Revealed O
the O
location-specific O
flow B-CONPRI
patterns E-CONPRI
and O
quantified O
the O
speeds O
of O
various O
types O
of O
flow O
. O


Reconstructed O
three-dimensional S-CONPRI
flow B-CONPRI
pattern E-CONPRI
under O
both O
conduction-mode O
melting S-MANP
and O
depression-mode O
melting S-MANP
. O


Experimentally O
analyzed O
the O
prevailing O
physical B-CONPRI
processes E-CONPRI
at O
different O
locations O
in O
the O
melt B-MATE
pool E-MATE
. O


Melt B-CONPRI
flow E-CONPRI
plays O
a O
critical O
role O
in O
laser B-MANP
metal I-MANP
additive I-MANP
manufacturing E-MANP
, O
yet O
the O
melt B-CONPRI
flow E-CONPRI
behavior O
within O
the O
melt B-MATE
pool E-MATE
has O
never O
been O
explicitly O
presented O
. O


Here O
, O
we O
report O
in-situ S-CONPRI
characterization O
of O
melt-flow B-CONPRI
dynamics E-CONPRI
in O
every O
location O
of O
the O
entire O
melt B-MATE
pool E-MATE
in O
laser B-MANP
metal I-MANP
additive I-MANP
manufacturing E-MANP
by O
populous O
and O
uniformly O
dispersed O
micro-tracers O
through O
in-situ S-CONPRI
high-resolution S-PARA
synchrotron O
x-ray B-CHAR
imaging E-CHAR
. O


The O
location-specific O
flow B-CONPRI
patterns E-CONPRI
in O
different O
regions O
of O
the O
melt B-MATE
pool E-MATE
are O
revealed O
and O
quantified O
under O
both O
conduction-mode O
and O
depression-mode O
melting S-MANP
. O


The O
physical B-CONPRI
processes E-CONPRI
at O
different O
locations O
in O
the O
melt B-MATE
pool E-MATE
are O
identified O
. O


The O
full-field O
melt-flow S-CONPRI
mapping O
approach O
reported O
here O
opens O
the O
way O
to O
study O
the O
detailed O
melt-flow B-CONPRI
dynamics E-CONPRI
under O
real O
additive B-MANP
manufacturing E-MANP
conditions O
. O


The O
results O
obtained O
provide O
crucial O
insights O
into O
laser B-MANP
additive I-MANP
manufacturing E-MANP
processes O
and O
are O
critical O
for O
developing O
reliable O
high-fidelity S-CONPRI
computational B-ENAT
models E-ENAT
. O


High B-PARA
resolution E-PARA
X-ray O
tomography O
was O
used O
to O
evaluate O
the O
efficiency O
of O
Hot B-MANP
Isostatic I-MANP
Pressing E-MANP
. O


Full O
consolidation S-CONPRI
of O
large O
internal O
cavities O
filled O
with O
unmelted O
powder S-MATE
was O
demonstrated O
. O


Design S-FEAT
of O
such O
cavities O
with O
unmelted O
powder S-MATE
could O
improve O
production S-MANP
rates O
by O
eliminating O
the O
need O
for O
some O
fraction S-CONPRI
of O
hatch O
melting S-MANP
in O
the O
interior O
of O
additively-manufactured O
structures O
. O


HIP S-MANP
is O
highly O
effective O
at O
closing O
most O
typical O
porosity S-PRO
distributions S-CONPRI
. O


Exceptions O
are O
highly O
interconnected O
pores S-PRO
and O
pores S-PRO
near O
the O
surface S-CONPRI
. O


Hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
of O
additively B-MANP
manufactured E-MANP
metals O
is O
a O
widely O
adopted O
and O
effective O
method O
to O
improve O
the O
density S-PRO
and O
microstructure S-CONPRI
homogeneity O
within O
geometrically-complex S-CONPRI
metal O
structures O
fabricated S-CONPRI
with O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
. O


The O
role O
of O
pores S-PRO
in O
the O
fatigue S-PRO
performance O
of O
additively B-MANP
manufactured E-MANP
metal O
parts O
is O
increasingly O
being O
recognized O
as S-MATE
a O
critical B-PRO
factor E-PRO
and O
HIP S-MANP
post-processing O
is O
now O
heralded O
as S-MATE
a O
method O
to O
eliminate O
pores S-PRO
, O
especially O
for O
high-criticality O
applications O
such O
as S-MATE
in O
the O
aerospace B-APPL
industry E-APPL
. O


Despite O
the O
widely O
reported O
positive O
influence O
on O
fatigue S-PRO
performance O
and O
high O
efficiency O
of O
pore S-PRO
closure O
, O
examples O
have O
been O
reported O
in O
which O
pores S-PRO
have O
not O
been O
entirely O
closed O
or O
have O
subsequently O
re-opened O
upon O
heat B-MANP
treatment E-MANP
. O


A O
variety O
of O
porosity S-PRO
distributions S-CONPRI
and O
types O
of O
pores S-PRO
may O
be S-MATE
present O
in O
parts O
produced O
by O
LBPF O
and O
the O
effectiveness S-CONPRI
of O
pore S-PRO
closure O
may O
differ O
depending O
on O
these O
pore S-PRO
characteristics O
. O


In O
this O
work O
, O
X-ray B-CHAR
tomography E-CHAR
was O
employed O
to O
provide O
insights O
into O
pore S-PRO
closure O
efficiency O
by O
HIP S-MANP
for O
an O
intentional O
and O
artificially-induced O
cavity O
as S-MATE
well O
as S-MATE
for O
a O
range S-PARA
of O
typical O
process-induced O
pores S-PRO
( O
lack O
of O
fusion S-CONPRI
, O
keyhole O
, O
contour S-FEAT
pores O
, O
etc O
. O


) O
in O
coupon O
samples S-CONPRI
of O
Ti6Al4V S-MATE
. O


The O
same O
samples S-CONPRI
were O
imaged O
non-destructively O
before O
and O
after O
HIP S-MANP
and O
aligned O
carefully O
for O
side-by-side O
viewing O
. O


High O
pore S-PRO
closure O
efficiency O
is O
demonstrated O
for O
all O
types O
of O
cavities O
and O
pores S-PRO
investigated O
, O
but O
near-surface O
pores S-PRO
of O
all O
types O
are O
shown O
to O
be S-MATE
problematic O
to O
varying O
degrees O
, O
in O
some O
cases O
perforating S-CONPRI
the O
superficial O
surface S-CONPRI
and O
creating O
new O
external O
notches S-FEAT
. O


Subsequent O
heat B-MANP
treatments E-MANP
( O
annealing S-MANP
after O
HIP S-MANP
) O
in O
some O
cases O
resulted O
in O
internal O
pore S-PRO
reopening O
for O
previously O
closed O
internal O
pores S-PRO
as S-MATE
well O
as S-MATE
a O
new O
“ O
blistering O
” O
effect O
observed O
for O
some O
near-surface O
pores S-PRO
, O
which O
the O
authors O
believe O
is O
reported O
for O
the O
first O
time O
. O


Implications O
of O
these O
results O
for O
quality B-CONPRI
control E-CONPRI
and O
HIP S-MANP
processing O
of O
LPBF S-MANP
parts O
are O
discussed O
. O


Finally O
, O
the O
utility O
of O
using O
HIP S-MANP
to O
consolidate O
intentionally-unmelted O
powder S-MATE
in O
order O
to O
improve O
production S-MANP
rates O
of O
powder B-MANP
bed I-MANP
fusion E-MANP
has O
great O
potential O
and O
is O
preliminarily O
demonstrated O
. O


Direct B-MANP
Energy I-MANP
Deposition E-MANP
( O
DED S-MANP
) O
systems O
are O
currently O
used O
to O
repair O
and O
maintain O
existing O
parts O
in O
the O
aerospace S-APPL
and O
automotive B-APPL
industries E-APPL
. O


This O
paper O
discusses O
an O
effort O
to O
scale O
up O
the O
DED S-MANP
technique O
in O
order O
to O
Additively B-MANP
Manufacture E-MANP
( O
AM S-MANP
) O
molds S-MACEQ
and O
dies S-MACEQ
used O
in O
the O
composite B-MANP
manufacturing E-MANP
industry O
. O


The O
US O
molds S-MACEQ
and O
dies S-MACEQ
market O
has O
been O
in O
a O
rapid O
decline O
over O
the O
last O
decade O
due O
to O
outsourcing S-CONPRI
to O
non-US O
entities O
. O


Oak O
Ridge O
National O
Laboratory S-CONPRI
( O
ORNL O
) O
, O
Wolf O
Robotics S-APPL
and O
Lincoln O
Electric O
have O
developed O
a O
Metal B-MANP
Big I-MANP
Area I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
MBAAM S-MANP
) O
system O
that O
uses O
a O
high B-PARA
deposition I-PARA
rate E-PARA
and O
a O
low-cost O
wire B-MATE
feedstock I-MATE
material E-MATE
. O


In O
this O
work O
we O
used O
the O
MBAAM S-MANP
system O
with O
a O
mild B-MATE
steel E-MATE
wire O
, O
ER70S-6 S-MATE
, O
to O
fabricate S-MANP
a O
compression B-MANP
molding E-MANP
mold O
for O
composite B-CONPRI
structures E-CONPRI
used O
in O
automotive S-APPL
and O
mass-transit S-APPL
applications O
. O


In O
addition O
, O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
AM S-MANP
structure O
were O
investigated O
, O
and O
it O
was O
found O
that O
the O
MBAAM S-MANP
process O
delivers O
parts O
with O
high O
planar O
isotropic S-PRO
behavior O
. O


The O
paper O
investigates S-CONPRI
the O
microstructure S-CONPRI
and O
grain S-CONPRI
of O
the O
printed O
articles O
to O
confirm O
the O
roots O
of O
the O
observed O
planar O
isotropic S-PRO
properties O
. O


The O
manufactured S-CONPRI
AM B-MACEQ
mold E-MACEQ
was O
used O
to O
fabricate S-MANP
50 O
composite S-MATE
parts O
with O
no O
observed O
mold S-MACEQ
deformations S-CONPRI
. O


Wire O
feed S-PARA
metal O
additive B-MANP
manufacturing E-MANP
offers O
advantages O
, O
such O
as S-MATE
large O
build B-PARA
volumes E-PARA
and O
high O
build B-CHAR
rates E-CHAR
, O
over O
powder B-MACEQ
bed E-MACEQ
and O
blown O
powder S-MATE
techniques O
, O
but O
it O
has O
its O
own O
disadvantages O
, O
i.e. O
, O
lower O
feature S-FEAT
resolution O
and O
bead B-CONPRI
morphology E-CONPRI
control O
issues O
. O


A O
new O
wire O
feed S-PARA
metal O
additive B-MANP
manufacturing I-MANP
process E-MANP
called O
Metal B-MANP
Big I-MANP
Area I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
mBAAM S-MANP
) O
uses O
a O
Gas B-MANP
Metal I-MANP
Arc I-MANP
Weld E-MANP
system O
on O
an O
articulated O
robot B-MACEQ
arm E-MACEQ
to O
increase O
build B-PARA
volume E-PARA
and O
deposition B-PARA
rate E-PARA
in O
comparison O
to O
powder B-MANP
bed I-MANP
techniques E-MANP
. O


The O
high B-PARA
deposition I-PARA
rate E-PARA
implies O
a O
low-resolution O
process S-CONPRI
; O
therefore O
, O
parts O
designed S-FEAT
for O
mBAAM S-MANP
must O
incorporate O
the O
use O
of O
machining S-MANP
to O
achieve O
certain O
features O
. O


This O
paper O
presents O
an O
introduction O
to O
how O
design B-CONPRI
rules E-CONPRI
, O
such O
as S-MATE
overhang O
constraint O
, O
large O
weld B-CONPRI
bead E-CONPRI
thickness O
, O
and O
support B-FEAT
structure E-FEAT
, O
for O
mBAAM S-MANP
interact O
in O
the O
context O
of O
an O
excavator B-MACEQ
arm E-MACEQ
case B-CONPRI
study E-CONPRI
, O
which O
was O
designed S-FEAT
using O
topology B-FEAT
optimization E-FEAT
. O


Interactive O
database S-ENAT
for O
mechanical B-CONPRI
properties E-CONPRI
of O
metal S-MATE
lattice B-FEAT
structures E-FEAT
. O


Lattice S-CONPRI
Unit-cell O
Characterization O
Interface S-CONPRI
for O
Engineering S-APPL
compiles O
69 O
sources O
. O


Lattice B-FEAT
structure E-FEAT
data S-CONPRI
compiled O
from O
analytical O
, O
experimental S-CONPRI
, O
and O
finite B-CONPRI
element E-CONPRI
. O


Data S-CONPRI
compilation O
includes O
nearly O
1650 O
experimental S-CONPRI
and O
finite B-CONPRI
element I-CONPRI
data I-CONPRI
points E-CONPRI
. O


Lattice B-CONPRI
data E-CONPRI
incorporates O
18 O
different O
common O
unit B-CONPRI
cell I-CONPRI
topologies E-CONPRI
. O


With O
the O
ever-increasing O
resolution S-PARA
of O
metal B-MANP
additive I-MANP
manufacturing E-MANP
processes O
, O
the O
ability O
to O
design S-FEAT
and O
fabricate S-MANP
cellular O
or O
lattice B-FEAT
structures E-FEAT
is O
readily O
improving O
. O


While O
there O
are O
few O
limits S-CONPRI
to O
the O
variety O
of O
unit B-CONPRI
cell I-CONPRI
topologies E-CONPRI
that O
can O
feasibly O
be S-MATE
manufactured O
, O
there O
is O
little O
known O
about O
the O
effect O
that O
the O
underlying O
unit B-CONPRI
cell I-CONPRI
topology E-CONPRI
has O
on O
lattice B-FEAT
structure E-FEAT
mechanical O
performance S-CONPRI
. O


Increased O
knowledge O
of O
lattice B-FEAT
structure E-FEAT
performance O
based O
on O
the O
unit B-CONPRI
cell I-CONPRI
topology E-CONPRI
can O
aid O
in O
appropriate O
unit B-CONPRI
cell E-CONPRI
selection O
to O
achieve O
desired O
lattice B-FEAT
structure E-FEAT
mechanical O
properties S-CONPRI
. O


The O
objective O
in O
this O
work O
is O
to O
compile O
metal S-MATE
additively B-MANP
manufactured E-MANP
lattice O
structure B-CHAR
characterization E-CHAR
data S-CONPRI
found O
in O
the O
literature O
into O
Ashby-style O
plots O
that O
can O
be S-MATE
used O
to O
differentiate O
unit B-CONPRI
cell I-CONPRI
topologies E-CONPRI
and O
guide O
unit B-CONPRI
cell E-CONPRI
selection O
. O


Data S-CONPRI
gathered O
from O
literature O
encompasses O
over O
69 O
papers O
describing O
18 O
different O
unit B-CONPRI
cell I-CONPRI
topologies E-CONPRI
. O


Data S-CONPRI
on O
mechanical B-CONPRI
properties E-CONPRI
such O
as S-MATE
the O
effective O
modulus O
, O
Poisson O
’ O
s S-MATE
ratio O
, O
yield B-PRO
strength E-PRO
, O
buckling B-PRO
strength E-PRO
, O
and O
plateau O
strength S-PRO
, O
of O
lattice B-FEAT
structures E-FEAT
from O
analytical O
models O
based O
on O
mathematical S-CONPRI
derivations O
, O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
, O
and O
experimental S-CONPRI
characterization O
was O
gathered O
and O
synthesized O
. O


In O
total O
, O
nearly O
1,650 O
data S-CONPRI
points O
for O
experimental S-CONPRI
and O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
were O
compiled O
along O
with O
a O
variety O
of O
analytical O
models O
for O
18 O
different O
unit B-CONPRI
cell I-CONPRI
topologies E-CONPRI
. O


The O
process S-CONPRI
of O
gathering O
the O
data S-CONPRI
from O
the O
literature O
along O
with O
the O
assumptions O
used O
to O
compile O
the O
data S-CONPRI
are O
discussed O
. O


A O
graphical O
user O
interface S-CONPRI
and O
database S-ENAT
were O
developed O
that O
allows O
for O
comparison O
of O
different O
lattice B-FEAT
structure E-FEAT
mechanical O
properties S-CONPRI
based O
on O
their O
unit B-CONPRI
cell I-CONPRI
topology E-CONPRI
. O


The O
Lattice S-CONPRI
Unit-cell O
Characterization O
Interface S-CONPRI
for O
Engineers O
( O
LUCIE O
) O
provides O
a O
simple S-MANP
format O
to O
guide O
engineers O
, O
scientists O
, O
and O
others O
towards O
understanding O
the O
relationships O
of O
the O
unit B-CONPRI
cell I-CONPRI
topology E-CONPRI
and O
the O
lattice B-FEAT
structure E-FEAT
mechanical O
properties S-CONPRI
, O
with O
the O
intent O
of O
guiding O
appropriate O
unit B-CONPRI
cell E-CONPRI
selection O
. O


Three O
cases O
studies O
are O
shown O
for O
using O
LUCIE O
to O
differentiate O
unit B-CONPRI
cell I-CONPRI
topologies E-CONPRI
for O
improved O
understanding O
of O
experimental S-CONPRI
and O
simulation-based O
results O
( O
Case B-CONPRI
Study E-CONPRI
1 O
) O
, O
to O
identify O
unit B-CONPRI
cell I-CONPRI
topology E-CONPRI
options O
for O
reducing O
weight S-PARA
while O
maintaining O
yield B-PRO
stress E-PRO
or O
increasing O
yield B-PRO
stress E-PRO
without O
reducing O
weight S-PARA
( O
Case B-CONPRI
Study E-CONPRI
2 O
) O
, O
and O
for O
quickly O
narrowing O
multiple O
options O
to O
an O
appropriate O
unit B-CONPRI
cell I-CONPRI
topology E-CONPRI
( O
Case B-CONPRI
Study E-CONPRI
3 O
) O
. O


Drop-on-demand B-MANP
jetting E-MANP
of O
metals S-MATE
offers O
a O
fully O
digital B-MANP
manufacturing E-MANP
approach O
to O
surpass O
the O
limitations O
of O
the O
current O
generation O
powder-based B-MANP
additive I-MANP
manufacturing E-MANP
technologies O
. O


However O
, O
research S-CONPRI
on O
this O
topic O
has O
been O
restricted O
mainly O
to O
near-net O
shaping S-MANP
of O
relatively O
low O
melting B-PARA
temperature E-PARA
metals O
. O


Here O
it O
is O
proposed O
a O
novel O
approach O
to O
jet O
molten B-MATE
metals E-MATE
at O
high-temperatures O
( O
> O
1000 O
°C O
) O
to O
enable O
the O
direct B-MANP
digital I-MANP
additive I-MANP
fabrication E-MANP
of O
micro- S-CHAR
to O
macro-scale O
objects O
. O


The O
technique O
used O
in O
our O
research S-CONPRI
– O
“ O
MetalJet O
” O
- O
is O
discussed O
by O
studying O
the O
ejection S-CONPRI
and O
the O
deposition S-CONPRI
of O
two O
example O
metals S-MATE
, O
tin S-MATE
and O
silver S-MATE
. O


The O
applicability O
of O
this O
new O
technology S-CONPRI
to O
additive B-MANP
manufacturing E-MANP
is O
evaluated O
through O
the O
study O
of O
the O
interface S-CONPRI
formed O
between O
the O
droplets S-CONPRI
and O
the O
substrate S-MATE
, O
the O
inter-droplets O
bonding S-CONPRI
, O
the O
microstructure S-CONPRI
and O
the O
geometrical B-CONPRI
fidelity E-CONPRI
of O
the O
printed O
objects O
. O


The O
research S-CONPRI
shows O
that O
the O
integrity S-CONPRI
of O
the O
samples S-CONPRI
( O
in O
terms O
of O
density S-PRO
as S-MATE
well O
as S-MATE
metallurgy O
) O
varies O
dramatically O
in O
the O
two O
investigated O
materials S-CONPRI
due O
to O
the O
different O
conditions O
that O
are O
required O
to O
melt S-CONPRI
the O
interface S-CONPRI
of O
the O
stacked O
droplets S-CONPRI
. O


Nevertheless O
the O
research S-CONPRI
shows O
that O
by O
a O
careful O
choice O
of O
the O
jetting S-MANP
strategy O
and O
sintering S-MANP
treatments O
3D B-CONPRI
structures E-CONPRI
of O
various O
complexity S-CONPRI
can O
be S-MATE
formed O
. O


This O
research S-CONPRI
paves O
the O
way O
towards O
the O
next O
generation O
metal B-MANP
additive I-MANP
manufacturing E-MANP
where O
various O
printing O
resolutions O
and O
multi-material S-CONPRI
capabilities O
could O
be S-MATE
used O
to O
obtain O
functional B-CONPRI
components E-CONPRI
for O
applications O
in O
printed B-CONPRI
electronics E-CONPRI
, O
medicine S-CONPRI
and O
the O
automotive B-APPL
sectors E-APPL
. O


Metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
as S-MATE
an O
emerging O
manufacturing S-MANP
technique O
has O
been O
gradually O
accepted O
to O
manufacture S-CONPRI
end-use O
components S-MACEQ
. O


However O
, O
one O
of O
the O
most O
critical O
issues O
preventing O
its O
broad O
applications O
is O
build B-CHAR
failure E-CHAR
resulting O
from O
residual B-PRO
stress E-PRO
accumulation O
in O
manufacturing B-MANP
process E-MANP
. O


The O
goal O
of O
this O
work O
is O
to O
investigate O
the O
feasibility S-CONPRI
of O
using O
topology B-FEAT
optimization E-FEAT
to O
design S-FEAT
support O
structure S-CONPRI
to O
mitigate O
residual B-PRO
stress E-PRO
induced O
build B-CHAR
failure E-CHAR
. O


To O
make O
topology B-FEAT
optimization E-FEAT
computationally O
tractable O
, O
the O
inherent O
strain S-PRO
method O
is O
employed O
to O
perform O
fast O
prediction S-CONPRI
of O
residual B-PRO
stress E-PRO
in O
an O
AM S-MANP
build O
. O


Graded O
lattice B-FEAT
structure E-FEAT
optimization O
is O
utilized O
to O
design S-FEAT
the O
support B-FEAT
structure E-FEAT
due O
to O
the O
open-celled S-CONPRI
and O
self-supporting S-FEAT
nature O
of O
periodic O
lattice B-FEAT
structure E-FEAT
. O


The O
objective O
for O
the O
optimization S-CONPRI
is O
to O
minimize O
the O
mass O
of O
sacrificial O
support B-FEAT
structure E-FEAT
under O
stress S-PRO
constraint O
. O


By O
limiting O
the O
maximum O
stress S-PRO
under O
the O
yield B-PRO
strength E-PRO
, O
cracking S-CONPRI
resulting O
from O
residual B-PRO
stress E-PRO
can O
be S-MATE
prevented O
. O


To O
show O
the O
feasibility S-CONPRI
of O
the O
proposed O
method O
, O
the O
support B-FEAT
structure E-FEAT
of O
a O
double-cantilever B-MACEQ
beam E-MACEQ
and O
a O
hip B-APPL
implant E-APPL
is O
designed S-FEAT
, O
respectively O
. O


The O
support B-FEAT
structure E-FEAT
after O
optimization S-CONPRI
can O
achieve O
a O
weight S-PARA
reduction S-CONPRI
of O
approximately O
60 O
% O
. O


The O
components S-MACEQ
with O
optimized O
support B-FEAT
structures E-FEAT
no O
longer O
suffer O
from O
stress-induced B-CONPRI
cracking E-CONPRI
after O
the O
designs S-FEAT
are O
realized O
by O
AM S-MANP
, O
which O
proves O
the O
effectiveness S-CONPRI
of O
the O
proposed O
method O
. O


Additive S-MATE
friction O
stir O
deposition S-CONPRI
( O
AFSD O
) O
is O
an O
emerging O
solid-state S-CONPRI
metal B-MANP
additive I-MANP
manufacturing E-MANP
technology O
renowned O
for O
strong O
interface S-CONPRI
adhesion S-PRO
and O
isotropic S-PRO
mechanical O
properties S-CONPRI
. O


This O
is O
postulated O
to O
result O
from O
the O
material S-MATE
flow O
phenomena O
near O
the O
interface S-CONPRI
, O
but O
experimental S-CONPRI
corroboration O
has O
remained O
absent O
. O


Here O
, O
we O
seek O
to O
understand O
the O
interface S-CONPRI
formed O
in O
AFSD O
via O
morphological O
and O
microstructural S-CONPRI
investigation O
, O
wherein O
the O
non-planar O
interfacial O
morphology S-CONPRI
is O
characterized O
on O
the O
track-scale O
( O
centimeter O
scale O
) O
using O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
and O
the O
material S-MATE
deformation S-CONPRI
history O
is O
explored O
by O
microstructure S-CONPRI
mapping O
at O
the O
interfacial O
regions O
. O


X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
reveals O
unique O
3D S-CONPRI
features O
at O
the O
interface S-CONPRI
with O
significant O
macroscopic S-CONPRI
material O
mixing S-CONPRI
. O


In O
the O
out-of-plane O
direction O
, O
the O
deposited O
material S-MATE
inserts S-MACEQ
below O
the O
initial O
substrate S-MATE
surface O
in O
the O
feed-rod O
zone O
, O
while O
the O
substrate S-MATE
surface O
surges O
upwards O
in O
the O
tool S-MACEQ
protrusion-affected O
zone O
. O


Complex O
3D B-CONPRI
structures E-CONPRI
like O
fins O
and O
serrations O
form O
on O
the O
advancing O
side O
, O
leading O
to O
structural O
interlocking O
; O
on O
the O
retreating O
side O
, O
the O
interface S-CONPRI
manifests O
as S-MATE
a O
smooth O
sloped O
surface S-CONPRI
. O


Microstructure S-CONPRI
mapping O
reveals O
a O
uniform O
thermomechanical S-CONPRI
history O
for O
the O
deposited O
material S-MATE
, O
which O
develops O
a O
homogeneous S-CONPRI
, O
almost O
fully O
recrystallized S-MANP
microstructure S-CONPRI
. O


The O
substrate S-MATE
surface O
develops O
partially O
recrystallized S-MANP
microstructures S-MATE
that O
are O
location-dependent O
; O
more O
intra-granular O
orientation S-CONPRI
gradients O
are O
found O
in O
the O
regions O
further O
away O
from O
the O
centerline O
of O
the O
deposition S-CONPRI
track O
. O


From O
these O
observations O
, O
we O
discuss O
the O
mechanisms O
for O
interfacial O
material S-MATE
flow O
and O
interface S-CONPRI
morphology O
formation O
during O
AFSD O
. O


Embedded B-ENAT
electronics E-ENAT
and O
sensors S-MACEQ
are O
becoming O
increasingly O
important O
for O
the O
development O
of O
Industry B-ENAT
4.0 E-ENAT
. O


For O
small O
components S-MACEQ
, O
space O
constraints O
lead S-MATE
to O
full O
3D B-CONPRI
integration E-CONPRI
requirements O
that O
are O
only O
achievable O
through O
Additive B-MANP
Manufacturing E-MANP
. O


Manufacturing S-MANP
metal O
components S-MACEQ
usually O
require O
high O
temperatures S-PARA
incompatible O
with O
electronics S-CONPRI
but O
Ultrasonic B-MANP
Additive I-MANP
Manufacturing E-MANP
( O
UAM S-MANP
) O
can O
produce O
components S-MACEQ
with O
mechanical B-CONPRI
properties E-CONPRI
close O
to O
bulk O
, O
but O
with O
the O
integration O
of O
internal O
embedded B-ENAT
electronics E-ENAT
, O
sensors S-MACEQ
or O
optics S-APPL
. O


This O
paper O
describes O
a O
novel O
manufacturing S-MANP
route O
for O
embedding O
electronics S-CONPRI
with O
3D S-CONPRI
via O
connectors O
in O
an O
aluminium B-MATE
matrix E-MATE
. O


Metal S-MATE
foils O
with O
printed O
conductors S-MATE
and O
insulators S-MATE
were O
prepared O
separately O
from O
the O
UAM S-MANP
process S-CONPRI
thereby O
separating O
the O
electronics S-CONPRI
preparation O
from O
the O
part B-CONPRI
consolidation E-CONPRI
. O


A O
dual O
material S-MATE
polymer O
layer S-PARA
exhibited O
the O
best O
electrically S-CONPRI
insulating O
properties S-CONPRI
, O
while O
providing O
mechanical S-APPL
protection O
of O
printed B-MACEQ
conductive E-MACEQ
tracks O
stable O
up O
to O
100 O
°C O
. O


General O
design S-FEAT
and O
UAM S-MANP
process S-CONPRI
recommendations O
are O
given O
for O
3D S-CONPRI
embedded O
electronics S-CONPRI
in O
a O
metal B-CONPRI
matrix E-CONPRI
. O


Functionally B-MATE
graded I-MATE
metals E-MATE
fabricated S-CONPRI
using O
high-temperature O
additive B-MANP
manufacturing E-MANP
can O
form O
intermetallics S-MATE
that O
fracture S-CONPRI
during O
printing O
due O
to O
thermal B-PRO
stresses E-PRO
generated O
by O
the O
heat B-CONPRI
source E-CONPRI
. O


To O
address O
this O
problem O
, O
we O
introduce O
a O
new O
class O
of O
non-equilibrium B-CONPRI
phase I-CONPRI
diagrams E-CONPRI
, O
termed O
Scheil B-CONPRI
Ternary I-CONPRI
Projection E-CONPRI
( O
STeP S-CONPRI
) O
diagrams O
, O
for O
designing O
optimal O
composition B-CONPRI
gradients E-CONPRI
that O
avoid O
brittle S-PRO
phases O
. O


Using O
the O
Fe-Cr-Al S-MATE
ternary O
as S-MATE
a O
model S-CONPRI
system O
, O
we O
compare O
the O
phase S-CONPRI
fields O
in O
equilibrium S-CONPRI
and O
STeP B-CONPRI
diagrams E-CONPRI
to O
show O
that O
intermetallic S-MATE
phase O
fields O
are O
dramatically O
expanded O
under O
the O
rapid B-MANP
solidification E-MANP
conditions O
in O
melt-based O
additive B-MANP
manufacturing E-MANP
, O
an O
important O
effect O
that O
must O
be S-MATE
accounted O
for O
when O
designing O
composition B-CONPRI
gradients E-CONPRI
. O


We O
present O
the O
results O
of O
3D S-CONPRI
modeling O
of O
the O
laser S-ENAT
and O
electron B-CONPRI
beam E-CONPRI
powder O
bed B-MANP
fusion E-MANP
process O
at O
the O
mesoscale S-CONPRI
with O
an O
in-house O
developed O
advanced O
multiphysical O
numerical O
tool S-MACEQ
. O


The O
hydrodynamics O
and O
thermal B-PRO
conductivity E-PRO
core S-MACEQ
of O
the O
tool S-MACEQ
is O
based O
on O
the O
lattice S-CONPRI
Boltzmann O
method O
. O


The O
numerical O
tool S-MACEQ
takes O
into O
account O
the O
random O
distributions S-CONPRI
of O
powder B-MATE
particles E-MATE
by O
size O
in O
a O
layer S-PARA
and O
the O
propagation O
of O
the O
laser S-ENAT
( O
electron B-CONPRI
beam E-CONPRI
) O
with O
a O
full O
ray O
tracing O
( O
Monte O
Carlo O
) O
model S-CONPRI
that O
includes O
multiple O
reflections O
, O
phase S-CONPRI
transitions O
, O
thermal B-PRO
conductivity E-PRO
, O
and O
detailed O
liquid O
dynamics O
of O
the O
molten B-MATE
metal E-MATE
, O
influenced O
by O
evaporation S-CONPRI
of O
the O
metal S-MATE
and O
the O
recoil O
pressure S-CONPRI
. O


We O
numerically O
demonstrate O
a O
strong O
dependence O
of O
the O
net O
energy B-CHAR
absorption E-CHAR
of O
the O
incoming O
heat B-CONPRI
source E-CONPRI
beam S-MACEQ
by O
the O
powder B-MACEQ
bed E-MACEQ
and O
melt B-MATE
pool E-MATE
on O
the O
beam S-MACEQ
power O
. O


We O
show O
the O
ability O
of O
our O
model S-CONPRI
to O
predict O
the O
measurable O
properties S-CONPRI
of O
a O
single O
track O
on O
a O
bare O
substrate S-MATE
as S-MATE
well O
as S-MATE
on O
a O
powder S-MATE
layer S-PARA
. O


We O
obtain O
good O
agreement O
with O
experimental B-CONPRI
data E-CONPRI
for O
the O
depth O
, O
width O
and O
shape O
of O
a O
track O
for O
a O
number O
of O
materials S-CONPRI
and O
a O
wide O
range S-PARA
of O
energy O
source S-APPL
parameters S-CONPRI
. O


We O
further O
apply O
our O
model S-CONPRI
to O
the O
simulation S-ENAT
of O
the O
entire O
layer S-PARA
formation O
and O
demonstrate O
the O
strong O
dependence O
of O
the O
resulting O
layer S-PARA
morphology O
on O
the O
hatch B-PARA
spacing E-PARA
. O


The O
presented O
model S-CONPRI
could O
be S-MATE
very O
helpful O
for O
optimizing O
the O
additive S-MATE
process O
without O
carrying O
out O
a O
large O
number O
of O
experiments O
in O
a O
common O
trial-and-error S-CONPRI
method O
, O
developing O
process B-CONPRI
parameters E-CONPRI
for O
new O
materials S-CONPRI
, O
and O
assessing O
novel O
modalities O
of O
powder B-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
. O


The O
particle S-CONPRI
size O
and O
shape O
distributions S-CONPRI
of O
metal B-MATE
powders E-MATE
used O
in O
additive B-MANP
manufacturing E-MANP
powder O
bed B-MANP
fusion E-MANP
processes O
are O
of O
technological O
importance O
for O
the O
final O
built O
product O
. O


Current O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
measurements O
of O
these O
distributions S-CONPRI
assume O
a O
spherical S-CONPRI
shape O
, O
while O
techniques O
that O
measure O
both O
size O
and O
shape O
are O
always O
two-dimensional S-CONPRI
( O
2D S-CONPRI
) O
measurements O
of O
particle B-CONPRI
projections E-CONPRI
. O


This O
paper O
describes O
a O
set S-APPL
of O
techniques O
using O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
, O
combined O
with O
various O
mathematical B-CONPRI
algorithms E-CONPRI
, O
to O
measure O
the O
3D S-CONPRI
size O
, O
shape O
, O
and O
internal O
porosity S-PRO
of O
individual O
particles S-CONPRI
. O


Calibrated S-CONPRI
by O
a O
limited O
amount O
of O
visual B-CHAR
examination E-CHAR
of O
3D B-CONPRI
images E-CONPRI
of O
individual O
particles S-CONPRI
, O
these O
techniques O
can O
classify O
powder B-MATE
particles E-MATE
as S-MATE
single O
near-spherical O
( O
SnS S-CONPRI
) O
particles S-CONPRI
, O
and O
non-spherical S-CONPRI
( O
NS S-MATE
) O
particles S-CONPRI
, O
which O
consist O
of O
either O
single O
highly O
non-spherical S-CONPRI
particles O
or O
multi-particles S-CONPRI
, O
where O
two O
or O
more O
smaller O
particles S-CONPRI
have O
been O
joined O
together O
. O


From O
this O
3D B-CONPRI
data E-CONPRI
, O
other O
algorithms S-CONPRI
can O
generate O
2D B-MATE
particle E-MATE
size O
and O
shape O
information O
to O
compare O
with O
the O
results O
of O
2D B-ENAT
measurement I-ENAT
techniques E-ENAT
. O


These O
techniques O
are O
applied O
to O
two O
metal B-MATE
powders E-MATE
composed O
of O
a O
specific O
alloy S-MATE
of O
titanium S-MATE
with O
aluminum S-MATE
and O
vanadium S-MATE
, O
denoted O
as S-MATE
Ti64 O
, O
which O
is O
in O
common O
use O
as S-MATE
a O
powder S-MATE
for O
selective B-MANP
laser E-MANP
or O
electron B-MANP
beam I-MANP
melting E-MANP
powder O
bed S-MACEQ
additive B-MANP
manufacturing E-MANP
. O


One O
powder S-MATE
was O
made O
with O
a O
gas-atomization B-CONPRI
process E-CONPRI
, O
the O
other O
with O
a O
plasma-atomization B-CONPRI
process E-CONPRI
, O
both O
have O
been O
recycled S-CONPRI
, O
and O
both O
pass O
the O
specifications S-PARA
for O
additive B-MANP
manufacturing E-MANP
use O
. O


The O
powders S-MATE
differ O
in O
the O
fraction S-CONPRI
of O
NS S-MATE
particles O
and O
porous S-PRO
particles S-CONPRI
, O
in O
their O
size O
and O
shape O
distributions S-CONPRI
, O
and O
in O
average S-CONPRI
shape O
and O
size O
statistics S-CONPRI
. O


The O
SnS/NS O
classification S-CONPRI
enables O
one O
to O
show O
how O
these O
classes O
contribute O
to O
the O
overall O
particle B-CONPRI
size I-CONPRI
distributions E-CONPRI
, O
even O
for O
a O
single O
powder S-MATE
type O
, O
and O
is O
useful O
for O
comparing O
different O
sources O
of O
powder S-MATE
as S-MATE
well O
as S-MATE
studying O
how O
the O
size/shape O
distributions S-CONPRI
of O
a O
powder S-MATE
might O
change O
over O
multiple O
recycling S-CONPRI
events O
. O


Electrochemical S-CONPRI
microstructuring O
enables O
the O
production S-MANP
of O
polymer-metal B-MATE
hybrids E-MATE
by O
means O
of O
Material B-MANP
Extrusion E-MANP
without O
the O
need O
of O
coatings S-APPL
. O


The O
contact S-APPL
temperature O
between O
the O
metal S-MATE
sheet O
and O
the O
deposited O
polymer S-MATE
significantly O
influences O
the O
resulting O
component S-MACEQ
behavior O
. O


A O
consolidation S-CONPRI
roll O
improves O
the O
filling O
of O
microstructures S-MATE
for O
low O
contact S-APPL
temperatures O
. O


The O
development O
towards O
higher O
individualization O
and O
functional O
density S-PRO
pushes O
the O
need O
towards O
a O
flexible B-CONPRI
production E-CONPRI
of O
multi-material S-CONPRI
and O
lightweight S-CONPRI
components S-MACEQ
. O


In O
this O
paper O
, O
extrusion S-MANP
based O
additive B-MANP
manufacturing E-MANP
was O
used O
to O
produce O
polymer-metal B-MATE
hybrids E-MATE
with O
polypropylene S-MATE
and O
aluminum B-MATE
alloy E-MATE
. O


For O
this O
purpose O
, O
a O
screw-driven B-MACEQ
extruder E-MACEQ
on O
a O
six-axis B-MACEQ
robot E-MACEQ
was O
used O
. O


Due O
to O
the O
adhesion S-PRO
incompatibility O
of O
polypropylene S-MATE
and O
untreated O
metals S-MATE
, O
the O
surface S-CONPRI
of O
the O
aluminum B-MATE
sheets E-MATE
was O
electrochemically S-CONPRI
micro-structured O
. O


The O
investigations O
show O
that O
this O
enables O
a O
mechanically O
stressable S-PRO
joint S-CONPRI
through O
the O
filling O
of O
the O
surface S-CONPRI
microstructures S-MATE
with O
polymer S-MATE
. O


Investigations O
on O
lap B-CONPRI
shear I-CONPRI
joints E-CONPRI
reveal O
a O
distinct O
influence O
of O
the O
contact S-APPL
temperature O
between O
the O
polymer S-MATE
and O
metal S-MATE
onto O
the O
lap B-PRO
shear I-PRO
strength E-PRO
. O


A O
sufficient O
contact S-APPL
temperature O
is O
required O
for O
filling O
surface S-CONPRI
microstructures S-MATE
. O


Thus O
, O
increased O
metal S-MATE
and O
extrusion S-MANP
temperatures O
favor O
higher O
strengths S-PRO
. O


Furthermore O
, O
the O
use O
of O
a O
consolidation S-CONPRI
roll O
shows O
beneficial O
influences O
in O
lower O
temperature B-PARA
ranges E-PARA
due O
to O
the O
application O
of O
higher O
pressures S-CONPRI
during O
the O
polymer S-MATE
strand O
deposition S-CONPRI
. O


A O
virtual B-MACEQ
binocular E-MACEQ
vision O
sensor S-MACEQ
is O
developed O
to O
monitor S-CONPRI
molten B-PARA
pool I-PARA
width E-PARA
. O


A O
closed-loop B-MACEQ
controller E-MACEQ
is O
designed S-FEAT
for O
molten B-PARA
pool I-PARA
width E-PARA
control O
. O


Comparison O
tests O
between O
open O
and O
closed-loop B-MACEQ
control E-MACEQ
are O
carried O
out O
. O


Gas B-MANP
metal I-MANP
arc E-MANP
( O
GMA S-MANP
) O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
one O
of O
the O
significant O
wire B-MANP
and I-MANP
arc I-MANP
AM E-MANP
processes S-CONPRI
with O
the O
ability O
to O
produce O
large-scale O
metal S-MATE
parts O
in O
a O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
fashion S-CONPRI
. O


Despite O
this O
fact O
, O
techniques O
to O
realize O
process S-CONPRI
sensing O
and O
geometry S-CONPRI
control O
have O
not O
been O
perfectly O
developed O
. O


This O
study O
aims O
at O
molten B-PARA
pool I-PARA
width E-PARA
control O
in O
GMA B-MANP
AM E-MANP
using O
a O
passive B-CONPRI
vision I-CONPRI
sensing E-CONPRI
technique O
. O


A O
virtual B-ENAT
binocular I-ENAT
vision I-ENAT
sensing E-ENAT
system O
consisting O
of O
a O
biprism S-MACEQ
and O
a O
camera S-MACEQ
is O
designed S-FEAT
to O
monitor S-CONPRI
the O
molten B-PARA
pool I-PARA
geometry E-PARA
. O


The O
molten B-PARA
pool I-PARA
width E-PARA
in O
a O
captured O
image S-CONPRI
pair O
is O
extracted S-CONPRI
by O
a O
series O
of O
procedures O
, O
such O
as S-MATE
sensor O
calibration S-CONPRI
, O
image S-CONPRI
pair O
rectification O
, O
disparity O
calculation O
, O
and O
width O
reconstruction S-CONPRI
. O


A O
verification B-CHAR
test E-CHAR
is O
conducted O
and O
reveals O
that O
the O
detection O
error S-CONPRI
of O
the O
sensing B-CHAR
system E-CHAR
is O
less O
than O
3 O
% O
. O


To O
keep O
consistent O
layer S-PARA
width O
in O
each O
layer S-PARA
, O
the O
deviation O
of O
the O
molten B-PARA
pool I-PARA
width E-PARA
is O
compensated O
by O
designing O
a O
fuzzy B-MACEQ
intelligent I-MACEQ
controller E-MACEQ
to O
adjust O
the O
arc B-CONPRI
current E-CONPRI
in O
real O
time O
. O


The O
effectiveness S-CONPRI
of O
the O
controller S-MACEQ
is O
evaluated O
via O
the O
deposition S-CONPRI
of O
thin-walled B-FEAT
parts E-FEAT
. O


The O
results O
indicate O
that O
the O
consistency S-CONPRI
of O
the O
molten B-PARA
pool I-PARA
width E-PARA
in O
GMA B-MANP
AM E-MANP
can O
be S-MATE
improved O
when O
employing O
the O
fuzzy B-MACEQ
controller E-MACEQ
. O


Porosity S-PRO
in O
additively B-MANP
manufactured E-MANP
metals O
can O
reduce O
material B-PRO
strength E-PRO
and O
is O
generally O
undesirable O
. O


Although O
studies O
have O
shown O
relationships O
between O
process B-CONPRI
parameters E-CONPRI
and O
porosity S-PRO
, O
monitoring B-CONPRI
strategies E-CONPRI
for O
defect S-CONPRI
detection O
and O
pore S-PRO
formation O
are O
still O
needed O
. O


In O
this O
paper O
, O
instantaneous B-CONPRI
anomalous E-CONPRI
conditions O
are O
detected O
in-situ S-CONPRI
via O
pyrometry S-CHAR
during O
laser B-MANP
powder I-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
and O
correlated S-CONPRI
with O
voids S-CONPRI
observed O
using O
post-build O
micro-computed B-CHAR
tomography E-CHAR
. O


Large O
two-color O
pyrometry S-CHAR
data S-CONPRI
sets O
were O
used O
to O
estimate O
instantaneous O
temperatures S-PARA
, O
melt B-MATE
pool E-MATE
orientations O
and O
aspect B-FEAT
ratios E-FEAT
. O


Machine B-ENAT
learning I-ENAT
algorithms E-ENAT
were O
then O
applied O
to O
processed S-CONPRI
pyrometry O
data S-CONPRI
to O
detect O
outlier O
images S-CONPRI
and O
conditions O
. O


It O
is O
shown O
that O
melt B-MATE
pool E-MATE
outliers O
are O
good O
predictors O
of O
voids S-CONPRI
observed O
post-build O
. O


With O
this O
approach O
, O
real O
time O
process B-CONPRI
monitoring E-CONPRI
can O
be S-MATE
incorporated O
into O
systems O
to O
detect O
defect S-CONPRI
and O
void S-CONPRI
formation O
. O


Alternatively O
, O
using O
the O
methodology S-CONPRI
presented O
here O
, O
pyrometry S-CHAR
data S-CONPRI
can O
be S-MATE
post O
processed S-CONPRI
for O
porosity S-PRO
assessment O
. O


This O
paper O
proposes O
an O
additive B-MANP
manufacturing E-MANP
method O
that O
combines O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
3D B-MANP
printing E-MANP
and O
an O
electroforming S-MANP
technology O
to O
fabricate S-MANP
multi-material O
structures O
composed O
of O
resin S-MATE
and O
metal S-MATE
. O


In O
this O
method O
, O
an O
FFF B-MACEQ
3D I-MACEQ
printer E-MACEQ
prints O
a O
resin S-MATE
mold S-MACEQ
that O
functions O
as S-MATE
a O
structural B-CONPRI
unit E-CONPRI
in O
a O
multi-material B-FEAT
structure E-FEAT
and O
as S-MATE
a O
sacrificial B-MACEQ
plastic I-MACEQ
mold E-MACEQ
for O
the O
addition O
of O
the O
metal B-MATE
material E-MATE
. O


This O
sacrificial O
mold S-MACEQ
is O
eventually O
removed O
. O


Electroforming S-MANP
the O
interior O
of O
a O
printed B-CONPRI
resin E-CONPRI
mold S-MACEQ
enables O
the O
fabrication S-MANP
of O
multi-material B-FEAT
structures E-FEAT
using O
resin S-MATE
and O
metal B-MATE
materials E-MATE
. O


The O
fabrication S-MANP
conditions O
for O
multi-material B-FEAT
structures E-FEAT
when O
using O
the O
proposed O
method O
were O
investigated O
and O
the O
surfaces S-CONPRI
of O
the O
resulting O
structures O
were O
evaluated O
. O


The O
fabrication S-MANP
conditions O
for O
the O
specified B-CONPRI
thickness E-CONPRI
per O
process S-CONPRI
and O
the O
total O
thicknesses O
from O
all O
the O
processes S-CONPRI
were O
determined O
. O


Furthermore O
, O
our O
results O
indicated O
that O
the O
shape O
of O
the O
side O
of O
the O
metal S-MATE
portion O
depended O
on O
the O
forming S-MANP
precision O
of O
the O
FFF B-MACEQ
3D I-MACEQ
printer E-MACEQ
. O


We O
present O
an O
example O
of O
the O
fabrication S-MANP
of O
a O
gear S-MACEQ
shape O
from O
resin S-MATE
and O
metal S-MATE
. O


X-ray B-CHAR
CT E-CHAR
and O
image B-CONPRI
analysis E-CONPRI
enable O
full O
surface B-CHAR
characterization E-CHAR
of O
LPBF S-MANP
channels O
. O


Novel O
methodology S-CONPRI
enables O
roughness S-PRO
profile S-FEAT
extraction O
from O
3D B-CONPRI
deviation I-CONPRI
data E-CONPRI
. O


360° O
roughness S-PRO
characterization O
enables O
predictive B-CONPRI
models E-CONPRI
for O
LPBF S-MANP
channels O
. O


The O
increasingly O
complex B-PRO
shapes E-PRO
and O
geometries S-CONPRI
being O
produced O
using O
additive B-MANP
manufacturing E-MANP
necessitate O
new O
characterization O
techniques O
that O
can O
address O
the O
corresponding O
challenges O
. O


Standard S-CONPRI
techniques O
for O
roughness S-PRO
and O
texture S-FEAT
measurements O
are O
inept O
at O
characterizing O
the O
internal O
surfaces S-CONPRI
in O
freeform B-CONPRI
geometries E-CONPRI
. O


Hence O
, O
this O
work O
presents O
a O
new O
methodology S-CONPRI
for O
extracting S-CONPRI
and O
quantitatively S-CONPRI
characterizing O
the O
roughness S-PRO
on O
internal O
surfaces S-CONPRI
. O


The O
methodology S-CONPRI
links O
X-ray B-CHAR
CT E-CHAR
with O
complete O
roughness S-PRO
characterization O
of O
channels O
manufactured S-CONPRI
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
through O
a O
novel O
image B-CONPRI
analysis E-CONPRI
approach O
of O
X-ray B-CHAR
CT E-CHAR
data S-CONPRI
. O


Global O
and O
local B-CONPRI
orientation E-CONPRI
parameters O
are O
defined O
to O
enable O
a O
full O
360° O
description O
of O
the O
roughness S-PRO
inside O
additively B-MANP
manufactured E-MANP
channels O
. O


X-ray B-CHAR
CT E-CHAR
data S-CONPRI
is O
analyzed O
to O
generate O
3D B-CONPRI
deviation I-CONPRI
data E-CONPRI
– O
based O
on O
which O
multiple O
local O
roughness S-PRO
profiles S-FEAT
are O
extracted S-CONPRI
and O
analyzed O
in O
accordance O
with O
the O
ISO S-MANS
4287:1997 O
standard S-CONPRI
. O


To O
demonstrate O
the O
proposed O
methodology S-CONPRI
, O
seven O
circular O
17-4 B-MATE
PH I-MATE
stainless I-MATE
steel E-MATE
channels O
produced O
at O
different O
inclinations S-FEAT
and O
with O
a O
diameter S-CONPRI
of O
2 O
mm S-MANP
are O
investigated O
as S-MATE
a O
case B-CONPRI
study E-CONPRI
. O


Qualitative S-CONPRI
and O
quantitative S-CONPRI
characterization O
of O
the O
roughness S-PRO
is O
obtained O
through O
the O
use O
of O
the O
proposed O
methodology S-CONPRI
. O


A O
strong O
dependence O
of O
the O
local O
roughness S-PRO
on O
the O
corresponding O
α O
and O
β O
orientations S-CONPRI
is O
found O
. O


A O
simple B-CONPRI
regression I-CONPRI
model E-CONPRI
is O
subsequently O
extracted S-CONPRI
from O
the O
calculated O
roughness B-PRO
values E-PRO
and O
allows O
prediction S-CONPRI
of O
Ra-values S-CONPRI
in O
the O
channels O
for O
the O
ranges O
between O
0° O
≤ O
α O
≤ O
90° O
and O
80° O
≤ O
β O
≤ O
280° O
. O


In O
addition O
to O
decreasing O
the O
effective O
hydraulic B-CONPRI
diameter E-CONPRI
of O
a O
cooling B-MACEQ
channel E-MACEQ
, O
the O
surface B-PRO
roughness E-PRO
also O
influences O
the O
local B-CONPRI
Nusselt I-CONPRI
number E-CONPRI
, O
which O
is O
quantified O
using O
the O
extracted S-CONPRI
regression O
model S-CONPRI
. O


This O
paper O
reports O
on O
the O
results O
of O
a O
round B-CHAR
robin I-CHAR
test E-CHAR
conducted O
by O
ten O
X-ray B-CHAR
micro I-CHAR
computed I-CHAR
tomography E-CHAR
( O
micro-CT S-CHAR
) O
laboratories S-CONPRI
with O
the O
same O
three O
selected O
titanium B-MATE
alloy E-MATE
( O
Ti6Al4V S-MATE
) O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
test O
parts O
. O


These O
parts O
were O
a O
10-mm O
cube S-CONPRI
, O
a O
60-mm O
long O
and O
40-mm O
high O
complex-shaped S-CONPRI
bracket S-MACEQ
, O
and O
a O
15-mm O
diameter S-CONPRI
rod O
. O


Previously O
developed O
protocols S-CONPRI
for O
micro-CT B-CHAR
analysis E-CHAR
of O
these O
parts O
were O
provided O
to O
all O
participants O
, O
including O
suggested O
scanning B-CONPRI
parameters E-CONPRI
and O
image B-CONPRI
analysis E-CONPRI
steps O
. O


No O
further O
information O
on O
the O
samples S-CONPRI
were O
provided O
, O
and O
they O
were O
selected O
from O
a O
variety O
of O
parts O
from O
a O
previous O
different O
type O
of O
round B-CHAR
robin E-CHAR
study O
where O
various O
L-PBF S-MANP
laboratories S-CONPRI
provided O
identical O
parts O
for O
micro-CT B-CHAR
analysis E-CHAR
at O
one O
laboratory S-CONPRI
. O


In O
this O
new O
micro-CT B-CHAR
round I-CHAR
robin I-CHAR
test E-CHAR
which O
involves O
various O
micro-CT S-CHAR
laboratories S-CONPRI
, O
parts O
from O
the O
previous O
work O
were O
selected O
such O
that O
each O
part O
had O
a O
different O
characteristic O
flaw S-CONPRI
type O
, O
and O
all O
laboratories S-CONPRI
involved O
in O
the O
study O
analyzed O
the O
same O
set S-APPL
of O
parts O
. O


The O
10-mm O
cube S-CONPRI
contained O
subsurface O
pores S-PRO
just O
under O
its O
top O
surface S-CONPRI
( O
relative O
to O
build B-PARA
direction E-PARA
) O
, O
and O
all O
participants O
could O
positively O
identify O
this O
. O


The O
complex O
bracket S-MACEQ
had O
contour S-FEAT
pores O
around O
its O
outer O
vertical S-CONPRI
sides O
, O
and O
was O
warped O
with O
two O
arms O
deflected O
towards O
one O
another O
. O


The O
15-mm O
diameter S-CONPRI
rod O
had O
a O
layered O
stop/start O
flaw S-CONPRI
, O
which O
was O
also O
positively O
identified O
by O
all O
participants O
. O


Differences O
were O
found O
among O
participants O
for O
quantitative S-CONPRI
evaluations O
, O
ranging O
from O
no O
quantitative B-CHAR
measurement E-CHAR
made O
, O
to O
under O
and O
overestimation S-CONPRI
of O
the O
values O
in O
all O
analyses O
attempted O
. O


This O
round B-CHAR
robin E-CHAR
provides O
the O
opportunity O
to O
highlight O
typical O
causes O
of O
errors S-CONPRI
in O
micro-CT B-CHAR
scanning E-CHAR
and O
image B-CONPRI
analysis E-CONPRI
as S-MATE
applied O
to O
additively B-MANP
manufactured E-MANP
parts O
. O


Some O
workflow B-CONPRI
variations E-CONPRI
, O
sources O
of O
error S-CONPRI
and O
ways O
to O
increase O
the O
reproducibility S-CONPRI
of O
such O
analysis O
workflows S-CONPRI
are O
discussed O
. O


The O
ultimate O
aim O
of O
this O
work O
is O
to O
advance O
the O
efficient O
use O
of O
micro-CT S-CHAR
facilities O
for O
process B-CONPRI
optimization E-CONPRI
and O
quality S-CONPRI
inspections S-CHAR
for O
additively B-MANP
manufactured I-MANP
products E-MANP
. O


The O
results O
provide O
confidence O
in O
the O
use O
of O
laboratory S-CONPRI
micro-CT O
but O
also O
indicate O
the O
need O
for O
further O
development O
of O
standards S-CONPRI
, O
protocols S-CONPRI
and O
image B-CONPRI
analysis E-CONPRI
workflows O
for O
quantitative B-CHAR
assessment E-CHAR
, O
especially O
for O
direct O
and O
quantitative S-CONPRI
comparisons O
between O
different O
laboratories S-CONPRI
. O


Very O
limited O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
have O
been O
developed O
for O
production S-MANP
of O
Metal B-MATE
Matrix I-MATE
Composites E-MATE
( O
MMCs S-MATE
) O
reinforced S-CONPRI
by O
ceramic S-MATE
. O


Most O
of O
these O
processes S-CONPRI
use O
different O
mixing S-CONPRI
techniques O
to O
mix O
metal S-MATE
and O
ceramic B-MATE
powder I-MATE
particles E-MATE
in O
order O
to O
be S-MATE
used O
in O
an O
existing O
AM B-MANP
process E-MANP
such O
as S-MATE
Selective O
Laser S-ENAT
Melting O
( O
SLM S-MANP
) O
process S-CONPRI
. O


The O
current O
AM B-MANP
techniques E-MANP
for O
MMCs S-MATE
fabrication S-MANP
have O
limitations O
due O
to O
material S-MATE
mixing O
and O
the O
AM B-MANP
process E-MANP
limitations O
itself O
. O


This O
paper O
introduces O
a O
novel O
AM S-MANP
method O
for O
fabrication S-MANP
of O
MMCs S-MATE
by O
Thermal B-MANP
Decomposition E-MANP
of O
Salts S-MATE
( O
TDS S-CHAR
) O
. O


In O
this O
method O
inorganic B-MATE
salts E-MATE
are O
printed O
on O
metal B-MATE
powder E-MATE
bed S-MACEQ
to O
fabricate S-MANP
green O
part O
. O


The O
green B-PRO
part E-PRO
undergoes O
bulk B-MANP
sintering E-MANP
. O


During O
bulk B-MANP
sintering E-MANP
the O
printed O
inorganic B-MATE
salts E-MATE
are O
decomposed O
to O
fine B-MATE
ceramic E-MATE
particles O
to O
form O
MMC S-MATE
. O


This O
process S-CONPRI
is O
capable O
of O
generating O
MMC S-MATE
structures O
with O
uniformly O
distributed O
and O
dispersed O
ultra-fine O
ceramic S-MATE
particles O
in O
the O
metal B-CONPRI
matrix E-CONPRI
with O
less O
limitations O
and O
lower O
cost O
compared O
to O
other O
existing O
AM B-MANP
techniques E-MANP
. O


In O
this O
paper O
, O
bronze-alumina S-MATE
MMC O
was O
fabricated S-CONPRI
and O
studied O
by O
the O
TDS B-CONPRI
process E-CONPRI
to O
validate O
the O
proposed O
process S-CONPRI
. O


It O
was O
also O
shown O
that O
the O
TDS B-CONPRI
process E-CONPRI
can O
be S-MATE
used O
to O
fabricate S-MANP
other O
types O
of O
MMCs S-MATE
besides O
bronze-alumina S-MATE
due O
to O
the O
nature O
of O
the O
process S-CONPRI
. O


Design B-CONPRI
of I-CONPRI
Experiments E-CONPRI
methodology O
was O
used O
to O
study O
and O
model S-CONPRI
the O
effects O
of O
sintering S-MANP
parameters S-CONPRI
on O
the O
properties S-CONPRI
of O
the O
bronze-alumina S-MATE
fabricated O
by O
the O
TDS B-CONPRI
process E-CONPRI
. O


Due O
to O
MMCs S-MATE
unique O
properties S-CONPRI
combined O
with O
AM S-MANP
benefits O
, O
this O
novel O
method O
will O
be S-MATE
of O
great O
interest O
to O
various O
industries S-APPL
such O
as S-MATE
aerospace S-APPL
applications O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
promises O
rapid O
development O
cycles O
and O
fabrication S-MANP
of O
ready-to-use S-CONPRI
, O
geometrically-complex S-CONPRI
parts O
. O


The O
metallic B-MACEQ
parts E-MACEQ
produced O
by O
AM S-MANP
often O
contain O
highly O
non-equilibrium O
microstructures S-MATE
, O
e.g O
. O


chemical O
microsegregation S-CONPRI
and O
residual B-CONPRI
dislocation E-CONPRI
networks O
. O


While O
such O
microstructures S-MATE
can O
enhance O
some O
material B-CONPRI
properties E-CONPRI
, O
they O
are O
often O
undesirable O
. O


Many O
AM B-MACEQ
parts E-MACEQ
are O
thus O
heat-treated S-MANP
after O
fabrication S-MANP
, O
a O
process S-CONPRI
that O
significantly O
slows O
production S-MANP
. O


This O
study O
investigated O
if O
electropulsing S-CONPRI
, O
the O
process S-CONPRI
of O
sending O
high-current-density S-CONPRI
electrical B-CONPRI
pulses E-CONPRI
through O
a O
metallic B-MACEQ
part E-MACEQ
, O
could O
be S-MATE
used O
to O
modify O
the O
microstructures S-MATE
of O
AM S-MANP
316 O
L O
stainless B-MATE
steel E-MATE
( O
SS S-MATE
) O
and O
AlSi10Mg S-MATE
parts O
fabricated S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
more O
rapidly O
than O
thermal B-MANP
annealing E-MANP
. O


Electropulsing S-CONPRI
has O
shown O
promise O
as S-MATE
a O
rapid O
postprocessing S-CONPRI
method O
for O
materials B-CONPRI
fabricated E-CONPRI
using O
conventional O
methods O
, O
e.g O
. O


casting S-MANP
and O
rolling S-MANP
, O
but O
has O
never O
been O
applied O
to O
AM B-MATE
materials E-MATE
. O


For O
both O
the O
materials S-CONPRI
used O
in O
this O
study O
, O
as-fabricated O
SLM S-MANP
parts O
contained O
significant O
chemical B-CONPRI
heterogeneity E-CONPRI
, O
either O
chemical O
microsegregation S-CONPRI
( O
316 B-MATE
L I-MATE
SS E-MATE
) O
or O
a O
cellular B-CONPRI
interdendritic E-CONPRI
phase O
( O
AlSi10Mg S-MATE
) O
. O


In O
both O
cases O
, O
annealing S-MANP
times O
on O
the O
order O
of O
hours O
at O
high O
homologous B-CHAR
temperatures E-CHAR
are O
necessary O
for O
homogenization S-MANP
. O


Using O
electropulsing S-CONPRI
, O
chemical O
microsegregation S-CONPRI
was O
eliminated O
in O
316 B-MATE
L I-MATE
SS E-MATE
samples O
after O
10 O
, O
16 O
ms O
electrical B-CONPRI
pulses E-CONPRI
. O


In O
AlSi10Mg S-MATE
parts O
, O
electropulsing S-CONPRI
produced O
spheroidized S-MANP
Si-rich O
particles S-CONPRI
after O
as S-MATE
few O
as S-MATE
15 O
, O
16 O
ms O
electrical B-CONPRI
pulses E-CONPRI
with O
a O
corresponding O
increase O
in O
ductility S-PRO
. O


This O
study O
demonstrated O
that O
electropulsing S-CONPRI
can O
be S-MATE
used O
to O
modify O
the O
microstructures S-MATE
of O
AM B-MANP
metals E-MANP
. O


Architected O
structural O
metamaterials S-MATE
, O
also O
known O
as S-MATE
lattice O
, O
truss S-MACEQ
, O
or O
acoustic B-MATE
materials E-MATE
, O
provide O
opportunities O
to O
produce O
tailored O
effective O
properties S-CONPRI
that O
are O
not O
achievable O
in O
bulk O
monolithic B-MATE
materials E-MATE
. O


These O
topologies S-CONPRI
are O
typically O
designed S-FEAT
under O
the O
assumption O
of O
uniform O
, O
isotropic S-PRO
base O
material B-CONPRI
properties E-CONPRI
taken O
from O
reference O
databases S-ENAT
and O
without O
consideration O
for O
sub-optimal O
as-printed O
properties S-CONPRI
or O
off-nominal O
dimensional O
heterogeneities S-CONPRI
. O


However O
, O
manufacturing B-CONPRI
imperfections E-CONPRI
such O
as S-MATE
surface O
roughness S-PRO
are O
present O
throughout O
the O
lattices S-CONPRI
and O
their O
constituent O
struts S-MACEQ
create O
significant O
variability S-CONPRI
in O
mechanical B-CONPRI
properties E-CONPRI
and O
part O
performance S-CONPRI
. O


This O
study O
utilized O
a O
customized O
tensile B-MACEQ
bar E-MACEQ
with O
a O
gauge B-MACEQ
section E-MACEQ
consisting O
of O
five O
parallel O
struts S-MACEQ
loaded O
in O
a O
stretch O
( O
tensile S-PRO
) O
orientation S-CONPRI
to O
examine O
the O
impact S-CONPRI
of O
manufacturing S-MANP
heterogeneities S-CONPRI
on O
quasi-static B-CONPRI
deformation E-CONPRI
of O
the O
struts S-MACEQ
, O
with O
a O
focus O
on O
ultimate B-PRO
tensile I-PRO
strength E-PRO
and O
ductility S-PRO
. O


The O
customized O
tensile B-MACEQ
specimen E-MACEQ
was O
designed S-FEAT
to O
prevent O
damage S-PRO
during O
handling O
, O
despite O
the O
sub-millimeter O
thickness O
of O
each O
strut S-MACEQ
, O
and O
to O
enable O
efficient O
, O
high-throughput O
mechanical B-CHAR
testing E-CHAR
. O


The O
strut S-MACEQ
tensile O
specimens O
and O
reference O
monolithic S-PRO
tensile O
bars O
were O
manufactured S-CONPRI
using O
a O
direct B-MANP
metal I-MANP
laser I-MANP
sintering E-MANP
( O
also O
known O
as S-MATE
laser O
powder B-MANP
bed I-MANP
fusion E-MANP
or O
selective B-MANP
laser I-MANP
melting E-MANP
) O
process S-CONPRI
in O
a O
precipitation B-MANP
hardened E-MANP
stainless O
steel B-MATE
alloy E-MATE
, O
17-4PH S-MATE
, O
with O
minimum B-PARA
feature I-PARA
sizes E-PARA
ranging O
from O
0.5-0.82 O
mm S-MANP
, O
comparable O
to O
minimum O
allowable O
dimensions S-FEAT
for O
the O
process S-CONPRI
. O


Over O
70 O
tensile B-CHAR
stress-strain I-CHAR
tests E-CHAR
were O
performed O
revealing O
that O
the O
effective O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
struts S-MACEQ
were O
highly O
stochastic S-CONPRI
, O
considerably O
inferior O
to O
the O
properties S-CONPRI
of O
larger O
as-printed O
reference O
tensile B-MACEQ
bars E-MACEQ
, O
and O
well O
below O
the O
minimum O
allowable O
values O
for O
the O
alloy S-MATE
. O


Pre- O
and O
post-test O
non-destructive B-CHAR
analyses E-CHAR
revealed O
that O
the O
primary B-CONPRI
source E-CONPRI
of O
the O
reduced O
properties S-CONPRI
and O
increased O
variability S-CONPRI
was O
attributable O
to O
heterogeneous S-CONPRI
surface O
topography S-CHAR
with O
stress-concentrating S-CONPRI
contours S-FEAT
and O
commensurate O
reduction S-CONPRI
in O
effective O
load-bearing B-FEAT
area E-FEAT
. O


This O
study O
investigates S-CONPRI
the O
feasibility S-CONPRI
of O
achieving O
high B-PARA
deposition I-PARA
rate E-PARA
using O
wire B-MANP
+ I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
in O
stainless B-MATE
steel E-MATE
to O
reduce O
lead B-PARA
time E-PARA
and O
cost B-CONPRI
of I-CONPRI
manufacturing E-CONPRI
. O


The O
pulse O
MIG B-MANP
welding E-MANP
technique O
with O
a O
tandem B-MACEQ
torch E-MACEQ
was O
used O
for O
depositing O
martensitic B-MATE
stainless I-MATE
steel E-MATE
17-4 O
pH S-CONPRI
. O


The O
mechanical S-APPL
and O
metallurgical S-APPL
properties O
of O
the O
manufactured S-CONPRI
component S-MACEQ
were O
analysed O
to O
evaluate O
the O
limitations O
and O
the O
extent O
to O
which O
the O
rate B-CONPRI
of I-CONPRI
deposition E-CONPRI
reaches O
a O
maximum O
without O
any O
failure S-CONPRI
or O
defect S-CONPRI
being O
evident O
in O
the O
manufactured S-CONPRI
component S-MACEQ
. O


Deposition B-PARA
rate E-PARA
of O
9.5 O
kg/h O
was O
achieved O
. O


The O
hardness S-PRO
was O
matched O
for O
the O
as S-MATE
deposited O
condition O
. O


Thermal B-PRO
conductivities E-PRO
of O
metal B-MATE
powders E-MATE
for O
additive B-MANP
manufacturing E-MANP
were O
measured O
. O


Infiltrating B-CONPRI
gas E-CONPRI
pressure O
and O
composition S-CONPRI
influence O
the O
powder S-MATE
thermal O
conductivity S-PRO
. O


He O
infiltration S-CONPRI
yields O
200 O
% O
higher O
thermal B-PRO
conductivity E-PRO
than O
Ar S-ENAT
or O
N2 S-MATE
at O
1 O
atm S-CHAR
. O


Powder S-MATE
thermal O
conductivities O
depend O
weakly O
on O
temperature S-PARA
from O
295 O
K S-MATE
to O
470 O
K. O
Gas-enhanced O
thermal B-PRO
conductivity E-PRO
is O
consistent O
with O
an O
effective O
medium O
model S-CONPRI
. O


The O
thermal B-PRO
conductivities E-PRO
of O
five O
metal B-MATE
powders E-MATE
for O
powder B-MANP
bed I-MANP
additive I-MANP
manufacturing E-MANP
( O
Inconel B-MATE
718 E-MATE
, O
17-4 B-MATE
stainless I-MATE
steel E-MATE
, O
Inconel B-MATE
625 E-MATE
, O
Ti-6Al-4V S-MATE
, O
and O
316L B-MATE
stainless I-MATE
steel E-MATE
) O
were O
measured O
using O
the O
transient S-CONPRI
hot B-CHAR
wire I-CHAR
method E-CHAR
. O


These O
measurements O
were O
conducted O
with O
three O
infiltrating B-CONPRI
gases E-CONPRI
( O
argon S-MATE
, O
nitrogen S-MATE
, O
and O
helium S-MATE
) O
within O
a O
temperature B-PARA
range E-PARA
of O
295–470 O
K S-MATE
and O
a O
gas S-CONPRI
pressure O
range S-PARA
of O
1.4–101 O
kPa O
. O


The O
measurements O
of O
thermal B-PRO
conductivity E-PRO
indicate O
that O
the O
pressure S-CONPRI
and O
the O
composition S-CONPRI
of O
the O
gas S-CONPRI
have O
a O
significant O
influence O
on O
the O
effective B-PARA
thermal I-PARA
conductivity E-PARA
of O
the O
powder S-MATE
, O
but O
that O
the O
metal B-MATE
powder E-MATE
properties O
and O
temperature S-PARA
do O
not O
. O


Our O
measurements O
improve O
the O
accuracy S-CHAR
upon O
which O
laser S-ENAT
parameters O
can O
be S-MATE
optimized O
in O
order O
to O
improve O
thermal B-CONPRI
control E-CONPRI
of O
powder B-MACEQ
beds E-MACEQ
in O
selective B-MANP
laser I-MANP
melting I-MANP
processes E-MANP
, O
especially O
in O
overhanging O
and O
cellular O
geometries S-CONPRI
where O
heat B-CONPRI
dissipation E-CONPRI
by O
the O
powder S-MATE
is O
critical O
. O


A O
fundamental O
understanding O
of O
spatial O
and O
temporal O
thermal B-CONPRI
distributions E-CONPRI
is O
crucial O
for O
predicting O
solidification S-CONPRI
and O
solid-state B-CONPRI
microstructural E-CONPRI
development O
in O
parts O
made O
by O
additive B-MANP
manufacturing E-MANP
. O


While O
sophisticated O
numerical B-CONPRI
techniques E-CONPRI
that O
are O
based O
on O
finite B-CONPRI
element E-CONPRI
or O
finite B-CONPRI
volume I-CONPRI
methods E-CONPRI
are O
useful O
for O
gaining O
insight O
into O
these O
phenomena O
at O
the O
length B-CHAR
scale E-CHAR
of O
the O
melt B-MATE
pool E-MATE
( O
100–500 O
μm O
) O
, O
they O
are O
ill-suited O
for O
predicting O
engineering S-APPL
trends O
over O
full O
part O
cross-sections S-CONPRI
( O
> O
10 O
× O
10 O
cm O
) O
or O
many O
layers O
over O
long O
process B-CONPRI
times E-CONPRI
( O
> O
many O
days O
) O
due O
to O
the O
necessity O
of O
fully O
resolving O
the O
heat B-CONPRI
source E-CONPRI
characteristics O
. O


On O
the O
other O
hand O
, O
it O
is O
extremely O
difficult O
to O
resolve O
the O
highly O
dynamic S-CONPRI
nature O
of O
the O
process S-CONPRI
using O
purely O
in-situ S-CONPRI
characterization O
techniques O
[ O
1 O
] O
. O


This O
paper O
proposes O
a O
pragmatic O
alternative O
based O
on O
a O
semi-analytical B-CONPRI
approach E-CONPRI
to O
predicting O
the O
transient B-CONPRI
heat I-CONPRI
conduction E-CONPRI
during O
powder B-MANP
bed I-MANP
metal I-MANP
additive I-MANP
manufacturing I-MANP
processes E-MANP
. O


The O
model S-CONPRI
calculations O
were O
theoretically O
verified O
for O
selective B-MANP
laser I-MANP
melting E-MANP
of O
AlSi10Mg S-MATE
and O
electron B-MANP
beam I-MANP
melting E-MANP
of O
IN718 S-MATE
powders O
for O
simple S-MANP
cross-sectional B-CONPRI
geometries E-CONPRI
and O
the O
transient S-CONPRI
results O
are O
compared O
to O
steady B-CONPRI
state E-CONPRI
predictions S-CONPRI
from O
the O
Rosenthal B-CONPRI
equation E-CONPRI
. O


It O
is O
shown O
that O
the O
transient S-CONPRI
effects O
of O
the O
scan O
strategy O
create O
significant O
variations S-CONPRI
in O
the O
melt B-MATE
pool E-MATE
geometry S-CONPRI
and O
solid-liquid B-CONPRI
interface I-CONPRI
velocity E-CONPRI
, O
especially O
as S-MATE
the O
thermal B-CONPRI
diffusivity E-CONPRI
of O
the O
material S-MATE
decreases O
and O
the O
pre-heat S-CONPRI
of O
the O
process S-CONPRI
increases O
. O


With O
positive O
verification S-CONPRI
of O
the O
strategy O
, O
the O
model S-CONPRI
was O
then O
experimentally B-CONPRI
validated E-CONPRI
to O
simulate O
two O
point-melt S-CONPRI
scan O
strategies O
during O
electron B-MANP
beam I-MANP
melting E-MANP
of O
IN718 S-MATE
, O
one O
intended O
to O
produce O
a O
columnar O
and O
one O
an O
equiaxed B-CONPRI
grain E-CONPRI
structure O
. O


Through O
comparison O
of O
the O
solidification S-CONPRI
conditions O
( O
i.e O
. O


transient S-CONPRI
and O
spatial B-FEAT
variations E-FEAT
of O
thermal B-PARA
gradient E-PARA
and O
liquid-solid B-CONPRI
interface E-CONPRI
velocity O
) O
predicted S-CONPRI
by O
the O
model S-CONPRI
to O
phenomenological S-CONPRI
CET B-CONPRI
theory E-CONPRI
, O
the O
model B-CONPRI
accurately E-CONPRI
predicted O
the O
experimental S-CONPRI
grain O
structures O
. O


Existing O
commercial O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
printing O
systems O
based O
on O
powder B-MANP
bed I-MANP
fusion E-MANP
approach O
can O
normally O
only O
print S-MANP
a O
single O
material S-MATE
in O
each O
component S-MACEQ
. O


In O
this O
paper O
, O
functionally B-MATE
gradient I-MATE
materials E-MATE
( O
FGM S-MANP
) O
with O
composition S-CONPRI
variation O
from O
a O
copper B-MATE
alloy E-MATE
to O
a O
soda-lime B-MATE
glass E-MATE
were O
manufactured S-CONPRI
using O
a O
proprietary O
nozzle-based O
multi-material B-MANP
selective I-MANP
laser I-MANP
melting E-MANP
( O
MMSLM S-MANP
) O
system O
. O


An O
in B-CONPRI
situ E-CONPRI
powder O
mixing S-CONPRI
system O
was O
designed S-FEAT
to O
mix O
both O
metal S-MATE
and O
glass S-MATE
powders O
at O
selective O
ratios O
and O
the O
mixed O
powders S-MATE
were O
dispensed O
with O
an O
ultrasonic B-MACEQ
vibration I-MACEQ
powder I-MACEQ
feeding I-MACEQ
system E-MACEQ
with O
multiple O
nozzles S-MACEQ
. O


From O
the O
cross B-CONPRI
section E-CONPRI
analysis O
of O
the O
gradient B-CONPRI
structures E-CONPRI
, O
glass S-MATE
proportion O
increased O
gradually O
from O
the O
metallic B-MATE
matrix I-MATE
composite E-MATE
( O
MMC S-MATE
) O
, O
transition B-CONPRI
phase E-CONPRI
to O
ceramic B-MATE
matrix I-MATE
composite E-MATE
( O
CMC S-MATE
) O
. O


The O
pure O
copper B-MATE
alloy E-MATE
joined O
the O
MMC S-MATE
part O
and O
the O
pure O
glass S-MATE
phase O
penetrated O
into O
the O
CMC S-MATE
part O
during O
laser B-CONPRI
processing E-CONPRI
, O
which O
anchored O
the O
glass S-MATE
phase O
, O
as S-MATE
the O
main O
mechanism S-CONPRI
of O
combining O
pure B-MATE
metal E-MATE
and O
pure O
glass S-MATE
by O
FGM S-MANP
in O
3D B-APPL
printed I-APPL
parts E-APPL
. O


From O
results O
of O
indentation S-CONPRI
, O
tensile S-PRO
and O
shear B-CHAR
tests E-CHAR
on O
the O
gradient O
material S-MATE
samples O
, O
it O
showed O
that O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
FGM S-MANP
gradually O
changed O
from O
ductility S-PRO
( O
metal S-MATE
side O
) O
to O
brittle S-PRO
( O
glass S-MATE
side O
) O
. O


The O
weakest O
part O
of O
the O
FGM S-MANP
structure O
occurred O
at O
the O
interface S-CONPRI
between O
transition B-CONPRI
phase E-CONPRI
and O
the O
CMC S-MATE
, O
which O
was O
also O
the O
interface S-CONPRI
between O
the O
ductile S-PRO
and O
brittle S-PRO
phases O
. O


The O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
metal B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
can O
quickly O
produce O
complex O
parts O
with O
mechanical B-CONPRI
properties E-CONPRI
comparable O
to O
that O
of O
wrought B-MATE
materials E-MATE
. O


However O
, O
thermal B-PRO
stress E-PRO
accumulated O
during O
Metal S-MATE
PBF O
may O
induce O
part O
distortion S-CONPRI
and O
even O
cause O
failure S-CONPRI
of O
the O
entire O
process S-CONPRI
. O


This O
manuscript S-CONPRI
is O
the O
second O
part O
of O
two O
companion O
manuscripts S-CONPRI
that O
collectively O
present O
a O
part-scale O
simulation S-ENAT
method O
for O
fast O
prediction S-CONPRI
of O
thermal B-CONPRI
distortion E-CONPRI
in O
Metal S-MATE
PBF O
. O


The O
first O
part O
provides O
a O
fast O
prediction S-CONPRI
of O
the O
temperature S-PARA
history O
in O
the O
part O
via O
a O
thermal B-CONPRI
circuit I-CONPRI
network E-CONPRI
( O
TCN S-CONPRI
) O
model S-CONPRI
. O


This O
second O
part O
uses O
the O
temperature S-PARA
history O
from O
the O
TCN S-CONPRI
to O
inform O
a O
model S-CONPRI
of O
thermal B-CONPRI
distortion E-CONPRI
using O
a O
quasi-static B-CONPRI
thermo-mechanical I-CONPRI
model E-CONPRI
( O
QTM S-CONPRI
) O
. O


The O
QTM B-CONPRI
model E-CONPRI
distinguished O
two O
periods O
of O
Metal S-MATE
PBF O
, O
the O
thermal B-CONPRI
loading E-CONPRI
period O
and O
the O
stress B-CONPRI
relaxation E-CONPRI
period O
. O


In O
the O
thermal B-CONPRI
loading E-CONPRI
period O
, O
the O
layer-by-layer S-CONPRI
build B-PARA
cycles E-PARA
of O
Metal S-MATE
PBF O
are O
simulated O
, O
and O
the O
thermal B-PRO
stress E-PRO
accumulated O
in O
the O
build S-PARA
process O
is O
predicted S-CONPRI
. O


In O
the O
stress B-CONPRI
relaxation E-CONPRI
period O
, O
the O
removal O
of O
parts O
from O
the O
substrate S-MATE
is O
simulated O
, O
and O
the O
off-substrate O
part O
distortion S-CONPRI
and O
residual B-PRO
stress E-PRO
are O
predicted S-CONPRI
. O


Validation S-CONPRI
of O
part O
distortion S-CONPRI
predicted O
by O
the O
QTM B-CONPRI
model E-CONPRI
against O
both O
experiment S-CONPRI
and O
data S-CONPRI
in O
literature O
showed O
a O
relative B-CONPRI
error E-CONPRI
less O
than O
20 O
% O
. O


This O
QTM S-CONPRI
, O
together O
with O
the O
TCN S-CONPRI
, O
offers O
a O
framework S-CONPRI
for O
rapid O
, O
part-scale O
simulations S-ENAT
of O
Metal S-MATE
PBF O
that O
can O
be S-MATE
used O
to O
optimize O
the O
build S-PARA
process O
and O
parameters S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
are O
subject O
to O
lower O
stability S-PRO
compared O
to O
their O
traditional O
counterparts O
. O


The O
process S-CONPRI
inconsistency O
leads O
to O
anomalies S-CONPRI
in O
the O
build S-PARA
, O
which O
hinders O
AM S-MANP
’ O
s S-MATE
broader O
adoption O
to O
critical O
structural B-CONPRI
component E-CONPRI
manufacturing S-MANP
. O


Therefore O
, O
it O
is O
crucial O
to O
detect O
any O
process B-CONPRI
change/anomaly E-CONPRI
in O
a O
timely O
and O
accurate S-CHAR
manner O
for O
potential O
corrective O
operations O
. O


Real-time O
thermal B-FEAT
image E-FEAT
streams O
captured O
from O
AM B-MANP
processes E-MANP
are O
regarded O
as S-MATE
most O
informative O
signatures O
of O
the O
process S-CONPRI
stability O
. O


Existing O
state-of-the-art S-CONPRI
studies O
on O
thermal B-FEAT
image E-FEAT
streams O
focus O
merely O
on O
in B-CONPRI
situ E-CONPRI
sensing O
, O
feature B-ENAT
extraction E-ENAT
, O
and O
their O
relationship O
with O
process S-CONPRI
setup O
parameters S-CONPRI
and O
material B-CONPRI
properties E-CONPRI
. O


The O
objective O
of O
this O
paper O
is O
to O
develop O
a O
statistical B-CONPRI
process I-CONPRI
control E-CONPRI
( O
SPC S-CONPRI
) O
approach O
to O
detect O
process S-CONPRI
changes O
as S-MATE
soon O
as S-MATE
it O
occurs O
based O
on O
predefined O
distribution S-CONPRI
of O
the O
monitoring O
statistics S-CONPRI
. O


There O
are O
two O
major O
challenges O
: O
1 O
) O
complex O
spatial B-CONPRI
interdependence E-CONPRI
exists O
in O
the O
thermal B-FEAT
images E-FEAT
and O
current O
engineering B-CONPRI
knowledge E-CONPRI
is O
not O
sufficient O
to O
describe O
all O
the O
variability S-CONPRI
, O
and O
2 O
) O
the O
thermal B-FEAT
images E-FEAT
suffer O
from O
a O
large O
data S-CONPRI
volume O
, O
a O
low O
signal-to-noise B-PARA
ratio E-PARA
, O
and O
an O
ill O
structure S-CONPRI
with O
missing O
data S-CONPRI
. O


To O
tackle O
these O
challenges O
, O
multilinear B-CONPRI
principal I-CONPRI
component I-CONPRI
analysis E-CONPRI
( O
MPCA S-CONPRI
) O
approach O
is O
used O
to O
extract O
low O
dimensional O
features O
and O
residuals S-CONPRI
. O


Subsequently O
, O
an O
online O
dual O
control B-CONPRI
charting E-CONPRI
system O
is O
proposed O
by O
leveraging O
multivariate S-CONPRI
T2 O
and O
Q O
control B-CONPRI
charts E-CONPRI
to O
detect O
changes O
in O
extracted S-CONPRI
low O
dimensional O
features O
and O
residuals S-CONPRI
, O
respectively O
. O


A O
real-world O
case B-CONPRI
study E-CONPRI
of O
thin O
wall O
fabrication S-MANP
using O
a O
Laser B-MANP
Engineered I-MANP
Net I-MANP
Shaping E-MANP
( O
LENS S-MANP
) O
process S-CONPRI
is O
used O
to O
illustrate O
the O
effectiveness S-CONPRI
of O
the O
proposed O
approach O
, O
and O
the O
accuracy S-CHAR
of O
process S-CONPRI
anomaly S-CONPRI
detection O
is O
validated O
based O
on O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
information O
collected O
from O
the O
final O
build S-PARA
offline O
. O


In O
order O
to O
establish O
modeling S-ENAT
and O
simulation S-ENAT
( O
M B-ENAT
& I-ENAT
S E-ENAT
) O
in O
support S-APPL
of O
Additive B-MANP
Manufacturing I-MANP
Processes E-MANP
( O
AMP S-MANP
) O
control O
for O
tailoring O
functional B-CONPRI
component E-CONPRI
performance O
by O
design S-FEAT
, O
a O
methodology S-CONPRI
is O
introduced O
for O
identifying O
relevant O
M B-ENAT
& I-ENAT
S E-ENAT
challenges O
. O


This O
exercise O
is O
meant O
to O
spur O
research S-CONPRI
addressing O
the O
specific O
issue O
of O
tailoring O
functional B-CONPRI
component E-CONPRI
performance O
by O
design S-FEAT
, O
as S-MATE
well O
as S-MATE
AMP-related S-MANP
process O
optimization S-CONPRI
more O
generally O
. O


A O
composition B-CONPRI
abstraction E-CONPRI
that O
connects O
process B-CONPRI
control E-CONPRI
with O
functional O
performance S-CONPRI
of O
the O
multiscale B-CONPRI
modeling E-CONPRI
processes O
is O
presented O
, O
from O
both O
the O
forward O
and O
inverse B-CONPRI
analysis E-CONPRI
perspectives O
. O


A O
brief O
ontology S-CONPRI
is O
introduced O
that O
describes O
the O
ordering O
of O
dependency O
and O
membership O
of O
all O
components S-MACEQ
of O
a O
model S-CONPRI
, O
which O
serves O
the O
purpose O
of O
isolating S-CONPRI
potential O
challenge O
areas S-PARA
. O


Certain O
features O
of O
AMPs S-MANP
that O
are O
usually O
ignored O
by O
the O
community O
during O
modeling S-ENAT
are O
a O
specific O
focus O
. O


Furthermore O
, O
two O
semantically S-CONPRI
reduced O
modeling S-ENAT
approaches O
involving O
continuum B-CONPRI
abstractions E-CONPRI
for O
the O
computational B-CONPRI
domains E-CONPRI
are O
presented O
. O


The O
solutions O
of O
the O
relevant O
system O
of O
coupled O
partial B-CONPRI
differential I-CONPRI
equations E-CONPRI
are O
used O
to O
demonstrate O
both O
the O
positive O
and O
negative O
implications O
of O
a O
series O
of O
assumptions O
routinely O
made O
in O
M B-ENAT
& I-ENAT
S E-ENAT
of O
AMPs S-MANP
. O


Finally O
, O
a O
discrete B-CONPRI
element I-CONPRI
method I-CONPRI
model E-CONPRI
is O
presented O
to O
highlight O
the O
challenges O
introduced O
by O
the O
specific O
nature O
of O
this O
approach O
. O


The O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
metal B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
can O
quickly O
produce O
complex O
parts O
with O
mechanical B-CONPRI
properties E-CONPRI
comparable O
to O
wrought B-MATE
materials E-MATE
. O


However O
, O
thermal B-PRO
stress E-PRO
accumulated O
during O
PBF S-MANP
induces O
part O
distortion S-CONPRI
, O
potentially O
yielding O
parts O
out O
of O
specification S-PARA
and O
frequently O
process B-CONPRI
failure E-CONPRI
. O


This O
manuscript S-CONPRI
is O
the O
first O
of O
two O
companion O
manuscripts S-CONPRI
that O
introduce O
a O
computationally O
efficient O
distortion S-CONPRI
and O
stress S-PRO
prediction B-CONPRI
algorithm E-CONPRI
that O
is O
designed S-FEAT
to O
drastically O
reduce O
compute B-PARA
time E-PARA
when O
integrated O
in O
to O
a O
process B-CONPRI
design I-CONPRI
optimization E-CONPRI
routine O
. O


In O
this O
first O
manuscript S-CONPRI
, O
we O
introduce O
a O
thermal B-CONPRI
circuit I-CONPRI
network E-CONPRI
( O
TCN S-CONPRI
) O
model S-CONPRI
to O
estimate O
the O
part O
temperature S-PARA
history O
during O
PBF S-MANP
, O
a O
major O
computational O
bottleneck S-CONPRI
in O
PBF B-CONPRI
simulation E-CONPRI
. O


In O
the O
TCN B-CONPRI
model E-CONPRI
, O
we O
are O
modeling S-ENAT
conductive B-CONPRI
heat I-CONPRI
transfer E-CONPRI
through O
both O
the O
part O
and O
support B-FEAT
structure E-FEAT
by O
dividing O
the O
part O
into O
thermal B-CONPRI
circuit I-CONPRI
elements E-CONPRI
( O
TCEs S-CONPRI
) O
, O
which O
consists O
of O
thermal O
nodes O
represented O
by O
thermal B-CONPRI
capacitances E-CONPRI
that O
are O
connected O
by O
resistors S-MACEQ
, O
and O
then O
building O
the O
TCN S-CONPRI
in O
a O
layer-by-layer S-CONPRI
manner O
to O
replicate O
the O
PBF S-MANP
process O
. O


In O
comparison O
to O
conventional O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
( O
FEM S-CONPRI
) O
thermal B-CONPRI
modeling E-CONPRI
, O
the O
TCN B-CONPRI
model E-CONPRI
predicts O
the O
temperature S-PARA
history O
of O
metal S-MATE
PBF O
AM B-MACEQ
parts E-MACEQ
with O
more O
than O
two O
orders O
of O
magnitude S-PARA
faster O
computational B-PARA
speed E-PARA
, O
while O
sacrificing O
less O
than O
15 O
% O
accuracy S-CHAR
. O


The O
companion O
manuscript S-CONPRI
illustrates O
how O
the O
temperature S-PARA
history O
is O
integrated O
into O
a O
thermomechanical B-CONPRI
model E-CONPRI
to O
predict O
thermal B-PRO
stress E-PRO
and O
distortion S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
a O
set S-APPL
of O
emerging O
technologies S-CONPRI
that O
can O
produce O
physical O
objects O
with O
complex O
geometrical O
shapes O
directly O
from O
a O
digital O
model S-CONPRI
. O


However O
, O
achieving O
the O
full O
potential O
of O
AM S-MANP
is O
hampered O
by O
many O
challenges O
, O
including O
the O
lack O
of O
predictive B-CONPRI
models E-CONPRI
that O
correlate O
processing O
parameters S-CONPRI
with O
the O
properties S-CONPRI
of O
the O
processed S-CONPRI
part O
. O


We O
develop O
a O
Gaussian S-CONPRI
process-based O
predictive B-CONPRI
model E-CONPRI
for O
the O
learning O
and O
prediction S-CONPRI
of O
the O
porosity S-PRO
in O
metallic B-MACEQ
parts E-MACEQ
produced O
using O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
– O
a O
laser-based O
AM B-MANP
process E-MANP
) O
. O


More O
specifically O
, O
a O
spatial O
Gaussian S-CONPRI
process O
regression B-CONPRI
model E-CONPRI
is O
first O
developed O
to O
model S-CONPRI
part O
porosity S-PRO
as S-MATE
a O
function O
of O
SLM S-MANP
process B-CONPRI
parameters E-CONPRI
. O


Next O
, O
a O
Bayesian O
inference B-CONPRI
framework E-CONPRI
is O
used O
to O
estimate O
the O
statistical O
model S-CONPRI
parameters O
, O
and O
the O
porosity S-PRO
of O
the O
part O
at O
any O
given O
setting O
is O
predicted S-CONPRI
using O
the O
Kriging O
method O
. O


A O
case B-CONPRI
study E-CONPRI
is O
conducted O
to O
validate O
this O
predictive O
framework S-CONPRI
through O
predicting O
the O
porosity S-PRO
of O
17-4 B-MATE
PH I-MATE
stainless I-MATE
steel E-MATE
manufacturing O
on O
a O
ProX O
100 O
selective B-MANP
laser I-MANP
melting E-MANP
system O
. O


This O
paper O
presents O
a O
concept O
of O
solidifying O
small O
quantities O
of O
metal B-MATE
powders E-MATE
in O
an O
additive S-MATE
manner O
, O
using O
localized O
microwave S-ENAT
heating S-MANP
( O
LMH O
) O
. O


The O
experimental S-CONPRI
results O
show O
solidification S-CONPRI
of O
metal B-MATE
powders E-MATE
in O
forms O
of O
spheres O
and O
rods O
( O
of O
∼2 O
mm S-MANP
diameter S-CONPRI
) O
and O
extension O
of O
these O
rods O
by O
adding O
batches O
of O
powder S-MATE
and O
consolidating O
them O
locally O
as S-MATE
building O
blocks O
by O
LMH O
. O


A O
theoretical B-CONPRI
model E-CONPRI
applied O
for O
the O
LMH O
interaction O
with O
metal B-MATE
powders E-MATE
attributes O
a O
magnetic O
heating S-MANP
effect O
also O
to O
powders S-MATE
made O
of O
non-magnetic O
metals S-MATE
, O
due O
to O
eddy O
currents O
. O


The O
experimental S-CONPRI
observations O
and O
numerical O
results O
also O
suggest O
that O
micro-plasma O
discharges O
between O
the O
powder B-MATE
particles E-MATE
initiate O
their O
heating S-MANP
process O
. O


The O
additive S-MATE
LMH O
approach O
presented O
here O
is O
intended O
to O
extend O
microwave B-MANP
sintering E-MANP
capabilities O
, O
mainly O
known O
in O
volumetric O
molds S-MACEQ
, O
also O
to O
applications O
in O
the O
framework S-CONPRI
of O
rapid B-ENAT
prototyping E-ENAT
, O
additive B-MANP
manufacturing E-MANP
, O
and O
3D-printing S-MANP
. O


Oscillating O
laser-arc O
hybrid O
additive B-MANP
manufacturing E-MANP
( O
O-LHAM O
) O
is O
developed O
. O


Surface B-PRO
roughness E-PRO
of O
O-LHAM O
reduces O
to O
20 O
% O
of O
WAAM S-MANP
via O
laser-arc O
synergic O
effects O
. O


High O
porosity S-PRO
easily O
occurs O
within O
laser-arc O
hybrid O
additive B-MANP
manufacturing E-MANP
( O
LHAM O
) O
can O
be S-MATE
suppressed O
via O
periodical O
beam S-MACEQ
oscillation O
. O


O-LHAM O
has O
better O
tensile B-PRO
properties E-PRO
because O
of O
finer B-FEAT
microstructure E-FEAT
and O
lower O
texture S-FEAT
content O
. O


A O
novel O
additive B-MANP
manufacturing E-MANP
approach O
integrating O
an O
oscillating O
laser B-CONPRI
beam E-CONPRI
and O
a O
cold B-MANP
metal I-MANP
transfer E-MANP
arc S-CONPRI
was O
developed O
to O
balance O
the O
surface B-CHAR
accuracy E-CHAR
, O
deposition S-CONPRI
efficiency O
, O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
deposited O
parts O
. O


The O
new O
method O
was O
termed O
as S-MATE
oscillating O
laser-arc O
hybrid O
additive B-MANP
manufacturing E-MANP
( O
O-LHAM O
) O
. O


The O
sample S-CONPRI
properties S-CONPRI
of O
the O
wire-arc B-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
, O
laser-arc O
hybrid O
additive B-MANP
manufacturing E-MANP
( O
LHAM O
) O
, O
and O
O-LHAM O
processes S-CONPRI
were O
compared O
. O


First O
, O
both O
the O
surface B-PRO
roughness E-PRO
and O
minimum O
processing O
margin O
of O
the O
O-LHAM O
sample S-CONPRI
were O
reduced O
to O
20 O
% O
of O
the O
WAAM S-MANP
sample S-CONPRI
, O
because O
the O
droplet S-CONPRI
transfer O
was O
stabilized O
by O
the O
laser-arc O
synergic O
effects O
. O


Second O
, O
the O
grains S-CONPRI
were O
refined O
, O
and O
the O
{ O
001 O
} O
< O
100 O
> O
-cube O
texture S-FEAT
content O
was O
decreased O
to O
1.6 O
% O
, O
as S-MATE
the O
oscillation O
induced O
a O
strong O
stirring O
effect O
on O
the O
molten B-CONPRI
pool E-CONPRI
. O


The O
nondestructive O
X-ray S-CHAR
test O
suggested O
that O
the O
visible O
porosity S-PRO
within O
the O
O-LHAM O
sample S-CONPRI
was O
suppressed O
by O
beam S-MACEQ
oscillation O
when O
the O
periodically O
oscillated O
laser S-ENAT
keyhole O
could O
“ O
capture O
” O
the O
bubbles O
, O
while O
the O
porosity S-PRO
within O
the O
LHAM O
sample S-CONPRI
reached O
24 O
% O
. O


Due O
to O
the O
microstructure S-CONPRI
changes O
and O
the O
porosity S-PRO
suppression O
, O
the O
O-LHAM O
almost O
eliminated O
the O
anisotropy S-PRO
of O
tensile B-PRO
strength E-PRO
and O
improved O
the O
elongation S-PRO
by O
up O
to O
34 O
% O
. O


Despite O
recent O
advances O
in O
our O
understanding O
of O
the O
unique O
mechanical S-APPL
behavior O
of O
natural O
structural O
materials S-CONPRI
such O
as S-MATE
nacre O
and O
human O
bone S-BIOP
, O
traditional B-MANP
manufacturing E-MANP
strategies O
limit S-CONPRI
our O
ability O
to O
mimic S-MACEQ
such O
nature-inspired O
structures O
using O
existing O
structural O
materials S-CONPRI
and O
manufacturing B-MANP
processes E-MANP
. O


To O
this O
end O
, O
we O
introduce O
a O
customizable O
single-step O
approach O
for O
additively O
fabricating S-MANP
geometrically-free O
metallic-based O
structural O
composites S-MATE
showing O
directionally-tailored O
, O
location-specific O
properties S-CONPRI
. O


To O
exemplify O
this O
capability O
, O
we O
present O
a O
layered O
metal-ceramic O
composite S-MATE
not O
previously O
reported O
exhibiting O
significant O
directional O
and O
site-specific O
dependence O
of O
properties S-CONPRI
along O
with O
crack O
arrest O
ability O
difficult O
to O
achieve O
using O
traditional B-MANP
manufacturing E-MANP
approaches O
. O


Our O
results O
indicate O
that O
nature-inspired O
microstructural S-CONPRI
designs S-FEAT
towards O
directional O
properties S-CONPRI
can O
be S-MATE
realized O
in O
structural B-CONPRI
components E-CONPRI
using O
a O
novel O
additive B-MANP
manufacturing E-MANP
approach O
. O


Additive B-MANP
Layer I-MANP
Manufacturing E-MANP
( O
ALM S-MANP
) O
of O
metals S-MATE
is O
rapidly O
changing O
the O
landscape O
of O
industrial S-APPL
manufacturing O
. O


This O
paper O
presents O
the O
PALMS O
process S-CONPRI
, O
derived O
from O
electrolytic O
plasma S-CONPRI
polishing O
, O
as S-MATE
a O
solution S-CONPRI
to O
this O
problem O
. O


The O
viability O
of O
the O
process S-CONPRI
on O
a O
scale O
compatible O
with O
commercial O
use O
is O
demonstrated O
with O
a O
prototype S-CONPRI
industrial S-APPL
implementation O
. O


PALMS O
was O
applied O
on O
AISI O
316 O
stainless B-MATE
steel E-MATE
pieces O
produced O
either O
by O
ALM S-MANP
or O
by O
conventional B-MANP
machining E-MANP
( O
CM O
. O


) O
Surface S-CONPRI
states O
, O
microstructures S-MATE
and O
other O
properties S-CONPRI
were O
compared O
pre- O
and O
post-PALMS O
. O


Significant O
improvements O
in O
surface S-CONPRI
state O
were O
observed O
after O
a O
10 O
min O
treatment O
, O
with O
a O
5-fold O
reduction S-CONPRI
in O
roughness S-PRO
. O


ALM S-MANP
surfaces O
were O
not O
affected O
negatively O
by O
PALMS O
in O
any O
way O
measured O
, O
and O
showed O
slight O
improvements O
in O
hardness S-PRO
and O
pore B-PRO
density E-PRO
. O


Two O
PVD S-MANP
coatings S-APPL
( O
TiN S-MATE
and O
WCC O
) O
were O
finally O
applied O
Post-PALMS O
, O
to O
test O
the O
compatibility O
of O
the O
process S-CONPRI
with O
further O
industrially O
relevant O
surface B-MANP
treatments E-MANP
. O


PALMS O
enables O
good O
coating S-APPL
adhesion S-PRO
on O
ALM S-MANP
pieces O
, O
with O
improved O
friction S-CONPRI
and O
wear B-CONPRI
properties E-CONPRI
compared O
to O
their O
CM O
counterparts O
. O


As S-MATE
metal O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
becomes O
more O
widely O
adopted O
in O
the O
aerospace S-APPL
and O
orthopedic O
industries S-APPL
, O
there O
is O
increasing O
demand O
to O
improve O
part O
quality S-CONPRI
and O
reduce O
overall O
cost O
. O


The O
high O
cost O
of O
powder B-MACEQ
feedstock E-MACEQ
has O
raised O
interest O
in O
recovering O
unmelted O
powder S-MATE
in O
the O
build B-PARA
chamber E-PARA
and O
its O
reuse O
in O
subsequent O
builds S-CHAR
. O


While O
degradation S-CONPRI
in O
powder S-MATE
properties O
with O
recovery O
and O
reuse O
can O
cause O
degradation S-CONPRI
in O
part O
properties S-CONPRI
, O
this O
topic O
has O
received O
rather O
limited O
attention O
. O


In O
this O
study O
the O
properties S-CONPRI
of O
Ti6Al4V S-MATE
metal B-MATE
powder E-MATE
are O
evaluated O
over O
30 O
build B-PARA
cycles E-PARA
in O
Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM S-MANP
) O
AM S-MANP
. O


The O
morphological O
, O
microstructural S-CONPRI
, O
mechanical S-APPL
, O
and O
chemical O
changes O
are O
evaluated O
in O
cross-sectioned O
powder B-MATE
particles E-MATE
and O
compared O
to O
isolated O
control O
samples S-CONPRI
to O
understand O
the O
mechanisms O
of O
degradation S-CONPRI
. O


Results O
show O
that O
in O
response O
to O
the O
elevated O
build B-PARA
chamber E-PARA
temperature O
, O
the O
powder S-MATE
undergoes O
a O
sub-beta-transus O
aging O
heat B-MANP
treatment E-MANP
with O
powder S-MATE
reuse O
. O


Based O
on O
nanoindentation S-CHAR
hardness S-PRO
measurements O
, O
the O
particles S-CONPRI
undergo O
an O
increase O
in O
near-surface O
hardness S-PRO
( O
up O
to O
2 O
GPa S-PRO
) O
with O
respect O
to O
the O
core S-MACEQ
. O


Moreover O
, O
tint O
etching S-MANP
revealed O
an O
oxidized S-MANP
surface O
layers O
consistent O
with O
alpha O
case O
formation O
. O


The O
particle S-CONPRI
hardening S-MANP
appears O
to O
result O
from O
oxygen S-MATE
diffusion S-CONPRI
during O
powder S-MATE
recovery O
and O
not O
work B-MANP
hardening E-MANP
related O
to O
the O
mechanical S-APPL
aspects O
of O
that O
process S-CONPRI
. O


These O
results O
demonstrate O
the O
importance O
of O
managing/mitigating O
oxidation S-MANP
of O
metal B-MATE
powder E-MATE
feedstock S-MATE
to O
improve O
its O
reusability O
and O
increasing O
its O
overall O
lifetime O
. O


Components S-MACEQ
manufactured O
via O
Wire B-MANP
+ I-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
are O
usually O
characterised O
by O
large O
columnar B-PRO
grains E-PRO
. O


This O
can O
be S-MATE
mitigated O
by O
introducing O
in-process O
cold B-MANP
rolling E-MANP
; O
in O
fact O
, O
the O
associated O
local B-CONPRI
plastic I-CONPRI
deformation E-CONPRI
leads O
to O
a O
reduction S-CONPRI
of O
distortion S-CONPRI
and O
residual B-PRO
stresses E-PRO
, O
and O
to O
microstructural S-CONPRI
refinement O
. O


In O
this O
research S-CONPRI
, O
inter-pass O
rolling S-MANP
was O
applied O
with O
a O
load O
of O
50 O
kN O
to O
a O
tantalum S-MATE
linear O
structure S-CONPRI
to O
assess O
rolling S-MANP
’ O
s S-MATE
effectiveness S-CONPRI
in O
changing O
the O
grain B-CONPRI
structure E-CONPRI
from O
columnar O
to O
equiaxed O
, O
as S-MATE
well O
as S-MATE
in O
refining O
the O
grain B-PRO
size E-PRO
. O


An O
average S-CONPRI
grain O
size O
of O
650 O
μm O
has O
been O
obtained O
after O
five O
cycles O
of O
inter-pass O
rolling S-MANP
and O
deposition S-CONPRI
. O


When O
the O
deformed S-MANP
layer O
was O
reheated O
during O
the O
subsequent O
deposition S-CONPRI
, O
recrystallisation O
occurred O
, O
leading O
to O
the O
growth O
of O
new O
strain-free O
equiaxed B-CONPRI
grains E-CONPRI
. O


The O
depth O
of O
the O
refined O
region O
has O
been O
characterised O
and O
correlated S-CONPRI
to O
the O
hardness S-PRO
profile O
developed O
after O
rolling S-MANP
. O


Furthermore O
, O
a O
random O
texture S-FEAT
was O
formed O
after O
rolling S-MANP
, O
which O
should O
contribute O
to O
obtaining O
isotropic S-PRO
mechanical O
properties S-CONPRI
. O


Wire B-MANP
+ I-MANP
Arc I-MANP
Additive I-MANP
Manufacture E-MANP
demonstrated O
the O
ability O
to O
deposit O
sound O
refractory B-MATE
metal E-MATE
components S-MACEQ
and O
the O
possibility O
to O
improve O
the O
microstructure S-CONPRI
when O
coupled O
with O
cold O
inter-pass O
rolling S-MANP
. O


An O
innovative O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
variant O
based O
on O
plastic B-PRO
deformation E-PRO
at O
high O
temperatures S-PARA
was O
developed O
. O


This O
new O
variant O
is O
capable O
of O
collapsing O
pores S-PRO
that O
have O
been O
formed O
during O
the O
deposition B-MANP
process E-MANP
. O


The O
in-situ S-CONPRI
hot O
forging S-MANP
technique O
refines O
the O
grain B-CONPRI
structure E-CONPRI
and O
improve O
mechanical B-CONPRI
properties E-CONPRI
in O
the O
deposited B-CHAR
layer E-CHAR
. O


In O
this O
study O
, O
we O
propose O
a O
new O
variant O
of O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
based O
on O
hot O
forging S-MANP
. O


During O
WAAM S-MANP
, O
the O
material S-MATE
is O
locally O
forged O
immediately O
after O
deposition S-CONPRI
, O
and O
in-situ S-CONPRI
viscoplastic O
deformation S-CONPRI
occurs O
at O
high O
temperatures S-PARA
. O


In O
the O
subsequent O
layer S-PARA
deposition S-CONPRI
, O
recrystallization S-CONPRI
of O
the O
previous O
solidification S-CONPRI
structure O
occurs O
that O
refines O
the O
microstructure S-CONPRI
. O


Because O
of O
its O
similarity O
with O
hot O
forging S-MANP
, O
this O
variant O
was O
named O
hot O
forging S-MANP
wire O
and O
arc B-MANP
additive I-MANP
manufacturing E-MANP
( O
HF-WAAM O
) O
. O


A O
customized O
WAAM S-MANP
torch O
was O
developed O
, O
manufactured S-CONPRI
, O
and O
tested O
in O
the O
production S-MANP
of O
samples S-CONPRI
of O
AISI316 O
L O
stainless B-MATE
steel E-MATE
. O


Forging S-MANP
forces S-CONPRI
of O
17 O
N S-MATE
and O
55 O
N S-MATE
were O
applied O
to O
plastically O
deform O
the O
material S-MATE
. O


The O
results O
showed O
that O
this O
new O
variant O
refines O
the O
solidification B-CONPRI
microstructure E-CONPRI
and O
reduce O
texture S-FEAT
effects O
, O
as S-MATE
determined O
via O
high O
energy O
synchrotron S-ENAT
X-ray O
diffraction S-CHAR
experiments O
, O
without O
interrupting O
the O
additive B-MANP
manufacturing I-MANP
process E-MANP
. O


Mechanical S-APPL
characterization O
was O
performed O
and O
improvements O
on O
both O
yield B-PRO
strength E-PRO
and O
ultimate B-PRO
tensile I-PRO
strength E-PRO
were O
achieved O
. O


Furthermore O
, O
it O
was O
observed O
that O
HF-WAAM O
significantly O
affects O
porosity S-PRO
; O
pores S-PRO
formed O
during O
the O
process S-CONPRI
were O
closed O
by O
the O
hot O
forging S-MANP
process O
. O


Because O
deformation S-CONPRI
occurs O
at O
high O
temperatures S-PARA
, O
the O
forces S-CONPRI
involved O
are O
small O
, O
and O
the O
WAAM S-MANP
equipment S-MACEQ
does O
not O
have O
specific O
requirements O
with O
respect O
to O
stiffness S-PRO
, O
thereby O
allowing O
the O
incorporation O
of O
this O
new O
variant O
into O
conventional O
moving O
equipment S-MACEQ
such O
as S-MATE
multi-axis O
robots S-MACEQ
or O
3-axis O
table O
used O
in O
WAAM S-MANP
. O


A O
bimetallic O
additively-manufactured O
structure S-CONPRI
( O
BAMS O
) O
is O
a O
type O
of O
functionally-graded O
multi-material B-FEAT
structure E-FEAT
used O
for O
achieving O
different O
complementary O
material B-CONPRI
properties E-CONPRI
within O
the O
same O
structure S-CONPRI
as S-MATE
well O
as S-MATE
cost O
optimization S-CONPRI
. O


Wire B-MANP
+ I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
offers O
the O
capability O
to O
fabricate S-MANP
the O
BAMS O
in O
a O
simultaneous O
or O
sequential O
way O
. O


To O
fully O
utilize O
the O
benefits O
of O
the O
BAMS O
, O
the O
interfacial O
joint S-CONPRI
should O
be S-MATE
strong O
, O
and O
each O
of O
the O
constituents O
should O
have O
reasonable O
mechanical B-PRO
integrity E-PRO
. O


For O
this O
, O
a O
BAMS O
of O
low-carbon B-MATE
steel E-MATE
and O
austenitic-stainless O
steel S-MATE
was O
fabricated S-CONPRI
using O
a O
gas-metal-arc-welding O
( O
GMAW S-MANP
) O
-based O
WAAM S-MANP
process S-CONPRI
. O


Then O
, O
the O
BAMS O
was O
heat-treated S-MANP
at O
a O
range S-PARA
of O
800 O
°C O
to O
1100 O
°C O
and O
30 O
min O
to O
2 O
h. O
This O
resulted O
in O
35 O
% O
and O
250 O
% O
increases O
in O
the O
ultimate B-PRO
tensile I-PRO
strength E-PRO
and O
elongation S-PRO
, O
compared O
to O
the O
as-deposited O
BAMS O
. O


Scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
, O
energy-dispersive O
X-ray S-CHAR
spectroscopy S-CONPRI
( O
EDAx O
) O
, O
and O
the O
Vickers B-PRO
hardness E-PRO
test O
were O
used O
to O
characterize O
the O
BAMS O
. O


The O
additive B-MANP
manufacturing E-MANP
of O
metals B-MATE
and I-MATE
ceramics E-MATE
generally O
uses O
a O
concentrated O
laser B-PARA
heat E-PARA
source O
to O
form O
a O
local O
melt B-MATE
pool E-MATE
that O
moves O
quickly O
during O
the O
process S-CONPRI
. O


The O
material S-MATE
is O
deposited O
by O
fast O
cooling S-MANP
and O
progressive O
solidification S-CONPRI
. O


In O
this O
study O
, O
the O
effects O
of O
temperature B-PARA
gradient E-PARA
and O
progressive O
solidification S-CONPRI
on O
residual B-PRO
stress E-PRO
were O
analyzed O
using O
numerical O
finite-element O
models O
for O
a O
single O
rapidly O
solidifying O
bead S-CHAR
during O
the O
deposition B-MANP
process E-MANP
. O


Conceptual O
two- O
and O
three-dimensional S-CONPRI
finite B-CONPRI
element I-CONPRI
models E-CONPRI
are O
proposed O
, O
considering O
the O
solidification S-CONPRI
effect O
. O


Based O
on O
the O
numerical O
results O
, O
a O
reduced-order O
modeling S-ENAT
strategy O
was O
proposed O
to O
efficiently O
reproduce O
the O
final O
residual B-PRO
stress E-PRO
state O
of O
single-bead O
deposition B-MANP
processes E-MANP
in O
additive B-MANP
manufacturing E-MANP
, O
i.e O
. O


sequential O
solidification S-CONPRI
. O


Although O
additive B-MANP
manufacturing E-MANP
technology O
is O
available O
for O
the O
direct O
fabrication S-MANP
of O
metal S-MATE
parts O
, O
the O
process S-CONPRI
is O
still O
in O
a O
juvenile O
state O
compared O
to O
older O
metal S-MATE
fabrication S-MANP
methods O
such O
as S-MATE
sand O
casting S-MANP
. O


Therefore O
, O
limited O
standards S-CONPRI
are O
available O
stipulating O
the O
use O
of O
additively-manufactured O
parts O
in O
critical O
service O
conditions O
such O
as S-MATE
extreme O
environments O
or O
safety S-CONPRI
components S-MACEQ
. O


However O
, O
since O
sand B-MANP
casting E-MANP
is O
suited O
for O
multiple O
units O
of O
parts O
, O
the O
time O
and O
resources O
needed O
to O
produce O
a O
single O
part O
through O
sand B-MANP
casting E-MANP
is O
not O
ideal O
for O
a O
competitive O
market O
. O


Although O
additive B-MANP
manufacturing E-MANP
or O
“ O
3D B-MANP
printing E-MANP
” O
has O
been O
combined O
with O
metal S-MATE
casting S-MANP
in O
the O
past O
through O
“ O
rapid O
casting S-MANP
” O
to O
fabricate S-MANP
sand O
molds S-MACEQ
directly O
, O
the O
sand S-MATE
used O
is O
stipulated O
by O
the O
3D B-MACEQ
printer E-MACEQ
. O


The O
use O
of O
specialized O
sand S-MATE
may O
result O
in O
changes O
to O
infrastructure O
and O
large O
amounts O
of O
additional O
sand S-MATE
required O
to O
be S-MATE
stored O
on O
location O
. O


The O
main O
question O
we O
sought O
to O
answer O
was O
if O
traditional O
foundry S-MANP
sand O
or O
“ O
non-standard O
” O
sand S-MATE
could O
be S-MATE
used O
within O
a O
3D B-MANP
printing E-MANP
system O
? O
We O
report O
herein O
that O
the O
although O
the O
increase O
in O
surface B-PRO
roughness E-PRO
may O
be S-MATE
tolerable O
, O
the O
use O
of O
foundry S-MANP
sand O
within O
a O
3D B-MACEQ
printer E-MACEQ
produces O
molds S-MACEQ
with O
less O
than O
optimal O
results O
, O
mainly O
due O
to O
the O
absence O
of O
compaction S-MANP
. O


Binder S-MATE
bleeding O
via O
the O
liquid B-MATE
binder E-MATE
jetting S-MANP
process O
also O
contributes O
to O
a O
loss O
in O
dimensional O
quality S-CONPRI
. O


The O
behavior O
of O
high O
performance S-CONPRI
super O
duplex O
stainless B-MATE
steel E-MATE
( O
SDSS O
) O
during O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
has O
been O
investigated O
using O
a O
novel O
arc S-CONPRI
heat O
treatment O
technique O
. O


Tungsten B-MANP
inert I-MANP
gas E-MANP
( O
TIG S-MANP
) O
arc S-CONPRI
pulses O
were O
applied O
on O
a O
disc O
shaped O
sample S-CONPRI
mounted O
on O
a O
water-cooled O
chamber O
to O
physically O
simulate O
AM S-MANP
thermal O
cycles O
. O


SDSS O
base B-MATE
metal E-MATE
and O
a O
duplicated O
additively B-MANP
manufactured E-MANP
structure O
( O
DAMS O
) O
were O
used O
as S-MATE
initial O
microstructures S-MATE
. O


Samples S-CONPRI
were O
melted S-CONPRI
one O
, O
five O
, O
or O
15 O
times O
by O
arc S-CONPRI
heat O
treatment O
. O


Microstructure S-CONPRI
characterization O
and O
modelling S-ENAT
were O
performed O
to O
study O
the O
evolution S-CONPRI
of O
microstructure S-CONPRI
and O
properties S-CONPRI
with O
successive O
AM S-MANP
cycles O
. O


Microstructural S-CONPRI
changes O
were O
dependent O
on O
the O
number O
of O
reheating O
cycles O
, O
cooling B-PARA
rate E-PARA
, O
and O
peak O
temperature S-PARA
. O


In O
particular O
, O
the O
DAMS O
austenite S-MATE
morphology O
and O
fraction S-CONPRI
changed O
after O
reheating O
to O
peak O
temperatures S-PARA
above O
700 O
°C O
. O


Nitrides S-MATE
and O
sigma O
were O
observed O
in O
the O
high O
and O
low O
temperature S-PARA
heat B-CONPRI
affected I-CONPRI
zones E-CONPRI
, O
respectively O
. O


Sensitization O
to O
corrosion S-CONPRI
was O
more O
pronounced O
in O
reheated O
DAMS O
than O
in O
the O
base B-MATE
metal E-MATE
. O


Hardness S-PRO
was O
increased O
more O
by O
multiple O
remelting/reheating O
than O
by O
slow O
cooling S-MANP
. O


It O
was O
found O
that O
AM S-MANP
thermal O
cycles O
significantly O
affect O
SDSS O
properties S-CONPRI
especially O
for O
an O
initial O
microstructure S-CONPRI
similar O
to O
that O
produced O
by O
AM S-MANP
. O


Additive B-MANP
manufacturing E-MANP
is O
a O
promising O
and O
rapidly O
rising O
technology S-CONPRI
in O
metal S-MATE
processing O
. O


In O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
, O
the O
most O
applied O
metal B-MANP
additive I-MANP
manufacturing E-MANP
process O
, O
the O
repetitive O
heating S-MANP
and O
cooling S-MANP
cycles O
induce O
severe O
strains O
in O
the O
built O
material S-MATE
, O
which O
can O
have O
a O
number O
of O
adverse O
consequences O
such O
as S-MATE
deformation O
, O
cracking S-CONPRI
and O
decreased O
fatigue B-PRO
life E-PRO
that O
might O
lead S-MATE
to O
severe O
failure S-CONPRI
even O
already O
during O
processing O
. O


It O
has O
been O
reported O
recently O
that O
the O
application O
of O
laser S-ENAT
shock O
peening S-MANP
( O
LSP O
) O
can O
counteract O
efficiently O
the O
named O
issues O
of O
LPBF S-MANP
through O
the O
introduction O
of O
beneficial O
compressive O
residual B-PRO
stresses E-PRO
in O
the O
surface S-CONPRI
regions O
mostly O
affected O
by O
tensile B-PRO
stresses E-PRO
from O
the O
manufacturing B-MANP
process E-MANP
. O


Here O
we O
demonstrate O
how O
lattice S-CONPRI
strains O
implied O
by O
LPBF S-MANP
and O
LSP O
can O
efficiently O
be S-MATE
characterized O
through O
diffraction S-CHAR
contrast O
neutron S-CONPRI
imaging S-APPL
. O


Despite O
the O
spatial O
resolution S-PARA
need O
with O
regards O
to O
the O
significant O
gradients O
of O
the O
stress B-PRO
distribution E-PRO
and O
the O
specific O
microstructure S-CONPRI
, O
which O
prevent O
the O
application O
of O
more O
conventional O
methods O
, O
Bragg O
edge O
imaging S-APPL
succeeds O
to O
provide O
essential O
two-dimensionally O
spatial O
resolved O
strain S-PRO
maps O
in O
full O
field O
single O
exposure S-CONPRI
measurements O
. O


Two-wire O
TOP-TIG O
additive B-MANP
manufacturing E-MANP
of O
titanium B-MATE
aluminide I-MATE
alloys E-MATE
was O
proposed O
. O


The O
Al S-MATE
wire O
was O
fed O
in O
TOP-TIG O
welding S-MANP
mode O
but O
the O
Ti6Al4V S-MATE
wire O
was O
fed O
in O
conventional O
TIG B-MANP
welding E-MANP
mode O
. O


The O
main O
microstructure S-CONPRI
of O
the O
as-fabricated O
component S-MACEQ
is O
α2/γ O
lamellae S-MATE
. O


The O
different O
Al S-MATE
content O
results O
in O
the O
different O
content O
and O
distribution S-CONPRI
of O
the O
α2 O
phase S-CONPRI
and O
the O
γ O
phase S-CONPRI
. O


50 O
at. O
% O
Al S-MATE
content O
provides O
better O
mechanical B-CONPRI
properties E-CONPRI
. O


Titanium B-MATE
aluminide E-MATE
( O
TiAl O
) O
alloys S-MATE
are O
promising O
high-temperature O
structural O
materials S-CONPRI
in O
the O
aerospace S-APPL
field O
. O


Additive B-MANP
manufacturing E-MANP
is O
a O
desirable O
process S-CONPRI
for O
fabricating S-MANP
TiAl O
alloys S-MATE
. O


In O
the O
process S-CONPRI
of O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
of O
TiAl O
alloys S-MATE
, O
Al-based O
and O
Ti-based O
wires O
were O
used O
as S-MATE
the O
feedstocks S-MATE
. O


However O
, O
it O
is O
hard O
to O
ensure O
the O
two O
different O
wires O
melt S-CONPRI
synchronously O
under O
the O
heat S-CONPRI
of O
one O
single O
arc S-CONPRI
, O
so O
the O
desired O
microstructures S-MATE
with O
γ O
( O
TiAl O
) O
phase S-CONPRI
and O
α2 O
( O
Ti3Al O
) O
phase S-CONPRI
are O
hard O
to O
obtain O
. O


A O
two-wire O
TOP-TIG-based O
additive B-MANP
manufacturing I-MANP
process E-MANP
for O
TiAl O
alloys S-MATE
was O
proposed O
in O
this O
paper O
. O


The O
Ti6Al4V S-MATE
wire O
and O
pure O
Al S-MATE
wire O
were O
used O
as S-MATE
the O
feedstocks S-MATE
. O


The O
Al S-MATE
wire O
was O
fed O
in O
TOP-TIG O
mode O
behind O
the O
molten B-CONPRI
pool E-CONPRI
, O
while O
the O
Ti6Al4V S-MATE
wire O
was O
fed O
in O
conventional O
TIG S-MANP
mode O
in O
front O
of O
the O
molten B-CONPRI
pool E-CONPRI
. O


The O
two O
wires O
melt S-CONPRI
synchronously O
in O
a O
broad O
range S-PARA
of O
parameters S-CONPRI
. O


The O
compositions O
of O
the O
component S-MACEQ
can O
be S-MATE
controlled O
by O
adjusting O
the O
two-wire O
feeding O
speeds O
. O


The O
main O
microstructures S-MATE
of O
the O
as-fabricated O
component S-MACEQ
contain O
α2/γ O
lamellae S-MATE
colonies O
, O
equiaxed O
γ O
grains S-CONPRI
, O
and O
α2 O
grains S-CONPRI
. O


In O
the O
top O
and O
middle O
regions O
, O
when O
the O
Al S-MATE
content O
is O
45 O
at. O
% O
, O
the O
structures O
are O
full O
α2/γ O
lamellae S-MATE
; O
as S-MATE
the O
Al S-MATE
content O
increases O
to O
50 O
at. O
% O
, O
some O
equiaxed O
γ O
distributed O
at O
the O
grain B-CONPRI
boundaries E-CONPRI
; O
the O
component S-MACEQ
with O
55 O
at. O
% O
Al S-MATE
content O
exhibits O
the O
structures O
consists O
of O
equiaxed O
γ O
with O
snowflake-shaped O
α2/γ O
lamellae S-MATE
colonies O
. O


In O
the O
bottom O
region O
, O
all O
components S-MACEQ
exhibit O
the O
coarse O
equiaxed O
α2 O
grains S-CONPRI
with O
γ O
laths O
. O


As S-MATE
the O
Al S-MATE
content O
increases O
, O
the O
α2 O
phase S-CONPRI
decreases O
, O
but O
the O
γ O
phase S-CONPRI
increases O
, O
and O
from O
the O
top O
region O
to O
the O
bottom O
region O
, O
the O
proportion O
of O
the O
α2 O
increases O
by O
about O
52 O
at. O
% O
. O


As S-MATE
the O
Al S-MATE
content O
increases O
, O
the O
hardness S-PRO
decreases O
. O


The O
component S-MACEQ
with O
50 O
at. O
% O
Al S-MATE
exhibits O
the O
highest O
compressive B-PRO
strength E-PRO
with O
1762 O
MPa S-CONPRI
and O
a O
compressive O
ratio O
with O
26.1 O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
enables O
the O
fabrication S-MANP
of O
complex O
designs S-FEAT
that O
are O
difficult O
to O
create O
by O
other O
means O
. O


Metal S-MATE
parts O
manufactured S-CONPRI
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
can O
incorporate O
intricate O
design S-FEAT
features O
and O
demonstrate O
desirable O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
process S-CONPRI
of O
iteratively O
converging O
on O
the O
appropriate O
build B-PARA
parameters E-PARA
increases O
the O
time O
and O
cost O
of O
creating O
functional O
LPBF S-MANP
manufactured O
parts O
. O


This O
paper O
describes O
a O
fast O
, O
scalable O
method O
for O
part-scale O
process B-CONPRI
optimization E-CONPRI
of O
arbitrary O
geometries S-CONPRI
. O


The O
computational O
approach O
uses O
feature B-ENAT
extraction E-ENAT
to O
identify O
scan O
vectors O
in O
need O
of O
parameter S-CONPRI
adaptation O
and O
applies O
results O
from O
simulation-based O
feed S-PARA
forward O
control O
models O
. O


This O
method O
provides O
a O
framework S-CONPRI
to O
quickly O
optimize O
complex O
parts O
through O
the O
targeted O
application O
of O
models O
with O
a O
range S-PARA
of O
fidelity O
and O
by O
automating O
the O
transfer O
of O
optimization S-CONPRI
strategies O
to O
new O
part O
designs S-FEAT
. O


The O
computational O
approach O
and O
algorithmic O
framework S-CONPRI
are O
described O
, O
a O
software S-CONPRI
package O
is O
implemented O
, O
the O
method O
is O
applied O
to O
parts O
with O
complex O
features O
, O
and O
parts O
are O
printed O
on O
a O
customized O
open O
architecture S-APPL
LPBF O
machine S-MACEQ
. O


CrC-Ni O
successfully O
deposited O
onto O
an O
AM S-MANP
stainless O
steel S-MATE
using O
cold O
spray O
coating S-APPL
. O


The O
CrC-Ni O
coating S-APPL
reduced O
equivalent O
residual B-PRO
stresses E-PRO
in O
the O
substrate S-MATE
surface O
. O


CrC-Ni O
coating S-APPL
improved O
the O
surface B-PARA
quality E-PARA
of O
an O
AM S-MANP
produced O
stainless B-MATE
steel E-MATE
. O


Crack B-CONPRI
growth E-CONPRI
mechanism O
is O
changed O
due O
to O
the O
deposition S-CONPRI
of O
the O
CrC-Ni O
coating S-APPL
. O


Multiaxial O
fatigue B-PRO
life E-PRO
of O
AM S-MANP
stainless O
steel S-MATE
significantly O
improved O
by O
the O
CrC-Ni O
coating S-APPL
. O


Integration O
of O
metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
and O
cold O
spray O
( O
CS O
) O
technologies S-CONPRI
provide O
an O
unprecedented O
opportunity O
to O
manufacture S-CONPRI
coated S-APPL
material O
systems O
with O
complex O
geometrical B-FEAT
features E-FEAT
. O


The O
application O
of O
these O
material S-MATE
systems O
in O
functionally O
critical O
components S-MACEQ
requires O
adequate O
structural B-PRO
integrity E-PRO
, O
particularly O
in O
the O
presence O
of O
cyclic B-PRO
loading E-PRO
. O


This O
work O
aims O
to O
study O
the O
multiaxial O
fatigue S-PRO
( O
axial-torsional O
cyclic B-PRO
loading E-PRO
) O
behavior O
of O
a O
coated S-APPL
material O
system O
consists O
of O
15Cr-5Ni O
PH S-CONPRI
stainless O
steel S-MATE
( O
15-5 O
PH S-CONPRI
SS O
) O
substrate S-MATE
additively B-MANP
manufactured E-MANP
by O
direct B-MANP
metal I-MANP
laser I-MANP
sintering E-MANP
with O
a O
layer S-PARA
of O
newly O
commercialized O
chromium B-MATE
carbide E-MATE
nickel O
( O
CrC-Ni O
) O
barrier O
coating S-APPL
deposited O
by O
CS O
coating S-APPL
. O


The O
influence O
of O
AM S-MANP
and O
CS-induced O
residual B-PRO
stresses E-PRO
on O
fatigue S-PRO
performance O
of O
test O
specimens O
was O
thoroughly O
studied O
. O


Additionally O
, O
the O
effect O
of O
surface B-PRO
roughness E-PRO
and O
processes S-CONPRI
induced O
defects S-CONPRI
were O
considered O
to O
explain O
the O
crack B-CONPRI
growth E-CONPRI
mechanism O
. O


Stresses O
assessed O
by O
synchrotron S-ENAT
X-ray O
diffraction S-CHAR
indicated O
a O
substantial O
accumulation O
of O
the O
residual B-PRO
stresses E-PRO
, O
particularly O
in O
the O
outer O
surface S-CONPRI
of O
the O
as S-MATE
fabricated O
15-5 O
PH S-CONPRI
SS O
specimens O
. O


The O
state O
of O
residual B-PRO
stress E-PRO
was O
changed O
notably O
following O
the O
deposition S-CONPRI
of O
CrC-Ni O
coating S-APPL
in O
the O
axial O
, O
hoop O
, O
and O
radial O
directions O
of O
the O
fatigue B-CHAR
test E-CHAR
specimen O
. O


Also O
, O
CS O
deposition S-CONPRI
of O
CrC-Ni O
coating S-APPL
caused O
significant O
improvement O
in O
the O
surface B-PARA
quality E-PARA
of O
the O
additively B-MANP
manufactured E-MANP
components O
. O


Fatigue B-CHAR
test E-CHAR
results O
indicated O
that O
the O
CS O
deposition S-CONPRI
of O
CrC-Ni O
substantially O
enhances O
the O
fatigue B-PRO
life E-PRO
of O
the O
AM-produced O
15-5 O
PH S-CONPRI
SS O
substrate S-MATE
in O
all O
loading O
conditions O
, O
particularly O
in O
the O
high O
cycle O
fatigue S-PRO
regime O
. O


The O
improvement O
in O
the O
fatigue B-PRO
life E-PRO
of O
the O
specimens O
with O
coating S-APPL
was O
associated O
with O
the O
reduced O
surface S-CONPRI
equivalent O
residual B-PRO
stress E-PRO
and O
improvement O
in O
the O
specimens O
' O
surface S-CONPRI
condition O
( O
i.e. O
, O
reduced O
surface B-PRO
roughness E-PRO
) O
. O


In O
addition O
, O
the O
fractographic B-CHAR
analysis E-CHAR
of O
the O
specimen O
indicated O
although O
the O
crack O
tends O
to O
initiate O
in O
the O
surface S-CONPRI
of O
both O
as S-MATE
fabricated O
and O
cold O
sprayed S-MANP
specimens O
, O
the O
mechanism S-CONPRI
of O
crack B-CONPRI
growth E-CONPRI
differs O
notably O
following O
the O
CS O
coating S-APPL
. O


While O
the O
cracks O
tend O
to O
propagate O
in O
the O
planes O
parallel O
or O
with O
a O
small O
deviation O
from O
the O
build B-PARA
layers E-PARA
of O
the O
AM S-MANP
produced O
specimens O
, O
deposition S-CONPRI
of O
CrC-Ni O
coating S-APPL
increased O
the O
deviation O
of O
crack B-CONPRI
growth E-CONPRI
plane O
from O
the O
build B-PARA
layers E-PARA
of O
the O
substrate S-MATE
. O


Electromagnetic O
wave O
based O
laser-powder O
particle S-CONPRI
interactions O
. O


Powder S-MATE
features O
are O
associated O
with O
additive B-MANP
manufacturing I-MANP
process E-MANP
. O


New O
heat B-CONPRI
source E-CONPRI
model O
considering O
powder S-MATE
effects O
. O


A O
modified O
heat-source O
model S-CONPRI
based O
on O
electromagnetic O
wave O
theory O
was O
proposed O
to O
investigate O
the O
interactions O
between O
powder B-MATE
particles E-MATE
and O
a O
laser B-CONPRI
beam E-CONPRI
, O
considering O
the O
spatial B-CHAR
distribution E-CHAR
of O
particles S-CONPRI
inside O
the O
beam S-MACEQ
. O


The O
absorption S-CONPRI
of O
energy O
by O
these O
particles S-CONPRI
in O
laser B-MANP
directed I-MANP
energy I-MANP
deposition I-MANP
additive I-MANP
manufacturing E-MANP
was O
calculated O
using O
the O
proposed O
model S-CONPRI
, O
which O
was O
validated O
experimentally O
. O


Both O
numerical O
model S-CONPRI
and O
experiment S-CONPRI
were O
used O
to O
study O
the O
effects O
of O
powder S-MATE
velocities O
on O
the O
temperature S-PARA
variations O
in O
the O
additive B-MANP
manufacturing I-MANP
process E-MANP
. O


Results O
indicate O
that O
the O
direct O
heat B-CONPRI
transfer E-CONPRI
from O
the O
laser S-ENAT
to O
a O
target O
can O
be S-MATE
increased O
if O
the O
size O
distribution S-CONPRI
is O
wider O
; O
it O
also O
increases O
with O
the O
velocity O
of O
the O
particles S-CONPRI
. O


However O
, O
with O
the O
increase O
of O
powder-flow O
rate O
, O
the O
rate O
of O
mass O
transfer O
decreases O
the O
heat B-CONPRI
transfer E-CONPRI
. O


Melt-pool O
depth O
in O
melting S-MANP
and O
re-melting O
processes S-CONPRI
can O
therefore O
be S-MATE
controlled O
by O
varying O
these O
parameters S-CONPRI
. O


Wire‐arc O
additive B-MANP
manufacturing E-MANP
is O
a O
metal B-MANP
additive I-MANP
manufacturing E-MANP
process O
that O
enables O
the O
production S-MANP
of O
large O
components S-MACEQ
at O
a O
high B-PARA
deposition I-PARA
rate E-PARA
. O


This O
process S-CONPRI
transfers O
a O
large O
amount O
of O
heat S-CONPRI
to O
the O
workpiece S-CONPRI
, O
requiring O
the O
introduction O
of O
idle O
times O
between O
the O
deposition S-CONPRI
of O
subsequent O
layers O
so O
that O
the O
workpiece S-CONPRI
cools O
down O
. O


This O
procedure O
prevents O
the O
workpiece S-CONPRI
from O
collapsing O
and O
ensures O
a O
suitable O
interpass B-PARA
temperature E-PARA
. O


The O
main O
challenge O
is O
the O
selection O
of O
such O
an O
idle O
time O
capable O
of O
ensuring O
the O
required O
interpass B-PARA
temperature E-PARA
, O
because O
the O
cooling B-PARA
rate E-PARA
of O
the O
workpiece S-CONPRI
changes O
throughout O
the O
process S-CONPRI
, O
entailing O
the O
need O
for O
a O
different O
idle O
time O
between O
the O
deposition S-CONPRI
of O
subsequent O
layers O
to O
achieve O
a O
constant O
interpass S-PARA
temperature.This O
paper O
proposes O
an O
innovative O
approach O
to O
schedule O
the O
deposition S-CONPRI
of O
interlayer O
idle O
times O
for O
wire‐arc O
additive B-MANP
manufacturing I-MANP
process E-MANP
. O


The O
technique O
is O
based O
on O
a O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
of O
the O
thermal O
behavior O
of O
the O
workpiece S-CONPRI
, O
by O
solving O
the O
heat B-CONPRI
transfer E-CONPRI
equations O
. O


The O
simulation S-ENAT
data S-CONPRI
are O
processed S-CONPRI
using O
the O
developed O
algorithm S-CONPRI
to O
compute O
specific O
idle O
times O
for O
the O
deposition S-CONPRI
of O
each O
layer S-PARA
, O
thereby O
ensuring O
a O
constant O
interpass B-PARA
temperature E-PARA
. O


The O
effectiveness S-CONPRI
of O
the O
proposed O
technique O
is O
validated O
by O
experiments O
performed O
on O
a O
test O
case O
component S-MACEQ
. O


The O
temperature S-PARA
data S-CONPRI
measured O
during O
the O
process S-CONPRI
are O
compared O
with O
the O
FE S-MATE
simulation O
results O
to O
verify O
the O
accuracy S-CHAR
of O
the O
model S-CONPRI
. O


There O
is O
a O
growing O
interest O
in O
using O
recycled B-CONPRI
materials E-CONPRI
and O
economically O
produced O
powder S-MATE
in O
additive B-MANP
manufacturing I-MANP
processes E-MANP
. O


State-of-the-art S-CONPRI
powder B-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
processes O
typically O
use O
spherical S-CONPRI
powder S-MATE
that O
are O
produced O
using O
an O
atomization S-MANP
process O
. O


However O
, O
using O
irregularly O
shaped O
Ti-6Al-4V B-MATE
powder E-MATE
from O
the O
Hydride-Dehydride O
( O
HDH O
) O
process S-CONPRI
is O
more O
economical O
because O
fewer O
processing O
steps O
are O
required O
and O
it O
can O
use O
recycled B-CONPRI
material E-CONPRI
as S-MATE
feedstock O
. O


In O
this O
work O
, O
the O
use O
of O
HDH O
powder S-MATE
in O
the O
electron B-MANP
beam I-MANP
additive I-MANP
manufacturing E-MANP
( O
EBAM S-MANP
) O
process S-CONPRI
is O
investigated O
. O


Deposition S-CONPRI
parameters O
for O
the O
HDH O
powder S-MATE
were O
developed O
, O
followed O
by O
a O
detailed O
study O
of O
as-built O
porosity S-PRO
and O
microstructure S-CONPRI
. O


The O
powder S-MATE
flow O
characteristics O
were O
also O
studied O
, O
and O
the O
as-built O
part O
porosity S-PRO
was O
compared O
to O
the O
parts O
built O
using O
spherical S-CONPRI
atomized S-ENAT
powder O
. O


This O
work O
demonstrates O
the O
successful O
use O
of O
non-spherical S-CONPRI
HDH O
powder S-MATE
in O
the O
EBAM S-MANP
process O
. O


The O
extension O
of O
metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
to O
non-weldable O
Ni-based O
superalloys S-MATE
remains O
a O
challenge O
for O
the O
electron B-MANP
beam I-MANP
melting E-MANP
process O
. O


Various O
cracking S-CONPRI
mechanisms O
, O
including O
solidification S-CONPRI
, O
liquation O
, O
strain-age O
, O
and O
ductility S-PRO
dip O
cracking S-CONPRI
, O
make O
it O
difficult O
to O
fabricate S-MANP
traditionally O
non-weldable O
Ni-based O
superalloys S-MATE
using O
the O
AM B-MANP
process E-MANP
. O


Because O
airfoil O
geometries S-CONPRI
are O
highly O
complicated O
, O
the O
correspondingly O
complex O
thermal O
signatures O
lead S-MATE
to O
various O
types O
of O
cracking S-CONPRI
in O
geometries S-CONPRI
that O
are O
under O
severe O
mechanical S-APPL
restraints O
during O
the O
printing B-MANP
process E-MANP
. O


This O
work O
aims O
to O
understand O
the O
correlations O
between O
cracking S-CONPRI
, O
scan O
strategy O
, O
and O
part O
geometry S-CONPRI
in O
airfoil O
geometries S-CONPRI
. O


Crack O
locations O
were O
monitored O
via O
an O
in-situ S-CONPRI
near-infrared O
camera S-MACEQ
during O
printing O
. O


A O
part-scale O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
( O
FEM S-CONPRI
) O
was O
used O
to O
reveal O
cracking S-CONPRI
mechanisms O
. O


New O
scan O
strategies O
that O
avoided O
cracking S-CONPRI
were O
utilized O
in O
an O
FEM S-CONPRI
simulation O
. O


The O
present O
work O
demonstrates O
the O
potential O
for O
scan O
strategy O
optimization S-CONPRI
to O
manipulate O
stress B-PRO
distribution E-PRO
and O
the O
resultant O
microstructure S-CONPRI
of O
parts O
for O
industrial S-APPL
applications O
. O


Recent O
work O
in O
metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
suggests O
that O
mechanical B-CONPRI
properties E-CONPRI
may O
vary O
with O
feature B-PARA
size E-PARA
; O
however O
, O
these O
studies O
do O
not O
provide O
a O
statistically O
robust O
description O
of O
this O
phenomenon O
, O
nor O
do O
they O
provide O
a O
clear O
causal O
mechanism S-CONPRI
. O


Because O
of O
the O
huge O
design B-CONPRI
freedom E-CONPRI
afforded O
by O
3D B-MANP
printing E-MANP
, O
AM B-MACEQ
parts E-MACEQ
typically O
contain O
a O
range S-PARA
of O
feature B-PARA
sizes E-PARA
, O
with O
particular O
interest O
in O
smaller O
features O
, O
so O
the O
size B-CONPRI
effect E-CONPRI
must O
be S-MATE
well O
understood O
in O
order O
to O
make O
informed O
design S-FEAT
decisions O
. O


This O
work O
investigates S-CONPRI
the O
effect O
of O
feature B-PARA
size E-PARA
on O
the O
stochastic S-CONPRI
mechanical S-APPL
performance O
of O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
tensile O
specimens O
. O


A O
high-throughput O
tensile B-CHAR
testing E-CHAR
method O
was O
used O
to O
characterize O
the O
effect O
of O
specimen O
size O
on O
strength S-PRO
, O
elastic B-PRO
modulus E-PRO
and O
elongation S-PRO
in O
a O
statistically O
meaningful O
way O
. O


The O
effective O
yield B-PRO
strength E-PRO
, O
ultimate B-PRO
tensile I-PRO
strength E-PRO
and O
modulus O
decreased O
strongly O
with O
decreasing O
specimen O
size O
: O
all O
three O
properties S-CONPRI
were O
reduced O
by O
nearly O
a O
factor O
of O
two O
as S-MATE
feature O
dimensions S-FEAT
were O
scaled O
down O
from O
6.25 O
mm S-MANP
to O
0.4 O
mm S-MANP
. O


Hardness S-PRO
and O
microstructural B-CHAR
observations E-CHAR
indicate O
that O
this O
size O
dependence O
was O
not O
due O
to O
an O
intrinsic O
change O
in O
material B-CONPRI
properties E-CONPRI
, O
but O
instead O
the O
effects O
of O
surface B-PRO
roughness E-PRO
on O
the O
geometry S-CONPRI
of O
the O
specimens O
. O


Finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
using O
explicit O
representations O
of O
surface B-CONPRI
topography E-CONPRI
shows O
the O
critical O
role O
surface S-CONPRI
features O
play O
in O
creating O
stress B-CHAR
concentrations E-CHAR
that O
trigger O
deformation S-CONPRI
and O
subsequent O
fracture S-CONPRI
. O


The O
experimental S-CONPRI
and O
finite B-CONPRI
element E-CONPRI
results O
provide O
the O
tools S-MACEQ
needed O
to O
make O
corrections O
in O
the O
design B-CONPRI
process E-CONPRI
to O
more O
accurately S-CHAR
predict O
the O
performance S-CONPRI
of O
AM S-MANP
components O
. O


A O
hybrid B-CONPRI
manufacturing E-CONPRI
supply O
chain O
based O
on O
metal B-MANP
Additive I-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
is O
proposed O
. O


Adding O
capacity S-CONPRI
to O
existing O
AM S-MANP
hubs O
is O
preferred O
over O
establishing O
new O
AM S-MANP
hubs O
at O
current O
demand O
. O


The O
ever-growing O
applications O
of O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
in O
the O
production S-MANP
of O
low O
volume- O
high O
value O
metal S-MATE
parts O
can O
be S-MATE
attributed O
to O
improving O
AM S-MANP
processing O
capabilities O
and O
complex O
design B-CONPRI
freedom E-CONPRI
. O


However O
, O
secondary O
post-processing S-CONPRI
using O
traditional O
processes S-CONPRI
such O
as S-MATE
machining O
, O
grinding S-MANP
, O
heat B-MANP
treatment E-MANP
and O
hot B-MANP
isostatic I-MANP
pressing E-MANP
, O
i.e. O
, O
Hybrid B-CONPRI
Manufacturing E-CONPRI
, O
is O
required O
to O
achieve O
Geometric B-CONPRI
Dimensioning E-CONPRI
and O
Tolerancing O
( O
GD S-MATE
& O
T O
) O
, O
surface B-FEAT
finish E-FEAT
and O
desired O
mechanical B-CONPRI
properties E-CONPRI
. O


It O
is O
often O
challenging O
for O
most O
traditional O
manufacturers O
to O
participate O
in O
the O
rapidly O
evolving O
supply B-CONPRI
chain E-CONPRI
of O
direct B-MANP
digital I-MANP
manufacturing E-MANP
( O
DDM S-CONPRI
) O
through O
in-house O
investments O
in O
cost O
prohibitive O
metal B-MANP
AM E-MANP
. O


This O
research B-CONPRI
investigates E-CONPRI
a O
system O
of O
strategically-located O
AM S-MANP
hubs O
which O
can O
integrate O
hybrid-AM O
with O
the O
capabilities O
and O
excess O
capacity S-CONPRI
in O
multiple O
traditional B-MANP
manufacturing E-MANP
facilities O
. O


Using O
North O
American O
Industry S-APPL
Classification S-CONPRI
System O
( O
NAICS O
) O
data S-CONPRI
for O
machine S-MACEQ
shops O
in O
the O
U.S. O
, O
an O
uncapacitated O
facility O
location O
model S-CONPRI
is O
used O
to O
determine O
the O
optimal O
locations O
for O
AM S-MANP
hub O
centers O
based O
on O
: O
( O
1 O
) O
geographical O
data S-CONPRI
, O
( O
2 O
) O
demand O
and O
( O
3 O
) O
cost O
of O
hybrid-AM O
processing O
. O


Results O
from O
this O
study O
have O
identified O
: O
( O
a O
) O
candidate O
US O
counties O
to O
build S-PARA
AM S-MANP
hubs O
, O
( O
b S-MATE
) O
total O
cost O
( O
fixed O
, O
operational O
and O
transportation O
) O
and O
( O
c S-MATE
) O
capacity S-CONPRI
utilization O
of O
the O
AM S-MANP
hubs O
. O


It O
was O
found O
that O
uncapacitated O
facility O
location O
models O
identified O
demand O
centroid O
as S-MATE
the O
optimal O
location O
and O
was O
affected O
only O
by O
AM S-MANP
utilization O
rate O
whereas O
a O
constrained O
p-median O
model S-CONPRI
identified O
22 O
AM S-MANP
hub O
locations O
as S-MATE
the O
initial O
sites O
for O
AM S-MANP
hubs O
which O
grows O
to O
44 O
AM S-MANP
hubs O
as S-MATE
demand O
increases O
. O


It O
was O
also O
found O
that O
transportation O
cost O
was O
not O
a O
significant O
factor O
in O
the O
hybrid-AM O
supply B-CONPRI
chain E-CONPRI
. O


Findings O
from O
this O
study O
will O
help O
both O
AM S-MANP
companies O
and O
traditional O
manufacturers O
to O
determine O
location O
in O
the O
U.S O
and O
key O
factors O
to O
advance O
the O
metal S-MATE
hybrid-AM O
supply B-CONPRI
chain E-CONPRI
. O


In O
this O
paper O
, O
maraging B-MATE
steel E-MATE
powder O
was O
deposited O
on O
top O
of O
an O
H13 B-MATE
tool I-MATE
steel E-MATE
using O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
technique O
. O


The O
mechanical B-CONPRI
properties E-CONPRI
, O
microstructure S-CONPRI
, O
and O
interfacial O
characteristics O
of O
the O
additively B-MANP
manufactured E-MANP
MS1-H13 O
bimetals O
were O
investigated O
using O
different O
mechanical S-APPL
and O
microstructural S-CONPRI
techniques O
. O


Several O
uniaxial O
tensile B-CHAR
tests E-CHAR
and O
micro-hardness O
indentations O
were O
performed O
to O
identify O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
additively B-MANP
manufactured E-MANP
bimetal O
. O


Advanced O
electron B-CHAR
microscopy E-CHAR
techniques O
including O
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
and O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
were O
used O
to O
identify O
the O
mechanism S-CONPRI
of O
interface S-CONPRI
formation O
. O


In O
addition O
, O
the O
microstructure S-CONPRI
of O
the O
additively B-MANP
manufactured E-MANP
maraging O
steel S-MATE
along O
with O
the O
conventionally O
fabricated S-CONPRI
substrate-H13 O
were O
studied O
. O


It O
was O
concluded O
that O
, O
a O
very O
narrow O
interface S-CONPRI
was O
formed O
between O
the O
additively B-MANP
manufactured E-MANP
maraging O
steel S-MATE
and O
the O
conventional O
H13 S-MATE
without O
forming S-MANP
cracks O
or O
discontinuities O
. O


The O
first O
deposited B-CHAR
layers E-CHAR
possessed O
the O
highest O
hardness S-PRO
due O
to O
grain B-PRO
size E-PRO
refinement O
, O
solid B-MATE
solution E-MATE
strengthening O
, O
and O
cellular O
solidification S-CONPRI
structure O
. O


Finally O
, O
under O
uniaxial O
tensile S-PRO
loading O
, O
the O
additively B-MANP
manufactured E-MANP
bimetal O
steel S-MATE
failed O
from O
the O
underlying O
tool S-MACEQ
steel S-MATE
, O
indicating O
a O
robust O
interface S-CONPRI
. O


Thermomechanical S-CONPRI
analyses O
of O
WAAM S-MANP
by O
implicit O
FEM S-CONPRI
and O
explicit O
FEM S-CONPRI
were O
compared O
. O


Explicit O
FEM S-CONPRI
can O
be S-MATE
greatly O
accelerated O
( O
30,000× O
) O
using O
time O
scaling O
technique O
. O


Real-time O
simulation S-ENAT
of O
WAAM S-MANP
was O
achieved O
for O
a O
large-scale O
build S-PARA
( O
500 O
× O
40 O
× O
5 O
mm3 O
) O
. O


Developed O
FEMs O
all O
showed O
high O
accuracy S-CHAR
in O
predicting O
residual B-PRO
stress E-PRO
and O
distortion S-CONPRI
. O


This O
study O
aims O
to O
advance O
the O
structural B-CHAR
analysis E-CHAR
of O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
by O
considering O
the O
thermomechanical S-CONPRI
features O
inherent O
in O
direct B-MANP
energy I-MANP
deposition E-MANP
. O


Simulation S-ENAT
approaches O
including O
the O
iterative O
substructure O
method O
( O
ISM O
) O
, O
dynamic S-CONPRI
mesh O
refining O
method O
( O
DMRM O
) O
, O
and O
graphics O
processing O
unit O
( O
GPU O
) O
based O
explicit O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
( O
FEM S-CONPRI
) O
were O
developed O
for O
accelerating O
additive B-MANP
manufacturing E-MANP
stress O
analysis O
that O
is O
very O
time O
consuming O
by O
conventional O
numerical O
methods O
. O


The O
residual B-PRO
stress E-PRO
and O
distortion S-CONPRI
of O
two O
large O
builds S-CHAR
were O
analyzed O
, O
showing O
very O
consistent O
numerical O
results O
and O
good O
agreement O
with O
experiments O
. O


Compared O
with O
the O
commercial O
software S-CONPRI
Abaqus S-ENAT
, O
the O
novel O
approaches O
reduced O
the O
computational O
cost O
substantially O
without O
compromising O
accuracy S-CHAR
. O


Such O
high-fidelity S-CONPRI
modeling O
approaches O
will O
be S-MATE
very O
useful O
for O
building O
up O
a O
digital O
twin O
of O
WAAM S-MANP
to O
reduce O
development O
time O
and O
cost O
. O


WAAM S-MANP
( O
Wire-Arc-Additive-Manufacturing O
) O
is O
a O
metal B-MANP
additive I-MANP
manufacturing E-MANP
process O
using O
arc B-MANP
welding E-MANP
to O
create O
large O
components S-MACEQ
with O
high B-PARA
deposition I-PARA
rate E-PARA
. O


The O
workpiece B-CONPRI
quality E-CONPRI
and O
the O
process S-CONPRI
productivity O
are O
strongly O
dependent O
both O
on O
the O
process B-CONPRI
parameters E-CONPRI
( O
wire O
feed S-PARA
speed O
, O
voltage O
and O
current O
) O
and O
on O
the O
selected O
deposition B-PARA
path E-PARA
. O


Currently O
, O
the O
CAM S-ENAT
( O
Computer-Aided-Manufacturing O
) O
software S-CONPRI
dedicated O
to O
WAAM S-MANP
rely O
on O
a O
multi-pass O
strategy O
to O
create O
the O
component S-MACEQ
layers O
, O
i.e O
. O


each O
layer S-PARA
is O
built O
overlapping O
multiple O
welding S-MANP
passes O
. O


However O
, O
since O
WAAM S-MANP
can O
create O
wide O
layers O
, O
a O
single O
pass O
strategy O
can O
improve O
the O
process S-CONPRI
efficiency O
when O
dealing O
with O
thin O
walled O
components S-MACEQ
. O


This O
paper O
proposes O
CAM S-ENAT
software O
dedicated O
to O
WAAM S-MANP
, O
using O
a O
single O
pass O
strategy O
. O


The O
proposed O
solution S-CONPRI
uses O
a O
midsurface O
representation O
of O
the O
workpiece S-CONPRI
as S-MATE
input O
, O
to O
generate O
the O
deposition S-CONPRI
toolpath O
. O


A O
specific O
strategy O
is O
developed O
and O
proposed O
for O
each O
one O
of O
the O
selected O
features O
, O
with O
the O
aim O
of O
minimizing O
the O
geometrical O
errors S-CONPRI
and O
to O
ensure O
the O
required O
machining B-PARA
allowances E-PARA
for O
the O
subsequent O
finishing B-MANP
operations E-MANP
. O


The O
effectiveness S-CONPRI
of O
the O
proposed O
strategy O
is O
verified O
manufacturing S-MANP
a O
test O
case O
. O


The O
Wire-Arc B-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
process S-CONPRI
is O
an O
increasingly O
attractive O
method O
for O
producing O
porosity-free O
metal S-MATE
components S-MACEQ
. O


However O
, O
the O
residual B-PRO
stresses E-PRO
and O
distortions O
resulting O
from O
the O
WAAM S-MANP
process S-CONPRI
are O
major O
concerns O
as S-MATE
they O
not O
only O
influence O
the O
part O
tolerance S-PARA
but O
can O
also O
cause O
premature O
failure S-CONPRI
in O
the O
final O
component S-MACEQ
during O
service O
. O


The O
current O
paper O
presents O
a O
method O
for O
using O
neutron B-CHAR
diffraction E-CHAR
to O
measure O
residual B-PRO
stresses E-PRO
in O
Fe3Al O
intermetallic S-MATE
wall O
components S-MACEQ
that O
have O
been O
in-situ S-CONPRI
additively O
fabricated S-CONPRI
using O
the O
WAAM S-MANP
process S-CONPRI
with O
different O
post-production O
treatments O
. O


By O
using O
averaging O
methods O
during O
the O
experimental S-CONPRI
setup O
and O
data S-CONPRI
processing O
, O
more O
reliable O
residual B-PRO
stress E-PRO
results O
are O
obtained O
from O
the O
acquired O
neutron B-CHAR
diffraction E-CHAR
data S-CONPRI
. O


In O
addition O
, O
the O
present O
study O
indicates O
that O
the O
normal O
residual B-PRO
stresses E-PRO
are O
significant O
compared O
to O
normal O
butt/fillet O
welding S-MANP
samples S-CONPRI
, O
which O
is O
caused O
by O
the O
large O
temperature B-PARA
gradient E-PARA
in O
this O
direction O
during O
the O
additive S-MATE
layer O
depositions O
. O


Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
presents O
unprecedented O
opportunities O
to O
enable O
design B-CONPRI
freedom E-CONPRI
in O
parts O
that O
are O
unachievable O
via O
conventional B-MANP
manufacturing E-MANP
. O


However O
, O
AM-processed O
components S-MACEQ
generally O
lack O
the O
necessary O
performance S-CONPRI
metrics O
for O
widespread O
commercial O
adoption O
. O


We O
present O
a O
novel O
AM S-MANP
processing O
and O
design S-FEAT
approach O
using O
removable O
heat B-MACEQ
sink E-MACEQ
artifacts O
to O
tailor O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
traditionally O
low O
strength S-PRO
and O
low O
ductility S-PRO
alloys S-MATE
. O


The O
design S-FEAT
approach O
is O
demonstrated O
with O
the O
Fe-50 O
at. O
% O
Co S-MATE
alloy S-MATE
, O
as S-MATE
a O
model B-CONPRI
material E-CONPRI
of O
interest O
for O
electromagnetic O
applications O
. O


AM-processed O
components S-MACEQ
exhibited O
unprecedented O
performance S-CONPRI
, O
with O
a O
300 O
% O
increase O
in O
strength S-PRO
and O
an O
order-of-magnitude O
improvement O
in O
ductility S-PRO
relative O
to O
conventional O
wrought B-MATE
material E-MATE
. O


These O
results O
are O
discussed O
in O
the O
context O
of O
product O
performance S-CONPRI
, O
production S-MANP
yield O
, O
and O
manufacturing S-MANP
implications O
toward O
enabling O
the O
design S-FEAT
and O
processing O
of O
high-performance O
, O
next-generation O
components S-MACEQ
, O
and O
alloys S-MATE
. O


Rib-web O
structures O
are O
used O
for O
lightweight S-CONPRI
design S-FEAT
in O
various O
applications O
. O


The O
most O
prominent O
cases O
are O
found O
in O
aerospace S-APPL
engineering O
, O
where O
intricate O
structures O
are O
produced O
by O
forging S-MANP
and O
subsequent O
machining S-MANP
or O
by O
machining S-MANP
from O
solid O
blocks O
of O
material S-MATE
. O


Due O
to O
the O
large O
scrap O
rate O
involved O
in O
conventional B-MANP
manufacturing E-MANP
, O
rib-web O
structures O
are O
suitable O
applications O
for O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
. O


Among O
the O
AM B-MANP
processes E-MANP
, O
wire-arc B-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
is O
highly O
suitable O
for O
rib-web O
structures O
due O
to O
its O
high B-PARA
deposition I-PARA
rate E-PARA
and O
the O
potential O
to O
manufacture S-CONPRI
large-size O
parts O
. O


In O
WAAM S-MANP
, O
the O
welding S-MANP
strategy O
greatly O
influences O
the O
properties S-CONPRI
and O
quality S-CONPRI
of O
deposited O
parts O
. O


With O
an O
increasing O
number O
of O
starts O
and O
stops O
, O
the O
danger O
of O
uneven O
material S-MATE
build-up O
and O
welding B-CONPRI
defects E-CONPRI
increases O
. O


This O
study O
presents O
a O
novel O
strategy O
for O
generating O
optimal O
tool B-CONPRI
paths E-CONPRI
for O
WAAM S-MANP
of O
lightweight S-CONPRI
rib-web O
structures O
, O
mitigating O
the O
disadvantages O
of O
discontinuous O
welding S-MANP
paths O
such O
as S-MATE
welding O
defects S-CONPRI
and O
uneven O
build-up O
. O


When O
two O
or O
more O
weld B-CONPRI
beads E-CONPRI
are O
deposited O
on O
each O
edge O
, O
the O
vertices S-PARA
of O
the O
rib-web O
structure S-CONPRI
may O
suffer O
from O
underfilling O
. O


It O
is O
shown O
that O
this O
can O
be S-MATE
avoided O
by O
a O
correction O
strategy O
, O
which O
consists O
in O
manufacturing S-MANP
the O
part O
once O
, O
evaluating O
the O
size O
of O
voids S-CONPRI
in O
the O
junctions S-APPL
, O
and O
computing O
a O
correction O
to O
deposit O
the O
required O
amount O
of O
material S-MATE
into O
the O
center O
of O
the O
junction S-APPL
. O


While O
this O
strategy O
may O
be S-MATE
used O
if O
a O
single O
part O
is O
considered O
, O
it O
is O
shown O
that O
the O
tool B-CONPRI
path E-CONPRI
correction O
to O
be S-MATE
applied O
to O
arbitrary O
junction S-APPL
geometries S-CONPRI
can O
be S-MATE
represented O
by O
a O
neural B-CONPRI
network E-CONPRI
that O
is O
derived O
from O
an O
experimental S-CONPRI
database S-ENAT
consisting O
of O
representative O
junction S-APPL
types O
. O


With O
this O
approach O
, O
paths O
for O
any O
rib-web O
geometry S-CONPRI
can O
be S-MATE
generated O
, O
which O
saves O
lead B-PARA
time E-PARA
in O
variant-rich O
production S-MANP
. O


Locally O
dispensing O
fine O
and O
irregular O
dry O
powders S-MATE
with O
a O
stable O
and O
continuous O
flow B-PARA
rate E-PARA
for O
additive B-MANP
manufacturing E-MANP
purposes O
is O
challenging O
. O


Ultrasonic B-PARA
vibration E-PARA
is O
an O
effective O
tool S-MACEQ
to O
deposit O
spherical S-CONPRI
powders S-MATE
. O


However O
, O
the O
existing O
single O
ultrasonic B-PARA
vibration E-PARA
actuated O
powder S-MATE
dispenser O
could O
cause O
powder S-MATE
jamming O
and O
blockage O
when O
dispensing O
irregularly O
shaped O
ceramic S-MATE
particles O
. O


In O
this O
study O
, O
we O
demonstrate O
a O
hybrid O
ultrasonic O
and O
motor O
vibration O
integrated O
dispensing O
method O
to O
successfully O
deposit O
irregularly O
shaped O
silicon B-MATE
carbide E-MATE
( O
SiC S-MATE
) O
powder S-MATE
and O
SiC S-MATE
and O
metal B-MATE
powder E-MATE
mixtures O
. O


Flow B-PARA
rate E-PARA
experiments O
on O
mixed O
SiC-316 O
L O
powders S-MATE
with O
SiC S-MATE
volume O
fractions O
of O
25 O
vol O
% O
, O
40 O
vol O
% O
, O
and O
50 O
vol O
% O
, O
indicated O
that O
the O
powder B-PARA
flow I-PARA
rate E-PARA
was O
determined O
by O
powder S-MATE
packing O
density S-PRO
after O
pre-mixing O
and O
before O
deposition S-CONPRI
. O


A O
lower O
packing O
density S-PRO
resulted O
in O
a O
higher O
powder B-PARA
flow I-PARA
rate E-PARA
. O


Both O
the O
SiC S-MATE
particle S-CONPRI
size O
and O
SiC S-MATE
volume O
fraction S-CONPRI
affected O
the O
final O
mixed O
powder S-MATE
packing O
density S-PRO
. O


The O
SiC-316 O
L O
mixture O
with O
40 O
vol O
% O
of O
320 O
grit O
SiC B-MATE
powder E-MATE
had O
the O
highest O
powder B-PARA
flow I-PARA
rate E-PARA
( O
37.53 O
μL/s O
) O
. O


Finally O
, O
the O
new O
powder S-MATE
deposition S-CONPRI
approach O
was O
successfully O
used O
for O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
manufacturing O
of O
a O
double O
helix O
structure S-CONPRI
made O
of O
a O
316 O
L O
stainless B-MATE
steel E-MATE
and O
a O
SiC-316 O
L O
mixture O
. O


Such O
a O
powder S-MATE
dispensing O
technology S-CONPRI
has O
the O
potential O
to O
be S-MATE
applied O
in O
powder B-MATE
materials E-MATE
involved O
in O
additive B-MANP
manufacturing E-MANP
and O
pharmacy O
industries S-APPL
. O


Direct O
observation O
and O
quantification O
of O
melt B-MATE
pool E-MATE
evolution S-CONPRI
during O
LPBF S-MANP
through O
in-situ S-CONPRI
x-ray O
imaging S-APPL
. O


Melt B-MATE
pool E-MATE
undergoes O
different O
melt S-CONPRI
regimes O
and O
exhibits O
orders-of-magnitude O
volume S-CONPRI
change O
under O
a O
constant O
input O
energy B-PARA
density E-PARA
. O


Laser S-ENAT
absorption S-CONPRI
variation O
under O
constant O
input O
energy B-PARA
density E-PARA
is O
an O
important O
cause O
of O
melt B-MATE
pool E-MATE
variation O
. O


Laser S-ENAT
absorption S-CONPRI
variation O
stems O
from O
the O
separate O
effects O
of O
laser B-PARA
power E-PARA
and O
scan B-PARA
speed E-PARA
on O
depression O
zone O
development O
. O


Size O
and O
shape O
of O
a O
melt B-MATE
pool E-MATE
play O
a O
critical O
role O
in O
determining O
the O
microstructure S-CONPRI
in O
additively B-MANP
manufactured E-MANP
metals O
. O


However O
, O
it O
is O
very O
challenging O
to O
directly O
characterize O
the O
size O
and O
shape O
of O
the O
melt B-MATE
pool E-MATE
beneath O
the O
surface S-CONPRI
of O
the O
melt B-MATE
pool E-MATE
during O
the O
additive B-MANP
manufacturing I-MANP
process E-MANP
. O


Here O
, O
we O
report O
the O
direct O
observation O
and O
quantification O
of O
melt B-MATE
pool E-MATE
variation O
during O
the O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
additive B-MANP
manufacturing I-MANP
process E-MANP
under O
constant O
input O
energy B-PARA
density E-PARA
by O
in-situ S-CONPRI
high-speed O
high-energy O
x-ray B-CHAR
imaging E-CHAR
. O


We O
show O
that O
the O
melt B-MATE
pool E-MATE
can O
undergo O
different O
melting S-MANP
regimes O
and O
both O
the O
melt B-PARA
pool I-PARA
dimension E-PARA
and O
melt B-MATE
pool E-MATE
volume O
can O
have O
orders-of-magnitude O
change O
under O
a O
constant O
input O
energy B-PARA
density E-PARA
. O


Our O
analysis O
shows O
that O
the O
significant O
melt B-MATE
pool E-MATE
variation O
can O
not O
be S-MATE
solely O
explained O
by O
the O
energy O
dissipation O
rate O
. O


We O
found O
that O
energy B-CHAR
absorption E-CHAR
changes O
significantly O
under O
a O
constant O
input O
energy B-PARA
density E-PARA
, O
which O
is O
another O
important O
cause O
of O
melt B-MATE
pool E-MATE
variation O
. O


Our O
further O
analysis O
reveals O
that O
the O
significant O
change O
in O
energy B-CHAR
absorption E-CHAR
originates O
from O
the O
separate O
roles O
of O
laser B-PARA
power E-PARA
and O
scan B-PARA
speed E-PARA
in O
depression O
zone O
development O
. O


The O
results O
reported O
here O
are O
important O
for O
understanding O
the O
laser B-MANP
powder I-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing I-MANP
process E-MANP
and O
guiding O
the O
development O
of O
better O
metrics O
for O
processing O
parameter S-CONPRI
design S-FEAT
. O


Successful O
round B-CHAR
robin I-CHAR
test E-CHAR
conducted O
using O
various O
additive B-APPL
manufactured I-APPL
part E-APPL
producers O
of O
the O
same O
test O
parts O
. O


Various O
intentional O
and O
unintentional O
defects S-CONPRI
identified O
. O


Porosity/defect O
distribution S-CONPRI
extends O
from O
coupon O
samples S-CONPRI
to O
complex O
parts O
in O
general O
. O


Micro O
computed B-CHAR
tomography E-CHAR
( O
microCT S-CHAR
) O
allows O
non-destructive O
insights O
into O
the O
quality S-CONPRI
of O
additively B-MANP
manufactured E-MANP
parts O
and O
the O
processes S-CONPRI
that O
produce O
them O
. O


A O
round B-CHAR
robin I-CHAR
test E-CHAR
was O
conducted O
as S-MATE
follows O
: O
a O
series O
of O
standard S-CONPRI
test O
procedures O
( O
part O
sizes O
and O
shapes O
and O
test O
protocols S-CONPRI
) O
were O
applied O
– O
using O
one O
microCT S-CHAR
system O
– O
to O
identical O
parts O
produced O
on O
a O
variety O
of O
metal B-MANP
additive I-MANP
manufacturing E-MANP
systems O
( O
specifically O
laser B-MACEQ
powder I-MACEQ
bed I-MACEQ
fusion I-MACEQ
systems E-MACEQ
) O
. O


These O
are O
simple S-MANP
parts O
: O
a O
10 O
mm S-MANP
cube S-CONPRI
, O
a O
15 O
mm S-MANP
diameter S-CONPRI
vertical-built O
cylinder O
and O
a O
basic O
topology S-CONPRI
optimized O
example O
part O
– O
a O
bracket S-MACEQ
. O


The O
15 O
mm S-MANP
diameter S-CONPRI
cylinder O
acts O
as S-MATE
witness O
specimen O
for O
the O
build S-PARA
of O
the O
complex O
part O
. O


All O
these O
were O
produced O
in O
Ti6Al4V S-MATE
, O
and O
in O
some O
cases O
parts O
were O
provided O
with O
variations S-CONPRI
in O
process B-CONPRI
parameters E-CONPRI
or O
manufacturing S-MANP
conditions O
which O
led S-APPL
to O
different O
types O
of O
intentional O
manufacturing S-MANP
flaws S-CONPRI
or O
defects S-CONPRI
. O


The O
major O
result O
shown O
is O
that O
the O
analysis O
of O
a O
simple S-MANP
10 O
mm S-MANP
cube S-CONPRI
clearly O
identifies O
incorrect O
process B-CONPRI
parameters E-CONPRI
even O
for O
very O
low O
levels O
of O
porosity S-PRO
, O
with O
unique O
porosity S-PRO
distributions S-CONPRI
and O
characteristics O
. O


The O
witness O
specimen O
( O
15 O
mm S-MANP
cylinder O
) O
allows O
clear O
identification O
of O
layered O
stop-start O
flaws S-CONPRI
, O
at O
a O
resolution S-PARA
better O
than O
a O
complex O
part O
built O
alongside O
it O
, O
allowing O
to O
identify O
defective O
builds S-CHAR
. O


The O
results O
indicate O
a O
successful O
first O
step S-CONPRI
at O
standardized O
microCT S-CHAR
analysis O
procedures O
for O
improvement O
of O
processes S-CONPRI
and O
quality B-CONPRI
control E-CONPRI
in O
additive B-MANP
manufacturing E-MANP
. O


Understanding O
microstructural S-CONPRI
development O
in O
additive B-MANP
manufacturing E-MANP
under O
highly O
non-equilibrium O
cooling S-MANP
conditions O
and O
the O
consequent O
effects O
on O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
final O
component S-MACEQ
is O
critical O
for O
accelerating O
industrial S-APPL
adoption O
of O
these O
manufacturing S-MANP
techniques O
. O


In O
this O
study O
, O
simple S-MANP
but O
effective O
theoretical B-CONPRI
solidification E-CONPRI
models O
are O
recalled O
to O
evaluate O
their O
ability O
to O
predict O
of O
microstructural S-CONPRI
features O
in O
additive B-MANP
manufacturing E-MANP
applications O
. O


As S-MATE
a O
case B-CONPRI
study E-CONPRI
, O
the O
resulting O
solidification B-CONPRI
microstructure E-CONPRI
selection O
maps O
are O
created O
to O
predict O
the O
stable O
growth O
modality O
and O
the O
columnar O
to O
equiaxed O
transition S-CONPRI
( O
CET O
) O
of O
an O
Al-10Si-0.5Mg B-MATE
alloy E-MATE
processed O
via O
Selective B-MANP
Laser I-MANP
Melting E-MANP
. O


The O
potential O
of O
this O
method O
in O
microstructural S-CONPRI
predictions O
for O
additively B-MANP
manufactured I-MANP
products E-MANP
, O
as S-MATE
well O
as S-MATE
outstanding O
challenges O
and O
limitations O
, O
are O
discussed O
. O


The O
present O
theoretical/experimental O
investigation O
deals O
with O
the O
problem O
of O
performing O
the O
static O
assessment O
of O
notched O
components S-MACEQ
made O
of O
additively B-MANP
manufactured E-MANP
Acrylonitrile B-MATE
Butadiene I-MATE
Styrene E-MATE
( O
ABS S-MATE
) O
. O


The O
notch S-FEAT
strength O
of O
this O
3D-printed S-MANP
material O
was O
investigated O
by O
testing S-CHAR
a O
large O
number O
of O
specimens O
, O
with O
the O
experiments O
being O
run O
not O
only O
under O
tension O
, O
but O
also O
under O
three-point B-CHAR
bending E-CHAR
. O


The O
samples S-CONPRI
contained O
geometrical B-FEAT
features E-FEAT
of O
different O
sharpness O
and O
were O
manufactured S-CONPRI
( O
flat O
on O
the O
build B-MACEQ
plate E-MACEQ
) O
by O
changing O
the O
printing O
direction O
. O


Being O
supported O
by O
the O
experimental S-CONPRI
evidence O
, O
the O
hypothesis O
was O
formed O
that O
the O
mechanical B-CONPRI
response E-CONPRI
of O
3D-printed S-MANP
ABS O
can O
be S-MATE
modelled O
effectively O
by O
treating O
it O
as S-MATE
a O
material S-MATE
that O
is O
linear-elastic O
, O
brittle S-PRO
, O
homogenous O
and O
isotropic S-PRO
. O


This O
simplifying O
hypothesis O
allowed O
the O
Theory O
of O
Critical O
Distances O
to O
be S-MATE
employed O
also O
to O
assess O
static O
strength S-PRO
of O
3D-printed S-MANP
ABS O
containing O
geometrical B-FEAT
features E-FEAT
. O


The O
validation S-CONPRI
exercise O
based O
on O
the O
experimental S-CONPRI
results O
being O
generated O
demonstrates O
that O
this O
theory O
is O
highly O
accurate S-CHAR
, O
with O
its O
use O
leading O
to O
predictions S-CONPRI
falling O
mainly O
within O
an O
error S-CONPRI
interval O
of O
about O
±20 O
% O
. O


This O
level O
of O
accuracy S-CHAR
is O
certainly O
satisfactory O
especially O
because O
this O
static O
assessment O
methodology S-CONPRI
can O
be S-MATE
used O
in O
situations O
of O
engineering S-APPL
relevance O
by O
making O
use O
of O
the O
results O
obtained O
by O
solving O
standard S-CONPRI
linear-elastic O
Finite B-CONPRI
Element I-CONPRI
models E-CONPRI
. O


Material S-MATE
calibration S-CONPRI
was O
carried O
out O
for O
DMLS-MS1 O
and O
hybrid O
DMLS-MS1-H13 O
. O


Finite B-CONPRI
element E-CONPRI
modeling O
for O
Rockwell B-CHAR
hardness I-CHAR
test E-CHAR
was O
implemented O
. O


A O
combined O
FEM-analytical O
approach O
was O
developed O
to O
calculate O
fatigue B-PRO
life E-PRO
of O
DMLS-MS1 O
. O


Finite B-CONPRI
element I-CONPRI
model E-CONPRI
of O
welding S-MANP
process S-CONPRI
on O
DMLS-MS1 O
was O
accomplished O
. O


Fatigue B-PRO
life E-PRO
of O
welded S-MANP
DMLS-MS1 O
was O
calculated O
using O
the O
developed O
FE S-MATE
framework O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
has O
been O
recently O
used O
to O
deposit O
metal B-MATE
powder E-MATE
on O
top O
of O
conventional O
metals S-MATE
. O


Of O
particular O
interest O
is O
hybrid O
additively B-MATE
manufactured I-MATE
steels E-MATE
which O
were O
found O
to O
be S-MATE
a O
suitable O
solution S-CONPRI
to O
benefit O
from O
features O
of O
each O
metal S-MATE
at O
different O
spots O
of O
a O
mechanical S-APPL
component S-MACEQ
. O


Due O
to O
its O
superior O
mechanical S-APPL
characteristics O
, O
maraging B-MATE
steel E-MATE
( O
MS1 O
) O
has O
recently O
attracted O
tremendous O
attention O
for O
additive B-MANP
manufacturing E-MANP
applications O
mainly O
in O
aerospace S-APPL
, O
tool S-MACEQ
and O
die S-MACEQ
, O
and O
marine B-APPL
industries E-APPL
or O
to O
be S-MATE
3D B-MANP
printed E-MANP
on O
top O
of O
other O
metals S-MATE
as S-MATE
a O
hybrid O
product O
using O
different O
techniques O
such O
as S-MATE
Direct O
Metal S-MATE
Laser B-MANP
Sintering E-MANP
( O
DMLS S-MANP
) O
. O


In O
this O
paper O
a O
predictive O
finite B-CONPRI
element E-CONPRI
( O
FE S-MATE
) O
model S-CONPRI
and O
a O
combined O
analytical-numerical O
framework S-CONPRI
were O
developed O
to O
evaluate O
the O
mechanical S-APPL
performance O
of O
hybrid O
additively B-MANP
manufactured E-MANP
components O
and O
facilitate O
the O
prediction S-CONPRI
of O
hardness S-PRO
and O
fatigue B-PRO
life E-PRO
of O
these O
parts O
. O


The O
proposed O
tools S-MACEQ
were O
employed O
in O
two O
scopes O
: O
First O
to O
simulate O
the O
indentation B-CHAR
hardness I-CHAR
test E-CHAR
of O
hybrid O
DMLS-MS1-H13 O
steels S-MATE
; O
and O
second O
to O
calculate O
fatigue S-PRO
crack O
nucleation S-CONPRI
life O
of O
maraging B-MATE
steel E-MATE
including O
defects S-CONPRI
( O
i.e O
. O


welding S-MANP
residual B-PRO
stresses E-PRO
) O
. O


Parameters S-CONPRI
such O
as S-MATE
local O
and O
global O
displacements O
, O
changes O
in O
Young O
’ O
s S-MATE
modulus O
, O
and O
hardness S-PRO
, O
high O
cycle O
fatigue B-PRO
life E-PRO
, O
welding S-MANP
temperature S-PARA
distribution S-CONPRI
, O
and O
residual B-PRO
stress E-PRO
were O
investigated O
. O


The O
hardness S-PRO
experiments O
were O
carried O
out O
to O
improve O
the O
reported O
data S-CONPRI
found O
in O
similar O
studies O
, O
which O
were O
used O
as S-MATE
the O
main O
resource O
to O
validate O
the O
proposed O
numerical O
framework S-CONPRI
. O


The O
capabilities O
of O
the O
presented O
frameworks O
enable O
this O
work O
to O
target O
existing O
ambiguities O
in O
additively B-MANP
manufactured E-MANP
mechanical O
components S-MACEQ
. O


A O
net-shape O
synthesis O
process S-CONPRI
has O
been O
used O
to O
convert O
different O
isovolumetric O
precursor S-MATE
mixtures O
composed O
of O
either O
100 O
vol O
% O
86/14 O
molar O
Cr/Cr2O3 O
or O
50 O
vol O
% O
86/14 O
molar O
Cr/Cr2O3 O
with O
50 O
vol O
% O
Cr3C2 O
to O
form O
multilayer O
chromium B-MATE
carbide E-MATE
materials O
suitable O
for O
reactive O
powder B-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
. O


Selective O
deposition S-CONPRI
was O
performed O
by O
patterning O
precursor S-MATE
layers O
using O
a O
masked O
high-volume O
, O
low-pressure O
slurry S-MATE
spray O
deposition S-CONPRI
technique O
. O


Following O
deposition S-CONPRI
, O
each O
layer S-PARA
was O
thermochemically O
converted O
to O
Cr3C2 O
at O
950 O
°C O
in O
a O
gas S-CONPRI
atmosphere O
containing O
76 O
vol. O
% O
Ar S-ENAT
, O
4 O
vol. O
% O
H2 O
, O
20 O
% O
vol. O
% O
CH4 O
. O


This O
process S-CONPRI
was O
repeated O
multiple O
times O
to O
construct O
layered B-CONPRI
structures E-CONPRI
representative O
of O
additively B-MANP
manufactured E-MANP
refractory O
ceramics S-MATE
. O


X-ray B-CHAR
diffraction E-CHAR
characterization O
and O
quantitative B-CONPRI
phase E-CONPRI
analysis O
of O
each O
converted O
layer S-PARA
indicated O
that O
the O
average S-CONPRI
phase O
fraction S-CONPRI
of O
Cr3C2 O
present O
in O
the O
multi-layered O
samples S-CONPRI
following O
conversion O
from O
Cr/Cr2O3 O
and O
Cr3C2/Cr/Cr2O3 O
precursors O
was O
94.5 O
wt O
% O
( O
SD O
= O
0.92 O
) O
and O
98.8 O
wt O
% O
( O
SD O
= O
0.21 O
) O
respectively O
. O


Despite O
the O
higher O
phase B-CONPRI
fraction E-CONPRI
of O
Cr3C2 O
produced O
by O
the O
three-component O
precursor S-MATE
system O
, O
SEM S-CHAR
imaging S-APPL
of O
the O
sample S-CONPRI
microstructures S-MATE
and O
fracture S-CONPRI
analysis O
indicated O
that O
increased O
bonding S-CONPRI
occurred O
in O
Cr3C2 O
produced O
by O
conversion O
of O
Cr/Cr2O3 O
. O


This O
reaction-induced O
bonding S-CONPRI
enhanced O
the O
interlayer O
mechanical B-PRO
integrity E-PRO
. O


The O
results O
in O
this O
work O
demonstrate O
the O
use O
of O
isovolumetric O
reaction O
synthesis O
techniques O
that O
are O
broadly O
applicable O
for O
non-oxide S-MATE
ceramic S-MATE
production O
using O
reactive O
additive B-MANP
manufacturing E-MANP
methods O
. O


A O
novel O
hydrodynamic O
cavitation S-CONPRI
abrasive S-MATE
finishing O
( O
HCAF O
) O
process S-CONPRI
was O
developed O
. O


Internal O
surface B-MANP
finishing E-MANP
was O
done O
using O
cavitation-aided O
microparticle O
abrasion O
. O


Synergistic O
effects O
enhanced O
the O
material S-MATE
removal O
and O
surface B-FEAT
finish E-FEAT
up O
to O
80 O
% O
. O


Surface B-MANP
finishing E-MANP
additive-manufactured O
( O
AM S-MANP
) O
internal O
channels O
is O
challenging O
. O


In O
this O
study O
, O
a O
novel O
hydrodynamic O
cavitation S-CONPRI
abrasive S-MATE
finishing O
( O
HCAF O
) O
technique O
is O
proposed O
and O
its O
feasibility S-CONPRI
for O
surface B-MANP
finishing E-MANP
is O
analyzed O
. O


Surface B-MANP
finishing E-MANP
is O
performed O
using O
controlled O
hydrodynamic O
cavitation S-CONPRI
erosion O
and O
microparticle O
abrasion O
phenomena O
. O


Various O
surface-finishing O
conditions O
were O
employed O
to O
investigate O
material S-MATE
removal O
and O
surface B-FEAT
finish E-FEAT
enhancement O
via O
synergistic O
effects O
in O
the O
HCAF O
process S-CONPRI
. O


To O
quantify O
the O
contributions O
from O
each O
erosion O
mechanism S-CONPRI
, O
additively B-MANP
manufactured E-MANP
AlSi10Mg O
internal O
channels O
were O
surface S-CONPRI
finished O
in O
isolated O
conditions O
of O
a O
) O
liquid O
impingement O
, O
b S-MATE
) O
absolute O
cavitation S-CONPRI
erosion O
, O
c S-MATE
) O
absolute O
abrasion O
, O
and O
d O
) O
cavitation-assisted O
microparticle O
abrasion O
. O


The O
erosion O
rate O
and O
total O
thickness O
loss O
were O
established O
as S-MATE
the O
measurands O
to O
quantify O
the O
intensity O
of O
the O
surface B-FEAT
finish E-FEAT
. O


A O
synergy O
map O
is O
proposed O
to O
quantify O
the O
contribution O
from O
the O
synergistic O
effects O
from O
hydrodynamic O
cavitation S-CONPRI
abrasive S-MATE
finishing O
. O


The O
synergistic O
material-removal O
mechanism S-CONPRI
is O
explained O
using O
surface B-CHAR
morphology E-CHAR
observations O
. O


Hydrodynamic O
cavitation S-CONPRI
gradually O
removed O
loosely O
attached O
surface B-CONPRI
asperities E-CONPRI
in O
AM S-MANP
internal O
channels O
. O


The O
findings O
suggest O
that O
the O
synergistic O
effects O
in O
hydrodynamic O
cavitation S-CONPRI
abrasive S-MATE
finishing O
are O
effective O
in O
enhancing O
the O
material S-MATE
removal O
and O
surface-finish O
quality S-CONPRI
of O
AM S-MANP
components O
. O


Tracking O
codes O
are O
embedded O
inside O
3D B-APPL
printed I-APPL
parts E-APPL
for O
product O
authentication O
. O


Imaging S-APPL
method O
like O
micro-CT S-CHAR
can O
retrieve O
the O
internal O
tracking O
code O
information O
. O


Micro-CT S-CHAR
images S-CONPRI
of O
the O
code O
present O
poor O
contrast O
and O
imaging S-APPL
artifact O
challenges O
. O


Pre- O
and O
post-processing S-CONPRI
enable O
automatic O
and O
robust O
image S-CONPRI
reading O
and O
verification S-CONPRI
. O


The O
developed O
image S-CONPRI
processing O
methods O
have O
no O
dependence O
on O
the O
original O
image S-CONPRI
. O


The O
layer-by-layer S-CONPRI
printing O
process S-CONPRI
of O
additive B-MANP
manufacturing E-MANP
methods O
provides O
new O
opportunities O
to O
embed O
identification O
codes O
inside O
parts O
during O
manufacture S-CONPRI
. O


The O
availability O
of O
reverse B-CONPRI
engineering E-CONPRI
tools O
has O
increased O
the O
risk O
of O
counterfeit O
part O
production S-MANP
and O
new O
authentication O
technologies S-CONPRI
such O
as S-MATE
the O
one O
proposed O
in O
this O
paper O
are O
required O
for O
many O
applications O
including O
aerospace B-MACEQ
components E-MACEQ
and O
medical B-APPL
implants E-APPL
and O
devices O
. O


The O
embedded O
codes O
are O
read O
by O
imaging S-APPL
techniques O
such O
as S-MATE
micro-Computed O
Tomography O
( O
micro-CT S-CHAR
) O
scanners O
or O
radiography S-ENAT
. O


The O
work O
presented O
in O
this O
paper O
is O
focused O
on O
developing O
methods O
that O
can O
improve O
the O
quality S-CONPRI
of O
the O
recovered O
micro-CT S-CHAR
scanned O
code O
images S-CONPRI
such O
that O
they O
can O
be S-MATE
interpreted O
by O
standard S-CONPRI
code O
reader O
technology S-CONPRI
. O


Inherent O
low O
contrast O
and O
the O
presence O
of O
imaging S-APPL
artifacts O
are O
the O
main O
challenges O
that O
need O
to O
be S-MATE
addressed O
. O


Image S-CONPRI
processing O
methods O
are O
developed O
to O
address O
these O
challenges O
using O
titanium S-MATE
and O
aluminum B-MATE
alloy E-MATE
specimens O
containing O
embedded O
quick O
response O
( O
QR O
) O
codes O
. O


The O
proposed O
techniques O
for O
recovering O
the O
embedded O
codes O
are O
based O
on O
a O
combination O
of O
Mathematical S-CONPRI
Morphology O
and O
an O
innovative O
de-noising O
algorithm S-CONPRI
based O
on O
optimal O
image S-CONPRI
filtering O
techniques O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
commonly O
referred O
to O
as S-MATE
3D B-MANP
printing E-MANP
, O
was O
originally O
used O
for O
rapid B-ENAT
prototyping E-ENAT
. O


However O
, O
research S-CONPRI
into O
new O
technologies S-CONPRI
has O
allowed O
AM S-MANP
to O
become O
applicable O
far O
beyond O
prototype S-CONPRI
fabrication S-MANP
. O


Oak O
Ridge O
National O
Laboratory S-CONPRI
( O
ORNL O
) O
, O
sponsored O
by O
the O
Office O
of O
Naval O
Research S-CONPRI
, O
has O
designed S-FEAT
and O
developed O
an O
anthropomorphic O
seven O
degree-of-freedom O
( O
DOF O
) O
dual O
arm O
hydraulic O
manipulator S-MACEQ
using O
metal B-MANP
AM E-MANP
technologies O
. O


The O
titanium S-MATE
manipulators S-MACEQ
are O
designed S-FEAT
for O
subsea O
use O
. O


This O
article O
will O
detail O
the O
novel O
AM S-MANP
design O
of O
the O
hydraulic O
manipulator S-MACEQ
system O
. O


It O
will O
cover O
the O
manipulators S-MACEQ
’ O
pitch O
and O
rotary O
link O
designs S-FEAT
, O
custom O
valves O
, O
hydraulic O
power S-PARA
unit O
, O
and O
the O
motivation O
for O
a O
dual O
arm O
design S-FEAT
. O


In O
all O
manufacturing B-MANP
processes E-MANP
, O
there O
are O
several O
factors O
for O
which O
the O
final O
product O
exhibits O
dimensional O
and O
shape O
deviations O
from O
its O
ideal O
nominal O
geometry S-CONPRI
. O


In O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
and O
3D B-MANP
printing E-MANP
, O
a O
part O
is O
built O
layerwise O
in O
a O
single O
manufacturing S-MANP
step O
and O
is O
often O
net-shaped O
. O


In O
most O
cases O
, O
no O
finishing B-MANP
operation E-MANP
is O
applied O
to O
change O
the O
dimensions S-FEAT
of O
the O
product O
, O
apart O
from O
a O
reduction S-CONPRI
of O
the O
superficial O
roughness S-PRO
through O
sandblasting O
or O
polishing S-MANP
. O


Therefore O
, O
knowing O
the O
dimensional B-CHAR
tolerance E-CHAR
of O
AM B-MANP
processes E-MANP
in O
advance O
is O
of O
fundamental O
importance O
, O
but O
little O
information O
is O
currently O
available O
in O
the O
literature O
. O


A O
benchmarking O
analysis O
of O
three O
different O
AM S-MANP
systems O
for O
polymers S-MATE
is O
presented O
in O
this O
paper O
. O


The O
compared O
machines S-MACEQ
are O
based O
on O
different O
AM B-MANP
techniques E-MANP
which O
are O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
, O
selective B-MANP
laser I-MANP
sintering E-MANP
( O
SLS S-MANP
) O
and O
Arburg O
plastic S-MATE
freeforming O
( O
APF O
) O
. O


The O
dimensional B-CHAR
accuracy E-CHAR
of O
the O
machines S-MACEQ
has O
been O
defined O
using O
the O
ISO S-MANS
IT O
grades O
of O
a O
reference O
artifact O
. O


In O
the O
analysis O
of O
the O
benchmarking O
results O
, O
a O
specific O
focus O
is O
made O
on O
the O
importance O
of O
the O
thermal O
household O
in O
SLS S-MANP
and O
a O
parameter S-CONPRI
named O
SLS S-MANP
modulus O
is O
proposed O
to O
identify O
critical O
heat S-CONPRI
concentrations O
in O
the O
powder B-MACEQ
bed E-MACEQ
that O
may O
influence O
the O
dimensional B-CHAR
accuracy E-CHAR
of O
the O
manufactured S-CONPRI
part O
. O


Wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
, O
which O
is O
an O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
that O
uses O
metal B-MATE
materials E-MATE
, O
has O
a O
higher O
fabricated S-CONPRI
volume O
per O
unit O
time O
but O
a O
lower O
fabricated S-CONPRI
shape O
accuracy S-CHAR
compared O
with O
other O
methods O
. O


With O
this O
process S-CONPRI
, O
the O
surface B-PRO
roughness E-PRO
of O
fabricated S-CONPRI
objects O
is O
several O
hundred O
micrometers O
or O
more O
, O
and O
a O
finishing B-MANP
process E-MANP
is O
necessary O
. O


However O
, O
the O
fabricated S-CONPRI
objects O
after O
finishing S-MANP
can O
have O
uncut O
areas S-PARA
or O
can O
be S-MATE
overcut O
during O
the O
finishing B-MANP
process E-MANP
owing O
to O
the O
large O
difference O
between O
the O
target O
and O
actual O
fabricated S-CONPRI
shapes O
. O


Therefore O
, O
the O
objective O
of O
this O
study O
is O
to O
develop O
a O
cooperative O
system O
for O
WAAM S-MANP
and O
machining S-MANP
that O
includes O
a O
process S-CONPRI
that O
measures O
the O
shape O
of O
the O
fabricated S-CONPRI
object O
. O


First O
, O
the O
three-dimensional S-CONPRI
( O
3-D S-CONPRI
) O
shape O
of O
the O
fabricated S-CONPRI
object O
was O
measured O
by O
structure S-CONPRI
from O
motion O
( O
SfM O
) O
and O
compared O
with O
the O
3-D S-CONPRI
computer-aided O
design S-FEAT
( O
CAD S-ENAT
) O
data S-CONPRI
. O


Second O
, O
the O
original O
design S-FEAT
was O
modified O
, O
and O
the O
amount O
of O
material S-MATE
removed O
during O
finish O
cutting S-MANP
was O
optimized O
with O
the O
developed O
software S-CONPRI
. O


Finally O
, O
the O
fabricated S-CONPRI
hollow O
object O
was O
finished O
by O
milling S-MANP
to O
obtain O
a O
uniform O
wall B-FEAT
thickness E-FEAT
without O
any O
defects S-CONPRI
. O


A O
3-D S-CONPRI
fabricated O
object O
was O
measured O
by O
SfM O
, O
and O
it O
was O
observed O
that O
the O
measurement S-CHAR
accuracy S-CHAR
was O
sufficiently O
high O
for O
the O
requirements O
of O
the O
system O
. O


In O
addition O
, O
a O
fabricated S-CONPRI
hollow O
quadrangular O
pyramid O
with O
a O
closed O
shape O
was O
machined S-MANP
with O
a O
computer B-ENAT
numerical I-ENAT
control E-ENAT
( O
CNC S-ENAT
) O
machine B-MACEQ
tool E-MACEQ
with O
the O
modification O
of O
the O
work O
origin O
. O


As S-MATE
a O
result O
, O
the O
amount O
of O
material S-MATE
removed O
during O
finish O
cutting S-MANP
was O
optimized O
, O
and O
the O
inclined O
wall B-FEAT
thickness E-FEAT
was O
uniform O
compared O
with O
that O
without O
modification O
. O


In O
addition O
, O
a O
hollow O
turbine B-APPL
blade E-APPL
with O
a O
freeform S-CONPRI
shape O
was O
successfully O
finished O
without O
any O
defects S-CONPRI
. O


A O
wire O
arc S-CONPRI
additive B-MANP
manufactured E-MANP
sample O
with O
intentional O
defects S-CONPRI
is O
studied O
. O


Owing O
to O
a O
lack O
of O
standards S-CONPRI
and O
codes O
, O
a O
calibration S-CONPRI
method O
was O
introduced O
. O


The O
known O
size O
defects S-CONPRI
were O
used O
for O
calibration S-CONPRI
of O
the O
ultrasonic O
system O
. O


In O
this O
study O
, O
Wire B-MANP
+ I-MANP
Arc I-MANP
Additive I-MANP
Manufacture E-MANP
( O
WAAM S-MANP
) O
was O
employed O
to O
manufacture S-CONPRI
a O
steel S-MATE
specimen O
with O
intentionally O
embedded O
defects S-CONPRI
which O
were O
subsequently O
used O
for O
calibration S-CONPRI
of O
an O
ultrasonic O
phased O
array O
system O
and O
defect S-CONPRI
sizing O
. O


An O
ABB O
robot S-MACEQ
was O
combined O
with O
the O
Cold B-MANP
Metal I-MANP
Transfer E-MANP
( O
CMT S-MANP
) O
Gas B-MANP
Metal I-MANP
Arc E-MANP
( O
GMA S-MANP
) O
process S-CONPRI
to O
deposit O
20 O
layers O
of O
mild B-MATE
steel E-MATE
. O


Tungsten-carbide O
balls O
( O
ø1-3 O
mm S-MANP
) O
were O
intentionally O
embedded O
inside O
the O
additive S-MATE
structure O
after O
the O
4th O
, O
8th O
, O
12th O
and O
18th O
layers O
to O
serve O
as S-MATE
ultrasonic O
reflectors O
, O
simulating O
defects S-CONPRI
within O
the O
WAAM S-MANP
sample S-CONPRI
. O


An O
ultrasonic O
phased O
array O
system O
, O
consisting O
of O
a O
5 O
MHz O
64 O
Element S-MATE
phased O
array O
transducer S-MACEQ
, O
was O
used O
to O
inspect O
the O
WAAM S-MANP
sample S-CONPRI
non-destructively O
. O


The O
majority O
of O
the O
reflectors O
were O
detected O
successfully O
using O
Total O
Focusing O
Method O
( O
TFM O
) O
, O
proving O
that O
the O
tungsten B-MACEQ
carbide I-MACEQ
balls E-MACEQ
were O
successfully O
embedded O
during O
the O
WAAM S-MANP
process S-CONPRI
and O
also O
that O
these O
are O
good O
ultrasonic O
reflectors O
. O


Owing O
to O
a O
lack O
of O
standards S-CONPRI
and O
codes O
for O
the O
ultrasonic B-CHAR
inspection E-CHAR
of O
WAAM S-MANP
samples S-CONPRI
( O
Lopez O
et O
al. O
, O
2018 O
) O
, O
a O
calibration S-CONPRI
method O
and O
step-by-step O
inspection S-CHAR
strategy O
were O
introduced O
and O
then O
used O
to O
estimate O
the O
size O
and O
shape O
of O
an O
unknown O
lack O
of O
fusion S-CONPRI
( O
LoF O
) O
indication O
. O


Corrosion B-PRO
behavior E-PRO
and O
biocompatibility S-PRO
of O
AM S-MANP
( O
SLM S-MANP
) O
and O
wrought B-MATE
316 I-MATE
L I-MATE
SS E-MATE
are O
evaluated O
in O
physiological O
environment O
containing O
complexing O
agent O
i.e O
. O


Ecorr O
for O
the O
SLM S-MANP
316 B-MATE
L I-MATE
SS E-MATE
is O
consistently O
higher O
and O
breakdown O
potential O
, O
Ebd O
, O
is O
more O
than O
3 O
times O
higher O
compared O
to O
the O
wrought S-CONPRI
. O


SLM S-MANP
sample S-CONPRI
exhibits O
wider O
passive O
region O
and O
higher O
charge O
transfer O
resistance S-PRO
( O
Rt S-MANP
) O
( O
approximately O
1.5 O
to O
2.5 O
times O
) O
. O


The O
SLM S-MANP
part O
shows O
better O
cell S-APPL
proliferation O
. O


In O
order O
to O
mitigate O
potential O
implant S-APPL
failures O
, O
it O
is O
essential O
to O
determine O
the O
corrosion B-PRO
behavior E-PRO
of O
biomaterials S-MATE
in O
a O
realistic O
physiological O
environment O
. O


In O
order O
to O
simulate O
the O
real O
oxidative O
nature O
of O
human O
body O
fluid S-MATE
, O
this O
research S-CONPRI
considers O
the O
effects O
of O
a O
complexing O
agent O
while O
determining O
the O
corrosion B-PRO
behavior E-PRO
of O
316L B-MATE
stainless I-MATE
steel E-MATE
( O
SS S-MATE
) O
that O
has O
been O
fabricated S-CONPRI
by O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
process S-CONPRI
. O


the O
citrate O
ion S-CONPRI
, O
in O
Phosphate S-MATE
Buffer S-CONPRI
Saline O
( O
PBS S-MATE
) O
solution S-CONPRI
strongly O
affects O
the O
passivation S-CONPRI
behavior O
of O
316L O
SS S-MATE
by O
complex O
species O
formation O
. O


However O
, O
due O
to O
a O
rapid B-CONPRI
solidification I-CONPRI
process E-CONPRI
, O
the O
microstructural S-CONPRI
properties O
of O
the O
additively B-MANP
manufactured E-MANP
metal O
are O
not O
similar O
to O
that O
of O
the O
conventionally O
manufactured S-CONPRI
counterpart O
. O


The O
microstructure S-CONPRI
of O
the O
SLM S-MANP
316L O
SS S-MATE
contains O
refined O
sub-grains O
within O
each O
coarse O
grain S-CONPRI
and O
the O
formation O
of O
micro-inclusions O
i.e O
. O


The O
SLM S-MANP
316L O
SS S-MATE
had O
better O
pitting S-CONPRI
resistance O
and O
passive O
film O
stability S-PRO
. O


Ecorr O
for O
the O
SLM S-MANP
316L O
SS S-MATE
was O
consistently O
higher O
and O
the O
breakdown O
potential O
, O
Ebd O
, O
was O
more O
than O
three O
times O
higher O
compared O
to O
the O
wrought S-CONPRI
counterpart O
as S-MATE
determined O
by O
cyclic O
potentiodynamic B-CHAR
polarization E-CHAR
. O


Moreover O
, O
the O
SLM S-MANP
sample S-CONPRI
had O
a O
wider O
passive O
region O
and O
higher O
charge O
transfer O
resistance S-PRO
( O
Rt S-MANP
) O
( O
approximately O
1.5 O
to O
2.5 O
times O
) O
as S-MATE
determined O
by O
cyclic B-CHAR
voltammetry E-CHAR
and O
electrochemical S-CONPRI
impedance O
spectroscopy S-CONPRI
, O
respectively O
. O


In O
addition O
, O
the O
attachment O
and O
proliferation O
tendency O
of O
MC3T3-E1 O
pre-osteoblast O
cells S-APPL
were O
studied O
to O
evaluate O
biocompatibility S-PRO
. O


The O
SLM S-MANP
part O
had O
better O
cell S-APPL
proliferation O
. O


To O
summarize O
, O
in O
a O
physiological O
environment O
, O
the O
SLM S-MANP
316L O
SS S-MATE
outperformed O
the O
conventional O
wrought S-CONPRI
316L O
SS S-MATE
in O
terms O
of O
corrosion B-CONPRI
resistance E-CONPRI
and O
biocompatibility S-PRO
. O


Wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
has O
become O
a O
promising O
metal S-MATE
3D B-ENAT
printing I-ENAT
technology E-ENAT
for O
fabricating S-MANP
large-scale O
and O
complex-shaped S-CONPRI
components O
. O


One O
major O
problem O
that O
limits S-CONPRI
the O
application O
of O
WAAM S-MANP
is O
the O
difficulty O
in O
controlling O
the O
dimensional B-CHAR
accuracy E-CHAR
under O
constantly O
changing O
interlayer O
temperatures S-PARA
. O


During O
the O
deposition B-MANP
process E-MANP
, O
as S-MATE
the O
wall O
height O
increases O
, O
the O
heat S-CONPRI
accumulates O
on O
the O
upper O
layers O
, O
which O
leads O
to O
the O
variation S-CONPRI
of O
the O
layer S-PARA
dimensions S-FEAT
. O


Normal O
practices O
such O
as S-MATE
introducing O
idle O
time O
and O
actively O
cooling S-MANP
the O
workpiece S-CONPRI
to O
mitigate O
such O
problems O
lack O
efficiency O
and O
practicality O
, O
respectively O
. O


A O
novel O
process B-CONPRI
planning E-CONPRI
strategy O
is O
proposed O
in O
this O
paper O
and O
aims O
to O
achieve O
a O
continuous O
deposition B-MANP
process E-MANP
while O
ensuring O
dimensional B-CHAR
accuracy E-CHAR
. O


With O
the O
aid O
of O
a O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
, O
the O
typical O
thermal O
transfer O
cycle O
of O
the O
workpiece S-CONPRI
was O
analyzed O
and O
then O
divided O
into O
different O
stages O
. O


When O
depositing O
material S-MATE
, O
the O
interlayer O
temperature S-PARA
of O
the O
subsequent O
layers O
can O
be S-MATE
predicted O
using O
the O
developed O
algorithm S-CONPRI
. O


Hence O
, O
the O
process B-CONPRI
parameters E-CONPRI
( O
e.g. O
, O
wire O
feed S-PARA
speed O
and O
travel O
speed O
) O
can O
be S-MATE
varied O
according O
to O
the O
predicted S-CONPRI
interlayer O
temperature S-PARA
using O
the O
developed O
adaptive O
process B-CONPRI
model E-CONPRI
, O
and O
this O
will O
ensure O
the O
uniform O
layer S-PARA
dimensions S-FEAT
. O


The O
result O
shows O
that O
such O
technique O
succeeds O
in O
a O
continuous O
fabrication S-MANP
of O
the O
component S-MACEQ
with O
high O
accuracy S-CHAR
and O
efficiency O
. O


2219-Al O
specimens O
with O
no O
cracks O
and O
less O
pores S-PRO
were O
fabricated S-CONPRI
by O
novel O
laser-TIG O
hybrid O
additive B-MANP
manufacturing E-MANP
. O


The O
mechanical B-CONPRI
properties E-CONPRI
were O
higher O
than O
that O
fabricated S-CONPRI
by O
conventional O
TIG S-MANP
, O
CMT S-MANP
or O
SLM S-MANP
. O


The O
presence O
of O
laser S-ENAT
could O
refine O
grains S-CONPRI
and O
improve O
the O
uniformity O
of O
elements S-MATE
and O
eutectics O
. O


Owing O
to O
its O
high O
strength B-PRO
to I-PRO
weight I-PRO
ratio E-PRO
, O
Al–Cu O
alloy S-MATE
is O
extensively O
used O
in O
the O
aeronautic O
and O
aerospace B-APPL
industries E-APPL
. O


However O
, O
there O
are O
some O
shortcomings O
in O
the O
additive B-MANP
manufacturing E-MANP
of O
Al–Cu O
alloy S-MATE
, O
such O
as S-MATE
cracks O
and O
poor O
strength S-PRO
. O


In O
this O
work O
, O
Al–Cu O
( O
2219-Al O
) O
specimens O
with O
excellent O
mechanical B-CONPRI
properties E-CONPRI
were O
fabricated S-CONPRI
by O
laser-Tungsten O
Inert B-CONPRI
Gas E-CONPRI
( O
TIG S-MANP
) O
hybrid O
additive B-MANP
manufacturing E-MANP
. O


From O
the O
microstructural S-CONPRI
studies O
, O
the O
average S-CONPRI
grain O
size O
in O
the O
laser S-ENAT
zone O
( O
LZ O
) O
decreased O
to O
14.4 O
μm O
, O
which O
was O
approximately O
40.3 O
% O
smaller O
than O
that O
in O
the O
arc S-CONPRI
zone O
( O
AZ O
) O
. O


Its O
crystal B-PRO
orientation E-PRO
relationship O
was O
described O
as S-MATE
[ O
110 O
] O
α∥ O
[ O
002 O
] O
θ O
, O
( O
110 O
) O
α∥ O
( O
002 O
) O
θ O
between O
the O
α-Al O
matrix O
and O
the O
θ O
phase S-CONPRI
. O


Meanwhile O
, O
the O
θ′ O
phase S-CONPRI
characterized O
a O
good O
coherent O
relationship O
with O
the O
α-Al O
matrix O
, O
which O
resulted O
in O
low O
phase B-CONPRI
boundary E-CONPRI
energy O
. O


Furthermore O
, O
the O
deposited O
specimens O
exhibited O
a O
yield B-PRO
strength E-PRO
of O
155.5 O
± O
7.9 O
MPa S-CONPRI
and O
an O
ultimate B-PRO
tensile I-PRO
strength E-PRO
of O
301.5 O
± O
16.7 O
MPa S-CONPRI
, O
with O
an O
elongation S-PRO
of O
12.8 O
± O
2.8 O
% O
. O


These O
mechanical B-CONPRI
properties E-CONPRI
were O
higher O
than O
in O
specimens O
fabricated S-CONPRI
by O
TIG S-MANP
, O
CMT S-MANP
and O
SLM S-MANP
methods O
. O


The O
improved O
properties S-CONPRI
were O
predominately O
related O
to O
the O
smaller O
size O
of O
eutectics O
, O
the O
uniform O
distribution S-CONPRI
of O
Cu S-MATE
and O
the O
semi-coherent O
θ′ O
phases O
in O
the O
LZ O
. O


The O
combined O
effect O
of O
laser S-ENAT
and O
arc S-CONPRI
can O
yield O
components S-MACEQ
with O
excellent O
mechanical B-CONPRI
properties E-CONPRI
, O
promoting O
the O
material S-MATE
for O
an O
expansive O
range S-PARA
of O
applications O
. O


New O
microstructural S-CONPRI
features O
were O
found O
in O
the O
TiAl O
alloy S-MATE
manufactured O
using O
the O
gas S-CONPRI
tungsten O
arc S-CONPRI
welding-based O
additive B-MANP
manufacturing E-MANP
technology O
. O


The O
ion-irradiation O
responses O
of O
the O
new O
microstructure S-CONPRI
features O
were O
investigated O
in-situ S-CONPRI
via O
irradiation S-MANP
with O
1 O
MeV O
Kr2+ O
ions O
at O
room O
and O
873 O
K. O
Examination O
of O
the O
microstructure S-CONPRI
showed O
that O
the O
typical O
lamellar S-CONPRI
microstructure O
consisting O
of O
α2-Ti3Al O
and O
γ-TiAl O
phases O
formed O
α2/γ O
lamellar S-CONPRI
interfaces O
and O
γ/γ O
twin O
boundaries S-FEAT
. O


Apart O
from O
this O
, O
the O
γ O
lamellae S-MATE
were O
also O
found O
to O
form O
γ/γ O
lamellar S-CONPRI
boundaries S-FEAT
with O
the O
two O
γ O
lamellae S-MATE
in O
the O
same O
orientation S-CONPRI
or O
the O
< O
10-1 O
> O
// O
< O
411 O
> O
orientation S-CONPRI
relationship O
. O


This O
is O
not O
observed O
in O
the O
TiAl O
alloys S-MATE
fabricated O
using O
traditional O
alloy S-MATE
fabrication O
methods O
. O


Kr O
ion-irradiation O
at O
room O
and O
elevated O
temperatures S-PARA
resulted O
in O
no O
significant O
difference O
in O
the O
morphologies S-CONPRI
of O
most O
radiation-induced O
defects S-CONPRI
in O
the O
< O
411 O
> O
orientated O
γ O
lamellae S-MATE
and O
the O
< O
10-1 O
> O
orientated O
γ O
lamellae S-MATE
. O


However O
, O
the O
areas S-PARA
of O
the O
new O
boundaries S-FEAT
exhibited O
different O
damage S-PRO
morphologies O
in O
comparison O
with O
the O
traditional O
γ/γ O
twin O
boundaries S-FEAT
. O


The O
formation O
mechanisms O
of O
the O
new O
microstructural S-CONPRI
features O
formed O
in O
the O
additive B-MANP
manufacturing I-MANP
process E-MANP
and O
their O
irradiation S-MANP
behaviour O
are O
investigated O
and O
discussed O
. O


Additive B-MANP
manufacturing E-MANP
can O
produce O
parts O
with O
complex B-CONPRI
geometries E-CONPRI
in O
fewer O
steps O
than O
conventional O
processing O
, O
which O
leads O
to O
cost B-CONPRI
reduction E-CONPRI
and O
a O
higher O
quality S-CONPRI
of O
goods O
. O


One O
potential O
application O
is O
the O
production S-MANP
of O
molds S-MACEQ
and O
dies S-MACEQ
with O
conformal B-CONPRI
cooling E-CONPRI
for O
injection B-MANP
molding E-MANP
, O
die B-MANP
casting E-MANP
, O
and O
forging S-MANP
. O


AISI O
H13 B-MATE
tool I-MATE
steel E-MATE
is O
typically O
used O
in O
these O
applications O
because O
of O
its O
high O
hardness S-PRO
at O
elevated O
temperatures S-PARA
, O
high O
wear B-PRO
resistance E-PRO
, O
and O
good O
toughness S-PRO
. O


However O
, O
available O
data S-CONPRI
on O
the O
processing O
of O
H13 B-MATE
steel E-MATE
by O
additive B-MANP
manufacturing E-MANP
are O
still O
scarce O
. O


Thus O
, O
this O
study O
focused O
on O
the O
processability O
of O
H13 B-MATE
tool I-MATE
steel E-MATE
by O
powder B-MANP
bed I-MANP
fusion E-MANP
and O
its O
microstructural B-CHAR
characterization E-CHAR
. O


Laser B-PARA
power E-PARA
( O
97−216 O
W O
) O
and O
scan B-PARA
speed E-PARA
( O
300−700 O
mm/s O
) O
were O
varied O
, O
and O
the O
consolidation S-CONPRI
of O
parts O
, O
common O
defects S-CONPRI
, O
solidification S-CONPRI
structure O
, O
microstructure S-CONPRI
, O
and O
hardness S-PRO
were O
evaluated O
. O


Over O
the O
range S-PARA
of O
processing O
parameters S-CONPRI
, O
microstructural S-CONPRI
features O
were O
mostly O
identical O
, O
consisting O
of O
a O
predominantly O
cellular O
solidification S-CONPRI
structure O
of O
martensite S-MATE
and O
19.8 O
% O
–25.9 O
% O
of O
retained B-MATE
austenite E-MATE
. O


Cellular/dendritic O
solidification S-CONPRI
structure O
displayed O
C S-MATE
, O
Cr S-MATE
, O
and O
V S-MATE
segregation S-CONPRI
toward O
cell S-APPL
walls O
. O


The O
thermal B-PARA
cycle E-PARA
resulted O
in O
alternating O
layers O
of O
heat-affected O
zones O
, O
which O
varied O
somewhat O
in O
hardness S-PRO
and O
microstructure S-CONPRI
. O


Retained B-MATE
austenite E-MATE
was O
correlated S-CONPRI
to O
the O
solidification S-CONPRI
structure O
and O
displayed O
a O
preferential O
orientation S-CONPRI
with O
{ O
001 O
} O
//build O
direction O
. O


Density B-FEAT
and I-FEAT
porosity E-FEAT
maps O
were O
obtained O
by O
helium S-MATE
gas S-CONPRI
pycnometry O
and O
light O
optical B-CHAR
microscopy E-CHAR
, O
respectively O
, O
and O
, O
along O
with O
linear O
crack O
density S-PRO
, O
were O
used O
to O
determine O
appropriate O
processing O
parameters S-CONPRI
for O
H13 B-MATE
tool I-MATE
steel E-MATE
. O


Thermal B-CONPRI
diffusivity E-CONPRI
, O
thermal B-PRO
conductivity E-PRO
, O
and O
thermal O
capacity S-CONPRI
were O
measured O
to O
determine O
dimensionless O
processing O
parameters S-CONPRI
, O
which O
were O
then O
compared O
to O
others O
reported O
in O
the O
literature O
. O


The O
complex O
, O
nonequilibrium O
physical O
, O
chemical O
, O
and O
metallurgical S-APPL
nature O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
tends O
to O
lead S-MATE
to O
uncontrollable O
and O
unpredictable O
material S-MATE
and O
structural O
properties S-CONPRI
. O


In O
this O
study O
, O
we O
investigated O
a O
laser S-ENAT
opto-ultrasonic O
dual O
( O
LOUD O
) O
detection O
approach O
for O
simultaneous O
and O
real-time O
detection O
of O
elemental O
compositions O
, O
structural B-CONPRI
defects E-CONPRI
, O
and O
residual B-PRO
stress E-PRO
in O
aluminium S-MATE
( O
Al S-MATE
) O
alloy S-MATE
components O
during O
wire B-MANP
+ I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
processes S-CONPRI
. O


In O
this O
approach O
, O
a O
pulsed-laser O
beam S-MACEQ
was O
used O
to O
excite O
the O
surfaces S-CONPRI
of O
Al B-MATE
alloy E-MATE
samples O
to O
generate O
ultrasound O
and O
optical B-CHAR
spectra E-CHAR
. O


As S-MATE
a O
result O
, O
the O
compositional O
information O
can O
be S-MATE
obtained O
from O
the O
optical B-CHAR
spectra E-CHAR
, O
while O
the O
structural B-CONPRI
defects E-CONPRI
and O
residual B-PRO
stress E-PRO
distributions S-CONPRI
can O
be S-MATE
extracted O
from O
the O
ultrasonic O
signals O
. O


The O
silicon S-MATE
( O
Si S-MATE
) O
and O
copper S-MATE
( O
Cu S-MATE
) O
compositions O
obtained O
from O
optical S-CHAR
spectral O
analyses O
are O
consistent O
with O
those O
obtained O
from O
the O
electron-probe O
microanalyses O
( O
EPMA S-CHAR
) O
. O


The O
1 O
mm S-MANP
blowhole S-CONPRI
and O
the O
residual B-PRO
stress E-PRO
distribution S-CONPRI
of O
the O
sample S-CONPRI
were O
detected O
by O
the O
ultrasonic O
signals O
in O
the O
LOUD O
detection O
, O
which O
shows O
consistency S-CONPRI
with O
the O
conventional O
ultrasonic O
testing S-CHAR
( O
UT S-PRO
) O
. O


Both O
results O
indicate O
that O
the O
LOUD O
detection O
holds O
the O
promising O
of O
becoming O
an O
effective O
testing S-CHAR
method O
for O
AM B-MANP
processes E-MANP
to O
ensure O
quality B-CONPRI
control E-CONPRI
and O
process S-CONPRI
feedback S-PARA
. O


Wire B-MANP
+ I-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
has O
already O
proven O
to O
be S-MATE
successful O
for O
the O
production S-MANP
of O
large O
metal S-MATE
parts O
. O


However O
, O
there O
are O
still O
no O
specific O
standards S-CONPRI
available O
to O
label O
the O
quality S-CONPRI
requirements O
of O
the O
parts O
produced O
by O
WAAM S-MANP
and O
this O
is O
preventing O
a O
more O
widespread O
adoption O
of O
the O
technique.A O
crucial O
step S-CONPRI
towards O
the O
quality S-CONPRI
assurance O
of O
WAAM S-MANP
parts O
will O
be S-MATE
the O
development O
of O
Non-Destructive B-CHAR
Testing E-CHAR
( O
NDT S-CONPRI
) O
systems O
capable O
of O
identifying O
defects S-CONPRI
while O
parts O
are O
being O
produced O
. O


In O
this O
regard O
, O
Eddy B-CHAR
Current I-CHAR
Testing E-CHAR
( O
ECT O
) O
can O
play O
a O
significant O
role O
, O
by O
allowing O
the O
inspection S-CHAR
of O
both O
ferromagnetic O
and O
non-ferromagnetic O
materials S-CONPRI
, O
with O
high O
speeds O
and O
without O
contact S-APPL
with O
the O
material S-MATE
surface O
. O


The O
limitation O
here O
is O
that O
commercial O
ECT O
targets O
only O
the O
inspection S-CHAR
of O
surface S-CONPRI
and O
subsurface O
defects.This O
study O
is O
focused O
on O
the O
development O
of O
a O
NDT S-CONPRI
system O
which O
includes O
customized O
ECT O
probes S-MACEQ
for O
the O
inline O
layer-by-layer S-CONPRI
detection O
of O
defects S-CONPRI
in O
aluminium S-MATE
WAAM O
samples S-CONPRI
. O


Results O
revealed O
that O
the O
developed O
EC O
probes S-MACEQ
were O
able O
to O
locate O
artificial O
defects S-CONPRI
: O
at O
depths O
up O
to O
5 O
mm S-MANP
; O
with O
a O
thickness O
as S-MATE
small O
as S-MATE
350 O
μm O
; O
with O
the O
probe S-MACEQ
up O
to O
5 O
mm S-MANP
away O
from O
the O
inspected O
sample S-CONPRI
surface.The O
developed O
ECT O
probes S-MACEQ
proved O
to O
surpass O
the O
limitation O
of O
commercial O
ones O
. O


Also O
, O
these O
probes S-MACEQ
were O
able O
to O
overcome O
the O
limitations O
caused O
by O
the O
surface B-PRO
roughness E-PRO
of O
the O
samples S-CONPRI
and O
the O
high O
temperatures S-PARA
involved O
in O
the O
deposition B-MANP
process E-MANP
. O


These O
preliminary O
results O
represent O
an O
important O
step S-CONPRI
for O
the O
development O
of O
NDT S-CONPRI
systems O
for O
WAAM S-MANP
. O


By O
using O
filaments S-MATE
comprising O
metal S-MATE
or O
ceramic B-MATE
powders E-MATE
and O
polymer B-MATE
binders E-MATE
, O
solid O
metal S-MATE
and O
ceramic S-MATE
parts O
can O
be S-MATE
created O
by O
combining O
low-cost O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
with O
debinding S-CONPRI
and O
sintering S-MANP
. O


In O
this O
work O
, O
we O
explored O
a O
fabrication S-MANP
route O
using O
a O
FFF S-MANP
filament O
filled O
with O
316 O
L O
steel B-MATE
powder E-MATE
at O
55 O
vol.- O
% O
. O


We O
investigated O
the O
printing O
, O
debinding S-CONPRI
and O
sintering S-MANP
parameters S-CONPRI
and O
optimized O
them O
with O
respect O
to O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
final O
part O
. O


Special O
focus O
was O
placed O
on O
debinding S-CONPRI
and O
sintering S-MANP
in O
order O
to O
obtain O
components S-MACEQ
of O
low O
residual S-CONPRI
porosity S-PRO
. O


Solvent O
debinding S-CONPRI
of O
the O
printed O
green B-CONPRI
bodies E-CONPRI
created O
an O
internal O
network O
of O
interconnected O
pores S-PRO
and O
was O
followed O
by O
thermal B-CHAR
debinding E-CHAR
. O


Thermal B-CHAR
debinding E-CHAR
allowed O
for O
complete O
removal O
of O
the O
remaining O
binder S-MATE
and O
produced O
mechanically O
stable O
brown B-CHAR
parts E-CHAR
. O


Sintering S-MANP
at O
1360 O
°C O
provided O
densification S-MANP
of O
the O
parts O
and O
generated O
nearly O
isotropic S-PRO
linear O
shrinkage S-CONPRI
of O
about O
20 O
% O
. O


Using O
optimized O
parameters S-CONPRI
, O
it O
was O
possible O
to O
fabricate S-MANP
316 O
L O
steel S-MATE
components S-MACEQ
with O
a O
density S-PRO
greater O
than O
95 O
% O
via O
the O
material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
, O
debinding S-CONPRI
and O
sintering S-MANP
route O
, O
with O
achievable O
deflections O
in O
a O
3-point O
bending B-CHAR
test E-CHAR
similar O
to O
rolled O
sheet B-MATE
material E-MATE
, O
albeit O
at O
lower O
strength S-PRO
. O


Fabricating S-MANP
a O
magnesium B-MATE
alloy E-MATE
using O
wire-and-arc-based O
additive B-MANP
manufacturing E-MANP
was O
successfully O
conducted O
. O


Suitable O
processing O
conditions O
for O
realizing O
a O
solid O
structure S-CONPRI
with O
few O
weld S-FEAT
defects S-CONPRI
were O
clarified O
. O


Fabricated S-CONPRI
object O
has O
sufficient O
tensile B-PRO
strength E-PRO
compared O
with O
the O
bulk O
material S-MATE
. O


Microstructure S-CONPRI
at O
the O
boundary S-FEAT
between O
the O
substrate S-MATE
and O
the O
fabricated S-CONPRI
object O
is O
finer O
than O
that O
on O
the O
top O
layer S-PARA
. O


Material B-CONPRI
properties E-CONPRI
, O
such O
as S-MATE
porosity O
, O
tensile B-PRO
strength E-PRO
, O
and O
microstructure S-CONPRI
, O
of O
magnesium-alloy O
components S-MACEQ
fabricated O
using O
wire-and-arc-based O
additive-manufacturing O
techniques O
, O
which O
essentially O
represent O
a O
form O
of O
arc-welding O
technology S-CONPRI
have O
been O
examined O
. O


In O
the O
proposed O
method O
, O
the O
wire O
material S-MATE
is O
melted S-CONPRI
by O
arc S-CONPRI
discharge O
, O
and O
the O
molten B-MATE
metal E-MATE
is O
subsequently O
solidified O
and O
accumulated O
. O


Magnesium S-MATE
wire O
developed O
in O
this O
study O
facilitated O
fabrication S-MANP
of O
magnesium-alloy O
components S-MACEQ
using O
the O
said O
additive-manufacturing O
process S-CONPRI
. O


Subsequently O
, O
combinations O
of O
fabrication S-MANP
conditions O
, O
such O
as S-MATE
the O
welding S-MANP
current O
, O
torch O
feed S-PARA
speed O
, O
and O
cross O
feed S-PARA
of O
the O
torch O
, O
were O
explored O
, O
and O
suitable O
conditions O
for O
realizing O
a O
solid O
structure S-CONPRI
with O
fewer O
weld S-FEAT
defects S-CONPRI
compared O
to O
those O
observed O
when O
using O
die-casting O
and O
other O
manufacturing S-MANP
methods O
, O
were O
determined O
. O


Tensile B-CHAR
tests E-CHAR
and O
microstructure S-CONPRI
observations O
were O
also O
performed O
to O
elucidate O
mechanical B-CONPRI
properties E-CONPRI
of O
magnesium B-MATE
alloy E-MATE
components S-MACEQ
fabricated O
via O
the O
said O
wire-and-arc-based O
technique O
. O


It O
was O
demonstrated O
that O
the O
fabricated S-CONPRI
object O
possesses O
sufficient O
tensile B-PRO
strength E-PRO
compared O
to O
the O
observed O
standard S-CONPRI
value O
of O
the O
bulk O
material S-MATE
. O


Furthermore O
, O
results O
from O
microstructure S-CONPRI
observations O
demonstrated O
that O
the O
higher O
the O
torch O
feed S-PARA
speed O
, O
the O
finer O
is O
the O
microstructure S-CONPRI
. O


Moreover O
, O
the O
observed O
microstructure S-CONPRI
at O
the O
boundary S-FEAT
between O
the O
substrate S-MATE
and O
fabricated S-CONPRI
object O
was O
finer O
compared O
to O
that O
at O
the O
top O
layer S-PARA
. O


WAAM S-MANP
( O
Wire B-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
) O
is O
a O
metal B-MANP
AM E-MANP
( O
Additive B-MANP
Manufacturing E-MANP
) O
technology S-CONPRI
that O
allows O
high B-PARA
deposition I-PARA
rates E-PARA
and O
the O
manufacturability S-CONPRI
of O
very O
large O
components S-MACEQ
, O
compared O
to O
other O
AM B-MANP
technologies E-MANP
. O


Distortions O
and O
residual B-PRO
stresses E-PRO
affecting O
the O
manufactured S-CONPRI
parts O
represent O
the O
main O
drawbacks O
of O
this O
AM B-MANP
technique E-MANP
. O


FE S-MATE
( O
Finite B-CONPRI
Element E-CONPRI
) O
modeling S-ENAT
could O
represent O
an O
effective O
tool S-MACEQ
to O
tackle O
such O
issues O
, O
since O
it O
can O
be S-MATE
used O
to O
optimize O
process B-CONPRI
parameters E-CONPRI
, O
deposition B-PARA
paths E-PARA
and O
to O
test O
alternative O
mitigation O
strategies O
. O


Nevertheless O
, O
specific O
modeling S-ENAT
strategies O
are O
needed O
to O
reduce O
the O
computational O
cost O
of O
the O
process B-ENAT
simulation E-ENAT
, O
such O
as S-MATE
reducing O
the O
number O
of O
elements S-MATE
used O
in O
discretizing O
the O
model S-CONPRI
. O


The O
proposed O
technique O
is O
based O
on O
dividing O
the O
substrate S-MATE
in O
several O
zones O
, O
separately O
discretized O
and O
then O
connected O
by O
means O
of O
a O
double O
sided O
contact S-APPL
algorithm S-CONPRI
. O


This O
strategy O
allows O
to O
achieve O
a O
significant O
reduction S-CONPRI
of O
the O
number O
of O
elements S-MATE
required O
, O
without O
affecting O
their O
quality B-CONPRI
parameters E-CONPRI
. O


The O
geometry S-CONPRI
and O
dimension S-FEAT
of O
the O
mesh O
zones O
are O
identified O
through O
a O
dedicated O
algorithm S-CONPRI
that O
allows O
to O
achieve O
an O
accurate S-CHAR
temperature O
prediction S-CONPRI
with O
the O
minimum O
element S-MATE
number O
. O


The O
effectiveness S-CONPRI
of O
the O
proposed O
technique O
was O
tested O
by O
means O
of O
both O
numerical O
and O
experimental S-CONPRI
validation O
tests O
. O


AlCoFeNiSmTiV O
based O
new O
high O
entropy O
alloys S-MATE
were O
designed S-FEAT
and O
fabricated S-CONPRI
using O
additive B-MANP
manufacturing E-MANP
technique O
. O


Elevated O
temperature S-PARA
corrosion S-CONPRI
performance O
of O
these O
alloys S-MATE
were O
studied O
. O


Phase S-CONPRI
analysis O
results O
indicated O
the O
presence O
of O
a O
single O
FCC S-CONPRI
phase O
in O
these O
HEAs O
after O
enduring O
corrosive S-PRO
atmospheres O
. O


High O
entropy O
alloys S-MATE
have O
attracted O
great O
interest O
due O
to O
their O
great O
stability S-PRO
and O
exceptional O
mechanical B-CONPRI
properties E-CONPRI
. O


Due O
to O
growing O
demand O
of O
novel O
engineering B-MATE
materials E-MATE
, O
which O
can O
endure O
harsh O
corrosive S-PRO
atmospheres O
, O
HEAs O
have O
been O
studied O
extensively O
to O
meet O
the O
demands O
of O
challenging O
industrial S-APPL
environments O
. O


Current O
manufacturing S-MANP
techniques O
of O
HEAs O
include O
arc-melting O
or O
spark B-MANP
plasma I-MANP
sintering E-MANP
, O
which O
are O
limited O
by O
factors O
such O
as S-MATE
high O
energy O
, O
grain B-CHAR
refinement E-CHAR
, O
alloying S-FEAT
, O
and O
size O
limitations O
. O


In O
this O
study O
we O
report O
elevated O
temperature S-PARA
corrosion B-PRO
behavior E-PRO
of O
two O
new O
HEAs O
AlCoFeNiTiV0.9Sm0.1 O
and O
AlCoFeNiV0.9Sm0.1 O
, O
produced O
by O
laser-based B-MANP
additive I-MANP
manufacturing E-MANP
, O
which O
offers O
high O
freedom O
of O
design S-FEAT
, O
fast O
prototyping S-CONPRI
, O
and O
rapid O
quenching S-MANP
rates O
that O
are O
ideal O
for O
many O
industrial S-APPL
applications O
. O


These O
alloys S-MATE
were O
tested O
in O
corrosive S-PRO
syngas O
atmosphere O
at O
elevated O
temperatures S-PARA
to O
explore O
their O
applicability O
in O
such O
harsh O
environments O
. O


Phase S-CONPRI
analysis O
results O
indicated O
the O
presence O
of O
a O
single O
FCC S-CONPRI
phase O
in O
these O
HEAs O
with O
no O
major O
surface S-CONPRI
cracks O
after O
enduring O
such O
corrosive S-PRO
atmospheres O
. O


These O
alloys S-MATE
exhibited O
good O
corrosion B-CONPRI
resistance E-CONPRI
as S-MATE
revealed O
by O
electrochemical S-CONPRI
testing O
methods O
. O


CALPHAD O
and O
DFT S-CHAR
simulations O
were O
also O
performed O
to O
reveal O
the O
phase S-CONPRI
stability O
and O
crystal B-PRO
structures E-PRO
to O
further O
corroborate O
our O
experimental S-CONPRI
results O
. O


Wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
is O
an O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technology S-CONPRI
that O
uses O
wire-form O
materials S-CONPRI
and O
arc S-CONPRI
discharges O
as S-MATE
the O
energy O
source S-APPL
. O


AM B-MANP
techniques E-MANP
can O
fabricate S-MANP
complicated O
shapes O
that O
can O
not O
be S-MATE
obtained O
via O
conventional O
processing O
. O


Building O
lattice B-FEAT
structures E-FEAT
inside O
components S-MACEQ
enables O
weight S-PARA
reduction S-CONPRI
while O
maintaining O
high O
strength S-PRO
. O


Strut S-MACEQ
shapes O
must O
be S-MATE
constructed O
to O
form O
these O
lattice B-FEAT
structures E-FEAT
using O
WAAM S-MANP
. O


For O
fabricating S-MANP
strut O
shapes O
with O
high O
accuracy S-CHAR
, O
the O
process B-CONPRI
parameters E-CONPRI
should O
be S-MATE
optimized O
. O


However O
, O
the O
relationship O
between O
layer S-PARA
geometry S-CONPRI
and O
process B-CONPRI
parameters E-CONPRI
is O
not O
clear O
. O


Therefore O
, O
in O
this O
study O
, O
struts S-MACEQ
were O
fabricated S-CONPRI
under O
various O
process S-CONPRI
conditions O
to O
investigate O
the O
influences O
of O
process B-CONPRI
parameters E-CONPRI
on O
the O
built O
object O
geometry S-CONPRI
. O


The O
results O
showed O
that O
fabrication S-MANP
of O
strut S-MACEQ
shapes O
depends O
on O
the O
heat S-CONPRI
input O
condition O
. O


Moreover O
, O
it O
was O
found O
that O
the O
arc S-CONPRI
discharge O
time O
had O
the O
highest O
influence O
on O
the O
layer B-PARA
height E-PARA
and O
diameter S-CONPRI
. O


The O
inclination B-FEAT
angle E-FEAT
of O
an O
overhanging O
shape O
had O
little O
influence O
on O
the O
dimensional B-CHAR
accuracy E-CHAR
of O
the O
built O
object O
. O


In O
addition O
, O
computer-aided B-ENAT
manufacturing E-ENAT
( O
CAM S-ENAT
) O
system O
was O
developed O
for O
the O
fabrication S-MANP
of O
lattice B-FEAT
structures E-FEAT
, O
and O
the O
lattice B-FEAT
structures E-FEAT
were O
successfully O
built O
using O
WAAM S-MANP
. O


The O
build S-PARA
accuracy S-CHAR
was O
measured O
using O
an O
x-ray B-CHAR
computed I-CHAR
tomography E-CHAR
( O
CT S-ENAT
) O
scanner O
; O
the O
deviation O
in O
the O
structures O
designed S-FEAT
using O
the O
CAM S-ENAT
system O
and O
the O
actual O
fabricated S-CONPRI
structures O
measured O
using O
the O
CT S-ENAT
scanner O
was O
lower O
than O
approximately O
±2.3 O
mm S-MANP
. O


The O
integration O
of O
coaxial O
connectors O
into O
the O
filter S-APPL
and O
waveguide O
designs S-FEAT
via O
3D B-MANP
printing E-MANP
eliminates O
the O
need O
for O
two O
additional O
bulky O
external O
SMA-to-waveguide O
transitions O
, O
and O
allows O
for O
customizable O
integrated O
SMA-to-waveguide O
transitions O
that O
minimize O
impedance O
mismatch O
. O


Four O
designs S-FEAT
, O
including O
air-filled O
and O
polycarbonate S-MATE
( O
PC S-MATE
) O
dielectric-filled O
waveguides O
and O
two-pole O
filters S-APPL
, O
are O
modeled O
and O
manufactured S-CONPRI
using O
additive B-MANP
manufacturing E-MANP
to O
demonstrate O
this O
integrative O
approach O
. O


PC S-MATE
dielectric S-MACEQ
posts O
are O
also O
incorporated O
into O
the O
device O
to O
provide O
additional O
reinforcement S-PARA
to O
the O
coaxial O
connectors O
without O
impacting O
the O
radio B-CONPRI
frequency E-CONPRI
( O
RF O
) O
performance S-CONPRI
. O


This O
paper O
discusses O
the O
topology B-FEAT
optimization E-FEAT
and O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
specific O
re-design O
of O
a O
metallic S-MATE
C-frame O
as S-MATE
it O
is O
used O
in O
the O
riveting O
process S-CONPRI
in O
the O
automotive B-APPL
industry E-APPL
. O


The O
main O
objective O
of O
the O
optimization S-CONPRI
and O
re-design O
process S-CONPRI
is O
the O
reduction S-CONPRI
of O
the O
structural O
weight S-PARA
where O
special O
attention O
needs O
to O
be S-MATE
paid O
to O
the O
specific O
manufacturing B-MANP
process E-MANP
of O
powder B-MANP
bed I-MANP
fusion E-MANP
which O
is O
a O
powder S-MATE
based O
layerwise O
additive B-MANP
manufacturing I-MANP
process E-MANP
. O


The O
initial O
optimization S-CONPRI
and O
AM S-MANP
specific O
re-design O
are O
performed O
under O
consideration O
of O
a O
number O
of O
free O
parameters S-CONPRI
that O
drive O
the O
performance S-CONPRI
and O
weight S-PARA
of O
the O
C-frame O
, O
and O
several O
generated O
solutions O
are O
compared O
under O
special O
consideration O
of O
the O
weight S-PARA
, O
the O
mechanical S-APPL
performance O
and O
the O
general O
manufacturability S-CONPRI
using O
powder B-MANP
bed I-MANP
fusion E-MANP
. O


The O
selected O
optimized O
solution S-CONPRI
then O
undergoes O
a O
final O
detailed O
re-design O
which O
focusses O
on O
given O
manufacturing S-MANP
restrictions O
. O


The O
mechanical S-APPL
performance O
of O
the O
optimized O
C-frame O
is O
assessed O
employing O
detailed O
finite B-CONPRI
element E-CONPRI
simulations O
by O
evaluating O
the O
stress S-PRO
and O
deformation S-CONPRI
state O
. O


The O
general O
manufacturability S-CONPRI
of O
the O
optimized O
part O
by O
powder B-MANP
bed I-MANP
fusion E-MANP
is O
demonstrated O
by O
the O
manufacturing S-MANP
of O
a O
scaled O
prototype S-CONPRI
. O


In O
order O
to O
enable O
a O
comparison O
of O
the O
new O
AM S-MANP
solution O
with O
a O
classical O
manufacturing B-MANP
process E-MANP
, O
an O
optimized O
C-frame O
geared O
towards O
classical O
milling S-MANP
is O
established O
as S-MATE
well O
. O


Both O
solutions O
are O
compared O
concerning O
weight S-PARA
, O
mechanical S-APPL
performance O
, O
manufacturability S-CONPRI
and O
economic O
aspects O
, O
and O
it O
can O
be S-MATE
shown O
that O
the O
AM S-MANP
solution O
offers O
a O
number O
of O
advantages O
that O
can O
not O
be S-MATE
exploited O
when O
employing O
classical O
means O
of O
manufacturing S-MANP
. O


This O
paper O
may O
serve O
as S-MATE
an O
introduction O
to O
the O
rather O
complex O
field O
of O
AM S-MANP
design O
of O
load O
bearing O
structures O
and O
is O
an O
illustrated O
case B-CONPRI
study E-CONPRI
thereof O
which O
can O
be S-MATE
of O
use O
for O
engineers O
working O
in O
this O
specific O
field O
that O
is O
still O
the O
topic O
of O
global O
academic O
and O
industrial S-APPL
research O
. O


Multifunctional O
lattice S-CONPRI
materials O
exhibit O
functionalities O
beyond O
conventional O
load-bearing S-FEAT
usage O
and O
are O
usually O
fabricated S-CONPRI
by O
additive B-MANP
manufacturing E-MANP
. O


This O
work O
introduces O
a O
new O
class O
of O
functional O
lattice S-CONPRI
materials O
called O
liquid B-MATE
metal E-MATE
lattice S-CONPRI
materials O
. O


These O
lattice S-CONPRI
materials O
consist O
of O
liquid B-MATE
metals E-MATE
and O
elastomers S-MATE
organized O
in O
a O
core-shell O
manner O
. O


This O
hybrid O
design S-FEAT
induces O
a O
shape B-PRO
memory I-PRO
effect E-PRO
by O
harnessing O
the O
solid-liquid O
phase S-CONPRI
transition O
of O
liquid B-MATE
metals E-MATE
. O


Consequently O
, O
several O
remarkable O
functionalities O
are O
achieved O
such O
as S-MATE
recoverable O
energy B-CHAR
absorption E-CHAR
, O
tunable O
rigidity O
, O
and O
reconfigurable O
behaviors O
. O


These O
liquid B-MATE
metal E-MATE
lattice S-CONPRI
materials O
are O
fabricated S-CONPRI
by O
using O
a O
hybrid B-CONPRI
manufacturing E-CONPRI
approach O
, O
which O
integrates O
the O
3D B-MANP
printing E-MANP
, O
vacuum B-MANP
casting E-MANP
, O
and O
conformal O
coating S-APPL
techniques O
. O


A O
variety O
of O
lattice B-FEAT
structures E-FEAT
are O
presented O
to O
demonstrate O
the O
capability O
of O
this O
hybrid B-CONPRI
manufacturing E-CONPRI
method O
and O
the O
functionalities O
of O
liquid B-MATE
metal E-MATE
lattice S-CONPRI
materials O
. O


This O
new O
class O
of O
lattice S-CONPRI
materials O
have O
promising O
applications O
in O
aerospace S-APPL
, O
robotics S-APPL
, O
tunable O
metamaterials S-MATE
, O
etc O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
of O
tungsten S-MATE
carbide-cobalt O
( O
WC-Co O
) O
is O
explored O
starting O
with O
WC S-MATE
preforms O
shaped O
with O
binder S-MATE
jet O
additive B-MANP
manufacturing E-MANP
( O
BJAM O
) O
followed O
by O
melt B-CONPRI
infiltration E-CONPRI
of O
Co S-MATE
. O


The O
research S-CONPRI
objective O
is O
to O
demonstrate O
the O
ability O
to O
net-shape O
WC-Co O
composites S-MATE
through O
BJAM O
of O
a O
WC S-MATE
preform O
followed O
by O
backfilling O
with O
cobalt S-MATE
via O
pressureless O
infiltration S-CONPRI
. O


This O
method O
also O
has O
the O
potential O
to O
minimize O
shrinkage S-CONPRI
and O
grain B-CONPRI
growth E-CONPRI
compared O
to O
other O
AM B-MANP
techniques E-MANP
. O


The O
effects O
of O
sintering S-MANP
, O
Co S-MATE
content O
, O
and O
infiltration S-CONPRI
time O
on O
the O
net O
shaping S-MANP
and O
properties S-CONPRI
of O
processed S-CONPRI
composites S-MATE
are O
shown O
. O


The O
best O
shaped O
material S-MATE
had O
an O
average S-CONPRI
grain O
size O
of O
5.1 O
μm O
, O
32 O
vol. O
% O
Co S-MATE
, O
density S-PRO
of O
98.54 O
% O
theoretical S-CONPRI
, O
fracture S-CONPRI
toughness O
of O
23.2 O
MPa S-CONPRI
m1/2 O
, O
and O
hardness S-PRO
of O
9.0 O
GPa S-PRO
. O


Data S-CONPRI
presented O
illustrates O
that O
the O
proposed O
approach O
results O
in O
favorable O
ceramic-metal S-MATE
( O
cermet S-MATE
) O
properties S-CONPRI
and O
is O
viable O
for O
fabricating S-MANP
cermets S-MATE
of O
other O
material S-MATE
combinations O
. O


Successful O
AM S-MANP
of O
cermets S-MATE
provides O
complex B-CONPRI
geometries E-CONPRI
, O
high O
throughout O
, O
and O
low O
costs O
. O


Online O
nondestructive B-CHAR
testing E-CHAR
for O
quality B-CONPRI
control E-CONPRI
is O
a O
critical O
direction O
for O
research S-CONPRI
in O
additive B-MANP
manufacturing E-MANP
in O
the O
future O
. O


In O
this O
study O
, O
for O
the O
first O
time O
, O
optical S-CHAR
emission S-CHAR
spectroscopy O
was O
employed O
to O
probe S-MACEQ
the O
arc S-CONPRI
characteristics O
in O
the O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
of O
an O
Al B-MATE
alloy E-MATE
and O
to O
detect O
its O
structural O
features O
. O


The O
arc S-CONPRI
characteristics O
, O
such O
as S-MATE
spectral O
intensity O
, O
electron O
density S-PRO
, O
and O
electron O
temperature S-PARA
, O
were O
calculated O
based O
on O
the O
atomic O
emission S-CHAR
spectral O
lines O
. O


The O
resulting O
structural O
features O
of O
the O
deposited B-CHAR
layers E-CHAR
, O
namely O
the O
forming S-MANP
width O
, O
composition S-CONPRI
, O
grain B-PRO
size E-PRO
, O
and O
porosity S-PRO
defects S-CONPRI
, O
were O
analyzed O
, O
and O
a O
correlation O
between O
the O
arc S-CONPRI
characteristics O
and O
the O
structural O
features O
was O
proposed O
. O


The O
arc S-CONPRI
cathode O
size O
, O
which O
changed O
with O
the O
number O
of O
deposited B-CHAR
layers E-CHAR
, O
controlled O
the O
arc S-CONPRI
energy O
distribution S-CONPRI
. O


Hence O
, O
the O
forming S-MANP
width O
had O
an O
approximately O
linear O
relation O
with O
the O
spectral O
intensity O
of O
Mg S-MATE
( O
a O
constituent O
of O
the O
alloy S-MATE
used O
for O
the O
wire O
feed S-PARA
) O
and O
the O
electron O
density S-PRO
. O


The O
porosity S-PRO
in O
the O
alloy S-MATE
was O
observed O
to O
be S-MATE
caused O
by O
H O
, O
which O
was O
a O
dominant O
pollutant O
in O
the O
process S-CONPRI
. O


Furthermore O
, O
the O
correlation O
between O
the O
porosity S-PRO
and O
H O
spectral O
intensity O
was O
observed O
to O
be S-MATE
approximately O
linear O
. O


However O
, O
no O
significant O
correlation O
between O
the O
grain B-PRO
size E-PRO
and O
the O
spectrum O
was O
noticeable O
. O


The O
results O
from O
this O
study O
establish O
the O
applicability O
of O
spectral O
diagnosis O
of O
the O
forming S-MANP
size O
and O
the O
porosity S-PRO
in O
WAAM S-MANP
. O


Specification S-PARA
and O
analysis O
of O
the O
system O
structure S-CONPRI
and O
components S-MACEQ
of O
a O
desktop O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
system O
. O


Physical O
modeling S-ENAT
of O
the O
energy O
consumption O
behavior O
of O
the O
desktop O
AM S-MANP
system O
using O
function-oriented O
bond O
graph O
. O


Development O
of O
an O
energy O
simulation S-ENAT
tool O
for O
the O
desktop O
AM S-MANP
system O
using O
MATLAB®/Simulink® O
platform S-MACEQ
. O


Experimental S-CONPRI
validation O
of O
the O
simulation B-CHAR
accuracy E-CHAR
of O
the O
developed O
simulation S-ENAT
approach O
. O


The O
assessment O
and O
minimization O
of O
energy O
consumptions O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
are O
currently O
emerging O
research S-CONPRI
tasks O
. O


It O
is O
evident O
that O
the O
energy O
consumption O
of O
an O
AM B-MANP
process E-MANP
can O
be S-MATE
one O
or O
two O
orders O
of O
magnitude S-PARA
higher O
than O
conventional B-MANP
manufacturing E-MANP
processes O
. O


For O
improving O
the O
sustainability B-CONPRI
performance E-CONPRI
of O
AM S-MANP
, O
the O
energy O
use O
of O
AM S-MANP
should O
be S-MATE
evaluated O
and O
optimized O
in O
the O
design S-FEAT
phase O
for O
planning S-MANP
products O
and O
AM B-MANP
processes E-MANP
. O


In O
order O
to O
support S-APPL
the O
quantification O
and O
evaluation O
of O
the O
energy O
consumption O
of O
AM S-MANP
, O
we O
have O
developed O
an O
energy O
simulation S-ENAT
of O
a O
desktop O
AM S-MANP
system O
by O
using O
a O
physical O
modeling S-ENAT
approach O
. O


Moreover O
, O
experiments O
have O
been O
carried O
out O
to O
validate O
and O
confirm O
the O
simulation B-CHAR
accuracy E-CHAR
and O
reliability S-CHAR
. O


The O
result O
of O
the O
experimental S-CONPRI
validation O
has O
shown O
that O
the O
accuracy S-CHAR
of O
the O
developed O
simulation S-ENAT
approach O
can O
be S-MATE
up O
to O
approximately O
98 O
% O
. O


Metal B-MANP
additive I-MANP
manufacturing E-MANP
is O
moving O
from O
rapid B-ENAT
prototyping E-ENAT
to O
on-demand O
manufacturing S-MANP
and O
even O
to O
serial O
production S-MANP
. O


Consistent O
part O
quality S-CONPRI
and O
development O
of O
a O
wider O
range S-PARA
of O
available O
materials S-CONPRI
are O
key O
for O
wider O
adoption O
. O


This O
requires O
control O
and O
optimization S-CONPRI
of O
various O
laser S-ENAT
and O
scanning B-CONPRI
parameters E-CONPRI
. O


Therefore O
, O
process B-CONPRI
modeling E-CONPRI
has O
been O
extensively O
pursued O
to O
reduce O
experimental S-CONPRI
runs O
in O
the O
search O
for O
parameters S-CONPRI
that O
produce O
dense O
, O
high-quality O
parts O
for O
the O
given O
alloy S-MATE
. O


However O
, O
these O
optimal O
parameters S-CONPRI
remain O
machine-specific O
if O
conditions O
defined O
by O
the O
machine S-MACEQ
architecture S-APPL
are O
not O
considered O
. O


Previous O
studies O
have O
shown O
that O
shielding O
gas S-CONPRI
flow O
is O
one O
such O
parameter S-CONPRI
that O
affects O
porosity S-PRO
and O
mechanical B-CONPRI
properties E-CONPRI
of O
parts O
produced O
with O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
. O


In O
this O
study O
, O
the O
effect O
of O
shielding O
gas S-CONPRI
flow O
velocity O
on O
porosity S-PRO
and O
melt B-MATE
pool E-MATE
geometry S-CONPRI
in O
laser B-MANP
powder I-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
is O
studied O
. O


As S-MATE
the O
vapor O
plume O
, O
and O
how O
effectively O
it O
is O
removed O
by O
the O
shielding O
gas S-CONPRI
flow O
, O
have O
a O
significant O
effect O
on O
the O
melt B-MATE
pool E-MATE
geometry S-CONPRI
in O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
, O
models O
aiming O
at O
predicting O
the O
melt B-MATE
pool E-MATE
geometry S-CONPRI
and O
attempts O
to O
transfer O
process B-CONPRI
parameters E-CONPRI
from O
one O
machine S-MACEQ
to O
another O
should O
consider O
the O
effect O
of O
the O
shielding O
gas S-CONPRI
flow O
. O


Nickel B-MATE
Aluminum I-MATE
Bronze E-MATE
square O
bars O
were O
printed O
via O
wire-arc B-MANP
additive I-MANP
manufacturing E-MANP
. O


Formation O
of O
various O
κ-phases O
were O
discussed O
and O
compared O
with O
cast S-MANP
alloy S-MATE
. O


Additive B-MANP
Manufactured E-MANP
( O
AM S-MANP
) O
alloy S-MATE
has O
fine O
solidification S-CONPRI
structure O
. O


AM-NAB O
exhibited O
superior O
tensile B-PRO
properties E-PRO
than O
the O
cast-NAB O
. O


As S-MATE
a O
step S-CONPRI
forward O
toward O
the O
development O
of O
the O
next O
generation O
of O
nickel B-MATE
aluminum I-MATE
bronze E-MATE
( O
NAB S-MATE
) O
components S-MACEQ
using O
wire-arc B-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
, O
square O
bars O
were O
printed O
in O
the O
vertical S-CONPRI
direction O
. O


The O
as-built O
microstructure S-CONPRI
was O
characterized O
using O
multi-scale O
electron B-CHAR
microscopy E-CHAR
techniques O
, O
where O
the O
differences O
in O
phase S-CONPRI
formation O
were O
compared O
to O
the O
reference O
cast-NAB O
based O
on O
the O
solidification S-CONPRI
characteristics O
. O


The O
as-cast O
microstructure S-CONPRI
typically O
consists O
of O
Cu-rich O
α-matrix O
, O
and O
four O
types O
of O
intermetallic S-MATE
particles O
referred O
to O
as S-MATE
κ-phases O
. O


In O
the O
WAAM-NAB O
, O
the O
formation O
of O
κI O
was O
suppressed O
due O
to O
high O
cooling B-PARA
rates E-PARA
. O


The O
microstructure S-CONPRI
was O
finer O
and O
the O
volume B-PARA
fraction E-PARA
of O
intermetallic S-MATE
particles O
was O
significantly O
lower O
than O
that O
of O
the O
cast-NAB O
. O


Based O
on O
energy B-CHAR
dispersive I-CHAR
spectroscopy E-CHAR
( O
EDS S-CHAR
) O
technique O
and O
diffraction B-CHAR
pattern E-CHAR
analysis O
using O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
TEM S-CHAR
) O
, O
the O
phases O
formed O
in O
the O
interdendritic O
regions O
were O
identified O
as S-MATE
κII O
( O
globular O
Fe3Al O
) O
and O
κIII O
( O
lamellar S-CONPRI
NiAl O
) O
, O
whereas O
numerous O
fine O
( O
5–10 O
nm O
) O
Fe-rich O
κIV O
particles S-CONPRI
were O
precipitated O
uniformly O
within O
the O
α-matrix O
. O


Electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
analysis O
revealed O
weak O
texture S-FEAT
on O
both O
parallel O
and O
perpendicular O
planes O
to O
the O
building B-PARA
direction E-PARA
with O
( O
100 O
) O
poles O
rotated O
away O
from O
the O
build B-PARA
direction E-PARA
. O


The O
WAAM-NAB O
sample S-CONPRI
exhibited O
considerably O
higher O
yield B-PRO
strength E-PRO
( O
˜88 O
MPa S-CONPRI
) O
and O
elongation S-PRO
( O
˜10 O
% O
) O
than O
the O
cast-NAB O
, O
but O
the O
gain S-PARA
in O
the O
ultimate B-PRO
tensile I-PRO
strength E-PRO
was O
marginal O
. O


Processing O
of O
Inconel B-MATE
718 E-MATE
and O
copper B-MATE
alloy E-MATE
GRCop-84 O
as S-MATE
a O
bimetallic O
structure S-CONPRI
using O
laser B-MANP
engineered I-MANP
net I-MANP
shaping E-MANP
( O
LENS S-MANP
) O
. O


A O
compositionally O
gradient O
layer S-PARA
with O
high O
laser B-CONPRI
energy E-CONPRI
input O
helped O
to O
process S-CONPRI
these O
bimetallic O
structures O
. O


The O
bimetallic O
structure S-CONPRI
resulted O
in O
high O
thermal B-CONPRI
diffusivity E-CONPRI
as S-MATE
compared O
to O
pure O
Inconel B-MATE
718 E-MATE
. O


Deposition S-CONPRI
of O
GRCop-84 O
Increased O
the O
thermal B-CONPRI
diffusivity E-CONPRI
of O
Inconel B-MATE
718 E-MATE
by O
∼250 O
% O
. O


To O
understand O
processing O
ability O
and O
measure O
resultant O
interfacial O
and O
thermal B-CONPRI
properties E-CONPRI
of O
Inconel B-MATE
718 E-MATE
and O
copper B-MATE
alloy E-MATE
GRCop-84 O
, O
bimetallic O
structures O
were O
fabricated S-CONPRI
using O
laser S-ENAT
engineering S-APPL
net O
shaping S-MANP
( O
LENS™ O
) O
, O
a O
commercially O
available O
additive B-MANP
manufacturing E-MANP
technique O
. O


It O
was O
hypothesized O
that O
additively O
combining O
the O
two O
aerospace S-APPL
alloys O
would O
form O
a O
unique O
bimetallic O
structure S-CONPRI
with O
improved O
thermophysical O
properties S-CONPRI
compared O
to O
the O
Inconel B-MATE
718 I-MATE
alloy E-MATE
. O


Two O
approaches O
were O
used O
: O
the O
direct O
deposition S-CONPRI
of O
GRCop-84 O
on O
Inconel B-MATE
718 E-MATE
and O
the O
compositional O
gradation O
of O
the O
two O
alloys S-MATE
. O


Scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
, O
energy B-CHAR
dispersive I-CHAR
spectroscopy E-CHAR
( O
EDS S-CHAR
) O
, O
X-ray B-CHAR
Diffraction E-CHAR
( O
XRD S-CHAR
) O
, O
Vickers O
microhardness S-CONPRI
and O
flash S-MATE
thermal O
diffusivity S-CHAR
were O
used O
to O
characterize O
these O
bimetallic O
structures O
to O
validate O
our O
hypothesis O
. O


The O
compositional O
gradation O
approach O
showed O
a O
gradual O
transition S-CONPRI
of O
Inconel B-MATE
718 E-MATE
and O
GRCop-84 O
elements S-MATE
at O
the O
interface S-CONPRI
, O
which O
was O
also O
reflected O
in O
the O
cross-sectional O
hardness S-PRO
profile O
across O
the O
bimetallic O
interface S-CONPRI
. O


SEM S-CHAR
images S-CONPRI
showed O
columnar B-PRO
grain E-PRO
structures O
at O
the O
interfaces O
with O
Cr2Nb O
precipitate S-MATE
accumulation O
along O
grain B-CONPRI
boundaries E-CONPRI
and O
the O
substrate-deposit O
interface S-CONPRI
. O


The O
average S-CONPRI
thermal O
diffusivity S-CHAR
of O
the O
bimetallic O
structure S-CONPRI
was O
measured O
at O
11.33 O
mm2/s O
for O
the O
temperature B-PARA
range E-PARA
of O
50 O
°C–300 O
°C O
; O
a O
250 O
% O
increase O
in O
diffusivity S-CHAR
when O
compared O
to O
the O
pure O
Inconel B-MATE
718 I-MATE
alloy E-MATE
at O
3.20 O
mm2/s O
. O


Conductivity S-PRO
of O
the O
bimetallic O
structures O
increased O
by O
almost O
300 O
% O
compared O
to O
Inconel B-MATE
718 E-MATE
as S-MATE
well O
. O


Such O
structures O
with O
designed S-FEAT
compositional O
gradation O
and O
tailored O
thermal B-CONPRI
properties E-CONPRI
opens O
up O
the O
possibilities O
of O
multi-material S-CONPRI
metal B-MANP
additive I-MANP
manufacturing E-MANP
for O
next O
generation O
of O
aerospace S-APPL
structures O
. O


Depth-sensing O
( O
instrumented O
) O
indentation S-CONPRI
testing O
technique O
is O
a O
robust O
, O
reliable O
, O
convenient O
and O
non-destructive O
characterization O
method O
to O
study O
small-scale O
mechanical B-CONPRI
properties E-CONPRI
and O
rate-dependent O
plastic B-PRO
deformation E-PRO
in O
metals S-MATE
and O
alloys S-MATE
at O
ambient O
and O
elevated O
temperatures S-PARA
. O


In O
the O
present O
paper O
, O
depth-sensing O
indentation S-CONPRI
creep B-PRO
behavior E-PRO
of O
an O
additively B-MANP
manufactured E-MANP
, O
via O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
method O
, O
Ti-6Al-4V B-MATE
alloy E-MATE
is O
studied O
at O
ambient O
temperature S-PARA
. O


Indentation S-CONPRI
creep B-CHAR
tests E-CHAR
were O
performed O
through O
a O
dual-stage O
scheme O
( O
loading O
followed O
by O
a O
constant O
load-holding O
and O
unloading O
) O
at O
different O
peak O
loads O
of O
250 O
mN S-MATE
, O
350 O
mN S-MATE
, O
and O
450 O
mN S-MATE
with O
holding O
time O
of O
400 O
s. O
Creep S-PRO
parameters O
including O
creep S-PRO
rate O
, O
creep S-PRO
stress O
exponent O
, O
and O
indentation S-CONPRI
size O
effect O
were O
analyzed O
, O
according O
to O
the O
Oliver O
and O
Pharr O
method O
, O
at O
different O
additive B-MANP
manufacturing E-MANP
scan O
directions O
and O
scan O
sizes O
. O


To O
assess O
processing O
parameter/ O
microstructure/ O
creep S-PRO
property O
correlations O
in O
the O
additively B-MANP
manufacture E-MANP
Ti-6Al-4V O
alloy S-MATE
, O
microstructural S-CONPRI
quantitative O
analyses O
( O
i.e O
. O


optical B-CHAR
microscopy E-CHAR
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
) O
were O
performed O
as S-MATE
well O
. O


The O
findings O
of O
this O
study O
, O
according O
to O
stress S-PRO
exponent O
values O
, O
showed O
that O
the O
controlling O
mechanism S-CONPRI
of O
the O
creep S-PRO
at O
ambient O
temperature S-PARA
for O
the O
examined O
L-PBF S-MANP
Ti-6Al-4V O
is O
mainly O
glide-controlled O
dislocation S-CONPRI
creep S-PRO
. O


These O
findings O
were O
compared O
against O
traditionally O
processed S-CONPRI
Ti-6Al-4V O
as S-MATE
well O
. O


Additively B-MANP
manufactured E-MANP
, O
short B-MATE
fiber I-MATE
reinforced I-MATE
polymer I-MATE
composites E-MATE
have O
advantages O
over O
traditional O
continuous B-MATE
fiber I-MATE
composites E-MATE
, O
which O
include O
low O
cost O
and O
design B-CONPRI
flexibility E-CONPRI
. O


However O
, O
these O
composites S-MATE
suffer O
from O
low O
strength S-PRO
and O
stiffness S-PRO
as S-MATE
compared O
to O
their O
continuous B-MATE
fiber E-MATE
counterparts O
due O
to O
the O
limitation O
of O
low O
fiber S-MATE
volume O
. O


This O
direct O
write O
additive B-MANP
manufacturing E-MANP
technique O
allowed O
us O
to O
fabricate S-MANP
short O
fiber S-MATE
reinforced O
thermoset O
composites S-MATE
in O
intricate O
geometries S-CONPRI
, O
with O
unprecedented O
high O
compression B-PRO
strength E-PRO
( O
673 O
MPa S-CONPRI
) O
, O
flexural B-PRO
strength E-PRO
( O
401 O
MPa S-CONPRI
) O
, O
flexural O
stiffness S-PRO
( O
53 O
GPa S-PRO
) O
, O
and O
fiber S-MATE
volume O
ratio O
( O
46 O
% O
) O
. O


Milled B-MATE
carbon I-MATE
fibers E-MATE
were O
used O
as S-MATE
the O
reinforcing B-MATE
fibers E-MATE
, O
which O
were O
considered O
too O
short O
to O
have O
the O
ability O
to O
enhance O
the O
mechanical B-PRO
strength E-PRO
of O
composites S-MATE
. O


However O
, O
in O
this O
study O
we O
show O
for O
the O
first O
time O
that O
milled B-MATE
carbon I-MATE
fibers E-MATE
have O
the O
ability O
to O
significantly O
reinforce O
the O
thermoset O
matrix O
and O
the O
composites S-MATE
reinforced O
with O
these O
fibers S-MATE
achieve O
mechanical S-APPL
performances O
similar O
to O
those O
of O
composites S-MATE
reinforced O
with O
longer O
fibers S-MATE
. O


We O
believe O
that O
a O
transformation O
takes O
place O
at O
high O
fiber S-MATE
volumes O
on O
the O
load O
transport S-CHAR
mechanism S-CONPRI
within O
the O
composites S-MATE
, O
leading O
to O
higher O
levels O
of O
strength S-PRO
and O
a O
stiffness S-PRO
enhancement O
. O


This O
pseudo O
transformation O
can O
give O
rise O
to O
short B-MATE
fibers E-MATE
that O
act O
as S-MATE
if O
they O
are O
longer O
, O
which O
aids O
in O
the O
effective O
transfer O
of O
tensile B-CHAR
loads E-CHAR
from O
the O
matrix O
phase S-CONPRI
to O
the O
fibers S-MATE
. O


This O
study O
also O
showed O
that O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
additively O
fabricated S-CONPRI
thermoset O
composites S-MATE
match O
those O
of O
ubiquitous O
, O
denser O
structural O
metals S-MATE
, O
and O
these O
properties S-CONPRI
show O
nearly O
isotropic S-PRO
behavior O
. O


Therefore O
, O
these O
systems O
have O
great O
potential O
to O
find O
immediate O
applications O
where O
weight S-PARA
reduction S-CONPRI
and O
component S-MACEQ
complexity S-CONPRI
are O
both O
desired O
. O


Lattice B-FEAT
structures E-FEAT
are O
excellent O
candidates O
for O
lightweight S-CONPRI
, O
energy O
absorbing O
applications O
such O
as S-MATE
personal O
protective O
equipment S-MACEQ
. O


In O
this O
paper O
we O
explore O
several O
important O
aspects O
of O
lattice B-FEAT
design E-FEAT
and O
production S-MANP
by O
metal B-MANP
additive I-MANP
manufacturing E-MANP
, O
including O
the O
choice O
of O
cell B-PRO
size E-PRO
and O
the O
application O
of O
a O
post-manufacture O
heat B-MANP
treatment E-MANP
. O


Key O
results O
include O
the O
characterisation O
of O
several O
failure B-PRO
modes E-PRO
in O
double O
gyroid O
lattices S-CONPRI
made O
of O
Al-Si10-Mg O
, O
the O
elimination O
of O
brittle B-CONPRI
fracture E-CONPRI
and O
low-strain O
failure S-CONPRI
by O
the O
application O
of O
a O
heat B-MANP
treatment E-MANP
, O
and O
the O
calculation O
of O
specific B-CONPRI
energy I-CONPRI
absorption E-CONPRI
under O
compressive O
deformation S-CONPRI
( O
16 O
× O
106 O
J O
m−3 O
up O
to O
50 O
% O
strain S-PRO
) O
. O


These O
results O
demonstrate O
the O
suitability O
of O
double O
gyroid O
lattices S-CONPRI
for O
energy O
absorbing O
applications O
, O
and O
will O
enable O
the O
design S-FEAT
and O
manufacture S-CONPRI
of O
more O
efficient O
lightweight S-CONPRI
parts O
in O
the O
future O
. O


Minimizing O
the O
residual B-PRO
stress E-PRO
build-up O
in O
metal-based O
additive B-MANP
manufacturing E-MANP
plays O
a O
pivotal O
role O
in O
selecting O
a O
particular O
material S-MATE
and O
technique O
for O
making O
an O
industrial S-APPL
part O
. O


In O
beam-based O
additive B-MANP
manufacturing E-MANP
, O
although O
a O
great O
deal O
of O
effort O
has O
been O
made O
to O
minimize O
the O
residual B-PRO
stresses E-PRO
, O
it O
is O
still O
elusive O
how O
to O
do O
so O
by O
simply O
optimizing O
the O
manufacturing S-MANP
parameters O
, O
such O
as S-MATE
beam O
size O
, O
beam S-MACEQ
power O
, O
and O
scan B-PARA
speed E-PARA
. O


With O
reference O
to O
the O
Ti6Al4V B-MATE
alloy E-MATE
and O
manufacturing S-MANP
by O
electron B-MANP
beam I-MANP
melting E-MANP
, O
we O
perform O
systematic O
finite B-CONPRI
element E-CONPRI
modeling O
of O
one-pass O
scanning S-CONPRI
to O
study O
the O
effects O
of O
beam S-MACEQ
size O
, O
beam S-MACEQ
power O
density S-PRO
, O
beam S-MACEQ
scan O
speed O
, O
and O
chamber O
bed S-MACEQ
temperature O
on O
the O
magnitude S-PARA
and O
distribution S-CONPRI
of O
residual B-PRO
stresses E-PRO
. O


Our O
study O
elucidates O
both O
qualitative S-CONPRI
and O
quantitative S-CONPRI
features O
of O
the O
residual B-PRO
stress E-PRO
fields O
originated O
by O
these O
manufacturing S-MANP
parameters O
. O


Our O
findings O
can O
serve O
as S-MATE
useful O
guidelines O
for O
engineers O
and O
designers O
to O
deal O
with O
residual B-PRO
stress E-PRO
build-up O
during O
additive B-MANP
manufacturing E-MANP
of O
Ti6Al4V S-MATE
. O


LCAs O
of O
ten O
3D B-MACEQ
printers E-MACEQ
were O
compared O
in O
different O
temporal O
& O
spatial O
utilizations O
. O


Utilization O
alone O
is O
not O
enough O
; O
energy O
use O
and O
print S-MANP
materials S-CONPRI
are O
also O
critical O
. O


Previous O
studies O
on O
the O
environmental O
impacts O
of O
polymeric O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
have O
shown O
that O
higher O
printer S-MACEQ
utilization O
dramatically O
improves O
impacts O
per O
part—so O
much O
so O
that O
it O
might O
dominate O
all O
other O
interventions O
if O
taken O
to O
an O
extreme O
. O


In O
this O
study O
, O
life B-CONPRI
cycle E-CONPRI
assessments O
( O
LCAs O
) O
were O
performed O
for O
an O
inkjet S-MANP
fusion S-CONPRI
printer O
with O
exceptionally O
high O
spatial O
utilization O
capacity S-CONPRI
and O
were O
compared O
to O
previous O
LCAs O
of O
nine O
printers S-MACEQ
printing O
with O
eight O
materials S-CONPRI
. O


Comparisons O
were O
performed O
in O
different O
utilizations O
, O
both O
temporal O
and O
spatial O
, O
to O
determine O
if O
high O
utilization O
reduces O
the O
environmental O
impact S-CONPRI
of O
AM S-MANP
more O
than O
other O
interventions O
, O
such O
as S-MATE
using O
sustainable S-CONPRI
print S-MANP
materials S-CONPRI
. O


For O
the O
inkjet S-MANP
fusion S-CONPRI
printer O
, O
maximum O
utilization O
dramatically O
reduced O
the O
environmental O
impact S-CONPRI
per O
part O
to O
less O
than O
1 O
% O
of O
its O
impact S-CONPRI
in O
lowest O
utilization O
; O
this O
was O
below O
the O
impacts O
of O
other O
printers S-MACEQ
in O
low O
utilizations O
. O


However O
, O
when O
compared O
in O
the O
same O
utilization O
scenarios O
, O
the O
inkjet S-MANP
fusion S-CONPRI
printer O
still O
caused O
a O
higher O
environmental O
impact S-CONPRI
per O
part O
than O
almost O
all O
printers S-MACEQ
, O
primarily O
due O
to O
high O
energy O
use O
. O


The O
lowest-impact O
printer S-MACEQ
used O
both O
high O
spatial O
utilization O
and O
low-impact O
materials S-CONPRI
that O
also O
enabled O
a O
low-energy O
printing B-MANP
process E-MANP
. O


Therefore O
, O
printer S-MACEQ
utilization O
is O
not O
the O
overriding O
factor O
and O
must O
be S-MATE
combined O
with O
energy O
efficiency O
and O
material S-MATE
choice O
. O


Ultrasonic O
cavitation S-CONPRI
abrasive S-MATE
finishing O
reduced O
Ra O
on O
metal S-MATE
additively B-MANP
manufactured E-MANP
sloping O
and O
side O
surfaces S-CONPRI
by O
up O
to O
40 O
% O
. O


No O
excessive O
removal O
occurs O
in O
UCAF O
as S-MATE
mass O
and O
dimensional O
changes O
induced O
by O
UCAF O
are O
dependent O
on O
the O
initial O
surface B-CHAR
morphology E-CHAR
. O


Internal O
surfaces S-CONPRI
of O
a O
3 O
mm S-MANP
diameter S-CONPRI
channel S-APPL
were O
finished O
to O
less O
than O
4 O
μm O
Ra O
. O


Moderate O
abrasive S-MATE
size O
and O
concentration O
led S-APPL
to O
a O
balance O
between O
the O
two O
mechanisms O
of O
surface B-PRO
roughness E-PRO
improvement O
. O


The O
poor O
and O
non-uniform O
surface B-PARA
quality E-PARA
of O
parts O
produced O
by O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
processes S-CONPRI
remains O
a O
huge O
limitation O
in O
additive B-MANP
manufacturing E-MANP
. O


Here O
we O
show O
that O
ultrasonic O
cavitation S-CONPRI
abrasive S-MATE
finishing O
( O
UCAF O
) O
could O
improve O
the O
surface B-FEAT
integrity E-FEAT
of O
PBF S-MANP
surfaces O
built O
at O
various O
orientations S-CONPRI
–0° O
, O
45° O
and O
90° O
. O


Average S-CONPRI
surface O
roughness S-PRO
, O
Ra O
, O
was O
reduced O
from O
as S-MATE
high O
as S-MATE
6.5 O
μm O
on O
side O
surfaces S-CONPRI
( O
90° O
) O
to O
3.8 O
μm O
. O


Surface S-CONPRI
morphological O
observations O
showed O
extensive O
removals O
of O
surface S-CONPRI
irregularities O
and O
peak O
reduction S-CONPRI
on O
sloping O
( O
45° O
) O
and O
side O
surfaces S-CONPRI
. O


The O
micro-hardness O
of O
the O
first O
100 O
μm O
of O
the O
surface S-CONPRI
layer S-PARA
was O
enhanced O
up O
to O
15 O
% O
post-UCAF O
. O


A O
parametric O
study O
further O
showed O
the O
effect O
of O
abrasive S-MATE
size O
, O
abrasive S-MATE
concentration O
, O
ultrasonic O
amplitude O
and O
working O
gap O
on O
UCAF O
’ O
s S-MATE
performance S-CONPRI
. O


A O
moderate O
abrasive S-MATE
size O
at O
12.5 O
μm O
and O
concentration O
level O
at O
5 O
wt O
% O
resulted O
in O
the O
lowest O
final O
Ra O
; O
as S-MATE
the O
two O
dominant O
material S-MATE
removal O
mechanisms O
– O
direct O
cavitation S-CONPRI
erosion O
and O
micro-abrasive O
impacts O
– O
were O
balanced O
. O


Finally O
, O
UCAF O
was O
demonstrated O
to O
result O
in O
20 O
% O
Ra O
improvement O
of O
internal O
surfaces S-CONPRI
of O
a O
3 O
mm S-MANP
diameter S-CONPRI
channel S-APPL
. O


Microstructure S-CONPRI
of O
an O
additively B-MANP
manufactured E-MANP
AlSi10Mg O
through O
direct B-MANP
metal I-MANP
laser I-MANP
sintering E-MANP
( O
DMLS S-MANP
) O
process S-CONPRI
is O
studied O
using O
multi-scale O
characterization O
techniques O
including O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
, O
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
, O
and O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
. O


The O
microstructure S-CONPRI
of O
DMLS-AlSi10Mg O
consists O
of O
hierarchical O
characteristics O
, O
spanning O
three O
order O
of O
magnitude S-PARA
, O
where O
nanometer S-FEAT
sized O
to O
sub-millimeter O
scaled O
features O
exist O
in O
the O
structure S-CONPRI
. O


These O
characteristics O
included O
grain S-CONPRI
and O
cell S-APPL
structures O
, O
nanoscale O
Si S-MATE
precipitates S-MATE
and O
pre-existing O
dislocation S-CONPRI
networks O
. O


Dynamic S-CONPRI
mechanical O
behavior O
of O
the O
material S-MATE
is O
studied O
using O
a O
Split O
Hopkinson O
Pressure S-CONPRI
Bar O
apparatus O
over O
a O
range S-PARA
of O
strain B-CONPRI
rates E-CONPRI
varying O
between O
800 O
s−1 O
and O
3200 O
s−1 O
. O


Investigation O
of O
the O
deformed S-MANP
microstructures O
reveals O
the O
role O
of O
hierarchical O
microstructure S-CONPRI
on O
the O
dynamic S-CONPRI
behavior O
of O
the O
material S-MATE
. O


The O
high O
strain-rate O
deformation S-CONPRI
is O
accommodated O
by O
dynamic S-CONPRI
recovery O
( O
DRV O
) O
process S-CONPRI
, O
where O
low O
angle O
grain B-CONPRI
boundaries E-CONPRI
evolve O
due O
to O
the O
generation O
of O
dislocations S-CONPRI
, O
evolution S-CONPRI
of O
dislocation S-CONPRI
networks O
, O
and O
annihilation O
of O
dislocations S-CONPRI
. O


Both O
cell S-APPL
walls O
and O
Si S-MATE
precipitates S-MATE
contribute O
to O
impeding O
the O
dislocation B-CONPRI
motion E-CONPRI
and O
development O
of O
dislocation S-CONPRI
networks O
. O


At O
high O
strain B-CONPRI
rates E-CONPRI
, O
dislocation S-CONPRI
networks O
evolve O
in O
the O
nanoscale O
DRVed O
subgrains S-CONPRI
. O


Metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
a O
rapidly O
growing O
field O
aimed O
to O
produce O
high-performance O
net-shaped O
parts O
. O


Therefore O
, O
bulk O
metallic B-MATE
glasses E-MATE
( O
BMGs O
) O
, O
known O
for O
their O
superlative O
mechanical B-CONPRI
properties E-CONPRI
, O
are O
of O
remarkable O
interest O
for O
integration O
with O
AM B-MANP
technology E-MANP
. O


In O
this O
study O
, O
we O
pioneer O
the O
utilization O
of O
commercially O
available O
BMG O
sheetmetal O
as S-MATE
feedstock O
for O
AM S-MANP
, O
using O
laser S-ENAT
foil S-MATE
printing O
( O
LFP S-MATE
) O
technology S-CONPRI
. O


LFP S-MATE
and O
traditional O
casting S-MANP
were O
used O
to O
produce O
samples S-CONPRI
for O
four-point O
bending S-MANP
and O
Vickers B-PRO
hardness E-PRO
measurements O
to O
rigorously O
compare O
the O
mechanical S-APPL
performance O
of O
samples S-CONPRI
resulting O
from O
these O
two O
fabrication S-MANP
techniques O
. O


Through O
LFP S-MATE
, O
fully O
amorphous O
BMG O
samples S-CONPRI
with O
dimensions S-FEAT
larger O
than O
the O
critical O
casting S-MANP
thickness O
of O
the O
same O
master O
alloy S-MATE
were O
successfully O
made O
, O
while O
exhibiting O
high O
yield B-PRO
strength E-PRO
and O
toughness S-PRO
in O
bending S-MANP
. O


This O
work O
exemplifies O
a O
potential O
method O
to O
fabricate S-MANP
high-value O
BMG O
commercial O
parts O
, O
like O
gears S-MACEQ
or O
mechanisms O
, O
where O
the O
parts O
are O
conventionally O
machined S-MANP
after O
printing O
, O
and O
greatly O
benefit O
from O
utilizing O
novel O
materials S-CONPRI
. O


In O
industry S-APPL
, O
Design B-FEAT
for I-FEAT
Additive I-FEAT
Manufacturing E-FEAT
( O
DfAM O
) O
is O
currently O
synonymous O
with O
expert O
knowledge O
and O
external O
consultants O
for O
many O
companies S-APPL
. O


Particularly O
in O
higher O
cost O
technologies S-CONPRI
, O
such O
as S-MATE
metal O
powder B-MANP
bed I-MANP
fusion E-MANP
, O
component S-MACEQ
design O
requires O
extensive O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
knowledge O
. O


If O
a O
part O
is O
improperly O
designed S-FEAT
, O
then O
it O
can O
cause O
thousands O
of O
dollars O
of O
lost O
time O
and O
material S-MATE
through O
a O
failed O
print S-MANP
. O


To O
avoid O
this O
situation O
, O
specialists O
must O
be S-MATE
consulted O
throughout O
the O
printing B-MANP
process E-MANP
; O
however O
, O
the O
shortage O
of O
trained O
personnel O
familiar O
with O
AM S-MANP
can O
create O
a O
bottleneck S-CONPRI
during O
design S-FEAT
. O


In O
order O
to O
help O
businesses O
identify O
candidate O
parts O
for O
Powder B-MANP
Bed I-MANP
Fusion E-MANP
( O
PBF S-MANP
) O
AM S-MANP
, O
this O
paper O
presents O
a O
DfAM O
worksheet O
to O
help O
engineers O
, O
drafters O
, O
and O
designers O
select O
good O
part O
candidates O
with O
little O
prior O
knowledge O
of O
the O
specific O
technology S-CONPRI
. O


This O
worksheet O
uses O
data S-CONPRI
from O
the O
literature O
to O
support S-APPL
the O
values O
used O
for O
design S-FEAT
guidance O
. O


Example O
components S-MACEQ
are O
shown O
to O
demonstrate O
the O
worksheet O
process S-CONPRI
. O


Ratings O
of O
these O
components S-MACEQ
are O
then O
compared O
with O
expert O
raters O
’ O
assessments O
of O
their O
suitability O
for O
fabrication S-MANP
with O
PBF S-MANP
from O
a O
geometric O
standpoint O
. O


In O
recent O
years O
, O
combining O
additive S-MATE
and O
subtractive B-MANP
manufacturing E-MANP
technologies O
has O
attracted O
much O
attention O
from O
both O
industrial S-APPL
and O
academic O
sectors O
. O


Thereafter O
, O
the O
design S-FEAT
of O
process B-CONPRI
planning E-CONPRI
for O
combining O
additive S-MATE
and O
subtractive B-MANP
manufacturing E-MANP
processes S-CONPRI
is O
focused O
. O


This O
allows O
achieving O
the O
geometry S-CONPRI
and O
quality S-CONPRI
of O
final O
part O
from O
the O
existing O
part O
. O


The O
methodology S-CONPRI
for O
process B-CONPRI
planning E-CONPRI
design S-FEAT
is O
developed O
in O
two O
major O
steps O
using O
the O
manufacturing S-MANP
feature S-FEAT
concept O
, O
the O
knowledge O
of O
manufacturing B-MANP
processes E-MANP
, O
technological O
requirements O
, O
and O
available O
resources O
. O


In O
the O
first O
step S-CONPRI
, O
manufacturing S-MANP
features O
( O
i.e O
. O


machining S-MANP
and O
additive B-MANP
manufacturing E-MANP
features O
) O
are O
extracted S-CONPRI
from O
the O
information O
of O
the O
existing O
and O
final O
parts O
. O


In O
the O
second O
step S-CONPRI
, O
the O
process B-CONPRI
planning E-CONPRI
is O
generated O
from O
extracted S-CONPRI
features O
by O
respecting O
the O
relationships O
of O
features O
and O
the O
manufacturing S-MANP
precedence O
constraints O
. O


Finally O
, O
a O
case B-CONPRI
study E-CONPRI
is O
used O
to O
illustrate O
the O
proposed O
methodology S-CONPRI
. O


Although O
vibration-assisted O
powder B-MACEQ
delivery I-MACEQ
systems E-MACEQ
have O
been O
developed O
and O
studied O
in O
the O
literature O
, O
their O
characteristics O
and O
principles O
of O
operation O
are O
generally O
not O
well O
suited O
for O
powder-based B-MANP
additive I-MANP
manufacturing E-MANP
operations O
mainly O
because O
of O
their O
powder S-MATE
flows O
and O
deposition S-CONPRI
characteristics O
. O


The O
flow B-PARA
rate E-PARA
, O
one O
of O
the O
key O
parameters S-CONPRI
in O
these O
processes S-CONPRI
, O
was O
used O
to O
evaluate O
the O
system O
. O


Its O
sensitivity S-PARA
and O
dependence O
on O
powder B-MATE
particle E-MATE
size O
, O
piezo O
excitation S-CHAR
frequency O
and O
amplitude O
, O
hopper O
volume S-CONPRI
, O
nozzle S-MACEQ
size O
, O
and O
humidity O
were O
assessed O
. O


The O
results O
, O
using O
316 B-MATE
L I-MATE
stainless I-MATE
steel I-MATE
powders E-MATE
, O
have O
shown O
that O
the O
mass O
powder B-PARA
flow I-PARA
rate E-PARA
can O
be S-MATE
effectively O
controlled O
and O
that O
it O
is O
most O
prominently O
influenced O
by O
the O
piezo O
excitation S-CHAR
frequency O
. O


Ti6Al4V S-MATE
+ O
Al12Si O
compositionally O
graded O
cylindrical S-CONPRI
structures O
were O
fabricated S-CONPRI
on O
a O
Ti6Al4V B-MATE
substrate E-MATE
using O
laser B-MANP
engineered I-MANP
net I-MANP
shaping E-MANP
( O
LENS™ O
) O
process S-CONPRI
. O


LENS™ O
fabricated S-CONPRI
materials O
had O
two O
regions O
of O
Ti6Al4V S-MATE
+ O
Al12Si O
compositions O
, O
a O
pure O
Al12Si O
, O
and O
a O
pure O
Ti6Al4V S-MATE
area S-PARA
. O


Microstructural S-CONPRI
changes O
were O
affected O
by O
both O
laser B-PARA
power E-PARA
and O
compositional O
variations S-CONPRI
. O


In O
addition O
, O
TiSi2 O
and O
Ti3Al O
phase S-CONPRI
formations O
were O
also O
identified O
in O
low O
and O
high O
laser B-PARA
power E-PARA
processed O
Ti6Al4V S-MATE
+ O
Al12Si O
sections O
, O
respectively O
. O


Moreover O
, O
the O
high O
laser B-PARA
power E-PARA
processed O
Ti6Al4V S-MATE
+ O
Al12Si O
section O
showed O
the O
highest O
hardness S-PRO
value O
of O
685.6 O
± O
10.6 O
HV0.1 O
, O
which O
was O
caused O
due O
to O
the O
formation O
of O
new O
intermetallic S-MATE
phases O
. O


This O
high O
hardness S-PRO
section O
exhibited O
brittle B-CONPRI
failure E-CONPRI
modes O
during O
compression B-CHAR
tests E-CHAR
, O
while O
the O
pure O
Al12Si O
sections O
showed O
ductile S-PRO
deformation S-CONPRI
. O


The O
maximum O
compressive B-PRO
strengths E-PRO
of O
Ti6Al4V S-MATE
+ O
Al12Si O
compositionally O
graded O
material S-MATE
was O
507.8 O
± O
52.0 O
MPa S-CONPRI
. O


Our O
results O
show O
that O
compositionally O
gradient O
bulk O
structures O
of O
Ti6Al4V S-MATE
and O
Al12Si O
can O
be S-MATE
directly O
manufactured S-CONPRI
using O
additive B-MANP
manufacturing E-MANP
, O
however O
, O
performances O
can O
vary O
significantly O
based O
on O
process B-CONPRI
parameters E-CONPRI
and O
compositional O
variations S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
enables O
highly O
complex-shaped S-CONPRI
and O
functionally O
optimized O
parts O
. O


However O
, O
as S-MATE
today O
’ O
s S-MATE
computer-aided B-ENAT
design E-ENAT
( O
CAD S-ENAT
) O
tools S-MACEQ
are O
still O
based O
on O
low-level O
, O
geometric O
primitives O
, O
the O
modeling S-ENAT
of O
complex B-CONPRI
geometries E-CONPRI
requires O
many O
repetitive O
, O
manual O
steps O
. O


As S-MATE
a O
consequence O
, O
the O
need O
for O
an O
automated O
design S-FEAT
approach O
is O
emphasized O
and O
regarded O
as S-MATE
a O
key O
enabler O
to O
quickly O
create O
different O
concepts O
, O
allow O
iterative O
design S-FEAT
changes O
, O
and O
customize O
parts O
at O
reduced O
effort O
. O


Topology B-FEAT
optimization E-FEAT
exists O
as S-MATE
a O
computational O
design S-FEAT
approach O
but O
usually O
demands O
a O
manual O
interpretation O
and O
redesign O
of O
a O
CAD B-ENAT
model E-ENAT
and O
may O
not O
be S-MATE
applicable O
to O
problems O
such O
as S-MATE
the O
design S-FEAT
of O
parts O
with O
multiple O
integrated O
flows O
. O


This O
work O
presents O
a O
computational O
design S-FEAT
synthesis O
framework S-CONPRI
to O
automate O
the O
design S-FEAT
of O
complex-shaped S-CONPRI
multi-flow O
nozzles S-MACEQ
. O


The O
framework S-CONPRI
provides O
AM S-MANP
users O
a O
toolbox O
with O
design S-FEAT
elements O
, O
which O
are O
used O
as S-MATE
building O
blocks O
to O
generate O
finished O
3D B-APPL
part E-APPL
geometries O
. O


The O
elements S-MATE
are O
organized O
in O
a O
hierarchical O
architecture S-APPL
and O
implemented O
using O
object-oriented O
programming O
. O


As S-MATE
the O
layout S-CONPRI
of O
the O
elements S-MATE
is O
defined O
with O
a O
visual O
interface S-CONPRI
, O
the O
process S-CONPRI
is O
accessible O
to O
non-experts O
. O


As S-MATE
a O
proof O
of O
concept O
, O
the O
framework S-CONPRI
is O
applied O
to O
successfully O
generate O
a O
variety O
of O
customized O
AM S-MANP
nozzles O
that O
are O
tested O
using O
co-extrusion O
of O
clay S-MATE
. O


Finally O
, O
the O
work O
discusses O
the O
framework S-CONPRI
’ O
s S-MATE
benefits O
and O
limitations O
, O
the O
impact S-CONPRI
on O
product B-CONPRI
development E-CONPRI
and O
novel O
AM S-MANP
applications O
, O
and O
the O
transferability O
to O
other O
domains O
. O


17-4PH S-MATE
stainless O
steel S-MATE
thin-walled O
samples S-CONPRI
were O
additively B-MANP
manufactured E-MANP
by O
SLM S-MANP
Samples S-CONPRI
parallel O
and O
at O
45˚ O
to O
the O
scan O
axes O
gave O
beam S-MACEQ
path O
lengths O
of O
19 O
- O
0.8 O
mm S-MANP
Longer O
beam S-MACEQ
paths O
gave O
microstructures S-MATE
comprising O
mostly O
coarse-grained O
ferrite S-MATE
The O
shortest O
beam S-MACEQ
paths O
gave O
structures O
with O
mostly O
austenite S-MATE
and O
some O
martensite S-MATE
Re-heating O
of O
ferrite S-MATE
leads O
to O
austenite S-MATE
, O
with O
martensite S-MATE
forming S-MANP
during O
cooling S-MANP
Components S-MACEQ
with O
varying O
dimensions S-FEAT
are O
found O
in O
numerous O
applications O
. O


The O
current O
work O
examines O
how O
microstructures S-MATE
and O
phases O
change O
for O
additively B-MANP
manufactured E-MANP
17-4PH S-MATE
thin O
walls O
as S-MATE
a O
function O
of O
laser S-ENAT
path O
length O
, O
path O
direction O
, O
and O
wall B-FEAT
thickness E-FEAT
. O


Two O
sample S-CONPRI
sets O
were O
designed S-FEAT
, O
each O
consisting O
of O
four O
walls O
with O
thicknesses O
of O
6.4 O
mm S-MANP
to O
0.8 O
mm S-MANP
. O


In O
the O
first O
set S-APPL
, O
the O
wall O
axes O
were O
parallel O
to O
the O
scan O
axes O
, O
such O
that O
the O
laser S-ENAT
path O
length O
varied O
from O
layer S-PARA
to O
layer S-PARA
with O
the O
laser S-ENAT
path O
either O
being O
parallel O
or O
perpendicular O
to O
the O
wall O
. O


In O
the O
second O
set S-APPL
, O
the O
walls O
lay S-CONPRI
at O
45° O
to O
the O
scan O
axes O
, O
such O
that O
the O
laser S-ENAT
path O
had O
the O
same O
length O
in O
all O
layers O
and O
gradually O
decreased O
with O
wall B-FEAT
thickness E-FEAT
. O


Substantial O
changes O
in O
phase S-CONPRI
stability O
and O
microstructure S-CONPRI
are O
observed O
as S-MATE
the O
wall B-FEAT
thickness E-FEAT
decreases O
, O
with O
ferritic S-MATE
phases O
and O
coarse O
grains S-CONPRI
changing O
to O
fine O
grains S-CONPRI
and O
an O
increasing O
volume B-PARA
fraction E-PARA
of O
austenite S-MATE
. O


These O
changes O
are O
attributed O
to O
changes O
in O
the O
local O
temperature-time O
profile S-FEAT
as S-MATE
the O
length O
of O
the O
laser S-ENAT
paths O
change O
from O
19 O
mm S-MANP
to O
0.8 O
mm S-MANP
. O


These O
observations O
demonstrate O
the O
range S-PARA
of O
microstructure S-CONPRI
and O
phase S-CONPRI
control O
options O
available O
in O
additive B-MANP
manufacturing E-MANP
with O
judicious O
selections O
of O
part O
layouts O
on O
build B-MACEQ
plates E-MACEQ
and O
of O
laser B-CONPRI
beam E-CONPRI
directions O
. O


In O
this O
paper O
, O
the O
anisotropy S-PRO
in O
the O
nickel-aluminum O
bronze S-MATE
( O
NAB S-MATE
) O
component S-MACEQ
manufactured O
by O
WAAM S-MANP
process S-CONPRI
has O
been O
shown O
and O
investigated O
by O
different O
methods O
including O
material S-MATE
and O
mechanical B-CHAR
tests E-CHAR
. O


The O
quenching S-MANP
and O
tempering S-MANP
heat B-MANP
treatments E-MANP
have O
been O
used O
in O
this O
paper O
to O
reduce O
the O
anisotropy S-PRO
. O


Results O
have O
indicated O
that O
the O
quenching S-MANP
and O
tempering S-MANP
heat B-MANP
treatments E-MANP
can O
effectively O
reduce O
the O
anisotropy S-PRO
in O
the O
NAB S-MATE
component S-MACEQ
. O


Results O
have O
shown O
that O
the O
additively B-MANP
manufactured E-MANP
materials O
possess O
relatively O
better O
tensile S-PRO
performances O
. O


In O
this O
paper O
, O
a O
nickel-aluminum O
bronze B-MATE
alloy E-MATE
component O
is O
built O
using O
wire-arc B-MANP
additive I-MANP
manufacturing I-MANP
process E-MANP
. O


In O
order O
to O
investigate O
the O
influence O
of O
anisotropy S-PRO
introduced O
by O
the O
wire-arc B-MANP
additive I-MANP
manufacturing I-MANP
process E-MANP
, O
the O
layer-by-layer S-CONPRI
manufactured O
components S-MACEQ
with O
different O
post-production O
heat B-MANP
treatments E-MANP
are O
characterized O
by O
optical S-CHAR
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
morphologies S-CONPRI
, O
X-ray B-CHAR
diffraction E-CHAR
and O
mechanical B-CHAR
tests E-CHAR
in O
longitudinal O
, O
transverse O
and O
normal O
directions O
. O


Also O
, O
the O
ductility S-PRO
of O
the O
alloy S-MATE
is O
significantly O
improved O
with O
the O
designed S-FEAT
quenching O
and O
tempering S-MANP
method O
, O
and O
competitive O
mechanical B-CONPRI
properties E-CONPRI
are O
achieved O
when O
tempering S-MANP
temperature S-PARA
reaches O
650 O
°C O
. O


In O
addition O
, O
the O
anisotropy S-PRO
in O
the O
additively B-MANP
manufactured E-MANP
alloy O
can O
be S-MATE
effectively O
modified O
by O
the O
quenching S-MANP
and O
tempering S-MANP
heat B-MANP
treatments E-MANP
. O


Selective B-MANP
laser I-MANP
sintering E-MANP
( O
SLS S-MANP
) O
is O
one O
of O
the O
most O
popular O
industrial S-APPL
polymer O
additive B-MANP
manufacturing I-MANP
processes E-MANP
with O
applications O
in O
aerospace S-APPL
, O
biomedical S-APPL
, O
tooling S-CONPRI
, O
prototyping S-CONPRI
, O
and O
beyond O
. O


SLS S-MANP
is O
capable O
of O
creating O
unique O
, O
functional O
parts O
with O
little O
waste O
and O
no O
tooling S-CONPRI
by O
using O
a O
high-powered O
laser S-ENAT
to O
selectively O
melt S-CONPRI
powdered O
polymer S-MATE
into O
desired O
shapes O
. O


This O
process S-CONPRI
relies O
heavily O
on O
understanding O
and O
controlling O
the O
thermodynamics O
of O
the O
polymer B-MATE
melt E-MATE
process O
. O


One O
of O
the O
biggest O
challenges O
SLS S-MANP
faces O
is O
lack O
of O
adequate O
process B-CONPRI
control E-CONPRI
, O
which O
leads O
to O
comparatively O
high O
component S-MACEQ
variations O
. O


It O
has O
been O
shown O
that O
implementing O
more O
advanced O
laser S-ENAT
control O
techniques O
enable O
a O
higher O
level O
of O
control O
over O
the O
processing O
temperatures S-PARA
and O
lead S-MATE
to O
more O
uniform O
components S-MACEQ
. O


Currently O
, O
there O
are O
no O
commercial O
options O
for O
a O
laser B-PARA
power E-PARA
controller S-MACEQ
that O
allows O
continuously O
variable O
power S-PARA
to O
be S-MATE
used O
as S-MATE
a O
galvanometer O
system O
adjusts O
the O
laser S-ENAT
position O
. O


Process B-CONPRI
consistency E-CONPRI
and O
control O
are O
bottleneck S-CONPRI
issues O
to O
wider O
insertion O
of O
powder-bed O
fusion S-CONPRI
additive B-MANP
manufacturing E-MANP
in O
the O
industrial S-APPL
shopfloor O
. O


Of O
particular O
interest O
is O
the O
porosity S-PRO
of O
the O
components S-MACEQ
, O
which O
remains O
the O
limiting O
factor O
to O
high-cycle O
fatigue S-PRO
performance O
. O


Recent O
experiments O
have O
shown O
that O
, O
with O
increasing O
energy B-PARA
density E-PARA
, O
a O
surge O
in O
porosity S-PRO
is O
seen O
in O
selectively O
laser S-ENAT
melted O
metals S-MATE
. O


In O
this O
high-energy O
density S-PRO
regime O
, O
porosity S-PRO
must O
originate O
from O
mechanisms O
that O
are O
different O
from O
the O
well-known O
incomplete O
melting S-MANP
in O
the O
low O
energy B-PARA
density E-PARA
regime O
. O


To O
shed O
light O
on O
this O
interesting O
phenomenon O
, O
this O
paper O
first O
discusses O
the O
mechanism S-CONPRI
of O
bubble O
formation O
in O
the O
melt B-MATE
pool E-MATE
and O
possible O
trapping O
during O
the O
solidification S-CONPRI
, O
and O
then O
formulates O
a O
predictive B-CONPRI
model E-CONPRI
for O
porosity S-PRO
in O
this O
regime O
. O


To O
compare O
with O
experimental S-CONPRI
results O
, O
we O
perform O
computer S-ENAT
modeling O
and O
simulations S-ENAT
which O
have O
been O
fully O
validated O
by O
experiments O
to O
determine O
the O
parameters S-CONPRI
in O
the O
model S-CONPRI
. O


We O
show O
that O
the O
model S-CONPRI
predictions O
are O
in O
good O
qualitative S-CONPRI
and O
quantitative S-CONPRI
agreement O
with O
the O
experimental S-CONPRI
measurements O
. O


Hence O
, O
the O
proposed O
model S-CONPRI
can O
be S-MATE
used O
as S-MATE
a O
tool S-MACEQ
to O
predict O
the O
porosity S-PRO
, O
and O
further O
to O
control O
and O
possibly O
reduce O
porosity S-PRO
in O
laser S-ENAT
powder-bed O
fusion S-CONPRI
additive B-MANP
manufacturing E-MANP
, O
paving O
the O
way O
for O
its O
wider O
adoption O
in O
manufacturing S-MANP
shopfloors O
. O


Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
uses O
a O
focused O
, O
high O
power S-PARA
laser S-ENAT
to O
repeatedly O
scan O
geometric O
patterns O
on O
thin O
layers O
of O
metal B-MATE
powder E-MATE
, O
which O
build S-PARA
up O
to O
a O
final O
, O
solid O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
part O
. O


This O
process S-CONPRI
is O
somewhat O
limited O
in O
that O
the O
parts O
tend O
to O
have O
poorer O
surface B-FEAT
finish E-FEAT
( O
compared O
to O
machining S-MANP
or O
grinding S-MANP
) O
and O
distortion S-CONPRI
due O
to O
residual B-PRO
stress E-PRO
, O
as S-MATE
well O
as S-MATE
multiple O
other O
deficiencies O
. O


Typical O
laser B-ENAT
scan E-ENAT
strategies O
are O
relatively O
simple S-MANP
and O
use O
constant O
laser B-PARA
power E-PARA
levels O
. O


This O
elicits O
local O
variations S-CONPRI
in O
the O
melt B-MATE
pool E-MATE
size O
, O
shape O
, O
or O
temperature S-PARA
, O
particularly O
near O
sharp O
geometric O
features O
or O
overhang S-PARA
structures O
due O
to O
the O
relatively O
higher O
thermal B-PRO
conductivity E-PRO
of O
solid O
metal S-MATE
compared O
to O
metal B-MATE
powder E-MATE
. O


In O
this O
paper O
, O
we O
present O
a O
new O
laser B-PARA
power E-PARA
control O
algorithm S-CONPRI
, O
which O
scales O
the O
laser B-PARA
power E-PARA
to O
a O
value O
called O
the O
geometric O
conductance O
factor O
( O
GCF O
) O
. O


The O
GCF O
is O
calculated O
based O
on O
the O
amount O
of O
solid O
vs. O
powder B-MATE
material E-MATE
near O
the O
melt B-MATE
pool E-MATE
. O


Then O
, O
we O
detail O
the O
hardware O
and O
software S-CONPRI
implementation O
on O
the O
National O
Institute O
of O
Standards S-CONPRI
and O
Technology S-CONPRI
( O
NIST O
) O
additive B-MANP
manufacturing E-MANP
metrology O
testbed O
( O
AMMT O
) O
, O
which O
includes O
co-axial O
melt B-MATE
pool E-MATE
monitoring O
using O
a O
high-speed O
camera S-MACEQ
. O


Six O
parts O
were O
fabricated S-CONPRI
out O
of O
nickel S-MATE
superalloy O
625 O
( O
IN625 O
) O
with O
the O
same O
nominal O
laser B-PARA
power E-PARA
, O
but O
with O
varying O
GCF O
algorithm S-CONPRI
parameters O
. O


We O
demonstrate O
the O
effect O
of O
tailored O
laser B-PARA
power E-PARA
on O
reducing O
the O
variability S-CONPRI
of O
melt B-MATE
pool E-MATE
intensity O
measured O
throughout O
the O
3D S-CONPRI
build O
. O


Finally O
, O
we O
contrast O
the O
difference O
between O
the O
‘ O
optimized O
’ O
part O
vs. O
the O
standard S-CONPRI
build B-PARA
parameters E-PARA
, O
including O
the O
deflection O
of O
the O
final O
part O
top O
surface S-CONPRI
near O
the O
overhang S-PARA
and O
the O
variation S-CONPRI
of O
surface B-FEAT
finish E-FEAT
on O
the O
down-facing O
surfaces S-CONPRI
. O


Ultimately O
, O
the O
improvements O
to O
the O
in-situ S-CONPRI
process O
monitoring O
and O
part O
qualities O
demonstrate O
the O
utility O
and O
future O
potential O
tuning O
and O
optimizing O
more O
complex O
laser B-ENAT
scan E-ENAT
strategies O
. O


Powder-fed O
laser B-MANP
additive I-MANP
manufacturing E-MANP
( O
LAM S-MANP
) O
based O
on O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
technology S-CONPRI
is O
used O
to O
produce O
S316-L O
austenitic S-MATE
, O
and O
S410-L O
martensitic B-MATE
stainless I-MATE
steel E-MATE
structures O
by O
3D-printing S-MANP
through O
a O
layer-upon-layer O
fashion S-CONPRI
. O


The O
microstructural S-CONPRI
features O
and O
crystallographic O
textural O
components S-MACEQ
are O
studied O
via O
electron O
backscattering O
diffraction S-CHAR
( O
EBSD S-CHAR
) O
analysis O
, O
hardness S-PRO
indentation O
and O
tensile B-CHAR
testing E-CHAR
. O


The O
results O
are O
compared O
with O
commercial O
rolled O
sheets S-MATE
of O
austenitic S-MATE
and O
martensitic B-MATE
stainless I-MATE
steels E-MATE
. O


A O
well-developed O
< O
200 O
> O
direction O
solidification S-CONPRI
texture O
( O
with O
a O
J-index O
of O
∼11.5 O
) O
is O
observed O
for O
the O
austenitic S-MATE
structure O
produced O
by O
the O
LAM S-MANP
process O
, O
compared O
to O
a O
J-index O
of O
∼2.0 O
for O
the O
commercial O
austenitic S-MATE
rolled O
sheet S-MATE
. O


Such O
a O
texture S-FEAT
in O
the O
LAM S-MANP
process O
is O
caused O
by O
equiaxed B-CONPRI
grain E-CONPRI
formation O
in O
the O
middle O
of O
each O
layer S-PARA
followed O
by O
columnar O
growth O
during O
layer-upon-layer O
deposition S-CONPRI
. O


A O
quite O
strong O
preferred O
orientation S-CONPRI
( O
J-index O
of O
17.5 O
) O
is O
noticed O
for O
martensitic O
steel S-MATE
developed O
by O
LAM S-MANP
. O


Large O
laths O
of O
martensite S-MATE
exhibit O
a O
dominant O
textural O
component S-MACEQ
of O
{ O
011 O
} O
< O
111 O
> O
in O
the O
α-phase O
, O
which O
is O
mainly O
controlled O
by O
transformation O
during O
layer-by-layer B-CONPRI
deposition E-CONPRI
. O


On O
the O
other O
hand O
, O
the O
martensitic O
commercial O
sheet S-MATE
consists O
of O
equiaxed B-CONPRI
grains E-CONPRI
without O
any O
preferred O
orientation S-CONPRI
or O
completely O
random O
orientations S-CONPRI
. O


In O
the O
case O
of O
the O
austenitic S-MATE
steel O
, O
mechanical B-CONPRI
properties E-CONPRI
such O
as S-MATE
tensile O
strength S-PRO
, O
hardness S-PRO
and O
ductility S-PRO
were O
severely O
deteriorated O
during O
the O
LAM S-MANP
deposition S-CONPRI
. O


A O
ductility S-PRO
loss O
of O
about O
50 O
% O
is O
recorded O
compared O
to O
the O
commercially O
rolled O
sheets S-MATE
that O
is O
attributed O
to O
the O
cast/solidified O
structure S-CONPRI
. O


However O
, O
LAM S-MANP
manufacturing O
of O
martensitic B-MATE
stainless I-MATE
steel E-MATE
structures O
leads O
to O
a O
considerably O
enhanced O
mechanical B-PRO
strength E-PRO
( O
more O
than O
double O
) O
at O
the O
expense O
of O
reduced O
ductility S-PRO
, O
because O
of O
martensitic O
phase S-CONPRI
transformations O
under O
higher O
cooling B-PARA
rates E-PARA
. O


Electrophoretic B-MANP
deposition E-MANP
( O
EPD O
) O
is O
a O
widely O
used O
industrial S-APPL
coating S-APPL
technique O
for O
depositing O
polymer S-MATE
, O
ceramic S-MATE
, O
and O
metal S-MATE
thin O
films O
. O


Recently O
, O
there O
has O
been O
interested O
in O
using O
EPD O
for O
additive B-MANP
manufacturing E-MANP
using O
reconfigurable O
electrodes S-MACEQ
. O


We O
demonstrate O
a O
resolution S-PARA
limit S-CONPRI
of O
10 O
μm O
for O
the O
deposited O
feature S-FEAT
, O
which O
corresponds O
to O
the O
limits S-CONPRI
of O
the O
optical S-CHAR
system O
. O


Furthermore O
, O
the O
first O
3D S-CONPRI
overhanging O
structure S-CONPRI
made O
with O
EPD O
is O
presented O
, O
which O
points O
to O
the O
ability O
to O
create O
architected O
cellular B-MATE
materials E-MATE
. O


These O
improvements O
open O
the O
possibility O
for O
EPD O
to O
be S-MATE
a O
true O
3D S-CONPRI
additive O
manufacturing S-MANP
technique O
. O


Addresses O
thermal B-MANP
annealing E-MANP
of O
additively B-MANP
manufactured E-MANP
polymer O
parts O
. O


Demonstrates O
significant O
enhancement O
in O
thermal B-PRO
conductivity E-PRO
. O


Data S-CONPRI
quantify O
dependence O
of O
enhancement O
on O
annealing S-MANP
time O
and O
temperature S-PARA
. O


Develops O
a O
theoretical S-CONPRI
thermal O
model S-CONPRI
, O
with O
good O
agreement O
with O
measurements O
. O


Results O
may O
help O
improve O
thermal O
performance S-CONPRI
of O
polymer S-MATE
AM B-MACEQ
parts E-MACEQ
. O


While O
additive B-MANP
manufacturing E-MANP
offers O
significant O
advantages O
compared O
to O
traditional B-MANP
manufacturing E-MANP
technologies S-CONPRI
, O
deterioration O
in O
thermal O
and O
mechanical B-CONPRI
properties E-CONPRI
compared O
to O
properties S-CONPRI
of O
the O
underlying O
materials S-CONPRI
is O
a O
serious O
concern O
. O


In O
the O
context O
of O
polymer B-MANP
extrusion E-MANP
based O
additive B-MANP
manufacturing E-MANP
, O
post-process S-CONPRI
approaches O
, O
such O
as S-MATE
thermal O
annealing S-MANP
have O
been O
reported O
for O
improving O
mechanical B-CONPRI
properties E-CONPRI
based O
on O
reptation O
of O
polymer S-MATE
chains O
and O
enhanced O
filament-to-filament O
adhesion S-PRO
. O


However O
, O
there O
is O
a O
lack O
of O
similar O
work O
for O
improving O
thermal B-CONPRI
properties E-CONPRI
such O
as S-MATE
thermal O
conductivity S-PRO
. O


This O
paper O
reports O
significant O
enhancement O
in O
build-direction O
thermal B-PRO
conductivity E-PRO
of O
polymer B-MANP
extrusion E-MANP
based O
parts O
as S-MATE
a O
result O
of O
thermal B-MANP
annealing E-MANP
. O


A O
theoretical B-CONPRI
model E-CONPRI
based O
on O
Arrhenius O
kinetics O
for O
neck O
growth O
and O
a O
heat B-CONPRI
transfer E-CONPRI
model O
for O
the O
consequent O
impact S-CONPRI
on O
inter-layer O
thermal O
contact S-APPL
resistance O
is O
developed O
. O


Predicted S-CONPRI
thermal O
conductivity S-PRO
enhancement O
is O
found O
to O
be S-MATE
in O
good O
agreement O
with O
experimental B-CONPRI
data E-CONPRI
for O
a O
wide O
range S-PARA
of O
annealing S-MANP
temperature O
and O
time O
. O


The O
theoretical B-CONPRI
model E-CONPRI
may O
play O
a O
key O
role O
in O
developing O
practical O
thermal B-MANP
annealing E-MANP
strategies O
that O
account O
for O
the O
multiple O
constraints O
involved O
in O
annealing S-MANP
of O
polymer S-MATE
parts O
. O


This O
work O
may O
facilitate O
the O
use O
of O
polymer B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
for O
producing O
enhanced O
thermal B-PRO
conductivity E-PRO
parts O
capable O
of O
withstanding O
thermal O
loads O
. O


Additively B-MANP
manufactured E-MANP
metamaterials O
such O
as S-MATE
lattices O
offer O
unique O
physical B-PRO
properties E-PRO
such O
as S-MATE
high O
specific B-PRO
strengths E-PRO
and O
stiffnesses O
. O


However O
, O
additively B-MANP
manufactured E-MANP
parts O
, O
including O
lattices S-CONPRI
, O
exhibit O
a O
higher O
variability S-CONPRI
in O
their O
mechanical B-CONPRI
properties E-CONPRI
than O
wrought B-MATE
materials E-MATE
, O
placing O
more O
stringent O
demands O
on O
inspection S-CHAR
, O
part O
quality S-CONPRI
verification O
, O
and O
product O
qualification O
. O


Previous O
research S-CONPRI
on O
anomaly S-CONPRI
detection O
has O
primarily O
focused O
on O
using O
in-situ S-CONPRI
monitoring O
of O
the O
additive B-MANP
manufacturing I-MANP
process E-MANP
or O
post-process S-CONPRI
( O
ex-situ O
) O
x-ray B-CHAR
computed I-CHAR
tomography E-CHAR
. O


In O
this O
work O
, O
we O
show O
that O
convolutional O
neural B-CONPRI
networks E-CONPRI
( O
CNN O
) O
, O
a O
machine B-ENAT
learning I-ENAT
algorithm E-ENAT
, O
can O
directly O
predict O
the O
energy O
required O
to O
compressively O
deform O
gyroid O
and O
octet O
truss S-MACEQ
metamaterials S-MATE
using O
only O
optical S-CHAR
images S-CONPRI
. O


Using O
the O
tiled O
nature O
of O
engineered O
lattices S-CONPRI
, O
the O
relatively O
small O
data S-CONPRI
set O
( O
43 O
to O
48 O
lattices S-CONPRI
) O
can O
be S-MATE
augmented O
by O
systematically O
subdividing O
the O
original O
image S-CONPRI
into O
many O
smaller O
sub-images O
. O


During O
testing S-CHAR
of O
the O
CNN O
, O
the O
prediction S-CONPRI
from O
these O
sub-images O
can O
be S-MATE
combined O
using O
an O
ensemble-like O
technique O
to O
predict O
the O
deformation S-CONPRI
work O
of O
the O
entire O
lattice S-CONPRI
. O


This O
approach O
provides O
a O
fast O
and O
inexpensive O
screening O
tool S-MACEQ
for O
predicting O
properties S-CONPRI
of O
3D B-MANP
printed E-MANP
lattices O
. O


Importantly O
, O
this O
artificial O
intelligence O
strategy O
goes O
beyond O
‘ O
inspection S-CHAR
’ O
, O
since O
it O
accurately S-CHAR
estimates O
product O
performance S-CONPRI
metrics O
, O
not O
just O
the O
existence O
of O
defects S-CONPRI
. O


Plaster O
Binder B-MANP
Jetting E-MANP
( O
BJ S-MANP
) O
is O
one O
of O
the O
major O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
which O
has O
been O
in O
use O
since O
the O
1990s O
. O


It O
has O
many O
advantages O
such O
as S-MATE
the O
ability O
to O
print S-MANP
in O
full O
color O
CMY O
( O
K S-MATE
) O
, O
no O
support B-FEAT
structures E-FEAT
, O
and O
is O
relatively O
faster O
and O
less O
expensive O
when O
compared O
to O
other O
AM B-MANP
technologies E-MANP
. O


Since O
there O
is O
no O
phase S-CONPRI
transformation O
( O
e.g O
. O


powder S-MATE
to O
molten B-CONPRI
pool E-CONPRI
in O
powder B-MANP
bed I-MANP
fusion E-MANP
, O
directed B-MANP
energy I-MANP
deposition E-MANP
) O
, O
BJ S-MANP
does O
not O
require O
support B-FEAT
structures E-FEAT
and O
enables O
higher O
packing O
density S-PRO
in O
the O
build B-PARA
volume E-PARA
. O


However O
, O
relatively O
lower O
mechanical B-PRO
strength E-PRO
when O
compared O
to O
other O
AM B-MANP
processes E-MANP
has O
mostly O
limited O
it O
to O
non-functional O
applications O
such O
as S-MATE
prototyping O
. O


This O
paper O
investigates S-CONPRI
novel O
methods O
to O
improve O
the O
mechanical S-APPL
and O
temperature S-PARA
performance S-CONPRI
of O
plaster O
BJ S-MANP
additive B-APPL
manufactured I-APPL
parts E-APPL
via O
improved O
infiltration S-CONPRI
processes O
and O
incorporation O
of O
infiltrants O
with O
higher O
strength S-PRO
. O


Potential O
applications O
include O
functional O
end O
use O
products O
, O
including O
tooling S-CONPRI
, O
jigs S-MACEQ
and O
fixtures O
for O
higher O
temperature S-PARA
applications O
. O


Three O
2-part O
epoxy S-MATE
resin O
systems O
were O
evaluated O
as S-MATE
infiltrants O
in O
comparison O
to O
epoxy S-MATE
and O
cyanoacrylate O
( O
CA S-MATE
) O
resins S-MATE
recommended O
by O
the O
original O
equipment S-MACEQ
manufacturer O
( O
OEM O
) O
. O


Multiple O
impregnation S-MANP
methods O
including O
hot O
and O
wet O
vacuum O
were O
evaluated O
on O
their O
infiltration B-CONPRI
effectiveness E-CONPRI
. O


The O
best O
impregnation S-MANP
method O
was O
then O
used O
to O
prepare O
tensile S-PRO
, O
flexural O
and O
compressive O
samples S-CONPRI
for O
additional O
evaluation O
of O
each O
resin S-MATE
. O


Both O
resins S-MATE
and O
infiltrated O
samples S-CONPRI
were O
individually O
evaluated O
using O
Differential O
Scanning S-CONPRI
Calorimetry O
( O
DSC S-CHAR
) O
to O
determine O
glass B-CONPRI
transition I-CONPRI
temperatures E-CONPRI
and O
other O
thermal O
events O
. O


Infiltrated O
specimens O
of O
the O
best O
performing O
resins S-MATE
were O
evaluated O
for O
Heat B-CONPRI
Deflection E-CONPRI
Temperature O
( O
HDT O
) O
performance S-CONPRI
utilizing O
Dynamic B-CONPRI
Mechanical I-CONPRI
Analysis E-CONPRI
( O
DMA S-CONPRI
) O
. O


It O
was O
found O
that O
infiltration S-CONPRI
is O
anisotropic S-PRO
, O
with O
the O
higher O
penetration B-PARA
depth E-PARA
from O
the O
sides O
( O
between O
layers O
) O
than O
top O
and O
bottom O
( O
across O
layers O
) O
. O


Vacuum O
impregnation S-MANP
resulted O
in O
the O
highest O
infiltration S-CONPRI
depth O
by O
fully O
impregnating O
the O
25 O
mm S-MANP
cubic O
samples S-CONPRI
. O


The O
best O
performing O
epoxy S-MATE
showed O
a O
10 O
% O
increase O
in O
mechanical B-PRO
strength E-PRO
over O
the O
OEM O
epoxy S-MATE
at O
76 O
% O
reduction S-CONPRI
in O
cost O
. O


The O
OEM O
cyanoacrylate O
had O
the O
lowest O
mechanical B-PRO
strength E-PRO
across O
all O
tests O
. O


DSC S-CHAR
analysis O
revealed O
that O
the O
plaster O
and O
gypsum S-MATE
base O
material S-MATE
will O
start O
to O
dehydrate O
above O
100 O
°C O
and O
will O
ultimately O
limit S-CONPRI
the O
parts O
’ O
high O
temperature S-PARA
capabilities O
. O


The O
OEM O
epoxy S-MATE
showed O
the O
highest O
HDT O
. O


High O
residual B-PRO
stresses E-PRO
are O
typical O
in O
additively B-MANP
manufactured E-MANP
metals O
and O
can O
reach O
levels O
as S-MATE
high O
as S-MATE
the O
yield B-PRO
strength E-PRO
, O
leading O
to O
distortions O
and O
even O
cracks O
. O


Here O
, O
an O
in B-CONPRI
situ E-CONPRI
method O
for O
controlling O
residual B-PRO
stress E-PRO
during O
laser B-MANP
powder I-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
was O
demonstrated O
. O


By O
illuminating O
the O
surface S-CONPRI
of O
a O
build S-PARA
with O
homogeneously O
intense O
, O
shaped O
light O
from O
a O
set S-APPL
of O
laser S-ENAT
diodes S-APPL
, O
the O
thermal O
history O
was O
controlled O
thereby O
reducing O
the O
residual B-PRO
stress E-PRO
in O
as-built O
parts O
. O


316L B-MATE
stainless I-MATE
steel E-MATE
bridge-shaped O
parts O
were O
built O
to O
characterize O
the O
effect O
of O
in B-CONPRI
situ E-CONPRI
annealing S-MANP
on O
the O
residual B-PRO
stress E-PRO
. O


A O
reduction S-CONPRI
in O
the O
overall O
residual B-PRO
stress E-PRO
value O
of O
up O
to O
90 O
% O
was O
realized O
without O
altering O
the O
as-built O
grain B-CONPRI
structure E-CONPRI
( O
no O
grain B-CONPRI
growth E-CONPRI
) O
. O


Some O
annealing S-MANP
effects O
on O
the O
cellular-dendritic O
solidification S-CONPRI
structure O
( O
patterns O
of O
higher O
solute O
content O
) O
occurred O
in O
areas S-PARA
that O
experienced O
prolonged O
exposure S-CONPRI
to O
elevated O
temperature S-PARA
. O


A O
comparison O
of O
the O
in B-CONPRI
situ E-CONPRI
process O
to O
conventional O
post-build O
annealing S-MANP
demonstrated O
equivalent O
stress S-PRO
reduction S-CONPRI
compared O
to O
rule-of-thumb O
thermal B-MANP
treatments E-MANP
. O


Use O
of O
this O
method O
could O
reduce O
or O
remove O
the O
need O
for O
post B-CONPRI
processing E-CONPRI
to O
remove O
residual B-PRO
stresses E-PRO
. O


Metallic S-MATE
cellular O
solids O
are O
a O
class O
of O
materials S-CONPRI
known O
for O
their O
high O
specific O
mechanical B-CONPRI
properties E-CONPRI
, O
being O
desirable O
in O
applications O
where O
a O
combination O
of O
high O
strength S-PRO
or O
stiffness S-PRO
and O
low O
density S-PRO
are O
important O
. O


These O
lightweight S-CONPRI
materials O
are O
often O
stochastic S-CONPRI
and O
manufactured S-CONPRI
by O
foaming O
or O
casting S-MANP
. O


If O
regular O
( O
periodic O
) O
lattice B-FEAT
structures E-FEAT
are O
desired O
, O
they O
may O
be S-MATE
manufactured O
by O
metallic B-MANP
additive I-MANP
manufacturing E-MANP
techniques O
. O


However O
, O
these O
have O
characteristic O
issues O
, O
such O
as S-MATE
un-melted O
powders S-MATE
, O
porosity S-PRO
and O
heterogeneous S-CONPRI
microstructures O
. O


This O
study O
reports O
a O
novel O
low-cost O
route O
for O
producing O
regular O
lattice B-FEAT
structures E-FEAT
by O
an O
additive B-MANP
manufacturing E-MANP
assisted O
investment B-MANP
casting E-MANP
technique O
. O


Fused B-MANP
filament I-MANP
fabrication E-MANP
is O
used O
to O
produce O
the O
lattice B-FEAT
structure E-FEAT
pattern O
which O
is O
infiltrated O
with O
plaster O
. O


The O
pattern S-CONPRI
is O
then O
burnt O
off O
and O
the O
aluminum S-MATE
is O
cast S-MANP
in O
vacuum O
. O


In O
this O
way O
we O
can O
manufacture S-CONPRI
non-stochastic O
metallic S-MATE
lattices S-CONPRI
having O
fine O
struts/ribs O
( O
0.6 O
mm S-MANP
cross-section O
using O
a O
0.4 O
mm S-MANP
nozzle O
) O
and O
relative B-PRO
densities E-PRO
down O
to O
0.036 O
. O


X-ray B-CHAR
micro I-CHAR
computed I-CHAR
tomography E-CHAR
( O
μCT O
) O
showed O
that O
as-cast O
A356 O
Aluminium B-MATE
alloy E-MATE
frameworks O
have O
high O
dimensional B-CHAR
tolerances E-CHAR
and O
fine O
detail O
control O
. O


Frameworks O
based O
on O
units O
of O
six O
connected O
struts S-MACEQ
ranging O
from O
intruding O
( O
auxetic O
) O
to O
protruding O
( O
hexagonal S-FEAT
) O
strut S-MACEQ
angles O
are O
studied O
. O


Vertical S-CONPRI
struts S-MACEQ
are O
finer O
than O
expected O
, O
reducing O
their O
moment O
of O
area S-PARA
which O
could O
impact S-CONPRI
their O
compressive B-PRO
strength E-PRO
. O


This O
new O
, O
low O
cost O
, O
route O
for O
producing O
high O
precision S-CHAR
metallic S-MATE
cellular O
lattices S-CONPRI
offers O
an O
attractive O
alternative O
to O
other O
additive B-MANP
manufacturing E-MANP
techniques O
( O
e.g O
. O


selective B-MANP
laser E-MANP
and O
electron B-MANP
beam I-MANP
melting E-MANP
) O
. O


Fine O
equiaxed O
dendrites S-BIOP
and O
discrete O
Laves B-CONPRI
phase E-CONPRI
were O
obtained O
using O
alow O
pulse O
frequency O
. O


Discrete O
distribution S-CONPRI
of O
δ-phase O
and O
high-density O
precipitation S-CONPRI
of O
γ″-Ni3Nb O
were O
obtained O
. O


A O
good O
combination O
of O
strength S-PRO
and O
ductility S-PRO
was O
obtained O
by O
optimizing O
the O
microstructures S-MATE
. O


Controlling O
of O
Nb-rich O
intermetallics S-MATE
is O
an O
important O
topic O
for O
laser B-MANP
additive I-MANP
manufacturing E-MANP
( O
LAM S-MANP
) O
of O
Inconel B-MATE
718 E-MATE
. O


In O
the O
present O
work O
, O
a O
novel O
quasi-continuous-wave O
LAM S-MANP
( O
QCW-LAM O
) O
with O
different O
pulse O
frequencies O
is O
used O
to O
control O
the O
morphology S-CONPRI
, O
distribution S-CONPRI
and O
amount O
of O
Nb-rich O
phases O
of O
Inconel B-MATE
718 E-MATE
. O


The O
results O
show O
that O
dispersively O
distributed O
Nb-rich O
Laves B-CONPRI
phases E-CONPRI
are O
produced O
by O
introducing O
equiaxed O
dendrites S-BIOP
at O
a O
low O
pulse O
frequency O
while O
a O
high O
pulse O
frequency O
results O
in O
coarse O
and O
chain-like O
Laves B-CONPRI
phases E-CONPRI
. O


The O
samples S-CONPRI
featured O
by O
fine O
and O
discrete O
Laves B-CONPRI
phases E-CONPRI
show O
a O
good O
response O
to O
the O
post O
solution-aging O
treatment O
in O
which O
the O
dissolution O
of O
Laves-phase O
and O
subsequently O
discrete O
precipitations O
of O
δ-phase O
as S-MATE
well O
as S-MATE
high-density O
precipitation S-CONPRI
of O
γ″-Ni3Nb O
strengthening B-CONPRI
phase E-CONPRI
are O
promoted O
. O


Thus O
, O
a O
good O
combination O
of O
strength S-PRO
and O
ductility S-PRO
is O
achieved O
for O
the O
QCW-LAM O
fabricated S-CONPRI
Inconel O
718 O
. O


This O
study O
shows O
a O
desired O
mechanical B-CONPRI
property E-CONPRI
can O
be S-MATE
obtained O
by O
synergistically O
optimizing O
the O
microstructures S-MATE
in O
which O
various O
Nb-rich O
phases O
are O
involved O
even O
though O
the O
formation O
of O
brittle S-PRO
Laves O
phases O
is O
hardly O
avoided O
during O
LAM S-MANP
of O
Inconel B-MATE
718 E-MATE
. O


This O
paper O
discusses O
the O
effects O
of O
process B-CONPRI
parameters E-CONPRI
in O
TIG S-MANP
based O
WAAM S-MANP
for O
specimens O
created O
using O
Hastelloy S-MATE
X O
alloy S-MATE
( O
Haynes O
International O
) O
welding S-MANP
wire O
and O
304 O
stainless-steel O
plate O
as S-MATE
the O
substrate S-MATE
. O


The O
Taguchi B-CONPRI
method E-CONPRI
and O
ANOVA O
were O
used O
to O
determine O
the O
effects O
of O
travel O
speed O
, O
wire O
feed S-PARA
rate O
, O
current O
, O
and O
argon S-MATE
flow O
rate O
on O
the O
responses O
including O
bead S-CHAR
shape O
and O
size O
, O
bead S-CHAR
roughness O
, O
oxidation S-MANP
levels O
, O
melt S-CONPRI
through O
depth O
, O
and O
the O
microstructure S-CONPRI
. O


Increasing O
travel O
speed O
or O
decreasing O
current O
caused O
a O
decrease O
in O
melt S-CONPRI
through O
depth O
and O
an O
increase O
in O
roughness S-PRO
. O


No O
observable O
interface S-CONPRI
between O
the O
layers O
was O
present O
suggesting O
a O
complete O
fusion S-CONPRI
between O
layers O
with O
no O
oxidation S-MANP
. O


The O
zones O
were O
characterized O
by O
the O
size O
and O
distribution S-CONPRI
of O
the O
molybdenum B-MATE
carbide E-MATE
formations O
within O
the O
matrix O
grain S-CONPRI
formations O
. O


Reactive-deposition O
additive B-MANP
manufacturing E-MANP
was O
employed O
to O
manufacture S-CONPRI
titanium-based O
metal B-MATE
matrix I-MATE
composites E-MATE
for O
improving O
the O
wear B-PRO
resistance E-PRO
and O
temperature S-PARA
capability O
of O
commercially O
pure O
titanium S-MATE
( O
CPTi O
) O
; O
a O
standard S-CONPRI
material S-MATE
in O
the O
aerospace S-APPL
, O
biomedical S-APPL
, O
and O
marine B-APPL
industries E-APPL
, O
among O
others O
. O


Composites S-MATE
were O
manufactured S-CONPRI
by O
leveraging O
in B-CONPRI
situ E-CONPRI
high-temperature O
reactions O
between O
CPTi O
, O
zirconium S-MATE
( O
Zr S-MATE
) O
, O
and O
boron B-MATE
nitride E-MATE
( O
BN S-MATE
) O
powders S-MATE
during O
laser-based O
directed-energy-deposition O
( O
DED S-MANP
) O
3D-printing S-MANP
. O


The O
effect O
of O
Zr S-MATE
and O
BN S-MATE
on O
the O
processability O
, O
phase S-CONPRI
formation O
( O
s S-MATE
) O
, O
surface S-CONPRI
wear O
, O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
3D-printed S-MANP
titanium O
was O
studied O
by O
printing O
commercially-pure O
titanium S-MATE
with O
premixed O
additions O
of O
20 O
wt O
% O
Zr S-MATE
and O
10 O
wt O
% O
BN S-MATE
using O
Laser B-MANP
Engineered I-MANP
Net I-MANP
Shaping E-MANP
( O
LENS™ O
) O
. O


In O
the O
as-printed O
BN-containing O
structures O
, O
phase S-CONPRI
analysis O
revealed O
reinforcing O
ceramic S-MATE
phases O
TiN S-MATE
, O
TiB O
, O
and O
TiB2 O
, O
whose O
presence O
was O
substantiated O
through O
first-principles O
analysis O
. O


The O
combined O
addition O
of O
Zr S-MATE
and O
BN S-MATE
produced O
a O
Ti-Zr O
alloy S-MATE
matrix O
with O
BN-particle O
and O
in B-CONPRI
situ E-CONPRI
phase-reinforced O
microstructure S-CONPRI
with O
450 O
% O
higher O
hardness S-PRO
( O
from O
318 O
± O
26 O
HV0.1/15 O
to O
1424 O
± O
361 O
HV0.5/15 O
) O
, O
a O
stabilized O
sliding−COF O
within O
50 O
m O
of O
reciprocating O
wear S-CONPRI
testing S-CHAR
, O
and O
9x O
lower O
final O
wear S-CONPRI
rate O
in O
comparison O
to O
LENS™ O
deposited O
titanium S-MATE
. O


Zr-addition O
alone O
revealed O
a O
combined O
alloyed O
and O
particle-reinforced O
composite S-MATE
with O
12 O
% O
higher O
hardness S-PRO
, O
23 O
% O
higher O
compressive O
yield B-PRO
strength E-PRO
, O
and O
an O
11 O
% O
decrease O
in O
final O
wear S-CONPRI
rate O
compared O
to O
LENS™-produced O
titanium S-MATE
. O


Our O
results O
demonstrate O
that O
reactive-deposition O
based O
additive B-MANP
manufacturing E-MANP
can O
be S-MATE
exploited O
to O
create O
unique O
coatings S-APPL
and O
net-shape O
alloyed O
structures O
to O
enhance O
the O
surface S-CONPRI
and O
bulk O
properties S-CONPRI
of O
standard S-CONPRI
engineering B-MATE
materials E-MATE
such O
as S-MATE
titanium O
. O


We O
propose O
a O
simple S-MANP
method O
to O
construct O
a O
process S-CONPRI
map O
for O
additive B-MANP
manufacturing E-MANP
using O
a O
support S-APPL
vector O
machine S-MACEQ
. O


By O
observing O
the O
surface S-CONPRI
of O
the O
built O
parts O
and O
classifying O
them O
into O
two O
classes O
( O
good O
or O
bad O
) O
, O
this O
method O
enables O
a O
process S-CONPRI
map O
to O
be S-MATE
constructed O
in O
order O
to O
predict O
a O
process S-CONPRI
condition O
that O
is O
effective O
at O
fabricating S-MANP
a O
part O
with O
low O
pore B-PRO
density E-PRO
. O


This O
proposed O
method O
is O
demonstrated O
in O
a O
biomedical S-APPL
CoCr O
alloy S-MATE
system O
. O


This O
study O
also O
shows O
that O
the O
value O
of O
a O
decision O
function O
in O
a O
support S-APPL
vector O
machine S-MACEQ
has O
a O
physical O
meaning O
( O
at O
least O
in O
the O
proposed O
method O
) O
and O
is O
a O
semi-quantitative O
guideline O
for O
porosity B-PRO
density E-PRO
of O
parts O
fabricated S-CONPRI
by O
additive B-MANP
manufacturing E-MANP
. O


In O
binder B-MANP
jetting I-MANP
additive I-MANP
manufacturing E-MANP
( O
BJAM O
) O
, O
the O
part O
geometry S-CONPRI
is O
generated O
via O
a O
binding O
agent O
during O
printing O
and O
structural B-PRO
integrity E-PRO
is O
imparted O
during O
sintering S-MANP
at O
a O
later O
stage O
. O


This O
separation O
between O
shape O
generation O
and O
thermal O
processing O
allows O
the O
sintering S-MANP
process S-CONPRI
to O
be S-MATE
uniquely O
controlled O
and O
the O
final O
microstructural S-CONPRI
characteristics O
to O
be S-MATE
tailored O
. O


The O
separation O
between O
the O
printing O
and O
consolidation S-CONPRI
steps O
offers O
a O
unique O
opportunity O
to O
print S-MANP
responsive O
materials S-CONPRI
that O
are O
later O
“ O
activated O
” O
by O
temperature S-PARA
and/or O
environment O
. O


This O
concept O
is O
preliminarily O
demonstrated O
using O
a O
foaming O
copper S-MATE
feedstock O
, O
such O
that O
the O
copper S-MATE
is O
printed O
, O
sintered S-MANP
and O
then O
foamed O
via O
intraparticle O
expansion O
in O
separate O
steps O
. O


The O
integration O
of O
foaming O
feedstock S-MATE
in O
BJAM O
could O
allow O
for O
creation O
of O
ultra-lightweight O
structures O
that O
offer O
hierarchical O
porosity S-PRO
, O
graded O
density S-PRO
, O
and/or O
tailored O
absorption S-CONPRI
properties O
. O


This O
work O
investigates S-CONPRI
processing O
protocol S-CONPRI
for O
copper S-MATE
foam O
structures O
to O
achieve O
the O
highest O
porosity S-PRO
. O


The O
copper S-MATE
feedstock O
was O
prepared O
by O
distributing O
copper B-MATE
oxides E-MATE
through O
the O
copper S-MATE
matrix O
via O
mechanical B-MANP
milling E-MANP
, O
and O
that O
powder S-MATE
was O
then O
printed O
into O
a O
green O
geometry S-CONPRI
through O
BJAM O
. O


The O
printed O
green B-PRO
parts E-PRO
were O
then O
heat S-CONPRI
treated O
using O
different O
thermal B-PARA
cycles E-PARA
to O
investigate O
the O
porosity S-PRO
evolution S-CONPRI
relative O
to O
various O
heating S-MANP
conditions O
. O


The O
heat S-CONPRI
treated O
parts O
were O
then O
examined O
for O
their O
resulting O
properties S-CONPRI
including O
porosity S-PRO
, O
microstructural B-CONPRI
evolution E-CONPRI
, O
and O
volumetric O
shrinkage S-CONPRI
. O


Parts O
that O
were O
initially O
sintered S-MANP
in O
air O
and O
then O
annealed O
in O
a O
hydrogen O
atmosphere O
led S-APPL
to O
higher O
porosity S-PRO
compared O
to O
those O
sintered S-MANP
in O
hydrogen O
alone O
. O


Anisotropy S-PRO
in O
linear O
shrinkage S-CONPRI
in O
X O
, O
Y S-MATE
, O
and O
Z O
direction O
was O
also O
observed O
in O
the O
heat S-CONPRI
treated O
parts O
with O
the O
largest O
linear O
shrinkage S-CONPRI
occurring O
in O
the O
Z O
direction O
. O


Additive B-MANP
manufacturing E-MANP
that O
allows O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
shaping O
of O
complex B-CONPRI
structures E-CONPRI
is O
of O
rapidly O
increasing O
interest O
in O
production S-MANP
technology O
. O


A O
particularly O
rapid B-ENAT
prototyping E-ENAT
technique O
of O
additive B-MANP
manufacturing E-MANP
is O
laser B-CONPRI
beam E-CONPRI
melting O
( O
LBM O
) O
. O


This O
3D B-MANP
printing E-MANP
method O
is O
based O
on O
a O
powder B-MANP
bed I-MANP
fusion E-MANP
technique O
, O
using O
a O
high-powered O
laser S-ENAT
to O
melt S-CONPRI
and O
consolidate O
metallic B-MATE
powders E-MATE
. O


The O
process S-CONPRI
needs O
a O
tightly O
controlled O
atmosphere O
of O
inert B-CONPRI
gas E-CONPRI
, O
which O
requires O
a O
confined O
space O
of O
a O
building B-PARA
chamber E-PARA
. O


This O
and O
more O
process S-CONPRI
related O
factors O
like O
elevated O
temperatures S-PARA
, O
laser S-ENAT
radiation O
or O
the O
resulting O
light O
intensity O
caused O
by O
the O
melting S-MANP
of O
metals S-MATE
, O
make O
a O
closed-loop O
quality B-CONPRI
control E-CONPRI
very O
ambitious O
. O


In O
this O
paper O
, O
we O
propose O
a O
new O
in-process O
approach O
for O
quality B-CONPRI
control E-CONPRI
with O
high O
precision S-CHAR
metrology S-CONPRI
based O
on O
structured O
light O
. O


The O
precise O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
dimensional O
measurement S-CHAR
of O
both O
the O
printed O
part O
and O
the O
powder S-MATE
deposition S-CONPRI
, O
allows O
for O
process S-CONPRI
assessment O
in- O
or O
off-line O
. O


For O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
additive B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
metals S-MATE
, O
residual S-CONPRI
stress-induced O
cracking S-CONPRI
often O
occurs O
at O
the O
interface S-CONPRI
between O
the O
solid O
and O
lattice S-CONPRI
support O
, O
and O
hence O
it O
is O
important O
to O
characterize O
the O
as-built O
critical O
J-integral O
of O
the O
interface S-CONPRI
to O
prevent O
cracking S-CONPRI
to O
occur O
. O


However O
, O
the O
standard S-CONPRI
testing O
method O
for O
the O
critical O
J-integral O
of O
the O
interface S-CONPRI
( O
ASTM O
E1820-01 O
) O
does O
not O
work O
well O
in O
this O
situation O
for O
four O
reasons O
: O
1 O
) O
standard S-CONPRI
test O
blocks O
consisting O
of O
half O
solid O
and O
half O
lattice S-CONPRI
support O
crack O
during O
the O
printing B-MANP
process E-MANP
; O
2 O
) O
even O
after O
reinforcing O
the O
block O
with O
side O
walls O
to O
prevent O
cracking S-CONPRI
, O
post-stress O
relief O
causes O
the O
yield B-PRO
strength E-PRO
to O
change O
significantly O
, O
which O
would O
affect O
J-integral O
significantly O
; O
3 O
) O
post-build O
machining S-MANP
processes O
to O
obtain O
the O
required O
standard S-CONPRI
specimen O
geometry S-CONPRI
release O
a O
significant O
amount O
of O
residual B-PRO
stress E-PRO
, O
which O
also O
gives O
incorrect O
J-integral O
value O
; O
4 O
) O
the O
interface S-CONPRI
is O
so O
brittle S-PRO
that O
it O
is O
very O
difficult O
to O
machine S-MACEQ
it O
to O
the O
required O
standard S-CONPRI
configuration S-CONPRI
. O


Hence O
a O
more O
effective O
method O
that O
combines O
printing O
experiments O
and O
residual B-PRO
stress E-PRO
simulation O
is O
proposed O
to O
determine O
the O
as-built O
critical O
J-integral O
of O
the O
interface S-CONPRI
. O


Next O
, O
the O
experimentally-validated O
modified B-CONPRI
inherent I-CONPRI
strain I-CONPRI
method E-CONPRI
is O
utilized O
to O
simulate O
residual B-PRO
stress E-PRO
and O
compute O
the O
critical O
J-integral O
at O
where O
the O
interfacial O
cracking S-CONPRI
occurs O
. O


The O
proposed O
method O
is O
subsequently O
validated O
using O
the O
obtained O
critical O
J-integral O
to O
predict O
cracking S-CONPRI
in O
different O
geometries S-CONPRI
. O


This O
method O
eliminates O
the O
uncertainties O
associated O
with O
stress B-CONPRI
relaxation E-CONPRI
by O
heat B-MANP
treatment E-MANP
and O
machining S-MANP
on O
mechanical B-CONPRI
properties E-CONPRI
, O
as S-MATE
well O
as S-MATE
sheds O
light O
on O
crack O
prediction S-CONPRI
for O
as-built O
L-PBF S-MANP
components S-MACEQ
. O


This O
study O
aims O
to O
investigate O
the O
fabrication S-MANP
feasibility O
of O
a O
conventionally O
rolled O
low-carbon O
low-alloy O
shipbuilding O
steel S-MATE
plate O
( O
EH36 O
) O
by O
emerging O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
technology S-CONPRI
using O
ER70S O
feedstock S-MATE
wire O
. O


Following O
the O
fabrication S-MANP
process O
, O
different O
heat B-MANP
treatment E-MANP
cycles O
, O
including O
air-cooling O
and O
water-quenching O
from O
the O
intercritical O
austenitizing S-MANP
temperature O
of O
800 O
°C O
, O
were O
applied O
to O
both O
conventionally O
rolled O
and O
WAAM S-MANP
samples S-CONPRI
. O


Microstructural S-CONPRI
features O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
both O
rolled O
and O
WAAM S-MANP
fabricated S-CONPRI
ship O
plates O
were O
comprehensively O
characterized O
and O
compared O
before O
and O
after O
different O
heat B-MANP
treatment E-MANP
cycles O
. O


Both O
air-cooling O
and O
water-quenching O
heat B-MANP
treatments E-MANP
resulted O
in O
the O
formation O
of O
hard O
martensite-austenite O
( O
MA O
) O
constituents O
in O
the O
microstructure S-CONPRI
of O
the O
rolled O
ship O
plate O
, O
leading O
to O
the O
increased O
hardness S-PRO
and O
tensile B-PRO
strength E-PRO
and O
reduced O
ductility S-PRO
of O
the O
component S-MACEQ
. O


On O
the O
other O
hand O
, O
air-cooling O
heat B-MANP
treatment E-MANP
was O
found O
to O
homogenize O
the O
microstructure S-CONPRI
of O
the O
WAAM S-MANP
ship O
plate O
, O
causing O
a O
slight O
decrease O
in O
the O
hardness S-PRO
and O
tensile B-PRO
strength E-PRO
, O
while O
the O
water-quenching O
cycle O
led S-APPL
to O
the O
formation O
of O
acicular O
ferrite S-MATE
and O
intergranular O
pearlite S-MATE
, O
contributing O
to O
the O
improved O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
part O
. O


Therefore O
, O
the O
enhanced O
mechanical B-PRO
integrity E-PRO
of O
the O
water-quenched O
WAAM S-MANP
component S-MACEQ
as S-MATE
compared O
to O
its O
rolled O
counterpart O
verified O
the O
fabrication S-MANP
feasibility O
of O
the O
ship O
plates O
by O
the O
WAAM S-MANP
. O


The O
ability O
to O
combine O
multiple O
materials S-CONPRI
( O
MM S-MANP
) O
into O
a O
single O
component S-MACEQ
to O
expand O
its O
range S-PARA
of O
functional O
properties S-CONPRI
is O
of O
tremendous O
value O
to O
the O
ceaseless O
optimization S-CONPRI
of O
engineering S-APPL
systems O
. O


Although O
fusion S-CONPRI
and O
solid-state S-CONPRI
joining S-MANP
techniques O
have O
been O
typically O
used O
to O
join O
dissimilar O
metals S-MATE
, O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
has O
the O
potential O
to O
produce O
MM S-MANP
parts O
with O
a O
complex O
spatial B-CHAR
distribution E-CHAR
of O
materials S-CONPRI
and O
properties S-CONPRI
that O
is O
otherwise O
unachievable O
. O


In O
this O
work O
, O
the O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
process S-CONPRI
was O
used O
to O
manufacture S-CONPRI
MM O
parts O
which O
feature S-FEAT
steep O
material S-MATE
transitions O
from O
316L B-MATE
stainless I-MATE
steel E-MATE
( O
SS S-MATE
) O
to O
Ti-6Al-4V S-MATE
( O
TiA O
) O
through O
an O
interlayer O
of O
HOVADUR® O
K220 O
copper–alloy O
( O
CuA O
) O
. O


The O
microstructure S-CONPRI
in O
both O
the O
CuA/SS O
and O
TiA/CuA O
interfaces O
were O
examined O
in O
detail O
and O
the O
latter O
was O
found O
to O
be S-MATE
the O
critical O
interface S-CONPRI
as S-MATE
it O
contained O
three O
detrimental O
phases O
( O
i.e O
. O


L21 O
ordered O
phase S-CONPRI
, O
amorphous O
phase S-CONPRI
, O
and O
Ti2Cu O
) O
which O
limit S-CONPRI
the O
mechanical B-PRO
strength E-PRO
of O
the O
overall O
MM S-MANP
part O
. O


By O
making O
use O
of O
the O
non-homogeneity O
within O
the O
melt B-MATE
pool E-MATE
and O
limiting O
the O
laser B-CONPRI
energy E-CONPRI
input O
, O
the O
relatively O
tougher O
interfacial O
α′-Ti O
phase S-CONPRI
can O
be S-MATE
increased O
at O
the O
expense O
of O
other O
brittle S-PRO
phases O
, O
forming S-MANP
what O
is O
essentially O
a O
composite B-CONPRI
structure E-CONPRI
at O
the O
TiA/CuA O
interface S-CONPRI
. O


During O
tensile B-CHAR
testing E-CHAR
, O
the O
interfacial O
α′-Ti O
phase S-CONPRI
is O
capable O
of O
deflecting O
cracks O
from O
the O
relatively O
brittle S-PRO
TiA/CuA O
interface S-CONPRI
towards O
the O
ductile S-PRO
CuA O
interlayer O
and O
an O
overall O
tensile B-PRO
strength E-PRO
in O
excess O
of O
500 O
MPa S-CONPRI
can O
be S-MATE
obtained O
. O


This O
method O
of O
introducing O
an O
interfacial O
composite B-CONPRI
structure E-CONPRI
to O
improve O
MM S-MANP
bonding S-CONPRI
is O
envisioned O
to O
be S-MATE
applicable O
for O
the O
SLM S-MANP
of O
other O
metallic S-MATE
combinations O
as S-MATE
well O
. O


A O
stereolithographic O
approach O
based O
on O
thiol-ene O
click O
chemistry S-CONPRI
is O
developed O
to O
3D B-MANP
print E-MANP
preceramic O
polymers S-MATE
into O
infusible O
thermosets O
. O


Three O
classes O
of O
preceramic O
polymers S-MATE
, O
including O
siloxane O
, O
carbosilane O
and O
carbosilazane O
, O
are O
additively B-MANP
manufactured E-MANP
. O


Upon O
pyrolysis S-MANP
, O
thermosets O
transform O
into O
glassy O
ceramics S-MATE
with O
uniform O
shrinkage S-CONPRI
and O
high O
density S-PRO
. O


A O
fabricated S-CONPRI
SiOC O
honeycomb S-CONPRI
exhibits O
a O
significantly O
higher O
compressive B-PRO
strength E-PRO
to O
weight S-PARA
ratio O
in O
comparison O
to O
other O
porous S-PRO
ceramics S-MATE
. O


Here O
we O
introduce O
a O
versatile O
stereolithographic O
route O
to O
produce O
three O
different O
kinds O
of O
Si-containing O
thermosets O
that O
yield O
high O
performance S-CONPRI
ceramics S-MATE
upon O
thermal B-MANP
treatment E-MANP
. O


Due O
to O
the O
rapidity O
and O
efficiency O
of O
the O
thiol-ene O
click O
reactions O
, O
this O
additive B-MANP
manufacturing I-MANP
process E-MANP
can O
be S-MATE
effectively O
carried O
out O
using O
conventional O
light B-MACEQ
sources E-MACEQ
on O
benchtop O
printers S-MACEQ
. O


Through O
pyrolysis S-MANP
the O
thermosets O
transform O
into O
glassy O
ceramics S-MATE
with O
uniform O
shrinkage S-CONPRI
and O
high O
density S-PRO
. O


The O
obtained O
ceramic S-MATE
structures O
are O
nearly O
fully B-PARA
dense E-PARA
, O
have O
smooth B-CONPRI
surfaces E-CONPRI
, O
and O
are O
free O
from O
macroscopic S-CONPRI
voids O
and O
defects S-CONPRI
. O


A O
fabricated S-CONPRI
SiOC O
honeycomb S-CONPRI
was O
shown O
to O
exhibit O
a O
significantly O
higher O
compressive B-PRO
strength E-PRO
to O
weight S-PARA
ratio O
in O
comparison O
to O
other O
porous S-PRO
ceramics S-MATE
. O


Schematic O
representation O
of O
the O
stereolithographic O
additive B-MANP
manufacturing E-MANP
of O
preceramic O
polymers S-MATE
into O
intricately O
patterned O
thermosets O
assisted O
by O
thiol-ene O
click O
chemistry S-CONPRI
and O
their O
subsequent O
conversion O
into O
ceramics.Download O
: O
Download O
high-res B-CONPRI
image E-CONPRI
( O
189 O
Advances O
in O
multi-material B-MANP
additive I-MANP
manufacturing E-MANP
have O
enabled O
advancements O
in O
the O
manufacture S-CONPRI
of O
composite B-MATE
materials E-MATE
. O


In O
this O
work O
, O
a O
family O
of O
thermite-based O
reactive B-MATE
materials E-MATE
is O
created O
and O
evaluated O
for O
the O
suitability O
as S-MATE
composite O
energetic O
structures O
. O


The O
burn O
rate O
with O
respect O
to O
binder S-MATE
ratio O
is O
observed O
to O
be S-MATE
highly O
predictable S-CONPRI
and O
exponential O
( O
coefficients O
of O
determination O
of O
rTi2=0.984 O
and O
rAl2=0.973 O
) O
, O
with O
composites S-MATE
transitioning O
from O
one O
binder S-MATE
mass O
fraction S-CONPRI
to O
another O
. O


To O
create O
composites S-MATE
, O
a O
single O
layered O
syringe S-MACEQ
and O
nozzle S-MACEQ
are O
used O
in O
conjunction O
with O
continuous O
filament S-MATE
direct O
ink S-MATE
writing O
. O


The O
resulting O
prints O
show O
success O
in O
composite B-CONPRI
structure E-CONPRI
with O
a O
transition S-CONPRI
zone O
between O
printed O
materials S-CONPRI
. O


These O
results O
show O
both O
a O
variety O
of O
thermite-based O
energetics O
with O
easily O
modifiable O
reaction B-PARA
rates E-PARA
and O
a O
technique O
to O
print S-MANP
said O
reactive B-MATE
materials E-MATE
to O
create O
composite B-CONPRI
structures E-CONPRI
. O


Space O
agencies O
are O
looking O
for O
advanced O
technologies S-CONPRI
to O
build S-PARA
light O
weight S-PARA
and O
stiff O
payload O
components S-MACEQ
to O
bear O
space O
environment O
and O
launch O
loads O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
techniques O
like O
Direct B-MANP
Metal I-MANP
Laser I-MANP
Sintering E-MANP
( O
DMLS S-MANP
) O
is O
one O
of O
the O
suitable O
option O
which O
can O
be S-MATE
explored O
for O
space O
applications O
. O


This O
paper O
highlights O
the O
development O
process S-CONPRI
of O
Antenna O
Feed S-PARA
Array O
( O
AFA O
) O
using O
DMLS S-MANP
as S-MATE
an O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
technique O
. O


Such O
horns O
are O
preferred O
for O
this O
development O
as S-MATE
they O
are O
the O
prime O
choice O
for O
feed S-PARA
elements S-MATE
in O
High O
Throughput S-CHAR
satellites O
( O
HTS O
) O
that O
employ O
Multibeam O
Antennas O
. O


In O
the O
development O
process S-CONPRI
, O
certain O
design B-CONPRI
rules E-CONPRI
of O
AM S-MANP
are O
adopted O
based O
on O
consideration O
to O
produce O
self-sustaining O
structures O
. O


AFA O
realized O
by O
DMLS S-MANP
is O
evaluated O
by O
functional O
testing S-CHAR
, O
vibration O
testing S-CHAR
for O
space O
qualification O
test O
levels O
. O


Variations S-CONPRI
in O
local O
processing O
parameters S-CONPRI
and O
conditions O
in O
additively B-MANP
manufactured E-MANP
materials O
make O
mechanical B-CONPRI
properties E-CONPRI
difficult O
to O
characterize O
. O


Microtensile O
testing S-CHAR
is O
providing O
a O
wealth O
of O
information O
on O
these O
local O
property B-CONPRI
variations E-CONPRI
. O


Here O
we O
utilize O
spatial O
autocorrelation O
techniques O
to O
show O
autocorrelation O
of O
grain B-PRO
sizes E-PRO
and O
mechanical B-CONPRI
properties E-CONPRI
with O
build B-PARA
height E-PARA
in O
a O
specially-designed O
, O
additively B-MANP
manufactured E-MANP
AlSi10Mg O
part O
. O


This O
result O
suggests O
that O
, O
at O
least O
in O
some O
cases O
, O
an O
interplay O
between O
local O
part O
geometry S-CONPRI
and O
the O
fabrication S-MANP
process O
occurs O
that O
affects O
local O
mechanical B-CONPRI
properties E-CONPRI
. O


Complex O
thermal O
behaviour O
during O
fabrication S-MANP
plays O
an O
import O
role O
in O
the O
geometrical O
formation O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
Ti6Al4V S-MATE
components S-MACEQ
manufactured O
using O
Wire B-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
technology S-CONPRI
. O


In O
this O
study O
, O
through O
in-situ S-CONPRI
temperature O
measurement S-CHAR
, O
the O
heat B-PRO
accumulation E-PRO
and O
thermal O
behaviour O
during O
the O
gas S-CONPRI
tungsten O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
GT-WAAM O
) O
process S-CONPRI
are O
presented O
. O


The O
effects O
of O
heat B-PRO
accumulation E-PRO
on O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
additively B-MANP
manufactured E-MANP
Ti6Al4V O
parts O
were O
studied O
by O
means O
of O
optical B-CHAR
microscopy E-CHAR
( O
OM S-CHAR
) O
, O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
, O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
, O
energy B-CHAR
dispersive I-CHAR
spectrometer E-CHAR
( O
EDS S-CHAR
) O
and O
standard S-CONPRI
tensile O
tests O
, O
aiming O
to O
explore O
the O
feasibility S-CONPRI
of O
fabricating S-MANP
Ti6Al4V O
parts O
by O
GT-WAAM O
using O
localized O
gas S-CONPRI
shielding O
. O


The O
results O
show O
that O
due O
to O
the O
influences O
of O
thermal O
accumulation O
, O
the O
layer S-PARA
’ O
s S-MATE
surface O
oxidation S-MANP
, O
microstructural B-CONPRI
evolution E-CONPRI
, O
grain B-PRO
size E-PRO
, O
and O
crystalline O
phase S-CONPRI
vary O
along O
the O
building B-PARA
direction E-PARA
of O
the O
as-fabricated O
wall O
, O
which O
creates O
variations S-CONPRI
in O
mechanical B-CONPRI
properties E-CONPRI
and O
fracture S-CONPRI
features O
. O


It O
has O
also O
been O
found O
that O
it O
is O
necessary O
to O
maintain O
the O
process S-CONPRI
interpass B-PARA
temperature E-PARA
below O
200 O
°C O
to O
ensure O
an O
acceptable O
quality S-CONPRI
of O
Ti6Al4V S-MATE
part O
fabricated S-CONPRI
using O
only O
localized O
gas S-CONPRI
shielding O
in O
an O
otherwise O
open O
atmosphere O
. O


This O
research S-CONPRI
provides O
a O
better O
understanding O
of O
the O
effects O
of O
heat B-PRO
accumulation E-PRO
on O
targeted O
deposition S-CONPRI
properties O
during O
the O
WAAM S-MANP
process S-CONPRI
, O
which O
will O
benefit O
future O
process B-CONPRI
control E-CONPRI
, O
improvement O
, O
and O
optimization S-CONPRI
. O


A O
novel O
binder-free S-CONPRI
3D B-MANP
printing E-MANP
method O
with O
zero O
process B-MATE
contaminants E-MATE
is O
developed O
. O


The O
first O
ever O
study O
on O
employing O
microwave S-ENAT
( O
MW S-CONPRI
) O
sintering S-MANP
for O
inkjet B-MANP
3D I-MANP
printing E-MANP
. O


Reduction S-CONPRI
of O
sintering B-PARA
time E-PARA
up O
to O
four O
times O
compared O
to O
conventional O
sintering S-MANP
. O


Discussion O
on O
thermal O
and O
non-thermal O
effects O
in O
MW B-MANP
sintering E-MANP
of O
3D B-APPL
printed I-APPL
parts E-APPL
. O


3D B-MANP
printing E-MANP
( O
3DP S-MANP
) O
is O
a O
two-step O
additive B-MANP
manufacturing E-MANP
technique O
( O
AM S-MANP
) O
in O
which O
additively B-MANP
manufactured E-MANP
green O
parts O
in O
the O
first O
step S-CONPRI
are O
transformed O
into O
functional O
parts O
during O
the O
second O
step S-CONPRI
. O


Here O
we O
use O
capillary-mediated B-MANP
binderless I-MANP
3DP E-MANP
as S-MATE
a O
novel O
method O
to O
additively B-MANP
manufacture E-MANP
green O
parts O
of O
Mg-5.06Zn-0.15 B-MATE
Zr E-MATE
powder O
. O


A O
unified O
perspective O
on O
the O
development O
steps O
of O
process B-CONPRI
parameters E-CONPRI
to O
obtain O
sufficient O
handling B-PRO
strength E-PRO
and O
a O
high O
level O
of O
dimensional B-CHAR
accuracy E-CHAR
in O
the O
green B-PRO
parts E-PRO
without O
compromising O
its O
chemical B-CONPRI
composition E-CONPRI
is O
established O
by O
using O
a O
scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
, O
X-ray B-CHAR
micro-tomography E-CHAR
, O
vibrational B-ENAT
spectroscopy E-ENAT
, O
and O
chemical B-CHAR
analysis E-CHAR
. O


For O
the O
first O
time O
, O
microwave S-ENAT
( O
MW S-CONPRI
) O
sintering S-MANP
is O
successfully O
used O
for O
densification S-MANP
of O
the O
green B-PRO
parts E-PRO
with O
centimeter-scale B-CONPRI
dimensions E-CONPRI
in O
which O
the O
primary O
chemical B-CONPRI
composition E-CONPRI
of O
the O
Mg-Zn-Zr B-MATE
powder E-MATE
is O
retrieved O
from O
the O
green B-PRO
parts E-PRO
, O
resulting O
in O
a O
compositionally O
zero-sum O
AM B-MANP
process E-MANP
. O


It O
is O
found O
that O
swelling S-CONPRI
leads O
to O
loss O
of O
shape B-CONPRI
fidelity E-CONPRI
during O
MW B-MANP
sintering E-MANP
of O
the O
green B-PRO
parts E-PRO
at O
temperatures S-PARA
≥ O
510 O
°C O
. O


As S-MATE
discussed O
in O
the O
context O
of O
thermal O
and O
non-thermal O
effects O
, O
MW S-CONPRI
significantly O
reduced O
sintering B-PARA
time E-PARA
by O
a O
factor O
of O
three O
to O
four O
times O
when O
compared O
to O
sintering S-MANP
in O
a O
conventional B-MACEQ
furnace E-MACEQ
. O


The O
results O
of O
this O
study O
suggest O
the O
notion O
of O
capillary-mediated B-MANP
binderless I-MANP
3DP E-MANP
as S-MATE
well O
as S-MATE
MW O
sintering S-MANP
as S-MATE
a O
potential O
alternative O
for O
the O
first O
and O
second O
steps O
of O
3DP S-MANP
, O
respectively O
. O


Wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
of O
HSLA O
steel S-MATE
was O
performed O
. O


Microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
were O
related O
to O
the O
thermal B-PARA
cycles E-PARA
. O


No O
preferential O
texture S-FEAT
was O
developed O
, O
leading O
to O
near-isotropic O
mechanical B-CONPRI
properties E-CONPRI
. O


As-built O
parts O
exhibited O
excellent O
ductility S-PRO
and O
high O
mechanical B-PRO
strength E-PRO
. O


Wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
is O
a O
viable O
technique O
for O
the O
manufacture S-CONPRI
of O
large O
and O
complex O
dedicated O
parts O
used O
in O
structural O
applications O
. O


High-strength O
low-alloy O
( O
HSLA O
) O
steels S-MATE
are O
well-known O
for O
their O
applications O
in O
the O
tool S-MACEQ
and O
die S-MACEQ
industries O
and O
as S-MATE
power-plant O
components S-MACEQ
. O


The O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
as-built O
parts O
are O
investigated O
, O
and O
are O
correlated S-CONPRI
with O
the O
thermal B-PARA
cycles E-PARA
involved O
in O
the O
process S-CONPRI
. O


The O
heat S-CONPRI
input O
is O
found O
to O
affect O
the O
cooling B-PARA
rates E-PARA
, O
interlayer O
temperatures S-PARA
, O
and O
residence O
times O
in O
the O
800–500 O
°C O
interval O
when O
measured O
using O
an O
infrared S-CONPRI
camera S-MACEQ
. O


The O
microstructural B-CHAR
characterization E-CHAR
performed O
by O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
reveals O
that O
the O
microstructural S-CONPRI
constituents O
of O
the O
sample S-CONPRI
remain O
unchanged O
. O


i.e. O
, O
the O
same O
microstructural S-CONPRI
constituents—ferrite O
, O
bainite S-MATE
, O
martensite S-MATE
, O
and O
retained B-MATE
austenite E-MATE
are O
present O
for O
all O
heat S-CONPRI
inputs O
. O


Electron O
backscattered O
diffraction S-CHAR
analysis O
shows O
that O
no O
preferential O
texture S-FEAT
has O
been O
developed O
in O
the O
samples S-CONPRI
. O


Because O
of O
the O
homogeneity O
in O
the O
microstructural S-CONPRI
features O
of O
the O
as-built O
parts O
, O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
as-built O
parts O
are O
found O
to O
be S-MATE
nearly O
isotropic S-PRO
. O


Mechanical B-CHAR
testing E-CHAR
of O
samples S-CONPRI
shows O
excellent O
ductility S-PRO
and O
high O
mechanical B-PRO
strength E-PRO
. O


This O
is O
the O
first O
study O
elucidating O
on O
the O
effect O
of O
thermal B-PARA
cycles E-PARA
on O
the O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
during O
WAAM S-MANP
of O
HSLA O
steel S-MATE
. O


Components S-MACEQ
produced O
by O
near B-MANP
net I-MANP
shape I-MANP
additive I-MANP
manufacturing E-MANP
processes O
often O
require O
subsequent O
subtractive B-MANP
finishing I-MANP
operations E-MANP
to O
satisfy O
requisite O
surface B-FEAT
finish E-FEAT
and O
geometric B-FEAT
tolerances E-FEAT
. O


It O
is O
well O
established O
that O
the O
microstructure S-CONPRI
and O
properties S-CONPRI
of O
the O
as-built O
component S-MACEQ
are O
sensitive O
to O
the O
additive S-MATE
processing O
history O
. O


Therefore O
, O
downstream O
secondary O
processes S-CONPRI
may O
be S-MATE
affected O
by O
the O
as-built O
components S-MACEQ
’ O
mechanical S-APPL
behavior O
. O


In O
this O
work O
we O
study O
the O
sensitivity S-PARA
of O
secondary O
machining S-MANP
operations O
on O
CoCrMo O
samples S-CONPRI
produced O
via O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
. O


Utilizing O
novel O
high-throughput O
mechanical B-CHAR
testing E-CHAR
, O
microstructure S-CONPRI
characterization O
, O
and O
a O
rigorous O
statistical O
analysis O
we O
investigate O
the O
degree O
of O
material S-MATE
anisotropy S-PRO
present O
in O
the O
as-built O
material S-MATE
. O


We O
then O
study O
the O
effects O
of O
this O
anisotropy S-PRO
on O
secondary O
processing O
via O
slot O
milling S-MANP
experiments O
. O


Our O
results O
indicate O
that O
mechanical B-PRO
anisotropy E-PRO
is O
driven O
by O
both O
the O
morphology S-CONPRI
of O
the O
microstructure S-CONPRI
as S-MATE
well O
as S-MATE
crystallographic O
texture S-FEAT
. O


The O
machining S-MANP
force S-CONPRI
response O
is O
correspondingly O
sensitive O
to O
these O
sources O
of O
anisotropy S-PRO
, O
which O
has O
the O
potential O
to O
impact S-CONPRI
how O
manufacturers O
finish O
additively O
built O
parts O
. O


This O
study O
presents O
a O
detailed O
characterization O
of O
room O
temperature S-PARA
bulk O
microstructure S-CONPRI
and O
texture S-FEAT
of O
additively B-MANP
manufactured E-MANP
Ti-6Al-4V O
alloy S-MATE
samples O
with O
the O
neutron S-CONPRI
time-of-flight O
diffractometer O
HIPPO O
. O


A O
comparison O
is O
made O
between O
samples S-CONPRI
that O
were O
manufactured S-CONPRI
by O
two O
different O
methods O
utilizing O
selective B-MANP
laser I-MANP
melting E-MANP
and O
electron B-MANP
beam I-MANP
melting E-MANP
. O


Analysis O
of O
the O
orientation S-CONPRI
distribution S-CONPRI
function O
shows O
a O
dependency O
upon O
the O
particular O
fabrication S-MANP
technique O
used O
as S-MATE
well O
as S-MATE
on O
the O
location O
within O
the O
built O
body O
and O
orientation S-CONPRI
relative O
to O
the O
build B-PARA
direction E-PARA
. O


It O
is O
shown O
that O
the O
texture S-FEAT
components S-MACEQ
strength O
in O
the O
hexagonal S-FEAT
phase O
depends O
on O
the O
relative O
tilt B-FEAT
angle E-FEAT
between O
the O
build B-PARA
direction E-PARA
and O
that O
the O
overall O
texture S-FEAT
of O
samples S-CONPRI
prepared O
with O
the O
electron B-CONPRI
beam E-CONPRI
method O
is O
weaker O
than O
those O
prepared O
with O
the O
selective B-MANP
laser I-MANP
melting E-MANP
. O


Such O
knowledge O
on O
the O
bulk O
microstructure S-CONPRI
allows O
to O
optimize O
additive B-MANP
manufacturing I-MANP
process E-MANP
parameters O
. O


One O
rapidly O
advancing O
technology S-CONPRI
with O
high O
space O
resource O
utilization O
potential O
is O
additive B-MANP
manufacturing E-MANP
. O


Additive B-MANP
manufacturing E-MANP
is O
already O
prevalent O
in O
the O
aerospace B-APPL
industry E-APPL
and O
is O
an O
enabling O
technology S-CONPRI
of O
significant O
potential O
for O
weight S-PARA
savings O
, O
cost B-CONPRI
reduction E-CONPRI
, O
tool S-MACEQ
repair O
, O
and O
just-in-time O
manufacturing S-MANP
. O


In O
the O
last O
few O
years O
, O
institutions O
such O
as S-MATE
ASTM O
International O
and O
NASA O
have O
released O
standards S-CONPRI
for O
additive B-MANP
manufacturing E-MANP
, O
but O
research S-CONPRI
done O
in O
the O
field O
of O
additive B-MANP
manufacturing E-MANP
with O
space O
resources O
is O
still O
in O
its O
infancy O
. O


Among O
the O
technologies S-CONPRI
under O
investigation O
, O
powder B-MANP
bed I-MANP
fusion E-MANP
technologies O
for O
melting S-MANP
regolith O
show O
particular O
promise O
due O
to O
their O
efficiency O
and O
freedom O
from O
binder S-MATE
material O
. O


As S-MATE
strict O
material S-MATE
and O
process B-CONPRI
control E-CONPRI
is O
difficult O
with O
space O
resource O
utilization O
focused O
technology S-CONPRI
, O
the O
lessons O
learned O
by O
terrestrial O
manufacturing S-MANP
experts O
are O
still O
being O
adapted O
for O
use O
in O
the O
burgeoning O
field.Proposed O
is O
a O
framework S-CONPRI
for O
adapting O
existing O
standards S-CONPRI
for O
use O
with O
space O
resources O
by O
identifying O
specific O
risks O
and O
fundamental O
factors O
for O
part O
quality S-CONPRI
, O
determining O
part O
criticality O
, O
and O
documenting O
material S-MATE
, O
process B-CONPRI
controls E-CONPRI
, O
environmental O
conditions O
, O
and O
other O
influencing O
factors O
. O


This O
research S-CONPRI
explored O
the O
influences O
of O
shielding O
gases O
on O
the O
appearance O
of O
weld B-CONPRI
beads E-CONPRI
and O
the O
microstructures S-MATE
and O
mechanical B-CONPRI
properties E-CONPRI
of O
thin-wall O
samples S-CONPRI
using O
conventional O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
as S-MATE
the O
heat B-CONPRI
source E-CONPRI
by O
using O
5356 O
aluminium B-MATE
alloy E-MATE
welding O
wire O
as S-MATE
the O
raw B-MATE
materials E-MATE
and O
nitrogen S-MATE
( O
N2 S-MATE
) O
and O
argon S-MATE
( O
Ar S-ENAT
) O
as S-MATE
the O
shielding O
gases O
. O


The O
results O
showed O
that O
under O
the O
same O
parameters S-CONPRI
and O
after O
mono-layer O
single-bead O
welding S-MANP
was O
performed O
using O
N2 S-MATE
as S-MATE
the O
shielding O
gas S-CONPRI
, O
the O
bead S-CHAR
height O
was O
higher O
, O
the O
bead B-CHAR
width E-CHAR
was O
narrower O
, O
and O
the O
penetration B-PARA
depth E-PARA
was O
shallower O
. O


The O
grain B-PRO
size E-PRO
of O
the O
thin-wall O
sample S-CONPRI
protected O
by O
N2 S-MATE
was O
43.5–47.8 O
% O
smaller O
than O
that O
obtained O
under O
Ar S-ENAT
protection O
. O


However O
, O
the O
sample S-CONPRI
protected O
by O
N2 S-MATE
contained O
many O
flaky O
nitrides S-MATE
, O
whose O
presence O
improved O
the O
microhardness S-CONPRI
but O
reduced O
the O
ultimate B-PRO
tensile I-PRO
strength E-PRO
( O
UTS S-PRO
) O
and O
plasticity S-PRO
. O


The O
average S-CONPRI
UTS O
of O
the O
thin-wall O
sample S-CONPRI
protected O
by O
N2 S-MATE
in O
the O
horizontal O
direction O
was O
82.5 O
% O
of O
the O
UTS S-PRO
of O
the O
samples S-CONPRI
shielded O
using O
Ar S-ENAT
. O


However O
, O
the O
average S-CONPRI
elongation O
in O
the O
horizontal O
direction O
of O
the O
samples S-CONPRI
protected O
by O
N2 S-MATE
was O
18.6 O
% O
of O
that O
of O
the O
samples S-CONPRI
shielded O
by O
Ar S-ENAT
. O


The O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
sample S-CONPRI
protected O
by O
argon S-MATE
were O
more O
excellent O
. O


An O
eco-design O
for O
AM S-MANP
framework O
based O
on O
energy O
performance S-CONPRI
assessment O
has O
been O
proposed O
. O


A O
simulation S-ENAT
tool O
has O
been O
proposed O
to O
predict O
energy O
consumption O
of O
AM S-MANP
. O


Design S-FEAT
mechanisms O
and O
the O
workflow S-CONPRI
for O
eco-design O
for O
AM S-MANP
have O
been O
discussed O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
has O
been O
considered O
as S-MATE
a O
promising O
technology S-CONPRI
with O
higher O
resource O
efficiency O
and O
better O
ecological O
benefits O
in O
production B-ENAT
systems E-ENAT
. O


If O
the O
parameters S-CONPRI
are O
not O
designed S-FEAT
appropriately O
, O
the O
ecological O
performance S-CONPRI
of O
AM S-MANP
can O
be S-MATE
worse O
than O
conventional B-MANP
manufacturing E-MANP
processes O
. O


To O
ensure O
the O
ecological O
benefits O
of O
AM S-MANP
, O
eco-design O
based O
on O
Life B-CONPRI
Cycle E-CONPRI
Assessment O
( O
LCA O
) O
is O
a O
promising O
approach O
to O
analyze O
and O
minimize O
the O
environmental O
impacts O
of O
AM S-MANP
. O


However O
, O
LCA O
can O
only O
be S-MATE
carried O
out O
at O
the O
later O
stage O
of O
the O
design B-CONPRI
process E-CONPRI
after O
most O
design S-FEAT
and O
decision O
operations O
are O
already O
made O
because O
the O
implementation O
of O
LCA O
requires O
detailed O
process S-CONPRI
and O
inventory O
information O
of O
the O
entire O
life B-CONPRI
cycle E-CONPRI
. O


If O
users O
attempt O
to O
optimize O
the O
ecological O
performance S-CONPRI
of O
their O
design S-FEAT
solutions O
, O
they O
need O
to O
repeat O
almost O
the O
entire O
design B-CONPRI
process E-CONPRI
. O


The O
proposed O
approach O
uses O
a O
holistic O
framework S-CONPRI
consisting O
of O
three O
parts O
: O
a O
simulation S-ENAT
tool O
for O
energy O
consumption O
prediction S-CONPRI
of O
AM S-MANP
, O
an O
assessment O
model S-CONPRI
for O
energy O
performance S-CONPRI
of O
AM S-MANP
, O
and O
general O
workflows S-CONPRI
of O
eco-design O
for O
AM S-MANP
. O


Since O
the O
energy O
performance S-CONPRI
quantification O
and O
assessment O
of O
AM S-MANP
require O
less O
process S-CONPRI
information O
, O
it O
can O
be S-MATE
integrated O
earlier O
and O
easier O
into O
the O
eco-design O
for O
AM S-MANP
. O


Additionally O
, O
an O
example O
of O
use O
case O
is O
provided O
that O
confirms O
the O
feasibility S-CONPRI
of O
this O
framework S-CONPRI
. O


By O
employing O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
, O
we O
demonstrate O
how O
Sn3Ag4Ti O
alloy S-MATE
can O
robustly O
bond O
to O
silicon S-MATE
via O
additive B-MANP
manufacturing E-MANP
. O


With O
this O
technology S-CONPRI
, O
heat S-CONPRI
removal O
devices O
( O
e.g. O
, O
vapor O
chamber O
evaporators O
, O
heat S-CONPRI
pipes O
, O
micro-channels O
) O
can O
be S-MATE
directly O
printed O
onto O
the O
electronic O
package O
without O
using O
thermal O
interface S-CONPRI
materials O
. O


This O
reduces O
operating O
temperature S-PARA
, O
saving O
power S-PARA
and O
reducing O
electronic-waste O
. O


The O
bonding S-CONPRI
of O
common O
metal B-MATE
alloys E-MATE
used O
in O
additive B-MANP
manufacturing E-MANP
onto O
silicon S-MATE
is O
relatively O
weak O
and O
generally O
possesses O
high O
contact S-APPL
angles O
( O
poor O
wetting O
and O
interfacial O
strength S-PRO
) O
. O


By O
using O
the O
proper O
interlayer O
material S-MATE
, O
wettability S-CONPRI
and O
reactivity O
with O
the O
silicon S-MATE
substrate O
increase O
drastically O
. O


Unlike O
conventional O
dissimilar O
material S-MATE
brazing S-APPL
that O
can O
take O
tens O
of O
minutes O
to O
form O
a O
strong O
bond O
, O
this O
study O
demonstrates O
how O
this O
kinetic O
limitation O
can O
be S-MATE
overcome O
to O
form O
a O
good O
bond O
in O
sub-milliseconds O
via O
intense O
laser S-ENAT
heating S-MANP
. O


The O
mechanism S-CONPRI
for O
rapid O
bonding S-CONPRI
lies O
in O
using O
an O
alloy S-MATE
that O
can O
form O
a O
strong O
intermetallic S-MATE
bond O
to O
the O
substrate S-MATE
at O
a O
low O
temperature S-PARA
, O
and O
exposing O
the O
sample S-CONPRI
multiple O
times O
to O
give O
sufficient O
diffusion S-CONPRI
time O
for O
a O
strong O
bond O
. O


Bonding S-CONPRI
of O
Sn3Ag4Ti O
to O
silicon S-MATE
occurs O
through O
the O
formation O
of O
a O
thin O
( O
∼μm O
) O
titanium-silicide O
interfacial O
layer S-PARA
that O
makes O
the O
silicon S-MATE
wettable O
to O
the O
Sn3Ag4Ti O
. O


These O
printed O
parts O
are O
mechanically O
resistant O
to O
thermal B-PARA
cycling E-PARA
, O
with O
no O
mechanical B-PRO
failures E-PRO
visible O
after O
over O
a O
week O
of O
continuous O
thermal B-PARA
cycling E-PARA
( O
−40 O
°C O
and O
130 O
°C O
) O
. O


Additively B-MANP
manufactured E-MANP
low O
porosity S-PRO
equiatomic O
CoCrFeMnNi O
alloy S-MATE
parts O
. O


Parts O
are O
single O
phase S-CONPRI
with O
inter-cellular O
regions O
enriched O
in O
Mn S-MATE
and O
Ni S-MATE
. O


Tensile B-PRO
properties E-PRO
exceeded O
most O
previous O
work O
on O
similar O
alloys S-MATE
. O


Initiation O
of O
pitting S-CONPRI
for O
CoCrFeMnNi O
alloy S-MATE
was O
comparable O
to O
304 O
L O
stainless B-MATE
steel E-MATE
. O


This O
study O
investigates S-CONPRI
the O
mechanical S-APPL
and O
corrosion B-PRO
properties E-PRO
of O
as-built O
and O
annealed O
equiatomic O
CoCrFeMnNi O
alloy S-MATE
produced O
by O
laser-based O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
. O


The O
high O
cooling B-PARA
rates E-PARA
of O
DED S-MANP
produced O
a O
single-phase O
, O
cellular O
microstructure S-CONPRI
with O
cells S-APPL
on O
the O
order O
of O
4 O
μm O
in O
diameter S-CONPRI
and O
inter-cellular O
regions O
that O
were O
enriched O
in O
Mn S-MATE
and O
Ni S-MATE
. O


Annealing S-MANP
created O
a O
chemically O
homogeneous S-CONPRI
recrystallized O
microstructure S-CONPRI
with O
a O
high O
density S-PRO
of O
annealing S-MANP
twins O
. O


The O
average S-CONPRI
yield O
strength S-PRO
of O
the O
as-built O
condition O
was O
424 O
MPa S-CONPRI
and O
exceeded O
the O
annealed O
condition O
( O
232 O
MPa S-CONPRI
) O
, O
however O
; O
the O
strain B-MANP
hardening E-MANP
rate O
was O
lower O
for O
the O
as-built O
material S-MATE
stemming O
from O
higher O
dislocation B-PRO
density E-PRO
associated O
with O
DED S-MANP
parts O
and O
the O
fine O
cell B-PRO
size E-PRO
. O


In O
general O
, O
the O
yield B-PRO
strength E-PRO
, O
ultimate B-PRO
tensile I-PRO
strength E-PRO
, O
and O
elongation-to-failure O
for O
the O
as-built O
material S-MATE
exceeded O
values O
from O
previous O
studies O
that O
explored O
other O
AM B-MANP
techniques E-MANP
to O
produce O
the O
CoCrFeMnNi O
alloy S-MATE
. O


Ductile B-CONPRI
fracture E-CONPRI
occurred O
for O
all O
specimens O
with O
dimple O
initiation O
associated O
with O
nanoscale O
oxide B-MATE
inclusions E-MATE
. O


The O
breakdown O
potential O
( O
onset O
of O
pitting B-CONPRI
corrosion E-CONPRI
) O
was O
similar O
for O
the O
as-built O
and O
annealed O
conditions O
at O
0.40 O
VAg/AgCl O
when O
immersed O
in O
0.6 O
M O
NaCl S-MATE
. O


A O
passive O
oxide S-MATE
film O
depleted O
in O
Cr S-MATE
cations O
with O
substantial O
incorporation O
of O
Mn S-MATE
cations O
is O
proposed O
as S-MATE
the O
primary O
mechanism S-CONPRI
for O
local O
corrosion S-CONPRI
susceptibility O
of O
the O
CoCrFeMnNi O
alloy S-MATE
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
enables O
the O
fabrication S-MANP
of O
complex O
lattice B-FEAT
structures E-FEAT
, O
for O
which O
a O
single O
part O
may O
have O
hundreds O
or O
thousands O
of O
individual O
geometric O
features O
. O


Conventional O
methods O
for O
measuring O
part O
geometry S-CONPRI
and O
performing O
quality B-CONPRI
control E-CONPRI
, O
which O
typically O
use O
a O
small O
number O
of O
low-dimensional O
measurements O
, O
are O
not O
well O
suited O
for O
lattice B-FEAT
structures E-FEAT
. O


This O
paper O
describes O
a O
method O
for O
scanning S-CONPRI
and O
automatically O
extracting S-CONPRI
individual O
features O
of O
the O
lattice S-CONPRI
and O
applies O
this O
method O
to O
characterize O
AM S-MANP
lattice O
structures O
in O
both O
two-dimensional S-CONPRI
and O
three-dimensional B-CONPRI
lattices E-CONPRI
. O


The O
research S-CONPRI
measured O
94 O
lattice S-CONPRI
parts O
fabricated S-CONPRI
from O
3 O
materials S-CONPRI
in O
9 O
different O
designs S-FEAT
using O
either O
a O
high-resolution S-PARA
document O
scanner O
or O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
( O
CT S-ENAT
) O
. O


A O
statistical O
analysis O
considered O
manufacturing S-MANP
variances O
as S-MATE
a O
function O
of O
material S-MATE
type O
and O
part O
design S-FEAT
on O
a O
subset O
of O
the O
data S-CONPRI
, O
comprising O
the O
size O
and O
location O
of O
over O
15,000 O
individual O
features O
. O


We O
studied O
the O
geometric O
variations S-CONPRI
of O
these O
struts S-MACEQ
in O
uniform O
, O
hierarchical O
and O
gradated O
parts O
. O


For O
a O
single O
design S-FEAT
and O
material S-MATE
, O
the O
standard B-CHAR
deviation E-CHAR
of O
lattice S-CONPRI
feature B-PARA
size E-PARA
is O
quite O
small O
. O


For O
example O
, O
a O
lattice S-CONPRI
strut O
with O
thickness O
0.5 O
mm S-MANP
has O
a O
standard B-CHAR
deviation E-CHAR
of O
30 O
μm O
. O


However O
, O
when O
the O
same O
process S-CONPRI
is O
used O
to O
manufacture S-CONPRI
multiple O
parts O
having O
different O
designs S-FEAT
and O
from O
different O
materials S-CONPRI
, O
the O
standard B-CHAR
deviation E-CHAR
of O
feature B-PARA
size E-PARA
can O
be S-MATE
larger O
by O
2X O
or O
more O
. O


This O
type O
of O
automated B-ENAT
measurement E-ENAT
and O
analysis O
may O
allow O
for O
rigorous O
monitoring O
, O
qualification O
and O
control O
of O
AM S-MANP
lattice O
parts O
in O
production S-MANP
. O


The O
adhesion S-PRO
and O
merging O
of O
adjacent O
filaments S-MATE
in O
polymer B-MANP
extrusion E-MANP
based O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
plays O
a O
key O
role O
in O
determining O
the O
thermal O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
built O
part O
. O


It O
is O
well O
known O
that O
maintaining O
the O
deposited O
filaments S-MATE
at O
a O
high O
temperature S-PARA
aids O
in O
the O
process S-CONPRI
of O
adhesion S-PRO
and O
merging O
. O


While O
external O
mechanisms O
such O
as S-MATE
laser O
and O
infrared S-CONPRI
heating S-MANP
have O
been O
used O
in O
the O
past O
to O
heat S-CONPRI
up O
deposited O
filaments S-MATE
, O
this O
paper O
presents O
a O
simpler O
, O
less O
invasive O
and O
in B-CONPRI
situ E-CONPRI
mechanism O
for O
heating S-MANP
of O
previously O
deposited B-CHAR
layers E-CHAR
using O
a O
hot O
metal S-MATE
block O
integrated O
with O
and O
rastering O
together O
with O
the O
filament-dispensing O
nozzle S-MACEQ
. O


Infrared S-CONPRI
thermography O
based O
quantitative B-CHAR
measurement E-CHAR
of O
temperature S-PARA
field O
along O
the O
raster O
line O
is O
carried O
out O
for O
two O
configurations O
– O
a O
preheater O
and O
a O
postheater O
traveling O
ahead O
of O
or O
behind O
the O
nozzle S-MACEQ
respectively O
. O


In O
each O
case O
, O
significant O
temperature S-PARA
rise O
in O
the O
deposited O
filaments S-MATE
is O
shown O
. O


The O
measured O
temperature S-PARA
rise O
is O
shown O
to O
be S-MATE
a O
function O
of O
process B-CONPRI
parameters E-CONPRI
such O
as S-MATE
raster O
speed O
and O
heater-to-base O
gap O
. O


Experimental S-CONPRI
measurements O
are O
shown O
to O
agree O
well O
with O
theoretical S-CONPRI
and O
simulation S-ENAT
models O
. O


Cross-section O
imaging S-APPL
of O
samples S-CONPRI
printed O
without O
and O
with O
the O
in B-CONPRI
situ E-CONPRI
heating S-MANP
clearly O
show O
significant O
improvement O
in O
neck O
growth O
and O
filament-to-filament O
merging O
compared O
to O
the O
baseline O
case O
. O


Improvement O
in O
thermal O
and O
structural B-CHAR
performance E-CHAR
of O
printed O
samples S-CONPRI
is O
also O
demonstrated O
. O


The O
improved O
temperature S-PARA
field O
and O
consequently O
enhanced O
filament S-MATE
adhesion S-PRO
reported O
here O
may O
help O
design S-FEAT
and O
build S-PARA
parts O
with O
superior O
thermal O
and O
mechanical B-CONPRI
properties E-CONPRI
using O
polymer S-MATE
AM S-MANP
. O


Pore S-PRO
structures O
of O
additively B-MANP
manufactured E-MANP
metal O
parts O
were O
investigated O
with O
X-ray B-CHAR
Computed I-CHAR
Tomography E-CHAR
( O
XCT O
) O
. O


Disks O
made O
of O
a O
cobalt-chrome O
alloy S-MATE
were O
produced O
using O
laser-based O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
processes S-CONPRI
. O


The O
additive B-MANP
manufacturing E-MANP
processing O
parameters S-CONPRI
( O
scan B-PARA
speed E-PARA
and O
hatch B-PARA
spacing E-PARA
) O
were O
varied O
in O
order O
to O
have O
porosities S-PRO
varying O
from O
0.1 O
% O
to O
70 O
% O
so O
as S-MATE
to O
see O
the O
effects O
of O
processing O
parameters S-CONPRI
on O
the O
formation O
of O
pores S-PRO
and O
cracks O
. O


The O
XCT O
images S-CONPRI
directly O
show O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
pore S-PRO
structure O
, O
along O
with O
cracks O
. O


Qualitative S-CONPRI
visualization O
is O
useful O
; O
however O
, O
quantitative S-CONPRI
results O
depend O
on O
accurately S-CHAR
segmenting O
the O
XCT O
images S-CONPRI
. O


Methods O
of O
segmentation O
and O
image B-CONPRI
analysis E-CONPRI
were O
carefully O
developed O
based O
, O
as S-MATE
much O
as S-MATE
possible O
, O
on O
aspects O
of O
the O
images S-CONPRI
themselves O
. O


These O
enabled O
quantitative S-CONPRI
measures O
of O
porosity S-PRO
, O
including O
how O
porosity S-PRO
varies O
in O
and O
across O
the O
build B-PARA
direction E-PARA
, O
pore B-PARA
size E-PARA
distribution S-CONPRI
, O
how O
pore S-PRO
structure O
varies O
between O
parts O
with O
similar O
porosity S-PRO
levels O
but O
different O
processing O
parameters S-CONPRI
, O
pore S-PRO
shape O
, O
and O
particle B-CONPRI
size I-CONPRI
distribution E-CONPRI
of O
un-melted O
powder S-MATE
trapped O
in O
pores S-PRO
. O


These O
methods O
could O
possibly O
serve O
as S-MATE
the O
basis O
for O
standard S-CONPRI
segmentation O
and O
image B-CONPRI
analysis E-CONPRI
methods O
for O
metallic S-MATE
additively B-MANP
manufactured E-MANP
parts O
, O
enabling O
accurate S-CHAR
and O
reliable O
defect S-CONPRI
detection O
and O
quantitative S-CONPRI
measures O
of O
pore S-PRO
structure O
, O
which O
are O
critical O
aspects O
of O
qualification O
and O
certification O
. O


The O
aluminium B-MATE
alloy E-MATE
wire O
2319 O
is O
commonly O
used O
for O
Wire B-MANP
+ I-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
. O


It O
is O
oversaturated O
with O
copper S-MATE
, O
like O
other O
alloys S-MATE
of O
the O
precipitation B-MANP
hardening E-MANP
2 O
# O
# O
# O
series O
, O
which O
are O
used O
for O
structural O
applications O
in O
aviation O
. O


Residual B-PRO
stress E-PRO
and O
distortion S-CONPRI
are O
one O
of O
the O
biggest O
challanges O
in O
metal B-MANP
additive I-MANP
manufacturing E-MANP
, O
however O
this O
topic O
is O
not O
widely O
investigated O
for O
aluminium B-MATE
alloys E-MATE
. O


Neutron B-CHAR
diffraction E-CHAR
measurements O
showed O
that O
the O
as-built O
component S-MACEQ
can O
contain O
constant O
tensile B-PRO
residual I-PRO
stresses E-PRO
along O
the O
height O
of O
the O
wall O
, O
which O
can O
reach O
the O
materials S-CONPRI
' O
yield B-PRO
strength E-PRO
. O


These O
stresses O
cause O
bending S-MANP
distortion O
after O
unclamping O
the O
part O
from O
the O
build B-MACEQ
platform E-MACEQ
. O


Two O
different O
rolling S-MANP
techniques O
were O
used O
to O
control O
residual B-PRO
stress E-PRO
and O
distortion S-CONPRI
. O


Vertical S-CONPRI
rolling S-MANP
was O
applied O
inter-pass O
on O
top O
of O
the O
wall O
to O
deform O
each O
layer S-PARA
after O
its O
deposition S-CONPRI
. O


This O
technique O
virtually O
elimiated O
the O
distortion S-CONPRI
, O
but O
produced O
a O
characteristic O
residual B-PRO
stress E-PRO
profile S-FEAT
. O


Side O
rolling S-MANP
instead O
was O
applied O
on O
the O
side O
surface S-CONPRI
of O
the O
wall O
, O
after O
it O
has O
been O
completed O
. O


An O
interesting O
observation O
from O
the O
neutron B-CHAR
diffraction E-CHAR
measurements O
of O
the O
stress-free O
reference O
was O
the O
significantly O
larger O
FCC S-CONPRI
aluminium S-MATE
unit O
cell S-APPL
dimension O
in O
the O
inter-pass O
rolled O
walls O
as S-MATE
compared O
to O
the O
as-build O
condition O
. O


This O
is O
a O
result O
of O
less O
copper S-MATE
in O
solid B-MATE
solution E-MATE
with O
aluminium S-MATE
, O
indicating O
greater O
precipitation S-CONPRI
and O
thus O
, O
potentially O
contibuting O
to O
improve O
the O
strenght O
of O
the O
material S-MATE
. O


This O
work O
demonstrates O
the O
feasibility S-CONPRI
of O
fabricating S-MANP
bulk O
nanostructured O
high O
modulus O
steels S-MATE
in-situ S-CONPRI
by O
additive B-MANP
manufacturing E-MANP
. O


This O
ideal O
match O
of O
novel O
processes S-CONPRI
and O
alloy S-MATE
concepts O
opens O
up O
new O
pathways O
for O
lightweight S-CONPRI
design S-FEAT
by O
producing O
light O
, O
stiff O
, O
strong O
and O
ductile S-PRO
components S-MACEQ
with O
minimal O
geometric O
restraints O
. O


On O
the O
example O
of O
an O
Fe S-MATE
– O
Ti S-MATE
– O
B S-MATE
alloy S-MATE
, O
a O
conventional O
processing O
sequence O
of O
melting S-MANP
and O
casting S-MANP
pre-alloys O
, O
gas-atomisation O
and O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
selective B-MANP
laser I-MANP
melting E-MANP
) O
led S-APPL
to O
finely O
dispersed O
metastable S-PRO
particle O
and O
matrix O
phases O
. O


A O
simple B-MANP
annealing E-MANP
step O
transformed O
them O
into O
the O
desired O
equilibrium S-CONPRI
constituents O
of O
ductile S-PRO
ferrite O
( O
matrix O
) O
and O
light O
and O
stiff O
TiB2 O
( O
particles S-CONPRI
) O
, O
with O
only O
minimal O
changes O
in O
particle S-CONPRI
size O
( O
about O
20–150 O
nm O
in O
diameter S-CONPRI
) O
and O
distribution S-CONPRI
( O
mainly O
on O
the O
matrix O
grain B-CONPRI
boundaries E-CONPRI
) O
. O


This O
nano-scaled O
composite B-CONPRI
structure E-CONPRI
promises O
an O
extremely O
attractive O
property S-CONPRI
profile S-FEAT
, O
i.e O
. O


an O
increased O
stiffness/ratio O
at O
elevated O
strength S-PRO
and O
without O
deteriorated O
ductility S-PRO
. O


However O
, O
the O
not O
yet O
optimized O
parameters S-CONPRI
of O
the O
laser S-ENAT
fusion S-CONPRI
process O
led S-APPL
to O
the O
formation O
of O
few O
pores S-PRO
and O
cracks O
, O
which O
prevented O
the O
complete O
assessment O
of O
the O
property S-CONPRI
profile S-FEAT
of O
the O
manufactured S-CONPRI
samples O
. O


Material S-MATE
and O
processing O
strategies O
for O
the O
further O
development O
of O
this O
promising O
lightweight S-CONPRI
design S-FEAT
approach O
– O
including O
the O
suitability O
of O
other O
powder B-MANP
metallurgy E-MANP
processing O
routes O
– O
are O
outlined O
and O
discussed O
. O


Metal B-MANP
Additive I-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
have O
made O
it O
possible O
to O
build S-PARA
parts O
with O
complex O
geometric O
features O
by O
adopting O
a O
layer-by-layer S-CONPRI
approach O
. O


However O
, O
additional O
support B-FEAT
structures E-FEAT
are O
needed O
to O
support S-APPL
overhanging O
surfaces S-CONPRI
and O
reduce O
distortion S-CONPRI
that O
may O
occur O
in O
these O
parts O
. O


This O
increases O
the O
overall O
build B-PARA
time E-PARA
of O
the O
part O
and O
leads O
to O
additional O
post B-CONPRI
processing E-CONPRI
efforts O
for O
removal B-MANP
of I-MANP
support E-MANP
structures O
. O


Further O
, O
support B-FEAT
structures E-FEAT
have O
a O
detrimental O
effect O
on O
the O
surface B-FEAT
finish E-FEAT
on O
the O
areas S-PARA
of O
the O
part O
that O
come O
in O
contact S-APPL
with O
the O
supports S-APPL
. O


Thus O
, O
minimizing O
the O
need O
for O
support B-FEAT
structures E-FEAT
and O
ensuring O
its O
maximum O
removal O
is O
essential O
for O
an O
efficient O
part O
build S-PARA
in O
AM S-MANP
. O


Part O
build B-PARA
orientation E-PARA
is O
the O
main O
parameter S-CONPRI
that O
influences O
the O
need O
for O
support B-FEAT
structures E-FEAT
to O
build S-PARA
a O
part O
. O


This O
paper O
presents O
an O
approach O
to O
identify O
the O
best O
build B-PARA
orientation E-PARA
for O
a O
part O
such O
that O
the O
overall O
part O
build B-PARA
time E-PARA
is O
minimized O
while O
ensuring O
maximum O
removal B-MANP
of I-MANP
supports E-MANP
and O
minimizing O
the O
contact S-APPL
area S-PARA
between O
the O
part O
surface S-CONPRI
and O
supports S-APPL
. O


A O
hierarchical O
octree O
data S-CONPRI
structure O
has O
been O
used O
to O
analyze O
support S-APPL
accessibility O
and O
the O
area S-PARA
of O
support S-APPL
in O
contact S-APPL
with O
part O
. O


A O
2D S-CONPRI
setup O
map O
highlighting O
the O
feasible O
directions O
of O
setups O
for O
support S-APPL
removal O
has O
also O
been O
presented O
. O


The O
estimation O
for O
overhang B-PARA
angle E-PARA
of O
a O
3D S-CONPRI
structural O
surface S-CONPRI
is O
established O
by O
fitting O
the O
local B-CONPRI
element I-CONPRI
density I-CONPRI
distribution E-CONPRI
with O
a O
density S-PRO
hyperplane O
in O
ℝ4 O
space O
. O


The O
3D S-CONPRI
hanging O
feature S-FEAT
issue O
is O
resolved O
by O
the O
combination O
of O
horizontal O
minimum O
length O
constraint O
and O
overhang B-PARA
angle E-PARA
constraint O
. O


A O
constraint-based O
approach O
for O
3D S-CONPRI
topology O
optimization S-CONPRI
with O
a O
large O
number O
of O
element-wise O
constraints O
is O
proposed O
to O
obtain O
an O
accurate S-CHAR
solution O
. O


This O
paper O
studies O
additive B-MANP
manufacturing E-MANP
oriented O
structural O
topology B-FEAT
optimization E-FEAT
with O
SIMP O
approach O
and O
aims O
at O
3D S-CONPRI
high-resolution O
printable O
structural O
topology S-CONPRI
design S-FEAT
with O
overhang S-PARA
and O
horizontal O
minimum O
length O
control O
for O
minimum O
compliance.To O
start O
with O
, O
we O
construct O
a O
hyperplane O
in O
ℝ4 O
by O
fitting O
a O
local B-CONPRI
element I-CONPRI
density I-CONPRI
distribution E-CONPRI
in O
the O
18 O
Elements S-MATE
Scheme O
, O
use O
its O
gradient O
to O
estimate O
the O
overhang B-PARA
angle E-PARA
, O
the O
directional-dependent O
overhang B-PARA
angle E-PARA
and O
formulate O
the O
corresponding O
constraints O
. O


Next O
, O
we O
propose O
a O
Horizontal O
Square O
Scheme O
and O
four O
support S-APPL
sets O
around O
the O
concerned O
element S-MATE
. O


The O
horizontal O
minimum O
length O
was O
controlled O
by O
forbidding O
the O
concerned O
element S-MATE
’ O
s S-MATE
density S-PRO
to O
be S-MATE
larger O
than O
the O
average S-CONPRI
density O
of O
the O
elements S-MATE
in O
one O
of O
the O
support S-APPL
sets O
. O


By O
combining O
these O
two O
constraints O
, O
the O
hanging O
feature S-FEAT
is O
well O
suppressed.A O
new O
implementation O
scheme O
with O
an O
improved O
weight S-PARA
function O
is O
proposed O
to O
meet O
these O
element S-MATE
wise O
AM S-MANP
constraints O
well O
. O


To O
get O
high B-PARA
resolution E-PARA
structural O
boundaries S-FEAT
with O
low O
computational O
efforts O
, O
this O
paper O
applies O
the O
multiresolution O
topology B-FEAT
optimization E-FEAT
( O
MTOP O
) O
method.The O
structural O
TO O
problem O
is O
solved O
by O
MMA O
. O


A O
number O
of O
numerical O
examples O
and O
AM S-MANP
experiments O
show O
the O
effectiveness S-CONPRI
of O
this O
method O
. O


The O
present O
approach O
works O
efficiently O
when O
the O
building B-PARA
direction E-PARA
is O
in O
slight O
misalignment O
with O
the O
vertical S-CONPRI
direction O
. O


The O
columnar O
to O
equiaxed O
transition S-CONPRI
( O
CET O
) O
of O
grain B-CONPRI
structures E-CONPRI
associated O
with O
processing O
conditions O
has O
been O
observed O
during O
metallic B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
. O


However O
, O
the O
formation O
mechanisms O
of O
these O
grain B-CONPRI
structures E-CONPRI
have O
not O
been O
well O
understood O
under O
rapid B-MANP
solidification E-MANP
conditions O
, O
especially O
for O
AM S-MANP
of O
superalloys S-MATE
. O


This O
paper O
aims O
to O
uncover O
the O
underlying O
mechanisms O
that O
govern O
the O
CET O
of O
AM B-MANP
metals E-MANP
, O
using O
a O
well-tested O
multiscale O
phase-field O
model S-CONPRI
where O
heterogeneous B-CONPRI
nucleation E-CONPRI
, O
grain S-CONPRI
selection O
and O
grain S-CONPRI
epitaxial S-PRO
growth O
are O
considered O
. O


Using O
In718 S-MATE
as S-MATE
an O
example O
, O
the O
simulated O
results O
show O
that O
the O
CET O
is O
critically O
controlled O
by O
the O
undercooling O
, O
involving O
constitutional O
supercooling S-CONPRI
, O
thermal O
and O
curvature O
undercoolings O
in O
the O
melt B-MATE
pool E-MATE
, O
which O
dictates O
the O
extent O
of O
heterogeneous B-CONPRI
nucleation E-CONPRI
with O
respect O
to O
the O
grain S-CONPRI
epitaxial S-PRO
growth O
during O
rapid B-MANP
solidification E-MANP
. O


Laser B-MANP
Additive I-MANP
Manufacturing E-MANP
( O
LAM S-MANP
) O
of O
light B-MATE
metals E-MATE
such O
as S-MATE
high-strength O
Al-based O
alloys S-MATE
offers O
tremendous O
potential O
for O
e.g O
. O


weight S-PARA
reduction S-CONPRI
and O
associated O
reduced O
fuel O
consumptions O
for O
the O
transportation O
industry S-APPL
. O


Typically O
, O
commercial O
Sc-containing O
alloys S-MATE
, O
such O
as S-MATE
Scalmalloy® O
, O
rely O
on O
precipitation B-MANP
hardening E-MANP
to O
increase O
their O
strength S-PRO
. O


Conventional O
processing O
involves O
controlled O
ageing O
during O
which O
ordered O
and O
coherent O
Al3Sc O
precipitates S-MATE
form O
from O
a O
Sc-supersaturated O
solid B-MATE
solution E-MATE
. O


Here O
we O
show O
how O
the O
intrinsic O
heat B-MANP
treatment E-MANP
( O
IHT O
) O
of O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
can O
be S-MATE
used O
to O
trigger O
the O
precipitation S-CONPRI
of O
Al3Sc O
already O
during O
the O
LAM S-MANP
process O
. O


High O
number O
densities O
of O
1023 O
nano-precipitates O
per O
m3 O
can O
be S-MATE
realized O
through O
solid-state B-CONPRI
phase E-CONPRI
transformation O
from O
the O
supersaturated O
Al-Sc O
matrix O
that O
results O
from O
the O
fast O
cooling B-PARA
rate E-PARA
in O
LAM S-MANP
. O


Yet O
, O
the O
IHT O
causes O
precipitates S-MATE
to O
coarsen O
, O
hence O
reducing O
their O
strengthening S-MANP
effect O
. O


We O
implement O
alternative O
solidification S-CONPRI
conditions O
to O
exploit O
the O
IHT O
to O
form O
a O
Zr-rich O
shell S-MACEQ
around O
the O
Al3Sc O
precipitates S-MATE
that O
prevents O
coarsening O
. O


Our O
approach O
is O
applicable O
to O
a O
wide O
range S-PARA
of O
precipitation-hardened O
alloys S-MATE
to O
trigger O
in-situ S-CONPRI
precipitation O
during O
LAM S-MANP
. O


Thermo-mechanical S-CONPRI
finite B-CONPRI
element E-CONPRI
modeling O
of O
additive B-MANP
manufacturing I-MANP
processes E-MANP
, O
such O
as S-MATE
Directed O
Energy O
Deposition S-CONPRI
and O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
, O
has O
been O
widely O
applied O
for O
the O
prediction S-CONPRI
and O
mitigation O
of O
part O
distortion S-CONPRI
. O


However O
, O
as S-MATE
the O
size O
of O
modeled O
geometries S-CONPRI
gets O
larger O
, O
the O
number O
of O
nodes O
and O
elements S-MATE
required O
in O
the O
finite B-CONPRI
element E-CONPRI
mesh O
increases O
significantly O
. O


Because O
runtime O
will O
increase O
as S-MATE
more O
nodes O
are O
added O
, O
it O
is O
not O
practical O
to O
conduct O
full O
simulations S-ENAT
of O
large O
builds S-CHAR
using O
standard S-CONPRI
static O
meshes O
. O


Advanced O
meshing O
strategy O
is O
required O
to O
reduce O
the O
run O
time O
and O
to O
retain O
the O
accuracy S-CHAR
of O
the O
prediction S-CONPRI
. O


In O
this O
work O
, O
a O
mesh O
coarsening O
strategy O
is O
evaluated O
for O
predicting O
temperature S-PARA
, O
distortion S-CONPRI
, O
and O
residual B-PRO
stress E-PRO
in O
additive B-MANP
manufacturing E-MANP
, O
aiming O
to O
achieve O
feasible O
run O
times O
with O
reasonable O
accuracy S-CHAR
on O
large O
builds S-CHAR
. O


Directed B-MANP
Energy I-MANP
Deposition E-MANP
of O
thin O
wall O
geometries S-CONPRI
built O
from O
Inconel® O
625 O
and O
Ti6Al4V S-MATE
is O
used O
as S-MATE
a O
reference O
and O
models O
with O
2 O
levels O
of O
Octree O
mesh O
coarsening O
are O
investigated O
. O


The O
thermal O
history O
, O
in B-CONPRI
situ E-CONPRI
distortion S-CONPRI
, O
residual B-PRO
stress E-PRO
, O
and O
run O
times O
are O
compared O
with O
previously O
experimentally B-CONPRI
validated E-CONPRI
static O
mesh O
results O
. O


Two O
levels O
of O
mesh O
coarsening O
is O
found O
to O
be S-MATE
the O
most O
effective O
case O
for O
both O
materials S-CONPRI
reducing O
the O
computational O
time O
by O
75 O
% O
while O
reporting O
less O
than O
2.5 O
% O
error S-CONPRI
for O
the O
peak O
distortion S-CONPRI
and O
negligible O
error S-CONPRI
for O
the O
thermal O
history O
difference O
as S-MATE
compared O
to O
the O
static O
mesh O
. O


Keeping O
two O
fine O
layers O
of O
elements S-MATE
underneath O
the O
heat B-CONPRI
source E-CONPRI
is O
found O
to O
be S-MATE
the O
most O
efficient O
in O
terms O
of O
prediction S-CONPRI
accuracy S-CHAR
and O
run O
time O
. O


Cork S-MATE
powder O
residues O
were O
used O
to O
produce O
a O
biodegradable O
filament S-MATE
for O
additive B-MANP
manufacturing E-MANP
. O


The O
addition O
of O
a O
maleic O
anhydride-based O
coupling O
agent O
to O
the O
PLA S-MATE
matrix O
improved O
the O
mechanical S-APPL
behavior O
of O
CPC O
. O


A O
cork-like O
filament S-MATE
fully O
biodegradable O
and O
filled O
with O
low O
granulometry O
cork S-MATE
powder O
residues O
was O
developed O
. O


Cork-polymer O
composites S-MATE
( O
CPC O
) O
were O
prepared O
using O
a O
Brabender O
type O
mixer O
incorporating O
15 O
% O
( O
w/w O
) O
of O
cork S-MATE
powder O
( O
corresponding O
to O
55 O
% O
( O
v/v O
) O
) O
and O
having O
polylactic B-MATE
acid E-MATE
( O
PLA S-MATE
) O
as S-MATE
matrix O
. O


In O
order O
to O
promote O
a O
chemical O
adhesion S-PRO
between O
cork S-MATE
particles O
and O
PLA S-MATE
, O
the O
effect O
of O
maleic O
anhydride O
grafted O
PLA S-MATE
( O
MAgPLA O
) O
was O
studied O
. O


Fourier B-ENAT
Transform I-ENAT
Infrared E-ENAT
– O
Attenuated O
Total O
Reflection S-CHAR
( O
FTIR-ATR O
) O
analysis O
was O
used O
to O
evaluate O
the O
functionalization O
of O
MAgPLA O
onto O
the O
polymeric O
chain O
. O


The O
addition O
of O
MAgPLA O
enhanced O
the O
mechanical S-APPL
behavior O
by O
increasing O
tensile B-PRO
properties E-PRO
while O
improving O
the O
dispersion S-CONPRI
of O
cork S-MATE
particles O
within O
PLA S-MATE
matrix O
. O


In O
addition O
, O
cork S-MATE
particles O
and O
MAgPLA O
acted O
as S-MATE
nucleating O
agents O
during O
PLA S-MATE
melting S-MANP
process O
. O


To O
evaluate O
the O
printability S-PARA
of O
the O
developed O
CPC O
filament S-MATE
, O
specimens O
were O
printed O
by O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
and O
compared O
to O
those O
obtained O
by O
injection B-MANP
molding E-MANP
( O
IM O
) O
. O


FFF S-MANP
allowed O
to O
preserve O
the O
cork S-MATE
alveolar O
structure S-CONPRI
in O
the O
specimens O
, O
benefiting O
CPC O
mechanical S-APPL
behavior O
. O


3D B-APPL
parts E-APPL
could O
be S-MATE
printed O
with O
the O
CPC O
filament S-MATE
thereby O
demonstrating O
the O
usefulness O
of O
the O
fully O
biodegradable O
cork-based O
filament S-MATE
here O
developed O
. O


3D B-APPL
printed I-APPL
parts E-APPL
exhibit O
unique O
characteristics O
, O
such O
as S-MATE
a O
nonplastic O
and O
warm O
touch O
, O
a O
natural O
colour O
and O
the O
release O
of O
a O
pleasant O
odour O
during O
the O
printing B-MANP
process E-MANP
. O


AISI O
316L O
steel S-MATE
was O
tested O
under O
high O
Hertzian O
loads O
at O
different O
temperatures S-PARA
. O


The O
3D B-MANP
printed E-MANP
material O
presents O
higher O
wear B-PRO
resistance E-PRO
. O


The O
triboxides O
present O
the O
same O
chemical B-CONPRI
composition E-CONPRI
. O


The O
material S-MATE
produced O
using O
SLM S-MANP
presents O
a O
thinner O
strain-hardened O
layer S-PARA
. O


The O
3D B-MANP
printed E-MANP
material O
begins O
dynamic S-CONPRI
recrystallization O
at O
higher O
temperatures S-PARA
. O


This O
material S-MATE
is O
also O
suitable O
for O
use O
in O
the O
3D B-MANP
printing E-MANP
of O
metal S-MATE
components.In O
this O
study O
, O
the O
wear S-CONPRI
behavior O
of O
AISI O
316L O
steel S-MATE
produced O
using O
Selective B-MANP
Laser I-MANP
Melting E-MANP
technology O
was O
investigated O
in O
order O
to O
determine O
its O
metallurgical S-APPL
evolution S-CONPRI
under O
high O
Hertzian O
stress S-PRO
. O


The O
results O
were O
compared O
to O
AISI O
316L O
that O
was O
classically O
forged.A O
preliminary O
mechanical S-APPL
and O
microstructural B-CHAR
characterization E-CHAR
was O
carried O
out O
in O
order O
to O
characterize O
the O
material S-MATE
and O
compare O
the O
properties S-CONPRI
of O
3D B-MANP
printed E-MANP
with O
material S-MATE
that O
has O
been O
forged O
. O


The O
wear S-CONPRI
rates O
were O
then O
calculated O
using O
a O
stylus B-MACEQ
profilometer E-MACEQ
. O


The O
wear S-CONPRI
tracks O
were O
characterized O
in O
the O
top O
view O
to O
determine O
the O
composition S-CONPRI
of O
the O
triboxide O
layer S-PARA
using O
SEM-EDXS O
and O
Raman B-CHAR
spectroscopy E-CHAR
. O


Cross B-CONPRI
sections E-CONPRI
of O
the O
samples S-CONPRI
were O
then O
used O
to O
conduct O
SEM S-CHAR
analysis O
in O
order O
to O
determine O
the O
thickness O
of O
the O
tribolayer O
and O
the O
characteristics O
of O
the O
strain S-PRO
hardened S-MANP
layer O
. O


EBSD S-CHAR
mapping O
was O
also O
conducted O
on O
the O
same O
samples S-CONPRI
to O
determine O
the O
regions O
in O
which O
recrystallization S-CONPRI
had O
taken O
place.The O
results O
showed O
that O
the O
3D B-MANP
printed E-MANP
material O
has O
lower O
wear S-CONPRI
rates O
than O
the O
forged O
material S-MATE
, O
due O
to O
the O
finer B-FEAT
microstructure E-FEAT
of O
the O
material S-MATE
produced O
by O
3D S-CONPRI
. O


In O
addition O
, O
the O
triboxides O
formed O
on O
the O
additively B-MANP
manufactured E-MANP
component O
were O
finer O
, O
although O
the O
nature O
of O
the O
oxide S-MATE
was O
the O
same O
. O


The O
3D B-MANP
printed E-MANP
material O
showed O
a O
dynamic S-CONPRI
recrystallization O
at O
600 O
°C O
, O
while O
the O
forged O
material S-MATE
started O
to O
recrystallize O
at O
200 O
°C O
. O


Medium O
powered O
LPBF S-MANP
machines O
can O
process S-CONPRI
pure O
Cu S-MATE
to O
an O
acceptable O
level O
. O


Resistivity S-PRO
of O
as-built O
Cu S-MATE
increases O
by O
33 O
% O
depending O
on O
build B-PARA
orientation E-PARA
. O


Resistivity S-PRO
can O
be S-MATE
reduced O
by O
over O
50 O
% O
from O
as-built O
conditions O
via O
heat B-MANP
treatment E-MANP
. O


Electrical B-CHAR
resistivity E-CHAR
values O
once O
heat S-CONPRI
treated O
are O
lower O
than O
AlSi10Mg S-MATE
values O
. O


Pure O
copper S-MATE
is O
an O
excellent O
thermal O
and O
electrical S-APPL
conductor S-MATE
, O
however O
, O
attempts O
to O
process S-CONPRI
it O
with O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
have O
seen O
various O
levels O
of O
success O
. O


While O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
has O
successfully O
processed S-CONPRI
pure O
copper S-MATE
to O
high O
densities O
, O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
has O
had O
difficulties O
achieving O
the O
same O
results O
without O
the O
use O
of O
very O
high O
power S-PARA
lasers O
. O


This O
requirement O
has O
hampered O
the O
exploration O
of O
using O
LPBF S-MANP
with O
pure O
copper S-MATE
as S-MATE
most O
machines S-MACEQ
are O
equipped O
with O
lasers O
that O
have O
low O
to O
medium O
laser B-PARA
power E-PARA
densities O
. O


In O
this O
work O
, O
experiments O
were O
conducted O
to O
process S-CONPRI
pure O
copper S-MATE
with O
a O
200 O
W O
LPBF S-MANP
machine O
with O
a O
small O
laser S-ENAT
spot O
diameter S-CONPRI
resulting O
in O
an O
above O
average S-CONPRI
laser O
power S-PARA
density S-PRO
in O
order O
to O
maximise O
density S-PRO
and O
achieve O
low O
electrical B-CHAR
resistivity E-CHAR
. O


The O
effects O
of O
initial O
build B-PARA
orientation E-PARA
and O
post O
heat B-MANP
treatment E-MANP
were O
also O
investigated O
to O
explore O
their O
influence O
on O
electrical B-CHAR
resistivity E-CHAR
. O


It O
was O
found O
that O
despite O
issues O
with O
high O
porosity S-PRO
, O
heat S-CONPRI
treated O
specimens O
had O
a O
lower O
electrical B-CHAR
resistivity E-CHAR
than O
other O
common O
AM B-MATE
materials E-MATE
such O
as S-MATE
the O
aluminium B-MATE
alloy I-MATE
AlSi10Mg E-MATE
. O


By O
conducting O
these O
tests O
, O
it O
was O
found O
that O
despite O
having O
approximately O
double O
the O
resistivity S-PRO
of O
commercially O
pure O
copper S-MATE
, O
the O
resistivity S-PRO
was O
sufficiently O
low O
enough O
to O
demonstrate O
the O
potential O
to O
use O
AM S-MANP
to O
process S-CONPRI
copper S-MATE
suitable O
for O
electrical B-APPL
applications E-APPL
. O


Large O
Area S-PARA
Additive B-MANP
Manufacturing E-MANP
now O
enables O
the O
fabrication S-MANP
of O
structures O
that O
are O
dramatically O
more O
substantial O
than O
those O
produced O
with O
standard S-CONPRI
3D B-MANP
printing E-MANP
. O


As S-MATE
the O
use O
of O
support B-FEAT
structure E-FEAT
is O
generally O
not O
appropriate O
when O
printing O
at O
these O
scales O
, O
understanding O
the O
limits S-CONPRI
of O
overhanging B-FEAT
feature E-FEAT
angles O
is O
necessary O
to O
establish O
the O
economic O
case O
for O
using O
large O
3D B-MANP
printing E-MANP
. O


Additionally O
, O
understanding O
the O
physics S-CONPRI
of O
the O
process S-CONPRI
is O
paramount O
to O
avoiding O
expensive O
failed O
prints O
. O


Rapid O
sequential O
layers O
can O
result O
in O
slumping O
as S-MATE
the O
structure S-CONPRI
retains O
excessive O
heat S-CONPRI
when O
the O
next O
layer S-PARA
is O
printed O
. O


The O
model S-CONPRI
can O
be S-MATE
used O
to O
insert S-MACEQ
additional O
dwell B-PARA
times E-PARA
after O
each O
layer S-PARA
so O
that O
the O
next O
layer S-PARA
of O
printing O
initiates O
after O
the O
previous O
layer S-PARA
is O
sufficiently O
cool O
such O
that O
the O
existing O
structure S-CONPRI
is O
appropriately O
solidified O
. O


Inputs O
to O
the O
model S-CONPRI
include O
the O
feedstock B-MATE
material E-MATE
, O
the O
number O
of O
beads S-CHAR
in O
the O
overhanging O
wall O
, O
the O
angle O
of O
overhang S-PARA
and O
the O
threshold O
of O
failure S-CONPRI
represented O
as S-MATE
out-of-plane O
displacement O
from O
the O
intended O
geometry S-CONPRI
. O


The O
proposed O
thermal O
model S-CONPRI
can O
then O
be S-MATE
used O
with O
slicing S-CONPRI
software O
to O
insert S-MACEQ
pauses O
a O
priori O
, O
or O
can O
be S-MATE
leveraged O
during O
the O
print S-MANP
in O
conjunction O
with O
infrared S-CONPRI
imaging S-APPL
in O
order O
to O
provide O
in B-CONPRI
situ E-CONPRI
process O
control O
to O
improve O
quality S-CONPRI
and O
yield O
. O


Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
as S-MATE
an O
additive B-MANP
manufacturing I-MANP
process E-MANP
can O
fabricate S-MANP
near O
to O
net B-MANP
shape E-MANP
metallic S-MATE
components S-MACEQ
directly O
from O
Computer B-ENAT
aided I-ENAT
design E-ENAT
models O
, O
which O
may O
be S-MATE
difficult O
to O
fabricate S-MANP
using O
conventional B-MANP
manufacturing E-MANP
methods O
. O


In O
this O
work O
, O
the O
powdered B-MATE
metals E-MATE
used O
as S-MATE
the O
raw B-MATE
material E-MATE
feedstock S-MATE
in O
the O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
process S-CONPRI
were O
studied O
. O


SLM B-MANP
manufacturing E-MANP
processibility O
of O
nickel S-MATE
based O
super B-MATE
alloy E-MATE
, O
powders S-MATE
related O
to O
the O
particle B-CONPRI
Size I-CONPRI
Distribution E-CONPRI
( O
PSD O
) O
, O
flow O
ability O
, O
mechanical B-CONPRI
properties E-CONPRI
and O
microstructures S-MATE
was O
investigated O
. O


Different O
powder S-MATE
characterisation O
methods O
were O
also O
investigated O
to O
establish O
which O
might O
be S-MATE
most O
useful O
for O
SLM S-MANP
application O
. O


Three O
different O
Inconel B-MATE
625 E-MATE
( O
IN625 O
) O
powder B-MACEQ
feedstock E-MACEQ
materials S-CONPRI
have O
been O
accounted O
for O
this O
study O
. O


Firstly O
, O
three O
different O
IN625 O
powders S-MATE
were O
fully O
characterised O
for O
chemical B-CONPRI
composition E-CONPRI
, O
particle B-CONPRI
size I-CONPRI
distribution E-CONPRI
and O
flow O
ability O
using O
different O
types O
of O
characterisation O
techniques O
. O


It O
has O
been O
found O
that O
the O
presence O
of O
any O
significant O
proportion O
of O
powder B-MATE
particles E-MATE
smaller O
than O
10-μm O
diameter S-CONPRI
, O
leads O
to O
severe O
agglomeration O
and O
make O
SLM S-MANP
processing O
difficult O
. O


Secondly O
, O
coupons O
were O
manufactured S-CONPRI
using O
SLM S-MANP
from O
each O
powder S-MATE
with O
different O
process B-CONPRI
parameter E-CONPRI
, O
which O
were O
analysed O
for O
porosity S-PRO
and O
mechanical B-CONPRI
behaviour E-CONPRI
. O


Next O
, O
the O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
, O
electron O
back O
scattering O
diffraction S-CHAR
( O
EBSD S-CHAR
) O
are O
employed O
to O
investigate O
the O
microstructures S-MATE
. O


Finally O
, O
data S-CONPRI
analysis O
was O
employed O
on O
the O
data S-CONPRI
collected O
by O
metal B-MATE
powders E-MATE
characterization O
, O
SLM B-MANP
manufacturing E-MANP
, O
SEM/EBSD O
study O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
IN625 O
. O


It O
has O
been O
observed O
that O
the O
powder S-MATE
characteristics O
, O
as S-MATE
well O
as S-MATE
SLM O
process B-CONPRI
parameters E-CONPRI
influences O
on O
the O
quality S-CONPRI
of O
the O
IN625 O
fabricated S-CONPRI
. O


Binder B-MANP
jetting I-MANP
additive I-MANP
manufacturing E-MANP
( O
BJAM O
) O
is O
a O
comparatively O
low-cost O
process S-CONPRI
that O
enables O
manufacturing S-MANP
of O
complex O
and O
customizable O
metal S-MATE
parts O
. O


This O
process S-CONPRI
is O
applied O
to O
low-cost O
water-atomized O
iron S-MATE
powder O
with O
the O
goal O
of O
understanding O
the O
effects O
of O
printing O
parameters S-CONPRI
and O
sintering S-MANP
schedule O
on O
maximizing O
the O
green O
and O
sintered S-MANP
densities O
of O
manufactured S-CONPRI
samples O
, O
respectively O
. O


The O
powder S-MATE
is O
characterized O
by O
using O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
and O
particle S-CONPRI
size O
analysis O
( O
Camsizer O
X2 O
) O
. O


In O
the O
AM B-MANP
process E-MANP
, O
the O
effects O
of O
powder S-MATE
compaction S-MANP
, O
layer B-PARA
thickness E-PARA
, O
and O
liquid B-MATE
binder E-MATE
level O
on O
green B-PRO
part E-PRO
density S-PRO
are O
investigated O
. O


Post-process B-CONPRI
heat E-CONPRI
treatment O
is O
applied O
to O
selected O
samples S-CONPRI
, O
and O
suitable O
debinding S-CONPRI
parameters O
are O
studied O
by O
using O
thermo-gravimetric O
analysis O
( O
TGA S-CHAR
) O
. O


Sintering S-MANP
at O
various O
temperatures S-PARA
and O
durations O
results O
in O
densities O
of O
up O
to O
91.3 O
% O
. O


Image S-CONPRI
processing O
of O
x-ray B-CHAR
computed I-CHAR
tomography E-CHAR
( O
μCT O
) O
scans O
of O
the O
samples S-CONPRI
reveals O
that O
porosity S-PRO
distribution S-CONPRI
is O
affected O
by O
powder S-MATE
spreading O
, O
and O
gradients O
in O
pore S-PRO
distribution S-CONPRI
in O
the O
sample S-CONPRI
are O
largely O
reduced O
after O
sintering S-MANP
. O


The O
results O
indicate O
that O
the O
sintering S-MANP
temperature O
and O
time O
might O
be S-MATE
tailored O
to O
achieve O
target O
densities O
anywhere O
in O
the O
range S-PARA
of O
64 O
% O
and O
91 O
% O
, O
with O
possibly O
higher O
densities O
by O
increasing O
sintering B-PARA
time E-PARA
. O


Binder-jetting O
, O
an O
additive B-MANP
manufacturing I-MANP
process E-MANP
and O
relatively O
low-cost B-PRO
technology E-PRO
is O
utilized O
to O
deposit O
complex-shaped S-CONPRI
thin O
ceramic B-MACEQ
cores E-MACEQ
. O


In O
this O
study O
, O
for O
enhancing O
sintering S-MANP
quality S-CONPRI
, O
a O
decomposable O
binder S-MATE
was O
prepared O
using O
binder-jetting O
by O
dispersing O
different O
contents O
of O
zirconium S-MATE
basic O
carbonate O
( O
ZBC O
) O
into O
an O
inorganic O
colloidal B-MATE
binder E-MATE
. O


The O
effects O
of O
different O
ZBC O
contents O
on O
the O
printability S-PARA
of O
the O
binder S-MATE
and O
the O
performance S-CONPRI
characteristics O
of O
the O
ceramic B-MACEQ
cores E-MACEQ
by O
binder-jetting O
were O
investigated O
. O


The O
results O
show O
that O
the O
surface B-PRO
tension E-PRO
of O
the O
binder S-MATE
decreases O
with O
the O
increasing O
of O
ZBC O
contents O
, O
indicating O
that O
the O
addition O
of O
ZBC O
particles S-CONPRI
perturbs O
the O
interaction O
between O
water O
molecules O
. O


The O
presence O
of O
newly O
generated O
ZrO2 S-MATE
particles S-CONPRI
decomposed O
by O
ZBC O
demonstrated O
a O
significant O
effect O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
ceramic B-MACEQ
cores E-MACEQ
. O


The O
sintered S-MANP
density S-PRO
increased O
by O
about O
44 O
% O
, O
the O
bending B-PRO
strength E-PRO
improved O
from O
60 O
to O
79 O
MPa S-CONPRI
, O
and O
linear O
shrinkage S-CONPRI
decreased O
from O
20 O
to O
13 O
% O
after O
sintering S-MANP
at O
1500 O
°C O
as S-MATE
the O
ZBC O
content O
was O
increased O
from O
0 O
to O
35 O
wt O
% O
. O


Purposely O
introduced O
gas S-CONPRI
pores O
in O
wire B-MANP
+ I-MANP
arc I-MANP
additive I-MANP
manufactured E-MANP
titanium S-MATE
( O
WAAM S-MANP
Ti-6Al-4 B-MATE
V E-MATE
) O
. O


Interrupted O
fatigue B-CHAR
testing E-CHAR
with O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
scanning S-CONPRI
at O
intervals O
. O


Changes O
in O
porosity S-PRO
morphology S-CONPRI
observed O
with O
fatigue S-PRO
loading O
cycles O
. O


Cyclic O
stress-strain O
response O
in O
the O
vicinity O
of O
gas S-CONPRI
pores O
calculated O
by O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
. O


Fatigue B-PRO
life E-PRO
predicted O
using O
the O
traditional O
notch S-FEAT
fatigue S-PRO
approach O
. O


Porosity S-PRO
defects S-CONPRI
remain O
a O
challenge O
to O
the O
structural B-PRO
integrity E-PRO
of O
additive B-MANP
manufactured E-MANP
materials O
, O
particularly O
for O
parts O
under O
fatigue S-PRO
loading O
applications O
. O


Although O
the O
wire B-MANP
+ I-MANP
arc I-MANP
additive I-MANP
manufactured E-MANP
Ti-6Al-4 B-MATE
V E-MATE
builds S-CHAR
are O
typically O
fully B-PARA
dense E-PARA
, O
occurrences O
of O
isolated O
pores S-PRO
may O
not O
be S-MATE
completely O
avoided O
due O
to O
feedstock S-MATE
contamination O
. O


This O
study O
used O
contaminated O
wires O
to O
build S-PARA
the O
gauge B-MACEQ
section E-MACEQ
of O
fatigue S-PRO
specimens O
to O
purposely O
introduce O
spherical B-PRO
gas I-PRO
pores E-PRO
in O
the O
size O
range S-PARA
of O
120–250 O
micrometres O
. O


Changes O
in O
the O
defect S-CONPRI
morphology O
were O
monitored O
via O
interrupted O
fatigue B-CHAR
testing E-CHAR
with O
periodic O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
( O
CT S-ENAT
) O
scanning S-CONPRI
. O


Prior O
to O
specimen O
failure S-CONPRI
, O
the O
near O
surface S-CONPRI
pores S-PRO
grew O
by O
approximately O
a O
factor O
of O
2 O
and O
tortuous O
fatigue S-PRO
cracks O
were O
initiated O
and O
propagated O
towards O
the O
nearest O
free B-CONPRI
surface E-CONPRI
. O


Elastic-plastic O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
showed O
cyclic O
plastic B-PRO
deformation E-PRO
at O
the O
pore S-PRO
root O
as S-MATE
a O
result O
of O
stress B-CHAR
concentration E-CHAR
; O
consequently O
for O
an O
applied O
tension-tension O
cyclic B-PRO
stress E-PRO
( O
stress S-PRO
ratio O
0.1 O
) O
, O
the O
local O
stress S-PRO
at O
the O
pore S-PRO
root O
became O
a O
tension-compression O
nature O
( O
local O
stress S-PRO
ratio O
−1.0 O
) O
. O


Fatigue B-PRO
life E-PRO
was O
predicted S-CONPRI
using O
the O
notch S-FEAT
fatigue S-PRO
approach O
and O
validated O
with O
experimental S-CONPRI
test O
results O
. O


Processing-structure-property O
relationships O
in O
material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
are O
complex O
, O
non-linear O
, O
and O
poorly O
understood O
. O


In O
this O
work O
, O
we O
designed S-FEAT
an O
informatics O
workflow S-CONPRI
for O
the O
collection O
of O
high O
pedigree O
data S-CONPRI
from O
each O
stage O
of O
the O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
printing B-MANP
process E-MANP
. O


In O
conjunction O
with O
a O
design B-CONPRI
of I-CONPRI
experiments E-CONPRI
, O
we O
applied O
the O
workflow S-CONPRI
to O
investigate O
the O
influences O
of O
processing O
parameters S-CONPRI
on O
weld B-PRO
strength E-PRO
across O
three O
commercially O
available O
FFF S-MANP
printers O
. O


Environmental O
, O
material S-MATE
, O
and O
print S-MANP
conditions O
that O
may O
impact S-CONPRI
performance O
were O
monitored O
to O
ensure O
that O
relevant O
data S-CONPRI
were O
collected O
in O
a O
consistent O
manner O
. O


Acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
filament S-MATE
was O
used O
to O
print S-MANP
ASTM O
D638-14 O
Type O
V S-MATE
tensile B-MACEQ
bars E-MACEQ
. O


Data S-CONPRI
were O
analyzed O
using O
multivariate S-CONPRI
statistical O
techniques O
, O
including O
principal O
component S-MACEQ
analysis O
. O


The O
magnitude S-PARA
of O
the O
effects O
of O
extrusion S-MANP
temperature O
, O
layer B-PARA
thickness E-PARA
, O
print S-MANP
bed S-MACEQ
temperature O
, O
and O
print S-MANP
speed O
on O
the O
tensile B-PRO
properties E-PRO
of O
the O
final O
print S-MANP
were O
determined O
. O


The O
results O
demonstrated O
that O
printer S-MACEQ
selection O
is O
important O
and O
changes O
the O
impact S-CONPRI
of O
print S-MANP
parameters S-CONPRI
. O


Non-destructive O
dielectric S-MACEQ
imaging O
during O
additive B-MANP
manufacturing E-MANP
. O


3D S-CONPRI
characterization O
of O
relative O
dielectric S-MACEQ
permittivity O
within O
printed O
devices O
. O


Integrated O
, O
in-line O
quality B-CONPRI
control E-CONPRI
technique O
for O
AM B-MANP
processes E-MANP
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
techniques O
are O
used O
increasingly O
for O
the O
direct O
fabrication S-MANP
of O
microwave S-ENAT
devices O
, O
such O
as S-MATE
graded O
index O
lenses O
and O
dielectric S-MACEQ
resonator O
antennas O
, O
which O
have O
spatially-varying O
dielectric S-MACEQ
properties O
( O
i.e O
. O


However O
, O
there O
is O
no O
effective O
method O
to O
characterize O
the O
spatial B-CHAR
distribution E-CHAR
of O
permittivity O
within O
the O
printed O
component S-MACEQ
, O
either O
during O
manufacture S-CONPRI
or O
once O
the O
component S-MACEQ
is O
complete O
. O


Therefore O
it O
is O
not O
possible O
to O
confirm O
the O
extent O
to O
which O
the O
manufactured S-CONPRI
spatial O
distribution S-CONPRI
of O
permittivity O
meets O
the O
intended O
design S-FEAT
. O


We O
report O
the O
integration O
of O
a O
novel O
split O
ring O
resonator S-APPL
( O
SRR O
) O
surface S-CONPRI
mapping O
technique O
directly O
into O
an O
AM B-MANP
process E-MANP
to O
make O
non-destructive O
in-line O
measurements O
of O
the O
local O
relative O
dielectric S-MACEQ
permittivity O
( O
ϵr O
) O
within O
3D B-APPL
objects E-APPL
as O
they O
are O
formed O
. O


We O
then O
reconstruct O
these O
data S-CONPRI
into O
3D S-CONPRI
dielectric O
“ O
images S-CONPRI
” O
of O
the O
printed O
component S-MACEQ
. O


Detailed O
insights O
into O
the O
dielectric S-MACEQ
imaging O
principle O
, O
data S-CONPRI
processing/analysis O
, O
as S-MATE
well O
as S-MATE
limitations O
and O
opportunities O
related O
to O
the O
technique O
are O
described O
. O


The O
work O
aims O
to O
accelerate O
the O
design-make-test O
cycle O
for O
advanced O
microwave S-ENAT
devices O
, O
and O
suggests O
the O
possibility O
for O
real-time O
, O
closed-loop B-MACEQ
control E-MACEQ
of O
dielectric S-MACEQ
properties O
during O
AM S-MANP
. O


Variation S-CONPRI
of O
texture S-FEAT
in O
Ti-6Al-4V S-MATE
samples S-CONPRI
produced O
by O
three O
different O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
has O
been O
studied O
by O
neutron S-CONPRI
time-of-flight O
( O
TOF O
) O
diffraction S-CHAR
. O


The O
investigated O
AM B-MANP
processes E-MANP
were O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
, O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
and O
laser S-ENAT
metal O
wire O
deposition S-CONPRI
( O
LMwD O
) O
. O


Additionally O
, O
for O
the O
LMwD O
material S-MATE
separate O
measurements O
were O
done O
on O
samples S-CONPRI
from O
the O
top O
and O
bottom O
pieces O
in O
order O
to O
detect O
potential O
texture S-FEAT
variations O
between O
areas S-PARA
close O
to O
and O
distant O
from O
the O
supporting O
substrate S-MATE
in O
the O
manufacturing B-MANP
process E-MANP
. O


Electron O
backscattered O
diffraction S-CHAR
( O
EBSD S-CHAR
) O
was O
also O
performed O
on O
material S-MATE
parallel O
and O
perpendicular O
to O
the O
build B-PARA
direction E-PARA
to O
characterize O
the O
microstructure S-CONPRI
. O


Understanding O
the O
context O
of O
texture S-FEAT
for O
AM B-MANP
processes E-MANP
is O
of O
significant O
relevance O
as S-MATE
texture O
can O
be S-MATE
linked O
to O
anisotropic S-PRO
mechanical O
behavior O
. O


It O
was O
found O
that O
LMwD O
had O
the O
strongest O
texture S-FEAT
while O
the O
two O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
processes S-CONPRI
EBM S-MANP
and O
SLM S-MANP
displayed O
comparatively O
weaker O
texture S-FEAT
. O


The O
texture S-FEAT
of O
EBM S-MANP
and O
SLM S-MANP
was O
of O
the O
same O
order O
of O
magnitude S-PARA
. O


These O
results O
correlate O
well O
with O
previous O
microstructural S-CONPRI
studies O
. O


Additionally O
, O
texture S-FEAT
variations O
were O
found O
in O
the O
LMwD O
sample S-CONPRI
, O
where O
the O
part O
closest O
to O
the O
substrate S-MATE
featured O
stronger O
texture S-FEAT
than O
the O
corresponding O
top O
part O
. O


The O
crystal O
direction O
of O
the O
α O
phase S-CONPRI
with O
the O
strongest O
texture S-FEAT
component S-MACEQ
was O
[ O
112¯3 O
] O
. O


Carries O
out O
in B-CONPRI
situ E-CONPRI
high O
speed O
imaging S-APPL
of O
polymer B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
. O


Measures O
thermal B-PRO
conductivity E-PRO
of O
built O
part O
as S-MATE
a O
function O
of O
process B-CONPRI
parameters E-CONPRI
. O


Develops O
correlation O
between O
process S-CONPRI
, O
microstructure S-CONPRI
and O
thermal B-CONPRI
properties E-CONPRI
. O


Results O
show O
strong O
dependence O
of O
thermal B-CONPRI
property E-CONPRI
on O
raster O
speed O
& O
layer B-PARA
height E-PARA
. O


Results O
may O
be S-MATE
helpful O
for O
process B-CONPRI
optimization E-CONPRI
to O
obtain O
novel O
, O
functional O
parts O
. O


Additive B-MANP
manufacturing E-MANP
has O
gained O
significant O
research S-CONPRI
attention O
due O
to O
multiple O
advantages O
over O
traditional B-MANP
manufacturing E-MANP
technologies S-CONPRI
. O


A O
fundamental O
understanding O
of O
the O
relationships O
between O
process B-CONPRI
parameters E-CONPRI
, O
microstructure S-CONPRI
and O
functional O
properties S-CONPRI
of O
built O
parts O
is O
critical O
for O
optimizing O
the O
additive B-MANP
manufacturing I-MANP
process E-MANP
and O
building O
parts O
with O
desired O
properties S-CONPRI
. O


This O
is O
also O
critical O
for O
a O
multi-functional O
part O
where O
the O
process S-CONPRI
needs O
to O
be S-MATE
optimized O
with O
respect O
to O
disparate O
performance S-CONPRI
requirements O
such O
as S-MATE
mechanical O
strength S-PRO
and O
thermal B-PRO
conductivity E-PRO
. O


This O
paper O
presents O
in B-CONPRI
situ E-CONPRI
high O
speed O
imaging S-APPL
and O
build-direction O
thermal B-PRO
conductivity E-PRO
measurements O
of O
polymer B-MANP
extrusion E-MANP
based O
additively B-MANP
manufactured E-MANP
parts O
in O
order O
to O
understand O
the O
effect O
of O
process B-CONPRI
parameters E-CONPRI
such O
as S-MATE
raster O
speed O
, O
infill B-PARA
percentage E-PARA
and O
layer B-PARA
height E-PARA
on O
build-direction O
thermal B-PRO
conductivity E-PRO
. O


Measurements O
of O
thermal B-PRO
conductivity E-PRO
using O
a O
one-dimensional O
heat B-CONPRI
flux E-CONPRI
method O
are O
correlated S-CONPRI
with O
in B-CONPRI
situ E-CONPRI
process O
images S-CONPRI
obtained O
from O
a O
high O
speed O
camera S-MACEQ
as S-MATE
well O
as S-MATE
cross O
section O
images S-CONPRI
of O
the O
built O
part O
. O


Results O
indicate O
strong O
dependence O
of O
build-direction O
thermal B-PRO
conductivity E-PRO
on O
raster O
speed O
, O
layer B-PARA
thickness E-PARA
and O
infill B-PARA
percentage E-PARA
, O
which O
is O
corroborated O
by O
high O
speed O
imaging S-APPL
of O
the O
printing B-MANP
process E-MANP
at O
different O
values O
of O
these O
process B-CONPRI
parameters E-CONPRI
. O


Key O
trade-offs O
between O
process S-CONPRI
throughput O
and O
thermal B-CONPRI
properties E-CONPRI
are O
also O
identified O
. O


In O
addition O
to O
enhancing O
our O
fundamental O
understanding O
of O
polymer B-MANP
extrusion E-MANP
based O
additive B-MANP
manufacturing E-MANP
and O
its O
influence O
on O
thermal B-CONPRI
properties E-CONPRI
of O
built O
parts O
, O
results O
presented O
here O
may O
facilitate O
process B-CONPRI
optimization E-CONPRI
towards O
parts O
with O
desired O
thermal O
and O
multi-functional O
properties S-CONPRI
. O


Lightweight S-CONPRI
design S-FEAT
is O
an O
area S-PARA
of O
mechanical B-APPL
engineering E-APPL
that O
becomes O
increasingly O
important O
in O
many O
industries S-APPL
, O
as S-MATE
they O
pursue O
reduced O
mass O
and O
more O
efficient O
parts O
. O


A O
special O
class O
of O
materials S-CONPRI
for O
load-bearing S-FEAT
structures O
are O
metallic S-MATE
cellular B-MATE
materials E-MATE
with O
cubic O
unit B-CONPRI
cells E-CONPRI
, O
which O
can O
be S-MATE
manufactured O
conveniently O
through O
laser B-CONPRI
beam E-CONPRI
melting O
( O
LBM O
) O
. O


Such O
materials S-CONPRI
exhibit O
a O
rather O
complex O
microstructure S-CONPRI
and O
can O
be S-MATE
analysed O
using O
analytical O
and O
numerical O
methods O
wherein O
the O
determination O
of O
properties S-CONPRI
such O
as S-MATE
relative O
density S-PRO
, O
effective O
elastic B-PRO
and I-PRO
yield I-PRO
strength E-PRO
properties O
is O
of O
special O
interest O
. O


This O
paper O
addresses O
closed-form O
analytical O
methods O
based O
on O
beam S-MACEQ
theories O
for O
the O
determination O
of O
the O
effective O
properties S-CONPRI
of O
additively B-MANP
manufactured E-MANP
microstructures O
such O
as S-MATE
lattices O
, O
and O
a O
comparison O
with O
experimental S-CONPRI
results O
[ O
1 O
] O
, O
[ O
2 O
] O
which O
leads O
to O
excellent O
agreements O
for O
relative B-PRO
densities E-PRO
lower O
than O
40 O
% O
, O
although O
results O
reveal O
a O
great O
dependency O
on O
the O
manufacturing S-MANP
strategy O
. O


Lastly O
, O
a O
classification S-CONPRI
concerning O
the O
topology S-CONPRI
of O
the O
cellular O
units O
is O
presented O
as S-MATE
well O
in O
order O
to O
help O
the O
engineer O
choose O
appropriate O
geometries S-CONPRI
for O
specific O
application O
purposes O
. O


In O
conclusion O
, O
this O
structural O
concept O
may O
be S-MATE
applied O
in O
many O
fields O
such O
as S-MATE
bioengineering O
and O
in O
functional B-MATE
graded I-MATE
materials E-MATE
as S-MATE
they O
are O
applied O
in O
lightweight S-CONPRI
engineering S-APPL
. O


Polymeric O
Pellet-Based O
Additive B-MANP
Manufacturing E-MANP
( O
PPBAM O
) O
systems O
are O
increasing O
in O
the O
field O
of O
3D B-MANP
printing E-MANP
as O
a O
result O
of O
the O
evolution S-CONPRI
of O
additive B-ENAT
technologies E-ENAT
as O
their O
development O
process S-CONPRI
consolidates O
and O
expands O
. O


New O
opportunities O
for O
industrial S-APPL
integration O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
are O
identified O
, O
including O
AM S-MANP
of O
large O
polymeric O
parts O
. O


The O
PPBAM O
process S-CONPRI
consists O
of O
adapting O
a O
pellet-fed O
extrusion S-MANP
mechanism O
to O
a O
displacement O
system O
, O
either O
a O
Cartesian O
mechanism S-CONPRI
or O
a O
robotic B-MACEQ
arm E-MACEQ
system O
, O
building O
parts O
in O
a O
multi-layered O
approach O
. O


This O
use O
is O
justified O
by O
the O
extruded S-MANP
filament O
sizes O
required O
and O
the O
material S-MATE
costs O
when O
facing S-MANP
large-format O
prints O
. O


In O
this O
article O
, O
a O
pellet S-CONPRI
extrusion S-MANP
based O
printer S-MACEQ
prototype O
is O
presented O
together O
with O
a O
case B-CONPRI
study E-CONPRI
. O


The O
case B-CONPRI
study E-CONPRI
consists O
of O
the O
development O
of O
a O
two O
cubic O
meter S-MANS
capacity S-CONPRI
plastic O
part O
for O
the O
naval O
industry S-APPL
with O
a O
topology B-FEAT
optimization E-FEAT
design S-FEAT
approach O
and O
material S-MATE
selection O
and O
validation B-CONPRI
methodology E-CONPRI
for O
a O
large-volume O
pellet S-CONPRI
based O
extrusion S-MANP
system O
. O


Two O
functional B-CONPRI
prototypes E-CONPRI
were O
developed O
with O
the O
selected O
materials S-CONPRI
from O
the O
explained O
methodology S-CONPRI
a O
PLA S-MATE
and O
a O
flame B-MATE
retardant E-MATE
ABS S-MATE
, O
and O
post O
processed S-CONPRI
to O
full O
fill O
the O
actual O
product´s O
specifications S-PARA
. O


The O
first O
report O
on O
the O
fatigue S-PRO
behavior O
of O
additively O
manfacutred O
( O
AM S-MANP
) O
biodegradable O
porous S-PRO
Mg B-MATE
alloy E-MATE
( O
WE43 O
) O
and O
how O
it O
is O
affected O
by O
biodegradation O
. O


Biodegradation O
decreased O
the O
fatigue B-PRO
strength E-PRO
of O
the O
porous B-MATE
material E-MATE
from O
30 O
% O
to O
20 O
% O
of O
its O
yield B-PRO
strength E-PRO
. O


Moreover O
, O
cyclic B-PRO
loading E-PRO
significantly O
increased O
its O
biodegradation O
rate O
. O


The O
mechanistic O
aspects O
of O
how O
biodegradation O
and O
cyclic B-PRO
loading E-PRO
interacted O
with O
each O
other O
on O
both O
micro O
and O
macro B-CONPRI
scales E-CONPRI
were O
revealed O
. O


Additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
biodegradable B-MATE
metals E-MATE
with O
topologically S-CONPRI
ordered O
porous S-PRO
structures O
hold O
unprecedented O
promise O
as S-MATE
potential O
bone S-BIOP
substitutes O
. O


There O
is O
, O
however O
, O
no O
information O
available O
in O
the O
literature O
regarding O
their O
mechanical S-APPL
performance O
under O
cyclic B-PRO
loading E-PRO
or O
the O
interactions O
between O
biodegradation O
and O
cyclic B-PRO
loading E-PRO
. O


We O
therefore O
used O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
to O
fabricate S-MANP
porous O
magnesium B-MATE
alloy E-MATE
( O
WE43 O
) O
scaffolds S-FEAT
based O
on O
diamond S-MATE
unit O
cells S-APPL
. O


The O
microstructure S-CONPRI
of O
the O
resulting O
material S-MATE
was O
examined O
using O
electron O
back-scattered O
diffraction S-CHAR
, O
scanning B-CHAR
transmission I-CHAR
electron I-CHAR
microscopy E-CHAR
, O
and O
X-ray B-CHAR
diffraction E-CHAR
. O


The O
fatigue S-PRO
behaviors O
of O
the O
material S-MATE
in O
air O
and O
in O
revised O
simulated O
body O
fluid S-MATE
( O
r-SBF O
) O
were O
evaluated O
and O
compared O
. O


Biodegradation O
decreased O
the O
fatigue B-PRO
strength E-PRO
of O
the O
porous B-MATE
material E-MATE
from O
30 O
% O
to O
20 O
% O
of O
its O
yield B-PRO
strength E-PRO
. O


Moreover O
, O
cyclic B-PRO
loading E-PRO
significantly O
increased O
its O
biodegradation O
rate O
. O


The O
mechanistic O
aspects O
of O
how O
biodegradation O
and O
cyclic B-PRO
loading E-PRO
interacted O
with O
each O
other O
on O
different O
scales O
were O
revealed O
as S-MATE
well O
. O


In O
addition O
, O
dislocations S-CONPRI
became O
more O
tangled O
after O
the O
fatigue B-CHAR
tests E-CHAR
. O


On O
the O
macro-scale O
, O
cracks O
preferred O
initiating O
at O
the O
strut S-MACEQ
junctions S-APPL
where O
tensile B-PRO
stress E-PRO
concentrations O
were O
present O
, O
as S-MATE
revealed O
by O
the O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
of O
the O
porous B-MATE
material E-MATE
under O
compressive B-PRO
loading E-PRO
. O


Further O
improvements O
in O
the O
biodegradation-affected O
fatigue S-PRO
performance O
of O
the O
AM S-MANP
porous O
Mg B-MATE
alloy E-MATE
may O
therefore O
be S-MATE
realized O
by O
optimizing O
both O
the O
topological B-FEAT
design E-FEAT
of O
the O
porous S-PRO
structure O
and O
the O
laser-processing O
parameters S-CONPRI
that O
determine O
the O
microstructure S-CONPRI
of O
the O
SLM S-MANP
porous B-MATE
material E-MATE
. O


Additive B-MANP
manufacturing E-MANP
workflow O
was O
employed O
for O
fabrication S-MANP
of O
patient-specific O
fracture S-CONPRI
fixation O
implants S-APPL
. O


Orthotropic S-MATE
material B-CONPRI
properties E-CONPRI
of O
AM S-MANP
implants O
along O
with O
their O
biomechanical S-APPL
behavior O
were O
investigated O
using O
experimental S-CONPRI
and O
computational B-ENAT
methods E-ENAT
. O


medial O
fracture S-CONPRI
gap O
displacement O
) O
by O
47.2 O
% O
and O
risk O
of O
screw S-MACEQ
cut-out O
by O
14.6 O
% O
when O
compared O
to O
the O
conventional O
plate O
design S-FEAT
. O


Recent O
advancements O
in O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
have O
motivated O
researchers O
to O
consider O
this O
fabrication S-MANP
technique O
as S-MATE
a O
solution S-CONPRI
for O
challenges O
in O
patient-specific O
orthopaedic S-APPL
needs O
. O


Although O
there O
is O
an O
increasing O
trend S-CONPRI
in O
the O
applications O
of O
AM S-MANP
in O
medical S-APPL
fields O
, O
there O
is O
a O
critical O
need O
to O
understand O
the O
biomechanical S-APPL
performance O
of O
AM S-MANP
implants O
. O


In O
particular O
, O
design S-FEAT
opportunities O
, O
anisotropic B-PRO
material I-PRO
properties E-PRO
and O
resulting O
stability S-PRO
of O
AM S-MANP
implant O
constructs O
for O
large O
bone B-BIOP
defects E-BIOP
such O
as S-MATE
osteosarcoma O
, O
comminuted O
fractures O
and O
infections O
are O
unexplored O
. O


This O
study O
aims O
to O
evaluate O
metal B-MANP
AM E-MANP
for O
complex O
fracture S-CONPRI
fixation O
using O
both O
computational O
and O
experimental S-CONPRI
methods O
. O


In O
addition O
, O
this O
research S-CONPRI
highlights O
the O
role O
of O
AM S-MANP
in O
the O
entire O
workflow S-CONPRI
to O
fabricate S-MANP
metal O
AM S-MANP
fixation O
plates O
for O
treatment O
of O
comminuted O
proximal O
humerus O
fractures O
. O


A O
new O
AM-centric O
patient-specific O
implant S-APPL
design S-FEAT
for O
reducing O
common O
postoperative O
complications O
such O
as S-MATE
varus O
collapse O
and O
screw S-MACEQ
cutout O
is O
investigated O
. O


Biocompatible S-PRO
316L B-MATE
stainless I-MATE
steel E-MATE
specimens O
processed S-CONPRI
in O
laser-powder O
bed B-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
is O
subjected O
to O
tensile B-CHAR
testing E-CHAR
and O
post-hoc O
microhardness S-CONPRI
to O
obtain O
orthotropic S-MATE
material B-CONPRI
properties E-CONPRI
of O
the O
AM S-MANP
implants O
. O


Subsequently O
, O
risk O
of O
screw S-MACEQ
cut-out O
is O
evaluated O
using O
finite B-CHAR
element I-CHAR
modelling E-CHAR
( O
FEM S-CONPRI
) O
of O
AM S-MANP
implant-bone O
constructs O
. O


medial O
fracture S-CONPRI
gap O
displacement O
) O
by O
47.2 O
% O
and O
risk O
of O
screw S-MACEQ
cut-out O
by O
14.6 O
% O
when O
compared O
to O
the O
conventional O
plate O
design S-FEAT
. O


Findings O
from O
this O
study O
can O
be S-MATE
extended O
to O
other O
patient O
anatomy O
, O
loading O
conditions O
, O
and O
AM B-MANP
processes E-MANP
. O


The O
feasibility S-CONPRI
of O
a O
hybrid O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
method O
combining O
material B-MANP
extrusion E-MANP
and O
powder B-MANP
bed I-MANP
binder I-MANP
jetting E-MANP
( O
PBBJ O
) O
techniques O
for O
fabrication S-MANP
of O
structures O
made O
of O
silicone S-MATE
( O
polysiloxane O
) O
is O
investigated O
in O
this O
paper O
. O


A O
full O
factorial O
experimental B-CONPRI
design E-CONPRI
was O
conducted O
to O
maximize O
the O
geometrical O
accuracy S-CHAR
of O
the O
parts O
. O


The O
rheological S-PRO
and O
morphological O
properties S-CONPRI
of O
the O
silicone B-MATE
powders E-MATE
, O
the O
thermal O
characteristics O
of O
the O
liquid O
silicone B-MATE
binder E-MATE
, O
and O
mechanical S-APPL
characterization O
the O
additively B-MANP
manufactured E-MANP
parts O
are O
reported O
. O


Using O
this O
hybrid O
AM S-MANP
method O
, O
porous S-PRO
cylindrical S-CONPRI
structures O
( O
5 O
mm S-MANP
diameter S-CONPRI
( O
D O
) O
× O
3 O
mm S-MANP
height O
( O
H O
) O
) O
with O
potential O
applications O
in O
biomedical B-APPL
industry E-APPL
were O
additively B-MANP
manufactured E-MANP
. O


The O
final O
structures O
are O
composed O
of O
∼60 O
% O
silicone B-MATE
powder E-MATE
, O
∼ O
30 O
% O
silicone B-MATE
binder E-MATE
, O
and O
< O
10 O
% O
air O
voids S-CONPRI
. O


These O
three O
phases O
are O
distributed O
throughout O
the O
structure S-CONPRI
in O
a O
non-uniform O
fashion S-CONPRI
. O


Powder B-MANP
bed I-MANP
binder I-MANP
jetting I-MANP
additive I-MANP
manufacturing E-MANP
was O
used O
for O
the O
first O
time O
to O
produce O
porous S-PRO
silicone O
( O
polysiloxane O
) O
structures.Download O
: O
Download O
high-res B-CONPRI
image E-CONPRI
( O
285 O
Additive B-MANP
manufacturing E-MANP
of O
soft O
magnetic O
materials S-CONPRI
and O
components S-MACEQ
based O
on O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
offers O
new O
opportunities O
for O
soft O
magnetic O
core S-MACEQ
materials O
in O
efficient O
energy O
converters O
. O


For O
more O
favorable O
material S-MATE
compositions O
like O
FeSi6.7 O
( O
strategy O
1 O
) O
with O
larger O
electrical B-CHAR
resistivity E-CHAR
and O
close-to-zero O
magnetostriction S-PRO
a O
maximum O
permeability S-PRO
of O
μmax O
= O
31,000 O
, O
minimum O
coercivity O
of O
Hc O
= O
16 O
A/m O
and O
hysteresis S-PRO
losses O
of O
0.7 O
W/kg O
at O
1 O
T O
and O
50 O
Hz O
have O
been O
realized O
. O


Feasibility S-CONPRI
, O
functionality O
and O
potential O
of O
the O
different O
strategies O
( O
and O
combinations O
thereof O
) O
are O
discussed O
based O
on O
first O
prototypes S-CONPRI
and O
supporting O
simulations S-ENAT
. O


The O
results O
are O
compared O
to O
conventional O
electrical S-APPL
steel O
and O
SMC O
( O
soft O
magnetic O
composites S-MATE
) O
. O


This O
work O
investigates S-CONPRI
the O
feasibility S-CONPRI
of O
a O
binderless O
, O
extrusion-based O
additive B-MANP
manufacturing E-MANP
approach O
to O
fabricate S-MANP
alumina S-MATE
( O
Al2O3 S-MATE
) O
parts O
from O
nanopowder O
. O


Traditional O
manufacture S-CONPRI
of O
ceramics S-MATE
with O
subtractive S-MANP
methods O
is O
limited O
due O
to O
their O
inherent O
hardness S-PRO
and O
brittleness O
, O
inevitably O
leading O
to O
ceramic S-MATE
parts O
with O
less-than-optimal O
geometries S-CONPRI
for O
the O
specific O
application O
. O


With O
an O
additive B-MANP
manufacturing E-MANP
approach O
, O
ceramic S-MATE
parts O
with O
complex O
3D B-FEAT
geometries E-FEAT
, O
including O
overhangs S-PARA
or O
hollow O
enclosures O
, O
become O
possible O
. O


These O
complex O
ceramic S-MATE
parts O
are O
highly O
valuable O
in O
heat B-MACEQ
exchanger E-MACEQ
, O
condenser O
, O
biomedical S-APPL
implant O
, O
chemical O
reactant O
vessel O
, O
and O
electrical S-APPL
isolation O
applications O
. O


This O
research S-CONPRI
employed O
direct O
coagulation S-CONPRI
of O
alumina S-MATE
nanopowder O
slurries O
with O
the O
polyvalent O
salt S-MATE
tri-ammonium O
citrate O
providing O
the O
solidification B-CONPRI
mechanism E-CONPRI
in O
an O
extrusion-based O
printing B-MANP
process E-MANP
. O


The O
viscosity S-PRO
of O
the O
slurries O
was O
adjusted O
from O
∼35 O
Pa-s O
to O
∼1000 O
Pa-s O
by O
adjusting O
pH S-CONPRI
from O
∼9 O
to O
∼4 O
, O
resulting O
in O
a O
paste O
that O
is O
suitable O
for O
extrusion S-MANP
, O
which O
retains O
near-net O
geometry S-CONPRI
. O


It O
was O
shown O
that O
the O
direct O
coagulation S-CONPRI
approach O
can O
be S-MATE
used O
to O
create O
a O
suspension O
with O
tuneable O
flow O
characteristics O
and O
coagulation S-CONPRI
rate O
, O
and O
a O
mechanism S-CONPRI
describing O
the O
process S-CONPRI
was O
proposed O
. O


The O
direct O
coagulation S-CONPRI
printing O
( O
DCP O
) O
method O
is O
described O
in O
detail O
, O
including O
how O
slurry S-MATE
is O
extruded S-MANP
, O
solidified O
, O
and O
printed O
in O
complex B-CONPRI
geometries E-CONPRI
, O
and O
sintered S-MANP
to O
full O
density S-PRO
. O


Parts O
were O
printed O
with O
a O
sintered S-MANP
resolution S-PARA
of O
450 O
μm O
and O
green O
densities O
as S-MATE
high O
as S-MATE
65 O
% O
. O


Mechanical B-CONPRI
properties E-CONPRI
were O
characterized O
with O
a O
comparison O
to O
different O
materials S-CONPRI
and O
methods O
from O
literature O
, O
showing O
hardness S-PRO
and O
flexural O
modulus O
up O
to O
∼1800 O
HV O
and O
400 O
GPa S-PRO
, O
respectively O
. O


Heat B-CONPRI
transfer E-CONPRI
in O
standoff S-MACEQ
region O
between O
nozzle S-MACEQ
tip O
and O
bed S-MACEQ
is O
critical O
. O


Carries O
out O
infrared S-CONPRI
based O
temperature S-PARA
measurement S-CHAR
in O
standoff S-MACEQ
region O
. O


Develops O
analytical O
model S-CONPRI
to O
predict O
temperature S-PARA
distribution S-CONPRI
in O
standoff S-MACEQ
region O
. O


Shows O
good O
agreement O
between O
measurements O
and O
model S-CONPRI
in O
wide O
range S-PARA
of O
parameters S-CONPRI
. O


Contributes O
towards O
accurate S-CHAR
thermal O
design S-FEAT
of O
polymer B-MANP
additive I-MANP
manufacturing E-MANP
. O


Dispensing O
of O
a O
polymer B-MATE
filament E-MATE
above O
its O
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
is O
a O
critical O
step S-CONPRI
in O
several O
polymer-based O
additive B-MANP
manufacturing E-MANP
techniques O
. O


While O
the O
nozzle S-MACEQ
assembly S-MANP
heats O
up O
the O
filament S-MATE
prior O
to O
dispense O
, O
it O
is O
important O
to O
minimize O
cooling S-MANP
down O
of O
the O
filament S-MATE
in O
the O
standoff S-MACEQ
distance O
between O
the O
nozzle S-MACEQ
tip O
and O
bed S-MACEQ
. O


While O
heat B-CONPRI
transfer E-CONPRI
processes O
within O
the O
nozzle S-MACEQ
assembly S-MANP
, O
such O
as S-MATE
filament O
melting S-MANP
, O
and O
on O
the O
bed S-MACEQ
, O
such O
as S-MATE
thermally-driven O
filament-to-filament O
adhesion S-PRO
, O
have O
been O
well O
studied O
, O
there O
is O
a O
lack O
of O
work O
on O
heat B-CONPRI
transfer E-CONPRI
in O
the O
filament S-MATE
in O
the O
standoff S-MACEQ
region O
. O


This O
paper O
presents O
infrared S-CONPRI
thermography O
based O
measurement S-CHAR
of O
temperature S-PARA
distribution S-CONPRI
in O
the O
filament S-MATE
in O
the O
standoff S-MACEQ
region O
, O
and O
an O
analytical O
model S-CONPRI
for O
heat B-CONPRI
transfer E-CONPRI
in O
this O
region O
. O


The O
analytical O
model S-CONPRI
, O
based O
on O
a O
balance O
between O
thermal O
advection O
and O
convective/radiative O
heat S-CONPRI
loss O
predicts O
an O
exponentially O
decaying O
temperature S-PARA
distribution S-CONPRI
, O
the O
nature O
of O
which O
is O
governed O
by O
the O
characteristic O
length O
, O
a O
parameter S-CONPRI
that O
combines O
multiple O
process B-CONPRI
parameters E-CONPRI
such O
as S-MATE
mass O
flowrate O
, O
filament B-PARA
diameter E-PARA
, O
heat B-CONPRI
capacity E-CONPRI
and O
cooling S-MANP
conditions O
. O


Experimental B-CONPRI
data E-CONPRI
in O
a O
wide O
range S-PARA
of O
process B-CONPRI
parameters E-CONPRI
are O
found O
to O
be S-MATE
in O
very O
good O
agreement O
with O
the O
analytical O
model S-CONPRI
. O


The O
thermal O
design B-CONPRI
space E-CONPRI
for O
ensuring O
minimal O
temperature S-PARA
drop O
in O
the O
standoff S-MACEQ
region O
is O
explored O
based O
on O
the O
analytical O
model S-CONPRI
. O


Experimental B-CONPRI
data E-CONPRI
and O
theoretical S-CONPRI
modeling S-ENAT
presented O
here O
improve O
our O
fundamental O
understanding O
of O
heat B-CONPRI
transfer E-CONPRI
in O
polymer B-MANP
additive I-MANP
manufacturing E-MANP
, O
and O
may O
contribute O
towards O
design S-FEAT
tools O
for O
thermal O
optimization S-CONPRI
of O
these O
processes S-CONPRI
. O


A O
complete O
understanding O
of O
processing-structure-property-performance O
relationship O
of O
additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
components S-MACEQ
are O
critical O
from O
an O
application O
standpoint O
. O


Therefore O
, O
in O
the O
current O
investigation O
, O
a O
comprehensive O
microstructural B-CHAR
characterization E-CHAR
and O
mechanical B-CONPRI
properties E-CONPRI
( O
tensile S-PRO
, O
fatigue S-PRO
and O
impact S-CONPRI
toughness O
) O
evaluation O
of O
nickel B-MATE
alloy E-MATE
718 O
AM S-MANP
by O
the O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
technique O
have O
been O
performed O
. O


AM S-MANP
builds O
were O
made O
from O
powders S-MATE
manufactured S-CONPRI
via O
different O
atomization S-MANP
conditions O
. O


Although O
the O
standard S-CONPRI
post-heat O
treatment O
procedure O
led S-APPL
to O
the O
removal O
of O
severe O
interdendritic O
segregation S-CONPRI
both O
grain B-CONPRI
boundary E-CONPRI
and O
intra-grain O
precipitation S-CONPRI
of O
δ O
phase S-CONPRI
occurred O
. O


Regardless O
of O
δ O
phase S-CONPRI
presence O
, O
axial O
fatigue S-PRO
properties O
of O
both O
the O
AM S-MANP
builds O
were O
similar O
to O
design S-FEAT
handbook O
wrought S-CONPRI
fatigue S-PRO
data S-CONPRI
. O


However O
, O
due O
to O
the O
δ O
phase S-CONPRI
, O
impact S-CONPRI
toughness O
properties S-CONPRI
were O
comparable O
to O
the O
wrought B-MATE
material E-MATE
conditions O
that O
exhibited O
δ O
phase S-CONPRI
. O


Fractured O
surfaces S-CONPRI
of O
Charpy O
impact S-CONPRI
samples O
exhibited O
crack B-CONPRI
propagation E-CONPRI
extensively O
along O
the O
boundaries S-FEAT
decorated O
by O
δ O
precipitates S-MATE
. O


Variability S-CONPRI
in O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
additively B-MANP
manufactured E-MANP
metal O
parts O
is O
a O
key O
concern O
for O
their O
application O
in O
service O
. O


One O
of O
the O
parameters S-CONPRI
affecting O
the O
above-mentioned O
property S-CONPRI
is O
solidification S-CONPRI
texture O
which O
is O
driven O
by O
scan B-PARA
patterns E-PARA
and O
other O
process S-CONPRI
variables O
. O


Understanding O
of O
how O
these O
textures O
arise O
in O
the O
AM B-MANP
process E-MANP
can O
provide O
a O
pathway O
to O
control O
these O
features O
which O
ultimately O
decide O
the O
final O
structural O
material B-CONPRI
properties E-CONPRI
. O


In O
this O
work O
, O
a O
Cellular O
Automata O
( O
CA S-MATE
) O
based O
two-dimensional B-CONPRI
microstructure E-CONPRI
model S-CONPRI
is O
formulated O
and O
implemented O
to O
understand O
grain B-CONPRI
evolution E-CONPRI
in O
AM S-MANP
. O


Grain B-CONPRI
evolution E-CONPRI
in O
multilayer O
depositions O
using O
various O
scan B-PARA
patterns E-PARA
in O
Directed B-MANP
Energy I-MANP
Deposition E-MANP
( O
DED S-MANP
) O
, O
Metal S-MATE
Laser S-ENAT
Sintering/Selective O
Laser S-ENAT
Melting O
( O
MLS/SLM O
) O
, O
and O
Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM S-MANP
) O
is O
presented O
and O
qualitatively O
compared O
with O
reported O
literature O
. O


Results O
show O
strong O
correlation O
of O
scan B-PARA
patterns E-PARA
with O
evolving O
grain S-CONPRI
orientations O
. O


Variability S-CONPRI
in O
grain B-PRO
size E-PRO
and O
orientation B-CONPRI
evolution E-CONPRI
during O
SLM S-MANP
and O
EBM S-MANP
processing O
of O
metallic B-MATE
materials E-MATE
showed O
direct O
influence O
by O
exposure S-CONPRI
to O
different O
cooling B-PARA
rates E-PARA
and O
thermal B-PARA
gradients E-PARA
. O


The O
similarities O
between O
the O
simulated O
and O
reported O
results O
lead S-MATE
us O
to O
conclude O
CA S-MATE
based O
modeling S-ENAT
for O
predicting O
grain S-CONPRI
orientation O
and O
size O
in O
metal B-MANP
AM E-MANP
processes O
is O
useful O
for O
prediction S-CONPRI
of O
continuum S-CONPRI
level O
structural O
properties S-CONPRI
at O
global O
and O
local O
length B-CHAR
scales E-CHAR
. O


This O
paper O
presents O
the O
methodology S-CONPRI
and O
findings O
of O
a O
novel O
piece O
of O
research S-CONPRI
with O
the O
purpose O
of O
understanding O
and O
mitigating O
distortion S-CONPRI
caused O
by O
the O
combined O
processes S-CONPRI
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
and O
post O
machining S-MANP
to O
final O
specifications S-PARA
. O


The O
research S-CONPRI
work O
started O
with O
the O
AM S-MANP
building O
of O
a O
stainless B-MATE
steel E-MATE
316 O
L O
industrial S-APPL
impeller O
that O
was O
then O
machined S-MANP
by O
removing O
around O
0.5 O
mm S-MANP
from O
certain O
surfaces S-CONPRI
of O
the O
impeller O
’ O
s S-MATE
blades O
and O
hub O
. O


Distortion S-CONPRI
and O
residual B-PRO
stresses E-PRO
were O
experimentally O
measured.The O
manufacture S-CONPRI
of O
the O
impeller O
by O
AM S-MANP
and O
then O
machining S-MANP
was O
numerically O
simulated O
by O
applying O
the O
finite B-CONPRI
element E-CONPRI
( O
FE S-MATE
) O
method O
. O


Distortion S-CONPRI
and O
residual B-PRO
stresses E-PRO
were O
simulated O
and O
validated O
. O


The O
FE S-MATE
distortion S-CONPRI
was O
then O
used O
in O
a O
numerical O
procedure O
to O
reverse O
distortion S-CONPRI
directions O
in O
order O
to O
produce O
a O
new O
impeller O
with O
mitigated O
distortion S-CONPRI
. O


A O
2-stage O
hybrid B-CONPRI
manufacturing E-CONPRI
supply O
chain O
based O
on O
metal B-MANP
Additive I-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
is O
proposed O
which O
includes O
AM S-MANP
hubs O
, O
Heat B-MANP
Treatment E-MANP
( O
HT O
) O
facilities O
and O
machine S-MACEQ
shops O
. O


p-median O
models O
are O
applied O
to O
identify O
the O
optimal O
location O
for O
metal B-MANP
AM E-MANP
hubs O
in O
the O
U.S. O
that O
would O
serve O
as S-MATE
near-net O
manufacturers O
to O
supply O
processed S-CONPRI
build B-MACEQ
plates E-MACEQ
to O
HT O
facilities O
who O
will O
ship O
it O
to O
machine S-MACEQ
shops O
after O
HT O
. O


Fewer O
number O
of O
heat B-MANP
treatment E-MANP
facilities O
require O
concentrated O
locations O
and O
fewer O
AM S-MANP
hubs O
. O


Hybrid B-CONPRI
Manufacturing E-CONPRI
is O
defined O
as S-MATE
the O
integration O
of O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
, O
specifically O
metal B-MANP
AM E-MANP
, O
with O
traditional B-MANP
manufacturing E-MANP
post-processing S-CONPRI
such O
as S-MATE
heat O
treatment O
and O
machining S-MANP
. O


Hybrid O
AM S-MANP
enables O
Small O
and O
Medium O
Enterprises O
( O
SME O
) O
who O
can O
offer O
post-processing S-CONPRI
services O
to O
integrate O
into O
the O
growing O
AM S-MANP
supply O
chain O
. O


Most O
near-net O
metal B-MANP
AM E-MANP
parts O
require O
heat B-MANP
treatment E-MANP
processes O
( O
e.g O
. O


residual B-PRO
stress E-PRO
relieving/annealing O
) O
before O
machining S-MANP
to O
achieve O
final O
engineering S-APPL
specification O
. O


This O
research B-CONPRI
investigates E-CONPRI
a O
two-stage O
facility O
model S-CONPRI
to O
optimize O
the O
locations O
and O
capacities O
for O
new O
metal B-MANP
AM E-MANP
hubs O
which O
require O
two O
sequential O
post-processing S-CONPRI
services O
: O
heat B-MANP
treatment E-MANP
and O
machining S-MANP
. O


Using O
North O
American O
Industry S-APPL
Classification S-CONPRI
System O
( O
NAICS O
) O
data S-CONPRI
for O
machine S-MACEQ
shops O
and O
heat B-MANP
treatment E-MANP
facilities O
in O
the O
U.S. O
, O
a O
p-median O
location O
model S-CONPRI
is O
used O
to O
determine O
the O
optimal O
locations O
for O
AM S-MANP
hub O
centers O
based O
on O
: O
( O
1 O
) O
geographical O
data S-CONPRI
, O
( O
2 O
) O
demand O
and O
( O
3 O
) O
fixed O
and O
operational O
costs O
of O
hybrid-AM O
processing O
. O


Results O
from O
this O
study O
have O
identified O
: O
( O
a O
) O
candidate O
US O
counties O
to O
locate O
metal B-MANP
AM E-MANP
hubs O
, O
( O
b S-MATE
) O
total O
cost O
( O
fixed O
, O
operational O
and O
transportation O
) O
, O
( O
c S-MATE
) O
capacity S-CONPRI
utilization O
of O
the O
AM S-MANP
hubs O
and O
( O
d O
) O
demand O
assignments O
across O
machine S-MACEQ
shops O
– O
heat B-MANP
treatment E-MANP
facilities O
– O
AM S-MANP
hubs O
. O


It O
was O
found O
that O
2-stage O
p-Median O
model S-CONPRI
identified O
22 O
A O
M O
hub O
locations O
as S-MATE
the O
initial O
sites O
for O
AM S-MANP
hubs O
which O
grows O
to O
35 O
A O
M O
hubs O
as S-MATE
demand O
increases O
. O


It O
was O
also O
found O
that O
relatively O
fewer O
number O
of O
heat B-MANP
treatment E-MANP
facilities O
than O
machine S-MACEQ
shops O
resulted O
in O
a O
more O
concentrated O
locations O
of O
AM S-MANP
hubs O
. O


In O
addition O
, O
transportation O
costs O
were O
not O
adversely O
affected O
by O
the O
inclusion S-MATE
of O
as-build O
plates O
and O
showed O
that O
including O
heat B-MANP
treatment E-MANP
facilities O
as S-MATE
part O
of O
the O
hybrid O
AM S-MANP
supply O
chain O
will O
be S-MATE
mutually O
beneficial O
to O
all O
stakeholders O
of O
metal S-MATE
hybrid O
AM S-MANP
supply O
chain O
, O
i.e O
. O


AM S-MANP
→ O
Heat B-MANP
treatment E-MANP
→ O
Machining S-MANP
. O


Wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
is O
a O
promising O
direct B-MANP
energy I-MANP
deposition E-MANP
technology O
to O
produce O
high-value O
material S-MATE
components S-MACEQ
with O
a O
low O
buy-to-fly O
ratio O
. O


WAAM S-MANP
is O
able O
to O
produce O
thin-walled O
structures O
of O
large O
scale O
and O
also O
truss S-MACEQ
structures O
without O
any O
support S-APPL
. O


To O
manufacture S-CONPRI
complex O
parts O
, O
process S-CONPRI
reliability O
and O
repeatability S-CONPRI
are O
still O
a O
necessity O
and O
this O
often O
leads O
to O
long O
developing O
times O
. O


In O
this O
paper O
, O
a O
method O
is O
proposed O
to O
automatically O
manufacture S-CONPRI
complex O
truss S-MACEQ
structures O
with O
point O
by O
point O
arc B-MANP
additive I-MANP
manufacturing E-MANP
and O
a O
six O
axis O
robot S-MACEQ
. O


Computer B-ENAT
aided I-ENAT
manufacturing E-ENAT
( O
CAM S-ENAT
) O
software S-CONPRI
is O
designed S-FEAT
to O
manage O
( O
i O
) O
material S-MATE
deposition S-CONPRI
at O
intersections O
and O
( O
ii O
) O
collisions O
between O
the O
part O
under O
construction S-APPL
and O
the O
torch O
. O


Because O
it O
is O
difficult O
to O
model S-CONPRI
the O
deposition B-MANP
process E-MANP
, O
the O
bead B-CHAR
geometry E-CHAR
is O
monitored O
using O
video O
imaging S-APPL
. O


Image S-CONPRI
treatment O
program O
detects O
the O
contour S-FEAT
of O
the O
deposit O
and O
computes O
its O
current O
position O
. O


With O
this O
position O
, O
the O
CAM S-ENAT
software O
corrects O
the O
geometry S-CONPRI
of O
the O
part O
for O
future O
deposition S-CONPRI
. O


Simple S-MANP
case B-CONPRI
studies E-CONPRI
are O
tested O
to O
validate O
the O
algorithm S-CONPRI
. O


Two O
solid O
free O
form O
geometries S-CONPRI
designed S-FEAT
by O
topology B-FEAT
optimization E-FEAT
are O
manufactured S-CONPRI
with O
this O
skeleton O
arc B-MANP
additive I-MANP
manufacturing E-MANP
process O
. O


Ti-6Al-4V B-MATE
powders E-MATE
from O
six O
different O
vendors O
were O
compared O
with O
respect O
to O
their O
microstructures S-MATE
, O
size-distributions O
, O
chemistries O
, O
surface S-CONPRI
appearances O
, O
flow O
behavior O
, O
and O
packing O
densities O
. O


The O
analysis O
approaches O
followed O
closely O
ASTM O
F3049 O
, O
the O
standard S-CONPRI
guide O
for O
characterization O
of O
additive B-MANP
manufacturing E-MANP
metal O
powders S-MATE
. O


Chemistries O
, O
including O
impurity S-PRO
content O
, O
agreed O
well O
with O
the O
standard S-CONPRI
requirements O
. O


Powder B-MATE
particle E-MATE
microstructures S-MATE
revealed O
acicular O
alpha O
prime O
for O
all O
vendors O
. O


Quantificational O
analysis O
of O
porosity S-PRO
in O
the O
WAAM S-MANP
2319 O
alloy S-MATE
was O
revealed O
by O
XCT O
. O


The O
formation O
and O
evolution S-CONPRI
of O
micropores O
are O
affected O
by O
microstructures S-MATE
. O


Evolution S-CONPRI
mechanisms O
include O
particles S-CONPRI
dissolution O
, O
H O
pore S-PRO
precipitation O
and O
growth O
. O


Majority O
of O
the O
micropores O
were O
adjacent O
to O
second B-MATE
phase I-MATE
particles E-MATE
. O


Given O
its O
detrimental O
influence O
on O
mechanical B-CONPRI
properties E-CONPRI
, O
porosity S-PRO
defect S-CONPRI
is O
a O
major O
problem O
for O
wire B-MANP
+ I-MANP
arc I-MANP
additively I-MANP
manufactured E-MANP
( O
WAAM S-MANP
) O
Al S-MATE
components O
. O


We O
performed O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
, O
optical B-CHAR
microscopy E-CHAR
, O
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
to O
observe O
the O
spatial B-CHAR
distribution E-CHAR
, O
size O
, O
and O
shape O
of O
micropores O
and O
reveal O
their O
formation O
and O
evolution S-CONPRI
mechanisms O
during O
the O
deposition S-CONPRI
and O
heat B-MANP
treatment E-MANP
of O
the O
WAAM S-MANP
2319 O
Al B-MATE
alloys E-MATE
. O


Key O
findings O
demonstrated O
that O
thehydrogenmicropores O
and O
solidification S-CONPRI
microvoids O
existed O
in O
as-deposited O
alloys S-MATE
. O


The O
amounts O
and O
morphologies S-CONPRI
of O
hydrogen O
micropores O
and O
solidification S-CONPRI
microvoids O
varied O
from O
the O
top O
, O
middle O
, O
and O
bottom O
of O
the O
wall O
sample S-CONPRI
because O
of O
the O
distinct O
microstructure S-CONPRI
and O
second-phase O
distribution S-CONPRI
in O
each O
section O
. O


After O
the O
heat B-MANP
treatment E-MANP
, O
a O
significant O
variation S-CONPRI
in O
micropores O
involving O
three O
main O
evolution S-CONPRI
mechanisms O
, O
namely O
, O
hydrogen O
micropore O
precipitation S-CONPRI
, O
phase B-CONPRI
particle E-CONPRI
dissolution O
, O
and O
micropore O
growth O
, O
was O
observed O
. O


Results O
of O
this O
research S-CONPRI
may O
provide O
a O
solid O
foundation O
for O
the O
safe O
application O
of O
WAAM S-MANP
Al B-MATE
alloy E-MATE
structures O
. O


In O
this O
study O
, O
the O
heterogeneous S-CONPRI
anisotropic S-PRO
microstructure O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
additively B-MANP
manufactured E-MANP
( O
CoCrFeMnNi O
) O
99C1 O
high-entropy O
alloy S-MATE
( O
HEA O
) O
are O
comprehensively O
investigated O
using O
experimental S-CONPRI
and O
theoretical S-CONPRI
analyses O
. O


For O
the O
present O
alloys S-MATE
, O
the O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
process S-CONPRI
produced O
orthogonally O
anisotropic S-PRO
microstructure O
with O
not O
only O
strong O
macroscopic S-CONPRI
morphological O
but O
also O
sharp O
microscopic O
crystallographic O
textures O
. O


Moreover O
, O
due O
to O
the O
complex O
thermal B-PARA
gradient E-PARA
and O
history O
in O
the O
melt B-MATE
pools E-MATE
, O
the O
columnar B-PRO
grains E-PRO
were O
heterogeneously S-CONPRI
evolved O
along O
the O
building B-PARA
direction E-PARA
with O
alternatively O
arranged O
layers O
of O
fine O
and O
coarse O
grains S-CONPRI
parallel O
to O
the O
laser S-ENAT
scanning O
direction O
. O


This O
unique O
morphological O
texture S-FEAT
played O
a O
dominant O
factor O
for O
the O
big O
difference O
in O
tensile B-PRO
properties E-PRO
between O
different O
loading O
directions O
in O
the O
early O
stage O
of O
deformation S-CONPRI
. O


In O
particular O
, O
the O
alternatively O
arrangement O
of O
fine O
and O
coarse O
grains S-CONPRI
could O
generate O
high O
hetero-deformation O
induced O
( O
HDI O
) O
hardening S-MANP
along O
the O
scanning S-CONPRI
direction O
in O
the O
as-built O
samples S-CONPRI
by O
profuse O
evolution S-CONPRI
of O
geometrically O
necessary O
dislocation S-CONPRI
at O
the O
boundaries S-FEAT
of O
each O
layer S-PARA
. O


On O
the O
other O
hand O
, O
upon O
the O
last O
stage O
of O
plastic B-PRO
deformation E-PRO
, O
the O
crystallographic O
texture S-FEAT
played O
a O
crucial O
role O
in O
directional O
flow O
behavior O
by O
modulating O
twinning S-CONPRI
activity O
. O


The O
combined O
contribution O
of O
the O
various O
anisotropic S-PRO
microstructural O
factors O
to O
the O
tensile B-PRO
properties E-PRO
of O
the O
SLM-processed O
HEAs O
was O
clarified O
both O
qualitatively O
and O
quantitatively S-CONPRI
. O


This O
work O
will O
shed O
light O
on O
effective O
utilization O
of O
both O
heterogeneity S-CONPRI
and O
anisotropy S-PRO
of O
the O
structural O
parts O
for O
customized O
performance S-CONPRI
via O
expanding O
multi-scale O
freedom O
of O
design S-FEAT
in O
additive B-MANP
manufacturing E-MANP
. O


IN625 O
grains S-CONPRI
grew O
epitaxially O
on O
the O
fine O
grains S-CONPRI
of O
SS316L O
forming S-MANP
Type-I O
interface S-CONPRI
. O


Bidirectional O
nucleation S-CONPRI
from O
IN625 O
and O
mushy B-CONPRI
zone E-CONPRI
at O
SS316L O
formed O
Type-II O
interface S-CONPRI
. O


Cracking S-CONPRI
was O
formed O
at O
Type-II O
interface S-CONPRI
and O
in O
the O
SS316L O
tracks O
. O


Cracking S-CONPRI
mechanisms O
include O
solidification S-CONPRI
, O
liquidation O
, O
and O
ductility S-PRO
dip O
cracking S-CONPRI
. O


This O
research S-CONPRI
illustrates O
the O
rationale O
of O
adopting O
a O
preferred O
printing O
sequence O
by O
examining O
crack O
generation O
predominated O
by O
resultant O
interfaces O
and O
microstructural S-CONPRI
inhomogeneity O
, O
through O
underlying O
governing O
mechanisms O
in O
directed B-MANP
energy I-MANP
deposition E-MANP
of O
316L O
stainless O
steel/Inconel O
625 O
( O
SS316L/IN625 O
) O
bimetals O
. O


For O
this O
purpose O
, O
microstructural S-CONPRI
and O
crystallographic O
characterizations O
augmented O
by O
numerical B-ENAT
simulations E-ENAT
were O
employed O
on O
additively B-MANP
manufactured E-MANP
two O
distinct O
interfaces O
, O
i.e O
. O


Type-I O
( O
IN625 O
deposition S-CONPRI
on O
SS316L O
) O
and O
Type-II O
( O
SS316L O
deposition S-CONPRI
on O
IN625 O
) O
. O


Changing O
the O
printing O
sequence O
generated O
these O
two O
types O
of O
interfaces O
with O
unique O
morphologies S-CONPRI
, O
which O
was O
found O
attributable O
to O
the O
compositional O
variations S-CONPRI
and O
mismatch O
in O
thermal B-CONPRI
properties E-CONPRI
. O


Type-I O
interface S-CONPRI
was O
typified O
by O
gradual-change O
composition S-CONPRI
in O
the O
transition S-CONPRI
zone O
, O
causing O
the O
IN625 O
grains S-CONPRI
to O
grow O
epitaxially O
on O
the O
grains S-CONPRI
of O
SS316L O
. O


Type-II O
interface S-CONPRI
was O
characterized O
as S-MATE
a O
compositional O
sudden-change O
zone O
( O
CSCZ O
) O
adjacent O
to O
SS316L O
, O
leading O
to O
merging O
bidirectional O
nucleation S-CONPRI
and O
grain B-CONPRI
growth E-CONPRI
from O
the O
bottom O
IN625 O
and O
upper O
CSCZ O
, O
and O
lack O
of O
epitaxial S-PRO
growth O
. O


Additionally O
, O
high O
cracking S-CONPRI
susceptibility O
occurred O
near O
the O
Type-II O
interface S-CONPRI
rather O
than O
the O
Type-I O
interface S-CONPRI
, O
which O
was O
related O
to O
solidification S-CONPRI
and O
liquidation O
cracking S-CONPRI
, O
and O
further O
promoted O
ductility S-PRO
dip O
cracking S-CONPRI
. O


This O
research S-CONPRI
will O
provide O
a O
guideline O
for O
the O
additive B-MANP
manufacturing E-MANP
of O
bimetals O
with O
the O
consideration O
of O
printing O
sequence O
to O
control O
interface S-CONPRI
formation O
for O
a O
crack-free O
structure S-CONPRI
. O


X-ray S-CHAR
μCT O
used O
for O
non-destructive O
measurement S-CHAR
of O
porosity S-PRO
through O
the O
multiple O
stages O
of O
the O
CEAM O
. O


Porosity S-PRO
was O
quantified O
and O
mapped O
within O
the O
parts O
by O
using O
image B-CONPRI
analysis E-CONPRI
. O


Vertical S-CONPRI
and O
radial O
gradient O
of O
porosity S-PRO
and O
pore B-PARA
size E-PARA
observed O
in O
green O
, O
de-bound O
and O
sintered S-MANP
samples S-CONPRI
. O


The O
microscopic O
and O
macroscopic S-CONPRI
quality O
of O
samples S-CONPRI
improves O
through O
the O
process S-CONPRI
stages O
. O


Ceramic S-MATE
Extrusion O
Additive B-MANP
Manufacturing E-MANP
( O
CEAM O
) O
enables O
the O
die-less O
fabrication S-MANP
of O
small O
ceramic S-MATE
parts O
, O
with O
a O
process B-ENAT
chain E-ENAT
that O
includes O
four O
consecutive O
stages O
: O
the O
3D B-MANP
printing E-MANP
, O
solvent O
de-binding O
, O
thermal O
de-binding O
, O
and O
sintering S-MANP
. O


The O
3D B-MANP
printing E-MANP
process O
was O
implemented O
through O
Ephestus O
, O
a O
specially O
developed O
EAM O
machine S-MACEQ
for O
the O
manufacturing S-MANP
of O
parts O
from O
alumina S-MATE
feedstock O
. O


A O
test O
part O
was O
designed S-FEAT
, O
and O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
( O
μ-CT O
) O
was O
used O
to O
quantify O
its O
characteristics O
through O
the O
processing O
stages O
of O
the O
EAM O
. O


The O
porosity S-PRO
distribution S-CONPRI
and O
the O
distribution S-CONPRI
of O
void S-CONPRI
size O
and O
shape O
were O
determined O
throughout O
the O
samples S-CONPRI
at O
each O
stage O
, O
using O
image B-CONPRI
analysis E-CONPRI
techniques O
. O


Furthermore O
, O
the O
evolution S-CONPRI
of O
some O
macroscopic S-CONPRI
quality O
properties S-CONPRI
was O
measured.The O
results O
show O
that O
both O
microscopic O
( O
porosity S-PRO
) O
and O
macroscopic S-CONPRI
( O
geometry S-CONPRI
, O
density S-PRO
) O
properties S-CONPRI
of O
the O
samples S-CONPRI
improve O
through O
the O
process S-CONPRI
stages O
. O


A O
vertical S-CONPRI
gradient O
of O
porosity S-PRO
is O
present O
in O
green O
and O
de-bound O
samples S-CONPRI
, O
with O
porosity S-PRO
decreasing O
with O
increasing O
sample S-CONPRI
height O
. O


After O
sintering S-MANP
, O
the O
vertical S-CONPRI
gradient O
of O
porosity S-PRO
disappears O
. O


The O
sphericity O
and O
the O
diameter S-CONPRI
of O
voids S-CONPRI
are O
negatively O
correlated S-CONPRI
and O
dispersed O
over O
a O
wide O
range S-PARA
in O
the O
green O
state O
. O


The O
sintering S-MANP
process S-CONPRI
has O
a O
homogenization S-MANP
effect O
on O
the O
void S-CONPRI
shape O
distribution S-CONPRI
. O


The O
geometrical O
deviation O
from O
the O
nominal O
designed S-FEAT
dimensions O
and O
the O
surface B-PARA
quality E-PARA
of O
parts O
improves O
when O
moving O
from O
the O
green O
to O
the O
sintered S-MANP
state O
. O


Experimental S-CONPRI
investigation O
of O
porosities S-PRO
in O
additive B-MANP
manufactured E-MANP
ceramics O
parts.Download O
: O
Download O
high-res B-CONPRI
image E-CONPRI
( O
178 O
In O
this O
paper O
, O
the O
authors O
explore O
the O
use O
of O
impedance-based O
monitoring O
techniques O
for O
in-situ S-CONPRI
detection O
of O
additive B-MANP
manufacturing E-MANP
build O
defects S-CONPRI
. O


By O
physically O
coupling O
a O
piezoceramic O
( O
PZT S-MATE
) O
sensor S-MACEQ
to O
the O
part O
being O
fabricated S-CONPRI
, O
the O
measured O
electrical S-APPL
impedance O
of O
the O
PZT S-MATE
can O
be S-MATE
directly O
linked O
to O
the O
mechanical S-APPL
impedance O
of O
the O
part O
. O


It O
is O
hypothesized O
that O
one O
can O
detect O
build S-PARA
defects O
in O
geometry S-CONPRI
or O
material B-CONPRI
properties E-CONPRI
in-situ S-CONPRI
by O
comparing O
the O
signatures O
collected O
during O
printing O
of O
parts O
with O
that O
of O
a O
defect-free O
control O
sample S-CONPRI
. O


In O
this O
paper O
, O
the O
authors O
explore O
the O
layer-to-layer O
sensitivity S-PARA
for O
both O
PZT S-MATE
sensors O
embedded O
into O
printed O
parts O
and O
for O
a O
fixture-based O
PZT S-MATE
sensor O
. O


For O
this O
work O
, O
this O
concept O
is O
evaluated O
in O
context O
of O
material B-MANP
jetting E-MANP
. O


A O
set S-APPL
of O
control O
samples S-CONPRI
is O
created O
and O
used O
to O
establish O
a O
baseline O
signature O
. O


( O
e.g. O
, O
internal B-CONPRI
voids E-CONPRI
) O
are O
fabricated S-CONPRI
and O
their O
layer-to-layer O
signatures O
are O
compared O
to O
a O
control O
sample S-CONPRI
. O


Using O
this O
technique O
, O
the O
authors O
demonstrate O
an O
ability O
to O
track O
print S-MANP
progress O
and O
detect O
defects S-CONPRI
as S-MATE
they O
occur O
. O


For O
embedded O
sensors S-MACEQ
the O
defects S-CONPRI
were O
detectable O
at O
2.28 O
% O
of O
the O
part O
volume S-CONPRI
( O
95.6 O
mm3 O
) O
and O
by O
fixture-based O
sensors S-MACEQ
when O
it O
affected O
1.38 O
% O
of O
the O
part O
volume S-CONPRI
. O


Surface B-PRO
roughness E-PRO
of O
an O
as S-MATE
produced O
AM S-MANP
component O
is O
very O
high O
, O
which O
prohibits O
the O
direct O
utilization O
of O
additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
components S-MACEQ
for O
the O
intended O
applications O
. O


Reducing O
surface B-PRO
roughness E-PRO
is O
exponentially O
more O
challenging O
for O
the O
internal O
surfaces S-CONPRI
of O
an O
AM S-MANP
component O
. O


This O
paper O
reports O
our O
research S-CONPRI
in O
the O
area S-PARA
of O
postprocessing S-CONPRI
of O
interior O
surfaces S-CONPRI
of O
an O
AM S-MANP
component O
. O


We O
have O
investigated O
electropolishing S-MANP
and O
chemical B-MANP
polishing E-MANP
( O
chempolishing O
) O
methods O
to O
reduce O
the O
surface B-PRO
roughness E-PRO
of O
the O
internal O
surface S-CONPRI
. O


We O
found O
that O
chempolishing O
was O
effective O
in O
simultaneously O
reducing O
the O
internal O
and O
external O
surface B-PRO
roughness E-PRO
of O
316 O
steel S-MATE
AM S-MANP
components O
. O


Chempolishing O
is O
found O
suitable O
for O
any O
complicated O
AM S-MANP
shape O
and O
geometry S-CONPRI
. O


Our O
electropolishing S-MANP
methodology O
was O
effective O
in O
reducing O
the O
surface B-PRO
roughness E-PRO
of O
the O
internal O
or O
external O
surfaces S-CONPRI
provided O
that O
a O
counter O
electrode S-MACEQ
could O
be S-MATE
positioned O
in O
the O
proximity O
of O
the O
surface S-CONPRI
to O
be S-MATE
polished O
. O


We O
have O
performed O
optical S-CHAR
profilometry O
, O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
, O
and O
contact S-APPL
angle O
measurement S-CHAR
study O
to O
investigate O
the O
difference O
between O
electropolishing S-MANP
and O
chemical B-MANP
polishing E-MANP
methods O
. O


Modelling S-ENAT
of O
wire-arc B-MANP
additive I-MANP
manufacturing I-MANP
process E-MANP
is O
an O
effective O
way O
for O
adapting O
the O
optimum O
parameters S-CONPRI
as S-MATE
well O
as S-MATE
understanding O
and O
managing O
the O
sequences O
of O
layer-by-layer B-CONPRI
deposition E-CONPRI
. O


Some O
of O
these O
parameters S-CONPRI
such O
as S-MATE
toolpath O
, O
deposition S-CONPRI
intervals O
and O
heat B-CONPRI
source E-CONPRI
power O
play O
important O
roles O
in O
improving O
the O
process S-CONPRI
viability O
and O
cost O
efficiency O
. O


In O
this O
article O
, O
we O
have O
studied O
Al-5Mg O
, O
Al-3Si O
alloys S-MATE
as O
demonstrators O
, O
from O
both O
experimental S-CONPRI
and O
modelling S-ENAT
perspectives O
, O
to O
benchmark S-MANS
different O
deposition S-CONPRI
parameters O
and O
provided O
guidelines O
for O
optimising O
the O
process S-CONPRI
conditions O
. O


Physical O
values O
such O
as S-MATE
total O
distortion S-CONPRI
and O
residual B-PRO
stress E-PRO
were O
selected O
as S-MATE
indicators O
for O
the O
manufacturability S-CONPRI
of O
the O
structure S-CONPRI
. O


The O
simulations S-ENAT
were O
performed O
by O
Simufact O
Welding S-MANP
software S-CONPRI
, O
that O
is O
outfitted O
with O
the O
MARC O
solver O
and O
the O
experiments O
were O
executed O
in O
a O
robotic O
cell S-APPL
. O


We O
have O
introduced O
a O
method O
for O
optimising O
the O
process B-CONPRI
parameters E-CONPRI
based O
on O
the O
heat B-CONPRI
source E-CONPRI
power O
modification O
and O
selection O
of O
unique O
parameters S-CONPRI
for O
each O
deposition B-PARA
layer E-PARA
. O


This O
was O
performed O
by O
monitoring O
the O
evolution S-CONPRI
of O
the O
molten B-CONPRI
pool E-CONPRI
size O
and O
geometry S-CONPRI
when O
building O
a O
wall O
structure S-CONPRI
. O


The O
results O
suggest O
that O
achieving O
an O
uninterrupted O
deposition B-MANP
process E-MANP
entails O
modification O
of O
the O
heat S-CONPRI
input O
for O
each O
layer S-PARA
. O


Thus O
, O
a O
simple S-MANP
analytical O
method O
was O
proposed O
to O
estimate O
the O
heat S-CONPRI
input O
reduction S-CONPRI
coefficient O
for O
a O
wall O
structure S-CONPRI
as S-MATE
a O
function O
of O
molten B-PARA
pool I-PARA
geometry E-PARA
and O
the O
height O
at O
which O
, O
a O
new O
layer S-PARA
is O
being O
deposited O
. O


It O
was O
also O
shown O
that O
a O
generic O
selection O
of O
parameters S-CONPRI
for O
aluminium B-MATE
alloys E-MATE
may O
impair O
the O
eventual O
quality S-CONPRI
for O
some O
of O
the O
alloys S-MATE
due O
to O
their O
inherent O
physical B-PRO
properties E-PRO
such O
as S-MATE
high O
temperature S-PARA
flowability O
. O


In O
the O
current O
investigation O
, O
an O
ultrasonic O
imaging S-APPL
system O
originally O
developed O
for O
visualization O
of O
microstructures S-MATE
in O
sheet B-MATE
metals E-MATE
, O
with O
capabilities O
of O
generating O
plane O
two-dimensional B-CONPRI
images E-CONPRI
at O
spatial O
resolutions O
between O
1 O
and O
200 O
μm O
, O
was O
used O
to O
quantitatively S-CONPRI
evaluate O
a O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
processed B-CONPRI
3D E-CONPRI
test O
part O
. O


For O
the O
ultrasonic O
system O
, O
a O
custom O
software S-CONPRI
program O
was O
written O
to O
control O
all O
components S-MACEQ
of O
the O
inspection S-CHAR
schemes O
in O
a O
continuous O
scan O
mode O
, O
including O
the O
movement O
of O
three O
orthogonal O
translational O
stages O
, O
as S-MATE
well O
as S-MATE
display O
a O
live O
ultrasonic O
image S-CONPRI
during O
scanning S-CONPRI
and O
provide O
tools S-MACEQ
for O
advanced O
post-processing S-CONPRI
of O
the O
recorded O
ultrasonic O
signals O
. O


Prior O
to O
collecting O
ultrasonic O
data S-CONPRI
for O
a O
selected O
test O
specimen O
, O
an O
optical S-CHAR
flat O
reference O
standard S-CONPRI
was O
used O
to O
characterize O
the O
ultrasonic O
probes S-MACEQ
and O
to O
quantify O
the O
system O
’ O
s S-MATE
mechanical S-APPL
stability O
, O
repeatability S-CONPRI
, O
and O
accuracy S-CHAR
when O
measuring O
the O
physical O
dimensions S-FEAT
of O
features O
. O


Ultrasonic O
data S-CONPRI
collected O
at O
different O
spatial O
resolutions O
were O
used O
to O
characterize O
a O
part O
’ O
s S-MATE
surface O
flatness S-PRO
, O
internal O
defects S-CONPRI
, O
and O
fusion S-CONPRI
conditions O
; O
and O
to O
measure O
the O
physical O
dimensions S-FEAT
of O
intended O
features O
. O


Finally O
, O
a O
suggestion O
is O
made O
for O
adopting O
a O
process S-CONPRI
to O
qualify O
or O
certify O
FFF S-MANP
based O
additive B-MACEQ
manufacturing I-MACEQ
machines E-MACEQ
in O
the O
market O
by O
applying O
a O
reliable O
NDE O
validation S-CONPRI
method O
to O
a O
standardized O
part O
with O
various O
features O
of O
different O
shapes O
and O
physical O
dimensions S-FEAT
. O


Successful O
printing O
of O
high-performance O
material S-MATE
with O
suitable O
properties S-CONPRI
using O
additive B-MANP
manufacturing E-MANP
methods O
such O
as S-MATE
Fused O
Filament S-MATE
Fabrication S-MANP
( O
FFF S-MANP
) O
can O
create O
many O
advanced O
applications O
in O
industries S-APPL
. O


However O
, O
the O
high O
viscosity S-PRO
of O
high-performance O
polymers S-MATE
causes O
complications O
during O
the O
FFF S-MANP
process O
and O
reduces O
the O
final O
print B-CONPRI
quality E-CONPRI
. O


To O
overcome O
this O
challenge O
, O
Inorganic O
Fullerene S-MATE
Tungsten O
Sulphide O
( O
IF-WS2 O
) O
nanoparticles S-CONPRI
are O
applied O
in O
this O
study O
to O
enhance O
the O
flowability O
of O
poly-ether-ketone-ketone O
( O
PEEK S-MATE
) O
without O
compromising O
its O
mechanical S-APPL
and O
thermal B-CONPRI
properties E-CONPRI
. O


In O
the O
first O
step S-CONPRI
, O
different O
loadings O
of O
IF-WS2 O
nanoparticles S-CONPRI
are O
melt S-CONPRI
compounded O
with O
PEEK S-MATE
and O
the O
nanocomposites O
are O
characterized O
. O


SEM S-CHAR
and O
EDX S-CHAR
images O
of O
fractured O
surfaces S-CONPRI
indicate O
that O
a O
good O
dispersion S-CONPRI
of O
nanoparticles S-CONPRI
is O
achieved O
without O
any O
pre-treatment O
or O
pre-dispersion O
. O


A O
reduction S-CONPRI
in O
melt S-CONPRI
viscosity O
of O
25 O
% O
, O
and O
a O
simultaneous O
growth O
in O
storage O
modulus O
, O
crystallization S-CONPRI
and O
degradation S-CONPRI
temperature O
of O
about O
60 O
% O
, O
53 O
% O
and O
100 O
°C O
is O
found O
with O
addition O
of O
2 O
wt O
% O
IF-WS2 O
to O
PEEK S-MATE
, O
respectively O
. O


This O
great O
achievement O
is O
mainly O
ascribed O
to O
the O
unique O
characteristics O
of O
IF-WS2 O
nanoparticles S-CONPRI
, O
acting O
as S-MATE
both O
reinforcing O
and O
lubricating O
agents O
, O
indicated O
by O
a O
reduction S-CONPRI
in O
coefficient B-PRO
of I-PRO
friction E-PRO
. O


There O
is O
no O
significant O
increase O
of O
crystallization S-CONPRI
and O
melting B-PARA
temperatures E-PARA
with O
the O
addition O
of O
IF-WS2 O
nanoparticles S-CONPRI
, O
which O
is O
beneficial O
in O
the O
FFF S-MANP
process O
. O


In O
the O
second O
step S-CONPRI
, O
the O
PEEK S-MATE
nanocomposite O
filaments S-MATE
are O
printed O
via O
FFF S-MANP
. O


The O
print B-CONPRI
quality E-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
printed O
PEEK S-MATE
are O
also O
improved O
with O
the O
incorporation O
of O
IF-WS2 O
nanoparticles S-CONPRI
. O


Hence O
, O
incorporation O
of O
IF-WS2 O
nanoparticles S-CONPRI
into O
PEEK S-MATE
via O
melt S-CONPRI
compounding O
is O
an O
effective O
approach O
for O
the O
development O
of O
suitable O
high-performance O
engineering B-MATE
materials E-MATE
for O
FFF S-MANP
. O


Dislocation S-CONPRI
structures O
, O
chemical O
segregation S-CONPRI
, O
γ′ O
, O
γ″ O
, O
δ O
precipitates S-MATE
, O
and O
Laves B-CONPRI
phase E-CONPRI
were O
quantified O
within O
the O
microstructures S-MATE
of O
Inconel B-MATE
718 E-MATE
( O
IN718 S-MATE
) O
produced O
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
and O
subjected O
to O
standard S-CONPRI
, O
direct O
aging O
, O
and O
modified O
multi-step O
heat B-MANP
treatments E-MANP
. O


Additionally O
, O
heat-treated S-MANP
samples O
still O
attached O
to O
the O
build B-MACEQ
plates E-MACEQ
vs. O
those O
removed O
were O
also O
documented O
for O
a O
standard S-CONPRI
heat B-MANP
treatment E-MANP
. O


The O
effects O
of O
the O
different O
resulting O
microstructures S-MATE
on O
room O
temperature S-PARA
strengths S-PRO
and O
elongations O
to O
failure S-CONPRI
are O
revealed O
. O


Knowledge O
derived O
from O
these O
process-structure-property O
relationships O
was O
used O
to O
engineer O
a O
super-solvus O
solution S-CONPRI
anneal O
at O
1020 O
°C O
for O
15 O
min O
, O
followed O
by O
aging O
at O
720 O
°C O
for O
24 O
h O
heat B-MANP
treatment E-MANP
for O
AM-IN718 O
that O
eliminates O
Laves S-CONPRI
and O
δ O
phases O
, O
preserves O
AM-specific O
dislocation S-CONPRI
cells S-APPL
that O
are O
shown O
to O
be S-MATE
stabilized O
by O
MC S-MATE
carbide S-MATE
particles O
, O
and O
precipitates S-MATE
dense O
γ′ O
and O
γ″ O
nanoparticle O
populations O
. O


This O
“ O
optimized O
for O
AM-IN718 O
heat B-MANP
treatment E-MANP
” O
results O
in O
superior O
properties S-CONPRI
relative O
to O
wrought/additively O
manufactured S-CONPRI
, O
then O
industry-standard O
heat S-CONPRI
treated O
IN718 S-MATE
: O
relative O
increases O
of O
7/10 O
% O
in O
yield B-PRO
strength E-PRO
, O
2/7 O
% O
in O
ultimate B-PRO
strength E-PRO
, O
and O
23/57 O
% O
in O
elongation S-PRO
to O
failure S-CONPRI
are O
realized O
, O
respectively O
, O
regardless O
of O
as-printed O
vs. O
machined S-MANP
surface O
finishes O
. O


In O
this O
work O
the O
effect O
of O
manufacturing S-MANP
strategy O
and O
post O
process S-CONPRI
treatment O
on O
the O
high O
strain B-CONPRI
rate E-CONPRI
( O
HSR O
) O
compressive O
deformation S-CONPRI
behavior O
of O
additively B-MANP
manufactured E-MANP
powder O
bed B-MANP
fusion E-MANP
17-4PH S-MATE
stainless O
steel S-MATE
is O
studied O
. O


Specimens O
were O
fabricated S-CONPRI
using O
three O
different O
laser S-ENAT
vector O
path O
strategies O
to O
impart O
different O
thermal O
histories O
and O
resulting O
microstructures S-MATE
in O
the O
material S-MATE
. O


The O
effect O
of O
post B-CONPRI
processing E-CONPRI
in O
the O
form O
of O
hot B-MANP
isostatic I-MANP
pressing E-MANP
and O
heat B-MANP
treatment E-MANP
and O
their O
effect O
on O
HSR O
compressive O
deformation S-CONPRI
response O
of O
the O
material S-MATE
was O
studied O
. O


Defect S-CONPRI
characteristics O
were O
quantified O
using O
x-ray B-CHAR
micro I-CHAR
computed I-CHAR
tomography E-CHAR
. O


It O
was O
found O
that O
the O
laser S-ENAT
vector O
strategy O
had O
a O
strong O
influence O
on O
the O
development O
of O
microstructure S-CONPRI
and O
defect S-CONPRI
characteristics O
and O
spatial B-CHAR
distribution E-CHAR
in O
the O
materials S-CONPRI
which O
strongly O
influence O
the O
HSR O
response O
and O
the O
HSR O
compressive O
flow B-PRO
stresses E-PRO
of O
the O
materials S-CONPRI
varied O
by O
as S-MATE
much O
as S-MATE
43 O
% O
in O
the O
regimes O
tested O
. O


This O
work O
proposes O
a O
finite B-CONPRI
element E-CONPRI
( O
FE S-MATE
) O
analysis O
workflow S-CONPRI
to O
simulate O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
additive B-MANP
manufacturing E-MANP
at O
a O
macroscopic S-CONPRI
length B-CHAR
scale E-CHAR
( O
i.e O
. O


part O
length B-CHAR
scale E-CHAR
) O
and O
to O
predict O
thermal O
conditions O
during O
manufacturing S-MANP
, O
as S-MATE
well O
as S-MATE
distortions O
, O
strength S-PRO
and O
residual B-PRO
stresses E-PRO
at O
the O
completion O
of O
manufacturing S-MANP
. O


The O
proposed O
analysis O
method O
incorporates O
a O
multi-step O
FE S-MATE
workflow O
to O
elucidate O
the O
thermal O
and O
mechanical B-CONPRI
responses E-CONPRI
in O
laser B-MANP
engineered I-MANP
net I-MANP
shaping E-MANP
( O
LENS S-MANP
) O
manufacturing S-MANP
. O


For O
each O
time O
step S-CONPRI
, O
a O
thermal O
element S-MATE
activation O
scheme O
captures O
the O
material S-MATE
deposition B-MANP
process E-MANP
. O


Then O
, O
activated O
elements S-MATE
and O
their O
associated O
geometry S-CONPRI
are O
analyzed O
first O
thermally O
for O
heat S-CONPRI
flow O
due O
to O
radiation S-MANP
, O
convection O
, O
and O
conduction O
, O
and O
then O
mechanically O
for O
the O
resulting O
stresses O
, O
displacements O
, O
and O
material B-CONPRI
property E-CONPRI
evolution S-CONPRI
. O


Simulations S-ENAT
agree O
with O
experimentally O
measured O
in B-CONPRI
situ E-CONPRI
thermal O
measurements O
for O
simple S-MANP
cylindrical S-CONPRI
build S-PARA
geometries O
, O
as S-MATE
well O
as S-MATE
general O
trends S-CONPRI
of O
local O
hardness S-PRO
distribution S-CONPRI
and O
plastic S-MATE
strain O
accumulation O
( O
represented O
by O
relative O
distribution S-CONPRI
of O
geometrically O
necessary O
dislocations S-CONPRI
) O
. O


Residual B-PRO
stresses E-PRO
play O
an O
important O
role O
for O
the O
structural B-PRO
integrity E-PRO
of O
engineering S-APPL
components S-MACEQ
. O


In O
this O
study O
residual B-PRO
stresses E-PRO
were O
determined O
in O
titanium B-MATE
alloy E-MATE
( O
Ti-6Al-4V S-MATE
) O
and O
Inconel B-MATE
718 E-MATE
samples O
produced O
using O
selective-laser-melting O
( O
SLM S-MANP
) O
additive B-MANP
manufacturing E-MANP
. O


The O
contour S-FEAT
method O
and O
a O
numerical B-ENAT
simulation E-ENAT
approach O
( O
inherent-strain-based O
method O
) O
were O
used O
to O
determine O
the O
residual B-PRO
stress E-PRO
distributions S-CONPRI
. O


The O
inherent-strain-based O
method O
reduces O
the O
computational O
time O
compared O
to O
weakly-coupled O
thermo-mechanical S-CONPRI
simulations S-ENAT
. O


Results O
showed O
the O
presence O
of O
high O
tensile B-PRO
residual I-PRO
stresses E-PRO
at O
and O
near O
the O
surface S-CONPRI
of O
both O
titanium S-MATE
and O
Inconel B-MATE
alloys E-MATE
samples O
, O
whereas O
compressive O
residual B-PRO
stresses E-PRO
were O
seen O
at O
the O
center O
region O
. O


A O
good O
agreement O
was O
seen O
between O
the O
results O
obtained O
from O
contour S-FEAT
method O
and O
the O
numerical B-ENAT
simulation E-ENAT
, O
particularly O
1 O
mm S-MANP
below O
the O
surface S-CONPRI
of O
the O
samples S-CONPRI
. O


This O
study O
presents O
an O
automated O
thresholding O
method O
for O
analyzing O
and O
quantifying O
the O
internal O
composition S-CONPRI
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
parts O
using O
computed B-CHAR
tomography E-CHAR
( O
CT S-ENAT
) O
data S-CONPRI
. O


A O
mixed O
skewed-Gaussian O
distribution S-CONPRI
( O
MSGD O
) O
algorithm S-CONPRI
, O
derived O
from O
a O
statistical O
image B-CONPRI
analysis E-CONPRI
technique O
called O
Mixed O
Gaussian S-CONPRI
Distribution S-CONPRI
( O
MGD O
) O
clustering O
, O
integrates O
a O
mixture O
of O
skewed-Gaussian O
distributions S-CONPRI
to O
model S-CONPRI
the O
internal O
phases O
from O
CT S-ENAT
data O
. O


The O
parameters S-CONPRI
of O
the O
MSGD O
algorithm S-CONPRI
( O
i.e O
. O


probability S-CONPRI
, O
mean O
, O
standard B-CHAR
deviation E-CHAR
, O
and O
skew O
) O
are O
inferred O
from O
the O
measured O
grayscale O
histogram O
using O
least-squares O
fitting O
and O
are O
assigned O
to O
phases O
present O
in O
the O
CT S-ENAT
data O
. O


From O
the O
MSGD O
fitted O
and O
thresholded O
CT S-ENAT
data O
, O
phase S-CONPRI
volume O
percentages O
and O
spatial B-FEAT
variations E-FEAT
of O
density S-PRO
of O
the O
phases O
are O
quantified O
. O


The O
MSGD O
algorithm S-CONPRI
was O
validated O
using O
previously O
reported O
CT S-ENAT
analysis O
and O
experimental S-CONPRI
porosity O
measurements O
of O
two O
Cobalt B-MATE
Chrome E-MATE
( O
CoCr O
) O
specimens O
( O
∼1 O
% O
and O
∼13 O
% O
porosity S-PRO
) O
fabricated S-CONPRI
by O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
. O


Compared O
with O
the O
1.1 O
% O
and O
13.7 O
% O
porosity S-PRO
of O
the O
specimens O
measured O
by O
the O
Archimedes B-CHAR
method E-CHAR
, O
the O
MSGD O
method O
predicted S-CONPRI
a O
porosity S-PRO
of O
1.6 O
% O
+/− O
0.7 O
% O
and O
14.5 O
% O
+/− O
1.9 O
% O
, O
a O
measured O
increase O
of O
0.5 O
% O
and O
0.8 O
% O
, O
respectively O
. O


These O
results O
show O
a O
similarity O
in O
predicted S-CONPRI
porosity S-PRO
between O
Archimedes O
and O
MSGD O
method O
indicating O
that O
CT S-ENAT
and O
the O
MSGD O
method O
may O
provide O
a O
reasonable O
estimate O
for O
part O
porosity S-PRO
. O


Developed O
a O
design S-FEAT
and O
fabrication S-MANP
workflow O
for O
DM-based O
FGM S-MANP
structures O
. O


The O
workflow S-CONPRI
integrates O
material S-MATE
as S-MATE
well O
as S-MATE
structural O
design S-FEAT
with O
fabrication S-MANP
. O


Used O
a O
simplified O
regression-based O
model S-CONPRI
to O
predict O
the O
mechanical S-APPL
behavior O
of O
DMs O
. O


Experimentally B-CONPRI
validated E-CONPRI
the O
workflow S-CONPRI
with O
the O
help O
of O
voxel S-CONPRI
printed O
FGM S-MANP
structures O
. O


Voxel-based O
multimaterial B-MANP
jetting I-MANP
additive I-MANP
manufacturing E-MANP
allows O
fabrication S-MANP
of O
digital B-CONPRI
materials E-CONPRI
( O
DMs O
) O
at O
the O
meso-scale O
( O
∼1 O
mm S-MANP
) O
by O
controlling O
the O
deposition S-CONPRI
patterns O
of O
soft O
elastomeric O
and O
rigid O
glassy O
polymers S-MATE
at O
the O
voxel-scale O
( O
∼90 O
μm O
) O
. O


The O
digital B-CONPRI
materials E-CONPRI
can O
then O
be S-MATE
used O
to O
create O
heterogeneous S-CONPRI
functionally B-MATE
graded I-MATE
material E-MATE
( O
FGM S-MANP
) O
structures O
at O
the O
macro-scale O
( O
∼10 O
mm S-MANP
) O
programmed O
to O
behave O
in O
a O
predefined O
manner O
. O


This O
offers O
huge O
potential O
for O
design S-FEAT
and O
fabrication S-MANP
of O
novel O
and O
complex O
bespoke O
mechanical S-APPL
structures.This O
paper O
presents O
a O
complete O
design S-FEAT
and O
manufacturing S-MANP
workflow O
that O
simultaneously O
integrates O
material S-MATE
design S-FEAT
, O
structural B-FEAT
design E-FEAT
, O
and O
product O
fabrication S-MANP
of O
FGM S-MANP
structures O
based O
on O
digital B-CONPRI
materials E-CONPRI
. O


This O
is O
enabled O
by O
a O
regression B-CONPRI
analysis E-CONPRI
of O
the O
experimental B-CONPRI
data E-CONPRI
on O
mechanical S-APPL
performance O
of O
the O
DMs O
i.e. O
, O
Young O
’ O
s S-MATE
modulus O
, O
tensile B-PRO
strength E-PRO
and O
elongation S-PRO
at O
break O
. O


This O
allows O
us O
to O
express O
the O
material S-MATE
behavior O
simply O
as S-MATE
a O
function O
of O
the O
microstructural S-CONPRI
descriptors O
( O
in O
this O
case O
, O
just O
volume B-PARA
fraction E-PARA
) O
without O
having O
to O
understand O
the O
underlying O
microstructural S-CONPRI
mechanics O
while O
simultaneously O
connecting O
it O
to O
the O
process S-CONPRI
parameters.Our O
proposed O
design S-FEAT
and O
manufacturing B-MANP
approach E-MANP
is O
then O
demonstrated O
and O
validated O
in O
two O
series O
of O
design S-FEAT
exercises O
to O
devise O
complex O
FGM S-MANP
structures O
. O


First O
, O
we O
design S-FEAT
, O
computationally O
predict O
and O
experimentally O
validate O
the O
behavior O
of O
prescribed O
designs S-FEAT
of O
FGM S-MANP
tensile O
structures O
with O
different O
material B-CONPRI
gradients E-CONPRI
. O


Second O
, O
we O
present O
a O
design S-FEAT
automation S-CONPRI
approach O
for O
optimal O
FGM S-MANP
structures O
. O


The O
comparison O
between O
the O
simulations S-ENAT
and O
the O
experiments O
with O
the O
FGM S-MANP
structures O
shows O
that O
the O
presented O
design S-FEAT
and O
fabrication S-MANP
workflow O
based O
on O
our O
modeling S-ENAT
approach O
for O
DMs O
at O
meso-scale O
can O
be S-MATE
effectively O
used O
to O
design S-FEAT
and O
predict O
the O
performance S-CONPRI
of O
FGMs O
at O
macro-scale O
. O


Porous S-PRO
titanium O
and O
tantalum S-MATE
structures O
were O
fabricated S-CONPRI
by O
additive B-MANP
manufacturing E-MANP
with O
30 O
% O
volume B-PARA
fraction E-PARA
designed S-FEAT
porosity O
. O


Nanotubes S-CONPRI
were O
formed O
on O
the O
surface S-CONPRI
of O
the O
porous S-PRO
titanium O
using O
anodization S-MANP
process O
( O
TNT S-MATE
) O
. O


Porous S-PRO
TNT O
and O
porous S-PRO
Ta O
showed O
comparable O
new O
bone S-BIOP
formation O
as S-MATE
early O
as S-MATE
5 O
weeks O
after O
surgery S-APPL
in O
a O
rat O
distal O
femur O
model S-CONPRI
. O


Our O
findings O
for O
TNT S-MATE
pave O
a O
way O
to O
avoid O
high O
manufacturing B-CONPRI
cost E-CONPRI
related O
to O
biomedical B-APPL
application E-APPL
of O
tantalum S-MATE
. O


Material B-CONPRI
properties E-CONPRI
of O
implants S-APPL
such O
as S-MATE
volume O
porosity S-PRO
and O
nanoscale O
surface B-MANP
modification E-MANP
have O
been O
shown O
to O
enhance O
cell-material O
interactions O
in O
vitro O
and O
osseointegration S-PRO
in O
vivo O
. O


Porous S-PRO
tantalum O
( O
Ta S-MATE
) O
and O
titanium S-MATE
( O
Ti S-MATE
) O
coatings S-APPL
are O
widely O
used O
for O
non-cemented O
implants S-APPL
, O
which O
are O
fabricated S-CONPRI
using O
different O
processing O
routes O
. O


In O
recent O
years O
, O
some O
of O
those O
implants S-APPL
are O
being O
manufactured S-CONPRI
using O
additive B-MANP
manufacturing E-MANP
. O


However O
, O
limited O
knowledge O
is O
available O
on O
direct O
comparison O
of O
additively B-MANP
manufactured E-MANP
porous O
Ta S-MATE
and O
Ti S-MATE
structures O
towards O
early O
stage O
osseointegration S-PRO
. O


In O
this O
study O
, O
we O
have O
fabricated S-CONPRI
porous O
Ta S-MATE
and O
Ti6Al4V S-MATE
( O
Ti64 S-MATE
) O
implants S-APPL
using O
laser B-MANP
engineered I-MANP
net I-MANP
shaping E-MANP
( O
LENS™ O
) O
with O
similar O
volume B-PARA
fraction E-PARA
porosity S-PRO
to O
compare O
the O
influence O
of O
surface S-CONPRI
characteristics O
and O
material S-MATE
chemistry S-CONPRI
on O
in O
vivo O
response O
using O
a O
rat O
distal O
femur O
model S-CONPRI
for O
5 O
and O
12 O
weeks O
. O


We O
have O
also O
assessed O
whether O
surface B-MANP
modification E-MANP
on O
Ti64 S-MATE
can O
elicit O
similar O
in O
vivo O
response O
as S-MATE
porous O
Ta S-MATE
in O
a O
rat O
distal O
femur O
model S-CONPRI
for O
5 O
and O
12 O
weeks O
. O


The O
harvested O
implants S-APPL
were O
histologically O
analyzed O
for O
osteoid O
surface S-CONPRI
per O
bone S-BIOP
surface O
. O


Field B-CHAR
emission I-CHAR
scanning I-CHAR
electron I-CHAR
microscopy E-CHAR
( O
FESEM S-CHAR
) O
was O
done O
to O
assess O
the O
bone-implant B-FEAT
interface E-FEAT
. O


The O
results O
presented O
here O
indicate O
comparable O
performance S-CONPRI
of O
porous S-PRO
Ta O
and O
surface B-MANP
modified E-MANP
porous S-PRO
Ti64 O
implants S-APPL
towards O
early O
stage O
osseointegration S-PRO
at O
5 O
weeks O
post O
implantation S-MANP
through O
seamless O
bone-material O
interlocking O
. O


Design B-FEAT
for I-FEAT
Additive I-FEAT
Manufacturing E-FEAT
( O
DfAM O
) O
allows O
optimising O
parts O
by O
integrating O
complexity S-CONPRI
. O


DfAM O
adds O
value O
to O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
manufacturing S-MANP
in O
terms O
of O
cost O
, O
manufacturing S-MANP
lead B-PARA
time E-PARA
, O
and O
productivity S-CONPRI
. O


Material S-MATE
usage O
is O
the O
main O
cost O
driver O
in O
metal S-MATE
PBF O
and O
is O
determined O
by O
part O
volume S-CONPRI
and O
lattice S-CONPRI
volume O
fraction S-CONPRI
. O


DfAM O
can O
reduce O
the O
manufacturing B-CONPRI
cost E-CONPRI
by O
53.7 O
% O
, O
manufacturing S-MANP
time O
by O
54.3 O
% O
, O
and O
overall O
weight S-PARA
by O
52.5 O
% O
. O


DfAM O
is O
necessary O
to O
increase O
the O
economic O
feasibility S-CONPRI
of O
AM S-MANP
business O
cases O
. O


The O
cost-effectiveness O
of O
metal B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
systems O
in O
high-throughput O
production S-MANP
are O
dominated O
by O
the O
high O
cost O
of O
metallic B-MATE
powder E-MATE
materials S-CONPRI
. O


Metal S-MATE
PBF O
technologies S-CONPRI
become O
more O
competitive O
in O
production S-MANP
scenarios O
when O
Design B-FEAT
for I-FEAT
Additive I-FEAT
Manufacturing E-FEAT
( O
DfAM O
) O
is O
integrated O
to O
embed O
functionality O
through O
shape B-FEAT
complexity E-FEAT
, O
weight S-PARA
, O
and O
material S-MATE
reduction O
through O
topology B-FEAT
optimization E-FEAT
and O
lattice S-CONPRI
structures.This O
study O
investigates S-CONPRI
the O
value O
of O
DfAM O
in O
terms O
of O
unit O
cost O
and O
manufacturing S-MANP
time O
reduction S-CONPRI
. O


Input O
design S-FEAT
parameters O
, O
such O
as S-MATE
lattice O
design-type O
, O
part O
size O
, O
volume B-PARA
fraction E-PARA
, O
material S-MATE
type O
and O
production S-MANP
volumes O
are O
included O
in O
a O
Design-of-Experiment O
to O
model S-CONPRI
their O
impact S-CONPRI
. O


The O
performance S-CONPRI
variables O
for O
cost O
and O
manufacturing S-MANP
time O
were O
assessed O
for O
two O
scenarios O
: O
( O
i O
) O
outsourcing S-CONPRI
scenario O
using O
an O
online O
quotation O
system O
, O
and O
( O
ii O
) O
in-house O
scenario O
utilizing O
a O
decision O
support S-APPL
system O
( O
DSS O
) O
for O
metal S-MATE
PBF.The O
results O
indicate O
that O
the O
size O
of O
the O
part O
and O
the O
lattice S-CONPRI
volume O
fraction S-CONPRI
are O
the O
most O
significant O
parameters S-CONPRI
that O
contribute O
to O
time O
and O
cost O
savings O
. O


This O
study O
shows O
that O
full O
utilization O
of O
build B-MACEQ
platforms E-MACEQ
by O
volume-optimized O
parts O
, O
high O
production S-MANP
volumes O
, O
and O
reduction S-CONPRI
of O
volume B-PARA
fraction E-PARA
lead S-MATE
to O
substantial O
benefits O
for O
metal S-MATE
PBF O
industrialization O
. O


Integration O
of O
DfAM O
and O
lattice B-FEAT
designs E-FEAT
for O
lightweight S-CONPRI
part O
production S-MANP
can O
decrease O
the O
unit O
cost O
of O
production S-MANP
down O
to O
70.6 O
% O
and O
manufacturing S-MANP
time O
can O
be S-MATE
reduced O
significantly O
down O
to O
71.7 O
% O
depending O
on O
the O
manufacturing S-MANP
scenarios O
and O
design S-FEAT
constraints O
when O
comparing O
to O
solid O
infill S-PARA
designs S-FEAT
. O


The O
study O
also O
provides O
a O
case O
example O
of O
a O
bracket S-MACEQ
design O
whose O
cost O
is O
reduced O
by O
53.7 O
% O
, O
manufacturing S-MANP
time O
is O
reduced O
by O
54.3 O
% O
, O
and O
the O
overall O
weight S-PARA
is O
reduced O
significantly O
with O
the O
use O
of O
lattices S-CONPRI
structures O
and O
topology B-FEAT
optimization E-FEAT
. O


The O
capability O
to O
manufacture S-CONPRI
items O
in O
space O
is O
an O
exploration O
enabling O
advancement O
, O
and O
will O
be S-MATE
crucial O
for O
sustainable S-CONPRI
human O
exploration O
as S-MATE
we O
progress O
beyond O
Earth O
orbit O
. O


The O
extrusion S-MANP
based O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
method O
using O
thermoplastics S-MATE
represents O
a O
robust O
and O
simple S-MANP
methodology S-CONPRI
applicable O
to O
printing O
parts O
for O
both O
current O
and O
future O
human O
spaceflight O
exploration O
missions O
. O


Understanding O
the O
performance S-CONPRI
and O
behaviour O
of O
the O
FFF S-MANP
process O
under O
varying O
gravity O
loads O
is O
therefore O
an O
important O
knowledge O
gap O
that O
needs O
to O
be S-MATE
addressed O
in O
order O
to O
fully O
appreciate O
the O
characteristics O
of O
space O
manufactured S-CONPRI
elements S-MATE
. O


In O
this O
study O
, O
we O
detail O
an O
experiment S-CONPRI
conducted O
on O
a O
parabolic O
flight O
campaign O
( O
PFC O
) O
wherein O
we O
produced O
a O
number O
of O
FFF S-MANP
polylactic O
acid O
( O
PLA S-MATE
) O
polymer S-MATE
test O
articles O
and O
compared O
them O
to O
terrestrially O
fabricated S-CONPRI
articles O
. O


We O
report O
on O
the O
methodology S-CONPRI
and O
the O
operational O
parameters S-CONPRI
used O
, O
as S-MATE
well O
as S-MATE
presenting O
an O
analysis O
of O
the O
samples S-CONPRI
via O
optical B-CHAR
microscopy E-CHAR
and O
tomography O
. O


Compressive O
, O
tensile S-PRO
and O
other O
technical O
properties S-CONPRI
are O
reported O
herein O
. O


An O
approach O
to O
teaching O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
course O
for O
engineering S-APPL
students O
is O
suggested O
. O


A O
pedagogical O
model S-CONPRI
was O
developed O
, O
based O
on O
PDL O
strategy O
, O
for O
a O
14-week O
AM S-MANP
course O
. O


The O
students O
designed S-FEAT
and O
3D B-MANP
printed E-MANP
devices O
helping O
people O
with O
disabilities O
. O


The O
projects O
served O
as S-MATE
useful O
collaborative O
learning O
experiences O
for O
AM S-MANP
education O
. O


The O
course O
demonstrates O
the O
potential O
of O
AM B-MANP
technologies E-MANP
as O
innovative O
environment O
. O


The O
present O
study O
suggests O
an O
approach O
to O
teaching O
a O
novel O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
course O
for O
engineering S-APPL
students O
at O
the O
graduate O
level O
, O
developed O
in O
2015 O
and O
taught O
currently O
at O
Afeka O
Academic O
College O
of O
Engineering S-APPL
. O


The O
proposed O
course O
is O
dedicated O
to O
the O
fundamentals O
, O
methods O
, O
materials S-CONPRI
, O
standards S-CONPRI
and O
industrial S-APPL
applications O
of O
AM S-MANP
, O
and O
involves O
introduction O
lectures O
, O
special O
topic O
lectures O
organized O
with O
industry S-APPL
and O
academic O
experts O
, O
laboratory S-CONPRI
training O
and O
final O
engineering S-APPL
projects O
. O


The O
first O
project O
proposed O
by O
the O
students O
was O
to O
develop O
and O
build S-PARA
an O
opener O
for O
medicine S-CONPRI
containers O
; O
the O
second O
was O
to O
design S-FEAT
and O
build S-PARA
a O
device O
for O
pouring O
liquids O
for O
people O
with O
Parkinson O
’ O
s S-MATE
disease O
; O
and O
the O
third O
was O
to O
design S-FEAT
and O
construct O
a O
3D S-CONPRI
puzzle O
for O
blind O
or O
visually O
impaired O
people O
. O


All O
three O
projects O
were O
designed S-FEAT
with O
a O
computer-aided B-ENAT
design E-ENAT
program O
and O
then O
printed O
using O
the O
ABS B-MATE
material E-MATE
. O


Quality B-CONPRI
control E-CONPRI
( O
three-point B-CHAR
bending I-CHAR
tests E-CHAR
and O
light O
microscopy S-CHAR
) O
was O
routinely O
conducted O
on O
standard S-CONPRI
specimens O
printed O
on O
the O
same O
tray O
with O
the O
components S-MACEQ
. O


The O
learning O
process S-CONPRI
included O
two O
iteration O
steps O
that O
were O
executed O
to O
improve O
and O
optimize O
the O
structural B-FEAT
design E-FEAT
. O


The O
final O
3D B-MANP
printed E-MANP
objects O
, O
the O
students O
’ O
presentations O
, O
their O
experience O
, O
as S-MATE
reflected O
in O
their O
final O
reports O
, O
and O
their O
personal O
written O
evaluations O
, O
lead S-MATE
to O
the O
conclusion O
that O
the O
projects O
served O
as S-MATE
useful O
learning O
experience O
for O
engineering S-APPL
education O
. O


Here O
we O
report O
a O
pre-fractal O
antenna O
design S-FEAT
based O
on O
the O
Sierpinski O
tetrahedron O
that O
has O
been O
developed O
with O
additive B-MANP
manufacturing E-MANP
. O


The O
Sierpinski O
tetrahedron-based O
antenna O
was O
simulated O
with O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
( O
FEM S-CONPRI
) O
modeling S-ENAT
and O
experimentally O
tested O
to O
highlight O
its O
potential O
for O
wideband O
communications O
. O


The O
Sierpinski O
tetrahedron-based O
antennas O
were O
fabricated S-CONPRI
by O
two O
methods O
, O
the O
first O
involves O
printing O
the O
antenna O
out O
of O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
, O
followed O
by O
spin O
casting S-MANP
a O
coating S-APPL
of O
an O
ABS S-MATE
solution O
containing O
graphene S-MATE
flakes S-CONPRI
produced O
through O
electrochemical S-CONPRI
exfoliation O
, O
the O
second O
method O
involves O
3D B-MANP
printing E-MANP
the O
antenna O
from O
graphene-impregnated O
polylactic B-MATE
acid E-MATE
( O
PLA S-MATE
) O
filament S-MATE
directly O
without O
any O
coating S-APPL
. O


These O
antennas O
incorporate O
the O
advantages O
of O
3D B-MANP
printing E-MANP
which O
allows O
for O
rapid B-ENAT
prototyping E-ENAT
and O
the O
development O
of O
devices O
with O
complex B-CONPRI
geometries E-CONPRI
. O


Due O
to O
these O
manufacturing S-MANP
advantages O
, O
self-similar O
antennas O
like O
the O
Sierpinski O
tetrahedron O
can O
be S-MATE
realized O
which O
provide O
increased O
gain S-PARA
and O
multi-band O
performance S-CONPRI
. O


Lattice B-FEAT
structures E-FEAT
fabricated S-CONPRI
via O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
offer O
improved O
performance S-CONPRI
over O
traditional B-MANP
manufacturing E-MANP
methods O
, O
however O
, O
predicting O
their O
mechanical B-CONPRI
behaviour E-CONPRI
both O
accurately S-CHAR
and O
with O
acceptable O
computational B-CONPRI
efficiency E-CONPRI
remains O
a O
challenge O
. O


AM S-MANP
associated O
defects S-CONPRI
combined O
with O
multiple O
high O
aspect-ratio O
strut S-MACEQ
elements S-MATE
require O
fine O
3D S-CONPRI
finite-element O
( O
FE S-MATE
) O
meshes O
; O
resulting O
in O
high O
computational O
complexity S-CONPRI
that O
limits S-CONPRI
the O
number O
of O
lattice B-FEAT
unit E-FEAT
cells S-APPL
that O
can O
be S-MATE
practically O
simulated O
. O


Alternatively O
, O
Euler-Bernoulli O
or O
Timoshenko O
beam S-MACEQ
elements O
can O
be S-MATE
specified O
to O
reduce O
computational O
complexity S-CONPRI
. O


However O
, O
these O
beam S-MACEQ
elements O
are O
typically O
based O
on O
idealised O
representations O
that O
exclude O
AM S-MANP
associated O
defects S-CONPRI
. O


This O
research S-CONPRI
proposes O
a O
novel O
method O
which O
combines O
data S-CONPRI
driven O
AM S-MANP
defect O
modelling S-ENAT
, O
Markov O
Chains O
and O
Monte O
Carlo O
( O
MCS O
) O
simulation S-ENAT
techniques O
to O
predict O
the O
stiffness S-PRO
of O
an O
AM S-MANP
lattice O
structure S-CONPRI
. O


Furthermore O
, O
this O
method O
accommodates O
stochastic B-CONPRI
distributions E-CONPRI
of O
AM S-MANP
associated O
defects S-CONPRI
within O
computationally O
effective O
beam S-MACEQ
models O
; O
thereby O
enabling O
the O
simulation S-ENAT
of O
large-scale O
lattice B-FEAT
structures E-FEAT
at O
a O
relatively O
low O
computational O
cost O
. O


The O
proposed O
method O
is O
aimed O
at O
reliability S-CHAR
analysis O
or O
a O
probabilistic O
approach O
to O
structural B-CHAR
analysis E-CHAR
of O
AM S-MANP
lattice O
structures O
. O


The O
combination O
of O
generating O
AM S-MANP
strut O
digital O
realisations O
and O
MCS O
, O
resulted O
in O
a O
variety O
of O
possible O
strut S-MACEQ
deformation S-CONPRI
shapes O
and O
effective O
diameters O
under O
axial O
compression S-PRO
. O


The O
propagation O
of O
effective O
diameter S-CONPRI
variability O
to O
the O
lattice-scale O
level O
displayed O
the O
possible O
variation S-CONPRI
in O
the O
mechanical B-CONPRI
response E-CONPRI
of O
AM S-MANP
lattice O
structure S-CONPRI
. O


Simulations S-ENAT
are O
validated O
and O
insight O
into O
how O
a O
lattice B-FEAT
structures E-FEAT
unit O
cell B-CONPRI
topology E-CONPRI
affects O
simulation B-CHAR
accuracy E-CHAR
is O
discussed O
. O


The O
use O
of O
laser B-MANP
additive I-MANP
manufacturing E-MANP
based O
on O
melting S-MANP
of O
injected O
zirconium B-MATE
powder E-MATE
under O
localized O
shielding O
was O
evaluated O
in O
terms O
of O
microstructures S-MATE
and O
mechanical B-CONPRI
properties E-CONPRI
of O
thin O
wall O
structures O
. O


The O
material S-MATE
was O
characterized O
in O
both O
the O
laser S-ENAT
travel O
and O
the O
build B-PARA
directions E-PARA
. O


The O
microstructures S-MATE
, O
tensile B-PRO
properties E-PRO
and O
fracture S-CONPRI
behavior O
were O
assessed O
for O
deposits O
made O
using O
as-received O
and O
recycled S-CONPRI
powder S-MATE
. O


Electron O
backscattered O
diffraction S-CHAR
and O
transmission S-CHAR
electron O
microcopy O
revealed O
a O
fine O
structure S-CONPRI
of O
Zr-α O
laths O
with O
nano-scale S-CONPRI
iron-rich O
precipitates S-MATE
at O
the O
lath O
interfaces O
. O


The O
properties S-CONPRI
of O
the O
fabricated S-CONPRI
components S-MACEQ
, O
which O
were O
made O
using O
new O
as-received O
powder S-MATE
were O
comparable O
to O
a O
Zr-2.5Nb O
alloy S-MATE
substrate O
, O
with O
yield B-PRO
strengths E-PRO
of O
over O
569 O
MPa S-CONPRI
and O
uniform O
strains O
up O
to O
the O
ultimate O
tensile B-PRO
stress E-PRO
ranging O
from O
8.5 O
to O
9.9 O
% O
. O


However O
, O
when O
recycled S-CONPRI
powder S-MATE
was O
used O
, O
the O
ductility S-PRO
dropped O
with O
total O
strains O
to O
failure S-CONPRI
of O
1.0–7.5 O
% O
, O
as S-MATE
a O
result O
of O
porosity S-PRO
and O
unmelted O
powder B-MATE
particles E-MATE
serving O
as S-MATE
brittle O
inclusions S-MATE
in O
the O
deposited O
material S-MATE
. O


3D B-MANP
printed E-MANP
AlSi10Mg O
can O
be S-MATE
used O
in O
electrical B-APPL
applications E-APPL
once O
heat S-CONPRI
treated O
Electrical B-CHAR
resistivity E-CHAR
values O
once O
heat S-CONPRI
treated O
are O
comparable O
to O
cast S-MANP
alloy S-MATE
values O
Resistivity S-PRO
of O
as-built O
AlSi10Mg S-MATE
increases O
by O
27 O
% O
depending O
on O
build B-PARA
orientation E-PARA
Heat O
treatment O
can O
reduce O
as-built O
resistivity S-PRO
by O
33 O
% O
Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
opens O
up O
a O
design B-CONPRI
freedom E-CONPRI
beyond O
the O
limits S-CONPRI
of O
traditional B-MANP
manufacturing E-MANP
techniques O
. O


Electrical S-APPL
windings O
created O
through O
AM S-MANP
could O
lead S-MATE
to O
more O
powerful O
and O
compact S-MANP
electric O
motors O
, O
but O
only O
if O
the O
electrical B-CONPRI
properties E-CONPRI
of O
the O
AM S-MANP
printed O
part O
can O
be S-MATE
shown O
to O
be S-MATE
similar O
to O
conventionally O
manufactured S-CONPRI
systems O
. O


Until O
now O
, O
no O
study O
has O
reported O
on O
the O
suitability O
of O
AM B-MACEQ
parts E-MACEQ
for O
electrical B-APPL
applications E-APPL
as S-MATE
there O
are O
few O
appropriate O
materials S-CONPRI
available O
to O
AM S-MANP
for O
this O
purpose O
. O


AlSi10Mg S-MATE
is O
a O
relatively O
good O
electrical S-APPL
conductor S-MATE
that O
does O
not O
have O
the O
same O
reported O
issues O
associated O
with O
processing O
pure O
aluminium S-MATE
or O
copper S-MATE
via O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
. O


Here O
, O
experiments O
were O
conducted O
to O
test O
the O
effects O
of O
geometry S-CONPRI
and O
heat B-MANP
treatments E-MANP
on O
the O
resistivity S-PRO
of O
AlSi10Mg S-MATE
processed O
by O
SLM S-MANP
. O


It O
was O
found O
that O
post O
heat B-MANP
treatments E-MANP
resulted O
in O
a O
resistivity S-PRO
that O
was O
33 O
% O
lower O
than O
the O
as-built O
material S-MATE
. O


The O
heat B-MANP
treatment E-MANP
also O
eliminated O
variance O
in O
the O
resistivity S-PRO
of O
as-built O
parts O
due O
to O
initial O
build B-PARA
orientation E-PARA
. O


By O
conducting O
these O
tests O
, O
it O
was O
found O
that O
, O
with O
this O
material S-MATE
, O
there O
is O
no O
penalty O
in O
terms O
of O
higher O
resistivity S-PRO
for O
using O
AM S-MANP
in O
electrical B-APPL
applications E-APPL
, O
thus O
allowing O
more O
design B-CONPRI
freedom E-CONPRI
in O
future O
electrical B-APPL
applications E-APPL
. O


Future O
exploration O
missions O
beyond O
low-Earth O
orbit O
would O
significantly O
benefit O
from O
a O
closed O
loop O
recyclable S-CONPRI
Additive B-MANP
Manufactured E-MANP
capability O
, O
allowing O
the O
production S-MANP
of O
general O
purpose O
tools S-MACEQ
and O
items O
in O
a O
time O
and O
cost O
effective O
manner O
. O


To O
realize O
this O
ambition O
, O
we O
present O
a O
feasibility S-CONPRI
study O
of O
a O
Solvent-Cast O
Direct-Write O
method O
using O
Polyvinyl O
Alcohol O
as S-MATE
biodegradable O
material S-MATE
. O


Process B-CONPRI
parameters E-CONPRI
such O
as S-MATE
solution O
viscosity S-PRO
, O
evaporation B-CHAR
rate E-CHAR
, O
print S-MANP
pressure S-CONPRI
and O
scan B-PARA
speed E-PARA
are O
optimized O
in O
order O
to O
achieve O
a O
consistent O
and O
reliable O
print S-MANP
outcome O
. O


We O
demonstrate O
the O
process S-CONPRI
by O
fabricating S-MANP
test O
complex B-CONPRI
geometries E-CONPRI
of O
sample S-CONPRI
specimens O
. O


Moreover O
, O
we O
report O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
printed O
geometries S-CONPRI
as S-MATE
well O
as S-MATE
the O
recyclability S-CONPRI
aspects O
. O


The O
aerospace S-APPL
, O
automotive S-APPL
and O
medical B-APPL
industries E-APPL
are O
suffering O
from O
significant O
number O
of O
counterfeited O
metallic S-MATE
products O
that O
not O
only O
have O
caused O
financial O
losses O
but O
also O
endanger O
lives O
. O


The O
rapid O
development O
of O
additive B-MANP
manufacturing E-MANP
technologies O
makes O
such O
a O
situation O
even O
worse O
. O


In O
this O
investigation O
, O
we O
successfully O
applied O
a O
novel O
hybrid O
powder S-MATE
delivery O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
approach O
to O
embed O
dissimilar O
tagging O
material S-MATE
( O
Cu10Sn O
copper B-MATE
alloy E-MATE
) O
safety S-CONPRI
features O
( O
e.g O
. O


QR O
code O
) O
into O
metallic S-MATE
components S-MACEQ
made O
of O
316 O
L O
stainless B-MATE
steel E-MATE
. O


X-ray B-CHAR
imaging E-CHAR
was O
found O
to O
be S-MATE
a O
suitable O
method O
for O
the O
identification O
of O
the O
embedded O
safety S-CONPRI
features O
up O
to O
15 O
mm S-MANP
in O
depth O
. O


X-ray S-CHAR
fluorescence S-CHAR
was O
used O
for O
the O
chemical B-CONPRI
composition E-CONPRI
identification O
of O
the O
imbedded O
security O
tagging O
material S-MATE
. O


A O
criterion O
for O
the O
selection O
of O
tagging O
material S-MATE
, O
its O
dimensions S-FEAT
and O
imbedding O
depth O
is O
proposed O
. O


The O
multiple O
material S-MATE
SLM O
technology S-CONPRI
was O
shown O
to O
offer O
the O
potential O
to O
be S-MATE
integrated O
into O
metallic S-MATE
component S-MACEQ
production O
for O
embedding O
anti-counterfeiting O
features O
. O


The O
development O
of O
cooling S-MANP
devices O
is O
important O
for O
many O
industrial S-APPL
products O
, O
and O
the O
lattice B-FEAT
structure E-FEAT
fabricated S-CONPRI
by O
additive B-MANP
manufacturing E-MANP
is O
expected O
to O
be S-MATE
useful O
for O
effective O
liquid O
cooling S-MANP
. O


However O
, O
lattice B-FEAT
density E-FEAT
should O
be S-MATE
carefully O
designed S-FEAT
for O
an O
effective O
arrangement O
of O
coolant S-MATE
flow O
. O


In O
this O
research S-CONPRI
, O
we O
optimize O
the O
lattice B-FEAT
density E-FEAT
distribution S-CONPRI
using O
a O
lattice B-FEAT
structure E-FEAT
approximation O
and O
the O
gradient O
method O
. O


Fluid B-PRO
flow E-PRO
is O
approximated O
by O
deriving O
effective O
properties S-CONPRI
from O
the O
Darcy–Forchheimer O
law O
and O
analyzing O
the O
flow O
according O
to O
the O
Brinkman–Forchheimer O
equation O
. O


We O
use O
a O
simple S-MANP
basic O
lattice S-CONPRI
shape O
composed O
of O
pillars O
, O
optimizing O
only O
its O
density B-PRO
distribution E-PRO
by O
setting O
the O
pillar O
diameter S-CONPRI
as S-MATE
the O
design S-FEAT
variable O
. O


Steady-state O
pressure S-CONPRI
and O
temperature S-PARA
reductions O
are O
treated O
as S-MATE
multi-objective O
functions O
. O


Through O
2D S-CONPRI
and O
3D S-CONPRI
numerical O
studies O
, O
we O
discuss O
the O
validity O
and O
limitations O
of O
the O
proposed O
method O
. O


Although O
observable O
errors S-CONPRI
in O
accuracy S-CHAR
exist O
between O
the O
results O
obtained O
from O
the O
optimization S-CONPRI
and O
full O
scale O
models O
, O
relative O
performance B-CONPRI
optimization E-CONPRI
was O
considered O
successful O
. O


Additive B-MANP
manufacturing E-MANP
has O
seen O
large O
growth O
due O
to O
its O
numerous O
process S-CONPRI
advantages O
, O
yet O
some O
undesirable O
defects S-CONPRI
in O
additive B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
products O
include O
pores S-PRO
and O
micro-cracks S-CONPRI
. O


These O
defects S-CONPRI
weaken O
the O
high O
temperature S-PARA
oxidation B-PRO
resistance E-PRO
of O
the O
final O
parts O
. O


In O
this O
work O
, O
laser S-ENAT
shock O
peening S-MANP
( O
LSP O
) O
is O
used O
as S-MATE
a O
post-treatment S-MANP
method O
to O
change O
the O
surface S-CONPRI
characteristics O
of O
selective B-MANP
laser I-MANP
melted E-MANP
( O
SLM S-MANP
) O
nano-TiC O
particle-reinforced O
Inconel B-MATE
625 E-MATE
nanocomposites O
( O
TiC/IN625 O
) O
. O


The O
effects O
of O
LSP O
on O
surface B-CHAR
morphology E-CHAR
, O
residual B-PRO
stress E-PRO
, O
microhardness S-CONPRI
, O
microstructure S-CONPRI
, O
and O
high O
temperature S-PARA
oxidation S-MANP
behavior O
of O
fabricated S-CONPRI
parts O
are O
studied O
. O


The O
results O
indicate O
pores S-PRO
in O
the O
as-built O
sample S-CONPRI
can O
be S-MATE
closed O
by O
the O
severe O
plastic B-PRO
deformation E-PRO
, O
which O
is O
induced O
by O
LSP O
. O


The O
maximum O
hardness S-PRO
is O
found O
to O
reach O
462 O
± O
7 O
HV O
with O
a O
∼ O
460 O
μm O
hardened S-MANP
layer O
, O
and O
the O
surface S-CONPRI
stress S-PRO
state O
transforms O
from O
tensile S-PRO
to O
compressive O
after O
LSP O
. O


The O
full O
width O
at O
half O
maximum O
( O
FWHM O
) O
values O
of O
the O
( O
111 O
) O
and O
( O
200 O
) O
diffraction S-CHAR
broaden O
, O
which O
can O
be S-MATE
attributed O
to O
grain B-CHAR
refinement E-CHAR
and O
an O
increase O
in O
lattice S-CONPRI
strain O
in O
the O
LSP O
samples S-CONPRI
. O


Dislocation S-CONPRI
walls O
and O
dislocation S-CONPRI
tangles O
with O
high O
dislocation B-PRO
density E-PRO
form O
in O
the O
LSP O
sample S-CONPRI
. O


Compared O
with O
as-built O
sample S-CONPRI
, O
the O
LSP O
samples S-CONPRI
exhibit O
lower O
mass O
gain S-PARA
after O
oxidation S-MANP
at O
900 O
°C O
for O
100 O
h O
, O
indicating O
that O
LSP O
samples S-CONPRI
have O
greater O
oxidation B-PRO
resistance E-PRO
at O
high O
temperature S-PARA
. O


The O
underlying O
mechanism S-CONPRI
governing O
the O
high O
temperature S-PARA
oxidation B-PRO
resistance E-PRO
is O
proposed O
based O
on O
the O
experimental S-CONPRI
results O
. O


This O
study O
shows O
that O
LSP O
can O
be S-MATE
used O
as S-MATE
an O
effective O
method O
to O
modify O
the O
surface S-CONPRI
characteristics O
of O
SLM S-MANP
TiC/IN625 O
. O


Many O
applications O
require O
structures O
composed O
of O
layers O
of O
heterogeneous S-CONPRI
materials O
and O
prefabricated O
components S-MACEQ
embedded O
between O
the O
layers O
. O


The O
existing O
additive B-MANP
manufacturing I-MANP
process E-MANP
based O
on O
layered O
object O
manufacturing S-MANP
is O
not O
able O
to O
handle O
multiple O
layer S-PARA
materials O
and O
can O
not O
embed O
prefabricated O
components S-MACEQ
. O


Moreover O
, O
the O
existing O
process S-CONPRI
imposes O
restrictions O
on O
the O
material S-MATE
options O
. O


This O
significantly O
limits S-CONPRI
the O
type O
of O
heterogeneous S-CONPRI
structures O
that O
can O
be S-MATE
manufactured O
using O
traditional O
additive B-MANP
manufacturing E-MANP
. O


This O
paper O
presents O
an O
extension O
of O
sheet B-MANP
lamination E-MANP
object O
manufacturing B-MANP
process E-MANP
by O
using O
a O
robotic O
cell S-APPL
to O
perform O
the O
sheet S-MATE
manipulation O
and O
handling O
. O


It O
makes O
the O
following O
three O
advances O
: O
( O
1 O
) O
enabling O
the O
use O
of O
multi-material S-CONPRI
layers O
and O
inclusion S-MATE
of O
prefabricated O
components S-MACEQ
between O
the O
layers O
, O
( O
2 O
) O
developing O
an O
algorithmic O
foundation O
to O
facilitate O
automated O
generation O
of O
robot S-MACEQ
instructions O
, O
and O
( O
3 O
) O
identifying O
the O
relevant O
process S-CONPRI
constraints O
related O
to O
speed O
, O
accuracy S-CHAR
, O
and O
strength S-PRO
. O


We O
demonstrate O
the O
system O
capabilities O
by O
using O
three O
case B-CONPRI
studies E-CONPRI
. O


Pure O
Zn S-MATE
bulk O
samples S-CONPRI
of O
good O
formation O
quality S-CONPRI
and O
high O
tensile B-PRO
properties E-PRO
were O
produced O
. O


The O
effect O
of O
scanning B-PARA
speed E-PARA
on O
grain B-PRO
size E-PRO
, O
morphology S-CONPRI
and O
texture S-FEAT
was O
clarified O
. O


Crystallographic O
effects O
resulted O
to O
strong O
anisotropy S-PRO
in O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
existence O
of O
tiny O
pores S-PRO
in O
LPBF S-MANP
samples O
influenced O
corrosion B-PRO
behavior E-PRO
. O


Corrosion S-CONPRI
rate O
increased O
with O
increasing O
scanning B-PARA
speed E-PARA
at O
the O
initial O
stage O
of O
immersion O
, O
and O
the O
gap O
narrowed O
as S-MATE
immersion O
time O
passed O
. O


Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
has O
been O
previously O
used O
to O
produce O
customized O
medical B-APPL
implants E-APPL
from O
biodegradable O
Zn S-MATE
and O
its O
alloys S-MATE
. O


In O
this O
study O
, O
we O
investigated O
the O
effect O
of O
the O
grain B-CONPRI
structure E-CONPRI
on O
the O
mechanical B-CONPRI
properties E-CONPRI
and O
in O
vitro O
corrosion B-PRO
behavior E-PRO
of O
pure O
Zn S-MATE
samples S-CONPRI
, O
by O
varying O
the O
scanning B-PARA
speed E-PARA
and O
building B-PARA
direction E-PARA
during O
the O
LPBF S-MANP
process O
. O


Increasing O
the O
scanning B-PARA
speed E-PARA
from O
300 O
to O
700 O
mm/s O
resulted O
in O
finer O
grains S-CONPRI
, O
irregular O
grain S-CONPRI
morphology O
, O
and O
a O
weaker O
grain S-CONPRI
texture O
, O
which O
enhanced O
the O
strength S-PRO
and O
ductility S-PRO
. O


Vertically O
built O
LPBF S-MANP
Zn O
tensile S-PRO
samples S-CONPRI
had O
higher O
strength S-PRO
and O
ductility S-PRO
compared O
with O
horizontally O
built O
samples S-CONPRI
, O
indicating O
strong O
anisotropy S-PRO
of O
the O
mechanical B-CONPRI
properties E-CONPRI
. O


Electrochemical B-CHAR
tests E-CHAR
revealed O
that O
the O
in O
vitro O
corrosion B-PRO
behavior E-PRO
was O
not O
strongly O
correlated S-CONPRI
with O
the O
scanning B-PARA
speed E-PARA
. O


This O
was O
attributable O
to O
the O
random O
distribution S-CONPRI
of O
tiny O
pores S-PRO
on O
the O
surface S-CONPRI
of O
the O
LPBF S-MANP
samples O
, O
although O
immersion O
tests O
showed O
that O
the O
sample S-CONPRI
prepared O
with O
the O
highest O
scanning B-PARA
speed E-PARA
exhibited O
the O
highest O
corrosion S-CONPRI
rate O
. O


With O
increasing O
immersion O
time O
in O
Hank O
’ O
s S-MATE
solution O
, O
the O
Zn2+ O
concentrations O
of O
the O
samples S-CONPRI
produced O
with O
different O
scanning B-PARA
speeds E-PARA
increased O
, O
their O
pH S-CONPRI
stabilized O
, O
and O
the O
differences O
between O
the O
corrosion S-CONPRI
rates O
narrowed O
. O


The O
effects O
of O
the O
processing O
parameters S-CONPRI
on O
the O
final O
performance S-CONPRI
of O
the O
samples S-CONPRI
could O
be S-MATE
well O
explained O
by O
the O
grain B-CONPRI
structures E-CONPRI
. O


The O
findings O
of O
this O
study O
afford O
bases O
for O
selecting O
the O
processing O
parameters S-CONPRI
for O
optimizing O
the O
properties S-CONPRI
of O
LPBF-produced O
Zn S-MATE
parts O
for O
biodegradable O
applications O
. O


Existing O
powder B-MACEQ
feedstock E-MACEQ
metrics O
for O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
are O
related O
to O
packing O
efficiency O
and O
flowability O
, O
and O
newer O
techniques O
, O
such O
as S-MATE
powder O
rheometry O
and O
dynamic S-CONPRI
avalanche O
testing S-CHAR
, O
have O
received O
recent O
attention O
in O
the O
literature O
. O


To O
date O
, O
however O
, O
no O
powder S-MATE
characterization O
technique O
is O
able O
to O
predict O
the O
spreadability O
of O
AM S-MANP
feedstock O
. O


This O
study O
endeavored O
to O
establish O
viable O
powder S-MATE
spreadability O
metrics O
through O
the O
development O
of O
a O
spreadability O
testing S-CHAR
rig O
that O
emulates O
the O
recoating O
conditions O
present O
in O
commercial O
PBF B-MANP
AM E-MANP
systems O
. O


As S-MATE
no O
metrics O
for O
spreadability O
currently O
exist O
, O
four O
potential O
metrics O
were O
evaluated O
in O
a O
3∙23 O
split O
plot O
experimental B-CONPRI
design E-CONPRI
. O


These O
four O
metrics O
were O
: O
( O
1 O
) O
the O
percentage O
of O
the O
build B-MACEQ
plate E-MACEQ
covered O
by O
spread S-CONPRI
powder S-MATE
, O
( O
2 O
) O
the O
rate O
of O
powder S-MATE
deposition S-CONPRI
, O
( O
3 O
) O
the O
average S-CONPRI
avalanching O
angle O
of O
the O
powder S-MATE
, O
and O
( O
4 O
) O
the O
rate O
of O
change O
of O
the O
avalanching O
angle O
. O


Three O
samples S-CONPRI
of O
gas B-MANP
atomized E-MANP
, O
Al-10Si-0.5 O
Mg S-MATE
PBF O
powder S-MATE
representing O
differing O
degrees O
of O
quality S-CONPRI
were O
used O
as S-MATE
the O
levels O
of O
the O
powder S-MATE
quality O
input O
variable O
. O


As S-MATE
no O
powder S-MATE
quality O
metrics O
have O
been O
shown O
to O
be S-MATE
indicative O
of O
powder S-MATE
spreadability O
in O
PBF S-MANP
, O
various O
bulk O
powder S-MATE
characteristics O
were O
used O
as S-MATE
the O
powder S-MATE
quality O
indicator O
during O
ANOVA O
. O


Of O
the O
four O
metrics O
tested O
, O
the O
average S-CONPRI
avalanching O
angle O
, O
while O
statistically O
dependent O
of O
the O
powders S-MATE
angle O
of O
repose O
, O
showed O
poor O
correlation O
with O
experimental B-CONPRI
data E-CONPRI
. O


poor O
build B-MACEQ
plate E-MACEQ
coverage O
and O
powder S-MATE
clumping O
, O
as S-MATE
measured O
by O
the O
viable O
spreading O
metrics O
. O


Other O
processing O
parameters S-CONPRI
, O
such O
as S-MATE
the O
recoating O
speed O
and O
the O
recoater B-MACEQ
blade E-MACEQ
material S-MATE
were O
shown O
to O
also O
influence O
the O
spread B-CONPRI
quality E-CONPRI
. O


A O
design S-FEAT
strategy O
for O
lattice S-CONPRI
cell S-APPL
configurations O
beyond O
Maxwell B-CONPRI
criterion E-CONPRI
. O


Established O
theoretical B-CONPRI
models E-CONPRI
to O
predict O
compressive O
modulus O
and O
strength S-PRO
. O


Compressive B-CHAR
tests E-CHAR
and O
μ-CT O
to O
assess O
mechanical B-CONPRI
properties E-CONPRI
and O
defects S-CONPRI
. O


A O
finite B-CONPRI
element E-CONPRI
modeling O
method O
based O
on O
inherent O
manufacturing S-MANP
defects S-CONPRI
. O


A O
comparison O
of O
experimental S-CONPRI
and O
theoretical S-CONPRI
results O
rendered O
minimal O
deviation O
. O


The O
development O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technology S-CONPRI
exhibits O
potential O
for O
the O
design S-FEAT
and O
manufacturing S-MANP
of O
complex O
lattice B-FEAT
structures E-FEAT
. O


Herein O
, O
a O
novel O
design S-FEAT
strategy O
is O
proposed O
for O
the O
lattice B-FEAT
unit E-FEAT
cell S-APPL
configurations O
, O
including O
triangular O
prism O
( O
T O
) O
, O
quadrangular O
prism O
( O
Q O
) O
and O
hexagonal S-FEAT
prism O
( O
H O
) O
, O
by O
considering O
the O
tight O
spatial O
arrangement O
and O
manufacturing B-CONPRI
constraints E-CONPRI
. O


Moreover O
, O
the O
influence O
of O
altering O
the O
degree O
of O
freedom O
of O
nodes O
, O
caused O
by O
additional O
struts S-MACEQ
, O
on O
mechanical S-APPL
performance O
and O
energy B-CHAR
absorption I-CHAR
capacity E-CHAR
is O
systematically O
investigated O
by O
theoretical S-CONPRI
modeling S-ENAT
, O
experimental S-CONPRI
characterization O
and O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
. O


A O
series O
of O
lattice B-FEAT
core E-FEAT
sandwich O
panels O
is O
designed S-FEAT
and O
manufactured S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
. O


X-ray B-CHAR
micro-computed I-CHAR
tomography E-CHAR
( O
μ-CT O
) O
is O
carried O
out O
to O
obtain O
the O
realistic O
geometrical O
information O
. O


Quasi-static S-CONPRI
uniaxial O
compressive B-CHAR
tests E-CHAR
are O
performed O
to O
investigate O
the O
failure B-PRO
mechanism E-PRO
and O
mechanical S-APPL
performance O
. O


The O
results O
reveal O
that O
the O
joint S-CONPRI
connectivity O
of O
the O
unit B-CONPRI
cell E-CONPRI
increased O
with O
the O
increase O
of O
the O
number O
of O
the O
struts S-MACEQ
, O
resulting O
in O
superior O
compressive O
modulus O
and O
ultimate B-PRO
strength E-PRO
. O


The O
main O
deformation S-CONPRI
mode O
of O
cells S-APPL
is O
gradually O
changed O
from O
bending-dominated O
to O
stretch-dominated O
with O
the O
increase O
of O
the O
joint S-CONPRI
connectivity O
. O


The O
proposed O
design S-FEAT
ensures O
the O
performance B-CONPRI
consistency E-CONPRI
of O
the O
manufactured S-CONPRI
struts O
and O
facilitates O
the O
theoretical B-CONPRI
predictions E-CONPRI
and O
analysis O
. O


Furthermore O
, O
the O
specific B-CONPRI
energy I-CONPRI
absorption E-CONPRI
of O
the O
structure S-CONPRI
also O
increased O
with O
the O
increase O
of O
joint S-CONPRI
connectivity O
. O


In O
the O
case O
of O
unit B-CONPRI
cells E-CONPRI
with O
different O
configurations O
, O
T O
series O
rendered O
superior O
specific B-PRO
strength E-PRO
and O
specific B-CONPRI
energy I-CONPRI
absorption E-CONPRI
, O
whereas O
Q O
series O
exhibited O
excellent O
specific B-PRO
stiffness E-PRO
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
rapidly O
moving O
from O
research S-CONPRI
to O
commercial O
applications O
due O
to O
its O
ability O
to O
produce O
geometric O
features O
difficult O
or O
impossible O
to O
generate O
by O
conventional B-MANP
machining E-MANP
. O


Fielded O
components S-MACEQ
need O
to O
endure O
fatigue S-PRO
loadings O
over O
long O
operational O
lifetimes O
. O


This O
work O
evaluates O
the O
ability O
of O
shot O
and O
laser B-MANP
peening E-MANP
to O
enhance O
the O
fatigue S-PRO
lifetime O
and O
strength S-PRO
of O
AM B-MACEQ
parts E-MACEQ
. O


As S-MATE
previously O
shown O
, O
peening S-MANP
processes O
induce O
beneficial O
microstructure S-CONPRI
and O
residual B-PRO
stress E-PRO
enhancement O
; O
this O
work O
takes O
a O
step S-CONPRI
to O
demonstrate O
the O
fatigue S-PRO
enhancement O
of O
peening S-MANP
including O
for O
the O
case O
of O
geometric O
stress S-PRO
risers S-MACEQ
as S-MATE
expected O
for O
fielded O
AM S-MANP
components O
. O


We O
present O
AM S-MANP
sample O
fatigue S-PRO
results O
with O
and O
without O
a O
stress S-PRO
riser S-MACEQ
using O
untreated O
baseline O
samples S-CONPRI
and O
shot O
and O
laser B-MANP
peening E-MANP
surface O
treatments O
. O


Laser B-MANP
peening E-MANP
is O
clearly O
shown O
to O
provide O
superior O
fatigue B-PRO
life E-PRO
and O
strength S-PRO
. O


We O
also O
investigated O
the O
ability O
of O
analysis O
to O
select O
laser B-MANP
peening E-MANP
parameters O
and O
coverage O
that O
can O
shape O
and/or O
correctively O
reshape O
AM S-MANP
components O
to O
a O
high O
degree O
of O
precision S-CHAR
. O


We O
demonstrated O
this O
potential O
by O
shaping S-MANP
and O
shape O
correction O
using O
our O
finite B-CONPRI
element E-CONPRI
based O
predictive O
modeling S-ENAT
and O
highly O
controlled O
laser B-MANP
peening E-MANP
. O


The O
present O
work O
addressed O
the O
challenges O
of O
identifying O
applicable O
Non-Destructive B-CHAR
Testing E-CHAR
( O
NDT S-CONPRI
) O
techniques O
suitable O
for O
inspection S-CHAR
and O
materials S-CONPRI
characterization O
techniques O
for O
Wire B-MANP
and I-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
parts O
. O


With O
the O
view O
of O
transferring O
WAAM S-MANP
to O
the O
industry S-APPL
and O
qualifying O
the O
manufacturing B-MANP
process E-MANP
for O
applications O
such O
as S-MATE
structural O
components S-MACEQ
, O
the O
quality S-CONPRI
of O
the O
produced O
parts O
needs O
to O
be S-MATE
assured O
. O


Thus O
, O
the O
main O
objective O
of O
this O
paper O
is O
to O
review O
the O
main O
NDT S-CONPRI
techniques O
and O
assess O
the O
capability O
of O
detecting O
WAAM S-MANP
defects S-CONPRI
, O
for O
inspection S-CHAR
either O
in O
a O
monitoring O
, O
in-process O
or O
post-process S-CONPRI
scenario O
. O


Radiography S-ENAT
and O
ultrasonic O
testing S-CHAR
were O
experimentally O
tested O
on O
reference O
specimens O
in O
order O
to O
compare O
the O
techniques O
capabilities O
. O


Metallographic O
, O
hardness S-PRO
and O
electrical B-PRO
conductivity E-PRO
analysis O
were O
also O
applied O
to O
the O
same O
specimens O
for O
material S-MATE
characterization O
. O


Experimental S-CONPRI
outcomes O
prove O
that O
typical O
WAAM S-MANP
defects S-CONPRI
can O
be S-MATE
detected O
by O
the O
referred O
techniques O
. O


The O
electrical B-PRO
conductivity E-PRO
measurement O
may O
complement O
or O
substitute O
some O
destructive O
methods O
used O
in O
AM S-MANP
processing O
. O


Compressive O
creep S-PRO
properties O
of O
AlSi10Mg S-MATE
parts O
produced O
by O
additive B-MANP
manufacturing E-MANP
selective O
laser S-ENAT
melting O
( O
AM-SLM O
) O
were O
studied O
using O
a O
spark B-MANP
plasma I-MANP
sintering E-MANP
( O
SPS S-MANP
) O
apparatus O
, O
capable O
of O
performing O
uniaxial O
compressive O
creep B-CHAR
tests E-CHAR
. O


Stress S-PRO
relief-treated O
specimens O
were O
tested O
under O
an O
applied O
stress S-PRO
of O
100–130 O
MPa S-CONPRI
in O
the O
175–225 O
°C O
temperature B-PARA
range E-PARA
. O


The O
creep S-PRO
parameters O
( O
i.e. O
, O
stress S-PRO
exponent O
n S-MATE
and O
apparent O
activation O
energy O
Q O
) O
, O
were O
empirically O
determined O
. O


The O
experimental S-CONPRI
results O
, O
together O
with O
microstructural S-CONPRI
examination O
of O
specimens O
, O
indicate O
that O
plastic B-PRO
deformation E-PRO
was O
controlled O
by O
dislocation S-CONPRI
activity O
. O


Furthermore O
, O
it O
is O
suggested O
that O
the O
annihilation O
process S-CONPRI
of O
dislocations S-CONPRI
during O
creep S-PRO
was O
enhanced O
by O
the O
electric O
current O
. O


This O
experimental S-CONPRI
study O
investigates S-CONPRI
the O
combined O
effect O
of O
the O
three O
primary O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
build B-PARA
orientations E-PARA
( O
0° O
, O
45° O
, O
and O
90° O
) O
and O
an O
extensive O
array O
of O
heat B-MANP
treatment E-MANP
plans O
on O
the O
plastic S-MATE
anisotropy S-PRO
of O
maraging B-MATE
steel E-MATE
300 O
( O
MS1 O
) O
fabricated S-CONPRI
on O
the O
EOSINT O
M280 O
Direct B-MANP
Metal I-MANP
Laser I-MANP
Sintering E-MANP
( O
DMLS S-MANP
) O
system O
. O


The O
alloy S-MATE
's O
microstructure S-CONPRI
, O
hardness S-PRO
, O
tensile B-PRO
properties E-PRO
and O
plastic S-MATE
strain O
behaviour O
have O
been O
examined O
for O
various O
strengthening S-MANP
heat-treatment O
plans O
to O
assess O
the O
influence O
of O
the O
time O
and O
temperature S-PARA
combinations O
on O
plastic S-MATE
anisotropy S-PRO
and O
mechanical B-CONPRI
properties E-CONPRI
( O
e.g O
. O


strength S-PRO
, O
ductility S-PRO
) O
. O


A O
comprehensive O
visual O
representation O
of O
the O
material S-MATE
's O
overall O
mechanical B-CONPRI
properties E-CONPRI
, O
for O
all O
three O
AM S-MANP
build O
orientations S-CONPRI
, O
against O
the O
various O
heat B-MANP
treatment E-MANP
plans O
is O
offered O
through O
time O
– O
temperature S-PARA
contour S-FEAT
maps O
. O


Considerable O
plastic S-MATE
anisotropy S-PRO
has O
been O
confirmed O
in O
the O
as-built O
condition O
, O
which O
can O
be S-MATE
reduced O
by O
aging O
heat-treatment O
, O
as S-MATE
verified O
in O
this O
study O
. O


However O
, O
it O
has O
identified O
that O
a O
degree O
of O
transverse O
strain B-PRO
anisotropy E-PRO
is O
likely O
to O
remain O
due O
to O
the O
AM S-MANP
alloy S-MATE
's O
fabrication S-MANP
history O
, O
a O
finding O
that O
has O
not O
been O
previously O
reported O
in O
the O
literature O
. O


Moreover O
, O
the O
heat B-MANP
treatment E-MANP
plan O
( O
6h O
at O
490 O
°C O
) O
recommended O
by O
the O
DMLS S-MANP
system O
manufacturer S-CONPRI
has O
been O
found O
not O
to O
be S-MATE
the O
optimal O
in O
terms O
of O
achieving O
high O
strength S-PRO
, O
hardness S-PRO
, O
ductility S-PRO
and O
low O
anisotropy S-PRO
for O
the O
MS1 O
material S-MATE
. O


With O
the O
use O
of O
the O
comprehensive O
experimental B-CONPRI
data E-CONPRI
collected O
and O
analysed O
in O
this O
study O
, O
and O
presented O
in O
the O
constructed O
contour S-FEAT
maps O
, O
the O
alloy S-MATE
's O
heat B-MANP
treatment E-MANP
parameters O
( O
time O
, O
temperature S-PARA
) O
can O
be S-MATE
tailored O
to O
meet O
the O
desired O
strength/ductility/anisotropy O
design S-FEAT
requirements O
, O
either O
for O
research S-CONPRI
or O
part O
production S-MANP
purposes O
. O


We O
have O
investigated O
the O
relationship O
between O
structure S-CONPRI
and O
thermal B-PRO
conductivity E-PRO
in O
additively B-MANP
manufactured E-MANP
interpenetrating O
A356/316L O
composites S-MATE
. O


We O
used O
X-ray S-CHAR
microcomputed O
tomography O
to O
characterize O
the O
pore S-PRO
structure O
in O
as-fabricated O
composites S-MATE
, O
finding O
microporosity S-PRO
in O
both O
constituents O
as S-MATE
well O
as S-MATE
a O
50 O
μm O
thick O
layer S-PARA
of O
interfacial O
porosity S-PRO
separating O
the O
constituents O
. O


We O
measured O
the O
thermal B-PRO
conductivity E-PRO
of O
a O
43 O
vol O
% O
316L O
composite S-MATE
to O
be S-MATE
53 O
Wm−1K−1 O
, O
which O
is O
significantly O
less O
than O
that O
predicted S-CONPRI
by O
a O
simple S-MANP
rule-of-mixtures O
approximation O
, O
presumably O
because O
of O
the O
residual S-CONPRI
porosity S-PRO
. O


Motivated O
by O
these O
experimental S-CONPRI
results O
we O
used O
periodic O
homogenization S-MANP
theory O
to O
determine O
the O
combined O
effects O
of O
porosity S-PRO
and O
unit B-CONPRI
cell E-CONPRI
structure S-CONPRI
on O
the O
effective B-PARA
thermal I-PARA
conductivity E-PARA
. O


This O
analysis O
showed O
that O
in O
fully B-PARA
dense E-PARA
composites S-MATE
, O
the O
topology S-CONPRI
of O
the O
constituents O
has O
a O
weak O
effect O
on O
the O
thermal B-PRO
conductivity E-PRO
, O
whereas O
in O
composites S-MATE
with O
interfacial O
porosity S-PRO
, O
the O
size O
and O
structure S-CONPRI
of O
the O
unit B-CONPRI
cell E-CONPRI
strongly O
influence O
the O
thermal B-PRO
conductivity E-PRO
. O


We O
also O
found O
that O
an O
approximation O
formula O
of O
the O
strong O
contrast O
expansion O
method O
gives O
excellent O
estimates O
of O
the O
effective B-PARA
thermal I-PARA
conductivity E-PARA
of O
these O
composites S-MATE
, O
providing O
a O
powerful O
tool S-MACEQ
for O
designing O
functionally B-CONPRI
graded E-CONPRI
composites S-MATE
and O
for O
identifying O
mesostructures O
with O
optimal O
thermal B-PRO
conductivity E-PRO
values O
. O


In O
this O
work O
, O
the O
performance S-CONPRI
of O
a O
focus O
variation S-CONPRI
instrument O
for O
measurement S-CHAR
of O
areal O
topography S-CHAR
of O
metal S-MATE
additive S-MATE
surfaces O
was O
investigated O
. O


Samples S-CONPRI
were O
produced O
using O
both O
laser S-ENAT
and O
electron B-CONPRI
beam E-CONPRI
powder O
bed B-MANP
fusion E-MANP
processes O
with O
some O
of O
the O
most O
common O
additive S-MATE
materials O
: O
Al-Si-10Mg O
, O
Inconel B-MATE
718 E-MATE
and O
Ti-6Al-4V S-MATE
. O


Surfaces S-CONPRI
parallel O
and O
orthogonal O
to O
the O
build B-PARA
direction E-PARA
were O
investigated O
. O


Measurement S-CHAR
performance O
was O
qualified O
by O
visually O
inspecting O
the O
topographic O
models O
obtained O
from O
measurement S-CHAR
and O
quantified O
by O
computing O
the O
number O
of O
non-measured O
data S-CONPRI
points O
, O
by O
estimating O
local O
repeatability B-CONPRI
error E-CONPRI
in O
topography S-CHAR
height O
determination O
and O
by O
computing O
the O
value O
of O
the O
areal O
field O
texture S-FEAT
parameter S-CONPRI
Sa O
. O


Variations S-CONPRI
captured O
through O
such O
indicators O
were O
investigated O
as S-MATE
focus O
variation-specific O
measurement S-CHAR
control O
parameters S-CONPRI
were O
varied O
. O


Changes O
in O
magnification S-CONPRI
, O
illumination O
type O
, O
vertical S-CONPRI
resolution S-PARA
and O
lateral O
resolution S-PARA
were O
investigated O
. O


The O
experimental S-CONPRI
campaign O
was O
created O
through O
full O
factorial B-CONPRI
design E-CONPRI
of O
experiments O
, O
and O
regression B-CONPRI
models E-CONPRI
were O
used O
to O
link O
the O
selected O
measurement S-CHAR
process O
control O
parameters S-CONPRI
to O
the O
measured O
performance S-CONPRI
indicators O
. O


The O
results O
indicate O
that O
focus O
variation S-CONPRI
microscopy S-CHAR
measurement S-CHAR
of O
metal S-MATE
additive S-MATE
surfaces O
is O
robust O
to O
changes O
of O
the O
measurement S-CHAR
control O
parameters S-CONPRI
when O
the O
Sa O
texture S-FEAT
parameter S-CONPRI
is O
considered O
, O
with O
variations S-CONPRI
confined O
to O
sub-micrometre O
scales O
and O
within O
5 O
% O
of O
the O
average S-CONPRI
parameter O
value O
for O
the O
same O
surface S-CONPRI
and O
objective O
. O


The O
number O
of O
non-measured O
points O
and O
the O
local O
repeatability B-CONPRI
error E-CONPRI
were O
more O
affected O
by O
the O
choice O
of O
measurement S-CHAR
control O
parameters S-CONPRI
. O


However O
, O
such O
changes O
could O
be S-MATE
predicted O
by O
the O
regression B-CONPRI
models E-CONPRI
, O
and O
proved O
consistent O
once O
material S-MATE
, O
type O
of O
additive S-MATE
process O
and O
orientation S-CONPRI
of O
the O
measured O
surface S-CONPRI
are O
set S-APPL
. O


Hot B-MANP
Isostatic I-MANP
Pressing E-MANP
( O
HIP S-MANP
) O
is O
a O
technique O
of O
applying O
high O
pressures S-CONPRI
through O
a O
fluid S-MATE
medium O
at O
high O
temperatures S-PARA
to O
enclosed O
powders S-MATE
, O
castings O
and O
pre-sintered S-PRO
metal S-MATE
parts O
to O
eliminate O
porosity S-PRO
. O


Due O
to O
uniform O
volumetric O
shrinkage S-CONPRI
expected O
from O
this O
process S-CONPRI
, O
it O
can O
be S-MATE
a O
useful O
post-processing S-CONPRI
technique O
for O
complex-geometry O
parts O
fabricated S-CONPRI
using O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
techniques O
. O


In O
order O
for O
the O
technique O
to O
work O
effectively O
, O
parts O
are O
typically O
required O
to O
have O
a O
minimum O
density S-PRO
of O
92 O
% O
, O
where O
surface S-CONPRI
porosity S-PRO
is O
closed O
. O


While O
HIP S-MANP
has O
been O
used O
in O
conjunction O
with O
powder B-MANP
bed I-MANP
fusion I-MANP
AM I-MANP
processes E-MANP
, O
its O
use O
for O
parts O
made O
using O
Binder B-MANP
Jetting E-MANP
( O
BJ S-MANP
) O
has O
not O
been O
investigated O
in O
detail O
due O
to O
the O
limitations O
of O
BJ S-MANP
in O
fabricating S-MANP
sufficiently O
high-density O
parts O
without O
infiltration S-CONPRI
. O


In O
this O
work O
, O
detailed O
investigations O
on O
the O
effect O
of O
HIP S-MANP
on O
BJ S-MANP
parts O
printed O
from O
three O
different O
powder S-MATE
configurations O
, O
which O
led S-APPL
to O
varying O
levels O
of O
porosity S-PRO
, O
are O
performed O
. O


The O
effects O
of O
HIP S-MANP
on O
the O
density S-PRO
, O
microstructure S-CONPRI
, O
tensile B-PRO
strength E-PRO
, O
and O
ductility S-PRO
of O
the O
resulting O
parts O
is O
reported O
. O


A O
maximum O
density S-PRO
of O
97.32 O
% O
was O
achieved O
by O
HIP S-MANP
of O
printed O
and O
sintered S-MANP
parts O
created O
via O
bimodal O
powders S-MATE
. O


Both O
the O
tensile B-PRO
strength E-PRO
and O
ductility S-PRO
were O
found O
to O
improve O
following O
HIP S-MANP
, O
which O
suggests O
that O
the O
reduction S-CONPRI
in O
porosity S-PRO
is O
predominant O
compared O
to O
the O
detrimental O
effects O
of O
grain S-CONPRI
coarsening O
. O


Control O
of O
the O
atomic B-PRO
structure E-PRO
, O
as S-MATE
measured O
by O
the O
extent O
of O
the O
embrittling O
B2 O
chemically O
ordered O
phase S-CONPRI
, O
is O
demonstrated O
in O
intermetallic B-MATE
alloys E-MATE
through O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
and O
characterized O
using O
high O
fidelity O
neutron B-CHAR
diffraction E-CHAR
. O


As S-MATE
a O
layer-by-layer S-CONPRI
rapid O
solidification B-MANP
process E-MANP
, O
AM S-MANP
was O
employed O
to O
suppress O
the O
extent O
of O
chemically O
ordered O
B2 O
phases O
in O
a O
soft O
ferromagnetic O
Fe-Co O
alloy S-MATE
, O
as S-MATE
a O
model B-CONPRI
material E-CONPRI
system O
of O
interest O
to O
electromagnetic O
applications O
. O


The O
extent O
of O
atomic O
ordering O
was O
found O
to O
be S-MATE
insensitive O
to O
the O
spatial O
location O
within O
specimens O
and O
suggests O
that O
the O
thermal O
conditions O
within O
only O
a O
few O
AM S-MANP
layers O
were O
most O
influential O
in O
controlling O
the O
microstructure S-CONPRI
, O
in O
agreement O
with O
the O
predictions S-CONPRI
from O
a O
thermal O
model S-CONPRI
for O
welding S-MANP
. O


Analysis O
of O
process B-CONPRI
parameter E-CONPRI
effects O
on O
ordering O
found O
that O
suppression O
of O
B2 O
phase S-CONPRI
was O
the O
result O
of O
an O
increased O
average S-CONPRI
cooling O
rate O
during O
processing O
. O


AM S-MANP
processing O
parameters S-CONPRI
, O
namely O
interlayer O
interval O
time O
and O
build S-PARA
velocity O
, O
were O
used O
to O
systematically O
control O
the O
relative O
fraction S-CONPRI
of O
ordered O
B2 O
phase S-CONPRI
in O
specimens O
from O
0.49 O
to O
0.72 O
. O


Hardness S-PRO
of O
AM S-MANP
specimens O
was O
more O
than O
150 O
% O
higher O
than O
conventionally O
processed S-CONPRI
bulk O
material S-MATE
. O


Implications O
for O
tailoring O
microstructures S-MATE
of O
intermetallic B-MATE
alloys E-MATE
are O
discussed O
. O


Wire–arc O
additive B-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
is O
an O
emergent O
method O
for O
the O
production S-MANP
and O
repair O
of O
high O
value O
components S-MACEQ
. O


Introduction O
of O
plastic S-MATE
strain O
by O
inter-pass O
rolling S-MANP
has O
been O
shown O
to O
produce O
grain B-CHAR
refinement E-CHAR
and O
improve O
mechanical B-CONPRI
properties E-CONPRI
, O
however O
suitable O
quality B-CONPRI
control E-CONPRI
techniques O
are O
required O
to O
demonstrate O
the O
refinement O
non-destructively O
. O


Specifically O
, O
undeformed O
and O
rolled O
specimens O
have O
been O
analysed O
by O
spatially O
resolved O
acoustic O
spectroscopy S-CONPRI
( O
SRAS O
) O
, O
allowing O
the O
efficacy O
of O
the O
rolling B-MANP
process E-MANP
to O
be S-MATE
observed O
in O
velocity O
maps O
. O


The O
work O
has O
three O
primary O
outcomes O
( O
i O
) O
differentiation O
of O
texture S-FEAT
due O
to O
rolling S-MANP
force S-CONPRI
, O
( O
ii O
) O
understanding O
the O
acoustic O
wave O
velocity O
response O
in O
the O
textured O
material S-MATE
including O
the O
underlying O
crystallography S-MANP
, O
( O
iii O
) O
extraction O
of O
an O
additional O
build S-PARA
metric O
such O
as S-MATE
layer O
height O
from O
acoustic O
maps O
and O
further O
useful O
material S-MATE
information O
such O
as S-MATE
minimum O
stiffness S-PRO
direction O
. O


Variations S-CONPRI
in O
acoustic O
response O
due O
to O
grain B-CHAR
refinement E-CHAR
and O
crystallographic O
orientation S-CONPRI
have O
been O
explored O
. O


This O
allowed O
prior-β O
grains S-CONPRI
to O
be S-MATE
resolved O
. O


A O
basic O
algorithm S-CONPRI
has O
been O
proposed O
for O
the O
automated B-ENAT
measurement E-ENAT
, O
which O
could O
be S-MATE
used O
for O
in-line O
closed B-CONPRI
loop I-CONPRI
control E-CONPRI
. O


Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
professionals O
often O
throw O
around O
the O
notion O
that O
complexity S-CONPRI
is O
free O
. O


Indeed O
, O
complexity S-CONPRI
is O
much O
easier O
and O
potentially O
cheaper O
to O
achieve O
through O
AM S-MANP
than O
through O
traditional B-MANP
manufacturing E-MANP
, O
but O
it O
is O
not O
free O
. O


Upon O
attempting O
to O
manufacture S-CONPRI
complex O
designs S-FEAT
, O
it O
is O
quickly O
found O
that O
certain O
features O
, O
or O
topologies S-CONPRI
, O
are O
more O
manufacturable S-CONPRI
than O
others O
, O
with O
sacrificial O
support B-MATE
material E-MATE
required O
for O
many O
complex O
designs S-FEAT
. O


This O
will O
significantly O
increase O
machining S-MANP
costs O
. O


Topology B-FEAT
Optimization E-FEAT
( O
TO O
) O
is O
a O
freeform S-CONPRI
computational O
design S-FEAT
methodology O
which O
is O
ideal O
for O
designing O
lightweight B-MACEQ
structures E-MACEQ
through O
a O
combination O
of O
modeling S-ENAT
and O
rigorous O
optimization S-CONPRI
. O


While O
AM S-MANP
can O
realize O
many O
complex O
topologies S-CONPRI
, O
there O
still O
remain O
AM S-MANP
manufacturing O
limitations O
( O
such O
as S-MATE
overhangs O
) O
, O
which O
require O
customized O
TO O
design S-FEAT
algorithms S-CONPRI
beyond O
freeform S-CONPRI
TO O
. O


In O
this O
work O
, O
a O
projection-based O
TO O
methodology S-CONPRI
is O
presented O
to O
design S-FEAT
for O
3D S-CONPRI
self-supporting O
structures O
– O
i.e O
. O


structures O
that O
do O
not O
require O
sacrificial O
support B-MATE
material E-MATE
. O


The O
foundation O
of O
the O
presented O
methodology S-CONPRI
is O
a O
2D S-CONPRI
overhang O
projection O
framework S-CONPRI
. O


In O
addition O
to O
expanding O
the O
methodology S-CONPRI
to O
three O
dimensions S-FEAT
, O
the O
algorithm S-CONPRI
is O
drastically O
improved O
through O
( O
1 O
) O
adopting O
a O
new O
overhang S-PARA
mapping O
scheme O
which O
allows O
for O
exact O
specification S-PARA
of O
allowable O
overhang B-PARA
angle E-PARA
, O
and O
( O
2 O
) O
implementing O
an O
adjoint O
approach O
to O
sensitivity S-PARA
calculations O
to O
speed O
up O
calculation O
drastically O
and O
to O
allow O
for O
scalability O
. O


Using O
several O
examples O
, O
it O
is O
shown O
that O
the O
presented O
methodology S-CONPRI
generates O
self-supporting S-FEAT
structures O
( O
given O
a O
prescribed O
printable O
overhang B-PARA
angle E-PARA
) O
which O
are O
entirely O
manufacturable S-CONPRI
without O
any O
added O
sacrificial O
support B-MATE
material E-MATE
. O


Upon O
printing O
a O
couple O
topologies S-CONPRI
with O
mixed O
success O
, O
further O
customization O
of O
the O
algorithm S-CONPRI
is O
proposed O
for O
situations O
where O
multiple O
directional-dependent O
overhang B-PARA
angles E-PARA
are O
possible O
in O
a O
single O
AM S-MANP
system O
. O


An O
analytical O
process B-CONPRI
model E-CONPRI
for O
predicting O
the O
layer B-PARA
height E-PARA
and O
wall O
width O
from O
the O
process B-CONPRI
parameters E-CONPRI
was O
developed O
for O
wire B-MANP
+ I-MANP
arc I-MANP
additive I-MANP
manufacture E-MANP
of O
Ti-6Al-4V S-MATE
, O
which O
includes O
inter-pass O
temperature S-PARA
and O
material B-CONPRI
properties E-CONPRI
. O


Capillarity O
theory O
predicted S-CONPRI
that O
cylindrical S-CONPRI
deposits O
were O
produced O
where O
the O
wall O
width O
was O
less O
than O
12 O
mm S-MANP
( O
radius O
< O
6 O
mm S-MANP
) O
due O
to O
the O
large O
value O
of O
the O
surface B-PRO
tension E-PRO
. O


Power S-PARA
was O
predicted S-CONPRI
with O
an O
accuracy S-CHAR
of O
±20 O
% O
for O
a O
wide O
range S-PARA
of O
conditions O
for O
pulsed O
TIG S-MANP
and O
plasma B-CONPRI
deposition E-CONPRI
. O


Interesting O
differences O
in O
the O
power S-PARA
requirements O
were O
observed O
where O
a O
surface S-CONPRI
depression O
was O
produced O
with O
the O
plasma S-CONPRI
process O
due O
to O
differences O
in O
melting S-MANP
efficiency O
and/or O
convection O
effects O
. O


Finally O
, O
it O
was O
estimated O
the O
impact S-CONPRI
of O
controlling O
the O
workpiece S-CONPRI
temperature S-PARA
on O
the O
accuracy S-CHAR
of O
the O
deposit O
geometry S-CONPRI
. O


Processing O
of O
Si S-MATE
and O
hydroxyapatite S-MATE
reinforced O
Ti6Al4Vmatrix O
compositesusinglaser-based O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
from O
powder B-MATE
blends E-MATE
. O


Si S-MATE
addition O
helped O
form O
in B-CONPRI
situ E-CONPRI
reactive O
phases O
of O
titanium B-MATE
silicides E-MATE
and O
vanadium S-MATE
silicides S-MATE
Composites S-MATE
showed O
higher O
hardness S-PRO
, O
lower O
coefficient B-PRO
of I-PRO
friction E-PRO
and O
better O
wear B-PRO
resistance E-PRO
. O


Directed-energy O
deposition S-CONPRI
( O
DED S-MANP
) O
-based O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
was O
explored O
for O
composite S-MATE
development O
using O
silicon S-MATE
( O
Si S-MATE
) O
and O
hydroxyapatite S-MATE
( O
HA O
) O
in O
Ti-6Al-4 B-MATE
V E-MATE
( O
Ti64 S-MATE
) O
matrix O
for O
articulating O
surfaces S-CONPRI
of O
load-bearing S-FEAT
implants S-APPL
. O


Specifically O
, O
laser B-MANP
engineered I-MANP
net I-MANP
shaping E-MANP
( O
LENSTM O
) O
– O
a O
commercially O
available O
DED-based O
AM B-MANP
technique E-MANP
– O
was O
used O
to O
fabricate S-MANP
composites S-MATE
from O
premixed-feedstock O
powders S-MATE
. O


The O
AM S-MANP
’ O
d O
composites S-MATE
proved O
to O
not O
only O
improve O
upon O
Ti64 S-MATE
’ O
s S-MATE
mechanical B-CONPRI
properties E-CONPRI
but O
also O
produced O
an O
in-situ S-CONPRI
Si-based O
tribofilm O
during O
tribological S-CONPRI
testing S-CHAR
that O
minimized O
wear S-CONPRI
induced O
damage S-PRO
. O


Additionally O
, O
it O
was O
found O
that O
with O
the O
introduction O
of O
Si S-MATE
, O
titanium B-MATE
silicides E-MATE
and O
vanadium S-MATE
silicides S-MATE
were O
formed O
; O
allowing O
for O
114 O
% O
increased O
hardness S-PRO
, O
decreased O
coefficient B-PRO
of I-PRO
friction E-PRO
( O
COF O
) O
and O
a O
reduction S-CONPRI
of O
wear S-CONPRI
rate O
of O
38.1 O
% O
and O
70.8 O
% O
, O
respectively O
, O
for O
a O
10 O
wt. O
% O
Si S-MATE
presence O
. O


The O
produced O
composites S-MATE
also O
displayed O
a O
positive O
shift O
in O
open-circuit O
potential O
( O
OCP O
) O
during O
linear O
wear S-CONPRI
, O
along O
with O
a O
reduction S-CONPRI
in O
the O
change O
of O
OCP O
from O
idle O
to O
linear O
wear S-CONPRI
conditions O
. O


Additionally O
, O
contact S-APPL
resistance O
( O
CR S-MATE
) O
values O
increased O
with O
a O
maximum O
value O
of O
1500 O
ohms O
due O
to O
the O
formation O
of O
Si-based O
tribofilm O
on O
the O
wear S-CONPRI
surface S-CONPRI
. O


Such O
composite S-MATE
development O
approach O
using O
DED-based O
AM S-MANP
can O
open O
up O
the O
possibilities O
of O
innovating O
next-generation O
implants S-APPL
that O
are O
designed S-FEAT
and O
manufactured S-CONPRI
via O
multi-material S-CONPRI
AM S-MANP
. O


We O
investigate O
experimentally O
and O
numerically O
the O
influence O
of O
the O
processing O
conditions O
on O
the O
cross-section O
of O
a O
strand O
printed O
by O
material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
. O


The O
parts O
manufactured S-CONPRI
by O
this O
method O
generally O
suffer O
from O
a O
poor O
surface B-FEAT
finish E-FEAT
and O
a O
low O
dimensional B-CHAR
accuracy E-CHAR
, O
coming O
from O
the O
lack O
of O
control O
over O
the O
shape O
of O
the O
printed O
strands O
. O


Using O
optical B-CHAR
microscopy E-CHAR
, O
we O
have O
measured O
the O
cross-sections S-CONPRI
of O
the O
extruded S-MANP
strands O
, O
for O
different O
layer B-PARA
heights E-PARA
and O
printing B-PARA
speeds E-PARA
. O


For O
the O
first O
time O
, O
we O
have O
compared O
the O
measurements O
of O
strands O
’ O
cross-sections S-CONPRI
to O
the O
numerical O
results O
of O
a O
three-dimensional S-CONPRI
computational B-CHAR
fluid I-CHAR
dynamics E-CHAR
model O
of O
the O
deposition S-CONPRI
flow O
. O


The O
proposed O
numerical O
model S-CONPRI
shows O
good O
agreement O
with O
the O
experimental S-CONPRI
results O
and O
is O
able O
to O
capture O
the O
changes O
of O
the O
strand O
morphology S-CONPRI
observed O
for O
the O
different O
processing O
conditions O
. O


The O
combination O
of O
additive B-MANP
manufacturing E-MANP
principles O
and O
electron B-CONPRI
beam E-CONPRI
( O
EB O
) O
technology S-CONPRI
allows O
complex O
metal S-MATE
parts O
, O
featuring O
excellent O
quality S-CONPRI
material S-MATE
, O
to O
be S-MATE
produced O
, O
whenever O
traditional O
methods O
are O
expensive O
or O
difficult O
to O
apply O
. O


Today O
, O
the O
optimization S-CONPRI
of O
process B-CONPRI
parameters E-CONPRI
, O
for O
a O
given O
metal B-MATE
powder E-MATE
, O
is O
generally O
attained O
through O
an O
empirical S-CONPRI
trial O
and O
error S-CONPRI
approach O
. O


Process B-ENAT
simulation E-ENAT
can O
be S-MATE
used O
as S-MATE
a O
tool S-MACEQ
for O
decision-making O
and O
process B-CONPRI
optimization E-CONPRI
, O
since O
a O
virtual O
analysis O
can O
help O
to O
facilitate O
the O
possibility O
of O
exploring O
“ O
what O
if O
” O
scenarios O
. O


In O
this O
work O
, O
a O
new O
type O
of O
modelling S-ENAT
has O
been O
introduced O
for O
energy O
source S-APPL
and O
powder B-MATE
material E-MATE
properties O
and O
it O
has O
been O
included O
in O
a O
thermal O
numerical O
model S-CONPRI
in O
order O
to O
improve O
the O
effectiveness S-CONPRI
and O
reliability S-CHAR
of O
Electon O
Beam S-MACEQ
Melting O
( O
EBM S-MANP
) O
FE S-MATE
simulation O
. O


Several O
specific O
subroutines O
have O
been O
developed O
to O
automatically O
calculate O
the O
powder S-MATE
properties O
as S-MATE
temperature O
functions O
, O
and O
to O
consider O
the O
position O
of O
the O
beam S-MACEQ
during O
scanning S-CONPRI
as S-MATE
well O
as S-MATE
the O
material S-MATE
state O
changes O
from O
powder S-MATE
to O
liquid O
in O
the O
melting S-MANP
phase O
and O
from O
liquid O
to O
solid O
during O
cooling S-MANP
. O


A O
comparison O
of O
the O
numerical O
results O
and O
experimental B-CONPRI
data E-CONPRI
taken O
from O
literature O
has O
shown O
a O
good O
forecasting O
capability O
. O


The O
average S-CONPRI
deviations O
of O
the O
simulation S-ENAT
from O
an O
experimental S-CONPRI
scan O
line O
width O
have O
been O
found O
to O
be S-MATE
below O
about O
15 O
% O
. O


ISO B-MANS
25178-2 E-MANS
surface O
texture S-FEAT
from O
X-ray B-CHAR
CT E-CHAR
, O
interlaboratory O
comparison O
, O
is O
presented O
. O


Less O
than O
0.5 O
% O
Sa O
areal O
roughness S-PRO
between O
metrology S-CONPRI
CT S-ENAT
and O
focus O
variation S-CONPRI
values O
. O


Artefact O
design S-FEAT
allows O
separation O
of O
surface S-CONPRI
determination O
and O
scaling O
errors S-CONPRI
. O


The O
study O
compared O
the O
results O
obtained O
for O
the O
extraction O
of O
areal O
surface B-FEAT
texture E-FEAT
data S-CONPRI
per O
ISO B-MANS
25178-2 E-MANS
from O
five O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
( O
CT S-ENAT
) O
volume S-CONPRI
measurements O
from O
each O
of O
four O
laboratories S-CONPRI
. O


Two O
Ti6Al4V S-MATE
ELI O
( O
extra-low O
interstitial O
) O
components S-MACEQ
were O
included O
in O
each O
of O
the O
CT S-ENAT
acquisitions O
. O


The O
first O
component S-MACEQ
was O
an O
additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
cube S-CONPRI
manufactured O
using O
an O
Arcam O
Q10 O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
machine S-MACEQ
. O


Surface B-FEAT
texture E-FEAT
data S-CONPRI
was O
extracted S-CONPRI
from O
CT S-ENAT
scans O
of O
this O
part O
. O


The O
values O
of O
selected O
parameters S-CONPRI
per O
ISO B-MANS
25178-2 E-MANS
are O
reported O
, O
including O
Sa O
, O
the O
arithmetic B-CONPRI
mean E-CONPRI
height O
, O
for O
which O
the O
values O
from O
the O
Nikon O
MCT O
225 O
metrology S-CONPRI
CT S-ENAT
measurements O
were O
all O
within O
0.5 O
% O
of O
the O
mean O
reference O
focus O
variation S-CONPRI
measurement S-CHAR
. O


CT S-ENAT
resolution O
requirements O
are O
discussed O
. O


The O
second O
component S-MACEQ
was O
a O
machined S-MANP
dimensional O
test O
artefact O
designed S-FEAT
to O
facilitate O
independent O
analysis O
of O
CT S-ENAT
global O
voxel S-CONPRI
scaling O
errors S-CONPRI
and O
surface S-CONPRI
determination O
errors S-CONPRI
. O


The O
results O
of O
mathematical S-CONPRI
global O
scaling O
and O
surface S-CONPRI
determination O
correction O
of O
the O
dimensional O
artefact O
data S-CONPRI
is O
reported O
. O


The O
dimensional O
test O
artefact O
errors S-CONPRI
for O
the O
XT O
H O
225 O
commercial O
CT S-ENAT
for O
length O
, O
outside O
diameter S-CONPRI
and O
inside O
diameter S-CONPRI
reduced O
from O
-0.27 O
% O
, O
-0.83 O
% O
and O
-0.54 O
% O
respectively O
to O
less O
than O
0.02 O
% O
after O
performing O
mathematical S-CONPRI
correction O
. O


This O
work O
will O
assist O
the O
development O
of O
surface B-FEAT
texture E-FEAT
correction O
protocols S-CONPRI
, O
help O
define O
surface-from-CT O
measurement S-CHAR
envelope O
limits S-CONPRI
and O
provide O
valuable O
information O
for O
an O
expanded O
Stage O
2 O
interlaboratory O
comparison O
, O
which O
will O
include O
a O
more O
diverse O
range S-PARA
of O
CT S-ENAT
systems O
and O
technologies S-CONPRI
, O
further O
expanding O
the O
surface-from-CT O
knowledge O
base O
. O


Bimetallic O
structures O
belong O
to O
a O
class O
of O
multi-material B-FEAT
structures E-FEAT
, O
and O
they O
potentially O
offer O
unique O
solutions O
to O
many O
engineering S-APPL
problems O
. O


In O
this O
work O
, O
bimetallic O
structures O
of O
Inconel B-MATE
718 E-MATE
and O
Ti6Al4V S-MATE
( O
Ti64 S-MATE
) O
alloys S-MATE
were O
processed S-CONPRI
using O
laser B-MANP
engineered I-MANP
net I-MANP
shaping E-MANP
( O
LENS™ O
) O
. O


During O
LENS™ O
processing O
, O
three O
build B-CONPRI
strategies E-CONPRI
were O
attempted O
: O
direct O
deposition S-CONPRI
, O
compositional O
gradation O
and O
use O
of O
an O
intermediate O
bond O
layer S-PARA
. O


Inconel B-MATE
718 E-MATE
and O
Ti64 B-MATE
alloys E-MATE
exhibit O
thermal B-CONPRI
properties E-CONPRI
mismatch O
along O
with O
brittle S-PRO
intermetallic O
phase S-CONPRI
formation O
at O
the O
interface S-CONPRI
resulting O
in O
delamination S-CONPRI
. O


For O
a O
successful O
build S-PARA
, O
the O
use O
of O
a O
compositional O
bond O
layer S-PARA
( O
CBL O
) O
was O
employed O
, O
which O
was O
a O
mixture O
of O
a O
third O
material S-MATE
- O
Vanadium B-MATE
Carbide E-MATE
- O
with O
the O
parent O
alloys S-MATE
to O
form O
an O
intermediate O
layer S-PARA
used O
in O
bonding S-CONPRI
the O
two O
immiscible O
alloys S-MATE
. O


A O
crack-free O
bimetallic O
structure S-CONPRI
of O
Inconel B-MATE
718 E-MATE
and O
Ti64 S-MATE
was O
demonstrated O
. O


Scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
, O
energy B-CHAR
dispersive I-CHAR
spectroscopy E-CHAR
( O
EDS S-CHAR
) O
, O
X-ray B-CHAR
diffraction E-CHAR
and O
Vickers B-PRO
hardness E-PRO
were O
used O
to O
characterize O
these O
bimetallic O
structures O
. O


XRD S-CHAR
analysis O
indicated O
presence O
of O
Cr3C2 O
phases O
. O


CBL O
improved O
the O
bonding B-PRO
strength E-PRO
by O
avoiding O
formation O
of O
brittle S-PRO
intermetallic O
phases O
such O
as S-MATE
TiNi3 O
and O
Ti2Ni O
as S-MATE
well O
as S-MATE
reducing O
thermal B-PRO
stresses E-PRO
at O
the O
interface S-CONPRI
. O


Our O
results O
successfully O
demonstrate O
the O
formation O
of O
Inconel B-MATE
718 E-MATE
and O
Ti64 S-MATE
bimetallic O
structures O
using O
a O
laser-based O
commercially O
available O
additive B-MANP
manufacturing E-MANP
approach O
. O


Additive B-MANP
manufacturing E-MANP
, O
also O
known O
as S-MATE
3D B-MANP
printing E-MANP
, O
is O
a O
new O
technology S-CONPRI
that O
obliterates O
the O
geometrical B-FEAT
limits E-FEAT
of O
the O
produced O
workpieces O
and O
promises O
low O
running O
costs O
as S-MATE
compared O
to O
traditional B-MANP
manufacturing E-MANP
methods O
. O


Hence O
, O
additive B-MANP
manufacturing E-MANP
technology O
has O
high O
expectations O
in O
industry S-APPL
. O


Unfortunately O
, O
the O
lack O
of O
a O
proper O
quality S-CONPRI
monitoring O
prohibits O
the O
penetration S-CONPRI
of O
this O
technology S-CONPRI
into O
an O
extensive O
practice O
. O


This O
work O
investigates S-CONPRI
the O
feasibility S-CONPRI
of O
using O
acoustic B-CONPRI
emission E-CONPRI
for O
quality S-CONPRI
monitoring O
and O
combines O
a O
sensitive O
acoustic B-CONPRI
emission E-CONPRI
sensor O
with O
machine S-MACEQ
learning O
. O


The O
acoustic O
signals O
were O
recorded O
using O
a O
fiber S-MATE
Bragg O
grating O
sensor S-MACEQ
during O
the O
powder B-MANP
bed I-MANP
additive I-MANP
manufacturing E-MANP
process O
in O
a O
commercially O
available O
selective B-MANP
laser I-MANP
melting E-MANP
machine S-MACEQ
. O


The O
process B-CONPRI
parameters E-CONPRI
were O
intentionally O
tuned O
to O
invoke O
different O
processing O
regimes O
that O
lead S-MATE
to O
the O
formation O
of O
different O
types O
and O
concentrations O
of O
pores S-PRO
( O
1.42 O
± O
0.85 O
% O
, O
0.3 O
± O
0.18 O
% O
and O
0.07 O
± O
0.02 O
% O
) O
inside O
the O
workpiece S-CONPRI
. O


The O
classifier O
, O
based O
on O
spectral O
convolutional O
neural B-CONPRI
network E-CONPRI
, O
was O
trained O
to O
differentiate O
the O
acoustic O
features O
of O
dissimilar O
quality S-CONPRI
. O


In O
view O
of O
the O
narrow O
range S-PARA
of O
porosity S-PRO
, O
the O
results O
can O
be S-MATE
considered O
as S-MATE
promising O
and O
they O
showed O
the O
feasibility S-CONPRI
of O
the O
quality S-CONPRI
monitoring O
using O
acoustic B-CONPRI
emission E-CONPRI
with O
the O
sub-layer O
spatial O
resolution S-PARA
. O


An O
automated O
python O
script O
to O
slice S-CONPRI
a O
macro-scale O
part O
into O
micro-scale S-CONPRI
layers O
and O
assign O
boundary B-CONPRI
conditions E-CONPRI
steps O
for O
each O
layer S-PARA
is O
presented O
. O


Key O
parameter S-CONPRI
interdependencies O
of O
resolution S-PARA
, O
energy O
and O
time O
are O
investigated O
in O
a O
series O
of O
layer-scaling O
thermomechanical B-CONPRI
process E-CONPRI
models O
. O


Guidelines O
for O
simulation S-ENAT
the O
thermal O
and O
stress S-PRO
results O
of O
higher B-PARA
resolution E-PARA
by O
lower O
resolution S-PARA
for O
the O
LPBF S-MANP
modelling O
are O
proposed O
. O


A O
novel O
efficient O
method O
for O
simulating O
powder-solid O
heat B-CONPRI
conduction E-CONPRI
by O
interface S-CONPRI
surface O
convection O
is O
presented O
. O


The O
Laser B-CONPRI
Beam E-CONPRI
Powder O
Bed B-MANP
Fusion E-MANP
( O
PBF-LB O
) O
category O
of O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
is O
currently O
receiving O
much O
attention O
for O
computational O
process S-CONPRI
modelling S-ENAT
. O


Major O
challenges O
exist O
in O
how O
to O
reconcile O
resolution S-PARA
, O
energy O
and O
time O
in O
a O
real O
build S-PARA
, O
with O
the O
practical O
limitations O
of O
resolution S-PARA
( O
layer B-PARA
height E-PARA
and O
mesh O
resolution S-PARA
) O
, O
energy O
( O
heat S-CONPRI
format O
and O
magnitude S-PARA
) O
and O
time O
( O
heating S-MANP
and O
cooling S-MANP
step O
times O
) O
in O
the O
computational O
space O
. O


A O
novel O
thermomechanical S-CONPRI
PBF-LB O
process B-CONPRI
model E-CONPRI
including O
an O
efficient O
powder-interface O
heat S-CONPRI
loss O
mechanism S-CONPRI
was O
developed O
. O


The O
effect O
of O
variations S-CONPRI
in O
layer B-PARA
height E-PARA
( O
layer S-PARA
scaling O
) O
, O
energy O
and O
time O
on O
the O
temperature S-PARA
and O
stress S-PRO
evolution S-CONPRI
was O
investigated O
. O


The O
influence O
of O
heating S-MANP
step O
time O
and O
cooling S-MANP
step O
time O
was O
characterised O
and O
the O
recommended O
ratio O
of O
element B-PARA
size E-PARA
to O
layer S-PARA
scaling O
was O
presented O
, O
based O
on O
a O
macroscale B-CONPRI
2D E-CONPRI
model O
. O


The O
layer S-PARA
scaling O
method O
was O
effective O
when O
scaling O
up O
to O
4 O
times O
the O
layer B-PARA
thickness E-PARA
and O
appropriately O
also O
scaling O
the O
cooling S-MANP
step O
time O
. O


This O
research S-CONPRI
provides O
guidelines O
and O
a O
framework S-CONPRI
for O
layer S-PARA
scaling O
for O
finite B-CHAR
element I-CHAR
modelling E-CHAR
of O
the O
PBF-LB O
process S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
a O
rapidly O
growing O
technology S-CONPRI
that O
enables O
the O
fast O
production S-MANP
of O
complex O
and O
near-net-shaped O
( O
NNS O
) O
components S-MACEQ
. O


Among O
the O
many O
applicable O
AM S-MANP
methods O
( O
particularly O
powder B-MACEQ
bed E-MACEQ
technologies O
) O
, O
electron-beam O
melting S-MANP
( O
EBM S-MANP
) O
is O
gaining O
increased O
interest O
mainly O
in O
aerospace S-APPL
and O
medical B-APPL
industries E-APPL
, O
due O
to O
its O
inherent O
advantages O
for O
the O
printing O
of O
Ti-6Al-4V B-MATE
alloy E-MATE
. O


Although O
major O
strides O
have O
been O
made O
towards O
understanding O
the O
effect O
of O
hot O
isostatic O
pressure S-CONPRI
( O
HIP S-MANP
) O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
Ti-6Al-4V S-MATE
produced O
by O
AM S-MANP
, O
its O
effect O
on O
corrosion S-CONPRI
performance O
remains O
relatively O
unexplored O
. O


To O
date O
, O
the O
reported O
corrosion S-CONPRI
studies O
remain O
essentially O
limited O
to O
the O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
process S-CONPRI
, O
while O
the O
corrosion B-PRO
behavior E-PRO
of O
EBM S-MANP
Ti-6Al-4V O
and O
particularly O
HIPed O
EBM S-MANP
Ti-6Al-4V O
have O
not O
been O
fully O
realized O
. O


This O
paper O
provides O
a O
detailed O
analysis O
of O
this O
corrosion S-CONPRI
performance O
, O
including O
the O
stress-corrosion O
susceptibility S-PRO
of O
EBM S-MANP
Ti-6Al-4V O
in O
as-build O
condition O
and O
after O
HIP B-MANP
heat I-MANP
treatment E-MANP
. O


Microstructure S-CONPRI
and O
phase S-CONPRI
identifications O
were O
examined O
by O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
and O
X-ray B-CHAR
diffraction I-CHAR
analysis E-CHAR
. O


Corrosion S-CONPRI
performance O
was O
evaluated O
by O
electrochemical B-CHAR
measurements E-CHAR
, O
including O
open-circuit O
potential O
( O
OCP O
) O
, O
potentiodynamic B-CHAR
polarization E-CHAR
analysis O
and O
impedance B-CHAR
spectroscopy E-CHAR
( O
EIS S-CHAR
) O
, O
as S-MATE
well O
as S-MATE
stress-corrosion O
examination O
in O
terms O
of O
slow O
strain-rate O
testing S-CHAR
( O
SSRT S-CONPRI
) O
. O


All O
of O
the O
corrosion S-CONPRI
tests O
were O
carried O
out O
in O
a O
3.5 O
wt. O
% O
NaCl S-MATE
solution O
at O
ambient O
temperature S-PARA
. O


Owing O
to O
the O
natural O
excellent O
corrosion B-CONPRI
resistance E-CONPRI
of O
Ti-6Al-4V S-MATE
, O
the O
obtained O
results O
revealed O
that O
the O
HIP S-MANP
process O
has O
only O
a O
slight O
positive O
effect O
on O
the O
corrosion B-CONPRI
resistance E-CONPRI
of O
Ti-6Al-4V S-MATE
produced O
by O
EBM S-MANP
. O


This O
minor O
improvement O
may O
be S-MATE
related O
to O
the O
improved O
efficiency O
of O
the O
passivation S-CONPRI
layer S-PARA
that O
was O
attributed O
to O
the O
increased O
β-phase O
content O
and O
the O
reduction S-CONPRI
of O
α/β O
interfaces O
. O


In O
terms O
of O
stress S-PRO
corrosion S-CONPRI
sensitivity O
, O
the O
HIPed O
specimens O
exhibited O
extended O
time-to-failure O
( O
TTF O
) O
at O
the O
low O
strain B-CONPRI
rate E-CONPRI
at O
2.5 O
10-7 O
1/sec O
, O
where O
the O
effect O
of O
the O
corrosive S-PRO
environment O
was O
more O
dominant O
. O


We O
study O
linearity S-CONPRI
assumptions O
in O
the O
transient B-CONPRI
macroscale E-CONPRI
mechanical S-APPL
aspect O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process B-ENAT
simulation E-ENAT
. O


Linearity S-CONPRI
assumptions O
are O
often O
resorted O
to O
in O
combination O
with O
calibrated S-CONPRI
inelastic O
deformation S-CONPRI
components S-MACEQ
to O
arrive O
at O
computationally O
tractable O
yet O
reasonably O
accurate S-CHAR
AM O
process B-CONPRI
models E-CONPRI
. O


We O
point O
out O
that O
linearity S-CONPRI
assumptions O
permit O
the O
independent O
computation S-CONPRI
of O
the O
response O
increment O
in O
each O
step S-CONPRI
of O
the O
AM B-MANP
process E-MANP
, O
and O
the O
total O
mechanical B-CONPRI
response E-CONPRI
is O
the O
superposition O
of O
all O
the O
process-step O
increments O
. O


In O
effect O
, O
process-step O
increments O
are O
computed O
with O
respect O
to O
the O
stress-free O
reference O
configuration S-CONPRI
in O
each O
step S-CONPRI
. O


The O
implication O
is O
that O
the O
mechanical B-CONPRI
response E-CONPRI
increment O
in O
each O
linearised O
AM B-MANP
process E-MANP
step O
may O
be S-MATE
computed O
in O
parallel O
. O


geometric O
or O
material S-MATE
) O
is O
modelled O
. O


Distortions O
in O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
Laser B-MANP
Metal I-MANP
Deposition E-MANP
( O
LMD S-MANP
) O
occur O
in O
the O
newly-built O
component S-MACEQ
due O
to O
rapid O
heating S-MANP
and O
solidification S-CONPRI
and O
can O
lead S-MATE
to O
shape O
deviations O
and O
cracking S-CONPRI
. O


Digital B-CONPRI
Image I-CONPRI
Correlation E-CONPRI
( O
DIC S-CONPRI
) O
is O
applied O
together O
with O
optical S-CHAR
filters S-APPL
to O
measure O
in-situ S-CONPRI
distortions O
directly O
on O
a O
wall O
geometry S-CONPRI
produced O
with O
LMD S-MANP
. O


The O
wall O
shows O
cyclic O
expansion O
and O
shrinking O
with O
the O
edges O
bending S-MANP
inward O
and O
the O
top O
of O
the O
sample S-CONPRI
exhibiting O
a O
slight O
u‐shape O
as S-MATE
residual O
distortions O
. O


Subsequently O
, O
a O
structural O
Finite B-CONPRI
Element I-CONPRI
Analysis E-CONPRI
( O
FEA O
) O
of O
the O
experiment S-CONPRI
is O
established O
, O
calibrated S-CONPRI
against O
experimental S-CONPRI
temperature O
profiles S-FEAT
and O
used O
to O
predict O
the O
in-situ S-CONPRI
distortions O
of O
the O
sample S-CONPRI
. O


A O
comparison O
of O
the O
experimental S-CONPRI
and O
numerical O
results O
reveals O
a O
good O
agreement O
in O
length O
direction O
of O
the O
sample S-CONPRI
and O
quantitative S-CONPRI
deviations O
in O
height O
direction O
, O
which O
are O
attributed O
to O
the O
material S-MATE
model O
used O
. O


The O
suitability O
of O
the O
novel O
experimental S-CONPRI
approach O
for O
measurements O
on O
an O
AM S-MANP
sample O
is O
shown O
and O
the O
potential O
for O
the O
validated O
numerical O
model S-CONPRI
as S-MATE
a O
predictive O
tool S-MACEQ
to O
reduce O
trial-and-error S-CONPRI
and O
improve O
part O
quality S-CONPRI
is O
evaluated O
. O


In O
this O
paper O
we O
investigate O
the O
use O
of O
passive B-CONPRI
stabilization E-CONPRI
to O
support S-APPL
stereolithography S-MANP
( O
SLA S-MACEQ
) O
printing O
aboard O
a O
moving B-MACEQ
vessel E-MACEQ
at O
sea O
. O


3D B-MANP
printing E-MANP
is O
a O
useful O
technology S-CONPRI
onboard O
a O
seagoing S-APPL
vessel O
to O
support S-APPL
engineering B-CONPRI
development E-CONPRI
, O
shipboard B-CONPRI
maintenance E-CONPRI
, O
and O
other O
applications O
when O
land-based B-CONPRI
manufacturing E-CONPRI
resources O
are O
unavailable O
. O


SLA S-MACEQ
printed O
material S-MATE
is O
particularly O
suited O
for O
underwater B-APPL
applications E-APPL
requiring O
sealed B-MACEQ
housings E-MACEQ
, O
since O
SLA B-MACEQ
printers E-MACEQ
are O
capable O
of O
producing O
high-resolution S-PARA
models O
that O
are O
fully O
solid O
and O
impervious S-CONPRI
to O
water O
. O


Hydrostatic B-PARA
pressure E-PARA
can O
quickly O
compromise O
parts O
created O
using O
standard S-CONPRI
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
3D B-MANP
printing E-MANP
. O


However O
, O
the O
dynamic S-CONPRI
environment O
onboard O
a O
moving B-MACEQ
vessel E-MACEQ
could O
impact S-CONPRI
the O
ability O
of O
an O
SLA B-MACEQ
printer E-MACEQ
to O
selectively O
cure S-CONPRI
voxels O
in O
a O
liquid B-CONPRI
resin I-CONPRI
bath E-CONPRI
as S-MATE
it O
undergoes O
constant O
motion O
, O
and O
can O
cause O
spilling S-CONPRI
over O
the O
walls O
of O
the O
resin B-CONPRI
tank E-CONPRI
. O


Using O
passive B-MACEQ
stabilization I-MACEQ
platforms E-MACEQ
onboard O
moving O
research B-MACEQ
vessels E-MACEQ
, O
we O
successfully O
printed O
a O
number O
of O
parts O
with O
no O
discernable S-CONPRI
differences O
from O
those O
produced O
in O
a O
traditional O
land-based B-CONPRI
laboratory E-CONPRI
. O


As S-MATE
a O
practical O
demonstration O
of O
this O
capability O
, O
we O
printed O
at O
sea O
underwater B-MACEQ
pressure I-MACEQ
housings E-MACEQ
that O
remained O
sealed O
to O
200 O
m O
water B-CONPRI
depth E-CONPRI
with O
functional O
integrated B-MACEQ
internal I-MACEQ
electronics E-MACEQ
. O


No O
post-print B-MANP
machining E-MANP
was O
required O
to O
create O
the O
sealed B-MACEQ
housings E-MACEQ
. O


This O
work O
lays O
the O
foundation O
for O
lithographic B-MANP
3D I-MANP
printing E-MANP
in O
seagoing B-APPL
oceanographic E-APPL
and O
naval B-APPL
applications E-APPL
, O
and O
additionally O
presents O
an O
economical O
approach O
for O
producing O
custom O
waterproof S-CONPRI
pressure B-MACEQ
housings E-MACEQ
in O
the O
field O
. O


Direct O
printing O
of O
microstructures S-MATE
using O
material B-MANP
jetting E-MANP
based O
additive B-MANP
manufacturing E-MANP
( O
3D B-MANP
printing E-MANP
) O
onto O
PMMA O
substrates O
. O


Substrate S-MATE
surface O
free O
energy O
contributes O
to O
both O
microstructure S-CONPRI
resolution O
and O
adhesion S-PRO
. O


Surface B-MANP
modification E-MANP
is O
an O
effective O
mechanism S-CONPRI
to O
tailor O
build S-PARA
– O
substrate S-MATE
interactions O
. O


The O
ability O
to O
directly O
print S-MANP
3D S-CONPRI
microstructures O
across O
the O
surface S-CONPRI
of O
large O
dimension S-FEAT
substrates O
opens O
up O
numerous O
possibilities O
not O
feasible O
with O
conventional O
2D S-CONPRI
or O
2.5D O
printing O
or O
coating S-APPL
techniques O
. O


Demonstrated O
herein O
is O
a O
method O
to O
print S-MANP
3D S-CONPRI
microstructures O
onto O
clear O
poly O
( O
methyl O
methacrylate O
) O
( O
PMMA O
) O
plates O
using O
material B-MANP
jetting E-MANP
technologies O
. O


Contact S-APPL
angle O
and O
profilometry O
analysis O
indicated O
that O
the O
VeroCyan™ O
photopolymer S-MATE
had O
enhanced O
wetting O
of O
the O
PMMA O
surface S-CONPRI
leading O
to O
greater O
droplet S-CONPRI
spreading O
affecting O
the O
geometries S-CONPRI
printed O
compared O
to O
VeroCyan™ O
integrated O
models O
. O


The O
surface S-CONPRI
chemistry S-CONPRI
and O
wetting O
behaviour O
played O
a O
crucial O
role O
in O
influencing O
interfacial O
interactions O
with O
the O
VeroCyan™ O
photopolymer S-MATE
hence O
its O
adhesion S-PRO
to O
the O
PMMA O
surface S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
has O
facilitated O
fabrication S-MANP
of O
complex O
and O
patient-specific O
metallic S-MATE
meta-biomaterials O
that O
offer O
an O
unprecedented O
collection O
of O
mechanical S-APPL
, O
mass O
transport S-CHAR
, O
and O
biological O
properties S-CONPRI
as S-MATE
well O
as S-MATE
a O
fully O
interconnected O
porous S-PRO
structure O
. O


However O
, O
applying O
meta-biomaterials O
for O
addressing O
unmet O
clinical O
needs O
in O
orthopedic O
surgery S-APPL
requires O
additional O
surface S-CONPRI
functionalities O
that O
should O
be S-MATE
induced O
through O
tailor-made O
coatings S-APPL
. O


Here O
, O
we O
developed O
multi-functional O
layer-by-layer S-CONPRI
coatings S-APPL
to O
simultaneously O
prevent O
implant-associated O
infections O
and O
stimulate O
bone B-CONPRI
tissue I-CONPRI
regeneration E-CONPRI
. O


We O
applied O
multiple O
layers O
of O
gelatin- O
and O
chitosan-based O
coatings S-APPL
containing O
either O
bone S-BIOP
morphogenetic O
protein O
( O
BMP O
) O
-2 O
or O
vancomycin O
on O
the O
surface S-CONPRI
of O
selective B-MANP
laser I-MANP
melted E-MANP
porous S-PRO
structures O
made O
from O
commercial O
pure O
Titanium S-MATE
( O
CP O
Ti S-MATE
) O
and O
designed S-FEAT
using O
a O
triply B-CONPRI
periodic I-CONPRI
minimal I-CONPRI
surface E-CONPRI
( O
i.e. O
, O
sheet S-MATE
gyroid O
) O
. O


The O
additive B-MANP
manufacturing I-MANP
process E-MANP
resulted O
in O
a O
porous S-PRO
structure O
and O
met O
the O
the O
design S-FEAT
values O
comparatively O
. O


X-ray B-CHAR
photoelectron I-CHAR
spectroscopy E-CHAR
spectra O
confirmed O
the O
presence O
and O
composition S-CONPRI
of O
the O
coating S-APPL
layers O
. O


The O
osteogenic O
differentiation O
of O
mesenchymal B-MATE
stem I-MATE
cells E-MATE
was O
enhanced O
, O
as S-MATE
shown O
by O
two-fold O
increase O
in O
the O
alkaline O
phosphatase O
activity O
and O
up O
to O
four-fold O
increase O
in O
the O
mineralization O
of O
all O
experimental S-CONPRI
groups O
containing O
BMP-2 O
. O


Eight-week O
subcutaneous S-BIOP
implantation S-MANP
in O
vivo O
showed O
no O
signs O
of O
a O
foreign O
body O
response O
, O
while O
connective O
tissue O
ingrowth O
was O
promoted O
by O
the O
layer-by-layer S-CONPRI
coating S-APPL
. O


These O
results O
unequivocally O
confirm O
the O
superior O
multi-functional O
performance S-CONPRI
of O
the O
developed O
biomaterials S-MATE
. O


The O
feasibility S-CONPRI
of O
in B-CONPRI
situ E-CONPRI
quantitative O
multielemental O
analysis O
during O
additive B-MANP
manufacturing I-MANP
process E-MANP
has O
been O
demonstrated O
for O
the O
first O
time O
. O


The O
specially O
designed S-FEAT
laser O
induced O
breakdown O
spectroscopy S-CONPRI
( O
LIBS O
) O
instrument O
was O
equipped O
the O
laser B-MANP
cladding E-MANP
head O
installed O
at O
an O
industrial B-MACEQ
robot E-MACEQ
. O


Melt B-MATE
pool E-MATE
surface O
sampling S-CONPRI
by O
LIBS O
probe S-MACEQ
was O
demonstrated O
to O
be S-MATE
the O
only O
choice O
for O
quantitative S-CONPRI
elemental B-CHAR
analysis E-CHAR
. O


On-line O
LIBS O
quantitative S-CONPRI
analysis O
of O
carbon S-MATE
and O
tungsten S-MATE
has O
been O
demonstrated O
during O
the O
synthesis O
of O
wear S-CONPRI
resistant O
coatings S-APPL
. O


Online O
LIBS O
results O
were O
in O
good O
agreement O
with O
offline O
analysis O
by O
conventional O
techniques O
( O
EDX S-CHAR
, O
XRF O
and O
combustion O
infrared B-CHAR
absorption E-CHAR
method O
) O
. O


The O
feasibility S-CONPRI
of O
in B-CONPRI
situ E-CONPRI
quantitative O
multi-elemental O
analysis O
during O
the O
additive B-MANP
manufacturing I-MANP
process E-MANP
has O
been O
demonstrated O
for O
the O
first O
time O
using O
laser S-ENAT
induced O
breakdown O
spectroscopy S-CONPRI
( O
LIBS O
) O
. O


The O
coaxial O
laser B-MANP
cladding E-MANP
technique O
was O
utilized O
for O
the O
production S-MANP
of O
highly O
wear-resistant O
coatings S-APPL
( O
nickel B-MATE
alloy E-MATE
reinforced O
with O
tungsten B-MATE
carbide E-MATE
grains S-CONPRI
) O
. O


High-quality O
production S-MANP
as S-MATE
well O
as S-MATE
gradient O
composition S-CONPRI
coating S-APPL
synthesis O
required O
an O
online O
technique O
for O
quantitative S-CONPRI
elemental B-CHAR
analysis E-CHAR
. O


A O
low-weight O
, O
compact S-MANP
LIBS O
probe S-MACEQ
was O
designed S-FEAT
to O
equip O
the O
laser B-MANP
cladding E-MANP
head O
installed O
at O
an O
industrial B-MACEQ
robot E-MACEQ
. O


Hot O
solidified O
clad O
as S-MATE
well O
as S-MATE
a O
melt B-MATE
pool E-MATE
surface O
was O
sampled O
by O
the O
LIBS O
probe S-MACEQ
but O
meaningful O
analytical O
results O
were O
achieved O
only O
for O
the O
latter O
case O
due O
to O
non-uniform O
distribution S-CONPRI
of O
tungsten B-MATE
carbide E-MATE
grains S-CONPRI
in O
the O
upper O
surface S-CONPRI
layer S-PARA
. O


LIBS O
sampling S-CONPRI
inside O
the O
melt B-MATE
pool E-MATE
did O
not O
affect O
the O
clad O
properties S-CONPRI
according O
to O
optical B-CHAR
microscopy E-CHAR
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
measurements O
. O


On-line O
LIBS O
quantitative S-CONPRI
analysis O
of O
key O
components S-MACEQ
( O
carbon S-MATE
and O
tungsten S-MATE
) O
was O
demonstrated O
during O
the O
synthesis O
of O
highly O
wear-resistant O
coatings S-APPL
and O
obtained O
results O
were O
in O
good O
agreement O
with O
offline O
analysis O
performed O
by O
electron O
energy B-CHAR
dispersive I-CHAR
X-ray I-CHAR
spectroscopy E-CHAR
, O
X-ray S-CHAR
fluorescence S-CHAR
spectroscopy O
, O
and O
the O
combustion O
infrared B-CHAR
absorption E-CHAR
method O
. O


In B-CONPRI
situ E-CONPRI
quantitative O
multielemental O
analysis O
by O
LIBS O
is O
a O
perspective O
control O
or/and O
feedback S-PARA
tool O
to O
improve O
quality S-CONPRI
of O
compositionally O
graded O
materials S-CONPRI
in O
additive B-MANP
manufacturing E-MANP
. O


Our O
objective O
herein O
is O
to O
investigate O
laser-based B-MANP
additive I-MANP
manufacturing E-MANP
to O
fabricate S-MANP
application-optimized O
machine-tools O
that O
perform O
comparably O
to O
commercially-available O
products O
. O


To O
demonstrate O
this O
technology S-CONPRI
, O
multi-layer O
Stellite™ O
( O
Co-Cr-W O
superalloy O
) O
structures O
were O
deposited O
on O
a O
stainless-steel O
substrate S-MATE
via O
directed B-MANP
energy I-MANP
deposition E-MANP
technique O
to O
be S-MATE
used O
as S-MATE
a O
tool S-MACEQ
for O
cutting S-MANP
applications O
requiring O
high-temperature O
strength S-PRO
and O
ductility S-PRO
, O
an O
area S-PARA
where O
conventional O
carbide S-MATE
and O
high-speed O
steel S-MATE
tools O
are O
challenged O
. O


The O
as-printed O
structures O
were O
free O
of O
large-scale O
defects S-CONPRI
and O
voids S-CONPRI
, O
and O
were O
further O
characterized O
and O
compared O
to O
commercial O
Blackalloy O
525 O
barstock O
( O
B525 O
) O
, O
a O
Co-Cr-W O
alloy S-MATE
tool O
of O
similar O
composition S-CONPRI
. O


The O
Stellite™ O
contained O
mostly O
Co-rich O
( O
α-phase O
) O
dendrites S-BIOP
, O
as S-MATE
well O
as S-MATE
inter-dendritic O
Cr7C3 O
and O
Cr23C6 O
phases O
. O


The O
B525 O
composition S-CONPRI
consisted O
of O
a O
range S-PARA
of O
lamellar-eutectic O
microstructure S-CONPRI
comprised O
of O
Co-phase O
with O
W6C O
reinforcement S-PARA
. O


During O
a O
turning S-MANP
operation O
of O
SS304L O
, O
the O
Stellite™ O
6 O
tool S-MACEQ
demonstrated O
consistent O
chip S-MATE
formation O
and O
more O
consistent O
rake-face O
and O
cratering O
wear S-CONPRI
in O
comparison O
to O
the O
B525 O
tool S-MACEQ
, O
indicating O
its O
adequacy O
for O
service O
in O
this O
application O
. O


Our O
results O
demonstrate O
for O
the O
first O
time O
that O
directed-energy-deposition O
can O
be S-MATE
utilized O
to O
fabricate S-MANP
advanced O
cutting B-APPL
tool E-APPL
concepts O
for O
job-specific O
applications O
. O


The O
influence O
of O
geometry S-CONPRI
and O
scan B-PARA
pattern E-PARA
on O
the O
microstructure B-CONPRI
evolution E-CONPRI
and O
magnetic O
performance S-CONPRI
of O
additively B-MANP
manufactured E-MANP
Fe-3Si O
components S-MACEQ
was O
investigated O
. O


To O
reduce O
eddy O
current O
losses O
, O
novel O
geometries S-CONPRI
were O
designed S-FEAT
and O
built O
and O
the O
microstructure S-CONPRI
and O
properties S-CONPRI
of O
these O
samples S-CONPRI
were O
characterized O
. O


The O
laser B-ENAT
scan E-ENAT
pattern O
was O
shown O
to O
strongly O
influence O
both O
the O
as-built O
grain B-CONPRI
structure E-CONPRI
and O
strength S-PRO
of O
the O
crystallographic O
texture S-FEAT
, O
resulting O
in O
measurable O
changes O
in O
the O
as-built O
magnetic O
performance S-CONPRI
. O


In O
thin O
wall O
samples S-CONPRI
, O
heat B-MANP
treatment E-MANP
resulted O
in O
an O
increase O
in O
the O
maximum O
relative O
magnetic O
permeability S-PRO
and O
decrease O
in O
power S-PARA
losses O
in O
most O
samples S-CONPRI
, O
consistent O
with O
grain B-CONPRI
growth E-CONPRI
. O


Compared O
to O
simple S-MANP
parallel O
plate O
construction S-APPL
and O
a O
mesh O
structure S-CONPRI
, O
a O
novel O
cross-section O
design S-FEAT
based O
on O
the O
Hilbert O
space O
filling O
curve O
was O
found O
to O
produce O
the O
lowest O
power S-PARA
losses O
. O


The O
mechanisms O
behind O
these O
results O
were O
explored O
using O
a O
combination O
of O
heat B-CONPRI
conduction E-CONPRI
and O
electromagnetic O
simulations S-ENAT
, O
providing O
a O
route O
for O
future O
component S-MACEQ
and O
process B-CONPRI
optimization E-CONPRI
. O


In O
this O
study O
, O
a O
laser-based B-MANP
additive I-MANP
manufacturing E-MANP
route O
of O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
was O
applied O
to O
fabricate S-MANP
carbon B-MATE
nanotubes E-MATE
( O
CNTs S-MATE
) O
reinforced S-CONPRI
Al-based O
nanocomposites O
with O
tailored O
microstructures S-MATE
and O
excellent O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
densification S-MANP
behavior O
, O
microstructure S-CONPRI
features O
and O
mechanical B-CONPRI
properties E-CONPRI
were O
investigated O
and O
the O
relationship O
between O
process S-CONPRI
and O
property S-CONPRI
was O
established O
. O


The O
results O
showed O
that O
the O
applied O
laser B-PARA
power E-PARA
and O
scan B-PARA
speed E-PARA
were O
the O
governing O
factors O
of O
the O
densification S-MANP
behavior O
of O
SLM-processed O
Al-based O
nanocomposites O
. O


SLM S-MANP
processing O
of O
0.5 O
wt. O
% O
CNTs/AlSi10Mg O
nanocomposite O
powder S-MATE
led S-APPL
to O
the O
formation O
of O
three O
typical O
microstructures S-MATE
including O
the O
primary O
Al9Si O
cellular O
dendrites S-BIOP
decorated O
with O
fibrous S-PRO
Si O
, O
the O
in B-CONPRI
situ E-CONPRI
Al4C3 O
covered O
on O
CNTs S-MATE
, O
and O
the O
precipitated O
Si S-MATE
inside O
the O
cellular B-CONPRI
grains E-CONPRI
. O


As S-MATE
the O
optimal O
SLM S-MANP
processing O
parameters S-CONPRI
of O
laser B-PARA
power E-PARA
of O
350 O
W O
and O
scan B-PARA
speed E-PARA
of O
2.0 O
m/s O
were O
applied O
, O
the O
fully B-PARA
dense E-PARA
SLM-processed O
CNTs/Al-based O
nanocomposites O
exhibited O
high O
microhardness S-CONPRI
of O
154.12 O
HV0.2 O
, O
tensile B-PRO
strength E-PRO
of O
420.8 O
MPa S-CONPRI
and O
elongation S-PRO
of O
8.87 O
% O
, O
due O
to O
the O
formation O
of O
high O
densification S-MANP
and O
ultrafine O
microstructure S-CONPRI
. O


The O
grain B-CHAR
refinement E-CHAR
effect O
, O
Orowan B-CONPRI
looping E-CONPRI
system O
and O
load O
transfer O
are O
considered O
as S-MATE
three O
strengthening B-CONPRI
mechanisms E-CONPRI
occurred O
simultaneously O
during O
tensile B-CHAR
tests E-CHAR
, O
leading O
to O
excellent O
mechanical B-CONPRI
properties E-CONPRI
of O
SLM-processed O
CNTs/Al-based O
nanocomposites O
. O


A O
skeleton O
sand S-MATE
mold S-MACEQ
which O
includes O
lattice-shell O
type O
, O
rib O
enforced O
type O
and O
air O
pockets O
structure S-CONPRI
was O
presented O
. O


These O
sand S-MATE
molds S-MACEQ
can O
save O
mold S-MACEQ
sand O
and O
control O
the O
time O
of O
casting S-MANP
. O


These O
sand S-MATE
molds S-MACEQ
make O
it O
possible O
to O
adjust O
the O
cooling S-MANP
and O
solidification S-CONPRI
conditions O
of O
castings O
. O


These O
sand S-MATE
molds S-MACEQ
can O
improve O
production S-MANP
efficiency O
, O
and O
reduce O
deformation S-CONPRI
, O
residual B-PRO
stress E-PRO
and O
defects S-CONPRI
of O
castings O
. O


The O
advance O
of O
additive B-MANP
manufacturing E-MANP
drives O
the O
design S-FEAT
of O
molds S-MACEQ
for O
castings O
. O


The O
shell S-MACEQ
forms O
the O
cavity O
for O
a O
casting S-MANP
and O
the O
surrounding O
ribs O
or O
lattices S-CONPRI
support O
and O
enforce O
the O
shell S-MACEQ
. O


This O
type O
of O
mold S-MACEQ
structure O
design S-FEAT
results O
in O
fast O
and O
uniform O
cooling S-MANP
of O
a O
casting S-MANP
, O
which O
can O
improve O
production S-MANP
efficiency O
and O
reduce O
the O
deformation S-CONPRI
and O
residual B-PRO
stress E-PRO
of O
a O
casting S-MANP
. O


In O
addition O
, O
it O
provides O
more O
space O
and O
flexibility S-PRO
to O
adjust O
the O
cooling S-MANP
conditions O
of O
interested O
locations O
of O
a O
casting S-MANP
. O


The O
thickness O
of O
the O
shell S-MACEQ
can O
be S-MATE
varied O
according O
to O
the O
local O
geometries S-CONPRI
of O
a O
casting S-MANP
. O


The O
support S-APPL
is O
designed S-FEAT
based O
on O
the O
hydrostatic B-PARA
pressure E-PARA
before O
solidification S-CONPRI
and O
the O
weight S-PARA
after O
solidification S-CONPRI
. O


An O
air O
pocket O
( O
hollow O
structure S-CONPRI
) O
in O
the O
shell S-MACEQ
was O
designed S-FEAT
for O
the O
riser S-MACEQ
to O
postpone O
its O
solidification S-CONPRI
and O
then O
facilitate O
shrinkage S-CONPRI
feeding O
. O


The O
experimental S-CONPRI
results O
revealed O
that O
the O
new O
design S-FEAT
of O
sand S-MATE
molds S-MACEQ
saved O
at O
least O
60 O
% O
sand S-MATE
and O
shortened O
the O
shakeout O
time O
by O
at O
least O
20 O
% O
. O


Local O
hollow O
structure S-CONPRI
prolonged O
its O
solidification B-MANP
process E-MANP
by O
approximately O
15 O
% O
. O


For O
the O
first O
time O
, O
a O
method O
of O
comparing O
quantitatively B-CHAR
measurement E-CHAR
apparatus O
for O
additive B-MANP
manufacture E-MANP
is O
defined O
. O


Novel O
instrumentation O
is O
subject O
to O
this O
analysis O
by O
way O
of O
case B-CONPRI
studies E-CONPRI
. O


Results O
allow O
researchers O
and O
industrial S-APPL
users O
alike O
to O
quickly O
assess O
the O
compatibility O
of O
an O
NDE O
technique O
with O
additive B-MANP
manufacturing I-MANP
processes E-MANP
. O


Cs O
and O
Ct S-ENAT
, O
the O
spatial O
and O
temporal O
capability O
, O
respectively O
, O
are O
shown O
to O
be S-MATE
useful O
analysis O
methods O
for O
integration O
feasibility S-CONPRI
efforts O
. O


Unlike O
more O
established O
subtractive S-MANP
or O
constant O
volume S-CONPRI
manufacturing B-MANP
technologies E-MANP
, O
additive B-MANP
manufacturing E-MANP
methods O
suffer O
from O
a O
lack O
of O
in-situ S-CONPRI
monitoring O
methodologies O
which O
can O
provide O
information O
relating O
to O
process B-CONPRI
performance E-CONPRI
and O
the O
formation O
of O
defects S-CONPRI
. O


In-process O
evaluation O
for O
additive B-MANP
manufacturing E-MANP
is O
becoming O
increasingly O
important O
in O
order O
to O
assure O
the O
integrity S-CONPRI
of O
parts O
produced O
in O
this O
way O
. O


This O
paper O
addresses O
the O
generic O
performance S-CONPRI
of O
inspection S-CHAR
methods O
suitable O
for O
additive B-MANP
manufacturing E-MANP
. O


Key O
process S-CONPRI
and O
measurement S-CHAR
parameters O
are O
explored O
and O
the O
impacts O
these O
have O
upon O
production S-MANP
rates O
are O
defined O
. O


A O
new O
method O
of O
benchmarking O
in-situ S-CONPRI
inspection O
instruments O
and O
characterising O
their O
suitability O
for O
additive B-MANP
manufacturing I-MANP
processes E-MANP
is O
presented O
to O
act O
as S-MATE
a O
design S-FEAT
tool O
to O
accommodate O
end O
user O
requirements O
. O


Two O
inspection S-CHAR
examples O
are O
presented O
: O
spatially O
resolved O
acoustic O
spectroscopy S-CONPRI
and O
optical S-CHAR
coherence O
tomography O
for O
scanning S-CONPRI
selective O
laser S-ENAT
melting O
and O
selective B-MANP
laser I-MANP
sintering E-MANP
parts O
, O
respectively O
. O


Observations O
made O
from O
the O
analyses O
presented O
show O
that O
the O
spatial O
capability O
arising O
from O
scanning B-CONPRI
parameters E-CONPRI
affects O
the O
temporal O
penalty O
and O
hence O
impact S-CONPRI
upon O
production S-MANP
rates O
. O


A O
case B-CONPRI
study E-CONPRI
, O
created O
from O
simulated O
data S-CONPRI
, O
has O
been O
used O
to O
outline O
the O
spatial O
performance S-CONPRI
of O
a O
generic O
nondestructive O
evaluation O
method O
and O
to O
show O
how O
a O
decrease O
in O
data S-CONPRI
capture O
resolution S-PARA
reduces O
the O
accuracy S-CHAR
of O
measurement S-CHAR
. O


While O
copper S-MATE
is O
a O
potent O
strengthener O
in O
titanium B-MATE
alloys E-MATE
, O
its O
use O
in O
commercial O
alloys S-MATE
has O
been O
severely O
restricted O
due O
to O
the O
strong O
tendency O
for O
segregation S-CONPRI
during O
solidification S-CONPRI
, O
leading O
to O
heterogeneous S-CONPRI
microstructures O
and O
what O
has O
often O
been O
referred O
to O
as S-MATE
the O
“ O
beta-fleck O
” O
problem O
. O


This O
problem O
can O
be S-MATE
largely O
obviated O
by O
using O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
for O
processing O
Ti-Cu O
alloys S-MATE
. O


This O
study O
focuses O
on O
AM S-MANP
of O
a O
binary S-CONPRI
Ti-4Cu O
and O
a O
ternary O
Ti-4Cu-4Al O
alloy S-MATE
using O
the O
laser B-MANP
engineered I-MANP
net I-MANP
shaping E-MANP
( O
LENS S-MANP
) O
process S-CONPRI
. O


The O
influence O
of O
post-deposition O
annealing B-MANP
treatments E-MANP
and O
the O
subsequent O
cooling B-PARA
rate E-PARA
on O
the O
microstructure S-CONPRI
and O
tensile B-PRO
properties E-PRO
of O
these O
alloys S-MATE
has O
been O
investigated O
in O
detail O
. O


The O
phase B-CONPRI
fraction E-CONPRI
of O
the O
eutectoid S-CONPRI
alpha O
+ O
Ti2Cu O
product O
is O
dependent O
on O
the O
cooling B-PARA
rate E-PARA
from O
above O
the O
beta O
transus O
temperature S-PARA
. O


Additionally O
, O
the O
Ti2Cu O
phase S-CONPRI
exhibited O
a O
far-from O
equilibrium B-CONPRI
composition E-CONPRI
in O
case O
of O
the O
water-quenched O
Ti-4Cu-4Al O
alloy S-MATE
. O


Both O
the O
yield B-PRO
stress E-PRO
( O
∼550−650 O
MPa S-CONPRI
) O
as S-MATE
well O
as S-MATE
the O
ductility S-PRO
( O
∼15–18 O
% O
) O
were O
also O
higher O
in O
case O
of O
the O
ternary B-MATE
alloy E-MATE
. O


The O
high O
strengths S-PRO
exhibited O
by O
the O
water-quenched O
samples S-CONPRI
of O
both O
alloys S-MATE
, O
while O
maintaining O
appreciable O
tensile B-PRO
ductility E-PRO
, O
could O
be S-MATE
attributed O
to O
clustering O
of O
Cu S-MATE
within O
the O
α O
laths O
, O
revealed O
by O
atom B-CHAR
probe I-CHAR
tomography E-CHAR
. O


Powder B-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technology S-CONPRI
, O
such O
as S-MATE
electron O
beam S-MACEQ
melting O
( O
EBM S-MANP
) O
and O
selective B-MANP
laser I-MANP
melting E-MANP
, O
has O
attracted O
tremendous O
academic O
and O
industrial S-APPL
interests O
because O
of O
its O
capacity S-CONPRI
to O
fabricate S-MANP
components S-MACEQ
with O
greater O
complexity S-CONPRI
compared O
with O
traditional O
processes S-CONPRI
, O
without O
significantly O
increasing O
the O
cost O
. O


It O
provides O
significantly O
higher O
design B-CONPRI
freedom E-CONPRI
to O
the O
designers O
and O
can O
make O
the O
built O
components S-MACEQ
closer O
to O
the O
optimum O
design S-FEAT
in O
theory O
when O
compared O
with O
traditional O
processes S-CONPRI
. O


However O
, O
the O
mechanical S-APPL
performance O
of O
the O
new O
design S-FEAT
fabricated O
by O
AM S-MANP
has O
not O
been O
clarified O
yet O
. O


Here O
, O
we O
report O
the O
fabrication S-MANP
and O
tensile S-PRO
deformation S-CONPRI
behavior O
of O
the O
EBM-built O
lightweight S-CONPRI
car S-CHAR
suspension O
double O
wishbone O
for O
both O
conventional O
and O
optimized O
designs S-FEAT
. O


EBM S-MANP
process O
is O
an O
effective O
method O
to O
produce O
a O
highly-dense O
Ti-6Al-4V S-MATE
lightweight S-CONPRI
design S-FEAT
component S-MACEQ
with O
good O
reproducibility S-CONPRI
and O
fine O
α/β O
duplex O
microstructure S-CONPRI
. O


A O
poor O
mechanical S-APPL
performance O
in O
the O
optimized O
design S-FEAT
is O
observed O
, O
which O
results O
from O
the O
build S-PARA
thickness-dependent O
mechanical S-APPL
performance O
that O
is O
caused O
by O
both O
various O
microstructures S-MATE
and O
rough O
surfaces S-CONPRI
in O
the O
Ti-6Al-4V S-MATE
parts O
. O


Notably O
, O
the O
rough O
surface S-CONPRI
plays O
a O
dominant O
role O
in O
premature O
failure S-CONPRI
when O
the O
build S-PARA
thickness O
is O
below O
2 O
mm S-MANP
. O


Based O
on O
these O
findings O
, O
the O
degraded O
mechanical S-APPL
performance O
in O
the O
optimized O
design S-FEAT
is O
discussed O
. O


The O
experimental S-CONPRI
results O
and O
analyses O
provide O
a O
guideline O
for O
the O
design S-FEAT
of O
lightweight B-MACEQ
structures E-MACEQ
that O
are O
mainly O
comprised O
of O
thin O
walls O
and/or O
struts S-MACEQ
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
allows O
engineers O
to O
design S-FEAT
and O
manufacture S-CONPRI
complex O
weight S-PARA
saving O
lattice B-FEAT
structures E-FEAT
with O
relative O
ease O
. O


A O
non-destructive B-CHAR
testing E-CHAR
and O
evaluation O
method O
used O
to O
assess O
material B-CONPRI
properties E-CONPRI
and O
quality S-CONPRI
is O
the O
focus O
of O
this O
paper O
, O
namely O
acoustic O
resonance O
( O
AR S-ENAT
) O
testing S-CHAR
. O


For O
this O
research S-CONPRI
, O
AR S-ENAT
testing O
was O
conducted O
on O
weight S-PARA
saving O
lattice B-FEAT
structures E-FEAT
( O
fine O
and O
coarse O
) O
manufactured S-CONPRI
by O
powder B-MANP
bed I-MANP
fusion E-MANP
. O


The O
suitability O
of O
AR S-ENAT
testing O
was O
assessed O
through O
a O
combined O
approach O
of O
experimental S-CONPRI
testing O
and O
FE S-MATE
modelling O
. O


A O
sensitivity S-PARA
study O
was O
conducted O
on O
the O
FE S-MATE
model O
to O
quantify O
the O
influence O
of O
element S-MATE
coarseness O
on O
the O
resonant O
frequency O
prediction S-CONPRI
and O
this O
needs O
to O
be S-MATE
taken O
into O
account O
in O
the O
application O
and O
analysis O
of O
the O
technique O
. O


The O
AR S-ENAT
and O
FE S-MATE
modelling O
modulus B-PRO
of I-PRO
elasticity E-PRO
values O
were O
validated O
using O
specimens O
of O
known O
properties S-CONPRI
. O


There O
was O
fair O
agreement O
between O
the O
FE S-MATE
and O
compression B-CHAR
test E-CHAR
extracted O
values O
of O
effective O
modulus O
for O
the O
coarse O
lattice S-CONPRI
. O


For O
the O
fine O
lattice S-CONPRI
, O
there O
was O
agreement O
in O
the O
values O
of O
effective O
modulus O
extracted S-CONPRI
from O
AR S-ENAT
, O
3-point O
bend O
, O
and O
compression S-PRO
experimental O
tests O
carried O
out O
. O


It O
was O
found O
that O
loose O
powder S-MATE
fusing S-CONPRI
from O
AM S-MANP
resulted O
in O
the O
fine O
lattice B-FEAT
structure E-FEAT
having O
a O
higher O
density S-PRO
( O
at O
least O
1.5 O
times O
greater O
) O
than O
calculated O
due O
to O
the O
effect O
of O
loose O
powder S-MATE
adhesion S-PRO
. O


This O
effect O
resulted O
in O
an O
increased O
stiffness S-PRO
of O
the O
fine O
lattice B-FEAT
structure E-FEAT
. O


AR S-ENAT
can O
be S-MATE
used O
as S-MATE
a O
measure O
of O
determining O
loose O
powder S-MATE
adhesion S-PRO
and O
other O
unique O
structural O
characteristics O
resulting O
from O
AM S-MANP
. O


Increasing O
performance S-CONPRI
requirements O
of O
advanced O
components S-MACEQ
demands O
versatile O
fabrication S-MANP
techniques O
to O
meet O
application-specific O
needs O
. O


Composite B-MATE
material E-MATE
processing O
via O
laser-based B-MANP
additive I-MANP
manufacturing E-MANP
offers O
high O
processing-flexibility O
and O
limited O
tooling S-CONPRI
requirements O
to O
meet O
this O
need O
, O
but O
limited O
information O
exists O
on O
the O
processing-property O
relationships O
for O
these O
materials S-CONPRI
as S-MATE
well O
as S-MATE
how O
to O
exploit O
them O
for O
application-specific O
needs O
. O


In O
this O
study O
, O
Ti/B4C O
+ O
BN S-MATE
composites O
are O
developed O
for O
high-temperature O
applications O
by O
designed-incorporation O
of O
ceramic B-MATE
reinforcement E-MATE
( O
5 O
wt O
% O
total O
) O
into O
commercially-pure O
titanium S-MATE
to O
form O
combined O
particle S-CONPRI
and O
in B-CONPRI
situ E-CONPRI
reinforcing O
phases O
. O


We O
combine O
both O
B4C S-MATE
( O
limited O
reactivity O
with O
matrix O
) O
and O
BN S-MATE
( O
high O
reactivity O
with O
matrix O
) O
reinforcements O
to O
understand O
the O
processing O
characteristics O
, O
in B-CONPRI
situ E-CONPRI
phase O
formations O
, O
and O
combinatorial O
effect O
of O
the O
multiphase O
microstructures S-MATE
on O
thermomechanical B-CONPRI
properties E-CONPRI
and O
high-temperature O
oxidation B-PRO
resistance E-PRO
. O


Combined O
reinforcement S-PARA
in O
this O
new O
composite B-MATE
material E-MATE
leads O
to O
superior O
yield B-PRO
strength E-PRO
and O
wear B-PRO
resistance E-PRO
in O
comparison O
to O
the O
other O
compositions O
and O
matrix O
, O
as S-MATE
well O
as S-MATE
comparable O
oxidation S-MANP
characteristics O
to O
commercially-developed O
high O
temperature S-PARA
titanium O
alloys S-MATE
, O
alleviating O
the O
need O
for O
multiple O
rare-earth O
alloying B-MATE
elements E-MATE
that O
significantly O
raises O
costs O
for O
manufacturers O
. O


Tubular S-FEAT
structures O
are O
fabricated S-CONPRI
to O
demonstrate O
the O
ease O
of O
site-specific O
composition S-CONPRI
and O
dimensional O
tolerancing O
using O
this O
method O
. O


Our O
results O
indicate O
that O
tailored O
ceramic B-MATE
reinforcement E-MATE
in O
titanium S-MATE
via O
laser-based O
AM S-MANP
could O
lead S-MATE
to O
significantly O
enhanced O
engineering S-APPL
structures O
, O
particularly O
for O
developing O
higher O
temperature S-PARA
titanium-based O
materials S-CONPRI
. O


Previous O
research S-CONPRI
on O
the O
powder B-MANP
bed I-MANP
fusion I-MANP
electron I-MANP
beam I-MANP
additive I-MANP
manufacturing E-MANP
of O
Inconel B-MATE
718 E-MATE
has O
established O
a O
definite O
correlation O
between O
the O
processing O
conditions O
and O
the O
solidification B-CONPRI
microstructure E-CONPRI
of O
components S-MACEQ
. O


However O
, O
the O
direct O
role O
of O
physical O
phenomena O
such O
as S-MATE
fluid O
flow O
and O
vaporization O
on O
determining O
the O
solidification B-CONPRI
morphology E-CONPRI
have O
not O
been O
investigated O
quantitatively S-CONPRI
. O


Here O
we O
investigate O
the O
transient S-CONPRI
and O
spatial O
evolution S-CONPRI
of O
the O
fusion B-CONPRI
zone E-CONPRI
geometry O
, O
temperature B-PARA
gradients E-PARA
, O
and O
solidification S-CONPRI
growth O
rates O
during O
pulsed O
electron B-MANP
beam I-MANP
melting E-MANP
of O
the O
powder B-MACEQ
bed E-MACEQ
with O
a O
focus O
on O
the O
role O
of O
key O
physical O
phenomena O
. O


The O
effect O
of O
spot O
density S-PRO
during O
pulsing O
, O
which O
relates O
to O
the O
amount O
of O
heating S-MANP
of O
the O
build B-PARA
area E-PARA
during O
processing O
, O
on O
the O
columnar-to-equiaxed O
transition S-CONPRI
of O
the O
solidification S-CONPRI
structure O
was O
studied O
both O
experimentally O
and O
theoretically O
. O


Predictions S-CONPRI
and O
the O
evaluation O
of O
the O
role O
of O
heat B-CONPRI
transfer E-CONPRI
and O
fluid B-PRO
flow E-PRO
were O
established O
using O
existing O
solidification S-CONPRI
theories O
combined O
with O
transient S-CONPRI
, O
three-dimensional S-CONPRI
numerical O
heat B-CONPRI
transfer E-CONPRI
and O
fluid B-PRO
flow E-PRO
modeling O
. O


Metallurgical S-APPL
characteristics O
of O
the O
alloy S-MATE
’ O
s S-MATE
solidification O
are O
extracted S-CONPRI
from O
the O
transient S-CONPRI
temperature S-PARA
fields O
, O
and O
microstructure S-CONPRI
is O
predicted S-CONPRI
and O
validated O
using O
optical S-CHAR
images S-CONPRI
and O
electron O
backscattered O
diffraction S-CHAR
data S-CONPRI
from O
the O
experimental S-CONPRI
results O
. O


While O
conductive B-CONPRI
heat I-CONPRI
transfer E-CONPRI
dominates O
in O
the O
mushy O
region O
, O
both O
the O
pool O
geometry S-CONPRI
and O
the O
solidification B-CONPRI
parameters E-CONPRI
are O
affected O
by O
convective O
heat B-CONPRI
transfer E-CONPRI
. O


Finally O
, O
increased O
spot O
density S-PRO
during O
processing O
is O
shown O
to O
increase O
the O
time O
of O
solidification S-CONPRI
, O
lowering O
temperature B-PARA
gradients E-PARA
and O
increasing O
the O
probability S-CONPRI
of O
equiaxed B-CONPRI
grain E-CONPRI
formation O
. O


In O
this O
paper O
we O
have O
used O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
to O
manufacture S-CONPRI
and O
characterize O
metal S-MATE
microwave O
components S-MACEQ
. O


Here O
we O
focus O
on O
a O
2.5 O
GHz O
microwave S-ENAT
cavity O
resonator S-APPL
, O
manufactured S-CONPRI
by O
PBF S-MANP
from O
the O
alloy S-MATE
AlSi10Mg O
. O


Of O
particular O
interest O
is O
its O
thermal B-PRO
expansion I-PRO
coefficient E-PRO
, O
especially O
since O
many O
microwave S-ENAT
applications O
for O
PBF S-MANP
produced O
components S-MACEQ
will O
be S-MATE
in O
satellite O
systems O
where O
extreme O
ranges O
of O
temperature S-PARA
are O
experienced O
. O


We O
exploit O
the O
inherent O
resonant O
frequency O
dependence O
on O
cavity O
geometry S-CONPRI
, O
using O
a O
number O
of O
TM O
cavity O
modes O
, O
to O
determine O
the O
thermal B-PRO
expansion I-PRO
coefficient E-PRO
over O
the O
temperature B-PARA
range E-PARA
6–450 O
K. O
Our O
results O
compare O
well O
with O
literature O
values O
and O
show O
that O
the O
material S-MATE
under O
test O
exhibits O
lower O
thermal B-CONPRI
expansion E-CONPRI
when O
compared O
with O
a O
bulk O
aluminium B-MATE
alloy E-MATE
alternative O
( O
6063 O
) O
. O


Metal B-MANP
additive I-MANP
manufacturing E-MANP
is O
an O
emerging O
method O
to O
fabricate S-MANP
components S-MACEQ
used O
in O
the O
aerospace S-APPL
and O
biomedical B-APPL
industries E-APPL
. O


However O
, O
one O
of O
the O
significant O
challenges O
in O
this O
approach O
is O
the O
surface B-PARA
quality E-PARA
of O
the O
fabricated S-CONPRI
components S-MACEQ
. O


After O
metal B-MANP
additive I-MANP
manufacturing E-MANP
operations O
, O
post-processing S-CONPRI
is O
essential O
to O
meet O
the O
expected O
surface B-PARA
quality E-PARA
. O


This O
study O
presents O
the O
surface S-CONPRI
characteristics O
of O
as-built O
specimens O
manufactured S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
, O
where O
improvement O
of O
the O
surface S-CONPRI
can O
be S-MATE
achieved O
by O
post-processing S-CONPRI
operations O
. O


The O
post-processing S-CONPRI
operations O
in O
focus O
are O
finish B-MANP
machining E-MANP
( O
FM O
) O
, O
vibratory O
surface B-MANP
finishing E-MANP
( O
VSF O
) O
and O
drag S-MACEQ
finishing O
( O
DF O
) O
operations O
. O


Surface B-CONPRI
topography E-CONPRI
, O
average S-CONPRI
surface O
roughness S-PRO
, O
microhardness S-CONPRI
, O
microstructure S-CONPRI
and O
XRD S-CHAR
analysis O
have O
been O
carried O
out O
to O
examine O
the O
surface S-CONPRI
characteristics O
resulting O
from O
the O
post-processing S-CONPRI
operations O
. O


This O
study O
demonstrates O
that O
the O
drag S-MACEQ
finishing O
operation O
can O
be S-MATE
used O
for O
post-processing S-CONPRI
to O
meet O
the O
surface B-PARA
quality E-PARA
requirement O
of O
SLM S-MANP
manufactured S-CONPRI
parts O
. O


In-process O
deformation S-CONPRI
methods O
such O
as S-MATE
rolling O
can O
be S-MATE
used O
to O
refine O
the O
large O
columnar B-PRO
grains E-PRO
that O
form O
when O
wire B-MANP
+ I-MANP
arc I-MANP
additively I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
titanium B-MATE
alloys E-MATE
. O


Due O
to O
the O
laterally O
restrained O
geometry S-CONPRI
, O
application O
to O
thick O
walls O
and O
intersecting O
features O
required O
the O
development O
of O
a O
new O
‘ O
inverted O
profile S-FEAT
’ O
roller S-MACEQ
. O


A O
larger O
radii O
roller S-MACEQ
increased O
the O
extent O
of O
the O
recrystallised O
area S-PARA
, O
providing O
a O
more O
uniform O
grain B-PRO
size E-PRO
, O
and O
higher O
loads O
increased O
the O
amount O
of O
refinement O
. O


Electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
showed O
that O
the O
majority O
of O
the O
strain S-PRO
is O
generated O
toward O
the O
edges O
of O
the O
rolled O
groove O
, O
up O
to O
3 O
mm S-MANP
below O
the O
rolled O
surface S-CONPRI
. O


These O
results O
will O
help O
facilitate O
future O
optimisation O
of O
the O
rolling B-MANP
process E-MANP
and O
industrialisation O
of O
WAAM S-MANP
for O
large-scale O
titanium S-MATE
components S-MACEQ
. O


In O
this O
contribution O
, O
a O
simplified O
macroscopic S-CONPRI
and O
semi-analytical O
thermal B-CHAR
analysis E-CHAR
of O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
is O
presented O
to O
obtain O
computationally O
efficient O
simulations S-ENAT
of O
the O
entire O
process S-CONPRI
. O


Solidification S-CONPRI
and O
solid-state B-CONPRI
phase E-CONPRI
transitions O
are O
taken O
into O
account O
. O


The O
model S-CONPRI
is O
derived O
for O
laser S-ENAT
metal O
powder S-MATE
directed B-MANP
energy I-MANP
deposition E-MANP
, O
although O
it O
can O
be S-MATE
simply O
adapted O
for O
other O
focused O
thermal B-CONPRI
energy E-CONPRI
( O
e.g. O
, O
electron B-CONPRI
beam E-CONPRI
, O
or O
plasma B-CONPRI
arc E-CONPRI
) O
. O


The O
gas S-CONPRI
flow O
used O
for O
carrying O
the O
powder S-MATE
significantly O
influences O
cooling S-MANP
conditions O
, O
which O
is O
included O
in O
the O
model S-CONPRI
. O


The O
proposed O
simulation S-ENAT
strategy O
applies O
to O
multilayer O
composites S-MATE
with O
a O
wide O
range S-PARA
of O
shapes O
in O
the O
horizontal O
plane O
and O
arbitrary O
laser S-ENAT
scanning O
strategies O
( O
continuous O
way O
, O
back O
and O
forth O
, O
etc. O
) O
. O


The O
proposed O
work O
provides O
a O
simple S-MANP
tool O
to O
study O
the O
influence O
of O
most O
process B-CONPRI
parameters E-CONPRI
, O
design S-FEAT
in O
situ O
experiments O
and O
in O
turn O
develop O
optimization S-CONPRI
loops O
to O
reach O
material S-MATE
requirements O
and O
specific O
microstructures S-MATE
. O


In B-CONPRI
situ E-CONPRI
pyrometer O
measurements O
have O
been O
compared O
to O
the O
model S-CONPRI
, O
and O
good O
agreement O
has O
been O
observed O
with O
2.6 O
% O
error S-CONPRI
in O
average S-CONPRI
. O


The O
model S-CONPRI
is O
used O
to O
demonstrate O
the O
effect O
of O
various O
process B-CONPRI
parameters E-CONPRI
for O
a O
simple S-MANP
cylindrical S-CONPRI
geometry O
and O
a O
more O
complex O
auxetic O
cell S-APPL
. O


Additive B-MANP
manufacturing E-MANP
using O
nanoparticles S-CONPRI
( O
NPs O
) O
is O
a O
growing O
field O
due O
to O
the O
ever-increasing O
demand O
for O
parts O
with O
smaller O
and O
smaller O
features O
. O


Of O
particular O
interest O
are O
copper S-MATE
nanoparticles O
( O
Cu S-MATE
NPs O
) O
due O
to O
the O
ubiquitous O
use O
of O
Cu S-MATE
in O
microelectronics S-CONPRI
applications O
. O


There O
are O
numerous O
methods O
currently O
available O
to O
synthesize O
Cu S-MATE
NPs O
in O
both O
powder S-MATE
and O
ink S-MATE
forms O
. O


However O
, O
the O
effect O
of O
how O
the O
NPs O
are O
manufactured S-CONPRI
on O
the O
sintering S-MANP
properties S-CONPRI
of O
the O
NPs O
produced O
is O
not O
well O
understood O
. O


This O
paper O
shows O
that O
NP O
size O
, O
morphology S-CONPRI
, O
and O
synthesis O
method O
can O
have O
a O
significant O
effect O
on O
the O
sintering S-MANP
temperature O
and O
sintering S-MANP
quality S-CONPRI
for O
Cu S-MATE
NPs O
. O


In O
addition O
, O
surface S-CONPRI
coatings S-APPL
and O
surfactants O
used O
in O
Cu S-MATE
NP O
inks O
can O
help O
to O
reduce O
agglomeration O
in O
the O
dried S-MANP
NP O
samples S-CONPRI
, O
prevent O
oxidation S-MANP
of O
the O
Cu S-MATE
NPs O
, O
and O
restrict O
the O
sintering S-MANP
of O
the O
Cu S-MATE
NPs O
at O
lower O
temperatures S-PARA
due O
to O
the O
need O
to O
thermally O
remove O
the O
surface S-CONPRI
coatings S-APPL
before O
sintering S-MANP
can O
occur O
. O


Therefore O
, O
these O
coatings S-APPL
improve O
the O
Cu S-MATE
NP O
packing O
density S-PRO
and O
increase O
the O
temperature S-PARA
required O
for O
necking S-CONPRI
to O
occur O
which O
leads O
to O
better O
sintering S-MANP
of O
the O
Cu S-MATE
NP O
ink S-MATE
samples O
. O


It O
is O
also O
observed O
in O
this O
paper O
that O
most O
of O
these O
surface S-CONPRI
coatings S-APPL
are O
removed O
during O
the O
sintering S-MANP
processes S-CONPRI
leaving O
the O
sintered S-MANP
parts O
with O
a O
much O
higher O
Cu S-MATE
percentage O
than O
contained O
in O
the O
original O
NPs O
. O


However O
, O
at O
temperatures S-PARA
near O
the O
melting B-PARA
temperature E-PARA
of O
the O
Cu S-MATE
NPs O
, O
the O
surface S-CONPRI
coatings S-APPL
can O
start O
to O
graphitize O
and O
hinder O
the O
fusion S-CONPRI
of O
the O
NPs O
. O


Therefore O
, O
the O
optimal O
sintering S-MANP
conditions O
for O
Cu S-MATE
NP O
inks O
are O
at O
temperature S-PARA
high O
enough O
to O
break O
down O
the O
polymer S-MATE
surface O
coating S-APPL
on O
the O
NPs O
but O
low O
enough O
that O
the O
Cu S-MATE
NPs O
do O
not O
start O
to O
melt S-CONPRI
and O
that O
graphitizing O
of O
the O
surface S-CONPRI
coatings S-APPL
does O
not O
start O
to O
occur O
. O


In O
the O
present O
study O
, O
420 B-MATE
stainless I-MATE
steel E-MATE
parts O
with O
different O
porosities S-PRO
in O
the O
range S-PARA
of O
∼6 O
% O
to O
∼ O
54 O
% O
were O
fabricated S-CONPRI
via O
the O
binder S-MATE
jet O
printing B-ENAT
technology E-ENAT
followed O
by O
pre-sintering S-MANP
between O
1000 O
and O
1400 O
°C O
. O


Initially O
, O
during O
the O
pre-sintering S-MANP
at O
1150 O
°C O
, O
evidences O
of O
neck O
formation O
between O
the O
420 B-MATE
stainless I-MATE
steel E-MATE
particles O
were O
observed O
. O


Later O
, O
when O
pre-sintered S-PRO
at O
higher O
temperature S-PARA
between O
1300 O
and O
1350 O
°C O
, O
the O
parts O
were O
found O
with O
3D S-CONPRI
interconnected O
open-porous O
channels O
. O


Finally O
, O
pre-sintering S-MANP
at O
1400 O
°C O
led S-APPL
to O
closed/isolated O
pores S-PRO
within O
the O
parts O
. O


Subsequent O
bronze S-MATE
infiltration O
into O
the O
as-built O
( O
without O
pre-sintering S-MANP
) O
and O
pre-sintered S-PRO
( O
< O
1350 O
°C O
) O
420 B-MATE
stainless I-MATE
steel E-MATE
parts O
with O
open O
porous S-PRO
channels O
were O
carried O
out O
successfully O
and O
their O
corresponding O
microstructures S-MATE
and O
mechanical B-CONPRI
properties E-CONPRI
were O
presented O
and O
discussed O
. O


Relatively O
more O
uniform O
bronze S-MATE
infiltration O
was O
able O
to O
be S-MATE
achieved O
for O
the O
parts O
pre-sintered S-PRO
between O
1300 O
and O
1350 O
°C O
due O
to O
the O
presence O
of O
3D S-CONPRI
interconnected O
open-porous O
channels O
. O


When O
compared O
to O
the O
as-built O
parts O
, O
the O
combination O
of O
pre-sintering S-MANP
at O
1350 O
°C O
and O
subsequent O
bronze S-MATE
infiltration O
led S-APPL
to O
a O
significant O
increase O
in O
the O
tensile B-PRO
properties E-PRO
exhibiting O
a O
maximum O
tensile S-PRO
yield O
strength S-PRO
and O
ultimate B-PRO
tensile I-PRO
strength E-PRO
of O
∼ O
647 O
and O
∼ O
1053 O
MPa S-CONPRI
, O
respectively O
. O


The O
fractured O
surfaces S-CONPRI
indicated O
a O
typical O
brittle S-PRO
mode O
of O
fracture S-CONPRI
with O
cleavages O
on O
the O
420 B-MATE
stainless I-MATE
steel E-MATE
matrix O
whereas O
dimples O
and O
ridges O
were O
observed O
within O
the O
bronze S-MATE
phase O
. O


Characterization O
of O
the O
local O
deformation S-CONPRI
of O
the O
microstructure S-CONPRI
of O
316L B-MATE
stainless I-MATE
steel E-MATE
single-track O
thickness O
walls O
. O


EBSD S-CHAR
and O
DIC S-CONPRI
analysis O
of O
material B-MATE
elements E-MATE
under O
in B-CONPRI
situ E-CONPRI
SEM O
tensile S-PRO
loading O
. O


Crystallographic O
morphology S-CONPRI
and O
texture S-FEAT
aligned O
with O
heat B-CONPRI
flow I-CONPRI
pattern E-CONPRI
induced O
by O
printing O
strategy O
. O


Statistical O
analysis O
of O
morphology S-CONPRI
and O
strain S-PRO
patterns O
for O
small O
and O
large O
grains S-CONPRI
. O


Relationship O
between O
grain S-CONPRI
's O
morphology S-CONPRI
, O
strain S-PRO
patterns O
and O
anisotropy S-PRO
of O
macroscopic S-CONPRI
behavior O
. O


In O
additive B-MANP
manufacturing E-MANP
, O
the O
process B-CONPRI
parameters E-CONPRI
have O
a O
direct O
impact S-CONPRI
on O
the O
microstructure S-CONPRI
of O
the O
material S-MATE
and O
consequently O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
manufactured S-CONPRI
parts O
. O


The O
purpose O
of O
this O
paper O
is O
to O
explore O
this O
relation O
by O
characterizing O
the O
local O
microstructural S-CONPRI
response O
via O
in B-CONPRI
situ E-CONPRI
tensile O
test O
under O
a O
scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
( O
SEM S-CHAR
) O
combined O
with O
high B-PARA
resolution E-PARA
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
( O
HR-DIC O
) O
and O
Electron B-CHAR
Backscatter I-CHAR
Diffraction E-CHAR
( O
EBSD S-CHAR
) O
maps O
. O


The O
specimens O
under O
scrutiny O
were O
extracted S-CONPRI
from O
bidirectionally-printed O
single-track O
thickness O
316L B-MATE
stainless I-MATE
steel E-MATE
walls O
built O
by O
directed B-MANP
energy I-MANP
deposition E-MANP
. O


The O
morphologic O
and O
crystallographic O
textures O
of O
the O
grains S-CONPRI
were O
characterized O
by O
statistical O
analysis O
and O
associated O
with O
the O
particular O
heat B-CONPRI
flow I-CONPRI
pattern E-CONPRI
of O
the O
process S-CONPRI
. O


Grains S-CONPRI
were O
sorted O
according O
to O
their O
size O
into O
large O
columnar B-PRO
grains E-PRO
located O
within O
the O
printed O
layer S-PARA
and O
small O
equiaxed B-CONPRI
grains E-CONPRI
located O
at O
the O
interfaces O
between O
successive O
layers O
. O


In B-CONPRI
situ E-CONPRI
tensile O
experiments O
were O
performed O
with O
a O
loading O
direction O
either O
perpendicular O
or O
along O
the O
printing O
direction O
and O
exhibit O
different O
mechanisms O
of O
deformation S-CONPRI
. O


A O
statistical O
analysis O
of O
the O
average S-CONPRI
deformation O
per O
grain S-CONPRI
indicates O
that O
for O
a O
tensile S-PRO
loading O
along O
the O
building B-PARA
direction E-PARA
, O
small O
grains S-CONPRI
deform O
less O
than O
the O
large O
ones O
. O


In O
addition O
, O
HR-DIC O
combined O
with O
EBSD S-CHAR
maps O
showed O
strain S-PRO
localization O
situated O
at O
the O
interface S-CONPRI
between O
layers O
in O
the O
absence O
of O
small O
grains S-CONPRI
either O
individual O
or O
in O
clusters O
. O


For O
tensile B-CHAR
loads E-CHAR
along O
the O
printing O
direction O
, O
the O
strain S-PRO
localization O
was O
present O
in O
several O
particular O
large O
grains S-CONPRI
. O


These O
observations O
permit O
to O
justify O
the O
differences O
in O
yield O
and O
ultimate B-PRO
strength E-PRO
noticed O
during O
macroscopic S-CONPRI
tensile O
tests O
for O
both O
configurations O
. O


Moreover O
, O
they O
indicate O
that O
an O
optimization S-CONPRI
of O
the O
process B-CONPRI
parameters E-CONPRI
could O
trigger O
the O
control O
of O
microstructure S-CONPRI
and O
consequently O
the O
macroscopic S-CONPRI
mechanical O
behavior O
. O


Strategies O
for O
fabricating S-MANP
iron-based O
materials S-CONPRI
with O
high O
strength S-PRO
and O
ductility S-PRO
are O
rare O
despite O
intense O
research S-CONPRI
efforts O
within O
the O
last O
decades O
. O


This O
study O
provides O
a O
novel O
approach O
to O
achieve O
the O
synthesis O
of O
highly O
strong O
and O
ductile S-PRO
iron-based O
composites S-MATE
reinforced O
with O
a O
high O
weight S-PARA
fraction S-CONPRI
of O
WC S-MATE
particles S-CONPRI
( O
20 O
wt O
% O
) O
utilizing O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
as S-MATE
processing O
technique O
. O


Thereby O
, O
the O
LPBF-fabricated O
composite B-MATE
material E-MATE
has O
a O
multi-phase O
microstructure S-CONPRI
consisting O
of O
ductile S-PRO
austenite S-MATE
( O
main O
phase S-CONPRI
) O
, O
highly O
strong O
martensite S-MATE
and O
carbidic O
precipitations O
extending O
across O
different O
length-scales O
. O


The O
precipitation S-CONPRI
of O
( O
Fe S-MATE
, O
W O
) O
3C O
type O
carbide S-MATE
at O
the O
Fe/WC O
interface S-CONPRI
is O
well O
controlled O
. O


Thus O
, O
a O
very O
thin O
reaction O
layer S-PARA
( O
< O
500 O
nm O
) O
forms O
between O
the O
WC S-MATE
particles S-CONPRI
and O
iron-based O
matrix O
. O


These O
iron-based O
composites S-MATE
synthesized O
by O
LPBF S-MANP
show O
an O
excellent O
compressive B-PRO
strength E-PRO
of O
about O
2833 O
MPa S-CONPRI
and O
large O
fracture S-CONPRI
strain O
of O
about O
32 O
% O
. O


The O
following O
mechanisms O
contribute O
to O
the O
improved O
mechanical B-CONPRI
properties E-CONPRI
: O
( O
1 O
) O
multiphase O
material S-MATE
system O
, O
( O
2 O
) O
grain B-CHAR
refinement E-CHAR
, O
( O
3 O
) O
substructures O
, O
( O
4 O
) O
coherent O
multiscale O
interfaces O
and O
( O
5 O
) O
nano-precipitations O
. O


Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
is O
a O
proven O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technology S-CONPRI
for O
producing O
metallic S-MATE
components S-MACEQ
with O
complex B-PRO
shapes E-PRO
using O
layer-by-layer S-CONPRI
manufacture O
principle O
. O


However O
, O
the O
fabrication S-MANP
of O
crack-free O
high-performance O
Ni-based O
superalloys S-MATE
such O
as S-MATE
Hastelloy O
X O
( O
HX O
) O
using O
LPBF S-MANP
technology O
remains O
a O
challenge O
because O
of O
these O
materials S-CONPRI
’ O
susceptibility S-PRO
to O
hot B-CONPRI
cracking E-CONPRI
. O


This O
paper O
addresses O
the O
above O
problem O
by O
proposing O
a O
novel O
method O
of O
introducing O
1 O
wt. O
% O
titanium B-MATE
carbide E-MATE
( O
TiC O
) O
nanoparticles S-CONPRI
. O


The O
findings O
reveal O
that O
the O
addition O
of O
TiC O
nanoparticles S-CONPRI
results O
in O
the O
elimination O
of O
microcracks S-CONPRI
in O
the O
LPBF-fabricated O
enhanced O
HX O
samples S-CONPRI
; O
i.e O
. O


the O
0.65 O
% O
microcracks S-CONPRI
that O
were O
formed O
in O
the O
as-fabricated O
original O
HX O
were O
eliminated O
in O
the O
as-fabricated O
enhanced O
HX O
, O
despite O
the O
0.14 O
% O
residual S-CONPRI
pores S-PRO
formed O
. O


It O
also O
contributes O
to O
a O
21.8 O
% O
increase O
in O
low-angle O
grain B-CONPRI
boundaries E-CONPRI
( O
LAGBs O
) O
and O
a O
98 O
MPa S-CONPRI
increase O
in O
yield B-PRO
strength E-PRO
. O


The O
study O
revealed O
that O
segregated O
carbides S-MATE
were O
unable O
to O
trigger O
hot B-CONPRI
cracking E-CONPRI
without O
sufficient O
thermal O
residual B-PRO
stresses E-PRO
; O
the O
significantly O
increased O
subgrains S-CONPRI
and O
low-angle O
grain B-CONPRI
boundaries E-CONPRI
played O
a O
key O
role O
in O
the O
hot B-CONPRI
cracking E-CONPRI
elimination O
. O


These O
findings O
offer O
a O
new O
perspective O
on O
the O
elimination O
of O
hot B-CONPRI
cracking E-CONPRI
of O
nickel-based B-MATE
superalloys E-MATE
and O
other O
industrially O
relevant O
crack-susceptible O
alloys S-MATE
. O


The O
findings O
also O
have O
significant O
implications O
for O
the O
design S-FEAT
of O
new O
alloys S-MATE
, O
particularly O
for O
high-temperature O
industrial S-APPL
applications O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
has O
the O
potential O
to O
construct O
complex B-CONPRI
geometries E-CONPRI
through O
the O
simple S-MANP
and O
highly O
repetitive O
process S-CONPRI
of O
layer-by-layer B-CONPRI
deposition E-CONPRI
. O


The O
process S-CONPRI
is O
repetitive O
and O
fully O
automated O
, O
but O
the O
interactions O
between O
layers O
during O
deposition S-CONPRI
are O
tightly O
coupled O
. O


To O
unravel O
these O
interactions O
, O
the O
computational B-ENAT
models E-ENAT
of O
the O
manufacturing B-MANP
process E-MANP
are O
critically O
needed O
. O


However O
, O
current O
state-of-the-art S-CONPRI
physics-based B-CONPRI
models E-CONPRI
are O
computationally O
demanding O
and O
can O
not O
be S-MATE
used O
for O
any O
realistic O
optimization S-CONPRI
. O


To O
address O
this O
challenge O
, O
we O
built O
a O
surrogate O
model S-CONPRI
( O
SM S-MATE
) O
of O
thermal B-CONPRI
profiles E-CONPRI
that O
significantly O
reduced O
the O
computational O
cost O
. O


We O
built O
this O
model S-CONPRI
based O
on O
the O
observation O
that O
any O
AM B-MANP
process E-MANP
exhibits O
a O
high O
level O
of O
redundancy O
and O
periodicity O
, O
making O
it O
an O
ideal O
problem O
for O
machine S-MACEQ
learning O
and O
surrogate O
modeling.We O
introduced O
a O
unique O
geometry S-CONPRI
representation O
that O
is O
the O
key O
insight O
for O
this O
work O
. O


Rather O
than O
directly O
using O
the O
part O
geometry S-CONPRI
, O
we O
directly O
use O
the O
GCode O
and O
translate O
it O
into O
a O
set S-APPL
of O
features O
( O
local O
distances O
from O
heat B-CONPRI
sources E-CONPRI
, O
e.g. O
, O
extruder S-MACEQ
, O
and O
sinks O
, O
e.g. O
, O
cooling S-MANP
surfaces O
) O
. O


This O
set S-APPL
of O
features O
is O
directly O
used O
as S-MATE
an O
input O
for O
the O
SM S-MATE
of O
thermal O
history O
. O


Since O
this O
set S-APPL
can O
be S-MATE
calculated O
a O
priori O
from O
GCode O
, O
the O
explicit O
geometry S-CONPRI
considerations O
are O
largely O
factored O
out O
. O


Moreover O
, O
we O
leveraged O
the O
analytical B-CONPRI
solution E-CONPRI
to O
the O
moving O
heat B-CONPRI
source E-CONPRI
model O
to O
determine O
heat S-CONPRI
influence O
zone O
( O
HIZ O
) O
. O


We O
showed O
that O
for O
fused B-MANP
filament I-MANP
fabrication E-MANP
, O
the O
size O
of O
HIZ O
is O
small O
; O
thus O
, O
the O
number O
of O
input O
variables O
for O
the O
SM S-MATE
is O
small O
as S-MATE
well.To O
build S-PARA
the O
SM S-MATE
, O
we O
first O
generated O
the O
thermal O
data S-CONPRI
using O
a O
physics-based B-CONPRI
model E-CONPRI
and O
use O
it O
to O
train O
an O
artificial B-ENAT
neural I-ENAT
network E-ENAT
model O
. O


We O
trained O
the O
SM S-MATE
and O
demonstrate O
its O
high O
predictive O
power S-PARA
and O
low O
computational O
cost O
. O


With O
such O
performance S-CONPRI
, O
this O
model S-CONPRI
opens O
the O
possibility O
of O
optimization S-CONPRI
as S-MATE
well O
as S-MATE
process O
planning S-MANP
, O
and O
in B-CONPRI
situ E-CONPRI
monitoring O
for O
closed-loop B-MACEQ
control E-MACEQ
. O


In O
the O
context O
of O
additive B-MANP
manufacturing E-MANP
, O
there O
is O
an O
exponential O
use O
of O
thermoplastic B-MATE
materials E-MATE
in O
the O
industrial S-APPL
and O
public O
open-source S-CONPRI
additive B-MANP
manufacturing E-MANP
sector O
, O
leading O
to O
an O
increase O
in O
global O
polymer S-MATE
consumption O
and O
waste O
generation O
. O


However O
, O
the O
coupling O
of O
the O
open-source S-CONPRI
3D B-MACEQ
printers E-MACEQ
with O
polymer S-MATE
processing O
could O
potentially O
offer O
the O
basis O
for O
a O
new O
paradigm O
of O
distributed O
recycling B-CONPRI
process E-CONPRI
. O


It O
could O
be S-MATE
a O
complementary O
alternative O
to O
the O
traditional O
paradigm O
of O
centralized O
recycling S-CONPRI
of O
polymers S-MATE
, O
which O
is O
often O
uneconomical O
and O
energy O
intensive O
due O
to O
transportation O
embodied O
energy O
. O


In O
order O
to O
achieve O
this O
goal O
, O
a O
first O
step S-CONPRI
is O
to O
prove O
the O
technical O
feasibility S-CONPRI
to O
recycle O
thermoplastic B-MATE
material E-MATE
intended O
for O
open-source S-CONPRI
3D B-MANP
printing E-MANP
feedstock.The O
contribution O
of O
the O
present O
study O
is O
twofold O
: O
first O
, O
a O
general O
methodology S-CONPRI
to O
evaluate O
the O
recyclability S-CONPRI
of O
thermoplastics S-MATE
used O
as S-MATE
feedstock O
in O
open-source S-CONPRI
3D B-MANP
printing E-MANP
machines O
is O
proposed O
. O


Then O
, O
the O
proposed O
methodology S-CONPRI
is O
applied O
to O
the O
recycling S-CONPRI
study O
of O
polylactic B-MATE
acid E-MATE
( O
PLA S-MATE
) O
material S-MATE
addressed O
to O
the O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
technique O
, O
which O
is O
currently O
the O
most O
widely O
used O
. O


The O
main O
results O
of O
this O
application O
contribute O
to O
the O
understanding O
of O
the O
influence O
of O
the O
material S-MATE
's O
physico-chemical O
degradation S-CONPRI
on O
its O
mechanical B-CONPRI
properties E-CONPRI
as S-MATE
well O
as S-MATE
its O
potential O
distributed O
recyclability S-CONPRI
. O


Additively B-MANP
manufactured E-MANP
internal O
lattice B-FEAT
structures E-FEAT
offer O
a O
unique O
approach O
to O
lightweight S-CONPRI
components S-MACEQ
and O
adding O
multi-functionality O
. O


Design S-FEAT
methods O
for O
parts O
based O
on O
lattices S-CONPRI
are O
emerging O
and O
include O
a O
family O
of O
topology B-FEAT
optimization E-FEAT
schemes O
for O
tailoring O
local O
cell B-FEAT
density E-FEAT
to O
service O
loadings O
. O


In O
order O
to O
gain S-PARA
confidence O
, O
these O
methods O
must O
be S-MATE
validated O
in O
a O
controlled O
manner O
. O


In O
this O
paper O
, O
we O
report O
optimization S-CONPRI
, O
analysis O
, O
manufacturing S-MANP
, O
and O
mechanical B-CHAR
test E-CHAR
validation O
of O
a O
casing-like O
test O
article O
. O


The O
test O
article O
was O
optimized O
using O
a O
stress-based O
homogenized S-MANP
topology O
optimization S-CONPRI
approach O
and O
achieved O
a O
53 O
% O
weight S-PARA
reduction S-CONPRI
versus O
a O
solid O
, O
fully-dense O
casing O
with O
the O
same O
form O
factor O
. O


The O
optimized O
geometry S-CONPRI
was O
studied O
with O
high-fidelity B-CONPRI
finite I-CONPRI
element I-CONPRI
analysis E-CONPRI
and O
then O
additively B-MANP
manufactured E-MANP
. O


Mechanical B-CHAR
testing E-CHAR
was O
performed O
and O
demonstrated O
good O
correlation O
between O
the O
homogenized S-MANP
finite B-CONPRI
element I-CONPRI
model E-CONPRI
used O
for O
optimization S-CONPRI
, O
the O
high-fidelity B-CONPRI
finite I-CONPRI
element I-CONPRI
model E-CONPRI
, O
and O
experimental S-CONPRI
results O
. O


The O
findings O
validate O
the O
optimization S-CONPRI
approach O
for O
the O
particular O
use O
and O
load O
case O
and O
start O
to O
build S-PARA
confidence O
in O
the O
approach O
as S-MATE
an O
accepted O
method O
. O


This O
work O
explores O
the O
feasibility S-CONPRI
of O
using O
the O
Abrasive S-MATE
Fluidized O
Bed S-MACEQ
( O
AFB O
) O
method O
to O
finish O
flat O
AlSi10Mg S-MATE
substrates O
manufactured S-CONPRI
by O
Direct B-MANP
Metal I-MANP
Laser I-MANP
Sintering E-MANP
( O
DMLS S-MANP
) O
. O


Finishing S-MANP
was O
performed O
by O
rotating O
the O
substrates O
inside O
a O
fluidized B-CONPRI
bed E-CONPRI
of O
abrasives S-MATE
at O
high O
speeds O
. O


The O
interaction O
between O
the O
fluidized O
abrasives S-MATE
and O
AlSi10Mg S-MATE
substrates O
has O
been O
investigated O
to O
analyze O
the O
influence O
of O
the O
operational O
parameters S-CONPRI
, O
namely O
, O
abrasive S-MATE
type O
and O
rotational O
speed O
, O
on O
the O
finishing S-MANP
performance O
. O


The O
morphological O
features O
of O
the O
substrates O
and O
geometrical O
tolerances S-PARA
have O
been O
inspected O
by O
field O
emission S-CHAR
gun–scanning O
electron B-CHAR
microscopy E-CHAR
( O
FEG–SEM O
) O
and O
contact S-APPL
gauge O
profilometry O
. O


After O
short O
finishing S-MANP
cycles O
, O
the O
substrates O
featured O
a O
smoother O
surface B-CHAR
morphology E-CHAR
, O
while O
the O
edges O
were O
only O
influenced O
slightly O
by O
the O
abrasive S-MATE
impacts O
. O


Abrasive S-MATE
Fluidized O
Bed S-MACEQ
( O
AFB O
) O
can O
therefore O
be S-MATE
considered O
a O
potential O
easy-to-automate O
, O
low O
cost O
, O
low O
time O
consuming O
and O
sustainable S-CONPRI
finishing S-MANP
technology O
for O
metal S-MATE
parts O
obtained O
through O
additive B-MANP
manufacturing E-MANP
. O


A O
texture S-FEAT
prediction S-CONPRI
method O
was O
proposed O
for O
epitaxial B-PRO
columnar I-PRO
grains E-PRO
in O
SLM S-MANP
. O


The O
texture S-FEAT
prediction S-CONPRI
method O
was O
combined O
with O
the O
melt B-MATE
pool E-MATE
prediction O
. O


Process S-CONPRI
and O
microstructure S-CONPRI
were O
linked O
quantitatively S-CONPRI
for O
the O
metal S-MATE
SLM O
AM B-MANP
process E-MANP
. O


Texture S-FEAT
evolution S-CONPRI
with O
the O
number B-PARA
of I-PARA
layers E-PARA
for O
SLM S-MANP
AlSi10Mg S-MATE
was O
simulated O
. O


The O
simulated O
texture S-FEAT
showed O
pattern S-CONPRI
and O
intensity O
similar O
to O
experiment S-CONPRI
results O
. O


Metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
such O
as S-MATE
selective O
laser S-ENAT
melting O
( O
SLM S-MANP
) O
has O
the O
powerful O
capability O
to O
produce O
very O
different O
microstructural S-CONPRI
features O
, O
hence O
different O
mechanical B-CONPRI
properties E-CONPRI
in O
metals S-MATE
using O
the O
same O
feedstock B-MATE
material E-MATE
but O
different O
values O
of O
process B-CONPRI
parameters E-CONPRI
. O


The O
lack O
of O
a O
reliable O
theoretical B-CONPRI
model E-CONPRI
of O
the O
processing-microstructure O
relationship O
of O
AM B-MATE
material E-MATE
is O
preventing O
AM B-MANP
technology E-MANP
from O
being O
widely O
adopted O
by O
the O
manufacturing S-MANP
community O
. O


Hence O
, O
the O
goal O
of O
this O
work O
is O
to O
establish O
the O
link O
between O
the O
microstructure S-CONPRI
( O
texture S-FEAT
) O
and O
the O
process B-CONPRI
parameters E-CONPRI
( O
laser B-PARA
power E-PARA
, O
scanning B-PARA
speed E-PARA
, O
preheat O
and O
scanning B-CONPRI
strategy E-CONPRI
) O
of O
a O
metal S-MATE
SLM O
process S-CONPRI
. O


To O
achieve O
the O
above O
goal O
, O
a O
quantitative S-CONPRI
semi-empirical O
method O
is O
proposed O
to O
predict O
the O
texture S-FEAT
of O
the O
epitaxial B-PRO
columnar I-PRO
grains E-PRO
grown O
from O
polycrystal O
substrates O
. O


Combined O
with O
the O
melt B-MATE
pool E-MATE
prediction O
by O
the O
Rosenthal B-CONPRI
solution E-CONPRI
, O
the O
processing O
and O
microstructure S-CONPRI
were O
linked O
together O
quantitatively S-CONPRI
. O


The O
proposed O
method O
is O
used O
to O
estimate O
the O
texture S-FEAT
evolution S-CONPRI
with O
the O
number B-PARA
of I-PARA
layers E-PARA
for O
EOS-DMLS-processed O
AlSi10Mg S-MATE
( O
unidirectional B-CONPRI
scanning E-CONPRI
direction O
in O
one O
layer S-PARA
and O
no O
rotation O
of O
scanning S-CONPRI
direction O
between O
layers O
) O
. O


The O
texture S-FEAT
reaches O
a O
steady B-CONPRI
state E-CONPRI
after O
five O
layers O
, O
and O
the O
steady B-CONPRI
state E-CONPRI
texture O
has O
similar O
pattern S-CONPRI
and O
intensity O
to O
that O
obtained O
from O
the O
experiment S-CONPRI
using O
the O
same O
process B-CONPRI
parameter E-CONPRI
values O
and O
scanning B-CONPRI
strategy E-CONPRI
. O


The O
severe O
thermal B-PARA
gradients E-PARA
associated O
with O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
generate O
large O
residual B-PRO
stresses E-PRO
( O
RS O
) O
that O
geometrically O
distort O
and O
otherwise O
alter O
the O
performance S-CONPRI
of O
printed O
parts O
. O


Despite O
broad O
research S-CONPRI
interest O
in O
this O
field O
, O
it O
has O
remained O
challenging O
to O
measure O
warpage S-CONPRI
in O
general O
as S-MATE
well O
as S-MATE
RS O
distributions S-CONPRI
in O
situ O
, O
which O
has O
obfuscated O
the O
mechanisms O
of O
stress S-PRO
formation O
during O
the O
printing B-MANP
process E-MANP
. O


In O
pursuit O
of O
this O
goal O
, O
we O
have O
developed O
a O
non-destructive O
framework S-CONPRI
for O
RS B-CHAR
measurement E-CHAR
in O
SLM S-MANP
parts O
using O
three-dimensional S-CONPRI
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
( O
3D-DIC O
) O
to O
capture O
in B-CONPRI
situ E-CONPRI
surface O
distortion S-CONPRI
. O


A O
two-dimensional S-CONPRI
analytical O
model S-CONPRI
was O
developed O
to O
convert O
DIC S-CONPRI
surface O
curvature O
measurements O
to O
estimates O
of O
in-plane O
residual B-PRO
stresses E-PRO
. O


Experimental S-CONPRI
validation O
using O
stainless B-MATE
steel E-MATE
316 O
L O
“ O
inverted-cone O
” O
parts O
demonstrated O
that O
residual B-PRO
stress E-PRO
varied O
across O
the O
surface S-CONPRI
of O
the O
printed O
part O
, O
and O
strongly O
interacted O
with O
the O
component S-MACEQ
geometry O
. O


The O
3D-DIC O
based O
RS B-CHAR
measurements E-CHAR
were O
validated O
by O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
, O
with O
an O
average S-CONPRI
error O
of O
6 O
% O
between O
measured O
and O
analytically O
derived O
stresses O
. O


Systematic O
variation S-CONPRI
in O
RS O
was O
attributed O
to O
the O
sector-based O
laser S-ENAT
raster O
strategy O
, O
which O
was O
supported O
by O
complementary O
finite B-CONPRI
element E-CONPRI
calculations O
. O


Calculations O
showed O
that O
the O
heterogeneous S-CONPRI
RS O
distribution S-CONPRI
in O
the O
parts O
emerged O
from O
the O
sequential O
re-heating O
and O
cooling S-MANP
of O
the O
new O
surface S-CONPRI
, O
and O
changed O
dynamically O
between O
layers O
. O


The O
unique O
DIC S-CONPRI
based O
RS O
methodology S-CONPRI
brings O
substantial O
benefits O
over O
alternatively O
proposed O
in B-CONPRI
situ E-CONPRI
AM S-MANP
RS O
measurements O
, O
and O
should O
facilitate O
enhanced O
process B-CONPRI
optimization E-CONPRI
and O
understanding O
leading O
towards O
AM B-MACEQ
part E-MACEQ
qualification O
. O


The O
interior O
porous S-PRO
defects S-CONPRI
formed O
during O
the O
layer-by-layer S-CONPRI
fabrication S-MANP
process O
have O
attracted O
increasing O
attention O
for O
different O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
techniques O
and O
are O
regarded O
as S-MATE
a O
crucial O
factor O
affecting O
the O
overall O
performance S-CONPRI
. O


In O
this O
work O
, O
aiming O
at O
the O
cold O
spray O
Ti6Al4V S-MATE
bulk O
materials S-CONPRI
, O
the O
hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
treatment O
is O
adopted O
to O
reduce O
the O
interior O
defects S-CONPRI
, O
adjust O
the O
microstructure S-CONPRI
, O
and O
improve O
the O
mechanical B-CONPRI
properties E-CONPRI
. O


To O
characterize O
the O
pore S-PRO
morphologies S-CONPRI
and O
porosity S-PRO
evolution S-CONPRI
, O
the O
CS O
Ti6Al4V S-MATE
sample S-CONPRI
is O
characterized O
by O
optical B-CHAR
microscopy E-CHAR
and O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
( O
XCT O
) O
. O


The O
3D S-CONPRI
reconstructions O
by O
XCT O
show O
that O
the O
fully B-PARA
dense E-PARA
Ti6Al4V O
alloy S-MATE
can O
be S-MATE
obtained O
through O
the O
high O
temperature S-PARA
diffusion S-CONPRI
and O
high O
pressure S-CONPRI
compacting O
of O
the O
HIP S-MANP
sample O
. O


After O
the O
HIP S-MANP
treatment O
, O
the O
severely O
deformed S-MANP
grains O
experience O
an O
obvious O
growth O
with O
the O
uniformly O
distributed O
β O
precipitates S-MATE
around O
equiaxed O
α O
grains S-CONPRI
. O


The O
tensile B-CHAR
test E-CHAR
shows O
that O
the O
strength S-PRO
of O
CS O
Ti6Al4V B-MATE
alloys E-MATE
can O
be S-MATE
largely O
improved O
by O
the O
enhanced O
diffusion S-CONPRI
and O
resultant O
metallurgical B-CONPRI
bonding E-CONPRI
. O


With O
the O
HIP S-MANP
treatment O
, O
the O
CS O
samples S-CONPRI
exhibit O
highly O
densified S-MANP
morphology O
and O
adjusted O
microstructure S-CONPRI
that O
can O
benefit O
the O
improvement O
of O
mechanical B-CONPRI
properties E-CONPRI
. O


A O
number O
of O
strategies O
that O
enable O
lattice B-FEAT
structures E-FEAT
to O
be S-MATE
derived O
from O
Topology B-FEAT
Optimisation E-FEAT
( O
TO O
) O
results O
suitable O
for O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
are O
presented O
. O


The O
proposed O
strategies O
are O
evaluated O
for O
mechanical S-APPL
performance O
and O
assessed O
for O
AM S-MANP
specific O
design S-FEAT
related O
manufacturing S-MANP
considerations O
. O


Results O
from O
Finite B-CONPRI
Element E-CONPRI
( O
FE S-MATE
) O
analysis O
for O
the O
two O
loading O
scenarios O
considered O
: O
intended O
loading O
, O
and O
variability S-CONPRI
in O
loading O
, O
provide O
insight O
into O
the O
solution S-CONPRI
optimality O
and O
robustness S-PRO
of O
the O
design S-FEAT
strategies O
. O


Lattice S-CONPRI
strategies O
that O
capitalised O
on O
TO O
results O
were O
found O
to O
be S-MATE
considerably O
( O
∼40–50 O
% O
) O
superior O
in O
terms O
of O
specific B-PRO
stiffness E-PRO
when O
compared O
to O
the O
structures O
where O
this O
was O
not O
the O
case O
. O


The O
Graded O
strategy O
was O
found O
to O
be S-MATE
the O
most O
desirable O
from O
both O
the O
design S-FEAT
and O
manufacturing S-MANP
perspective O
. O


The O
presented O
pros-and-cons O
for O
the O
various O
proposed O
design S-FEAT
strategies O
aim O
to O
provide O
insight O
into O
their O
suitability O
in O
meeting O
the O
challenges O
faced S-MANP
by O
the O
AM S-MANP
design O
community O
. O


Accompanying O
the O
increasing O
advances O
and O
interest O
in O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
is O
an O
increasing O
demand O
for O
an O
industrial S-APPL
workforce O
that O
is O
knowledgeable O
about O
the O
technologies S-CONPRI
and O
how O
to O
apply O
them O
to O
solve O
real-world O
problems O
. O


As S-MATE
a O
step S-CONPRI
towards O
addressing O
this O
knowledge O
gap O
, O
a O
workshop O
was O
held O
at O
the O
National O
Science O
Foundation O
( O
NSF O
) O
to O
discuss O
the O
educational O
needs O
to O
prepare O
industry S-APPL
for O
AM S-MANP
and O
its O
use O
in O
different O
fields O
. O


The O
workshop O
participants O
– O
66 O
representatives O
from O
academia O
, O
industry S-APPL
, O
and O
government O
– O
identified O
several O
key O
educational O
themes O
: O
( O
1 O
) O
AM B-MANP
processes E-MANP
and O
process/material O
relationships O
, O
( O
2 O
) O
engineering S-APPL
fundamentals O
with O
an O
emphasis O
on O
materials S-CONPRI
science O
and O
manufacturing S-MANP
, O
( O
3 O
) O
professional O
skills O
for O
problem O
solving O
and O
critical O
thinking O
, O
( O
4 O
) O
design S-FEAT
practices O
and O
tools S-MACEQ
that O
leverage O
the O
design B-CONPRI
freedom E-CONPRI
enabled O
by O
AM S-MANP
, O
and O
( O
5 O
) O
cross-functional O
teaming O
and O
ideation O
techniques O
to O
nurture O
creativity O
. O


First O
, O
ensure O
that O
all O
AM S-MANP
curricula O
provide O
students O
with O
an O
understanding O
of O
( O
i O
) O
AM S-MANP
and O
traditional B-MANP
manufacturing E-MANP
processes S-CONPRI
to O
enable O
them O
to O
effectively O
select O
the O
appropriate O
process S-CONPRI
for O
product O
realization O
; O
( O
ii O
) O
the O
relationships O
between O
AM B-MANP
processes E-MANP
and O
material B-CONPRI
properties E-CONPRI
; O
and O
( O
iii O
) O
“ O
Design S-FEAT
for O
AM S-MANP
” O
, O
including O
computational B-CONPRI
tools E-CONPRI
for O
AM S-MANP
design O
as S-MATE
well O
as S-MATE
frameworks O
for O
process B-CONPRI
selection E-CONPRI
, O
costing O
, O
and O
solution S-CONPRI
generation O
that O
take O
advantage O
of O
AM S-MANP
capabilities O
. O


Second O
, O
establish O
a O
national O
network O
for O
AM S-MANP
education O
that O
, O
by O
leveraging O
existing O
“ O
distributed O
” O
educational O
models O
and O
NSF O
’ O
s S-MATE
Advanced O
Technology S-CONPRI
Education O
( O
ATE O
) O
Programs O
, O
provides O
open O
source S-APPL
resources O
as S-MATE
well O
as S-MATE
packaged O
activities O
, O
courses O
, O
and O
curricula O
for O
all O
educational O
levels O
( O
K-Gray O
) O
. O


Fourth O
, O
provide O
support S-APPL
for O
collaborative O
and O
community-oriented O
maker O
spaces O
that O
promote O
awareness O
of O
AM S-MANP
among O
the O
public O
and O
provide O
AM S-MANP
training O
programs O
for O
incumbent O
workers O
in O
industry S-APPL
and O
students O
seeking O
alternative O
pathways O
to O
gain S-PARA
AM S-MANP
knowledge O
and O
experience O
. O


The O
dynamic S-CONPRI
tensile O
properties S-CONPRI
of O
additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
and O
cast S-MANP
Al-10Si-Mg O
alloy S-MATE
were O
investigated O
using O
high-speed O
synchrotron S-ENAT
X-ray O
imaging S-APPL
coupled O
with O
a O
modified O
Kolsky O
bar O
apparatus O
. O


A O
controlled O
tensile S-PRO
loading O
( O
strain B-CONPRI
rate E-CONPRI
≈ O
750 O
s−1 O
) O
was O
applied O
using O
the O
Kolsky O
bar O
apparatus O
and O
the O
deformation S-CONPRI
and O
fracture S-CONPRI
behavior O
were O
recorded O
using O
the O
high-speed O
X-ray B-CHAR
imaging E-CHAR
setup O
. O


The O
synchrotron S-ENAT
X-ray O
computed B-CHAR
tomography E-CHAR
( O
CT S-ENAT
) O
and O
high-speed O
imaging S-APPL
results O
worked O
together O
to O
identify O
the O
location O
of O
the O
critical O
flaw S-CONPRI
and O
to O
capture O
the O
dynamics O
of O
crack B-CONPRI
propagation E-CONPRI
. O


In O
all O
experiments O
, O
the O
critical O
flaw S-CONPRI
was O
located O
on O
the O
surface S-CONPRI
of O
each O
specimen O
. O


The O
AM S-MANP
specimens O
showed O
significantly O
higher O
crack B-CONPRI
propagation E-CONPRI
speed O
, O
yield B-PRO
strength E-PRO
, O
ultimate B-PRO
tensile I-PRO
strength E-PRO
, O
strain B-MANP
hardening E-MANP
coefficient O
, O
and O
yet O
lower O
ductility S-PRO
compared O
to O
the O
cast S-MANP
specimens O
under O
dynamic S-CONPRI
tension O
. O


Although O
the O
strength S-PRO
values O
were O
higher O
for O
the O
AM S-MANP
specimens O
, O
the O
critical O
mode O
I O
stress S-PRO
intensity O
factors O
were O
comparable O
for O
both O
specimens O
. O


The O
microstructures S-MATE
of O
the O
samples S-CONPRI
were O
characterized O
by O
CT S-ENAT
and O
scanning S-CONPRI
electron O
microcopy O
. O


The O
correlation O
between O
the O
dynamic S-CONPRI
fracture O
behavior O
of O
the O
samples S-CONPRI
and O
the O
microstructure S-CONPRI
of O
the O
samples S-CONPRI
is O
analyzed O
and O
discussed O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
uniquely O
suitable O
for O
healthcare O
applications O
due O
to O
its O
design B-CONPRI
flexibility E-CONPRI
and O
cost O
effectiveness S-CONPRI
for O
creating O
complex B-CONPRI
geometries E-CONPRI
. O


Successful O
arthroplasty O
requires O
integration O
of O
the O
prosthetic S-APPL
implant S-APPL
with O
the O
bone S-BIOP
to O
replace O
the O
damaged O
joint S-CONPRI
. O


Bone-mimetic O
biomaterials S-MATE
are O
utilised O
due O
to O
their O
mechanical B-CONPRI
properties E-CONPRI
and O
porous S-PRO
structure O
that O
allows O
bone B-CONPRI
ingrowth E-CONPRI
and O
implant S-APPL
fixation O
. O


The O
predictability O
of O
predetermined O
interconnected O
porous S-PRO
structures O
produced O
by O
AM S-MANP
ensures O
the O
required O
shape O
, O
size O
and O
properties S-CONPRI
that O
are O
suitable O
for O
tissue O
ingrowth O
and O
prevention O
of O
the O
implant S-APPL
loosening O
. O


The O
quality S-CONPRI
of O
the O
manufacturing B-MANP
process E-MANP
needs O
to O
be S-MATE
established O
before O
the O
utilisation O
of O
the O
parts O
in O
healthcare O
. O


This O
paper O
demonstrates O
a O
novel O
examination O
method O
of O
acetabular O
hip B-MACEQ
prosthesis E-MACEQ
cups O
based O
on O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
( O
CT S-ENAT
) O
and O
image S-CONPRI
processing O
. O


The O
method O
was O
developed O
based O
on O
an O
innovative O
hip B-MACEQ
prosthesis E-MACEQ
acetabular O
cup O
prototype S-CONPRI
with O
a O
prescribed O
non-uniform O
lattice B-FEAT
structure E-FEAT
forming S-MANP
struts O
over O
the O
surface S-CONPRI
, O
with O
the O
interconnected O
porosity S-PRO
encouraging O
bone S-BIOP
adhesion S-PRO
. O


This O
non-destructive O
, O
non-contact O
examination O
method O
can O
provide O
information O
of O
the O
interconnectivity O
of O
the O
porous S-PRO
structure O
, O
the O
standard B-CHAR
deviation E-CHAR
of O
the O
size O
of O
the O
pores S-PRO
and O
struts S-MACEQ
, O
the O
local O
thickness O
of O
the O
lattice B-FEAT
structure E-FEAT
in O
its O
size O
and O
spatial B-CHAR
distribution E-CHAR
. O


Fatigue S-PRO
limit O
of O
L-PBF S-MANP
maraging O
steels S-MATE
was O
characterized O
by O
infrared S-CONPRI
thermography O
. O


Different O
manufacturing S-MANP
strategies O
led S-APPL
to O
varying O
fatigue S-PRO
limit O
values O
. O


Printing B-MANP
process E-MANP
optimization S-CONPRI
with O
respect O
to O
fatigue S-PRO
performance O
can O
be S-MATE
envisaged O
. O


This O
paper O
deals O
with O
the O
fatigue S-PRO
performance O
of O
maraging B-MATE
steels E-MATE
manufactured S-CONPRI
by O
Powder B-MANP
Bed I-MANP
Fusion E-MANP
using O
a O
laser B-CONPRI
beam E-CONPRI
( O
L-PBF S-MANP
) O
. O


The O
objective O
of O
the O
study O
was O
to O
develop O
a O
method O
for O
the O
rapid O
and O
reliable O
characterization O
of O
the O
produced O
material S-MATE
’ O
s S-MATE
fatigue S-PRO
limit O
using O
infrared S-CONPRI
( O
IR S-CHAR
) O
thermography O
. O


Next O
, O
fatigue B-CHAR
tests E-CHAR
instrumented O
by O
IR S-CHAR
camera S-MACEQ
were O
processed S-CONPRI
using O
heat B-CONPRI
source E-CONPRI
reconstruction O
to O
measure O
the O
mechanical S-APPL
dissipation O
due O
to O
fatigue B-PRO
damage E-PRO
. O


A O
statistical O
model S-CONPRI
was O
then O
proposed O
to O
identify O
the O
fatigue S-PRO
limit O
of O
the O
material S-MATE
. O


Finally O
, O
a O
practical O
application O
was O
performed O
to O
compare O
different O
manufacturing S-MANP
strategies O
using O
the O
same O
powder S-MATE
, O
opening O
perspectives O
for O
the O
rapid O
optimization S-CONPRI
of O
the O
printing B-MANP
process E-MANP
with O
respect O
to O
the O
fatigue S-PRO
performance O
of O
the O
parts O
produced O
. O


Magnetically O
isotropic S-PRO
bonded O
magnets S-APPL
with O
a O
high O
loading O
fraction S-CONPRI
of O
70 O
vol. O
% O
Nd-Fe-B O
are O
fabricated S-CONPRI
via O
an O
extrusion-based O
additive B-MANP
manufacturing E-MANP
, O
or O
3D B-MANP
printing E-MANP
system O
that O
enables O
rapid O
production S-MANP
of O
large O
parts O
. O


The O
density S-PRO
of O
the O
printed O
magnet S-APPL
is O
∼ O
5.2 O
g/cm3 O
. O


The O
as-printed O
magnets S-APPL
are O
then O
coated S-APPL
with O
two O
types O
of O
polymers S-MATE
, O
both O
of O
which O
improve O
the O
thermal B-PRO
stability E-PRO
as S-MATE
revealed O
by O
flux S-MATE
aging O
loss O
measurements O
. O


Tensile B-CHAR
tests E-CHAR
performed O
at O
25 O
°C O
and O
100 O
°C O
show O
that O
the O
ultimate O
tensile B-PRO
stress E-PRO
( O
UTS S-PRO
) O
increases O
with O
increasing O
loading O
fraction S-CONPRI
of O
the O
magnet S-APPL
powder O
, O
and O
decreases O
with O
increasing O
temperature S-PARA
. O


AC O
magnetic B-CHAR
susceptibility E-CHAR
and O
resistivity S-PRO
measurements O
show O
that O
the O
3D B-MANP
printed E-MANP
Nd-Fe-B O
bonded O
magnets S-APPL
exhibit O
extremely O
low O
eddy O
current O
loss O
and O
high O
resistivity S-PRO
. O


Finally O
, O
we O
demonstrate O
the O
performance S-CONPRI
of O
the O
3D B-MANP
printed E-MANP
magnets O
in O
a O
DC S-CHAR
motor O
configuration S-CONPRI
via O
back O
electromotive O
force S-CONPRI
measurements O
. O


During O
solidification S-CONPRI
of O
many O
so-called O
high-performance O
engineering S-APPL
alloys S-MATE
, O
such O
as S-MATE
6000 O
and O
7000 O
series O
aluminum B-MATE
alloys E-MATE
, O
which O
are O
also O
unweldable O
autogenously O
, O
volumetric O
solidification B-CONPRI
shrinkage E-CONPRI
and O
thermal O
contraction S-CONPRI
produces O
voids S-CONPRI
and O
cracks O
. O


During O
additive B-MANP
manufacturing E-MANP
processing O
, O
these O
defects S-CONPRI
can O
span O
the O
length O
of O
columnar B-PRO
grains E-PRO
, O
as S-MATE
well O
as S-MATE
intergranular O
regions O
. O


In O
this O
research S-CONPRI
, O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
of O
aluminum B-MATE
alloy E-MATE
( O
AA O
) O
6061 O
used O
powder B-MACEQ
bed E-MACEQ
heating S-MANP
at O
500 O
°C O
in O
combination O
with O
other O
experimentally O
determined O
processing O
parameters S-CONPRI
to O
produce O
crack-free O
components S-MACEQ
. O


In O
addition O
, O
melt-pool O
banding O
, O
which O
is O
a O
normal O
solidification S-CONPRI
feature S-FEAT
in O
LPBF S-MANP
, O
was O
eliminated O
, O
illustrating O
solidification B-MANP
process E-MANP
modification O
as S-MATE
a O
consequence O
of O
powder B-MACEQ
bed E-MACEQ
heating S-MANP
. O


Corresponding O
microindentation O
hardness S-PRO
and O
tensile B-CHAR
testing E-CHAR
of O
the O
as-fabricated O
AA6061 S-MATE
components O
indicated O
an O
average S-CONPRI
Vickers O
hardness S-PRO
of O
HV O
54 O
, O
and O
tensile S-PRO
yield O
, O
ultimate B-PRO
strength E-PRO
, O
and O
elongation B-PRO
values E-PRO
of O
60 O
MPa S-CONPRI
, O
130 O
MPa S-CONPRI
, O
and O
15 O
% O
, O
respectively O
. O


These O
mechanical B-CONPRI
properties E-CONPRI
and O
those O
of O
heat S-CONPRI
treated O
parts O
showed O
values O
comparable O
to O
annealed O
and O
T6 O
heat S-CONPRI
treated O
wrought S-CONPRI
products O
, O
respectively O
. O


X-ray B-CHAR
diffraction E-CHAR
and O
optical B-CHAR
microscopy E-CHAR
revealed O
columnar B-PRO
grain E-PRO
growth O
in O
the O
build B-PARA
direction E-PARA
with O
the O
as-fabricated O
, O
powder-bed O
heated O
product O
microstructure S-CONPRI
characterized O
by O
[ O
100 O
] O
textured O
, O
elongated O
grains S-CONPRI
( O
∼ O
25 O
μm O
wide O
by O
400 O
μm O
in O
length O
) O
, O
and O
both O
intragranular O
and O
intergranular O
, O
noncoherent O
Al-Si-O O
precipitates S-MATE
which O
did O
not O
contribute O
significantly O
to O
the O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
results O
of O
this O
study O
are O
indicative O
that O
powder B-MACEQ
bed E-MACEQ
heating S-MANP
may O
be S-MATE
used O
to O
assist O
with O
successful O
fabrication S-MANP
of O
AA6061 S-MATE
and O
other O
alloy S-MATE
systems O
susceptible O
to O
additive B-CONPRI
manufacturing I-CONPRI
solidification E-CONPRI
cracking O
. O


Recent O
developments O
in O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
involving O
heat S-CONPRI
and O
mass O
deposition S-CONPRI
have O
exposed O
the O
need O
for O
computationally O
efficient O
modeling S-ENAT
of O
thermal O
field O
histories O
. O


This O
is O
due O
to O
the O
effect O
of O
such O
histories O
on O
resulting O
morphologies S-CONPRI
and O
quantities O
of O
interest O
, O
such O
as S-MATE
micro- O
and O
meso-structure O
, O
residual S-CONPRI
strains O
and O
stresses O
, O
as S-MATE
well O
as S-MATE
on O
material S-MATE
and O
structural O
properties S-CONPRI
and O
associated O
functional O
performance S-CONPRI
at O
the O
macro-scale O
. O


Consequently O
, O
in O
this O
paper O
, O
analytic O
solutions O
are O
enriched O
and O
then O
used O
to O
model S-CONPRI
the O
thermal O
aspects O
of O
AM S-MANP
, O
in O
a O
manner O
that O
demonstrates O
both O
high O
computational O
performance S-CONPRI
and O
fidelity O
required O
to O
enable O
“ O
in O
the O
loop O
” O
use O
for O
feedback S-PARA
control O
of O
AM B-MANP
processes E-MANP
. O


It O
is O
first O
shown O
that O
the O
utility O
of O
existing O
analytical B-CONPRI
solutions E-CONPRI
is O
limited O
due O
to O
their O
underlying O
assumptions O
, O
some O
of O
which O
are O
their O
derivation O
based O
on O
a O
homogeneous S-CONPRI
semi-infinite O
domain S-CONPRI
and O
temperature S-PARA
independent O
material B-CONPRI
properties E-CONPRI
among O
others O
. O


These O
solutions O
must O
therefore O
be S-MATE
enriched O
in O
order O
to O
capture O
the O
actual O
thermal O
physics S-CONPRI
associated O
with O
the O
relevant O
AM B-MANP
processes E-MANP
. O


Enrichments O
introduced O
herein O
include O
the O
handling O
of O
strong O
nonlinear O
variations S-CONPRI
in O
material B-CONPRI
properties E-CONPRI
due O
to O
their O
dependence O
on O
temperature S-PARA
, O
finite O
non-convex O
solution S-CONPRI
domains O
, O
behavior O
of O
heat B-CONPRI
sources E-CONPRI
very O
near O
domain S-CONPRI
boundaries S-FEAT
, O
and O
mass O
accretion O
coupled O
to O
the O
thermal O
problem O
. O


Design B-FEAT
for I-FEAT
additive I-FEAT
manufacturing E-FEAT
( O
AM S-MANP
) O
requires O
knowledge O
of O
the O
constraints O
associated O
with O
your O
targeted O
AM B-MANP
process E-MANP
. O


One O
important O
design S-FEAT
concern O
is O
the O
unintentional O
trapping O
of O
parasitic O
mass O
in O
occluded O
void B-CONPRI
geometries E-CONPRI
with O
either O
uncured O
or O
non-solidified O
material S-MATE
, O
or O
in O
some O
cases O
, O
sacrificial O
support B-MATE
material E-MATE
. O


These O
occluded O
features O
create O
the O
need O
to O
physically O
alter O
the O
optimal O
topology S-CONPRI
to O
remove O
the O
material S-MATE
. O


In O
this O
work O
, O
a O
projection-based O
topology B-FEAT
optimization E-FEAT
design S-FEAT
formulation O
is O
proposed O
to O
eliminate O
occluded O
void S-CONPRI
topological O
features O
in O
optimal O
AM S-MANP
designs O
. O


The O
algorithm S-CONPRI
is O
based O
on O
the O
combination O
and O
enhancement O
of O
two O
existing O
algorithms S-CONPRI
: O
a O
projection-based O
, O
overhang-constrained O
algorithm S-CONPRI
to O
design S-FEAT
self-supporting O
structures O
in O
AM S-MANP
, O
and O
a O
void S-CONPRI
projection O
algorithm S-CONPRI
to O
design S-FEAT
topologies O
through O
control O
of O
the O
void B-CONPRI
phase E-CONPRI
. O


The O
combined O
algorithm S-CONPRI
results O
in O
topologies S-CONPRI
with O
void S-CONPRI
regions O
that O
always O
possess O
an O
exit O
path O
to O
predefined O
outer O
surfaces S-CONPRI
– O
i.e O
. O


Solutions O
are O
first O
demonstrated O
in O
two O
dimensions S-FEAT
, O
with O
increasing O
design B-CONPRI
freedom E-CONPRI
allowed O
through O
algorithm S-CONPRI
enhancements O
. O


The O
algorithm S-CONPRI
is O
then O
adapted O
to O
3D S-CONPRI
, O
adopting O
a O
multi-phase O
TO O
approach O
to O
not O
only O
regain O
control O
of O
the O
solid O
phase S-CONPRI
length B-CHAR
scale E-CHAR
, O
but O
also O
to O
drive O
toward O
superior O
performing O
topologies S-CONPRI
with O
minimal O
impact S-CONPRI
on O
the O
part O
performance S-CONPRI
. O


Steel S-MATE
– O
Inconel S-MATE
multi-scale O
multilayer O
by O
liquid B-MATE
metal E-MATE
dispersed O
powder B-MANP
bed I-MANP
fusion E-MANP
. O


Nano-scale B-CONPRI
microstructural E-CONPRI
design S-FEAT
by O
reactive O
additive B-MANP
manufacturing E-MANP
. O


Gradients O
of O
microstructure S-CONPRI
, O
texture S-FEAT
, O
residual B-PRO
stresses E-PRO
and O
chemical B-CONPRI
composition E-CONPRI
. O


Zig-zag O
columnar B-PRO
grains E-PRO
, O
grain B-CONPRI
boundaries E-CONPRI
and O
crack O
formation O
. O


Multi-scale O
correlative O
characterization O
of O
additively B-MANP
manufactured E-MANP
gradient O
structures O
. O


Synthesis O
of O
multi-metal O
hybrid O
structures O
with O
narrow O
heat B-CONPRI
affected I-CONPRI
zones E-CONPRI
, O
limited O
residual B-PRO
stresses E-PRO
and O
secondary O
phase S-CONPRI
occurrence O
represents O
a O
serious O
scientific O
and O
technological O
challenge O
. O


In O
this O
work O
, O
liquid O
dispersed O
metal B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
was O
used O
to O
additively B-MANP
manufacture E-MANP
a O
multilayered O
structure S-CONPRI
based O
on O
alternating O
Inconel B-MATE
625 I-MATE
alloy E-MATE
( O
IN625 O
) O
and O
316L B-MATE
stainless I-MATE
steel E-MATE
( O
316L O
) O
layers O
on O
a O
316L O
base O
plate O
. O


Analytical O
scanning S-CONPRI
and O
transmission B-CHAR
electron I-CHAR
microscopies E-CHAR
, O
high-energy O
synchrotron S-ENAT
X-ray O
diffraction S-CHAR
and O
nanoindentation S-CHAR
analysis O
reveal O
sharp O
compositional O
, O
structural O
and O
microstructural S-CONPRI
boundaries S-FEAT
between O
alternating O
60 O
μm O
thick O
alloys S-MATE
’ O
sub-regions O
and O
unique O
microstructures S-MATE
at O
macro- O
, O
micro- S-CHAR
and O
nano-scales S-FEAT
. O


The O
periodic O
occurrence O
of O
IN625 O
and O
316L O
sub-regions O
is O
correlated S-CONPRI
with O
a O
cross-sectional O
hardness S-PRO
increase O
and O
decrease O
and O
compressive B-PRO
stress E-PRO
decrease O
and O
increase O
, O
respectively O
. O


The O
laser S-ENAT
scanning O
strategy O
induced O
a O
growth O
of O
elongated O
grains S-CONPRI
separated O
by O
zig-zag O
low-angle O
grain B-CONPRI
boundaries E-CONPRI
, O
which O
correlate O
with O
the O
occurrence O
of O
zig-zag O
cracks O
propagating O
in O
the O
growth O
direction O
. O


The O
occurrence O
of O
the O
C-like O
stress S-PRO
gradient O
with O
a O
pronounced O
surface S-CONPRI
tensile O
stress S-PRO
of O
about O
500 O
MPa S-CONPRI
is O
interpreted O
by O
the O
temperature B-CONPRI
gradient I-CONPRI
mechanism E-CONPRI
model S-CONPRI
. O


Chemical B-CHAR
analysis E-CHAR
indicates O
a O
formation O
of O
reinforcing O
spherical S-CONPRI
chromium-metal-oxide O
nano-dispersoids O
and O
demonstrates O
a O
possibility O
for O
reactive O
additive B-MANP
manufacturing E-MANP
and O
microstructural S-CONPRI
design S-FEAT
at O
the O
nanoscale O
, O
as S-MATE
a O
remarkable O
attribute O
of O
the O
deposition B-MANP
process E-MANP
. O


Finally O
, O
the O
study O
shows O
that O
the O
novel O
approach O
represents O
an O
effective O
tool S-MACEQ
to O
combine O
dissimilar O
metallic B-MATE
alloys E-MATE
into O
unique O
bionic O
hierarchical O
microstructures S-MATE
with O
possible O
synergetic O
properties S-CONPRI
. O


Binder B-MANP
jetting E-MANP
( O
BJ S-MANP
) O
is O
a O
high O
build-rate O
additive B-MANP
manufacturing I-MANP
process E-MANP
with O
growing O
commercial O
interest O
. O


Growth O
in O
BJ S-MANP
applications O
is O
driven O
by O
the O
use O
of O
finer O
powders S-MATE
and O
improved O
post-processing S-CONPRI
methods O
that O
can O
produce O
dense O
, O
homogenous O
final O
parts O
. O


This O
paper O
considers O
the O
impact S-CONPRI
of O
in-process O
drying S-MANP
, O
part O
geometry S-CONPRI
, O
and O
droplet B-PARA
size E-PARA
on O
a O
key O
printing O
parameter S-CONPRI
: O
binder S-MATE
saturation O
. O


Parts O
of O
varying O
thicknesses O
are O
printed O
with O
a O
range S-PARA
of O
saturation O
levels O
under O
various O
heating S-MANP
conditions O
. O


In O
unheated O
powder B-MACEQ
beds E-MACEQ
, O
part O
mass O
increases O
linearly O
with O
printing O
saturation O
levels O
across O
the O
range S-PARA
tested O
( O
30 O
% O
–130 O
% O
) O
. O


However O
, O
when O
the O
powder S-MATE
is O
heated O
between O
layers O
, O
there O
is O
a O
wide O
range S-PARA
of O
print S-MANP
saturation O
levels O
( O
30–80 O
% O
) O
over O
which O
increasing O
binder S-MATE
saturation O
or O
droplet S-CONPRI
volume O
does O
not O
increase O
the O
part O
mass O
. O


This O
stable O
part O
mass O
corresponds O
to O
accurate S-CHAR
part O
geometries S-CONPRI
without O
bleeding O
and O
is O
likely O
due O
to O
enhanced O
evaporation S-CONPRI
of O
the O
binder S-MATE
solvent O
between O
layers O
. O


Smaller O
droplet S-CONPRI
volume O
( O
42 O
pl S-CHAR
) O
was O
also O
shown O
to O
decrease O
saturation O
levels O
in O
unheated O
powder B-MACEQ
bed E-MACEQ
and O
in O
single O
layer S-PARA
parts O
. O


The O
differences O
in O
part O
mass O
with O
print S-MANP
saturation O
and O
droplet S-CONPRI
volume O
are O
most O
pronounced O
in O
thin O
parts O
. O


These O
observations O
lead S-MATE
to O
a O
simple S-MANP
method O
for O
determining O
an O
appropriate O
print S-MANP
saturation O
parameter S-CONPRI
for O
a O
powder/binder O
combination O
in O
thick O
parts O
. O


Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
is O
widely O
gaining O
popularity O
as S-MATE
an O
alternative O
manufacturing S-MANP
technique O
for O
complex O
and O
customised O
parts O
. O


AM B-MATE
materials E-MATE
are O
used O
for O
various O
medical B-APPL
applications E-APPL
in O
both O
metal S-MATE
and O
polymer S-MATE
options O
. O


Adenosine O
Triphosphate O
( O
ATP O
) O
bioluminescence O
technology S-CONPRI
is O
a O
rapid O
, O
user-friendly O
method O
of O
quantifying O
surface S-CONPRI
cleanliness O
and O
was O
used O
in O
this O
study O
to O
gather O
quantitative B-CONPRI
data E-CONPRI
on O
levels O
of O
contamination O
on O
AM B-MATE
materials E-MATE
at O
three O
different O
stage O
processes S-CONPRI
: O
post O
build S-PARA
, O
post O
cleaning S-MANP
and O
post O
sterilization O
. O


The O
surface S-CONPRI
cleanliness O
of O
eleven O
AM B-MATE
materials E-MATE
, O
three O
metals S-MATE
and O
eight O
polymers S-MATE
, O
was O
tested O
. O


ATP O
bioluminescence O
provided O
the O
sensitivity S-PARA
to O
evaluate O
different O
material S-MATE
surface O
characteristics O
, O
and O
specifically O
the O
impact S-CONPRI
of O
surface B-MANP
finishing E-MANP
techniques O
on O
overall O
cleanliness O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
provides O
flexibility S-PRO
in O
creating O
novel O
metal-matrix O
composites S-MATE
( O
MMCs S-MATE
) O
with O
unique O
microstructures S-MATE
and O
enhanced O
mechanical B-CONPRI
properties E-CONPRI
over O
conventionally O
manufactured S-CONPRI
MMGs O
. O


In O
this O
study O
, O
a O
Zr-based O
metallic B-MATE
glass E-MATE
( O
MG S-MATE
) O
decorated O
Ti6Al4V S-MATE
( O
Ti64 S-MATE
) O
composite S-MATE
with O
a O
unique O
hybrid O
nanostructure O
and O
enhanced O
mechanical B-CONPRI
properties E-CONPRI
and O
wear B-PRO
resistance E-PRO
was O
fabricated S-CONPRI
using O
SLM S-MANP
. O


The O
results O
revealed O
that O
a O
near-full O
dense O
and O
crack-free O
Ti-based O
composite S-MATE
was O
produced O
, O
with O
its O
reinforcements O
consisting O
of O
ultrafine O
β O
dendrites S-BIOP
set O
with O
partially O
crystallized O
MG S-MATE
nanobands O
uniformly O
distributed O
along O
the O
boundaries S-FEAT
of O
the O
melt B-MATE
pool E-MATE
. O


The O
addition O
of O
MG S-MATE
significantly O
affected O
the O
solidification S-CONPRI
behavior O
of O
the O
Ti-liquid O
because O
of O
its O
higher O
dynamic S-CONPRI
viscosity O
and O
density S-PRO
as S-MATE
well O
as S-MATE
compositional O
effect O
on O
the O
phase S-CONPRI
stability O
. O


With O
such O
a O
unique O
nanostructured O
reinforcement S-PARA
, O
the O
Ti64/MG O
composite S-MATE
exhibited O
an O
enhanced O
yield B-PRO
strength E-PRO
( O
> O
1 O
GPa S-PRO
) O
with O
reasonable O
ductility S-PRO
and O
fracture S-CONPRI
toughness O
. O


On O
the O
basis O
of O
the O
result O
of O
a O
theoretical S-CONPRI
analysis O
, O
we O
attributed O
the O
main O
strengthening B-CONPRI
mechanism E-CONPRI
to O
Orowan O
strengthening S-MANP
. O


The O
wear B-PRO
resistance E-PRO
was O
also O
much O
improved O
in O
the O
Ti64/MG O
composite S-MATE
, O
arising O
from O
the O
higher O
hardness S-PRO
of O
the O
nanostructured O
reinforcement S-PARA
and O
the O
formation O
of O
a O
more O
protective O
tribo-oxide O
layer S-PARA
during O
sliding O
. O


The O
confinement O
of O
the O
3D S-CONPRI
distributed O
reinforcement S-PARA
phase S-CONPRI
played O
a O
crucial O
role O
in O
preventing O
the O
delamination S-CONPRI
of O
the O
tribo-layer O
on O
the O
matrix O
. O


This O
work O
opens O
a O
pathway O
to O
the O
design S-FEAT
of O
novel O
additively B-MANP
manufactured E-MANP
MMCs O
with O
outstanding O
mechanical B-CONPRI
properties E-CONPRI
. O


Fatigue S-PRO
of O
laser B-CONPRI
beam E-CONPRI
powder O
bed S-MACEQ
fused O
( O
LB-PBF O
) O
316 O
L O
stainless B-MATE
steel E-MATE
is O
investigated O
. O


Effects O
of O
build B-PARA
orientation E-PARA
and O
surface B-PRO
roughness E-PRO
are O
examined O
. O


Fractography S-CHAR
and O
failure S-CONPRI
analysis O
on O
fatigue S-PRO
specimens O
are O
conducted O
. O


A O
fracture S-CONPRI
mechanics-based O
approach O
is O
employed O
to O
explain O
the O
fatigue S-PRO
results O
. O


The O
effects O
of O
layer S-PARA
orientation O
and O
surface B-PRO
roughness E-PRO
on O
the O
mechanical B-CONPRI
properties E-CONPRI
and O
fatigue B-PRO
life E-PRO
of O
316L B-MATE
stainless I-MATE
steel E-MATE
( O
SS S-MATE
) O
fabricated S-CONPRI
via O
a O
laser B-CONPRI
beam E-CONPRI
powder O
bed B-MANP
fusion E-MANP
( O
LB-PBF O
) O
additive B-MANP
manufacturing I-MANP
process E-MANP
were O
investigated O
. O


Quasi-static S-CONPRI
tensile O
and O
uniaxial O
fatigue B-CHAR
tests E-CHAR
were O
conducted O
on O
LB-PBF O
316L O
SS S-MATE
specimens O
fabricated S-CONPRI
in O
vertical S-CONPRI
and O
diagonal O
directions O
in O
their O
as-built O
surface S-CONPRI
condition O
, O
as S-MATE
well O
as S-MATE
in O
horizontal O
, O
vertical S-CONPRI
, O
and O
diagonal O
directions O
where O
the O
surface S-CONPRI
had O
been O
machined S-MANP
to O
remove O
any O
effects O
of O
surface B-PRO
roughness E-PRO
. O


Similarly O
, O
in O
the O
as-built O
condition O
, O
vertical S-CONPRI
specimens O
demonstrated O
better O
fatigue S-PRO
resistance O
when O
compared O
to O
diagonal O
specimens O
. O


Furthermore O
, O
the O
detrimental O
effects O
of O
surface B-PRO
roughness E-PRO
on O
fatigue B-PRO
life E-PRO
of O
LB-PBF O
316L O
SS S-MATE
specimens O
was O
not O
significant O
, O
which O
may O
be S-MATE
due O
to O
the O
presence O
of O
large O
internal O
defects S-CONPRI
in O
the O
specimens O
. O


Anisotropy S-PRO
of O
LB-PBF O
316L O
SS S-MATE
specimens O
was O
attributed O
to O
the O
variation S-CONPRI
in O
layer S-PARA
orientation O
, O
affecting O
defects S-CONPRI
’ O
directionality O
with O
respect O
to O
the O
loading O
direction O
. O


These O
defect S-CONPRI
characteristics O
can O
significantly O
influence O
the O
stress B-CHAR
concentration E-CHAR
and O
, O
consequently O
, O
fatigue S-PRO
behavior O
of O
additive B-APPL
manufactured I-APPL
parts E-APPL
. O


Therefore O
, O
the O
elastic-plastic O
energy O
release O
rates O
, O
a O
fracture S-CONPRI
mechanics-based O
concept O
that O
incorporates O
size O
, O
location O
, O
and O
projected O
area S-PARA
of O
defects S-CONPRI
on O
the O
loading O
plane O
, O
were O
determined O
to O
correlate O
the O
fatigue S-PRO
data S-CONPRI
and O
acceptable O
results O
were O
achieved O
. O


As-built O
microstructure S-CONPRI
of O
L-PBF B-MANP
AM E-MANP
consists O
of O
fine O
dendrites S-BIOP
and O
precipitates S-MATE
. O


Precipitates S-MATE
comprise O
mostly O
Laves B-CONPRI
phase E-CONPRI
and O
small O
amount O
of O
NbC O
carbide S-MATE
. O


Uniformly O
distributed O
hardness S-PRO
for O
samples S-CONPRI
built O
with O
and O
without O
support S-APPL
. O


Calculations O
show O
heat S-CONPRI
build-up O
of O
487 O
K S-MATE
with O
support S-APPL
versus O
353 O
K S-MATE
without O
support S-APPL
. O


Solidification B-PARA
cooling I-PARA
rate E-PARA
6.57 O
× O
105 O
K/s O
with O
support S-APPL
versus O
8.45 O
× O
105 O
K/s O
without O
. O


INCONEL® O
718 O
cubes O
with O
and O
without O
structural O
support S-APPL
were O
built O
by O
laser-powder O
bed B-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
additive B-MANP
manufacturing E-MANP
. O


The O
effect O
of O
support S-APPL
on O
the O
as-built O
microstructure S-CONPRI
was O
studied O
based O
on O
the O
microstructural S-CONPRI
characteristics O
and O
micro-hardness O
variations S-CONPRI
. O


Specifically O
, O
the O
microstructure S-CONPRI
was O
examined O
by O
optical B-CHAR
microscopy E-CHAR
, O
and O
scanning S-CONPRI
and O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
. O


The O
precipitates S-MATE
were O
identified O
via O
selected O
area S-PARA
diffraction O
supplemented O
by O
high-resolution S-PARA
energy B-CHAR
dispersive I-CHAR
X-ray I-CHAR
spectroscopy E-CHAR
. O


Micro-hardness O
distributions S-CONPRI
on O
cross B-CONPRI
sections E-CONPRI
parallel O
and O
perpendicular O
to O
the O
build B-PARA
direction E-PARA
were O
mapped O
. O


In O
addition O
, O
analytical O
equations O
, O
taking O
into O
account O
various O
laser B-CONPRI
processing E-CONPRI
parameters O
, O
material B-CONPRI
properties E-CONPRI
and O
support S-APPL
geometries S-CONPRI
, O
were O
developed O
to O
calculate O
the O
heat S-CONPRI
build-up O
and O
cooling S-MANP
conditions O
during O
L-PBF S-MANP
. O


The O
results O
of O
microstructure S-CONPRI
characterization O
and O
analytical O
calculation O
showed O
a O
marginal O
effect O
of O
the O
support S-APPL
on O
the O
local O
microstructure S-CONPRI
and O
hardness S-PRO
due O
to O
the O
low O
heat S-CONPRI
input O
in O
L-PBF S-MANP
. O


Moreover O
, O
the O
comprehensive O
set S-APPL
of O
microstructure B-CONPRI
data E-CONPRI
is O
useful O
for O
future O
work O
of O
modelling S-ENAT
processing-microstructure O
relation O
as S-MATE
well O
as S-MATE
optimizing O
post-fabrication O
heat B-MANP
treatment E-MANP
. O


The O
ability O
to O
simulate O
the O
thermal O
, O
mechanical S-APPL
, O
and O
material S-MATE
response O
in O
additive B-MANP
manufacturing E-MANP
offers O
tremendous O
utility O
for O
gaining O
a O
deeper O
understanding O
of O
the O
process S-CONPRI
, O
while O
also O
having O
significant O
practical O
application O
. O


The O
approach O
and O
progress O
in O
establishing O
an O
integrated O
computational O
system O
for O
simulating O
additive B-MANP
manufacturing E-MANP
of O
metallic S-MATE
components S-MACEQ
are O
discussed O
, O
with O
the O
primary O
focus O
directed O
at O
the O
computational O
intensive O
components S-MACEQ
, O
which O
include O
the O
process S-CONPRI
and O
material S-MATE
models O
. O


SRAS O
optical S-CHAR
data S-CONPRI
was O
used O
for O
defect S-CONPRI
characterisation O
of O
an O
SLM S-MANP
layer S-PARA
. O


A O
bespoke O
algorithm S-CONPRI
was O
developed O
to O
target O
defects S-CONPRI
for O
rework O
. O


A O
hatch O
pattern S-CONPRI
rework O
showed O
to O
be S-MATE
the O
most O
effective O
method O
for O
rework O
. O


A O
general O
framework S-CONPRI
for O
targeted O
rework O
in O
AM B-MANP
processes E-MANP
is O
presented O
. O


A O
major O
factor O
limiting O
the O
adoption O
of O
powder-bed-fusion O
additive B-MANP
manufacturing E-MANP
for O
production S-MANP
of O
parts O
is O
the O
control O
of O
build S-PARA
process O
defects S-CONPRI
and O
the O
effect O
these O
have O
upon O
the O
certification O
of O
parts O
for O
structural O
applications O
. O


In O
response O
to O
this O
, O
new O
methods O
for O
detecting O
defects S-CONPRI
and O
to O
monitor S-CONPRI
process O
performance S-CONPRI
are O
being O
developed O
. O


However O
, O
effective O
utilisation O
of O
such O
methods O
to O
rework O
parts O
in O
process S-CONPRI
has O
yet O
to O
be S-MATE
demonstrated.This O
study O
investigates S-CONPRI
the O
use O
of O
spatially O
resolved O
acoustic O
spectroscopy S-CONPRI
( O
SRAS O
) O
scan O
data S-CONPRI
to O
inform O
repair O
strategies O
within O
a O
commercial O
selective B-MANP
laser I-MANP
melting E-MANP
machine S-MACEQ
. O


New O
methodologies O
which O
allow O
for O
rework O
of O
the O
most O
common O
defects S-CONPRI
observed O
in O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
manufacturing S-MANP
are O
proposed O
and O
demonstrated O
. O


Three O
rework O
methodologies O
are O
applied O
to O
targeted O
surface S-CONPRI
breaking O
pores S-PRO
: O
a O
hatch O
pattern S-CONPRI
, O
a O
spiral O
pattern S-CONPRI
and O
a O
single O
shot O
exposure S-CONPRI
. O


The O
work O
presented O
shows O
that O
it O
is O
possible O
to O
correct O
surface S-CONPRI
breaking O
pores S-PRO
using O
targeted O
re-melting O
, O
reducing O
the O
depth O
of O
defects S-CONPRI
whilst O
minimising O
changes O
in O
local O
texture S-FEAT
. O


This O
work O
is O
part O
of O
a O
programme O
to O
develop O
a O
method O
by O
which O
defects S-CONPRI
can O
be S-MATE
detected O
and O
the O
part O
reworked O
in-process O
during O
SLM S-MANP
to O
enable O
defect S-CONPRI
specification O
targets O
to O
be S-MATE
met O
. O


Despite O
the O
rapid O
adoption O
of O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
Additive B-MANP
Manufacturing E-MANP
by O
industry S-APPL
, O
current O
processes S-CONPRI
remain O
largely O
open-loop O
, O
with O
limited O
real-time O
monitoring O
capabilities O
. O


While O
some O
machines S-MACEQ
offer O
powder B-MACEQ
bed E-MACEQ
visualization O
during O
builds S-CHAR
, O
they O
lack O
automated O
analysis O
capability O
. O


This O
work O
presents O
an O
approach O
for O
in-situ S-CONPRI
monitoring O
and O
analysis O
of O
powder B-MACEQ
bed E-MACEQ
images S-CONPRI
with O
the O
potential O
to O
become O
a O
component S-MACEQ
of O
a O
real-time O
control B-MACEQ
system E-MACEQ
in O
an O
LPBF S-MANP
machine O
. O


Specifically O
, O
a O
computer B-CONPRI
vision I-CONPRI
algorithm E-CONPRI
is O
used O
to O
automatically O
detect O
and O
classify O
anomalies S-CONPRI
that O
occur O
during O
the O
powder S-MATE
spreading O
stage O
of O
the O
process S-CONPRI
. O


Anomaly S-CONPRI
detection O
and O
classification S-CONPRI
are O
implemented O
using O
an O
unsupervised O
machine B-ENAT
learning I-ENAT
algorithm E-ENAT
, O
operating O
on O
a O
moderately-sized O
training O
database S-ENAT
of O
image S-CONPRI
patches O
. O


The O
performance S-CONPRI
of O
the O
final O
algorithm S-CONPRI
is O
evaluated O
, O
and O
its O
usefulness O
as S-MATE
a O
standalone O
software S-CONPRI
package O
is O
demonstrated O
with O
several O
case B-CONPRI
studies E-CONPRI
. O


The O
mechanical S-APPL
, O
metallurgical S-APPL
and O
corrosion B-PRO
properties E-PRO
of O
Alloy S-MATE
625 O
produced O
using O
the O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
manufacturing B-MANP
process E-MANP
were O
investigated O
and O
compared O
with O
typical O
performance S-CONPRI
of O
the O
alloy S-MATE
produced O
using O
conventional O
forging S-MANP
processes O
. O


Test O
specimens O
were O
produced O
near B-MANP
net I-MANP
shape E-MANP
along O
with O
several O
demonstration O
pieces O
that O
were O
produced O
to O
examine O
the O
geometric O
complexity S-CONPRI
that O
could O
be S-MATE
achieved O
with O
the O
process S-CONPRI
. O


The O
additively B-MANP
manufactured E-MANP
specimens O
exhibited O
strength S-PRO
, O
fracture S-CONPRI
toughness O
and O
impact S-CONPRI
toughness O
that O
was O
equal O
to O
or O
better O
than O
properties S-CONPRI
typically O
achieved O
for O
wrought S-CONPRI
product O
. O


There O
was O
no O
evidence O
of O
stress B-CONPRI
corrosion I-CONPRI
cracking E-CONPRI
susceptibility O
in O
3.5 O
% O
NaCl S-MATE
solution O
at O
stress S-PRO
intensities O
up O
to O
70 O
ksi-in1/2 O
after O
700 O
h O
exposure S-CONPRI
. O


The O
microstructure S-CONPRI
was O
equiaxed O
in O
the O
plane O
of O
the O
powder B-MACEQ
bed I-MACEQ
build I-MACEQ
platform E-MACEQ
( O
X–Y O
) O
and O
exhibited O
a O
columnar O
shape O
in O
the O
Z O
direction O
although O
there O
was O
not O
any O
significant O
evidence O
of O
anisotropy S-PRO
in O
the O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
high O
hardness S-PRO
, O
melting B-PARA
temperature E-PARA
and O
environmental O
resistance S-PRO
of O
most O
ceramic B-MATE
materials E-MATE
makes O
them O
well-suited O
for O
propulsion O
, O
tribilogical O
and O
protective O
applications O
. O


However O
, O
these O
same O
attributes O
pose O
difficulties O
for O
manufacturing S-MANP
and O
machining S-MANP
of O
ceramics S-MATE
and O
ultimately O
limit S-CONPRI
the O
achievable O
design B-CONPRI
space E-CONPRI
of O
these O
materials S-CONPRI
. O


Recently O
, O
a O
new O
class O
of O
preceramic O
photopolymers S-MATE
has O
been O
developed O
that O
enables O
additive B-MANP
manufacturing E-MANP
of O
ceramics S-MATE
using O
commercially O
available O
stereolithography S-MANP
systems O
. O


By O
consolidating O
preceramic O
monomers O
via O
layer-wise O
exposure S-CONPRI
to O
ultraviolet B-CONPRI
light E-CONPRI
and O
subsequently O
pyrolyzing O
under O
an O
inert O
atmosphere O
to O
form O
a O
ceramic S-MATE
, O
this O
method O
allows O
for O
complex B-CONPRI
geometry E-CONPRI
parts O
that O
can O
not O
be S-MATE
produced O
with O
traditional O
sintering S-MANP
, O
pressing S-MANP
or O
vapor O
infiltration S-CONPRI
processes O
. O


To O
this O
end O
, O
we O
present O
x-ray B-CHAR
micro-computed I-CHAR
tomography E-CHAR
( O
micro-CT S-CHAR
) O
measurements O
of O
the O
dimensional O
stability S-PRO
and O
uniformity O
of O
additively B-MANP
manufactured E-MANP
silicon-based O
ceramics S-MATE
as S-MATE
a O
function O
of O
geometry S-CONPRI
and O
processing O
conditions O
. O


Laser S-ENAT
polishing O
( O
LP O
) O
is O
an O
emerging O
technique O
with O
the O
potential O
to O
be S-MATE
used O
for O
post-build O
, O
or O
in-situ S-CONPRI
, O
precision S-CHAR
smoothing O
of O
rough O
, O
fatigue-initiation O
prone O
, O
surfaces S-CONPRI
of O
additive B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
components S-MACEQ
. O


LP O
uses O
a O
laser S-ENAT
to O
re-melt O
a O
thin O
surface S-CONPRI
layer S-PARA
and O
smooths O
the O
surface S-CONPRI
by O
exploiting O
surface B-PRO
tension E-PRO
effects O
in O
the O
melt B-MATE
pool E-MATE
. O


However O
, O
rapid O
re-solidification O
of O
the O
melted S-CONPRI
surface O
layer S-PARA
and O
the O
associated O
substrate S-MATE
thermal O
exposure S-CONPRI
can O
significantly O
modify O
the O
subsurface O
material S-MATE
. O


This O
study O
has O
used O
an O
electron B-CONPRI
beam E-CONPRI
melted O
( O
EBM S-MANP
) O
Ti6Al4V S-MATE
component S-MACEQ
, O
representing O
the O
worst O
case O
scenario O
in O
terms O
of O
roughness S-PRO
for O
a O
powder B-MACEQ
bed E-MACEQ
process O
, O
as S-MATE
an O
example O
to O
investigate O
these O
issues O
and O
evaluate O
the O
capability O
of O
the O
LP O
technique O
for O
improving O
the O
surface B-PARA
quality E-PARA
of O
AM B-MACEQ
parts E-MACEQ
. O


Experiments O
have O
shown O
that O
the O
surface B-PRO
roughness E-PRO
can O
be S-MATE
reduced O
to O
below O
Sa O
= O
0.51 O
μm O
, O
which O
is O
comparable O
to O
a O
CNC S-ENAT
machined O
surface S-CONPRI
, O
and O
high O
stress S-PRO
concentrating O
defects S-CONPRI
inherited O
from O
the O
AM B-MANP
process E-MANP
were O
removed O
by O
LP O
. O


However O
, O
the O
re-melted O
layer S-PARA
underwent O
a O
change O
in O
texture S-FEAT
, O
grain B-CONPRI
structure E-CONPRI
, O
and O
a O
martensitic O
transformation O
, O
which O
was O
subsequently O
tempered S-MANP
in-situ S-CONPRI
by O
repeated O
beam S-MACEQ
rastering O
and O
resulted O
in O
a O
small O
increase O
in O
sub-surface O
hardness S-PRO
. O


In O
addition O
, O
a O
high O
level O
of O
near-surface O
tensile B-PRO
residual I-PRO
stresses E-PRO
was O
generated O
by O
the O
process S-CONPRI
, O
although O
they O
could O
be S-MATE
relaxed O
to O
near O
zero O
by O
a O
standard S-CONPRI
stress O
relief O
heat B-MANP
treatment E-MANP
. O


Currently O
, O
additive B-MANP
manufacturing E-MANP
is O
a O
rapidly O
growing O
technique O
that O
should O
be S-MATE
explored O
for O
the O
development O
of O
various O
composites S-MATE
and O
alloys S-MATE
. O


Graphene S-MATE
is O
also O
simultaneously O
gaining O
considerable O
attention O
as S-MATE
a O
reinforcement S-PARA
material S-MATE
for O
metals S-MATE
due O
to O
its O
superior O
properties S-CONPRI
. O


In O
this O
study O
, O
a O
graphene/AlSi10Mg O
composite S-MATE
was O
developed O
using O
the O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
technique O
. O


The O
effect O
of O
graphene S-MATE
reinforcement O
and O
laser B-PARA
power E-PARA
variation O
was O
studied O
on O
the O
basis O
of O
the O
porosity S-PRO
, O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
composite S-MATE
. O


First O
, O
graphene S-MATE
( O
0.1 O
and O
0.2 O
wt. O
% O
) O
was O
mixed O
in O
AlSi10Mg S-MATE
powder O
by O
conducting O
low-energy O
ball B-MANP
milling E-MANP
. O


The O
resultant O
mixture O
was O
used O
for O
PBF S-MANP
at O
laser B-PARA
power E-PARA
values O
of O
200 O
, O
300 O
and O
400 O
W. O
The O
prepared O
samples S-CONPRI
were O
characterised O
by O
synchrotron-based O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
to O
observe O
their O
pore S-PRO
distribution S-CONPRI
and O
morphology S-CONPRI
. O


The O
observation O
results O
reveal O
that O
the O
energy O
( O
laser B-PARA
power E-PARA
) O
required O
for O
appropriate O
melting S-MANP
of O
the O
powder S-MATE
was O
increased O
after O
graphene S-MATE
incorporation O
. O


Electron O
backscattered O
diffraction S-CHAR
analysis O
revealed O
grain B-CHAR
refinement E-CHAR
and O
increase O
in O
fraction S-CONPRI
of O
high O
angle O
grain B-CONPRI
boundaries E-CONPRI
due O
to O
progressive O
addition O
of O
graphene S-MATE
. O


The O
strain S-PRO
developed O
after O
graphene S-MATE
incorporation O
was O
also O
validated O
using O
X-ray B-CHAR
diffraction I-CHAR
analysis E-CHAR
. O


The O
uniform O
distribution S-CONPRI
of O
graphene S-MATE
and O
its O
structural O
inherency O
was O
confirmed O
by O
Raman B-CHAR
analysis E-CHAR
. O


Moreover O
, O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
revealed O
a O
suitable O
graphene-matrix O
interface S-CONPRI
. O


The O
tensile B-PRO
properties E-PRO
were O
significantly O
influenced O
by O
the O
porosity S-PRO
induced O
in O
the O
samples S-CONPRI
irrespective O
of O
graphene S-MATE
reinforcement O
. O


However O
, O
a O
yield B-PRO
strength E-PRO
increase O
of O
22 O
% O
was O
observed O
in O
the O
composite S-MATE
compared O
with O
the O
strength S-PRO
of O
unreinforced O
sample S-CONPRI
of O
equivalent O
density S-PRO
. O


Hardness S-PRO
increased O
progressively O
with O
the O
graphene S-MATE
content O
and O
was O
unaffected O
by O
variation S-CONPRI
in O
the O
laser B-PARA
power E-PARA
. O


Material B-MANP
jetting I-MANP
3D I-MANP
printing E-MANP
is O
an O
additive B-MANP
manufacturing E-MANP
technique O
that O
allows O
producing O
complex O
parts O
without O
tooling S-CONPRI
and O
minimum O
material S-MATE
wastage O
. O


In O
this O
study O
, O
orientation S-CONPRI
control O
of O
randomly O
shaped O
, O
anisotropic S-PRO
hard O
magnetic O
ferrite S-MATE
particles O
is O
demonstrated O
for O
material S-MATE
jetting-based O
additive B-MANP
manufacturing I-MANP
processes E-MANP
using O
a O
developed O
particle S-CONPRI
alignment O
configuration S-CONPRI
. O


Strontium O
ferrite S-MATE
and O
PR-48 O
photosensitive B-MATE
resin E-MATE
were O
used O
as S-MATE
the O
base O
materials S-CONPRI
. O


An O
automated O
experimental S-CONPRI
setup O
with O
two O
neodymium S-MATE
permanent O
cube S-CONPRI
magnets O
capable O
of O
generating O
a O
dipolar O
magnetic B-CONPRI
field E-CONPRI
was O
built O
to O
align O
magnetic O
particles S-CONPRI
in O
the O
resin S-MATE
. O


Particle S-CONPRI
alignment O
was O
characterized O
for O
directionality O
using O
images S-CONPRI
obtained O
through O
real O
time O
optical B-CHAR
microscopy E-CHAR
. O


The O
orientation S-CONPRI
of O
magnetic O
particles S-CONPRI
was O
observed O
to O
be S-MATE
dependent O
on O
the O
distance O
of O
separation O
between O
the O
cube S-CONPRI
magnets O
and O
the O
magnetization O
time O
. O


X-ray B-CHAR
diffraction E-CHAR
was O
used O
to O
indicate O
the O
c-axis O
alignment O
of O
the O
hexagonal S-FEAT
strontium O
ferrite S-MATE
particles O
in O
the O
cured S-MANP
specimens O
. O


The O
influence O
of O
process B-CONPRI
parameters E-CONPRI
on O
particle S-CONPRI
orientation S-CONPRI
was O
evaluated O
, O
employing O
a O
full O
factorial O
experiment S-CONPRI
analysis O
. O


This O
fundamental O
research S-CONPRI
serves O
as S-MATE
a O
basis O
for O
constructing O
and O
optimizing O
the O
magnetic O
particle S-CONPRI
alignment O
setup O
for O
additive B-MANP
manufacturing I-MANP
processes E-MANP
. O


Measurements O
of O
the O
temperature S-PARA
and O
distortion S-CONPRI
evolution O
during O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
are O
taken O
as S-MATE
a O
function O
of O
time O
. O


In B-CONPRI
situ E-CONPRI
measurements O
have O
proven O
vital O
to O
the O
development O
and O
validation S-CONPRI
of O
FE S-MATE
( O
finite B-CONPRI
element E-CONPRI
) O
models O
for O
alternate O
forms O
of O
additive B-MANP
manufacturing E-MANP
. O


Due O
to O
powder S-MATE
obscuring O
all O
but O
the O
top O
layer S-PARA
of O
the O
part O
in O
LPBF S-MANP
, O
many O
non-contact O
measurement S-CHAR
techniques O
used O
for O
in B-CONPRI
situ E-CONPRI
measurement O
of O
additive B-MANP
manufacturing I-MANP
processes E-MANP
are O
impossible O
. O


Therefore O
, O
an O
enclosed O
instrumented O
system O
is O
designed S-FEAT
to O
allow O
for O
the O
in B-CONPRI
situ E-CONPRI
measurement O
of O
temperature S-PARA
and O
distortion S-CONPRI
in O
an O
LPBF S-MANP
machine O
without O
the O
need O
for O
altering O
the O
machine S-MACEQ
or O
the O
build S-PARA
process O
. O


By O
instrumenting O
a O
substrate S-MATE
from O
underneath O
, O
the O
spread S-CONPRI
powder S-MATE
does O
not O
affect O
measurements O
. O


Default O
processing O
parameters S-CONPRI
for O
the O
EOS S-APPL
M280 O
machine S-MACEQ
prescribe O
a O
rotating O
scan B-PARA
pattern E-PARA
of O
67° O
for O
each O
layer S-PARA
. O


One O
test O
is O
completed O
using O
the O
default O
rotating O
scan B-PARA
pattern E-PARA
and O
a O
second O
is O
completed O
using O
a O
constant O
scan B-PARA
pattern E-PARA
. O


Experimental S-CONPRI
observations O
for O
the O
build S-PARA
geometry O
tested O
showed O
that O
for O
Inconel® O
718 O
and O
a O
constant O
scan B-PARA
pattern E-PARA
produce O
results O
in O
a O
37.6 O
% O
increase O
in O
distortion S-CONPRI
as S-MATE
compared O
with O
a O
rotated O
scan B-PARA
pattern E-PARA
. O


The O
in B-CONPRI
situ E-CONPRI
measurements O
also O
show O
that O
the O
thermal B-PARA
cycles E-PARA
caused O
by O
the O
processing O
of O
a O
layer S-PARA
can O
impact S-CONPRI
the O
distortion S-CONPRI
accumulated O
during O
the O
deposition S-CONPRI
of O
the O
previous O
layers O
. O


The O
amount O
of O
distortion S-CONPRI
built O
per O
layer S-PARA
between O
the O
rotating O
and O
constant O
scan B-PARA
pattern E-PARA
cases O
highlights O
inter-layer O
effects O
not O
previously O
discovered O
in O
LPBF S-MANP
. O


The O
demonstrated O
inter-layer O
effects O
in O
the O
LPBF S-MANP
process O
should O
be S-MATE
considered O
in O
the O
development O
of O
thermo-mechanical B-CONPRI
models E-CONPRI
of O
the O
LPBF S-MANP
process O
. O


Increasing O
demand O
for O
high-quality O
additive B-APPL
manufactured I-APPL
parts E-APPL
in O
the O
aerospace S-APPL
, O
automotive S-APPL
, O
medical S-APPL
, O
and O
oil S-MATE
and O
gas S-CONPRI
industries O
requires O
careful O
control O
of O
the O
part O
microstructure S-CONPRI
, O
residual B-PRO
stress E-PRO
, O
and O
density S-PRO
homogeneity O
. O


In O
order O
to O
improve O
part O
quality S-CONPRI
, O
partial O
remelting O
of O
the O
as-built O
material S-MATE
during O
subsequent O
beam S-MACEQ
scans O
is O
desirable O
. O


Here O
, O
we O
make O
use O
of O
computer B-CONPRI
simulations E-CONPRI
to O
explicitly O
study O
remelting O
in O
laser- O
or O
electron O
beam-melting O
additive B-MANP
manufacturing E-MANP
. O


By O
explicitly O
implementing O
phase S-CONPRI
transformations O
between O
the O
powder S-MATE
, O
the O
liquid O
, O
and O
the O
bulk O
, O
we O
track O
the O
amount O
of O
material S-MATE
that O
is O
subject O
to O
remelting O
. O


The O
influence O
of O
the O
beam S-MACEQ
parameters O
, O
such O
as S-MATE
the O
beam S-MACEQ
size O
, O
scan B-PARA
speed E-PARA
and O
power S-PARA
, O
are O
investigated O
and O
both O
the O
cases O
of O
an O
exponential O
as S-MATE
well O
as S-MATE
a O
linear O
beam S-MACEQ
absorption S-CONPRI
profile O
are O
considered O
. O


We O
find O
that O
, O
at O
constant O
beam S-MACEQ
cross O
section O
, O
there O
is O
an O
optimal O
beam S-MACEQ
shape O
for O
remelting O
. O


Calculations O
are O
presented O
for O
the O
model S-CONPRI
case O
of O
AISI O
316L B-MATE
stainless I-MATE
steel E-MATE
but O
can O
be S-MATE
extended O
to O
a O
wide O
class O
of O
metals S-MATE
. O


Binder B-MANP
jetting E-MANP
technology O
enables O
the O
production S-MANP
of O
sand B-MANP
casting E-MANP
molds S-MACEQ
and O
cores S-MACEQ
without O
a O
pattern S-CONPRI
. O


Real-time O
inertial O
measurement S-CHAR
is O
demonstrated O
with O
encapsulated S-CONPRI
wireless O
sensors S-MACEQ
in O
sand S-MATE
cores S-MACEQ
. O


In O
this O
work O
, O
real-time O
in-process O
monitoring O
of O
core S-MACEQ
motion O
in O
metal S-MATE
castings O
is O
demonstrated O
through O
the O
use O
of O
two O
emerging O
technologies S-CONPRI
. O


3D S-CONPRI
sand O
printing O
( O
3DSP O
) O
is O
a O
binder B-MANP
jetting I-MANP
additive I-MANP
manufacturing E-MANP
process O
that O
is O
quickly O
manifesting O
itself O
as S-MATE
a O
technological O
disrupter O
in O
the O
metal S-MATE
casting S-MANP
industry O
. O


Based O
on O
its O
direct B-MANP
digital I-MANP
manufacturing E-MANP
principle O
, O
3DSP O
enables O
complex O
mold S-MACEQ
and O
core S-MACEQ
design O
freedom O
that O
has O
been O
previously O
unavailable O
to O
foundry S-MANP
engineers O
. O


In O
addition O
, O
the O
miniaturization O
and O
affordability O
of O
electronics S-CONPRI
and O
sensing S-APPL
equipment S-MACEQ
is O
rapidly O
accelerating O
. O


An O
experimental S-CONPRI
casting S-MANP
and O
mold S-MACEQ
were O
designed S-FEAT
in O
this O
research S-CONPRI
to O
demonstrate O
and O
evaluate O
wireless O
sensing S-APPL
of O
core S-MACEQ
shifts O
. O


With O
the O
use O
of O
3D S-CONPRI
sand O
printing O
, O
precisely O
sized O
and O
located O
pockets O
were O
manufactured S-CONPRI
inside O
of O
cores S-MACEQ
. O


Miniature O
wireless O
Bluetooth O
sensors S-MACEQ
capable O
of O
measuring O
acceleration O
and O
rotation O
were O
then O
embedded O
inside O
the O
cores S-MACEQ
. O


From O
these O
, O
high O
fidelity O
data S-CONPRI
were O
captured O
wirelessly O
from O
the O
sensors S-MACEQ
during O
the O
casting S-MANP
process O
. O


With O
strategically O
designed S-FEAT
core B-MACEQ
prints E-MACEQ
designed O
to O
allow O
varying O
levels O
of O
core S-MACEQ
motion O
, O
it O
is O
shown O
that O
core S-MACEQ
shifts O
can O
be S-MATE
measured O
and O
discriminated O
during O
casting S-MANP
in O
real O
time O
. O


The O
fracture S-CONPRI
properties O
( O
stress S-PRO
intensity O
factor O
and O
energy O
release O
rate O
) O
of O
additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
polylactic B-MATE
acid E-MATE
( O
PLA S-MATE
) O
and O
its O
short B-MATE
carbon I-MATE
fiber E-MATE
( O
CF O
) O
reinforced S-CONPRI
composites S-MATE
have O
been O
studied O
. O


The O
effects O
of O
CF O
reinforcement S-PARA
, O
nozzle S-MACEQ
geometry S-CONPRI
and O
bead S-CHAR
lay-up O
orientations S-CONPRI
in O
fracture S-CONPRI
properties O
, O
void S-CONPRI
contents O
, O
and O
interfacial B-CONPRI
bonding E-CONPRI
were O
investigated O
. O


The O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
-based O
AM S-MANP
specimens O
using O
both O
circular O
and O
square O
shaped O
nozzle S-MACEQ
were O
printed O
and O
compared O
with O
the O
conventional O
compression S-PRO
molded O
( O
CM O
) O
samples S-CONPRI
. O


Compact S-MANP
tension O
( O
CT S-ENAT
) O
specimens O
with O
different O
CF O
concentrations O
( O
0 O
wt. O
% O
, O
3 O
wt O
. O


% O
, O
5 O
wt. O
% O
, O
7 O
wt. O
% O
and O
10 O
wt. O
% O
) O
were O
printed O
with O
two O
bead S-CHAR
lay-up O
orientations S-CONPRI
( O
450/-450 O
and O
00/900 O
) O
using O
PLA S-MATE
and O
CF/PLA O
composite S-MATE
filaments O
. O


The O
results O
show O
significant O
improvement O
in O
fracture S-CONPRI
toughness O
and O
fracture S-CONPRI
energy O
for O
CF/PLA O
composites S-MATE
in O
comparison O
to O
neat O
PLA S-MATE
. O


The O
increase O
in O
fracture S-CONPRI
energy O
was O
observed O
to O
be S-MATE
about O
77 O
% O
for O
00/900 O
and O
88 O
% O
for O
450/-450 O
bead S-CHAR
orientations O
, O
respectively O
for O
the O
same O
fiber B-FEAT
reinforcement E-FEAT
( O
5 O
wt O
. O


Such O
improvement O
in O
fracture S-CONPRI
properties O
is O
expected O
to O
be S-MATE
higher O
for O
all O
900 O
bead S-CHAR
orientations O
. O


The O
samples S-CONPRI
printed O
by O
square-shaped O
nozzle S-MACEQ
showed O
enhanced O
fracture S-CONPRI
toughness O
with O
less O
inter-bead O
voids S-CONPRI
and O
larger O
bonded O
areas S-PARA
in O
comparison O
to O
the O
circular-shaped O
nozzle S-MACEQ
. O


Although O
the O
fracture S-CONPRI
toughness O
showed O
very O
negligible O
differences O
between O
00/900 O
and O
450/-450 O
specimens O
, O
distinguishable O
variation S-CONPRI
may O
be S-MATE
seen O
in O
the O
case O
of O
00 O
and O
900 O
bead S-CHAR
orientations O
. O


The O
crack B-CONPRI
propagation E-CONPRI
path O
and O
fracture S-CONPRI
mechanisms O
were O
studied O
using O
optical B-CHAR
microscopy E-CHAR
( O
OM S-CHAR
) O
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
examinations O
. O


Fractography S-CHAR
revealed O
different O
modes O
of O
failure S-CONPRI
with O
a O
very O
high O
fiber B-FEAT
orientation E-FEAT
along O
the O
printing O
direction O
and O
a O
relatively O
higher O
void S-CONPRI
contents O
for O
7 O
and O
10 O
wt O
. O


% O
fiber B-FEAT
reinforcement E-FEAT
. O


The O
advent O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
also O
often O
referred O
to O
as S-MATE
3D B-MANP
printing E-MANP
, O
has O
enabled O
the O
rapid O
production S-MANP
of O
parts O
with O
complex B-CONPRI
geometries E-CONPRI
that O
are O
either O
labor-intensive O
or O
unrealizable O
by O
traditional B-MANP
manufacturing E-MANP
methods O
. O


Many O
existing O
3D B-ENAT
printing I-ENAT
technologies E-ENAT
, O
however O
, O
only O
allow O
one O
material S-MATE
to O
be S-MATE
printed O
at O
one O
time O
, O
while O
many O
applications O
require O
the O
integration O
of O
different O
materials S-CONPRI
, O
which O
sometimes O
can O
not O
be S-MATE
printed O
by O
one O
AM B-MANP
technology E-MANP
. O


In O
this O
paper O
, O
a O
novel O
multi-material S-CONPRI
multi-method O
( O
m4 S-MANP
) O
3D B-MACEQ
printer E-MACEQ
comprised O
of O
multiple O
AM B-MANP
technologies E-MANP
is O
presented O
as S-MATE
a O
solution S-CONPRI
to O
the O
current O
limitations O
. O


This O
printer S-MACEQ
fosters O
the O
advancement O
of O
AM S-MANP
by O
combining O
materials S-CONPRI
traditionally O
unable O
to O
be S-MATE
printed O
concurrently O
while O
adding O
functionality O
to O
printed O
parts O
. O


The O
m4 S-MANP
3D B-MACEQ
printer E-MACEQ
integrates O
four O
AM B-MANP
technologies E-MANP
and O
two O
complementary O
technologies S-CONPRI
onto O
one O
single O
platform S-MACEQ
, O
including O
inkjet S-MANP
( O
IJ O
) O
, O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
, O
direct O
ink S-MATE
writing O
( O
DIW S-MANP
) O
, O
and O
aerosol O
jetting S-MANP
( O
AJ O
) O
, O
along O
with O
robotic B-MACEQ
arms E-MACEQ
for O
pick-and-place O
( O
PnP O
) O
and O
photonic O
curing S-MANP
for O
intense O
pulsed O
light O
( O
IPL O
) O
sintering S-MANP
. O


The O
integration O
of O
these O
AM B-MANP
technologies E-MANP
and O
PnP O
into O
a O
single O
platform S-MACEQ
allows O
for O
rapid B-MANP
fabrication E-MANP
of O
complex O
devices O
, O
providing O
a O
wide O
range S-PARA
of O
functionalities O
with O
applications O
ranging O
from O
soft B-APPL
robotics E-APPL
and O
flexible O
electronics S-CONPRI
to O
medical B-APPL
devices E-APPL
. O


Magnesium B-MATE
alloys E-MATE
are O
highly O
attractive O
in O
aerospace S-APPL
and O
auto O
industries S-APPL
due O
to O
their O
high O
strength-to-weight O
ratio O
. O


Additive B-MANP
manufacturing E-MANP
of O
Mg B-MATE
alloys E-MATE
can O
further O
save O
cost O
from O
materials S-CONPRI
and O
machining S-MANP
time O
. O


This O
paper O
investigates S-CONPRI
the O
microstructure S-CONPRI
and O
dynamic S-CONPRI
mechanical O
behavior O
of O
WE-43 O
Mg B-MATE
alloy E-MATE
built O
through O
the O
powder B-MANP
bed I-MANP
fusion I-MANP
process E-MANP
. O


Samples S-CONPRI
from O
four O
different O
combinations O
of O
processing O
parameters S-CONPRI
were O
built O
. O


These O
builds S-CHAR
were O
studied O
in O
both O
as-built O
and O
hot O
isostatically O
pressed S-MANP
conditions O
. O


The O
resultant O
complex O
microstructures S-MATE
were O
studied O
under O
scanning S-CONPRI
and O
transmission B-CHAR
electron I-CHAR
microscopes E-CHAR
while O
their O
dynamic S-CONPRI
mechanical O
behavior O
was O
evaluated O
using O
a O
split-Hopkinson O
pressure S-CONPRI
bar O
testing S-CHAR
system O
. O


Effects O
of O
initial O
porosity S-PRO
and O
microstructural B-CONPRI
evolution E-CONPRI
during O
HIP S-MANP
treatment O
on O
mechanical B-CONPRI
response E-CONPRI
are O
discussed O
. O


Any O
literature O
investigation O
of O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
( O
L-PBF S-MANP
) O
manufacturing S-MANP
of O
metal S-MATE
parts O
would O
reveal O
that O
the O
development O
of O
internal B-PRO
stresses E-PRO
is O
a O
serious O
limitation O
in O
the O
application O
of O
this O
technology S-CONPRI
. O


Researchers O
have O
used O
a O
variety O
of O
different O
methods O
to O
quantify O
this O
stress S-PRO
and O
investigate O
scanning B-CONPRI
strategies E-CONPRI
aimed O
at O
reducing O
or O
distributing O
this O
stress S-PRO
more O
evenly O
in O
the O
part O
. O


These O
techniques O
provide O
a O
rapid O
method O
to O
give O
a O
quantitative S-CONPRI
comparison O
of O
scan O
strategies O
and O
parameters S-CONPRI
. O


Non-destructive O
diffraction S-CHAR
based O
methods O
can O
be S-MATE
used O
to O
calculate O
the O
profile S-FEAT
of O
stress S-PRO
in O
a O
part O
but O
these O
are O
often O
prohibitively O
expensive O
or O
difficult O
to O
use O
on O
a O
large O
scale O
. O


This O
study O
presents O
a O
methodology S-CONPRI
which O
combines O
deflection O
based O
methods O
with O
either O
the O
hole B-MANP
drilling E-MANP
or O
contour S-FEAT
methods O
. O


Results O
show O
that O
these O
experiments O
can O
be S-MATE
completed O
in O
a O
cost O
effective O
manner O
, O
with O
standard S-CONPRI
lab O
based O
equipment S-MACEQ
to O
generate O
a O
through O
thickness O
measurement S-CHAR
of O
residual B-PRO
stress E-PRO
. O


To O
benefit O
from O
the O
fascinating O
properties S-CONPRI
of O
multi-material B-FEAT
structures E-FEAT
, O
the O
interfacial O
joint S-CONPRI
should O
exhibit O
good O
mechanical B-PRO
strength E-PRO
. O


Evaluating O
the O
shear B-PRO
strength E-PRO
of O
a O
bimetallic O
joint S-CONPRI
via O
conventional O
methods O
is O
usually O
complex O
, O
and O
in O
most O
cases O
produces O
unreliable O
data S-CONPRI
due O
to O
induced O
bending S-MANP
stress O
among O
others O
. O


In O
this O
work O
, O
a O
novel O
single-shear O
test O
device O
was O
designed S-FEAT
and O
fabricated S-CONPRI
to O
measure O
shear B-PRO
strength E-PRO
of O
bimetallic O
joints O
. O


The O
device O
was O
first O
standardized O
by O
shearing S-MANP
standard O
materials S-CONPRI
, O
and O
the O
results O
were O
in O
good O
agreement O
with O
published O
data S-CONPRI
. O


Subsequently O
, O
the O
shear B-PRO
strength E-PRO
of O
Inconel S-MATE
718/copper O
alloy S-MATE
( O
GRCop-84 O
) O
bimetallic O
joint S-CONPRI
built O
via O
laser B-MANP
engineered I-MANP
net I-MANP
shaping E-MANP
( O
LENS™ O
) O
was O
evaluated O
. O


Compression B-CHAR
test E-CHAR
on O
the O
bimetallic O
joint S-CONPRI
was O
carried O
out O
as S-MATE
well O
for O
more O
mechanical S-APPL
characterization O
. O


Both O
shear O
and O
compressive O
yield B-PRO
strengths E-PRO
of O
the O
bimetallic O
joints O
were O
compared O
with O
the O
base O
materials S-CONPRI
in O
addition O
to O
influence O
of O
thermal B-PARA
cycling E-PARA
on O
the O
joint S-CONPRI
strength O
. O


Inconel S-MATE
718/GRCop-84 O
bimetallic-joint O
shear B-PRO
strength E-PRO
was O
220 O
± O
18 O
MPa S-CONPRI
and O
231 O
± O
27 O
MPa S-CONPRI
for O
as-printed O
sample S-CONPRI
and O
after O
thermal B-PARA
cycling E-PARA
, O
respectively O
. O


Likewise O
, O
the O
bimetallic O
yield B-PRO
strength E-PRO
after O
compression B-CHAR
test E-CHAR
was O
232 O
± O
3 O
MPa S-CONPRI
and O
337 O
± O
15 O
MPa S-CONPRI
. O


No O
cracking S-CONPRI
through O
or O
along O
the O
interface S-CONPRI
was O
observed O
even O
after O
thermal B-PARA
cycling E-PARA
, O
which O
indicates O
no O
thermal O
degradation S-CONPRI
at O
the O
bimetallic O
interfacial O
joint S-CONPRI
. O


Increase O
in O
compressive O
yield B-PRO
strength E-PRO
after O
thermal B-PARA
cycling E-PARA
could O
be S-MATE
attributed O
to O
precipitation S-CONPRI
of O
Cr2Nb O
particles S-CONPRI
in O
GRCop-84 O
matrix O
along O
with O
strengthening S-MANP
due O
to O
gamma O
phases O
in O
Inconel B-MATE
718 E-MATE
. O


Scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
and O
backscatter O
electron O
imaging S-APPL
were O
used O
to O
examine O
the O
interfacial O
microstructures S-MATE
and O
failure B-PRO
modes E-PRO
. O


EDS S-CHAR
was O
used O
as S-MATE
well O
to O
analyze O
the O
interface S-CONPRI
elemental O
composition S-CONPRI
. O


The O
development O
of O
the O
single-shear O
test O
device O
can O
provide O
an O
added O
opportunity O
to O
effectively O
evaluate O
mechanical S-APPL
behavior O
, O
reliability S-CHAR
and O
performance S-CONPRI
of O
additively B-MANP
manufactured E-MANP
multi-material O
structures O
through O
bond B-CONPRI
strength E-CONPRI
analysis O
. O


In O
this O
work O
, O
we O
develop O
a O
simple S-MANP
model S-CONPRI
to O
determine O
the O
upper O
bound O
of O
feed S-PARA
rates O
that O
do O
not O
cause O
jamming O
in O
material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
, O
also O
known O
as S-MATE
fused O
deposition B-CONPRI
modeling E-CONPRI
( O
FDM S-MANP
) O
™ O
or O
fused-filament B-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
. O


We O
first O
derive O
a O
relation O
between O
the O
tube O
temperature S-PARA
and O
Péclet O
number O
for O
the O
solid O
portion O
of O
polymer B-MATE
filaments E-MATE
. O


We O
focus O
on O
the O
boundary S-FEAT
between O
the O
solid O
and O
molten O
polymer S-MATE
in O
the O
heated O
portion O
of O
the O
tube O
. O


We O
find O
the O
Péclet O
number O
that O
corresponds O
to O
the O
point O
at O
which O
this O
boundary S-FEAT
makes O
contact S-APPL
with O
the O
nozzle S-MACEQ
, O
and O
identify O
this O
as S-MATE
the O
upper O
bound O
of O
the O
feed S-PARA
rate O
. O


We O
compare O
our O
predictions S-CONPRI
to O
experimental S-CONPRI
results O
. O


We O
find O
good O
agreement O
for O
tube O
temperatures S-PARA
sufficiently O
above O
the O
glass-transition O
temperature S-PARA
, O
which O
is O
the O
temperature S-PARA
region O
of O
typical O
additive B-MANP
manufacturing E-MANP
. O


Additive B-MANP
manufacturing E-MANP
potential O
of O
cold O
spray O
technology S-CONPRI
was O
used O
to O
fabricate S-MANP
freestanding O
samples S-CONPRI
of O
a O
copper B-MATE
alloy E-MATE
. O


Different O
volume B-PARA
fractions E-PARA
of O
micro O
and O
nanocrystalline O
powder B-MATE
particles E-MATE
were O
used O
to O
obatin O
a O
bimodal O
structure S-CONPRI
with O
heterogeneous S-CONPRI
arrangement O
of O
crystalline O
phases O
. O


The O
effects O
of O
volume B-PARA
fractions E-PARA
of O
each O
phase S-CONPRI
were O
investigated O
on O
the O
microstructural S-CONPRI
arrangement O
, O
porosity S-PRO
, O
microhardness S-CONPRI
, O
residual B-PRO
stresses E-PRO
, O
and O
mechanical B-PRO
strength E-PRO
of O
the O
deposited O
materials S-CONPRI
. O


A O
series O
of O
finite B-CONPRI
element E-CONPRI
simulations O
were O
developed O
and O
validated O
by O
experimental B-CONPRI
data E-CONPRI
to O
describe O
the O
influence O
of O
volume B-PARA
fraction E-PARA
, O
morphology S-CONPRI
, O
and O
spatial B-CHAR
distribution E-CHAR
of O
the O
phases O
on O
the O
global O
strength S-PRO
of O
the O
samples S-CONPRI
under O
tensile S-PRO
loading O
. O


The O
obtained O
results O
evidence O
the O
possibility O
of O
tailoring O
the O
mechanical B-CONPRI
response E-CONPRI
of O
freestanding O
cold O
spray O
deposits O
, O
adopting O
a O
heterogeneous S-CONPRI
phase O
structure S-CONPRI
. O


Optimized O
fabrication S-MANP
parameters O
and O
post-processing S-CONPRI
strategies O
should O
be S-MATE
studied O
to O
further O
enhance O
the O
performance S-CONPRI
of O
the O
designed S-FEAT
bimodal O
materials S-CONPRI
and O
overcome O
the O
intrinsic O
brittleness O
of O
cold O
spray O
deposits O
. O


In O
this O
article O
, O
we O
propose O
a O
model S-CONPRI
that O
can O
account O
for O
the O
effect O
of O
porosity S-PRO
and O
high O
surface B-PRO
roughness E-PRO
on O
the O
fatigue S-PRO
crack O
initiation O
of O
AM S-MANP
Ti6Al4V O
alloys S-MATE
in O
moderate O
and O
high O
cycle O
fatigue S-PRO
regimes O
. O


Within O
these O
fatigue S-PRO
regimes O
, O
the O
applied O
force S-CONPRI
to O
the O
component S-MACEQ
is O
below O
the O
yield B-PRO
stress E-PRO
, O
however O
, O
defective O
features O
, O
viz. O
, O
porosity S-PRO
and O
high O
surface B-PRO
roughness E-PRO
, O
can O
act O
as S-MATE
stress O
raisers O
. O


As S-MATE
a O
consequence O
, O
local O
plasticity S-PRO
can O
occur O
. O


To O
capture O
this O
phenomenon O
, O
a O
nonlinear O
isotropic S-PRO
kinematic O
hardening S-MANP
elasto-plasticity O
model S-CONPRI
is O
employed O
in O
our O
finite B-CONPRI
element E-CONPRI
( O
FE S-MATE
) O
model S-CONPRI
. O


For O
creating O
the O
geometry S-CONPRI
of O
the O
FE S-MATE
models O
, O
inputs O
from O
fractography S-CHAR
analyses O
and O
surface B-PRO
roughness E-PRO
measurements O
are O
needed O
. O


From O
fractography S-CHAR
analyses O
, O
the O
shape O
of O
pores S-PRO
formed O
by O
gas S-CONPRI
bubbles O
during O
manufacture S-CONPRI
appears O
quite O
regular O
. O


Thus O
, O
these O
pores S-PRO
are O
modeled O
as S-MATE
circles O
in O
FE S-MATE
models O
. O


The O
size O
of O
these O
pores S-PRO
and O
their O
distance O
to O
a O
free B-CONPRI
surface E-CONPRI
of O
the O
tested O
specimens O
are O
extracted S-CONPRI
from O
Scanning B-MACEQ
Electron I-MACEQ
Microscope E-MACEQ
images S-CONPRI
. O


Moreover O
, O
it O
has O
been O
mentioned O
in O
the O
literature O
that O
statistical O
parameters S-CONPRI
of O
surface B-PRO
roughness E-PRO
can O
not O
fully O
describe O
the O
detrimental O
effect O
of O
this O
type O
of O
defect S-CONPRI
to O
the O
fatigue B-PRO
life E-PRO
of O
the O
associated O
component S-MACEQ
. O


Thus O
, O
in O
our O
FE S-MATE
model O
, O
the O
surface B-CONPRI
topography E-CONPRI
, O
which O
was O
measured O
using O
stylus-based O
profilometer S-MACEQ
, O
is O
explicitly O
modeled O
. O


The O
finite B-CONPRI
element E-CONPRI
results O
are O
then O
post-processed O
by O
our O
in-house O
software S-CONPRI
to O
extract O
the O
Smith–Watson–Topper O
( O
SWT O
) O
fatigue S-PRO
indicator O
parameter S-CONPRI
( O
FIP O
) O
. O


The O
SWT O
parameter S-CONPRI
is O
calculated O
at O
each O
element S-MATE
centroid O
of O
the O
FE S-MATE
mesh O
, O
i.e. O
, O
the O
local O
indicator O
. O


Afterward O
, O
an O
average S-CONPRI
value O
of O
the O
SWT O
parameter S-CONPRI
over O
a O
so-called O
critical O
area S-PARA
whose O
center O
is O
located O
at O
the O
considered O
centroid O
is O
also O
calculated O
, O
i.e. O
, O
the O
average S-CONPRI
indicator O
. O


The O
results O
show O
that O
the O
local O
SWT O
indicator O
is O
too O
conservative O
in O
predicting O
the O
fatigue B-PRO
life E-PRO
of O
the O
AM S-MANP
Ti64 O
alloys S-MATE
while O
the O
average S-CONPRI
SWT O
one O
can O
provide O
good O
results O
. O


A O
complete O
metallurgical S-APPL
and O
mechanical S-APPL
assessment O
of O
additively-manufactured O
maraging S-MANP
tool O
steels S-MATE
has O
been O
undertaken O
, O
beginning O
with O
the O
initial O
powder S-MATE
and O
ending O
at O
hybrid O
builds S-CHAR
. O


The O
effect O
of O
powder S-MATE
recycling O
on O
powder S-MATE
characteristics O
is O
investigated O
using O
flowability O
, O
size O
distribution S-CONPRI
, O
and O
density B-CHAR
measurements E-CHAR
. O


Virgin O
and O
re-used O
powder S-MATE
have O
similar O
characteristics O
in O
terms O
of O
size O
distribution S-CONPRI
and O
chemical O
and O
phase S-CONPRI
homogeneity O
, O
but O
no O
flowability O
. O


A O
microstructural B-CHAR
characterization E-CHAR
of O
the O
as-built O
and O
heat-treated S-MANP
samples O
is O
undertaken O
, O
showing O
the O
phase B-CONPRI
evolution E-CONPRI
, O
and O
the O
formation O
of O
porosity S-PRO
between O
build B-PARA
layers E-PARA
. O


The O
age-hardening O
response O
of O
the O
alloy S-MATE
at O
490 O
°C O
and O
650 O
°C O
is O
demonstrated O
to O
be S-MATE
similar O
to O
the O
material S-MATE
in O
the O
wrought S-CONPRI
condition O
. O


Finally O
, O
hybrid O
build S-PARA
scenarios O
are O
examined O
– O
maraging B-MATE
steel E-MATE
powder O
deposited O
onto O
C300 O
maraging B-MATE
steel E-MATE
, O
as S-MATE
well O
as S-MATE
H13 O
tool S-MACEQ
steel S-MATE
substrates O
– O
using O
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
. O


In O
both O
cases O
, O
the O
interface S-CONPRI
remains O
coherent O
without O
any O
sign O
of O
de-bonding O
during O
tensile S-PRO
deformation S-CONPRI
. O


In O
the O
case O
of O
the O
maraging B-MATE
steel E-MATE
powder O
/ O
C300 O
substrate S-MATE
, O
the O
deformation S-CONPRI
is O
homogeneous S-CONPRI
throughout O
until O
failure S-CONPRI
localizes O
away O
from O
the O
interface S-CONPRI
. O


In O
the O
case O
of O
the O
maraging B-MATE
steel E-MATE
powder O
/ O
H13 S-MATE
substrate O
, O
the O
deformation S-CONPRI
is O
predominantly O
within O
the O
substrate S-MATE
until O
failure S-CONPRI
localizes O
at O
the O
interface S-CONPRI
. O


A O
heat B-MANP
treatment E-MANP
strategy O
for O
the O
maraging B-MATE
steel E-MATE
powder O
/ O
H13 B-MATE
tool I-MATE
steel E-MATE
substrate O
is O
proposed O
. O


The O
effect O
of O
electrode S-MACEQ
positive O
time O
cycle O
( O
% O
EP O
) O
of O
the O
alternating O
current O
TIG B-MANP
process E-MANP
has O
been O
investigated O
for O
aluminium S-MATE
wire O
+ O
arc S-CONPRI
additive B-MANP
manufacture E-MANP
of O
linear O
walls O
. O


The O
study O
considered O
the O
effect O
on O
oxide S-MATE
removal O
, O
linear O
wall O
dimensions S-FEAT
, O
microstructure S-CONPRI
, O
mechanical B-CONPRI
properties E-CONPRI
as S-MATE
well O
as S-MATE
the O
effect O
on O
electrode S-MACEQ
wear O
. O


Microstructure S-CONPRI
analysis O
showed O
a O
noticeable O
increase O
in O
the O
grain B-PRO
size E-PRO
for O
higher O
% O
EP O
. O


The O
study O
also O
showed O
that O
% O
EP O
had O
no O
significant O
effect O
on O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
study O
also O
indicated O
that O
there O
could O
be S-MATE
other O
contributing O
factors O
to O
wall O
dimensions S-FEAT
. O


For O
aluminium S-MATE
wire O
+ O
arc S-CONPRI
additive B-MANP
manufacture E-MANP
of O
linear O
walls O
, O
minimum O
cleaning S-MANP
ranged O
between O
10 O
% O
EP O
and O
20 O
% O
EP O
. O


Reverted O
austenite S-MATE
is O
a O
metastable S-PRO
phase O
that O
can O
be S-MATE
used O
in O
maraging B-MATE
steels E-MATE
to O
increase O
ductility S-PRO
via O
transformation-induced O
plasticity S-PRO
or O
TRIP O
effect O
. O


In O
the O
present O
study O
, O
18Ni O
maraging B-MATE
steel E-MATE
samples O
were O
built O
by O
selective B-MANP
laser I-MANP
melting E-MANP
, O
homogenized S-MANP
at O
820 O
°C O
and O
then O
subjected O
to O
different O
isothermal S-CONPRI
tempering O
cycles O
aiming O
for O
martensite-to-austenite O
reversion O
. O


Thermodynamic O
simulations S-ENAT
were O
used O
to O
estimate O
the O
inter-critical O
austenite S-MATE
+ O
ferrite S-MATE
field O
and O
to O
interpret O
the O
results O
obtained O
after O
tempering S-MANP
. O


In-situ S-CONPRI
synchrotron O
X-ray B-CHAR
diffraction E-CHAR
was O
performed O
during O
the O
heating S-MANP
, O
soaking O
and O
cooling S-MANP
of O
the O
samples S-CONPRI
to O
characterize O
the O
martensite-to-austenite O
reversion O
kinetics O
and O
the O
reverted O
austenite S-MATE
stability O
upon O
cooling S-MANP
to O
room O
temperature S-PARA
. O


The O
reverted O
austenite S-MATE
size O
and O
distribution S-CONPRI
were O
measured O
by O
Electron O
Backscattered O
Diffraction S-CHAR
. O


Results O
showed O
that O
the O
selected O
soaking O
temperatures S-PARA
of O
610 O
°C O
and O
650 O
°C O
promoted O
significant O
and O
gradual O
martensite-to-austenite O
reversion O
with O
high O
thermal B-PRO
stability E-PRO
. O


Tempering S-MANP
at O
690 O
°C O
caused O
massive O
and O
complete O
austenitization O
, O
resulting O
in O
low O
austenite S-MATE
stability O
upon O
cooling S-MANP
due O
to O
compositional O
homogenization S-MANP
. O


The O
process S-CONPRI
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
has O
rapidly O
developed O
over O
the O
past O
two O
decades O
and O
is O
now O
addressing O
the O
needs O
of O
industry S-APPL
for O
fast O
production S-MANP
of O
samples S-CONPRI
with O
tailored O
properties S-CONPRI
and O
complex B-CONPRI
geometries E-CONPRI
. O


One O
of O
the O
most O
common O
alloys S-MATE
fabricated O
from O
powder S-MATE
using O
the O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
( O
L-PBF S-MANP
) O
method O
is O
AlSi10Mg S-MATE
. O


The O
effects O
of O
the O
inherent O
anisotropy S-PRO
and O
existing O
porosity S-PRO
in O
AM S-MANP
AlSi10Mg S-MATE
were O
investigated O
in O
terms O
of O
thermophysical O
properties S-CONPRI
, O
namely O
thermal B-PRO
conductivity E-PRO
, O
diffusivity S-CHAR
, O
heat B-CONPRI
capacity E-CONPRI
and O
thermal B-CONPRI
expansion E-CONPRI
. O


In O
both O
cases O
, O
the O
sample S-CONPRI
showed O
abnormal O
thermal B-CONPRI
expansion E-CONPRI
and O
conductivity S-PRO
, O
as S-MATE
compared O
to O
a O
conventionally O
fabricated S-CONPRI
sample O
. O


After O
heat B-MANP
treatment E-MANP
, O
macro- O
and O
microstructure S-CONPRI
analysis O
confirmed O
that O
thermally O
induced O
porosity S-PRO
( O
TIP O
) O
had O
occurred O
. O


The O
anisotropic S-PRO
behaviors O
of O
thermal B-PRO
conductivity E-PRO
, O
diffusivity S-CHAR
and O
thermal B-CONPRI
expansion E-CONPRI
were O
found O
to O
be S-MATE
related O
to O
the O
texture S-FEAT
, O
preferred O
orientation S-CONPRI
and O
pore S-PRO
distribution S-CONPRI
of O
the O
aluminum S-MATE
grains O
in O
the O
L-PBF-treated O
samples S-CONPRI
. O


Design B-FEAT
for I-FEAT
additive I-FEAT
manufacturing E-FEAT
( O
DFAM O
) O
guidelines O
are O
important O
for O
helping O
designers O
avoid O
iterations O
and O
leverage O
the O
design B-CONPRI
freedoms E-CONPRI
afforded O
by O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
. O


This O
paper O
describes O
how O
quantitative S-CONPRI
design S-FEAT
guidelines O
are O
compiled O
for O
a O
polymer S-MATE
selective O
laser B-MANP
sintering E-MANP
( O
SLS S-MANP
) O
process S-CONPRI
via O
a O
metrology S-CONPRI
study O
. O


As S-MATE
part O
of O
the O
metrology S-CONPRI
study O
, O
a O
test O
part O
is O
designed S-FEAT
to O
focus O
specifically O
on O
geometric O
resolution S-PARA
and O
accuracy S-CHAR
of O
the O
polymer S-MATE
SLS O
process S-CONPRI
. O


The O
test O
part O
is O
compact S-MANP
, O
allowing O
it O
to O
be S-MATE
easily O
inserted O
into O
existing O
SLS S-MANP
builds S-CHAR
and O
therefore O
eliminating O
the O
need O
for O
dedicated O
metrology S-CONPRI
builds S-CHAR
. O


To O
build S-PARA
a O
statistical O
foundation O
upon O
which O
design S-FEAT
guidelines O
can O
be S-MATE
compiled O
, O
multiple O
copies O
of O
the O
test O
part O
are O
fabricated S-CONPRI
within O
existing O
commercial O
builds S-CHAR
in O
a O
factorial O
study O
with O
materials S-CONPRI
, O
build B-PARA
orientations E-PARA
, O
and O
locations O
within O
the O
build B-PARA
chamber E-PARA
as S-MATE
control O
factors O
. O


Enhancing O
the O
corrosion B-CONPRI
resistance E-CONPRI
and O
improving O
the O
biological O
response O
to O
316 O
L O
stainless B-MATE
steel E-MATE
is O
a O
long-standing O
and O
active O
area S-PARA
of O
biomedical S-APPL
research O
. O


Here O
, O
we O
analyzed O
the O
structure S-CONPRI
and O
corrosion S-CONPRI
tendency O
of O
selective B-MANP
laser E-MANP
melted-additively O
manufactured S-CONPRI
( O
AM S-MANP
) O
316 O
L O
stainless B-MATE
steel E-MATE
( O
AM S-MANP
316L O
SS S-MATE
) O
and O
its O
wrought S-CONPRI
counterpart O
. O


SEM S-CHAR
analysis O
showed O
a O
fine O
( O
500–800 O
nm O
) O
interconnected O
sub-granular O
structure S-CONPRI
for O
the O
AM S-MANP
316L O
SS S-MATE
, O
but O
a O
polygonal O
coarse-grained O
structure S-CONPRI
for O
the O
wrought B-CONPRI
sample E-CONPRI
. O


Relative O
to O
the O
wrought B-CONPRI
sample E-CONPRI
, O
the O
AM S-MANP
316L O
SS S-MATE
also O
exhibited O
a O
higher O
charge O
transfer O
resistance S-PRO
and O
higher O
breakdown O
potential O
( O
˜1000 O
mV O
vs. O
SCE O
) O
when O
tested O
in O
biological O
electrolytes S-APPL
, O
which O
included O
human O
serum O
, O
PBS S-MATE
, O
and O
0.9 O
M O
NaCl S-MATE
. O


A O
higher O
pitting S-CONPRI
resistance O
( O
extended O
passive O
region O
) O
and O
improved O
stability S-PRO
of O
the O
AM S-MANP
316L O
SS S-MATE
was O
attributed O
to O
its O
dense O
structure S-CONPRI
of O
oxide S-MATE
film O
and O
refined O
microstructure S-CONPRI
. O


Finally O
, O
material S-MATE
compatibility O
with O
pre-osteoblasts O
was O
analyzed O
. O


Large O
cytoplasmic O
extension O
of O
osteoblast B-BIOP
cells E-BIOP
and O
retention O
of O
stiller O
morphology S-CONPRI
was O
observed O
when O
cells S-APPL
were O
cultured O
on O
the O
AM S-MANP
316L O
SS S-MATE
as S-MATE
compared O
to O
its O
wrought S-CONPRI
counterpart O
, O
suggesting O
that O
the O
AM S-MANP
316L O
SS S-MATE
was O
a O
better O
substrate S-MATE
for O
cell S-APPL
spreading O
and O
differentiation O
. O


Runx2 O
, O
an O
anti–proliferative O
marker O
indicative O
of O
differentiation O
, O
was O
equivalent O
in O
cells S-APPL
cultured O
on O
either O
samples S-CONPRI
, O
but O
overall O
more O
cells S-APPL
were O
present O
on O
the O
AM S-MANP
316L O
SS S-MATE
. O


Given O
its O
higher O
corrosion B-CONPRI
resistance E-CONPRI
and O
ability O
to O
support S-APPL
osteoblast S-BIOP
adherence O
, O
spreading O
and O
differentiation O
, O
the O
AM S-MANP
316L O
SS S-MATE
has O
potential O
for O
use O
in O
the O
biomedical B-APPL
industry E-APPL
. O


Simulations S-ENAT
of O
the O
material S-MATE
deposition S-CONPRI
in O
extrusion-based O
additive B-MANP
manufacturing E-MANP
. O


Prediction S-CONPRI
of O
the O
strand O
cross-section O
as S-MATE
function O
of O
the O
processing O
parameters S-CONPRI
. O


Negative O
linear O
relationship O
between O
the O
printing O
force S-CONPRI
and O
the O
printing B-PARA
speed E-PARA
. O


We O
propose O
a O
numerical O
model S-CONPRI
to O
simulate O
the O
extrusion S-MANP
of O
a O
strand O
of O
semi-molten S-PRO
material S-MATE
on O
a O
moving O
substrate S-MATE
, O
within O
the O
computation S-CONPRI
fluid O
dynamics O
paradigm O
. O


According O
to O
the O
literature O
, O
the O
deposition S-CONPRI
flow O
of O
the O
strands O
has O
an O
impact S-CONPRI
on O
the O
inter-layer O
bond O
formation O
in O
extrusion-based O
additive B-MANP
manufacturing E-MANP
, O
as S-MATE
well O
as S-MATE
the O
surface B-PRO
roughness E-PRO
of O
the O
fabricated S-CONPRI
part O
. O


Under O
the O
assumptions O
of O
an O
isothermal S-CONPRI
Newtonian O
fluid S-MATE
and O
a O
creeping O
laminar O
flow O
, O
the O
deposition S-CONPRI
flow O
is O
controlled O
by O
two O
parameters S-CONPRI
: O
the O
gap O
distance O
between O
the O
extrusion S-MANP
nozzle O
and O
the O
substrate S-MATE
, O
and O
the O
velocity O
ratio O
of O
the O
substrate S-MATE
to O
the O
average S-CONPRI
velocity O
of O
the O
flow O
inside O
the O
nozzle S-MACEQ
. O


The O
numerical B-ENAT
simulation E-ENAT
fully O
resolves O
the O
deposition S-CONPRI
flow O
and O
provides O
the O
cross-section O
of O
the O
printed O
strand O
. O


The O
adoption O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
for O
fabricating S-MANP
biomedical S-APPL
implants O
at O
hospitals O
provides O
many O
potential O
benefits O
. O


Relative O
to O
biomedical S-APPL
implants O
fabricated S-CONPRI
via O
traditional B-MANP
manufacturing E-MANP
( O
TM O
) O
, O
typically O
available O
by O
suppliers O
out O
of O
the O
immediate O
region O
, O
biomedical S-APPL
implants O
fabricated S-CONPRI
through O
AM S-MANP
provides O
an O
opportunity O
to O
receive O
more O
patient-specific O
, O
customized O
parts O
with O
faster O
response O
, O
a O
lower O
inventory O
level O
, O
and O
reduced O
delivery O
costs O
. O


Despite O
the O
promising O
features O
of O
AM B-MANP
technologies E-MANP
, O
the O
make-or-buy O
decisions O
are O
not O
straightforward O
and O
require O
careful O
investigation O
due O
to O
the O
relatively O
high O
AM B-MACEQ
machine E-MACEQ
and O
production B-CONPRI
costs E-CONPRI
. O


No O
research S-CONPRI
efforts O
, O
to O
the O
best O
of O
our O
knowledge O
, O
have O
been O
dedicated O
to O
the O
quantitative S-CONPRI
analysis O
of O
the O
costs O
of O
supply B-CONPRI
chains E-CONPRI
integrated O
with O
AM S-MANP
facilities O
, O
e.g. O
, O
inventory O
cost O
, O
transportation O
cost O
, O
product O
lead B-PARA
time E-PARA
, O
etc O
. O


In O
this O
study O
, O
we O
propose O
a O
stochastic S-CONPRI
cost B-CONPRI
model E-CONPRI
to O
quantify O
the O
supply-chain O
level O
costs O
associated O
with O
the O
production S-MANP
of O
biomedical S-APPL
implants O
using O
AM B-MANP
techniques E-MANP
, O
and O
investigate O
the O
economic O
feasibility S-CONPRI
of O
using O
such O
technologies S-CONPRI
to O
fabricate S-MANP
biomedical S-APPL
implants O
at O
the O
sites O
of O
hospitals O
. O


The O
problem O
is O
formulated O
in O
the O
form O
of O
a O
stochastic S-CONPRI
programming O
model S-CONPRI
, O
which O
determines O
the O
number O
of O
AM S-MANP
facilities O
to O
be S-MATE
established O
and O
volume S-CONPRI
of O
product O
flow O
between O
manufacturing S-MANP
facilities O
and O
hospitals O
. O


A O
customized O
Sample S-CONPRI
Average B-CONPRI
Algorithm E-CONPRI
( O
SAA O
) O
is O
developed O
to O
obtain O
the O
solutions O
. O


We O
apply O
the O
cost B-CONPRI
model E-CONPRI
to O
a O
real-world O
case B-CONPRI
study E-CONPRI
that O
focuses O
on O
the O
use O
of O
biomedical S-APPL
implants O
for O
hospitals O
in O
the O
state O
of O
Mississippi O
( O
MS O
) O
, O
and O
identify O
the O
conditions O
and O
cost O
parameters S-CONPRI
that O
have O
significant O
impact S-CONPRI
on O
the O
economic O
feasibility S-CONPRI
of O
AM S-MANP
. O


We O
find O
that O
the O
ratio O
between O
the O
unit O
production B-CONPRI
costs E-CONPRI
of O
AM S-MANP
and O
TM O
( O
ATR O
) O
, O
as S-MATE
well O
as S-MATE
product O
lead B-PARA
time E-PARA
and O
demands O
, O
are O
key O
cost O
parameters S-CONPRI
that O
determine O
the O
economic O
feasibility S-CONPRI
of O
AM S-MANP
. O


Popular O
dialogue O
around O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
often O
assumes O
that O
AM S-MANP
will O
cause O
a O
move O
from O
centralized O
to O
distributed O
manufacturing S-MANP
. O


We O
combine O
a O
Process-Based O
Cost B-CONPRI
Model E-CONPRI
and O
an O
optimization B-CONPRI
model E-CONPRI
to O
analyze O
the O
optimal O
location O
and O
number O
of O
manufacturing S-MANP
sites O
, O
and O
the O
tradeoffs O
between O
production S-MANP
, O
transportation O
and O
inventory O
costs O
. O


We O
use O
as S-MATE
a O
case B-CONPRI
study E-CONPRI
the O
commercial O
aviation O
maintenance O
market O
and O
a O
titanium S-MATE
jet O
engine O
bracket S-MACEQ
as S-MATE
an O
exemplar O
of O
a O
class O
of O
parts O
that O
are O
not O
flight-critical O
. O


We O
run O
our O
analysis O
for O
three O
different O
scenarios O
, O
one O
corresponding O
to O
the O
current O
state O
of O
the O
technology S-CONPRI
, O
and O
two O
which O
represent O
potential O
improvements O
in O
AM B-MANP
technology E-MANP
. O


Our O
results O
suggest O
that O
the O
cost-minimizing O
number O
of O
manufacturing S-MANP
locations O
does O
not O
vary O
significantly O
when O
taking O
into O
account O
a O
range S-PARA
of O
plausible O
improvements O
in O
the O
technology S-CONPRI
. O


In O
this O
case O
, O
distributed O
manufacturing S-MANP
is O
only O
favorable O
for O
a O
set S-APPL
of O
non-critical O
components S-MACEQ
that O
can O
be S-MATE
produced O
on O
the O
same O
equipment S-MACEQ
with O
minimal O
certification O
requirements O
and O
whose O
annual O
demand O
is O
in O
the O
tens O
of O
thousands O
. O


Distributed O
manufacturing S-MANP
is O
attractive O
at O
lower O
volumes O
for O
components S-MACEQ
that O
require O
no O
hot B-MANP
isostatic I-MANP
pressing E-MANP
. O


Through O
the O
combination O
of O
in-situ S-CONPRI
alloying S-FEAT
and O
additive B-MANP
manufacturing E-MANP
with O
gas B-MANP
tungsten I-MANP
arc I-MANP
welding E-MANP
, O
a O
new O
approach O
to O
fabricating S-MANP
titanium O
aluminide O
alloys S-MATE
is O
proposed O
. O


This O
innovative O
and O
low O
cost O
process S-CONPRI
has O
many O
similarities O
to O
multipass O
welding S-MANP
. O


It O
has O
been O
a O
generally O
accepted O
practice O
to O
maintain O
a O
specified O
interpass B-PARA
temperature E-PARA
when O
multipass O
welding S-MANP
many O
different O
alloys S-MATE
to O
prevent O
defects S-CONPRI
such O
as S-MATE
cracks O
. O


Increasing O
the O
interpass B-PARA
temperature E-PARA
can O
facilitate O
phase S-CONPRI
transformation O
by O
extending O
the O
high O
temperature S-PARA
period O
and O
produce O
the O
desired O
weld S-FEAT
microstructure.This O
study O
examines O
the O
influence O
of O
different O
interpass B-PARA
temperatures E-PARA
on O
in-situ S-CONPRI
alloyed O
and O
additively B-MANP
manufactured E-MANP
γ-TiAl O
alloy S-MATE
. O


The O
microstructure S-CONPRI
, O
chemical B-CONPRI
composition E-CONPRI
, O
phase S-CONPRI
constitution O
and O
microhardness S-CONPRI
of O
all O
the O
test O
components S-MACEQ
were O
respectively O
examined O
by O
using O
light O
microscopy S-CHAR
, O
SEM-EDS O
, O
X-ray B-CHAR
diffraction E-CHAR
and O
a O
Duromain O
70 O
Hardness S-PRO
Tester O
. O


No O
appreciable O
changes O
in O
microstructure S-CONPRI
and O
composition S-CONPRI
were O
found O
as S-MATE
interpass O
temperature S-PARA
was O
changed O
. O


However O
, O
as S-MATE
the O
interpass B-PARA
temperature E-PARA
was O
increased O
from O
100 O
°C O
to O
400 O
°C O
, O
a O
decrease O
of O
α2 O
phase B-CONPRI
fraction E-CONPRI
was O
observed O
due O
to O
the O
lower O
cooling B-PARA
rate E-PARA
. O


Consequently O
, O
the O
microhardness S-CONPRI
value O
also O
decreased O
. O


A O
further O
increase O
of O
interpass B-PARA
temperature E-PARA
to O
500 O
°C O
produced O
only O
minor O
reductions O
in O
the O
brittle S-PRO
α2 O
phase B-CONPRI
fraction E-CONPRI
and O
the O
microhardness S-CONPRI
value O
. O


In O
view O
of O
these O
results O
, O
a O
suitable O
interpass B-PARA
temperature E-PARA
was O
found O
for O
producing O
crack-free O
components S-MACEQ
. O


Increasingly O
, O
metal S-MATE
parts O
made O
by O
additive B-MANP
manufacturing E-MANP
are O
produced O
using O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
. O


In O
this O
paper O
we O
report O
upon O
the O
combined O
effects O
of O
PBF S-MANP
parameters S-CONPRI
, O
including O
power S-PARA
and O
scan B-PARA
speed E-PARA
, O
in O
layer-by-layer S-CONPRI
manufacturing O
of O
gas B-MANP
atomized E-MANP
non-modulated O
( O
NM O
) O
Ni-Mn-Ga O
alloy S-MATE
. O


The O
effects O
of O
process B-CONPRI
parameters E-CONPRI
upon O
PBF S-MANP
is O
studied O
by O
applying O
nine O
different O
parameter S-CONPRI
sets O
in O
the O
as-printed O
state O
and O
after O
homogenization S-MANP
and O
ordering O
. O


The O
chemical B-CONPRI
composition E-CONPRI
of O
the O
samples S-CONPRI
is O
analyzed O
using O
EDX S-CHAR
attached O
to O
an O
SEM S-CHAR
, O
and O
the O
crystal B-PRO
structures E-PRO
are O
determined O
by O
X-ray B-CHAR
diffraction E-CHAR
. O


The O
phase S-CONPRI
transformation O
temperatures S-PARA
are O
measured O
using O
a O
low-field O
ac O
susceptibility S-PRO
measurement S-CHAR
system O
and O
the O
magnetic O
properties S-CONPRI
are O
measured O
with O
a O
vibrating O
sample S-CONPRI
magnetometer O
( O
VSM S-CHAR
) O
. O


Before O
the O
heat-treatment O
, O
all O
as-printed O
samples S-CONPRI
showed O
paramagnetic O
behavior O
with O
low O
magnetization O
and O
no O
phase S-CONPRI
transformations O
could O
be S-MATE
observed O
in O
the O
susceptibility S-PRO
measurements O
. O


After O
annealing S-MANP
, O
the O
samples S-CONPRI
recovered O
the O
ferromagnetic O
behavior O
with O
comparable O
magnetization O
to O
annealed O
gas B-MANP
atomized E-MANP
powder O
. O


The O
as-printed O
samples S-CONPRI
were O
composed O
of O
a O
mixture O
of O
different O
crystal B-PRO
structures E-PRO
. O


However O
, O
after O
annealing S-MANP
the O
original O
NM O
structure S-CONPRI
with O
a O
= O
b S-MATE
= O
5.47 O
Å O
and O
c S-MATE
= O
6.66 O
Å O
with O
a O
c/a O
-ratio O
of O
1.22 O
was O
recovered O
and O
crystallographic O
twins O
could O
be S-MATE
observed O
in O
an O
SEM S-CHAR
. O


Expanding O
on O
prior O
process S-CONPRI
mapping O
work O
by O
the O
authors O
, O
multiple O
melt B-MATE
pool E-MATE
cross-sections S-CONPRI
are O
measured O
at O
multiple O
process B-CONPRI
parameter E-CONPRI
combinations O
for O
the O
Inconel B-MATE
718 I-MATE
alloy E-MATE
in O
a O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
( O
L-PBF S-MANP
) O
process S-CONPRI
. O


Collection O
of O
such O
data S-CONPRI
enables O
the O
study O
of O
the O
variability S-CONPRI
of O
melt B-MATE
pool E-MATE
geometry S-CONPRI
( O
e.g O
. O


width O
, O
depth O
, O
and O
cross-sectional O
area S-PARA
) O
across O
process S-CONPRI
space O
. O


Furthermore O
, O
the O
statistical O
distribution S-CONPRI
of O
the O
measured O
melt B-MATE
pool E-MATE
geometries S-CONPRI
is O
compared O
to O
that O
of O
an O
equivalent O
normal O
distribution S-CONPRI
and O
intriguing O
outliers O
are O
observed O
. O


The O
cross-sectional O
morphology S-CONPRI
of O
the O
melt B-MATE
pools E-MATE
are O
associated O
with O
defects S-CONPRI
such O
as S-MATE
keyholing O
porosity S-PRO
and O
balling O
and O
the O
variability S-CONPRI
of O
the O
defects S-CONPRI
is O
quantified O
. O


The O
final O
product O
of O
this O
work O
is O
a O
robust O
description O
of O
L-PBF S-MANP
In718 S-MATE
melt O
pool O
behavior O
, O
based O
on O
ex-situ O
observations O
, O
which O
can O
be S-MATE
linked O
to O
in-situ S-CONPRI
observations O
of O
melt B-MATE
pool E-MATE
morphology O
in O
future O
work O
. O


This O
study O
evaluates O
the O
performance S-CONPRI
of O
continuous O
carbon S-MATE
, O
Kevlar S-MATE
and O
glass B-MATE
fibre E-MATE
reinforced O
composites S-MATE
manufactured O
using O
the O
fused B-CONPRI
deposition E-CONPRI
modelling O
( O
FDM S-MANP
) O
additive B-MANP
manufacturing E-MANP
technique O
. O


The O
fibre S-MATE
reinforced O
nylon B-MATE
composites E-MATE
were O
fabricated S-CONPRI
using O
a O
Markforged O
Mark O
One O
3D B-MANP
printing E-MANP
system O
. O


The O
mechanical S-APPL
performance O
of O
the O
composites S-MATE
was O
evaluated O
both O
in O
tension O
and O
flexure S-MACEQ
. O


The O
influence O
of O
fibre S-MATE
orientation O
, O
fibre S-MATE
type O
and O
volume B-PARA
fraction E-PARA
on O
mechanical B-CONPRI
properties E-CONPRI
were O
also O
investigated O
. O


The O
results O
were O
compared O
with O
that O
of O
both O
non-reinforced O
nylon S-MATE
control O
specimens O
, O
and O
known O
material B-CONPRI
property E-CONPRI
values O
from O
literature O
. O


It O
was O
demonstrated O
that O
of O
the O
fibres S-MATE
investigated O
, O
those O
fabricated S-CONPRI
using O
carbon B-MATE
fibre E-MATE
yielded O
the O
largest O
increase O
in O
mechanical B-PRO
strength E-PRO
per O
fibre S-MATE
volume O
. O


Its O
tensile B-PRO
strength E-PRO
values O
were O
up O
to O
6.3 O
times O
higher O
than O
those O
obtained O
with O
the O
non-reinforced O
nylon S-MATE
polymer O
. O


As S-MATE
the O
carbon S-MATE
and O
glass B-MATE
fibre E-MATE
volume O
fraction S-CONPRI
increased O
so O
too O
did O
the O
level O
of O
air O
inclusion S-MATE
in O
the O
composite S-MATE
matrix O
, O
which O
impacted O
on O
mechanical S-APPL
performance O
. O


As S-MATE
a O
result O
, O
a O
maximum O
efficiency O
in O
tensile B-PRO
strength E-PRO
was O
observed O
in O
glass S-MATE
specimen O
as S-MATE
fibre O
content O
approached O
22.5 O
% O
, O
with O
higher O
fibre S-MATE
contents O
( O
up O
to O
33 O
% O
) O
, O
yielding O
only O
minor O
increases O
in O
strength S-PRO
. O


Approaches O
used O
in O
Computational O
Welding S-MANP
Mechanics O
are O
applicable O
for O
additive B-MANP
Manufacturing E-MANP
. O


The O
model S-CONPRI
sizes O
pose O
additional O
challenges O
in O
case O
of O
simulating O
AM S-MANP
. O


Models O
must O
couple O
microstructural S-CONPRI
and O
material S-MATE
behavior O
. O


The O
paper O
describes O
the O
application O
of O
modeling S-ENAT
approaches O
used O
in O
Computational O
Welding S-MANP
Mechanics O
( O
CWM O
) O
applicable O
for O
simulating O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
. O


It O
focuses O
on O
the O
approximation O
of O
the O
behavior O
in O
the O
process S-CONPRI
zone O
and O
the O
behavior O
of O
the O
solid O
material S-MATE
, O
particularly O
in O
the O
context O
of O
changing O
microstructure S-CONPRI
. O


Two O
examples O
are O
shown O
, O
one O
for O
the O
precipitation B-MANP
hardening E-MANP
Alloy S-MATE
718 O
and O
one O
for O
Ti-6Al-4V S-MATE
. O


The O
latter O
alloy S-MATE
is O
subject O
to O
phase S-CONPRI
changes O
due O
to O
the O
thermal B-PARA
cycling E-PARA
. O


A O
model S-CONPRI
for O
additive B-MANP
manufacturing E-MANP
by O
selective B-MANP
laser I-MANP
melting E-MANP
of O
a O
powder B-MACEQ
bed E-MACEQ
with O
application O
to O
alumina S-MATE
ceramic O
is O
presented O
. O


Based O
on O
Beer–Lambert O
law O
, O
a O
volume S-CONPRI
heat B-CONPRI
source E-CONPRI
model O
taking O
into O
account O
the O
material S-MATE
absorption S-CONPRI
is O
derived O
. O


The O
level O
set S-APPL
method O
is O
used O
to O
track O
the O
shape O
of O
deposed O
bead S-CHAR
. O


Shrinkage S-CONPRI
during O
consolidation S-CONPRI
from O
powder S-MATE
to O
liquid O
and O
compact S-MANP
medium O
is O
modeled O
by O
a O
compressible O
Newtonian O
constitutive O
law O
. O


A O
semi-implicit O
formulation O
of O
surface B-PRO
tension E-PRO
is O
used O
, O
which O
permits O
a O
stable O
resolution S-PARA
to O
capture O
the O
liquid/gas O
interface S-CONPRI
. O


The O
influence O
of O
different O
process B-CONPRI
parameters E-CONPRI
on O
temperature S-PARA
distribution S-CONPRI
, O
melt B-MATE
pool E-MATE
profiles O
and O
bead S-CHAR
shapes O
is O
discussed O
. O


The O
effects O
of O
liquid O
viscosity S-PRO
and O
surface B-PRO
tension E-PRO
on O
melt B-MATE
pool E-MATE
dynamics O
are O
investigated O
. O


Three O
dimensional O
simulations S-ENAT
of O
several O
passes O
are O
also O
presented O
to O
study O
the O
influence O
of O
the O
scanning B-CONPRI
strategy E-CONPRI
. O


A O
wire-arc B-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
system O
is O
used O
to O
fabricate S-MANP
iron O
rich O
Fe–Al O
intermetallics S-MATE
with O
25 O
at O
% O
aluminum S-MATE
content O
. O


The O
alloy S-MATE
is O
produced O
in B-CONPRI
situ E-CONPRI
through O
controlled O
addition O
of O
the O
elemental O
iron S-MATE
and O
aluminum S-MATE
components O
into O
the O
welding S-MANP
process S-CONPRI
. O


The O
properties S-CONPRI
of O
the O
fabricated S-CONPRI
material O
are O
assessed O
using O
optical S-CHAR
microstructure S-CONPRI
analysis O
, O
hardness S-PRO
testing O
, O
tensile B-CHAR
testing E-CHAR
, O
X-ray B-CHAR
diffraction E-CHAR
phase S-CONPRI
characterization O
and O
electron O
dispersive O
spectrometry O
. O


It O
is O
shown O
that O
the O
WAAM B-MACEQ
system E-MACEQ
is O
capable O
of O
producing O
iron S-MATE
rich O
Fe–Al O
intermetallics S-MATE
with O
higher O
yield B-PRO
strength E-PRO
and O
similar O
room O
temperature S-PARA
ductility S-PRO
when O
compared O
to O
equivalent O
materials S-CONPRI
produced O
using O
powder B-MANP
metallurgy E-MANP
. O


Support B-FEAT
structures E-FEAT
are O
required O
in O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
additive B-MANP
manufacturing E-MANP
of O
metallic S-MATE
components S-MACEQ
with O
overhanging B-CONPRI
structures E-CONPRI
in O
order O
to O
reinforce O
and O
anchor O
the O
part O
, O
preventing O
warping S-CONPRI
during O
fabrication S-MANP
. O


In O
this O
study O
, O
we O
tested O
the O
tensile S-PRO
structural O
strength S-PRO
of O
support B-FEAT
structures E-FEAT
with O
four O
different O
2-dimensional O
lattice B-CONPRI
geometries E-CONPRI
by O
fabricating S-MANP
samples O
composed O
of O
solid O
material S-MATE
on O
the O
bottom O
, O
followed O
by O
support B-MATE
material E-MATE
in O
the O
middle O
, O
followed O
by O
solid O
material S-MATE
on O
the O
top O
. O


The O
support B-FEAT
structure E-FEAT
regions O
were O
fabricated S-CONPRI
with O
a O
lower O
linear O
heat S-CONPRI
input O
than O
the O
solid O
material S-MATE
, O
providing O
deliberate O
geometrical O
stress B-CHAR
concentrations E-CHAR
to O
enable O
the O
removal B-MANP
of I-MANP
support E-MANP
material S-MATE
after O
processing O
. O


These O
samples S-CONPRI
were O
subjected O
to O
tension O
in O
the O
vertical S-CONPRI
direction O
to O
measure O
the O
strengths S-PRO
of O
the O
support S-APPL
structure-solid O
material S-MATE
interfaces O
. O


Two O
strengths S-PRO
were O
computed O
: O
an O
effective O
structural O
strength S-PRO
defined O
as S-MATE
the O
total O
force S-CONPRI
that O
the O
structure S-CONPRI
withstood O
normalized O
by O
the O
full O
cross-sectional O
area S-PARA
, O
and O
a O
ligament O
structural O
strength S-PRO
, O
defined O
as S-MATE
the O
effective O
structural O
strength S-PRO
normalized O
by O
the O
density S-PRO
of O
the O
solid O
material S-MATE
, O
thereby O
ignoring O
the O
volume S-CONPRI
of O
the O
surrounding O
powder S-MATE
and O
voids S-CONPRI
that O
do O
not O
contribute O
to O
the O
strength S-PRO
of O
the O
lattice S-CONPRI
. O


The O
effective O
structural O
strength S-PRO
was O
14–32 O
% O
of O
the O
strength S-PRO
of O
fully B-PARA
dense E-PARA
Ti-6Al-4V O
made O
by O
PBF S-MANP
and O
the O
ligament O
structural O
strength S-PRO
was O
34–49 O
% O
of O
the O
strength S-PRO
of O
fully B-PARA
dense E-PARA
material O
. O


These O
interface S-CONPRI
strengths O
are O
lower O
than O
that O
of O
fully-dense O
material S-MATE
due O
to O
the O
stress B-CHAR
concentrations E-CHAR
at O
the O
support S-APPL
structure-solid O
material S-MATE
interfaces O
, O
not O
any O
intrinsic O
difference O
in O
the O
intrinsic O
strength S-PRO
of O
support B-FEAT
structure E-FEAT
versus O
solid O
material S-MATE
. O


These O
results O
can O
be S-MATE
used O
to O
tailor O
the O
support B-FEAT
structure E-FEAT
geometry S-CONPRI
to O
balance O
sufficient O
anchoring O
strength S-PRO
during O
fabrication S-MANP
and O
ease O
of O
part O
removal O
and O
subsequent O
machining S-MANP
during O
post-processing S-CONPRI
. O


In-situ S-CONPRI
detection O
of O
processing O
defects S-CONPRI
is O
a O
critical O
challenge O
for O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion I-MANP
Additive I-MANP
Manufacturing E-MANP
. O


Many O
of O
these O
defects S-CONPRI
are O
related O
to O
interactions O
between O
the O
recoater B-MACEQ
blade E-MACEQ
, O
which O
spreads O
the O
powder S-MATE
, O
and O
the O
powder B-MACEQ
bed E-MACEQ
. O


This O
work O
leverages O
Deep O
Learning O
, O
specifically O
a O
Convolutional O
Neural B-CONPRI
Network E-CONPRI
( O
CNN O
) O
, O
for O
autonomous O
detection O
and O
classification S-CONPRI
of O
many O
of O
these O
spreading O
anomalies S-CONPRI
. O


Importantly O
, O
the O
input O
layer S-PARA
of O
the O
CNN O
is O
modified O
to O
enable O
the O
algorithm S-CONPRI
to O
learn O
both O
the O
appearance O
of O
the O
powder B-MACEQ
bed E-MACEQ
anomalies S-CONPRI
as O
well O
as S-MATE
key O
contextual O
information O
at O
multiple O
size O
scales O
. O


These O
modifications O
to O
the O
CNN O
architecture S-APPL
are O
shown O
to O
improve O
the O
flexibility S-PRO
and O
overall O
classification S-CONPRI
accuracy S-CHAR
of O
the O
algorithm S-CONPRI
while O
mitigating O
many O
human O
biases O
. O


A O
case B-CONPRI
study E-CONPRI
is O
used O
to O
demonstrate O
the O
utility O
of O
the O
presented O
methodology S-CONPRI
and O
the O
overall O
performance S-CONPRI
is O
shown O
to O
be S-MATE
superior O
to O
that O
of O
methodologies O
previously O
reported O
by O
the O
authors O
. O


The O
observation O
of O
sub-grained O
cellular O
features O
in O
additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
/selectively O
laser S-ENAT
melted O
( O
SLM S-MANP
) O
316L B-MATE
stainless I-MATE
steel E-MATE
components O
has O
remained O
an O
interesting O
, O
though O
incompletely O
understood O
phenomenon O
. O


However O
, O
the O
recently O
observed O
correlation O
linking O
the O
presence O
of O
these O
features O
with O
significantly O
enhanced O
mechanical B-PRO
strength E-PRO
in O
SLM S-MANP
316L O
materials S-CONPRI
has O
driven O
a O
renewed O
interest O
and O
effort O
toward O
elucidating O
the O
mechanism S-CONPRI
( O
s S-MATE
) O
by O
which O
they O
are O
formed O
. O


These O
phenomena O
include O
SLM-induced O
intrinsic O
strain-aging O
, O
Cottrell O
atmosphere O
formation O
, O
and O
twin-boundary O
enhanced O
mass B-CONPRI
diffusion E-CONPRI
to O
structural B-CONPRI
defects E-CONPRI
. O


Furthermore O
, O
evidence O
is O
provided O
to O
support S-APPL
the O
proposed O
theory O
that O
the O
observed O
chemical B-CONPRI
heterogeneity E-CONPRI
coincident O
with O
dislocation S-CONPRI
cell S-APPL
structures O
is O
actually O
the O
result O
of O
local O
, O
strain S-PRO
energy B-PARA
density E-PARA
induced O
solid B-CONPRI
state I-CONPRI
diffusion E-CONPRI
. O


Numerical B-ENAT
simulation E-ENAT
of O
residual B-CONPRI
deformation E-CONPRI
in O
metallic S-MATE
components S-MACEQ
with O
dense O
lattice S-CONPRI
support O
structures O
by O
the O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
additive B-MANP
manufacturing I-MANP
process E-MANP
has O
been O
a O
significant O
challenge O
due O
to O
the O
very O
high O
computational O
expense O
in O
performing O
both O
finite B-CONPRI
element E-CONPRI
meshing O
and O
analysis O
. O


In O
this O
work O
, O
the O
modified B-CONPRI
inherent I-CONPRI
strain I-CONPRI
method E-CONPRI
is O
extended O
to O
enable O
efficient O
residual B-CONPRI
deformation E-CONPRI
simulation O
of O
l-PBF S-MANP
components S-MACEQ
with O
lattice S-CONPRI
support O
structures O
. O


The O
asymptotic O
homogenization B-MANP
method E-MANP
is O
employed O
to O
obtain O
the O
equivalent O
mechanical B-CONPRI
properties E-CONPRI
including O
the O
anisotropic S-PRO
elastic O
modulus O
and O
inherent O
strains O
given O
the O
topological O
configuration S-CONPRI
and O
laser S-ENAT
scanning O
strategy O
of O
the O
thin-walled O
lattice S-CONPRI
support O
structures O
. O


A O
key O
finding O
is O
that O
the O
in-plane O
homogenized S-MANP
inherent O
strain S-PRO
values O
decrease O
with O
increasing O
volume S-CONPRI
density S-PRO
, O
which O
can O
be S-MATE
attributed O
to O
the O
directional O
dependence O
of O
inherent O
strains O
for O
the O
AM-processed O
material S-MATE
. O


Based O
on O
the O
homogenized S-MANP
mechanical O
properties S-CONPRI
and O
inherent O
strains O
, O
the O
thin-walled O
lattice S-CONPRI
support O
structures O
can O
be S-MATE
considered O
to O
be S-MATE
an O
effective O
solid O
continuum S-CONPRI
so O
that O
the O
simulation S-ENAT
can O
be S-MATE
accelerated O
significantly O
to O
obtain O
residual B-CONPRI
deformation E-CONPRI
. O


Good O
accuracy S-CHAR
of O
the O
homogenized S-MANP
mechanical O
property S-CONPRI
and O
inherent O
strains O
is O
validated O
by O
comparing O
the O
simulated O
residual B-CONPRI
deformation E-CONPRI
with O
experimental B-CONPRI
deformation E-CONPRI
measurement O
of O
several O
lattice S-CONPRI
structured O
beams O
of O
different O
volume S-CONPRI
densities O
. O


In O
addition O
, O
the O
scalability O
of O
the O
proposed O
method O
is O
also O
verified O
through O
application O
to O
a O
complex O
L-PBF S-MANP
component S-MACEQ
fabricated O
with O
thin-walled O
support B-FEAT
structures E-FEAT
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
promises O
great O
potential O
benefits O
for O
industrial S-APPL
manufacturers O
who O
require O
low O
volume S-CONPRI
and O
functional O
, O
highly O
complex O
, O
end-use O
products O
. O


Commercial O
adoption O
of O
AM S-MANP
has O
been O
slow O
due O
to O
factors O
such O
as S-MATE
quality O
control O
, O
production S-MANP
rates O
, O
and O
repeatability S-CONPRI
. O


However O
, O
given O
AM S-MANP
's O
potential O
, O
numerous O
research S-CONPRI
efforts O
are O
underway O
to O
improve O
the O
quality S-CONPRI
of O
the O
product O
realization O
process S-CONPRI
. O


A O
major O
area S-PARA
of O
opportunity O
is O
to O
complement O
existing O
efforts O
with O
advancements O
in O
end-to-end O
digital O
implementations O
of O
AM B-MANP
processes E-MANP
. O


Systematically O
configured O
digital O
implementations O
would O
facilitate O
informational O
transformations O
through O
standard S-CONPRI
interfaces O
, O
streamlining O
the O
AM S-MANP
digital O
spectrum O
. O


Here O
, O
we O
propose O
the O
development O
of O
a O
federated O
, O
information O
systems O
architecture S-APPL
for O
additive B-MANP
manufacturing E-MANP
. O


We O
establish O
an O
information O
requirements O
workflow S-CONPRI
for O
streamlining O
information O
throughput S-CHAR
during O
product O
realization O
. O


The O
architecture S-APPL
is O
delivered O
through O
the O
development O
of O
a O
solution S-CONPRI
stack O
, O
including O
the O
identification O
of O
areas S-PARA
where O
advancements O
in O
information O
representations O
will O
have O
the O
highest O
impact S-CONPRI
. O


Common O
data S-CONPRI
structures O
and O
interfaces O
will O
allow O
developers O
and O
end O
users O
of O
additive B-MANP
manufacturing E-MANP
technologies O
to O
simplify O
, O
coordinate S-PARA
, O
validate O
, O
and O
verify O
end-to-end O
digital O
implementations O
. O


This O
paper O
investigates S-CONPRI
the O
development O
of O
a O
novel O
high O
temperature S-PARA
polymer B-MATE
composite E-MATE
material S-MATE
by O
modifying O
polyetherimide O
( O
PEI O
) O
ULTEM™ O
1010 O
with O
the O
addition O
of O
functional O
additives S-MATE
and O
processing O
it O
into O
filaments S-MATE
for O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
. O


Through O
twin-screw O
extrusion S-MANP
, O
four O
different O
formulations O
were O
obtained O
using O
combinations O
of O
hollow O
glass S-MATE
microspheres O
, O
nanoclay O
, O
and O
non-halogenated O
flame-retardant O
additives S-MATE
. O


These O
additives S-MATE
were O
designed S-FEAT
to O
create O
a O
material S-MATE
that O
exhibits O
low O
density S-PRO
, O
high O
char O
yield O
, O
and O
low O
flammability O
. O


Filament S-MATE
quality O
was O
characterized O
and O
reported O
. O


SiC S-MATE
particles S-CONPRI
were O
added O
in-situ S-CONPRI
during O
WAAM S-MANP
of O
an O
high B-MATE
strength I-MATE
low I-MATE
alloy I-MATE
steel E-MATE
. O


Cementite S-MATE
formed O
in O
the O
SiC-containing O
parts O
due O
to O
SiC S-MATE
dissociation O
in O
the O
melt B-MATE
pool E-MATE
. O


Non-melted O
SiC S-MATE
particles S-CONPRI
acted O
as S-MATE
nucleating O
agents O
promoting O
grain B-CHAR
refinement E-CHAR
. O


Improved O
mechanical B-CONPRI
properties E-CONPRI
were O
obtained O
upon O
the O
use O
of O
SiC S-MATE
. O


In O
this O
work O
, O
SiC S-MATE
particles S-CONPRI
were O
added O
to O
the O
molten B-CONPRI
pool E-CONPRI
during O
WAAM S-MANP
of O
a O
high B-MATE
strength I-MATE
low I-MATE
alloy I-MATE
steel E-MATE
. O


The O
introduction O
of O
these O
high O
melting B-PRO
point E-PRO
particles O
promoted O
grain B-CHAR
refinement E-CHAR
, O
and O
the O
precipitation S-CONPRI
of O
Fe3C O
due O
to O
SiC S-MATE
dissociation O
. O


The O
microstructural B-CONPRI
evolution E-CONPRI
was O
studied O
by O
optical S-CHAR
and O
electron B-CHAR
microscopy E-CHAR
techniques O
and O
high O
energy O
synchrotron S-ENAT
X-ray O
diffraction S-CHAR
. O


Additionally O
, O
mechanical B-CHAR
testing E-CHAR
and O
hardness S-PRO
profiles O
were O
obtained O
for O
the O
SiC-containing O
and O
SiC-free O
parts O
. O


An O
improvement O
in O
the O
mechanical B-PRO
strength E-PRO
of O
the O
SiC-added O
WAAM S-MANP
parts O
was O
observed O
, O
which O
was O
attributed O
to O
the O
refined O
grain B-CONPRI
structure E-CONPRI
and O
finely O
dispersed O
Fe3C O
. O


The O
present O
study O
systematically O
investigated O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
wire-based O
( O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
, O
known O
as S-MATE
WAAM O
) O
deposition S-CONPRI
of O
steel B-MATE
metals E-MATE
, O
both O
stainless B-MATE
steel E-MATE
304 O
and O
mild B-MATE
steel E-MATE
ER70S O
. O


Graded O
material B-CONPRI
properties E-CONPRI
of O
stainless B-MATE
steel E-MATE
304 O
were O
observed O
for O
wear S-CONPRI
and O
hardness S-PRO
in O
the O
direction O
of O
deposition S-CONPRI
and O
in O
Z O
height O
, O
due O
to O
variations S-CONPRI
in O
local O
thermal O
histories O
of O
the O
metal S-MATE
. O


The O
yield O
and O
ultimate B-PRO
strength E-PRO
, O
however O
, O
were O
not O
found O
to O
be S-MATE
statistically O
significantly O
different O
( O
p S-MATE
= O
0.55 O
) O
along O
the O
direction O
of O
deposition S-CONPRI
for O
SS304 O
. O


During O
wear S-CONPRI
testing S-CHAR
, O
a O
grain B-CHAR
refinement E-CHAR
was O
observed O
directly O
beneath O
the O
wear S-CONPRI
scar O
in O
these O
materials S-CONPRI
in O
a O
focused O
ion S-CONPRI
beam S-MACEQ
channel O
observed O
under O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
. O


Additionally O
, O
no O
significant O
difference O
in O
yield B-PRO
strength E-PRO
was O
observed O
in O
printed O
mild B-MATE
steel E-MATE
( O
ER70S O
) O
between O
vertical S-CONPRI
and O
horizontal B-BIOP
specimens E-BIOP
. O


The O
observed O
graded O
mechanical B-CONPRI
properties E-CONPRI
in O
stainless B-MATE
steel E-MATE
304 O
allow O
the O
opportunity O
for O
varying O
the O
processing O
conditions O
to O
design S-FEAT
parts O
with O
locally O
optimized O
or O
functionally B-CONPRI
graded E-CONPRI
mechanical O
properties S-CONPRI
. O


Lattice B-FEAT
structures E-FEAT
are O
frequently O
found O
in O
nature O
and O
engineering S-APPL
due O
to O
their O
myriad O
attractive O
properties S-CONPRI
, O
with O
applications O
ranging O
from O
molecular O
to O
architectural O
scales O
. O


Lattices S-CONPRI
have O
also O
become O
a O
key O
concept O
in O
additive B-MANP
manufacturing E-MANP
, O
which O
enables O
precise B-MANP
fabrication E-MANP
of O
complex O
lattices S-CONPRI
that O
would O
not O
be S-MATE
possible O
otherwise O
. O


While O
design S-FEAT
and O
simulation S-ENAT
tools O
for O
stiff O
lattices S-CONPRI
are O
common O
, O
here O
we O
present O
a O
digital O
design S-FEAT
and O
nonlinear O
simulation S-ENAT
approach O
for O
additive B-MANP
manufacturing E-MANP
of O
soft O
lattices S-CONPRI
structures O
subject O
to O
large O
deformations S-CONPRI
and O
instabilities O
, O
for O
which O
applications O
in O
soft B-APPL
robotics E-APPL
, O
healthcare O
, O
personal O
protection O
, O
energy B-CHAR
absorption E-CHAR
, O
fashion S-CONPRI
and O
design S-FEAT
are O
rapidly O
emerging O
. O


Our O
framework S-CONPRI
enables O
design S-FEAT
of O
soft O
lattices S-CONPRI
with O
curved O
members O
conforming O
to O
freeform B-CONPRI
geometries E-CONPRI
, O
and O
with O
variable O
, O
gradually O
changing O
member O
thickness O
and O
material S-MATE
, O
allowing O
the O
local O
control O
of O
stiffness S-PRO
. O


We O
model S-CONPRI
the O
lattice S-CONPRI
members O
as S-MATE
3D S-CONPRI
curved O
rods O
and O
using O
a O
spline-based O
isogeometric O
method O
that O
allows O
the O
efficient O
simulation S-ENAT
of O
nonlinear O
, O
large O
deformation S-CONPRI
behavior O
of O
these O
structures O
directly O
from O
the O
CAD S-ENAT
geometries O
. O


Furthermore O
, O
we O
enhance O
the O
formulation O
with O
a O
new O
joint S-CONPRI
stiffening O
approach O
, O
which O
is O
based O
on O
parameters S-CONPRI
derived O
from O
the O
actual O
node O
geometries S-CONPRI
. O


Simulation S-ENAT
results O
are O
verified O
against O
experiments O
with O
soft O
lattices S-CONPRI
realized O
by O
PolyJet B-CONPRI
multi-material E-CONPRI
polymer O
3D B-MANP
printing E-MANP
, O
highlighting O
the O
potential O
for O
simulation-driven S-ENAT
, O
digital O
design S-FEAT
and O
application O
of O
non-uniform O
and O
curved O
soft O
lattice B-FEAT
structures E-FEAT
. O


Premelting O
electron O
beam-assisted O
freeform B-MANP
fabrication E-MANP
( O
PEBF3 O
) O
method O
is O
proposed O
for O
the O
first O
time O
. O


Al S-MATE
and O
Ti S-MATE
are O
joined O
by O
PEBF3 O
with O
no O
defects S-CONPRI
. O


Meanwhile O
, O
TiAl3 O
reinforced S-CONPRI
aluminum S-MATE
matrix O
composites S-MATE
are O
obtained O
. O


TiAl3 O
reinforced S-CONPRI
aluminum S-MATE
matrix O
composites S-MATE
have O
better O
wear B-PRO
resistance E-PRO
than O
aluminum B-MATE
alloy E-MATE
with O
no O
TiAl3 O
. O


The O
reasons O
for O
the O
friction S-CONPRI
coefficient O
of O
the O
deposition S-CONPRI
with O
TiAl3 O
changes O
periodically O
are O
explained O
and O
verified O
. O


Premelting O
electron O
beam-assisted O
freeform B-MANP
fabrication E-MANP
, O
as S-MATE
a O
new O
method O
to O
avoid O
the O
direct O
coupling O
of O
wire-beam-molten O
pool O
during O
electron B-MANP
beam I-MANP
freeform I-MANP
fabrication E-MANP
, O
is O
proposed O
for O
the O
first O
time O
. O


The O
three O
factors O
referring O
to O
wire O
, O
beam S-MACEQ
and O
molten B-CONPRI
pool E-CONPRI
, O
are O
decomposed O
into O
two O
factors O
as S-MATE
wire O
and O
beam S-MACEQ
. O


The O
liquid B-MATE
metal E-MATE
is O
formed O
in O
the O
diversion O
nozzle S-MACEQ
, O
as S-MATE
the O
wire O
is O
heated O
and O
melted S-CONPRI
inside O
it O
by O
an O
electron B-CONPRI
beam E-CONPRI
, O
and O
, O
subsequently O
, O
is O
transferred O
to O
the O
substrate S-MATE
with O
solidification B-MANP
process E-MANP
. O


Finally O
, O
a O
continuous O
and O
stable O
process S-CONPRI
of O
premelting O
electron O
beam-assisted O
freeform B-MANP
fabrication E-MANP
is O
achieved O
. O


When O
an O
aluminum B-MATE
alloy E-MATE
was O
deposited O
on O
a O
TC4 O
substrate S-MATE
by O
premelting O
electron O
beam-assisted O
freeform B-MANP
fabrication E-MANP
, O
the O
TC4 O
base B-MATE
metal E-MATE
did O
not O
melt S-CONPRI
because O
the O
electron B-CONPRI
beam E-CONPRI
did O
not O
directly O
act O
on O
the O
TC4 O
substrate S-MATE
. O


There O
is O
no O
stirring O
of O
the O
electron B-CONPRI
beam E-CONPRI
inside O
the O
liquid O
deposition S-CONPRI
body O
, O
and O
the O
dissolution O
and O
diffusion S-CONPRI
of O
elemental O
Ti S-MATE
exists O
, O
which O
ensures O
the O
effective O
connection O
between O
the O
deposition S-CONPRI
and O
the O
TC4 O
substrate S-MATE
. O


Although O
TiAl3 O
intermetallic B-MATE
compounds E-MATE
were O
generated O
in O
the O
deposition S-CONPRI
, O
the O
interface S-CONPRI
between O
TiAl3 O
and O
the O
Al S-MATE
matrix O
was O
coherent O
, O
as S-MATE
( O
101 O
) O
TiAl3// O
( O
020 O
) O
Al S-MATE
was O
clearly O
detected O
in O
the O
center O
of O
the O
deposition S-CONPRI
. O


There O
are O
no O
cracks O
or O
other O
defects S-CONPRI
in O
the O
deposition S-CONPRI
. O


The O
acicular O
TiAl3 O
intermetallic B-MATE
compounds E-MATE
are O
dispersed O
in O
the O
deposition S-CONPRI
, O
which O
improves O
the O
wear B-PRO
resistance E-PRO
of O
the O
deposition S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
enables O
production S-MANP
of O
geometrically-complex S-CONPRI
elastomeric O
structures O
. O


The O
elastic B-CONPRI
recovery E-CONPRI
and O
strain-rate O
dependence O
of O
these O
materials S-CONPRI
means O
they O
are O
ideal O
for O
use O
in O
dynamic S-CONPRI
, O
repetitive O
mechanical B-CONPRI
loading E-CONPRI
. O


Their O
process-dependence O
, O
and O
the O
frequent O
emergence O
of O
new O
AM S-MANP
elastomers O
, O
commonly O
necessitates O
full O
material S-MATE
characterisation O
; O
however O
, O
accessing O
specialised O
equipment S-MACEQ
means O
this O
is O
often O
a O
time-consuming O
and O
expensive O
process S-CONPRI
. O


This O
work O
presents O
an O
innovative O
equi-biaxial O
rig O
that O
enables O
full O
characterisation O
via O
a O
conventional O
material S-MATE
testing O
machine S-MACEQ
( O
supplementing O
uni-axial O
tension O
and O
planar O
tension B-CHAR
tests E-CHAR
) O
. O


Combined O
with O
stress B-CONPRI
relaxation E-CONPRI
data S-CONPRI
, O
this O
provides O
a O
novel O
route O
for O
hyperelastic O
material S-MATE
modelling O
with O
viscoelastic S-PRO
components S-MACEQ
. O


This O
approach O
was O
validated O
by O
recording O
the O
force-displacement O
and O
deformation S-CONPRI
histories O
from O
finite B-CHAR
element I-CHAR
modelling E-CHAR
a O
honeycomb B-FEAT
structure E-FEAT
. O


These O
data S-CONPRI
compared O
favourably O
to O
experimental S-CONPRI
quasistatic O
and O
dynamic S-CONPRI
compression S-PRO
testing O
, O
validating O
this O
novel O
and O
convenient O
route O
for O
characterising O
complex O
elastomeric O
materials S-CONPRI
. O


Supported O
by O
data S-CONPRI
describing O
the O
potential O
for O
high O
build-quality O
production S-MANP
using O
an O
AM B-MANP
process E-MANP
with O
low O
barriers O
to O
entry O
, O
this O
study O
should O
serve O
to O
encourage O
greater O
exploitation O
of O
this O
emerging O
manufacturing B-MANP
process E-MANP
for O
fabricating S-MANP
elastomeric O
structures O
within O
industrial S-APPL
communities O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
allows O
for O
layer-by-layer S-CONPRI
fabrication S-MANP
of O
complex O
metallic B-MACEQ
parts E-MACEQ
with O
features O
typically O
unobtainable O
via O
conventional B-MANP
manufacturing E-MANP
. O


For O
heat B-MACEQ
exchangers E-MACEQ
, O
such O
complex O
features O
are O
desirable O
for O
enhancing O
their O
heat B-CONPRI
transfer E-CONPRI
capability O
and O
conformability O
to O
specific O
applications O
. O


In O
this O
case B-CONPRI
study E-CONPRI
, O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
, O
a O
laser-based B-MANP
additive I-MANP
manufacturing E-MANP
process O
, O
was O
utilized O
to O
fabricate S-MANP
a O
compact S-MANP
( O
5.08 O
cm O
× O
3.81 O
cm O
× O
1.58 O
cm O
) O
flat-plate O
oscillating O
heat S-CONPRI
pipe O
( O
FP-OHP O
) O
with O
innovative O
design S-FEAT
features O
, O
including O
a O
Ti–6Al–4V O
casing O
and O
a O
closed-loop O
, O
circular O
mini-channel O
( O
1.53 O
mm S-MANP
in O
diameter S-CONPRI
) O
consisting O
of O
four O
interconnected O
layers O
. O


Venting O
holes O
were O
integrated O
to O
intersect O
each O
layer S-PARA
to O
allow O
for O
a O
unique O
layer-by-layer S-CONPRI
, O
plug-and-pressurize O
de-powdering S-PRO
procedure O
. O


The O
device O
channel S-APPL
surface O
was O
inspected O
via O
Scanning B-CHAR
Electron I-CHAR
Microscopy E-CHAR
( O
SEM S-CHAR
) O
– O
and O
it O
was O
found O
that O
the O
channel S-APPL
wall O
consisted O
of O
partially O
un-melted O
particles S-CONPRI
, O
as S-MATE
well O
as S-MATE
amorphous O
melt S-CONPRI
regions O
; O
surface S-CONPRI
characteristics O
influential O
on O
surface/fluid O
capillarity O
and O
heat B-CONPRI
transfer E-CONPRI
. O


This O
study O
also O
highlights O
important O
design S-FEAT
and O
manufacturing S-MANP
concerns O
encountered O
during O
SLM S-MANP
of O
channel-embedded O
parts O
, O
such O
as S-MATE
channel O
surface B-PARA
quality E-PARA
and O
de-powdering S-PRO
. O


The O
Ti–6Al–4V O
FP-OHP O
was O
found O
to O
operate O
successfully O
with O
an O
effective B-PARA
thermal I-PARA
conductivity E-PARA
of O
approximately O
110 O
W/m O
K S-MATE
at O
a O
power S-PARA
input O
of O
50 O
W O
; O
demonstrating O
a O
400–500 O
% O
increase O
relative O
to O
solid O
Ti–6Al–4V O
. O


This O
paper O
addresses O
a O
comprehensive O
analytical O
model S-CONPRI
for O
the O
laser S-ENAT
powder-fed O
additive B-MANP
manufacturing E-MANP
( O
LPF-AM O
) O
process S-CONPRI
, O
also O
known O
as S-MATE
directed O
energy O
deposition S-CONPRI
AM S-MANP
. O


The O
model S-CONPRI
analytically O
couples O
the O
moving O
laser B-CONPRI
beam E-CONPRI
with O
Gaussian S-CONPRI
energy O
distribution S-CONPRI
, O
the O
powder S-MATE
stream O
and O
the O
semi-infinite O
substrate S-MATE
together O
, O
while O
considering O
the O
attenuated O
laser B-PARA
power E-PARA
intensity O
distribution S-CONPRI
, O
the O
heated O
powder S-MATE
spatial O
distribution S-CONPRI
and O
the O
melt B-MATE
pool E-MATE
3D S-CONPRI
shape O
with O
its O
boundary S-FEAT
variation O
. O


The O
particles S-CONPRI
concentration O
on O
transverse O
plane O
is O
modeled O
with O
Gaussian S-CONPRI
distribution S-CONPRI
based O
on O
optical B-CHAR
measurement E-CHAR
. O


The O
model S-CONPRI
can O
effectively O
be S-MATE
used O
for O
process S-CONPRI
development/optimization O
and O
controller S-MACEQ
design O
, O
while O
predicting O
adequate O
clad O
geometry S-CONPRI
as S-MATE
well O
as S-MATE
the O
catchment O
efficiency O
rapidly O
. O


Experimental S-CONPRI
validation O
through O
the O
deposition S-CONPRI
of O
Inconel B-MATE
625 E-MATE
proves O
the O
model S-CONPRI
can O
accurately S-CHAR
predict O
the O
clad O
geometry S-CONPRI
and O
catchment O
efficiency O
in O
the O
range S-PARA
of O
specific B-PRO
energy E-PRO
that O
is O
corresponding O
to O
high O
clad O
quality S-CONPRI
( O
maximum O
percentage O
difference O
is O
6.2 O
% O
for O
clad O
width O
, O
7.8 O
% O
for O
clad O
height O
and O
6.8 O
% O
for O
catchment O
efficiency O
) O
. O


To O
produce O
complex O
functional O
devices O
while O
eliminating O
the O
need O
for O
assembly S-MANP
calls O
for O
a O
multi-material B-MANP
additive I-MANP
manufacturing E-MANP
technology O
. O


This O
paper O
presented O
a O
3D-printing S-MANP
system O
that O
integrated O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
and O
laser-based O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
to O
produce O
hybrid O
metal S-MATE
and O
polymer S-MATE
components S-MACEQ
. O


PBF-printed O
metal S-MATE
and O
FFF-printed O
polymer S-MATE
, O
both O
of O
which O
differ O
in O
material B-CONPRI
properties E-CONPRI
, O
were O
joined O
through O
PBF-printed O
interlocking O
structures O
, O
with O
their O
joining S-MANP
strength O
enhanced O
by O
laser S-ENAT
heating S-MANP
. O


Tensile S-PRO
and O
shear B-CHAR
tests E-CHAR
confirmed O
good O
joint S-CONPRI
strength O
of O
the O
printed O
metal/polymer O
components S-MACEQ
, O
which O
were O
created O
without O
adhesives S-MATE
. O


In O
addition O
, O
metal B-MATE
powder E-MATE
deposition S-CONPRI
onto O
the O
top O
of O
polymer S-MATE
substrates O
through O
laser S-ENAT
melting O
was O
demonstrated O
. O


Finally O
, O
several O
3D S-CONPRI
components O
consisting O
of O
hybrid O
stainless B-MATE
steel E-MATE
( O
SS S-MATE
316L O
) O
, O
copper S-MATE
( O
Cu10Sn O
) O
and O
polymer S-MATE
( O
PLA S-MATE
, O
PET O
) O
were O
successfully O
printed O
and O
their O
potential O
applications O
were O
discussed O
. O


Depending O
on O
the O
available O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
system O
, O
and O
the O
intended O
application O
, O
the O
use O
of O
highly-optimized O
LPBF S-MANP
parameters O
to O
fabricate S-MANP
near-perfect O
density S-PRO
alloys S-MATE
may O
not O
be S-MATE
feasible O
, O
economical O
or O
required O
. O


Thus O
, O
it O
is O
important O
to O
understand O
how O
sub-optimal O
density S-PRO
and O
microstructure S-CONPRI
can O
simultaneously O
affect O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
alloys S-MATE
. O


Here O
we O
study O
the O
microstructure S-CONPRI
and O
properties S-CONPRI
of O
an O
AlSi10Mg B-MATE
alloy E-MATE
fabricated O
with O
sub-optimal O
parameters S-CONPRI
and O
investigate O
the O
effectiveness S-CONPRI
of O
post-processing S-CONPRI
by O
hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
and O
T6 O
heat B-MANP
treatment E-MANP
. O


Defects S-CONPRI
were O
characterized O
using O
micro-computed B-CHAR
tomography E-CHAR
while O
the O
microstructure S-CONPRI
was O
analysed O
using O
transmission S-CHAR
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
. O


The O
as-built O
microstructure S-CONPRI
features O
dendritically-arranged O
nano-crystalline O
Si S-MATE
particles S-CONPRI
that O
are O
favourable O
for O
high O
hardness S-PRO
, O
strength S-PRO
and O
impact S-CONPRI
toughness O
while O
T6 O
generally O
caused O
these O
properties S-CONPRI
to O
degrade O
. O


HIP S-MANP
was O
unable O
to O
close O
large O
defects S-CONPRI
due O
to O
trapped O
gases O
, O
which O
limited O
fatigue B-PRO
life E-PRO
improvements O
. O


Defects S-CONPRI
oriented O
normal O
to O
the O
loading O
axis O
( O
or O
parallel O
to O
the O
fracture S-CONPRI
plane O
) O
are O
very O
detrimental O
, O
but O
when O
oriented O
favourably O
, O
the O
alloy S-MATE
was O
still O
able O
to O
achieve O
comparable O
strength S-PRO
and O
ductility S-PRO
to O
results O
reported O
in O
literature O
for O
LPBF-fabricated O
AlSi10Mg B-MATE
alloys E-MATE
. O


Interestingly O
, O
the O
anisotropic S-PRO
nano-crystalline O
Si S-MATE
structures O
of O
the O
as-built O
alloy S-MATE
resulted O
in O
substantially O
improved O
toughness S-PRO
even O
when O
defects S-CONPRI
were O
oriented O
unfavourably O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
are O
being O
frequently O
used O
in O
industry S-APPL
as S-MATE
they O
allow O
the O
manufacture S-CONPRI
of O
complex O
parts O
with O
reduced O
lead B-PARA
times E-PARA
. O


Electron O
beam-powder O
bed B-MANP
fusion E-MANP
( O
EB-PBF O
) O
as S-MATE
an O
AM B-MANP
technology E-MANP
is O
known O
for O
its O
near-net-shape S-MANP
production O
capacity S-CONPRI
with O
low O
residual B-PRO
stress E-PRO
. O


However O
, O
the O
surface B-PARA
quality E-PARA
and O
geometrical O
accuracy S-CHAR
of O
the O
manufactured S-CONPRI
parts O
are O
major O
obstacles O
for O
the O
wider O
industrial S-APPL
adoption O
of O
this O
technology S-CONPRI
, O
especially O
when O
enhanced O
mechanical S-APPL
performance O
is O
taken O
into O
consideration O
. O


Identifying O
the O
origins O
of O
surface S-CONPRI
features O
such O
as S-MATE
satellite O
particles S-CONPRI
and O
sharp O
valleys O
on O
the O
parts O
manufactured S-CONPRI
by O
EB-PBF O
is O
important O
for O
a O
better O
understanding O
of O
the O
process S-CONPRI
and O
its O
capability O
. O


Moreover O
, O
understanding O
the O
influence O
of O
the O
contour S-FEAT
melting O
strategy O
, O
by O
altering O
process B-CONPRI
parameters E-CONPRI
, O
on O
the O
surface B-PRO
roughness E-PRO
of O
the O
parts O
and O
the O
number O
of O
near-surface O
defects S-CONPRI
is O
highly O
critical O
. O


In O
this O
study O
, O
processing O
parameters S-CONPRI
of O
the O
EB-PBF O
technique O
such O
as S-MATE
scanning O
speed O
, O
beam S-MACEQ
current O
, O
focus O
offset S-CONPRI
, O
and O
number O
of O
contours S-FEAT
( O
one O
or O
two O
) O
with O
the O
linear O
melting S-MANP
strategy O
were O
investigated O
. O


A O
sample S-CONPRI
manufactured S-CONPRI
using O
Arcam-recommended O
process B-CONPRI
parameters E-CONPRI
( O
three O
contours S-FEAT
with O
the O
spot O
melting S-MANP
strategy O
) O
was O
used O
as S-MATE
a O
reference O
. O


For O
the O
samples S-CONPRI
with O
one O
contour S-FEAT
, O
the O
scanning B-PARA
speed E-PARA
had O
the O
greatest O
effect O
on O
the O
arithmetical O
mean O
height O
( O
Sa O
) O
, O
and O
for O
the O
samples S-CONPRI
with O
two O
contours S-FEAT
, O
the O
beam S-MACEQ
current O
and O
focus O
offset S-CONPRI
had O
the O
greatest O
effect O
. O


For O
the O
samples S-CONPRI
with O
two O
contours S-FEAT
, O
a O
lower O
focus O
offset S-CONPRI
and O
lower O
scan B-PARA
speed E-PARA
( O
at O
a O
higher O
beam S-MACEQ
current O
) O
resulted O
in O
a O
lower O
Sa O
; O
however O
, O
increasing O
the O
scan B-PARA
speed E-PARA
for O
the O
samples S-CONPRI
with O
one O
contour S-FEAT
decreased O
Sa O
. O


In O
general O
, O
the O
samples S-CONPRI
with O
two O
contours S-FEAT
provided O
a O
lower O
Sa O
( O
∼22 O
% O
) O
but O
with O
slightly O
higher O
porosity S-PRO
( O
∼8 O
% O
) O
compared O
to O
the O
samples S-CONPRI
with O
one O
contour S-FEAT
. O


Fewer O
defects S-CONPRI
were O
detected O
with O
a O
lower O
scanning B-PARA
speed E-PARA
and O
higher O
beam S-MACEQ
current O
. O


The O
number O
of O
defects S-CONPRI
and O
the O
Sa O
value O
for O
the O
samples S-CONPRI
with O
two O
contours S-FEAT
manufactured O
using O
the O
linear O
melting S-MANP
strategy O
were O
∼85 O
% O
and O
16 O
% O
, O
respectively O
, O
lower O
than O
those O
of O
the O
reference O
samples B-CONPRI
manufactured E-CONPRI
using O
the O
spot O
melting S-MANP
strategy O
. O


Given O
the O
attention O
around O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
organizations O
want O
to O
know O
if O
their O
products O
should O
be S-MATE
fabricated O
using O
AM S-MANP
. O


To O
facilitate O
product B-CONPRI
development E-CONPRI
decisions O
, O
a O
reference O
system O
is O
shown O
describing O
the O
key O
attributes O
of O
a O
product O
from O
a O
manufacturability S-CONPRI
stand-point O
: O
complexity S-CONPRI
, O
customization O
, O
and O
production S-MANP
volume O
. O


A O
geometric O
complexity S-CONPRI
factor O
developed O
for O
cast S-MANP
parts O
is O
modified O
for O
a O
more O
general O
application O
. O


Parts O
with O
varying O
geometric O
complexity S-CONPRI
are O
then O
analyzed O
and O
mapped O
into O
regions O
of O
the O
complexity S-CONPRI
, O
customization O
, O
and O
production S-MANP
volume O
model S-CONPRI
. O


Implications O
for O
product B-CONPRI
development E-CONPRI
and O
manufacturing S-MANP
business O
approaches O
are O
discussed O
. O


Rod S-MACEQ
shaped O
samples S-CONPRI
of O
AlSi10Mg S-MATE
additively B-MANP
manufactured E-MANP
using O
recycled S-CONPRI
powder S-MATE
through O
direct B-MANP
metal I-MANP
laser I-MANP
sintering E-MANP
( O
DMLS S-MANP
) O
process S-CONPRI
showed O
higher O
quasi-static S-CONPRI
uniaxial O
tensile B-PRO
strength E-PRO
in O
both O
horizontal O
and O
vertical S-CONPRI
build B-PARA
directions E-PARA
than O
those O
of O
cast S-MANP
counterpart O
alloy S-MATE
. O


In O
addition O
, O
they O
offered O
mechanical B-CONPRI
properties E-CONPRI
within O
the O
range S-PARA
of O
other O
additively B-MANP
manufactured E-MANP
counterparts O
. O


TEM S-CHAR
showed O
that O
the O
microstructure S-CONPRI
of O
the O
as-built O
samples S-CONPRI
comprised O
of O
cell-like O
structures O
featured O
by O
dislocation S-CONPRI
networks O
and O
Si S-MATE
precipitates S-MATE
. O


HRTEM S-CHAR
studies O
revealed O
the O
semi-coherency O
characteristics O
of O
the O
Si S-MATE
precipitates S-MATE
. O


After O
deformation S-CONPRI
, O
the O
dislocation B-PRO
density E-PRO
increased O
as S-MATE
a O
result O
of O
generation O
of O
new O
dislocations S-CONPRI
due O
to O
dislocation B-CONPRI
motion E-CONPRI
. O


The O
dislocations S-CONPRI
bypassed O
the O
precipitates S-MATE
by O
bowing O
around O
them O
and O
penetrating O
the O
semi-coherent O
precipitates S-MATE
. O


Strengthening S-MANP
of O
recycled S-CONPRI
DMLS-AlSi10Mg O
alloys S-MATE
manufactured O
in O
both O
directions O
was O
attributed O
to O
Orowan O
mechanism S-CONPRI
( O
due O
to O
existence O
of O
Si S-MATE
precipitates S-MATE
) O
, O
Hall-Petch O
effect O
( O
due O
to O
eutectic S-CONPRI
cell S-APPL
walls O
) O
, O
and O
dislocation S-CONPRI
hardening O
( O
due O
to O
pre-existing O
dislocation S-CONPRI
networks O
) O
. O


Due O
to O
the O
slightly O
different O
microstructure S-CONPRI
, O
the O
contribution O
of O
each O
strengthening B-CONPRI
mechanism E-CONPRI
was O
slightly O
different O
in O
identical O
samples S-CONPRI
made O
with O
virgin B-MATE
powder E-MATE
. O


Three O
different O
AlSi10Mg_200C O
samples S-CONPRI
with O
near O
optimum O
process B-CONPRI
parameters E-CONPRI
were O
built O
. O


AlSi10Mg_200C O
samples S-CONPRI
with O
very O
low O
surface B-PRO
roughness E-PRO
were O
produced O
. O


AlSi10Mg_200C O
samples S-CONPRI
also O
possessed O
very O
low O
porosity S-PRO
levels O
. O


OM S-CHAR
and O
SEM S-CHAR
Microscopy S-CHAR
analyses O
were O
performed O
to O
investigate O
causality O
. O


Laser S-ENAT
sintered O
aluminum B-MATE
alloys E-MATE
produced O
by O
metal S-MATE
3D B-MACEQ
printers E-MACEQ
can O
replace O
cast B-MATE
aluminum I-MATE
alloys E-MATE
in O
aerospace S-APPL
, O
defense O
, O
and O
marine B-APPL
industries E-APPL
by O
offering O
better O
mechanical B-CONPRI
properties E-CONPRI
, O
less O
porosity S-PRO
, O
and O
competitive O
fatigue S-PRO
characteristics O
. O


One O
of O
the O
major O
issues O
currently O
is O
the O
considerable O
surface B-PRO
roughness E-PRO
of O
additively B-MANP
manufactured E-MANP
aluminum O
alloys S-MATE
demanding O
post-processing S-CONPRI
procedures O
such O
as S-MATE
bead O
blasting O
or O
machining S-MANP
. O


In O
the O
current O
study O
, O
the O
process B-CONPRI
parameters E-CONPRI
such O
as S-MATE
laser O
power S-PARA
, O
scan B-PARA
speed E-PARA
, O
and O
hatch B-PARA
spacing E-PARA
were O
altered O
such O
that O
better O
surface B-PRO
roughness E-PRO
could O
be S-MATE
achieved O
for O
AlSi10Mg_200C O
using O
a O
Direct B-MANP
Metal I-MANP
Laser I-MANP
Sintering E-MANP
( O
DMLS S-MANP
) O
system O
. O


The O
process B-CONPRI
parameters E-CONPRI
were O
chosen O
such O
that O
three O
samples S-CONPRI
with O
the O
same O
core S-MACEQ
properties O
but O
different O
upskin O
characteristics O
were O
produced O
. O


The O
achieved O
surface B-PRO
roughness E-PRO
of O
the O
additively B-MANP
manufactured E-MANP
aluminum O
samples S-CONPRI
were O
almost O
as S-MATE
low O
as S-MATE
one O
fifth O
of O
the O
regular O
samples B-CONPRI
manufactured E-CONPRI
using O
standard S-CONPRI
process B-CONPRI
parameters E-CONPRI
. O


The O
microstructure S-CONPRI
and O
the O
porosity S-PRO
level O
of O
the O
samples S-CONPRI
printed O
by O
different O
process B-CONPRI
parameters E-CONPRI
were O
studied O
to O
reveal O
the O
causality O
of O
the O
low O
surface B-PRO
roughness E-PRO
for O
the O
proposed O
process S-CONPRI
. O


Large-scale O
polymer S-MATE
AM S-MANP
is O
very O
susceptible O
to O
part O
failure S-CONPRI
due O
to O
thermal O
warping S-CONPRI
. O


A O
1D O
heat B-CONPRI
transfer E-CONPRI
model O
can O
predict O
the O
temperature S-PARA
evolution S-CONPRI
of O
thin O
walls O
. O


Parameter S-CONPRI
studies O
provide O
guidance O
for O
minimizing O
the O
likelihood O
of O
build B-CHAR
failure E-CHAR
. O


Higher O
thermal B-PRO
conductivity E-PRO
is O
shown O
to O
be S-MATE
detrimental O
to O
the O
success O
of O
the O
build S-PARA
. O


The O
incremental O
deposition B-MANP
process E-MANP
utilized O
by O
most O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
presents O
significant O
challenges O
related O
to O
residual B-PRO
stresses E-PRO
and O
warping S-CONPRI
which O
arise O
from O
repeated O
deposition S-CONPRI
of O
hot O
material S-MATE
onto O
cooler O
material S-MATE
. O


In O
this O
work O
we O
investigate O
the O
thermal O
evolution S-CONPRI
in O
thin O
walls O
of O
carbon S-MATE
fiber/acrylonitrile O
butadiene O
styrene O
( O
CF/ABS O
) O
composite B-MATE
materials E-MATE
fabricated O
via O
Big O
Area S-PARA
Additive B-MANP
Manufacturing E-MANP
( O
BAAM O
) O
. O


We O
measure O
the O
thermal O
evolution S-CONPRI
of O
composite S-MATE
parts O
during O
the O
build S-PARA
process O
using O
infrared S-CONPRI
imaging S-APPL
, O
and O
develop O
a O
simple S-MANP
1D O
transient S-CONPRI
thermal O
model S-CONPRI
to O
describe O
the O
build S-PARA
process O
. O


The O
model S-CONPRI
predictions O
are O
in O
excellent O
agreement O
with O
the O
observed O
temperature S-PARA
profiles S-FEAT
and O
from O
the O
results O
we O
develop O
criteria O
to O
guide O
deposition S-CONPRI
parameter O
selection O
to O
minimize O
the O
likelihood O
of O
cracking S-CONPRI
during O
printing O
. O


Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
was O
used O
to O
produce O
3D-printed S-MANP
net O
shape O
NdFeB O
( O
Neodymium S-MATE
Iron B-MATE
Boron E-MATE
) O
permanent B-MATE
magnets E-MATE
that O
exhibit O
relatively O
large O
internal O
permanent O
magnetization O
structures O
, O
without O
exposure S-CONPRI
to O
any O
external O
magnetizing O
field O
. O


The O
permanent O
magnetization O
can O
be S-MATE
detected O
via O
the O
stray O
field O
that O
appears O
after O
cutting S-MANP
the O
sample S-CONPRI
into O
pieces O
. O


Maximum O
magnetic O
flux S-MATE
densities O
of O
almost O
80 O
mT O
are O
recorded O
1 O
mm S-MANP
above O
the O
cut O
surfaces S-CONPRI
in O
the O
air O
. O


Dependencies O
of O
the O
effect O
on O
SLM S-MANP
process B-CONPRI
parameters E-CONPRI
, O
as S-MATE
well O
as S-MATE
on O
the O
sample B-CONPRI
size E-CONPRI
and O
shape O
are O
discussed O
. O


The O
discovered O
effect O
may O
offer O
new O
routes O
for O
producing O
magnetized O
rare O
earth-transition O
metal S-MATE
( O
RE-TM O
) O
permanent B-MATE
magnets E-MATE
without O
using O
a O
magnetizer O
, O
and O
it O
shows O
that O
the O
SLM B-MANP
3D-printing E-MANP
process S-CONPRI
can O
lead S-MATE
to O
new O
material S-MATE
behavior O
. O


Thermally O
induced O
residual B-PRO
stresses E-PRO
and O
residual B-CONPRI
distortions E-CONPRI
in O
the O
additive B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
parts O
are O
two O
of O
the O
major O
obstacles O
that O
are O
preventing O
AM B-MANP
technology E-MANP
from O
gaining O
wide O
adoption O
. O


In O
this O
work O
, O
a O
three-dimensional S-CONPRI
thermo-elastic-plastic O
model S-CONPRI
is O
proposed O
to O
predict O
the O
thermomechanical S-CONPRI
behavior O
in O
the O
laser B-MANP
engineered I-MANP
net I-MANP
shaping E-MANP
( O
LENS S-MANP
) O
process S-CONPRI
of O
Ti-6Al-4V S-MATE
using O
Finite B-CONPRI
Element I-CONPRI
Method E-CONPRI
( O
FEM S-CONPRI
) O
. O


It O
is O
shown O
that O
the O
computed O
thermal O
history O
and O
mechanical S-APPL
deformations S-CONPRI
are O
in O
good O
agreement O
with O
the O
experimental S-CONPRI
measurements O
. O


The O
main O
contributions O
of O
this O
study O
are O
: O
( O
I O
) O
in O
the O
past O
, O
a O
point-wise O
comparison O
between O
simulation S-ENAT
results O
and O
experimental S-CONPRI
measurements O
is O
more O
favored O
to O
validate O
the O
employed O
model S-CONPRI
, O
where O
the O
general O
picture O
is O
lost O
; O
rather O
, O
to O
validate O
the O
proposed O
model S-CONPRI
, O
the O
simulated O
distortion S-CONPRI
of O
the O
bottom O
surface S-CONPRI
of O
a O
thin O
substrate S-MATE
is O
compared O
with O
experimental S-CONPRI
measurements O
using O
a O
3D S-CONPRI
laser O
scanner O
, O
in O
terms O
of O
both O
magnitude S-PARA
and O
distribution S-CONPRI
map O
. O


( O
II O
) O
Rather O
few O
works O
have O
been O
done O
to O
show O
the O
effectiveness S-CONPRI
of O
widely O
employed O
quasi-static B-CONPRI
mechanical I-CONPRI
analysis E-CONPRI
in O
the O
transient S-CONPRI
LENS S-MANP
process O
; O
as S-MATE
such O
, O
both O
quasi-static S-CONPRI
and O
dynamic S-CONPRI
simulations O
are O
performed O
and O
compared O
mechanically O
to O
demonstrate O
the O
validity O
of O
using O
quasi-static S-CONPRI
modeling S-ENAT
to O
save O
computational O
cost O
. O


Additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
conformal B-MACEQ
cooling I-MACEQ
channels E-MACEQ
are O
currently O
the O
state O
of O
the O
art S-APPL
for O
high O
performing O
tooling S-CONPRI
with O
reduced O
cycle O
times O
. O


This O
paper O
introduces O
the O
concept O
of O
conformal B-CONPRI
cooling E-CONPRI
layers O
which O
challenges O
the O
status O
quo O
in O
providing O
higher O
heat B-CONPRI
transfer E-CONPRI
rates O
that O
also O
provide O
less O
variation S-CONPRI
in O
tooling S-CONPRI
temperatures.The O
cooling S-MANP
layers O
are O
filled O
with O
self-supporting S-FEAT
repeatable O
unit B-CONPRI
cells E-CONPRI
that O
form O
a O
lattice S-CONPRI
throughout O
the O
cooling S-MANP
layers O
. O


The O
lattices S-CONPRI
increase O
fluid S-MATE
vorticity O
which O
improves O
convective O
heat B-CONPRI
transfer E-CONPRI
. O


Mechanical B-CHAR
testing E-CHAR
of O
the O
lattices S-CONPRI
shows O
that O
the O
design S-FEAT
of O
the O
unit B-CONPRI
cell E-CONPRI
significantly O
varies O
the O
compression S-PRO
characteristics.A O
virtual O
case B-CONPRI
study E-CONPRI
of O
the O
injection B-MANP
moulding E-MANP
of O
a O
plastic S-MATE
enclosure O
is O
used O
to O
compare O
the O
performance S-CONPRI
of O
conformal B-CONPRI
cooling E-CONPRI
layers O
with O
that O
of O
conventional O
( O
drilled O
) O
cooling B-MACEQ
channels E-MACEQ
and O
conformal O
( O
AM S-MANP
) O
cooling B-MACEQ
channels E-MACEQ
. O


The O
results O
show O
the O
conformal O
layers O
reduce O
cooling S-MANP
time O
by O
26.34 O
% O
over O
conventional B-MACEQ
cooling I-MACEQ
channels E-MACEQ
. O


A O
wide O
range S-PARA
of O
materials S-CONPRI
is O
suitable O
for O
processing O
by O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
techniques O
. O


Among O
the O
latest O
formulations O
, O
maraging B-MATE
steel E-MATE
18Ni-300 O
, O
which O
is O
a O
martensite-hardenable O
alloy S-MATE
, O
is O
often O
used O
when O
both O
high O
fracture S-CONPRI
toughness O
and O
high O
strength S-PRO
are O
required O
, O
or O
if O
dimensional O
changes O
need O
to O
be S-MATE
minimised O
. O


In O
direct O
tooling S-CONPRI
, O
18Ni-300 O
can O
be S-MATE
successfully O
employed O
in O
numerous O
applications O
, O
for O
example O
in O
the O
production S-MANP
of O
dies S-MACEQ
for O
injection B-MANP
moulding E-MANP
and O
for O
casting S-MANP
of O
aluminium B-MATE
alloys E-MATE
; O
moreover O
, O
it O
is O
particularly O
valuable O
for O
high-performance O
engineering S-APPL
parts.Even O
though O
bibliographic O
data S-CONPRI
are O
available O
on O
the O
effects O
that O
parameters S-CONPRI
, O
employed O
in O
PBF S-MANP
processes O
, O
have O
on O
the O
obtained O
density S-PRO
, O
roughness S-PRO
, O
hardness S-PRO
and O
microstructure S-CONPRI
of O
18Ni-300 O
, O
there O
is O
still O
a O
lack O
of O
knowledge O
on O
the O
fatigue B-PRO
life E-PRO
of O
PBF S-MANP
manufactured S-CONPRI
parts O
. O


This O
paper O
describes O
the O
fatigue S-PRO
behaviour O
of O
18Ni-300 O
steel S-MATE
manufactured S-CONPRI
by O
PBF S-MANP
, O
as S-MATE
compared O
by O
forging S-MANP
. O


Relevant O
negative O
effects O
of O
the O
cross-contamination S-CONPRI
of O
the O
raw B-MATE
material E-MATE
are O
originally O
identified O
in O
this O
paper O
, O
which O
emphasizes O
the O
inadequacy O
of O
current O
acceptability O
protocols S-CONPRI
for O
PBF S-MANP
powders O
. O


In O
the O
absence O
of O
contamination O
, O
endurance O
achieved O
by O
PBF S-MANP
is O
found O
equal O
to O
that O
by O
forging S-MANP
and O
consistent O
with O
tooling S-CONPRI
requirements O
as S-MATE
set O
out O
by O
industrial S-APPL
partners O
, O
based O
on O
injection B-MANP
moulding E-MANP
process O
modelling S-ENAT
. O


Metal B-MATE
powder E-MATE
bed S-MACEQ
additive B-MANP
manufacturing E-MANP
technologies O
, O
such O
as S-MATE
the O
Electron B-MANP
Beam I-MANP
Melting E-MANP
process O
, O
facilitate O
a O
high O
degree O
of O
geometric O
flexibility S-PRO
and O
have O
been O
demonstrated O
as S-MATE
useful O
production S-MANP
techniques O
for O
metallic S-MATE
parts.However O
, O
the O
EBM S-MANP
process O
is O
typically O
associated O
with O
lower O
resolutions O
and O
higher O
surface B-PRO
roughness E-PRO
compared O
to O
similar O
laser-based O
powder B-MACEQ
bed E-MACEQ
metal S-MATE
processes O
. O


In O
part O
, O
this O
difference O
is O
related O
to O
the O
larger O
powder S-MATE
size O
distribution S-CONPRI
and O
thicker O
layers O
normally O
used O
. O


As S-MATE
part O
of O
an O
effort O
to O
improve O
the O
resolution S-PARA
and O
surface B-PRO
roughness E-PRO
of O
EBM S-MANP
fabricated O
components S-MACEQ
, O
this O
study O
investigates S-CONPRI
the O
feasibility S-CONPRI
of O
fabricating S-MANP
components S-MACEQ
with O
a O
smaller O
powder S-MATE
size O
fraction S-CONPRI
and O
layer B-PARA
thickness E-PARA
( O
similar O
to O
laser S-ENAT
based O
processes S-CONPRI
) O
. O


The O
surface B-CHAR
morphology E-CHAR
, O
microstructure S-CONPRI
and O
tensile B-PRO
properties E-PRO
of O
the O
produced O
samples S-CONPRI
were O
evaluated O
. O


The O
findings O
indicate O
that O
microstructure S-CONPRI
is O
dependent O
on O
wall-thickness O
and O
that O
, O
for O
thin B-CONPRI
walled I-CONPRI
structures E-CONPRI
, O
tensile B-PRO
properties E-PRO
can O
become O
dominated O
by O
variations S-CONPRI
in O
surface B-PRO
roughness E-PRO
. O


Additive B-MANP
manufacturing E-MANP
provides O
new O
chances O
in O
the O
manufacturing S-MANP
of O
highly O
complex O
, O
mass-customized O
structures O
with O
negligible O
wastes O
. O


Binder B-MANP
jetting E-MANP
holds O
distinctive O
promise O
among O
additive B-MANP
manufacturing E-MANP
technologies O
due O
to O
its O
fast O
, O
low-cost O
manufacturing S-MANP
; O
stress-free O
structures O
with O
complex O
internal O
and O
external O
geometries S-CONPRI
; O
and O
the O
isotropic S-PRO
properties O
of O
the O
final O
printed O
parts O
. O


An O
ExOne O
binder S-MATE
jet O
3D B-MACEQ
printer E-MACEQ
is O
used O
to O
produce O
frameworks O
for O
removable O
partial O
dentures S-APPL
from O
metallic B-MATE
powder E-MATE
. O


Initially O
, O
an O
existing O
framework S-CONPRI
is O
scanned O
using O
micro-computed B-CHAR
tomography E-CHAR
and O
then O
the O
obtained O
model S-CONPRI
is O
printed O
. O


Consolidation S-CONPRI
of O
the O
printed O
parts O
is O
achieved O
with O
the O
relative B-PRO
density E-PRO
higher O
than O
99 O
% O
density S-PRO
with O
controlled O
shrinkage S-CONPRI
. O


Presented O
results O
demonstrate O
that O
binder B-MANP
jetting E-MANP
may O
be S-MATE
used O
to O
produce O
mechanically O
sound O
complex-shaped S-CONPRI
structures O
as S-MATE
shown O
here O
on O
a O
denture S-APPL
metal O
framework S-CONPRI
model O
. O


Numerical B-ENAT
simulation E-ENAT
is O
used O
to O
understand O
the O
melting S-MANP
and O
pressurization O
mechanism S-CONPRI
in O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
. O


The O
results O
show O
the O
incoming O
fiber S-MATE
melts O
axisymmetrically O
, O
forming S-MANP
a O
cone O
of O
unmelted O
material S-MATE
in O
the O
center O
surrounded O
by O
melted S-CONPRI
polymer O
. O


Details O
of O
the O
simulation S-ENAT
reveal O
that O
a O
recirculating O
vortex O
of O
melted S-CONPRI
polymer O
is O
formed O
at O
the O
fiber S-MATE
entrance O
to O
the O
hot B-MACEQ
end E-MACEQ
. O


The O
Generalized O
Newtonian B-CONPRI
Fluid E-CONPRI
( O
GNF O
) O
model S-CONPRI
was O
appropriate O
for O
simulation S-ENAT
within O
the O
region O
that O
melts O
the O
fiber S-MATE
, O
however O
, O
a O
viscoelastic S-PRO
model S-CONPRI
, O
the O
Phan-Thien-Tanner O
( O
PTT O
) O
model S-CONPRI
, O
was O
required O
to O
capture O
flow O
within O
the O
nozzle S-MACEQ
. O


This O
is O
due O
to O
the O
presence O
of O
an O
elongational O
flow O
as S-MATE
molten O
material S-MATE
transitions O
from O
the O
melting S-MANP
region O
( O
diameter S-CONPRI
of O
3 O
mm S-MANP
) O
to O
the O
nozzle S-MACEQ
at O
the O
exit O
( O
diameter S-CONPRI
of O
0.5 O
mm S-MANP
) O
. O


Increased O
manufacturing S-MANP
rates O
are O
limited O
by O
high O
pressures S-CONPRI
, O
necessitating O
more O
consideration O
in O
the O
nozzle S-MACEQ
design S-FEAT
of O
future O
FFF S-MANP
printers O
. O


A O
unique O
and O
efficient O
semi-analytic O
method O
is O
presented O
for O
quickly O
predicting O
the O
three-dimensional S-CONPRI
thermal O
field O
produced O
by O
conduction O
from O
a O
heat B-CONPRI
source E-CONPRI
moving O
along O
an O
arbitrary O
path O
. O


A O
Green O
's O
function O
approach O
is O
used O
to O
decouple O
the O
solution S-CONPRI
at O
each O
time O
step S-CONPRI
into O
the O
analytical O
source S-APPL
contribution O
and O
a O
conduction O
contribution O
. O


The O
latter O
is O
solved O
numerically O
using O
efficient O
Gaussian S-CONPRI
convolution O
algorithms S-CONPRI
. O


This O
decoupling O
allows O
for O
boundary B-CONPRI
conditions E-CONPRI
on O
side O
boundaries S-FEAT
to O
be S-MATE
satisfied O
numerically O
and O
lowers O
computational O
expenses O
by O
allowing O
calculations O
to O
be S-MATE
localized O
around O
the O
heat B-CONPRI
source E-CONPRI
. O


The O
thermal O
field O
resulting O
from O
arbitrary O
scan O
paths O
is O
constructed O
using O
analytical B-CONPRI
solutions E-CONPRI
for O
elementary O
linear O
segments O
. O


The O
results O
of O
various O
scan B-PARA
patterns E-PARA
are O
presented O
and O
successfully O
verified O
against O
finite B-CONPRI
element E-CONPRI
simulations O
. O


The O
computational O
times O
of O
predictions S-CONPRI
are O
shown O
to O
be S-MATE
faster O
than O
the O
corresponding O
finite B-CONPRI
element E-CONPRI
simulation O
by O
an O
order O
of O
magnitude S-PARA
with O
less O
than O
1 O
% O
average S-CONPRI
error O
. O


Given O
its O
ability O
to O
quickly O
predict O
the O
thermal O
history O
and O
changes O
in O
melt B-MATE
pool E-MATE
geometry S-CONPRI
due O
to O
arbitrary O
scan O
paths O
, O
this O
method O
provides O
a O
potentially O
powerful O
tool S-MACEQ
for O
exploration O
and O
optimization S-CONPRI
of O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
processes O
. O


The O
origins O
of O
nano-scale S-CONPRI
oxide O
inclusions S-MATE
in O
316 O
L O
austenitic B-MATE
stainless I-MATE
steel E-MATE
( O
SS S-MATE
) O
manufactured S-CONPRI
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
was O
investigated O
by O
quantifying O
the O
possible O
intrusion O
pathways O
of O
oxygen S-MATE
contained O
in O
the O
precursor B-MATE
powder E-MATE
, O
extraneous O
oxygen S-MATE
from O
the O
process S-CONPRI
environment O
during O
laser B-CONPRI
processing E-CONPRI
, O
and O
moisture O
contamination O
during O
powder S-MATE
handling O
and O
storage O
. O


When O
processing O
the O
fresh O
, O
as-received O
powder S-MATE
in O
a O
well-controlled O
environment O
, O
the O
oxide B-MATE
inclusions E-MATE
contained O
in O
the O
precursor B-MATE
powder E-MATE
were O
the O
primary O
contributors O
to O
the O
formation O
of O
nano-scale S-CONPRI
oxides O
in O
the O
final O
additive B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
product O
. O


These O
oxide B-MATE
inclusions E-MATE
were O
found O
to O
be S-MATE
enriched O
with O
oxygen S-MATE
getter O
elements S-MATE
like O
Si S-MATE
and O
Mn S-MATE
. O


By O
controlling O
the O
extraneous O
oxygen S-MATE
level O
in O
the O
process S-CONPRI
environment O
, O
the O
oxygen S-MATE
level O
in O
AM S-MANP
produced O
parts O
was O
found O
to O
increase O
with O
the O
extraneous O
oxygen S-MATE
level O
. O


The O
intrusion O
pathway O
of O
this O
extra O
oxygen S-MATE
was O
found O
to O
be S-MATE
dominated O
by O
the O
incorporation O
of O
spatter S-CHAR
particles S-CONPRI
into O
the O
build S-PARA
during O
processing O
. O


Moisture O
induced O
oxidation S-MANP
during O
powder S-MATE
storage O
was O
also O
found O
to O
result O
in O
a O
higher O
oxide S-MATE
density S-PRO
in O
the O
AM S-MANP
produced O
parts O
. O


SS S-MATE
316 O
L O
powder S-MATE
free O
of O
Si S-MATE
and O
Mn S-MATE
oxygen O
getters O
was O
processed S-CONPRI
in O
a O
well-controlled O
environment O
and O
resulted O
in O
a O
similar O
level O
of O
oxygen S-MATE
intrusion O
. O


Microhardness S-CONPRI
testing O
indicated O
that O
the O
oxide S-MATE
volume O
fraction S-CONPRI
increase O
from O
extraneous O
oxygen S-MATE
did O
not O
influence O
hardness S-PRO
values O
. O


However O
, O
a O
marked O
decrease O
in O
hardness S-PRO
was O
found O
for O
the O
humidified O
and O
Si-Mn O
free O
AM S-MANP
processed O
parts O
. O


Laser B-MANP
Engineered I-MANP
Net I-MANP
Shaping E-MANP
( O
LENS® O
) O
is O
a O
metal B-MANP
Additive I-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
technique O
that O
carries O
great O
potential O
for O
the O
fabrication S-MANP
and O
repair O
of O
high-integrity O
structural O
and O
engine O
components S-MACEQ
. O


Confident O
application O
of O
the O
LENS S-MANP
technique O
requires O
a O
fundamental O
understanding O
of O
the O
microstructure S-CONPRI
and O
properties S-CONPRI
of O
the O
fabricated S-CONPRI
materials O
, O
as S-MATE
well O
as S-MATE
their O
correlations O
to O
processing O
conditions O
. O


In O
this O
study O
, O
two O
alloys S-MATE
fabricated O
by O
LENS S-MANP
, O
Ti-6Al-4V S-MATE
and O
Inconel B-MATE
718 E-MATE
, O
were O
examined O
and O
compared O
to O
their O
wrought S-CONPRI
counterparts O
. O


The O
differences O
between O
low O
and O
high O
laser B-PARA
power E-PARA
fabrications O
, O
as S-MATE
well O
as S-MATE
the O
effects O
of O
various O
post-LENS O
heat B-MANP
treatments E-MANP
were O
systematically O
investigated O
and O
discussed O
. O


The O
interfacial B-MATE
bond E-MATE
strength O
between O
LENS S-MANP
depositions O
and O
substrates O
were O
also O
evaluated O
for O
repair O
purposes O
. O


The O
residual S-CONPRI
porosity S-PRO
and O
surface B-PRO
roughness E-PRO
of O
metal B-MATE
materials E-MATE
generated O
via O
additive B-MANP
manufacturing E-MANP
are O
generally O
regarded O
as S-MATE
the O
major O
influence O
factors O
on O
the O
fatigue B-PRO
strength E-PRO
. O


The O
mechanical B-CONPRI
properties E-CONPRI
of O
specimens O
out O
of O
tool S-MACEQ
steel S-MATE
1.2344 O
were O
investigated O
. O


Tensile B-PRO
strength E-PRO
and O
hardness S-PRO
achieved O
results O
in O
the O
range S-PARA
of O
conventionally O
fabricated S-CONPRI
parts O
, O
whereas O
a O
significantly O
lower O
fatigue B-PRO
strength E-PRO
was O
observed O
. O


Cracks O
were O
induced O
by O
the O
present O
cavities O
as S-MATE
well O
as S-MATE
in O
the O
steel S-MATE
matrix O
. O


Further O
investigations O
of O
the O
oxygen S-MATE
content O
showed O
a O
high O
oxygen S-MATE
content O
of O
570 O
ppm O
homogeneously O
distributed O
inside O
the O
specimens O
potentially O
limiting O
the O
strength S-PRO
of O
the O
matrix O
itself O
. O


Process B-CONPRI
monitoring E-CONPRI
in O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
a O
crucial O
component S-MACEQ
in O
the O
mission O
of O
broadening O
AM S-MANP
industrialization O
. O


However O
, O
conventional O
part O
evaluation O
and O
qualification O
techniques O
, O
such O
as S-MATE
computed O
tomography O
( O
CT S-ENAT
) O
, O
can O
only O
be S-MATE
utilized O
after O
the O
build S-PARA
is O
complete O
, O
and O
thus O
eliminate O
any O
potential O
to O
correct O
defects S-CONPRI
during O
the O
build S-PARA
process O
. O


In O
contrast O
to O
post-build O
CT S-ENAT
, O
in B-CONPRI
situ E-CONPRI
defect S-CONPRI
detection O
based O
on O
in B-CONPRI
situ E-CONPRI
sensing O
, O
such O
as S-MATE
layerwise O
visual O
inspection S-CHAR
, O
enables O
the O
potential O
for O
in-process O
re-melting O
and O
correction O
of O
detected O
defects S-CONPRI
and O
thus O
facilitates O
in-process O
part O
qualification O
. O


This O
paper O
describes O
the O
development O
and O
implementation O
of O
such O
an O
in B-CONPRI
situ E-CONPRI
defect S-CONPRI
detection O
strategy O
for O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
AM S-MANP
using O
supervised O
machine S-MACEQ
learning.During O
the O
build S-PARA
process O
, O
multiple O
images S-CONPRI
were O
collected O
at O
each O
build B-PARA
layer E-PARA
using O
a O
high B-PARA
resolution E-PARA
digital O
single-lens O
reflex O
( O
DSLR O
) O
camera S-MACEQ
. O


For O
each O
neighborhood O
in O
the O
resulting O
layerwise O
image S-CONPRI
stack O
, O
multi-dimensional O
visual O
features O
were O
extracted S-CONPRI
and O
evaluated O
using O
binary S-CONPRI
classification O
techniques O
, O
i.e O
. O


a O
linear O
support S-APPL
vector O
machine S-MACEQ
( O
SVM O
) O
. O


Through O
binary S-CONPRI
classification O
, O
neighborhoods O
are O
then O
categorized O
as S-MATE
either O
a O
flaw S-CONPRI
, O
i.e O
. O


an O
undesirable O
interruption O
in O
the O
typical O
structure S-CONPRI
of O
the O
material S-MATE
, O
or O
a O
nominal O
build S-PARA
condition O
. O


the O
true O
location O
of O
flaws S-CONPRI
and O
nominal O
build B-PARA
areas E-PARA
, O
which O
are O
needed O
to O
train O
the O
binary S-CONPRI
classifiers O
, O
were O
obtained O
from O
post-build O
high-resolution S-PARA
3D S-CONPRI
CT O
scan O
data S-CONPRI
. O


In O
CT S-ENAT
scans O
, O
discontinuities O
, O
e.g O
. O


incomplete O
fusion S-CONPRI
, O
porosity S-PRO
, O
cracks O
, O
or O
inclusions S-MATE
, O
were O
identified O
using O
automated O
analysis O
tools S-MACEQ
or O
manual O
inspection S-CHAR
. O


After O
the O
classifier O
had O
been O
properly O
trained O
, O
in B-CONPRI
situ E-CONPRI
defect S-CONPRI
detection O
accuracies O
greater O
than O
80 O
% O
were O
demonstrated O
during O
cross-validation O
experiments O
. O


In O
this O
paper O
the O
heat B-CONPRI
transfer E-CONPRI
and O
residual B-PRO
stress E-PRO
evolution S-CONPRI
in O
the O
direct B-MANP
metal I-MANP
laser I-MANP
sintering E-MANP
process O
of O
the O
additive B-MANP
manufacturing E-MANP
of O
titanium B-MATE
alloy E-MATE
products O
are O
studied O
. O


A O
numerical O
model S-CONPRI
is O
developed O
in O
a O
COMSOL O
multiphysics O
environment O
considering O
the O
temperature-dependent O
material B-CONPRI
properties E-CONPRI
of O
TiAl6V4 O
. O


The O
thermo-mechanical S-CONPRI
coupled O
simulation S-ENAT
is O
performed O
. O


3-D S-CONPRI
simulation O
is O
used O
to O
study O
single-layer O
laser B-MANP
sintering E-MANP
. O


A O
2-D O
model S-CONPRI
is O
used O
to O
study O
the O
multi-layer O
effects O
of O
additive B-MANP
manufacturing E-MANP
. O


The O
results O
reveal O
the O
behavior O
of O
the O
melt B-MATE
pool E-MATE
size O
, O
temperature S-PARA
history O
, O
and O
change O
of O
the O
residual B-PRO
stresses E-PRO
of O
a O
single O
layer S-PARA
and O
among O
the O
multiple O
layers O
of O
the O
effects O
of O
the O
change O
of O
the O
local O
base O
temperature S-PARA
and O
laser B-PARA
power E-PARA
etc O
. O


The O
result O
of O
the O
simulation S-ENAT
provides O
a O
better O
understanding O
of O
the O
complex O
thermo-mechanical S-CONPRI
mechanisms O
of O
laser B-MANP
sintering I-MANP
additive I-MANP
manufacturing I-MANP
processes E-MANP
. O


Laser-matter O
interactions O
in O
laser B-MANP
additive I-MANP
manufacturing E-MANP
( O
LAM S-MANP
) O
occur O
on O
short O
time B-FEAT
scales E-FEAT
( O
10−6–10−3 O
s S-MATE
) O
and O
have O
traditionally O
proven O
difficult O
to O
characterise O
. O


We O
investigate O
these O
interactions O
during O
LAM S-MANP
of O
stainless B-MATE
steel E-MATE
SS316L O
and O
13-93 O
bioactive B-MATE
glass E-MATE
powders O
using O
a O
custom O
built O
LAM S-MANP
process O
replicator O
( O
LAMPR O
) O
with O
in B-CONPRI
situ E-CONPRI
and O
operando O
synchrotron S-ENAT
X-ray O
real-time O
radiography S-ENAT
. O


This O
reveals O
a O
wide O
range S-PARA
of O
melt S-CONPRI
track O
solidification S-CONPRI
phenomena O
as S-MATE
well O
as S-MATE
spatter O
and O
porosity S-PRO
formation O
. O


We O
hypothesise O
that O
the O
SS316L O
powder S-MATE
absorbs O
the O
laser B-CONPRI
energy E-CONPRI
at O
its O
surface S-CONPRI
while O
the O
trace B-MATE
elements E-MATE
in O
the O
13-93 O
bioactive B-MATE
glass E-MATE
powder O
absorb O
and O
remit O
the O
infra-red O
radiation S-MANP
. O


Our O
results O
show O
that O
a O
low O
viscosity S-PRO
melt S-CONPRI
, O
e.g O
. O


8 O
mPa S-CONPRI
s O
for O
SS316L O
, O
tends O
to O
generate O
spatter S-CHAR
( O
diameter S-CONPRI
up O
to O
250 O
μm O
and O
an O
average S-CONPRI
spatter O
velocity O
of O
0.26 O
m O
s−1 O
) O
and O
form O
a O
melt S-CONPRI
track O
by O
molten B-CONPRI
pool E-CONPRI
wetting O
. O


In O
contrast O
, O
a O
high O
viscosity S-PRO
melt S-CONPRI
, O
e.g O
. O


2 O
Pa S-CHAR
s O
for O
13-93 O
bioactive B-MATE
glass E-MATE
, O
inhibits O
spatter S-CHAR
formation O
by O
damping O
the O
Marangoni O
convection O
, O
forming S-MANP
a O
melt S-CONPRI
track O
via O
viscous O
flow O
. O


The O
viscous O
flow O
in O
13-93 O
bioactive B-MATE
glass E-MATE
resists O
pore S-PRO
transport O
; O
combined O
with O
the O
reboil O
effect O
, O
this O
promotes O
pore S-PRO
growth O
during O
LAM S-MANP
, O
resulting O
in O
a O
pore B-PARA
size E-PARA
up O
to O
600 O
times O
larger O
than O
that O
exhibited O
in O
the O
SS316L O
sample S-CONPRI
. O


An O
evaluation O
of O
low-cost O
, O
high-oxygen O
content O
Zr-Cu-Al-Nb O
bulk O
metallic B-MATE
glasses E-MATE
( O
BMGs O
) O
produced O
through O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
was O
performed O
. O


Four-point O
bending S-MANP
and O
wear B-PRO
resistance E-PRO
tests O
were O
used O
to O
compare O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
printed O
alloy S-MATE
with O
laboratory S-CONPRI
grade O
cast S-MANP
parts O
. O


It O
is O
shown O
that O
the O
laser S-ENAT
PBF O
parts O
, O
while O
not O
being O
able O
to O
be S-MATE
cast O
as S-MATE
a O
bulk O
glass S-MATE
, O
can O
be S-MATE
printed O
amorphous O
up O
to O
at O
least O
several O
millimeters O
thick O
and O
yet O
still O
have O
reasonable O
mechanical B-CONPRI
properties E-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
of O
highly O
viscous O
materials S-CONPRI
, O
e.g. O
, O
polysiloxane O
( O
silicone S-MATE
) O
has O
gained O
attention O
in O
academia O
and O
different O
industries S-APPL
, O
specifically O
the O
medical S-APPL
and O
healthcare O
sectors O
. O


Different O
AM B-MANP
processes E-MANP
including O
micro-syringe O
nozzle S-MACEQ
dispensing O
systems O
have O
demonstrated O
promising O
results O
in O
the O
deposition S-CONPRI
of O
highly O
viscous O
materials S-CONPRI
. O


This O
contact-based O
3D B-MANP
printing E-MANP
system O
has O
drawbacks O
such O
as S-MATE
overfilling O
of O
material S-MATE
at O
locations O
where O
there O
is O
a O
change O
in O
the O
direction O
of O
the O
trajectory O
, O
thereby O
reducing O
the O
printing O
quality S-CONPRI
. O


Modeling S-ENAT
the O
continuous O
flow O
of O
a O
highly O
viscous O
polysiloxane O
in O
the O
nozzle S-MACEQ
dispensing O
AM S-MANP
system O
using O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
will O
be S-MATE
the O
first O
step S-CONPRI
to O
solve O
this O
overfilling O
phenomenon O
. O


The O
results O
of O
simulation S-ENAT
can O
be S-MATE
used O
to O
predict O
the O
required O
variation S-CONPRI
in O
the O
value O
of O
pressure S-CONPRI
before O
the O
nozzle S-MACEQ
reaches O
a O
corner O
. O


The O
level-set O
method O
is O
employed O
for O
this O
simulation S-ENAT
, O
and O
the O
results O
are O
validated O
by O
comparing O
the O
flow O
profile S-FEAT
and O
geometrical O
parameters S-CONPRI
of O
the O
model S-CONPRI
with O
those O
of O
the O
experimental S-CONPRI
trials O
of O
the O
dispensing O
of O
polysiloxane O
. O


Comparisons O
show O
that O
the O
model S-CONPRI
is O
able O
to O
predict O
the O
location O
of O
the O
droplet S-CONPRI
before O
it O
reaches O
the O
substrate S-MATE
, O
as S-MATE
well O
as S-MATE
the O
height O
of O
the O
droplet S-CONPRI
generated O
on O
the O
substrate S-MATE
accurately S-CHAR
. O


To O
predict O
the O
width O
of O
the O
droplet S-CONPRI
, O
adjustment O
factors O
need O
to O
be S-MATE
considered O
in O
calculations O
based O
on O
the O
value O
of O
the O
pressure S-CONPRI
. O


A O
significant O
microstructural S-CONPRI
inhomogeneity O
in O
EBM S-MANP
fabricated O
Co-Cr-Mo O
alloy S-MATE
along O
building B-PARA
direction E-PARA
. O


Post-production O
heat B-MANP
treatment E-MANP
regime O
homogenized S-MANP
microstructures O
and O
enhanced O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
phase S-CONPRI
constituents O
significantly O
affected O
the O
mechanical S-APPL
behaviors O
of O
Co-Cr-Mo O
alloy S-MATE
. O


The O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
, O
a O
layer-by-layer S-CONPRI
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technique O
, O
has O
been O
recently O
utilized O
for O
fabricating S-MANP
metallic O
components S-MACEQ
with O
complex B-PRO
shape E-PRO
and O
geometry S-CONPRI
. O


However O
, O
the O
inhomogeneity O
in O
microstructures S-MATE
and O
mechanical B-CONPRI
properties E-CONPRI
are O
the O
main O
drawbacks O
constraining O
the O
serviceability O
of O
the O
EBM-built O
parts O
. O


In O
the O
present O
study O
, O
we O
found O
remarkable O
microstructural S-CONPRI
inhomogeneity O
along O
build B-PARA
direction E-PARA
in O
the O
EBM-built O
Co-based O
alloy S-MATE
, O
owing O
to O
the O
competitive O
grain B-CONPRI
growth E-CONPRI
and O
subsequent O
isothermal S-CONPRI
γ-fcc O
→ O
ε-hcp O
phase S-CONPRI
transformation O
, O
which O
affects O
the O
corresponding O
tensile B-PRO
properties E-PRO
significantly O
. O


Then O
, O
we O
succeeded O
in O
eliminating O
the O
inhomogeneities O
, O
modifying O
the O
phase S-CONPRI
structures O
and O
refining O
grain B-PRO
sizes E-PRO
via O
comprehensive O
post-production O
heat B-MANP
treatment E-MANP
regimes O
, O
which O
provides O
a O
valuable O
implication O
for O
improving O
the O
reliabilities O
of O
AM-built O
metals S-MATE
and O
alloys S-MATE
. O


The O
Co-based O
alloy S-MATE
can O
be S-MATE
selectively O
transformed O
into O
predominant O
ε O
or O
predominant O
γ O
phase S-CONPRI
by O
the O
regime O
, O
and O
the O
grains S-CONPRI
were O
refined O
to O
1/10 O
of O
the O
initial O
sizes O
by O
repeated O
heat B-MANP
treatment E-MANP
. O


Finally O
, O
we O
investigated O
the O
tensile B-PRO
properties E-PRO
and O
fracture S-CONPRI
behaviors O
of O
the O
alloy S-MATE
before O
and O
after O
each O
heat B-MANP
treatment E-MANP
. O


The O
γ O
→ O
ε O
strain-induced O
martensitic O
transformation O
is O
the O
major O
deformation S-CONPRI
mode O
of O
the O
γ O
phase S-CONPRI
, O
meanwhile O
the O
formation O
of O
stripped O
ε O
phase S-CONPRI
at O
{ O
111 O
} O
γ O
habit O
planes O
contributed O
to O
a O
good O
combination O
of O
strength S-PRO
and O
ductility S-PRO
. O


Nevertheless O
, O
the O
ε O
phase S-CONPRI
was O
deformed S-MANP
mainly O
by O
( O
0001 O
) O
ε O
< O
11 O
2¯0 O
> O
ε O
basal O
and O
{ O
1 O
1¯00 O
} O
ε O
< O
11 O
2¯0 O
> O
ε O
prismatic S-CONPRI
slip O
systems O
, O
exhibiting O
very O
limited O
ductility S-PRO
and O
strength S-PRO
. O


In O
addition O
, O
the O
ε O
grains S-CONPRI
act O
as S-MATE
secondary O
hardening S-MANP
factor O
in O
the O
samples S-CONPRI
consisting O
of O
dual O
γ/ε O
phase S-CONPRI
, O
leading O
to O
a O
non-uniform O
deformation S-CONPRI
behavior O
. O


Two O
new O
high-carbon O
high B-MATE
speed I-MATE
steel I-MATE
alloys E-MATE
; O
Febal-C-Cr-Mo-V S-MATE
and O
Febal−x-C-Cr-Mo-V-Wx O
were O
additively B-MANP
manufactured E-MANP
by O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
process S-CONPRI
. O


Micro-hardness O
( O
0.5 O
HV O
) O
measurement S-CHAR
of O
multilayer O
additively B-MANP
manufactured E-MANP
samples O
showed O
no O
softening O
of O
martensite S-MATE
matrix O
under O
complex O
thermal B-PARA
cycling E-PARA
. O


Due O
to O
larger O
phase B-CONPRI
fraction E-CONPRI
of O
metal B-MATE
carbides E-MATE
and O
formation O
of O
a O
relatively O
stable O
oxide S-MATE
layer S-PARA
, O
Febal−x-C-Cr-Mo-V-Wx O
showed O
better O
high O
temperature S-PARA
( O
500 O
°C O
) O
wear B-PRO
resistance E-PRO
than O
Febal-C-Cr-Mo-V. O
Neutron B-CHAR
diffraction E-CHAR
of O
powders S-MATE
and O
additively B-MANP
manufactured E-MANP
samples O
of O
Febal-C-Cr-Mo-V S-MATE
and O
Febal−x-C-Cr-Mo-V-Wx O
alloys S-MATE
showed O
weak O
scattering O
properties S-CONPRI
. O


The O
inconclusive O
strain S-PRO
scanning S-CONPRI
was O
either O
result O
of O
a O
strong O
crystallographic O
texture S-FEAT
in O
the O
bulk O
or O
due O
to O
existence O
of O
nano- O
or O
semi-crystalline O
phases O
. O


Directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
of O
two O
high-carbon O
high B-MATE
speed I-MATE
steel I-MATE
alloys E-MATE
Febal-C-Cr-Mo-V S-MATE
and O
Febal−x-C-Cr-Mo-V-Wx O
was O
performed O
by O
using O
a O
4 O
kW O
Nd B-MATE
: I-MATE
YAG E-MATE
laser B-MACEQ
source E-MACEQ
. O


The O
purpose O
of O
additive B-MANP
manufacturing E-MANP
was O
design S-FEAT
and O
evaluation O
of O
thermally O
stable O
– O
high O
temperature S-PARA
wear O
resistant O
alloys S-MATE
. O


High O
temperature S-PARA
( O
500 O
°C O
) O
pin-on-disc O
tests O
were O
conducted O
to O
investigate O
the O
effect O
of O
carbides S-MATE
phase O
fraction S-CONPRI
on O
friction S-CONPRI
and O
wear S-CONPRI
. O


Strain S-PRO
scanning S-CONPRI
of O
the O
powder S-MATE
and O
additively B-MANP
manufactured E-MANP
materials O
was O
carried O
out O
by O
Neutron S-CONPRI
diffraction.Microstructures O
of O
both O
alloys S-MATE
consisted O
of O
a O
martensitic O
matrix O
with O
networks O
of O
primary O
and O
eutectic S-CONPRI
carbides S-MATE
. O


Febal−x-C-Cr-Mo-V-Wx O
showed O
a O
better O
high O
temperature S-PARA
wear O
resistance S-PRO
due O
to O
greater O
phase B-CONPRI
fraction E-CONPRI
of O
VC S-MATE
and O
Mo2C O
carbides S-MATE
. O


Fracture S-CONPRI
surfaces O
of O
post-heat O
treated O
tensile S-PRO
samples S-CONPRI
of O
Febal-C-Cr-Mo-V S-MATE
and O
Febal−x-C-Cr-Mo-V-Wx O
revealed O
brittle B-CONPRI
failures E-CONPRI
with O
minimal O
plasticity S-PRO
. O


Neutron S-CONPRI
strain O
mapping O
of O
the O
metal B-MATE
powders E-MATE
and O
the O
additively B-MANP
manufactured E-MANP
materials O
resulted O
in O
a O
weak O
diffraction S-CHAR
signal O
and O
peak O
widening O
effect O
. O


Ti–6Al–4V O
parts O
made O
using O
additive B-MANP
manufacturing I-MANP
processes E-MANP
such O
as S-MATE
selective O
laser S-ENAT
melting O
( O
SLM S-MANP
) O
and O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
are O
subject O
to O
the O
inclusion S-MATE
of O
defects S-CONPRI
. O


This O
study O
purposely O
fabricated S-CONPRI
Ti–6Al–4V O
samples S-CONPRI
with O
defects S-CONPRI
by O
varying O
process B-CONPRI
parameters E-CONPRI
from O
the O
factory O
default O
settings O
in O
both O
SLM S-MANP
and O
EBM S-MANP
systems O
. O


Process B-CONPRI
parameters E-CONPRI
are O
classified O
according O
to O
their O
tendency O
to O
create O
certain O
types O
of O
porosity S-PRO
. O


Finally O
, O
defect S-CONPRI
characteristics O
are O
discussed O
with O
respect O
to O
defect S-CONPRI
generation O
mechanisms O
; O
and O
effective O
process S-CONPRI
windows O
for O
SLM S-MANP
and O
EBM S-MANP
system O
are O
discussed O
. O


Developed O
intra-layer O
, O
closed-loop B-MACEQ
control E-MACEQ
of O
additive B-MANP
manufacturing E-MANP
build O
plan O
. O


Control O
affected O
macrostructure O
, O
microstructure S-CONPRI
, O
and O
mechanical B-CONPRI
properties E-CONPRI
. O


Demonstrated O
reduced O
variability S-CONPRI
in O
microstructure S-CONPRI
and O
hardness S-PRO
with O
control O
. O


The O
location O
, O
timing O
, O
and O
arrangement O
of O
depositions O
paths O
used O
to O
build S-PARA
an O
additively B-MANP
manufactured E-MANP
component O
– O
collectively O
called O
the O
build S-PARA
plan O
– O
are O
known O
to O
impact S-CONPRI
local O
thermal O
history O
, O
microstructure S-CONPRI
, O
thermal B-CONPRI
distortion E-CONPRI
, O
and O
mechanical B-CONPRI
properties E-CONPRI
. O


In O
this O
work O
, O
a O
novel O
system O
architecture S-APPL
for O
intra-layer O
, O
closed-loop B-MACEQ
control E-MACEQ
of O
the O
build S-PARA
plan O
is O
introduced O
and O
demonstrated O
for O
directed-energy O
deposition S-CONPRI
of O
Ti–6Al–4V O
. O


The O
control O
strategy O
altered O
the O
build S-PARA
plan O
in O
real O
time O
to O
ensure O
that O
the O
temperature S-PARA
around O
the O
start O
point O
of O
each O
hatch O
, O
prior O
to O
deposition S-CONPRI
, O
was O
below O
a O
threshold O
temperature S-PARA
of O
415 O
°C O
. O


Compared O
with O
open-loop O
processing O
, O
closed-loop B-MACEQ
control E-MACEQ
resulted O
in O
vertical S-CONPRI
alignment O
of O
columnar O
prior-β O
grains S-CONPRI
, O
more O
uniform O
α-lath O
widths O
, O
and O
more-uniform O
microhardness S-CONPRI
values O
within O
the O
deposited O
component S-MACEQ
. O


Recently O
, O
laser-powder O
bed B-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
has O
been O
utilized O
to O
produce O
a O
NiTi S-MATE
shape O
memory O
alloy S-MATE
actuator S-MACEQ
with O
embedded O
channels O
for O
liquid B-MATE
metal E-MATE
forced O
fluid S-MATE
convection O
to O
increase O
actuator S-MACEQ
heat O
transfer O
rates O
. O


To O
enable O
further O
increases O
in O
performance S-CONPRI
, O
it O
is O
critical O
to O
characterize O
and O
control O
the O
surface B-PARA
quality E-PARA
of O
fully O
interior O
channels O
which O
have O
higher O
surface B-PRO
roughness E-PRO
compared O
to O
exterior O
top O
surfaces S-CONPRI
. O


This O
work O
utilizes O
a O
design B-CONPRI
of I-CONPRI
experiments E-CONPRI
methodology O
by O
varying O
laser B-PARA
power E-PARA
, O
scan B-PARA
speed E-PARA
, O
hatch O
space O
, O
scan B-PARA
pattern E-PARA
, O
channel S-APPL
orientation O
, O
and O
channel B-FEAT
diameter E-FEAT
on O
the O
as-fabricated O
surface B-PRO
roughness E-PRO
of O
the O
overhangs S-PARA
and O
walls O
of O
interior O
channels O
in O
NiTi S-MATE
. O


To O
enable O
post-process S-CONPRI
increases O
in O
surface B-PARA
quality E-PARA
, O
the O
channels O
are O
subjected O
to O
an O
electropolishing S-MANP
treatment O
and O
further O
characterized O
. O


Internal O
channel S-APPL
surfaces O
are O
characterized O
using O
optical S-CHAR
profilometry O
and O
SEM S-CHAR
imaging S-APPL
. O


It O
is O
concluded O
that O
channel S-APPL
orientation O
plays O
a O
prominent O
role O
in O
determining O
the O
surface B-PRO
roughness E-PRO
of O
as-fabricated O
interior O
channels O
, O
and O
a O
lower O
laser B-PARA
energy I-PARA
density E-PARA
results O
in O
the O
highest O
reduction S-CONPRI
in O
surface B-PRO
roughness E-PRO
after O
an O
electropolishing S-MANP
treatment O
. O


Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
additive B-MANP
manufacturing E-MANP
and O
laser B-MANP
welding E-MANP
are O
powerful O
metal S-MATE
processing O
techniques O
with O
broad O
applications O
in O
advanced O
sectors O
such O
as S-MATE
the O
biomedical S-APPL
and O
aerospace B-APPL
industries E-APPL
. O


One O
common O
process S-CONPRI
variable O
that O
can O
tune O
laser-material O
interaction O
dynamics O
in O
these O
two O
techniques O
is O
adjustment O
of O
the O
composition S-CONPRI
and O
pressure S-CONPRI
of O
the O
atmosphere O
in O
which O
the O
process S-CONPRI
is O
conducted O
. O


While O
some O
of O
the O
physical O
mechanisms O
that O
are O
governed O
by O
the O
ambient O
pressure S-CONPRI
are O
well O
known O
from O
the O
welding S-MANP
literature O
, O
it O
remains O
unclear O
how O
these O
mechanisms O
extend O
to O
the O
distinct O
process S-CONPRI
conditions O
of O
LPBF S-MANP
. O


In B-CONPRI
situ E-CONPRI
studies O
of O
the O
differences O
in O
subsurface O
structure S-CONPRI
and O
behavior O
are O
essential O
for O
understanding O
the O
effects O
of O
gas S-CONPRI
pressure O
and O
composition S-CONPRI
on O
the O
LPBF S-MANP
processes O
. O


This O
article O
reports O
the O
use O
of O
in B-CONPRI
situ E-CONPRI
X-ray O
imaging S-APPL
to O
directly O
probe S-MACEQ
the O
morphological O
evolution S-CONPRI
of O
the O
liquid-vapor O
interface S-CONPRI
during O
laser S-ENAT
melting O
as S-MATE
a O
function O
of O
ambient O
pressure S-CONPRI
and O
oxygen S-MATE
partial O
pressure S-CONPRI
under O
LPBF S-MANP
conditions O
in O
316 O
L O
steel S-MATE
, O
Ti-64 O
, O
aluminum S-MATE
6061 O
, O
and O
Nickel S-MATE
400 O
. O


We O
observe O
significant O
changes O
in O
melt B-MATE
pool E-MATE
morphology O
as S-MATE
a O
function O
of O
pressure S-CONPRI
. O


Furthermore O
, O
similar O
changes O
in O
morphology S-CONPRI
occur O
due O
to O
an O
increase O
in O
oxygen S-MATE
partial O
pressure S-CONPRI
in O
the O
process S-CONPRI
atmosphere O
. O


Temperature- O
and O
composition-dependent O
changes O
in O
surface B-PRO
tension E-PRO
of O
the O
liquid B-MATE
metal E-MATE
drive O
this O
change O
in O
behavior O
, O
which O
has O
the O
potential O
to O
influence O
defect S-CONPRI
creation O
and O
final O
morphology S-CONPRI
in O
LPBF S-MANP
parts O
. O


Electron B-MANP
beam I-MANP
additive I-MANP
manufacturing E-MANP
( O
EBAM S-MANP
) O
is O
a O
relatively O
new O
technology S-CONPRI
to O
produce O
metallic B-MACEQ
parts E-MACEQ
in O
a O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
fashion S-CONPRI
by O
melting S-MANP
and O
fusing S-CONPRI
the O
metallic B-MATE
powders E-MATE
. O


Ti–6Al–4V O
is O
one O
of O
the O
most O
used O
industrial S-APPL
alloys S-MATE
used O
for O
aerospace S-APPL
and O
biomedical B-APPL
application E-APPL
. O


EBAM S-MANP
is O
a O
rapid B-CONPRI
solidification I-CONPRI
process E-CONPRI
and O
the O
properties S-CONPRI
of O
the O
build B-MATE
material E-MATE
depend O
on O
the O
solidification S-CONPRI
behavior O
as S-MATE
well O
as S-MATE
the O
microstructure S-CONPRI
of O
the O
build B-MATE
material E-MATE
. O


Thus O
, O
the O
prediction S-CONPRI
of O
part O
microstructures S-MATE
during O
the O
process S-CONPRI
may O
be S-MATE
an O
important O
factor O
for O
process B-CONPRI
optimization E-CONPRI
. O


In O
this O
study O
, O
a O
phase S-CONPRI
field O
model S-CONPRI
is O
developed O
for O
microstructure B-CONPRI
evolution E-CONPRI
of O
Ti–6Al–4V O
powder S-MATE
in O
EBAM S-MANP
process O
. O


FORTRAN O
code O
is O
used O
to O
solve O
the O
phase S-CONPRI
field O
equations O
, O
which O
incorporates O
the O
temperature B-PARA
gradient E-PARA
and O
solidification B-PARA
velocity E-PARA
as S-MATE
the O
simulation S-ENAT
parameters S-CONPRI
. O


The O
effect O
of O
temperature B-PARA
gradient E-PARA
and O
the O
beam S-MACEQ
scan O
speed O
on O
microstructure S-CONPRI
is O
investigated O
through O
simulation S-ENAT
. O


The O
simulation S-ENAT
results O
are O
compared O
with O
the O
analytical O
model S-CONPRI
and O
experimental S-CONPRI
findings O
by O
measuring O
the O
spacing O
evolution S-CONPRI
under O
the O
solidification S-CONPRI
condition O
Exciting O
progress O
in O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technology S-CONPRI
, O
which O
enables O
fabrication S-MANP
of O
cellular B-FEAT
structures E-FEAT
with O
highly O
complex O
lattices S-CONPRI
and O
pores S-PRO
, O
has O
stimulated O
the O
development O
of O
lightweight S-CONPRI
structural O
products O
with O
improved O
performance S-CONPRI
and O
increased O
functionality O
. O


However O
, O
conventional O
design S-FEAT
and O
analysis O
tools S-MACEQ
lack O
the O
ability O
to O
optimize O
complex B-CONPRI
geometries E-CONPRI
efficiently O
and O
robustly O
. O


With O
this O
motivation O
, O
in O
this O
study O
, O
homogenized S-MANP
material O
models O
of O
open-cell O
polymeric O
foams O
with O
spherical S-CONPRI
cell S-APPL
architectures O
that O
are O
manufactured S-CONPRI
by O
using O
an O
AM B-MANP
technology E-MANP
are O
formulated O
through O
both O
experimental S-CONPRI
and O
numerical O
investigations O
, O
which O
in O
turn O
can O
be S-MATE
employed O
in O
a O
novel O
micromechanics O
based O
topology B-FEAT
optimization E-FEAT
algorithm S-CONPRI
developed O
for O
the O
optimization S-CONPRI
of O
cellular B-FEAT
structures E-FEAT
. O


In O
this O
regard O
, O
generating O
computer S-ENAT
aided O
drawing S-MANP
( O
CAD S-ENAT
) O
data S-CONPRI
, O
which O
is O
mandatory O
for O
AM S-MANP
, O
randomly O
intersected O
spherical S-CONPRI
ensemble O
method O
is O
employed O
. O


Several O
foam S-MATE
models O
with O
different O
porosities S-PRO
are O
generated O
, O
and O
utilized O
in O
nonlinear O
finite B-CONPRI
element I-CONPRI
analyses E-CONPRI
( O
FEAs O
) O
to O
determine O
constitutive O
elastic B-PARA
constants E-PARA
. O


Plastic S-MATE
stress-strain O
data S-CONPRI
for O
the O
bulk O
AM B-MATE
material E-MATE
are O
obtained O
through O
static O
tensile B-CHAR
tests E-CHAR
in O
a O
variety O
of O
different O
loading O
directions O
and O
these O
results O
used O
in O
FEA O
as S-MATE
true O
stress-strain O
data S-CONPRI
. O


Homogenization S-MANP
is O
performed O
based O
on O
a O
quadratic O
form O
of O
the O
widely O
used O
Gibson O
and O
Ashby O
foam S-MATE
model O
, O
which O
describes O
the O
Young O
’ O
s S-MATE
modulus O
E∗ O
and O
yield B-PRO
strength E-PRO
σpl∗ O
of O
cellular B-FEAT
structures E-FEAT
in O
terms O
of O
relative B-PRO
density E-PRO
. O


Predicting O
residual B-CONPRI
distortion E-CONPRI
in O
metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
important O
to O
ensure O
quality S-CONPRI
of O
the O
fabricated S-CONPRI
component S-MACEQ
. O


The O
inherent O
strain S-PRO
method O
is O
ideal O
for O
this O
purpose O
, O
but O
has O
not O
been O
well O
developed O
for O
AM B-MACEQ
parts E-MACEQ
yet O
. O


In O
this O
paper O
, O
a O
modified O
inherent O
strain S-PRO
model S-CONPRI
is O
proposed O
to O
estimate O
the O
inherent O
strains O
from O
detailed O
AM B-MANP
process E-MANP
simulation O
of O
single O
line O
depositions O
on O
top O
of O
each O
other O
. O


The O
obtained O
inherent O
strains O
are O
employed O
in O
a O
layer-by-layer S-CONPRI
static O
equilibrium S-CONPRI
analysis O
to O
simulate O
residual B-CONPRI
distortion E-CONPRI
of O
the O
AM B-MACEQ
part E-MACEQ
efficiently O
. O


To O
validate O
the O
model S-CONPRI
, O
depositions O
of O
a O
single O
wall O
and O
a O
rectangular O
contour S-FEAT
wall O
models O
with O
different O
number B-PARA
of I-PARA
layers E-PARA
deposited O
by O
a O
representative O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
process S-CONPRI
are O
studied O
. O


The O
proposed O
model S-CONPRI
is O
demonstrated O
to O
be S-MATE
accurate S-CHAR
by O
comparing O
with O
full-scale O
detailed O
process B-ENAT
simulation E-ENAT
and O
experimental S-CONPRI
results O
. O


Based O
on O
this O
approach O
, O
simulation S-ENAT
results O
applied O
to O
the O
rectangular O
contour S-FEAT
wall O
structures O
of O
different O
heights O
show O
that O
the O
modified B-CONPRI
inherent I-CONPRI
strain I-CONPRI
method E-CONPRI
is O
quite O
efficient O
, O
while O
the O
residual B-CONPRI
distortion E-CONPRI
of O
AM B-MACEQ
parts E-MACEQ
can O
be S-MATE
accurately S-CHAR
computed O
within O
a O
short O
time O
. O


The O
improvement O
of O
the O
computational B-CONPRI
efficiency E-CONPRI
can O
be S-MATE
up O
to O
80 O
times O
in O
some O
specific O
cases O
. O


Stainless B-MATE
steel E-MATE
316L O
dogbones O
produced O
using O
two O
production S-MANP
methods O
were O
studied O
. O


General O
corrosion S-CONPRI
was O
not O
considered O
to O
be S-MATE
a O
major O
form O
of O
corrosion S-CONPRI
after O
2184 O
h. O
Mechanical B-CONPRI
properties E-CONPRI
for O
the O
traditionally O
manufactured S-CONPRI
samples O
did O
not O
change O
. O


Mechanical B-CONPRI
properties E-CONPRI
for O
the O
AM S-MANP
samples O
decreased O
during O
the O
exposure S-CONPRI
time O
. O


Hydrogen B-CONPRI
embrittlement E-CONPRI
in O
the O
AM S-MANP
samples O
caused O
the O
mechanical B-CONPRI
properties E-CONPRI
decrease O
. O


The O
effects O
on O
the O
surface S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
stainless B-MATE
steel E-MATE
AISI316L O
dogbones O
created O
using O
either O
traditional B-MANP
manufacturing E-MANP
( O
TM O
) O
or O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
exposed O
to O
0.75 O
M O
sulfuric O
acid O
solution S-CONPRI
over O
2184 O
h O
were O
studied O
. O


General O
corrosion S-CONPRI
was O
not O
a O
major O
form O
of O
corrosion S-CONPRI
, O
based O
on O
surface S-CONPRI
feature S-FEAT
changes O
, O
surface B-PRO
roughness E-PRO
, O
and O
mass O
loss O
for O
either O
method O
. O


No O
change O
to O
the O
mechanical B-CONPRI
properties E-CONPRI
occurred O
for O
the O
TM O
samples S-CONPRI
. O


Both O
tensile B-PRO
stress E-PRO
and O
strain S-PRO
decreased O
for O
the O
LPBF S-MANP
samples O
. O


The O
decrease O
was O
caused O
by O
hydrogen B-CONPRI
embrittlement E-CONPRI
, O
due O
to O
the O
formation O
of O
large O
brittle S-PRO
particles O
, O
as S-MATE
demonstrated O
by O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
of O
complex O
tungsten S-MATE
carbide-cobalt O
( O
WC-Co O
) O
parts O
was O
achieved O
using O
binder S-MATE
jet O
additive B-MANP
manufacturing E-MANP
( O
BJAM O
) O
of O
WC S-MATE
powders S-MATE
followed O
by O
Co S-MATE
infiltration O
. O


Using O
BJAM O
with O
infiltration S-CONPRI
of O
the O
metal S-MATE
phase O
can O
limit S-CONPRI
shrinkage O
and O
grain B-CONPRI
growth E-CONPRI
in O
ceramic-metal S-MATE
( O
cermet S-MATE
) O
composites S-MATE
compared O
to O
other O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
methods O
. O


Knowledge O
of O
previous O
infiltration S-CONPRI
studies O
was O
used O
to O
help O
process S-CONPRI
parts O
to O
imitate O
production S-MANP
of O
parts O
. O


The O
properties S-CONPRI
such O
as S-MATE
density O
, O
microstructure S-CONPRI
, O
grain B-PRO
size E-PRO
, O
and O
hardness S-PRO
of O
the O
parts O
are O
characterized O
along O
the O
infiltration S-CONPRI
height O
. O


Fracture S-CONPRI
toughness O
is O
measured O
where O
applicable O
. O


This O
approach O
has O
the O
potential O
to O
achieve O
highly O
dense O
WC-Co O
parts O
that O
are O
net-shaped O
with O
some O
ternary O
phase S-CONPRI
and O
z-direction S-FEAT
distortion S-CONPRI
. O


This O
paper O
proposes O
a O
novel O
geometric O
based O
scanning B-CONPRI
strategy E-CONPRI
adopted O
in O
the O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
manufacturing B-MANP
technology E-MANP
aimed O
at O
reducing O
the O
level O
of O
residual B-PRO
stresses E-PRO
generated O
during O
the O
build-up O
process S-CONPRI
. O


A O
set S-APPL
of O
computer B-CONPRI
simulations E-CONPRI
of O
the O
build S-PARA
, O
based O
on O
different O
scans O
strategies O
, O
including O
temperature S-PARA
dependent O
material B-CONPRI
properties E-CONPRI
, O
and O
a O
moving O
heat B-CONPRI
flux E-CONPRI
, O
were O
performed O
. O


The O
research S-CONPRI
novelty O
explores O
intermittent O
scan O
strategies O
in O
order O
to O
analyze O
the O
effect O
of O
reduction S-CONPRI
on O
heat S-CONPRI
concentration O
on O
the O
residual B-PRO
stress E-PRO
and O
deformation S-CONPRI
. O


Coupled O
thermal-structural O
computations O
revealed O
a O
significant O
stress S-PRO
and O
warpage B-CONPRI
reduction E-CONPRI
on O
the O
proposed O
scanning S-CONPRI
scheme O
. O


Different O
powder B-MATE
material E-MATE
properties O
were O
investigated O
and O
the O
computational B-ENAT
model E-ENAT
was O
validated O
against O
published O
numerical O
and O
experimental S-CONPRI
studies O
. O


This O
study O
focuses O
on O
the O
microstructural B-CONPRI
evolution E-CONPRI
in O
additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
β O
titanium B-MATE
alloys E-MATE
due O
to O
solid-state B-CONPRI
phase E-CONPRI
transformations O
occurring O
during O
the O
reheating O
of O
previously O
deposited B-CHAR
layers E-CHAR
, O
directly O
influencing O
the O
uniformity O
of O
microstructure S-CONPRI
across O
the O
entire O
build S-PARA
. O


During O
the O
AM S-MANP
of O
titanium B-MATE
alloys E-MATE
of O
a O
wide O
variety O
of O
compositions O
, O
including O
α O
+ O
β O
alloys S-MATE
such O
as S-MATE
Ti-6Al-4 O
V S-MATE
, O
and O
β O
alloys S-MATE
, O
when O
the O
laser S-ENAT
or O
electron B-CONPRI
beam E-CONPRI
hits O
the O
sample S-CONPRI
, O
the O
grains S-CONPRI
in O
the O
previously O
deposited O
topmost O
layers O
either O
re-melt O
or O
transform O
into O
the O
β O
phase S-CONPRI
. O


Subsequently O
, O
during O
the O
cooling S-MANP
cycle O
, O
depending O
on O
the O
alloy S-MATE
composition O
, O
second-phase O
precipitation S-CONPRI
may O
occur O
within O
these O
layers O
via O
solid-state B-CONPRI
precipitation E-CONPRI
. O


The O
present O
study O
compares O
two O
binary S-CONPRI
β O
-Ti O
alloys S-MATE
, O
Ti-12Mo O
and O
Ti-20 O
V S-MATE
, O
that O
have O
been O
processed S-CONPRI
using O
laser B-MANP
engineered I-MANP
net I-MANP
shaping E-MANP
( O
LENS™ O
) O
, O
a O
directed B-MANP
energy I-MANP
deposition E-MANP
technique O
for O
AM S-MANP
. O


Compared O
to O
Ti-V O
, O
which O
exhibited O
grains S-CONPRI
of O
only O
the O
β O
phase S-CONPRI
in O
the O
as-built O
condition O
, O
the O
less O
β O
stabilized O
Ti-Mo O
had O
extensive O
second-phase O
α O
precipitation S-CONPRI
within O
the O
build S-PARA
. O


The O
location O
within O
the O
LENS™ O
build S-PARA
played O
a O
pivotal O
role O
in O
determining O
the O
size O
scale O
, O
area S-PARA
fraction O
, O
and O
morphology S-CONPRI
of O
the O
α O
precipitates S-MATE
. O


These O
changes O
have O
been O
attributed O
to O
the O
different O
thermal B-PARA
cycles E-PARA
experienced O
during O
the O
deposition B-MANP
process E-MANP
. O


Irrespective O
of O
the O
alloy S-MATE
composition O
, O
columnar B-PRO
grains E-PRO
were O
observed O
in O
the O
depositions O
with O
a O
strong O
[ O
001 O
] O
β O
texture S-FEAT
along O
the O
build B-PARA
direction E-PARA
. O


In O
the O
Ti-12Mo O
alloy S-MATE
, O
wherein O
second O
phase S-CONPRI
α O
precipitation S-CONPRI
takes O
place O
, O
there O
was O
no O
significant O
α O
texturing O
, O
with O
all O
twelve O
variants O
forming S-MANP
. O


Significant O
attention O
has O
been O
focused O
on O
modeling S-ENAT
of O
metallic B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
, O
with O
the O
initial O
aim O
of O
predicting O
local O
thermal O
history O
, O
and O
ultimately O
structure S-CONPRI
and O
properties S-CONPRI
. O


Existing O
models O
range S-PARA
greatly O
in O
physical O
complexity S-CONPRI
and O
computational O
cost O
, O
and O
the O
implications O
of O
various O
simplifying O
assumption O
often O
go S-MATE
unassessed O
. O


In O
the O
present O
work O
, O
we O
first O
formulate O
a O
fast O
acting O
Discrete O
Source S-APPL
Model S-CONPRI
( O
DSM O
) O
capable O
of O
handling O
the O
complex O
processing O
often O
encountered O
in O
metal B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
AM S-MANP
. O


We O
then O
assess O
implications O
of O
the O
source S-APPL
representation O
, O
details O
of O
the O
numeric O
implementation O
, O
as S-MATE
well O
as S-MATE
effects O
of O
boundary B-CONPRI
conditions E-CONPRI
and O
thermophysical O
parameters S-CONPRI
. O


While O
a O
number O
of O
approximations O
limit S-CONPRI
its O
quantitative S-CONPRI
accuracy S-CHAR
, O
the O
inexpensive O
nature O
and O
ability O
to O
treat O
complex O
processing O
plans O
suggests O
it O
will O
be S-MATE
useful O
for O
screening O
and O
identification O
of O
regions O
experiencing O
anomalous O
thermal O
history O
. O


Electron B-MANP
beam I-MANP
welding E-MANP
( O
EBW S-MANP
) O
is O
a O
high-density O
energy O
( O
low O
heat S-CONPRI
input O
) O
welding S-MANP
technique O
, O
resulting O
in O
a O
narrow O
heat B-CONPRI
affected I-CONPRI
zone E-CONPRI
( O
HAZ S-CONPRI
) O
, O
causing O
minimal O
metallurgical S-APPL
changes O
in O
the O
workpieces O
. O


The O
present O
research S-CONPRI
work O
investigates S-CONPRI
EB O
autogenous O
welded S-MANP
AlSi10Mg S-MATE
samples O
, O
produced O
by O
the O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
method O
, O
with O
emphasis O
on O
the O
characterization O
of O
the O
joint S-CONPRI
's O
macro- O
and O
microstructure S-CONPRI
. O


When O
comparing O
the O
EB O
welded S-MANP
AM B-MACEQ
parts E-MACEQ
to O
the O
EB O
welded B-MANP
cast E-MANP
samples S-CONPRI
two O
main O
differences O
were O
observed O
: O
weld B-MATE
metal E-MATE
porosity S-PRO
and O
a O
negligible O
HAZ S-CONPRI
in O
the O
AM S-MANP
joints O
and O
low O
porosity S-PRO
level O
but O
substantial O
HAZ S-CONPRI
in O
the O
welded B-MANP
cast E-MANP
parts O
. O


These O
preliminary O
results O
show O
for O
the O
first O
time O
the O
feasibility S-CONPRI
of O
the O
EBW S-MANP
technique O
on O
AM-SLM O
specimens O
. O


The O
material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
technique O
known O
as S-MATE
fused O
filament S-MATE
fabrication S-MANP
( O
FFF S-MANP
) O
is O
an O
interesting O
method O
to O
fabricate S-MANP
complex O
ceramic S-MATE
parts O
whereby O
feedstocks S-MATE
containing O
thermoplastic B-MATE
binders E-MATE
and O
ceramic B-MATE
powders E-MATE
are O
printed O
and O
the O
resulting O
parts O
are O
subjected O
to O
debinding S-CONPRI
and O
sintering S-MANP
. O


A O
limiting O
factor O
of O
this O
process S-CONPRI
is O
the O
debinding S-CONPRI
step O
, O
usually O
done O
thermally O
. O


Long O
thermal B-PARA
cycles E-PARA
are O
required O
to O
avoid O
defects S-CONPRI
such O
as S-MATE
cracks O
and O
blisters O
caused O
by O
trapped O
pyrolysis S-MANP
products O
. O


The O
current O
study O
addresses O
this O
issue O
by O
developing O
a O
novel O
FFF S-MANP
binder S-MATE
formulation O
for O
the O
production S-MANP
of O
zirconia S-MATE
parts O
with O
an O
intermediate O
solvent O
debinding S-CONPRI
step O
. O


Different O
unfilled O
binder S-MATE
systems O
were O
evaluated O
considering O
the O
mechanical S-APPL
and O
rheological B-PRO
properties E-PRO
required O
for O
the O
FFF S-MANP
process O
together O
with O
the O
solvent O
debinding S-CONPRI
performance O
of O
the O
parts O
. O


Subsequently O
, O
the O
same O
compounds O
were O
used O
in O
feedstocks S-MATE
filled O
with O
47 O
vol. O
% O
of O
zirconia B-MATE
powder E-MATE
, O
and O
the O
resulting O
morphology S-CONPRI
was O
studied O
. O


Finally O
, O
the O
most O
promising O
formulation O
, O
containing O
zirconia S-MATE
, O
styrene-ethylene/butylene-styrene O
copolymer S-MATE
, O
paraffin S-MATE
wax O
, O
stearic O
acid O
, O
and O
acrylic S-MATE
acid-grafted O
high B-MATE
density I-MATE
polyethylene E-MATE
was O
successfully O
processed S-CONPRI
by O
FFF S-MANP
. O


After O
solvent O
debinding S-CONPRI
, O
55.4 O
wt. O
% O
of O
the O
binder S-MATE
was O
dissolved O
in O
cyclohexane O
, O
creating O
an O
interconnected O
porosity S-PRO
of O
29 O
vol. O
% O
that O
allowed O
a O
successful O
thermal B-CHAR
debinding E-CHAR
and O
subsequent O
pre-sintering S-MANP
. O


The O
layered B-CONPRI
structure E-CONPRI
of O
Additive B-MANP
Manufacturing I-MANP
processes E-MANP
results O
in O
a O
stair- O
stepping O
effect O
of O
the O
surface B-CONPRI
topographies E-CONPRI
. O


In O
general O
, O
the O
impact S-CONPRI
of O
this O
effect O
strongly O
depends O
on O
the O
build S-PARA
angle O
of O
a O
surface S-CONPRI
, O
whereas O
the O
overall O
surface B-PRO
roughness E-PRO
is O
additionally O
caused O
by O
the O
resolution S-PARA
of O
the O
specific O
AM B-MANP
process E-MANP
. O


The O
aim O
of O
this O
work O
is O
the O
prediction S-CONPRI
of O
the O
surface B-PARA
quality E-PARA
in O
dependence O
of O
the O
building B-PARA
orientation E-PARA
of O
a O
part O
. O


These O
results O
can O
finally O
be S-MATE
used O
to O
optimize O
the O
orientation S-CONPRI
to O
get O
a O
desired O
surface B-PARA
quality E-PARA
. O


As S-MATE
not O
all O
parts O
of O
the O
component S-MACEQ
surface O
are O
equally O
important O
, O
a O
preselection O
of O
areas S-PARA
can O
be S-MATE
used O
to O
improve O
the O
overall O
surface B-PARA
quality E-PARA
of O
relevant O
areas S-PARA
. O


The O
model S-CONPRI
uses O
the O
digital O
AMF S-CONPRI
format O
of O
a O
part O
. O


Each O
triangle O
is O
assigned O
with O
a O
roughness B-PRO
value E-PRO
and O
by O
testing S-CHAR
different O
orientations S-CONPRI
the O
best O
one O
can O
be S-MATE
found O
. O


This O
approach O
needs O
a O
database S-ENAT
for O
the O
surface B-PARA
qualities E-PARA
. O


This O
must O
be S-MATE
done O
separately O
for O
each O
Additive B-MANP
Manufacturing I-MANP
process E-MANP
and O
is O
shown O
exemplarily O
with O
a O
surface B-CONPRI
topography E-CONPRI
simulation S-ENAT
for O
the O
laser B-MANP
sintering E-MANP
process.A O
validation S-CONPRI
of O
the O
model S-CONPRI
is O
done O
with O
a O
monitor S-CONPRI
bracket S-MACEQ
of O
EOS B-APPL
GmbH E-APPL
. O


Measurements O
of O
five O
different O
orientations S-CONPRI
of O
the O
part O
, O
optimized O
according O
selected O
surface B-PARA
areas E-PARA
, O
show O
a O
good O
accordance O
between O
the O
real O
surface B-PRO
roughness E-PRO
and O
the O
predicted S-CONPRI
roughness O
of O
the O
simulation S-ENAT
. O


3D B-MANP
printing E-MANP
using O
the O
materials B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
( O
ME-AM S-MANP
) O
process S-CONPRI
is O
highly O
nonisothermal O
. O


In O
this O
process S-CONPRI
, O
a O
solid O
polymer B-MATE
filament E-MATE
is O
mechanically O
drawn O
into O
a O
heated O
hot B-MACEQ
end E-MACEQ
( O
liquefier O
) O
where O
the O
polymer S-MATE
is O
ideally O
melted S-CONPRI
to O
a O
viscous O
liquid O
. O


This O
melt S-CONPRI
is O
extruded S-MANP
through O
an O
orifice O
using O
applied O
pressure S-CONPRI
of O
the O
solid O
filament S-MATE
that O
is O
continuously O
being O
drawn O
into O
the O
extruder S-MACEQ
. O


The O
extruded S-MANP
filament O
melt S-CONPRI
is O
deposited O
to O
build S-PARA
up O
the O
desired O
part O
. O


The O
poor O
thermal B-PRO
conductivity E-PRO
of O
most O
polymers S-MATE
inevitably O
leads O
to O
temperature B-PARA
gradients E-PARA
, O
in O
both O
the O
radial O
and O
axial O
directions O
. O


Here O
we O
quantify O
the O
temperature S-PARA
evolution S-CONPRI
of O
the O
polymer B-MATE
filament E-MATE
in O
axial O
direction O
using O
embedded O
fine O
thermocouples S-MACEQ
as S-MATE
a O
function O
of O
process B-CONPRI
parameters E-CONPRI
. O


Information O
about O
the O
radial O
gradients O
is O
obtained O
by O
introducing O
dye O
markers O
within O
the O
filament S-MATE
through O
understanding O
the O
flow O
behavior O
through O
the O
extruder S-MACEQ
by O
the O
deformation S-CONPRI
of O
the O
dye O
from O
a O
linear O
to O
pseudo O
parabolic O
profile S-FEAT
. O


The O
polymer S-MATE
is O
heated O
above O
the O
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
for O
less O
than O
30 O
s S-MATE
for O
reasonable O
print S-MANP
conditions O
with O
the O
center O
of O
the O
filament S-MATE
remaining O
cooler O
than O
the O
liquefier O
temperature S-PARA
throughout O
the O
process S-CONPRI
. O


These O
process S-CONPRI
measurements O
provide O
critical O
data S-CONPRI
to O
enable O
improved O
simulation S-ENAT
and O
modeling S-ENAT
of O
the O
ME-AM S-MANP
process O
and O
the O
properties S-CONPRI
of O
the O
printed O
parts O
. O


Dendrites S-BIOP
built O
from O
elongated O
cells S-APPL
lead O
to O
a O
dislocation S-CONPRI
cell S-APPL
structure O
After O
a O
solution B-MANP
heat I-MANP
treatment E-MANP
the O
dislocation B-PRO
density E-PRO
is O
significantly O
decreased O
Nitrided S-MANP
AM S-MANP
structures O
can O
be S-MATE
built O
to O
match O
the O
properties S-CONPRI
of O
conventional O
316 O
L O
A O
solution B-MANP
treatment E-MANP
prevents O
CrN S-MATE
precipitation O
by O
eliminating O
stress S-PRO
A O
solution B-MANP
treatment E-MANP
plus O
nitriding S-MANP
are O
beneficial O
for O
corrosion S-CONPRI
and O
wear B-CONPRI
properties E-CONPRI
Due O
to O
the O
limited O
wear S-CONPRI
and O
corrosion B-PRO
properties E-PRO
of O
the O
austenitic B-MATE
stainless I-MATE
steel E-MATE
AISI O
316 O
L O
, O
some O
applications O
require O
the O
benefits O
of O
nitriding S-MANP
. O


The O
aim O
of O
this O
work O
was O
to O
investigate O
whether O
the O
same O
positive O
effect O
of O
nitriding S-MANP
could O
be S-MATE
obtained O
for O
316 O
L O
that O
was O
additive B-MANP
manufactured E-MANP
using O
the O
laser S-ENAT
powder-bed O
fusion S-CONPRI
process O
and O
further O
solution S-CONPRI
treated O
at O
1060 O
°C O
for O
30 O
min O
, O
low-temperature O
plasma B-MANP
nitrided E-MANP
at O
430 O
°C O
or O
both O
. O


This O
study O
was O
designed S-FEAT
to O
better O
understand O
the O
additive-manufactured O
and O
solution-treated O
microstructures S-MATE
as S-MATE
well O
as S-MATE
developing O
a O
nitride S-MATE
and O
a O
diffusion S-CONPRI
layer O
. O


The O
comparison O
of O
the O
wear S-CONPRI
and O
corrosion B-CONPRI
resistance E-CONPRI
, O
the O
microhardness S-CONPRI
and O
the O
microstructure S-CONPRI
changes O
of O
the O
additive-manufactured O
steel S-MATE
in O
different O
post-treated O
conditions O
with O
a O
commercial O
steel S-MATE
was O
carried O
out O
. O


It O
was O
found O
that O
the O
post-treated O
low-temperature O
plasma B-MANP
nitriding E-MANP
improves O
the O
wear S-CONPRI
and O
corrosion B-CONPRI
resistance E-CONPRI
of O
the O
additive-manufactured O
samples S-CONPRI
. O


The O
obtained O
values O
are O
similar O
to O
the O
values O
of O
conventionally O
fabricated S-CONPRI
and O
nitrided S-MANP
316 O
L. O
The O
solution S-CONPRI
treating O
itself O
( O
without O
further O
nitriding S-MANP
) O
did O
not O
have O
any O
significant O
impact S-CONPRI
on O
these O
properties S-CONPRI
. O


It O
was O
possible O
to O
explain O
the O
microstructure S-CONPRI
at O
the O
nano S-FEAT
level O
as S-MATE
well O
as S-MATE
correlating O
the O
wear S-CONPRI
and O
corrosion B-PRO
properties E-PRO
. O


Control O
of O
laser B-PARA
power E-PARA
to O
improve O
part O
quality S-CONPRI
is O
critical O
for O
fabrication S-MANP
of O
complex O
components S-MACEQ
via O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
( O
LPBF S-MANP
) O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
. O


If O
the O
laser B-PARA
power E-PARA
is O
too O
low O
, O
it O
will O
result O
in O
a O
small O
melt B-MATE
pool E-MATE
and O
lack O
of O
fusion S-CONPRI
; O
on O
the O
other O
hand O
, O
if O
the O
laser B-PARA
power E-PARA
is O
too O
high O
, O
it O
will O
result O
in O
keyhole O
and O
material S-MATE
evaporation S-CONPRI
. O


This O
paper O
examines O
a O
model-based O
feed-forward O
control O
for O
laser B-PARA
power E-PARA
in O
LPBF S-MANP
to O
improve O
build S-PARA
quality O
by O
avoiding O
the O
onset O
of O
keyhole O
formation O
or O
reducing O
over-melting O
. O


First O
, O
an O
analytical O
, O
control-oriented O
model S-CONPRI
on O
the O
dynamics O
of O
melt-pool O
cross-sectional O
area S-PARA
in O
scanning S-CONPRI
a O
multi-track O
part O
was O
developed O
, O
and O
then O
a O
nonlinear O
inverse-dynamics O
controller S-MACEQ
was O
designed S-FEAT
to O
adjust O
laser B-PARA
power E-PARA
such O
that O
the O
melt-pool O
cross-sectional O
area S-PARA
can O
be S-MATE
regulated O
to O
a O
constant O
set S-APPL
point O
during O
the O
build S-PARA
process O
. O


The O
resulting O
control O
trajectory O
on O
laser B-PARA
power E-PARA
from O
the O
simulated O
closed-loop B-MACEQ
controller E-MACEQ
was O
then O
implemented O
in O
a O
LPBF S-MANP
process O
as S-MATE
a O
feed-forward O
( O
FF O
) O
controller S-MACEQ
for O
laser B-PARA
power E-PARA
. O


Multiple O
bead-on-plate O
samples S-CONPRI
of O
Inconel B-MATE
625 E-MATE
, O
with O
different O
number O
of O
tracks O
and O
track O
lengths O
, O
were O
then O
built O
on O
an O
EOSINT O
M O
280 O
AM S-MANP
system O
to O
evaluate O
the O
performance S-CONPRI
of O
the O
resulting O
FF-Analytic O
controller S-MACEQ
. O


Experimental S-CONPRI
results O
demonstrated O
that O
the O
proposed O
FF-Analytic O
control O
of O
laser B-PARA
power E-PARA
was O
able O
to O
avoid O
the O
onset O
of O
keyhole O
formation O
that O
occurred O
under O
a O
constant O
laser B-PARA
power E-PARA
for O
certain O
samples S-CONPRI
. O


Furthermore O
, O
the O
proposed O
FF-Analytic O
control O
was O
demonstrated O
to O
have O
significantly O
reduced O
over-melting O
at O
the O
returning O
ends O
of O
the O
laser B-ENAT
scan E-ENAT
path O
in O
scanning S-CONPRI
a O
multi-track O
part O
compared O
to O
applying O
a O
constant O
laser B-PARA
power E-PARA
, O
albeit O
with O
some O
over-compensation O
due O
to O
modeling S-ENAT
imperfection S-CONPRI
. O


Overall O
, O
the O
proposed O
FF-Analytic O
control O
of O
laser B-PARA
power E-PARA
had O
23–40 O
% O
lower O
average S-CONPRI
error O
rate O
than O
applying O
a O
constant O
laser B-PARA
power E-PARA
in O
regulating O
the O
melt-pool O
cross-sectional O
area S-PARA
to O
a O
constant O
reference O
value O
, O
in O
terms O
of O
measurements O
of O
cross-sections S-CONPRI
at O
track O
ends O
. O


Forming S-MANP
quality O
was O
compared O
for O
AM-built-IN718 O
samples S-CONPRI
using O
two O
types O
of O
powders S-MATE
. O


Samples S-CONPRI
built O
with O
imperfect O
spherical S-CONPRI
powders S-MATE
tend O
to O
be S-MATE
porous O
and O
uneven O
. O


Processing O
with O
spherical S-CONPRI
powders S-MATE
has O
a O
broad O
process S-CONPRI
window O
suppressing O
defect S-CONPRI
. O


High O
cooling S-MANP
and O
solidification B-PARA
rates E-PARA
suppress O
the O
interdendritic O
void S-CONPRI
formation O
. O


The O
characteristics O
of O
powder S-MATE
applied O
in O
electron B-CONPRI
beam E-CONPRI
powder-bed O
fusion S-CONPRI
( O
EB-PBF O
) O
play O
a O
vital O
role O
in O
the O
process S-CONPRI
stability O
and O
final O
part O
performance S-CONPRI
. O


We O
use O
two O
types O
of O
Inconel B-MATE
718 I-MATE
alloy E-MATE
powders O
for O
experiments O
, O
namely O
, O
( O
i O
) O
imperfect O
spherical S-CONPRI
and O
( O
ii O
) O
spherical S-CONPRI
powders S-MATE
. O


They O
have O
similar O
particle B-CONPRI
size I-CONPRI
distributions E-CONPRI
but O
are O
different O
in O
geometry S-CONPRI
and O
built-in O
defect S-CONPRI
. O


The O
forming S-MANP
qualities O
concerning O
surface B-CONPRI
topography E-CONPRI
, O
density S-PRO
, O
and O
internal O
defect S-CONPRI
of O
the O
EB-PBF-built O
samples S-CONPRI
prepared O
using O
two O
types O
of O
powders S-MATE
are O
characterized O
under O
the O
same O
processing O
conditions O
. O


In O
particular O
, O
the O
forming S-MANP
qualities O
are O
further O
compared O
under O
the O
optimal B-PARA
process E-PARA
condition O
to O
highlight O
the O
decisive O
role O
of O
powder S-MATE
features O
. O


Notably O
, O
different O
powder S-MATE
geometries S-CONPRI
with O
distinct O
surface S-CONPRI
feature S-FEAT
inevitably O
affect O
the O
heat B-CONPRI
transfer E-CONPRI
during O
melting S-MANP
. O


The O
significance O
of O
powder B-MACEQ
feedstock E-MACEQ
characteristics O
in O
defect S-CONPRI
suppression O
is O
clarified O
with O
the O
aid O
of O
numerical B-ENAT
simulations E-ENAT
. O


The O
experimental S-CONPRI
results O
show O
that O
compared O
to O
spherical S-CONPRI
powders S-MATE
, O
fabrication S-MANP
using O
imperfect O
spherical S-CONPRI
powders S-MATE
is O
more O
likely O
to O
evoke O
lack–of–fusion O
and O
excessive O
melting S-MANP
under O
low O
and O
high O
energy O
conditions O
, O
respectively O
. O


Thus O
, O
spherical S-CONPRI
powders S-MATE
have O
a O
broader O
process S-CONPRI
window O
in O
ensuring O
a O
higher O
density S-PRO
and O
smoother O
surface S-CONPRI
than O
that O
of O
imperfect O
spherical S-CONPRI
powders S-MATE
. O


Moreover O
, O
in O
the O
sample S-CONPRI
built O
with O
spherical S-CONPRI
powders S-MATE
, O
the O
high O
cooling S-MANP
and O
solidification B-PARA
rates E-PARA
evaluated O
by O
numerical B-ENAT
simulations E-ENAT
result O
in O
the O
suppression O
of O
the O
interdendritic O
voids S-CONPRI
. O


The O
use O
of O
feedstocks S-MATE
from O
metal B-MANP
injection I-MANP
molding E-MANP
( O
MIM O
) O
for O
the O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
of O
green B-PRO
parts E-PRO
, O
which O
are O
then O
debound O
and O
sintered S-MANP
in O
a O
process S-CONPRI
called O
shaping S-MANP
, O
debinding S-CONPRI
, O
and O
sintering S-MANP
( O
SDS O
) O
, O
is O
promising O
in O
terms O
of O
production B-CONPRI
costs E-CONPRI
of O
metallic B-MACEQ
parts E-MACEQ
. O


However O
, O
in O
order O
to O
use O
the O
cost-efficient O
AM B-MANP
technique E-MANP
fused O
filament S-MATE
fabrication S-MANP
( O
FFF S-MANP
) O
for O
SDS O
, O
powder-binder O
mixtures O
known O
for O
MIM O
feedstocks S-MATE
must O
be S-MATE
adapted O
to O
filament S-MATE
requirements O
resulting O
in O
adjustments O
to O
debinding S-CONPRI
and O
sintering S-MANP
. O


In O
contrast O
to O
FFF S-MANP
, O
screw-based O
material B-MANP
extrusion E-MANP
is O
capable O
of O
processing O
already O
available O
MIM O
feedstocks S-MATE
, O
but O
machine S-MACEQ
costs O
are O
high O
due O
to O
complex O
print B-MACEQ
heads E-MACEQ
. O


In O
this O
work O
, O
a O
new O
process S-CONPRI
called O
piston-based O
feedstock S-MATE
fabrication S-MANP
( O
PFF O
) O
is O
developed O
for O
processing O
already O
available O
MIM O
feedstocks S-MATE
at O
comparable O
costs O
to O
FFF S-MANP
. O


First O
, O
the O
state O
of O
the O
art S-APPL
is O
reviewed O
highlighting O
the O
potential O
of O
piston-based O
material B-MANP
extrusion E-MANP
for O
its O
usage O
in O
SDS O
. O


Experimental S-CONPRI
studies O
are O
performed O
to O
validate O
the O
developed O
PFF O
printer S-MACEQ
. O


As S-MATE
material O
, O
a O
Ti-6Al-4V S-MATE
MIM O
feedstock S-MATE
is O
used O
. O


Thresholds O
for O
piston S-APPL
speed O
( O
0.175 O
mm/min O
) O
, O
extrusion S-MANP
temperature O
( O
80 O
°C O
) O
, O
and O
nozzle B-CONPRI
diameter E-CONPRI
( O
0.4 O
mm S-MANP
) O
are O
determined O
to O
ensure O
a O
viscosity S-PRO
that O
allows O
to O
control O
the O
extrusion B-MANP
process E-MANP
via O
steps O
per O
mm S-MANP
. O


With O
these O
thresholds O
it O
is O
found O
that O
a O
constant O
extrusion B-MANP
process E-MANP
can O
be S-MATE
established O
in O
a O
filling O
range S-PARA
of O
the O
cylinder O
up O
to O
155 O
mm S-MANP
. O


Finally O
, O
the O
performance S-CONPRI
of O
the O
PFF O
system O
is O
evaluated O
in O
terms O
of O
nozzle S-MACEQ
geometry S-CONPRI
, O
print S-MANP
speed O
, O
and O
reproducibility S-CONPRI
showing O
that O
reproducible O
green B-PRO
part E-PRO
properties O
are O
achieved O
at O
a O
maximum O
speed O
of O
8.18 O
mm/s O
while O
using O
a O
tapered O
FFF S-MANP
nozzle O
. O


A O
thermo-mechanical B-CONPRI
model E-CONPRI
of O
directed B-MANP
energy I-MANP
deposition I-MANP
additive I-MANP
manufacturing E-MANP
of O
Ti–6Al–4V O
is O
developed O
using O
measurements O
of O
the O
surface S-CONPRI
convection O
generated O
by O
gasses O
flowing O
during O
the O
deposition S-CONPRI
. O


In O
directed B-MANP
energy I-MANP
deposition E-MANP
, O
material S-MATE
is O
injected O
into O
a O
melt B-MATE
pool E-MATE
that O
is O
traversed O
to O
fill O
in O
a O
cross-section O
of O
a O
part O
, O
building O
it O
layer-by-layer S-CONPRI
. O


This O
creates O
large O
thermal B-PARA
gradients E-PARA
that O
generate O
plastic B-PRO
deformation E-PRO
and O
residual B-PRO
stresses E-PRO
. O


Finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
( O
FEA O
) O
is O
often O
used O
to O
study O
these O
phenomena O
using O
simple S-MANP
assumptions O
of O
the O
surface S-CONPRI
convection O
. O


This O
work O
proposes O
that O
a O
detailed O
knowledge O
of O
the O
surface S-CONPRI
heat B-CONPRI
transfer E-CONPRI
is O
required O
to O
produce O
more O
accurate S-CHAR
FEA O
results O
. O


The O
surface S-CONPRI
convection O
generated O
by O
the O
deposition B-MANP
process E-MANP
is O
measured O
and O
implemented O
in O
the O
thermo-mechanical B-CONPRI
model E-CONPRI
. O


Three O
depositions O
with O
different O
geometries S-CONPRI
and O
dwell B-PARA
times E-PARA
are O
used O
to O
validate O
the O
model S-CONPRI
using O
in B-CONPRI
situ E-CONPRI
measurements O
of O
the O
temperature S-PARA
and O
deflection O
as S-MATE
well O
as S-MATE
post-process O
measurements O
of O
the O
residual B-PRO
stress E-PRO
. O


An O
additional O
model S-CONPRI
is O
developed O
using O
the O
assumption O
of O
free O
convection O
on O
all O
surfaces S-CONPRI
. O


The O
results O
show O
that O
a O
measurement-based O
convection O
model S-CONPRI
is O
required O
to O
produce O
accurate S-CHAR
simulation O
results O
. O


Easily O
segregated O
Cu-15Ni-8Sn O
alloy S-MATE
bulk O
material S-MATE
was O
fabricated S-CONPRI
using O
a O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
process S-CONPRI
. O


The O
microstructure S-CONPRI
of O
SLM-manufactured O
Cu-15Ni-8Sn O
alloy S-MATE
was O
investigated O
using O
optical B-CHAR
microscopy E-CHAR
( O
OM S-CHAR
) O
, O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
, O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
, O
and O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
TEM S-CHAR
) O
. O


Differences O
in O
the O
microstructures S-MATE
and O
elemental O
segregation S-CONPRI
of O
gas-atomized O
alloy S-MATE
powder O
, O
cast S-MANP
ingots O
, O
and O
SLM-manufactured O
samples S-CONPRI
were O
analyzed O
. O


The O
statistical O
average S-CONPRI
grain O
size O
of O
the O
SLM-manufactured O
Cu-15Ni-8Sn O
alloy S-MATE
was O
4.03 O
μm O
. O


Microstructures S-MATE
of O
the O
SLM-manufactured O
sample S-CONPRI
were O
mainly O
composed O
of O
epitaxially O
grown O
slender O
cellular B-FEAT
structures E-FEAT
with O
submicron O
widths O
. O


Microsegregation S-CONPRI
was O
detected O
by O
TEM S-CHAR
, O
and O
80- O
to O
200-nm O
Sn-enriched O
precipitates S-MATE
were O
dispersed O
between O
cellullar O
structures O
. O


Many O
dislocations S-CONPRI
and O
dislocation S-CONPRI
tangles O
appeared O
around O
the O
precipitates S-MATE
. O


An O
EBSD S-CHAR
test O
revealed O
that O
most O
local O
misorientations O
within O
3 O
degrees O
were O
concentrated O
in O
fusion S-CONPRI
line O
regions O
. O


Compared O
with O
cast S-MANP
ingots O
, O
the O
yield B-PRO
strength E-PRO
Rp0.2 O
, O
ultimate B-PRO
tensile I-PRO
strength E-PRO
Rm O
, O
elongation S-PRO
A O
, O
and O
elastic B-PRO
modulus E-PRO
E O
of O
the O
SLM-manufactured O
sample S-CONPRI
increased O
by O
67 O
% O
, O
24.6 O
% O
, O
360 O
% O
, O
and O
7 O
% O
, O
respectively O
. O


Moreover O
, O
the O
SLM-manufactured O
Cu-15Ni-8Sn O
alloy S-MATE
could O
be S-MATE
directly O
aged O
at O
350℃ O
for O
12 O
h O
, O
reaching O
Rm O
= O
991.1 O
MPa S-CONPRI
and O
A O
=3 O
% O
, O
with O
no O
need O
for O
solid B-MATE
solution E-MATE
treatment O
or O
cold B-MANP
working E-MANP
. O


A O
method O
for O
modeling S-ENAT
the O
effect O
of O
stress B-CONPRI
relaxation E-CONPRI
at O
high O
temperatures S-PARA
during O
laser S-ENAT
direct B-MANP
energy I-MANP
deposition E-MANP
processes O
is O
experimentally B-CONPRI
validated E-CONPRI
for O
Ti-6Al-4V S-MATE
samples S-CONPRI
subject O
to O
different O
inter-layer O
dwell B-PARA
times E-PARA
. O


The O
predicted S-CONPRI
mechanical B-CONPRI
responses E-CONPRI
are O
compared O
to O
those O
of O
Inconel® O
625 O
samples S-CONPRI
, O
which O
experience O
no O
allotropic O
phase S-CONPRI
transformation O
, O
deposited O
under O
identical O
process S-CONPRI
conditions O
. O


The O
thermal O
response O
of O
workpieces O
in O
additive B-MANP
manufacturing E-MANP
is O
known O
to O
be S-MATE
strongly O
dependent O
on O
dwell B-PARA
time E-PARA
. O


In O
this O
work O
the O
dwell B-PARA
times E-PARA
used O
vary O
from O
0 O
to O
40 O
s. O
Based O
on O
past O
research S-CONPRI
on O
ferretic O
steels S-MATE
and O
the O
additive B-MANP
manufacturing E-MANP
of O
titanium B-MATE
alloys E-MATE
it O
is O
assumed O
that O
the O
effect O
of O
transformation O
strain S-PRO
in O
Ti-6Al-4V S-MATE
acts O
to O
oppose O
all O
other O
strain S-PRO
components S-MACEQ
, O
effectively O
eliminating O
all O
residual B-PRO
stress E-PRO
at O
temperatures S-PARA
above O
690 O
°C O
. O


The O
model S-CONPRI
predicts O
that O
Inconel® O
625 O
exhibits O
increasing O
distortion S-CONPRI
with O
decreasing O
dwell B-PARA
times E-PARA
but O
that O
Ti-6Al-4V S-MATE
displays O
the O
opposite O
behavior O
, O
with O
distortion S-CONPRI
dramatically O
decreasing O
with O
lowering O
dwell B-PARA
time E-PARA
. O


These O
predictions S-CONPRI
are O
accurate S-CHAR
when O
compared O
with O
experimental S-CONPRI
in O
situ O
and O
post-process S-CONPRI
measurements O
. O


The O
present O
study O
demonstrates O
for O
the O
first O
time O
a O
unique O
UK-designed O
and O
built O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
hybrid B-ENAT
system E-ENAT
that O
combines O
polymer S-MATE
based O
structural O
deposition S-CONPRI
with O
digital O
deposition S-CONPRI
of O
electrically S-CONPRI
conductive O
elements S-MATE
. O


This O
innovative O
manufacturing B-CONPRI
system E-CONPRI
is O
based O
on O
a O
multi-planar O
build S-PARA
approach O
to O
improve O
on O
many O
of O
the O
limitations O
associated O
with O
AM S-MANP
, O
such O
as S-MATE
poor O
surface B-FEAT
finish E-FEAT
, O
low O
geometric B-FEAT
tolerance E-FEAT
and O
poor O
robustness S-PRO
. O


Specifically O
, O
the O
approach O
involves O
a O
multi-planar O
Material B-MANP
Extrusion E-MANP
( O
ME O
) O
process S-CONPRI
in O
which O
separated O
build S-PARA
stations O
with O
up O
to O
5 O
axes O
of O
motion O
replace O
traditional O
horizontally-sliced O
layer S-PARA
modelling O
. O


The O
construction S-APPL
of O
multi-material S-CONPRI
architectures O
also O
involved O
using O
multiple O
print S-MANP
systems O
in O
order O
to O
combine O
both O
ME O
and O
digital O
deposition S-CONPRI
of O
conductive O
material S-MATE
. O


To O
demonstrate O
multi-material B-MANP
3D I-MANP
Printing E-MANP
( O
3DP S-MANP
) O
we O
used O
three O
thermoplastics S-MATE
to O
print S-MANP
specimens O
, O
on O
top O
of O
which O
a O
unique O
Ag O
nano-particulate O
ink S-MATE
was O
printed O
using O
a O
non-contact O
jetting S-MANP
process O
, O
during O
which O
drop O
characteristics O
such O
as S-MATE
shape O
, O
velocity O
, O
and O
volume S-CONPRI
were O
assessed O
using O
a O
bespoke O
drop O
watching O
system O
. O


Electrical S-APPL
analysis O
of O
printed B-MACEQ
conductive E-MACEQ
tracks O
on O
polymer S-MATE
surfaces O
was O
performed O
during O
mechanical B-CHAR
testing E-CHAR
( O
static O
tensile S-PRO
and O
flexural O
testing S-CHAR
and O
dynamic S-CONPRI
fatigue O
testing S-CHAR
) O
to O
assess O
robustness S-PRO
of O
the O
printed O
circuits O
. O


Both O
serpentine O
and O
straight O
line O
patterns O
were O
used O
in O
the O
testing S-CHAR
of O
Ag O
particle S-CONPRI
loaded O
ink S-MATE
and O
they O
showed O
very O
similar O
resistance S-PRO
changes O
during O
mechanical S-APPL
exposure S-CONPRI
. O


Monitored O
resistance S-PRO
and O
stress S-PRO
changed O
as S-MATE
a O
function O
of O
strain S-PRO
exhibiting O
hysteresis S-PRO
with O
more O
prominent O
residual S-CONPRI
strain O
during O
stretching O
and O
compression S-PRO
cycles O
and O
3-point O
bending S-MANP
flexural O
tests O
of O
PA S-CHAR
and O
CoPA O
substrates O
. O


Bare O
and O
encapsulated S-CONPRI
tracks O
exhibited O
low O
electrical B-CHAR
resistivity E-CHAR
( O
1–3*10−6 O
Ω*m O
) O
, O
and O
its O
change O
was O
more O
rapid O
on O
ABS S-MATE
and O
minor O
on O
PA S-CHAR
and O
CoPA O
when O
increasing O
tensile S-PRO
and O
flexural O
strain S-PRO
up O
to O
1.2 O
% O
and O
0.8 O
% O
, O
respectively O
. O


Resistance S-PRO
of O
Ag O
tracks O
on O
ABS S-MATE
also O
increased O
rapidly O
during O
fatigue B-CHAR
testing E-CHAR
and O
the O
tracks O
easily O
fractured O
during O
repeated O
stretching-compression O
cycles O
at O
1 O
% O
and O
1.2 O
% O
strain S-PRO
. O


No O
resistance S-PRO
changes O
of O
Ag O
tracks O
printed O
on O
PA S-CHAR
and O
CoPA O
were O
observed O
at O
lower O
strain S-PRO
amplitudes O
whereas O
at O
higher O
strain S-PRO
amplitudes O
these O
changes O
were O
the O
lowest O
for O
conductive O
tracks O
on O
CoPA O
. O


Thermal B-CHAR
analyses E-CHAR
were O
conducted O
to O
determine O
the O
printed O
material S-MATE
’ O
s S-MATE
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
( O
Tg S-CHAR
) O
, O
stability S-PRO
and O
degradation S-CONPRI
behavior O
to O
find O
the O
optimum O
annealing S-MANP
conditions O
post O
printing O
. O


The O
novel O
AM S-MANP
printer O
has O
the O
ability O
to O
fabricate S-MANP
fully O
functional O
objects O
in O
one O
build S-PARA
, O
including O
integrated O
printed O
circuitry O
and O
embedded B-ENAT
electronics E-ENAT
. O


This O
new O
technology S-CONPRI
also O
gives O
the O
opportunity O
for O
designers O
to O
improve O
existing O
products O
, O
as S-MATE
well O
as S-MATE
create O
new O
products O
with O
the O
added O
advantages O
of O
geometrically O
unconstrained O
3DP S-MANP
. O


This O
paper O
proposes O
computational B-ENAT
models E-ENAT
of O
the O
direct B-MANP
energy I-MANP
deposition E-MANP
and O
powder B-MANP
bed I-MANP
fusion I-MANP
processes E-MANP
developed O
for O
process B-CONPRI
control E-CONPRI
applications O
. O


Both O
models O
are O
built O
upon O
a O
regression S-CONPRI
metamodel O
of O
heat B-CONPRI
transfer E-CONPRI
beneath O
the O
laser B-CONPRI
beam E-CONPRI
, O
to O
which O
an O
auxiliary O
thermal O
model S-CONPRI
is O
added O
to O
account O
for O
residual B-CONPRI
heat E-CONPRI
in O
track-to-track O
interactions O
. O


Both O
models O
are O
coupled O
by O
taking O
temperatures S-PARA
predicted S-CONPRI
with O
the O
auxiliary O
model S-CONPRI
and O
incorporating O
them O
as S-MATE
initial O
conditions O
for O
metamodel O
predictions S-CONPRI
of O
future O
laser B-ENAT
scans E-ENAT
. O


The O
synergy O
of O
the O
metamodel O
and O
the O
auxiliary O
model S-CONPRI
creates O
a O
high-fidelity S-CONPRI
model O
, O
which O
is O
used O
to O
generate O
training O
data S-CONPRI
for O
a O
model-free O
optimal O
controller S-MACEQ
. O


Simulation S-ENAT
results O
prove O
the O
capability O
of O
the O
proposed O
optimal O
controller S-MACEQ
to O
adjust O
scan B-PARA
speed E-PARA
to O
control O
temperature S-PARA
when O
accounting O
for O
track-to-track O
interactions O
. O


One O
of O
the O
serious O
obstacles O
preventing O
wide O
industrial S-APPL
use O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
in O
metals S-MATE
and O
alloys S-MATE
is O
a O
lack O
of O
materials S-CONPRI
available O
for O
this O
technology S-CONPRI
. O


It O
is O
particularly O
true O
for O
the O
Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM® O
) O
process S-CONPRI
, O
where O
only O
a O
few O
materials S-CONPRI
are O
commercially O
available O
, O
which O
significantly O
limits S-CONPRI
the O
use O
of O
the O
method O
. O


One O
of O
the O
dominant O
trends S-CONPRI
in O
AM S-MANP
today O
is O
developing O
processes S-CONPRI
for O
technological O
materials S-CONPRI
already O
widely O
used O
by O
other O
methods O
and O
developed O
for O
other O
industrial S-APPL
applications O
, O
gaining O
further O
advantages O
through O
the O
unique O
value O
added O
by O
additive B-MANP
manufacturing E-MANP
. O


Developing O
new O
materials S-CONPRI
specifically O
for O
additive B-MANP
manufacturing E-MANP
that O
can O
utilize O
the O
properties S-CONPRI
and O
specifics O
of O
the O
method O
in O
full O
is O
still O
a O
research S-CONPRI
and O
development O
subject O
, O
and O
such O
materials S-CONPRI
are O
yet O
far O
from O
full O
scale O
industrial S-APPL
usage O
. O


Stainless B-MATE
steels E-MATE
are O
widely O
used O
in O
industry S-APPL
due O
to O
good O
mechanical B-CONPRI
properties E-CONPRI
, O
corrosion B-CONPRI
resistance E-CONPRI
and O
low O
cost O
of O
material S-MATE
. O


Hence O
, O
there O
is O
potentially O
a O
market O
for O
this O
material S-MATE
and O
one O
possible O
business O
driver O
compared O
with O
casting S-MANP
for O
example O
is O
that O
lead B-PARA
times E-PARA
could O
be S-MATE
cut O
drastically O
by O
utilizing O
an O
additive S-MATE
approach O
for O
one-off O
or O
small O
series O
production S-MANP
. O


This O
paper O
presents O
results O
from O
the O
additive B-MANP
manufacturing E-MANP
of O
components S-MACEQ
from O
the O
known O
alloy S-MATE
316L O
using O
EBM® O
. O


Previously O
the O
samples S-CONPRI
of O
316L O
were O
made O
by O
laser-based O
AM B-MANP
technology E-MANP
. O


This O
work O
was O
performed O
as S-MATE
a O
part O
of O
the O
large O
project O
with O
the O
long O
term O
aim O
to O
use O
additively B-MANP
manufactured E-MANP
components O
in O
a O
nuclear O
fusion S-CONPRI
reactor O
. O


Components S-MACEQ
and O
test O
samples S-CONPRI
successfully O
made O
from O
316L B-MATE
stainless I-MATE
steel E-MATE
using O
EBM® O
process S-CONPRI
show O
promising O
mechanical B-CONPRI
properties E-CONPRI
, O
density S-PRO
and O
hardness S-PRO
compared O
to O
its O
counterpart O
made O
by O
powder B-MANP
metallurgy E-MANP
( O
hot B-MANP
isostatic I-MANP
pressing E-MANP
, O
HIP S-MANP
) O
. O


As S-MATE
with O
the O
other O
materials S-CONPRI
made O
by O
EBM® O
process S-CONPRI
, O
316L O
samples S-CONPRI
show O
rather O
low O
porosity S-PRO
. O


Present O
paper O
also O
reports O
on O
the O
hierarchical O
microstructure S-CONPRI
features O
of O
the O
316L O
material S-MATE
processed O
by O
EBM® O
characterized O
by O
optical S-CHAR
and O
electron B-CHAR
microscopy E-CHAR
. O


Roles O
of O
heat B-MANP
treatment E-MANP
and O
build B-PARA
direction E-PARA
are O
analyzed O
for O
SLM S-MANP
IN718 S-MATE
. O


The O
strength S-PRO
and O
anisotropic S-PRO
characteristics O
is O
explained O
via O
microstructure S-CONPRI
. O


High B-PARA
resolution E-PARA
tomography O
displays O
the O
prevalence O
of O
near O
surface S-CONPRI
porosity S-PRO
. O


Strain S-PRO
partitioning O
is O
observed O
based O
on O
the O
γ O
’ O
’ O
precipitates S-MATE
diffraction S-CHAR
spots O
. O


The O
benefits O
of O
additive B-MANP
manufacturing E-MANP
have O
been O
well O
documented O
, O
but O
prior O
to O
these O
materials S-CONPRI
being O
used O
in O
critical O
applications O
, O
the O
deformation S-CONPRI
mechanisms O
must O
be S-MATE
properly O
characterized O
. O


In O
this O
work O
, O
the O
role O
of O
heat B-MANP
treatment E-MANP
and O
build B-PARA
orientation E-PARA
of O
selective B-MANP
laser I-MANP
melting E-MANP
IN718 S-MATE
is O
investigated O
through O
detailed O
characterization O
. O


The O
microstructure S-CONPRI
of O
this O
material S-MATE
is O
probed O
through O
a O
combination O
of O
electron B-CHAR
microscopy E-CHAR
to O
identify O
the O
precipitate S-MATE
structure O
, O
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
to O
quantify O
the O
grain-level O
features O
, O
and O
synchrotron-based O
X-ray S-CHAR
microcomputed O
tomography O
to O
detect O
porosity S-PRO
. O


A O
high O
degree O
of O
porosity S-PRO
is O
observed O
spatially O
near O
the O
free B-CONPRI
surface E-CONPRI
of O
the O
part O
, O
where O
the O
contour S-FEAT
during O
the O
build S-PARA
process O
meets O
the O
interior O
hatch O
. O


Further O
, O
microstructure S-CONPRI
based O
deformation S-CONPRI
mechanisms O
are O
explored O
through O
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
relative O
to O
the O
grain S-CONPRI
features O
after O
monotonic O
and O
cyclic B-PRO
loading E-PRO
and O
in B-CONPRI
situ E-CONPRI
high-energy O
X-ray B-CHAR
diffraction E-CHAR
to O
identify O
the O
lattice S-CONPRI
strain O
evolution S-CONPRI
in O
these O
materials S-CONPRI
. O


Demarcations O
between O
the O
behaviors O
of O
the O
as-built O
versus O
post-processed O
materials S-CONPRI
are O
discussed O
; O
specifically O
, O
in O
terms O
of O
anisotropy S-PRO
with O
respect O
to O
build B-PARA
direction E-PARA
and O
values O
of O
the O
strength B-PRO
properties E-PRO
, O
based O
on O
the O
grain S-CONPRI
morphology O
, O
coherent O
twin O
formation O
, O
and O
precipitate S-MATE
structure O
. O


Lastly O
, O
the O
presence O
of O
dislocation S-CONPRI
sub-structures O
within O
the O
grains S-CONPRI
is O
observed O
to O
homogenize O
deformation S-CONPRI
within O
the O
as-built O
sample S-CONPRI
, O
while O
strain S-PRO
partitioning O
is O
observed O
during O
loading O
of O
the O
post-processed O
sample S-CONPRI
. O


A O
process S-CONPRI
is O
presented O
for O
the O
rapid O
production S-MANP
of O
microstructured O
monofilaments O
via O
thermal O
drawing S-MANP
of O
additively B-MANP
manufactured E-MANP
polymer O
preforms O
. O


Preforms O
are O
produced O
wholly O
, O
or O
in O
part O
, O
via O
fused B-MANP
filament I-MANP
fabrication E-MANP
of O
acrylonitrile-butadiene-styrene O
( O
ABS S-MATE
) O
and O
polycarbonate S-MATE
materials S-CONPRI
. O


Example O
monofilaments O
include O
“ O
microprinted O
” O
monofilaments O
that O
contain O
an O
arbitrary O
image S-CONPRI
embedded O
in O
the O
monofilament O
cross B-CONPRI
section E-CONPRI
; O
microfluidic O
monofilaments O
in O
which O
flow O
channels O
are O
formed O
by O
combining O
optically O
transparent S-CONPRI
and O
opaque O
materials S-CONPRI
; O
dual-material S-CONPRI
monofilaments O
that O
combine O
ABS S-MATE
and O
polycarbonate S-MATE
into O
a O
regular O
spoked O
geometry S-CONPRI
with O
five-fold O
symmetry O
; O
and O
a O
microfluidic O
preform O
co-fed O
with O
glass S-MATE
optical O
fiber S-MATE
, O
allowing O
both O
fluid S-MATE
and O
light O
transmission S-CHAR
through O
the O
monofilament O
. O


The O
primary O
advantages O
of O
this O
monofilament O
fabrication S-MANP
technique O
include O
short O
lead B-PARA
times E-PARA
; O
minimal O
investment O
in O
materials S-CONPRI
and O
equipment S-MACEQ
; O
a O
means O
of O
directly O
combining O
multiple O
materials S-CONPRI
into O
a O
single O
monofilament O
, O
even O
if O
the O
material S-MATE
components S-MACEQ
have O
different O
thermorheological O
properties S-CONPRI
; O
and O
the O
ability O
to O
create O
arbitrary O
and O
complex B-CONPRI
geometries E-CONPRI
. O


Energy O
system O
components S-MACEQ
with O
embedded O
sensors S-MACEQ
, O
or O
smart O
parts O
, O
can O
be S-MATE
a O
pathway O
in O
obtaining O
real-time O
system O
performance S-CONPRI
feedback S-PARA
and O
in B-CONPRI
situ E-CONPRI
monitoring O
during O
operation O
. O


Traditional O
surface S-CONPRI
contact S-APPL
or O
cavity O
placed O
sensors S-MACEQ
increase O
the O
possibility O
of O
disturbing O
the O
normal O
operation O
of O
energy O
systems O
due O
to O
changes O
in O
part O
design S-FEAT
required O
for O
sensor S-MACEQ
placement O
. O


The O
fabrication S-MANP
of O
smart O
parts O
using O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technology S-CONPRI
can O
allow O
the O
flexibility S-PRO
of O
embedding O
a O
sensor S-MACEQ
within O
a O
structure S-CONPRI
without O
compromising O
the O
structure S-CONPRI
and/or O
functionality O
. O


The O
embedding O
of O
a O
sensor S-MACEQ
within O
a O
desired O
location O
allows O
an O
end O
user O
the O
ability O
to O
monitor S-CONPRI
specific O
critical O
regions O
that O
are O
of O
interest O
such O
as S-MATE
high O
temperature S-PARA
and O
pressure S-CONPRI
( O
e.g. O
, O
combustor O
inlet S-MACEQ
conditions O
that O
can O
reach O
up O
to O
810 O
K S-MATE
and O
2760 O
kPa O
) O
. O


In O
addition O
, O
the O
non-intrusive O
placement O
of O
the O
sensor S-MACEQ
within O
a O
part O
’ O
s S-MATE
body O
can O
increase O
the O
sensor S-MACEQ
’ O
s S-MATE
life O
span O
by O
isolating S-CONPRI
the O
sensor S-MACEQ
from O
the O
aforementioned O
harsh O
operating O
environments O
. O


This O
paper O
focuses O
on O
the O
fabrication S-MANP
of O
smart O
parts O
using O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
AM B-MANP
technology E-MANP
as O
well O
as S-MATE
the O
characterization O
of O
the O
sensor S-MACEQ
’ O
s S-MATE
functionality O
. O


The O
development O
of O
a O
“ O
stop O
and O
go S-MATE
” O
process S-CONPRI
was O
explored O
that O
comprised O
of O
pausing O
a O
part O
’ O
s S-MATE
fabrication S-MANP
process O
to O
allow O
the O
placement O
of O
piezoelectric O
ceramic B-MATE
material E-MATE
into O
pre-designed O
cavities O
within O
a O
part O
’ O
s S-MATE
body O
, O
and O
resuming O
the O
process S-CONPRI
to O
complete O
the O
final O
product O
. O


A O
compression B-CHAR
test E-CHAR
was O
performed O
on O
the O
smart O
parts O
fabricated S-CONPRI
using O
EBM S-MANP
to O
demonstrate O
the O
sensor S-MACEQ
’ O
s S-MATE
capability O
of O
sensing S-APPL
external O
forces S-CONPRI
. O


A O
maximum O
sensing S-APPL
voltage O
response O
of O
approximately O
3 O
V S-MATE
was O
detected O
with O
a O
maximum O
pressure S-CONPRI
not O
exceeding O
40 O
MPa S-CONPRI
. O


This O
research S-CONPRI
work O
demonstrates O
the O
feasibility S-CONPRI
of O
fabricating S-MANP
smart O
parts O
with O
embedded O
sensors S-MACEQ
without O
the O
need O
of O
post-processing S-CONPRI
( O
e.g. O
, O
CNC B-MANP
machining E-MANP
and O
polishing S-MANP
) O
. O


In O
addition O
, O
the O
sensing S-APPL
capability O
of O
monitoring O
a O
component S-MACEQ
’ O
s S-MATE
performance S-CONPRI
has O
been O
validated O
, O
leading O
to O
the O
possibility O
of O
fabricating S-MANP
other O
smart O
parts O
that O
could O
impact S-CONPRI
industries O
such O
as S-MATE
energy O
, O
aerospace S-APPL
, O
automotive S-APPL
, O
and O
biomedical B-APPL
industries E-APPL
for O
applications O
like O
air/fuel O
pre-mixing O
, O
pressure B-MANP
tubes E-MANP
, O
and O
turbine B-APPL
blades E-APPL
. O


Recycling S-CONPRI
metal B-MATE
powders E-MATE
in O
the O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
is O
an O
important O
consideration O
in O
affordability O
with O
reference O
to O
traditional B-MANP
manufacturing E-MANP
. O


Metal B-MATE
powder E-MATE
recyclability O
has O
been O
studied O
before O
with O
respect O
to O
change O
in O
chemical B-CONPRI
composition E-CONPRI
of O
powders S-MATE
, O
effect O
on O
mechanical B-CONPRI
properties E-CONPRI
of O
produced O
parts O
, O
effect O
on O
flowability O
of O
powders S-MATE
and O
powder S-MATE
morphology S-CONPRI
. O


In O
this O
paper O
, O
we O
propose O
a O
data-driven O
method O
to O
understand O
in B-CONPRI
situ E-CONPRI
behavior O
of O
recycled S-CONPRI
powder S-MATE
on O
the O
build B-MACEQ
platform E-MACEQ
. O


Our O
method O
is O
based O
on O
comprehensive O
analysis O
of O
log O
file S-MANS
data S-CONPRI
from O
various O
sensors S-MACEQ
used O
in O
the O
process S-CONPRI
of O
printing O
metal S-MATE
parts O
in O
the O
Arcam O
Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM S-MANP
) O
® O
system O
. O


Using O
rake O
position O
data S-CONPRI
and O
rake O
sensor S-MACEQ
pulse O
data S-CONPRI
collected O
during O
Arcam O
builds S-CHAR
, O
we O
found O
that O
Inconel B-MATE
718 E-MATE
powders O
exhibit O
additional O
powder S-MATE
spreading O
operations O
with O
increased O
reuse O
cycles O
compared O
to O
Ti-6Al-4V B-MATE
powders E-MATE
. O


We O
substantiate O
differences O
found O
in O
in B-CONPRI
situ E-CONPRI
behavior O
of O
Ti-6Al-4V S-MATE
and O
Inconel B-MATE
718 E-MATE
powders O
using O
known O
sintering S-MANP
behavior O
of O
the O
two O
powders S-MATE
. O


The O
novelty O
of O
this O
work O
lies O
in O
the O
new O
approach O
to O
understanding O
powder S-MATE
behavior O
especially O
spreadability O
using O
in B-CONPRI
situ E-CONPRI
log O
file S-MANS
data S-CONPRI
that O
is O
regularly O
collected O
in O
Arcam O
EBM® O
builds S-CHAR
rather O
than O
physical O
testing S-CHAR
of O
parts O
and O
powders S-MATE
post O
build S-PARA
. O


In O
addition O
to O
studying O
powder S-MATE
recyclability O
, O
the O
proposed O
methodology S-CONPRI
has O
potential O
to O
be S-MATE
extended O
generically O
to O
monitor S-CONPRI
powder O
behavior O
in O
AM B-MANP
processes E-MANP
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
provides O
an O
economic O
approach O
to O
manufacturing S-MANP
Ni-base O
superalloy O
components S-MACEQ
for O
high-pressure O
gas B-MACEQ
turbines E-MACEQ
as S-MATE
well O
as S-MATE
repairing O
damaged O
blade O
sections O
during O
operation O
. O


In O
this O
study O
, O
two O
advanced O
processing O
routes O
are O
combined O
: O
SLM S-MANP
, O
to O
fabricate S-MANP
small O
specimens O
of O
the O
nonweldable O
CMSX-4 O
, O
and O
hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
with O
a O
rapid O
cooling B-PARA
rate E-PARA
as S-MATE
post-processing O
to O
heal O
defects S-CONPRI
while O
the O
target O
γ/γ´ O
microstructure S-CONPRI
is O
developed O
. O


An O
initial O
parametric O
study O
is O
carried O
out O
to O
investigate O
the O
influence O
of O
the O
SLM S-MANP
process B-CONPRI
parameters E-CONPRI
on O
the O
microstructure S-CONPRI
and O
defects S-CONPRI
occurring O
during O
SLM S-MANP
. O


Special O
emphasis O
is O
placed O
on O
understanding O
and O
characterizing O
the O
as-built O
SLM S-MANP
microstructures S-MATE
by O
means O
of O
high-resolution S-PARA
characterization O
techniques O
. O


The O
post-processing B-CONPRI
heat E-CONPRI
treatment O
is O
then O
optimized O
with O
respect O
to O
segregation S-CONPRI
and O
the O
γ/γ´ O
microstructure S-CONPRI
. O


This O
article O
proposes O
a O
new O
method O
for O
reducing O
the O
amount O
of O
support B-MATE
material E-MATE
required O
for O
3-D S-CONPRI
printing O
of O
complex O
designs S-FEAT
generated O
by O
topology B-FEAT
optimization E-FEAT
. O


This O
procedure O
relies O
on O
solving O
sequentially O
two O
structural B-CONPRI
optimization E-CONPRI
problems O
– O
the O
first O
on O
a O
discrete O
truss-based O
model S-CONPRI
and O
the O
second O
on O
a O
continuum-based O
model S-CONPRI
. O


In O
the O
optimization S-CONPRI
of O
the O
discrete O
model S-CONPRI
, O
the O
maximum O
overhang S-PARA
limitation O
is O
imposed O
based O
on O
geometrical O
parameters S-CONPRI
. O


The O
optimized O
discrete O
pattern S-CONPRI
is O
then O
projected O
on O
to O
the O
continuum S-CONPRI
so O
that O
it O
influences O
the O
material S-MATE
distribution S-CONPRI
in O
the O
continuum S-CONPRI
optimization O
. O


Numerical O
results O
indicate O
that O
the O
designs S-FEAT
obtained O
by O
this O
approach O
exhibit O
improved O
printability S-PARA
as S-MATE
they O
have O
fewer O
overhanging B-FEAT
features E-FEAT
. O


In O
some O
cases O
, O
practically O
no O
supporting O
material S-MATE
will O
be S-MATE
required O
for O
printing O
the O
optimized O
design S-FEAT
. O


The O
importance O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
to O
the O
future O
of O
product B-FEAT
design E-FEAT
and O
manufacturing S-MANP
infrastructure O
demands O
educational O
programs O
tailored O
to O
embrace O
its O
fundamental O
principles O
and O
its O
innovative O
potential O
. O


The O
lectures O
begin O
with O
in-depth O
technical O
analysis O
of O
the O
major O
AM B-MANP
processes E-MANP
and O
machine S-MACEQ
technologies O
, O
then O
focus O
on O
special O
topics O
including O
design S-FEAT
methods O
, O
machine S-MACEQ
controls O
, O
applications O
of O
AM S-MANP
to O
major O
industry S-APPL
needs O
, O
and O
emerging O
processes S-CONPRI
and O
materials S-CONPRI
. O


In O
lab O
sessions O
, O
students O
operate O
and O
characterize O
desktop O
AM B-MACEQ
machines E-MACEQ
, O
and O
work O
in O
teams O
to O
design S-FEAT
and O
fabricate S-MANP
a O
bridge S-APPL
having O
maximum O
strength S-PRO
per O
unit O
weight S-PARA
while O
conforming O
to O
geometric O
constraints O
. O


In O
a O
single O
semester O
of O
the O
course O
, O
teams O
created O
prototype S-CONPRI
machines S-MACEQ
for O
3D B-MANP
printing E-MANP
of O
molten B-MATE
glass E-MATE
, O
3D B-MANP
printing E-MANP
of O
soft-serve O
ice O
cream O
, O
robotic O
deposition S-CONPRI
of O
biodegradable B-PRO
material E-PRO
, O
direct-write O
deposition S-CONPRI
of O
continuous B-MATE
carbon I-MATE
fiber E-MATE
composites S-MATE
, O
large-area O
parallel O
extrusion S-MANP
of O
polymers S-MATE
, O
and O
in B-CONPRI
situ E-CONPRI
optical O
scanning S-CONPRI
during O
3D B-MANP
printing E-MANP
. O


Several O
of O
these O
projects O
led S-APPL
to O
patent S-CONPRI
applications O
, O
follow-on O
research S-CONPRI
, O
and O
peer-reviewed O
publications O
. O


We O
conclude O
that O
AM S-MANP
education O
, O
while O
arguably O
rooted O
in O
mechanical B-APPL
engineering E-APPL
, O
is O
truly O
multidisciplinary O
, O
and O
that O
education O
programs O
must O
embrace O
this O
context O
. O


A O
novel O
soft O
mold S-MACEQ
casting S-MANP
method O
for O
metal S-MATE
part O
fabrication S-MANP
is O
developed O
. O


The O
paste O
can O
be S-MATE
utilized O
with O
direct O
paste O
printing O
and O
soft O
mold S-MACEQ
casting S-MANP
. O


Three-dimensional S-CONPRI
metal S-MATE
parts O
can O
be S-MATE
obtained O
with O
good O
geometric O
precision S-CHAR
. O


Recently O
, O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
of O
metals S-MATE
has O
enjoyed O
significant O
advancement O
. O


While O
the O
mainstream O
AM S-MANP
methods O
utilize O
high-energy O
power S-PARA
beams O
to O
melt S-CONPRI
metal O
powders S-MATE
, O
other O
low-cost O
alternatives O
are O
also O
being O
developed O
( O
e.g. O
, O
direct O
ink B-MANP
printing E-MANP
) O
. O


In O
this O
study O
, O
a O
copper S-MATE
powder-binder O
paste O
is O
developed O
, O
which O
is O
not O
only O
capable O
to O
be S-MATE
used O
for O
direct O
printing O
, O
but O
also O
to O
be S-MATE
cast O
using O
soft O
molds S-MACEQ
. O


Dense O
three-dimensional S-CONPRI
parts O
can O
be S-MATE
obtained O
by O
sintering S-MANP
green B-CONPRI
bodies E-CONPRI
. O


The O
electrical S-APPL
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
sintered S-MANP
samples S-CONPRI
are O
evaluated O
by O
conductivity S-PRO
, O
hardness S-PRO
measurements O
and O
tensile B-CHAR
tests E-CHAR
, O
respectively O
. O


The O
results O
are O
comparable O
to O
other O
powder S-MATE
processed O
copper S-MATE
materials O
. O


The O
properties S-CONPRI
of O
3-D S-CONPRI
printed O
polymeric O
parts O
depend O
significantly O
on O
the O
processing O
conditions O
under O
which O
they O
are O
fabricated S-CONPRI
. O


This O
study O
aims O
to O
determine O
how O
the O
use O
of O
low-pressure O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processing O
conditions O
, O
influences O
the O
mechanical S-APPL
performance O
of O
printed O
polymeric O
parts O
. O


This O
polymer B-MATE
material E-MATE
extrusion S-MANP
( O
PME S-MANP
) O
study O
was O
carried O
out O
using O
an O
open-source S-CONPRI
desktop O
printer S-MACEQ
, O
under O
both O
low O
pressure S-CONPRI
( O
1 O
Pa S-CHAR
) O
and O
at O
atmospheric O
pressure S-CONPRI
. O


The O
printing O
study O
was O
carried O
out O
using O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
, O
polylactic B-MATE
acid E-MATE
( O
PLA S-MATE
) O
and O
a O
nylon S-MATE
co-polymer O
( O
PA6 O
) O
. O


The O
resultant O
polymer S-MATE
parts O
were O
compared O
based O
on O
their O
printed O
mass O
, O
density S-PRO
, O
volume S-CONPRI
, O
porosity S-PRO
, O
surface S-CONPRI
energy O
, O
ATR-IR O
analysis O
and O
thermal B-CONPRI
properties E-CONPRI
( O
DSC S-CHAR
) O
. O


As S-MATE
expected O
only O
minor O
differences O
in O
chemical O
functionality O
were O
observed O
between O
parts O
printed O
under O
the O
two O
processing O
pressures S-CONPRI
. O


Under O
low-pressure O
printing O
conditions O
, O
the O
polymer S-MATE
parts O
exhibited O
some O
physical O
changes O
, O
when O
compared O
to O
those O
, O
printed O
under O
atmospheric O
conditions O
, O
such O
as S-MATE
an O
increase O
in O
density S-PRO
and O
a O
decrease O
in O
porosity S-PRO
. O


Comparing O
low-pressure O
printed O
type O
V S-MATE
dog O
bones O
( O
ASTM O
D-638 O
) O
, O
with O
those O
printed O
at O
atmospheric O
pressure S-CONPRI
, O
it O
was O
observed O
that O
the O
ABS S-MATE
, O
PLA S-MATE
and O
PA6 O
exhibited O
an O
increase O
in O
Ultimate B-PRO
Tensile I-PRO
Strength E-PRO
of O
9 O
% O
, O
13 O
% O
and O
42 O
% O
respectively O
. O


It O
is O
proposed O
that O
the O
superior O
mechanical B-CONPRI
properties E-CONPRI
obtained O
for O
polymers S-MATE
printed O
under O
low O
pressure S-CONPRI
conditions O
, O
may O
be S-MATE
due O
to O
a O
combination O
of O
two O
factors O
. O


These O
are O
the O
reduction S-CONPRI
in O
porosity S-PRO
of O
the O
printed O
part O
and O
the O
reduction S-CONPRI
in O
heat S-CONPRI
loss O
at O
the O
printed O
polymer S-MATE
surface O
, O
yielding O
enhanced O
bonding S-CONPRI
between O
the O
polymer S-MATE
layers O
. O


In O
a O
further O
printing O
study O
carried O
out O
at O
atmospheric O
pressure S-CONPRI
in O
a O
nitrogen S-MATE
atmosphere O
, O
it O
was O
also O
demonstrated O
that O
any O
oxidation S-MANP
of O
the O
polymer S-MATE
layers O
during O
printing O
, O
did O
not O
significantly O
influence O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
resultant O
printed O
parts O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
are O
used O
to O
build S-PARA
structural O
components S-MACEQ
layer-by-layer O
. O


Cold O
spray O
is O
considered O
an O
AM B-MANP
process E-MANP
, O
whereby O
particles B-CONPRI
impact E-CONPRI
a O
substrate S-MATE
at O
high O
velocities O
to O
generate O
the O
deposition B-PARA
layer E-PARA
. O


Effect O
of O
spray O
angles O
on O
bonding B-PRO
strength E-PRO
at O
the O
cold O
spray O
deposit O
and O
substrate S-MATE
interface S-CONPRI
was O
experimentally O
investigated O
. O


The O
results O
showed O
that O
bonding B-PRO
strength E-PRO
increased O
with O
decreasing O
spray O
angle O
from O
the O
normal O
direction O
( O
90° O
spray O
angle O
) O
, O
and O
the O
maximum O
bonding B-PRO
strength E-PRO
was O
observed O
at O
45° O
spray O
angle O
; O
however O
, O
the O
deposition S-CONPRI
efficiency O
and O
strength S-PRO
of O
the O
bulk O
deposit O
material S-MATE
decreased O
with O
decreasing O
spray O
angle O
. O


3D S-CONPRI
finite O
element S-MATE
modeling O
of O
single-particle O
impact S-CONPRI
combined O
with O
experimental S-CONPRI
observation O
of O
“ O
splat O
” O
deposits O
was O
conducted O
to O
understand O
bonding S-CONPRI
process O
under O
different O
spray O
angles O
. O


The O
relationships O
between O
parameters S-CONPRI
contributing O
bonding S-CONPRI
formations O
( O
e.g. O
, O
plastic B-PRO
deformation E-PRO
and O
temperature S-PARA
rise O
due O
to O
impact S-CONPRI
) O
and O
processing O
parameters S-CONPRI
( O
e.g. O
, O
spray O
angles O
, O
impact S-CONPRI
velocity O
, O
pre-heating O
temperature S-PARA
) O
were O
established O
and O
discussed O
. O


These O
relationships O
are O
useful O
for O
understanding O
bonding B-CHAR
mechanisms E-CHAR
and O
strengths S-PRO
of O
deposits O
sprayed S-MANP
at O
different O
angles O
and O
can O
be S-MATE
used O
to O
define O
an O
optimized O
spray O
angle O
. O


The O
modeling S-ENAT
results O
also O
revealed O
that O
increasing O
particle S-CONPRI
impact S-CONPRI
velocity O
and O
pre-heating O
temperature S-PARA
promoted O
deposit O
quality S-CONPRI
, O
but O
in O
different O
respects O
. O


Finally O
, O
the O
influence O
of O
different O
primary O
accelerating O
gases O
( O
helium S-MATE
vs O
nitrogen S-MATE
) O
on O
the O
material B-CONPRI
properties E-CONPRI
of O
the O
deposits O
was O
investigated O
. O


The O
tensile B-CHAR
testing E-CHAR
showed O
that O
fully B-PARA
dense E-PARA
deposits O
produced O
with O
different O
gases O
had O
similar O
stiffness S-PRO
and O
yield B-PRO
strength E-PRO
, O
but O
different O
ductility S-PRO
. O


The O
particle S-CONPRI
impact S-CONPRI
model O
was O
further O
used O
to O
explain O
the O
different O
material S-MATE
behaviors O
, O
which O
also O
demonstrated O
feasibility S-CONPRI
to O
connect O
the O
spray O
parameters S-CONPRI
and O
the O
material B-CONPRI
properties E-CONPRI
via O
modeling S-ENAT
for O
optimizing O
cold O
spray O
process S-CONPRI
. O


Lithography-based O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
increasingly O
becoming O
the O
technology S-CONPRI
of O
choice O
for O
the O
small O
series O
or O
single O
unit O
production S-MANP
. O


At O
the O
TU O
Vienna O
a O
digital B-MANP
light I-MANP
processing E-MANP
( O
DLP S-MANP
) O
system O
was O
developed O
for O
the O
fabrication S-MANP
of O
complex O
technical O
ceramics S-MATE
, O
requiring O
high O
levels O
of O
detail O
and O
accuracy S-CHAR
. O


The O
DLP-system O
used O
in O
this O
study O
creates O
a O
ceramic S-MATE
green O
part O
by O
stacking O
up O
layers O
of O
a O
photo-curable B-MATE
resin E-MATE
with O
a O
solid O
loading O
of O
around O
45 O
vol. O
% O
zirconia S-MATE
. O


After O
a O
thermal B-CHAR
debinding E-CHAR
and O
sintering S-MANP
step O
the O
part O
turns O
into O
a O
dense O
ceramic S-MATE
and O
gains O
its O
final O
properties S-CONPRI
. O


The O
native O
resolution S-PARA
of O
the O
DLP S-MANP
process O
depends O
on O
the O
light O
engine O
's O
DMD S-MANP
( O
digital O
mirror O
device O
) O
chip S-MATE
and O
the O
optics S-APPL
employed O
. O


Currently O
it O
is O
possible O
to O
print S-MANP
3D-structures O
with O
a O
spatial O
resolution S-PARA
down O
to O
40 O
μm O
. O


A O
modification O
of O
the O
light B-MACEQ
source E-MACEQ
allows O
for O
the O
customization O
of O
the O
light O
curing S-MANP
strategy O
for O
each O
pixel O
of O
the O
exposed O
layers O
. O


This O
work O
presents O
methods O
to O
improve O
the O
geometrical O
accuracy S-CHAR
as O
well O
as S-MATE
the O
structural O
properties S-CONPRI
of O
the O
final O
3D-printed S-MANP
ceramic O
part O
by O
using O
the O
full O
capabilities O
of O
the O
light B-MACEQ
source E-MACEQ
. O


On O
the O
one O
hand O
, O
the O
feasibility S-CONPRI
to O
control O
the O
dimensional O
overgrowth O
to O
gain S-PARA
resolution O
below O
the O
native O
resolution S-PARA
of O
the O
light O
engine—a O
sub-pixel O
resolution—was O
evaluated O
. O


Overgrowth O
occurs O
due O
to O
light B-CONPRI
scattering E-CONPRI
and O
was O
found O
to O
be S-MATE
sensitive O
to O
both O
exposure S-CONPRI
time O
and O
exposed O
area S-PARA
. O


On O
the O
other O
hand O
, O
different O
light O
curing S-MANP
strategies O
( O
LCSs O
) O
and O
depths O
of O
cure S-CONPRI
( O
Cd S-MATE
) O
were O
used O
for O
the O
3D-printing S-MANP
of O
ceramic S-MATE
green O
parts O
and O
their O
influence O
on O
cracks O
in O
the O
final O
ceramic S-MATE
was O
evaluated O
. O


It O
was O
concluded O
that O
softstart O
LCSs O
, O
as S-MATE
well O
as S-MATE
higher O
values O
for O
Cd S-MATE
, O
reduce O
cracks O
in O
the O
final O
ceramic S-MATE
. O


Applying O
these O
findings O
within O
the O
3D-printing S-MANP
process O
may O
be S-MATE
another O
step S-CONPRI
toward O
flawless O
and O
highly O
accurate S-CHAR
ceramic O
parts O
. O


Direct O
additive B-MANP
manufacturing E-MANP
of O
ceramics S-MATE
using O
melt S-CONPRI
cast S-MANP
route O
. O


Fabrication S-MANP
of O
compositionally O
gradient O
ceramic-metal S-MATE
structure O
in O
one O
additive B-MANP
manufacturing E-MANP
operation O
. O


Characterization O
and O
defect S-CONPRI
analysis O
of O
AM S-MANP
processed O
parts O
. O


Laser B-MANP
Engineered I-MANP
Net I-MANP
Shaping E-MANP
( O
LENS™ O
) O
, O
which O
is O
a O
laser S-ENAT
based O
additive B-MANP
manufacturing E-MANP
method O
, O
was O
utilized O
to O
fabricate S-MANP
Ti-Al2O3 O
compositionally O
graded O
structures O
. O


The O
Ti-Al2O3 O
graded O
composites S-MATE
consisted O
of O
different O
sections O
−Ti6Al4V O
alloy S-MATE
, O
Ti6Al4V S-MATE
+ O
Al2O3 S-MATE
composites O
, O
and O
pure O
Al2O3 S-MATE
ceramic O
. O


After O
LENS™ O
processing O
, O
microstructural B-CHAR
characterization E-CHAR
, O
phase S-CONPRI
analysis O
, O
elemental O
distribution S-CONPRI
, O
and O
microhardness S-CONPRI
measurements O
were O
performed O
on O
the O
cross B-CONPRI
sections E-CONPRI
of O
Ti-Al2O3 O
graded O
composites S-MATE
. O


Each O
section O
had O
their O
unique O
microstructures S-MATE
and O
phases O
. O


Moreover O
, O
hardness S-PRO
measurements O
demonstrated O
that O
the O
pure O
Al2O3 S-MATE
section O
had O
the O
highest O
hardness S-PRO
of O
2365.5 O
± O
64.7 O
HV0.3 O
. O


Conventional O
ceramic B-MANP
processing E-MANP
requires O
extensive O
post-processing S-CONPRI
including O
high O
temperature S-PARA
sintering S-MANP
, O
which O
makes O
it O
difficult O
for O
direct O
fabrication S-MANP
of O
metal-ceramic O
multi-layer O
structures O
. O


The O
results O
demonstrate O
that O
LENS™ O
can O
be S-MATE
utilized O
to O
process B-CONPRI
multi-material E-CONPRI
metal B-MATE
ceramic E-MATE
composites S-MATE
in O
a O
single O
step S-CONPRI
while O
maintaining O
the O
size O
, O
shape O
and O
compositional O
variations S-CONPRI
based O
on O
computer B-ENAT
aided I-ENAT
design E-ENAT
files O
. O


Since O
this O
is O
a O
first-generation O
work O
, O
and O
limited O
research S-CONPRI
results O
are O
available O
in O
published O
literature O
related O
to O
LENS™ O
processing O
of O
both O
metals B-MATE
and I-MATE
ceramics E-MATE
in O
one O
operation O
, O
the O
demonstration O
of O
this O
work O
is O
expected O
to O
inspire O
future O
studies O
on O
manufacturing S-MANP
of O
multi-material S-CONPRI
composites S-MATE
using O
AM S-MANP
. O


A O
rather O
simple S-MANP
computational O
analysis O
for O
the O
thermomechanical S-CONPRI
simulation S-ENAT
of O
the O
EBM S-MANP
is O
presented O
. O


A O
new O
model S-CONPRI
is O
provided O
to O
account O
the O
powder B-MACEQ
bed E-MACEQ
behaviour O
during O
the O
melting S-MANP
. O


Shrinkage S-CONPRI
and O
porosity S-PRO
for O
both O
powder S-MATE
and O
bulk O
materials S-CONPRI
are O
considered O
. O


Experimental S-CONPRI
validations O
support S-APPL
strongly O
the O
effectiveness S-CONPRI
of O
the O
proposed O
model S-CONPRI
. O


The O
proposed O
approach O
might O
be S-MATE
useful O
for O
other O
powder-based O
AM B-MANP
processes E-MANP
as O
well O
. O


In O
this O
work O
, O
an O
improved O
but O
still O
rather O
simple S-MANP
computational O
analysis O
is O
presented O
for O
a O
more O
detailed O
prediction S-CONPRI
of O
Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM S-MANP
) O
process S-CONPRI
outcomes O
. O


A O
fully O
coupled O
thermomechanical S-CONPRI
analysis O
is O
developed O
in O
which O
nonlinearities O
due O
to O
the O
variation S-CONPRI
of O
material B-CONPRI
properties E-CONPRI
when O
the O
material S-MATE
melts O
are O
included O
. O


A O
new O
analytical O
approach O
is O
developed O
to O
emulate O
the O
volume S-CONPRI
variation S-CONPRI
of O
the O
powder B-MACEQ
bed E-MACEQ
during O
heating S-MANP
and O
melting S-MANP
. O


Particularly O
, O
the O
expansion O
of O
the O
powder B-MATE
particles E-MATE
and O
the O
porosity S-PRO
reduction O
within O
the O
powder B-MACEQ
bed E-MACEQ
are O
considered O
simultaneously O
. O


The O
thermal B-CONPRI
expansion E-CONPRI
and O
the O
shrinkage S-CONPRI
of O
solid O
material S-MATE
during O
heating S-MANP
and O
cooling S-MANP
and O
the O
stress S-PRO
formation O
within O
the O
solid O
material S-MATE
are O
also O
modelled O
. O


The O
model S-CONPRI
can O
predict O
the O
geometrical O
transformation O
of O
the O
powder S-MATE
into O
solid O
material S-MATE
in O
an O
efficient O
way O
. O


A O
comparison O
between O
experimental S-CONPRI
and O
simulated O
cross-sectional O
areas S-PARA
of O
melted S-CONPRI
single O
lines O
is O
presented O
. O


Both O
continues O
line O
melting S-MANP
and O
fractional O
line O
melting S-MANP
, O
multi O
beam S-MACEQ
melting O
, O
are O
considered O
. O


The O
model S-CONPRI
shows O
a O
good O
ability O
to O
provide O
consistent O
and O
accurate S-CHAR
forecasts O
. O


The O
main O
goal O
of O
this O
work O
is O
the O
adoption O
of O
additive B-MANP
manufacturing E-MANP
for O
the O
production S-MANP
of O
inexpensive O
rare-earth O
free O
MnAl-based O
permanent B-MATE
magnets E-MATE
. O


The O
use O
of O
more O
advanced O
binder-free S-CONPRI
additive B-MANP
manufacturing E-MANP
technique O
such O
as S-MATE
Electron O
Beam S-MACEQ
Melting O
( O
EBM S-MANP
) O
allows O
obtaining O
fully-dense O
magnetic O
materials S-CONPRI
with O
advanced O
topology S-CONPRI
and O
complex B-PRO
shapes E-PRO
. O


We O
focus O
on O
the O
feasibility S-CONPRI
of O
controlling O
the O
phase S-CONPRI
formation O
in O
additively B-MANP
manufactured E-MANP
Mn-Al O
alloys S-MATE
by O
employing O
post-manufacturing O
heat B-MANP
treatment E-MANP
. O


The O
as-manufactured O
EBM S-MANP
samples O
contain O
8 O
% O
of O
the O
desired O
ferromagnetic O
τ-MnAl O
phase S-CONPRI
. O


After O
the O
optimized O
annealing B-MANP
treatment E-MANP
, O
the O
content O
of O
the O
τ-phase O
was O
increased O
to O
90 O
% O
. O


This O
sample S-CONPRI
has O
a O
coercivity O
value O
of O
0.15 O
T O
, O
which O
is O
also O
the O
maximum O
achieved O
in O
conventionally O
produced O
binary S-CONPRI
MnAl O
magnets S-APPL
. O


Moreover O
, O
the O
EBM S-MANP
samples O
are O
fully B-PARA
dense E-PARA
and O
have O
the O
same O
density S-PRO
as S-MATE
the O
samples S-CONPRI
produced O
by O
conventional O
melting S-MANP
density S-PRO
. O


A O
modelling S-ENAT
strategy O
is O
proposed O
to O
evaluate O
the O
influence O
of O
defect S-CONPRI
morphology O
on O
the O
fatigue S-PRO
limit O
of O
additively B-MANP
manufactured E-MANP
Al O
alloys S-MATE
by O
: O
( O
i O
) O
obtaining O
an O
x-ray B-CHAR
micro-Computed I-CHAR
Tomography E-CHAR
( O
μ-CT O
) O
3D B-CONPRI
image E-CONPRI
of O
the O
material S-MATE
, O
( O
ii O
) O
computing O
the O
Equivalent O
Inertia O
Ellipsoid O
of O
each O
individual O
pore S-PRO
, O
( O
iii O
) O
modelling S-ENAT
the O
influence O
of O
the O
defect S-CONPRI
on O
the O
fatigue S-PRO
limit O
through O
the O
Defect S-CONPRI
Stress O
Gradient O
( O
DSG O
) O
approach O
coupled O
to O
the O
Eshelby O
theory O
and O
, O
( O
iv O
) O
3D S-CONPRI
mapping O
the O
criticality O
of O
each O
individual O
defect S-CONPRI
. O


For O
this O
fatigue S-PRO
study O
, O
an O
AlSi10Mg B-MATE
alloy E-MATE
was O
manufactured S-CONPRI
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
using O
sub-optimal O
deposition S-CONPRI
parameters O
in O
order O
to O
produce O
large O
lack-of-fusion O
defects S-CONPRI
. O


After O
a O
T6 O
heat B-MANP
treatment E-MANP
, O
tension-compression O
fatigue B-CHAR
tests E-CHAR
, O
with O
R O
= O
−1 O
, O
were O
conducted O
on O
specimens O
oriented O
with O
their O
loading O
axis O
either O
parallel O
or O
normal O
to O
the O
Z-axis S-CONPRI
of O
the O
additive B-MANP
manufacturing E-MANP
equipment O
. O


Two O
samples S-CONPRI
were O
characterised O
before O
μ-CT O
testing S-CHAR
in O
order O
to O
characterise O
the O
initial O
3D S-CONPRI
defect O
population S-BIOP
. O


Each O
sample S-CONPRI
was O
fatigued O
step S-CONPRI
by O
step S-CONPRI
in O
order O
to O
determine O
the O
fatigue S-PRO
limit O
. O


The O
fracture S-CONPRI
surface O
was O
observed O
in O
order O
to O
identify O
the O
critical O
defect S-CONPRI
in O
the O
initial O
μ-CT O
image S-CONPRI
. O


A O
comparison O
with O
the O
fatigue S-PRO
results O
led S-APPL
to O
the O
following O
conclusions O
: O
( O
i O
) O
when O
the O
longest O
axis O
of O
the O
defect S-CONPRI
is O
perpendicular O
to O
the O
loading O
axis O
, O
modelling S-ENAT
the O
defect S-CONPRI
as S-MATE
an O
equivalent O
inertia O
prolate O
ellipsoid O
gives O
better O
results O
( O
5 O
% O
error S-CONPRI
on O
the O
fatigue S-PRO
limit O
) O
than O
modelling S-ENAT
it O
as S-MATE
a O
simple S-MANP
equivalent O
sphere O
( O
22 O
% O
error S-CONPRI
on O
the O
fatigue S-PRO
limit O
) O
, O
( O
ii O
) O
the O
prolate O
ellipsoid O
is O
not O
relevant O
when O
the O
longest O
axis O
of O
the O
defect S-CONPRI
is O
oriented O
along O
the O
loading O
axis O
; O
in O
this O
case O
an O
oblate O
equivalent O
ellipsoid O
should O
be S-MATE
used O
, O
( O
iii O
) O
the O
concept O
of O
‘ O
size O
’ O
for O
a O
complex O
3D S-CONPRI
shaped O
defect S-CONPRI
should O
be S-MATE
linked O
to O
the O
inertia O
and O
the O
loading O
, O
( O
iv O
) O
with O
this O
approach O
, O
surface B-CONPRI
defects E-CONPRI
are O
shown O
to O
be S-MATE
more O
critical O
than O
internal O
ones O
for O
fatigue B-PRO
life E-PRO
and O
, O
( O
v S-MATE
) O
a O
3D S-CONPRI
defect O
criticality O
map O
of O
the O
entire O
sample S-CONPRI
can O
be S-MATE
plotted O
to O
provide O
visual O
feedback S-PARA
on O
which O
defects S-CONPRI
are O
the O
most O
critical O
for O
fatigue B-PRO
life E-PRO
. O


In O
common O
thermoplastic S-MATE
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
, O
a O
solid O
polymer B-MATE
filament E-MATE
is O
melted S-CONPRI
, O
extruded S-MANP
though O
a O
rastering O
nozzle S-MACEQ
, O
welded S-MANP
onto O
neighboring O
layers O
and O
solidified O
. O


The O
temperature S-PARA
of O
the O
polymer S-MATE
at O
each O
of O
these O
stages O
is O
the O
key O
parameter S-CONPRI
governing O
these O
non-equilibrium O
processes S-CONPRI
, O
but O
due O
to O
its O
strong O
spatial O
and O
temporal O
variations S-CONPRI
, O
it O
is O
difficult O
to O
measure O
accurately S-CHAR
. O


Here O
we O
utilize O
infrared S-CONPRI
( O
IR S-CHAR
) O
imaging S-APPL
– O
in O
conjunction O
with O
necessary O
reflection S-CHAR
corrections O
and O
calibration S-CONPRI
procedures O
– O
to O
measure O
these O
temperature S-PARA
profiles S-FEAT
of O
a O
model S-CONPRI
polymer O
during O
3D B-MANP
printing E-MANP
. O


From O
the O
temperature S-PARA
profiles S-FEAT
of O
the O
printed O
layer S-PARA
( O
road O
) O
and O
sublayers O
, O
the O
temporal O
profile S-FEAT
of O
the O
crucially O
important O
weld S-FEAT
temperatures S-PARA
can O
be S-MATE
obtained O
. O


Under O
typical O
printing O
conditions O
, O
the O
weld S-FEAT
temperature S-PARA
decreases O
at O
a O
rate O
of O
approximately O
100 O
°C/s O
and O
remains O
above O
the O
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
for O
approximately O
1 O
s. O
These O
measurement S-CHAR
methods O
are O
a O
first O
step S-CONPRI
in O
the O
development O
of O
strategies O
to O
control O
and O
model S-CONPRI
the O
printing B-MANP
processes E-MANP
and O
in O
the O
ability O
to O
develop O
models O
that O
correlate O
critical O
part O
strength S-PRO
with O
material S-MATE
and O
processing O
parameters S-CONPRI
. O


A O
novel O
compulsively O
constricted O
wire O
arc S-CONPRI
additive S-MATE
manufacturing（CC-WAAM）method O
was O
proposed O
with O
arc S-CONPRI
and O
droplets S-CONPRI
ejected O
out O
of O
a O
narrow O
space O
. O


Small-size O
liquid O
droplets S-CONPRI
were O
transferred O
to O
previous O
layer S-PARA
with O
stable O
path O
and O
direction O
with O
low O
heat S-CONPRI
input O
. O


Good O
shielding O
and O
heat S-CONPRI
preservation O
for O
high-temperature O
liquid O
droplets S-CONPRI
as S-MATE
well O
as S-MATE
the O
liquid O
pool O
were O
guaranteed O
by O
the O
ejected O
arc S-CONPRI
plasma O
. O


Uniform O
and O
fine O
microstructures S-MATE
were O
achieved O
in O
the O
deposited O
metal S-MATE
using O
mild B-MATE
steel E-MATE
filler O
wire O
in O
CC-WAAM O
. O


In O
order O
to O
realize O
oriented O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
featured O
by O
low O
heat S-CONPRI
input O
and O
small O
droplets S-CONPRI
, O
a O
novel O
compulsively O
constricted O
WAAM S-MANP
( O
CC-WAAM O
) O
method O
was O
proposed O
and O
investigated O
in O
this O
paper O
. O


The O
arc S-CONPRI
burned O
between O
a O
metallic S-MATE
wire O
and O
a O
tungsten S-MATE
electrode S-MACEQ
in O
a O
narrow-space O
nozzle S-MACEQ
. O


The O
proposed O
technology S-CONPRI
could O
provide O
compulsive O
constriction O
for O
arc S-CONPRI
plasma O
and O
liquid B-MATE
metal E-MATE
droplets S-CONPRI
using O
a O
cubic B-MATE
boron I-MATE
nitride E-MATE
( O
CBN S-MATE
) O
ceramic S-MATE
nozzle O
. O


The O
surrounding O
arc S-CONPRI
was O
ejected O
out O
of O
the O
nozzle S-MACEQ
and O
offered O
extra O
heating S-MANP
and O
a O
good O
shielding O
environment O
during O
the O
whole O
manufacturing B-MANP
process E-MANP
. O


The O
arc S-CONPRI
and O
metal S-MATE
transfer O
behaviors O
could O
be S-MATE
improved O
for O
better O
performance S-CONPRI
and O
higher O
quality S-CONPRI
. O


The O
economic O
and O
efficient O
new O
method O
is O
expected O
to O
solve O
the O
challenges O
faced S-MANP
by O
traditional O
WAAM S-MANP
such O
as S-MATE
excessive O
heat S-CONPRI
input O
and O
poor O
geometrical O
accuracy S-CHAR
. O


Preliminary O
experiments O
showed O
that O
the O
two O
AM S-MANP
layers O
produced O
by O
the O
novel O
method O
had O
homogeneous S-CONPRI
microstructure O
distribution S-CONPRI
and O
fine O
grains S-CONPRI
. O


The O
geometrical O
dimensions S-FEAT
of O
each O
layer S-PARA
can O
be S-MATE
effectively O
controlled O
by O
regulating O
the O
travel O
speed O
of O
the O
torch O
. O


The O
wide-range O
adjustable O
heat S-CONPRI
input O
can O
effectively O
control O
the O
state O
of O
the O
metallic S-MATE
formation O
, O
making O
it O
possible O
to O
realize O
an O
accurate S-CHAR
control O
of O
the O
microstructure S-CONPRI
and O
properties S-CONPRI
. O


Residual B-PRO
stress E-PRO
distribution S-CONPRI
in O
cold O
spray O
microparticles O
for O
additive B-MANP
manufacturing E-MANP
is O
studied O
. O


A O
simulation S-ENAT
model S-CONPRI
for O
cold-spray O
additive B-MANP
manufacturing E-MANP
based O
on O
arbitrary O
Lagrangian–Eulerian O
method O
is O
proposed O
. O


The O
residual B-PRO
stress E-PRO
formation O
mechanism S-CONPRI
in O
cold-spray O
additive B-MANP
manufacturing E-MANP
is O
explained O
in O
detail O
. O


Cold O
spray O
( O
CS O
) O
residual B-PRO
stress E-PRO
was O
measured O
by O
the O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
and O
contour S-FEAT
methods O
. O


The O
residual B-PRO
stress E-PRO
components S-MACEQ
SX O
and O
SY O
, O
perpendicular O
to O
the O
thickness O
, O
have O
similar O
distributions S-CONPRI
and O
approximately O
equal O
magnitudes O
. O


Both O
are O
compressive O
on O
the O
deposited O
surface S-CONPRI
and O
become O
tensile S-PRO
inside O
the O
structure S-CONPRI
. O


An O
advanced O
simulation S-ENAT
model S-CONPRI
based O
on O
the O
arbitrary O
Lagrangian–Eulerian O
( O
ALE O
) O
method O
was O
developed O
to O
investigate O
the O
residual B-PRO
stress E-PRO
distributions S-CONPRI
in O
a O
single O
CS O
microparticle O
and O
multi-layer O
CS O
microparticles O
and O
reveal O
the O
formation O
mechanism S-CONPRI
. O


The O
residual B-PRO
stress E-PRO
components S-MACEQ
SX O
and O
SY O
predicted S-CONPRI
by O
the O
proposed O
simulation S-ENAT
model S-CONPRI
have O
the O
same O
distribution S-CONPRI
as S-MATE
shown O
by O
the O
measurements O
, O
i.e. O
, O
compressive O
on O
the O
surface S-CONPRI
and O
tensile S-PRO
inside O
. O


As S-MATE
the O
number O
of O
deposition B-PARA
layers E-PARA
increases O
, O
the O
position O
of O
maximum O
tensile B-PRO
stress E-PRO
moves O
from O
the O
substrate S-MATE
to O
the O
deposited B-CHAR
layers E-CHAR
. O


The O
residual B-PRO
stress E-PRO
component S-MACEQ
SZ O
in O
the O
direction O
of O
the O
deposition S-CONPRI
thickness O
shows O
alternate O
tensile S-PRO
and O
compressive O
distributions S-CONPRI
in O
the O
transverse O
direction O
, O
which O
is O
quite O
different O
from O
that O
of O
the O
transverse O
component S-MACEQ
. O


The O
present O
work O
provides O
a O
guideline O
for O
effectively O
tailoring O
the O
residual B-PRO
stress E-PRO
in O
CS O
parts O
and O
thereby O
improving O
the O
fatigue S-PRO
lifetime O
. O


Because O
many O
of O
the O
most O
important O
defects S-CONPRI
in O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
( O
L-PBF S-MANP
) O
occur O
at O
the O
size O
and O
timescales O
of O
the O
melt B-MATE
pool E-MATE
itself O
, O
the O
development O
of O
methodologies O
for O
monitoring O
the O
melt B-MATE
pool E-MATE
is O
critical O
. O


This O
works O
examines O
the O
possibility O
of O
in-situ S-CONPRI
detection O
of O
keyholing O
porosity S-PRO
and O
balling O
instabilities O
. O


Specifically O
, O
a O
visible-light O
high O
speed O
camera S-MACEQ
with O
a O
fixed O
field O
of O
view O
is O
used O
to O
study O
the O
morphology S-CONPRI
of O
L-PBF S-MANP
melt O
pools O
in O
the O
Inconel B-MATE
718 E-MATE
material O
system O
. O


A O
scale-invariant O
description O
of O
melt B-MATE
pool E-MATE
morphology O
is O
constructed O
using O
Computer B-CONPRI
Vision E-CONPRI
techniques O
and O
unsupervised O
Machine S-MACEQ
Learning O
is O
used O
to O
differentiate O
between O
observed O
melt B-MATE
pools E-MATE
. O


By O
observing O
melt B-MATE
pools E-MATE
produced O
across O
process S-CONPRI
space O
, O
in-situ S-CONPRI
signatures O
are O
identified O
which O
may O
indicate O
flaws S-CONPRI
such O
as S-MATE
those O
observed O
ex-situ O
. O


This O
linkage O
of O
ex-situ O
and O
in-situ S-CONPRI
morphology O
enabled O
the O
use O
of O
supervised O
Machine S-MACEQ
Learning O
to O
classify O
melt B-MATE
pools E-MATE
observed O
( O
with O
the O
high O
speed O
camera S-MACEQ
) O
during O
fusion S-CONPRI
of O
non-bulk O
geometries S-CONPRI
such O
as S-MATE
overhangs O
. O


The O
ability O
to O
deposit O
a O
consistent O
and O
predictable S-CONPRI
solidification O
microstructure S-CONPRI
can O
greatly O
accelerate O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
qualification O
. O


Process S-CONPRI
mapping O
is O
an O
approach O
that O
represents O
process S-CONPRI
outcomes O
in O
terms O
of O
process S-CONPRI
variables O
. O


In O
this O
work O
, O
a O
solidification B-CONPRI
microstructure E-CONPRI
process S-CONPRI
map O
was O
developed O
using O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
for O
deposition S-CONPRI
of O
single O
beads S-CHAR
of O
Ti-6Al-4V S-MATE
via O
electron B-CONPRI
beam E-CONPRI
wire O
feed S-PARA
AM B-MANP
processes E-MANP
. O


Process S-CONPRI
variable O
combinations O
yielding O
constant O
beta O
grain B-PRO
size E-PRO
and O
morphology S-CONPRI
were O
identified O
. O


Comparison O
with O
a O
previously O
developed O
process S-CONPRI
map O
for O
melt B-MATE
pool E-MATE
geometry S-CONPRI
shows O
that O
maintaining O
a O
constant O
melt B-MATE
pool E-MATE
cross O
sectional O
area S-PARA
will O
also O
yield O
a O
constant O
grain B-PRO
size E-PRO
. O


Additionally O
, O
the O
grain S-CONPRI
morphology O
boundaries S-FEAT
are O
similar O
to O
curves O
of O
constant O
melt B-MATE
pool E-MATE
aspect B-FEAT
ratio E-FEAT
. O


Experimental S-CONPRI
results O
support S-APPL
the O
numerical O
predictions S-CONPRI
and O
identify O
a O
proportional O
size O
scaling O
between O
beta O
grain S-CONPRI
widths O
and O
melt B-MATE
pool E-MATE
widths O
. O


Results O
further O
demonstrate O
that O
in B-CONPRI
situ E-CONPRI
indirect O
control O
of O
solidification B-CONPRI
microstructure E-CONPRI
is O
possible O
through O
direct O
melt B-PARA
pool I-PARA
dimension E-PARA
control O
. O


The O
effects O
of O
electron B-CONPRI
beam E-CONPRI
manufactured O
( O
EBM S-MANP
) O
process-induced O
defects S-CONPRI
on O
local O
microstructural B-CONPRI
failure E-CONPRI
initiation O
and O
propagation O
in O
IN O
718 O
have O
been O
investigated O
. O


Predictions S-CONPRI
for O
transgranular B-CONPRI
fracture E-CONPRI
, O
based O
on O
local O
cleavage B-CONPRI
plane E-CONPRI
stresses O
, O
and O
for O
intergranular O
fracture S-CONPRI
, O
based O
on O
dislocation-grain O
boundary S-FEAT
( O
GB O
) O
interactions O
and O
evolving O
dislocation S-CONPRI
pileups O
, O
were O
combined O
with O
a O
crystalline O
dislocation-density O
plasticity S-PRO
approach O
to O
understand O
the O
influence O
of O
AM S-MANP
process-induced O
defects S-CONPRI
, O
such O
as S-MATE
porosity O
, O
NbC O
precipitates S-MATE
, O
and O
regions O
of O
dry O
powder S-MATE
. O


High O
local O
stresses O
along O
the O
peripheries O
of O
pores S-PRO
caused O
crack O
nucleation S-CONPRI
, O
and O
mismatches O
in O
deformation S-CONPRI
behavior O
between O
NbC O
precipitates S-MATE
and O
the O
surrounding O
matrix O
led S-APPL
to O
local O
stress S-PRO
gradients O
that O
induced O
crack O
nucleation S-CONPRI
and O
decohesion O
at O
precipitate/matrix O
interfaces O
. O


Regions O
of O
unmelted O
powder S-MATE
had O
significant O
stress S-PRO
accumulations O
that O
initiated O
failure S-CONPRI
at O
low O
nominal O
strains O
. O


Failure S-CONPRI
due O
to O
high O
localized O
stresses O
near O
regions O
of O
unmelted O
powder S-MATE
was O
dominant O
over O
precipitate/matrix O
decohesion O
and O
crack O
nucleation S-CONPRI
near O
pore S-PRO
peripheries O
. O


Based O
on O
the O
predictions S-CONPRI
, O
the O
mechanical S-APPL
behavior O
of O
AM S-MANP
alloys S-MATE
is O
governed O
by O
local O
dislocation-density O
evolution S-CONPRI
near O
process-induced O
defects S-CONPRI
, O
which O
preferentially O
nucleate O
material S-MATE
failure S-CONPRI
. O


Furthermore O
, O
interactions O
between O
these O
different O
defect S-CONPRI
types O
can O
significantly O
accelerate O
failure S-CONPRI
initiation O
and O
propagation O
. O


Lattice B-FEAT
structures E-FEAT
can O
add O
value O
to O
high-performance O
components S-MACEQ
manufactured O
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
due O
to O
their O
high O
specific B-PRO
strength E-PRO
and O
stiffness S-PRO
. O


A O
further O
use O
of O
lattice B-FEAT
structures E-FEAT
is O
in O
thermo-mechanical S-CONPRI
applications O
, O
where O
the O
high O
surface B-PARA
area E-PARA
of O
the O
lattice S-CONPRI
may O
aid O
heat B-CONPRI
transfer E-CONPRI
. O


However O
, O
little O
characterisation O
of O
lattices S-CONPRI
under O
thermal B-CONPRI
loading E-CONPRI
is O
currently O
available O
in O
the O
literature O
. O


In O
this O
study O
, O
a O
custom-built O
test O
rig O
was O
used O
to O
characterise O
the O
thermal O
conduction O
for O
three O
triply B-CONPRI
periodic I-CONPRI
minimal I-CONPRI
surface E-CONPRI
lattice S-CONPRI
types O
, O
namely O
: O
gyroid O
, O
diamond S-MATE
and O
Schwarz O
primitives O
, O
with O
unit B-CONPRI
cell E-CONPRI
size O
and O
volume B-PARA
fraction E-PARA
being O
varied.Results O
show O
that O
thermal B-PRO
conductivity E-PRO
is O
primarily O
a O
function O
of O
the O
material B-CONPRI
properties E-CONPRI
and O
volume B-PARA
fraction E-PARA
of O
the O
sample S-CONPRI
. O


However O
, O
some O
effects O
of O
the O
geometry S-CONPRI
, O
such O
as S-MATE
surface O
area S-PARA
to O
volume S-CONPRI
ratio O
, O
can O
be S-MATE
used O
to O
explain O
slight O
differences O
in O
the O
measured O
conductivity S-PRO
. O


The O
Schwarz O
primitive O
unit B-CONPRI
cell E-CONPRI
consistently O
gave O
the O
highest O
conductivity S-PRO
, O
with O
diamond S-MATE
and O
gyroid O
unit B-CONPRI
cells E-CONPRI
being O
marginally O
lower O
. O


Larger O
cell B-PRO
sizes E-PRO
typically O
gave O
higher O
conductivity S-PRO
than O
smaller O
cells S-APPL
, O
which O
can O
be S-MATE
attributed O
to O
greater O
intra-cell O
convective O
heat B-CONPRI
transfer E-CONPRI
and O
better O
interface S-CONPRI
coupling O
with O
the O
testing S-CHAR
apparatus.The O
experimental S-CONPRI
results O
are O
used O
to O
derive O
equations O
that O
allow O
samples S-CONPRI
with O
a O
specified O
thermal B-PRO
conductivity E-PRO
to O
be S-MATE
designed O
, O
thus O
demonstrating O
how O
a O
component S-MACEQ
may O
be S-MATE
manufactured O
with O
a O
custom O
thermal B-CONPRI
profile E-CONPRI
by O
varying O
the O
volume B-PARA
fraction E-PARA
of O
the O
lattice S-CONPRI
. O


Sensing S-APPL
and O
closed-loop B-MACEQ
control E-MACEQ
are O
critical O
attributes O
of O
a O
robust O
3D B-MANP
printing E-MANP
process O
, O
such O
as S-MATE
Directed O
Energy O
Deposition S-CONPRI
( O
DED S-MANP
) O
, O
in O
which O
it O
is O
necessary O
to O
manage O
geometry S-CONPRI
, O
material B-CONPRI
properties E-CONPRI
, O
and O
residual B-PRO
stress E-PRO
and O
distortion S-CONPRI
. O


The O
present O
research S-CONPRI
demonstrates O
multiple O
modes O
of O
closed-loop O
melt B-MATE
pool E-MATE
size O
control O
in O
laser-wire O
based O
DED S-MANP
, O
a O
form O
of O
large-scale O
metal B-MANP
additive I-MANP
manufacturing E-MANP
. O


First O
, O
real-time O
closed-loop O
melt B-MATE
pool E-MATE
size O
control O
through O
laser B-PARA
power E-PARA
modulation O
was O
demonstrated O
for O
intralayer O
control O
of O
bead B-CHAR
geometry E-CHAR
. O


Next O
, O
an O
interlayer O
trend S-CONPRI
in O
laser B-PARA
power E-PARA
during O
the O
printing O
of O
layered O
components S-MACEQ
was O
documented O
, O
which O
inspired O
the O
development O
of O
novel O
modes O
of O
control O
. O


A O
controller S-MACEQ
that O
modulates O
print S-MANP
speed O
and O
deposition B-PARA
rate E-PARA
on O
a O
per-layer O
basis O
was O
developed O
and O
demonstrated O
, O
enabling O
the O
control O
of O
either O
average S-CONPRI
melt O
pool O
size O
alone O
or O
average S-CONPRI
laser O
power S-PARA
in O
coordination O
with O
real-time O
melt B-MATE
pool E-MATE
size O
control O
. O


This O
work O
demonstrates O
that O
accumulated O
heat S-CONPRI
in O
components S-MACEQ
under O
construction S-APPL
can O
be S-MATE
exploited O
to O
maintain O
process S-CONPRI
stability O
as S-MATE
print O
speed O
and O
deposition B-PARA
rate E-PARA
are O
automatically O
increased O
under O
closed-loop B-MACEQ
control E-MACEQ
. O


This O
has O
major O
implications O
for O
overall O
production S-MANP
efficiency O
. O


Control O
modes O
are O
characterized O
in O
terms O
of O
their O
effect O
on O
local O
bead B-CHAR
geometry E-CHAR
, O
global O
part O
geometry S-CONPRI
, O
and O
interlayer O
effect O
on O
energy B-PARA
density E-PARA
, O
among O
other O
factors O
. O


Quality B-CONPRI
control E-CONPRI
in O
metal B-MANP
additive I-MANP
manufacturing E-MANP
prioritizes O
the O
development O
of O
advanced O
inspection S-CHAR
schemes O
to O
characterize O
the O
defect S-CONPRI
evolution O
during O
processing O
and O
post-processing S-CONPRI
. O


This O
involves O
grand O
challenges O
in O
detecting O
internal O
defects S-CONPRI
and O
analyzing O
large O
and O
complex O
defect S-CONPRI
datasets O
in O
macroscopic S-CONPRI
samples O
. O


Here O
, O
we O
present O
an O
inspection S-CHAR
pipeline O
that O
integrates O
( O
i O
) O
fast O
, O
micro O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
reconstruction S-CONPRI
, O
( O
ii O
) O
automated O
3D S-CONPRI
morphology O
analysis O
, O
and O
( O
iii O
) O
machine S-MACEQ
learning-based O
big O
data S-CONPRI
analysis O
. O


X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
and O
automated O
computer B-CONPRI
vision E-CONPRI
result O
in O
a O
holistic O
defect S-CONPRI
morphology O
database S-ENAT
for O
the O
inspected O
macroscopic S-CONPRI
volume O
, O
based O
on O
which O
machine S-MACEQ
learning O
analysis O
is O
employed O
to O
reveal O
quantitative S-CONPRI
insights O
into O
the O
global O
evolution S-CONPRI
of O
defect S-CONPRI
characteristics O
beyond O
qualitative S-CONPRI
human O
observations O
. O


We O
demonstrate O
this O
pipeline O
by O
examining O
the O
global-scale O
pore S-PRO
evolution S-CONPRI
in O
post-processing S-CONPRI
of O
binder B-MANP
jetting I-MANP
additive I-MANP
manufacturing E-MANP
, O
from O
the O
green O
state O
, O
to O
the O
sintered S-MANP
state O
, O
and O
to O
the O
hot O
isostatic O
pressed S-MANP
state O
of O
copper S-MATE
. O


The O
pipeline O
is O
shown O
to O
be S-MATE
effective O
at O
detecting O
and O
processing O
the O
information O
associated O
with O
a O
large O
number O
( O
∼105 O
) O
of O
pores S-PRO
in O
macroscopic S-CONPRI
volumes O
. O


By O
quantifying O
the O
evolution S-CONPRI
of O
( O
i O
) O
the O
weight S-PARA
of O
pore S-PRO
morphology S-CONPRI
parameters O
and O
( O
ii O
) O
the O
pore S-PRO
number O
and O
volume B-PARA
fraction E-PARA
of O
each O
categorized O
group O
, O
new O
understandings O
are O
developed O
regarding O
the O
effects O
of O
sintering S-MANP
and O
hot B-MANP
isostatic I-MANP
pressing E-MANP
on O
pore B-PRO
decomposition E-PRO
, O
shrinkage S-CONPRI
, O
and O
smoothing O
during O
post-processing S-CONPRI
of O
binder B-MANP
jetting E-MANP
. O


Pore S-PRO
structures O
with O
isotropic S-PRO
stiffness O
fabricated S-CONPRI
via O
selective B-MANP
laser I-MANP
melting E-MANP
. O


The O
structures O
were O
based O
on O
topology B-FEAT
optimization E-FEAT
and O
additive B-MANP
manufacturing E-MANP
. O


The O
stiffness S-PRO
was O
experimentally O
verified O
. O


The O
stiffness S-PRO
and O
strength S-PRO
were O
higher O
than O
conventional O
porous B-MATE
metals E-MATE
. O


Recent O
additive B-MANP
manufacturing E-MANP
technologies O
can O
be S-MATE
used O
to O
fabricate S-MANP
porous O
metals S-MATE
with O
precise O
internal O
pore S-PRO
structures O
and O
effective O
performance S-CONPRI
. O


We O
use O
topology B-FEAT
optimization E-FEAT
to O
derive O
an O
optimal O
pore S-PRO
structure O
shape O
with O
high O
stiffness S-PRO
that O
is O
verified O
experimentally O
. O


The O
design S-FEAT
maximizes O
the O
effective O
bulk B-PRO
modulus E-PRO
and O
isotropic S-PRO
stiffness O
, O
and O
the O
performance S-CONPRI
is O
compared O
with O
Hashin–Shtrikman O
( O
HS S-MATE
) O
bounds O
. O


The O
optimized O
structure S-CONPRI
is O
fabricated S-CONPRI
via O
selective B-MANP
laser I-MANP
melting E-MANP
of O
maraging B-MATE
steel E-MATE
, O
which O
is O
a O
high-strength O
, O
iron-nickel O
steel S-MATE
that O
can O
not O
easily O
be S-MATE
made O
porous S-PRO
with O
conventional O
methods O
. O


The O
optimal O
porous S-PRO
structure O
achieved O
85 O
% O
of O
the O
performance S-CONPRI
of O
the O
HS S-MATE
upper O
bound O
in O
numerical B-ENAT
simulations E-ENAT
, O
and O
at O
least O
90 O
% O
of O
them O
were O
realized O
in O
compressive O
testing S-CHAR
. O


Finally O
, O
the O
performance S-CONPRI
is O
discussed O
relative O
to O
that O
of O
other O
metals S-MATE
. O


In O
metal B-MANP
additive I-MANP
manufacturing E-MANP
, O
microstructural S-CONPRI
inhomogeneities O
, O
like O
anisotropic S-PRO
mechanical O
strength S-PRO
and O
geometric O
limitations O
in O
directed B-MANP
energy I-MANP
deposition E-MANP
, O
electron B-MANP
beam I-MANP
melting E-MANP
, O
or O
selective B-MANP
laser I-MANP
sintering E-MANP
, O
have O
led S-APPL
to O
the O
exploration O
of O
alternative O
techniques O
in O
recent O
years O
. O


Among O
these O
techniques O
, O
fused B-MANP
filament I-MANP
fabrication E-MANP
is O
an O
attractive O
alternative O
due O
to O
its O
successes O
in O
producing O
dense O
parts O
, O
approaching O
traditional B-MANP
manufacturing E-MANP
specifications S-PARA
. O


Despite O
this O
success O
, O
many O
challenges O
remain O
to O
produce O
reliable O
parts O
with O
reproducible O
properties S-CONPRI
using O
FFF S-MANP
, O
particularly O
in O
the O
thermal B-MANP
treatment E-MANP
for O
part O
densification S-MANP
. O


% O
Ti-6Al-4V B-MATE
powder E-MATE
to O
create O
a O
printable O
filament S-MATE
. O


Printed O
Ti-6Al-4V S-MATE
parts O
using O
these O
filaments S-MATE
were O
sintered S-MANP
at O
temperatures S-PARA
ranging O
from O
900 O
to O
1340 O
°C O
and O
evaluated O
by O
x-ray B-CHAR
diffraction E-CHAR
, O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
and O
optical B-CHAR
microscopy E-CHAR
. O


The O
sintered S-MANP
samples S-CONPRI
demonstrated O
a O
linear O
decrease O
in O
β-phase O
from O
15 O
to O
11 O
vol O
. O


% O
with O
increasing O
temperature S-PARA
, O
while O
residual B-PRO
stress E-PRO
and O
Young O
’ O
s S-MATE
modulus O
increased O
. O


Additionally O
, O
the O
density S-PRO
of O
printed O
and O
sintered S-MANP
Ti-6Al-4V O
parts O
could O
be S-MATE
increased O
up O
to O
91 O
% O
of O
the O
theoretical S-CONPRI
density S-PRO
of O
Ti-6Al-4V S-MATE
by O
increasing O
the O
sintering S-MANP
temperature O
up O
to O
1340 O
°C O
. O


Samples S-CONPRI
that O
were O
sintered S-MANP
at O
1340 O
°C O
showed O
a O
higher O
Young O
’ O
s S-MATE
modulus O
compared O
to O
SLM S-MANP
samples S-CONPRI
, O
likely O
due O
to O
the O
increased O
α-phase O
in O
samples S-CONPRI
sintered O
at O
1340 O
°C O
. O


The O
microstructures S-MATE
of O
additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
metal S-MATE
components S-MACEQ
have O
been O
shown O
to O
be S-MATE
heterogeneous O
and O
spatially O
variable O
when O
compared O
to O
conventionally O
manufactured S-CONPRI
counterparts O
. O


Consequently O
, O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
AM-metal O
parts O
are O
expected O
to O
vary O
locally O
within O
their O
volume S-CONPRI
. O


For O
AM S-MANP
structural O
components S-MACEQ
intended O
to O
operate O
in O
extreme O
environments O
, O
including O
high-strain-rate O
loading O
scenarios O
, O
there O
is O
a O
need O
to O
quantify O
variability S-CONPRI
of O
mechanical S-APPL
behavior O
within O
the O
same O
AM-build O
domain S-CONPRI
at O
quasi-static S-CONPRI
and O
dynamic S-CONPRI
strain-rates O
as S-MATE
well O
as S-MATE
the O
effect O
of O
heat B-MANP
treatment E-MANP
on O
the O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
objective O
of O
this O
study O
is O
to O
investigate O
the O
effect O
of O
loading O
direction O
and O
direct-age O
hardening S-MANP
heat O
treatment O
on O
quasi-static S-CONPRI
and O
dynamic S-CONPRI
mechanical O
response O
within O
an O
Inconel B-MATE
718 E-MATE
volume O
produced O
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
using O
manufacturer-recommended O
processing O
parameters S-CONPRI
. O


Uniaxial O
compression B-CHAR
tests E-CHAR
and O
a O
split-Hopkinson O
pressure S-CONPRI
bar O
( O
SHPB O
) O
were O
used O
to O
investigate O
the O
quasi-static S-CONPRI
and O
dynamic S-CONPRI
response O
, O
respectively O
, O
of O
as-built O
and O
heat-treated S-MANP
specimens O
extracted S-CONPRI
along O
the O
three O
principal O
processing O
directions O
. O


Electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
measurements O
were O
made O
for O
representative O
specimens O
within O
the O
build S-PARA
domain O
to O
correlate O
microstructural S-CONPRI
features O
to O
observed O
location-specific O
mechanical S-APPL
deformation S-CONPRI
. O


Results O
from O
both O
quasi-static S-CONPRI
and O
dynamic S-CONPRI
loading O
show O
that O
the O
recommended O
processing O
parameters S-CONPRI
yield O
a O
homogeneous S-CONPRI
stress-strain O
response O
throughout O
the O
material S-MATE
volume O
in O
the O
as-built O
condition O
. O


Deformed S-MANP
specimen O
geometries S-CONPRI
showed O
a O
systematic O
and O
repeatable O
preferential O
deformation S-CONPRI
along O
the O
build B-PARA
direction E-PARA
, O
regardless O
of O
condition O
or O
loading O
strain B-CONPRI
rate E-CONPRI
when O
loading O
was O
applied O
in O
either O
of O
the O
two O
orthogonal O
processing O
directions O
. O


The O
deformation S-CONPRI
dependence O
is O
found O
to O
be S-MATE
related O
to O
the O
underlying O
, O
process-induced O
crystallographic O
texture S-FEAT
and O
grain S-CONPRI
morphology O
. O


Two O
different O
honeycomb B-FEAT
structures E-FEAT
are O
manufactured S-CONPRI
with O
LENS S-MANP
system O
from O
Ti-6Al-4V B-MATE
alloy E-MATE
. O


Mechanical B-CONPRI
properties E-CONPRI
of O
the O
Ti-6Al-4V B-MATE
alloy E-MATE
are O
determined O
. O


Procedure O
for O
acquiring O
proper O
data S-CONPRI
for O
the O
elasto-visco-plastic O
constitutive O
model S-CONPRI
is O
presented O
. O


Energy-absorption O
properties S-CONPRI
of O
the O
honeycomb S-CONPRI
cellular B-FEAT
structures E-FEAT
are O
assessed O
during O
experimental S-CONPRI
and O
numerical O
testing S-CHAR
. O


The O
paper O
presents O
a O
methodology S-CONPRI
investigation O
of O
honeycomb S-CONPRI
cellular B-FEAT
structures E-FEAT
deformation O
process S-CONPRI
in O
quasi-static S-CONPRI
compression B-CHAR
tests E-CHAR
. O


Two O
honeycomb S-CONPRI
topologies O
with O
different O
elementary O
cells S-APPL
were O
designed S-FEAT
and O
manufactured S-CONPRI
from O
Ti-6Al-4 B-MATE
V I-MATE
alloy E-MATE
powder S-MATE
with O
the O
use O
of O
Laser B-MANP
Engineered I-MANP
Net I-MANP
Shaping E-MANP
( O
LENS S-MANP
) O
system O
and O
compressed O
using O
a O
universal O
strength S-PRO
machine S-MACEQ
. O


To O
simulate O
the O
deformation S-CONPRI
process O
with O
LS-Dyna O
software S-CONPRI
, O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
material S-MATE
were O
assessed O
and O
correlated S-CONPRI
. O


An O
elasto-visco-plastic O
material S-MATE
model O
( O
Mat_Plasticity_With_Damage O
) O
was O
used O
for O
predicting O
the O
material S-MATE
behavior O
. O


The O
results O
of O
experimental S-CONPRI
tests O
and O
numerical B-ENAT
simulations E-ENAT
were O
compared O
. O


A O
reasonable O
agreement O
between O
deformation S-CONPRI
, O
failure S-CONPRI
and O
force S-CONPRI
histories O
was O
obtained O
. O


Additionally O
, O
both O
the O
topologies S-CONPRI
were O
compared O
for O
their O
energy B-CHAR
absorption E-CHAR
capabilities O
. O


The O
validated O
numerical O
modelling S-ENAT
with O
the O
adopted O
constitutive O
model S-CONPRI
will O
be S-MATE
used O
in O
the O
further O
studies O
to O
analyze O
different O
cellular B-FEAT
structures E-FEAT
topologies O
subjected O
to O
dynamic S-CONPRI
loading O
. O


A O
novel O
technique O
was O
developed O
to O
control O
the O
microstructure B-CONPRI
evolution E-CONPRI
in O
Alloy S-MATE
718 O
processed S-CONPRI
using O
Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM S-MANP
) O
. O


In B-CONPRI
situ E-CONPRI
solution O
treatment O
and O
aging O
of O
Alloy S-MATE
718 O
was O
performed O
by O
heating S-MANP
the O
top O
surface S-CONPRI
of O
the O
build S-PARA
after O
build S-PARA
completion O
scanning S-CONPRI
an O
electron B-CONPRI
beam E-CONPRI
to O
act O
as S-MATE
a O
planar O
heat B-CONPRI
source E-CONPRI
during O
the O
cool B-PARA
down E-PARA
process O
. O


Results O
demonstrate O
that O
the O
measured O
hardness S-PRO
( O
478 O
± O
7 O
HV O
) O
of O
the O
material S-MATE
processed O
using O
in B-CONPRI
situ E-CONPRI
heat B-MANP
treatment E-MANP
similar O
to O
that O
of O
peak-aged O
Inconel B-MATE
718 E-MATE
. O


Large O
solidification B-CONPRI
grains E-CONPRI
and O
cracks O
formed O
, O
which O
are O
identified O
as S-MATE
the O
likely O
mechanism S-CONPRI
leading O
to O
failure S-CONPRI
of O
tensile B-CHAR
tests E-CHAR
of O
the O
in B-CONPRI
situ E-CONPRI
heat B-MANP
treatment E-MANP
material O
under O
loading O
. O


Despite O
poor O
tensile S-PRO
performance S-CONPRI
, O
the O
technique O
proposed O
was O
shown O
to O
successively O
age O
Alloy S-MATE
718 O
( O
increase O
precipitate S-MATE
size O
and O
hardness S-PRO
) O
without O
removing O
the O
sample S-CONPRI
from O
the O
process S-CONPRI
chamber O
, O
which O
can O
reduce O
the O
number O
of O
process S-CONPRI
steps O
in O
producing O
a O
part O
. O


Tighter O
controls O
on O
processing O
temperature S-PARA
during O
layer S-PARA
melting O
to O
lower O
process S-CONPRI
temperature O
and O
selective O
heating S-MANP
during O
in B-CONPRI
situ E-CONPRI
heat B-MANP
treatment E-MANP
to O
reduce O
over-sintering O
are O
proposed O
as S-MATE
methods O
for O
improving O
the O
process S-CONPRI
. O


Lattice B-FEAT
structures E-FEAT
with O
isotropic S-PRO
stiffness O
fabricated S-CONPRI
via O
electron B-MANP
beam I-MANP
melting E-MANP
. O


The O
structures O
were O
based O
on O
topology B-FEAT
optimization E-FEAT
and O
additive B-MANP
manufacturing E-MANP
. O


The O
designed S-FEAT
isotropic O
stiffness S-PRO
was O
experimentally O
verified O
. O


The O
strength S-PRO
was O
also O
isotropic S-PRO
as S-MATE
the O
same O
with O
stiffness S-PRO
. O


Electron-beam O
melting S-MANP
( O
EBM S-MANP
) O
exhibits O
advantages O
over O
other O
metal-additive O
manufacturing S-MANP
techniques O
owing O
to O
its O
low O
residual B-PRO
stress E-PRO
, O
rapid B-MANP
fabrication E-MANP
speed O
, O
and O
high O
energy O
efficiency O
. O


However O
, O
in O
EBM S-MANP
, O
metal B-MATE
powder E-MATE
is O
preheated O
and O
sintered S-MANP
to O
stabilize O
the O
temperature B-PARA
gradient E-PARA
and O
powder S-MATE
position O
during O
melting S-MANP
with O
a O
high-power O
electron B-CONPRI
beam E-CONPRI
. O


When O
making O
a O
lattice B-FEAT
structure E-FEAT
by O
EBM S-MANP
, O
a O
certain O
size O
of O
the O
powder-removing O
hole O
is O
required O
to O
remove O
the O
sintered S-MANP
remaining O
metal B-MATE
powder E-MATE
from O
the O
lattice S-CONPRI
. O


However O
, O
a O
large O
powder-removing O
hole O
can O
reduce O
the O
lattice S-CONPRI
mechanical O
performance S-CONPRI
. O


We O
conducted O
topology B-FEAT
optimization E-FEAT
to O
derive O
an O
optimal O
lattice B-FEAT
structure E-FEAT
shape O
with O
high O
isotropic S-PRO
stiffness O
assuming O
fabrication S-MANP
by O
EBM S-MANP
and O
minimizing O
the O
performance S-CONPRI
reduction O
owing O
to O
fixed O
large O
powder-removing O
holes O
. O


The O
optimized O
structure S-CONPRI
was O
fabricated S-CONPRI
via O
the O
EBM S-MANP
of O
a O
Ti–6Al–4V O
alloy S-MATE
. O


The O
optimal O
lattice B-FEAT
structure E-FEAT
achieved O
83 O
% O
of O
the O
performance S-CONPRI
of O
the O
Hashin–Shtrikman O
upper O
bound O
in O
numerical B-ENAT
simulations E-ENAT
, O
but O
an O
approximate O
20 O
% O
stiffness S-PRO
reduction S-CONPRI
was O
observed O
in O
the O
experiments O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
a O
commonly O
used O
powder B-MANP
bed I-MANP
fusion E-MANP
metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
. O


Although O
SLM S-MANP
is O
preferred O
due O
to O
its O
near-net-shape S-MANP
part O
commitment O
, O
the O
deposition B-PARA
rate E-PARA
of O
this O
process S-CONPRI
is O
slower O
compared O
with O
alternative O
metal S-MATE
processes O
. O


A O
higher O
deposition B-PARA
rate E-PARA
of O
SLM S-MANP
can O
be S-MATE
obtained O
by O
increasing O
the O
laser S-ENAT
scanning O
velocity O
and O
laser B-PARA
power E-PARA
; O
however O
, O
this O
results O
in O
decreased O
part O
quality S-CONPRI
due O
to O
the O
SLM S-MANP
process S-CONPRI
’ O
s S-MATE
physical O
limits S-CONPRI
. O


This O
study O
presents O
the O
conditions O
for O
a O
higher O
deposition B-PARA
rate E-PARA
for O
various O
process B-CONPRI
parameters E-CONPRI
with O
defocused O
beams O
to O
eliminate O
the O
void B-CONPRI
defects E-CONPRI
due O
to O
keyholing O
formed O
in O
the O
melt B-MATE
pool E-MATE
. O


Single O
bead S-CHAR
experiments O
were O
conducted O
, O
and O
the O
thresholds O
of O
the O
process B-CONPRI
parameters E-CONPRI
resulting O
in O
voids S-CONPRI
were O
identified O
. O


A O
melt B-MATE
pool E-MATE
depth-to-width O
ratio O
of O
0.85 O
was O
found O
to O
be S-MATE
a O
critical O
value O
for O
preventing O
voids S-CONPRI
in O
the O
process S-CONPRI
. O


The O
melt B-MATE
pool E-MATE
aspect B-FEAT
ratio E-FEAT
was O
related O
with O
the O
process B-CONPRI
parameters E-CONPRI
by O
using O
the O
normalized O
enthalpy O
and O
the O
volumetric O
energy B-PARA
density E-PARA
. O


The O
threshold O
values O
of O
the O
normalized O
enthalpy O
due O
to O
voids S-CONPRI
were O
independent O
from O
the O
beam B-PARA
diameters E-PARA
. O


Moreover O
, O
unstable O
single O
bead S-CHAR
track O
thresholds O
were O
plotted O
as S-MATE
a O
function O
of O
the O
beam B-PARA
diameters E-PARA
. O


In O
addition O
to O
the O
experiments O
, O
a O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
model O
was O
built O
with O
calibrated S-CONPRI
absorptivity O
and O
heat B-CONPRI
source E-CONPRI
parameters O
to O
predict O
the O
melt B-MATE
pool E-MATE
geometries S-CONPRI
for O
a O
wide O
range S-PARA
of O
process B-CONPRI
parameters E-CONPRI
( O
power S-PARA
= O
100–370 O
W O
, O
velocity O
= O
200–2000 O
mm/s O
, O
and O
beam B-PARA
diameter E-PARA
= O
100–260 O
μm O
) O
. O


A O
new O
laser S-ENAT
metal O
desposition O
process S-CONPRI
based O
on O
an O
inside-laser O
coaxial O
powder B-MACEQ
feeding I-MACEQ
system E-MACEQ
was O
successfully O
applied O
to O
manufacture S-CONPRI
reduced O
activation O
steel S-MATE
, O
which O
is O
featured O
with O
fine O
microstructure S-CONPRI
and O
excellent O
mechanical B-CONPRI
properties E-CONPRI
. O


In O
addition O
, O
infrared S-CONPRI
thermal O
imaging S-APPL
experiments O
and O
Abaqus S-ENAT
numerical O
simulation S-ENAT
were O
conducted O
to O
characterize O
the O
complex O
thermal O
history O
during O
the O
laser B-MANP
metal I-MANP
deposition E-MANP
process O
. O


The O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
reduced O
activation O
steel S-MATE
were O
systematically O
investigated O
in O
the O
as-fabricated O
and O
heat-treated S-MANP
samples O
. O


The O
results O
indicat O
that O
the O
peak O
temperature S-PARA
increased O
and O
the O
cooling B-PARA
rate E-PARA
decreased O
in O
the O
melt B-MATE
pool E-MATE
when O
the O
additional O
layers O
were O
deposited O
as S-MATE
a O
result O
of O
a O
cumulative O
effect O
of O
heat S-CONPRI
in O
the O
fabricated S-CONPRI
thin O
wall O
samples S-CONPRI
. O


The O
reduced O
cooling B-PARA
rate E-PARA
directly O
contributed O
to O
the O
decreased O
heterogeneous B-CONPRI
nucleation E-CONPRI
rate O
and O
the O
coarsening O
of O
austenite S-MATE
grains O
in O
the O
top O
domain S-CONPRI
. O


The O
differences O
in O
terms O
of O
microstructure S-CONPRI
and O
hardness S-PRO
of O
the O
as-fabricated O
samples S-CONPRI
along O
the O
building B-PARA
direction E-PARA
were O
also O
in O
a O
good O
agreement O
with O
the O
evolution S-CONPRI
of O
temperature S-PARA
field O
. O


The O
thermal B-PARA
cycling E-PARA
experimental S-CONPRI
and O
cyclic O
heat B-MANP
treatment E-MANP
results O
confirmed O
that O
in-situ S-CONPRI
thermal O
cycles O
were O
unable O
to O
trigger O
recrystallization S-CONPRI
because O
the O
stored O
strain S-PRO
energy O
was O
insufficient O
to O
induce O
nucleation S-CONPRI
of O
new O
austenite S-MATE
grains O
during O
laser B-MANP
directed I-MANP
energy I-MANP
deposition E-MANP
. O


Additive B-MANP
manufacture E-MANP
of O
sand S-MATE
molds S-MACEQ
via O
binder B-MANP
jetting E-MANP
enables O
the O
casting S-MANP
of O
complex O
metal S-MATE
geometries S-CONPRI
. O


Various B-MATE
material E-MATE
systems O
have O
been O
created O
for O
3D B-MANP
printing E-MANP
of O
sand S-MATE
molds S-MACEQ
; O
however O
, O
a O
formal O
study O
of O
the O
materials S-CONPRI
’ O
effects O
on O
cast S-MANP
products O
has O
not O
yet O
been O
conducted O
. O


In O
this O
paper O
the O
authors O
investigate O
potential O
differences O
in O
material B-CONPRI
properties E-CONPRI
( O
microstructure S-CONPRI
, O
porosity S-PRO
, O
mechanical B-PRO
strength E-PRO
) O
of O
A356 O
– O
T6 O
castings O
resulting O
from O
two O
different O
commercially O
available O
3D B-MANP
printing E-MANP
media O
. O


In O
addition O
, O
the O
material B-CONPRI
properties E-CONPRI
of O
cast S-MANP
products O
from O
traditional O
“ O
no-bake O
” O
silica B-MATE
sand E-MATE
is O
used O
as S-MATE
a O
basis O
for O
comparison O
of O
castings O
produced O
by O
the O
3D B-MANP
printed E-MANP
molds O
. O


It O
was O
determined O
that O
resultant O
castings O
yielded O
statistically O
equivalent O
results O
in O
four O
of O
the O
seven O
tests O
performed O
: O
dendrite S-BIOP
arm O
spacing O
, O
porosity S-PRO
, O
surface B-PRO
roughness E-PRO
, O
and O
tensile B-PRO
strength E-PRO
and O
differed O
in O
sand S-MATE
tensile O
strength S-PRO
, O
hardness S-PRO
, O
and O
density S-PRO
. O


As S-MATE
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
advances O
rapidly O
towards O
new O
materials S-CONPRI
and O
applications O
, O
it O
is O
vital O
to O
understand O
the O
performance B-CONPRI
limits E-CONPRI
of O
AM B-MANP
technologies E-MANP
and O
to O
overcome O
these O
limits S-CONPRI
via O
improved O
machine S-MACEQ
design S-FEAT
and O
process S-CONPRI
integration O
. O


Extrusion-based O
AM S-MANP
( O
i.e. O
, O
fused B-MANP
filament I-MANP
fabrication E-MANP
, O
FFF S-MANP
) O
is O
compatible O
with O
a O
wide O
variety O
of O
thermoplastic B-MATE
polymer E-MATE
and O
composite B-MATE
materials E-MATE
, O
and O
can O
be S-MATE
deployed O
across O
a O
wide O
range S-PARA
of O
length B-CHAR
scales E-CHAR
. O


However O
, O
the O
build B-CHAR
rate E-CHAR
of O
both O
desktop O
and O
professional O
FFF S-MANP
systems O
is O
comparable O
( O
∼10 O
’ O
s S-MATE
of O
cm3/h O
at O
∼0.2 O
mm S-MANP
layer B-PARA
thickness E-PARA
) O
, O
suggesting O
that O
fundamental O
aspects O
of O
the O
machine S-MACEQ
design S-FEAT
and O
process B-CONPRI
physics E-CONPRI
limit S-CONPRI
system O
performance S-CONPRI
. O


We O
determine O
the O
rate O
limits S-CONPRI
to O
FFF S-MANP
by O
analysis O
of O
machine S-MACEQ
modules O
: O
the O
filament S-MATE
extrusion S-MANP
mechanism O
, O
the O
heater O
and O
nozzle S-MACEQ
, O
and O
the O
motion O
system O
. O


We O
determine O
, O
by O
direct O
measurements O
and O
numerical O
analysis O
, O
that O
FFF S-MANP
build B-CHAR
rate E-CHAR
is O
influenced O
by O
the O
coincident O
module-level O
limits S-CONPRI
to O
traction O
force S-CONPRI
exerted O
on O
the O
filament S-MATE
, O
conduction O
heat B-CONPRI
transfer E-CONPRI
to O
the O
filament S-MATE
core S-MACEQ
, O
and O
gantry O
velocity O
for O
positioning O
the O
printhead O
. O


Our O
findings O
are O
validated O
by O
direct O
measurements O
of O
build B-CHAR
rate E-CHAR
versus O
part O
complexity S-CONPRI
using O
desktop O
FFF S-MANP
systems O
. O


Last O
, O
we O
study O
the O
scaling O
of O
the O
rate O
limits S-CONPRI
using O
finite B-CONPRI
element E-CONPRI
simulations O
of O
thermoplastic S-MATE
flow O
through O
the O
extruder S-MACEQ
. O


We O
map O
the O
scaling O
of O
extrusion S-MANP
force O
, O
polymer S-MATE
exit O
temperature S-PARA
, O
and O
average S-CONPRI
printhead O
velocity O
onto O
a O
unifying O
trade-space O
of O
build B-CHAR
rate E-CHAR
versus O
resolution S-PARA
. O


This O
approach O
validates O
the O
build B-CHAR
rate E-CHAR
performance O
of O
current O
FFF S-MANP
systems O
, O
and O
suggests O
that O
significant O
enhancements O
in O
FFF S-MANP
build B-CHAR
rate E-CHAR
with O
targeted O
quality S-CONPRI
specifications O
are O
possible O
via O
mutual O
improvements O
to O
the O
extrusion S-MANP
and O
heating S-MANP
mechanism O
along O
with O
high-speed O
motion O
systems O
. O


The O
ability O
to O
design S-FEAT
complex O
copper S-MATE
( O
Cu S-MATE
) O
parts O
into O
the O
most O
efficient O
thermal O
structures O
is O
an O
old O
dream O
, O
but O
difficult O
to O
realize O
with O
conventional B-MANP
manufacturing E-MANP
techniques O
. O


The O
recent O
development O
of O
laser S-ENAT
3D B-MANP
printing E-MANP
techniques O
makes O
it O
possible O
to O
fully O
explore O
intricate O
designs S-FEAT
and O
maximize O
the O
thermal O
performance S-CONPRI
of O
Cu-based O
thermal O
management O
components S-MACEQ
but O
present O
significant O
challenges O
due O
to O
its O
high O
optical S-CHAR
reflectivity O
. O


In O
this O
study O
, O
we O
demonstrated O
the O
laser S-ENAT
3D B-MANP
printing E-MANP
of O
pure O
Cu S-MATE
with O
a O
moderate O
laser B-PARA
power E-PARA
( O
400 O
W O
) O
. O


Dense O
Cu S-MATE
parts O
( O
95 O
% O
) O
with O
smooth B-CONPRI
surface E-CONPRI
finishing S-MANP
( O
Ra O
∼18 O
μm O
) O
were O
obtained O
at O
a O
scan B-PARA
speed E-PARA
of O
400 O
mm/s O
, O
a O
hatch B-PARA
distance E-PARA
of O
0.12 O
mm S-MANP
, O
and O
a O
layer B-PARA
thickness E-PARA
of O
0.03 O
mm S-MANP
. O


The O
hardness S-PRO
, O
electrical S-APPL
, O
and O
thermal B-PRO
conductivity E-PRO
of O
the O
printed O
Cu S-MATE
parts O
are O
108 O
MPa S-CONPRI
, O
5.71 O
× O
107 O
S/m O
, O
and O
368 O
W/m·K O
, O
respectively O
which O
are O
close O
to O
those O
of O
bulk O
Cu S-MATE
. O


Additionally O
, O
complex O
heat B-MACEQ
sink E-MACEQ
structures O
were O
printed O
with O
large O
surface B-PARA
areas E-PARA
( O
600 O
mm2/g O
) O
, O
and O
their O
cooling S-MANP
performances O
were O
compared O
to O
a O
commercial O
heat B-MACEQ
sink E-MACEQ
with O
a O
smaller O
surface B-PARA
area E-PARA
( O
286 O
mm2/g O
) O
on O
an O
electronic O
chip S-MATE
. O


The O
complex O
heat B-MACEQ
sinks E-MACEQ
printed O
cools O
the O
electronic O
chip S-MATE
45 O
% O
more O
efficiently O
than O
the O
commercial O
one O
. O


The O
introduction O
of O
selective B-MANP
laser I-MANP
melting E-MANP
to O
additively O
manufacturing S-MANP
Cu S-MATE
heat O
sinks O
offers O
the O
promise O
to O
enhance O
the O
performance S-CONPRI
beyond O
the O
scope O
of O
exciting O
thermal O
management O
components S-MACEQ
. O


Control O
of O
microstructure S-CONPRI
in O
a O
TiAl O
alloy S-MATE
was O
conducted O
by O
electron B-MANP
beam I-MANP
melting E-MANP
( O
82/85 O
) O
. O


An O
unique O
layered O
microstructure S-CONPRI
was O
created O
by O
the O
proposed O
EBM S-MANP
process O
( O
74/85 O
) O
. O


The O
room O
temperature S-PARA
ductility S-PRO
was O
greater O
than O
2 O
% O
under O
an O
appropriate O
condition O
( O
83/85 O
) O
. O


As-EBM O
specimens O
exhibited O
high O
yield B-PRO
strength E-PRO
and O
good O
ductility S-PRO
at O
800 O
°C O
( O
76/85 O
) O
. O


This O
paper O
clarified O
a O
novel O
strategy O
to O
improve O
the O
tensile B-PRO
properties E-PRO
of O
the O
Ti-48Al-2Cr-2Nb O
alloys S-MATE
fabricated O
by O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
, O
via O
the O
finding O
of O
the O
development O
of O
unique O
layered O
microstructure S-CONPRI
composed O
of O
duplex-like O
fine O
grains S-CONPRI
layers O
and O
coarser O
γ O
grains S-CONPRI
layers O
. O


It O
was O
clarified O
that O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
alloy S-MATE
fabricated O
by O
EBM S-MANP
can O
be S-MATE
controlled O
by O
varying O
an O
angle O
θ O
between O
EBM-building O
directions O
and O
stress S-PRO
loading O
direction O
. O


At O
room O
temperature S-PARA
, O
the O
yield B-PRO
strength E-PRO
exhibits O
high O
values O
more O
than O
550 O
MPa S-CONPRI
at O
all O
the O
loading O
orientations S-CONPRI
investigated O
( O
θ O
= O
0 O
, O
45 O
and O
90° O
) O
. O


The O
anisotropy S-PRO
of O
the O
yield B-PRO
strength E-PRO
decreased O
with O
increasing O
temperature S-PARA
. O


All O
the O
examined O
alloys S-MATE
exhibited O
a O
brittle-ductile O
transition S-CONPRI
temperature S-PARA
of O
approximately O
750 O
°C O
and O
the O
yield B-PRO
strength E-PRO
and O
tensile B-PRO
elongation E-PRO
at O
800 O
°C O
were O
over O
350 O
MPa S-CONPRI
and O
40 O
% O
, O
respectively.By O
the O
detailed O
observation O
of O
the O
microstructure S-CONPRI
, O
the O
formation O
mechanism S-CONPRI
of O
the O
unique O
layered O
microstructure S-CONPRI
was O
found O
to O
be S-MATE
closely O
related O
to O
the O
repeated O
local O
heat B-MANP
treatment E-MANP
effect O
during O
the O
EBM S-MANP
process O
, O
and O
thus O
its O
control O
is O
further O
possible O
by O
the O
tuning-up O
of O
the O
process B-CONPRI
parameters E-CONPRI
. O


The O
results O
demonstrate O
that O
the O
EBM S-MANP
process O
enables O
not O
only O
the O
fabrication S-MANP
of O
TiAl O
products O
with O
complex B-PRO
shape E-PRO
but O
also O
the O
control O
of O
the O
tensile B-PRO
properties E-PRO
associated O
with O
the O
peculiar O
microstructure S-CONPRI
formed O
during O
the O
process S-CONPRI
. O


Ti-1Al-8V-5Fe O
( O
Ti-185 O
) O
and O
other O
Fe S-MATE
containing O
β O
-Ti O
alloys S-MATE
are O
attractive O
because O
of O
their O
high O
strength S-PRO
and O
low O
cost O
. O


These O
alloys S-MATE
, O
however O
, O
can O
not O
be S-MATE
produced O
through O
ingot S-MATE
casting S-MANP
due O
to O
strong O
Fe S-MATE
segregation O
and O
the O
formation O
of O
β O
flecks O
. O


Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
was O
successfully O
used O
to O
produce O
Ti-185 O
components S-MACEQ
starting O
from O
elemental O
Ti S-MATE
and O
Fe S-MATE
powders O
, O
and O
an O
Al-V O
master O
alloy S-MATE
powder O
with O
irregular O
shape O
. O


Microstructure S-CONPRI
analysis O
of O
the O
as-built O
components S-MACEQ
demonstrated O
that O
SLM S-MANP
can O
be S-MATE
used O
to O
produce O
a O
very O
fine O
grain S-CONPRI
microstructure O
with O
nano-scale S-CONPRI
precipitates O
and O
non-detrimental O
Fe S-MATE
segregation O
. O


The O
findings O
are O
interpreted O
in O
terms O
of O
the O
rapid B-MANP
solidification E-MANP
conditions O
during O
SLM S-MANP
. O


Compression B-CHAR
test E-CHAR
results O
reveal O
that O
ultra-high O
strength S-PRO
and O
reasonable O
ductility S-PRO
can O
be S-MATE
achieved O
in O
the O
as-built O
as S-MATE
well O
as S-MATE
heat O
treated O
samples S-CONPRI
. O


Residual B-CONPRI
distortion E-CONPRI
is O
a O
major O
technical O
challenge O
for O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
since O
excessive O
distortion S-CONPRI
can O
cause O
build B-CHAR
failure E-CHAR
, O
cracks O
and O
loss O
in O
structural B-PRO
integrity E-PRO
. O


However O
, O
residual B-CONPRI
distortion E-CONPRI
can O
hardly O
be S-MATE
avoided O
due O
to O
the O
rapid O
heating S-MANP
and O
cooling S-MANP
inherent O
in O
this O
AM B-MANP
process E-MANP
. O


Thus O
, O
fast O
and O
accurate S-CHAR
distortion O
prediction S-CONPRI
is O
an O
effective O
way O
to O
ensure O
manufacturability S-CONPRI
and O
build S-PARA
quality O
. O


This O
paper O
proposes O
a O
multiscale O
process B-CONPRI
modeling E-CONPRI
framework S-CONPRI
for O
efficiently O
and O
accurately S-CHAR
simulating O
residual B-CONPRI
distortion E-CONPRI
and O
stress S-PRO
at O
the O
part-scale O
for O
the O
direct B-MANP
metal I-MANP
laser I-MANP
sintering E-MANP
( O
DMLS S-MANP
) O
process S-CONPRI
. O


In O
this O
framework S-CONPRI
, O
inherent O
strains O
are O
extracted S-CONPRI
from O
detailed O
process B-ENAT
simulation E-ENAT
of O
micro-scale S-CONPRI
model O
based O
on O
the O
recently O
proposed O
modified O
inherent O
strain S-PRO
model S-CONPRI
. O


The O
micro-scale S-CONPRI
detailed O
process B-ENAT
simulation E-ENAT
employs O
the O
actual O
parameters S-CONPRI
of O
the O
DMLS S-MANP
process O
such O
as S-MATE
laser O
power S-PARA
, O
velocity O
, O
and O
scanning S-CONPRI
path O
. O


Uniform O
but O
anisotropic S-PRO
strains O
are O
then O
applied O
to O
the O
part O
in O
a O
layer-by-layer B-CONPRI
fashion E-CONPRI
in O
a O
quasi-static B-CONPRI
equilibrium I-CONPRI
finite I-CONPRI
element I-CONPRI
analysis E-CONPRI
, O
in O
order O
to O
predict O
residual S-CONPRI
distortion/stress O
for O
the O
entire O
AM S-MANP
build O
. O


Effectiveness S-CONPRI
of O
this O
proposed O
framework S-CONPRI
is O
demonstrated O
by O
simulating O
a O
double O
cantilever B-MACEQ
beam E-MACEQ
and O
a O
canonical O
part O
with O
varying O
wall B-FEAT
thicknesses E-FEAT
and O
comparing O
with O
experimental S-CONPRI
measurements O
which O
show O
very O
good O
agreement O
. O


The O
metallurgy S-CONPRI
of O
selected O
metal S-MATE
and O
alloy S-MATE
components O
fabricated S-CONPRI
by O
additive S-MATE
metallurgy O
using O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
is O
presented O
for O
a O
range S-PARA
of O
examples O
including O
Ti-6Al-4V S-MATE
, O
Co-Cr-Mo O
super B-MATE
alloy E-MATE
, O
Ni-base O
super B-MATE
alloy E-MATE
systems O
( O
Inconel B-MATE
625 E-MATE
, O
718 O
and O
Rene S-MATE
142 O
) O
, O
Nb S-MATE
and O
Fe S-MATE
. O


Precursor S-MATE
and O
pre-alloyed O
powders S-MATE
are O
preheated O
and O
selectively O
melted S-CONPRI
using O
a O
range S-PARA
of O
EBM S-MANP
process O
parameters S-CONPRI
including O
beam S-MACEQ
scan O
strategies O
, O
beam S-MACEQ
current O
variations S-CONPRI
, O
and O
cooling B-PARA
rate E-PARA
features O
. O


Microstructures S-MATE
and O
residual B-PRO
mechanical I-PRO
properties E-PRO
are O
discussed O
for O
selected O
systems O
in O
contrast O
to O
more O
conventional O
wrought S-CONPRI
and O
cast S-MANP
products O
. O


Novel O
features O
of O
EBM S-MANP
fabrication O
include O
columnar O
microstructural S-CONPRI
architectures O
which O
result O
by O
layer-by-layer S-CONPRI
melt-solidification O
phenomena O
. O


Combining O
electrical S-APPL
and O
magnetic O
materials S-CONPRI
in O
the O
same O
part O
has O
been O
a O
challenge O
in O
3D B-MANP
printing E-MANP
due O
to O
difficulties O
co-printing O
complex O
materials S-CONPRI
in O
many O
additive B-MANP
manufacturing I-MANP
processes E-MANP
. O


Past O
3D B-MANP
printed E-MANP
inductors O
and O
other O
similar O
magnetic O
devices O
have O
therefore O
either O
lacked O
the O
magnetic O
materials S-CONPRI
necessary O
for O
improved O
performance S-CONPRI
, O
or O
required O
sintering S-MANP
at O
high O
temperatures S-PARA
for O
extended O
periods O
, O
beyond O
the O
capability O
of O
most O
3D S-CONPRI
printable O
polymers S-MATE
. O


In O
this O
work O
, O
we O
demonstrate O
a O
room O
temperature S-PARA
process S-CONPRI
for O
incorporating O
conductive O
and O
magnetic O
materials S-CONPRI
into O
the O
same O
3D B-MANP
printed E-MANP
device O
. O


A O
multi-stage O
fabrication S-MANP
process O
based O
on O
3D B-MANP
printing E-MANP
followed O
by O
fill O
with O
magnetic O
and O
conductive O
fluids S-MATE
is O
proposed O
. O


Multi-layer O
microfluidic O
channels O
for O
magnetic O
passives O
are O
first O
printed O
in O
a O
stereolithography S-MANP
process S-CONPRI
. O


The O
microfluidic O
systems O
are O
then O
filled O
with O
room O
temperature S-PARA
liquid B-MATE
metal E-MATE
, O
a O
gallium S-MATE
alloy S-MATE
liquid O
at O
room O
temperature S-PARA
, O
and O
ferrofluid O
to O
create O
inductors O
, O
transformers O
and O
wireless O
power S-PARA
coils O
. O


3D S-CONPRI
finite O
element S-MATE
modeling O
of O
LSFF O
process S-CONPRI
is O
presented O
based O
on O
a O
moving O
mesh O
approach O
. O


Temporal O
behaviors O
of O
stress S-PRO
fields O
and O
temperature S-PARA
distributions S-CONPRI
are O
explored O
for O
different O
deposited B-CHAR
layers E-CHAR
. O


Effects O
of O
preheating S-MANP
and O
addition O
of O
nano S-FEAT
particles O
are O
thoroughly O
investigated O
. O


Scanning S-CONPRI
velocity O
of O
the O
laser S-ENAT
plays O
a O
key O
role O
on O
the O
clad O
shape O
. O


Gas B-MACEQ
turbine E-MACEQ
blades O
, O
turbine O
shafts O
and O
centrifugal O
compressor O
impellers O
are O
often O
damaged O
by O
erosion O
and/or O
corrosion S-CONPRI
. O


By O
laser B-MANP
cladding E-MANP
technique O
, O
a O
coating S-APPL
layer O
can O
be S-MATE
deposited O
on O
the O
base O
material S-MATE
in O
order O
to O
rebuild O
, O
repair O
and O
improve O
anti-erosion O
or O
anti-corrosion O
properties S-CONPRI
of O
the O
sensitive O
machine S-MACEQ
parts O
. O


In O
this O
paper O
, O
a O
three-dimensional S-CONPRI
finite B-CONPRI
element E-CONPRI
modeling O
of O
the O
laser S-ENAT
solid O
freeform B-MANP
fabrication E-MANP
( O
LSFF O
) O
process S-CONPRI
for O
nickel B-MATE
alloy E-MATE
625 O
powder S-MATE
mixed O
with O
nano-CeO2 O
on O
AISI O
4140 O
steel S-MATE
is O
extensively O
studied O
. O


Using O
Comsol O
Multiphysics O
software S-CONPRI
and O
the O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
( O
FEM S-CONPRI
) O
, O
the O
heat B-CONPRI
transfer E-CONPRI
equation O
, O
moving O
mesh O
equation O
and O
stress S-PRO
tensor O
are O
numerically O
solved O
. O


Clad O
shape O
, O
temperature S-PARA
distribution S-CONPRI
and O
stress S-PRO
fields O
are O
obtained O
. O


The O
effects O
of O
preheating S-MANP
as S-MATE
well O
as S-MATE
addition O
of O
nano-CeO2 O
are O
investigated O
. O


Dependence O
of O
the O
clad O
height O
on O
the O
scanning S-CONPRI
velocity O
of O
the O
laser S-ENAT
is O
also O
studied O
. O


This O
paper O
demonstrates O
the O
ability O
to O
3D B-MANP
print E-MANP
a O
fluoropolymer O
based O
energetic O
material S-MATE
which O
could O
be S-MATE
used O
as S-MATE
part O
of O
a O
multifunctional O
reactive O
structure S-CONPRI
. O


The O
work O
presented O
lays O
the O
technical O
foundation O
for O
the O
3D B-MANP
printing E-MANP
of O
reactive B-MATE
materials E-MATE
using O
fusion S-CONPRI
based O
material B-MANP
extrusion E-MANP
. O


A O
reactive O
filament S-MATE
comprising O
of O
a O
polyvinylidene O
fluoride O
( O
PVDF O
) O
binder S-MATE
with O
20 O
% O
mass O
loading O
of O
aluminum S-MATE
( O
Al S-MATE
) O
was O
prepared O
using O
a O
commercial O
filament S-MATE
extruder S-MACEQ
and O
printed O
using O
a O
Makerbot O
Replicator O
2X O
. O


Printing B-CONPRI
performance E-CONPRI
of O
the O
energetic O
samples S-CONPRI
was O
compared O
with O
standard S-CONPRI
3D B-MANP
printing E-MANP
materials O
, O
with O
metrics O
including O
the O
bead-to-bead O
adhesion S-PRO
and O
surface B-PARA
quality E-PARA
of O
the O
printed O
samples S-CONPRI
. O


The O
reactivity O
and O
burning O
rates O
of O
the O
filaments S-MATE
and O
the O
printed O
samples S-CONPRI
were O
comparable O
. O


Differential O
scanning S-CONPRI
calorimetry O
and O
thermal O
gravimetric O
analysis O
showed O
that O
the O
onset O
temperature S-PARA
for O
the O
reactions O
was O
above O
350 O
°C O
, O
which O
is O
well O
above O
the O
operation O
temperature S-PARA
of O
both O
the O
filament S-MATE
extruder S-MACEQ
and O
the O
fused B-CONPRI
deposition E-CONPRI
printer O
. O


A O
lattice S-CONPRI
Boltzmann O
( O
LB O
) O
method O
to O
simulate O
melt B-MATE
pool E-MATE
dynamics O
and O
a O
cellular O
automaton O
( O
CA S-MATE
) O
to O
simulate O
the O
solidification B-MANP
process E-MANP
are O
coupled O
to O
predict O
the O
microstructure B-CONPRI
evolution E-CONPRI
during O
selective B-MANP
electron I-MANP
beam I-MANP
melting E-MANP
( O
SEBM S-MANP
) O
. O


The O
resulting O
CALB O
model S-CONPRI
takes O
into O
account O
powder S-MATE
related O
stochastic S-CONPRI
effects O
, O
energy B-CHAR
absorption E-CHAR
and O
evaporation S-CONPRI
, O
melt B-MATE
pool E-MATE
dynamics O
and O
solidification B-CONPRI
microstructure E-CONPRI
evolution S-CONPRI
. O


Several O
physical O
phenomena O
are O
observed O
during O
grain S-CONPRI
solidification O
, O
e.g. O
, O
initial O
grain S-CONPRI
selection O
starting O
at O
the O
base O
plate O
, O
grain B-CONPRI
boundary E-CONPRI
perturbation O
, O
grain S-CONPRI
nucleation O
due O
to O
unmolten O
powder B-MATE
particles E-MATE
in O
the O
bulk O
, O
grain S-CONPRI
penetration O
from O
the O
surface S-CONPRI
of O
the O
part O
or O
grain S-CONPRI
alignment O
dependent O
on O
the O
beam S-MACEQ
scanning O
strategy O
. O


The O
effect O
of O
process B-CONPRI
parameters E-CONPRI
on O
the O
final O
grain B-CONPRI
structure E-CONPRI
and O
texture S-FEAT
evolution S-CONPRI
is O
presented O
. O


Manufacturing S-MANP
of O
ceramic S-MATE
components O
with O
a O
geometrically O
complex O
3D S-CONPRI
architecture O
and O
highly O
detailed O
features O
for O
use O
in O
a O
variety O
of O
practical O
applications O
is O
still O
a O
challenge O
. O


In O
our O
investigation O
, O
we O
adopted O
a O
synergistic O
strategy O
for O
fabricating S-MANP
SiOC O
ceramics S-MATE
with O
intricate O
3D S-CONPRI
morphologies O
by O
additive B-MANP
manufacturing E-MANP
and O
origami O
technique O
or O
assemblage O
, O
taking O
advantage O
of O
the O
high O
printability S-PARA
and O
flexibility S-PRO
of O
a O
commercially O
available O
silicone B-MATE
elastomer E-MATE
. O


Secondary O
shaping S-MANP
using O
origami O
of O
different O
2D S-CONPRI
layers O
with O
varied O
design S-FEAT
allowed O
the O
manufacturing S-MANP
of O
spiral O
, O
flower-like O
and O
polyhedron O
architectures O
, O
which O
are O
difficult O
to O
fabricate S-MANP
without O
adding O
supports S-APPL
or O
by O
any O
conventional O
ceramic S-MATE
fabrication O
processes S-CONPRI
. O


Produced O
samples S-CONPRI
showed O
no O
cracks O
or O
pores S-PRO
and O
fully O
retained O
the O
given O
shape O
after O
pyrolysis S-MANP
. O


Origami-assisted O
3D B-MANP
printing E-MANP
enables O
easy O
fabrication S-MANP
of O
complex O
SiOC O
ceramic S-MATE
structures O
without O
requiring O
any O
supports S-APPL
. O


The O
potential O
of O
adding O
fillers O
into O
the O
silicone B-MATE
material E-MATE
used O
in O
this O
work O
could O
expand O
the O
applicability O
of O
the O
manufactured S-CONPRI
structures O
introducing O
additional O
functional O
properties.Download O
: O
Download O
high-res B-CONPRI
image E-CONPRI
( O
212 O
The O
aim O
of O
this O
paper O
is O
to O
investigate O
the O
evolution S-CONPRI
of O
a O
matrix-filler O
interface S-CONPRI
during O
the O
processing O
of O
novel O
composites S-MATE
formed O
by O
a O
matrix O
of O
polylactic B-MATE
acid E-MATE
( O
PLA S-MATE
) O
and O
Mg S-MATE
particles O
, O
when O
they O
are O
manufactured S-CONPRI
by O
Materials S-CONPRI
Extrusion S-MANP
. O


The O
particles S-CONPRI
addition O
to O
the O
PLA S-MATE
was O
carried O
out O
through O
the O
preparation O
of O
a O
Magnesium S-MATE
stable O
suspension O
in O
the O
polymer S-MATE
solution O
. O


To O
improve O
the O
Mg S-MATE
dispersion S-CONPRI
, O
the O
surfaces S-CONPRI
of O
the O
particles S-CONPRI
were O
previously O
modified O
by O
the O
adsorption S-CONPRI
of O
dispersants O
, O
namely O
Polyethylenimine O
( O
PEI O
) O
and O
Cetyltrimethylammonium O
bromide O
( O
CTAB O
) O
in O
aqueous O
suspension O
. O


The O
physical O
and O
mechanical S-APPL
characterization O
of O
PLA/Mg O
composites S-MATE
show O
that O
the O
Mg S-MATE
surface O
modification O
is O
the O
key O
to O
its O
successful O
dispersion S-CONPRI
due O
to O
the O
formation O
of O
ionic O
interactions O
between O
the O
dispersants O
and O
the O
matrix O
. O


This O
is O
favoured O
by O
the O
seeding O
effect O
of O
the O
PEI-modified O
Mg S-MATE
particles O
over O
the O
PLA S-MATE
re-precipitation O
during O
the O
composite S-MATE
shaping O
. O


Moreover O
, O
a O
PEI-PLA O
covalent B-CONPRI
bond E-CONPRI
appeared O
in O
the O
printed O
scaffolds S-FEAT
as S-MATE
a O
consequence O
of O
the O
temperature S-PARA
applied O
( O
165 O
°C O
) O
during O
extrusion S-MANP
and O
printing O
. O


Consequently O
, O
the O
matrix-filler O
strengthened O
interface S-CONPRI
improved O
the O
extrusion B-MANP
process E-MANP
and O
permits O
the O
printing O
of O
3D S-CONPRI
customized O
pieces O
. O


At O
the O
same O
time O
, O
particle S-CONPRI
agglomeration O
and O
the O
nozzle S-MACEQ
blocking S-CONPRI
is O
prevented O
. O


To O
reveal O
the O
mechanism S-CONPRI
of O
oxidation S-MANP
and O
the O
effect O
of O
inclusion S-MATE
characteristics O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
additively-manufactured O
metal B-CONPRI
matrix E-CONPRI
, O
two O
groups O
of O
AISI O
316 O
L O
stainless B-MATE
steel E-MATE
samples S-CONPRI
were O
fabricated S-CONPRI
under O
different O
flow B-PARA
rates E-PARA
of O
shielding O
gas S-CONPRI
( O
Ar S-ENAT
) O
at O
two O
intensities O
of O
laser B-CONPRI
beam E-CONPRI
. O


As S-MATE
flow O
rates O
of O
shielding O
gas S-CONPRI
increased O
from O
5 O
L/min O
to O
25 O
L/min O
, O
the O
oxygen S-MATE
content O
in O
the O
melt B-MATE
pool E-MATE
decreased O
from O
775 O
ppm O
to O
375 O
ppm O
at O
low O
intensity O
of O
laser B-CONPRI
beam E-CONPRI
( O
73 O
W/m2 O
) O
, O
and O
from O
677 O
ppm O
to O
1470 O
ppm O
at O
high O
intensity O
of O
laser B-CONPRI
beam E-CONPRI
( O
725 O
W/m2 O
) O
. O


Variation S-CONPRI
in O
oxygen S-MATE
content O
affected O
melt B-MATE
pool E-MATE
shape O
, O
solidification S-CONPRI
texture O
, O
and O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
material S-MATE
. O


In O
each O
intensity O
of O
laser B-CONPRI
beam E-CONPRI
group O
, O
optimal O
flow B-PARA
rates E-PARA
of O
shielding O
gas S-CONPRI
condition O
for O
tensile B-PRO
property E-PRO
existed O
. O


As S-MATE
inclusion O
number O
density S-PRO
increased O
from O
8866/mm2 O
to O
45909/mm2 O
, O
yield B-PRO
stress E-PRO
increased O
to O
26 O
% O
. O


A O
rapid O
drop O
in O
ductility S-PRO
occurred O
at O
flow B-PARA
rate E-PARA
5 O
L/min O
, O
because O
independently-nucleated O
spinel S-MATE
accelerated O
inclusion S-MATE
coalescence O
in O
the O
melt B-MATE
pool E-MATE
. O


Directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
is O
a O
metal B-MANP
additive I-MANP
manufacturing E-MANP
process O
, O
where O
dimensional B-CHAR
accuracy E-CHAR
and O
repeatability S-CONPRI
are O
traditionally O
challenging O
to O
achieve O
. O


Strategies O
for O
computationally O
inexpensive O
process S-CONPRI
modelling S-ENAT
and O
fast-response O
process B-CONPRI
controls E-CONPRI
of O
the O
laser S-ENAT
deposition B-MANP
process E-MANP
are O
necessary O
to O
keep O
the O
geometric O
features O
close O
to O
the O
required O
dimensional B-CHAR
tolerances E-CHAR
. O


The O
deposition S-CONPRI
geometry O
depends O
highly O
on O
the O
complex O
local O
laser-material O
interaction O
and O
global O
thermal O
history O
of O
the O
substrate S-MATE
. O


In O
order O
to O
control O
the O
deposition S-CONPRI
geometry O
, O
an O
accurate S-CHAR
and O
computationally O
inexpensive O
discretized O
state O
space O
thermal O
history O
model S-CONPRI
coupled O
with O
an O
analytical O
deposition S-CONPRI
geometry O
model S-CONPRI
is O
developed O
in O
this O
work O
. O


The O
model S-CONPRI
accounts O
for O
the O
local O
laser-material O
interaction O
using O
the O
mass O
and O
energy O
equilibrium S-CONPRI
equations O
coupled O
in O
a O
lumped O
parameter S-CONPRI
solution O
, O
as S-MATE
well O
as S-MATE
the O
global O
thermal O
history O
of O
the O
product O
using O
a O
state O
space O
thermomechanical S-CONPRI
discretization O
. O


In O
literature O
, O
studies O
have O
only O
focused O
on O
1D O
toolpaths O
with O
constant O
process B-CONPRI
parameters E-CONPRI
such O
as S-MATE
speed O
, O
powder S-MATE
feedrate O
, O
and O
laser B-PARA
power E-PARA
. O


As S-MATE
it O
is O
possible O
to O
achieve O
highly O
complex O
geometric B-FEAT
shapes E-FEAT
with O
additive B-MANP
manufacturing E-MANP
, O
it O
is O
important O
to O
have O
models O
compatible O
with O
2D/3D O
complex O
toolpaths O
. O


In O
this O
paper O
, O
an O
analytical O
thermomechanical B-CONPRI
model E-CONPRI
and O
a O
coupled O
deposition S-CONPRI
geometry O
model S-CONPRI
for O
DED S-MANP
process O
are O
presented O
and O
experimentally B-CONPRI
validated E-CONPRI
. O


As S-MATE
such O
, O
the O
thermal O
history O
of O
the O
deposited O
part O
is O
predicted S-CONPRI
throughout O
the O
process S-CONPRI
and O
the O
geometric O
features O
are O
predicted S-CONPRI
for O
2D S-CONPRI
toolpaths O
. O


Despite O
the O
ongoing O
success O
of O
metal B-MANP
additive I-MANP
manufacturing E-MANP
and O
especially O
the O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
technology S-CONPRI
, O
process-related O
defects S-CONPRI
, O
distortions O
and O
residual B-PRO
stresses E-PRO
impede O
its O
usability O
for O
fracture-critical O
applications O
. O


In O
this O
paper O
, O
results O
of O
in B-CONPRI
situ E-CONPRI
X-ray O
diffraction S-CHAR
experiments O
are O
presented O
that O
offer O
insights O
into O
the O
strain S-PRO
and O
stress S-PRO
formation O
during O
the O
manufacturing S-MANP
of O
multi-layer O
thin O
walls O
made O
from O
Inconel B-MATE
625 E-MATE
. O


Using O
different O
measuring O
modes O
and O
laser S-ENAT
scanning O
parameters S-CONPRI
, O
several O
experimental S-CONPRI
observations O
are O
discussed O
to O
validate O
and O
extend O
theoretical B-CONPRI
models E-CONPRI
and O
simulations S-ENAT
from O
the O
literature O
. O


As S-MATE
a O
sample S-CONPRI
is O
built-up O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
, O
the O
stress S-PRO
state O
changes O
continuously O
up O
until O
the O
last O
exposure S-CONPRI
. O


The O
localized O
energy O
input O
leads O
to O
a O
complex O
stress S-PRO
field O
around O
the O
heat B-CONPRI
source E-CONPRI
that O
involves O
alternating O
tensile S-PRO
and O
compressive B-PRO
stresses E-PRO
. O


The O
correlation O
of O
temperature S-PARA
and O
yield B-PRO
strength E-PRO
results O
in O
a O
stress S-PRO
maximum O
at O
a O
certain O
distance O
to O
the O
top O
layer S-PARA
. O


The O
present O
study O
demonstrates O
the O
potential O
of O
high-energy O
synchrotron S-ENAT
radiation S-MANP
diffraction S-CHAR
for O
in B-CONPRI
situ E-CONPRI
SLM O
research S-CONPRI
. O


Fabry-Pérot O
ultrasonic O
metamaterials S-MATE
have O
been O
additively B-MANP
manufactured E-MANP
using O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
to O
contain O
subwavelength O
holes O
with O
a O
high O
aspect-ratio O
of O
width O
to O
depth O
. O


Such O
metamaterials S-MATE
require O
the O
acoustic O
impedance O
mismatch O
between O
the O
structure S-CONPRI
and O
the O
immersion O
medium O
to O
be S-MATE
large O
. O


It O
is O
shown O
for O
the O
first O
time O
that O
metallic B-MACEQ
structures E-MACEQ
fulfil O
this O
criterion O
for O
applications O
in O
water O
over O
the O
200 O
– O
800 O
kHz O
frequency O
range S-PARA
. O


It O
is O
also O
demonstrated O
that O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
is O
a O
flexible O
fabrication S-MANP
method O
for O
the O
ceration O
of O
structures O
with O
different O
thicknesses O
, O
hole O
geometry S-CONPRI
and O
tapered O
openings O
, O
allowing O
the O
acoustic O
properties S-CONPRI
to O
be S-MATE
modified O
. O


It O
was O
confirmed O
via O
both O
finite B-CONPRI
element E-CONPRI
simulation O
and O
practical O
measurements O
that O
these O
structures O
supported O
Fabry-Pérot O
resonances O
, O
needed O
for O
metamaterial S-MATE
operation O
, O
at O
ultrasonic O
frequencies O
in O
water O
. O


Selective B-MANP
electron I-MANP
beam I-MANP
melting E-MANP
( O
SEBM S-MANP
) O
is O
shown O
to O
be S-MATE
a O
viable O
production S-MANP
route O
for O
titanium S-MATE
aluminides O
components S-MACEQ
. O


Fully B-PARA
dense E-PARA
and O
crack O
free O
parts O
can O
be S-MATE
produced O
. O


In O
the O
present O
paper O
a O
titanium B-MATE
aluminide I-MATE
alloy E-MATE
Ti-45Al-4Nb-C S-MATE
was O
investigated O
and O
the O
complete O
processing O
chain O
was O
developed O
, O
i.e O
. O


starting O
from O
the O
determination O
of O
the O
processing O
window O
, O
the O
evaluation O
of O
corresponding O
material B-CONPRI
properties E-CONPRI
for O
cube S-CONPRI
like O
specimens O
and O
finally O
the O
production S-MANP
of O
turbocharger O
wheels O
. O


The O
material B-CONPRI
properties E-CONPRI
were O
optimized O
by O
adjusting O
scanning B-CONPRI
strategy E-CONPRI
as S-MATE
well O
as S-MATE
heat O
treatment O
with O
particular O
consideration O
of O
the O
application O
to O
turbocharger O
wheels O
. O


The O
issue O
of O
dimensional B-CHAR
accuracy E-CHAR
and O
the O
feasibility S-CONPRI
of O
joining S-MANP
will O
be S-MATE
discussed O
and O
a O
proof O
test O
is O
performed O
. O


Cobalt-chromium-molybdenum O
( O
CoCrMo O
) O
alloys S-MATE
are O
widely O
used O
in O
load-bearing S-FEAT
implants S-APPL
; O
specifically O
, O
in O
hip S-MANP
, O
knee S-CONPRI
, O
and O
spinal O
applications O
due O
to O
their O
excellent O
wear B-PRO
resistance E-PRO
. O


However O
, O
due O
to O
in O
vivo O
corrosion S-CONPRI
and O
mechanically O
assisted O
corrosion S-CONPRI
, O
metal S-MATE
ion S-CONPRI
release O
occurs O
and O
accounts O
for O
poor O
biocompatibility S-PRO
. O


Therefore O
, O
a O
significant O
interest O
to O
improve O
upon O
CoCrMo B-MATE
alloy E-MATE
exists O
. O


In O
the O
present O
work O
we O
hypothesize O
that O
calcium B-MATE
phosphate E-MATE
( O
CaP O
) O
will O
behave O
as S-MATE
a O
solid O
lubricant S-MATE
in O
CoCrMo B-MATE
alloy E-MATE
under O
tribological S-CONPRI
testing S-CHAR
, O
thereby O
minimizing O
wear S-CONPRI
and O
metal S-MATE
ion S-CONPRI
release O
concerns O
associated O
with O
CoCrMo B-MATE
alloy E-MATE
. O


CoCrMo-CaP O
composite B-MATE
coatings E-MATE
were O
processed S-CONPRI
using O
laser B-MANP
engineered I-MANP
net I-MANP
shaping E-MANP
( O
LENS™ O
) O
system O
. O


After O
LENS™ O
processing O
, O
CoCrMo B-MATE
alloy E-MATE
was O
subjected O
to O
laser S-ENAT
surface O
melting S-MANP
( O
LSM S-MATE
) O
using O
the O
same O
LENS™ O
set-up O
. O


Samples S-CONPRI
were O
investigated O
for O
microstructural S-CONPRI
features O
, O
phase S-CONPRI
identification O
, O
and O
biocompatibility S-PRO
. O


It O
was O
found O
that O
LSM S-MATE
treated O
CoCrMo O
improved O
wear B-PRO
resistance E-PRO
by O
5 O
times O
. O


Our O
results O
show O
that O
careful O
surface B-MANP
modification E-MANP
treatments O
can O
simultaneously O
improve O
wear B-PRO
resistance E-PRO
and O
in O
vivo O
biocompatibility S-PRO
of O
CoCrMo B-MATE
alloy E-MATE
, O
which O
can O
correlate O
to O
a O
reduction S-CONPRI
of O
metal S-MATE
ion S-CONPRI
release O
in O
vivo O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
has O
several O
possible O
advantages O
over O
traditional B-MANP
manufacturing E-MANP
including O
increased O
design B-CONPRI
freedom E-CONPRI
, O
reduced O
material S-MATE
usage O
, O
and O
shorter O
lead-times O
. O


A O
noteworthy O
capability O
of O
AM S-MANP
is O
the O
ability O
to O
monitor S-CONPRI
the O
process S-CONPRI
during O
material S-MATE
deposition S-CONPRI
and O
interrupt O
the O
process S-CONPRI
during O
fabrication S-MANP
if O
necessary O
. O


Recently O
, O
such O
monitoring O
, O
feedback S-PARA
, O
and O
control O
have O
been O
made O
possible O
by O
implementing O
in B-CONPRI
situ E-CONPRI
infrared O
( O
IR S-CHAR
) O
thermography O
in O
powder B-MANP
bed I-MANP
fusion I-MANP
AM I-MANP
technologies E-MANP
. O


The O
purpose O
of O
the O
current O
research S-CONPRI
was O
to O
investigate O
the O
acquisition O
of O
absolute O
surface S-CONPRI
temperatures O
using O
in B-CONPRI
situ E-CONPRI
IR O
imaging S-APPL
of O
the O
melted S-CONPRI
or O
solid O
surfaces B-CONPRI
layer-by-layer E-CONPRI
during O
fabrication S-MANP
within O
an O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
system O
. O


The O
thermal O
camera S-MACEQ
was O
synchronized O
with O
the O
system O
's O
signal O
voltages O
of O
three O
synchronized O
events O
( O
pre-heating O
, O
melting S-MANP
, O
and O
raking O
) O
to O
automatically O
capture O
images S-CONPRI
. O


To O
acquire O
absolute O
temperature S-PARA
values O
from O
the O
IR S-CHAR
images S-CONPRI
, O
a O
calibration S-CONPRI
procedure O
was O
established O
to O
determine O
the O
solid O
material S-MATE
's O
emissivity O
and O
reflected O
temperature S-PARA
or O
mean O
radiant O
temperature S-PARA
of O
the O
build B-PARA
chamber E-PARA
, O
which O
are O
necessary O
input O
parameters S-CONPRI
for O
the O
IR S-CHAR
camera S-MACEQ
. O


A O
blackbody O
radiator O
was O
fabricated S-CONPRI
via O
EBM S-MANP
and O
was O
used O
as S-MATE
a O
tool S-MACEQ
to O
determine O
the O
emissivity O
of O
Ti–6Al–4V O
( O
determined O
to O
be S-MATE
0.26 O
in O
the O
temperature B-PARA
range E-PARA
of O
the O
current O
study O
) O
. O


heat S-CONPRI
shielding O
) O
that O
were O
used O
in O
calculating O
the O
mean O
radiant O
temperature S-PARA
of O
the O
manufacturing S-MANP
environment O
( O
∼342 O
°C O
) O
. O


Experimental S-CONPRI
validation O
of O
the O
model S-CONPRI
was O
performed O
using O
a O
thermocouple S-MACEQ
embedded O
during O
fabrication S-MANP
that O
showed O
a O
3.77 O
% O
difference O
in O
temperature S-PARA
. O


A O
temperature S-PARA
difference O
of O
∼366 O
°C O
( O
1038 O
°C O
vs. O
672 O
°C O
) O
was O
observed O
when O
comparing O
uncorrected O
IR S-CHAR
temperature O
data S-CONPRI
with O
corrected O
temperature S-PARA
data S-CONPRI
. O


Upon O
validation S-CONPRI
of O
the O
IR S-CHAR
parameters O
for O
a O
melted S-CONPRI
area S-PARA
, O
experimentation O
was O
conducted O
to O
also O
determine O
powder S-MATE
emissivity O
( O
found O
to O
be S-MATE
0.50 O
) O
. O


The O
thermal O
model S-CONPRI
presented O
here O
can O
be S-MATE
modified O
and O
implemented O
in O
other O
AM B-MANP
technologies E-MANP
for O
consideration O
of O
radiation S-MANP
energy O
to O
acquire O
absolute O
temperatures S-PARA
of O
layered O
surfaces S-CONPRI
, O
leading O
to O
improved O
thermal O
monitoring O
and O
control O
of O
the O
fabrication S-MANP
process O
. O


In-situ S-CONPRI
welding O
during O
powder B-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
process O
was O
proposed O
. O


Highly O
dense O
part O
without O
degrading O
of O
mechanical B-CONPRI
properties E-CONPRI
was O
fabricated S-CONPRI
by O
EBM S-MANP
. O


The O
applications O
of O
EBM S-MANP
technology O
was O
expanded O
using O
the O
in-situ S-CONPRI
welding O
concept O
. O


As S-MATE
one O
of O
the O
powder-bed-fusion O
additive B-MANP
manufacturing I-MANP
processes E-MANP
, O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
is O
able O
to O
produce O
metal S-MATE
parts O
directly O
. O


Many O
small O
volume S-CONPRI
components S-MACEQ
with O
high O
quality S-CONPRI
have O
been O
fabricated S-CONPRI
using O
the O
EBM S-MANP
technology O
. O


However O
, O
there O
are O
only O
few O
reports O
on O
the O
EBM S-MANP
fabrication O
of O
medium-sized O
components S-MACEQ
. O


This O
, O
in O
turn O
, O
drastically O
degrades O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
EBM S-MANP
printed O
parts O
. O


Here O
, O
we O
firstly O
report O
an O
in-situ S-CONPRI
welding O
process S-CONPRI
to O
overcome O
the O
lack O
of O
energy O
issue O
caused O
by O
the O
long O
scan O
length O
during O
EBM S-MANP
process O
. O


After O
the O
investigation O
of O
the O
corresponding O
microstructure S-CONPRI
, O
microhardness S-CONPRI
and O
tensile B-PRO
properties E-PRO
, O
it O
is O
revealed O
that O
the O
in-situ S-CONPRI
welding O
zone O
is O
fully O
joined O
and O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
in-situ S-CONPRI
welded O
part O
are O
comparable O
to O
that O
of O
the O
wrought S-CONPRI
counterpart O
. O


This O
implies O
that O
medium-sized O
components S-MACEQ
can O
be S-MATE
successfully O
fabricated S-CONPRI
using O
the O
EBM S-MANP
, O
with O
no O
compromise O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
. O


From O
pottery O
to O
clay S-MATE
tablets O
and O
building O
materials S-CONPRI
, O
clay S-MATE
easily O
qualifies O
as S-MATE
one O
of O
the O
most O
versatile O
materials S-CONPRI
in O
the O
history O
of O
human O
civilization O
. O


Clay S-MATE
owes O
this O
versatility O
to O
the O
distinct O
properties S-CONPRI
it O
exhibits O
before O
and O
after O
firing S-MANP
. O


Soft O
, O
unfired O
clay S-MATE
can O
morph O
into O
complex B-PRO
shapes E-PRO
, O
while O
fired S-MANP
clay S-MATE
offers O
a O
fixed O
shape O
and O
higher O
stiffness S-PRO
. O


Despite O
several O
potential O
applications O
, O
thus O
far O
, O
no O
designer O
materials S-CONPRI
with O
similar O
properties S-CONPRI
have O
been O
demonstrated O
. O


Here O
, O
we O
introduce O
the O
concept O
of O
metallic B-MATE
clay E-MATE
: O
a O
designer O
material S-MATE
that O
mimics O
the O
two-state O
behavior O
of O
clay S-MATE
. O


Metallic B-MATE
clay E-MATE
could O
initially O
morph O
into O
arbitrarily O
complex B-PRO
shapes E-PRO
owing O
to O
numerous O
degrees-of-freedom O
that O
its O
various O
kinematic O
( O
moving O
) O
and O
compliant O
( O
deformable O
) O
joints O
afford O
. O


The O
fabrication S-MANP
of O
metallic B-MATE
clay E-MATE
requires O
novel O
designs S-FEAT
of O
joints O
and O
locking O
mechanisms O
that O
are O
compatible O
with O
metal S-MATE
3D B-MANP
printing E-MANP
( O
additive B-MANP
manufacturing E-MANP
) O
techniques O
such O
that O
metallic B-MATE
clay E-MATE
can O
be S-MATE
fabricated O
through O
a O
single-step O
, O
non-assembly O
, O
and O
self-supporting S-FEAT
3D B-MANP
printing E-MANP
process O
. O


We O
designed S-FEAT
with O
3D B-MANP
printing E-MANP
17 O
prototypes S-CONPRI
using O
selective B-MANP
laser I-MANP
melting E-MANP
from O
a O
medical S-APPL
grade O
high O
strength S-PRO
titanium O
alloy S-MATE
( O
Ti-6Al-4V S-MATE
) O
to O
demonstrate O
the O
various O
aspects O
of O
metallic B-MATE
clay E-MATE
. O


Biomass-derived O
polymers S-MATE
have O
been O
rapidly O
developed O
for O
alleviating O
excessive O
fossil-fuel-based O
plastic S-MATE
consumption O
, O
as S-MATE
green O
manufacturing S-MANP
is O
required O
due O
to O
many O
environmental B-CONPRI
issues E-CONPRI
. O


Here O
, O
using O
a O
recently O
developed O
biopolymer S-MATE
, O
bio-based O
polycarbonate S-MATE
( O
bio O
PC S-MATE
) O
, O
we O
demonstrated O
the O
processability O
of O
filament-feedstock O
extrusion S-MANP
and O
extrusion-type O
3D B-MANP
printing E-MANP
. O


Under O
a O
set S-APPL
of O
optimal B-PARA
process E-PARA
conditions O
, O
the O
as-printed O
bio O
PC S-MATE
products O
showed O
superior O
tensile B-PRO
strength E-PRO
compared O
to O
other O
commercial O
polymers S-MATE
. O


We O
also O
confirmed O
the O
environmentally O
friendly O
characteristics O
of O
the O
thermoplastic S-MATE
processes S-CONPRI
of O
bio O
PC S-MATE
by O
measuring O
hazardous O
emissions O
during O
3D B-MANP
printing E-MANP
. O


Finally O
, O
considering O
sterilization O
of O
the O
as-printed O
consumer B-APPL
products E-APPL
, O
we O
tested O
the O
resistive O
properties S-CONPRI
of O
bio O
PC S-MATE
parts O
against O
heat S-CONPRI
and O
UV S-CONPRI
. O


Collectively O
, O
the O
good O
3D S-CONPRI
printability O
, O
low O
gas S-CONPRI
and O
particle S-CONPRI
emission S-CHAR
, O
and O
decent O
durability S-PRO
of O
the O
bio O
PC B-MATE
material E-MATE
indicate O
great O
potential O
applications O
for O
indoor O
home O
manufacturing S-MANP
of O
various O
consumer B-APPL
products E-APPL
. O


Process−property O
relationships O
in O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
play O
critical O
roles O
in O
process B-CONPRI
control E-CONPRI
and O
rapid O
certification O
. O


In O
laser-based O
directed B-MANP
energy I-MANP
deposition E-MANP
, O
powder S-MATE
mass O
flow O
into O
the O
melt B-MATE
pool E-MATE
influences O
the O
cooling S-MANP
behavior O
and O
properties S-CONPRI
of O
a O
built O
part O
. O


This O
study O
develops O
predictive O
computational B-ENAT
models E-ENAT
that O
provide O
the O
microhardness S-CONPRI
of O
AM S-MANP
components O
processed S-CONPRI
with O
miscible O
dissimilar B-MATE
alloys E-MATE
, O
and O
then O
investigates S-CONPRI
the O
influence O
of O
varying O
process B-CONPRI
parameters E-CONPRI
on O
properties S-CONPRI
in O
experiments O
and O
modeling S-ENAT
. O


Experimentally-determined O
clad O
dilution O
and O
microhardness S-CONPRI
results O
of O
Ni-based O
superalloy O
Inconel B-MATE
718 E-MATE
clads O
deposited O
onto O
1045 O
carbon B-MATE
steel E-MATE
substrates O
are O
compared O
to O
the O
values O
from O
a O
computational O
thermo-fluid O
dynamics O
( O
CtFD O
) O
model S-CONPRI
. O


The O
numerical O
model S-CONPRI
considers O
the O
fluidic O
mechanisms O
of O
molten B-MATE
metal E-MATE
during O
powder S-MATE
deposition S-CONPRI
and O
the O
resulting O
transient S-CONPRI
melt B-MATE
pool E-MATE
geometry S-CONPRI
changes O
. O


The O
model S-CONPRI
also O
handles O
the O
change O
in O
thermo-physical O
properties S-CONPRI
caused O
by O
the O
composition S-CONPRI
mixture O
between O
the O
powder S-MATE
and O
substrate B-MATE
materials E-MATE
in O
the O
melt B-MATE
pool E-MATE
. O


Based O
on O
the O
computed O
temperature S-PARA
and O
velocity O
distributions S-CONPRI
in O
the O
melt B-MATE
pool E-MATE
, O
cooling B-PARA
rate E-PARA
, O
dilution O
of O
the O
melt B-MATE
pool E-MATE
and O
microhardenss O
are O
evaluated O
. O


The O
capability O
to O
predict O
thermal O
histories O
in O
such O
models O
is O
calibrated S-CONPRI
and O
validated O
with O
experimental S-CONPRI
thermal O
imaging S-APPL
and O
microstructures S-MATE
of O
additive B-MANP
manufactured E-MANP
clads O
. O


In O
addition O
, O
the O
roles O
of O
cooling B-PARA
rate E-PARA
and O
alloy S-MATE
composition O
on O
the O
microhardness S-CONPRI
are O
examined O
. O


The O
results O
show O
that O
variation S-CONPRI
in O
microhardness S-CONPRI
is O
dominated O
by O
composition S-CONPRI
mixture O
between O
the O
powder S-MATE
and O
substrate B-MATE
materials E-MATE
, O
rather O
than O
cooling S-MANP
behavior O
or O
dendrite S-BIOP
arm O
spacing O
at O
liquid-solid B-CONPRI
interface E-CONPRI
in O
laser S-ENAT
deposited O
Inconel B-MATE
718 E-MATE
on O
AISI O
1045 O
carbon B-MATE
steel E-MATE
. O


A O
new O
one-way O
coupled O
thermal-mechanical O
finite B-CONPRI
element E-CONPRI
based O
model S-CONPRI
of O
direct B-MANP
metal I-MANP
laser I-MANP
sintering E-MANP
( O
DMLS S-MANP
) O
is O
developed O
to O
simulate O
the O
process S-CONPRI
, O
and O
predict O
distortion S-CONPRI
and O
cracking S-CONPRI
failure O
location O
in O
the O
fabricated S-CONPRI
components S-MACEQ
. O


The O
model S-CONPRI
takes O
into O
account O
the O
layer-by-layer S-CONPRI
additive B-MANP
manufacturing E-MANP
features O
, O
solidification S-CONPRI
and O
melting S-MANP
phenomena O
. O


The O
model S-CONPRI
is O
first O
validated O
using O
experimental B-CONPRI
data E-CONPRI
, O
then O
model S-CONPRI
is O
applied O
to O
a O
DMLS S-MANP
fabricated O
component S-MACEQ
. O


The O
study O
shows O
how O
the O
stress B-PRO
distribution E-PRO
at O
the O
support-solid O
interface S-CONPRI
is O
critical O
to O
contributing O
to O
cracking S-CONPRI
and O
distortion S-CONPRI
. O


During O
the O
DMLS S-MANP
process O
, O
thermal B-PRO
stress E-PRO
at O
the O
support-solid O
interface S-CONPRI
reaches O
its O
maximum O
during O
the O
printing B-MANP
process E-MANP
, O
particularly O
when O
the O
first O
solid O
layer S-PARA
is O
built O
above O
the O
support S-APPL
layer S-PARA
. O


This O
result O
suggests O
that O
cracking S-CONPRI
at O
the O
interface S-CONPRI
may O
occur O
during O
the O
printing B-MANP
process E-MANP
, O
which O
is O
consistent O
with O
experimental S-CONPRI
observation O
. O


Using O
a O
design S-FEAT
parametric O
study O
, O
a O
thick O
and O
low-density O
porous S-PRO
layer S-PARA
is O
found O
to O
reduce O
residual B-PRO
stress E-PRO
and O
distortion S-CONPRI
in O
the O
built O
component S-MACEQ
. O


The O
developed O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
can O
be S-MATE
used O
to O
future O
design S-FEAT
and O
optimize O
DMLS S-MANP
process O
. O


There O
is O
growing O
interest O
in O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
( O
L-PBF S-MANP
) O
or O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
manufacturing S-MANP
of O
high O
conductivity S-PRO
metals O
such O
as S-MATE
copper O
and O
refractory B-MATE
metals E-MATE
. O


SLM B-MANP
manufacturing E-MANP
of O
high O
thermal B-PRO
conductivity E-PRO
metals S-MATE
is O
particularly O
difficult O
. O


In O
case O
of O
refractory B-MATE
metals E-MATE
, O
the O
difficulty O
is O
amplified O
because O
of O
their O
high O
melting B-PRO
point E-PRO
and O
brittle S-PRO
behaviour O
. O


Rapid O
process S-CONPRI
development O
strategies O
are O
essential O
to O
identify O
suitable O
process B-CONPRI
parameters E-CONPRI
for O
achieving O
minimum O
porosities S-PRO
in O
these O
alloys S-MATE
, O
yet O
current O
strategies O
suffer O
from O
several O
limitations O
. O


We O
propose O
a O
simple S-MANP
approach O
for O
rapid O
process S-CONPRI
development O
using O
normalized O
process S-CONPRI
maps O
. O


Using O
plots O
of O
normalized O
energy B-PARA
density E-PARA
vs. O
normalized O
hatch B-PARA
spacing E-PARA
, O
we O
identify O
a O
wide O
processability O
window O
. O


This O
is O
further O
refined O
using O
analytical O
heat B-CONPRI
transfer E-CONPRI
models O
to O
predict O
melt B-MATE
pool E-MATE
size O
. O


Final O
optimization S-CONPRI
of O
the O
parameters S-CONPRI
is O
achieved O
by O
experiments O
based O
on O
statistical O
Design B-CONPRI
of I-CONPRI
Experiments E-CONPRI
concepts O
. O


In O
this O
article O
we O
demonstrate O
the O
use O
of O
our O
proposed O
approach O
for O
development O
of O
process B-CONPRI
parameters E-CONPRI
( O
hatch B-PARA
spacing E-PARA
, O
layer B-PARA
thickness E-PARA
, O
exposure S-CONPRI
time O
and O
point O
distance O
) O
for O
SLM B-MANP
manufacturing E-MANP
of O
molybdenum S-MATE
and O
aluminium S-MATE
. O


Relative B-PRO
densities E-PRO
of O
97.4 O
% O
and O
99.7 O
% O
are O
achieved O
using O
200 O
W O
pulsed B-MANP
laser E-MANP
and O
400 O
W O
continuous O
laser S-ENAT
respectively O
, O
for O
molybdenum S-MATE
and O
aluminium S-MATE
, O
demonstrating O
the O
effectiveness S-CONPRI
of O
our O
approach O
for O
SLM S-MANP
processing O
of O
high O
conductivity S-PRO
materials O
. O


Inconel B-MATE
718 E-MATE
, O
a O
widely O
used O
nickel S-MATE
based O
super B-MATE
alloy E-MATE
, O
is O
of O
special O
interest O
to O
the O
aerospace S-APPL
and O
automotive S-APPL
fields O
for O
its O
highly O
desirable O
and O
consistent O
material B-CONPRI
properties E-CONPRI
over O
a O
large O
range S-PARA
of O
temperatures S-PARA
. O


The O
objective O
of O
this O
research S-CONPRI
is O
to O
understand O
the O
effect O
of O
process B-CONPRI
parameters E-CONPRI
of O
a O
Direct B-MANP
Metal I-MANP
Laser I-MANP
Sintering E-MANP
( O
DMLS S-MANP
) O
machine S-MACEQ
, O
concerning O
mainly O
beam S-MACEQ
power O
between O
40 O
W O
and O
300 O
W O
and O
scan O
line O
speed O
between O
200 O
mm/s O
and O
2500 O
mm/s O
on O
scan O
line O
quality S-CONPRI
, O
line O
geometry S-CONPRI
and O
dimensions S-FEAT
, O
and O
melt B-MATE
pool E-MATE
geometry S-CONPRI
in O
laser S-ENAT
melted O
Inconel B-MATE
718 E-MATE
line O
scans O
. O


Higher O
power S-PARA
runs O
resulted O
in O
voids S-CONPRI
forming S-MANP
in O
the O
bottom O
of O
the O
melt B-MATE
pool E-MATE
and O
were O
consistent O
with O
either O
electron B-MANP
beam I-MANP
welding E-MANP
or O
melting S-MANP
processes O
operating O
at O
higher O
temperatures S-PARA
. O


Laser B-PARA
energy I-PARA
density E-PARA
( O
LED S-APPL
) O
, O
a O
method O
of O
correlating O
the O
effects O
of O
scan B-PARA
speed E-PARA
and O
beam S-MACEQ
power O
into O
one O
characteristic O
process B-CONPRI
parameter E-CONPRI
, O
was O
also O
investigated O
. O


This O
ratio O
of O
beam S-MACEQ
power O
to O
scan B-PARA
speed E-PARA
follows O
a O
second O
order O
polynomial O
trend S-CONPRI
line O
for O
melt B-MATE
pool E-MATE
width O
and O
a O
logarithmic O
trend S-CONPRI
for O
average S-CONPRI
line O
width O
. O


LED S-APPL
values O
for O
melt B-PARA
pool I-PARA
depth E-PARA
are O
separated O
to O
show O
two O
trend S-CONPRI
lines O
as S-MATE
two O
mechanisms O
operate O
at O
low O
values O
below O
0.25 O
J/mm O
and O
high O
values O
above O
0.25 O
J/mm O
. O


Process B-CONPRI
optimization E-CONPRI
has O
always O
been O
a O
crucial O
step S-CONPRI
for O
effective O
usage O
of O
metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
: O
it O
consists O
in O
establishing O
quantitative S-CONPRI
relations O
between O
final O
part O
's O
characteristics O
and O
process B-CONPRI
parameters E-CONPRI
to O
find O
their O
optimal O
combination O
and O
obtain O
a O
fully O
functional O
mechanical S-APPL
component S-MACEQ
. O


Experimental S-CONPRI
investigation O
techniques O
are O
usually O
employed O
for O
this O
purpose O
but O
they O
can O
be S-MATE
extremely O
expensive O
and O
time-consuming O
, O
especially O
when O
the O
output O
of O
the O
process S-CONPRI
depends O
on O
a O
large O
number O
of O
parameters S-CONPRI
, O
like O
for O
AM S-MANP
. O


Numerical B-ENAT
simulation E-ENAT
could O
represent O
an O
alternative O
solution S-CONPRI
: O
by O
reproducing O
the O
real O
process S-CONPRI
characteristics O
, O
a O
simulation S-ENAT
could O
provide O
useful O
insights O
, O
allowing O
to O
evaluate O
the O
performance S-CONPRI
of O
the O
process S-CONPRI
for O
different O
parameter S-CONPRI
combinations O
without O
relying O
exclusively O
on O
expensive O
experimental S-CONPRI
campaigns.In O
this O
work O
, O
a O
finite B-CONPRI
element E-CONPRI
AM S-MANP
simulation O
based O
on O
the O
inherent O
strain S-PRO
( O
IS O
) O
method O
was O
developed O
and O
the O
prediction B-CONPRI
performance E-CONPRI
in O
terms O
of O
part O
's O
residual B-CONPRI
deformation E-CONPRI
was O
evaluated O
by O
comparing O
the O
numerical O
results O
with O
the O
measurements O
carried O
out O
on O
an O
experimental S-CONPRI
campaign O
. O


A O
new O
model B-CONPRI
calibration E-CONPRI
approach O
for O
prediction S-CONPRI
improvement O
was O
also O
implemented O
and O
it O
allowed O
to O
discover O
an O
unexpected O
behaviour O
of O
the O
model S-CONPRI
that O
strongly O
affects O
the O
validity O
of O
this O
method O
for O
AM S-MANP
simulation O
. O


The O
role O
of O
volumetric O
energy B-PARA
density E-PARA
on O
the O
microstructural B-CONPRI
evolution E-CONPRI
, O
texture S-FEAT
and O
mechanical B-CONPRI
properties E-CONPRI
of O
304L O
stainless B-MATE
steel E-MATE
parts O
additively B-MANP
manufactured E-MANP
via O
selective B-MANP
laser I-MANP
melting I-MANP
process E-MANP
is O
investigated O
. O


304L O
is O
chosen O
because O
it O
is O
a O
potential O
candidate O
to O
be S-MATE
used O
as S-MATE
a O
matrix O
in O
a O
metal B-MATE
matrix I-MATE
composite E-MATE
with O
nanoparticles B-CONPRI
dispersion E-CONPRI
for O
energy O
and O
high O
temperature S-PARA
applications O
. O


The O
highest O
relative B-PRO
density E-PRO
of O
99 O
% O
±0.5 O
was O
achieved O
using O
a O
volumetric O
energy B-PARA
density E-PARA
of O
1400 O
J/mm3 O
. O


Both O
XRD S-CHAR
analysis O
and O
Scheil O
simulation S-ENAT
revealed O
the O
presence O
of O
a O
small O
trace O
of O
the O
delta O
ferrite S-MATE
phase O
, O
due O
to O
rapid B-MANP
solidification E-MANP
within O
the O
austenitic S-MATE
matrix O
of O
304L O
. O


A O
fine O
cellular O
substructure O
ranged O
between O
0.4–1.8 O
μm O
, O
was O
detected O
across O
different O
energy B-PARA
density E-PARA
values O
. O


At O
the O
highest O
energy B-PARA
density E-PARA
value O
, O
a O
strong O
texture S-FEAT
in O
the O
direction O
of O
[ O
100 O
] O
was O
identified O
. O


At O
lower O
energy B-PARA
density E-PARA
values O
, O
multicomponent O
texture S-FEAT
was O
found O
due O
to O
high O
nucleation S-CONPRI
rate O
and O
the O
existing O
defects S-CONPRI
. O


Yield B-PRO
strength E-PRO
, O
ultimate B-PRO
tensile I-PRO
strength E-PRO
, O
and O
microhardness S-CONPRI
of O
samples S-CONPRI
with O
a O
relative B-PRO
density E-PRO
of O
99 O
% O
were O
measured O
to O
be S-MATE
540 O
± O
15 O
MPa S-CONPRI
, O
660 O
± O
20 O
MPa S-CONPRI
and O
254 O
± O
7 O
HV O
, O
respectively O
and O
higher O
than O
mechanical B-CONPRI
properties E-CONPRI
of O
conventionally O
manufactured S-CONPRI
304L O
stainless B-MATE
steel E-MATE
. O


Heat B-MANP
treatment E-MANP
of O
the O
laser S-ENAT
melted O
304L O
at O
1200 O
°C O
for O
2 O
h O
, O
resulted O
in O
the O
nucleation S-CONPRI
of O
recrystallized S-MANP
equiaxed B-CONPRI
grains E-CONPRI
followed O
by O
a O
decrease O
in O
microhardness S-CONPRI
value O
from O
233 O
± O
3 O
HV O
to O
208 O
± O
8 O
HV O
due O
to O
disappearance O
of O
cellular O
substructure O
. O


In O
this O
work O
the O
process S-CONPRI
of O
Acoustoplastic O
Metal S-MATE
Direct-write O
( O
AMD O
) O
is O
introduced O
for O
the O
first O
time O
. O


Millimeter-scale O
3D S-CONPRI
aluminum O
articles O
were O
printed O
to O
demonstrate O
the O
process B-CONPRI
feasibility E-CONPRI
. O


Evidence O
of O
process-induced O
inter-layer O
and O
intra-layer O
mass O
transport S-CHAR
resulting O
in O
metallurgical B-CONPRI
bonding E-CONPRI
across O
voxels S-CONPRI
was O
obtained O
. O


During O
voxel S-CONPRI
formation O
, O
a O
process S-CONPRI
temperature O
rise O
of O
5 O
° O
Celsius O
from O
a O
process S-CONPRI
ambient O
temperature S-PARA
of O
25 O
° O
Celsius O
was O
recorded O
. O


In O
addition O
, O
acoustic O
energy-induced O
microstructural S-CONPRI
changes O
during O
process S-CONPRI
were O
observed O
in O
the O
material S-MATE
. O


The O
work O
presented O
here O
not O
only O
demonstrates O
the O
feasibility S-CONPRI
of O
a O
new O
non-melt O
fusion S-CONPRI
room O
temperature S-PARA
metal S-MATE
3D B-MANP
printing E-MANP
approach—capable O
of O
producing O
metals S-MATE
with O
more O
than O
99 O
percent O
density—but O
also O
presents O
both O
observational O
study O
and O
an O
initial O
theoretical S-CONPRI
basis O
upon O
which O
a O
new O
athermal O
microstructural S-CONPRI
transformation O
process S-CONPRI
may O
be S-MATE
understood O
Selective B-MANP
laser I-MANP
melting E-MANP
and O
other O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
techniques O
have O
recently O
attracted O
substantial O
interest O
of O
both O
researchers O
and O
the O
processing O
industry S-APPL
. O


In O
the O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
process S-CONPRI
, O
the O
components S-MACEQ
are O
produced O
layer-wise O
using O
a O
laser B-CONPRI
beam E-CONPRI
. O


SLM S-MANP
is O
a O
powder B-MACEQ
bed E-MACEQ
based O
AM B-MANP
process E-MANP
and O
is O
characterized O
by O
the O
complete O
melting S-MANP
of O
the O
utilized O
powder B-MATE
material E-MATE
. O


Employing O
SLM S-MANP
, O
complex O
three-dimensional S-CONPRI
parts O
and O
light O
weight S-PARA
structures O
can O
be S-MATE
produced O
directly O
from O
3D S-CONPRI
CAD O
data S-CONPRI
. O


However O
, O
although O
SLM S-MANP
is O
a O
very O
promising O
technology S-CONPRI
, O
there O
are O
still O
challenges O
to O
solve O
. O


Under O
cyclic B-PRO
loading E-PRO
, O
pores S-PRO
can O
act O
as S-MATE
stress O
raisers O
and O
lead S-MATE
to O
premature O
crack O
initiations O
, O
which O
reduce O
the O
fatigue B-PRO
strength E-PRO
of O
the O
material S-MATE
. O


Hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
offers O
the O
possibility O
to O
reduce O
the O
porosity S-PRO
. O


HIP S-MANP
combines O
high O
pressure S-CONPRI
and O
high O
temperature S-PARA
to O
produce O
materials S-CONPRI
with O
superior O
properties S-CONPRI
. O


The O
influence O
of O
the O
HIP S-MANP
process O
parameters S-CONPRI
on O
the O
density S-PRO
and O
microstructure S-CONPRI
of O
IN718 S-MATE
SLM O
components S-MACEQ
is O
investigated O
by O
means O
of O
micro O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
. O


The O
results O
of O
the O
experiments O
show O
that O
the O
majority O
of O
pores S-PRO
can O
be S-MATE
densified O
by O
means O
of O
HIP S-MANP
. O


On O
the O
other O
hand O
, O
some O
pores S-PRO
can O
not O
be S-MATE
densified O
. O


The O
reason O
for O
this O
is O
seen O
in O
entrapped O
argon S-MATE
gas O
from O
the O
SLM S-MANP
process S-CONPRI
. O


Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
additive B-MANP
manufacturing E-MANP
technology O
is O
sensitive O
to O
variations S-CONPRI
in O
powder B-MATE
particle E-MATE
morphology S-CONPRI
and O
size O
distribution S-CONPRI
. O


However O
, O
the O
absence O
of O
a O
clear O
link O
between O
the O
powder S-MATE
characteristics O
and O
the O
LPBF S-MANP
performances O
complicates O
the O
development O
, O
selection O
and O
quality B-CONPRI
control E-CONPRI
of O
LPBF S-MANP
powder O
feedstock S-MATE
. O


In O
this O
work O
, O
three O
Ti-6Al-4 B-MATE
V I-MATE
powder E-MATE
lots O
produced O
by O
two O
different O
techniques O
, O
namely O
, O
plasma S-CONPRI
atomization S-MANP
and O
gas B-MANP
atomization E-MANP
, O
were O
selected O
and O
characterized O
. O


Following O
the O
micro-computed B-CHAR
tomography E-CHAR
analysis O
of O
the O
powder B-MATE
particles E-MATE
’ O
morphology S-CONPRI
, O
size O
and O
density S-PRO
, O
the O
flowability O
of O
these O
powder S-MATE
lots O
was O
concurrently O
evaluated O
using O
Hall O
and O
Gustavsson O
flowmeters O
and O
an O
FT4 O
powder S-MATE
rheometer O
. O


Next O
, O
the O
same O
three O
powder S-MATE
lots O
were O
used O
to O
3D-print O
and O
post-process S-CONPRI
a O
series O
of O
testing S-CHAR
specimens O
with O
different O
layer B-PARA
thicknesses E-PARA
and O
build B-PARA
orientations E-PARA
, O
in O
order O
to O
establish O
a O
correlation O
between O
the O
powder S-MATE
characteristics O
and O
the O
geometric O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
a O
final O
product O
. O


This O
study O
demonstrates O
that O
the O
use O
of O
highly O
spherical S-CONPRI
powders S-MATE
with O
a O
limited O
amount O
of O
fine O
particles S-CONPRI
promotes O
their O
flowability O
and O
yields O
LPBF S-MANP
components S-MACEQ
with O
improved O
mechanical S-APPL
and O
geometric O
characteristics O
. O


Although O
the O
melt B-MATE
pool E-MATE
convection O
currents O
influence O
the O
dilution O
, O
porosity S-PRO
and O
distribution S-CONPRI
of O
potentially O
included O
hard O
phase B-CONPRI
particles E-CONPRI
such O
as S-MATE
carbide O
or O
other O
ceramic S-MATE
particles O
, O
which O
are O
added O
to O
increase O
the O
wear B-PRO
resistance E-PRO
of O
the O
deposited O
material S-MATE
, O
there O
is O
only O
limited O
knowledge O
of O
melt B-MATE
pool E-MATE
dynamics O
within O
blown O
powder S-MATE
additive B-MANP
manufacturing I-MANP
processes E-MANP
. O


In O
the O
pursuit O
of O
a O
deeper O
understanding O
, O
a O
high-speed O
camera S-MACEQ
has O
been O
used O
to O
observe O
melt B-MATE
pool E-MATE
dynamics O
during O
laser B-MANP
cladding E-MANP
at O
a O
frame O
rate O
of O
up O
to O
67 O
’ O
000 O
frames O
per O
second O
, O
allowing O
for O
the O
particles S-CONPRI
that O
swim O
on O
the O
surface S-CONPRI
to O
be S-MATE
traced O
automatically O
. O


The O
resulting O
videos O
allow O
for O
the O
melt B-MATE
pool E-MATE
surface O
behavior O
to O
be S-MATE
investigated O
using O
a O
specifically O
developed O
automated O
high-speed O
camera S-MACEQ
image O
evaluation O
technique O
. O


This O
method O
has O
been O
tested O
for O
reliability S-CHAR
and O
applied O
to O
investigate O
the O
process B-CONPRI
parameter E-CONPRI
influence O
on O
melt B-MATE
pool E-MATE
dynamics O
. O


The O
results O
show O
, O
that O
there O
is O
no O
pronounced O
laminar O
flow O
on O
the O
melt B-MATE
pool E-MATE
surface O
, O
instead O
a O
remarkable O
randomness O
to O
the O
direction O
of O
particle S-CONPRI
flow O
can O
be S-MATE
observed O
. O


That O
being O
said O
, O
it O
is O
still O
possible O
to O
identify O
certain O
flow O
tendencies O
that O
can O
be S-MATE
explained O
by O
surface B-PRO
tension E-PRO
phenomena O
like O
the O
Marangoni O
effect O
and O
which O
depend O
on O
the O
process B-CONPRI
parameters E-CONPRI
. O


Laser B-MANP
Metal I-MANP
Deposition E-MANP
is O
a O
near-net-shape S-MANP
processing O
technology S-CONPRI
, O
which O
allows O
remarkable O
freedom O
in O
multi-material S-CONPRI
processing O
. O


It O
has O
been O
shown O
that O
multi-material S-CONPRI
processing O
of O
the O
two O
alloys S-MATE
via O
discrete O
as S-MATE
well O
as S-MATE
via O
gradual O
material S-MATE
transition O
is O
possible O
without O
any O
cracks O
for O
manufacturing S-MANP
small O
cubes O
. O


Cross-sections S-CONPRI
of O
manufactured S-CONPRI
parts O
and O
tracks O
showed O
that O
a O
preheating S-MANP
temperature O
of O
at O
least O
400 O
°C O
is O
necessary O
to O
process S-CONPRI
crack O
free O
samples S-CONPRI
. O


EDX-analyses O
indicated O
that O
if O
a O
discrete O
material S-MATE
transition O
is O
required O
in O
multi-material S-CONPRI
processing O
, O
the O
material S-MATE
transition O
should O
be S-MATE
implemented O
in O
the O
vertical S-CONPRI
build-up O
direction O
because O
the O
mixing S-CONPRI
zone O
in O
this O
direction O
is O
significantly O
smaller O
than O
the O
mixing S-CONPRI
zone O
in O
the O
horizontal O
direction O
. O


Due O
to O
the O
stronger O
mixing S-CONPRI
effects O
in O
the O
horizontal O
direction O
, O
a O
gradual O
material S-MATE
transition O
by O
a O
linear O
progression O
should O
be S-MATE
implemented O
in O
this O
direction O
rather O
than O
in O
the O
vertical S-CONPRI
direction O
. O


The O
mixing S-CONPRI
effects O
are O
mainly O
caused O
by O
melt B-CONPRI
flow E-CONPRI
, O
while O
diffusion S-CONPRI
effects O
can O
be S-MATE
neglected O
. O


Processing O
of O
the O
low O
workability O
Fe-Co-1.5V O
( O
Hiperco® O
equivalent O
) O
alloy S-MATE
is O
demonstrated O
using O
the O
Laser B-MANP
Engineered I-MANP
Net I-MANP
Shaping E-MANP
( O
LENS S-MANP
) O
metals S-MATE
additive B-MANP
manufacturing E-MANP
technique O
. O


As S-MATE
an O
innovative O
and O
highly O
localized O
solidification B-MANP
process E-MANP
, O
LENS S-MANP
is O
shown O
to O
overcome O
workability O
issues O
that O
arise O
during O
conventional O
thermomechanical B-MANP
processing E-MANP
, O
enabling O
the O
production S-MANP
of O
bulk O
, O
near O
net-shape O
forms O
of O
the O
Fe-Co O
alloy S-MATE
. O


Bulk O
LENS S-MANP
structures O
appeared O
to O
be S-MATE
ductile O
with O
no O
significant O
macroscopic B-CONPRI
defects E-CONPRI
. O


Fine O
equiaxed B-CONPRI
grain E-CONPRI
structures O
were O
observed O
in O
as-built O
specimens O
following O
solidification S-CONPRI
, O
which O
then O
evolved O
toward O
a O
highly O
heterogeneous S-CONPRI
bimodal O
grain B-CONPRI
structure E-CONPRI
after O
annealing S-MANP
. O


The O
microstructure B-CONPRI
evolution E-CONPRI
in O
Fe-Co O
is O
discussed O
in O
the O
context O
of O
classical O
solidification S-CONPRI
theory O
and O
selective O
grain B-CONPRI
boundary E-CONPRI
pinning O
processes S-CONPRI
. O


Magnetic O
properties S-CONPRI
were O
also O
assessed O
and O
shown O
to O
fall O
within O
the O
extremes O
of O
conventionally O
processed S-CONPRI
Hiperco® O
alloys.Hiperco® O
is O
a O
registered O
trademark O
of O
Carpenter O
Technologies S-CONPRI
, O
Readings O
, O
PA S-CHAR
. O


The O
use O
of O
3D B-MANP
printing E-MANP
in O
architecture S-APPL
has O
grown O
tremendously O
over O
the O
last O
decade O
thanks O
to O
its O
strong O
reputation O
as S-MATE
a O
versatile O
, O
cheap O
and O
fast O
technology S-CONPRI
. O


Its O
durability S-PRO
, O
in O
fact O
, O
depends O
on O
several O
factors O
( O
above O
all O
design S-FEAT
accuracy S-CHAR
, O
quality S-CONPRI
of O
materials S-CONPRI
and O
environmental O
aggressiveness O
) O
, O
which O
may O
lead S-MATE
or O
contribute O
to O
rapid O
performance S-CONPRI
decay O
over O
time O
. O


With O
this O
in O
mind O
, O
the O
paper O
describes O
the O
design-to-production O
process S-CONPRI
for O
a O
façade O
shading O
system O
using O
additive B-MANP
manufacturing E-MANP
and O
the O
associated O
testing S-CHAR
campaign O
to O
assess O
the O
feasibility S-CONPRI
of O
the O
design S-FEAT
and O
durability S-PRO
of O
materials S-CONPRI
. O


Horizontal O
lamellas O
, O
with O
a O
complex O
curved O
geometry S-CONPRI
, O
were O
generated O
using O
computational O
design S-FEAT
optimised O
for O
additive B-MANP
manufacturing E-MANP
. O


In O
order O
to O
select O
the O
most O
suitable O
3D-printable O
material S-MATE
, O
tests O
were O
conducted O
on O
different O
polymers S-MATE
in O
a O
climatic O
chamber O
at O
Politecnico O
di O
Milano O
to O
monitor S-CONPRI
material S-MATE
performances O
over O
time O
at O
high O
temperatures S-PARA
such O
as S-MATE
the O
ones O
in O
Dubai O
. O


The O
data S-CONPRI
gathered O
from O
these O
tests O
was O
crucial O
to O
the O
correct O
design S-FEAT
of O
the O
façade O
manufacturing B-MANP
process E-MANP
. O


Lattice B-FEAT
structures E-FEAT
are O
advantageous O
in O
terms O
of O
their O
high O
specific B-PRO
stiffness E-PRO
and O
strength S-PRO
, O
and O
have O
been O
applied O
to O
the O
design S-FEAT
of O
lightweight B-MACEQ
structures E-MACEQ
owing O
to O
the O
recent O
development O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
. O


The O
unique O
design B-CONPRI
flexibility E-CONPRI
of O
AM S-MANP
has O
enabled O
the O
fabrication S-MANP
of O
a O
functionally B-FEAT
graded I-FEAT
lattice E-FEAT
( O
FGL O
) O
by O
gradually O
changing O
the O
lattice S-CONPRI
size O
and O
enhancing O
structural O
efficiency O
of O
lattice B-FEAT
structures E-FEAT
. O


Although O
FGLs O
have O
been O
generally O
designed S-FEAT
to O
reduce O
the O
compliance O
( O
i.e. O
, O
to O
increase O
the O
stiffness S-PRO
) O
, O
this O
study O
aims O
to O
develop O
soft O
polymeric O
lattices S-CONPRI
to O
widen O
the O
range S-PARA
of O
compliance O
for O
the O
development O
of O
FGLs O
. O


To O
develop O
soft O
lattice B-FEAT
structures E-FEAT
, O
various O
lattices S-CONPRI
were O
designed S-FEAT
and O
fabricated S-CONPRI
using O
a O
photo-polymerization O
type O
3D B-MACEQ
printer E-MACEQ
and O
photo-curable S-FEAT
polyurethane O
resin S-MATE
. O


Compression B-CHAR
tests E-CHAR
were O
conducted O
on O
these O
lattices S-CONPRI
, O
and O
their O
deformation S-CONPRI
behaviors O
were O
analyzed O
experimentally O
. O


The O
effects O
of O
various O
lattice B-FEAT
design E-FEAT
parameters O
and O
the O
curing B-PARA
time E-PARA
were O
also O
investigated O
, O
and O
the O
resulting O
changes O
in O
the O
compliance O
were O
analyzed O
. O


As S-MATE
a O
consequence O
, O
the O
compressive O
stiffness S-PRO
can O
vary O
widely O
, O
within O
a O
range S-PARA
of O
10−3 O
to O
102 O
N/mm O
. O


Two O
types O
of O
FGLs O
, O
which O
enabled O
the O
self-positioning O
and O
self-guided O
moving O
functions O
, O
were O
then O
developed O
by O
varying O
the O
lattice S-CONPRI
direction O
, O
strut B-PARA
diameter E-PARA
and O
curing B-PARA
time E-PARA
effectively O
. O


The O
thermal B-PRO
conductivity E-PRO
of O
AlSi10Mg S-MATE
made O
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
, O
and O
its O
modification O
via O
heat B-MANP
treatment E-MANP
, O
has O
received O
little O
attention O
despite O
possible O
applications O
for O
heat B-MACEQ
exchangers E-MACEQ
and O
thermo-mechanical S-CONPRI
components S-MACEQ
. O


Here O
, O
we O
show O
that O
heat B-MANP
treatment E-MANP
can O
increase O
the O
thermal B-PRO
conductivity E-PRO
of O
LPBF S-MANP
AlSi10Mg S-MATE
to O
that O
of O
cast S-MANP
material O
. O


Our O
results O
indicate O
that O
post-manufacture O
annealing S-MANP
eliminates O
the O
thermal B-PRO
conductivity E-PRO
anisotropy S-PRO
present O
in O
the O
as-built O
condition O
, O
and O
enhances O
the O
conductivity S-PRO
by O
close O
to O
30 O
% O
in O
the O
transverse O
direction O
( O
perpendicular O
to O
the O
LPBF S-MANP
build B-PARA
orientation E-PARA
) O
. O


A O
solution B-MANP
heat I-MANP
treatment E-MANP
increases O
the O
thermal B-PRO
conductivity E-PRO
further O
still O
( O
36 O
% O
compared O
to O
the O
as-built O
condition O
) O
, O
while O
a O
T6-like O
treatment O
provides O
the O
greatest O
increase O
( O
44 O
% O
compared O
to O
the O
as-built O
condition O
) O
. O


These O
improvements O
are O
related O
to O
the O
evolution S-CONPRI
of O
the O
AlSi10Mg S-MATE
microstructure O
, O
especially O
the O
breakdown O
of O
the O
Si S-MATE
cellular B-FEAT
structure E-FEAT
. O


Additionally O
, O
the O
thermal B-PRO
conductivities E-PRO
of O
gyroid O
lattice B-FEAT
structures E-FEAT
were O
examined O
in O
the O
as-built O
and O
annealed O
conditions O
. O


Contrary O
to O
solid O
specimens O
, O
the O
lattice B-FEAT
structures E-FEAT
exhibited O
almost O
isotropic S-PRO
thermal O
conductivity S-PRO
in O
the O
as-built O
condition O
. O


Their O
thermal B-PRO
conductivities E-PRO
were O
increased O
by O
the O
annealing B-MANP
treatment E-MANP
in O
proportion O
to O
their O
volume B-PARA
fraction E-PARA
. O


Our O
findings O
contribute O
to O
the O
development O
of O
a O
general O
design-for-additive-manufacturing O
( O
DfAM O
) O
framework S-CONPRI
which O
will O
make O
the O
best O
possible O
use O
of O
AM B-MATE
materials E-MATE
and O
lattice B-FEAT
structures E-FEAT
for O
heat B-CONPRI
transfer E-CONPRI
components S-MACEQ
. O


Building O
on O
a O
large O
scale O
with O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
is O
one O
of O
the O
biggest O
manufacturing S-MANP
challenges O
of O
our O
time O
. O


In O
the O
last O
decade O
, O
the O
proliferation O
of O
3D B-MANP
printing E-MANP
has O
allowed O
architects O
and O
engineers O
to O
imagine O
and O
develop O
constructions O
that O
can O
be S-MATE
produced O
additively O
. O


However O
, O
questions O
about O
the O
convenience O
of O
using O
this O
technology S-CONPRI
, O
and O
whether O
additive S-MATE
large-scale O
constructions O
can O
be S-MATE
feasible O
, O
efficient O
and O
sustainable S-CONPRI
are O
still O
open O
. O


In O
this O
research S-CONPRI
3D B-MANP
printing E-MANP
is O
considered O
not O
as S-MATE
a O
question O
, O
but O
as S-MATE
an O
answer O
to O
the O
increasing O
scarcity O
of O
material S-MATE
resources O
in O
the O
construction S-APPL
industry O
. O


This O
paper O
illustrates O
the O
overarching O
process S-CONPRI
from O
concept O
to O
the O
realisation O
of O
the O
Trabeculae S-MATE
Pavilion O
, O
a O
load-responsive O
architecture S-APPL
that O
is O
entirely O
designed S-FEAT
and O
optimized O
for O
3D B-MANP
printing E-MANP
, O
using O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
- O
one O
of O
the O
most O
cost-effective O
additive S-MATE
techniques O
of O
production S-MANP
. O


The O
research B-CONPRI
methodology E-CONPRI
is O
based O
on O
a O
multi-scale O
computational O
workflow S-CONPRI
that O
integrates O
several O
aspects O
, O
such O
as S-MATE
material O
testing S-CHAR
, O
bio-inspired B-CONPRI
design I-CONPRI
algorithms E-CONPRI
, O
multi-criteria O
optimization S-CONPRI
, O
and O
production S-MANP
management O
. O


The O
work O
culminates O
in O
the O
construction S-APPL
process O
of O
a O
full-scale O
architectural O
prototype S-CONPRI
; O
an O
anticlastic O
shell S-MACEQ
that O
features O
a O
cellular B-FEAT
structure E-FEAT
with O
increased O
material S-MATE
and O
structural O
efficiency O
. O


Microstructural B-CHAR
characterization E-CHAR
was O
carried O
out O
on O
AISI O
17-4 B-MATE
PH I-MATE
stainless I-MATE
steel E-MATE
fabricated O
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
in O
an O
argon S-MATE
environment O
. O


Conventionally O
, O
this O
steel S-MATE
exhibits O
a O
martensitic O
structure S-CONPRI
with O
a O
small O
fraction S-CONPRI
of O
δ O
ferrite S-MATE
. O


However O
, O
the O
combined O
findings O
of O
x-ray B-CHAR
diffraction E-CHAR
and O
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
( O
EBSD S-CHAR
) O
proved O
that O
SLM-ed O
17-4 O
PH S-CONPRI
steel O
has O
a O
fully O
ferritic S-MATE
microstructure O
, O
more O
specifically O
δ O
ferrite S-MATE
. O


The O
microstructure S-CONPRI
consists O
of O
coarse O
ferritic S-MATE
grains O
elongated O
along O
the O
build B-PARA
direction E-PARA
, O
with O
a O
pronounced O
solidification S-CONPRI
crystallographic O
texture S-FEAT
. O


These O
results O
were O
associated O
to O
the O
high O
cooling S-MANP
and O
heating S-MANP
rates O
experienced O
throughout O
the O
SLM S-MANP
process S-CONPRI
that O
suppressed O
the O
austenite S-MATE
formation O
and O
produced O
a O
“ O
by-passing O
” O
phenomenon O
of O
this O
phase S-CONPRI
during O
the O
numerous O
thermal B-PARA
cycles E-PARA
. O


Furthermore O
, O
the O
energy-dispersive O
X-ray S-CHAR
spectroscopy S-CONPRI
( O
EDS S-CHAR
) O
measurements O
revealed O
a O
uniform O
distribution S-CONPRI
of O
elements S-MATE
without O
any O
dendritic O
structure S-CONPRI
. O


The O
extremely O
high O
cooling S-MANP
kinetics O
induced O
a O
diffusionless O
solidification S-CONPRI
, O
resulting O
in O
a O
homogeneous S-CONPRI
elemental O
composition S-CONPRI
. O


It O
was O
also O
found O
that O
the O
ferritic S-MATE
SLM-ed O
material S-MATE
can O
be S-MATE
transformed O
to O
martensite S-MATE
again O
by O
re-austenitization O
at O
1050 O
°C O
followed O
by O
quenching S-MANP
. O


Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM S-MANP
) O
has O
the O
potentiality O
of O
being O
an O
effective O
system O
in O
terms O
of O
time O
and O
energy O
consumption O
. O


Among O
the O
different O
additive B-MANP
manufacturing I-MANP
processes E-MANP
that O
are O
available O
, O
the O
EBM S-MANP
process O
has O
shown O
the O
lowest O
Specific B-PRO
Energy E-PRO
Consumption O
( O
SEC O
) O
and O
the O
highest O
average S-CONPRI
Deposition O
Rate O
( O
DRa O
) O
. O


Moreover O
, O
all O
the O
literature O
studies O
have O
only O
an O
analysis O
of O
energy O
efficiency O
during O
the O
melting S-MANP
of O
the O
bulk O
material S-MATE
phase O
and O
have O
adopted O
a O
fixed O
job O
design S-FEAT
. O


A O
black-box O
approach O
is O
applied O
to O
provide O
a O
new O
model S-CONPRI
for O
the O
energy O
efficiency O
of O
the O
EBM S-MANP
process O
. O


Different O
jobs O
have O
been O
designed S-FEAT
to O
analyse O
the O
effect O
of O
a O
part O
and O
of O
manufacturing S-MANP
designs S-FEAT
. O


Bulk O
material S-MATE
, O
support S-APPL
and O
lattice B-FEAT
structures E-FEAT
have O
been O
included O
. O


The O
design S-FEAT
has O
therefore O
been O
aimed O
at O
investigating O
the O
effect O
of O
the O
building O
height O
, O
melted S-CONPRI
area S-PARA
and O
process S-CONPRI
themes O
on O
energy O
efficiency O
. O


The O
jobs O
have O
been O
produced O
using O
Arcam O
A2X O
and O
Standard S-CONPRI
Arcam O
Ti6Al4V B-MATE
powders E-MATE
. O


According O
to O
this O
research S-CONPRI
, O
the O
architecture S-APPL
of O
the O
machine S-MACEQ
and O
its O
control O
of O
the O
process S-CONPRI
have O
the O
main O
impact S-CONPRI
on O
the O
relationship O
between O
SEC O
and O
DRa O
. O


Additionally O
, O
the O
empirical S-CONPRI
approach O
applied O
to O
the O
machine S-MACEQ
subunits O
has O
highlighted O
that O
only O
a O
small O
part O
of O
the O
total O
energy O
demand O
is O
needed O
to O
power S-PARA
the O
electron B-CONPRI
beam E-CONPRI
during O
the O
melting S-MANP
phase O
, O
while O
the O
remaining O
part O
guarantees O
the O
good O
machine S-MACEQ
working O
conditions O
. O


Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
, O
is O
an O
additive B-MANP
manufacturing E-MANP
technology O
that O
is O
used O
in O
industry S-APPL
for O
rapid B-ENAT
prototyping E-ENAT
and O
manufacturing S-MANP
of O
aftermarket O
products O
, O
molds S-MACEQ
and O
special O
machine S-MACEQ
parts O
. O


Quality S-CONPRI
assurance O
and O
process S-CONPRI
stability O
still O
require O
improvement O
until O
this O
technology S-CONPRI
is O
ready O
for O
large O
scale O
serial O
production S-MANP
. O


Scan O
strategies O
and O
parameter S-CONPRI
sets O
for O
manufacturing S-MANP
are O
often O
fixed O
when O
certification O
processes S-CONPRI
are O
finished O
. O


Thus O
, O
it O
is O
important O
to O
test O
the O
manufacturability S-CONPRI
of O
specific O
design S-FEAT
features O
such O
as S-MATE
inner O
channels O
. O


In O
the O
following O
we O
will O
present O
the O
qualification O
of O
inner O
channels O
in O
different O
test O
parts O
for O
the O
aluminum B-MATE
alloy E-MATE
AlSi10Mg S-MATE
and O
the O
stainless B-MATE
steel E-MATE
1.4542 O
. O


The O
testing S-CHAR
includes O
different O
cleaning S-MANP
methods O
and O
air O
flow B-PARA
rate E-PARA
measurements O
. O


Additionally O
, O
we O
will O
compare O
such O
parts O
and O
LPBF S-MANP
specific O
problems O
to O
observations O
with O
a O
coaxial O
melt B-MATE
pool E-MATE
monitoring O
system O
. O


A O
system O
for O
the O
additive B-MANP
manufacturing E-MANP
of O
functionally B-MATE
graded I-MATE
concrete E-MATE
parts O
was O
developed O
. O


It O
is O
possible O
to O
3D B-MANP
print E-MANP
functionally O
graded O
concrete S-MATE
parts O
by O
varying O
the O
type O
and O
ratio O
of O
aggregates S-MATE
. O


Homogeneous S-CONPRI
and O
functionally B-CONPRI
graded E-CONPRI
parts O
were O
produced O
with O
the O
system O
. O


Cork S-MATE
is O
a O
viable O
natural B-MATE
aggregate E-MATE
for O
concrete B-MANP
printing E-MANP
. O


In O
recent O
years O
, O
the O
interest O
in O
developing O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
in O
the O
architecture S-APPL
, O
engineering S-APPL
and O
construction S-APPL
( O
AEC S-APPL
) O
industry S-APPL
has O
increased O
, O
motivated O
by O
the O
potential O
to O
support S-APPL
greater O
formal O
complexity S-CONPRI
. O


In O
this O
context O
, O
AM S-MANP
has O
been O
largely O
used O
to O
design S-FEAT
and O
fabricate S-MANP
physical O
parts O
with O
homogeneous B-MATE
materials E-MATE
. O


This O
paper O
proposes O
a O
new O
strategy O
, O
aimed O
at O
the O
design S-FEAT
and O
fabrication S-MANP
of O
functionally B-MATE
graded I-MATE
concrete E-MATE
parts O
with O
specific O
thermo-mechanical B-CONPRI
performance E-CONPRI
. O


The O
paper O
describes O
the O
development O
of O
the O
AM S-MANP
system O
to O
materialize S-CONPRI
such O
parts O
. O


The O
computational B-CONPRI
tool E-CONPRI
developed O
to O
design S-FEAT
the O
material S-MATE
to O
meet O
specific O
performance S-CONPRI
requirements O
, O
and O
the O
design S-FEAT
and O
testing S-CHAR
of O
the O
material S-MATE
are O
described O
elsewhere O
. O


A O
functionally B-MATE
graded I-MATE
concrete E-MATE
part O
obtained O
by O
replacing O
sand S-MATE
with O
cork S-MATE
was O
produced O
and O
is O
evaluated O
. O


Mechanical B-CONPRI
properties E-CONPRI
( O
tensile B-PRO
strength E-PRO
and O
creep S-PRO
) O
of O
AlSi10Mg S-MATE
specimens O
fabricated S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
in O
the O
Z-direction S-FEAT
were O
investigated O
in O
the O
25–400 O
°C O
temperature B-PARA
range E-PARA
. O


Specimens O
were O
tested O
after O
stress S-PRO
relief O
treatment O
. O


The O
results O
revealed O
that O
yield B-PRO
stress E-PRO
( O
YS O
) O
significantly O
decreases O
and O
the O
elongation S-PRO
increases O
at O
temperatures S-PARA
higher O
than O
200 O
°C O
. O


The O
ultimate O
tensile B-PRO
stress E-PRO
( O
UTS S-PRO
) O
continuously O
decreases O
with O
temperature S-PARA
. O


The O
creep S-PRO
parameters O
, O
namely O
stress S-PRO
exponent O
n S-MATE
and O
apparent O
activation O
energy O
Q O
, O
were O
found O
to O
be S-MATE
25 O
± O
2 O
and O
146 O
± O
20 O
kJ/mole O
, O
respectively O
. O


It O
was O
shown O
that O
plastic B-PRO
deformation E-PRO
during O
creep S-PRO
is O
governed O
by O
dislocation S-CONPRI
movements O
in O
primary O
aluminum S-MATE
grains O
. O


The O
tested O
material S-MATE
is O
actually O
an O
aluminum S-MATE
composite O
reinforced S-CONPRI
by O
sub-micron S-FEAT
Si S-MATE
particles S-CONPRI
. O


The O
creep S-PRO
resistance O
of O
AlSi10Mg B-MATE
alloy E-MATE
fabricated O
by O
selective B-MANP
laser I-MANP
melting E-MANP
is O
close O
to O
that O
for O
aluminum S-MATE
matrix O
particles S-CONPRI
reinforced O
composites S-MATE
. O


Recyclability S-CONPRI
of O
Ti-6Al-4 B-MATE
V I-MATE
powder E-MATE
by O
EBM S-MANP
process O
has O
been O
investigated O
. O


The O
effect O
of O
powder S-MATE
recycling O
was O
explored O
using O
metallographic O
and O
mechanical B-CHAR
testing E-CHAR
. O


Recycling S-CONPRI
causes O
various O
defects S-CONPRI
to O
appear O
in O
Ti-6Al-4 B-MATE
V I-MATE
powder E-MATE
, O
having O
a O
negative O
effect O
on O
the O
EBM S-MANP
process O
. O


HIP S-MANP
significantly O
improves O
the O
quality S-CONPRI
of O
the O
samples S-CONPRI
made O
from O
recycled S-CONPRI
powder S-MATE
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
also O
called O
3D-printing S-MANP
, O
is O
an O
innovative O
technology S-CONPRI
, O
as S-MATE
the O
printing O
of O
objects O
is O
performed O
by O
layer-by-layer B-CONPRI
deposition E-CONPRI
. O


A O
wide O
variety O
of O
materials S-CONPRI
can O
be S-MATE
used O
to O
produce O
a O
variety O
of O
shapes O
that O
can O
not O
be S-MATE
achieved O
using O
any O
other O
technology S-CONPRI
. O


AM S-MANP
started O
as S-MATE
a O
prototyping S-CONPRI
in O
plastics S-MATE
, O
and O
now O
it O
is O
successfully O
implemented O
with O
metals S-MATE
. O


AM S-MANP
in O
metals S-MATE
, O
first O
of O
all O
, O
in O
Titanium B-MATE
alloys E-MATE
, O
offers O
the O
potential O
to O
not O
only O
generate O
net-shape O
, O
complex O
geometrical O
and O
light-weight S-PRO
objects O
, O
but O
also O
to O
achieve O
enhanced O
mechanical B-CONPRI
properties E-CONPRI
, O
even O
better O
than O
achieved O
by O
traditional O
mass B-CONPRI
production E-CONPRI
, O
like O
casting.However O
, O
the O
priority O
of O
achieving O
good O
non-porous O
microstructure S-CONPRI
and O
the O
desired O
mechanical B-CONPRI
properties E-CONPRI
is O
a O
challenge O
for O
the O
main O
fields O
of O
applications O
of O
Titanium S-MATE
AM S-MANP
, O
such O
as S-MATE
the O
aerospace B-APPL
industry E-APPL
and O
production S-MANP
of O
medical B-APPL
implants E-APPL
. O


Thus O
, O
the O
quality S-CONPRI
of O
the O
powder S-MATE
and O
standardization O
of O
the O
AM B-MANP
process E-MANP
are O
the O
top O
priority O
. O


The O
potential O
recycling S-CONPRI
of O
the O
Ti-6Al-4 B-MATE
V I-MATE
powder E-MATE
as S-MATE
an O
inextricable O
part O
of O
the O
AM B-MANP
process E-MANP
needs O
to O
be S-MATE
explored.The O
influence O
of O
powder S-MATE
recycling O
on O
Ti-6Al-4 B-MATE
V E-MATE
additive B-MANP
manufacturing E-MANP
, O
the O
correct O
number O
of O
cycles O
, O
the O
requirements O
of O
the O
recycling S-CONPRI
procedures O
, O
and O
possible O
post B-CONPRI
processing E-CONPRI
procedures O
– O
are O
still O
open O
questions O
. O


This O
research S-CONPRI
aims O
to O
answer O
these O
questions O
. O


Two O
identical O
test O
cylinder O
sets O
were O
printed O
, O
one O
from O
recycled S-CONPRI
powder S-MATE
and O
one O
from O
the O
new O
powder S-MATE
batch O
. O


The O
cylinders O
were O
printed O
by O
the O
Arcam O
EBM S-MANP
A2X O
machine S-MACEQ
using O
a O
start O
platform S-MACEQ
of O
210 O
x O
210 O
mm S-MANP
in O
size O
. O


Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM S-MANP
) O
is O
a O
well-known O
effective O
manufacturing B-MANP
process E-MANP
. O


This O
AM B-MANP
technology E-MANP
utilizes O
high O
power S-PARA
electron B-CONPRI
beam E-CONPRI
to O
produce O
layer-by-layer S-CONPRI
metal O
parts O
for O
various O
applications O
, O
such O
as S-MATE
fabrication O
of O
biomedical S-APPL
implants O
and O
aerospace B-MACEQ
components E-MACEQ
. O


The O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
printed O
specimens O
from O
the O
two O
sets O
( O
new O
and O
recycled S-CONPRI
Ti-6Al-4 O
V S-MATE
powder S-MATE
) O
were O
investigated O
before O
and O
after O
heat B-MANP
treatment E-MANP
. O


A O
novel O
approach O
to O
fabricate S-MANP
ceramic S-MATE
structures O
at O
multiple O
scales O
in O
a O
single O
component S-MACEQ
, O
based O
on O
the O
hybridization O
of O
additive B-MANP
manufacturing E-MANP
technologies O
, O
was O
developed O
by O
combining O
3D S-CONPRI
macro-stereolithography O
( O
Digital B-MANP
Light I-MANP
Processing E-MANP
, O
DLP S-MANP
) O
with O
two-photon O
lithography S-CONPRI
( O
2PL O
) O
, O
to O
produce O
cm-sized O
sample S-CONPRI
geometries S-CONPRI
with O
sub-μm O
surface S-CONPRI
features O
. O


The O
preceramic O
structures O
in O
the O
sub-μm O
scale O
were O
realized O
by O
2PL O
directly O
on O
easily O
manageable O
DLP S-MANP
macro-sized O
samples S-CONPRI
of O
the O
same O
ceramic S-MATE
composition O
. O


In O
this O
way O
, O
preceramic O
structures O
presenting O
both O
features O
typical O
of O
DLP B-MACEQ
printers E-MACEQ
( O
with O
a O
minimum O
size O
of O
around O
50 O
μm O
) O
and O
features O
well O
below O
their O
resolution S-PARA
limit S-CONPRI
were O
realized O
. O


We O
report O
here O
, O
for O
the O
first O
time O
, O
the O
realization O
of O
polymer-derived O
ceramic S-MATE
SiOC O
ceramic S-MATE
components O
structured O
in O
3D S-CONPRI
across O
several O
length B-CHAR
scales E-CHAR
( O
with O
micron S-FEAT
and O
mesoscale B-CONPRI
3D E-CONPRI
features O
) O
, O
produced O
by O
pyrolysis S-MANP
at O
1000 O
°C O
of O
preceramic O
parts O
, O
without O
shape O
distortion S-CONPRI
during O
the O
pyrolysis S-MANP
step O
. O


The O
effect O
of O
varying O
the O
solids O
volume B-PARA
fraction E-PARA
of O
an O
aqueous O
clay S-MATE
paste O
suspension O
on O
its O
printability S-PARA
via O
an O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
or O
3D B-MANP
printing E-MANP
technique O
, O
Direct O
Ink S-MATE
Writing O
( O
DIW S-MANP
) O
or O
material B-MANP
extrusion E-MANP
, O
has O
been O
studied O
. O


DIW S-MANP
is O
a O
cost-effective O
and O
straightforward O
fabrication S-MANP
technology O
suitable O
for O
adoption O
at O
a O
larger-scale O
by O
the O
traditional B-MATE
ceramics E-MATE
industry S-APPL
and O
the O
creative O
community O
. O


The O
pastes O
were O
prepared O
with O
volume B-PARA
fraction E-PARA
of O
solids O
ranging O
from O
25 O
to O
57 O
vol O
% O
. O


Their O
rheological B-PRO
properties E-PRO
( O
storage O
modulus O
and O
apparent O
yield B-PRO
stress E-PRO
) O
were O
measured O
by O
dynamic S-CONPRI
oscillatory O
rheometry O
. O


The O
relationships O
between O
solids O
content O
, O
rheological S-PRO
behaviour O
and O
print S-MANP
parameters S-CONPRI
were O
evaluated O
. O


An O
equation O
based O
on O
rheological B-PRO
properties E-PRO
to O
delineate O
between O
printable O
and O
non-printable O
conditions O
has O
been O
proposed O
. O


In O
this O
study O
, O
we O
present O
the O
first O
results O
of O
a O
newly O
developed O
melt B-MATE
pool E-MATE
monitoring O
tool S-MACEQ
for O
selective B-MANP
laser I-MANP
melting E-MANP
, O
called O
DMP-meltpool O
. O


A O
manual O
data S-CONPRI
analysis O
method O
is O
given O
, O
and O
the O
events O
indicated O
by O
the O
analysis O
( O
DMP-meltpool O
events O
) O
are O
shown O
to O
correlate O
to O
the O
static O
tensile B-PRO
properties E-PRO
of O
the O
samples S-CONPRI
built O
. O


These O
events O
indicate O
the O
probability S-CONPRI
of O
material S-MATE
discontinuities O
( O
defects S-CONPRI
) O
in O
the O
metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
parts O
. O


In O
order O
to O
do O
so O
, O
cylindrical S-CONPRI
bars O
of O
Ti-6Al-4V S-MATE
ELI O
were O
built O
and O
monitored O
using O
DMP-meltpool O
. O


The O
tensile B-PRO
properties E-PRO
of O
the O
printed O
cylinders O
were O
correlated S-CONPRI
with O
the O
events O
detected O
by O
DMP-meltpool O
. O


An O
inverse O
relation O
between O
plastic S-MATE
elongation S-PRO
and O
the O
DMP-meltpool O
event O
density S-PRO
was O
observed O
. O


These O
results O
show O
that O
DMP-meltpool O
can O
be S-MATE
used O
to O
predict O
the O
quality S-CONPRI
of O
AM B-MACEQ
parts E-MACEQ
by O
detecting O
variations S-CONPRI
in O
the O
signals O
and O
tagging O
these O
events O
throughout O
the O
build S-PARA
as S-MATE
defects O
. O


Thus O
the O
technique O
can O
be S-MATE
employed O
for O
first O
stage O
in-line O
quality B-CONPRI
control E-CONPRI
of O
AM B-MACEQ
parts E-MACEQ
and O
for O
sorting O
out O
parts O
with O
potential O
defects S-CONPRI
non-destructively O
. O


The O
DMP-meltpool O
events O
could O
have O
significant O
correlations O
with O
other O
mechanical B-CONPRI
properties E-CONPRI
( O
like O
fatigue S-PRO
, O
hardness S-PRO
, O
fracture S-CONPRI
toughness O
, O
and O
crack B-CONPRI
propagation E-CONPRI
) O
since O
such O
properties S-CONPRI
are O
influenced O
by O
defects S-CONPRI
originating O
from O
the O
process S-CONPRI
instabilities O
. O


This O
study O
compares O
the O
mechanical B-CONPRI
response E-CONPRI
and O
microstructure S-CONPRI
of O
Co–Cr–Mo O
removable O
partial O
denture S-APPL
models O
made O
through O
conventional O
lost-wax O
casting S-MANP
and O
the O
selective B-MANP
laser I-MANP
melting E-MANP
additive B-MANP
manufacturing I-MANP
process E-MANP
. O


Co–Cr–Mo O
clasps O
for O
removal O
partial O
dentures S-APPL
, O
based O
on O
a O
wax S-MATE
model S-CONPRI
( O
BEGO O
USA O
) O
, O
were O
fabricated S-CONPRI
through O
lost-wax O
technique O
and O
selective B-MANP
laser I-MANP
melting E-MANP
, O
and O
subjected O
to O
mechanical S-APPL
bending S-MANP
experiments O
to O
determine O
their O
yield B-PRO
strength E-PRO
and O
maximum O
reversible O
deformation S-CONPRI
. O


Microstructure S-CONPRI
and O
chemical B-CONPRI
composition E-CONPRI
of O
the O
clasps O
were O
determined O
through O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
and O
wave-dispersive O
spectroscopy S-CONPRI
to O
rationalize O
the O
differences O
and O
similarities O
in O
the O
mechanical B-CHAR
testing E-CHAR
results O
from O
the O
two O
groups.It O
was O
found O
that O
the O
clasps O
made O
using O
lost-wax O
technique O
and O
selective B-MANP
laser I-MANP
melting E-MANP
exhibit O
comparable O
mean O
yield B-PRO
strengths E-PRO
and O
maximum O
elastic B-PRO
deformations E-PRO
, O
however O
the O
underlying O
microstructure S-CONPRI
of O
the O
cast S-MANP
clasps O
vastly O
differs O
from O
the O
laser-melted O
counterparts O
. O


Furthermore O
, O
the O
laser S-ENAT
melted O
clasps O
exhibit O
larger O
variability S-CONPRI
in O
their O
mechanical B-CONPRI
response E-CONPRI
. O


While O
selective B-MANP
laser I-MANP
melting E-MANP
is O
capable O
of O
producing O
removable O
partial O
denture S-APPL
clasps O
with O
similar O
average S-CONPRI
mechanical O
responses O
to O
those O
of O
lost-wax O
cast S-MANP
counterparts O
, O
additional O
studies O
should O
be S-MATE
conducted O
to O
minimize O
the O
variability S-CONPRI
in O
the O
laser S-ENAT
melted O
clasps O
in O
order O
to O
minimize O
unexpected O
failures O
. O


Optical S-CHAR
Emissions O
Spectroscopy S-CONPRI
and O
plume O
imaging S-APPL
were O
utilized O
to O
investigate O
flaws S-CONPRI
generated O
during O
directed B-MANP
energy I-MANP
deposition I-MANP
additive I-MANP
manufacturing E-MANP
. O


Ti-6Al–4 O
V S-MATE
coupons O
were O
built O
using O
varying O
laser B-PARA
power E-PARA
, O
powder B-PARA
flow I-PARA
rate E-PARA
, O
and O
hatching O
pattern S-CONPRI
to O
induce O
random O
and O
systematic O
flaws S-CONPRI
. O


X-Ray B-CHAR
Computed I-CHAR
Tomography E-CHAR
( O
CT S-ENAT
) O
scans O
were O
completed O
on O
each O
part O
to O
determine O
flaw S-CONPRI
density S-PRO
and O
flaw S-CONPRI
locations O
. O


For O
coupons O
built O
with O
constant O
laser B-PARA
power E-PARA
, O
variations S-CONPRI
in O
either O
powder B-PARA
flow I-PARA
rate E-PARA
or O
hatch O
pattern S-CONPRI
that O
led S-APPL
to O
an O
increase O
in O
flaw S-CONPRI
density S-PRO
were O
accompanied O
by O
an O
increase O
in O
median O
line-to-continuum O
ratios O
around O
430 O
and O
520 O
nm O
and O
in O
total O
plume O
area S-PARA
. O


These O
results O
present O
a O
path O
forward O
for O
real-time O
flaw B-CONPRI
detection E-CONPRI
and O
assessment O
of O
build S-PARA
quality O
in O
directed B-MANP
energy I-MANP
deposition E-MANP
and O
powder B-MANP
bed I-MANP
fusion I-MANP
processes E-MANP
. O


This O
study O
examines O
the O
impact S-CONPRI
of O
low-temperature O
heat-treatment O
on O
the O
microstructure S-CONPRI
and O
corrosion S-CONPRI
performance O
of O
direct B-MACEQ
metal I-MACEQ
laser E-MACEQ
sintered O
( O
DMLS S-MANP
) O
-AlSi10Mg O
alloy S-MATE
. O


Differential O
scanning S-CONPRI
calorimetry O
( O
DSC S-CHAR
) O
was O
used O
to O
determine O
the O
phase S-CONPRI
( O
s S-MATE
) O
transition S-CONPRI
temperatures S-PARA
in O
the O
alloy S-MATE
. O


Two O
exothermic O
phenomena O
were O
detected O
and O
associated O
with O
the O
Mg2Si S-MATE
precipitation O
and O
Si S-MATE
phase S-CONPRI
precipitation O
in O
the O
as-printed O
alloy S-MATE
. O


Based O
on O
DSC S-CHAR
results O
, O
thermal-treatments O
including O
below O
and O
above O
the O
active O
Si S-MATE
precipitation S-CONPRI
temperature O
at O
200 O
°C O
and O
300 O
°C O
, O
respectively O
, O
and O
350 O
°C O
as S-MATE
an O
upper O
limit S-CONPRI
temperature O
for O
3 O
h O
were O
applied O
to O
the O
as-printed O
samples S-CONPRI
. O


Scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
and O
X-ray B-CHAR
diffraction I-CHAR
analysis E-CHAR
confirmed O
that O
heat-treatment O
from O
200 O
°C O
to O
350 O
°C O
promotes O
the O
homogeneity O
of O
the O
microstructure S-CONPRI
, O
characterized O
by O
uniform O
distribution S-CONPRI
of O
eutectic S-CONPRI
Si O
in O
α-Al O
matrix O
. O


To O
investigate O
the O
impact S-CONPRI
of O
the O
applied O
heat-treatment O
cycles O
on O
corrosion B-CONPRI
resistance E-CONPRI
of O
DMLS-AlSi10Mg O
at O
early O
stage O
of O
immersion O
, O
anodic O
polarization O
testing S-CHAR
and O
electrochemical S-CONPRI
impedance O
spectroscopy S-CONPRI
were O
performed O
in O
aerated O
3.5 O
wt. O
% O
NaCl S-MATE
solution O
. O


The O
results O
revealed O
more O
uniformly O
distributed O
pitting S-CONPRI
attack O
on O
the O
corroded O
surfaces S-CONPRI
by O
increasing O
the O
heat-treatment O
temperature S-PARA
up O
to O
300 O
°C O
, O
attributed O
to O
the O
more O
protective O
nature O
of O
the O
spontaneously O
air-formed O
passive O
layer S-PARA
on O
the O
surface S-CONPRI
of O
the O
alloy S-MATE
at O
initial O
immersion O
time O
. O


Further O
increase O
of O
the O
heat B-MANP
treatment E-MANP
temperature O
to O
350 O
°C O
induced O
severe O
localized O
corrosion S-CONPRI
attacks O
near O
the O
coarse O
Si S-MATE
particles S-CONPRI
, O
ascribed O
to O
the O
increased O
potential O
difference O
between O
the O
coalesced O
Si S-MATE
particles S-CONPRI
and O
aluminum S-MATE
matrix O
galvanic O
couple O
. O


In O
comparison O
, O
the O
corrosion S-CONPRI
of O
the O
as-printed O
and O
200 O
°C O
heat S-CONPRI
treated O
samples S-CONPRI
was O
characterized O
by O
a O
penetrating O
selective O
attack O
along O
the O
melt B-CONPRI
pool I-CONPRI
boundaries E-CONPRI
, O
leading O
to O
a O
higher O
corrosion S-CONPRI
current O
density S-PRO
and O
an O
active O
surface S-CONPRI
at O
early O
exposure S-CONPRI
, O
associated O
with O
the O
weakness O
of O
the O
existing O
passive O
film O
on O
their O
surfaces S-CONPRI
. O


A O
testing S-CHAR
methodology S-CONPRI
was O
developed O
to O
expose O
photopolymer B-MATE
resins E-MATE
and O
measure O
the O
cured S-MANP
material O
to O
determine O
two O
key O
parameters S-CONPRI
related O
to O
the O
photopolymerization S-MANP
process O
: O
Ec O
( O
critical O
energy O
to O
initiate O
polymerization S-MANP
) O
and O
Dp O
( O
penetration B-PARA
depth E-PARA
of O
curing S-MANP
light O
) O
. O


Five O
commercially O
available O
resins S-MATE
were O
evaluated O
under O
exposure S-CONPRI
from O
365 O
nm O
and O
405 O
nm O
light O
at O
varying O
power S-PARA
densities O
and O
energies O
. O


Caliper S-MACEQ
measurements O
, O
stylus S-MACEQ
profilometry O
, O
and O
confocal O
laser S-ENAT
scanning O
microscopy S-CHAR
showed O
similar O
results O
for O
hard O
materials S-CONPRI
while O
caliper S-MACEQ
measurement O
of O
a O
soft O
, O
elastomeric O
material S-MATE
proved O
inaccurate O
. O


Working O
curves O
for O
the O
five O
photopolymers S-MATE
showed O
unique O
behavior O
both O
within O
and O
among O
the O
resins S-MATE
as S-MATE
a O
function O
of O
curing S-MANP
light O
wavelength S-CONPRI
. O


Ec O
and O
Dp O
for O
the O
five O
resins S-MATE
showed O
variations S-CONPRI
as S-MATE
large O
as S-MATE
10x O
. O


Variations S-CONPRI
of O
this O
magnitude S-PARA
, O
if O
unknown O
to O
the O
user O
and O
not O
controlled O
for O
, O
will O
clearly O
affect O
printed O
part O
quality S-CONPRI
. O


Rapid B-ENAT
prototyping E-ENAT
of O
smart O
objects O
with O
embedded B-ENAT
electronics E-ENAT
. O


Integrated O
additive B-MANP
manufacturing E-MANP
approach O
. O


Polymer/metal O
nanocomposite O
conductive O
lines O
with O
controlled O
electrical B-CONPRI
properties E-CONPRI
. O


Fabrication S-MANP
of O
conductive O
3D S-CONPRI
oblique O
paths O
, O
bridging S-CONPRI
vias O
and O
standard S-CONPRI
sockets O
. O


Freeform S-CONPRI
monolithic O
smart O
nightlight O
sensor S-MACEQ
. O


We O
present O
an O
integrated O
additive B-MANP
manufacturing E-MANP
approach O
for O
the O
rapid B-ENAT
prototyping E-ENAT
of O
objects O
with O
embedded O
electric O
circuits O
. O


Our O
approach O
relies O
on O
the O
combined O
use O
of O
standard S-CONPRI
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
for O
the O
production S-MANP
of O
thermoplastic S-MATE
3D S-CONPRI
freeform O
components S-MACEQ
, O
and O
supersonic O
cluster O
beam B-PARA
deposition E-PARA
( O
SCBD O
) O
for O
the O
fabrication S-MANP
of O
embedded O
electrical S-APPL
conducting O
lines O
and O
resistors S-MACEQ
with O
tailored O
conductivity S-PRO
. O


SCBD O
is O
an O
additive S-MATE
fabrication O
technique O
based O
on O
the O
deposition S-CONPRI
of O
neutral O
metallic S-MATE
clusters O
carried O
in O
a O
highly O
collimated O
supersonic O
beam S-MACEQ
. O


A O
multi-step O
fabrication S-MANP
procedure O
alternating O
FFF S-MANP
and O
SCBD O
was O
developed O
and O
optimized O
allowing O
the O
fabrication S-MANP
of O
conductive O
3D S-CONPRI
oblique O
paths O
, O
bridging S-CONPRI
vias O
, O
and O
sockets O
for O
standard S-CONPRI
electronic O
components S-MACEQ
fitting O
. O


This O
resulted O
in O
the O
simplification O
of O
the O
topology S-CONPRI
of O
planar O
electric O
circuits O
by O
enabling O
out-of-plane O
connections O
, O
minimizing O
the O
implementation O
of O
bulky O
passive O
electrical S-APPL
components S-MACEQ
and O
avoiding O
the O
use O
of O
soldering S-MANP
and O
conductive O
adhesives S-MATE
for O
the O
integration O
of O
active O
electronic O
components S-MACEQ
. O


A O
dark-activated O
light O
sensor S-MACEQ
was O
produced O
as S-MATE
a O
demonstrator O
. O


Polyolefin B-MATE
thermoplastics E-MATE
like O
high B-MATE
density I-MATE
polyethylene E-MATE
( O
HDPE S-MATE
) O
are O
the O
leaders O
in O
terms O
of O
world-scale O
plastics S-MATE
’ O
production S-MANP
, O
environmentally O
benign O
polymerization S-MANP
processes O
, O
recycling S-CONPRI
, O
and O
sustainability S-CONPRI
. O


However O
, O
additive B-MANP
manufacturing E-MANP
of O
HDPE S-MATE
by O
means O
of O
fused B-MANP
deposition I-MANP
modeling E-MANP
( O
FDM S-MANP
) O
also O
known O
as S-MATE
fused O
filament S-MATE
fabrication S-MANP
( O
FFF S-MANP
) O
has O
been O
problematic O
owing O
to O
its O
massive O
shrinkage S-CONPRI
, O
voiding S-CONPRI
and O
warpage S-CONPRI
problems O
accompanied O
by O
its O
poor O
adhesion S-PRO
to O
common O
build B-MACEQ
plates E-MACEQ
and O
to O
extruded S-MANP
HDPE O
strands O
. O


Herein O
we O
overcome O
these O
problems O
and O
improve O
Young O
’ O
s S-MATE
modulus O
, O
tensile B-PRO
strength E-PRO
and O
surface B-PARA
quality E-PARA
of O
3D B-MANP
printed E-MANP
HDPE O
by O
varying O
3D B-MANP
printing E-MANP
parameters O
like O
temperature S-PARA
and O
diameter S-CONPRI
of O
the O
nozzle S-MACEQ
, O
extrusion B-PARA
rate E-PARA
, O
build B-MACEQ
plate E-MACEQ
temperature O
, O
and O
build B-CONPRI
plate I-CONPRI
material E-CONPRI
. O


Both O
nozzle B-CONPRI
diameter E-CONPRI
and O
printing B-PARA
speed E-PARA
affect O
surface B-PARA
quality E-PARA
but O
do O
not O
impair O
mechanical B-CONPRI
properties E-CONPRI
. O


Particularly O
, O
an O
extrusion B-CONPRI
rate I-CONPRI
gradient E-CONPRI
prevents O
void S-CONPRI
formation O
. O


For O
the O
first O
time O
additive B-MANP
manufactured E-MANP
HDPE O
and O
injection-molded O
HDPE S-MATE
exhibit O
similar O
mechanical B-CONPRI
properties E-CONPRI
with O
exception O
of O
elongation S-PRO
at O
break O
. O


Excellent O
fusion S-CONPRI
of O
the O
extruded S-MANP
polymer O
strands O
and O
the O
absence O
of O
anisotropy S-PRO
are O
achieved O
, O
as S-MATE
verified O
by O
microscopic B-CONPRI
imaging E-CONPRI
and O
measuring O
the O
tensile B-PRO
strength E-PRO
parallel O
and O
perpendicular O
to O
the O
3D B-MANP
printing E-MANP
direction O
. O


Refractory S-APPL
elements S-MATE
have O
high O
melting B-PRO
points E-PRO
and O
are O
difficult O
to O
melt S-CONPRI
and O
cast S-MANP
. O


In O
this O
study O
it O
is O
successfully O
demonstrated O
for O
the O
first O
time O
that O
laser B-MANP
metal I-MANP
deposition E-MANP
can O
be S-MATE
used O
to O
produce O
TiZrNbHfTa O
high-entropy O
alloy S-MATE
from O
a O
blend S-MATE
of O
elemental O
powders S-MATE
by O
in-situ S-CONPRI
alloying S-FEAT
. O


Columnar O
specimens O
with O
a O
height O
of O
10 O
mm S-MANP
and O
a O
diameter S-CONPRI
of O
3 O
mm S-MANP
were O
deposited O
with O
a O
pulsed O
Nd B-MATE
: I-MATE
YAG E-MATE
laser S-ENAT
. O


The O
built-up O
specimen O
has O
near-equiatomic O
composition S-CONPRI
, O
nearly O
uniform O
grain B-PRO
size E-PRO
, O
equiaxed B-CONPRI
grain E-CONPRI
shape O
, O
is O
bcc S-CONPRI
single O
phase S-CONPRI
and O
exhibits O
a O
high O
hardness S-PRO
of O
509 O
HV0.2 O
. O


Material B-CONPRI
properties E-CONPRI
of O
parts O
made O
via O
selective B-MANP
laser I-MANP
melting E-MANP
are O
not O
the O
same O
as S-MATE
the O
well-established O
properties S-CONPRI
for O
bulk O
base O
materials S-CONPRI
, O
due O
to O
the O
unique O
processes S-CONPRI
used O
to O
produce O
the O
parts O
. O


Meanwhile O
, O
additive B-MANP
manufacturing E-MANP
is O
increasingly O
being O
used O
for O
heat B-MACEQ
exchangers E-MACEQ
and O
heat S-CONPRI
removal O
devices O
, O
which O
demand O
high O
thermal B-PRO
conductivities E-PRO
. O


The O
thermal B-CONPRI
properties E-CONPRI
are O
also O
important O
for O
many O
non-destructive B-CHAR
testing E-CHAR
technologies O
. O


The O
thermal B-PRO
conductivity E-PRO
of O
selective B-MANP
laser I-MANP
melted E-MANP
316 O
L O
stainless B-MATE
steel E-MATE
was O
studied O
as S-MATE
a O
function O
of O
processing O
conditions O
and O
build B-PARA
orientation E-PARA
. O


The O
porosity S-PRO
and O
thermal B-PRO
conductivity E-PRO
were O
measured O
versus O
processing O
conditions O
. O


A O
critical O
energy B-PARA
density E-PARA
of O
44.4 O
J/mm3 O
was O
observed O
below O
which O
the O
porosity S-PRO
increased O
and O
the O
thermal B-PRO
conductivity E-PRO
decreased O
. O


For O
the O
lowest-porosity O
sample S-CONPRI
, O
the O
local O
thermal B-PRO
conductivity E-PRO
map O
taken O
with O
frequency O
domain S-CONPRI
thermoreflectance O
showed O
a O
variation S-CONPRI
in O
the O
stainless B-MATE
steel E-MATE
thermal O
conductivity S-PRO
between O
10.4 O
and O
19.8 O
W/m-K O
, O
while O
the O
average S-CONPRI
thermal O
conductivity S-PRO
of O
14.3 O
W/m-K O
from O
the O
thermal B-PRO
conductivity E-PRO
map O
agreed O
, O
within O
measurement S-CHAR
uncertainty O
, O
with O
the O
bulk O
thermal B-PRO
conductivity E-PRO
measurements O
. O


The O
thermal B-PRO
conductivity E-PRO
trend O
was O
not O
fully O
explained O
by O
the O
porosity S-PRO
, O
as S-MATE
effective O
medium O
models O
fail O
to O
predict O
the O
trend S-CONPRI
. O


Amorphous O
stripes O
in O
the O
selective B-MANP
laser I-MANP
melted E-MANP
stainless O
steel S-MATE
grains S-CONPRI
were O
identified O
by O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
. O


These O
amorphous O
regions O
also O
resulted O
in O
decreased O
x-ray B-CHAR
diffraction E-CHAR
intensities O
with O
increasing O
porosity S-PRO
. O


The O
amorphous O
regions O
are O
hypothesized O
to O
lower O
the O
thermal B-PRO
conductivity E-PRO
at O
faster O
laser S-ENAT
scanning O
speeds O
due O
to O
less O
time O
at O
elevated O
temperatures S-PARA
. O


We O
also O
found O
that O
in-print O
plane O
and O
through-print O
plane O
thermal B-PRO
conductivities E-PRO
have O
the O
same O
value O
when O
the O
energy B-PARA
density E-PARA
is O
greater O
than O
this O
critical O
amount O
. O


When O
the O
energy B-PARA
density E-PARA
reduces O
below O
this O
critical O
amount O
, O
the O
in-plane O
conductivity S-PRO
exceeds O
the O
through-plane O
. O


Inconel B-MATE
718 I-MATE
alloy E-MATE
rods O
were O
fabricated S-CONPRI
by O
electron–beam O
melting S-MANP
( O
EBM S-MANP
) O
, O
where O
the O
cylindrical S-CONPRI
axes O
( O
CAs O
) O
deviated O
from O
the O
build B-PARA
directions E-PARA
( O
BD O
) O
by O
0° O
, O
45° O
, O
55° O
, O
and O
90° O
. O


The O
microstructures S-MATE
and O
high-temperature O
tensile B-PRO
properties E-PRO
of O
the O
rods O
were O
investigated O
by O
taking O
into O
account O
the O
effect O
of O
the O
BD O
. O


Columnar B-PRO
grain E-PRO
structures O
or O
mixtures O
of O
columnar O
and O
equiaxed B-CONPRI
grains E-CONPRI
were O
obtained O
in O
the O
rods O
. O


As S-MATE
a O
result O
, O
the O
crystal B-PRO
orientation E-PRO
of O
the O
rods O
could O
be S-MATE
controlled O
by O
appropriate O
choice O
of O
the O
CA S-MATE
. O


The O
highest O
strength S-PRO
was O
obtained O
for O
the O
< O
1 O
1 O
1 O
> O
oriented O
rod S-MACEQ
. O


The O
dependence O
of O
strength S-PRO
on O
the O
rod S-MACEQ
orientation S-CONPRI
could O
be S-MATE
explained O
in O
terms O
of O
the O
anisotropies O
in O
the O
crystal B-PRO
orientation E-PRO
, O
columnar B-PRO
grain E-PRO
structure O
, O
and O
arrangement O
of O
the O
precipitate S-MATE
particles S-CONPRI
. O


This O
paper O
presents O
the O
very O
first O
study O
on O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
of O
a O
high O
melting B-PRO
point E-PRO
near-eutectic O
V–9Si–5B O
alloy S-MATE
via O
direct B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
. O


Tailored O
V–9Si–5B O
powder B-MATE
material E-MATE
was O
produced O
by O
means O
of O
a O
gas B-MANP
atomization E-MANP
( O
GA S-MATE
) O
process S-CONPRI
. O


A O
novel O
setup O
for O
the O
DED S-MANP
experiments O
was O
developed O
and O
an O
overview O
of O
the O
production S-MANP
parameters S-CONPRI
for O
manufacturing S-MANP
of O
crack-free O
specimens O
is O
given O
. O


The O
microstructural B-CONPRI
evolution E-CONPRI
of O
the O
three-phase O
V–9Si–5B O
alloy S-MATE
is O
described O
by O
means O
of O
SEM S-CHAR
, O
EBSD S-CHAR
and O
STEM O
analyses O
during O
the O
entire O
process B-ENAT
chain E-ENAT
, O
i.e O
. O


the O
gas B-MANP
atomization E-MANP
of O
the O
powder B-MATE
material E-MATE
, O
the O
consolidation S-CONPRI
via O
DED S-MANP
and O
the O
heat B-MANP
treatment E-MANP
of O
the O
compacts S-MATE
. O


First O
mechanical B-CHAR
tests E-CHAR
demonstrate O
the O
high O
hardness S-PRO
and O
the O
competitive O
creep S-PRO
resistance O
of O
the O
AM S-MANP
V–9Si–5B O
material S-MATE
in O
comparison O
to O
other O
three-phase O
V-based O
alloys S-MATE
. O


Metal B-MANP
additive I-MANP
manufacturing E-MANP
offers O
a O
tool S-MACEQ
to O
bring O
formerly O
unmanufacturable O
, O
geometrically O
complex O
, O
engineered O
structures O
into O
existence O
. O


However O
, O
considerable O
challenges O
remain O
in O
controlling O
the O
unique O
microstructures S-MATE
, O
defects S-CONPRI
and O
properties S-CONPRI
that O
are O
created O
through O
this O
process S-CONPRI
. O


For O
the O
first O
time O
this O
work O
demonstrates O
how O
LaB6 O
nanoparticles S-CONPRI
can O
be S-MATE
used O
to O
control O
such O
features O
in O
Al B-MATE
alloys E-MATE
produced O
by O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
. O


A O
novel O
and O
efficient O
mechanical S-APPL
agitation S-CONPRI
process O
is O
used O
to O
inoculate O
AlSi10Mg S-MATE
powder O
with O
LaB6 O
nanoparticles S-CONPRI
which O
resulted O
in O
a O
homogenous O
, O
crack-free O
, O
equiaxed O
, O
very O
fine-grained O
as S-MATE
built O
microstructures S-MATE
. O


The O
substantial O
grain B-CHAR
refinement E-CHAR
is O
attributed O
to O
the O
good O
crystallographic O
atomic O
matching O
across O
the O
Al/LaB6 O
interfaces O
which O
facilitated O
Al S-MATE
nucleation O
on O
the O
LaB6 O
nanoparticles S-CONPRI
. O


The O
LaB6-inoculated O
AlSi10Mg S-MATE
exhibited O
near-isotropic O
mechanical B-CONPRI
properties E-CONPRI
with O
an O
improved O
plasticity S-PRO
compared O
with O
un O
modified O
AlSi10Mg S-MATE
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
has O
become O
one O
of O
the O
most O
commonly O
utilized O
processes S-CONPRI
in O
metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
. O


Despite O
its O
widespread O
use O
and O
capabilities O
, O
SLM S-MANP
parts O
are O
still O
being O
produced O
with O
excessive O
volumetric O
defects S-CONPRI
and O
flaws S-CONPRI
. O


The O
complex O
dependence O
of O
defect S-CONPRI
formation O
on O
process B-CONPRI
parameters E-CONPRI
, O
geometry S-CONPRI
, O
and O
material B-CONPRI
properties E-CONPRI
has O
inhibited O
effective O
quality S-CONPRI
assurance O
in O
SLM B-MANP
production E-MANP
. O


Exacerbating O
these O
issues O
are O
the O
difficulties O
thus O
far O
in O
accurately S-CHAR
detecting O
and O
identifying O
defects S-CONPRI
in-process O
so O
that O
parts O
may O
be S-MATE
qualified O
without O
destructive B-CHAR
testing E-CHAR
. O


Some O
of O
the O
most O
detrimental O
defects S-CONPRI
produced O
during O
SLM S-MANP
processing O
are O
lack O
of O
fusion S-CONPRI
( O
LoF O
) O
defects S-CONPRI
, O
which O
are O
frequently O
found O
to O
be S-MATE
in O
excess O
of O
100 O
μm O
in O
size O
, O
thus O
these O
defects S-CONPRI
are O
of O
critical O
importance O
to O
detect O
and O
remove O
. O


In O
this O
work O
, O
we O
have O
developed O
and O
demonstrated O
the O
capabilities O
of O
a O
novel O
in B-CONPRI
situ E-CONPRI
monitoring O
system O
using O
full-field O
infrared S-CONPRI
( O
IR S-CHAR
) O
thermography O
to O
monitor S-CONPRI
AlSi10Mg S-MATE
specimens O
during O
SLM B-MANP
production E-MANP
. O


Using O
layerwise O
relative O
surface S-CONPRI
temperature O
measurements O
, O
subsurface O
defects S-CONPRI
were O
identified O
via O
their O
retained O
thermal O
signature O
at O
the O
surface S-CONPRI
; O
transient S-CONPRI
thermal B-CONPRI
modeling E-CONPRI
was O
performed O
, O
which O
supported O
these O
observations O
. O


Parts O
were O
characterized O
using O
ex O
situ O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
to O
validate O
data S-CONPRI
identified O
defects S-CONPRI
and O
, O
critically O
, O
to O
estimate O
detection O
success O
. O


The O
IR S-CHAR
defect S-CONPRI
detection O
method O
was O
highly O
effective O
in O
identifying O
defects S-CONPRI
, O
with O
an O
82 O
% O
total O
success O
rate O
for O
LoF O
defects S-CONPRI
; O
detection O
success O
improved O
with O
increasing O
defect S-CONPRI
size O
. O


The O
method O
was O
also O
used O
statistically O
to O
analyze O
the O
presence O
of O
systematic O
process B-CONPRI
errors E-CONPRI
during O
SLM B-MANP
production E-MANP
, O
expanding O
the O
capabilities O
of O
IR S-CHAR
monitoring O
methods O
. O


This O
unique O
analysis O
method O
and O
simple S-MANP
integration O
for O
in B-CONPRI
situ E-CONPRI
IR O
monitoring O
can O
immediately O
improve O
non-destructive O
qualification O
methods O
in O
SLM S-MANP
processing O
. O


Additive B-MANP
manufacturing E-MANP
has O
opened O
doors O
for O
the O
efficient O
fabrication S-MANP
of O
individually O
tailored O
and O
complicated O
functional O
parts O
. O


However O
, O
the O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
printing B-MANP
process E-MANP
is O
vulnerable O
to O
defects S-CONPRI
generation O
, O
necessitating O
the O
need O
for O
in-situ S-CONPRI
monitoring O
and O
control O
technologies S-CONPRI
for O
quality S-CONPRI
assessment O
of O
parts O
. O


An O
in-situ S-CONPRI
monitoring O
system O
( O
IMS O
) O
based O
on O
optical S-CHAR
imaging S-APPL
was O
developed O
in-house O
for O
implementation O
on O
the O
selective B-MANP
laser I-MANP
melting I-MANP
process E-MANP
. O


A O
digital O
single O
lens S-MANP
reflex O
camera S-MACEQ
, O
mirror O
and O
several O
sets O
of O
light B-APPL
emitting I-APPL
diode E-APPL
strip O
lights O
formed O
the O
main O
constituents O
of O
the O
IMS O
. O


Cylindrical S-CONPRI
samples O
of O
316 O
L O
stainless B-MATE
steel E-MATE
were O
printed O
with O
variations S-CONPRI
in O
their O
energy B-PARA
density E-PARA
. O


Features O
taken O
in O
optical S-CHAR
images S-CONPRI
were O
extracted S-CONPRI
and O
evaluated O
via O
image S-CONPRI
processing O
. O


Micro O
computed B-CHAR
tomography E-CHAR
( O
CT S-ENAT
) O
, O
which O
is O
capable O
of O
assessing O
the O
internal O
defects S-CONPRI
and O
recovering O
the O
3D S-CONPRI
representation O
of O
a O
structure S-CONPRI
, O
was O
used O
as S-MATE
a O
validation S-CONPRI
method O
to O
correlate O
the O
features O
identified O
in O
the O
optical S-CHAR
images S-CONPRI
. O


Results O
have O
shown O
that O
features O
captured O
in-situ S-CONPRI
were O
correlated S-CONPRI
to O
defects S-CONPRI
detected O
by O
micro O
CT S-ENAT
, O
revealing O
the O
potential O
of O
using O
optical S-CHAR
images S-CONPRI
captured O
during O
printing O
as S-MATE
an O
indicator O
to O
the O
extent O
of O
defects S-CONPRI
present O
in O
selective B-MANP
laser I-MANP
melted E-MANP
parts O
. O


In O
recent O
years O
, O
the O
fabrication S-MANP
of O
aluminum B-MATE
alloy E-MATE
parts O
via O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
has O
been O
extensively O
considered O
in O
the O
biomedical S-APPL
, O
aerospace S-APPL
, O
and O
other O
industrial B-CONPRI
sectors E-CONPRI
, O
as S-MATE
it O
provides O
advantages O
such O
as S-MATE
the O
ability O
to O
manufacture S-CONPRI
complex B-PRO
shapes E-PRO
with O
high O
performance S-CONPRI
associated O
with O
lightweight S-CONPRI
design S-FEAT
. O


However O
, O
surface S-CONPRI
irregularities O
and O
sub-surface O
defects S-CONPRI
limit O
the O
full O
exploitation O
of O
such O
parts O
in O
fatigue-critical O
applications O
. O


Moreover O
, O
most O
of O
the O
commonly O
used O
metrological O
methods O
for O
surface B-CHAR
characterization E-CHAR
have O
proven O
to O
be S-MATE
unsuitable O
for O
determining O
important O
features O
such O
as S-MATE
undercuts O
and O
sub-surfaces O
pores S-PRO
. O


Hence O
, O
a O
comprehensive O
coupled O
investigation O
of O
metrological O
methods O
and O
cross-sectional O
analysis O
were O
performed O
in O
this O
study O
to O
evaluate O
the O
effects O
of O
surface S-CONPRI
features O
and O
volumetric O
defects S-CONPRI
typical O
of O
additively B-MANP
manufactured E-MANP
materials O
. O


Fatigue B-CHAR
tests E-CHAR
and O
fractographic B-CHAR
analyses E-CHAR
were O
conducted O
to O
support S-APPL
the O
finite B-CONPRI
element E-CONPRI
simulations O
and O
proposed O
fracture S-CONPRI
mechanics O
model S-CONPRI
. O


The O
results O
demonstrate O
that O
the O
standard S-CONPRI
metrological O
methods O
can O
not O
provide O
all O
of O
the O
data S-CONPRI
needed O
to O
model S-CONPRI
the O
fatigue S-PRO
behaviors O
of O
additively B-MANP
manufactured E-MANP
materials O
robustly O
. O


Moreover O
, O
a O
statistical O
model S-CONPRI
describing O
the O
competition O
between O
volumetric O
defects S-CONPRI
and O
surface S-CONPRI
irregularities O
was O
developed O
and O
validated O
. O


Different O
L-PBF S-MANP
process O
parameters S-CONPRI
were O
used O
to O
additively B-MANP
manufacture E-MANP
AHSS O
. O


FEM S-CONPRI
simulations O
quantified O
solidification B-CONPRI
parameters E-CONPRI
and O
melt B-MATE
pool E-MATE
shapes O
. O


High O
cooling B-PARA
rate E-PARA
parameters O
resulted O
in O
high O
GND O
densities O
and O
yield B-PRO
strength E-PRO
. O


M B-ENAT
& I-ENAT
S E-ENAT
scan O
strategy O
revealed O
a O
partial O
columnar O
to O
equiaxed O
transition S-CONPRI
. O


In O
this O
work O
, O
the O
additive B-MANP
manufacturing E-MANP
technique O
of O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
was O
used O
to O
build S-PARA
up O
X30Mn21 O
austenitic S-MATE
advanced O
high O
strength S-PRO
steel S-MATE
( O
AHSS O
) O
samples S-CONPRI
. O


Different O
L-PBF S-MANP
process O
parameters S-CONPRI
were O
used O
to O
understand O
the O
correlation O
between O
process S-CONPRI
, O
microstructure S-CONPRI
, O
texture S-FEAT
, O
and O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
influence O
of O
build B-MACEQ
platform E-MACEQ
preheating O
( O
200 O
°C–800 O
°C O
) O
, O
laser S-ENAT
speed O
( O
550 O
mm/s O
- O
950 O
mm/s O
) O
and O
scan O
strategy O
( O
bidirectional O
continuous O
and O
Mark O
& O
Sleep O
( O
M B-ENAT
& I-ENAT
S E-ENAT
) O
) O
on O
grain B-PRO
size E-PRO
, O
grain S-CONPRI
morphology O
, O
size O
of O
solidification S-CONPRI
cells S-APPL
, O
dislocation B-PRO
density E-PRO
, O
and O
texture S-FEAT
was O
studied O
. O


Local O
solidification B-CONPRI
parameters E-CONPRI
in O
the O
melt B-MATE
pool E-MATE
e.g O
. O


cooling B-PARA
rates E-PARA
, O
temperature B-PARA
gradients E-PARA
and O
solidification B-PARA
velocities E-PARA
were O
simulated O
by O
a O
FEM S-CONPRI
heat O
flow O
model S-CONPRI
and O
correlated S-CONPRI
with O
the O
solidification B-CONPRI
microstructure E-CONPRI
. O


By O
using O
SEM/EBSD O
analysis O
and O
tensile B-CHAR
testing E-CHAR
, O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
AHSS O
were O
assessed O
by O
considering O
microstructural S-CONPRI
aspects O
. O


It O
was O
found O
that O
AHSS O
, O
produced O
with O
higher O
laser S-ENAT
speeds O
and O
an O
alternative O
M B-ENAT
& I-ENAT
S E-ENAT
scan O
strategy O
, O
revealed O
a O
reduced O
grain B-PRO
size E-PRO
and O
texture S-FEAT
intensity O
. O


This O
was O
attributed O
to O
a O
partial O
columnar O
to O
equiaxed O
transition S-CONPRI
( O
CET O
) O
, O
as S-MATE
well O
as S-MATE
a O
significantly O
increased O
density S-PRO
of O
geometrically O
necessary O
dislocations S-CONPRI
. O


Preheating S-MANP
of O
the O
build B-MACEQ
platform E-MACEQ
promoted O
columnar B-PRO
grain E-PRO
growth O
with O
a O
more O
pronounced O
texture S-FEAT
, O
low O
dislocation B-PRO
densities E-PRO
, O
and O
reduced O
yield B-PRO
strength E-PRO
. O


The O
influence O
of O
cooling B-PARA
rate E-PARA
, O
temperature B-PARA
gradient E-PARA
and O
solidification B-PARA
velocity E-PARA
on O
microstructural S-CONPRI
and O
textural O
evolution S-CONPRI
is O
discussed O
based O
on O
fundamental O
solidification S-CONPRI
theories O
. O


The O
process B-ENAT
chain E-ENAT
of O
this O
method O
starts O
with O
injection B-MANP
molding E-MANP
. O


The O
polymer S-MATE
of O
this O
part O
is O
functionalized O
with O
LDS-additives O
which O
allow O
the O
part O
to O
be S-MATE
laser O
structured O
subsequently O
. O


This O
technique O
is O
less O
suitable O
for O
prototypes S-CONPRI
and O
small-scale O
productions O
of O
3D-MIDs O
because O
of O
its O
properties S-CONPRI
. O


Contrary O
to O
the O
injection B-MANP
molding E-MANP
process O
, O
the O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
such O
as S-MATE
powder O
bed S-MACEQ
based O
manufacturing B-MANP
processes E-MANP
, O
e.g O
. O


selective B-MANP
laser I-MANP
sintering E-MANP
( O
SLS S-MANP
) O
, O
is O
a O
constantly O
emerging O
processing O
technology S-CONPRI
for O
the O
fabrication S-MANP
of O
prototypes S-CONPRI
and O
small-scale O
productions O
. O


Unmodified O
polyamide B-MATE
12 E-MATE
( O
PA S-CHAR
12 O
) O
, O
e.g O
. O


PA2200 O
( O
supplier O
: O
EOS B-APPL
GmbH E-APPL
) O
is O
most O
commonly O
used O
for O
the O
SLS S-MANP
of O
polymer S-MATE
parts O
. O


The O
LPKF O
Laser S-ENAT
& O
Electronics S-CONPRI
AG O
in O
Garbsen O
, O
Germany O
, O
transferred O
the O
LDS-method O
to O
SLS-process O
. O


A O
standard S-CONPRI
SLS-polymer O
part O
is O
coated S-APPL
with O
a O
special O
paint O
, O
that O
contains O
the O
necessary O
LDS-additives O
. O


Once O
coated S-APPL
and O
dried S-MANP
, O
these O
parts O
can O
be S-MATE
laser O
direct O
structured O
similar O
to O
standard S-CONPRI
3D-MIDs O
. O


In O
this O
study O
, O
the O
authors O
use O
copper S-MATE
particles O
in O
order O
to O
functionalize O
a O
standard S-CONPRI
polyamide B-MATE
12 E-MATE
powder O
for O
laser S-ENAT
activation O
and O
selective O
metallization S-MANP
. O


The O
study O
shows O
, O
that O
the O
addition O
of O
copper S-MATE
particles O
enables O
the O
laser S-ENAT
direct O
structuring O
of O
polyamide B-MATE
12 E-MATE
. O


SLS-demonstrators O
were O
successfully O
laser S-ENAT
activated O
and O
selectively O
metallized O
. O


Furthermore O
, O
the O
copper S-MATE
particles O
enhance O
the O
mechanical B-CONPRI
properties E-CONPRI
as S-MATE
well O
as S-MATE
the O
heat B-PRO
conductivity E-PRO
of O
polyamide B-MATE
12 E-MATE
. O


Lattice B-FEAT
density E-FEAT
and O
fabric O
are O
combined O
to O
predict O
anisotropic S-PRO
mechanical O
properties S-CONPRI
. O


The O
resulting O
model S-CONPRI
is O
validated O
by O
mechanical B-CHAR
testing E-CHAR
in O
at O
least O
10 O
directions O
. O


Off-axis O
properties S-CONPRI
for O
Ti6Al4V S-MATE
and O
nylon S-MATE
lattices S-CONPRI
predicted O
to O
within O
13 O
and O
5.1 O
% O
. O


Predictions S-CONPRI
and O
mechanical S-APPL
data S-CONPRI
are O
correlated S-CONPRI
with O
R2 O
between O
0.84 O
and O
0.94 O
. O


Additive B-MANP
manufacturing E-MANP
methods O
present O
opportunities O
for O
structures O
to O
have O
tailored O
mechanical B-PRO
anisotropy E-PRO
by O
integrating O
controlled O
lattice B-FEAT
structures E-FEAT
into O
their O
design S-FEAT
. O


The O
ability O
to O
predict O
anisotropic S-PRO
mechanical O
properties S-CONPRI
of O
such O
lattice B-FEAT
structures E-FEAT
would O
help O
tailor O
anisotropy S-PRO
and O
ensure O
adequate O
off-axis O
strength S-PRO
at O
an O
early O
stage O
in O
the O
design B-CONPRI
process E-CONPRI
. O


A O
method O
is O
described O
for O
the O
development O
of O
a O
model S-CONPRI
to O
predict O
apparent O
modulus O
and O
strength S-PRO
based O
on O
structure S-CONPRI
density S-PRO
and O
fabric O
, O
taken O
from O
CAD S-ENAT
data O
. O


The O
model S-CONPRI
utilises O
a O
tensorial O
form O
of O
well-founded O
power-law O
relationships O
for O
these O
variables O
and O
is O
fit S-CONPRI
to O
mechanical B-CHAR
test E-CHAR
data S-CONPRI
for O
properties S-CONPRI
in O
the O
principal O
directions O
of O
manufactured S-CONPRI
titanium O
stochastic B-CONPRI
lattices E-CONPRI
and O
nylon S-MATE
rhombic O
dodecahedron O
structures O
. O


The O
results O
are O
validated O
against O
mechanical B-CHAR
testing E-CHAR
across O
at O
least O
7 O
additional O
off-axis O
directions O
. O


For O
stochastic S-CONPRI
structures O
, O
apparent O
modulus O
is O
predicted S-CONPRI
in O
10 O
directions O
with O
a O
mean O
error S-CONPRI
of O
13 O
% O
and O
strength S-PRO
predicted S-CONPRI
with O
a O
mean O
error S-CONPRI
of O
10 O
% O
. O


For O
rhombic O
dodecahedron O
structures O
apparent O
modulus O
and O
strength S-PRO
are O
predicted S-CONPRI
in O
15 O
directions O
with O
mean O
errors S-CONPRI
of O
4.2 O
% O
and O
5.1 O
% O
respectively O
. O


This O
model S-CONPRI
is O
the O
first O
to O
predict O
the O
anisotropic S-PRO
apparent O
modulus O
and O
strength S-PRO
of O
structures O
based O
on O
lattice B-FEAT
density E-FEAT
and O
fabric O
tensors O
and O
will O
be S-MATE
highly O
useful O
in O
the O
mechanical S-APPL
design S-FEAT
of O
lattice B-FEAT
structures E-FEAT
. O


A O
robotized O
laser/wire O
direct B-MANP
metal I-MANP
deposition E-MANP
system O
was O
utilized O
to O
fabricate S-MANP
316LSi O
coupons O
. O


The O
mechanical S-APPL
and O
microstructural S-CONPRI
properties O
were O
then O
characterized O
. O


It O
was O
found O
that O
different O
thermal O
histories O
caused O
by O
different O
inter-layer O
time O
intervals O
have O
significant O
impact S-CONPRI
on O
mechanical S-APPL
and O
microstructural S-CONPRI
properties O
. O


The O
thin-walled O
samples S-CONPRI
with O
lower O
cooling B-PARA
rates E-PARA
showed O
coarser O
columnar B-PRO
grains E-PRO
, O
lower O
ultimate B-PRO
tensile I-PRO
strength E-PRO
, O
and O
lower O
hardness S-PRO
compared O
to O
the O
block O
samples S-CONPRI
. O


The O
melt B-MATE
pool E-MATE
was O
monitored O
in O
real-time O
. O


An O
empirical S-CONPRI
correlation O
between O
the O
melt B-MATE
pool E-MATE
area S-PARA
and O
cooling B-PARA
rate E-PARA
was O
achieved O
that O
could O
enable O
control O
of O
scale O
of O
the O
final O
solidification S-CONPRI
structure O
by O
maintaining O
the O
melt B-MATE
pool E-MATE
size O
in O
real-time O
. O


Further O
, O
to O
study O
the O
anisotropic S-PRO
behavior O
, O
tensile S-PRO
samples S-CONPRI
were O
loaded O
in O
parallel O
and O
perpendicular O
directions O
with O
respect O
to O
the O
deposition B-PARA
direction E-PARA
. O


The O
results O
indicated O
that O
samples S-CONPRI
in O
the O
perpendicular O
direction O
had O
lower O
UTS S-PRO
and O
elongation S-PRO
for O
both O
coupon O
types O
, O
revealing O
a O
weaker O
bonding S-CONPRI
at O
inter-layer/bead O
interface S-CONPRI
due O
to O
the O
existence O
of O
lack-of-fusion O
pores S-PRO
. O


The O
capability O
to O
additively B-MANP
manufacture E-MANP
fully-functioning O
electronic O
circuits O
is O
a O
frontier O
in O
3D-printed S-MANP
electronics O
that O
will O
afford O
unprecedented O
scalability O
, O
miniaturization O
, O
and O
conformability O
of O
electronic O
circuits O
. O


In O
this O
paper O
, O
we O
report O
a O
novel O
procedure O
that O
employs O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
additive B-MANP
manufacturing E-MANP
techniques O
to O
fabricate S-MANP
high-frequency O
, O
tapered-solenoid O
type O
inductors O
for O
RF O
applications O
capable O
of O
wide O
bandwidth O
performance S-CONPRI
. O


The O
design S-FEAT
includes O
a O
polymer S-MATE
support O
structure S-CONPRI
to O
reduce O
the O
parasitic O
capacitance O
between O
the O
inductor S-APPL
and O
the O
substrate S-MATE
, O
a O
tapered O
solid O
core S-MACEQ
, O
and O
conducting O
windings O
. O


Each O
design S-FEAT
component S-MACEQ
is O
printed O
using O
aerosol-jet O
( O
AJ O
) O
printing O
methods O
on O
a O
grounded O
coplanar O
waveguide O
such O
that O
the O
small O
end O
of O
the O
conical-shaped O
inductor S-APPL
is O
connected O
to O
the O
transmission S-CHAR
line O
and O
the O
base O
of O
the O
inductor S-APPL
is O
connected O
to O
ground O
. O


Two O
types O
of O
solid-core O
inductors O
were O
fabricated S-CONPRI
: O
one O
with O
a O
printed O
polymer S-MATE
core S-MACEQ
and O
another O
with O
a O
non-printed O
iron S-MATE
core S-MACEQ
. O


Scattering O
parameter S-CONPRI
measurements O
establish O
that O
the O
polymer S-MATE
and O
iron-core O
inductors O
, O
combined O
with O
a O
45°-polymer O
support B-FEAT
structure E-FEAT
, O
can O
achieve O
usable O
bandwidths O
up O
to O
18 O
GHz O
and O
40 O
GHz O
, O
respectively O
, O
with O
low O
insertion O
loss O
. O


3D B-APPL
model E-APPL
and O
circuit O
model S-CONPRI
simulations O
were O
also O
carried O
out O
to O
study O
inductor S-APPL
performance O
in O
terms O
of O
self-resonance O
and O
insertion O
loss O
. O


The O
use O
of O
manufacturing S-MANP
to O
generate O
topology S-CONPRI
optimized O
components S-MACEQ
shows O
promise O
for O
designers O
. O


However O
, O
designers O
who O
assume O
that O
additive B-MANP
manufacturing E-MANP
follows O
traditional B-MANP
manufacturing E-MANP
techniques O
may O
be S-MATE
misled O
due O
to O
the O
nuances O
in O
specific O
techniques O
. O


Since O
commercial O
topology B-FEAT
optimization E-FEAT
software S-CONPRI
tools O
are O
neither O
designed S-FEAT
to O
consider O
orientation S-CONPRI
of O
the O
parts O
nor O
large O
variations S-CONPRI
in O
properties S-CONPRI
, O
the O
goal O
of O
this O
research S-CONPRI
is O
to O
evaluate O
the O
limitations O
of O
an O
existing O
commercial O
topology B-FEAT
optimization E-FEAT
software S-CONPRI
( O
i.e O
. O


Inspire® O
) O
using O
electron B-CONPRI
beam E-CONPRI
powder O
bed B-MANP
fusion E-MANP
( O
i.e O
. O


Arcam® O
) O
to O
produce O
optimized O
Ti-6Al-4V B-MATE
alloy E-MATE
components S-MACEQ
. O


Emerging O
qualification O
tools S-MACEQ
from O
Oak O
Ridge O
National O
Laboratory S-CONPRI
including O
in-situ S-CONPRI
near-infrared O
imaging S-APPL
and O
log O
file S-MANS
data S-CONPRI
analysis O
were O
used O
to O
rationalize O
the O
final O
performance S-CONPRI
of O
components S-MACEQ
. O


While O
the O
weight S-PARA
savings O
of O
each O
optimized O
part O
exceeded O
the O
initial O
criteria O
, O
the O
failure S-CONPRI
loads O
and O
locations O
proved O
instrumental O
in O
providing O
insight O
to O
additive B-MANP
manufacturing E-MANP
with O
topology B-FEAT
optimization E-FEAT
. O


This O
research S-CONPRI
has O
shown O
the O
need O
for O
a O
comprehensive O
understanding O
of O
correlations O
between O
geometry S-CONPRI
, O
additive B-MANP
manufacturing E-MANP
processing O
conditions O
, O
defect S-CONPRI
generation O
, O
and O
microstructure S-CONPRI
for O
characterization O
of O
complex O
components S-MACEQ
such O
as S-MATE
those O
designed S-FEAT
by O
topology B-FEAT
optimization E-FEAT
. O


Ni-Cu-base O
alloy S-MATE
plates O
have O
been O
obtained O
by O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
technology S-CONPRI
. O


Dendritic O
structure S-CONPRI
and O
particle S-CONPRI
precipitation O
have O
been O
found O
to O
significantly O
depend O
on O
alloy S-MATE
composition O
, O
in O
particular O
Mn S-MATE
, O
Ti S-MATE
and O
C S-MATE
contents O
. O


Higher O
hardness S-PRO
, O
strength S-PRO
, O
toughness S-PRO
and O
wear B-PRO
resistance E-PRO
in O
one O
of O
the O
tested O
alloys S-MATE
were O
associated O
with O
precipitation S-CONPRI
of O
TiCN O
particles S-CONPRI
. O


Moderate O
dependence O
of O
microstructural S-CONPRI
parameters O
and O
mechanical B-CONPRI
properties E-CONPRI
on O
deposition S-CONPRI
speed O
was O
observed O
within O
the O
tested O
speed O
range S-PARA
. O


Two O
Ni-Cu O
alloys S-MATE
( O
Monel S-MATE
K500 O
and O
FM O
60 O
) O
having O
various O
Mn S-MATE
, O
Fe S-MATE
, O
Al S-MATE
, O
Ti S-MATE
and O
C S-MATE
contents O
were O
deposited O
on O
a O
Monel S-MATE
K500 O
plate O
at O
three O
different O
speeds O
using O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
technique O
. O


Microstructure S-CONPRI
characterisation O
, O
in O
particular O
a O
detailed O
study O
of O
precipitates S-MATE
, O
was O
carried O
out O
using O
optical S-CHAR
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
. O


Mechanical B-CONPRI
properties E-CONPRI
were O
assessed O
using O
hardness S-PRO
, O
tensile S-PRO
and O
wear S-CONPRI
testing S-CHAR
. O


For O
similar O
deposition S-CONPRI
conditions O
, O
Monel S-MATE
K500 O
has O
exhibited O
smaller O
secondary B-MATE
dendrite E-MATE
arm O
spacing O
and O
higher O
number O
density S-PRO
of O
Ti-rich O
particles S-CONPRI
, O
although O
the O
Ti S-MATE
concentration O
in O
FM O
60 O
was O
higher O
. O


Finer B-FEAT
microstructure E-FEAT
and O
Ti S-MATE
precipitation S-CONPRI
led S-APPL
to O
superior O
hardness S-PRO
, O
tensile S-PRO
and O
wear B-PRO
resistance E-PRO
of O
Monel S-MATE
K500 O
compared O
to O
FM O
60 O
. O


The O
variation S-CONPRI
in O
microstructure-properties O
relationship O
with O
alloy S-MATE
composition O
is O
discussed O
. O


We O
devised O
a O
novel O
method O
to O
embed O
sensors S-MACEQ
or O
integrated B-MACEQ
circuit E-MACEQ
( O
IC O
) O
chips O
into O
metal S-MATE
components S-MACEQ
by O
using O
a O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
process S-CONPRI
. O


The O
concept O
of O
a O
protective B-APPL
layer E-APPL
is O
introduced O
to O
fabricate S-MANP
all O
parts O
without O
damaging O
the O
sensors S-MACEQ
during O
the O
laser B-ENAT
scanning I-ENAT
process E-ENAT
. O


The O
operation O
of O
sensors S-MACEQ
in O
the O
parts O
is O
analyzed O
from O
a O
computational O
analysis O
on O
the O
thermal O
influence O
of O
laser B-PARA
heat E-PARA
. O


The O
fabricated S-CONPRI
metal O
parts O
show O
continuous O
microstructures S-MATE
including O
grains S-CONPRI
and O
phases O
between O
the O
base O
part O
and O
the O
new O
part O
formed O
after O
embedding O
the O
sensor S-MACEQ
despite O
the O
intermittent O
SLM S-MANP
process S-CONPRI
. O


The O
embedded O
sensor S-MACEQ
operates O
properly O
when O
compared O
to O
bare O
sensors S-MACEQ
. O


Plastic S-MATE
circuit O
board-based O
IC O
components S-MACEQ
were O
embedded O
into O
an O
Inconel S-MATE
718C O
turbine B-APPL
blade E-APPL
, O
which O
accurately S-CHAR
distinguished O
three-dimensional S-CONPRI
vibration O
along O
the O
X O
, O
Y S-MATE
, O
and O
Z O
axes O
. O


Our O
results O
imply O
that O
the O
proposed O
process S-CONPRI
can O
open O
new O
avenues O
for O
SLM S-MANP
technology O
to O
realize O
metal S-MATE
components S-MACEQ
with O
a O
self-cognitive O
ability O
using O
integrated O
sensors S-MACEQ
. O


Printed O
free-standing O
pure O
Au S-MATE
structure O
with O
feature B-PARA
sizes E-PARA
of O
smaller O
than O
10 O
microns O
. O


Combination O
of O
laser-induced O
forward O
transfer O
of O
pure B-MATE
metals E-MATE
and O
chemical O
etching S-MANP
. O


Approach O
allows O
fully O
overhanging B-CONPRI
structures E-CONPRI
and O
reduces O
substrate S-MATE
contamination O
. O


Cu S-MATE
support O
structures O
can O
be S-MATE
selectively O
removed O
after O
LIFT-printing O
. O


A O
combined O
approach O
of O
laser-induced O
forward O
transfer O
( O
LIFT O
) O
and O
chemical O
etching S-MANP
of O
pure B-MATE
metal E-MATE
films O
is O
studied O
to O
fabricate S-MANP
complex O
, O
free-standing O
, O
3-dimensional O
gold S-MATE
structures O
on O
the O
few O
micron S-FEAT
scale O
. O


A O
picosecond O
pulsed B-MANP
laser E-MANP
source O
with O
515 O
nm O
central O
wavelength S-CONPRI
is O
used O
to O
deposit O
metal S-MATE
droplets S-CONPRI
of O
copper S-MATE
and O
gold S-MATE
in O
a O
sequential O
fashion S-CONPRI
. O


After O
transfer O
, O
chemical O
etching S-MANP
in O
ferric O
chloride O
completely O
removes O
the O
mechanical S-APPL
Cu S-MATE
support O
leaving O
a O
final O
free-standing O
gold S-MATE
structure O
. O


Unprecedented O
feature B-PARA
sizes E-PARA
of O
smaller O
than O
10 O
μm O
are O
achieved O
with O
surface B-PRO
roughness E-PRO
of O
0.3 O
to O
0.7 O
μm O
. O


Formation O
of O
interfacial O
mixing S-CONPRI
volumes O
between O
the O
two O
metals S-MATE
is O
not O
found O
confirming O
the O
viability O
of O
the O
approach O
. O


Additive B-MANP
manufacturing E-MANP
promises O
to O
revolutionize O
manufacturing S-MANP
industries S-APPL
. O


However O
, O
3D B-MANP
printing E-MANP
of O
novel O
build B-MATE
materials E-MATE
is O
currently O
limited O
by O
constraints O
inherent O
to O
printer S-MACEQ
designs S-FEAT
. O


In O
this O
work O
, O
a O
bench-top S-CONPRI
powder O
melt B-MANP
extrusion E-MANP
( O
PME S-MANP
) O
3D B-MACEQ
printer I-MACEQ
head E-MACEQ
was O
designed S-FEAT
and O
fabricated S-CONPRI
to O
print S-MANP
parts O
directly O
from O
powder-based B-MATE
materials E-MATE
rather O
than O
filament S-MATE
. O


The O
final O
design S-FEAT
of O
the O
PME B-MACEQ
printer I-MACEQ
head E-MACEQ
evolved O
from O
the O
Rich O
Rap O
Universal B-MACEQ
Pellet I-MACEQ
Extruder E-MACEQ
( O
RRUPE O
) O
design S-FEAT
and O
was O
realized O
through O
an O
iterative B-CONPRI
approach E-CONPRI
. O


The O
PME B-MACEQ
printer E-MACEQ
was O
made O
possible O
by O
modifications O
to O
the O
funnel O
shape O
, O
pressure S-CONPRI
applied O
to O
the O
extrudate S-MATE
by O
the O
auger S-MACEQ
, O
and O
hot B-MACEQ
end I-MACEQ
structure E-MACEQ
. O


Through O
comparison O
of O
parts O
printed O
with O
the O
PME B-MACEQ
printer E-MACEQ
with O
those O
from O
a O
commercially O
available O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
3D B-MACEQ
printer E-MACEQ
using O
common O
thermoplastics S-MATE
poly O
( O
lactide O
) O
( O
PLA S-MATE
) O
, O
high O
impact S-CONPRI
poly O
( O
styrene O
) O
( O
HIPS S-MATE
) O
, O
and O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
powders S-MATE
( O
< O
1 O
mm S-MANP
in O
diameter S-CONPRI
) O
, O
evaluation O
of O
the O
printer S-MACEQ
performance S-CONPRI
was O
performed O
. O


For O
each O
build B-MATE
material E-MATE
, O
the O
PME S-MANP
printed O
objects O
show O
comparable O
viscoelastic B-PRO
properties E-PRO
by O
dynamic B-CONPRI
mechanical I-CONPRI
analysis E-CONPRI
( O
DMA S-CONPRI
) O
to O
those O
of O
the O
FFF S-MANP
objects O
. O


However O
, O
due O
to O
a O
significant O
difference O
in O
printer B-PARA
resolution E-PARA
between O
PME S-MANP
( O
X–Y O
resolution S-PARA
of O
0.8 O
mm S-MANP
and O
a O
Z-layer B-CHAR
height I-CHAR
calibrated E-CHAR
to O
0.1 O
mm S-MANP
) O
and O
FFF S-MANP
( O
X–Y O
resolution S-PARA
of O
0.4 O
mm S-MANP
and O
a O
Z-layer B-PARA
height E-PARA
of O
0.18 O
mm S-MANP
) O
, O
as S-MATE
well O
as S-MATE
, O
an O
inherently O
more O
inconsistent O
feed S-PARA
of O
build B-MATE
material E-MATE
for O
PME S-MANP
than O
FFF S-MANP
, O
the O
resulting O
print B-CONPRI
quality E-CONPRI
, O
determined O
by O
a O
dimensional B-CHAR
analysis E-CHAR
and O
surface B-PRO
roughness E-PRO
comparisons O
, O
of O
the O
PME S-MANP
printed O
objects O
was O
lower O
than O
that O
of O
the O
FFF S-MANP
printed O
parts O
based O
on O
the O
print B-PARA
layer E-PARA
uniformity O
and O
structure S-CONPRI
. O


Further O
, O
due O
to O
the O
poorer O
print B-PARA
resolution E-PARA
and O
inherent O
inconsistent O
build B-MATE
material E-MATE
feed O
of O
the O
PME S-MANP
, O
the O
bulk O
tensile B-PRO
strength E-PRO
and O
Young O
’ O
s S-MATE
moduli O
of O
the O
objects O
printed O
by O
PME S-MANP
were O
lower O
and O
more O
inconsistent O
( O
49.2 O
± O
10.7 O
MPa S-CONPRI
and O
1620 O
± O
375 O
MPa S-CONPRI
, O
respectively O
) O
than O
those O
of O
FFF S-MANP
printed O
objects O
( O
57.7 O
± O
2.31 O
MPa S-CONPRI
and O
2160 O
± O
179 O
MPa S-CONPRI
, O
respectively O
) O
. O


Nevertheless O
, O
PME S-MANP
print O
methods O
promise O
an O
opportunity O
to O
provide O
a O
platform S-MACEQ
on O
which O
it O
is O
possible O
to O
rapidly O
prototype S-CONPRI
a O
myriad O
of O
thermoplastic B-MATE
materials E-MATE
for O
3D B-MANP
printing E-MANP
. O


Effects O
of O
laser S-ENAT
conditions O
on O
part O
qualities O
of O
a O
near-eutectic O
Al-Fe B-MATE
alloy E-MATE
fabricated O
via O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
was O
investigated O
. O


The O
much O
refined O
microstructure S-CONPRI
consisting O
of O
nano-scaled O
Al-Fe O
intertmetallics O
with O
different O
size O
and O
morphology S-CONPRI
was O
observed O
. O


P·v-1/2 O
based O
on O
deposited O
energy B-PARA
density E-PARA
model O
was O
proved O
to O
be S-MATE
a O
more O
appropriate O
design S-FEAT
parameter O
. O


An O
estimated O
threshold O
value O
of O
P·v-1/2 O
for O
fabricating S-MANP
satisfactory O
Al-2.5Fe O
( O
mass O
% O
) O
alloy S-MATE
parts O
could O
be S-MATE
identified O
. O


This O
study O
focused O
on O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
of O
the O
Al–Fe O
binary S-CONPRI
alloy S-MATE
samples O
with O
a O
near-eutectic O
composition S-CONPRI
of O
2.5 O
mass O
% O
Fe S-MATE
using O
the O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
process S-CONPRI
. O


The O
melt B-PARA
pool I-PARA
depth E-PARA
, O
relative B-PRO
density E-PRO
, O
and O
hardness S-PRO
of O
LPBF-fabricated O
Al–2.5Fe O
alloy S-MATE
samples O
under O
different O
laser B-PARA
power E-PARA
( O
P S-MATE
) O
and O
scan B-PARA
speed E-PARA
( O
v S-MATE
) O
conditions O
were O
systematically O
examined O
. O


The O
results O
provided O
optimum O
laser S-ENAT
parameter O
sets O
( O
P S-MATE
= O
204 O
W O
, O
v S-MATE
≤ O
800 O
mms-1 O
) O
for O
the O
fabrication S-MANP
of O
dense O
alloy S-MATE
samples O
with O
high O
relative B-PRO
densities E-PRO
> O
99 O
% O
. O


Additionally O
, O
Pv-1/2 O
, O
which O
is O
based O
on O
the O
deposited O
energy B-PARA
density E-PARA
model O
, O
was O
found O
to O
be S-MATE
a O
more O
appropriate O
parameter S-CONPRI
for O
additively O
manufacturing S-MANP
Al–2.5Fe O
alloy S-MATE
samples O
, O
and O
using O
it O
to O
simplify O
the O
relative B-PRO
densities E-PRO
of O
the O
samples S-CONPRI
made O
the O
determination O
of O
a O
threshold O
value O
for O
the O
laser S-ENAT
parameters O
required O
to O
fabricate S-MANP
dense O
alloy S-MATE
samples O
. O


The O
microstructural S-CONPRI
and O
crystallographic O
characterization O
of O
the O
LPBF-built O
Al–2.5Fe O
alloy S-MATE
samples O
revealed O
a O
characteristic O
microstructure S-CONPRI
consisting O
of O
multi-scan O
melt B-MATE
pools E-MATE
that O
resulted O
from O
local O
melting S-MANP
and O
rapid B-MANP
solidification E-MANP
owing O
to O
laser S-ENAT
irradiation S-MANP
during O
the O
LPBF S-MANP
process O
. O


Furthermore O
, O
a O
number O
of O
columnar B-PRO
grains E-PRO
with O
a O
mean O
width O
of O
∼ O
21 O
μm O
elongated O
along O
the O
building B-PARA
direction E-PARA
were O
also O
observed O
in O
the O
α-Al O
matrix O
. O


Numerous O
nano-sized O
particles S-CONPRI
of O
the O
metastable S-PRO
Al6Fe O
intermetallic S-MATE
phase O
with O
a O
mean O
size O
< O
100 O
nm O
were O
finely O
dispersed O
in O
the O
α-Al O
matrix O
. O


The O
hardness S-PRO
of O
the O
refined O
microstructure S-CONPRI
produced O
by O
the O
LPBF S-MANP
process O
was O
high O
at O
∼ O
90 O
HV O
, O
which O
is O
more O
than O
twofold O
higher O
than O
that O
of O
conventionally O
casted O
alloys S-MATE
that O
contain O
the O
coarsened O
plate-shaped O
Al13Fe4 O
intermetallic S-MATE
phase O
in O
equilibrium S-CONPRI
with O
the O
α-Al O
matrix O
. O


In-situ S-CONPRI
monitoring O
of O
metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
is O
a O
key O
issue O
to O
determine O
the O
quality S-CONPRI
and O
stability S-PRO
of O
the O
process S-CONPRI
during O
the O
layer-wise O
production S-MANP
of O
the O
part O
. O


The O
quantities O
that O
can O
be S-MATE
measured O
via O
in-situ S-CONPRI
sensing O
can O
be S-MATE
referred O
to O
as S-MATE
“ O
process S-CONPRI
signatures O
” O
, O
and O
can O
represent O
the O
source S-APPL
of O
information O
to O
detect O
possible O
defects S-CONPRI
. O


Most O
of O
the O
literature O
on O
in-situ S-CONPRI
monitoring O
of O
Laser B-MANP
Power I-MANP
Bed I-MANP
Fusion E-MANP
( O
LPBF S-MANP
) O
processes S-CONPRI
focuses O
on O
the O
melt-pool O
, O
laser S-ENAT
track O
and O
layer S-PARA
image S-CONPRI
as S-MATE
source O
of O
information O
to O
detect O
the O
onset O
of O
possible O
defects S-CONPRI
. O


High-speed O
image S-CONPRI
acquisition O
, O
coupled O
with O
image S-CONPRI
segmentation O
and O
feature B-ENAT
extraction E-ENAT
, O
is O
used O
to O
estimate O
different O
statistical O
descriptors O
of O
the O
spattering O
behaviour O
along O
the O
laser B-ENAT
scan E-ENAT
path O
. O


A O
logistic O
regression B-CONPRI
model E-CONPRI
is O
developed O
to O
determine O
the O
ability O
of O
spatter-related O
descriptors O
to O
classify O
different O
energy B-PARA
density E-PARA
conditions O
corresponding O
to O
different O
quality S-CONPRI
states O
. O


This O
is O
why O
future O
research S-CONPRI
on O
spatter S-CHAR
signature O
analysis O
and O
modelling S-ENAT
is O
highly O
encouraged O
to O
improve O
the O
effectiveness S-CONPRI
of O
in-situ S-CONPRI
monitoring O
tools S-MACEQ
. O


The O
metal B-MANP
additive I-MANP
manufacturing E-MANP
industry S-APPL
is O
rising O
and O
so O
is O
the O
interest O
in O
new O
lattice B-FEAT
structures E-FEAT
with O
unique O
mechanical B-CONPRI
properties E-CONPRI
. O


Many O
studies O
have O
already O
investigated O
lattice B-FEAT
structures E-FEAT
with O
different O
geometries S-CONPRI
and O
their O
influence O
on O
mechanical B-CONPRI
properties E-CONPRI
, O
but O
little O
is O
known O
about O
the O
effect O
of O
specific O
processing O
characteristics O
that O
are O
inherent O
to O
metal B-MANP
additive I-MANP
manufacturing E-MANP
. O


Therefore O
this O
study O
investigates S-CONPRI
the O
effect O
of O
two O
crucial O
steps O
in O
the O
manufacturing B-MANP
process E-MANP
: O
the O
build B-PARA
orientation E-PARA
selection O
and O
heat B-MANP
treatment E-MANP
. O


In O
total O
the O
microstructure S-CONPRI
and O
static O
mechanical B-CONPRI
properties E-CONPRI
of O
five O
different O
orientations S-CONPRI
and O
three O
heat B-MANP
treatment E-MANP
conditions O
were O
evaluated O
using O
Ti6Al4V B-MATE
diamond E-MATE
like O
lattice B-FEAT
structures E-FEAT
. O


The O
results O
show O
a O
significant O
decrease O
in O
mechanical B-PRO
strength E-PRO
for O
samples S-CONPRI
that O
are O
built O
diagonally O
and O
a O
transformation O
of O
the O
microstructure S-CONPRI
after O
a O
HIP S-MANP
( O
hot B-MANP
isostatic I-MANP
pressing E-MANP
) O
treatment O
, O
resulting O
in O
a O
lower O
maximum O
strength S-PRO
, O
but O
higher O
ductility S-PRO
. O


In O
general O
, O
horizontal B-FEAT
struts E-FEAT
should O
be S-MATE
avoided O
during O
manufacturing S-MANP
, O
unless O
the O
applied O
load O
after O
manufacturing S-MANP
can O
be S-MATE
properly O
supported O
by O
other O
struts S-MACEQ
. O


Both O
a O
stress S-PRO
relief O
heat B-MANP
treatment E-MANP
and O
a O
HIP S-MANP
treatment O
can O
be S-MATE
used O
in O
statically O
loaded O
applications O
, O
whereas O
a O
HIP S-MANP
treatment O
is O
believed O
to O
be S-MATE
beneficial O
for O
dynamically O
loaded O
applications O
. O


This O
study O
enables O
an O
appropriate O
selection O
of O
build B-PARA
orientation E-PARA
and O
heat B-MANP
treatment E-MANP
of O
lattice B-FEAT
structures E-FEAT
for O
different O
applications O
. O


We O
report O
the O
design S-FEAT
of O
a O
metal B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
system O
for O
in-situ S-CONPRI
monitoring O
of O
the O
build S-PARA
process O
during O
additive B-MANP
manufacture E-MANP
. O


Its O
open-architecture O
design S-FEAT
was O
originally O
determined O
to O
enable O
access O
for O
x-rays S-CONPRI
to O
the O
melt B-MATE
pool E-MATE
, O
but O
it O
also O
provides O
access O
to O
the O
build B-PARA
area E-PARA
for O
a O
range S-PARA
of O
other O
in-situ S-CONPRI
measurement O
techniques O
. O


The O
system O
is O
sufficiently O
automated O
to O
enable O
single O
tracks O
and O
high-density O
, O
multiple O
layer S-PARA
components S-MACEQ
to O
be S-MATE
built O
. O


It O
is O
easily O
transportable O
to O
enable O
measurements O
at O
different O
measurement S-CHAR
facilities O
and O
its O
modular S-CONPRI
design S-FEAT
enables O
straightforward O
modification O
for O
the O
specific O
measurements O
being O
made O
. O


We O
demonstrate O
that O
the O
system O
produces O
components S-MACEQ
with O
> O
99 O
% O
density S-PRO
. O


Hence O
the O
build S-PARA
conditions O
are O
representative O
to O
observe O
process S-CONPRI
fundamentals O
and O
to O
develop O
process B-CONPRI
control E-CONPRI
strategies O
. O


In O
this O
work O
a O
finite-element O
framework S-CONPRI
for O
the O
numerical B-ENAT
simulation E-ENAT
of O
the O
heat B-CONPRI
transfer E-CONPRI
analysis O
of O
additive B-MANP
manufacturing I-MANP
processes E-MANP
by O
powder-bed O
technologies S-CONPRI
, O
such O
as S-MATE
Selective O
Laser S-ENAT
Melting O
, O
is O
presented O
. O


These O
kind O
of O
technologies S-CONPRI
allow O
for O
a O
layer-by-layer S-CONPRI
metal O
deposition B-MANP
process E-MANP
to O
cost-effectively O
create O
, O
directly O
from O
a O
CAD B-ENAT
model E-ENAT
, O
complex O
functional O
parts O
such O
as S-MATE
turbine O
blades O
, O
fuel O
injectors O
, O
heat B-MACEQ
exchangers E-MACEQ
, O
medical B-APPL
implants E-APPL
, O
among O
others O
. O


The O
numerical O
model S-CONPRI
proposed O
accounts O
for O
different O
heat B-CONPRI
dissipation E-CONPRI
mechanisms O
through O
the O
surrounding O
environment O
and O
is O
supplemented O
by O
a O
finite-element O
activation O
strategy O
, O
based O
on O
the O
born-dead O
elements S-MATE
technique O
, O
to O
follow O
the O
growth O
of O
the O
geometry S-CONPRI
driven O
by O
the O
metal B-CONPRI
deposition E-CONPRI
process O
, O
in O
such O
a O
way O
that O
the O
same O
scanning B-PARA
pattern E-PARA
sent O
to O
the O
numerical B-ENAT
control E-ENAT
system O
of O
the O
AM B-MACEQ
machine E-MACEQ
is O
used O
. O


An O
experimental S-CONPRI
campaign O
has O
been O
carried O
out O
at O
the O
Monash O
Centre O
for O
Additive B-MANP
Manufacturing E-MANP
using O
an O
EOSINT-M280 O
machine S-MACEQ
where O
it O
was O
possible O
to O
fabricate S-MANP
different O
benchmark S-MANS
geometries O
, O
as S-MATE
well O
as S-MATE
to O
record O
the O
temperature S-PARA
measurements O
at O
different O
thermocouple S-MACEQ
locations O
. O


The O
experiment S-CONPRI
consisted O
in O
the O
simultaneous O
printing O
of O
two O
walls O
with O
a O
total O
deposition S-CONPRI
volume O
of O
107 O
cm3 O
in O
992 O
layers O
and O
about O
33,500 O
s S-MATE
build B-PARA
time E-PARA
. O


A O
large O
number O
of O
numerical B-ENAT
simulations E-ENAT
have O
been O
carried O
out O
to O
calibrate O
the O
thermal O
FE S-MATE
framework O
in O
terms O
of O
the O
thermophysical O
properties S-CONPRI
of O
both O
solid O
and O
powder B-MATE
materials E-MATE
and O
suitable O
boundary B-CONPRI
conditions E-CONPRI
. O


Furthermore O
, O
the O
large O
size O
of O
the O
experiment S-CONPRI
motivated O
the O
investigation O
of O
two O
different O
model S-CONPRI
reduction O
strategies O
: O
exclusion O
of O
the O
powder-bed O
from O
the O
computational B-CONPRI
domain E-CONPRI
and O
simplified O
scanning B-CONPRI
strategies E-CONPRI
. O


In O
August O
2018 O
, O
a O
demonstration/experiment O
was O
performed O
in O
Champaign O
, O
Illinois O
USA O
, O
at O
the O
Engineer O
Research S-CONPRI
and O
Development O
Center O
Construction S-APPL
Engineering O
Research B-CONPRI
Laboratory E-CONPRI
( O
ERDC-CERL O
) O
looking O
at O
the O
continuous O
printing O
of O
a O
512 O
ft2 O
( O
47.6 O
m2 O
) O
reinforced S-CONPRI
additively O
constructed O
concrete S-MATE
( O
RACC O
) O
building O
. O


Previously O
, O
in O
July O
of O
2017 O
, O
a O
more O
traditional O
building O
was O
3D B-MANP
printed E-MANP
using O
a O
discontinuous O
concrete B-MANP
printing E-MANP
approach O
. O


These O
demonstrations O
were O
performed O
to O
determine O
the O
feasibility S-CONPRI
of O
using O
additively O
constructed O
concrete S-MATE
( O
ACC O
) O
as S-MATE
a O
material S-MATE
for O
vertical S-CONPRI
structural O
elements S-MATE
. O


This O
study O
explores O
the O
differences O
and O
similarities O
of O
ACC O
with O
conventional O
concrete S-MATE
construction O
and O
concrete S-MATE
masonry O
unit O
construction S-APPL
. O


To O
validate O
the O
feasibility S-CONPRI
of O
ACC O
a O
cost O
comparison O
analysis O
was O
performed O
comparing O
the O
construction S-APPL
methods O
used O
in O
these O
demonstrations O
to O
conventional O
concrete S-MATE
masonry O
unit O
and O
cast-in-place O
concrete S-MATE
construction O
. O


Layered O
Assembly S-MANP
is O
a O
voxel-based O
additive B-MANP
manufacturing E-MANP
method O
in O
which O
premanufactured O
voxels S-CONPRI
serve O
as S-MATE
the O
feedstock S-MATE
for O
producing O
multi-material S-CONPRI
parts O
. O


Electrodes S-MACEQ
were O
nominally O
designed S-FEAT
for O
grasping O
voxels S-CONPRI
of O
3 O
× O
3 O
mm S-MANP
cross-section O
. O


Electrostatic O
field O
simulations S-ENAT
were O
performed O
in O
COMSOL O
Multiphysics O
for O
both O
single O
electrodes S-MACEQ
, O
and O
2 O
× O
2 O
electrode S-MACEQ
arrays O
. O


The O
selective O
gripping O
capability O
of O
the O
electrode S-MACEQ
arrays O
was O
tested O
at O
voltages O
in O
the O
75–800 O
V S-MATE
range S-PARA
and O
applied O
to O
both O
polymer S-MATE
and O
metallic S-MATE
voxels O
. O


A O
comparison O
of O
electrode S-MACEQ
performance O
in O
terms O
of O
geometry S-CONPRI
revealed O
that O
comb-shaped O
electrodes S-MACEQ
were O
superior O
, O
due O
to O
≈100 O
% O
reliability S-CHAR
when O
operating O
in O
the O
600–800 O
V S-MATE
range S-PARA
. O


Lack-of-fusion O
flaws S-CONPRI
can O
occur O
in O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
additive B-MANP
manufacturing E-MANP
of O
metal S-MATE
components S-MACEQ
. O


This O
paper O
demonstrates O
a O
method O
for O
detecting O
such O
flaws S-CONPRI
by O
monitoring O
the O
fabrication S-MANP
of O
every O
layer S-PARA
before O
and O
after O
laser S-ENAT
scanning O
with O
high B-PARA
resolution E-PARA
optical O
imaging S-APPL
. O


A O
binary S-CONPRI
template O
is O
created O
from O
the O
sliced O
3D B-APPL
model E-APPL
of O
the O
part O
. O


Using O
this O
template S-MACEQ
the O
optical S-CHAR
image B-CONPRI
data E-CONPRI
is O
indexed O
to O
the O
part O
geometry S-CONPRI
. O


The O
indexed O
image B-CONPRI
data E-CONPRI
is O
used O
to O
detect O
anomalies S-CONPRI
in O
the O
powder S-MATE
layer S-PARA
before O
laser S-ENAT
scanning O
and O
in O
the O
solidified O
material S-MATE
after O
scanning S-CONPRI
. O


Lack-of-fusion O
defects S-CONPRI
are O
identified O
from O
optical S-CHAR
data S-CONPRI
by O
correlating O
multiple O
images S-CONPRI
with O
different O
lighting O
conditions O
and O
from O
multiple O
layers O
. O


Pyrometry S-CHAR
showed O
an O
increase O
in O
intensity O
in O
CO2 S-MATE
atmosphere O
over O
Ar S-ENAT
atmosphere O
. O


At O
low O
levels O
of O
reactive O
gas S-CONPRI
atmospheres O
oxygen S-MATE
loss O
from O
spatter S-CHAR
dominates O
. O


Oxygen S-MATE
increased O
in O
samples S-CONPRI
from O
0.016 O
wt. O
% O
in O
Ar S-ENAT
to O
0.1 O
wt. O
% O
in O
CO2 S-MATE
. O


Average S-CONPRI
in-situ O
particle S-CONPRI
size O
in O
the O
samples S-CONPRI
were O
∼40 O
nm O
. O


There O
was O
a O
20 O
% O
increase O
in O
yield B-PRO
strength E-PRO
when O
samples S-CONPRI
were O
produced O
under O
CO2 S-MATE
. O


Traditionally O
, O
reactive O
gases O
such O
as S-MATE
oxygen O
( O
O2 O
) O
and O
carbon S-MATE
dioxide O
( O
CO2 S-MATE
) O
have O
been O
avoided O
during O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
of O
metals S-MATE
and O
alloys S-MATE
based O
on O
the O
notion O
that O
it O
may O
lead S-MATE
to O
defect S-CONPRI
formation O
and O
poor O
properties S-CONPRI
. O


Here O
we O
show O
that O
instead O
, O
these O
gases O
can O
be S-MATE
used O
to O
form O
sub-μm-sized O
oxide S-MATE
particles O
in-situ S-CONPRI
during O
the O
L-PBF S-MANP
process O
in O
an O
Fe-Cr-Al-Ti O
stainless B-MATE
steel E-MATE
and O
lead S-MATE
to O
improved O
room O
temperature S-PARA
and O
high-temperature O
mechanical B-CONPRI
properties E-CONPRI
. O


We O
manufactured B-CONPRI
cube E-CONPRI
samples O
using O
pure O
Ar S-ENAT
and O
various O
reactive O
gas S-CONPRI
atmospheres O
, O
namely O
an O
O2/Argon O
( O
Ar S-ENAT
) O
mixture O
containing O
0.2 O
% O
O2 O
and O
CO2/Ar O
mixtures O
containing O
up O
to O
100 O
% O
CO2 S-MATE
. O


Co-axial O
measurements O
of O
infrared S-CONPRI
radiation O
emitted O
from O
the O
melt B-MATE
pool E-MATE
showed O
correlation O
to O
the O
presence O
of O
O2 O
or O
CO2 S-MATE
in O
the O
gas S-CONPRI
mixture O
. O


Builds S-CHAR
produced O
under O
CO2-containing O
atmosphere O
contained O
complex O
oxides S-MATE
with O
an O
average S-CONPRI
diameter O
of O
∼40 O
nm O
, O
an O
Al-rich O
core S-MACEQ
and O
a O
Ti-rich O
shell S-MACEQ
. O


Due O
to O
the O
high O
cooling B-PARA
rates E-PARA
typical O
to O
L-PBF S-MANP
, O
agglomeration O
of O
oxides S-MATE
and O
slag S-MATE
formation O
on O
the O
surface S-CONPRI
of O
the O
samples S-CONPRI
could O
almost O
be S-MATE
entirely O
avoided O
. O


Compression B-CHAR
tests E-CHAR
at O
temperatures S-PARA
up O
to O
800 O
°C O
showed O
that O
the O
samples S-CONPRI
produced O
in O
100 O
% O
CO2 S-MATE
have O
about O
20 O
% O
higher O
yield B-PRO
stress E-PRO
compared O
to O
samples S-CONPRI
produced O
in O
Ar S-ENAT
. O


The O
paper O
concludes O
with O
a O
discussion O
of O
the O
formation O
mechanism S-CONPRI
of O
the O
observed O
oxides S-MATE
. O


Our O
results O
show O
that O
in-situ S-CONPRI
reactions O
during O
additive B-MANP
manufacturing I-MANP
processes E-MANP
are O
a O
promising O
pathway O
to O
the O
synthesis O
of O
particle-reinforced O
alloys S-MATE
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
, O
such O
as S-MATE
Selective O
Laser B-MANP
Sintering E-MANP
( O
SLS S-MANP
) O
, O
have O
enabled O
the O
fabrication S-MANP
of O
geometrically O
complicated O
designs S-FEAT
. O


However O
, O
undesired O
distortions O
due O
to O
thermally-induced O
residual B-PRO
stresses E-PRO
may O
lead S-MATE
to O
loss O
of O
tolerance S-PARA
or O
failure S-CONPRI
of O
the O
part O
. O


One O
potential O
failure B-PRO
mode E-PRO
is O
buckling S-PRO
, O
particularly O
when O
realizing O
high B-FEAT
aspect I-FEAT
ratio E-FEAT
features O
, O
like O
for O
infill S-PARA
, O
to O
minimize O
weight S-PARA
. O


In O
this O
paper O
, O
we O
address O
distortions O
and O
part O
failures O
due O
to O
buckling S-PRO
by O
using O
a O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
to O
predict O
residual B-PRO
stress E-PRO
distributions S-CONPRI
and O
sintering S-MANP
induced O
distortions O
. O


Initially O
, O
we O
conduct O
a O
transient S-CONPRI
thermal O
simulation S-ENAT
to O
determine O
the O
Heat B-CONPRI
Affected I-CONPRI
Zone E-CONPRI
( O
HAZ S-CONPRI
) O
, O
which O
is O
then O
used O
in O
the O
thermomechanical S-CONPRI
simulation S-ENAT
. O


In O
addition O
, O
we O
imposed O
perturbations O
on O
the O
mechanical S-APPL
mesh O
based O
on O
the O
buckling S-PRO
eigenmodes O
. O


Finally O
, O
a O
thermomechanical S-CONPRI
viscoplastic O
analysis O
was O
performed O
layer-by-layer S-CONPRI
to O
obtain O
the O
final O
residual B-PRO
stress E-PRO
state O
and O
subsequent O
distortions O
that O
occur O
after O
cooling S-MANP
down O
to O
ambient O
temperature S-PARA
. O


A O
model S-CONPRI
was O
used O
to O
describe O
the O
evolution S-CONPRI
of O
porosity S-PRO
due O
to O
laser B-MANP
sintering E-MANP
, O
and O
then O
a O
model S-CONPRI
of O
the O
effects O
of O
porosity S-PRO
on O
the O
viscoplastic O
constitutive O
properties S-CONPRI
of O
the O
sintered S-MANP
material S-MATE
was O
used O
in O
the O
thermomechanical S-CONPRI
simulation S-ENAT
. O


Modeling S-ENAT
results O
are O
compared O
against O
experimental S-CONPRI
specimens O
using O
a O
Durelli O
( O
aka O
, O
Theta O
) O
specimen O
geometry B-CONPRI
fabricated E-CONPRI
with O
a O
3D B-APPL
Systems E-APPL
ProX O
200 O
Selective B-MANP
Laser I-MANP
Sintering E-MANP
( O
SLS S-MANP
) O
machine S-MACEQ
. O


The O
geometry S-CONPRI
of O
the O
specimen O
represents O
an O
internal O
feature S-FEAT
with O
a O
high B-FEAT
aspect I-FEAT
ratio E-FEAT
that O
is O
prone O
to O
buckling S-PRO
, O
and O
the O
dimensions S-FEAT
were O
modified O
based O
on O
the O
simulation S-ENAT
results O
to O
confirm O
the O
ability O
of O
the O
modeling S-ENAT
approach O
to O
provide O
accurate S-CHAR
mitigation O
of O
buckling-induced O
distortions O
. O


This O
paper O
presents O
a O
process-microstructure O
finite B-CONPRI
element E-CONPRI
modeling O
framework S-CONPRI
for O
predicting O
the O
evolution S-CONPRI
of O
volumetric O
phase B-CONPRI
fractions E-CONPRI
and O
microhardness S-CONPRI
during O
laser B-MANP
directed I-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
additive B-MANP
manufacturing E-MANP
of O
Ti6Al4V S-MATE
. O


Based O
on O
recent O
experimental S-CONPRI
observations O
, O
the O
present O
microstructure B-CONPRI
evolution E-CONPRI
model O
is O
formulated O
to O
combine O
the O
formation O
and O
dissolution O
kinetics O
of O
grain B-CONPRI
boundary E-CONPRI
, O
Widmanstätten O
colony/basketweave O
, O
massive/martensitic O
alpha O
and O
beta O
phases O
of O
Ti6Al4V S-MATE
. O


The O
microstructure B-CONPRI
evolution E-CONPRI
algorithm S-CONPRI
is O
verified O
and O
embedded O
into O
a O
three-dimensional S-CONPRI
finite B-CONPRI
element E-CONPRI
process O
simulation S-ENAT
model S-CONPRI
to O
simulate O
thermally O
driven O
phase S-CONPRI
transformations O
during O
DED S-MANP
processing O
of O
a O
Ti6Al4V S-MATE
thin-walled O
rectangular O
sample S-CONPRI
. O


The O
simulated O
volumetric O
phase B-CONPRI
fractions E-CONPRI
and O
related O
microhardness S-CONPRI
distribution S-CONPRI
agree O
reasonably O
well O
with O
experimental S-CONPRI
measurements O
performed O
on O
the O
sample S-CONPRI
. O


Thus O
the O
proposed O
simulation S-ENAT
model S-CONPRI
could O
be S-MATE
useful O
for O
designers O
to O
understand O
and O
control O
process-microstructure-property O
relationships O
in O
a O
DED-processed O
part O
. O


The O
present O
research S-CONPRI
work O
has O
investigated O
the O
synthesis O
of O
ceramic S-MATE
structures O
based O
on O
inorganic O
, O
spherical-hollow O
microballoons O
using O
a O
binder S-MATE
jet O
printing B-MANP
process E-MANP
. O


Binder S-MATE
jet O
printing O
is O
a O
process S-CONPRI
that O
allows O
the O
synthesis O
process S-CONPRI
of O
complex O
and O
intricate O
parts O
with O
minimal O
waste O
of O
the O
feedstock B-MATE
material E-MATE
. O


The O
ceramic S-MATE
microballoons O
here O
investigated O
were O
based O
on O
a O
mullite S-MATE
derivative O
. O


The O
printed O
ceramic S-MATE
parts O
were O
cured S-MANP
and O
sintered S-MANP
as S-MATE
the O
precursor S-MATE
templates O
for O
metal B-CONPRI
matrix E-CONPRI
syntactic O
foams O
( O
MMSFs O
) O
. O


The O
MMSFs O
were O
manufactured S-CONPRI
by O
infiltrating S-CONPRI
the O
printed O
ceramic S-MATE
templates O
by O
molten O
aluminum S-MATE
. O


The O
flexural B-PRO
strength E-PRO
of O
the O
cured S-MANP
, O
sintered S-MANP
, O
and O
infiltrated O
structures O
were O
also O
investigated O
. O


It O
is O
proposed O
that O
binder S-MATE
jet O
printing O
followed O
by O
a O
sintering S-MANP
and O
pressureless O
infiltration S-CONPRI
process O
represents O
an O
advantageous O
technology S-CONPRI
for O
designing O
complex O
MMSF O
structures O
. O


The O
fused S-CONPRI
coating S-APPL
process O
is O
a O
new O
material B-MANP
jetting E-MANP
additive B-MANP
manufacturing E-MANP
technology O
that O
proposes O
to O
solve O
the O
problem O
of O
high O
cost O
, O
low O
efficiency O
and O
high O
material S-MATE
requirements O
of O
laser-based O
process S-CONPRI
and O
electron B-CONPRI
beam E-CONPRI
process O
. O


The O
structure S-CONPRI
and O
operating O
principles O
of O
the O
fused S-CONPRI
coating S-APPL
machine O
are O
explained O
in O
this O
paper O
. O


Sn63Pb37 O
is O
taken O
as S-MATE
the O
experimental S-CONPRI
material O
because O
of O
its O
low O
melting B-PARA
temperature E-PARA
, O
small O
surface B-PRO
tension E-PRO
coefficient O
and O
high O
viscosity S-PRO
. O


Tensile B-CHAR
test E-CHAR
specimens O
were O
made O
both O
parallel O
and O
perpendicular O
to O
the O
forming S-MANP
trajectory O
. O


Tensile B-PRO
strengths E-PRO
were O
measured O
and O
the O
corresponding O
fractographies O
were O
observed O
. O


It O
is O
found O
that O
large O
plastic B-PRO
deformation E-PRO
has O
occurred O
before O
the O
fracture S-CONPRI
, O
and O
the O
plasticity S-PRO
of O
fused S-CONPRI
components S-MACEQ
that O
the O
tensile S-PRO
direction O
parallel O
to O
the O
forming S-MANP
trajectory O
, O
is O
higher O
. O


The O
densification S-MANP
degree O
of O
fused S-CONPRI
coating S-APPL
component O
is O
measured O
by O
the O
drainage O
method O
. O


The O
average S-CONPRI
value O
is O
up O
to O
99.78 O
% O
which O
indicates O
that O
the O
internal B-PRO
structure E-PRO
is O
indistinguishable O
from O
extruded S-MANP
Sn63Pb37 O
. O


The O
Vickers B-PRO
hardness E-PRO
of O
the O
fused S-CONPRI
coated S-APPL
component O
and O
raw O
casted O
material S-MATE
were O
tested O
by O
5 O
points O
respectively O
, O
the O
results O
showed O
that O
the O
average S-CONPRI
Vickers O
hardness S-PRO
of O
the O
fused S-CONPRI
coating S-APPL
component O
is O
14.6 O
% O
higher O
than O
the O
casted O
one O
. O


Cellular B-MATE
materials E-MATE
, O
such O
as S-MATE
foams O
, O
can O
be S-MATE
used O
as S-MATE
load O
bearing O
members O
in O
civil O
construction S-APPL
and O
as S-MATE
protective O
energy O
absorbing O
structures O
for O
personnel O
and O
equipment S-MACEQ
. O


In O
the O
present O
study O
, O
novel O
lightweight S-CONPRI
closed-cell O
structures O
were O
designed S-FEAT
, O
and O
their O
mechanical B-CONPRI
properties E-CONPRI
and O
collapse O
mechanisms O
were O
investigated O
through O
a O
combination O
of O
experimental S-CONPRI
validation O
and O
finite B-CONPRI
element E-CONPRI
( O
FE S-MATE
) O
simulations S-ENAT
. O


Selected O
porous S-PRO
structure O
designs S-FEAT
were O
manufactured S-CONPRI
from O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
using O
additive B-MANP
manufacturing E-MANP
technology O
. O


These O
3D B-MANP
printed E-MANP
structures O
were O
subjected O
to O
quasi-static S-CONPRI
loading O
to O
determine O
the O
dependence O
of O
their O
elastic S-PRO
and O
plastic S-MATE
responses O
from O
their O
topological O
features O
. O


Deformation S-CONPRI
mechanisms O
were O
elucidated O
through O
quasi-static S-CONPRI
compression S-PRO
experiments O
and O
FE S-MATE
modelling O
. O


The O
appropriate O
distribution S-CONPRI
of O
the O
base O
material S-MATE
in O
the O
designed S-FEAT
closed-cell O
structures O
inherits O
the O
merits O
of O
uniform O
stress B-PRO
distribution E-PRO
and O
large O
deformations S-CONPRI
that O
lead S-MATE
to O
reaching O
high O
strengths S-PRO
and O
desirable O
energy B-CHAR
absorption E-CHAR
efficiencies O
. O


The O
effects O
of O
relative B-PRO
density E-PRO
and O
cell S-APPL
shape O
were O
studied O
in O
detail O
from O
elastic S-PRO
loading O
through O
the O
large O
plastic S-MATE
strain O
densification S-MANP
regions O
. O


The O
effects O
of O
cellular O
architecture S-APPL
on O
deformation S-CONPRI
mechanisms O
and O
energy B-CHAR
absorption E-CHAR
capabilities O
demonstrated O
the O
possibility O
of O
enhancing O
energy B-CHAR
absorption E-CHAR
efficiencies O
with O
appropriate O
design S-FEAT
criteria O
. O


Based O
on O
the O
experimental S-CONPRI
and O
numerical O
analyses O
, O
the O
most O
efficient O
energy O
absorbing O
closed-cell O
structure S-CONPRI
was O
proposed O
. O


The O
performance S-CONPRI
enhancement O
of O
parts O
produced O
using O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
is O
an O
important O
goal O
for O
various O
industrial S-APPL
applications O
. O


In O
order O
to O
achieve O
this O
goal O
, O
obtaining O
a O
homogeneous S-CONPRI
microstructure O
and O
eliminating O
material S-MATE
defects S-CONPRI
within O
the O
fabricated S-CONPRI
parts O
are O
important O
research S-CONPRI
issues O
. O


The O
objective O
of O
this O
experimental S-CONPRI
study O
is O
to O
evaluate O
the O
effect O
of O
thermal O
post-processing S-CONPRI
of O
AlSi10Mg S-MATE
parts O
, O
using O
recycled S-CONPRI
powder S-MATE
, O
with O
the O
aim O
of O
improving O
the O
microstructure S-CONPRI
homogeneity O
of O
the O
as-built O
parts O
. O


This O
work O
is O
essential O
for O
the O
cost-effective O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
of O
metal S-MATE
optics O
and O
optomechanical O
systems O
. O


To O
achieve O
this O
goal O
, O
a O
full O
characterization O
of O
fresh O
and O
recycled S-CONPRI
powder S-MATE
was O
performed O
, O
in O
addition O
to O
a O
microstructure S-CONPRI
assessment O
of O
the O
as-built O
fabricated S-CONPRI
samples O
. O


Annealing S-MANP
, O
solution B-MANP
heat I-MANP
treatment E-MANP
( O
SHT O
) O
and O
T6 O
heat B-MANP
treatment E-MANP
( O
T6 O
HT O
) O
were O
applied O
under O
different O
processing O
conditions O
. O


A O
micro-hardness O
map O
was O
developed O
to O
assist O
in O
the O
selection O
of O
the O
optimized O
post-processing B-CONPRI
parameters E-CONPRI
in O
order O
to O
satisfy O
the O
design S-FEAT
requirements O
of O
the O
part O
. O


Thermal B-APPL
barrier I-APPL
coatings E-APPL
( O
TBC S-APPL
) O
are O
regularly O
used O
today O
to O
protect O
and O
extend O
the O
service B-CONPRI
life E-CONPRI
of O
several O
superalloys S-MATE
which O
are O
extensively O
used O
in O
high O
temperature S-PARA
applications O
. O


The O
existing O
TBCs S-APPL
are O
typically O
between O
0.1 O
to O
0.5 O
mm S-MANP
in O
thickness O
, O
are O
deposited O
on O
metal S-MATE
substrates O
using O
plasma B-MANP
spray E-MANP
or O
electron B-CONPRI
beam E-CONPRI
vapor O
deposition S-CONPRI
, O
and O
can O
reduce O
temperatures S-PARA
at O
the O
substrate S-MATE
surface O
by O
up O
to O
300 O
°C O
. O


For O
greater O
temperature S-PARA
reductions O
there O
is O
a O
need O
for O
thicker O
TBCs S-APPL
. O


The O
building O
of O
thick O
TBCs S-APPL
has O
to O
date O
been O
stymied O
by O
poor O
adhesion S-PRO
, O
and O
cracking S-CONPRI
during O
deposition S-CONPRI
. O


It O
has O
been O
suggested O
that O
a O
functionally B-CONPRI
graded E-CONPRI
approach O
may O
reduce O
the O
residual B-PRO
stresses E-PRO
which O
result O
in O
these O
defects S-CONPRI
. O


To O
date O
there O
have O
been O
few O
reports O
on O
the O
deposition S-CONPRI
of O
ceramic S-MATE
or O
cermet S-MATE
coatings O
using O
laser S-ENAT
AM S-MANP
and O
none O
have O
reported O
on O
the O
phase S-CONPRI
stability O
of O
ceramic S-MATE
particles O
post-deposition O
. O


This O
paper O
is O
a O
first O
report O
on O
the O
phase S-CONPRI
stability O
of O
ceramic S-MATE
particles O
following O
the O
compositional O
segregation S-CONPRI
of O
elements S-MATE
during O
deposition S-CONPRI
using O
a O
powder S-MATE
feed S-PARA
additive B-MANP
manufacturing I-MANP
process E-MANP
. O


Functionally B-CONPRI
graded E-CONPRI
( O
FG O
) O
, O
thick O
TBCs S-APPL
( O
> O
3 O
mm S-MANP
) O
consisting O
of O
Inconel B-MATE
625 E-MATE
( O
IN625 O
) O
and O
yttria-partially O
stabilized O
zirconia S-MATE
( O
8YSZ O
) O
were O
deposited O
on O
an O
A516 O
steel S-MATE
substrate O
via O
laser S-ENAT
direct B-MANP
energy I-MANP
deposition E-MANP
( O
LDED O
) O
. O


Good O
interfaces O
were O
observed O
between O
the O
bond B-APPL
coat E-APPL
( O
BC O
) O
and O
first O
cermet S-MATE
layer O
and O
between O
the O
graded O
cermet S-MATE
layers O
. O


However O
, O
cermet S-MATE
layers O
deposited O
with O
10 O
wt. O
% O
or O
more O
YSZ S-MATE
developed O
a O
thin O
layer S-PARA
of O
YSZ S-MATE
on O
the O
surface S-CONPRI
. O


The O
thin O
layer S-PARA
of O
YSZ S-MATE
greatly O
hindered O
additional O
deposition S-CONPRI
of O
new O
cermet S-MATE
layers O
. O


In O
cermet S-MATE
layers O
that O
did O
exhibit O
good O
interfaces O
, O
fine O
, O
re-solidified O
, O
YSZ S-MATE
particles S-CONPRI
were O
homogenously O
distributed O
within O
the O
Inconel B-MATE
625 E-MATE
matrix O
. O


The O
YSZ S-MATE
particles S-CONPRI
exhibited O
a O
tetragonal B-FEAT
lattice I-FEAT
structure E-FEAT
and O
were O
depleted O
of O
yttrium S-MATE
. O


In O
contrast O
, O
the O
thin O
YSZ S-MATE
layer S-PARA
formed O
on O
a O
cermet S-MATE
surface O
showed O
no O
yttrium S-MATE
depletion O
. O


Some O
of O
the O
primary O
barriers O
to O
widespread O
adoption O
of O
metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
are O
persistent O
defect S-CONPRI
formation O
in O
built O
components S-MACEQ
, O
high O
material S-MATE
costs O
, O
and O
lack O
of O
consistency S-CONPRI
in O
powder B-MACEQ
feedstock E-MACEQ
. O


To O
generate O
more O
reliable O
, O
complex-shaped S-CONPRI
metal O
parts O
, O
it O
is O
crucial O
to O
understand O
how O
feedstock S-MATE
properties O
change O
with O
reuse O
and O
how O
that O
affects O
build S-PARA
mechanical O
performance S-CONPRI
. O


Powder B-MATE
particles E-MATE
interacting O
with O
the O
energy O
source S-APPL
, O
yet O
not O
consolidated O
into O
an O
AM B-MACEQ
part E-MACEQ
can O
undergo O
a O
range S-PARA
of O
dynamic S-CONPRI
thermal O
interactions O
, O
resulting O
in O
variable O
particle S-CONPRI
behavior O
if O
reused O
. O


In O
this O
work O
, O
we O
present O
a O
systematic O
study O
of O
316L O
powder S-MATE
properties O
from O
the O
virgin O
state O
through O
thirty O
powder S-MATE
reuses O
in O
the O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
process O
. O


Thirteen O
powder S-MATE
characteristics O
and O
the O
resulting O
AM S-MANP
build O
mechanical B-CONPRI
properties E-CONPRI
were O
investigated O
for O
both O
powder S-MATE
states O
. O


Results O
show O
greater O
variability S-CONPRI
in O
part O
ductility S-PRO
for O
the O
virgin O
state O
. O


The O
feedstock S-MATE
exhibited O
minor O
changes O
to O
size O
distribution S-CONPRI
, O
bulk O
composition S-CONPRI
, O
and O
hardness S-PRO
with O
reuse O
, O
but O
significant O
changes O
to O
particle S-CONPRI
morphology S-CONPRI
, O
microstructure S-CONPRI
, O
magnetic O
properties S-CONPRI
, O
surface S-CONPRI
composition S-CONPRI
, O
and O
oxide S-MATE
thickness O
. O


Additionally O
, O
sieved O
powder S-MATE
, O
along O
with O
resulting O
fume/condensate O
and O
recoil O
ejecta O
( O
spatter S-CHAR
) O
properties S-CONPRI
were O
characterized O
. O


It O
was O
discovered O
that O
spatter S-CHAR
leads O
to O
formation O
of O
single O
crystal O
ferrite S-MATE
through O
large O
degrees O
of O
supercooling S-CONPRI
and O
massive O
solidification S-CONPRI
. O


Ferrite S-MATE
content O
and O
consequently O
magnetic B-CHAR
susceptibility E-CHAR
of O
the O
powder S-MATE
also O
increases O
with O
reuse O
, O
suggesting O
potential O
for O
magnetic B-CONPRI
separation E-CONPRI
as S-MATE
a O
refining O
technique O
for O
altered O
feedstock S-MATE
. O


Tensile B-PRO
stress E-PRO
in O
selective B-MANP
laser I-MANP
melted E-MANP
( O
SLM S-MANP
) O
stainless B-MATE
steel E-MATE
316 O
( O
SS316 O
) O
bars O
was O
studied O
with O
neutron S-CONPRI
imaging S-APPL
methods O
for O
measurement S-CHAR
of O
attenuation O
, O
scattering O
, O
and O
diffraction S-CHAR
. O


The O
hypotheses O
for O
stress S-PRO
failure S-CONPRI
includes O
modifications O
to O
both O
the O
grain B-CONPRI
structure E-CONPRI
and O
residual S-CONPRI
porosity S-PRO
. O


Neutron S-CONPRI
Bragg O
edge O
imaging S-APPL
showed O
a O
change O
in O
crystallographic O
structure S-CONPRI
and/or O
texture S-FEAT
at O
a O
pre-existing O
fracture S-CONPRI
, O
but O
did O
not O
provide O
evidence O
for O
presumptive O
crack O
formation O
. O


A O
Talbot-Lau O
grating-based O
neutron S-CONPRI
interferometer O
yielded O
better O
than O
100 O
μm O
spatial O
resolution S-PARA
for O
the O
attenuation O
images S-CONPRI
and O
was O
tuned O
to O
an O
autocorrelation O
scattering O
length O
of O
1.97 O
μm O
for O
the O
dark-field O
( O
scattering O
) O
images S-CONPRI
. O


The O
interferometry S-CONPRI
imaging S-APPL
was O
performed O
with O
samples S-CONPRI
parallel O
and O
perpendicular O
to O
the O
linear O
grating O
, O
allowing O
assessment O
of O
scattering O
along O
and O
perpendicular O
to O
the O
additive B-MANP
manufacturing E-MANP
build O
direction O
. O


In O
the O
3D S-CONPRI
tomography O
dark-field O
volume S-CONPRI
of O
a O
tensile S-PRO
stressed O
bar O
, O
features O
were O
observed O
that O
suggested O
possible O
sites O
of O
crack O
formation O
. O


The O
features O
were O
quantified O
with O
line O
probes S-MACEQ
and O
found O
to O
be S-MATE
reproducible O
over O
three O
tomography O
experiments O
. O


After O
imaging S-APPL
, O
the O
half-stressed O
bar O
was O
pulled O
to O
failure S-CONPRI
; O
the O
fracture S-CONPRI
point O
is O
correlated S-CONPRI
with O
a O
feature S-FEAT
in O
the O
line O
probe S-MACEQ
having O
enhanced O
neutron B-CHAR
scattering E-CHAR
. O


Neutron S-CONPRI
interferometry S-CONPRI
, O
particularly O
the O
dark-field O
imaging S-APPL
modality O
, O
emerges O
as S-MATE
a O
powerful O
non-destructive O
method O
for O
detecting O
early O
crack O
formation O
in O
additive B-MANP
manufactured E-MANP
components O
. O


Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
is O
a O
method O
of O
joining S-MANP
metal/non-metals O
or O
composites S-MATE
layer O
by O
layer S-PARA
using O
different O
energy O
sources O
. O


Among O
the O
various O
AM B-MANP
processes E-MANP
, O
laser-based O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
is O
very O
popular O
, O
in O
which O
geometrically O
complex B-CONPRI
structures E-CONPRI
can O
be S-MATE
manufactured O
directly O
from O
CAD B-ENAT
models E-ENAT
. O


One O
of O
the O
least O
investigated O
areas S-PARA
in O
LPBF S-MANP
is O
the O
fatigue S-PRO
property O
of O
LPBF S-MANP
produced O
stainless B-MATE
steel E-MATE
parts O
, O
which O
find O
a O
variety O
of O
engineering S-APPL
and O
medical B-APPL
applications E-APPL
. O


In O
actual O
service O
conditions O
, O
many O
engineering S-APPL
components S-MACEQ
undergo O
variable O
cyclic B-PRO
loadings E-PRO
. O


Therefore O
, O
in O
order O
to O
widen O
industrial S-APPL
applications O
of O
LPBF S-MANP
process O
, O
effects O
of O
variable O
amplitude O
loading O
under O
both O
zero O
and O
tensile S-PRO
mean O
stresses O
on O
the O
fatigue B-PRO
life E-PRO
of O
LPBF S-MANP
produced O
15-5 O
precipitation B-MANP
hardened E-MANP
stainless O
steel S-MATE
parts O
have O
been O
examined O
in O
the O
present O
study O
. O


Further O
, O
different O
modes O
of O
failure S-CONPRI
, O
effects O
of O
load O
sequences O
on O
fatigue B-PRO
life E-PRO
and O
the O
cumulative O
damage S-PRO
during O
the O
process S-CONPRI
have O
also O
been O
studied O
. O


Fracture S-CONPRI
surfaces O
were O
studied O
using O
Scanning B-CHAR
Electron I-CHAR
Microscopy E-CHAR
to O
investigate O
the O
mode O
of O
failures O
and O
completely O
different O
fracture S-CONPRI
surface O
morphologies S-CONPRI
for O
these O
two O
cases O
explain O
the O
observed O
difference O
in O
number O
of O
cycles O
to O
failure S-CONPRI
with O
the O
reversal O
of O
the O
load O
sequence O
. O


Recent O
advances O
in O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
( O
XCT O
) O
have O
allowed O
for O
measurement S-CHAR
resolutions O
approaching O
the O
point O
where O
XCT O
can O
be S-MATE
used O
for O
measuring O
surface B-CONPRI
topography E-CONPRI
. O


These O
advances O
make O
XCT O
appealing O
for O
measuring O
hard-to-reach O
or O
internal O
surfaces S-CONPRI
, O
such O
as S-MATE
those O
often O
present O
in O
additively B-MANP
manufactured E-MANP
parts O
. O


To O
demonstrate O
the O
feasibility S-CONPRI
and O
potential O
of O
XCT O
for O
topography S-CHAR
measurement S-CHAR
, O
topography S-CHAR
datasets O
obtained O
using O
two O
XCT O
systems O
are O
compared O
to O
those O
acquired O
using O
coherence O
scanning B-CONPRI
interferometry E-CONPRI
and O
focus O
variation S-CONPRI
microscopy S-CHAR
. O


A O
hollow O
Ti6Al4V S-MATE
part O
produced O
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
is O
used O
as S-MATE
a O
measurement S-CHAR
artefact O
. O


The O
artefact O
comprises O
two O
component S-MACEQ
halves O
that O
can O
be S-MATE
separated O
to O
expose O
the O
internal O
surfaces S-CONPRI
. O


Measured O
surface S-CONPRI
datasets O
are O
accurately S-CHAR
aligned O
and O
similarly O
cropped O
, O
and O
compared O
by O
various O
qualitative S-CONPRI
and O
quantitative S-CONPRI
means O
, O
including O
the O
computation S-CONPRI
of O
ISO B-MANS
25178-2 E-MANS
areal O
surface B-FEAT
texture E-FEAT
parameters S-CONPRI
, O
commonly O
used O
in O
part O
quality S-CONPRI
assessment O
. O


Results O
show O
that O
XCT O
can O
non-destructively O
provide O
surface S-CONPRI
information O
comparable O
with O
more O
conventional O
surface S-CONPRI
measurement S-CHAR
technologies O
, O
thus O
representing O
a O
viable O
alternative O
to O
more O
conventional O
measurement S-CHAR
, O
particularly O
appealing O
for O
hard-to-reach O
and O
internal O
surfaces S-CONPRI
. O


Low-cost O
GMAW-based O
3-D S-CONPRI
printing O
slicing S-CONPRI
needed O
for O
diverse O
users O
. O


Upgraded O
free O
and O
open O
source S-APPL
CuraEngine O
into O
MOSTMetalCura O
. O


New O
slicer S-ENAT
track O
counts O
, O
avoid O
overlaps O
, O
infill S-PARA
to O
enable O
continous O
bead S-CHAR
. O


Also O
includes O
variable O
pauses O
, O
control O
of O
welder O
and O
set S-APPL
wire O
feed S-PARA
. O


The O
slicer S-ENAT
enables O
1 O
mm S-MANP
resolution O
printing O
of O
ER70S-6 S-MATE
steel O
. O


Low-cost O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
( O
GMAW S-MANP
) O
-based O
3-D S-CONPRI
printing O
has O
proven O
effective O
at O
additive B-MANP
manufacturing E-MANP
steel O
and O
aluminum S-MATE
parts O
. O


To O
enable O
automated O
slicing S-CONPRI
a O
3-D S-CONPRI
model O
and O
generating O
G-code S-ENAT
for O
an O
acceptable O
path O
for O
GMAW S-MANP
3-D S-CONPRI
printing O
, O
this O
paper O
reports O
on O
upgrading O
of O
the O
free O
and O
open O
source S-APPL
CuraEngine O
. O


The O
new O
slicer S-ENAT
, O
MOSTMetalCura O
, O
provides O
the O
following O
novel O
abilities O
necessary O
for O
GMAW S-MANP
3-D S-CONPRI
printing O
: O
i O
) O
change O
the O
perimeter O
metric O
from O
width O
to O
track O
count O
, O
ii O
) O
avoid O
movement O
that O
overlaps O
previous O
weld B-CONPRI
beads E-CONPRI
, O
iii O
) O
have O
infill S-PARA
start O
immediately O
after O
the O
perimeter O
finished O
and O
in O
the O
direction O
that O
eliminates O
translations O
, O
iv O
) O
add O
a O
variable O
pause O
between O
layers O
to O
allow O
for O
substrate S-MATE
cooling S-MANP
, O
v S-MATE
) O
configure O
GPIO O
pins O
to O
turn O
on/off O
the O
welder O
, O
and O
vi O
) O
set S-APPL
optimized O
wire O
feed S-PARA
speed O
and O
voltage O
of O
the O
welder O
based O
on O
printing B-PARA
speed E-PARA
, O
layer B-PARA
height E-PARA
, O
filament B-PARA
diameter E-PARA
, O
and O
tool S-MACEQ
track O
width O
. O


The O
process S-CONPRI
for O
initiating O
these O
changes O
are O
detailed O
and O
the O
new O
slicer S-ENAT
is O
used O
to O
help O
improve O
the O
function O
of O
the O
printer S-MACEQ
for O
ER70S-6 S-MATE
steel O
. O


To O
find O
the O
printing O
function O
with O
the O
smallest O
bead B-CHAR
width E-CHAR
based O
on O
volume S-CONPRI
of O
material S-MATE
, O
the O
line O
width O
, O
layer B-PARA
height E-PARA
, O
and O
printing B-PARA
speed E-PARA
are O
varied O
to O
provide O
wire O
feed S-PARA
speed O
calculated O
by O
MOSTMetalCura O
, O
then O
the O
settings O
are O
used O
to O
print S-MANP
3-D S-CONPRI
models O
. O


The O
results O
of O
3-D S-CONPRI
printing O
three O
case B-CONPRI
study E-CONPRI
objects O
of O
increasing O
geometric O
complexity S-CONPRI
using O
the O
process B-CONPRI
methodology E-CONPRI
improvements O
presented O
, O
which O
show O
resolution S-PARA
of O
1 O
mm S-MANP
bead B-CHAR
widths E-CHAR
. O


In O
the O
current O
study O
, O
cylindrical S-CONPRI
samples O
of O
AlSi10Mg B-MATE
alloy E-MATE
were O
fabricated S-CONPRI
using O
direct B-MANP
metal I-MANP
laser I-MANP
sintering E-MANP
( O
DMLS S-MANP
) O
technique O
in O
vertical S-CONPRI
and O
horizontal O
directions O
. O


The O
microstructure S-CONPRI
of O
the O
samples S-CONPRI
was O
analyzed O
using O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
, O
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
and O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
. O


It O
was O
observed O
that O
, O
by O
changing O
the O
building B-PARA
direction E-PARA
from O
vertical S-CONPRI
to O
horizontal O
, O
columnar O
to O
equiaxed O
transition S-CONPRI
( O
CET O
) O
occurred O
in O
the O
alloy S-MATE
. O


While O
75 O
% O
of O
the O
grains S-CONPRI
in O
the O
vertical B-CONPRI
sample E-CONPRI
were O
columnar O
, O
by O
changing O
the O
direction O
to O
horizontal O
, O
49 O
% O
of O
the O
grains S-CONPRI
evolved O
with O
columnar O
shape O
and O
51 O
% O
of O
them O
were O
equiaxed O
. O


Moreover O
, O
the O
texture S-FEAT
of O
DMLS-AlSi10Mg O
alloy S-MATE
changed O
due O
to O
CET O
. O


While O
{ O
001 O
} O
fiber S-MATE
texture O
evolved O
in O
the O
vertical B-CONPRI
sample E-CONPRI
, O
the O
< O
001 O
> O
direction O
tilted O
away O
from O
the O
building B-PARA
direction E-PARA
in O
the O
horizontal O
one O
. O


Using O
the O
fundamentals O
of O
solidification S-CONPRI
and O
constitutional O
undercooling O
, O
the O
solidification S-CONPRI
behavior O
of O
AlSi10Mg B-MATE
alloy E-MATE
during O
DMLS S-MANP
process O
was O
modeled O
. O


It O
was O
observed O
that O
, O
the O
determinant O
parameter S-CONPRI
in O
CET O
during O
DMLS S-MANP
of O
AlSi10Mg B-MATE
alloy E-MATE
is O
the O
angle O
between O
the O
nominal O
growth O
rate O
and O
< O
hkl O
> O
direction O
of O
the O
growing O
dendrite S-BIOP
, O
which O
is O
controlled O
by O
the O
geometry S-CONPRI
and O
building B-PARA
direction E-PARA
of O
the O
sample S-CONPRI
. O


Further O
TEM S-CHAR
studies O
confirmed O
that O
, O
CET O
alters O
the O
shape O
and O
coherency O
of O
Si S-MATE
precipitates S-MATE
and O
dislocation B-PRO
density E-PRO
inside O
the O
α-Al O
dendrites S-BIOP
in O
DMLS-AlSi10Mg O
alloy S-MATE
. O


Metal B-MANP
additive I-MANP
manufacturing E-MANP
, O
despite O
of O
offering O
unique O
capabilities O
e.g O
. O


unlimited O
design B-CONPRI
freedom E-CONPRI
, O
short O
manufacturing S-MANP
time O
, O
etc. O
, O
suffers O
from O
raft S-MACEQ
of O
intrinsic O
defects S-CONPRI
. O


Porosity S-PRO
is O
of O
the O
defects S-CONPRI
which O
can O
badly O
deteriorate O
a O
part O
’ O
s S-MATE
performance S-CONPRI
. O


To O
this O
end O
, O
in O
this O
work O
a O
combined O
numerical O
and O
experimental S-CONPRI
approach O
has O
been O
used O
to O
analyze O
the O
formation O
, O
evolution S-CONPRI
and O
disappearance O
of O
keyhole O
and O
keyhole-induced O
porosities S-PRO
along O
with O
their O
initiating O
mechanisms O
, O
during O
single O
track O
L-PBF S-MANP
of O
a O
Ti6Al4V B-MATE
alloy E-MATE
. O


In O
this O
respect O
, O
a O
high-fidelity S-CONPRI
numerical O
model S-CONPRI
based O
on O
the O
Finite B-CONPRI
Volume I-CONPRI
Method E-CONPRI
( O
FVM O
) O
and O
accomplished O
in O
the O
commercial O
software S-CONPRI
Flow-3D O
is O
developed O
. O


The O
model S-CONPRI
accounts O
for O
the O
major O
physics S-CONPRI
taking O
place O
during O
the O
laser-scanning O
step S-CONPRI
of O
the O
L-PBF S-MANP
process O
. O


The O
results O
show O
that O
during O
the O
keyhole O
regime O
, O
the O
heating S-MANP
rises O
dramatically O
compared O
to O
the O
shallow-depth O
melt B-MATE
pool E-MATE
regime O
due O
to O
the O
large O
entrapment O
of O
laser S-ENAT
rays O
in O
the O
keyhole O
cavities O
. O


Also O
a O
detailed O
parametric O
study O
is O
performed O
to O
investigate O
the O
effect O
of O
input O
power S-PARA
on O
thermal O
absorptivity O
, O
heat B-CONPRI
transfer E-CONPRI
and O
melt B-MATE
pool E-MATE
anatomy O
. O


Furthermore O
, O
an O
X-ray B-CHAR
Computed I-CHAR
Tomography E-CHAR
( O
X-CT O
) O
analysis O
is O
carried O
out O
to O
visualize O
the O
pores S-PRO
formed O
during O
the O
L-PBF S-MANP
process O
. O


It O
is O
shown O
, O
that O
the O
predicted S-CONPRI
shape O
, O
size O
and O
depth O
of O
the O
pores S-PRO
are O
in O
very O
good O
agreement O
with O
those O
found O
by O
either O
X-CT O
or O
optical S-CHAR
and O
3D S-CONPRI
digital O
microscopic O
images S-CONPRI
. O


Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
is O
a O
metal B-MANP
additive I-MANP
manufacturing E-MANP
process O
where O
parts O
are O
fabricated S-CONPRI
from O
metal B-MATE
powder E-MATE
based O
on O
CAD S-ENAT
data O
. O


Selection O
of O
the O
best O
process B-CONPRI
parameters E-CONPRI
for O
the O
pulsed O
SLM S-MANP
processes S-CONPRI
is O
a O
fundamental O
problem O
due O
to O
the O
increased O
number O
of O
parameters S-CONPRI
that O
have O
a O
direct O
impact S-CONPRI
on O
the O
melt B-MATE
pool E-MATE
compared O
to O
the O
continuous O
SLM S-MANP
processes S-CONPRI
. O


In O
previous O
studies O
, O
volumetric O
energy B-PARA
density E-PARA
or O
scan B-PARA
speed E-PARA
have O
been O
used O
as S-MATE
control O
variables O
for O
applied O
energy O
. O


In O
this O
paper O
, O
the O
process B-CONPRI
parameters E-CONPRI
( O
laser B-PARA
power E-PARA
, O
exposure S-CONPRI
time O
, O
point O
distance O
and O
hatching O
distance O
) O
were O
considered O
individually O
, O
in O
addition O
to O
particle B-CONPRI
size I-CONPRI
distribution E-CONPRI
and O
layer B-PARA
thickness E-PARA
. O


The O
Taguchi O
experimental B-CONPRI
design E-CONPRI
method O
was O
used O
to O
determine O
and O
optimise O
the O
effect O
of O
the O
selected O
input O
parameters S-CONPRI
. O


The O
effect O
of O
exposure S-CONPRI
time O
and O
its O
correlation O
with O
layer B-PARA
thickness E-PARA
and O
particle B-CONPRI
size I-CONPRI
distribution E-CONPRI
was O
then O
investigated O
. O


The O
results O
show O
the O
best O
combination O
of O
process B-CONPRI
parameters E-CONPRI
which O
can O
provide O
fully O
or O
near O
fully B-PARA
dense E-PARA
parts O
. O


The O
results O
also O
show O
the O
minimum O
exposure S-CONPRI
time O
that O
can O
be S-MATE
used O
with O
different O
powder S-MATE
types O
and O
layer B-PARA
thicknesses E-PARA
. O


The O
paper O
concludes O
with O
a O
study O
which O
shows O
the O
part B-CONPRI
location E-CONPRI
has O
a O
significant O
impact S-CONPRI
on O
sample S-CONPRI
quality S-CONPRI
. O


X-ray B-CHAR
microtomography E-CHAR
can O
be S-MATE
used O
to O
characterise O
objects O
undergoing O
fabrication S-MANP
by O
additive B-MANP
manufacturing E-MANP
. O


During O
the O
layer-by-layer S-CONPRI
building B-CHAR
process E-CHAR
, O
it O
can O
provide O
key O
information O
about O
geometry S-CONPRI
, O
roughness S-PRO
and O
it O
can O
even O
reveal O
typical O
defects S-CONPRI
such O
as S-MATE
lack-of-fusion O
porosity S-PRO
, O
gas S-CONPRI
pores O
or O
cracks O
. O


In O
the O
present O
work O
, O
we O
describe O
our O
custom-designed O
additive B-MANP
manufacturing E-MANP
chamber O
allowing O
in B-CONPRI
situ E-CONPRI
3D-non-destructive O
characterisation O
to O
be S-MATE
performed O
during O
layer-by-layer S-CONPRI
construction S-APPL
using O
synchrotron S-ENAT
X-ray O
microtomography O
. O


Scans O
before O
( O
subsequently O
to O
powder S-MATE
deposition S-CONPRI
) O
and O
after O
local O
laser S-ENAT
melting O
are O
acquired O
for O
every O
layer S-PARA
. O


Among O
the O
most O
popular O
additive B-MANP
manufacturing I-MANP
processes E-MANP
for O
metals S-MATE
, O
Powder B-MANP
bed I-MANP
fusion E-MANP
technology O
involves O
a O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
manufacturing O
approach O
utilizing O
a O
high O
power S-PARA
source O
, O
such O
as S-MATE
a O
laser S-ENAT
or O
an O
electron B-CONPRI
beam E-CONPRI
, O
interacting O
with O
the O
metal B-MATE
powder E-MATE
on O
selected O
surfaces S-CONPRI
. O


Beam-powder O
interaction O
brings O
up O
a O
handful O
of O
phenomena O
affecting O
the O
quality S-CONPRI
of O
the O
final O
part O
in O
its O
volume S-CONPRI
and O
surface S-CONPRI
. O


In O
this O
study O
, O
different O
surface S-CONPRI
features O
generated O
by O
Selective B-MANP
Laser I-MANP
Melting E-MANP
of O
an O
Al-Si7-Mg O
alloy S-MATE
are O
investigated O
and O
interpreted O
based O
on O
their O
morphology S-CONPRI
, O
microstructure S-CONPRI
and O
hardness S-PRO
to O
improve O
the O
general O
understanding O
of O
defect S-CONPRI
genesis O
. O


Ballings O
, O
spatter S-CHAR
particles S-CONPRI
and O
partially O
melted S-CONPRI
metal O
powders S-MATE
are O
distinguished O
by O
their O
morphology S-CONPRI
, O
size O
and O
microstructure S-CONPRI
. O


It O
is O
shown O
that O
these O
differences O
arise O
from O
different O
cooling B-PARA
rates E-PARA
during O
their O
generation O
. O


Ballings O
share O
the O
same O
microstructure S-CONPRI
with O
the O
bulk O
material S-MATE
both O
experiencing O
cooling S-MANP
in O
conduction O
mode O
. O


Spatters O
and O
partially O
melted S-CONPRI
powders O
show O
coarser O
microstructure S-CONPRI
driven O
by O
solidification S-CONPRI
mainly O
ruled O
by O
convection O
and O
radiation S-MANP
during O
their O
flight O
in O
the O
inert O
atmosphere O
of O
the O
process S-CONPRI
chamber O
. O


Long O
production S-MANP
times O
, O
the O
associated O
high O
costs O
of O
the O
products O
and O
product O
size O
limitations O
belong O
among O
current O
issues O
of O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
technology S-CONPRI
. O


Hybrid O
products O
containing O
small O
and O
complex-shaped S-CONPRI
parts O
deposited O
by O
SLM S-MANP
on O
the O
forged O
, O
rolled O
or O
hot O
stamped O
semi-products O
could O
offer O
a O
practical O
solution S-CONPRI
to O
these O
limitations O
. O


Cylindrical S-CONPRI
hybrid O
parts O
were O
additively B-MANP
manufactured E-MANP
by O
depositing O
18Ni300 O
maraging B-MATE
steel E-MATE
on O
the O
cylindrical S-CONPRI
semi-products O
of O
CMnAlNb O
low-alloy O
advanced O
high O
strength S-PRO
steel S-MATE
( O
AHSS O
) O
. O


The O
AHSS O
was O
used O
either O
in O
forged O
and O
air O
cooled O
condition O
or O
after O
heat B-MANP
treatments E-MANP
typically O
used O
for O
inducing O
the O
TRIP O
( O
transformation O
induced O
plasticity S-PRO
) O
effect O
. O


Various O
post-build O
heat B-MANP
treatments E-MANP
of O
the O
hybrid O
parts O
were O
performed O
. O


The O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
hybrid O
parts O
were O
determined O
by O
hardness S-PRO
measurement O
across O
the O
interface S-CONPRI
and O
by O
a O
tensile B-CHAR
test E-CHAR
of O
the O
dissimilar O
joints O
. O


All O
tensile S-PRO
samples S-CONPRI
fractured O
in O
the O
high-strength O
steel S-MATE
side O
, O
several O
millimetres O
from O
the O
interface S-CONPRI
. O


Microstructure S-CONPRI
analysis O
of O
both O
materials S-CONPRI
and O
the O
interface S-CONPRI
region O
was O
carried O
out O
using O
light O
and O
scanning B-MACEQ
electron I-MACEQ
microscopes E-MACEQ
. O


The O
hybrid O
parts O
had O
the O
ultimate B-PRO
tensile I-PRO
strengths E-PRO
of O
840−940 O
MPa S-CONPRI
, O
with O
total O
elongations O
of O
12–19 O
% O
. O


The O
best O
combination O
of O
tensile B-PRO
strength E-PRO
and O
elongation S-PRO
was O
obtained O
with O
two-step O
heat B-MANP
treatment E-MANP
of O
the O
TRIP B-MATE
steel E-MATE
prior O
to O
additive B-MANP
manufacturing E-MANP
with O
no O
post-build O
heat B-MANP
treatment E-MANP
of O
the O
hybrid O
part O
. O


In O
this O
paper O
, O
the O
potential O
of O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
of O
stainless B-MATE
steel E-MATE
CL S-CHAR
20ES O
powder S-MATE
was O
investigated O
with O
a O
focus O
on O
controlled O
fabrication S-MANP
of O
porous S-PRO
structures O
with O
strongly O
reduced O
pore B-PARA
sizes E-PARA
, O
i.e O
. O


feature B-PARA
sizes E-PARA
significantly O
below O
conventional O
minimum O
SLM S-MANP
feature B-PARA
sizes E-PARA
. O


By O
controlling O
laser B-ENAT
scan E-ENAT
properties O
interacting O
with O
the O
powder B-MACEQ
bed E-MACEQ
directly O
, O
porous S-PRO
structures O
can O
be S-MATE
generated O
by O
selectively O
sintering S-MANP
powder B-MATE
particles E-MATE
. O


A O
wide O
range S-PARA
of O
porous S-PRO
samples O
was O
manufactured S-CONPRI
following O
this O
strategy O
, O
aiming O
to O
increase O
porosity S-PRO
while O
keeping O
pore B-PARA
sizes E-PARA
low O
. O


The O
effect O
of O
process B-CONPRI
parameters E-CONPRI
, O
including O
laser B-PARA
power E-PARA
and O
focal O
point O
positioning O
, O
was O
evaluated O
for O
a O
fibre B-CONPRI
laser E-CONPRI
operated O
in O
pulsed O
wave O
( O
PW O
) O
emission S-CHAR
mode O
. O


The O
first O
part O
of O
this O
study O
focuses O
on O
characterization O
of O
key O
porous S-PRO
structure O
properties S-CONPRI
, O
i.e. O
, O
porosity S-PRO
, O
average S-CONPRI
mass O
density S-PRO
, O
average S-CONPRI
pore O
sizes O
and O
structures O
at O
microscopic O
scales O
. O


The O
second O
part O
deals O
with O
the O
influence O
of O
porosity S-PRO
and O
pore B-PARA
sizes E-PARA
on O
thermal O
and O
fluid B-PRO
properties E-PRO
, O
i.e. O
, O
the O
effective B-PARA
thermal I-PARA
conductivity E-PARA
( O
ETC O
) O
and O
wettability S-CONPRI
. O


We O
have O
quantified O
the O
directional O
dependence O
( O
build B-PARA
direction E-PARA
plane O
and O
scan O
direction O
plane O
) O
off O
the O
structural O
and O
thermophysical O
properties S-CONPRI
of O
porous S-PRO
structures O
. O


For O
a O
range S-PARA
of O
porosities S-PRO
and O
pore B-PARA
sizes E-PARA
, O
we O
have O
observed O
that O
porosity S-PRO
and O
surface B-CHAR
morphology E-CHAR
influence O
the O
thermal B-CONPRI
properties E-CONPRI
and O
contact S-APPL
angle O
of O
droplets S-CONPRI
on O
the O
printed O
surface S-CONPRI
. O


Thermal B-PRO
conductivity E-PRO
was O
measured O
and O
the O
associated O
analysis O
was O
compared O
with O
available O
models O
and O
correlations O
in O
literature O
. O


The O
average S-CONPRI
thermal O
conductivity S-PRO
of O
fabricated S-CONPRI
porous O
structures O
was O
determined O
between O
6-14 O
W/m·K O
and O
found O
to O
be S-MATE
a O
function O
of O
porosity S-PRO
. O


Furthermore O
, O
the O
capillary O
wicking O
performance S-CONPRI
of O
additively B-MANP
manufactured E-MANP
stainless O
steel S-MATE
porous S-PRO
structures O
having O
an O
average S-CONPRI
pore O
radius O
from O
9 O
to O
23 O
µm O
was O
determined O
. O


Typically O
, O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
are O
limited O
to O
a O
single O
material S-MATE
per O
build S-PARA
while O
many O
products O
benefit O
from O
the O
integration O
of O
multiple O
materials S-CONPRI
with O
varied O
properties S-CONPRI
. O


To O
achieve O
the O
benefits O
of O
multiple O
materials S-CONPRI
, O
the O
geometric B-CONPRI
freedom E-CONPRI
of O
AM S-MANP
could O
be S-MATE
used O
to O
build S-PARA
internal O
structures O
that O
emulate O
a O
range S-PARA
of O
different O
material B-CONPRI
properties E-CONPRI
such O
as S-MATE
stiffness O
, O
Poisson O
’ O
s S-MATE
ratio O
, O
and O
elastic S-PRO
limit O
using O
only O
a O
single O
build B-MATE
material E-MATE
. O


This O
paper O
examines O
a O
wide O
range S-PARA
of O
properties S-CONPRI
that O
can O
be S-MATE
achieved O
using O
diamond S-MATE
lattice O
structures O
manufactured S-CONPRI
from O
Nylon S-MATE
12 O
with O
a O
commercial O
laser B-MANP
sintering E-MANP
( O
LS O
) O
process S-CONPRI
. O


Stiffness S-PRO
and O
energy B-CHAR
absorption E-CHAR
were O
measured O
for O
all O
lattices S-CONPRI
and O
the O
stiffness S-PRO
response O
was O
compared O
to O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
( O
FEA O
) O
. O


Simulation S-ENAT
shows O
agreement O
with O
experimental S-CONPRI
results O
over O
a O
stiffness S-PRO
range S-PARA
of O
four O
orders O
of O
magnitude S-PARA
once O
a O
correction O
factor O
is O
applied O
. O


Experimental S-CONPRI
results O
also O
show O
a O
wide O
range S-PARA
of O
energy B-CHAR
absorption E-CHAR
for O
diamond S-MATE
lattice O
structures O
and O
a O
significant O
increase O
in O
the O
effective O
elastic S-PRO
limit O
of O
the O
build B-MATE
material E-MATE
, O
which O
compensates O
for O
the O
low O
ductility S-PRO
of O
many O
AM B-MATE
materials E-MATE
. O


The O
elastic S-PRO
limit O
decreases O
with O
an O
increasing O
t/L O
ratio O
meanwhile O
the O
degradation S-CONPRI
under O
cyclic B-PRO
loading E-PRO
is O
relatively O
independent O
of O
the O
t/L O
ratio O
. O


Extrapolating O
this O
data S-CONPRI
into O
lattice B-FEAT
structures E-FEAT
made O
from O
metal S-MATE
, O
these O
same O
structures O
could O
mimic S-MACEQ
a O
wide O
range S-PARA
of O
“ O
fully O
” O
dense B-FEAT
and I-FEAT
porous E-FEAT
materials O
with O
just O
the O
use O
of O
a O
single O
material S-MATE
. O


Since O
the O
diamond S-MATE
lattice O
is O
a O
cellular B-FEAT
structure E-FEAT
, O
the O
voids S-CONPRI
can O
also O
be S-MATE
filled O
with O
other O
materials S-CONPRI
or O
structures O
to O
add O
secondary O
control O
of O
embedded O
functions O
such O
as S-MATE
energy O
storage O
and O
sensing S-APPL
. O


Laser S-ENAT
wire O
deposits O
using O
Alloy S-MATE
625 O
modified O
with O
0.4 O
wt O
% O
B S-MATE
were O
manufactured S-CONPRI
on O
stainless B-MATE
steel E-MATE
304 O
substrates O
. O


A O
layer S-PARA
boundary S-FEAT
with O
a O
thickness O
of O
around O
250 O
μm O
was O
formed O
between O
the O
layer S-PARA
cores S-MACEQ
during O
deposition S-CONPRI
. O


Results O
show O
that O
the O
solidification S-CONPRI
features O
in O
the O
layer S-PARA
boundary S-FEAT
were O
coarser O
than O
the O
layer S-PARA
core S-MACEQ
due O
to O
the O
recalescence O
mechanism S-CONPRI
. O


Continuous O
eutectics O
were O
observed O
segregating O
the O
inter-dendritic O
regions O
in O
both O
the O
layer S-PARA
boundary S-FEAT
and O
the O
layer S-PARA
core S-MACEQ
. O


The O
eutectics O
consisted O
of O
mainly O
Laves B-CONPRI
phase E-CONPRI
with O
a O
small O
amount O
of O
NbC O
precipitates S-MATE
. O


Solidification S-CONPRI
front O
velocities O
( O
SFV O
) O
were O
calculated O
from O
the O
Kurz-Giovanola-Trivedi O
( O
KGT O
) O
model S-CONPRI
. O


Results O
showed O
that O
they O
developed O
in O
the O
layer S-PARA
boundary S-FEAT
and O
in O
the O
layer S-PARA
core S-MACEQ
at O
0.06 O
m/s O
and O
0.1 O
m/s O
respectively O
. O


Electron O
backscattered O
diffraction S-CHAR
( O
EBSD S-CHAR
) O
mapping O
revealed O
that O
small O
equiaxed B-CONPRI
grains E-CONPRI
nucleated O
in O
the O
layer S-PARA
boundary S-FEAT
, O
while O
large O
columnar B-PRO
grains E-PRO
were O
prevalent O
in O
the O
layer S-PARA
core S-MACEQ
. O


The O
columnar O
to O
equiaxed O
transition S-CONPRI
( O
CET O
) O
model S-CONPRI
developed O
by O
Hunts O
was O
considered O
and O
the O
results O
were O
in O
good O
agreement O
with O
the O
observed O
grain S-CONPRI
morphologies O
. O


Metallization S-MANP
has O
been O
widely O
used O
to O
enhance O
the O
aesthetics O
and O
performance S-CONPRI
of O
injection O
molded O
plastic S-MATE
parts O
, O
but O
the O
techniques O
have O
not O
been O
widely O
extended O
to O
3D B-APPL
printed I-APPL
parts E-APPL
due O
to O
intrinsic O
differences O
in O
surface S-CONPRI
chemistry S-CONPRI
and O
morphology S-CONPRI
. O


Here O
, O
we O
investigate O
direct O
metallization S-MANP
of O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
3D B-MANP
printed E-MANP
thermoplastic O
parts O
using O
low O
cost O
environmentally O
benign O
surface B-MANP
preparations E-MANP
and O
physical B-MANP
vapor I-MANP
deposition E-MANP
( O
PVD S-MANP
) O
to O
avoid O
the O
use O
of O
preparation O
with O
toxic O
chromic O
acid O
. O


Fourier B-ENAT
transform I-ENAT
infrared E-ENAT
( O
FTIR S-CHAR
) O
spectra O
are O
gathered O
for O
each O
surface B-MANP
preparation E-MANP
method O
prior O
to O
metallization S-MANP
. O


The O
metallized O
parts O
are O
then O
characterized O
for O
thin O
film O
adhesion S-PRO
, O
electrical B-CHAR
resistivity E-CHAR
, O
and O
optical S-CHAR
reflectivity O
. O


Additionally O
, O
each O
part O
is O
imaged O
using O
a O
scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
( O
SEM S-CHAR
) O
post-metallization O
. O


The O
results O
show O
that O
surface B-MANP
preparation E-MANP
with O
solvent O
results O
in O
a O
smooth O
and O
aesthetically O
pleasing O
surface S-CONPRI
, O
but O
metallic S-MATE
film O
adhesion S-PRO
is O
poor O
. O


Conversely O
, O
when O
2000 O
grit O
sandpaper S-MATE
is O
used O
to O
mechanically O
prepare O
the O
surfaces S-CONPRI
, O
the O
resulting O
films O
have O
poor O
electrical B-PRO
conductivity E-PRO
and O
optical S-CHAR
reflectance O
, O
but O
excellent O
adhesion S-PRO
. O


Atmospheric O
plasma S-CONPRI
treatment O
of O
the O
parts O
results O
in O
the O
highest O
overall O
performance S-CONPRI
, O
with O
superior O
adhesion S-PRO
strength O
and O
optical S-CHAR
reflectivity O
and O
low O
electrical B-CHAR
resistivity E-CHAR
. O


Electron B-CHAR
microscopy E-CHAR
and O
FTIR S-CHAR
reveal O
that O
the O
high O
adhesion S-PRO
resulting O
from O
atmospheric O
plasma S-CONPRI
is O
caused O
by O
modification O
surface B-CHAR
morphology E-CHAR
, O
but O
not O
surface S-CONPRI
chemical O
termination O
. O


The O
results O
indicate O
that O
direct O
metallization S-MANP
of O
3D B-MANP
printed E-MANP
ABS O
is O
a O
viable O
method O
for O
creating O
metallized O
parts O
with O
high O
performance S-CONPRI
and O
an O
aesthetically O
pleasing O
appearance O
and O
that O
the O
use O
of O
chromic O
acid O
in O
surface B-MANP
preparation E-MANP
is O
not O
necessary O
. O


The O
development O
and O
growth O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
have O
made O
the O
optimization S-CONPRI
of O
surface B-PARA
quality E-PARA
and O
properties S-CONPRI
of O
AM S-MANP
components O
critical O
. O


Laser S-ENAT
polishing O
represents O
a O
recent O
and O
novel O
application O
of O
laser S-ENAT
surface O
irradiation S-MANP
that O
can O
be S-MATE
used O
for O
precise O
, O
post-process S-CONPRI
smoothing O
of O
the O
rough O
surfaces S-CONPRI
commonly O
encountered O
on O
AM B-MACEQ
parts E-MACEQ
. O


Austenitic B-MATE
stainless I-MATE
steels E-MATE
are O
an O
important O
class O
of O
alloys S-MATE
frequently O
used O
in O
biomedical B-APPL
applications E-APPL
due O
to O
their O
corrosion B-CONPRI
resistance E-CONPRI
. O


Due O
to O
this O
, O
corrosion B-CONPRI
resistance E-CONPRI
advancements O
and O
improved O
bio-response O
to O
stainless B-MATE
steels E-MATE
are O
long-term O
active O
areas S-PARA
of O
research S-CONPRI
. O


In O
this O
study O
, O
the O
influence O
of O
laser S-ENAT
polishing O
on O
surface B-MANP
modification E-MANP
and O
corrosion B-PRO
behavior E-PRO
of O
additively B-MANP
manufactured E-MANP
316L O
has O
been O
investigated O
. O


Laser S-ENAT
scanning O
speed O
and O
number O
of O
passes O
were O
varied O
to O
evaluate O
their O
effect O
on O
the O
surface B-PARA
quality E-PARA
and O
corrosion B-CONPRI
resistance E-CONPRI
of O
the O
experimental S-CONPRI
samples O
. O


The O
results O
indicated O
that O
laser S-ENAT
polishing O
could O
enable O
reductions O
in O
surface B-PRO
roughness E-PRO
of O
over O
92 O
% O
( O
from O
4.75 O
μm O
to O
0.49 O
μm O
Sa O
) O
while O
also O
incorporating O
partially O
melted S-CONPRI
powders O
originally O
on O
the O
as-printed O
surface S-CONPRI
layer S-PARA
. O


The O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
results O
indicated O
that O
there O
was O
no O
considerable O
phase S-CONPRI
change O
after O
laser S-ENAT
polishing O
. O


Laser S-ENAT
polishing O
was O
observed O
to O
refine O
the O
columnar O
structure S-CONPRI
within O
the O
as-printed O
sample S-CONPRI
into O
a O
fine O
cellular B-FEAT
structure E-FEAT
. O


Additionally O
, O
the O
sub-surface O
microhardness S-CONPRI
of O
the O
laser S-ENAT
remelted O
layer S-PARA
increased O
from O
1.82 O
GPa S-PRO
to O
2.89 O
GPa S-PRO
. O


Moreover O
, O
the O
laser S-ENAT
polished O
samples S-CONPRI
exhibited O
greater O
corrosion B-CONPRI
resistance E-CONPRI
, O
which O
was O
believed O
to O
be S-MATE
due O
to O
a O
combination O
of O
a O
decrease O
in O
surface B-PRO
roughness E-PRO
and O
grain B-CHAR
refinement E-CHAR
. O


These O
results O
show O
that O
laser S-ENAT
polishing O
can O
improve O
the O
corrosion B-CONPRI
resistance E-CONPRI
of O
additive B-MANP
manufactured E-MANP
stainless O
steel S-MATE
while O
also O
decreasing O
surface B-PRO
roughness E-PRO
and O
increasing O
surface S-CONPRI
microhardness S-CONPRI
. O


Due O
to O
those O
enhancements O
, O
it O
represents O
a O
suitable O
multifaceted O
process S-CONPRI
for O
finishing S-MANP
additive B-APPL
manufactured I-APPL
parts E-APPL
. O


When O
it O
is O
difficult O
to O
deposit O
a O
material S-MATE
A O
on O
a O
material S-MATE
B S-MATE
, O
it O
is O
possible O
to O
create O
a O
Functionally B-MATE
Graded I-MATE
Material E-MATE
( O
FGM S-MANP
) O
using O
a O
buffer S-CONPRI
material O
between O
them O
to O
avoid O
the O
appearance O
of O
defects S-CONPRI
. O


The O
literature O
shows O
that O
it O
is O
very O
difficult O
, O
nay O
impossible O
, O
to O
have O
an O
efficient O
metallurgical B-CONPRI
bond E-CONPRI
between O
Ti6Al4V S-MATE
and O
Inconel-Mo O
alloys S-MATE
without O
cracks O
, O
porosities S-PRO
or O
delamination S-CONPRI
. O


Moreover O
, O
the O
understanding O
of O
the O
phenomena O
taking O
place O
at O
the O
interface S-CONPRI
allows O
the O
preservation O
of O
the O
structural B-PRO
integrity E-PRO
of O
a O
FGM S-MANP
made O
by O
additive B-MANP
manufacturing E-MANP
. O


CLAD® O
powder-based O
directed B-MANP
energy I-MANP
deposition E-MANP
allows O
the O
building B-CHAR
of I-CHAR
parts E-CHAR
containing O
FGM S-MANP
and/or O
buffer S-CONPRI
materials O
directly O
during O
the O
process S-CONPRI
. O


In O
this O
paper O
, O
the O
first O
interface S-CONPRI
100 O
Ti6Al4V S-MATE
/ O
25 O
Ti6Al4V S-MATE
– O
75 O
Mo S-MATE
( O
in O
wt O
% O
) O
is O
smooth O
, O
suggesting O
that O
there O
has O
been O
diffusion S-CONPRI
between O
both O
alloys S-MATE
. O


The O
second O
one O
, O
25 O
Ti6Al4V S-MATE
– O
75 O
Mo S-MATE
/ O
30 O
Inconel B-MATE
718 E-MATE
– O
70 O
Mo S-MATE
, O
contains O
numerous O
exotic O
structures O
between O
both O
alloys S-MATE
. O


Thus O
, O
EDS S-CHAR
, O
TKD O
and O
X-ray S-CHAR
crystallography S-MANP
were O
performed O
right O
on O
this O
interface S-CONPRI
and O
revealed O
three O
main O
structures O
: O
a O
hexagonal S-FEAT
matrix O
, O
a O
cubic B-FEAT
structure E-FEAT
and O
an O
ordered O
hexagonal S-FEAT
one O
. O


The O
hexagonal S-FEAT
matrix O
appears O
to O
consist O
of O
Ni3Ti O
and O
the O
ordered O
hexagonal S-FEAT
one O
of O
NiMo O
. O


Ultrasonic B-MANP
welding E-MANP
is O
a O
solid-state S-CONPRI
joining S-MANP
process O
which O
uses O
ultrasonic B-PARA
vibration E-PARA
to O
join O
materials S-CONPRI
at O
relatively O
low O
temperatures S-PARA
. O


Ultrasonic O
powder S-MATE
consolidation S-CONPRI
is O
a O
derivative O
of O
the O
ultrasonic O
additive S-MATE
process O
which O
consolidates O
powder B-MATE
material E-MATE
into O
a O
dense O
solid O
block O
without O
melting S-MANP
. O


During O
ultrasonic O
powder S-MATE
consolidation S-CONPRI
process O
, O
metal B-MATE
powder E-MATE
under O
a O
compressive O
load O
is O
subjected O
to O
transverse O
ultrasonic B-PARA
vibrations E-PARA
resulting O
in O
a O
fully-dense O
consolidated O
product O
. O


While O
ultrasonic O
powder S-MATE
consolidation S-CONPRI
process O
is O
employed O
in O
a O
wide O
variety O
of O
manufacturing B-MANP
processes E-MANP
, O
bonding B-CHAR
mechanism E-CHAR
of O
powder B-MATE
particles E-MATE
during O
the O
consolidation S-CONPRI
process O
is O
not O
clearly O
understood O
. O


This O
study O
uses O
a O
coupled O
thermo-mechanical S-CONPRI
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
technique O
to O
understand O
the O
underlying O
bonding B-CHAR
mechanism E-CHAR
involved O
in O
ultrasonic O
powder S-MATE
consolidation S-CONPRI
process O
. O


The O
study O
also O
investigates S-CONPRI
the O
effect O
of O
critical O
process B-CONPRI
parameters E-CONPRI
including O
vibrational O
amplitude O
and O
base O
temperature S-PARA
on O
the O
stress S-PRO
, O
strain S-PRO
, O
and O
particle S-CONPRI
temperature O
distribution S-CONPRI
during O
this O
process S-CONPRI
. O


Based O
on O
the O
results O
of O
the O
simulation S-ENAT
, O
a O
possible O
theory O
on O
the O
bonding B-CHAR
mechanism E-CHAR
involved O
in O
ultrasonic O
powder S-MATE
consolidation S-CONPRI
process O
is O
proposed O
. O


The O
outcomes O
of O
this O
study O
can O
be S-MATE
used O
to O
further O
the O
industrial S-APPL
applications O
of O
ultrasonic O
powder S-MATE
consolidation S-CONPRI
process O
as S-MATE
well O
as S-MATE
other O
ultrasonic B-MANP
welding E-MANP
based O
processes S-CONPRI
. O


Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
has O
significantly O
increased O
the O
design B-CONPRI
freedom E-CONPRI
available O
for O
metal S-MATE
parts O
and O
provides O
significant O
flexibility S-PRO
within O
each O
build S-PARA
to O
produce O
multiple O
components S-MACEQ
of O
varying O
size O
and O
shape O
. O


In O
order O
to O
obtain O
the O
highest O
build S-PARA
efficiency O
, O
it O
is O
ideal O
to O
print S-MANP
multiple O
parts O
together O
spanning O
the O
entire O
plate O
with O
as S-MATE
little O
spacing O
as S-MATE
possible O
between O
the O
parts O
. O


Work O
has O
been O
performed O
to O
characterize O
the O
variance O
of O
materials S-CONPRI
properties O
as S-MATE
a O
function O
of O
location O
within O
the O
build B-PARA
volume E-PARA
as S-MATE
well O
as S-MATE
component O
density S-PRO
on O
the O
build B-MACEQ
plate E-MACEQ
. O


This O
work O
utilizes O
mechanical S-APPL
, O
chemical O
, O
and O
microstructural B-CHAR
analysis E-CHAR
techniques O
to O
expand O
on O
previous O
work O
by O
statistically O
evaluating O
the O
impact S-CONPRI
of O
build S-PARA
location O
, O
and O
nearest O
neighbor O
proximity O
on O
tensile S-PRO
performance S-CONPRI
in O
Electron B-CONPRI
Beam E-CONPRI
Melted O
( O
EBM S-MANP
) O
Ti-6Al-4 O
V. O
Mechanical S-APPL
results O
are O
then O
correlated S-CONPRI
to O
structural O
phenomenon O
and O
the O
effectiveness S-CONPRI
of O
various O
strengthening B-CONPRI
mechanisms E-CONPRI
are O
determined O
. O


Results O
show O
that O
properties S-CONPRI
span O
a O
small O
range S-PARA
regardless O
of O
build S-PARA
design O
and O
that O
interstitial O
strengthening S-MANP
and O
lath O
spacing O
are O
the O
driving O
factors O
for O
mechanical B-PRO
strength E-PRO
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
are O
used O
in O
three O
dimensional O
( O
3D S-CONPRI
) O
printing O
of O
parts O
using O
thermo-plastic O
extruders O
, O
or O
laser S-ENAT
and O
electron B-CONPRI
beam E-CONPRI
based O
metal B-CONPRI
deposition E-CONPRI
methods O
. O


This O
paper O
presents O
an O
integrated O
methodology S-CONPRI
for O
planning S-MANP
of O
tangential O
path O
velocity O
, O
material S-MATE
deposition B-PARA
rate E-PARA
and O
temperature S-PARA
control O
of O
the O
extruded S-MANP
material O
which O
is O
deposited O
along O
curved O
paths O
. O


The O
tangential O
velocity O
along O
the O
path O
is O
smoothed O
and O
optimized O
while O
respecting O
the O
heater O
’ O
s S-MATE
and O
extruder S-MACEQ
’ O
s S-MATE
capacities O
, O
as S-MATE
well O
as S-MATE
the O
feed S-PARA
drives O
’ O
jerk O
, O
acceleration O
and O
velocity O
limits S-CONPRI
. O


The O
extrusion B-PARA
rate E-PARA
is O
controlled O
proportional O
to O
the O
tangential O
path O
velocity O
while O
keeping O
the O
temperature S-PARA
of O
the O
deposited O
thermo-plastic O
material S-MATE
at O
the O
desired O
temperature S-PARA
by O
adaptively O
controlling O
current O
supply O
to O
the O
heater O
. O


The O
experimentally O
proven O
algorithm S-CONPRI
leads O
to O
more O
uniform O
material S-MATE
deposition S-CONPRI
at O
sharp O
curvatures O
and O
resulting O
improved O
dimensional B-CHAR
accuracy E-CHAR
of O
printed O
parts O
. O


The O
proposed O
methodology S-CONPRI
can O
be S-MATE
extended O
to O
laser S-ENAT
and O
electron B-CONPRI
beam E-CONPRI
based O
metal S-MATE
printing O
applications O
. O


Directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
processes S-CONPRI
frequently O
rely O
on O
metallic B-MATE
powder E-MATE
and O
wire B-MATE
feedstock I-MATE
materials E-MATE
. O


Several O
grades O
of O
metallic S-MATE
strips O
are O
, O
however O
, O
commercially O
available O
but O
not O
yet O
largely O
utilized O
in O
DED S-MANP
. O


This O
paper O
introduces O
a O
newly O
developed O
laser S-ENAT
strip O
cladding S-MANP
process O
, O
which O
can O
be S-MATE
used O
for O
surfacing O
, O
repair O
and O
additive B-MANP
manufacturing E-MANP
. O


Cladding S-MANP
tests O
consisted O
of O
single-layer O
single- O
and O
multi-bead O
tests O
on O
planar O
and O
round O
bar O
type O
base O
materials S-CONPRI
using O
a O
30 O
mm S-MANP
wide O
solid O
Alloy S-MATE
625 O
strip O
. O


The O
results O
showed O
that O
with O
8 O
kW O
laser B-PARA
power E-PARA
34 O
mm S-MANP
wide O
and O
˜2 O
mm S-MANP
thick O
single O
beads S-CHAR
on O
steel S-MATE
could O
be S-MATE
produced O
with O
low O
dilution O
and O
fusion S-CONPRI
bond O
with O
high O
deposition S-CONPRI
( O
8 O
kg/h O
) O
rates O
. O


Corrosion S-CONPRI
performance O
of O
clad O
deposit O
was O
influenced O
by O
the O
inhomogeneous O
distribution S-CONPRI
of O
intermixed O
iron S-MATE
from O
the O
base O
material S-MATE
on O
a O
test O
surface S-CONPRI
. O


In O
addition O
to O
high O
productivity S-CONPRI
, O
the O
developed O
process S-CONPRI
takes O
advantage O
of O
large O
build B-PARA
volume E-PARA
( O
> O
1 O
m3 O
) O
and O
full O
material B-CHAR
utilization E-CHAR
as S-MATE
well O
as S-MATE
clean O
process S-CONPRI
conditions O
. O


Additive B-MANP
manufacturing E-MANP
has O
the O
potential O
to O
revolutionize O
the O
production S-MANP
of O
metallic S-MATE
components S-MACEQ
as S-MATE
it O
yields O
near B-MANP
net I-MANP
shape E-MANP
parts O
with O
complex B-CONPRI
geometries E-CONPRI
and O
minimizes O
waste O
. O


At O
the O
present O
day O
, O
additively B-MANP
manufactured E-MANP
components O
face S-CONPRI
qualification O
and O
certification O
challenges O
due O
to O
the O
difficulty O
in O
controlling O
defects S-CONPRI
. O


This O
has O
driven O
a O
significant O
research S-CONPRI
effort O
aimed O
at O
better O
understanding O
and O
improving O
processing O
controls O
– O
yielding O
a O
plethora O
of O
in-situ S-CONPRI
measurements O
aimed O
at O
correlating O
defects S-CONPRI
with O
material S-MATE
quality O
metrics O
of O
interest O
. O


In O
this O
work O
, O
we O
develop O
machine-learning O
methods O
to O
learn O
correlations O
between O
thermal O
history O
and O
subsurface O
porosity S-PRO
for O
a O
variety O
of O
print S-MANP
conditions O
in O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
. O


Un-normalized O
surface S-CONPRI
temperatures O
( O
in O
the O
form O
of O
black-body O
radiances O
) O
are O
obtained O
using O
high-speed O
infrared S-CONPRI
imaging S-APPL
and O
porosity S-PRO
formation O
is O
observed O
in O
the O
sample S-CONPRI
cross-section O
through O
synchrotron S-ENAT
x-ray O
imaging S-APPL
. O


To O
demonstrate O
the O
predictive O
power S-PARA
of O
these O
features O
, O
we O
present O
four O
statistical O
machine-learning O
models O
that O
correlate O
temperature S-PARA
histories O
to O
subsurface O
porosity S-PRO
formation O
in O
laser S-ENAT
fused S-CONPRI
Ti-6Al-4V O
powder S-MATE
. O


The O
aircraft O
engine O
industry S-APPL
manufactures O
many O
ring-like O
metal S-MATE
parts O
of O
large O
diameter S-CONPRI
but O
small O
cross-sectional O
area S-PARA
. O


Designers O
of O
these O
parts O
require O
increasingly O
complex B-CONPRI
geometries E-CONPRI
for O
improved O
aerodynamic O
efficiency O
and O
cooling S-MANP
while O
manufacturers O
of O
these O
parts O
require O
larger O
and O
faster O
equipment S-MACEQ
for O
high O
productivity S-CONPRI
and O
low O
cost O
. O


The O
combination O
of O
these O
industrial S-APPL
requirements O
inspired O
the O
development O
of O
a O
new O
Direct B-MANP
Metal I-MANP
Laser I-MANP
Melting E-MANP
( O
DMLM S-MANP
) O
architecture S-APPL
, O
reported O
here O
, O
which O
incorporates O
a O
rotating O
powder B-MACEQ
bed E-MACEQ
. O


The O
system O
coordinates S-PARA
the O
rotational O
motion O
of O
the O
powder B-MACEQ
bed E-MACEQ
with O
an O
ascending O
laser S-ENAT
scanner O
and O
recoater O
to O
build S-PARA
parts O
in O
a O
helical O
fashion S-CONPRI
. O


A O
single-point O
powder S-MATE
feeder S-MACEQ
delivers O
metal B-MATE
powder E-MATE
near O
the O
inner O
radius O
of O
an O
annular O
build B-PARA
volume E-PARA
, O
and O
a O
recoater O
spreads O
the O
powder S-MATE
to O
the O
outer O
radius O
in O
a O
“ O
snow O
plow O
” O
fashion S-CONPRI
. O


Encoder S-MACEQ
feedback O
from O
both O
the O
rotational O
stage O
and O
the O
galvanometers O
assures O
accuracy S-CHAR
of O
the O
laser B-ENAT
scan E-ENAT
path O
. O


Build B-CHAR
rates E-CHAR
were O
shown O
to O
triple O
conventional O
DMLM S-MANP
systems O
while O
powder S-MATE
requirements O
were O
decreased O
by O
more O
than O
4x O
. O


The O
production S-MANP
of O
magnesium B-MATE
alloy E-MATE
WE43 O
was O
achieved O
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
. O


The O
alloy S-MATE
was O
investigated O
after O
SLM S-MANP
, O
hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
, O
and O
solutionising O
heat B-MANP
treatment E-MANP
. O


The O
microstructure S-CONPRI
and O
corrosion S-CONPRI
behaviour O
of O
the O
specimens O
were O
carefully O
characterised O
, O
whilst O
assessed O
and O
contrast O
relative O
to O
the O
conventionally O
cast S-MANP
alloy S-MATE
counterpart O
. O


The O
SLM S-MANP
prepared O
specimens O
possess O
a O
unique O
microstructure S-CONPRI
comprising O
fine O
grains S-CONPRI
growing O
with O
a O
strong O
[ O
0001 O
] O
texture S-FEAT
along O
the O
building B-PARA
direction E-PARA
with O
a O
low O
fraction S-CONPRI
of O
process-induced O
and O
metallurgical S-APPL
defects S-CONPRI
, O
reaching O
< O
0.1 O
% O
, O
after O
optimising O
the O
SLM S-MANP
parameters S-CONPRI
and O
the O
HIP S-MANP
treatment O
. O


Electrochemical B-CHAR
measurements E-CHAR
demonstrated O
that O
the O
SLM S-MANP
prepared O
WE43 O
is O
cathodically O
more O
active O
as S-MATE
compared O
with O
its O
cast S-MANP
counterpart O
. O


It O
is O
proposed O
that O
this O
behaviour O
is O
due O
to O
a O
high O
density S-PRO
of O
zirconium-rich O
oxide S-MATE
particles O
uniformly O
distributed O
throughout O
the O
alloy S-MATE
microstructure O
as S-MATE
well O
as S-MATE
the O
alterations O
in O
the O
chemical B-CONPRI
composition E-CONPRI
of O
the O
solid-solution O
matrix O
originating O
from O
the O
high O
cooling B-PARA
rates E-PARA
of O
SLM S-MANP
. O


It O
was O
also O
noted O
that O
the O
oxide S-MATE
particles O
are O
mainly O
sourced O
by O
powder S-MATE
. O


The O
present O
results O
suggest O
that O
the O
corrosion S-CONPRI
of O
SLM S-MANP
prepared O
Mg B-MATE
alloys E-MATE
could O
be S-MATE
greatly O
improved O
once O
the O
influence O
of O
powder S-MATE
characteristics O
is O
further O
understood O
and O
controlled O
. O


A O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
thermomechanical S-CONPRI
coupled O
model S-CONPRI
for O
Laser S-ENAT
Solid O
Forming S-MANP
( O
LSF O
) O
of O
Ti-6Al-4V B-MATE
alloy E-MATE
has O
been O
calibrated S-CONPRI
through O
experiments O
of O
40-layers O
metal B-CONPRI
deposition E-CONPRI
using O
different O
scanning B-CONPRI
strategies E-CONPRI
. O


The O
sensitivity B-CONPRI
analysis E-CONPRI
of O
the O
mechanical S-APPL
parameters O
shows O
that O
the O
thermal B-PRO
expansion I-PRO
coefficient E-PRO
as S-MATE
well O
as S-MATE
the O
elastic S-PRO
limit O
of O
Ti-6Al-4V S-MATE
have O
a O
great O
impact S-CONPRI
on O
the O
mechanical S-APPL
behavior O
. O


Using O
the O
validated O
model S-CONPRI
and O
optimal O
mechanical S-APPL
parameters O
, O
the O
evolution S-CONPRI
of O
thermo-mechanical S-CONPRI
fields O
in O
LSF O
has O
been O
analyzed O
. O


It O
has O
been O
found O
that O
the O
stresses O
and O
distortions O
develop O
in O
two O
stages O
, O
after O
the O
deposition S-CONPRI
of O
the O
first O
layer S-PARA
and O
during O
the O
cooling S-MANP
phase O
after O
the O
manufacturing S-MANP
of O
the O
component S-MACEQ
. O


The O
cooling S-MANP
phase O
is O
the O
responsible O
of O
70 O
% O
of O
the O
residual B-PRO
stresses E-PRO
and O
60 O
% O
of O
the O
total O
distortions O
. O


The O
analyses O
indicate O
that O
by O
controlling O
the O
initial O
substrate S-MATE
temperature O
( O
pre-heating O
phase S-CONPRI
) O
and O
the O
final O
cooling S-MANP
phase O
it O
is O
possible O
to O
mitigate O
both O
distortion S-CONPRI
and O
residual B-PRO
stresses E-PRO
. O


The O
results O
show O
that O
increasing O
the O
pre-heating O
temperature S-PARA
of O
the O
substrate S-MATE
is O
the O
most O
effective O
way O
to O
reduce O
the O
distortions O
and O
residual B-PRO
stresses E-PRO
in O
Additive B-MANP
Manufacturing E-MANP
. O


A O
novel O
method O
that O
combines O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
and O
atomic B-MANP
layer I-MANP
deposition E-MANP
( O
ALD O
) O
. O


Space-grading O
plastic S-MATE
AM S-MANP
components O
enables O
faster O
and O
more O
complex O
designs S-FEAT
. O


The O
ALD O
coating S-APPL
seems O
to O
improve O
the O
flow O
properties S-CONPRI
of O
the O
tested O
AM S-MANP
fluidics O
restrictor O
. O


Results O
also O
indicate O
an O
improved O
structural B-PRO
integrity E-PRO
. O


There O
were O
indications O
the O
coating S-APPL
might O
slightly O
mitigate O
outgassing O
at O
higher O
temperatures S-PARA
, O
but O
results O
are O
inconclusive O
. O


Space O
technology S-CONPRI
has O
been O
an O
early O
adopter O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
as S-MATE
a O
way O
of O
quickly O
producing O
relatively O
complex O
systems O
and O
components S-MACEQ
that O
would O
otherwise O
require O
expensive O
and O
custom O
design S-FEAT
and O
production S-MANP
. O


Space O
as S-MATE
an O
environment O
and O
long-term O
survivability O
pose O
challenges O
to O
materials S-CONPRI
used O
in O
AM S-MANP
and O
these O
challenges O
need O
to O
be S-MATE
addressed O
. O


Atomic B-MANP
layer I-MANP
deposition E-MANP
( O
ALD O
) O
is O
an O
effective O
coating S-APPL
method O
enabling O
conformal O
and O
precise O
coating S-APPL
of O
the O
complete O
AM S-MANP
print O
. O


This O
work O
analyses O
how O
an O
ALD O
coating S-APPL
of O
aluminium S-MATE
oxide O
on O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
and O
polyamide S-MATE
PA S-CHAR
2200 O
plastic S-MATE
AM S-MANP
prints O
benefits O
and O
protects O
them O
. O


AM S-MANP
was O
performed O
with O
material B-MANP
extrusion E-MANP
and O
selective B-MANP
laser I-MANP
sintering E-MANP
methods O
that O
are O
commonly O
used O
. O


Tests O
were O
performed O
with O
a O
simple S-MANP
bang-bang O
controller S-MACEQ
test O
setup O
and O
a O
mass O
spectrometer O
, O
and O
the O
existence O
of O
the O
coating S-APPL
was O
confirmed O
with O
scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
imaging S-APPL
. O


First O
known O
study O
on O
design B-CONPRI
freedom E-CONPRI
offered O
by O
3D S-CONPRI
Sand-Printing O
process S-CONPRI
to O
redesign O
sprue S-MACEQ
in O
metal S-MATE
casting S-MANP
which O
causes O
agitation S-CONPRI
in O
melt B-CONPRI
flow E-CONPRI
. O


Numerical O
model S-CONPRI
and O
optimization B-CONPRI
algorithm E-CONPRI
for O
novel O
sprue S-MACEQ
profiles S-FEAT
are O
developed O
to O
reduce O
casting S-MANP
defects O
by O
99.5 O
% O
. O


Mechanical B-PRO
strength E-PRO
in O
castings O
improved O
by O
8.4 O
% O
when O
compared O
to O
traditional O
gating O
. O


The O
opportunity O
to O
improve O
the O
quality S-CONPRI
of O
metal S-MATE
castings O
by O
enabling O
fabrication S-MANP
of O
complex O
gating B-CONPRI
systems E-CONPRI
via O
3D S-CONPRI
Sand-Printing O
( O
3DSP O
) O
has O
been O
recently O
established O
. O


Among O
the O
different O
components S-MACEQ
of O
a O
gating B-CONPRI
system E-CONPRI
( O
often O
called O
rigging O
) O
, O
sprue S-MACEQ
design S-FEAT
offers O
a O
major O
opportunity O
to O
exploit O
the O
unlimited O
geometric B-CONPRI
freedom E-CONPRI
offered O
by O
3DSP O
process S-CONPRI
. O


In O
this O
study O
, O
conventional O
principles O
of O
casting S-MANP
hydrodynamics O
is O
advanced O
by O
validated O
novel O
numerical O
models O
for O
novel O
sprue S-MACEQ
designs S-FEAT
to O
improve O
melt B-CONPRI
flow E-CONPRI
control O
. O


Multiple O
approaches O
to O
integrate O
3DSP O
into O
conventional B-MANP
manufacturing E-MANP
to O
fabricate S-MANP
complex O
gating B-CONPRI
systems E-CONPRI
through O
“ O
Hybrid O
Molding S-MANP
” O
are O
presented O
. O


3DSP O
molds S-MACEQ
featuring O
two O
optimized O
sprue S-MACEQ
profiles S-FEAT
and O
a O
benchmark S-MANS
straight O
sprue S-MACEQ
are O
fabricated S-CONPRI
to O
pour O
17-4 B-MATE
stainless I-MATE
steel E-MATE
. O


Computed B-CHAR
tomography E-CHAR
scans O
( O
CT S-ENAT
) O
shows O
that O
parabolic O
sprue S-MACEQ
casting S-MANP
( O
PSC O
) O
and O
conical-helix O
sprue S-MACEQ
casting S-MANP
( O
CHSC O
) O
reduced O
overall O
casting S-MANP
defects O
by O
56 O
% O
and O
99.5 O
% O
respectively O
when O
compared O
to O
straight O
sprue S-MACEQ
casting S-MANP
( O
SSC O
) O
. O


Scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
analysis O
confirms O
the O
presence O
of O
globular O
oxide B-MATE
inclusions E-MATE
and O
that O
PSC O
and O
CHSC O
exhibits O
21 O
% O
and O
35 O
% O
reduced O
inclusion S-MATE
when O
compared O
to O
the O
SSC O
. O


Three O
point O
flexural O
testing S-CHAR
reveals O
that O
CHSC O
and O
PSC O
exhibits O
an O
increase O
of O
8.4 O
% O
and O
4.1 O
% O
respectively O
in O
average S-CONPRI
ultimate O
flexural B-PRO
strength E-PRO
than O
SSC O
. O


The O
findings O
from O
this O
study O
demonstrate O
that O
numerically O
optimized O
gating B-CONPRI
systems E-CONPRI
that O
can O
only O
be S-MATE
fabricated O
via O
3DSP O
have O
the O
potential O
to O
significantly O
improve O
both O
mechanical S-APPL
and O
metallurgical S-APPL
performance O
of O
sand B-MANP
castings E-MANP
. O


With O
increasing O
industrial S-APPL
application O
of O
additive B-MANP
manufacturing E-MANP
technologies O
, O
such O
as S-MATE
selective O
laser S-ENAT
melting O
, O
the O
requirements O
concerning O
the O
processes S-CONPRI
’ O
capabilities O
like O
productivity S-CONPRI
, O
robustness S-PRO
, O
part O
quality S-CONPRI
and O
the O
range S-PARA
of O
processable O
materials S-CONPRI
are O
increasing O
as S-MATE
well O
. O


But O
due O
to O
high O
cooling B-PARA
rates E-PARA
, O
high O
thermal B-PARA
gradients E-PARA
and O
a O
layer-wise O
processing O
, O
parts O
produced O
by O
selective B-MANP
laser I-MANP
melting E-MANP
are O
subject O
to O
different O
kinds O
of O
defects S-CONPRI
. O


These O
defects S-CONPRI
commonly O
lead S-MATE
to O
high O
porosity S-PRO
, O
distortion S-CONPRI
, O
cracking S-CONPRI
and O
rough O
surfaces S-CONPRI
. O


But O
when O
a O
second O
beam S-MACEQ
is O
used O
to O
heat S-CONPRI
the O
vicinity O
of O
the O
melt B-MATE
pool E-MATE
a O
homogenization S-MANP
of O
the O
temperature S-PARA
field O
, O
a O
reduction S-CONPRI
of O
the O
cooling S-MANP
speeds O
within O
the O
melt B-MATE
pool E-MATE
and O
in O
its O
vicinity O
as S-MATE
well O
as S-MATE
an O
improved O
wetting O
behavior O
is O
possible O
. O


A O
proof O
of O
concept O
is O
shown O
, O
discussing O
general O
trends S-CONPRI
and O
possibilities O
, O
like O
increased O
surface B-PARA
qualities E-PARA
or O
dense O
microstructures S-MATE
with O
low O
amounts O
of O
remelting O
, O
when O
these O
strategies O
are O
elaborated O
. O


Binder S-MATE
jet O
printed O
components S-MACEQ
typically O
have O
low O
overall O
density S-PRO
in O
the O
green O
state O
and O
high O
shrinkage S-CONPRI
and O
deformation S-CONPRI
after O
heat B-MANP
treatment E-MANP
. O


It O
has O
previously O
been O
demonstrated O
that O
, O
by O
including O
nanoparticles S-CONPRI
of O
the O
same O
material S-MATE
in O
the O
binder S-MATE
, O
these O
properties S-CONPRI
can O
be S-MATE
improved O
as S-MATE
the O
nanoparticles S-CONPRI
can O
fill O
the O
interstices O
and O
pore S-PRO
throats O
between O
the O
bed S-MACEQ
particles O
. O


The O
beneficial O
effects O
from O
using O
these O
additive S-MATE
binder O
particles S-CONPRI
can O
be S-MATE
improved O
by O
maximising O
the O
binder S-MATE
particle O
size O
, O
enabling O
the O
space O
within O
the O
powder B-MACEQ
bed E-MACEQ
to O
be S-MATE
filled O
with O
a O
higher O
packing O
efficiency O
. O


The O
selection O
of O
maximum O
particle S-CONPRI
size O
for O
a O
binder S-MATE
requires O
detailed O
knowledge O
of O
the O
pores S-PRO
and O
pore S-PRO
throats O
between O
the O
powder B-MACEQ
bed E-MACEQ
particles S-CONPRI
. O


In O
this O
paper O
, O
a O
raindrop O
model S-CONPRI
is O
used O
to O
determine O
the O
critical O
radius O
at O
which O
binder S-MATE
particles O
can O
pass O
between O
pores S-PRO
and O
penetrate O
the O
bed S-MACEQ
. O


The O
model S-CONPRI
is O
validated O
against O
helium S-MATE
psychometry O
measurements O
and O
binder S-MATE
particle O
drop O
tests O
. O


It O
is O
found O
that O
the O
critical O
radius O
can O
be S-MATE
predicted O
, O
with O
acceptable O
accuracy S-CHAR
, O
using O
a O
linear O
function O
of O
the O
mean O
and O
standard B-CHAR
deviation E-CHAR
of O
the O
particle S-CONPRI
radii O
. O


Percolation O
theory O
concepts O
have O
been O
employed O
in O
order O
to O
generalise O
the O
results O
for O
powder B-MACEQ
beds E-MACEQ
that O
have O
different O
mean O
particle S-CONPRI
sizes O
and O
size O
distributions S-CONPRI
. O


The O
results O
of O
this O
work O
can O
be S-MATE
employed O
to O
inform O
the O
selection O
of O
particle S-CONPRI
sizes O
required O
for O
binder S-MATE
formulations O
, O
to O
optimise O
density S-PRO
and O
reduce O
shrinkage S-CONPRI
in O
printed O
binder S-MATE
jet O
components S-MACEQ
. O


Electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
is O
a O
metal B-MANP
powder I-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technology S-CONPRI
that O
makes O
possible O
the O
fabrication S-MANP
of O
three-dimensional S-CONPRI
near-net-shaped O
parts O
directly O
from O
computer S-ENAT
models O
. O


EBM S-MANP
technology O
has O
been O
continuously O
evolving O
, O
optimizing O
the O
properties S-CONPRI
and O
the O
microstructure S-CONPRI
of O
the O
as-fabricated O
alloys S-MATE
. O


Ti-6Al-4V S-MATE
ELI O
( O
Extra O
Low O
Interstitials O
) O
titanium B-MATE
alloy E-MATE
is O
the O
most O
widely O
used O
and O
studied O
alloy S-MATE
for O
this O
technology S-CONPRI
and O
is O
the O
focus O
of O
this O
work O
. O


Several O
research S-CONPRI
works O
have O
been O
completed O
to O
study O
the O
mechanisms O
of O
microstructure S-CONPRI
formation O
, O
evolution S-CONPRI
, O
and O
its O
subsequent O
influence O
on O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
alloy S-MATE
. O


In O
this O
work O
, O
samples B-CONPRI
fabricated E-CONPRI
at O
different O
locations O
, O
orientations S-CONPRI
, O
and O
distances O
from O
the O
build B-MACEQ
platform E-MACEQ
have O
been O
characterized O
, O
studying O
the O
relationship O
of O
these O
variables O
with O
the O
resulting O
material S-MATE
intrinsic O
characteristics O
and O
properties S-CONPRI
( O
surface B-CONPRI
topography E-CONPRI
, O
microstructure S-CONPRI
, O
porosity S-PRO
, O
micro-hardness O
and O
static O
mechanical B-CONPRI
properties E-CONPRI
) O
. O


This O
study O
has O
revealed O
that O
porosity S-PRO
is O
the O
main O
factor O
controlling O
mechanical B-CONPRI
properties E-CONPRI
relative O
to O
the O
other O
studied O
variables O
. O


Therefore O
, O
in O
future O
process S-CONPRI
development O
, O
decreasing O
the O
porosity S-PRO
should O
be S-MATE
considered O
the O
primary O
goal O
in O
order O
to O
improve O
mechanical B-CONPRI
properties E-CONPRI
. O


In O
the O
rapidly O
growing O
field O
of O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
, O
the O
Laser B-MANP
Directed I-MANP
Energy I-MANP
Deposition E-MANP
( O
L-DED O
) O
process S-CONPRI
is O
the O
focus O
of O
intense O
technical O
attention O
due O
to O
its O
potential O
to O
generate O
high O
quality S-CONPRI
components S-MACEQ
with O
location O
specific O
composition S-CONPRI
and O
microstructural S-CONPRI
control O
. O


Despite O
the O
variety O
of O
experimental S-CONPRI
and O
modelling S-ENAT
efforts O
devoted O
to O
the O
subject O
, O
no O
studies O
directly O
observe O
the O
interactions O
between O
individual O
powder B-MATE
particles E-MATE
and O
the O
liquid O
pool O
of O
metal S-MATE
at O
a O
high O
enough O
temporal O
frequency O
to O
characterize O
these O
discrete O
contact S-APPL
events O
. O


Video O
images S-CONPRI
reveal O
that O
particles S-CONPRI
often O
impact S-CONPRI
and O
float O
on O
the O
surface S-CONPRI
of O
the O
melt B-MATE
pool E-MATE
for O
several O
hundreds O
of O
microseconds O
before O
melting S-MANP
into O
it O
. O


Further O
incoming O
particles S-CONPRI
were O
observed O
to O
rebound O
from O
the O
melt B-MATE
pool E-MATE
by O
these O
floating O
particles S-CONPRI
. O


Through O
modelling S-ENAT
this O
process S-CONPRI
analytically O
, O
particle S-CONPRI
self-shielding O
is O
shown O
to O
impose O
unavoidable O
upper O
limits S-CONPRI
on O
overall O
powder S-MATE
capture O
efficiency O
for O
the O
L-DED O
process S-CONPRI
. O


High O
entropy O
alloy S-MATE
AlCoCrFeNi O
was O
obtained O
by O
selective B-MANP
electron I-MANP
beam I-MANP
melting E-MANP
( O
SEBM S-MANP
) O
. O


The O
mechanical B-CONPRI
properties E-CONPRI
of O
SEBM S-MANP
specimens O
were O
improved O
compared O
with O
those O
of O
the O
cast S-MANP
specimen O
. O


The O
pitting S-CONPRI
potential O
of O
the O
AlCoCrFeNi O
SEBM S-MANP
specimens O
in O
artificial O
seawater O
was O
slightly O
lower O
than O
that O
of O
the O
cast S-MANP
specimen O
. O


The O
properties S-CONPRI
of O
the O
product O
were O
influenced O
by O
the O
microstructure B-CONPRI
evolution E-CONPRI
in O
the O
SEBM S-MANP
process S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
is O
expected O
to O
be S-MATE
the O
manufacturing S-MANP
method O
for O
components S-MACEQ
made O
with O
high-entropy O
alloys S-MATE
( O
HEAs O
) O
. O


In O
this O
study O
, O
the O
mechanical S-APPL
and O
electrochemical S-CONPRI
behaviors O
were O
investigated O
for O
equi-molar O
HEA O
( O
AlCoCrFeNi O
) O
obtained O
with O
selective B-MANP
electron I-MANP
beam I-MANP
melting E-MANP
( O
SEBM S-MANP
) O
. O


The O
mechanical B-CONPRI
properties E-CONPRI
of O
SEBM S-MANP
products O
were O
improved O
compared O
with O
those O
of O
a O
cast S-MANP
specimen O
. O


Electrochemical B-CHAR
measurements E-CHAR
in O
artificial O
seawater O
revealed O
the O
corrosion B-PRO
behaviors E-PRO
of O
HEA O
( O
AlCoCrFeNi O
) O
. O


The O
pitting S-CONPRI
potential O
of O
SEBM S-MANP
specimens O
( O
0.112 O
V S-MATE
vs. O
Ag/AgCl O
) O
was O
lower O
than O
that O
of O
a O
cast S-MANP
specimen O
( O
0.178 O
V S-MATE
vs. O
Ag/AgCl O
) O
. O


The O
mechanical S-APPL
and O
electrochemical S-CONPRI
properties O
of O
SEBM S-MANP
products O
were O
influenced O
by O
the O
phase B-CONPRI
morphologies E-CONPRI
formed O
during O
the O
SEBM S-MANP
process S-CONPRI
. O


This O
paper O
aims O
to O
understand O
the O
formation O
and O
the O
effect O
of O
residual B-PRO
stress E-PRO
on O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
parts O
. O


SLM S-MANP
is O
a O
powder B-MACEQ
bed E-MACEQ
based O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
and O
can O
be S-MATE
compared O
to O
a O
laser B-MANP
welding E-MANP
process O
. O


Due O
to O
the O
high O
temperature B-PARA
gradients E-PARA
and O
the O
densification S-MANP
ratio O
, O
which O
are O
characteristic O
of O
this O
process S-CONPRI
, O
residual B-PRO
stresses E-PRO
occur O
. O


The O
investigation O
of O
residual B-PRO
stress E-PRO
is O
performed O
using O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
for O
samples S-CONPRI
made O
of O
austenitic B-MATE
stainless I-MATE
steel E-MATE
AISI O
316L O
( O
EN O
1.4404 O
) O
. O


This O
research S-CONPRI
examines O
residual B-PRO
stress E-PRO
at O
different O
depths O
and O
at O
two O
outer O
surfaces S-CONPRI
. O


For O
the O
measurement S-CHAR
of O
stresses O
at O
different O
depths O
, O
the O
samples S-CONPRI
’ O
surface S-CONPRI
layers O
were O
removed O
by O
electropolishing S-MANP
. O


At O
sufficiently O
large O
distances O
from O
the O
top O
surface S-CONPRI
, O
the O
stresses O
in O
the O
area S-PARA
of O
the O
edge O
layer S-PARA
initially O
increase O
strongly O
and O
then O
decline O
again O
. O


The O
value O
and O
orientation S-CONPRI
of O
the O
resulting O
main O
stress S-PRO
components S-MACEQ
are O
dependent O
on O
the O
examined O
layer S-PARA
. O


At O
the O
top O
surface S-CONPRI
, O
the O
residual B-PRO
stresses E-PRO
are O
higher O
in O
scan O
direction O
than O
in O
perpendicular O
direction O
. O


In O
contrast O
, O
at O
the O
lateral O
surface S-CONPRI
the O
maximum O
main O
stress S-PRO
is O
perpendicular O
to O
the O
scan O
and O
parallel O
to O
the O
building B-PARA
direction E-PARA
. O


These O
two O
cases O
can O
be S-MATE
described O
very O
well O
by O
the O
two O
mechanisms O
in O
SLM S-MANP
, O
namely O
the O
temperature B-CONPRI
gradient I-CONPRI
mechanism E-CONPRI
( O
TGM S-CONPRI
) O
and O
the O
cool-down O
phase S-CONPRI
. O


It O
is O
also O
shown O
that O
at O
samples S-CONPRI
with O
a O
relative O
structural O
density S-PRO
of O
> O
99 O
% O
, O
the O
residual B-PRO
stress E-PRO
values O
are O
independent O
of O
the O
applied O
energy B-PARA
density E-PARA
. O


The O
rheology S-PRO
of O
a O
ceramic S-MATE
paste O
is O
known O
to O
be S-MATE
a O
key O
factor O
in O
the O
process S-CONPRI
of O
additive B-MANP
manufacturing E-MANP
of O
ceramic S-MATE
parts O
via O
extrusion S-MANP
freeforming O
. O


The O
rheological B-PRO
properties E-PRO
of O
ceramic S-MATE
pastes O
can O
be S-MATE
influenced O
by O
several O
formulation O
parameters S-CONPRI
. O


In O
this O
study O
, O
the O
mutual O
influence O
between O
formulation O
parameters S-CONPRI
, O
printing O
properties S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
ceramic S-MATE
pastes O
( O
Al2O3 S-MATE
) O
and O
the O
resulting O
green B-CONPRI
bodies E-CONPRI
are O
investigated O
. O


Special O
focus O
is O
set S-APPL
on O
elucidating O
the O
origins O
and O
causes O
of O
the O
altered O
paste O
properties S-CONPRI
to O
allow O
targeted O
material S-MATE
development O
of O
pastes O
for O
the O
use O
in O
extrusion S-MANP
freeforming O
. O


Glycerine O
and O
nanoparticulate O
boehmite O
needles O
are O
tested O
as S-MATE
additives S-MATE
and O
they O
successfully O
improve O
the O
printability S-PARA
in O
the O
extrusion S-MANP
freeforming O
process S-CONPRI
of O
the O
paste O
and O
compression B-PRO
strength E-PRO
of O
the O
green B-CONPRI
body E-CONPRI
. O


Considerable O
difference O
in O
the O
dependency O
of O
the O
mechanical B-CONPRI
properties E-CONPRI
on O
the O
formulation O
parameters S-CONPRI
was O
detected O
after O
a O
partial O
sintering S-MANP
of O
the O
green B-CONPRI
bodies E-CONPRI
at O
1000 O
°C O
. O


Dewatering O
, O
shrinkage S-CONPRI
during O
drying S-MANP
and O
a O
running O
of O
the O
deposited O
lines O
could O
be S-MATE
reduced O
successfully O
by O
adjusting O
the O
formulation O
. O


The O
impact S-CONPRI
of O
the O
formulation O
parameters S-CONPRI
on O
the O
printing B-CONPRI
performance E-CONPRI
could O
be S-MATE
linked O
to O
the O
dependency O
of O
the O
volume S-CONPRI
flow B-PARA
rate E-PARA
on O
the O
ratio O
of O
pressure S-CONPRI
over O
viscosity S-PRO
. O


Hollow O
microlattices O
constitute O
a O
model S-CONPRI
topology O
for O
architected O
materials S-CONPRI
, O
as S-MATE
they O
combine O
excellent O
specific B-PRO
stiffness E-PRO
and O
strength S-PRO
with O
relative O
ease O
of O
manufacturing S-MANP
. O


The O
most O
scalable O
manufacturing S-MANP
technique O
to O
date O
encompasses O
fabrication S-MANP
of O
a O
sacrificial O
polymeric O
template S-MACEQ
by O
the O
Self O
Propagating O
Photopolymer S-MATE
Waveguide O
( O
SPPW O
) O
process S-CONPRI
, O
followed O
by O
thin O
film O
coating S-APPL
and O
removal O
of O
the O
substrate S-MATE
. O


Accurate S-CHAR
modeling O
of O
mechanical B-CONPRI
properties E-CONPRI
( O
e.g. O
, O
stiffness S-PRO
, O
strength S-PRO
) O
of O
hollow O
microlattices O
is O
challenging O
, O
primarily O
due O
to O
the O
complex O
stress S-PRO
state O
around O
the O
hollow O
nodes O
and O
the O
existence O
of O
manufacturing-induced O
geometric O
imperfections S-CONPRI
( O
e.g O
. O


In O
this O
work O
, O
we O
use O
a O
variety O
of O
measuring O
techniques O
( O
SEM S-CHAR
imaging S-APPL
, O
CT S-ENAT
scanning O
, O
etc O
. O


) O
to O
characterize O
the O
geometric O
imperfections S-CONPRI
in O
a O
nickel-based O
ultralight O
hollow O
microlattice O
and O
investigate O
their O
effect O
on O
the O
compressive B-PRO
strength E-PRO
of O
the O
lattice S-CONPRI
. O


At O
the O
strut S-MACEQ
level O
, O
where O
a O
more O
quantitative S-CONPRI
description O
of O
geometric O
defects S-CONPRI
is O
available O
, O
the O
gathered O
data S-CONPRI
is O
used O
to O
build S-PARA
a O
stochastic S-CONPRI
field O
model S-CONPRI
of O
geometric O
imperfections S-CONPRI
using O
Proper O
Orthogonal O
Decomposition S-PRO
. O


Using O
Monte O
Carlo O
simulations S-ENAT
, O
the O
critical O
buckling B-CHAR
loads E-CHAR
of O
a O
large O
set S-APPL
of O
imperfect O
bars O
created O
using O
the O
stochastic B-CONPRI
model E-CONPRI
are O
then O
extracted S-CONPRI
by O
Finite B-CONPRI
Elements E-CONPRI
Analysis O
. O


The O
statistics S-CONPRI
of O
the O
buckling B-PRO
strength E-PRO
in O
artificially O
generated O
bars O
is O
then O
used O
to O
explain O
the O
scatter O
in O
the O
strength S-PRO
of O
CT-derived O
bars O
and O
its O
correlation O
with O
the O
lattice S-CONPRI
strength O
measured O
experimentally O
. O


Although O
the O
quantitative S-CONPRI
results O
are O
specific O
to O
microlattices O
fabricated S-CONPRI
by O
SPPW O
templating O
, O
the O
methodology S-CONPRI
presented O
herein O
is O
equally O
applicable O
to O
architected O
materials S-CONPRI
produced O
by O
other O
manufacturing B-MANP
processes E-MANP
. O


In O
order O
to O
study O
the O
special O
constriction O
effect O
and O
physical B-CONPRI
process E-CONPRI
features O
during O
compulsively O
constricted O
WAAM S-MANP
( O
CC-WAAM O
) O
, O
the O
dynamic S-CONPRI
behaviours O
of O
arc S-CONPRI
, O
droplets S-CONPRI
, O
and O
molten B-CONPRI
pool E-CONPRI
were O
visually O
investigated O
. O


Possible O
interactions O
inside O
the O
narrow O
space O
were O
discussed O
to O
explain O
the O
mechanism S-CONPRI
of O
the O
compulsive O
constriction O
on O
ejected O
plasma S-CONPRI
and O
droplets S-CONPRI
. O


Based O
on O
the O
captured O
images S-CONPRI
, O
the O
strong O
radiative O
emission S-CHAR
indicates O
that O
the O
ejected O
plasma S-CONPRI
was O
at O
high O
temperature S-PARA
at O
least O
6000 O
K. O
As S-MATE
the O
current O
increases O
higher-temperature O
plasma S-CONPRI
jets O
were O
expected O
, O
which O
would O
lead S-MATE
to O
a O
larger O
plasma S-CONPRI
volume O
in O
the O
absence O
of O
constriction O
. O


The O
relationship O
between O
current O
and O
droplet S-CONPRI
diameters O
was O
preliminarily O
established O
to O
enable O
prediction S-CONPRI
of O
the O
droplet B-PARA
size E-PARA
. O


An O
important O
feature S-FEAT
of O
small-size O
droplets S-CONPRI
( O
as S-MATE
low O
as S-MATE
0.89 O
mm S-MANP
) O
offered O
CC-WAAM O
a O
great O
potential O
to O
improve O
the O
precision S-CHAR
of O
the O
additive B-MANP
manufacturing E-MANP
layers O
, O
although O
the O
minimum O
width O
of O
the O
deposited B-CHAR
layer E-CHAR
is O
much O
larger O
than O
the O
droplet S-CONPRI
diameter S-CONPRI
due O
to O
liquid O
spreading O
and O
accumulation O
. O


The O
droplets S-CONPRI
were O
found O
to O
have O
a O
slight O
impact S-CONPRI
on O
the O
molten B-CONPRI
pool E-CONPRI
behaviours O
, O
which O
produces O
stable O
molten B-CONPRI
pool E-CONPRI
shapes O
. O


Under O
the O
wide-range O
parameters S-CONPRI
, O
the O
deposited B-CHAR
layers E-CHAR
showed O
good O
appearances O
, O
which O
indicates O
the O
good O
adaptability O
of O
this O
novel O
technology S-CONPRI
. O


In O
this O
study O
, O
laser B-MANP
metal I-MANP
deposition E-MANP
( O
LMD S-MANP
) O
was O
employed O
to O
explore O
a O
new O
fabrication S-MANP
process O
for O
producing O
a O
functionally B-MATE
graded I-MATE
material E-MATE
( O
FGM S-MANP
) O
from O
Ti-6Al-4V S-MATE
to O
SS316 O
. O


A O
transition B-CONPRI
composition E-CONPRI
route O
was O
introduced O
( O
Ti-6Al-4V→V→Cr→Fe→SS316 O
) O
to O
avoid O
the O
intermetallic S-MATE
phases O
between O
Ti-6Al-4V S-MATE
and O
SS316 O
. O


A O
thin O
wall O
sample S-CONPRI
was O
fabricated S-CONPRI
via O
LMD S-MANP
by O
following O
the O
transition B-CONPRI
composition E-CONPRI
route O
. O


Microstructure S-CONPRI
characterization O
and O
composition S-CONPRI
distribution O
analyses O
were O
performed O
by O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
and O
energy O
dispersive O
spectrometry O
( O
EDS S-CHAR
) O
. O


The O
SEM S-CHAR
images S-CONPRI
depicted O
the O
microstructural S-CONPRI
morphology O
of O
the O
FGM S-MANP
sample O
. O


The O
element S-MATE
gradient O
distribution S-CONPRI
determined O
by O
the O
EDS S-CHAR
results O
may O
reflect O
the O
FGM S-MANP
transition O
composition S-CONPRI
route O
design S-FEAT
. O


X-ray B-CHAR
diffraction E-CHAR
tests O
were O
conducted O
and O
the O
results O
demonstrated O
that O
the O
generation O
of O
intermetallic S-MATE
phases O
effectively O
avoided O
following O
the O
composition S-CONPRI
route O
. O


The O
Vickers B-PRO
hardness E-PRO
test O
was O
used O
to O
determine O
the O
Vickers B-PRO
hardness E-PRO
number O
( O
VHN O
) O
distribution S-CONPRI
from O
Ti-6Al-4V S-MATE
to O
SS316 O
. O


The O
VHN O
results O
showed O
that O
no O
significant O
formation O
of O
hard O
brittle S-PRO
phases O
occurred O
in O
the O
LMD S-MANP
procedure O
. O


Combining O
metal S-MATE
nanoparticle O
( O
NP O
) O
printing O
and O
additive B-MANP
manufacturing E-MANP
has O
high O
potential O
for O
integration O
of O
3D S-CONPRI
conductive O
elements S-MATE
and O
electronic O
devices O
inside O
objects O
. O


Current O
processes S-CONPRI
used O
to O
achieve O
desired O
electrical B-CHAR
resistivity E-CHAR
of O
the O
printed O
NP O
circuits O
entail O
a O
compromise O
between O
resistivity S-PRO
, O
throughput S-CHAR
, O
and O
thermal O
damage S-PRO
of O
the O
structure S-CONPRI
. O


We O
explore O
the O
mechanisms O
underlying O
the O
combination O
of O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
of O
Acrylonitrile B-MATE
Butadiene I-MATE
Styrene E-MATE
( O
ABS S-MATE
) O
and O
Polylactide O
( O
PLA S-MATE
) O
polymer S-MATE
structures O
, O
printing O
of O
silver S-MATE
NPs O
( O
mixed O
nanowires O
and O
nanospheres O
) O
, O
and O
out-of-chamber O
Intense O
Pulsed O
Light O
( O
IPL O
) O
sintering S-MANP
of O
the O
printed O
circuits O
. O


IPL O
of O
only-nanosphere O
based O
circuits O
on O
the O
FFF-made O
structure S-CONPRI
thermally O
damages O
the O
polymer S-MATE
without O
any O
resistivity S-PRO
reduction S-CONPRI
. O


In O
a O
significant O
advance O
, O
the O
addition O
of O
nanowires O
achieves O
a O
resistivity S-PRO
several O
times O
lesser O
than O
the O
state-of-the-art S-CONPRI
( O
13.1 O
μΩ-cm O
or O
8 O
x O
bulk O
silver S-MATE
) O
without O
any O
thermal O
damage S-PRO
and O
within O
0.75 O
s S-MATE
of O
IPL O
. O


Electromagnetic O
analysis O
and O
Molecular O
Dynamics O
simulations S-ENAT
show O
that O
nanowire O
addition O
concurrently O
reduces O
IPL O
temperature S-PARA
and O
accelerates O
the O
kinetics O
of O
resistivity S-PRO
reduction S-CONPRI
. O


Subsequent O
FFF S-MANP
over O
the O
post-IPL O
conductive O
pattern S-CONPRI
causes O
a O
non-monotonic O
change O
in O
resistivity S-PRO
, O
surprisingly O
effecting O
a O
resistivity S-PRO
reduction S-CONPRI
down O
to O
11.8 O
μΩ-cm O
. O


The O
developed O
approach O
is O
used O
to O
demonstrate O
multilayer O
sensing S-APPL
of O
internal O
temperature S-PARA
and O
a O
light O
sensing S-APPL
circuit O
with O
embedded O
interconnects O
. O


Finally O
, O
we O
discuss O
how O
these O
insights O
may O
guide O
the O
creation O
of O
a O
machine B-MACEQ
tool E-MACEQ
that O
creates O
a O
seamless O
form O
of O
the O
proposed O
process S-CONPRI
. O


Parts O
fabricated S-CONPRI
using O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
methods O
, O
such O
as S-MATE
laser-powder O
bed B-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
, O
receive O
highly O
localized O
heat B-CONPRI
fluxes E-CONPRI
from O
a O
laser S-ENAT
within O
a O
purged O
, O
inert O
environment O
during O
manufacture S-CONPRI
. O


These O
heat B-CONPRI
fluxes E-CONPRI
are O
used O
for O
melting S-MANP
metal O
powder B-MACEQ
feedstock E-MACEQ
, O
while O
remaining O
energy O
is O
transferred O
to O
the O
solidified O
part O
and O
adjoining O
gas S-CONPRI
environment O
. O


Using O
computational B-CHAR
fluid I-CHAR
dynamics E-CHAR
( O
CFD S-APPL
) O
, O
the O
local O
heat B-CONPRI
transfer E-CONPRI
between O
the O
adjoining O
shielding O
gas S-CONPRI
, O
laser-induced O
melt B-MATE
pool E-MATE
and O
surrounding O
heat B-CONPRI
affected I-CONPRI
zone E-CONPRI
is O
estimated O
. O


Simulations S-ENAT
are O
performed O
for O
the O
L-PBF S-MANP
of O
a O
single O
layer S-PARA
of O
Ti-6Al-4 O
V. O
Local O
temperature S-PARA
, O
temperature B-PARA
gradients E-PARA
, O
temperature S-PARA
time-rates-of-change O
( O
including O
cooling B-PARA
rates E-PARA
) O
, O
as S-MATE
well O
as S-MATE
dimensionless O
numbers O
descriptive O
of O
important O
thermophysics O
, O
are O
provided O
in O
order O
to O
quantify O
local O
convective O
heat B-CONPRI
transfer E-CONPRI
for O
various O
laser/gas O
motion O
directions O
. O


Results O
demonstrate O
that O
L-PBF S-MANP
track O
heat B-CONPRI
transfer E-CONPRI
is O
highly O
dependent O
on O
relative O
gas/laser O
direction O
which O
can O
impact S-CONPRI
the O
prior O
β O
grain B-PRO
sizes E-PRO
in O
Ti-6Al-4 B-MATE
V E-MATE
material S-MATE
by O
up O
to O
10 O
% O
. O


It O
is O
found O
that O
when O
the O
laser S-ENAT
and O
gas S-CONPRI
are O
moving O
in O
the O
same O
direction O
, O
convection O
heat B-CONPRI
transfer E-CONPRI
is O
the O
highest O
and O
a O
‘ O
leading O
thermal O
boundary S-FEAT
layer O
’ O
exists O
in O
front O
of O
the O
laser S-ENAT
which O
is O
capable O
of O
preheating S-MANP
downstream O
powder S-MATE
for O
a O
possible O
reduction S-CONPRI
in O
residual B-PRO
stress E-PRO
formation O
along O
the O
track O
. O


Presented O
results O
can O
aid O
ongoing O
L-PBF S-MANP
modeling O
efforts O
and O
assist O
manufacturing S-MANP
design S-FEAT
decisions O
( O
e.g O
. O


scan O
strategy O
, O
laser B-PARA
power E-PARA
, O
scanning B-PARA
speed E-PARA
, O
etc O
. O


) O
– O
especially O
for O
cases O
where O
homogeneous S-CONPRI
or O
controlled O
material S-MATE
traits O
are O
desired O
. O


Zinc S-MATE
and O
its O
alloys S-MATE
constitute O
the O
new O
generation O
of O
biodegradable O
metallic B-MATE
materials E-MATE
for O
biomedical S-APPL
implants O
. O


Biodegradable O
implants S-APPL
of O
Zn S-MATE
, O
customized O
for O
the O
specific O
patient O
can O
be S-MATE
potentially O
realised O
through O
additive B-MANP
manufacturing I-MANP
processes E-MANP
such O
as S-MATE
selective O
laser S-ENAT
melting O
( O
SLM S-MANP
) O
. O


However O
, O
Zn S-MATE
is O
characterized O
by O
low O
melting S-MANP
and O
boiling O
points O
, O
resulting O
in O
high O
porosity S-PRO
in O
the O
build S-PARA
parts O
. O


In O
this O
work O
, O
the O
SLM S-MANP
of O
pure O
Zn B-MATE
powder E-MATE
is O
studied O
to O
improve O
part O
density S-PRO
. O


A O
flexible O
prototype S-CONPRI
SLM O
system O
was O
used O
to O
determine O
process B-CONPRI
feasibility E-CONPRI
under O
different O
atmospheric O
conditions O
. O


Working O
in O
a O
closed B-MACEQ
chamber E-MACEQ
under O
inert B-CONPRI
gas E-CONPRI
was O
found O
to O
be S-MATE
inadequate O
. O


Process S-CONPRI
stability O
was O
obtained O
in O
an O
open O
chamber O
with O
an O
inert B-CONPRI
gas E-CONPRI
jet O
flow O
over O
the O
powder B-MACEQ
bed E-MACEQ
. O


The O
effect O
of O
laser S-ENAT
process O
parameters S-CONPRI
and O
powder S-MATE
size O
was O
studied O
in O
this O
condition O
. O


This O
paper O
demonstrates O
a O
simple S-MANP
, O
low-cost O
additive B-MANP
manufacturing E-MANP
technique O
for O
fabricating S-MANP
structures O
compatible O
with O
high-density O
packaging O
solutions O
. O


A O
T-line O
resonator S-APPL
is O
characterized O
to O
understand O
the O
transmission S-CHAR
line O
losses O
associated O
with O
the O
vertical S-CONPRI
bends O
. O


Details O
of O
the O
simulation S-ENAT
, O
fabrication S-MANP
, O
and O
measurements O
are O
presented O
. O


Simulations S-ENAT
are O
carried O
out O
using O
ANSYS S-APPL
High-Frequency O
Structure S-CONPRI
Simulator O
( O
HFSS® O
) O
, O
and O
structures O
are O
fabricated S-CONPRI
using O
a O
polyjet S-CONPRI
printing O
process S-CONPRI
. O


The O
measured O
results O
are O
in O
good O
agreement O
with O
the O
simulation S-ENAT
results O
, O
and O
overall O
a O
good O
performance S-CONPRI
is O
achieved O
for O
all O
the O
antenna O
designs S-FEAT
. O


Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
is O
the O
most O
prominent O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technology S-CONPRI
for O
metal S-MATE
part O
production S-MANP
. O


Among O
the O
high O
number O
of O
factors O
influencing O
part O
quality S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
, O
the O
inter O
layer S-PARA
time O
( O
ILT O
) O
between O
iterative O
melting S-MANP
of O
volume S-CONPRI
elements S-MATE
in O
subsequent O
layers O
is O
almost O
completely O
unappreciated O
in O
the O
relevant O
literature O
on O
L-PBF S-MANP
. O


This O
study O
investigates S-CONPRI
the O
effect O
of O
ILT O
with O
respect O
to O
build B-PARA
height E-PARA
and O
under O
distinct O
levels O
of O
volumetric O
energy B-PARA
density E-PARA
( O
VED O
) O
using O
the O
example O
of O
316L B-MATE
stainless I-MATE
steel E-MATE
. O


In-situ S-CONPRI
thermography O
is O
used O
to O
gather O
information O
on O
cooling S-MANP
conditions O
during O
the O
process S-CONPRI
, O
which O
is O
followed O
by O
an O
extensive O
metallographic O
analysis O
. O


Significant O
effects O
of O
ILT O
and O
build B-PARA
height E-PARA
on O
heat B-PRO
accumulation E-PRO
, O
sub-grain B-PARA
sizes E-PARA
, O
melt B-MATE
pool E-MATE
geometries S-CONPRI
and O
hardness S-PRO
are O
presented O
. O


Furthermore O
, O
the O
rise O
of O
defect S-CONPRI
densities O
can O
be S-MATE
attributed O
to O
a O
mutual O
interplay O
of O
build B-PARA
height E-PARA
and O
ILT O
. O


Hence O
, O
ILT O
has O
been O
identified O
as S-MATE
a O
crucial O
factor O
for O
L-PBF S-MANP
of O
real O
part O
components S-MACEQ
especially O
for O
those O
with O
small O
cross B-CONPRI
sections E-CONPRI
. O


Crack-free O
nickel-based O
single O
crystal O
superalloy O
samples S-CONPRI
were O
fabricated S-CONPRI
via O
directed B-MANP
energy I-MANP
deposition E-MANP
. O


Hot B-CONPRI
cracking E-CONPRI
occurred O
at O
high-angle O
grain B-CONPRI
boundaries E-CONPRI
and O
especially O
at O
low-angle O
grain B-CONPRI
boundaries E-CONPRI
. O


The O
existence O
conditions O
of O
the O
liquid O
film O
for O
hot B-CONPRI
cracking E-CONPRI
in O
CMSX-10 O
are O
calculated O
with O
analysis O
models O
. O


The O
hot B-CONPRI
cracking E-CONPRI
mechanism O
is O
related O
to O
the O
stability S-PRO
of O
liquid O
film O
, O
stress B-CHAR
concentration E-CHAR
and O
Re-rich O
precipitations O
. O


Hot B-CONPRI
cracking E-CONPRI
is O
a O
frequent O
and O
severe O
defect S-CONPRI
that O
occurs O
during O
the O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
of O
single-crystal O
superalloys S-MATE
. O


Understanding O
the O
cracking S-CONPRI
behavior O
and O
mechanism S-CONPRI
is O
key O
to O
avoiding O
these O
defects S-CONPRI
. O


Hot B-CONPRI
cracking E-CONPRI
occurred O
at O
high-angle O
grain B-CONPRI
boundaries E-CONPRI
and O
especially O
at O
low-angle O
grain B-CONPRI
boundaries E-CONPRI
. O


Hot B-CONPRI
cracking E-CONPRI
was O
determined O
to O
be S-MATE
caused O
by O
a O
stable O
liquid O
film O
, O
stress B-CHAR
concentration E-CHAR
, O
and O
Re-rich O
precipitates S-MATE
. O


The O
stability S-PRO
of O
the O
liquid O
film O
depended O
on O
dendrite S-BIOP
coalescence O
undercooling O
which O
was O
related O
to O
the O
misorientation O
angle O
. O


The O
dendrite S-BIOP
coalescence O
undercooling O
at O
low-angle O
grain B-CONPRI
boundary E-CONPRI
( O
misorientation O
angle O
6.9° O
) O
was O
178 O
K S-MATE
, O
which O
was O
far O
higher O
than O
the O
vulnerable O
temperature S-PARA
interval O
38 O
K S-MATE
for O
hot B-CONPRI
cracking E-CONPRI
within O
a O
single O
dendrite S-BIOP
. O


Stress B-CHAR
concentration E-CHAR
provided O
the O
driving O
force S-CONPRI
for O
crack O
initiation O
and O
propagation O
. O


Re-rich O
precipitates S-MATE
promoted O
crack O
initiation O
by O
a O
pinning O
effect O
on O
the O
liquid O
feed S-PARA
. O


These O
findings O
provide O
technical O
support S-APPL
for O
achieving O
high-quality O
additive B-MANP
manufacturing E-MANP
and O
repair O
of O
non-weldable O
Ni-based O
single-crystal O
superalloys S-MATE
. O


LMDed O
Ti-Mo O
alloy S-MATE
, O
from O
elemental O
powder S-MATE
mixture O
, O
presents O
an O
almost O
defect-free O
feature S-FEAT
. O


Phase S-CONPRI
transition O
from O
α O
to O
β O
appears O
as S-MATE
results O
of O
in-situ S-CONPRI
thermal O
cycling O
. O


Textural O
density S-PRO
of O
α O
phase S-CONPRI
increases O
significantly O
, O
given O
to O
the O
in-situ S-CONPRI
thermal O
cycling O
. O


The O
LMDed O
Ti-Mo O
present O
a O
graded O
tensile B-PRO
property E-PRO
. O


In O
this O
work O
, O
almost O
dense O
( O
over O
99.8 O
% O
) O
Ti-Mo O
alloy S-MATE
samples O
were O
manufactured S-CONPRI
by O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
from O
a O
mixture O
of O
pure O
Ti S-MATE
and O
pure O
Mo S-MATE
( O
7.5 O
wt. O
% O
) O
powders S-MATE
. O


As S-MATE
a O
consequence O
of O
thermal O
accumulation O
and O
in-situ B-CONPRI
heat E-CONPRI
treating O
during O
the O
DED S-MANP
process O
, O
as-deposited O
samples S-CONPRI
present O
a O
graded B-FEAT
microstructure E-FEAT
along O
the O
building B-PARA
direction E-PARA
along O
with O
a O
phase S-CONPRI
transition O
from O
hcp-α O
Ti S-MATE
to O
bbc-β O
Ti S-MATE
. O


Mechanical B-CONPRI
properties E-CONPRI
were O
determined O
by O
tensile B-CHAR
tests E-CHAR
from O
flat O
samples S-CONPRI
harvested O
at O
different O
altitude O
positions O
. O


As S-MATE
altitude O
increases O
from O
the O
base O
plate O
, O
yield B-PRO
strength E-PRO
decreases O
from O
681 O
MPa S-CONPRI
to O
579 O
MPa S-CONPRI
and O
ultimate B-PRO
tensile I-PRO
strength E-PRO
from O
791 O
MPa S-CONPRI
to O
686 O
MPa S-CONPRI
. O


Elongation S-PRO
of O
the O
as-deposited O
material S-MATE
increases O
from O
10 O
% O
to O
25 O
% O
while O
the O
Young O
’ O
s S-MATE
modulus O
keeps O
a O
low O
value O
of O
105 O
GPa S-PRO
for O
the O
entire O
DEDed O
sample S-CONPRI
. O


AM B-MACEQ
parts E-MACEQ
are O
fabricated S-CONPRI
with O
intentional O
inhomogeneities O
to O
create O
codes O
. O


The O
controlled O
and O
random O
process S-CONPRI
variation O
ensures O
a O
unique O
material S-MATE
structure O
. O


The O
L-PBF S-MANP
approach O
creates O
random O
pores S-PRO
by O
a O
reduced O
volume S-CONPRI
energy B-PARA
density E-PARA
. O


The O
L-DED O
approach O
utilizes O
the O
different O
magnetic O
permeability S-PRO
of O
two O
materials S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
technologies O
enable O
various O
possibilities O
to O
create O
and O
modify O
the O
material S-MATE
composition S-CONPRI
and O
structure S-CONPRI
on O
a O
local O
level O
, O
but O
are O
often O
prone O
to O
undesired O
defects S-CONPRI
and O
inhomogeneities O
. O


By O
controlled O
and O
random O
process S-CONPRI
variation O
, O
unique O
codes O
that O
can O
be S-MATE
read O
and O
authenticated O
by O
an O
eddy O
current O
device O
were O
produced O
with O
the O
processes S-CONPRI
of O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
and O
laser B-MANP
directed I-MANP
energy I-MANP
deposition E-MANP
( O
L-DED O
) O
. O


Two O
approaches O
are O
presented O
: O
First O
, O
volumetric O
, O
porous S-PRO
structures O
with O
a O
defined O
shape O
are O
manufactured S-CONPRI
with O
L-PBF S-MANP
. O


Second O
, O
coatings S-APPL
are O
fabricated S-CONPRI
by O
L-DED O
with O
alternating O
process B-CONPRI
parameters E-CONPRI
, O
leading O
to O
local O
deviations O
of O
the O
magnetic O
permeability S-PRO
. O


Counterfeiting O
becomes O
impossible O
due O
to O
the O
irreproducible O
melt B-MATE
pool E-MATE
dynamics O
. O


Laser-induced O
forward O
transfer O
( O
LIFT O
) O
, O
a O
3D S-CONPRI
additive O
manufacturing S-MANP
technique O
is O
implemented O
to O
fabricate S-MANP
a O
fully O
metallic S-MATE
functional O
micro O
device O
. O


Digital O
deposition S-CONPRI
of O
both O
structural O
and O
sacrificial O
metal S-MATE
constituents O
in O
the O
same O
setup O
arrangement O
is O
achieved O
. O


The O
final O
free-standing O
structure S-CONPRI
is O
released O
by O
selective O
chemical O
wet O
etching S-MANP
of O
the O
support B-MATE
material E-MATE
. O


Using O
this O
approach O
, O
a O
chevron-type O
electro O
thermal O
micro-actuator O
made O
of O
gold S-MATE
was O
successfully O
fabricated S-CONPRI
and O
its O
functionality O
was O
shown O
in O
experiment S-CONPRI
. O


Comparison O
of O
the O
measured O
responses O
with O
the O
model S-CONPRI
predictions O
indicates O
that O
the O
thermal B-PRO
conductivity E-PRO
of O
printed O
Au S-MATE
is O
approximately O
8 O
times O
lower O
than O
the O
bulk O
value O
. O


It O
is O
a O
first O
demonstration O
of O
a O
functional O
micron S-FEAT
scale O
actuator S-MACEQ
printed O
using O
LIFT O
. O


In O
this O
paper O
, O
a O
predictive B-CONPRI
model E-CONPRI
based O
on O
a O
cellular O
automaton O
( O
CA S-MATE
) O
-finite O
element S-MATE
( O
FE S-MATE
) O
method O
has O
been O
developed O
to O
simulate O
thermal O
history O
and O
microstructure B-CONPRI
evolution E-CONPRI
during O
metal S-MATE
solidification O
for O
a O
laser-based B-MANP
additive I-MANP
manufacturing E-MANP
process O
. O


The O
macroscopic S-CONPRI
FE S-MATE
calculation O
was O
designed S-FEAT
to O
update O
the O
temperature S-PARA
field O
and O
simulate O
a O
high O
cooling B-PARA
rate E-PARA
. O


In O
the O
microscopic O
CA S-MATE
model O
, O
heterogeneous B-CONPRI
nucleation E-CONPRI
sites O
, O
preferential O
growth O
orientation S-CONPRI
, O
and O
dendritic O
grain B-CONPRI
growth E-CONPRI
were O
simulated O
. O


The O
CA S-MATE
model O
was O
able O
to O
show O
the O
entrapment O
of O
neighboring O
cells S-APPL
and O
the O
relationship O
between O
undercooling O
and O
the O
grain B-CONPRI
growth E-CONPRI
rate O
. O


The O
model S-CONPRI
predicted O
the O
dendritic O
grain B-PRO
size E-PRO
, O
and O
morphological O
evolution S-CONPRI
during O
the O
solidification B-CONPRI
phase E-CONPRI
of O
the O
deposition B-MANP
process E-MANP
. O


The O
grain S-CONPRI
morphology O
result O
has O
been O
validated O
by O
the O
experiment S-CONPRI
. O


SLM S-MANP
process S-CONPRI
was O
optimized O
via O
polynomial O
regression B-CONPRI
model E-CONPRI
. O


Remelting O
step S-CONPRI
between O
SLM S-MANP
scans O
led S-APPL
to O
homogenization S-MANP
of O
the O
metal B-MATE
powders E-MATE
. O


Si S-MATE
addition O
increased O
the O
tensile B-PRO
strength E-PRO
while O
maintaining O
the O
ductility S-PRO
. O


Interaction O
between O
dislocation S-CONPRI
loops O
with O
dislocations S-CONPRI
strengthened O
the O
alloy S-MATE
. O


Effect O
of O
solid B-MATE
solution E-MATE
and O
dislocation S-CONPRI
loop O
on O
yield B-PRO
strength E-PRO
were O
quantified O
. O


To O
widen O
the O
applications O
of O
new O
materials S-CONPRI
in O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
the O
traditional O
method O
of O
printing O
using O
pre-alloyed O
powders S-MATE
should O
be S-MATE
improved O
because O
the O
pre-alloying O
process S-CONPRI
is O
expensive O
and O
makes O
it O
difficult O
to O
adjust O
the O
composition S-CONPRI
of O
new O
materials S-CONPRI
. O


This O
study O
investigates S-CONPRI
the O
synthesis O
of O
a O
FeCoCrNi O
high-entropy O
alloy S-MATE
( O
HEA O
) O
containing O
1.5 O
at. O
% O
Si S-MATE
in B-CONPRI
situ E-CONPRI
using O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
. O


A O
remelting O
strategy O
and O
process B-CONPRI
optimization E-CONPRI
based O
on O
polynomial O
regression S-CONPRI
modeling S-ENAT
allowed O
for O
the O
printing O
of O
almost O
fully B-PARA
dense E-PARA
( O
99.78 O
% O
) O
samples S-CONPRI
. O


The O
samples S-CONPRI
comprised O
columnar B-PRO
grains E-PRO
, O
each O
containing O
numerous O
subgrains S-CONPRI
of O
a O
single-phase O
face-centered O
cubic O
solid B-MATE
solution E-MATE
. O


No O
precipitation S-CONPRI
or O
segregation S-CONPRI
were O
observed O
. O


The O
room O
temperature S-PARA
tensile O
properties S-CONPRI
of O
the O
samples S-CONPRI
were O
excellent O
, O
with O
yields O
and O
tensile B-PRO
strengths E-PRO
reaching O
701 O
± O
14 O
and O
907 O
± O
25 O
MPa S-CONPRI
, O
respectively O
, O
and O
an O
elongation S-PRO
at O
fracture S-CONPRI
of O
30.8 O
± O
2 O
% O
. O


These O
properties S-CONPRI
were O
attributed O
to O
solid B-MATE
solution E-MATE
strengthening O
and O
novel O
dislocation S-CONPRI
loop O
strengthening B-CONPRI
mechanism E-CONPRI
. O


These O
findings O
demonstrate O
that O
HEAs O
with O
a O
high O
relative B-PRO
density E-PRO
and O
good O
mechanical B-CONPRI
properties E-CONPRI
can O
be S-MATE
directly O
synthesized O
by O
SLM S-MANP
using O
inexpensive O
pure B-MATE
metal E-MATE
powders S-MATE
, O
thereby O
extending O
the O
application O
potential O
of O
AM S-MANP
to O
manufacture S-CONPRI
new O
materials S-CONPRI
. O


This O
paper O
presents O
a O
new O
approach O
for O
modelling S-ENAT
additive B-MANP
layer I-MANP
manufacturing E-MANP
at O
component S-MACEQ
scale O
. O


The O
approach O
is O
applied O
to O
powder-bed O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
and O
validated O
, O
where O
the O
mechanical B-CONPRI
behaviour E-CONPRI
of O
macro-scale O
industrial S-APPL
components S-MACEQ
has O
been O
predicted S-CONPRI
and O
compared O
with O
experimental S-CONPRI
results O
. O


The O
novelty O
of O
the O
approach O
is O
based O
on O
using O
a O
calibrated S-CONPRI
analytical O
thermal O
model S-CONPRI
to O
derive O
functions O
that O
are O
implemented O
in O
a O
structural O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
( O
FEA O
) O
. O


The O
induced O
distortion S-CONPRI
in O
SLM S-MANP
has O
been O
compensated O
for O
by O
modifying O
the O
initial O
geometry S-CONPRI
using O
FE S-MATE
predicted O
distortion S-CONPRI
. O


A O
newly O
developed O
distortion B-PARA
compensation E-PARA
method O
, O
based O
on O
optical S-CHAR
3D S-CONPRI
scan O
measurements O
, O
has O
also O
been O
implemented O
. O


The O
two O
distortion B-PARA
compensation E-PARA
methods O
have O
been O
experimentally B-CONPRI
validated E-CONPRI
. O


In O
summary O
, O
the O
research S-CONPRI
presented O
in O
this O
paper O
shows O
that O
the O
mitigation O
of O
distortion S-CONPRI
in O
SLM S-MANP
is O
now O
possible O
on O
industrial S-APPL
macro-scale O
components S-MACEQ
. O


This O
paper O
reports O
on O
X-ray B-CHAR
tomography E-CHAR
of O
a O
series O
of O
coupon O
samples S-CONPRI
( O
5 O
mm S-MANP
cubes O
) O
produced O
under O
different O
process B-CONPRI
parameters E-CONPRI
, O
for O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
of O
Ti6Al4V S-MATE
. O


Different O
process B-CONPRI
parameters E-CONPRI
result O
in O
different O
pore S-PRO
formation O
mechanisms O
, O
each O
with O
characteristic O
pore B-PARA
sizes E-PARA
, O
shapes O
and O
locations O
within O
the O
5 O
mm S-MANP
cube S-CONPRI
samples O
. O


While O
keyhole O
pores S-PRO
, O
lack O
of O
fusion S-CONPRI
pores O
and O
metallurgical S-APPL
pores O
have O
been O
previously O
identified O
and O
illustrated O
using O
X-ray B-CHAR
tomography E-CHAR
, O
this O
work O
extends O
beyond O
prior O
work O
to O
show O
how O
each O
of O
these O
not O
only O
exist O
in O
extreme O
situations O
but O
how O
they O
vary O
in O
size O
and O
shape O
in O
the O
transition S-CONPRI
regimes O
. O


It O
is O
shown O
how O
keyhole O
mode O
porosity S-PRO
increases O
gradually O
with O
increasing O
power S-PARA
, O
and O
how O
this O
depends O
on O
the O
scan B-PARA
speed E-PARA
. O


Similarly O
, O
lack O
of O
fusion S-CONPRI
pores O
are O
shown O
to O
occur O
following O
scan O
tracks O
in O
situations O
of O
poor O
hatch O
overlap S-CONPRI
, O
or O
a O
similar O
but O
different O
distribution S-CONPRI
of O
lack O
of O
fusion S-CONPRI
porosity O
due O
to O
large O
layer B-PARA
height E-PARA
spacing O
, O
showing O
respectively O
vertical S-CONPRI
and O
horizontal O
lack O
of O
fusion S-CONPRI
pore O
morphologies S-CONPRI
. O


Insights O
from O
3D B-CONPRI
images E-CONPRI
allow O
improvements O
in O
parameter S-CONPRI
choices O
for O
optimized O
density S-PRO
of O
parts O
produced O
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
, O
and O
generally O
allow O
a O
better O
understanding O
of O
the O
porosity S-PRO
present O
in O
additively B-MANP
manufactured E-MANP
parts O
. O


This O
work O
investigates S-CONPRI
an O
additive B-MANP
manufacturing E-MANP
route O
of O
producing O
functional O
net O
shaped O
parts O
from O
pre-alloyed O
magnetic O
shape-memory O
Ni-Mn-Ga O
powders S-MATE
. O


Three O
types O
of O
Ni-Mn-Ga O
powders S-MATE
were O
used O
in O
this O
investigation O
: O
spark O
eroded O
in O
liquid O
nitrogen S-MATE
( O
LN2 O
) O
, O
spark O
eroded O
in O
liquid O
argon S-MATE
( O
LAr O
) O
, O
and O
ball O
milled S-MANP
( O
BM S-MATE
) O
. O


Additive B-MANP
manufacturing E-MANP
via O
powder B-MANP
bed I-MANP
binder I-MANP
jetting E-MANP
, O
also O
known O
as S-MATE
3D B-MANP
printing E-MANP
( O
3DP S-MANP
) O
, O
was O
used O
in O
this O
research S-CONPRI
due O
to O
both O
relatively O
easy O
control O
of O
part O
porosity S-PRO
and O
the O
possibility O
to O
obtain O
complex O
shaped O
parts O
from O
Ni-Mn-Ga O
alloys S-MATE
. O


The O
four-dimension O
( O
4D S-CONPRI
) O
is O
created O
by O
the O
predictable S-CONPRI
change O
in O
3D B-APPL
printed I-APPL
part E-APPL
configuration O
over O
time O
as S-MATE
the O
result O
of O
shape-memory O
functionality O
. O


Binder B-MANP
jetting E-MANP
of O
Ni-Mn-Ga O
powders S-MATE
followed O
by O
curing S-MANP
and O
sintering S-MANP
proved O
successful O
in O
producing O
net O
shaped O
porous S-PRO
structures O
( O
spring-like O
, O
3-D S-CONPRI
hierarchical O
lattice B-FEAT
structures E-FEAT
, O
etc O
. O


) O
with O
good O
mechanical B-PRO
strength E-PRO
. O


Parts O
with O
porosities S-PRO
between O
24.08 O
% O
and O
73.43 O
% O
have O
been O
obtained O
by O
using O
powders S-MATE
with O
distinct O
morphologies S-CONPRI
. O


Thermo-magneto-mechanical O
trained O
3D B-APPL
printed I-APPL
parts E-APPL
obtained O
from O
ball O
milled S-MANP
Ni-Mn-Ga O
powders S-MATE
showed O
reversible O
magnetic-field-induced O
strains O
( O
MFISs O
) O
of O
up O
to O
0.01 O
% O
. O


The O
additive B-MANP
manufacturing E-MANP
is O
a O
viable O
technology S-CONPRI
in O
solving O
the O
design S-FEAT
issues O
of O
functional O
parts O
made O
of O
Ni-Mn-Ga O
magnetic O
shape-memory O
alloys S-MATE
( O
MSMA O
) O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
are O
capable O
of O
fabricating S-MANP
custom O
parts O
with O
complex O
geometrical O
shapes O
in O
a O
short O
period O
of O
time O
relative O
to O
traditional O
fabrication S-MANP
processes O
that O
require O
expensive O
tooling S-CONPRI
and O
several O
post B-CONPRI
processing E-CONPRI
steps O
. O


Material B-MANP
extrusion I-MANP
AM E-MANP
, O
known O
commercially O
as S-MATE
Fused O
Filament S-MATE
Fabrication S-MANP
( O
FFF S-MANP
) O
technology S-CONPRI
, O
is O
a O
widely O
used O
polymer S-MATE
AM B-MANP
process E-MANP
, O
however O
, O
the O
effects O
of O
inherent O
porosity S-PRO
on O
mechanical B-PRO
strength E-PRO
continues O
to O
be S-MATE
researched O
to O
identify O
strength S-PRO
improvement O
solutions O
. O


To O
address O
the O
effect O
of O
porosity S-PRO
and O
layer S-PARA
adhesion S-PRO
on O
mechanical B-CONPRI
properties E-CONPRI
( O
which O
can O
sometimes O
result O
in O
27–35 O
% O
lower O
ultimate B-PRO
tensile I-PRO
strength E-PRO
when O
compared O
to O
plastic B-MANP
injection I-MANP
molding E-MANP
) O
, O
an O
approach O
was O
employed O
to O
reinforce O
3D B-MANP
printed E-MANP
polycarbonate O
( O
PC S-MATE
) O
parts O
with O
continuous B-MATE
carbon I-MATE
fiber E-MATE
( O
CF O
) O
bundles O
. O


Results O
demonstrated O
a O
maximum O
of O
77 O
% O
increase O
in O
tensile S-PRO
yield O
strength S-PRO
when O
PC S-MATE
was O
reinforced S-CONPRI
with O
three O
CF O
bundles O
and O
micrographs O
showed O
multiple O
regions O
with O
zero O
porosity S-PRO
due O
to O
the O
CF O
inclusion S-MATE
. O


PC S-MATE
with O
three O
bundles O
of O
CF O
( O
modulus O
of O
3.36 O
GPa S-PRO
) O
showed O
85 O
% O
higher O
modulus B-PRO
of I-PRO
elasticity E-PRO
than O
the O
neat O
PC S-MATE
specimens O
( O
modulus O
of O
1.82 O
GPa S-PRO
) O
. O


The O
manual O
placement O
of O
CF O
and O
its O
impact S-CONPRI
on O
mechanical B-CONPRI
properties E-CONPRI
motivated O
the O
development O
of O
an O
automated O
selective O
deposition S-CONPRI
method O
using O
an O
ultrasonic O
embedding O
apparatus O
. O


Substantial O
technology S-CONPRI
development O
towards O
the O
embedding O
process S-CONPRI
of O
continuous B-MATE
carbon I-MATE
fiber E-MATE
bundles O
using O
ultrasonic O
energy O
was O
achieved O
in O
an O
automated O
fashion S-CONPRI
which O
is O
complementary O
of O
digital B-MANP
manufacturing E-MANP
and O
novel O
when O
compared O
to O
other O
existing O
processes S-CONPRI
. O


Laser B-MANP
Engineered I-MANP
Net I-MANP
Shaping E-MANP
( O
LENS™ O
) O
is O
a O
commercially O
available O
additive B-MANP
manufacturing E-MANP
technique O
that O
was O
used O
for O
one O
step S-CONPRI
manufacturing S-MANP
of O
bimetallic O
structures O
of O
stainless B-MATE
steel E-MATE
and O
Ti6Al4V S-MATE
( O
Ti64 S-MATE
) O
alloy S-MATE
. O


In O
the O
first O
approach O
, O
direct O
deposition S-CONPRI
of O
Ti64 S-MATE
on O
SS410 O
substrate S-MATE
and O
compositionally O
graded O
bimetallic O
structures O
were O
attempted O
without O
any O
intermediate O
bond O
layer S-PARA
. O


In O
the O
second O
approach O
, O
an O
intermediate O
NiCr O
bond O
layer S-PARA
( O
of O
thickness O
∼750 O
μm O
) O
was O
deposited O
to O
minimize O
thermal O
and O
residual B-PRO
stresses E-PRO
for O
these O
bimetallic O
structures O
. O


Direct O
deposition S-CONPRI
of O
Ti64 S-MATE
was O
successful O
only O
for O
a O
couple O
of O
layers O
before O
the O
structures O
were O
delaminated O
. O


Compositionally O
graded O
bonding S-CONPRI
was O
unsuccessful O
with O
the O
formation O
of O
brittle S-PRO
intermetallics O
and O
related O
residual B-PRO
stresses E-PRO
causing O
delamination S-CONPRI
. O


Using O
an O
intermediate O
NiCr O
layer S-PARA
, O
bimetallic O
structures O
were O
successfully O
fabricated S-CONPRI
. O


Our O
work O
is O
focused O
on O
LENS™ O
based O
processing O
approach O
and O
related O
microstructural B-CONPRI
evolution E-CONPRI
towards O
bimetallic O
structures O
. O


Residual B-PRO
stresses E-PRO
are O
measured O
for O
different O
deposition S-CONPRI
patterns O
. O


The O
evolution S-CONPRI
of O
residual B-PRO
stresses E-PRO
and O
distortions O
are O
modelled O
in O
3D S-CONPRI
. O


The O
effect O
of O
convective O
flow O
inside O
the O
molten B-CONPRI
pool E-CONPRI
are O
examined O
. O


Susceptibilities O
to O
delamination S-CONPRI
& O
warping S-CONPRI
of O
Ti-6Al-4V S-MATE
& O
Inconel B-MATE
718 E-MATE
are O
examined O
. O


Since O
the O
deposition S-CONPRI
patterns O
affect O
the O
stresses O
and O
distortions O
, O
we O
examined O
their O
effects O
on O
multi-layer O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
of O
Ti-6Al-4V S-MATE
and O
Inconel B-MATE
718 E-MATE
components S-MACEQ
experimentally O
and O
theoretically O
. O


We O
measured O
residual B-PRO
stresses E-PRO
by O
hole B-MANP
drilling E-MANP
method O
in O
three O
identical O
components S-MACEQ
printed O
using O
different O
deposition S-CONPRI
patterns O
. O


In O
order O
to O
understand O
the O
origin O
and O
the O
temporal O
evolution S-CONPRI
of O
residual B-PRO
stresses E-PRO
and O
distortion S-CONPRI
, O
we O
used O
a O
well-tested O
thermo-mechanical B-CONPRI
model E-CONPRI
after O
validating O
the O
computed O
results O
with O
experimental B-CONPRI
data E-CONPRI
for O
different O
deposition S-CONPRI
patterns O
. O


Distortions O
were O
also O
examined O
based O
on O
non-dimensional O
analysis.We O
show O
that O
printing O
with O
short O
track O
lengths O
can O
minimize O
residual B-PRO
stresses E-PRO
and O
distortion S-CONPRI
among O
the O
three O
patterns O
investigated O
for O
both O
alloys S-MATE
. O


Both O
Ti-6Al-4V S-MATE
and O
Inconel B-MATE
718 E-MATE
had O
similar O
fusion B-CONPRI
zone E-CONPRI
shape O
and O
size O
and O
were O
equally O
susceptible O
to O
deformation S-CONPRI
and O
warping S-CONPRI
, O
although O
Ti-6Al-4V S-MATE
was O
relatively O
less O
vulnerable O
to O
delamination S-CONPRI
due O
to O
its O
higher O
yield B-PRO
strength E-PRO
. O


A O
dimensionless O
strain S-PRO
parameter S-CONPRI
accurately S-CHAR
predicted O
the O
effects O
of O
WAAM S-MANP
parameters S-CONPRI
on O
distortion S-CONPRI
and O
this O
approach O
is O
especially O
useful O
when O
the O
detailed O
thermo-mechanical S-CONPRI
calculations O
can O
not O
be S-MATE
undertaken O
. O


The O
present O
work O
aims O
to O
investigate O
the O
mechanism S-CONPRI
of O
crack O
initiation O
induced O
by O
internal O
pores S-PRO
, O
which O
are O
inevitable O
in O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
and O
the O
influence O
of O
internal O
pores S-PRO
on O
the O
fatigue S-PRO
performance O
of O
directed O
energy O
deposited O
( O
DED S-MANP
) O
Ti-6.5Al-2Zr-Mo-V. O
After O
fatigue B-CHAR
test E-CHAR
under O
constant O
amplitude O
alternating O
stress S-PRO
at O
three O
stress S-PRO
levels O
, O
thirty-one O
pieces O
of O
DED S-MANP
Ti-6.5Al-2Zr-Mo-V O
specimens O
were O
found O
that O
cracks O
initiating O
from O
internal O
pores S-PRO
. O


Scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
( O
SEM S-CHAR
) O
and O
its O
accessories O
, O
such O
as S-MATE
energy O
dispersive O
spectrometry O
( O
EDS S-CHAR
) O
and O
electron O
backscattered O
diffraction S-CHAR
( O
EBSD S-CHAR
) O
, O
were O
used O
to O
analyze O
the O
characteristics O
of O
pore S-PRO
defects S-CONPRI
and O
clarify O
the O
mechanism S-CONPRI
of O
crack O
initiation O
. O


The O
results O
show O
that O
the O
specificity O
of O
the O
microstructure S-CONPRI
affected O
by O
the O
DED S-MANP
process O
and O
pore S-PRO
defects S-CONPRI
, O
such O
as S-MATE
segregation O
of O
Al S-MATE
and O
the O
existence O
of O
incomplete O
grain B-CONPRI
boundaries E-CONPRI
, O
are O
the O
main O
causes O
of O
crack O
initiation O
. O


Then O
, O
the O
crack O
initiation O
modes O
were O
divided O
into O
three O
types O
, O
and O
a O
classification S-CONPRI
model O
was O
established O
that O
can O
make O
the O
effect O
of O
pore S-PRO
defects S-CONPRI
on O
fatigue B-PRO
life E-PRO
clearer O
and O
more O
intuitive O
. O


The O
current O
study O
presents O
low O
cost O
3D B-MANP
printed E-MANP
materials O
with O
desired O
electrical S-APPL
charactrestics O
for O
RF/microwave O
applications O
. O


In O
contrast O
to O
the O
traditional B-MANP
manufacturing E-MANP
techniques O
of O
fabrication S-MANP
in O
electronics S-CONPRI
, O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
a O
proper O
technology S-CONPRI
for O
making O
parts O
with O
more O
advanced O
complex O
features O
. O


In O
this O
study O
, O
different O
3D B-MANP
printed E-MANP
configurations O
( O
infill S-PARA
density S-PRO
and O
pattern S-CONPRI
) O
of O
materials S-CONPRI
were O
printed O
with O
Fused B-MANP
Deposition I-MANP
Modeling E-MANP
( O
FDM S-MANP
) O
technique O
to O
achieve O
different O
electrical S-APPL
characteristics O
, O
which O
is O
used O
in O
design S-FEAT
and O
fabrication S-MANP
of O
RF/microwave O
structures O
. O


By O
different O
filling O
configurations O
, O
a O
range S-PARA
of O
relative O
permittivity O
has O
been O
obtained O
by O
using O
Nylon S-MATE
6 O
as S-MATE
an O
input O
filament S-MATE
for O
3D B-MANP
printing E-MANP
. O


In O
fact O
, O
by O
use O
of O
a O
known O
material S-MATE
such O
as S-MATE
Nylon O
6 O
, O
complex B-CONPRI
geometries E-CONPRI
can O
be S-MATE
3D B-MANP
printed E-MANP
with O
different O
dielectric S-MACEQ
behavior O
. O


Mechanical B-CONPRI
properties E-CONPRI
of O
the O
structures O
were O
investigated O
in O
order O
to O
estimate O
the O
quality S-CONPRI
of O
the O
3D B-APPL
printed I-APPL
parts E-APPL
in O
electronics S-CONPRI
’ O
industry S-APPL
. O


Considering O
these O
properties S-CONPRI
has O
direct O
influence O
on O
decision O
making O
through O
the O
design S-FEAT
of O
a O
3D B-CONPRI
structure E-CONPRI
with O
required O
electrical S-APPL
characteristics O
, O
while O
the O
mechanical B-CONPRI
properties E-CONPRI
are O
also O
considered O
. O


Binder B-MANP
jetting E-MANP
, O
a O
commercial O
additive B-MANP
manufacturing I-MANP
process E-MANP
that O
selectively O
deposits O
a O
liquid B-MATE
binder E-MATE
onto O
a O
powder B-MACEQ
bed E-MACEQ
, O
can O
become O
a O
viable O
method O
to O
additively B-MANP
manufacture E-MANP
ceramics O
. O


part O
density S-PRO
and O
geometric O
resolution S-PARA
) O
have O
not O
been O
investigated O
and O
no O
methodical O
approach O
exists O
for O
the O
process S-CONPRI
development O
of O
new O
materials S-CONPRI
. O


In O
this O
work O
, O
a O
parametric O
study O
consisting O
of O
18 O
experiments O
with O
unique O
process S-CONPRI
input O
combinations O
explores O
the O
influence O
of O
seven O
process S-CONPRI
inputs O
on O
the O
relative B-PRO
densities E-PRO
of O
as-printed O
( O
green O
) O
alumina S-MATE
( O
Al2O3 S-MATE
) O
parts O
. O


Sensitivity B-CONPRI
analyses E-CONPRI
compare O
the O
influence O
of O
each O
input O
on O
green O
densities O
. O


Multivariable O
linear O
and O
Gaussian S-CONPRI
process O
regressions O
provide O
models O
for O
predicting O
green O
densities O
as S-MATE
a O
function O
of O
binder B-MANP
jetting E-MANP
process O
inputs O
. O


The O
multivariable O
linear O
and O
Gaussian S-CONPRI
process O
regression B-CONPRI
models E-CONPRI
indicate O
that O
the O
green O
densities O
of O
alumina S-MATE
builds O
can O
be S-MATE
increased O
by O
decreasing O
the O
recoat O
speed O
and O
increasing O
the O
oscillator O
speed O
. O


The O
Gaussian S-CONPRI
process O
regression B-CONPRI
model E-CONPRI
further O
suggests O
that O
the O
green O
densities O
have O
nonlinear O
dependence O
on O
the O
rest O
of O
the O
process B-CONPRI
parameters E-CONPRI
. O


The O
models O
produced O
can O
assist O
operators O
in O
selecting O
process S-CONPRI
inputs O
that O
will O
result O
in O
a O
desired O
green O
density S-PRO
, O
allowing O
for O
the O
control O
of O
porosity S-PRO
in O
printed O
parts O
with O
a O
high O
degree O
of O
accuracy S-CHAR
. O


The O
methodology S-CONPRI
reported O
in O
this O
study O
can O
be S-MATE
leveraged O
for O
other O
powder S-MATE
systems O
and O
machines S-MACEQ
to O
predict O
and O
control O
the O
porosity S-PRO
of O
binder S-MATE
jetted O
parts O
for O
applications O
such O
as S-MATE
filters O
, O
bearings O
, O
electronics S-CONPRI
, O
and O
medical B-APPL
implants E-APPL
. O


Electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
has O
emerged O
as S-MATE
an O
important O
additive B-MANP
manufacturing E-MANP
technique O
. O


In O
this O
study O
, O
Alloy S-MATE
718 O
produced O
by O
EBM S-MANP
was O
investigated O
in O
as-built O
and O
post-treated O
conditions O
for O
microstructural S-CONPRI
characteristics O
and O
hardness S-PRO
. O


The O
post-treatments O
investigated O
were O
hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
and O
combined O
HIP S-MANP
+ O
heat B-MANP
treatment E-MANP
( O
HIP S-MANP
+ O
HT O
) O
carried O
out O
as S-MATE
a O
single O
cycle O
inside O
the O
HIP S-MANP
vessel O
. O


Both O
the O
post-treatments O
resulted O
in O
significant O
decrease O
in O
defects S-CONPRI
inevitably O
present O
in O
the O
as-built O
material S-MATE
. O


The O
columnar B-PRO
grain E-PRO
structure O
of O
the O
as-built O
material S-MATE
was O
found O
to O
be S-MATE
maintained O
after O
post-treatment S-MANP
, O
with O
some O
sporadic O
localized O
grain S-CONPRI
coarsening O
noted O
. O


Although O
HIP S-MANP
led O
to O
complete O
dissolution O
of O
δ O
and O
γ′′ O
phase S-CONPRI
, O
stable O
NbC O
and O
TiN S-MATE
( O
occasionally O
present O
) O
particles S-CONPRI
were O
observed O
in O
the O
post-treated O
specimens O
. O


Significant O
precipitation S-CONPRI
of O
γ′′ O
phase S-CONPRI
was O
observed O
after O
HIP S-MANP
+ O
HT O
, O
which O
was O
attributed O
to O
the O
two-step O
aging O
heat B-MANP
treatment E-MANP
carried O
out O
during O
HIP S-MANP
+ O
HT O
. O


The O
presence O
of O
γ′′ O
phase S-CONPRI
or O
otherwise O
was O
correlated S-CONPRI
to O
the O
hardness S-PRO
of O
the O
material S-MATE
. O


While O
the O
HIP S-MANP
treatment O
resulted O
in O
drop O
in O
hardness S-PRO
, O
HIP S-MANP
+ O
HT O
led S-APPL
to O
‘ O
recovery O
’ O
of O
the O
hardness S-PRO
to O
values O
exceeding O
those O
exhibited O
by O
the O
as-built O
material S-MATE
. O


The O
cold O
spray O
has O
been O
shown O
to O
be S-MATE
one O
of O
the O
promising O
additive B-MANP
manufacturing E-MANP
technologies O
to O
process S-CONPRI
Ultra O
High O
Molecular O
Weight S-PARA
Polyethylene S-MATE
( O
UHMWPE O
) O
-metal O
integrated O
systems O
by O
successfully O
being O
able O
to O
coat O
UHMWPE O
on O
metals S-MATE
using O
fumed O
nano-alumina O
( O
FNA O
) O
as S-MATE
UHMWPE O
particle S-CONPRI
surface O
modifiers O
. O


However O
, O
the O
exact O
mechanism S-CONPRI
of O
UHMWPE O
deposition S-CONPRI
and O
role O
of O
FNA O
was O
widely O
unknown O
. O


This O
study O
aims O
at O
identifying O
the O
fundamental O
parameters S-CONPRI
involved O
in O
high O
strain-rate O
UHMWPE O
deposition S-CONPRI
and O
their O
role O
in O
successful O
adhesion S-PRO
by O
a O
technique O
called O
Isolated O
Particle S-CONPRI
Deposition S-CONPRI
( O
IPD O
) O
. O


Major O
parameters S-CONPRI
that O
influenced O
the O
UHMWPE O
deposition S-CONPRI
efficiency O
significantly O
were O
the O
particle S-CONPRI
temperature O
and O
velocity O
and O
net O
surface S-CONPRI
activity O
of O
FNA O
. O


The O
stored O
elastic S-PRO
energy O
of O
UHMWPE O
decreases O
with O
increase O
in O
temperature S-PARA
, O
and O
the O
deposition S-CONPRI
criterion O
for O
a O
successful O
UHMWPE O
deposition S-CONPRI
is O
not O
to O
have O
net O
stored O
elastic S-PRO
energy O
after O
impact S-CONPRI
. O


Effect O
of O
FNA O
was O
seen O
in O
generating O
H-bonds O
that O
helped O
to O
establish O
bridge S-APPL
bond O
at O
UHMWPE-substrate O
interface S-CONPRI
. O


Innovative O
fabrication S-MANP
of O
a O
< O
NiCrAlY-IN625 O
> O
system O
by O
SLM S-MANP
was O
demonstrated O
. O


Several O
criteria O
were O
used O
to O
select O
the O
most O
appropriate O
SLM S-MANP
process S-CONPRI
conditions O
. O


As-built O
coatings S-APPL
exhibited O
significant O
dilution O
characteristic O
of O
SLM S-MANP
remelting O
. O


Laser B-PARA
power E-PARA
P O
= O
250 O
W O
and O
scanning B-PARA
speed E-PARA
v O
= O
800 O
mm/s O
were O
found O
optimal O
. O


The O
present O
study O
investigated O
for O
the O
first O
time O
the O
feasibility S-CONPRI
of O
producing O
by O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
a O
NiCrAlY O
bond B-APPL
coat E-APPL
material O
directly O
onto O
an O
IN625 O
substrate S-MATE
itself O
produced O
by O
SLM S-MANP
. O


A O
typical O
parameters B-CONPRI
optimization E-CONPRI
was O
conducted O
by O
varying O
laser B-PARA
power E-PARA
( O
P S-MATE
) O
and O
scanning B-PARA
speed E-PARA
( O
v S-MATE
) O
. O


Single-line O
scanning S-CONPRI
tracks O
and O
two-layer O
coatings S-APPL
were O
carried O
out O
and O
analyzed O
for O
15 O
different O
P/v O
conditions O
. O


Several O
criteria O
were O
defined O
for O
the O
selection O
of O
appropriate O
SLM S-MANP
parameters S-CONPRI
. O


The O
results O
showed O
significant O
remelting O
of O
the O
underlying O
substrate S-MATE
, O
which O
is O
a O
typical O
feature S-FEAT
of O
SLM B-MANP
manufacturing E-MANP
. O


This O
led S-APPL
to O
the O
formation O
of O
an O
intermediate O
dilution O
zone O
characterized O
by O
substantial O
mixing S-CONPRI
between O
IN625 O
superalloy O
substrate S-MATE
and O
NiCrAlY O
bond B-APPL
coat E-APPL
suggesting O
excellent O
metallurgical B-CONPRI
bonding E-CONPRI
. O


Optimum O
processing O
conditions O
were O
found O
for O
P S-MATE
= O
250 O
W O
and O
v S-MATE
= O
800 O
mm/s O
. O


It O
produced O
a O
dense O
242 O
μm O
thick O
bond B-APPL
coat E-APPL
including O
a O
36 O
% O
dilution O
zone O
. O


The O
SLMed S-MANP
< O
NiCrAlY-IN625 O
> O
system O
exhibited O
a O
smooth O
microhardness S-CONPRI
profile O
slightly O
increasing O
from O
275 O
Hv O
in O
the O
bond B-APPL
coat E-APPL
to O
305 O
Hv O
in O
the O
substrate S-MATE
. O


A O
progressive O
Al S-MATE
concentration O
distribution S-CONPRI
between O
the O
phases O
and O
low O
residual B-PRO
stress E-PRO
levels O
were O
found O
in O
the O
system O
. O


This O
suggested O
that O
SLM S-MANP
might O
be S-MATE
a O
valuable O
alternative O
manufacturing B-MANP
process E-MANP
for O
bond B-APPL
coat E-APPL
systems O
promoting O
excellent O
adhesion S-PRO
for O
high O
temperature S-PARA
applications O
. O


Coupling O
3D S-CONPRI
Discrete O
Element S-MATE
and O
Monte O
Carlo O
Ray O
tracing O
methods O
to O
simulate O
the O
laser S-ENAT
polymer O
interaction O
. O


Multiphysics O
coupling O
: O
conductive O
and O
radiative O
heat B-CONPRI
transfers E-CONPRI
with O
scattering O
, O
phase S-CONPRI
changes O
, O
coalescence O
, O
air O
diffusion S-CONPRI
, O
in O
participating O
granular O
medium O
. O


Application O
to O
additive B-MANP
manufacturing I-MANP
process E-MANP
. O


3D S-CONPRI
Numerical O
and O
experimental S-CONPRI
validations O
. O


A O
numerical O
framework S-CONPRI
based O
on O
a O
modified O
Monte O
Carlo O
ray-tracing O
method O
and O
the O
Discrete B-CONPRI
Element I-CONPRI
Method E-CONPRI
( O
DEM O
) O
is O
developed O
to O
predict O
the O
physical O
behavior O
of O
discrete O
particles S-CONPRI
during O
the O
Powder B-MANP
Bed I-MANP
Fusion E-MANP
( O
SLS S-MANP
) O
process S-CONPRI
. O


A O
comprehensive O
model S-CONPRI
coupling O
all O
major O
aspects O
of O
the O
underlying O
physics S-CONPRI
and O
the O
corresponding O
numerical O
framework S-CONPRI
, O
accounting O
for O
radiative O
heat B-CONPRI
transfer E-CONPRI
, O
heat B-CONPRI
conduction E-CONPRI
, O
sintering S-MANP
and O
granular O
dynamics O
among O
others O
, O
is O
developed O
. O


The O
spatially O
and O
temporally O
varying O
distribution S-CONPRI
of O
heat S-CONPRI
and O
displacement O
within O
the O
additively B-MANP
manufactured E-MANP
object O
are O
captured O
in O
detail O
. O


The O
model S-CONPRI
is O
validated O
through O
the O
comparison O
of O
simulated O
results O
with O
existing O
experimental S-CONPRI
results O
in O
the O
literature O
. O


Inconsistent O
part O
quality S-CONPRI
is O
a O
challenge O
to O
the O
widespread O
adoption O
of O
powder-bed O
fusion S-CONPRI
additive B-MANP
manufacturing E-MANP
. O


Previous O
efforts O
to O
monitor S-CONPRI
the O
PBF S-MANP
process O
in B-CONPRI
situ E-CONPRI
have O
been O
mostly O
limited O
to O
single O
tracks O
. O


The O
lack O
of O
quantitative S-CONPRI
, O
in B-CONPRI
situ E-CONPRI
monitoring O
results O
from O
full O
3D S-CONPRI
PBF O
builds S-CHAR
remains O
a O
barrier O
to O
closed-loop B-MACEQ
control E-MACEQ
. O


We O
track O
morphology S-CONPRI
in B-CONPRI
situ E-CONPRI
using O
coherent O
imaging S-APPL
, O
providing O
an O
immediate O
check O
on O
surface B-PRO
roughness E-PRO
, O
recoater B-MACEQ
blade E-MACEQ
damage S-PRO
, O
and O
powder S-MATE
packing O
density S-PRO
. O


Defects S-CONPRI
are O
corrected O
through O
manual O
closed-loop B-MACEQ
control E-MACEQ
; O
protrusions O
and O
depressions O
identified O
by O
in B-CONPRI
situ E-CONPRI
imaging S-APPL
are O
compensated O
through O
laser B-MANP
ablation E-MANP
and O
refilling O
, O
respectively O
, O
during O
a O
3D S-CONPRI
build O
. O


Maximum O
surface B-PRO
roughness E-PRO
is O
reduced O
by O
54 O
% O
and O
the O
number B-PARA
of I-PARA
layers E-PARA
with O
increased O
surface B-PRO
roughness E-PRO
relative O
to O
the O
steady-state O
value O
is O
reduced O
by O
60 O
% O
. O


Manual O
closed-loop B-MACEQ
control E-MACEQ
, O
successfully O
achieved O
using O
coherent O
imaging S-APPL
of O
PBF S-MANP
layer S-PARA
morphology O
, O
is O
an O
important O
step S-CONPRI
towards O
full O
feedback S-PARA
control O
capabilities O
. O


Laser S-ENAT
direct O
deposition S-CONPRI
model O
simulates O
thermal O
behavior O
in O
Ti6Al4V S-MATE
depositions O
. O


Cellular O
automaton O
model S-CONPRI
predicts O
the O
solidification S-CONPRI
and O
distribution S-CONPRI
of O
β O
grains S-CONPRI
. O


Phase S-CONPRI
prediction O
model S-CONPRI
simulates O
the O
solid-state B-CONPRI
phase E-CONPRI
transformation O
of O
β→α/α O
’ O
. O


Microhardness S-CONPRI
was O
assessed O
based O
on O
the O
predicted S-CONPRI
volume O
fraction S-CONPRI
of O
α O
’ O
. O


Simulation S-ENAT
results O
were O
validated O
with O
experimental B-CONPRI
data E-CONPRI
in O
good O
agreement O
. O


In O
this O
paper O
, O
a O
multiphysics O
and O
multiscale O
integrated O
simulation S-ENAT
framework S-CONPRI
is O
established O
to O
link O
the O
thermal O
history O
with O
the O
microstructural B-CONPRI
evolution E-CONPRI
and O
resulting O
properties S-CONPRI
of O
Ti6Al4V S-MATE
in O
additive B-MANP
manufacturing I-MANP
processes E-MANP
by O
combining O
: O
( O
1 O
) O
a O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
multiphysics O
modeling S-ENAT
of O
quasi-steady-state O
deposition S-CONPRI
geometry O
and O
thermal O
history O
in O
the O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
process S-CONPRI
, O
( O
2 O
) O
a O
3D S-CONPRI
cellular O
automata O
modeling S-ENAT
of O
the O
solidification B-CONPRI
grain E-CONPRI
structure O
, O
and O
( O
3 O
) O
a O
diffusion/diffusionless O
kinetic O
modeling S-ENAT
of O
solid-state B-CONPRI
phase E-CONPRI
transformation O
and O
microhardness S-CONPRI
prediction O
based O
on O
the O
simulated O
phase S-CONPRI
volume O
fractions O
. O


By O
applying O
to O
Ti6Al4V S-MATE
, O
this O
integrated O
simulation S-ENAT
framework S-CONPRI
demonstrates O
its O
feasibility S-CONPRI
in O
modeling S-ENAT
complex O
microstructural B-CONPRI
evolution E-CONPRI
and O
phase S-CONPRI
transformation O
during O
the O
multi-track O
DED S-MANP
process O
. O


The O
simulated O
track O
geometry S-CONPRI
and O
thermal O
history O
agree O
well O
with O
experimental S-CONPRI
results O
. O


Coupled O
with O
the O
extracted S-CONPRI
temperature O
profiles S-FEAT
and O
heating/cooling O
rates O
, O
the O
competitive O
growth O
of O
β O
grains S-CONPRI
upon O
solidification S-CONPRI
of O
the O
molten B-CONPRI
pool E-CONPRI
is O
successfully O
predicted S-CONPRI
. O


The O
solid-state S-CONPRI
β→α/α´ O
transformation O
in O
the O
fusion B-CONPRI
zone E-CONPRI
and O
heat-affected O
zone O
is O
then O
captured O
by O
the O
kinetic O
solid-state B-CONPRI
phase I-CONPRI
prediction I-CONPRI
model E-CONPRI
. O


With O
the O
predicted S-CONPRI
volume O
fractions O
of O
α O
and O
α´ O
in O
the O
final O
microstructure S-CONPRI
, O
the O
microhardness S-CONPRI
is O
assessed O
, O
matching O
the O
experimental S-CONPRI
measurements O
. O


Laser B-MANP
sintering E-MANP
( O
LS O
) O
, O
as S-MATE
an O
additive B-MANP
manufacturing I-MANP
process E-MANP
for O
production S-MANP
of O
polymer S-MATE
structures O
, O
provides O
the O
possibility O
of O
directly O
manufacturing S-MANP
personalized O
, O
structural O
motorcycle O
components S-MACEQ
for O
motor O
sports O
. O


To O
create O
such O
lightweight B-MACEQ
structures E-MACEQ
, O
the O
wall B-FEAT
thickness E-FEAT
and O
position O
limits S-CONPRI
of O
the O
LS O
systems O
need O
to O
be S-MATE
investigated O
in O
detail O
. O


Appearing O
process-related O
flaws S-CONPRI
such O
as S-MATE
different O
amounts O
of O
crystallinity O
, O
surface B-PRO
roughness E-PRO
, O
and O
defects S-CONPRI
such O
as S-MATE
pores O
exhibit O
dimensions S-FEAT
similar O
to O
the O
wall B-FEAT
thickness E-FEAT
. O


To O
study O
the O
process-related O
effects O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
450 O
tensile B-CHAR
test E-CHAR
specimens O
in O
z-direction S-FEAT
, O
the O
build B-PARA
areas E-PARA
of O
two O
LS O
systems O
were O
screened O
and O
a O
detailed O
wall B-FEAT
thickness E-FEAT
investigation O
was O
conducted O
. O


In O
addition O
, O
dynamic B-CONPRI
mechanical I-CONPRI
analysis E-CONPRI
, O
differential O
scanning S-CONPRI
calorimetry O
, O
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
for O
several O
wall B-FEAT
thicknesses E-FEAT
similar O
to O
the O
spot B-PARA
size E-PARA
were O
conducted O
. O


The O
investigations O
showed O
that O
the O
Young O
's O
moduli O
and O
ultimate B-PRO
tensile I-PRO
strengths E-PRO
of O
the O
produced O
specimens O
of O
the O
two O
commercial O
EOS S-APPL
systems O
, O
P396 O
and O
P770 O
, O
are O
similar O
and O
evenly O
distributed O
. O


Furthermore O
, O
structures O
with O
a O
thickness O
below O
1 O
mm S-MANP
showed O
distinctive O
losses O
in O
stiffness S-PRO
, O
ultimate B-PRO
tensile I-PRO
strength E-PRO
, O
and O
elongation S-PRO
at O
break O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
an O
additive B-MANP
manufacturing E-MANP
and O
3D B-ENAT
printing I-ENAT
technology E-ENAT
which O
offers O
flexibility S-PRO
in O
geometric O
design S-FEAT
and O
rapid O
production S-MANP
of O
complex B-CONPRI
structures E-CONPRI
. O


Maraging B-MATE
steels E-MATE
have O
high O
strength S-PRO
and O
good O
ductility S-PRO
, O
and O
therefore O
have O
been O
widely O
used O
in O
aerospace S-APPL
and O
tooling S-CONPRI
sectors O
for O
many O
years O
. O


This O
work O
aims O
to O
study O
the O
influence O
of O
aging O
temperature S-PARA
and O
aging O
time O
on O
the O
microstructure S-CONPRI
, O
mechanical B-CONPRI
property E-CONPRI
( O
hardness S-PRO
, O
strength S-PRO
and O
ductility S-PRO
) O
and O
tribological B-CONPRI
property E-CONPRI
of O
SLM S-MANP
maraging S-MANP
18Ni-300 O
steel S-MATE
. O


The O
results O
reveal O
that O
the O
aging O
conditions O
had O
a O
significant O
impact S-CONPRI
on O
the O
strength S-PRO
and O
wear-resistance O
of O
the O
SLM S-MANP
maraging B-MATE
steel E-MATE
. O


The O
optimal O
aging O
conditions O
for O
the O
SLM S-MANP
maraging B-MATE
steel E-MATE
produced O
in O
this O
work O
were O
490 O
°C O
for O
3 O
h O
under O
which O
strength S-PRO
and O
wear-resistance O
were O
maximised O
. O


Lower O
or O
higher O
aging O
temperature S-PARA
led S-APPL
to O
under-aging O
or O
over-aging O
phenomena O
, O
reducing O
the O
strength S-PRO
and O
wear-resistance O
performance S-CONPRI
. O


Shorter O
or O
longer O
aging O
time O
also O
resulted O
in O
the O
decrease O
of O
strength S-PRO
and O
wear-resistance O
performance S-CONPRI
of O
the O
SLM S-MANP
maraging B-MATE
steel E-MATE
as S-MATE
compared O
with O
the O
optimal O
conditions O
. O


The O
variation S-CONPRI
of O
the O
mechanical S-APPL
and O
tribological B-CONPRI
properties E-CONPRI
is O
primarily O
due O
to O
changes O
in O
phase B-CONPRI
compositions E-CONPRI
and O
microstructures S-MATE
of O
the O
SLM S-MANP
maraging B-MATE
steels E-MATE
. O


The O
integration O
of O
novel O
additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
materials S-CONPRI
and O
processes S-CONPRI
with O
traditional O
materials S-CONPRI
and O
manufacturing S-MANP
techniques O
, O
including O
the O
insertion O
of O
commercial O
off-the-shelf O
( O
COTS O
) O
components S-MACEQ
such O
as S-MATE
resistors O
, O
switches O
, O
batteries O
and O
light B-APPL
emitting I-APPL
diodes E-APPL
( O
LEDs S-APPL
) O
, O
has O
led S-APPL
to O
the O
development O
of O
increasingly O
complex O
‘ O
hybrid O
’ O
electronics S-CONPRI
including O
: O
antennas O
, O
waveguides O
, O
radio B-CONPRI
frequency E-CONPRI
identification O
( O
RFID O
) O
tags O
, O
various O
sensors S-MACEQ
, O
circuits O
and O
devices O
. O


Here O
we O
examine O
the O
resiliency O
and O
radio B-CONPRI
frequency E-CONPRI
( O
RF O
) O
performance S-CONPRI
of O
two O
commercially O
available O
conductive O
inks O
( O
DuPont O
CB028 O
and O
KA801 O
) O
printed O
onto O
a O
radar O
transparent S-CONPRI
substrate S-MATE
( O
poly O
ether O
, O
ether O
ketone O
; O
PEEK S-MATE
) O
. O


The O
quality S-CONPRI
of O
ink S-MATE
adhesion S-PRO
, O
a O
factor O
found O
to O
directly O
correlate O
with O
antenna O
performance S-CONPRI
, O
is O
examined O
via O
adhesion S-PRO
testing O
after O
exposure S-CONPRI
to O
high O
accelerations O
up O
to O
20,000 O
g O
and O
temperature S-PARA
cycling O
from O
−54 O
°C O
to O
+71 O
°C O
. O


Overall O
, O
the O
designs S-FEAT
, O
procedures O
and O
results O
provide O
a O
framework S-CONPRI
for O
multi-materials O
resiliency O
assessment O
as S-MATE
well O
as S-MATE
aspects O
unique O
to O
materials S-CONPRI
resiliency O
under O
harsh O
environmental O
conditions O
. O


Lattice B-FEAT
structures E-FEAT
have O
been O
intensively O
researched O
for O
their O
light-weight S-PRO
properties O
and O
unique O
functions O
in O
specific O
applications O
such O
as S-MATE
for O
impact S-CONPRI
protection O
and O
biomedical-implant O
. O


The O
advancement O
of O
additive B-MANP
manufacturing E-MANP
simplifies O
the O
fabrication S-MANP
of O
lattice B-FEAT
structures E-FEAT
as S-MATE
opposed O
to O
conventional B-MANP
manufacturing E-MANP
and O
this O
opens O
doors O
to O
create O
more O
designs S-FEAT
. O


There O
are O
ample O
research S-CONPRI
opportunities O
to O
explore O
the O
mechanical S-APPL
performance O
of O
the O
lattice B-FEAT
structures E-FEAT
fabricated S-CONPRI
by O
this O
technology S-CONPRI
specific O
to O
each O
design S-FEAT
. O


This O
study O
filled O
the O
research S-CONPRI
gap O
by O
investigating O
the O
deformation S-CONPRI
behaviour O
and O
compressive O
properties S-CONPRI
of O
Ti-6Al-4V S-MATE
lattice B-FEAT
structures E-FEAT
fabricated S-CONPRI
by O
a O
powder B-MANP
bed I-MANP
fusion E-MANP
method O
from O
the O
aspects O
of O
design S-FEAT
, O
orientation S-CONPRI
and O
density S-PRO
. O


The O
results O
were O
compared O
between O
cubic O
and O
honeycomb S-CONPRI
unit O
designs S-FEAT
, O
between O
two O
orientations S-CONPRI
and O
across O
five O
different O
densities O
. O


Results O
showed O
that O
both O
cubic O
and O
honeycomb S-CONPRI
lattice O
deformed S-MANP
in O
a O
layer-by-layer S-CONPRI
manner O
for O
the O
first O
tested O
orientation S-CONPRI
, O
where O
vertical S-CONPRI
struts S-MACEQ
were O
parallel O
to O
the O
compression S-PRO
direction O
. O


In O
the O
second O
tested O
orientation S-CONPRI
, O
where O
lattice S-CONPRI
struts O
were O
angled O
with O
respect O
to O
the O
direction O
of O
compression S-PRO
, O
the O
deformation S-CONPRI
behaviour O
was O
observed O
as S-MATE
a O
single O
diagonal O
shear O
band O
. O


As S-MATE
the O
density S-PRO
of O
the O
structure S-CONPRI
increased O
, O
the O
deformation S-CONPRI
pattern O
shifted O
towards O
diagonal O
crack O
similar O
to O
a O
solid O
part O
. O


Honeycomb S-CONPRI
lattice O
structure S-CONPRI
had O
the O
highest O
density S-PRO
efficiency O
for O
energy B-CHAR
absorption E-CHAR
in O
both O
orientations S-CONPRI
and O
for O
first O
maximum O
compressive B-PRO
strength E-PRO
in O
the O
second O
orientation S-CONPRI
. O


Change O
of O
orientation S-CONPRI
significantly O
affected O
the O
efficiency O
in O
plateau O
stress S-PRO
for O
cubic O
lattice B-FEAT
structure E-FEAT
, O
and O
compressive O
property S-CONPRI
values O
for O
honeycomb S-CONPRI
lattice O
structure S-CONPRI
. O


Comparative O
studies O
showed O
that O
the O
first O
maximum O
compressive B-PRO
strength E-PRO
and O
energy B-CHAR
absorption E-CHAR
of O
the O
lattice B-FEAT
structures E-FEAT
in O
the O
first O
orientation S-CONPRI
were O
higher O
than O
most O
of O
the O
lattice B-FEAT
designs E-FEAT
from O
other O
literature O
. O


This O
paper O
describes O
a O
facile O
method O
to O
fabricate S-MANP
complex O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
antennas O
by O
vacuum O
filling O
gallium-based O
liquid B-MATE
metals E-MATE
into O
3D B-MANP
printed E-MANP
cavities O
at O
room O
temperature S-PARA
. O


To O
create O
the O
cavities O
, O
a O
commercial O
printer S-MACEQ
co-prints O
a O
sacrificial O
wax-like O
material S-MATE
with O
an O
acrylic S-MATE
resin O
. O


Dissolving O
the O
printed O
wax S-MATE
in O
oil S-MATE
creates O
cavities O
as S-MATE
small O
as S-MATE
500 O
μm O
within O
the O
acrylic S-MATE
monolith O
. O


Placing O
the O
entire O
structure S-CONPRI
under O
vacuum O
evacuates O
most O
of O
the O
air O
from O
these O
cavities O
through O
a O
reservoir O
of O
liquid B-MATE
metal E-MATE
that O
covers O
a O
single O
inlet S-MACEQ
. O


Returning O
the O
assembly S-MANP
to O
atmospheric O
pressure S-CONPRI
pushes O
the O
metal S-MATE
from O
the O
reservoir O
into O
the O
cavities O
due O
to O
the O
pressure S-CONPRI
differential O
. O


This O
method O
enables O
filling O
of O
the O
closed O
internal O
cavities O
to O
create O
planar O
and O
curved O
conductive O
3D B-FEAT
geometries E-FEAT
without O
leaving O
pockets O
of O
trapped O
air O
that O
lead S-MATE
to O
defects S-CONPRI
. O


An O
advantage O
of O
this O
technique O
is O
the O
ability O
to O
rapidly O
prototype B-CONPRI
3D E-CONPRI
embedded O
antennas O
and O
other O
microwave S-ENAT
components S-MACEQ
with O
metallic S-MATE
conductivity S-PRO
at O
room O
temperature S-PARA
using O
a O
simple S-MANP
process S-CONPRI
. O


Because O
the O
conductors S-MATE
are O
liquid O
, O
they O
also O
enable O
the O
possibility O
of O
manipulating O
the O
properties S-CONPRI
of O
such O
devices O
by O
flowing O
metal S-MATE
in O
or O
out O
of O
selected O
cavities O
. O


The O
measured O
electrical B-CONPRI
properties E-CONPRI
of O
fabricated S-CONPRI
devices O
match O
well O
to O
electromagnetic O
simulations S-ENAT
, O
indicating O
that O
the O
approach O
described O
here O
forms O
antenna O
geometries S-CONPRI
with O
high O
fidelity O
. O


Residual B-PRO
stresses E-PRO
and O
distortion S-CONPRI
in O
Additive B-MANP
Manufactured E-MANP
( O
AM S-MANP
) O
parts O
are O
two O
key O
obstacles O
which O
seriously O
hinder O
the O
wide O
application O
of O
this O
technology S-CONPRI
. O


Nowadays O
, O
understanding O
the O
thermomechanical S-CONPRI
behavior O
induced O
by O
the O
AM B-MANP
process E-MANP
is O
still O
a O
complex O
task O
which O
must O
take O
into O
account O
the O
effects O
of O
both O
the O
process S-CONPRI
and O
the O
material S-MATE
parameters O
, O
the O
microstructure B-CONPRI
evolution E-CONPRI
as S-MATE
well O
as S-MATE
the O
pre-heating O
strategy O
. O


One O
of O
the O
challenges O
of O
this O
work O
is O
to O
increase O
the O
complexity S-CONPRI
of O
the O
geometries S-CONPRI
used O
to O
study O
the O
thermomechanical S-CONPRI
behavior O
induced O
by O
the O
AM B-MANP
process E-MANP
. O


The O
samples S-CONPRI
have O
been O
fabricated S-CONPRI
by O
Directed B-MANP
Energy I-MANP
Deposition E-MANP
( O
DED S-MANP
) O
. O


In-situ S-CONPRI
thermal O
and O
distortion S-CONPRI
histories O
of O
the O
substrate S-MATE
are O
measured O
in O
order O
to O
calibrate O
the O
3D S-CONPRI
coupled O
thermo-mechanical B-CONPRI
model E-CONPRI
. O


Once O
the O
numerical O
results O
showed O
a O
good O
agreement O
with O
the O
temperature S-PARA
measurements O
, O
the O
validated O
model S-CONPRI
has O
been O
used O
to O
predict O
the O
residual B-PRO
stresses E-PRO
and O
distortions O
. O


Different O
process B-CONPRI
parameters E-CONPRI
have O
been O
analyzed O
to O
study O
their O
sensitivity S-PARA
to O
the O
process S-CONPRI
assessment O
. O


Different O
preheating S-MANP
strategies O
have O
been O
also O
analyzed O
to O
check O
their O
effectiveness S-CONPRI
on O
the O
mitigation O
of O
both O
distortions O
and O
residual B-PRO
stresses E-PRO
. O


Finally O
, O
some O
simplifications O
of O
the O
actual O
scanning S-CONPRI
sequence O
are O
proposed O
to O
reduce O
the O
computational O
cost O
without O
loss O
of O
the O
accuracy S-CHAR
of O
the O
simulation S-ENAT
framework S-CONPRI
. O


Laser-Powder O
Bed B-MANP
Fusion E-MANP
( O
L-PBF S-MANP
) O
, O
an O
additive B-MANP
manufacturing I-MANP
process E-MANP
, O
produces O
a O
distinctive O
microstructure S-CONPRI
that O
closely O
resembles O
the O
weld B-MATE
metal E-MATE
microstructure S-CONPRI
but O
at O
a O
much O
finer O
scale O
. O


The O
solidification B-CONPRI
parameters E-CONPRI
, O
particularly O
temperature B-PARA
gradient E-PARA
and O
solidification B-PARA
rate E-PARA
, O
are O
important O
to O
study O
the O
as-built O
microstructure S-CONPRI
. O


In O
the O
present O
study O
, O
a O
computational O
framework S-CONPRI
with O
meso-scale O
resolution S-PARA
is O
developed O
for O
L-PBF S-MANP
of O
Inconel® O
718 O
( O
IN718 S-MATE
) O
, O
a O
Ni-base O
superalloy O
. O


The O
framework S-CONPRI
combines O
a O
powder S-MATE
packing O
model S-CONPRI
based O
on O
Discrete B-CONPRI
Element I-CONPRI
Method E-CONPRI
and O
a O
3-D S-CONPRI
transient O
heat S-CONPRI
and O
fluid B-PRO
flow E-PRO
simulation O
. O


The O
latter O
, O
i.e. O
, O
the O
molten B-CONPRI
pool E-CONPRI
model S-CONPRI
, O
captures O
the O
interaction O
between O
laser B-CONPRI
beam E-CONPRI
and O
individual O
powder B-MATE
particles E-MATE
including O
free B-CONPRI
surface E-CONPRI
evolution S-CONPRI
, O
surface B-PRO
tension E-PRO
and O
evaporation S-CONPRI
. O


The O
solidification B-CONPRI
parameters E-CONPRI
, O
calculated O
from O
the O
temperature S-PARA
fields O
, O
are O
used O
to O
assess O
the O
solidification B-CONPRI
morphology E-CONPRI
and O
grain B-PRO
size E-PRO
using O
existing O
theoretical B-CONPRI
models E-CONPRI
. O


The O
IN718 S-MATE
coupon O
built O
by O
L-PBF S-MANP
are O
characterized O
using O
optical S-CHAR
and O
scanning B-CHAR
electron I-CHAR
microscopies E-CHAR
. O


The O
experimental B-CONPRI
data E-CONPRI
of O
molten B-CONPRI
pool E-CONPRI
size O
and O
solidification B-CONPRI
microstructure E-CONPRI
are O
compared O
to O
the O
corresponding O
simulation S-ENAT
results O
. O


Selective B-MANP
laser I-MANP
sintering E-MANP
, O
also O
called O
laser B-MANP
sintering E-MANP
( O
LS O
) O
, O
is O
an O
additive B-MANP
manufacturing I-MANP
process E-MANP
that O
requires O
micronized O
plastic S-MATE
powder O
. O


Recently O
, O
we O
showed O
poly O
( O
ethylene O
terephthalate O
( O
PET O
) O
powder S-MATE
is O
a O
suitable O
material S-MATE
for O
LS O
, O
with O
a O
comparable O
printing B-CONPRI
performance E-CONPRI
as S-MATE
the O
current O
front-runner O
, O
polyamide B-MATE
12 E-MATE
( O
PA12 S-MATE
) O
. O


However O
, O
the O
LS O
process S-CONPRI
, O
by O
its O
nature O
, O
leaves O
unused O
powder S-MATE
that O
has O
been O
exposed O
to O
heat S-CONPRI
for O
prolonged O
time O
, O
and O
this O
powder S-MATE
may O
not O
be S-MATE
fully O
re-usable O
due O
to O
degradation.In O
this O
work O
, O
the O
re-use O
potential O
of O
heat-exposed O
PET O
powder S-MATE
is O
established O
. O


This O
is O
a O
matter O
of O
crucial O
importance O
as S-MATE
powders O
suitable O
for O
LS O
are O
very O
expensive O
, O
and O
the O
powder S-MATE
left O
after O
a O
building O
episode O
has O
to O
be S-MATE
re-used O
. O


Heat-exposed O
PA12 S-MATE
has O
to O
be S-MATE
blended O
or O
refreshed O
with O
virgin B-MATE
powder E-MATE
, O
to O
avoid O
printing O
defects S-CONPRI
. O


In O
contrast O
, O
heat-exposed O
PET O
powder S-MATE
, O
after O
96 O
h O
at O
210 O
°C O
, O
could O
be S-MATE
used O
, O
without O
refreshing O
with O
a O
portion O
of O
virgin B-MATE
powder E-MATE
. O


The O
printed O
articles O
from O
heat-exposed O
powders S-MATE
were O
as S-MATE
good O
as S-MATE
those O
from O
the O
fresh O
powder S-MATE
. O


There O
was O
no O
cross-linking S-CONPRI
and O
there O
was O
only O
a O
minor O
increase O
in O
the O
molecular O
weight S-PARA
of O
the O
powder S-MATE
after O
96 O
h O
, O
at O
210 O
°C O
. O


Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM S-MANP
) O
is O
an O
increasingly O
used O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
technique O
employed O
by O
many O
industrial B-CONPRI
sectors E-CONPRI
, O
including O
the O
medical B-APPL
device E-APPL
and O
aerospace B-APPL
industries E-APPL
. O


The O
application O
of O
this O
technology S-CONPRI
is O
, O
however O
, O
challenged O
by O
the O
lack O
of O
process B-CONPRI
monitoring E-CONPRI
and O
control B-MACEQ
system E-MACEQ
that O
underpins O
process S-CONPRI
repeatability O
and O
part O
quality S-CONPRI
reproducibility O
. O


An O
electronic O
imaging S-APPL
system O
prototype S-CONPRI
has O
been O
developed O
to O
serve O
as S-MATE
an O
EBM S-MANP
monitoring O
equipment S-MACEQ
, O
the O
capabilities O
of O
which O
have O
been O
verified O
at O
room O
temperature S-PARA
and O
at O
320 O
± O
10 O
°C O
. O


Nevertheless O
, O
in O
order O
to O
fully O
assess O
the O
applicability O
of O
this O
technique O
, O
electronic O
imaging S-APPL
needs O
to O
be S-MATE
conducted O
at O
a O
range S-PARA
of O
elevated O
temperatures S-PARA
to O
fully O
understand O
the O
influence O
of O
temperature S-PARA
on O
electronic O
image S-CONPRI
quality O
. O


Building O
on O
top O
of O
the O
previous O
electronic O
imaging S-APPL
trials O
at O
room O
temperature S-PARA
, O
this O
paper O
disseminates O
the O
essential O
step S-CONPRI
changes O
to O
allow O
high O
temperature S-PARA
electronic O
imaging S-APPL
: O
( O
1 O
) O
modification O
of O
a O
signal O
amplifier O
to O
deal O
with O
high O
electron B-CONPRI
beam E-CONPRI
current O
during O
electron B-CONPRI
beam I-CONPRI
heating E-CONPRI
, O
and O
( O
2 O
) O
design S-FEAT
of O
an O
open-source S-CONPRI
electron B-CONPRI
beam I-CONPRI
heating E-CONPRI
algorithm S-CONPRI
to O
maximise O
flexibility S-PRO
for O
user-defined O
heating S-MANP
strategy O
. O


In O
this O
paper O
, O
electronic O
imaging S-APPL
pilot O
trials O
at O
elevated O
temperatures S-PARA
, O
ranging O
from O
room O
temperature S-PARA
to O
650°C O
, O
were O
carried O
out O
. O


Image S-CONPRI
quality O
measure O
Q O
of O
the O
digital O
electron O
images S-CONPRI
was O
evaluated O
, O
and O
the O
influence O
of O
temperature S-PARA
was O
investigated O
. O


In O
this O
study O
, O
raw O
electronic O
images S-CONPRI
generated O
at O
higher O
temperatures S-PARA
had O
greater O
Q O
values O
, O
i.e O
. O


better O
global O
image S-CONPRI
quality O
. O


It O
has O
been O
demonstrated O
that O
, O
for O
temperatures S-PARA
between O
30°C-650°C O
, O
the O
influence O
of O
temperature S-PARA
on O
electronic O
image S-CONPRI
quality O
was O
not O
adversely O
affecting O
the O
visual O
clarity O
of O
image S-CONPRI
features O
. O


It O
is O
thus O
envisaged O
that O
the O
prototype S-CONPRI
has O
a O
potential O
to O
contribute O
to O
in-process O
EBM S-MANP
monitoring O
, O
and O
this O
paper O
has O
served O
as S-MATE
a O
crucial O
precursor S-MATE
to O
the O
ultimate O
goal O
of O
carrying O
out O
electronic O
imaging S-APPL
under O
real O
EBM S-MANP
building O
condition O
. O


Local O
microstructure S-CONPRI
control O
in O
electron B-CONPRI
beam E-CONPRI
powder O
bed B-MANP
fusion E-MANP
( O
EB-PBF O
) O
is O
of O
great O
interest O
to O
the O
additive B-MANP
manufacturing E-MANP
community O
to O
realize O
complex O
part O
geometry S-CONPRI
with O
targeted O
performance S-CONPRI
. O


The O
local O
microstructure S-CONPRI
control O
relies O
on O
having O
a O
detailed O
understanding O
of O
local O
melt B-MATE
pool E-MATE
physics O
( O
e.g. O
, O
3-D S-CONPRI
melt O
pool O
shape O
as S-MATE
well O
as S-MATE
spatial O
and O
temporal O
variations S-CONPRI
of O
thermal B-PARA
gradient E-PARA
( O
G O
) O
and O
solidification B-PARA
rate E-PARA
( O
R O
) O
) O
. O


In O
this O
research S-CONPRI
, O
a O
new O
scan O
strategy O
referred O
to O
as S-MATE
ghost O
beam S-MACEQ
is O
numerically O
evaluated O
as S-MATE
a O
candidate O
to O
achieve O
the O
targeted O
G O
and O
R O
of O
IN718 B-MATE
alloy E-MATE
. O


The O
boundary B-CONPRI
conditions E-CONPRI
for O
simulations S-ENAT
, O
including O
the O
speed O
( O
490 O
mm/s O
) O
and O
spatial O
locations O
of O
the O
beam S-MACEQ
within O
a O
given O
layer S-PARA
, O
are O
obtained O
by O
using O
series O
of O
snapshot O
images S-CONPRI
, O
recorded O
at O
12,000 O
frames O
per O
second O
, O
using O
a O
high-speed O
camera S-MACEQ
. O


The O
heat B-CONPRI
transfer E-CONPRI
simulations O
were O
performed O
using O
TRUCHAS O
an O
open-source S-CONPRI
software O
deployed O
within O
a O
high-performance O
computational O
infrastructure O
. O


The O
simulation S-ENAT
results O
showed O
that O
reheating O
at O
short O
beam S-MACEQ
on-time O
and O
time O
delay O
decreases O
both O
G O
and O
R. O
Local O
variation S-CONPRI
of O
R O
at O
the O
center O
of O
the O
melt B-MATE
pool E-MATE
trailing O
edge O
showed O
periodic O
temporal O
fluctuations O
. O


This O
paper O
introduces O
continuous O
lattice S-CONPRI
fabrication S-MANP
( O
CLF O
) O
– O
a O
novel O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technique O
invented O
for O
fiber-reinforced O
thermoplastic B-MATE
composites E-MATE
– O
and O
demonstrates O
its O
ability O
to O
exploit O
anisotropic B-PRO
material I-PRO
properties E-PRO
in O
digitally O
fabricated S-CONPRI
structures O
. O


In O
contrast O
to O
the O
layer-by-layer S-CONPRI
approaches O
employed O
in O
most O
AM B-MANP
processes E-MANP
, O
CLF O
enables O
the O
directed O
orientation S-CONPRI
of O
the O
fibers S-MATE
in O
all O
spatial O
coordinates S-PARA
, O
that O
is O
in O
the O
x- O
, O
y- O
, O
and O
z-directions O
. O


Based O
on O
a O
serial O
pultrusion S-MANP
and O
extrusion S-MANP
approach O
, O
CLF O
consolidates O
commingled O
yarns O
in B-CONPRI
situ E-CONPRI
and O
allows O
for O
the O
continuous O
deposition S-CONPRI
of O
high O
fiber S-MATE
volume O
fraction S-CONPRI
( O
> O
50 O
% O
) O
materials S-CONPRI
along O
a O
programmable O
trajectory O
without O
the O
use O
of O
molds S-MACEQ
or O
sacrificial O
layers O
by O
exploiting O
the O
high O
viscosities O
of O
fiber-filled O
polymer B-MATE
melts E-MATE
. O


The O
capacity S-CONPRI
of O
CLF O
to O
produce O
high-performance O
structural B-CONPRI
components E-CONPRI
is O
demonstrated O
in O
the O
fabrication S-MANP
of O
an O
ultra-lightweight O
load-bearing S-FEAT
lattice B-FEAT
structure E-FEAT
with O
outstanding O
stiffness-to-density O
and O
strength-to-density O
performance S-CONPRI
( O
compression S-PRO
modulus O
of O
13.23 O
MPa S-CONPRI
and O
compressive B-PRO
strength E-PRO
of O
0.20 O
MPa S-CONPRI
at O
a O
core S-MACEQ
density O
of O
9 O
mg/cm3 O
) O
. O


This O
digital B-MANP
fabrication E-MANP
method O
enables O
new O
approaches O
in O
load-tailored O
design S-FEAT
, O
including O
the O
possibility O
to O
build S-PARA
freeform O
structures O
, O
which O
have O
previously O
been O
overlooked O
due O
to O
difficulties O
and O
limitations O
in O
modern O
fiber B-MATE
composite E-MATE
manufacturing O
capabilities O
. O


Additive B-MANP
Manufacturing E-MANP
provides O
many O
advantages O
in O
reduced O
lead B-PARA
times E-PARA
and O
increased O
geometric B-CONPRI
freedom E-CONPRI
compared O
to O
traditional B-MANP
manufacturing E-MANP
methods O
, O
but O
material B-CONPRI
properties E-CONPRI
are O
often O
reduced O
. O


This O
paper O
considers O
powder B-MANP
bed I-MANP
fusion E-MANP
of O
polyamide B-MATE
12 E-MATE
( O
PA12 S-MATE
, O
Nylon S-MATE
12 O
) O
produced O
by O
three O
different O
processes S-CONPRI
: O
laser B-MANP
sintering E-MANP
( O
LS O
) O
, O
multijet O
fusion S-CONPRI
( O
MJF S-MANP
) O
/high O
speed O
sintering S-MANP
( O
HSS S-MATE
) O
, O
and O
large O
area S-PARA
projection O
sintering S-MANP
( O
LAPS S-CONPRI
) O
. O


While O
all O
utilize O
similar O
PA12 S-MATE
materials S-CONPRI
, O
they O
are O
found O
to O
differ O
significantly O
in O
mechanical B-CONPRI
properties E-CONPRI
especially O
in O
elongation S-PRO
to O
break O
. O


The O
slower O
heating S-MANP
methods O
( O
MJF/HSS O
and O
LAPS S-CONPRI
) O
produce O
large O
elongation S-PRO
at O
break O
with O
the O
LAPS S-CONPRI
process O
showing O
10x O
elongation S-PRO
and O
MJF/HSS O
exhibiting O
2.5x O
the O
elongation S-PRO
when O
compared O
to O
commercial O
LS O
samples S-CONPRI
. O


While O
there O
are O
small O
differences O
in O
crystallinity O
between O
these O
samples S-CONPRI
, O
the O
difference O
may O
be S-MATE
attributed O
to O
changes O
in O
the O
heating S-MANP
and O
cooling B-PARA
rates E-PARA
of O
the O
LAPS S-CONPRI
samples O
. O


The O
maximum O
inlet S-MACEQ
velocity O
of O
the O
filament S-MATE
is O
determined O
according O
to O
the O
process B-CONPRI
parameters E-CONPRI
. O


The O
velocity O
field O
, O
shear O
rate O
and O
viscosity S-PRO
in O
the O
nozzle S-MACEQ
were O
determined O
by O
analytical O
study O
and O
numerical B-ENAT
simulation E-ENAT
. O


The O
extrudate S-MATE
shape O
agrees O
with O
the O
numerical B-ENAT
simulation E-ENAT
: O
the O
extrudate S-MATE
undergoes O
severe O
deformation S-CONPRI
at O
high O
shear O
rate O
. O


Fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
is O
one O
of O
the O
various O
types O
of O
additive B-MANP
manufacturing I-MANP
processes E-MANP
. O


Similar O
to O
other O
types O
, O
FFF S-MANP
enables O
free-form O
fabrication S-MANP
and O
optimised O
structures O
by O
using O
polymeric O
filaments S-MATE
as S-MATE
the O
raw B-MATE
material E-MATE
. O


This O
work O
aims O
to O
optimise O
the O
printing O
conditions O
of O
the O
FFF S-MANP
process O
based O
on O
reliable O
properties S-CONPRI
, O
such O
as S-MATE
printing O
parameters S-CONPRI
and O
physical B-PRO
properties E-PRO
of O
polymers S-MATE
. O


The O
selected O
polymer S-MATE
is O
poly O
( O
lactic O
) O
acid O
( O
PLA S-MATE
) O
, O
which O
is O
a O
biodegradable O
thermoplastic S-MATE
polyester S-MATE
derived O
from O
corn O
starch S-BIOP
and O
is O
one O
of O
the O
most O
common O
polymers S-MATE
in O
the O
FFF S-MANP
process O
. O


Firstly O
, O
the O
maximum O
inlet S-MACEQ
velocity O
of O
the O
filament S-MATE
in O
the O
liquefier O
was O
empirically O
determined O
according O
to O
process B-CONPRI
parameters E-CONPRI
, O
such O
as S-MATE
feed O
rate O
, O
nozzle B-CONPRI
diameter E-CONPRI
and O
dimensions S-FEAT
of O
the O
deposited O
segment O
. O


Secondly O
, O
the O
rheological S-PRO
behaviour O
of O
the O
PLA S-MATE
, O
including O
the O
velocity O
field O
, O
shear O
rate O
and O
viscosity S-PRO
distribution S-CONPRI
in O
the O
nozzle S-MACEQ
, O
was O
determined O
via O
analytical O
study O
and O
numerical B-ENAT
simulation E-ENAT
. O


Our O
results O
indicated O
the O
variation S-CONPRI
in O
the O
shear O
rate O
according O
to O
the O
diameter S-CONPRI
of O
the O
nozzle S-MACEQ
and O
the O
inlet S-MACEQ
velocity O
. O


Finally O
, O
the O
distribution S-CONPRI
of O
the O
viscosity S-PRO
along O
the O
radius O
of O
the O
nozzle S-MACEQ
was O
obtained O
. O


At O
high O
inlet S-MACEQ
velocity O
, O
several O
defects S-CONPRI
appeared O
at O
the O
surface S-CONPRI
of O
the O
extrudates O
. O


The O
defects S-CONPRI
predicted O
via O
numerical B-ENAT
simulation E-ENAT
were O
reasonably O
consistent O
with O
that O
observed O
from O
an O
optical S-CHAR
microscope S-MACEQ
. O


nozzle B-CONPRI
diameter E-CONPRI
, O
feed S-PARA
rate O
and O
layer B-PARA
height E-PARA
) O
to O
improve O
the O
quality S-CONPRI
of O
the O
manufactured S-CONPRI
parts O
. O


Optimized O
LPBF S-MANP
gives O
AA7075 O
parts O
with O
density S-PRO
99.5 O
% O
, O
but O
containing O
hot O
cracks O
. O


Preventing O
cracking S-CONPRI
requires O
optimization S-CONPRI
of O
chemical B-CONPRI
composition E-CONPRI
of O
the O
powder S-MATE
. O


High O
isostatic B-MANP
pressing E-MANP
is O
not O
effective O
in O
healing O
long O
cracks O
. O


Solidification B-CHAR
cracks E-CHAR
are O
formed O
by O
the O
liquid O
film O
rupture O
mode O
. O


Silicon S-MATE
impurity S-PRO
appears O
to O
significantly O
increase O
stability S-PRO
of O
the O
liquid O
film O
. O


Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
is O
an O
attractive O
technology S-CONPRI
of O
manufacturing S-MANP
highstrength O
aluminium B-MATE
alloy E-MATE
parts O
for O
the O
aircraft O
and O
automobile S-APPL
industries O
, O
limited O
by O
poor O
processability O
of O
these O
alloys S-MATE
. O


This O
work O
was O
aimed O
at O
finding O
the O
process S-CONPRI
window O
for O
the O
LPBF S-MANP
manufacturing O
of O
defect-free O
components S-MACEQ
of O
AA7075 O
alloy S-MATE
. O


Optimization S-CONPRI
of O
the O
parameters S-CONPRI
was O
performed O
at O
each O
stage O
of O
the O
multi-stage O
research S-CONPRI
, O
i.e O
. O


At O
each O
stage O
, O
the O
relation O
between O
LPBF S-MANP
parameters O
and O
defect S-CONPRI
formation O
with O
a O
focus O
on O
hot B-CONPRI
cracking E-CONPRI
was O
investigated O
and O
discussed O
. O


Due O
to O
the O
optimization S-CONPRI
of O
process B-CONPRI
parameters E-CONPRI
, O
the O
density S-PRO
of O
volumetric O
specimens O
above O
99 O
% O
was O
reached O
and O
vaporization O
losses O
of O
the O
alloying B-MATE
elements E-MATE
were O
significantly O
reduced O
, O
but O
solidification B-CHAR
cracks E-CHAR
could O
not O
be S-MATE
eliminated O
. O


It O
was O
found O
that O
solidification B-CHAR
cracks E-CHAR
were O
formed O
by O
the O
liquid O
film O
rupture O
mode O
, O
mainly O
along O
columnar B-CONPRI
grain I-CONPRI
boundaries E-CONPRI
. O


The O
EDS S-CHAR
microanalysis O
showed O
intergranular O
microsegregation S-CONPRI
, O
not O
only O
of O
the O
main O
alloying B-MATE
elements E-MATE
( O
Zn S-MATE
, O
Mg S-MATE
, O
Cu S-MATE
) O
but O
also O
of O
minor O
elements S-MATE
such O
as S-MATE
Si O
. O


Silicon S-MATE
may O
play O
a O
significant O
role O
in O
increasing O
susceptibility S-PRO
to O
cracking S-CONPRI
by O
increasing O
the O
stability S-PRO
of O
the O
liquid O
film O
. O


Reduction S-CONPRI
in O
the O
silicon S-MATE
impurity S-PRO
content O
in O
the O
AA7075 O
powder S-MATE
gives O
a O
chance O
to O
reduce O
susceptibility S-PRO
to O
cracking S-CONPRI
with O
no O
change O
of O
the O
alloy S-MATE
specification O
. O


316L O
steel B-MATE
powder E-MATE
reuse O
( O
several O
times O
) O
in O
SLM S-MANP
leads O
to O
the O
increase O
of O
δ-ferrite O
. O


Magnetic O
attractive O
interaction O
among O
δ-ferrite O
powder B-MATE
particles E-MATE
is O
noticed O
. O


Particle S-CONPRI
clustering O
causes O
poor O
packing O
and O
non-uniformities O
in O
the O
powder S-MATE
layer S-PARA
. O


Defect S-CONPRI
formation O
is O
more O
critical O
when O
the O
pin O
support B-FEAT
structure E-FEAT
is O
used O
. O


Magnetic B-CONPRI
separation E-CONPRI
allows O
separation O
of O
austenite S-MATE
and O
δ-ferrite O
powder S-MATE
fractions O
. O


The O
presence O
of O
δ-ferrite O
in O
316L B-MATE
stainless I-MATE
steel I-MATE
powder E-MATE
reused O
several O
times O
contributes O
to O
structural B-CONPRI
defect E-CONPRI
formation O
in O
selective B-MANP
laser I-MANP
melted E-MANP
parts O
built O
using O
the O
pin O
support B-FEAT
structure E-FEAT
. O


The O
virgin O
316L B-MATE
stainless I-MATE
steel I-MATE
powder E-MATE
is O
fully O
austenitic S-MATE
. O


After O
several O
powder S-MATE
reuse O
cycles O
, O
reused O
powder S-MATE
has O
a O
finer O
particle S-CONPRI
size O
and O
about O
6 O
vol O
. O


Phase S-CONPRI
change O
occurs O
due O
to O
the O
thermal B-PARA
cycles E-PARA
imposed O
on O
the O
particles S-CONPRI
near O
the O
melt B-MATE
pool E-MATE
, O
via O
spattering O
and O
further O
interaction O
of O
in-flight O
droplets S-CONPRI
with O
the O
laser B-CONPRI
beam E-CONPRI
. O


Phase S-CONPRI
transformation O
changes O
the O
magnetic O
behavior O
of O
the O
powder S-MATE
leading O
to O
particle S-CONPRI
clustering O
in O
the O
powder B-MACEQ
bed E-MACEQ
. O


The O
uniformity O
of O
the O
powder B-MACEQ
bed E-MACEQ
is O
affected O
causing O
defects S-CONPRI
such O
as S-MATE
porosity O
, O
delamination S-CONPRI
, O
warping S-CONPRI
and O
lack O
of O
fusion S-CONPRI
. O


These O
defects S-CONPRI
are O
more O
prone O
to O
occur O
at O
the O
beginning O
of O
the O
building B-CHAR
process E-CHAR
. O


The O
magnetic O
and O
non-magnetic O
fractions O
of O
the O
reused O
powder S-MATE
were O
separated O
from O
each O
other O
using O
magnetic B-CONPRI
separation E-CONPRI
. O


Powder S-MATE
characterization O
was O
performed O
using O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
, O
laser S-ENAT
scattering O
particle S-CONPRI
size O
analysis O
, O
X-ray B-CHAR
diffraction E-CHAR
, O
and O
magnetization O
measurements O
. O


An O
explanation O
for O
the O
formation O
of O
such O
defects S-CONPRI
based O
on O
the O
magnetic O
behavior O
of O
δ-ferrite O
powder B-MATE
particles E-MATE
is O
proposed O
. O


The O
results O
suggest O
that O
magnetic B-CONPRI
separation E-CONPRI
should O
be S-MATE
used O
to O
remove O
magnetic O
particles S-CONPRI
after O
several O
reuse O
cycles O
. O


In O
the O
context O
of O
additive B-MANP
manufacturing E-MANP
, O
we O
illustrate O
how O
computational O
multi-body O
dynamics O
( O
CMBD O
) O
analysis O
can O
( O
a O
) O
increase O
printing O
throughput S-CHAR
; O
and O
, O
( O
b S-MATE
) O
play O
a O
role O
in O
improving O
the O
quality S-CONPRI
of O
3D B-APPL
printed I-APPL
parts E-APPL
. O


Throughput S-CHAR
is O
increased O
by O
packing O
the O
printing O
volume S-CONPRI
with O
as S-MATE
many O
parts O
as S-MATE
possible O
. O


The O
problem O
becomes O
one O
of O
determining O
where O
each O
component S-MACEQ
that O
needs O
to O
be S-MATE
printed O
finds O
itself O
inside O
the O
printing O
volume S-CONPRI
. O


Finding O
the O
position O
and O
orientation S-CONPRI
of O
each O
part O
is O
accomplished O
through O
CMBD O
analysis O
, O
a O
point O
illustrated O
through O
an O
example O
in O
which O
an O
open-source S-CONPRI
dynamics O
engine O
called O
Chrono O
is O
used O
to O
simulate O
the O
filling O
of O
the O
active O
printing O
volume S-CONPRI
with O
a O
dress O
that O
is O
subsequently O
3D B-MANP
printed E-MANP
. O


In O
relation O
to O
( O
b S-MATE
) O
, O
we O
use O
million-body O
dynamics O
simulations S-ENAT
to O
gauge O
how O
various O
granular O
mixture O
parameters S-CONPRI
and O
rolling S-MANP
regimes O
combine O
to O
ultimately O
control O
the O
roughness S-PRO
of O
the O
surface S-CONPRI
being O
sintered S-MANP
. O


The O
quality S-CONPRI
assessment O
of O
AM B-MATE
materials E-MATE
containing O
defects S-CONPRI
is O
a O
complex O
topic O
. O


Multiple O
defect S-CONPRI
types O
were O
characterised O
by O
X-ray B-CHAR
CT E-CHAR
and O
metallographic O
analysis O
. O


The O
critical O
defects S-CONPRI
in O
fatigue S-PRO
samples O
were O
compared O
to O
the O
statistical O
estimates O
. O


Quality S-CONPRI
correctly O
assessed O
by O
both O
methods O
for O
material S-MATE
obtained O
by O
three O
processes S-CONPRI
. O


Better O
precision S-CHAR
and O
lower O
cost O
by O
CT S-ENAT
when O
similar O
volumes O
are O
investigated O
. O


While O
the O
adoption O
of O
metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
growing O
exponentially O
owing O
to O
its O
wide O
range S-PARA
of O
potential O
applications O
, O
its O
application O
to O
safety-critical O
and O
structural O
parts O
is O
significantly O
impeded O
by O
the O
lack O
of O
standards S-CONPRI
. O


Quality S-CONPRI
assessment O
of O
AM S-MANP
products O
is O
a O
crucial O
requirement O
, O
as S-MATE
the O
AM B-MANP
process E-MANP
induces O
internal O
defects S-CONPRI
that O
can O
have O
detrimental O
effects O
on O
the O
fatigue S-PRO
resistance.By O
evaluating O
the O
defect S-CONPRI
distribution O
, O
it O
is O
possible O
to O
perform O
a O
fracture S-CONPRI
mechanics O
assessment O
to O
estimate O
the O
fatigue B-PRO
strength E-PRO
and O
service O
lifetime O
of O
AM B-MATE
materials E-MATE
. O


This O
strategy O
has O
been O
successfully O
applied O
to O
selective O
laser-melted O
AlSi10Mg S-MATE
by O
performing O
X-ray B-CHAR
micro-computed I-CHAR
tomography E-CHAR
( O
μCT O
) O
and O
applying O
suitable O
statistical B-CONPRI
methods E-CONPRI
( O
i.e. O
, O
statistics S-CONPRI
of O
extremes O
) O
. O


The O
results O
showed O
that O
both O
techniques O
were O
able O
to O
pinpoint O
a O
significant O
difference O
in O
the O
prospective O
largest O
defect S-CONPRI
in O
a O
material S-MATE
volume O
corresponding O
to O
the O
gauge B-MACEQ
section E-MACEQ
of O
a O
specimen O
. O


However O
, O
extrapolation O
of O
the O
critical O
defect S-CONPRI
size O
for O
fatigue S-PRO
failure S-CONPRI
using O
PS O
data S-CONPRI
was O
less O
accurate S-CHAR
and O
less O
conservative O
than O
that O
using O
CT S-ENAT
data O
. O


Investigation O
of O
manufacturing S-MANP
continuous O
fiber O
reinforced S-CONPRI
thermoplastic O
polymer B-MATE
composites E-MATE
( O
CFRTPCs O
) O
through O
3D B-ENAT
printing I-ENAT
technologies E-ENAT
has O
attracted O
great O
attention O
in O
the O
past O
few O
years O
due O
to O
excellent O
properties S-CONPRI
of O
CFRTPCs O
, O
such O
as S-MATE
high O
strength-to-weight O
ratio O
and O
stiffness S-PRO
. O


It O
is O
found O
that O
the O
properties S-CONPRI
of O
CFRTPCs O
are O
affected O
not O
only O
by O
the O
properties S-CONPRI
of O
the O
individual O
parent O
materials S-CONPRI
but O
also O
by O
interfacial O
characteristics O
. O


Modification O
of O
the O
interface S-CONPRI
is O
a O
great O
method O
to O
improve O
the O
wettability S-CONPRI
between O
fiber S-MATE
and O
polymer S-MATE
and O
hence O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
CFRTPCs O
. O


In O
this O
work O
, O
an O
ultrasound-assisted O
3D B-MANP
printing E-MANP
device O
for O
CFRTPCs O
is O
developed O
. O


The O
changes O
of O
surface B-FEAT
profile E-FEAT
and O
chemical O
structure S-CONPRI
of O
carbon B-MATE
fiber E-MATE
and O
carbon B-MATE
fiber E-MATE
prepreg O
after O
ultrasonic O
treatment O
are O
studied O
. O


The O
effects O
of O
ultrasonic O
processing O
parameters S-CONPRI
on O
the O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
CFRTPCs O
are O
provided O
. O


It O
is O
found O
that O
the O
tensile S-PRO
and O
flexural B-PRO
strength E-PRO
of O
composite B-MATE
materials E-MATE
are O
improved O
by O
34 O
% O
and O
29 O
% O
, O
respectively O
, O
compared O
with O
untreated O
material S-MATE
by O
using O
the O
ultrasonic O
amplitude O
of O
40 O
μm O
, O
resin S-MATE
solution O
mass O
fraction S-CONPRI
of O
10 O
% O
, O
processing O
speed O
of O
15 O
mm/s O
. O


Direct O
osseous O
healing O
to O
prosthetic S-APPL
components S-MACEQ
is O
a O
prerequisite O
for O
the O
clinical O
success O
of O
uncemented O
treatment O
in O
total O
hip S-MANP
replacements O
( O
THR O
) O
. O


The O
demands O
imposed O
on O
the O
material B-CONPRI
properties E-CONPRI
are O
constantly O
being O
stepped O
up O
to O
withstand O
the O
impact S-CONPRI
of O
an O
active O
lifestyle O
and O
ensure O
lifelong O
integration O
. O


Cobalt–chromium–molybdenum O
( O
Co-Cr-Mo O
) O
materials S-CONPRI
are O
interesting O
for O
their O
excellent O
mechanical S-APPL
stability O
, O
corrosion B-CONPRI
resistance E-CONPRI
and O
possibility O
to O
be S-MATE
produced O
by O
additive B-MANP
manufacturing E-MANP
into O
complex O
designs S-FEAT
with O
modifiable O
stiffness S-PRO
. O


The O
bone S-BIOP
response O
to O
Co-Cr-Mo O
is O
regarded O
as S-MATE
inferior O
to O
that O
of O
titanium S-MATE
and O
are O
usually O
cemented O
in O
THR O
. O


The O
hypothesis O
in O
the O
present O
study O
was O
that O
a O
low O
amount O
of O
Zr S-MATE
in O
the O
Co-Cr-Mo O
alloy S-MATE
would O
improve O
the O
bone S-BIOP
response O
and O
biomechanical S-APPL
anchorage O
. O


The O
results O
showed O
significantly O
higher O
implant S-APPL
stability O
for O
the O
Co-Cr-Mo O
alloy S-MATE
with O
an O
addition O
of O
0.04 O
% O
Zr S-MATE
after O
eight O
weeks O
of O
healing O
in O
rabbits O
, O
while O
no O
major O
differences O
were O
observed O
in O
the O
amount O
of O
bone S-BIOP
formed O
around O
the O
implants S-APPL
. O


Further O
, O
bone S-BIOP
tissue O
grew O
into O
surface S-CONPRI
irregularities O
and O
in O
direct O
contact S-APPL
with O
the O
implant S-APPL
surfaces O
. O


It O
is O
concluded O
that O
additively B-MANP
manufactured E-MANP
Co-Cr-Mo O
alloy S-MATE
implants O
osseointegrate O
and O
that O
the O
addition O
of O
a O
low O
amount O
of O
Zr S-MATE
to O
the O
bulk O
Co-Cr-Mo O
further O
improves O
the O
bone S-BIOP
anchorage O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
a O
widely O
used O
additive B-MANP
manufacturing E-MANP
method O
for O
building O
metal S-MATE
parts O
in O
a O
layer-by-layer S-CONPRI
manner O
thereby O
imposing O
almost O
no O
limitations O
on O
the O
geometrical O
layout S-CONPRI
of O
the O
part O
. O


The O
SLM S-MANP
process S-CONPRI
has O
a O
crucial O
impact S-CONPRI
on O
the O
microstructure S-CONPRI
, O
strength S-PRO
, O
surface B-PARA
quality E-PARA
and O
even O
the O
shape O
of O
the O
part O
, O
all O
of O
which O
depend O
on O
the O
thermal O
history O
of O
material S-MATE
points O
within O
the O
part O
. O


In O
this O
paper O
, O
we O
present O
a O
computationally O
tractable O
thermal O
model S-CONPRI
for O
the O
SLM S-MANP
process S-CONPRI
which O
accounts O
for O
individual O
laser S-ENAT
scanning O
vectors O
. O


First O
, O
a O
closed O
form O
solution S-CONPRI
of O
a O
line O
heat B-CONPRI
source E-CONPRI
is O
calculated O
to O
represent O
the O
laser S-ENAT
scanning O
vectors O
in O
a O
semi-infinite O
space O
. O


The O
thermal O
boundary B-CONPRI
conditions E-CONPRI
are O
accounted O
for O
by O
a O
complimentary O
correction O
field O
, O
which O
is O
computed O
numerically O
. O


The O
proposed O
semi-analytical O
model S-CONPRI
can O
be S-MATE
used O
to O
simulate O
manufacturing S-MANP
geometrically O
complex O
parts O
and O
allows O
spatial O
discretisation O
to O
be S-MATE
much O
coarser O
than O
the O
characteristic O
length B-CHAR
scale E-CHAR
of O
the O
process S-CONPRI
: O
laser B-PARA
spot I-PARA
size E-PARA
, O
except O
in O
the O
vicinity O
of O
boundaries S-FEAT
. O


The O
underlying O
assumption O
of O
linearity S-CONPRI
of O
the O
heat S-CONPRI
equation O
in O
the O
proposed O
model S-CONPRI
is O
justified O
by O
comparisons O
with O
a O
fully O
non-linear O
model S-CONPRI
and O
experiments O
. O


The O
accuracy S-CHAR
of O
the O
proposed O
boundary S-FEAT
correction O
scheme O
is O
demonstrated O
by O
a O
dedicated O
numerical O
example O
on O
a O
simple S-MANP
cubic O
part O
. O


The O
influence O
of O
the O
part O
design S-FEAT
and O
scanning B-CONPRI
strategy E-CONPRI
on O
the O
temperature S-PARA
transients O
are O
subsequently O
analysed O
on O
a O
geometrically O
complex O
part O
. O


The O
results O
show O
that O
overhanging B-FEAT
features E-FEAT
of O
a O
part O
obstruct O
the O
heat S-CONPRI
flow O
towards O
the O
base-plate O
thereby O
creating O
local O
overheating O
which O
in O
turn O
decrease O
local O
cooling B-PARA
rate E-PARA
. O


Finally O
, O
a O
real O
SLM S-MANP
process S-CONPRI
for O
a O
part O
with O
an O
overhanging B-FEAT
feature E-FEAT
is O
modelled O
for O
validation S-CONPRI
of O
the O
proposed O
model S-CONPRI
. O


Reasonable O
agreement O
between O
the O
model S-CONPRI
predictions O
and O
the O
experimentally O
measured O
values O
can O
be S-MATE
observed O
. O


The O
emergence O
of O
4D B-MANP
printing E-MANP
has O
revolutionized O
the O
additive B-MANP
manufacturing E-MANP
industry O
by O
enabling O
dynamic S-CONPRI
shape O
memory O
effects O
ensured O
by O
the O
use O
of O
smart O
materials S-CONPRI
. O


In O
addition O
to O
3D S-CONPRI
fabrication O
, O
4D S-CONPRI
printed O
products O
need O
to O
undergo O
shape O
programming O
and O
recovery O
cycles O
to O
achieve O
desired O
shape B-PRO
memory I-PRO
effects E-PRO
. O


Due O
to O
the O
new O
process S-CONPRI
and O
material S-MATE
characteristics O
, O
energy O
consumption O
models O
established O
for O
3D B-MANP
printing E-MANP
are O
no O
longer O
applicable O
for O
4D B-MANP
printing E-MANP
. O


In O
current O
literature O
, O
the O
environmental O
sustainability S-CONPRI
for O
4D B-MANP
printing E-MANP
has O
not O
yet O
been O
evaluated O
, O
leading O
to O
unknown O
environmental O
impacts O
that O
could O
be S-MATE
caused O
by O
4D B-MANP
printing E-MANP
processes O
and/or O
materials S-CONPRI
. O


In O
this O
research S-CONPRI
, O
theoretical B-CONPRI
models E-CONPRI
for O
quantifying O
the O
energy O
consumption O
in O
4D B-MANP
printing E-MANP
thermal-responsive O
polymers S-MATE
are O
established O
by O
jointly O
considering O
the O
compositional O
design S-FEAT
for O
materials S-CONPRI
. O


Experiments O
and O
case B-CONPRI
studies E-CONPRI
are O
performed O
to O
validate O
the O
proposed O
models O
and O
further O
investigate O
some O
critical B-PRO
factors E-PRO
that O
can O
affect O
energy O
consumption O
, O
e.g. O
, O
values O
of O
process B-CONPRI
parameters E-CONPRI
like O
layer B-PARA
thickness E-PARA
, O
and O
thermo-temporal O
conditions O
in O
shape O
memory O
cycles O
. O


The O
case B-CONPRI
study E-CONPRI
results O
show O
that O
overall O
energy O
consumption O
can O
be S-MATE
reduced O
by O
1 O
) O
increasing O
the O
concentrations O
of O
multi-functional O
crosslinkers O
in O
material S-MATE
composition S-CONPRI
, O
and O
2 O
) O
setting O
the O
shape O
programming O
and O
recovery O
temperatures S-PARA
as S-MATE
10 O
to O
15℃ O
above O
the O
material S-MATE
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
without O
compromising O
the O
shape O
fixity O
and O
recovery O
ratios O
. O


In O
addition O
, O
by O
adjusting O
the O
influential O
parameters S-CONPRI
throughout O
different O
stages O
in O
4D B-MANP
printing E-MANP
, O
the O
total O
energy O
consumption O
can O
be S-MATE
reduced O
by O
37.33 O
% O
, O
which O
corresponds O
to O
a O
reduction S-CONPRI
of O
259.52 O
pounds O
of O
CO2 S-MATE
emissions O
per O
kilogram O
methacrylate O
resin S-MATE
. O


While O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
commonly O
known O
as S-MATE
3D B-MANP
printing E-MANP
, O
has O
been O
in O
existence O
commercially O
for O
∼30 O
years O
, O
desktop B-MACEQ
3D I-MACEQ
printers E-MACEQ
are O
a O
relatively O
new O
and O
rapidly O
growing O
market O
segment O
. O


This O
research S-CONPRI
highlights O
differences O
amongst O
45 O
desktop B-MACEQ
3D I-MACEQ
printers E-MACEQ
and O
suggests O
a O
method O
by O
which O
to O
evaluate O
such O
differences O
. O


For O
this O
, O
a O
standard S-CONPRI
part O
consisting O
of O
various O
geometric O
features O
was O
designed S-FEAT
and O
printed O
using O
each O
system O
. O


An O
updated O
version O
of O
a O
previously O
developed O
quantitative S-CONPRI
ranking O
model S-CONPRI
was O
utilized O
to O
rate O
the O
build S-PARA
precision O
of O
each O
system O
as S-MATE
well O
as S-MATE
other O
features O
, O
including O
build B-PARA
volume E-PARA
, O
size O
, O
cost O
, O
weight S-PARA
, O
and O
layer B-PARA
resolution E-PARA
. O


In O
addition O
, O
the O
research S-CONPRI
team O
observed O
part O
aesthetics O
and O
quantified O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
criteria O
evaluated O
in O
this O
ranking O
model S-CONPRI
may O
be S-MATE
modified O
by O
each O
user O
, O
to O
extend O
this O
methodology S-CONPRI
to O
other O
desktop O
AM S-MANP
systems O
, O
including O
professional-grade O
machines S-MACEQ
. O


As S-MATE
expected O
, O
the O
comparisons O
demonstrated O
that O
each O
model S-CONPRI
had O
slightly O
different O
rankings O
as S-MATE
compared O
to O
the O
model S-CONPRI
presented O
in O
this O
paper O
, O
with O
some O
outliers O
. O


Additive B-MANP
manufacturing E-MANP
of O
ceramics S-MATE
has O
been O
actively O
investigated O
with O
the O
objective O
of O
fabricating S-MANP
complex B-CONPRI
structures E-CONPRI
that O
compete O
in O
terms O
of O
material S-MATE
performance O
with O
traditionally O
manufactured S-CONPRI
ceramics S-MATE
but O
with O
the O
benefit O
of O
increased O
geometric B-CONPRI
freedom E-CONPRI
. O


More O
specifically O
, O
zirconia S-MATE
provides O
high O
fracture S-CONPRI
toughness O
and O
thermal B-PRO
stability E-PRO
. O


In O
addition O
, O
its O
dielectric S-MACEQ
permittivity O
may O
be S-MATE
the O
highest O
among O
materials S-CONPRI
available O
for O
3D B-MANP
printing E-MANP
, O
and O
may O
enable O
the O
next O
generation O
of O
complex O
electromagnetic O
structures O
. O


NanoParticle O
Jetting™ O
is O
a O
new O
material B-MANP
jetting E-MANP
process O
for O
selectively O
depositing O
nanoparticles S-CONPRI
and O
is O
capable O
of O
printing O
zirconia S-MATE
. O


Dense O
, O
fine-featured O
parts O
can O
be S-MATE
manufactured O
with O
layer B-PARA
thicknesses E-PARA
as S-MATE
small O
as S-MATE
10 O
μm O
and O
jetting S-MANP
resolution O
of O
20 O
μm O
after O
a O
final O
sintering S-MANP
step O
. O


For O
this O
study O
, O
3D B-MANP
printed E-MANP
zirconia O
using O
NanoParticle O
Jetting™ O
was O
characterized O
in O
terms O
of O
chemistry S-CONPRI
, O
density S-PRO
, O
crystallography S-MANP
, O
sintering S-MANP
shrinkage S-CONPRI
and O
dielectric S-MACEQ
properties O
as S-MATE
a O
foundation O
for O
developing O
high O
performance S-CONPRI
radio O
frequency O
( O
RF O
) O
components S-MACEQ
. O


The O
experimental S-CONPRI
results O
indicate O
a O
yttria-stabilized O
ZrO2 S-MATE
structure S-CONPRI
exhibiting O
a O
bulk O
relative O
permittivity O
of O
23 O
and O
a O
loss O
tangent O
of O
0.0013 O
at O
microwave S-ENAT
frequencies O
. O


A O
simple S-MANP
zirconia O
dielectric S-MACEQ
resonator O
antenna O
is O
measured O
, O
confirming O
the O
measured O
dielectric S-MACEQ
properties O
and O
illustrating O
a O
practical O
application O
of O
this O
material S-MATE
. O


The O
corrosion B-PRO
behavior E-PRO
of O
AISI316L O
AM B-MACEQ
parts E-MACEQ
is O
evaluated O
before O
and O
after O
the O
heat B-MANP
treatment E-MANP
then O
compared O
with O
the O
wrought B-CONPRI
samples E-CONPRI
. O


AM B-MACEQ
parts E-MACEQ
have O
a O
better O
corrosion B-PRO
behavior E-PRO
compared O
to O
the O
wrought S-CONPRI
ones O
due O
to O
the O
absence O
of O
non-equilibrium O
phases O
. O


The O
annealed O
AM S-MANP
sample O
has O
an O
improved O
corrosion B-PRO
behavior E-PRO
due O
to O
the O
decreasing O
of O
the O
residual B-PRO
stress E-PRO
level O
. O


The O
noticeable O
change O
in O
corrosion B-CONPRI
resistance E-CONPRI
for O
the O
wrought B-CONPRI
sample E-CONPRI
is O
a O
result O
of O
phase S-CONPRI
transformation O
. O


This O
paper O
presents O
the O
investigation O
of O
the O
corrosion B-PRO
behavior E-PRO
of O
AISI316L O
samples S-CONPRI
prepared O
by O
laser-based O
powder B-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
method O
. O


Both O
AM S-MANP
and O
conventional O
stainless B-MATE
steel E-MATE
316L O
samples S-CONPRI
were O
examined O
in O
NaCl S-MATE
3.5 O
% O
solution S-CONPRI
before O
and O
after O
the O
annealing S-MANP
process O
using O
Tafel O
curves O
, O
Electrochemical S-CONPRI
Impedance O
Spectroscopy S-CONPRI
, O
and O
X-ray B-CHAR
diffraction E-CHAR
. O


The O
results O
indicate O
that O
the O
AM B-MACEQ
parts E-MACEQ
have O
an O
improved O
corrosion B-PRO
behavior E-PRO
than O
the O
conventional O
wrought B-CONPRI
samples E-CONPRI
. O


Besides O
, O
the O
heat B-MANP
treatment E-MANP
process O
is O
found O
to O
further O
decrease O
the O
corrosion S-CONPRI
rate O
of O
the O
AM B-MACEQ
parts E-MACEQ
through O
the O
relieving O
of O
the O
residual B-PRO
stress E-PRO
. O


In O
contrast O
, O
the O
post O
annealing S-MANP
induced O
improvement O
to O
corrosion B-CONPRI
resistance E-CONPRI
for O
the O
wrought B-CONPRI
samples E-CONPRI
is O
due O
to O
the O
elimination O
of O
martensite S-MATE
phase O
which O
almost O
always O
exists O
after O
the O
plastic B-PRO
deformation E-PRO
during O
their O
production S-MANP
process S-CONPRI
. O


The O
IN718 S-MATE
sample O
with O
deposition B-PARA
rate E-PARA
of O
2.2 O
kg/h O
and O
height O
75 O
mm S-MANP
was O
prepared O
. O


δ O
, O
γ O
'' O
and O
γ O
' O
phase S-CONPRI
are O
precipitated O
in O
bottom O
and O
middle O
region O
due O
to O
thermal B-PARA
cycle E-PARA
. O


The O
microhardness S-CONPRI
and O
room O
temperature S-PARA
tensile O
properties S-CONPRI
exhibit O
a O
high O
value O
. O


In O
order O
to O
meet O
the O
requirements O
for O
rapid B-MANP
manufacturing E-MANP
of O
large-scale O
high-performance O
metal S-MATE
components S-MACEQ
, O
the O
unique O
advantages O
of O
high-deposition-rate O
laser B-MANP
directed I-MANP
energy I-MANP
deposition E-MANP
( O
HDR-LDED O
, O
deposition B-PARA
rate E-PARA
≥ O
1 O
kg/h O
) O
technology S-CONPRI
have O
been O
attracted O
great O
attention O
. O


HDR-LDED O
technology S-CONPRI
significantly O
improves O
the O
efficiency O
by O
simultaneously O
increasing O
the O
mass O
and O
energy O
input O
on O
basis O
of O
conventional O
laser B-MANP
directed I-MANP
energy I-MANP
deposition E-MANP
( O
C-LDED O
, O
deposition B-PARA
rate E-PARA
≤ O
0.3 O
kg/h O
) O
, O
which O
dramatically O
changes O
the O
solidification S-CONPRI
condition O
and O
thermal B-PARA
cycling E-PARA
effect O
compared O
to O
C-LDED O
processes S-CONPRI
. O


Based O
on O
this O
, O
Inconel B-MATE
718 E-MATE
bulk O
samples S-CONPRI
were O
fabricated S-CONPRI
with O
a O
deposition B-PARA
rate E-PARA
of O
2.2 O
kg/h O
and O
a O
height O
of O
75 O
mm S-MANP
. O


Through O
experimental S-CONPRI
observation O
combined O
with O
finite B-CONPRI
element E-CONPRI
simulation O
, O
the O
precipitation B-CONPRI
morphology E-CONPRI
, O
thermal B-PARA
cycling E-PARA
effect O
and O
tensile B-PRO
properties E-PRO
at O
room O
temperature S-PARA
of O
the O
block O
samples S-CONPRI
at O
heights O
of O
6 O
mm S-MANP
( O
bottom O
region O
) O
, O
37 O
mm S-MANP
( O
middle O
region O
) O
and O
69 O
mm S-MANP
( O
top O
region O
) O
from O
the O
substrate S-MATE
were O
investigated O
. O


The O
results O
show O
that O
both O
temperature S-PARA
interval O
and O
incubation O
time O
satisfy O
the O
precipitation S-CONPRI
conditions O
of O
the O
second O
phases O
because O
of O
the O
intense O
thermal B-PARA
cycling E-PARA
effect O
so O
that O
δ O
, O
γ O
'' O
and O
γ O
' O
phase S-CONPRI
are O
precipitated O
in O
the O
bottom O
and O
middle O
region O
of O
the O
as-deposited O
sample S-CONPRI
during O
the O
HDR-LDED O
process S-CONPRI
. O


As S-MATE
a O
result O
, O
the O
micro-hardness O
and O
the O
yield B-PRO
strength E-PRO
of O
the O
bottom O
region O
( O
385 O
HV O
; O
745.1 O
± O
5.2 O
MPa S-CONPRI
) O
are O
similar O
to O
those O
of O
the O
middle O
region O
( O
381 O
HV O
; O
752.2 O
± O
12.1 O
MPa S-CONPRI
) O
, O
respectively O
. O


The O
tensile S-PRO
fracture S-CONPRI
mechanism O
is O
shown O
in O
both O
fracture S-CONPRI
and O
debonding O
of O
the O
Laves B-CONPRI
phase E-CONPRI
. O


The O
inhomogeneous O
microstructures S-MATE
and O
corresponding O
mechanical B-CONPRI
property E-CONPRI
differences O
of O
Inconel B-MATE
718 E-MATE
fabricated S-CONPRI
by O
HDR-LDED O
along O
the O
deposition B-PARA
direction E-PARA
suggest O
the O
necessity O
to O
conduct O
further O
research S-CONPRI
of O
the O
post O
heat B-MANP
treatment E-MANP
in O
the O
future O
. O


We O
demonstrate O
that O
a O
low O
dielectric S-MACEQ
constant O
composite S-MATE
filament O
, O
useful O
for O
FFF S-MANP
printing O
, O
can O
be S-MATE
manufactured O
by O
combining O
a O
base O
thermoplastic B-MATE
polymer E-MATE
with O
hollow O
microspheres S-CONPRI
and O
a O
plasticizer S-MATE
. O


Experimental S-CONPRI
results O
are O
provided O
for O
filaments S-MATE
made O
from O
two O
different O
base O
polymers S-MATE
( O
i.e O
. O


ABS S-MATE
and O
HDPE S-MATE
) O
and O
varying O
volume B-PARA
fractions E-PARA
of O
hollow O
microspheres S-CONPRI
. O


We O
also O
describe O
an O
effective O
media O
model S-CONPRI
to O
predict O
the O
dielectric S-MACEQ
properties O
of O
the O
composite S-MATE
filaments O
as S-MATE
a O
function O
of O
the O
properties S-CONPRI
of O
the O
constituent O
materials S-CONPRI
( O
e.g O
. O


base O
polymer S-MATE
, O
hollow O
microspheres S-CONPRI
) O
and O
their O
relative O
volume B-PARA
fractions E-PARA
within O
the O
composite S-MATE
filament O
. O


Experimental S-CONPRI
test O
samples S-CONPRI
were O
printed O
using O
the O
new O
low-K O
filaments S-MATE
and O
experimental S-CONPRI
characterization O
results O
are O
provided O
that O
validate O
this O
approach O
. O


Proven O
real-time O
measurement S-CHAR
capability O
of O
an O
in-house O
interferometry S-CONPRI
for O
both O
exposure B-CONPRI
cured E-CONPRI
height O
and O
dark O
cured S-MANP
height O
in O
photopolymer S-MATE
AM S-MANP
. O


Demonstrated O
real-time O
closed-loop B-MACEQ
control E-MACEQ
of O
cured S-MANP
height O
in O
photopolymer S-MATE
AM S-MANP
with O
the O
interferometry S-CONPRI
and O
an O
empirical S-CONPRI
dark O
curing S-MANP
model O
. O


Thorough O
error S-CONPRI
analysis O
for O
future O
research S-CONPRI
on O
improving O
the O
process B-CONPRI
control E-CONPRI
. O


An O
exemplary O
study O
on O
a O
lab-scale O
parallel O
computing O
enabled O
cyber-physical O
system O
for O
AM B-MANP
process E-MANP
sensing O
, O
modeling S-ENAT
and O
control O
. O


Exposure S-CONPRI
Controlled O
Projection O
Lithography S-CONPRI
( O
ECPL O
) O
is O
an O
in-house O
additive B-MANP
manufacturing I-MANP
process E-MANP
that O
can O
cure S-CONPRI
microscale O
photopolymer S-MATE
parts O
on O
a O
stationary O
transparent S-CONPRI
substrate S-MATE
with O
a O
time O
sequence O
of O
patterned O
ultraviolet S-CONPRI
beams O
delivered O
from O
underneath O
. O


An O
in-situ S-CONPRI
interferometric O
curing S-MANP
monitoring O
and O
measurement S-CHAR
( O
ICM O
& O
M O
) O
system O
has O
been O
developed O
to O
measure O
the O
ECPL O
process S-CONPRI
output O
of O
cured S-MANP
height O
profile S-FEAT
. O


This O
study O
develops O
a O
real-time O
feedback S-PARA
control B-MACEQ
system E-MACEQ
that O
utilizes O
an O
empirical S-CONPRI
process O
model S-CONPRI
and O
an O
online O
ICM O
& O
M O
feedback S-PARA
to O
automatically O
and O
accurately S-CHAR
cure O
a O
part O
with O
targeted O
height O
. O


Due O
to O
the O
nature O
of O
photopolymerization S-MANP
, O
the O
total O
height O
of O
an O
ECPL O
cured S-MANP
part O
is O
divided O
into O
exposure B-CONPRI
cured E-CONPRI
height O
and O
dark O
cured S-MANP
height O
. O


The O
exposure B-CONPRI
cured E-CONPRI
height O
is O
controlled O
by O
a O
closed-loop O
feedback S-PARA
on-off O
controller S-MACEQ
. O


The O
dark O
cured S-MANP
height O
is O
compensated O
by O
an O
empirical S-CONPRI
process O
model S-CONPRI
obtained O
from O
the O
ICM O
& O
M O
measurements O
for O
a O
series O
of O
cured S-MANP
parts O
. O


A O
parallel O
computing O
software S-CONPRI
application O
is O
developed O
to O
implement O
the O
real-time O
measurement S-CHAR
and O
control O
simultaneously O
. O


The O
experimental S-CONPRI
results O
directly O
validate O
the O
ICM O
& O
M O
system O
’ O
s S-MATE
real-time O
capability O
in O
capturing O
the O
process S-CONPRI
dynamics O
and O
in O
sensing S-APPL
the O
process S-CONPRI
output O
. O


Meanwhile O
, O
it O
evidently O
demonstrates O
the O
feedback S-PARA
control B-MACEQ
system E-MACEQ
’ O
s S-MATE
satisfactory O
performance S-CONPRI
in O
achieving O
the O
setpoint O
of O
total O
height O
, O
despite O
the O
presence O
of O
ECPL O
process S-CONPRI
uncertainties O
, O
ICM O
& O
M O
noises O
and O
computing O
interruptions O
. O


Generally O
, O
the O
study O
establishes O
a O
paradigm O
of O
improving O
additive B-MANP
manufacturing E-MANP
with O
a O
real-time O
closed-loop O
measurement S-CHAR
and O
control B-MACEQ
system E-MACEQ
. O


Recent O
advances O
in O
additive B-MANP
manufacturing E-MANP
facilitated O
the O
fabrication S-MANP
of O
parts O
with O
great O
geometrical B-FEAT
complexity E-FEAT
and O
relatively O
small O
size O
, O
and O
allowed O
for O
the O
fabrication S-MANP
of O
topologies S-CONPRI
that O
could O
not O
have O
been O
achieved O
using O
traditional O
fabrication S-MANP
techniques O
. O


In O
this O
work O
, O
we O
explore O
the O
topology-property O
relationship O
of O
several O
classes O
of O
periodic O
cellular B-MATE
materials E-MATE
; O
the O
first O
class O
is O
strut-based S-FEAT
structures O
, O
while O
the O
second O
and O
third O
classes O
are O
derived O
from O
the O
mathematically O
created O
triply B-CONPRI
periodic I-CONPRI
minimal I-CONPRI
surfaces E-CONPRI
, O
namely O
; O
the O
skeletal-TPMS O
and O
sheet-TPMS O
cellular B-FEAT
structures E-FEAT
. O


Powder B-MANP
bed I-MANP
fusion E-MANP
technology O
was O
employed O
to O
fabricate S-MANP
the O
cellular B-FEAT
structures E-FEAT
of O
various O
relative B-PRO
densities E-PRO
out O
of O
Maraging B-MATE
steel E-MATE
. O


Scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
( O
SEM S-CHAR
) O
was O
also O
employed O
to O
assess O
the O
quality S-CONPRI
of O
the O
printed O
parts O
. O


Compressive O
testing S-CHAR
was O
performed O
to O
deduce O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
considered O
cellular B-FEAT
structures E-FEAT
. O


Results O
showed O
that O
the O
sheet-TPMS O
based O
cellular B-FEAT
structures E-FEAT
exhibited O
a O
near O
stretching-dominated O
deformation S-CONPRI
behavior O
, O
while O
skeletal-TPMS O
showed O
a O
bending-dominated O
behavior O
. O


Overall O
the O
sheet-TPMS O
based O
cellular B-FEAT
structures E-FEAT
showed O
superior O
mechanical B-CONPRI
properties E-CONPRI
among O
all O
the O
tested O
structures O
. O


The O
most O
interesting O
observation O
is O
that O
sheet-based O
Diamond S-MATE
TPMS O
structure S-CONPRI
showed O
the O
best O
mechanical S-APPL
performance O
with O
nearly O
independence O
of O
relative B-PRO
density E-PRO
. O


It O
was O
also O
observed O
that O
at O
decreased O
volume B-PARA
fractions E-PARA
the O
effect O
of O
geometry S-CONPRI
on O
the O
mechanical B-CONPRI
properties E-CONPRI
is O
more O
pronounced O
. O


Polyhydroxyalkanoate O
( O
PHA O
) O
composites S-MATE
containing O
siliceous O
sponge O
spicules O
( O
SSS O
) O
were O
prepared O
from O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
printing O
filaments S-MATE
. O


Mechanical S-APPL
and O
morphological B-CHAR
characterizations E-CHAR
indicated O
that O
the O
improved O
adhesion S-PRO
between O
the O
SSS O
and O
PHA-g-AA O
enhanced O
the O
tensile B-PRO
strength E-PRO
at O
failure S-CONPRI
and O
Young O
’ O
s S-MATE
modulus O
of O
the O
composite S-MATE
compared O
with O
that O
of O
PHA/SSS O
. O


The O
PHA-g-AA/SSS O
composites S-MATE
were O
also O
more O
water-resistant O
than O
the O
PHA/SSS O
composites S-MATE
. O


Human O
foreskin O
fibroblasts S-BIOP
( O
FBs O
) O
were O
seeded O
on O
two O
series O
of O
these O
composites S-MATE
to O
assess O
cytocompatibility O
. O


FB O
proliferation O
was O
greater O
for O
the O
PHA/SSS O
composites S-MATE
than O
the O
PHA-g-AA/SSS O
composites S-MATE
. O


Moreover O
, O
SSS O
enhanced O
the O
antioxidant O
, O
anti-inflammatory O
and O
antibacterial O
properties S-CONPRI
of O
PHA-g-AA/SSS O
and O
PHA/SSS O
composites S-MATE
, O
demonstrating O
the O
potential O
of O
PHA-g-AA/SSS O
and O
PHA/SSS O
composites S-MATE
for O
biomedical S-APPL
material O
applications O
. O


Refined O
microstructure S-CONPRI
of O
AlSi10Mg B-MATE
alloy E-MATE
by O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
technology S-CONPRI
. O


As-EBM-built O
AlSi10Mg B-MATE
alloy E-MATE
contains O
fine O
granular O
Si S-MATE
phase S-CONPRI
and O
bimodal O
Al S-MATE
grains O
. O


As-EBM-built O
AlSi10Mg B-MATE
alloy E-MATE
is O
strengthened O
by O
the O
nano-Si O
precipitates S-MATE
. O


Refining O
the O
microstructure S-CONPRI
to O
improve O
the O
ductility S-PRO
of O
an O
Al‒Si O
alloy S-MATE
is O
challenging O
. O


In O
this O
paper O
, O
we O
report O
for O
the O
first O
time O
a O
novel O
microstructure S-CONPRI
refinement O
approach O
for O
AlSi10Mg S-MATE
( O
wt O
% O
) O
alloys S-MATE
using O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
technology S-CONPRI
, O
without O
the O
addition O
of O
any O
modification O
elements S-MATE
. O


The O
synergetic O
effect O
of O
superheating O
, O
fast O
cooling S-MANP
, O
and O
preheating S-MANP
contributes O
to O
a O
refined O
Si S-MATE
phase S-CONPRI
with O
a O
fine O
granular O
structure S-CONPRI
( O
0.5–2 O
μm O
) O
within O
bimodal O
Al S-MATE
grains O
( O
40 O
μm O
grains S-CONPRI
and O
0.5–2 O
μm O
sub-grains O
) O
. O


A O
maximum O
ductility S-PRO
of O
approximately O
32.7 O
% O
with O
a O
tensile B-PRO
strength E-PRO
of O
approximately O
136 O
MPa S-CONPRI
was O
achieved O
for O
the O
as-built O
AlSi10Mg S-MATE
EBM O
alloy S-MATE
. O


After O
solution B-MANP
heat I-MANP
treatment E-MANP
and O
T6-like O
aging O
, O
nano-Si O
precipitates S-MATE
formed O
which O
strengthened O
the O
alloys S-MATE
. O


The O
pathway O
developed O
in O
this O
study O
for O
refining O
the O
Al–Si O
alloy S-MATE
microstructure O
to O
improve O
the O
tensile B-PRO
ductility E-PRO
will O
provide O
a O
feasible O
and O
fast O
manufacturing S-MANP
method O
for O
improving O
the O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
other O
low-melting O
temperature S-PARA
alloys S-MATE
in O
the O
near O
future O
using O
EBM S-MANP
technology O
. O


Lunar O
regolith O
simulant O
is O
used O
as S-MATE
feedstock O
in O
the O
dry O
aerosol O
deposition B-MANP
process E-MANP
. O


Dry O
aerosol O
deposition S-CONPRI
builds S-CHAR
thick O
films O
on O
steel S-MATE
, O
glass S-MATE
and O
polyimide O
substrates O
. O


Mineral O
mixture O
is O
transformed O
directly O
to O
fully B-PARA
dense E-PARA
, O
nano-grained O
ceramic S-MATE
film O
. O


Phase S-CONPRI
and O
chemical B-CONPRI
composition E-CONPRI
of O
ceramic S-MATE
films O
are O
uniform O
and O
homogeneous S-CONPRI
. O


Small O
change O
in O
composition S-CONPRI
occurs O
from O
powder S-MATE
to O
coating S-APPL
in O
aerosol O
deposition S-CONPRI
. O


Dry O
Aerosol O
Deposition S-CONPRI
( O
DAD O
) O
is O
a O
ceramic B-MATE
coating E-MATE
process O
with O
the O
ability O
to O
build S-PARA
films O
and O
low O
profile S-FEAT
3D B-CONPRI
structures E-CONPRI
layer O
by O
layer S-PARA
and O
is O
therefore O
a O
promising O
additive B-MANP
manufacturing E-MANP
technique O
. O


DAD O
is O
unique O
because O
it O
uses O
kinetic O
energy O
rather O
than O
thermal B-CONPRI
energy E-CONPRI
for O
densification S-MANP
, O
and O
the O
result O
is O
a O
nearly O
theoretically O
dense O
, O
nano-crystalline O
ceramic S-MATE
. O


Thick O
films O
were O
successfully O
deposited O
onto O
glass S-MATE
, O
steel S-MATE
and O
polyimide O
substrates O
via O
DAD O
. O


Surface B-PRO
roughness E-PRO
increased O
with O
thickness O
and O
with O
some O
influence O
from O
substrate B-MATE
material E-MATE
. O


Utilizing O
the O
DAD O
process S-CONPRI
, O
a O
very O
heterogeneous S-CONPRI
mixture O
of O
silicate S-MATE
and O
titanate O
mineral O
phases O
was O
transformed O
in O
a O
single O
step S-CONPRI
to O
a O
fully B-PARA
dense E-PARA
, O
nano-grained O
coating S-APPL
with O
spatially O
homogeneous B-CONPRI
composition E-CONPRI
at O
the O
micro-scale S-CONPRI
. O


The O
final O
composition S-CONPRI
of O
the O
coatings S-APPL
was O
found O
to O
deviate O
slightly O
from O
the O
feedstock S-MATE
powder O
, O
becoming O
richer O
in O
ilmenite S-MATE
( O
FeTiO3 O
) O
and O
poorer O
in O
plagioclase O
( O
feldspar S-MATE
) O
content O
. O


This O
work O
demonstrates O
the O
potential O
of O
DAD O
for O
in-space O
manufacturing S-MANP
and O
lunar O
In B-CONPRI
Situ E-CONPRI
Resource O
Utilization O
. O


Additive B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
porous B-MATE
materials E-MATE
behave O
quantitatively S-CONPRI
and O
qualitatively O
differently O
in O
fatigue S-PRO
than O
bulk O
materials S-CONPRI
, O
and O
the O
relationships O
normally O
used O
for O
the O
fatigue S-PRO
design S-FEAT
of O
continuous O
bulk O
materials S-CONPRI
are O
not O
applicable O
to O
AM S-MANP
porous O
materials S-CONPRI
particularly O
for O
low O
stiffness S-PRO
applications.This O
study O
investigated O
how O
the O
manufacturing S-MANP
methods O
and O
the O
material S-MATE
used O
during O
powder B-MANP
bed I-MANP
fusion E-MANP
affects O
the O
compressive B-PRO
strength E-PRO
and O
high O
cycle O
fatigue B-PRO
strength E-PRO
of O
a O
stochastic S-CONPRI
porous B-MATE
material E-MATE
for O
a O
given O
stiffness S-PRO
. O


Specimens O
were O
manufactured S-CONPRI
using O
varying O
laser S-ENAT
parameters O
, O
3 O
scan O
strategies O
( O
Contour S-FEAT
, O
Points O
, O
Pulsing O
) O
and O
4 O
materials S-CONPRI
. O


The O
materials S-CONPRI
investigated O
were O
two O
titanium B-MATE
alloys E-MATE
: O
commercially O
pure O
grade O
2 O
( O
CP-Ti O
) O
and O
Ti6Al4V S-MATE
ELI O
, O
commercially O
pure O
tantalum S-MATE
( O
Ta S-MATE
) O
and O
a O
titanium-tantalum O
alloy S-MATE
( O
Ti-30Ta O
) O
.The O
trends S-CONPRI
observed O
during O
fatigue B-CHAR
testing E-CHAR
for O
monolithic S-PRO
metals S-MATE
and O
statically O
for O
solid O
and O
porous S-PRO
AM B-MATE
materials E-MATE
were O
not O
always O
indicative O
of O
the O
high O
cycle O
fatigue S-PRO
behaviour O
of O
porous S-PRO
AM B-MATE
materials E-MATE
. O


Unlike O
their O
solid O
counterparts O
, O
porous S-PRO
tantalum O
and O
the O
titanium-tantalum O
alloy S-MATE
had O
the O
greatest O
fatigue B-PRO
strength E-PRO
for O
a O
given O
stiffness S-PRO
, O
8 O
% O
greater O
than O
CP-Ti O
and O
19 O
% O
greater O
than O
Ti6Al4V S-MATE
ELI O
. O


Optimisation O
of O
the O
laser S-ENAT
parameters O
and O
scan O
strategies O
was O
found O
to O
also O
increase O
the O
fatigue B-PRO
strength E-PRO
for O
a O
given O
stiffness S-PRO
of O
porous S-PRO
AM B-MATE
materials E-MATE
by O
7–8 O
% O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
an O
additive B-MANP
manufacturing E-MANP
technology O
which O
allows O
parts O
to O
be S-MATE
fabricated O
from O
metal B-MATE
powder E-MATE
using O
CAD S-ENAT
data O
. O


Today O
, O
standard S-CONPRI
metal B-MATE
powders E-MATE
like O
stainless B-MATE
steel E-MATE
, O
titanium S-MATE
, O
aluminium S-MATE
or O
copper S-MATE
are O
widely O
used O
with O
SLM S-MANP
technology O
. O


However O
, O
none O
of O
these O
materials S-CONPRI
is O
suitable O
for O
high-temperature O
applications O
up O
to O
more O
than O
2000 O
°C O
such O
as S-MATE
the O
diagnostic O
and O
inner O
wall O
materials S-CONPRI
of O
a O
fusion S-CONPRI
reactor O
or O
experiment S-CONPRI
. O


As S-MATE
a O
primary O
task O
at O
the O
Central O
Institute O
of O
Engineering S-APPL
, O
Electronics S-CONPRI
and O
Analytics O
, O
development O
and O
manufacturing S-MANP
of O
high-temperature O
components S-MACEQ
for O
experimental S-CONPRI
setups O
are O
essentially O
demanded O
using O
new O
technologies S-CONPRI
and O
materials S-CONPRI
. O


Therefore O
, O
molybdenum S-MATE
powder O
is O
investigated O
in O
terms O
of O
suitability O
for O
SLM S-MANP
technology O
in O
this O
study O
, O
due O
to O
the O
capability O
of O
molybdenum S-MATE
withstanding O
high O
temperature S-PARA
. O


Parameters S-CONPRI
like O
laser B-PARA
power E-PARA
, O
spot O
velocity O
and O
thickness O
of O
the O
powder S-MATE
layer S-PARA
are O
analysed O
to O
achieve O
high O
density S-PRO
of O
the O
parts O
. O


Being O
able O
to O
characterize O
the O
process S-CONPRI
signatures O
of O
powder B-MACEQ
bed E-MACEQ
based O
additive B-MANP
manufacturing I-MANP
process E-MANP
is O
key O
to O
improving O
the O
product B-CONPRI
quality E-CONPRI
. O


This O
paper O
demonstrates O
the O
implementation O
of O
a O
digital O
fringe O
projection O
technique O
to O
measure O
surface B-CONPRI
topography E-CONPRI
of O
the O
powder B-MACEQ
bed E-MACEQ
layers O
during O
the O
fabrication S-MANP
. O


We O
focus O
on O
developing O
the O
metrology S-CONPRI
tool O
and O
observing O
the O
types O
of O
information O
that O
can O
be S-MATE
extracted O
from O
such O
topographical O
data S-CONPRI
. O


The O
performance S-CONPRI
of O
the O
system O
is O
demonstrated O
with O
selected O
in B-CONPRI
situ E-CONPRI
measurements O
. O


Experimental S-CONPRI
results O
show O
this O
system O
is O
capable O
of O
measuring O
powder B-MACEQ
bed E-MACEQ
signatures O
including O
the O
powder S-MATE
layer S-PARA
flatness S-PRO
, O
surface B-FEAT
texture E-FEAT
, O
the O
average S-CONPRI
height O
drop O
of O
the O
fused S-CONPRI
regions O
, O
characteristic O
length B-CHAR
scales E-CHAR
on O
the O
surface S-CONPRI
, O
and O
splatter O
drop O
location O
and O
dimension S-FEAT
. O


Mask B-MANP
projection I-MANP
stereolithography E-MANP
is O
a O
digital B-ENAT
light I-ENAT
processing-based E-ENAT
additive B-MANP
manufacturing E-MANP
technique O
that O
has O
various O
advantages O
, O
such O
as S-MATE
high-resolution O
, O
scanning-free O
parallel O
process S-CONPRI
, O
wide O
material S-MATE
sets O
available O
, O
and O
support-structure-free S-CONPRI
three-dimensional O
( O
3D S-CONPRI
) O
printing O
. O


However O
, O
multi-material B-MANP
3D I-MANP
printing E-MANP
with O
mask B-MANP
projection I-MANP
stereolithography E-MANP
has O
been O
challenging O
due O
to O
difficulties O
of O
exchanging O
a O
liquid-state S-CONPRI
material O
in O
a O
vat S-MACEQ
. O


In O
this O
work O
, O
we O
report O
a O
rapid O
multi-material S-CONPRI
projection O
micro-stereolithography O
using O
dynamic B-CONPRI
fluidic I-CONPRI
control E-CONPRI
of O
multiple O
liquid B-MATE
photopolymers E-MATE
within O
an O
integrated O
fluidic B-MACEQ
cell E-MACEQ
. O


Highly O
complex O
multi-material S-CONPRI
3D B-CONPRI
micro-structures E-CONPRI
are O
rapidly B-MANP
fabricated E-MANP
through O
an O
active O
material B-CONPRI
exchange I-CONPRI
process E-CONPRI
. O


Material B-PARA
flow I-PARA
rate E-PARA
in O
the O
fluidic B-MACEQ
cell E-MACEQ
, O
material B-CONPRI
exchange I-CONPRI
efficiency E-CONPRI
, O
and O
the O
effects O
of O
energy B-CONPRI
dosage E-CONPRI
on O
curing B-PARA
depth E-PARA
are O
studied O
for O
various O
photopolymers S-MATE
. O


In O
addition O
, O
the O
degree O
of O
cross-contamination S-CONPRI
between O
different O
materials S-CONPRI
in O
a O
3D B-MANP
printed E-MANP
multi-material O
structure S-CONPRI
is O
evaluated O
to O
assess O
the O
quality S-CONPRI
of O
multi-material B-MANP
printing E-MANP
. O


The O
pressure-tight S-CONPRI
and O
leak-free S-CONPRI
fluidic B-MACEQ
cell E-MACEQ
enables O
active O
and O
fast O
switch O
between O
liquid B-MATE
photopolymers E-MATE
, O
even O
including O
micro-/nano-particle B-MATE
suspensions E-MATE
, O
which O
could O
potentially O
lead S-MATE
to O
facile O
3D B-MANP
printing E-MANP
of O
multi-material S-CONPRI
metallic/ceramic S-MATE
structures O
or O
heterogeneous B-MATE
biomaterials E-MATE
. O


In O
addition O
, O
a O
multi-responsive B-MATE
hydrogel E-MATE
micro-structure O
is O
printed O
using O
a O
thermo-responsive B-MATE
hydrogel E-MATE
and O
an O
electroactive B-MATE
hydrogel E-MATE
, O
showing O
various O
modes O
of O
swelling B-CONPRI
actuation E-CONPRI
in O
response O
to O
multiple O
external B-CONPRI
stimuli E-CONPRI
. O


This O
new O
ability O
to O
rapidly O
and O
heterogeneously S-CONPRI
integrate O
multiple B-MATE
functional I-MATE
materials E-MATE
in O
three-dimension S-CONPRI
at O
micro-scale S-CONPRI
has O
potential O
to O
accelerate O
advances O
in O
many O
emerging O
areas S-PARA
including O
3D B-MATE
metamaterials E-MATE
, O
tissue B-CONPRI
engineering E-CONPRI
, O
and O
soft B-APPL
robotics E-APPL
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
allows O
for O
the O
production S-MANP
of O
custom O
parts O
with O
previously O
impractical O
internal O
features O
, O
but O
comes O
with O
the O
additional O
possibility O
of O
internal O
defects S-CONPRI
due O
to O
print S-MANP
error S-CONPRI
, O
residual B-PRO
stress E-PRO
buildup O
, O
or O
cyber-attack O
by O
a O
malicious O
actor O
. O


Conventional O
post O
process S-CONPRI
analysis O
techniques O
have O
difficulty O
detecting O
these O
defects S-CONPRI
, O
often O
requiring O
destructive O
tests O
that O
compromise O
the O
integrity S-CONPRI
( O
and O
thus O
the O
purpose O
) O
of O
the O
part O
. O


Here O
, O
we O
present O
a O
“ O
certify-as-you-build O
” O
quality S-CONPRI
assurance O
system O
with O
the O
capability O
to O
monitor S-CONPRI
a O
part O
during O
the O
print S-MANP
process O
, O
capture O
the O
geometry S-CONPRI
using O
three-dimensional S-CONPRI
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
( O
3D-DIC O
) O
, O
and O
compare O
the O
printed O
geometry S-CONPRI
with O
the O
computer S-ENAT
model O
to O
detect O
print S-MANP
errors S-CONPRI
in O
situ O
. O


A O
test O
case O
using O
a O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
3D B-MACEQ
printer E-MACEQ
was O
implemented O
, O
demonstrating O
in B-CONPRI
situ E-CONPRI
error S-CONPRI
detection O
of O
localized O
and O
global O
defects S-CONPRI
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
a O
powder-based B-MANP
additive I-MANP
manufacturing E-MANP
technique O
which O
creates O
parts O
by O
fusing S-CONPRI
together O
successive O
layers O
of O
powder S-MATE
with O
a O
laser S-ENAT
. O


The O
quality S-CONPRI
of O
produced O
parts O
is O
highly O
dependent O
on O
the O
proper O
selection O
of O
processing O
parameters S-CONPRI
, O
requiring O
significant O
testing S-CHAR
and O
experimentation O
to O
determine O
parameters S-CONPRI
for O
a O
given O
machine S-MACEQ
and O
material S-MATE
. O


Computational O
modeling S-ENAT
could O
potentially O
be S-MATE
used O
to O
shorten O
this O
process S-CONPRI
by O
identifying O
parameters S-CONPRI
through O
simulation S-ENAT
. O


However O
, O
simulating O
complete O
SLM S-MANP
builds S-CHAR
is O
challenging O
due O
to O
the O
difference O
in O
scale O
between O
the O
size O
of O
the O
particles S-CONPRI
and O
laser S-ENAT
used O
in O
the O
build S-PARA
and O
the O
size O
of O
the O
part O
produced O
. O


Often O
, O
continuum B-CONPRI
models E-CONPRI
are O
employed O
which O
approximate O
the O
powder S-MATE
as S-MATE
a O
continuous O
medium O
to O
avoid O
the O
need O
to O
model S-CONPRI
powder O
particles S-CONPRI
individually O
. O


While O
computationally O
expedient O
, O
continuum B-CONPRI
models E-CONPRI
require O
as S-MATE
inputs O
effective O
material B-CONPRI
properties E-CONPRI
for O
the O
powder S-MATE
which O
are O
often O
difficult O
to O
obtain O
experimentally O
. O


Building O
on O
previous O
works O
which O
have O
developed O
methods O
for O
estimating O
these O
effective O
properties S-CONPRI
along O
with O
their O
uncertainties O
through O
the O
use O
of O
detailed O
models O
, O
this O
work O
presents O
a O
part O
scale O
continuum B-CONPRI
model E-CONPRI
capable O
of O
predicting O
residual S-CONPRI
thermal O
stresses O
in O
an O
SLM S-MANP
build S-PARA
with O
uncertainty O
estimates O
. O


Model S-CONPRI
predictions O
are O
compared O
to O
experimental S-CONPRI
measurements O
from O
the O
literature O
. O


Processing O
of O
high-speed O
steel S-MATE
by O
SLM S-MANP
was O
successfully O
performed O
with O
low O
porosity S-PRO
. O


Preheating S-MANP
temperatures O
of O
200 O
°C O
or O
300 O
°C O
are O
necessary O
for O
low O
crack O
density S-PRO
. O


Microstructure S-CONPRI
consists O
of O
a O
cellular O
, O
fine O
dendritic O
structure S-CONPRI
after O
SLM S-MANP
. O


Hardness S-PRO
tempering O
behavior O
of O
the O
SLM-densified O
material S-MATE
is O
promising O
. O


The O
tribological B-CONPRI
properties E-CONPRI
of O
SLM S-MANP
specimens O
are O
highly O
promising O
compared O
to O
the O
references O
. O


In O
this O
work O
, O
the O
influence O
of O
different O
manufacturing S-MANP
techniques O
of O
M3:2 O
high-speed O
steel S-MATE
on O
the O
resulting O
microstructure S-CONPRI
and O
the O
associated O
material B-CONPRI
properties E-CONPRI
was O
investigated O
. O


Therefore O
, O
microstructure S-CONPRI
as S-MATE
well O
as S-MATE
the O
mechanical S-APPL
and O
tribological B-CONPRI
properties E-CONPRI
of O
cast S-MANP
steel O
( O
with O
subsequent O
hot-forming O
) O
and O
steel B-MATE
powder E-MATE
processed S-CONPRI
by O
two O
techniques O
: O
hot-isostatic O
pressing S-MANP
( O
HIP S-MANP
) O
and O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
were O
compared O
. O


A O
detailed O
SLM S-MANP
parameter S-CONPRI
analysis O
revealed O
that O
the O
porosity S-PRO
of O
SLM S-MANP
specimens O
can O
be S-MATE
decreased O
towards O
a O
smaller O
point O
distance O
and O
a O
longer O
exposure S-CONPRI
time O
( O
high O
energy O
input O
) O
. O


A O
rise O
in O
preheating S-MANP
temperature O
is O
associated O
with O
a O
reduction S-CONPRI
in O
the O
crack O
density S-PRO
or O
the O
complete O
avoidance O
of O
cracks O
. O


In O
this O
context O
, O
the O
high-speed O
steel S-MATE
showed O
outstanding O
densification S-MANP
behavior O
by O
SLM S-MANP
, O
even O
though O
this O
steel S-MATE
is O
considered O
to O
be S-MATE
hardly O
processable O
by O
SLM S-MANP
due O
to O
its O
high O
content O
of O
carbon S-MATE
and O
hard O
phase-forming O
elements S-MATE
. O


In O
addition O
, O
the O
reusability O
of O
steel B-MATE
powder E-MATE
for O
SLM S-MANP
processing O
was O
investigated O
. O


The O
results O
indicated O
that O
multiple O
reuse O
is O
possible O
, O
but O
only O
in O
combination O
with O
powder S-MATE
processing O
( O
mechanical S-APPL
sieving O
) O
after O
each O
SLM S-MANP
cycle O
. O


The O
microstructure S-CONPRI
of O
SLM-densified O
high-speed O
steel S-MATE
consists O
of O
a O
cellular O
, O
fine O
dendritic O
subgrain O
segregation S-CONPRI
structure O
( O
submicro O
level O
) O
that O
is O
not O
significantly O
affected O
by O
preheating S-MANP
the O
base O
plate O
. O


The O
mechanical S-APPL
and O
tribological B-CONPRI
properties E-CONPRI
were O
examined O
in O
relation O
to O
the O
manufacturing S-MANP
technique O
and O
the O
subsequent O
heat B-MANP
treatment E-MANP
. O


Our O
investigations O
revealed O
promising O
behavior O
with O
respect O
to O
hardness S-PRO
tempering O
( O
position O
of O
the O
secondary O
hardness S-PRO
peak O
) O
and O
tribology S-CONPRI
of O
the O
M3:2 O
steel S-MATE
processed S-CONPRI
by O
SLM S-MANP
compared O
to O
the O
HIP S-MANP
and O
cast S-MANP
conditions O
. O


A O
hybrid-part O
made O
of O
two O
materials S-CONPRI
was O
fabricated S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
of O
AlSi10Mg S-MATE
on O
an O
Al-Cu-Ni-Fe-Mg O
cast S-MANP
alloy S-MATE
substrate O
. O


The O
microstructure S-CONPRI
of O
the O
two-material O
component S-MACEQ
and O
the O
interface S-CONPRI
is O
investigated O
using O
multi-scale O
characterization O
techniques O
including O
optical B-CHAR
microscopy E-CHAR
( O
OM S-CHAR
) O
, O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
, O
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
( O
EBSD S-CHAR
) O
, O
and O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
TEM S-CHAR
) O
. O


The O
microstructure S-CONPRI
of O
SLM-AlSi10Mg O
consists O
of O
fine O
cellular O
dendrites S-BIOP
and O
columnar B-PRO
grains E-PRO
, O
developed O
along O
the O
building B-PARA
direction E-PARA
, O
where O
the O
substrate S-MATE
cast S-MANP
alloy S-MATE
is O
featured O
by O
large O
equiaxed B-CONPRI
grains E-CONPRI
. O


OM S-CHAR
and O
SEM S-CHAR
studies O
of O
the O
interface S-CONPRI
show O
a O
sound O
metallurgical B-CONPRI
bonding E-CONPRI
as S-MATE
a O
result O
of O
the O
melting S-MANP
of O
AlSi10Mg S-MATE
powder O
and O
partial O
melting S-MANP
of O
the O
cast S-MANP
substrate O
assisted O
by O
the O
circulate O
flows O
and O
Marangoni O
convection O
. O


The O
circulate O
flows O
cause O
complex O
phenomena O
at O
the O
interface S-CONPRI
, O
which O
lead S-MATE
to O
the O
dilution O
of O
alloying B-MATE
elements E-MATE
and O
a O
variation S-CONPRI
in O
the O
microstructure S-CONPRI
of O
the O
first O
consolidated O
layer S-PARA
of O
SLM-AlSi10Mg O
( O
as S-MATE
a O
result O
of O
variation S-CONPRI
in O
thermal B-PARA
gradient E-PARA
and O
solidification B-PARA
rate E-PARA
) O
. O


TEM S-CHAR
investigations O
of O
the O
interface S-CONPRI
reveal O
segregation S-CONPRI
of O
alloying B-MATE
elements E-MATE
at O
the O
interdendritic O
regions O
after O
solidification S-CONPRI
. O


Moreover O
, O
no O
precipitate S-MATE
is O
formed O
on O
top O
of O
the O
interface S-CONPRI
, O
due O
to O
the O
rapid B-MANP
solidification E-MANP
and O
dilution O
of O
the O
alloying B-MATE
elements E-MATE
. O


EBSD S-CHAR
analysis O
of O
the O
interface S-CONPRI
shows O
substantial O
differences O
in O
the O
grain B-CONPRI
structure E-CONPRI
of O
SLM-AlSi10Mg O
and O
the O
cast S-MANP
substrate O
, O
in O
terms O
of O
size O
and O
morphology S-CONPRI
. O


Mechanical B-CONPRI
properties E-CONPRI
of O
the O
hybrid O
material S-MATE
are O
studied O
afterwards O
using O
Vickers O
microhardness S-CONPRI
measurements O
, O
nanoindentation S-CHAR
and O
quasi-static S-CONPRI
uniaxial O
tensile B-CHAR
tests E-CHAR
. O


The O
SLM-AlSi10Mg O
side O
of O
the O
hybrid-part O
possesses O
better O
performance S-CONPRI
, O
mainly O
due O
to O
its O
finer O
and O
hierarchical O
microstructure S-CONPRI
. O


Inkjet B-MANP
printing E-MANP
of O
multiple O
materials S-CONPRI
is O
usually O
processed S-CONPRI
in O
multiple O
steps O
due O
to O
various O
jetting S-MANP
and O
curing/sintering O
conditions O
. O


The O
ink S-MATE
consists O
of O
iron B-MATE
oxide E-MATE
( O
Fe3O4 S-MATE
) O
nanoparticles S-CONPRI
( O
nominal O
particle S-CONPRI
size O
50–100 O
nm O
) O
suspended O
within O
a O
UV S-CONPRI
curable O
matrix O
resin S-MATE
. O


The O
viscosity S-PRO
and O
surface B-PRO
tension E-PRO
of O
the O
inks O
were O
tuned O
to O
sit O
within O
the O
inkjet S-MANP
printability O
range.Multiple O
layers O
of O
the O
electromagnetic O
active O
ink S-MATE
were O
printed O
alongside O
passive O
UV-curable O
ink S-MATE
in O
a O
single O
manufacturing B-MANP
process E-MANP
to O
form O
a O
multi-material S-CONPRI
waffle O
shape O
. O


The O
real O
permittivity O
of O
the O
cured S-MANP
passive O
ink S-MATE
, O
active O
ink S-MATE
and O
waffle O
structure S-CONPRI
at O
a O
frequency O
of O
8–12 O
GHz O
were O
2.25 O
, O
2.73 O
and O
2.65 O
F/m O
, O
respectively O
. O


This O
shows O
the O
potential O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
to O
form O
multi-material B-FEAT
structures E-FEAT
with O
tunable O
electromagnetic O
properties S-CONPRI
. O


A O
side-viewing O
vision O
monitoring O
methodology S-CONPRI
using O
high-speed O
camera S-MACEQ
for O
powder B-MANP
bed I-MANP
fusion I-MANP
process E-MANP
is O
proposed O
. O


A O
novel O
method O
is O
designed S-FEAT
to O
extract O
features O
from O
melt B-MATE
pool E-MATE
, O
plume O
and O
spatters O
. O


The O
characteristics O
of O
the O
features O
of O
melt B-MATE
pool E-MATE
, O
plume O
and O
spatters O
are O
investigated O
. O


The O
results O
demonstrated O
that O
the O
extracted S-CONPRI
features O
are O
potential O
indicators O
for O
process S-CONPRI
quality O
assessment O
. O


With O
the O
development O
of O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
additive B-MANP
manufacturing E-MANP
technique O
for O
functional O
parts O
production S-MANP
, O
process B-CONPRI
monitoring E-CONPRI
and O
diagnosis O
is O
highly O
demanded O
to O
ensure O
its O
process S-CONPRI
reliability O
and O
repeatability S-CONPRI
. O


An O
optical S-CHAR
filter S-APPL
with O
350 O
nm–800 O
nm O
cut-off O
was O
used O
to O
enhance O
the O
image S-CONPRI
contrast O
between O
the O
plume O
and O
the O
melt B-MATE
pool E-MATE
. O


A O
new O
image S-CONPRI
processing O
method O
was O
designed S-FEAT
to O
extract O
features O
from O
the O
melt B-MATE
pool E-MATE
, O
plume O
and O
spatters O
, O
respectively O
. O


Kalman O
filter S-APPL
tracking O
was O
used O
to O
pinpoint O
the O
exact O
melt B-MATE
pool E-MATE
position O
, O
and O
image S-CONPRI
segmentation O
algorithm S-CONPRI
was O
developed O
to O
segment O
the O
melt B-MATE
pool E-MATE
, O
plume O
and O
spatters O
from O
each O
other O
; O
a O
new O
tracking O
method O
was O
utilized O
to O
remove O
the O
spatters O
generated O
in O
the O
previous O
frame O
. O


After O
image S-CONPRI
processing O
, O
the O
features O
of O
melt B-MATE
pool E-MATE
intensity O
, O
plume O
area S-PARA
, O
plume O
orientation S-CONPRI
, O
spatter S-CHAR
number O
, O
spatter S-CHAR
area S-PARA
, O
spatter S-CHAR
orientation S-CONPRI
and O
spatter S-CHAR
velocity O
were O
extracted S-CONPRI
and O
their O
correlations O
with O
the O
scanning B-CONPRI
quality E-CONPRI
were O
investigated O
. O


The O
results O
indicated O
that O
these O
features O
were O
potential O
indicators O
for O
scanning B-CONPRI
quality E-CONPRI
assessment O
. O


The O
proposed O
method O
could O
be S-MATE
used O
to O
further O
study O
the O
characteristics O
of O
plume O
and O
spatter S-CHAR
and O
to O
explore O
the O
diagnosis O
performance S-CONPRI
based O
on O
the O
fusion S-CONPRI
of O
melt B-MATE
pool E-MATE
, O
plume O
and O
spatter S-CHAR
information O
. O


It O
provides O
a O
promising O
means O
for O
in-situ S-CONPRI
monitoring O
and O
control O
of O
PBF S-MANP
process O
. O


This O
paper O
presents O
the O
computational B-CHAR
fluid I-CHAR
dynamics E-CHAR
modeling O
of O
an O
additive B-MANP
manufacturing I-MANP
process E-MANP
that O
is O
candidate O
for O
the O
production S-MANP
of O
Gen B-MACEQ
IV E-MACEQ
nuclear O
reactor O
fuels O
. O


The O
modeled O
process S-CONPRI
combines O
the O
internal B-CONPRI
gelation E-CONPRI
to O
produce O
metal B-MATE
hydrous I-MATE
oxides E-MATE
with O
the O
3D B-MANP
ceramic I-MANP
printing E-MANP
to O
create O
a O
green B-CONPRI
body E-CONPRI
from O
these O
gelled B-MATE
oxides E-MATE
as S-MATE
described O
by O
Pouchon O
( O
2016 O
) O
. O


The O
objective O
of O
the O
simulations S-ENAT
is O
to O
optimize O
the O
process B-CONPRI
parameters E-CONPRI
: O
microfluidic B-CONPRI
mixing E-CONPRI
of O
the O
internal B-CONPRI
gelation E-CONPRI
reagents O
and O
generation O
of O
droplets S-CONPRI
of O
the O
mixed O
solutions O
. O


The O
simulations S-ENAT
were O
performed O
using O
the O
OpenFOAM O
software S-CONPRI
, O
and O
to O
perform O
these O
simulations S-ENAT
with O
the O
correct O
solution B-CONPRI
parameters E-CONPRI
, O
the O
properties S-CONPRI
of O
the O
fluids S-MATE
of O
interest O
were O
measured O
. O


The O
results O
show O
that O
a O
thorough O
mixing S-CONPRI
of O
the O
metal S-MATE
solution O
and O
the O
methenamine S-MATE
and O
urea S-MATE
mixture O
in O
a O
microfluidic B-MACEQ
mixer E-MACEQ
can O
be S-MATE
achieved O
in O
tens O
of O
milliseconds O
by O
either O
winding S-CONPRI
the O
mixing B-MACEQ
channel E-MACEQ
to O
create O
secondary B-CONPRI
flows E-CONPRI
or O
splitting O
the O
solutions O
inlets S-MACEQ
to O
yield O
additional O
diffusion B-CONPRI
interfaces E-CONPRI
. O


The O
optimal O
droplet B-PARA
size E-PARA
is O
achieved O
by O
using O
a O
mechanically B-CONPRI
vibrating E-CONPRI
3D B-MACEQ
printing I-MACEQ
head E-MACEQ
that O
leads O
to O
a O
frequency-following O
Rayleigh B-CONPRI
instability E-CONPRI
. O


The O
results O
of O
the O
simulations S-ENAT
suggest O
the O
parameters S-CONPRI
( O
micromixer B-PARA
geometry E-PARA
, O
flow B-PARA
rate E-PARA
, O
vibration B-PARA
frequency E-PARA
and O
others O
) O
that O
will O
optimize O
the O
mixing B-CONPRI
efficiency E-CONPRI
in O
a O
microfluidic B-MACEQ
mixer E-MACEQ
and O
the O
droplet B-CONPRI
generation E-CONPRI
process O
from O
a O
3D B-MACEQ
printing I-MACEQ
head E-MACEQ
. O


Metal S-MATE
Laser B-MANP
Sintering E-MANP
( O
LS O
) O
is O
a O
powder B-MANP
bed I-MANP
fusion I-MANP
process E-MANP
that O
can O
be S-MATE
used O
to O
produce O
manufactured S-CONPRI
parts O
of O
complex B-PRO
shapes E-PRO
directly O
from O
metallic B-MATE
powders E-MATE
. O


One O
of O
the O
major O
problems O
of O
such O
powder B-MANP
bed I-MANP
fusion I-MANP
processes E-MANP
is O
that O
during O
the O
continuous O
movement O
of O
the O
laser B-CONPRI
beam E-CONPRI
, O
temperature S-PARA
distribution S-CONPRI
becomes O
inhomogeneous O
and O
instable O
in O
the O
powder S-MATE
. O


It O
leads O
to O
greater O
residual B-PRO
stresses E-PRO
in O
the O
solidified O
layer S-PARA
. O


Thus O
, O
temperature S-PARA
analyses O
must O
be S-MATE
performed O
to O
better O
understand O
the O
heating-cooling O
process S-CONPRI
of O
the O
powder B-MACEQ
bed E-MACEQ
as S-MATE
well O
as S-MATE
the O
interactions O
of O
different O
laser S-ENAT
scanning O
paths O
within O
a O
sintering S-MANP
pattern S-CONPRI
. O


A O
transient B-CONPRI
3D I-CONPRI
Finite I-CONPRI
Element E-CONPRI
( O
FE S-MATE
) O
model S-CONPRI
of O
the O
LS O
process S-CONPRI
has O
been O
developed O
with O
the O
commercial O
FE S-MATE
code O
ABAQUS S-ENAT
. O


The O
model S-CONPRI
takes O
into O
account O
the O
different O
physical O
phenomena O
involved O
in O
this O
powder B-MANP
bed I-MANP
fusion E-MANP
technology O
( O
including O
thermal O
conduction O
, O
radiation S-MANP
and O
convection O
) O
. O


A O
moving O
thermal O
source S-APPL
, O
modeling S-ENAT
the O
laser B-ENAT
scan E-ENAT
, O
is O
implemented O
with O
the O
user O
scripting O
subroutine O
DFLUX O
in O
this O
FE S-MATE
code O
. O


The O
material S-MATE
’ O
s S-MATE
thermal O
behavior O
is O
also O
defined O
via O
the O
subroutine O
UMATHT O
. O


As S-MATE
the O
material B-CONPRI
properties E-CONPRI
change O
due O
to O
the O
powder B-MANP
bed I-MANP
fusion I-MANP
process E-MANP
, O
the O
model S-CONPRI
takes O
it O
into O
account O
. O


In O
this O
way O
, O
the O
calculation O
of O
a O
temperature-dependent O
behavior O
is O
undertaken O
for O
the O
packed O
powder B-MACEQ
bed E-MACEQ
, O
within O
its O
effective B-PARA
thermal I-PARA
conductivity E-PARA
and O
specific B-PRO
heat E-PRO
. O


Furthermore O
, O
the O
model S-CONPRI
accounts O
for O
the O
latent O
heat S-CONPRI
due O
to O
phase S-CONPRI
change O
of O
the O
metal B-MATE
powder E-MATE
. O


Finally O
, O
a O
time- O
and O
temperature-dependent O
formulation O
for O
the O
material S-MATE
’ O
s S-MATE
density S-PRO
is O
also O
computed O
, O
which O
is O
then O
integrated O
along O
with O
the O
other O
thermal B-CONPRI
properties E-CONPRI
in O
the O
heat S-CONPRI
equation O
. O


FE S-MATE
simulations O
have O
been O
applied O
to O
the O
case O
of O
titanium B-MATE
powder E-MATE
and O
show O
predictions S-CONPRI
in O
good O
agreement O
with O
experimental S-CONPRI
results O
. O


The O
effects O
of O
process B-CONPRI
parameters E-CONPRI
on O
the O
temperature S-PARA
and O
on O
the O
density B-PRO
distribution E-PRO
are O
also O
presented O
. O


The O
lattice B-FEAT
structure E-FEAT
is O
a O
type O
of O
cellular B-MATE
material E-MATE
that O
can O
achieve O
a O
variety O
of O
promising O
physical B-PRO
properties E-PRO
. O


Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
has O
relieved O
the O
difficulty O
of O
fabricating S-MANP
lattice O
structures O
with O
complex B-CONPRI
geometries E-CONPRI
. O


However O
, O
the O
quality S-CONPRI
of O
the O
AM S-MANP
fabricated O
lattice B-FEAT
structure E-FEAT
still O
needs O
improvement O
. O


In O
this O
paper O
, O
the O
influence O
of O
parameters S-CONPRI
of O
the O
Fused B-MANP
Deposition I-MANP
Modeling E-MANP
( O
FDM S-MANP
) O
process S-CONPRI
on O
lattice B-FEAT
structures E-FEAT
was O
investigated O
by O
the O
Taguchi B-CONPRI
method E-CONPRI
. O


It O
was O
found O
that O
the O
optimum O
level O
and O
significance O
of O
each O
process B-CONPRI
parameter E-CONPRI
vary O
for O
horizontal O
and O
inclined O
struts S-MACEQ
. O


In O
addition O
, O
compression B-CHAR
tests E-CHAR
investigate O
the O
influence O
of O
process B-CONPRI
parameters E-CONPRI
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
lattice B-FEAT
structures E-FEAT
. O


The O
results O
show O
that O
process B-CONPRI
parameters E-CONPRI
optimized O
by O
print B-CONPRI
quality E-CONPRI
can O
also O
improve O
the O
elastic B-PRO
modulus E-PRO
and O
the O
ultimate B-PRO
strength E-PRO
of O
these O
lattice B-FEAT
structures E-FEAT
. O


Laser B-MANP
cladding E-MANP
induces O
high O
tensile B-PRO
residual I-PRO
stress E-PRO
( O
RS O
) O
, O
which O
can O
compromise O
the O
quality S-CONPRI
of O
a O
specimen O
. O


Therefore O
, O
it O
is O
critical O
to O
accurately S-CHAR
predict O
the O
RS O
distribution S-CONPRI
in O
cladding S-MANP
and O
understand O
its O
formation O
mechanism S-CONPRI
. O


In O
this O
study O
, O
functionally B-MATE
graded I-MATE
material E-MATE
( O
FGM S-MANP
) O
layers O
were O
successfully O
deposited O
on O
the O
surface S-CONPRI
of O
a O
titanium B-MATE
alloy I-MATE
Ti6Al4V I-MATE
sheet E-MATE
by O
laser B-MANP
cladding E-MANP
technology O
. O


A O
corresponding O
thermo-mechanical S-CONPRI
coupling O
simulation S-ENAT
model S-CONPRI
of O
the O
laser B-MANP
cladding E-MANP
process O
was O
developed O
to O
investigate O
the O
formation O
mechanism S-CONPRI
of O
RS O
in O
the O
laser B-MANP
cladding E-MANP
FGM B-MATE
layers E-MATE
. O


The O
results O
show O
that O
high O
tensile S-PRO
RS O
forms O
in O
cladding S-MANP
components O
. O


Subsequent O
cladding S-MANP
can O
effectively O
alleviate O
the O
RS O
in O
cladding S-MANP
components O
although O
the O
position O
of O
maximum O
RS O
remains O
unchanged O
. O


The O
measurement S-CHAR
results O
of O
the O
longitudinal O
RS O
on O
the O
top O
and O
bottom O
surfaces S-CONPRI
of O
cladding S-MANP
components O
by O
the O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
method O
agreed O
with O
the O
simulation S-ENAT
results O
, O
thereby O
proving O
the O
accuracy S-CHAR
of O
the O
simulation S-ENAT
. O


In O
addition O
, O
the O
formation O
mechanism S-CONPRI
of O
RS O
in O
the O
laser B-MANP
cladding E-MANP
FGM B-MATE
layers E-MATE
was O
revealed O
by O
discussing O
the O
individual O
impact S-CONPRI
of O
each O
material B-CONPRI
property E-CONPRI
on O
RS O
. O


It O
was O
indicated O
that O
the O
RS O
distribution S-CONPRI
in O
the O
laser B-MANP
cladding E-MANP
FGM B-MATE
layers E-MATE
was O
significantly O
affected O
by O
material B-CONPRI
properties E-CONPRI
( O
in O
particular O
, O
coefficient B-PRO
of I-PRO
thermal I-PRO
expansion E-PRO
and O
Young O
’ O
s S-MATE
modulus O
) O
, O
except O
for O
the O
temperature B-PARA
gradient E-PARA
induced O
by O
the O
laser B-MANP
cladding E-MANP
process O
. O


The O
material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
process O
, O
i.e. O
, O
fused B-MANP
deposition I-MANP
modeling E-MANP
( O
FDM S-MANP
) O
, O
as S-MATE
opposed O
to O
traditional B-MANP
subtractive I-MANP
manufacturing E-MANP
, O
offers O
a O
superior O
way O
of O
manufacturing S-MANP
tooling O
components S-MACEQ
in O
terms O
of O
great O
design B-CONPRI
flexibility E-CONPRI
, O
rapid B-MANP
tooling E-MANP
development O
, O
material S-MATE
requirement O
reduction S-CONPRI
and O
significant O
cost O
savings O
. O


However O
, O
it O
is O
always O
challenging O
to O
design S-FEAT
a O
tool S-MACEQ
structure S-CONPRI
with O
minimized O
material S-MATE
and O
labor B-CONPRI
cost E-CONPRI
while O
maintaining O
satisfactory O
tooling B-CONPRI
performance E-CONPRI
. O


In O
the O
current O
study O
, O
a O
comprehensive O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
was O
developed O
for O
ULTEM O
9085 O
FDM S-MANP
tools O
subjected O
to O
applied O
pressure S-CONPRI
and O
elevated O
temperature S-PARA
for O
vacuum O
assisted O
resin B-MANP
transfer I-MANP
molding E-MANP
( O
VARTM O
) O
process S-CONPRI
. O


Both O
solid-build O
and O
sparse-build O
tools S-MACEQ
were O
studied O
. O


Material B-CONPRI
properties E-CONPRI
of O
the O
tools S-MACEQ
were O
obtained O
from O
solid O
coupon O
testing S-CHAR
at O
elevated O
temperatures S-PARA
. O


The O
thermo-mechanical S-CONPRI
behavior O
of O
tools S-MACEQ
during O
the O
VARTM O
process S-CONPRI
was O
investigated O
using O
the O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
. O


The O
ULTEM O
tools S-MACEQ
were O
manufactured S-CONPRI
using O
Stratasys S-APPL
Fortus O
400mc O
FDM S-MANP
machine O
. O


Thermal B-PARA
cycling E-PARA
of O
the O
tools S-MACEQ
was O
performed O
at O
elevated O
temperatures S-PARA
( O
180 O
°F O
and O
250 O
°F O
) O
. O


Dimensional B-CHAR
analysis E-CHAR
and O
surface B-PRO
roughness E-PRO
of O
the O
tools S-MACEQ
were O
evaluated O
after O
thermal B-PARA
cycling E-PARA
. O


This O
study O
on O
the O
performance S-CONPRI
of O
FDM S-MANP
tooling O
for O
VARTM O
composite B-MANP
manufacturing E-MANP
process O
can O
be S-MATE
extended O
to O
other O
composite B-MANP
manufacturing E-MANP
processes O
. O


The O
low O
alloy B-MATE
steel E-MATE
AISI O
4140 O
( O
German O
grade O
42CrMo4 O
) O
is O
one O
of O
the O
most O
frequently O
used O
Quench O
& O
Tempering S-MANP
( O
Q O
& O
T O
) O
steels S-MATE
with O
a O
wide O
range S-PARA
of O
applicability O
. O


Until O
now O
, O
commercially O
available O
iron S-MATE
powders O
for O
additive B-MANP
manufacturing E-MANP
can O
be S-MATE
summed O
up O
by O
their O
low O
amount O
of O
carbon S-MATE
. O


Fusion B-MANP
welding E-MANP
of O
Q O
& O
T O
steels S-MATE
often O
leads O
to O
cracks O
due O
to O
brittle S-PRO
martensitic O
transformation O
and O
the O
associated O
volume S-CONPRI
change O
. O


Therefore O
, O
the O
selection O
of O
appropriate O
process B-CONPRI
parameters E-CONPRI
in O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
plays O
a O
key O
role O
for O
the O
final O
material B-CONPRI
properties E-CONPRI
and O
is O
achieved O
through O
utilization O
of O
a O
new O
process S-CONPRI
development O
strategy O
and O
evaluation O
of O
microstructural S-CONPRI
features O
of O
test O
cubes O
. O


In O
this O
work O
tensile B-MACEQ
specimens E-MACEQ
were O
successfully O
produced O
with O
optimal B-PARA
process E-PARA
parameters O
and O
mechanical B-CHAR
tests E-CHAR
of O
additively O
built O
samples S-CONPRI
indicate O
mechanical S-APPL
performance O
comparable O
with O
a O
450 O
°C O
tempered S-MANP
state O
of O
conventionally O
cast S-MANP
material O
. O


By O
correlating O
the O
measured O
mechanical B-CONPRI
properties E-CONPRI
of O
LPBF S-MANP
samples O
to O
those O
of O
a O
conventional O
Q O
& O
T O
state O
, O
an O
estimation O
of O
the O
intrinsic O
heat B-MANP
treatment E-MANP
during O
LPBF S-MANP
was O
carried O
out O
using O
an O
inverse O
transient S-CONPRI
Hollomon–Jaffe O
approach O
. O


This O
is O
also O
in O
accordance O
with O
the O
finely O
dispersed O
carbide S-MATE
precipitates O
in O
the O
as S-MATE
built O
condition O
. O


Furthermore O
, O
the O
effect O
of O
bed S-MACEQ
pre-heating O
on O
the O
final O
material S-MATE
tempering O
state O
was O
found O
to O
be S-MATE
negligible O
. O


This O
shows O
the O
importance O
of O
a O
balanced O
match O
between O
LPBF S-MANP
process O
parameters S-CONPRI
and O
subsequent O
application O
demands O
as S-MATE
well O
as S-MATE
necessary O
postprocessing S-CONPRI
steps O
. O


Alumina S-MATE
toughened O
zirconia S-MATE
( O
ATZ O
) O
parts O
were O
produced O
via O
a O
laser-based O
powder B-MANP
bed I-MANP
fusion E-MANP
technology O
using O
a O
conventional O
Nd-YAG O
continuous B-CONPRI
wave E-CONPRI
laser O
. O


The O
powder S-MATE
was O
produced O
using O
a O
spray B-MANP
drying E-MANP
process S-CONPRI
and O
the O
laser S-ENAT
matter O
interaction O
was O
enhanced O
by O
a O
binder S-MATE
pyrolysis O
. O


Thermal O
post-processing S-CONPRI
to O
further O
increase O
the O
part O
density S-PRO
was O
investigated O
using O
dilatometry O
. O


The O
microstructure S-CONPRI
was O
analysed O
using O
X-ray B-CHAR
powder I-CHAR
diffraction E-CHAR
measurements O
. O


The O
mechanical B-CONPRI
properties E-CONPRI
were O
assessed O
using O
a O
four-point O
bending B-CHAR
test E-CHAR
on O
ten O
specimens O
, O
reaching O
a O
bending B-PRO
strength E-PRO
of O
31 O
± O
11 O
MPa S-CONPRI
. O


Laser-based O
direct O
metal S-MATE
addition O
( O
LBDMA O
) O
is O
a O
promising O
directed B-MANP
energy I-MANP
deposition E-MANP
technology O
that O
is O
well O
suited O
for O
the O
production S-MANP
of O
complex O
metal S-MATE
structures O
, O
low-volume O
manufacturing S-MANP
, O
and O
high-value O
component S-MACEQ
repair O
or O
modification O
. O


LBDMA O
is O
finding O
wide O
application O
in O
the O
automotive S-APPL
, O
biomedical S-APPL
, O
and O
aerospace B-APPL
industries E-APPL
. O


However O
, O
the O
process S-CONPRI
reliability O
and O
the O
repeatability S-CONPRI
of O
finished O
components S-MACEQ
are O
still O
problems O
. O


This O
work O
offers O
a O
solution S-CONPRI
by O
developing O
a O
sensing S-APPL
and O
control B-MACEQ
system E-MACEQ
for O
the O
robotically O
controlled O
8-axis O
LBDMA O
system O
developed O
at O
the O
Research S-CONPRI
Center O
for O
Advanced O
Manufacturing S-MANP
of O
Southern O
Methodist O
University O
, O
Dallas O
, O
TX O
. O


The O
developed O
system O
consists O
of O
sensing S-APPL
and O
control O
units O
for O
the O
powder B-PARA
flow I-PARA
rate E-PARA
and O
the O
molten B-CONPRI
pool E-CONPRI
size O
. O


An O
optoelectronic O
sensor S-MACEQ
was O
developed O
to O
sense O
the O
powder B-PARA
flow I-PARA
rate E-PARA
. O


It O
is O
a O
main O
component S-MACEQ
in O
an O
on-line O
control B-MACEQ
system E-MACEQ
of O
powder B-PARA
flow I-PARA
rate E-PARA
in O
a O
LBDMA O
system O
. O


An O
infrared S-CONPRI
imaging S-APPL
setup O
was O
installed O
on O
the O
laser S-ENAT
head O
to O
monitor S-CONPRI
the O
top O
full-field O
view O
of O
the O
molten B-CONPRI
pool E-CONPRI
. O


A O
simple S-MANP
proportional O
integral O
derivative O
( O
PID O
) O
controller S-MACEQ
, O
combined O
with O
feed-forward O
compensation O
was O
used O
to O
build S-PARA
a O
closed-loop B-MACEQ
control E-MACEQ
system O
for O
achieving O
a O
uniform O
molten B-CONPRI
pool E-CONPRI
size O
. O


Two O
L-shaped O
single-bead O
walls O
were O
built O
with O
and O
without O
closed-loop B-MACEQ
control E-MACEQ
, O
respectively O
. O


A O
good O
performance S-CONPRI
on O
achieving O
uniform O
geometry S-CONPRI
by O
closed-loop B-MACEQ
control E-MACEQ
of O
the O
molten B-CONPRI
pool E-CONPRI
size O
was O
approved O
. O


Selective B-MANP
laser I-MANP
sintering E-MANP
( O
LS O
) O
of O
thermoplastic B-MATE
powders E-MATE
allows O
for O
the O
construction S-APPL
of O
complex O
parts O
with O
higher O
mechanical B-CONPRI
properties E-CONPRI
and O
durability S-PRO
compared O
to O
other O
additive B-MANP
manufacturing E-MANP
methods O
. O


According O
to O
the O
current O
model S-CONPRI
of O
isothermal S-CONPRI
laser O
sintering S-MANP
, O
semi-crystalline O
thermoplastics S-MATE
need O
to O
be S-MATE
processed O
within O
a O
certain O
temperature B-PARA
range E-PARA
, O
resulting O
in O
the O
simultaneous O
presence O
of O
the O
material S-MATE
both O
in O
a O
molten O
and O
solid B-CONPRI
state E-CONPRI
, O
which O
is O
present O
during O
part O
building O
. O


Based O
on O
this O
process B-CONPRI
model E-CONPRI
, O
high O
cycle O
times O
ranging O
from O
hours O
to O
days O
are O
a O
thought O
to O
be S-MATE
a O
necessity O
to O
avoid O
warpage.In O
this O
paper O
, O
the O
limited O
validity O
of O
the O
model S-CONPRI
of O
isothermal S-CONPRI
laser O
sintering S-MANP
is O
shown O
by O
various O
experiments O
, O
as S-MATE
ongoing O
solidification S-CONPRI
could O
be S-MATE
detected O
a O
few O
layers O
below O
the O
powder B-MACEQ
bed E-MACEQ
surface O
. O


The O
results O
indicate O
that O
crystallization S-CONPRI
and O
material S-MATE
solidification O
is O
initiated O
at O
high O
temperatures S-PARA
and O
further O
progresses O
throughout O
part O
build-up O
in O
z-direction S-FEAT
. O


Therefore O
, O
a O
process-adapted O
material S-MATE
characterization O
was O
performed O
to O
identify O
the O
isothermal B-CONPRI
crystallization E-CONPRI
kinetics O
at O
processing O
temperature S-PARA
and O
to O
track O
changes O
of O
the O
material S-MATE
state O
over O
time O
. O


A O
dual O
approach O
on O
measuring O
surface S-CONPRI
temperatures O
by O
infrared S-CONPRI
thermography O
and O
additional O
thermocouple S-MACEQ
measurements O
in O
z-direction S-FEAT
was O
performed O
to O
identify O
further O
influences O
on O
the O
material S-MATE
solidification O
. O


A O
model B-CONPRI
experiment E-CONPRI
revealed O
that O
a O
few O
millimeters O
below O
the O
surface S-CONPRI
, O
components S-MACEQ
produced O
by O
LS O
are O
already O
solidified O
. O


Based O
on O
these O
results O
, O
the O
authors O
present O
an O
enhanced O
process B-CONPRI
model E-CONPRI
of O
isothermal S-CONPRI
laser O
sintering S-MANP
, O
which O
considers O
material S-MATE
solidification O
in O
z-direction S-FEAT
during O
part O
build-up O
. O


Additive B-MANP
manufacturing E-MANP
( O
3D B-MANP
printing E-MANP
) O
enables O
the O
designing O
and O
producing O
of O
complex B-CONPRI
geometries E-CONPRI
in O
a O
layer-by-layer S-CONPRI
approach O
. O


The O
layered B-CONPRI
structure E-CONPRI
leads O
to O
anisotropic S-PRO
behaviour O
in O
the O
material S-MATE
. O


To O
accommodate O
anisotropic S-PRO
behaviour O
, O
geometrical O
optimization S-CONPRI
is O
needed O
so O
that O
the O
3D B-MANP
printed E-MANP
object O
meets O
the O
pre-set O
strength S-PRO
and O
quality S-CONPRI
requirements O
. O


In O
this O
article O
a O
material S-MATE
description O
for O
polymer S-MATE
powder O
bed S-MACEQ
fused O
also O
or O
selective B-MANP
laser E-MANP
sintered O
( O
SLS S-MANP
) O
PA12 S-MATE
( O
Nylon-12 O
) O
, O
which O
is O
a O
common O
3D B-MANP
printing E-MANP
plastic O
, O
was O
investigated O
, O
using O
the O
Finite B-CONPRI
Element I-CONPRI
Method E-CONPRI
( O
FEM S-CONPRI
) O
. O


The O
Material S-MATE
Model O
parameters S-CONPRI
were O
obtained O
by O
matching O
them O
to O
the O
test O
results O
of O
multipurpose O
test O
specimens O
( O
dumb-bells O
or O
dog O
bones O
) O
and O
the O
model S-CONPRI
was O
then O
used O
to O
simulate/predict O
the O
mechanical S-APPL
performance O
of O
the O
SLS S-MANP
printed O
lower-leg O
prosthesis O
components S-MACEQ
, O
pylon O
and O
support S-APPL
. O


For O
verification S-CONPRI
purposes O
, O
two O
FEM S-CONPRI
designs S-FEAT
for O
a O
support S-APPL
were O
SLS S-MANP
printed O
together O
with O
additional O
test O
specimens O
in O
order O
to O
validate O
the O
used O
Material S-MATE
Model O
. O


The O
SLS S-MANP
printed O
prosthesis O
pieces O
were O
tested O
according O
to O
ISO S-MANS
10328 O
Standard S-CONPRI
. O


The O
FEM S-CONPRI
simulations O
, O
together O
with O
the O
Material S-MATE
Model O
, O
was O
found O
to O
give O
good O
estimations O
for O
the O
location O
of O
a O
failure S-CONPRI
and O
its O
load O
. O


It O
was O
also O
noted O
that O
there O
were O
significant O
variations S-CONPRI
among O
individual O
SLS S-MANP
printed O
test O
specimens O
, O
which O
impacted O
on O
the O
material S-MATE
parameters O
and O
the O
FEM S-CONPRI
simulations O
. O


Hence O
, O
to O
enable O
reliable O
FEM S-CONPRI
simulations O
for O
the O
designing O
of O
3D B-MANP
printed E-MANP
products O
, O
better O
control O
of O
the O
SLS B-MANP
process E-MANP
with O
regards O
to O
porosity S-PRO
, O
pore S-PRO
morphology S-CONPRI
and O
pore S-PRO
distribution S-CONPRI
is O
needed O
. O


Water-atomized O
and O
gas-atomized O
17-4 B-MATE
PH I-MATE
stainless I-MATE
steel E-MATE
powder O
were O
used O
as S-MATE
feedstock O
in O
selective B-MANP
laser I-MANP
melting I-MANP
process E-MANP
. O


Gas B-MANP
atomized E-MANP
powder O
revealed O
single O
martensitic O
phase S-CONPRI
after O
printing O
and O
heat B-MANP
treatment E-MANP
independent O
of O
energy B-PARA
density E-PARA
. O


As-printed O
water B-MANP
atomized E-MANP
powder S-MATE
contained O
dual O
martensitic O
and O
austenitic S-MATE
phase O
regardless O
of O
energy B-PARA
density E-PARA
. O


The O
H900 O
heat B-MANP
treatment E-MANP
cycle O
was O
not O
effective O
in O
enhancing O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
water-atomized O
powder S-MATE
after O
laser S-ENAT
melting O
. O


However O
, O
after O
solutionizing O
at O
1315ºC O
and O
aging O
at O
482 O
°C O
fully O
martensitic O
structure S-CONPRI
was O
observed O
with O
hardness S-PRO
( O
40.2 O
HRC O
) O
, O
yield B-PRO
strength E-PRO
( O
1000 O
MPa S-CONPRI
) O
and O
ultimate B-PRO
tensile I-PRO
strength E-PRO
( O
1261 O
MPa S-CONPRI
) O
comparable O
to O
those O
of O
gas B-MANP
atomized E-MANP
( O
42.7 O
HRC O
, O
1254 O
MPa S-CONPRI
and O
1300 O
MPa S-CONPRI
) O
and O
wrought S-CONPRI
alloy S-MATE
( O
39 O
HRC O
, O
1170 O
MPa S-CONPRI
and O
1310 O
MPa S-CONPRI
) O
, O
respectively O
. O


Improved O
mechanical B-CONPRI
properties E-CONPRI
in O
water-atomized O
powder S-MATE
was O
found O
to O
be S-MATE
related O
to O
presence O
of O
finer O
martensite S-MATE
and O
higher O
volume B-PARA
fraction E-PARA
of O
fine O
Cu-enriched O
precipitates S-MATE
. O


Our O
results O
imply O
that O
water-atomized O
powder S-MATE
is O
a O
promising O
cheaper O
feedstock S-MATE
alternative O
to O
gas-atomized O
powder S-MATE
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
offer O
new O
processing O
routes O
for O
functionally B-MATE
graded I-MATE
materials E-MATE
. O


At O
present O
, O
parts O
built O
using O
these O
processes S-CONPRI
often O
require O
additional O
processing O
as S-MATE
a O
result O
of O
the O
characteristic O
surface B-FEAT
finish E-FEAT
limitations O
synonymous O
with O
AM B-MANP
processes E-MANP
. O


A O
difficulty O
thus O
arises O
in O
the O
post B-CONPRI
processing E-CONPRI
of O
these O
components S-MACEQ
as S-MATE
volumes O
within O
the O
part O
have O
differing O
material B-CONPRI
properties E-CONPRI
by O
definition O
and O
will O
therefore O
exhibit O
variable O
machinability.In O
this O
study O
, O
machining S-MANP
of O
functionally B-CONPRI
graded E-CONPRI
Ti6Al4V/ O
WC S-MATE
components S-MACEQ
consisting O
of O
a O
metal B-MATE
matrix I-MATE
composite E-MATE
( O
MMC S-MATE
) O
region O
and O
a O
single O
alloy S-MATE
region O
produced O
via O
direct B-MANP
energy I-MANP
deposition E-MANP
using O
commercially O
available O
tooling S-CONPRI
is O
explored O
. O


The O
influence O
of O
post B-CONPRI
processing E-CONPRI
on O
surface B-FEAT
integrity E-FEAT
is O
investigated O
and O
reported O
. O


The O
effect O
of O
material S-MATE
variation O
on O
cutting B-CONPRI
forces E-CONPRI
and O
tool S-MACEQ
response O
along O
the O
component S-MACEQ
is O
also O
analysed O
and O
reported O
. O


Cutting B-CONPRI
forces E-CONPRI
within O
the O
MMC S-MATE
region O
are O
found O
to O
increase O
by O
as S-MATE
much O
as S-MATE
40 O
% O
which O
has O
been O
subsequently O
related O
to O
the O
periodic O
changes O
in O
microstructure S-CONPRI
generated O
by O
the O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
build B-CONPRI
strategy E-CONPRI
. O


Tool B-CONPRI
wear E-CONPRI
mechanisms O
are O
investigated O
and O
the O
influence O
of O
material S-MATE
pull O
out O
on O
surface B-FEAT
integrity E-FEAT
of O
both O
MMC S-MATE
and O
single O
material S-MATE
regions O
is O
explored O
. O


This O
study O
provides O
an O
insight O
into O
how O
the O
layer S-PARA
building O
strategies O
, O
particularly O
with O
multiple O
materials S-CONPRI
and O
the O
resulting O
variation S-CONPRI
in O
microstructure S-CONPRI
influences O
the O
machining S-MANP
of O
resulting O
components S-MACEQ
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
gaining O
popularity O
because O
of O
its O
ability O
to O
manufacture S-CONPRI
complex O
parts O
in O
less O
time O
. O


Despite O
recent O
research S-CONPRI
involving O
designs S-FEAT
of O
experiments O
( O
DOEs O
) O
to O
characterize O
the O
relationships O
between O
some O
AM B-MANP
process E-MANP
parameters O
and O
various O
part O
quality S-CONPRI
characteristics O
, O
to O
date O
, O
there O
seems O
to O
be S-MATE
no O
universally O
accepted O
comprehensive O
model S-CONPRI
that O
relates O
process B-CONPRI
parameters E-CONPRI
to O
part O
quality S-CONPRI
. O


In O
this O
paper O
, O
to O
support S-APPL
the O
goal O
of O
manufacturing S-MANP
parts O
right O
the O
first O
time O
, O
a O
Bayesian O
network O
in O
continuous O
domain S-CONPRI
is O
developed O
which O
relates O
four O
process B-CONPRI
parameters E-CONPRI
( O
laser B-PARA
power E-PARA
, O
scan B-PARA
speed E-PARA
, O
hatch B-PARA
spacing E-PARA
, O
and O
layer B-PARA
thickness E-PARA
) O
and O
five O
part O
quality S-CONPRI
characteristics O
( O
density S-PRO
, O
hardness S-PRO
, O
top O
layer S-PARA
surface O
roughness S-PRO
, O
ultimate B-PRO
tensile I-PRO
strength E-PRO
in O
the O
build B-PARA
direction E-PARA
and O
ultimate B-PRO
tensile I-PRO
strength E-PRO
perpendicular O
to O
the O
build B-PARA
direction E-PARA
) O
. O


A O
machine B-ENAT
learning I-ENAT
algorithm E-ENAT
is O
used O
to O
train O
the O
network O
on O
a O
database S-ENAT
mined O
from O
a O
large O
number O
of O
publications O
with O
experimental B-CONPRI
data E-CONPRI
from O
parts O
built O
using O
316L O
with O
selective B-MANP
laser I-MANP
melting E-MANP
. O


The O
network O
is O
validated O
by O
retaining O
a O
subset O
of O
the O
training O
data S-CONPRI
for O
testing S-CHAR
and O
comparing O
the O
network O
’ O
s S-MATE
predictions S-CONPRI
to O
the O
known O
values O
. O


Accuracy S-CHAR
is O
optimized O
by O
continually O
re-training O
the O
network O
using O
parts O
built O
with O
a O
specific O
machine S-MACEQ
of O
interest O
. O


The O
industrial S-APPL
relevance O
of O
this O
research S-CONPRI
is O
outlined O
with O
respect O
to O
four O
current O
challenges O
in O
AM S-MANP
, O
including O
the O
length O
of O
time O
to O
determine O
optimal B-PARA
process E-PARA
parameters O
for O
a O
new O
machine S-MACEQ
, O
ability O
to O
organize O
relevant O
knowledge O
, O
quantification O
of O
machine S-MACEQ
variability O
, O
and O
transfer O
of O
knowledge O
to O
new O
operators O
. O


Reclaimed O
materials S-CONPRI
such O
as S-MATE
waste O
plastics S-MATE
can O
be S-MATE
utilized O
in O
additive B-MANP
manufacturing E-MANP
to O
improve O
the O
self-reliance O
of O
warfighters O
on O
forward O
operating O
bases O
by O
cutting S-MANP
costs O
and O
decreasing O
the O
demand O
for O
the O
frequent O
resupplying O
of O
parts O
by O
the O
supply B-CONPRI
chain E-CONPRI
. O


In O
addition O
, O
the O
use O
of O
waste O
materials S-CONPRI
in O
additive B-MANP
manufacturing E-MANP
in O
the O
private O
sector O
would O
reduce O
cost O
and O
increase O
sustainability S-CONPRI
, O
providing O
a O
high-value O
output O
for O
used O
plastics S-MATE
. O


Experimentation O
is O
conducted O
to O
process S-CONPRI
polyethylene B-MATE
terephthalate E-MATE
bottles O
and O
packaging O
into O
filament S-MATE
that O
can O
then O
be S-MATE
used O
for O
additive B-MANP
manufacturing E-MANP
methods O
like O
fused B-MANP
filament I-MANP
fabrication E-MANP
, O
without O
the O
use O
of O
additives S-MATE
or O
modification O
to O
the O
polymer S-MATE
. O


The O
chemistry S-CONPRI
of O
different O
polyethylene B-MATE
terephthalate E-MATE
recycled O
feedstocks S-MATE
was O
evaluated O
and O
found O
to O
be S-MATE
identical O
, O
and O
thus O
mixed O
feedstock S-MATE
processing O
is O
a O
suitable O
approach O
. O


Rheological S-PRO
data S-CONPRI
showed O
drying S-MANP
of O
the O
recycled S-CONPRI
polyethylene B-MATE
terephthalate E-MATE
led S-APPL
to O
an O
increase O
in O
the O
polymer S-MATE
’ O
s S-MATE
viscosity O
. O


Thermal O
and O
mechanical B-CONPRI
properties E-CONPRI
were O
evaluated O
for O
filament S-MATE
with O
different O
processing O
conditions O
, O
as S-MATE
well O
as S-MATE
printed O
and O
molded O
specimens O
. O


Crystallinity O
ranged O
from O
12.2 O
for O
the O
water O
cooled O
filament S-MATE
, O
compared O
to O
24.9 O
% O
for O
the O
filament S-MATE
without O
any O
active O
cooling S-MANP
. O


Tensile S-PRO
results O
show O
that O
the O
elongation S-PRO
to O
failure S-CONPRI
was O
similar O
to O
an O
injection O
molded O
part O
( O
3.5 O
% O
) O
and O
tensile B-PRO
strength E-PRO
of O
35.1 O
± O
8 O
MPa S-CONPRI
was O
comparable O
to O
commercial O
polycarbonate-ABS O
filament S-MATE
, O
demonstrating O
the O
robustness S-PRO
of O
the O
material S-MATE
. O


In O
addition O
, O
three B-CONPRI
point I-CONPRI
bending E-CONPRI
tests O
showed O
a O
similar O
load O
at O
failure S-CONPRI
for O
a O
select O
long-lead O
military S-APPL
part O
printed O
from O
the O
recycled S-CONPRI
filament S-MATE
compared O
to O
parts O
printed O
from O
commercial O
filament S-MATE
. O


Thus O
filament S-MATE
from O
recycled S-CONPRI
polyethylene B-MATE
terephthalate E-MATE
has O
the O
capability O
for O
replacing O
commercial O
filament S-MATE
in O
printing O
a O
diverse O
range S-PARA
of O
plastic S-MATE
parts O
. O


The O
incorporation O
of O
electrical S-APPL
components S-MACEQ
into O
3D B-MANP
printed E-MANP
products O
such O
as S-MATE
sensors O
or O
printing O
of O
circuits O
requires O
the O
use O
of O
3D S-CONPRI
printable O
conductive O
materials S-CONPRI
. O


However O
, O
most O
conductive O
materials S-CONPRI
available O
for O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
have O
conductivities O
of O
less O
than O
1000 O
S/m O
. O


Here O
, O
we O
describe O
the O
study O
of O
conductive O
thermoplastic B-MATE
composites E-MATE
comprising O
either O
nylon S-MATE
– O
6 O
or O
polyethylene S-MATE
( O
PE S-MANP
) O
matrix O
. O


The O
fillers O
used O
were O
nickel S-MATE
and O
Sn95Ag4Cu1 O
, O
a O
low O
melting B-PRO
point E-PRO
metal O
alloy S-MATE
. O


The O
combination O
of O
nickel B-MATE
metal E-MATE
particles O
and O
tin B-MATE
alloy E-MATE
allows O
for O
higher O
metal S-MATE
loading O
at O
lower O
melt S-CONPRI
viscosity O
, O
compared O
to O
composites S-MATE
of O
nickel B-MATE
metal E-MATE
particles O
alone O
. O


% O
metal S-MATE
loading O
was O
processable O
by O
a O
single O
screw B-MACEQ
extruder E-MACEQ
. O


Embedded O
conductive O
tracks O
of O
various O
geometries S-CONPRI
were O
easily O
printed O
via O
FFF S-MANP
. O


Electrical B-PRO
conductivity E-PRO
of O
embedded O
conductive O
track O
has O
been O
investigated O
as S-MATE
a O
function O
of O
geometrical O
variation S-CONPRI
, O
where O
conductive O
tracks O
printed O
along O
a O
horizontal O
axis O
show O
resistance S-PRO
of O
≤ O
1 O
Ω. O
Porosity S-PRO
of O
the O
printed O
track O
is O
shown O
to O
increase O
with O
prints O
along O
the O
vertical S-CONPRI
axis O
, O
leading O
to O
a O
reduction S-CONPRI
in O
electrical B-PRO
conductivity E-PRO
of O
more O
than O
two O
orders O
of O
magnitude S-PARA
. O


Rapid O
melt B-MATE
pool E-MATE
formation O
and O
solidification S-CONPRI
during O
the O
metal B-MATE
powder E-MATE
bed S-MACEQ
process O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
generates O
large O
thermal B-PARA
gradients E-PARA
that O
can O
in O
turn O
lead S-MATE
to O
increased O
residual B-PRO
stress E-PRO
formation O
within O
a O
component S-MACEQ
. O


Metal S-MATE
anchors O
or O
supports S-APPL
are O
required O
to O
be S-MATE
built O
in-situ S-CONPRI
and O
forcibly O
hold O
SLM S-MANP
structures O
in O
place O
and O
minimise O
geometric O
distortion/warpage O
as S-MATE
a O
result O
of O
this O
thermal O
residual B-PRO
stress E-PRO
. O


Anchors O
are O
often O
costly O
, O
difficult O
and O
time O
consuming O
to O
remove O
and O
limit S-CONPRI
the O
geometric B-CONPRI
freedom E-CONPRI
of O
this O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
. O


A O
novel O
method O
known O
as S-MATE
Anchorless O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
ASLM O
) O
maintains O
processed B-CONPRI
material E-CONPRI
within O
a O
stress S-PRO
relieved O
state O
throughout O
the O
duration O
of O
a O
build S-PARA
. O


As S-MATE
a O
result O
metal S-MATE
components S-MACEQ
formed O
using O
ASLM O
do O
not O
require O
support B-FEAT
structures E-FEAT
or O
anchors O
. O


ASLM O
locally O
melts O
two O
or O
more O
powdered O
materials S-CONPRI
that O
alloy S-MATE
under O
the O
action O
of O
the O
laser S-ENAT
and O
can O
form O
into O
various O
combinations O
of O
eutectic/hypo/hyper O
eutectic S-CONPRI
alloys S-MATE
with O
a O
new O
lower O
solidification S-CONPRI
temperature O
. O


This O
new O
alloy S-MATE
is O
maintained O
in O
a O
semi-solid O
or O
stress S-PRO
reduced O
state O
throughout O
the O
build S-PARA
with O
the O
assistance O
of O
elevated O
powder B-MACEQ
bed E-MACEQ
pre-heating O
. O


In O
this O
paper O
the O
ASLM O
methodology S-CONPRI
is O
detailed O
and O
investigations O
into O
processing O
of O
a O
low O
temperature S-PARA
eutectic S-CONPRI
Al-Si S-MATE
binary O
casting B-MATE
alloy E-MATE
is O
explored O
. O


Two O
types O
of O
Al S-MATE
powders O
were O
compared O
; O
pre-alloyed O
AlSi12 S-MATE
and O
elemental O
mix O
Al S-MATE
+ O
12 O
wt O
% O
Si S-MATE
. O


The O
study O
established O
an O
understanding O
of O
the O
laser S-ENAT
in-situ S-CONPRI
alloying S-FEAT
process O
and O
confirmed O
successful O
alloy S-MATE
formation O
within O
the O
process S-CONPRI
. O


Differential O
thermal B-CHAR
analysis E-CHAR
, O
microscopy S-CHAR
and O
X-Ray B-CHAR
diffraction E-CHAR
were O
used O
to O
further O
understand O
the O
nature O
of O
alloying S-FEAT
within O
the O
process S-CONPRI
. O


Residual B-PRO
stress E-PRO
reduction S-CONPRI
was O
observed O
within O
ASLM O
processed S-CONPRI
elemental O
Al S-MATE
+ O
Si12 O
and O
geometries S-CONPRI
produced O
without O
the O
requirement O
for O
anchors O
. O


Heterogeneous B-CONPRI
grain I-CONPRI
structure E-CONPRI
is O
a O
source S-APPL
of O
the O
inhomogeneity O
in O
structure S-CONPRI
and O
properties S-CONPRI
of O
the O
metallic S-MATE
components S-MACEQ
made O
by O
multi-layer O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
. O


During O
AM S-MANP
, O
repeated O
heating S-MANP
and O
cooling S-MANP
during O
multi-layer O
deposition S-CONPRI
, O
local O
temperature B-PARA
gradient E-PARA
and O
solidification S-CONPRI
growth O
rate O
, O
deposit O
geometry S-CONPRI
, O
and O
molten B-CONPRI
pool E-CONPRI
shape O
and O
size O
govern O
the O
evolution S-CONPRI
of O
the O
grain B-CONPRI
structure E-CONPRI
. O


Here O
the O
effects O
of O
these O
causative O
factors O
on O
the O
heterogeneous S-CONPRI
grain B-CONPRI
growth E-CONPRI
during O
multi-layer O
laser S-ENAT
deposition S-CONPRI
of O
Inconel B-MATE
718 E-MATE
are O
examined O
by O
a O
Monte O
Carlo O
method O
based O
grain B-CONPRI
growth E-CONPRI
model O
. O


It O
is O
found O
that O
epitaxial B-PRO
columnar I-PRO
grain E-PRO
growth O
occurs O
from O
the O
substrate S-MATE
or O
previously O
deposited B-CHAR
layer E-CHAR
to O
the O
curved O
top O
surface S-CONPRI
of O
the O
deposit O
. O


The O
growth O
direction O
of O
these O
columnar B-PRO
grains E-PRO
is O
controlled O
by O
the O
molten B-CONPRI
pool E-CONPRI
shape O
and O
size O
. O


The O
grains S-CONPRI
in O
the O
previously O
deposited B-CHAR
layers E-CHAR
continue O
to O
grow O
because O
of O
the O
repeated O
heating S-MANP
and O
cooling S-MANP
during O
the O
deposition S-CONPRI
of O
the O
successive O
layers O
. O


Average S-CONPRI
longitudinal O
grain S-CONPRI
area S-PARA
decreases O
by O
approximately O
80 O
% O
when O
moving O
from O
the O
center O
to O
the O
edge O
of O
the O
deposit O
due O
to O
variable O
growth O
directions O
dependent O
on O
the O
local O
curvatures O
of O
the O
moving O
molten B-CONPRI
pool E-CONPRI
. O


The O
average S-CONPRI
horizontal O
grain S-CONPRI
area S-PARA
increases O
with O
the O
distance O
from O
the O
substrate S-MATE
, O
with O
a O
20 O
% O
increase O
in O
the O
horizontal O
grain S-CONPRI
area S-PARA
in O
a O
short O
distance O
from O
the O
third O
to O
the O
eighth O
layer S-PARA
, O
due O
to O
competitive O
solid-state S-CONPRI
grain B-CONPRI
growth E-CONPRI
causes O
increased O
grain B-PRO
size E-PRO
in O
previous O
layers O
. O


Powder S-MATE
quality O
in O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
of O
Ti-6Al-4V S-MATE
components S-MACEQ
is O
crucial O
in O
determining O
the O
critical O
material B-CONPRI
properties E-CONPRI
of O
the O
end O
item O
. O


In O
this O
study O
, O
we O
report O
on O
the O
effect O
of O
powder S-MATE
oxidation S-MANP
on O
the O
Charpy O
impact S-CONPRI
energy O
of O
Ti-6Al-4V S-MATE
parts O
manufactured S-CONPRI
using O
EBM S-MANP
. O


In O
addition O
to O
oxidation S-MANP
, O
the O
effects O
on O
impact S-CONPRI
energy O
due O
to O
hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
, O
specimen O
orientation S-CONPRI
, O
and O
EBM S-MANP
process O
defects S-CONPRI
were O
also O
investigated O
. O


This O
research S-CONPRI
has O
shown O
that O
excessive O
powder S-MATE
oxidation S-MANP
( O
oxygen S-MATE
mass O
fraction S-CONPRI
above O
0.25 O
% O
and O
up O
to O
0.46 O
% O
) O
dramatically O
decreases O
the O
impact S-CONPRI
energy O
. O


It O
was O
determined O
that O
the O
room O
temperature S-PARA
impact S-CONPRI
energy O
of O
the O
parts O
after O
excessive O
oxidation S-MANP
was O
reduced O
by O
about O
seven O
times O
. O


We O
also O
report O
that O
HIP S-MANP
post-processing O
significantly O
increases O
the O
impact S-CONPRI
toughness O
, O
especially O
for O
specimens O
with O
lower O
or O
normal O
oxygen S-MATE
content O
. O


The O
specimen O
orientation S-CONPRI
effect O
was O
found O
to O
be S-MATE
more O
significant O
for O
low O
oxidation S-MANP
levels O
. O


Material B-MANP
extrusion I-MANP
3D I-MANP
printing E-MANP
( O
ME3DP O
) O
, O
based O
on O
fused B-MANP
deposition I-MANP
modeling E-MANP
( O
FDM S-MANP
) O
technology S-CONPRI
is O
currently O
the O
most O
widely O
available O
3D B-MANP
printing E-MANP
platform O
. O


As S-MATE
is O
the O
case O
with O
other O
3D B-MANP
printing E-MANP
methods O
, O
parts O
fabricated S-CONPRI
from O
ME3DP O
will O
exhibit O
physical B-PRO
property E-PRO
anisotropy S-PRO
where O
build B-PARA
direction E-PARA
has O
an O
effect O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
a O
given O
part O
. O


The O
work O
presented O
in O
this O
paper O
analyzes O
the O
effect O
of O
physical O
property-altering O
additives S-MATE
to O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
on O
mechanical B-CONPRI
property E-CONPRI
anisotropy S-PRO
. O


A O
total O
of O
six O
ABS-based O
polymer B-MATE
matrix I-MATE
composites E-MATE
and O
four O
polymer B-MATE
blends E-MATE
were O
created O
and O
evaluated O
. O


Tensile B-CHAR
test E-CHAR
specimens O
were O
printed O
in O
two O
build B-PARA
orientations E-PARA
and O
the O
differences O
in O
ultimate B-PRO
tensile I-PRO
strength E-PRO
and O
% O
elongation S-PRO
at O
break O
were O
compared O
between O
the O
two O
test O
sample S-CONPRI
versions O
. O


Fracture S-CONPRI
surface O
analysis O
was O
performed O
via O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
which O
gave O
insight O
to O
the O
failure B-PRO
modes E-PRO
and O
rheology S-PRO
of O
the O
novel O
material S-MATE
systems O
as S-MATE
compared O
to O
specimens O
fabricated S-CONPRI
from O
the O
same O
ABS S-MATE
base O
resin S-MATE
. O


Here O
it O
was O
found O
that O
a O
ternary O
blend S-MATE
of O
ABS S-MATE
combined O
with O
styrene O
ethylene O
butadiene O
styrene O
( O
SEBS O
) O
and O
ultra O
high O
molecular O
weight S-PARA
polyethylene S-MATE
( O
UHMWPE O
) O
lowered O
the O
mechanical B-CONPRI
property E-CONPRI
anisotropy S-PRO
in O
terms O
of O
relative O
UTS S-PRO
to O
a O
difference O
of O
22 O
± O
2.07 O
% O
as S-MATE
compared O
to O
47 O
± O
7.23 O
% O
for O
samples S-CONPRI
printed O
from O
ABS S-MATE
. O


The O
work O
here O
demonstrates O
the O
mitigation O
of O
a O
problem O
associated O
with O
3D B-MANP
printing E-MANP
as O
a O
whole O
through O
novel O
materials S-CONPRI
development O
and O
analyzes O
the O
effects O
of O
adding O
a O
wide O
variety O
of O
materials S-CONPRI
on O
the O
physical B-PRO
properties E-PRO
of O
a O
thermoplastic S-MATE
base O
resin S-MATE
. O


Moisture O
affects O
the O
flow O
behavior O
of O
AM B-MANP
metal E-MANP
powders O
, O
where O
AlSi10Mg S-MATE
is O
the O
most O
sensitive O
to O
water O
and O
oxygen S-MATE
pick O
up O
. O


The O
powder S-MATE
morphology S-CONPRI
influences O
to O
a O
large O
extent O
the O
moisture O
pick O
up O
and O
flow O
behavior O
. O


The O
flowability O
measured O
with O
traditional O
tools S-MACEQ
is O
not O
representative O
for O
powder B-MANP
bed I-MANP
fusion I-MANP
processes E-MANP
. O


Two O
new O
flowability O
tools S-MACEQ
that O
mimic S-MACEQ
the O
powder S-MATE
spreading O
mechanism S-CONPRI
of O
powder B-MANP
bed I-MANP
fusion E-MANP
systems O
are O
proposed O
and O
tested O
. O


Air O
drying S-MANP
and O
vacuum O
drying S-MANP
treatments O
to O
remove O
the O
moisture O
prior O
to O
the O
build S-PARA
process O
are O
investigated O
. O


For O
AM S-MANP
processes—specifically O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
( O
L-PBF S-MANP
) O
processes—powder O
flowability O
is O
essential O
for O
the O
product B-CONPRI
quality E-CONPRI
, O
as S-MATE
these O
processes S-CONPRI
are O
based O
on O
a O
thin O
layer S-PARA
spreading O
mechanism S-CONPRI
. O


However O
, O
the O
available O
techniques O
to O
measure O
this O
flowability O
do O
not O
accurately S-CHAR
represent O
the O
spreading O
mechanism S-CONPRI
. O


Hence O
, O
this O
paper O
presents O
two O
novel O
applicator O
tools S-MACEQ
specifically O
designed S-FEAT
to O
test O
the O
spreadability O
of O
l-PBF S-MANP
powders O
in O
thin O
layer S-PARA
application O
. O


The O
results O
were O
checked O
by O
running O
standard S-CONPRI
tests O
to O
analyze O
the O
powder S-MATE
morphology S-CONPRI
, O
moisture O
content O
, O
chemical B-CONPRI
composition E-CONPRI
and O
flowability O
using O
the O
Hall-flowmeter O
. O


For O
this O
study O
, O
four O
common O
l-PBF S-MANP
metal O
powders S-MATE
were O
selected O
: O
Inconel B-MATE
718 E-MATE
, O
Ti6Al4V S-MATE
, O
AlSi10Mg S-MATE
and O
Scalmalloy O
. O


From O
the O
as-received O
state O
, O
drying S-MANP
( O
vacuum O
and O
air O
) O
and O
moisturizing O
treatments O
were O
applied O
to O
compare O
four O
humidity O
states O
and O
investigate O
the O
feasibility S-CONPRI
of O
pre-treating O
the O
powders S-MATE
to O
remove O
moisture O
, O
which O
is O
known O
to O
cause O
problems O
with O
flowability O
, O
porosity S-PRO
formation O
and O
enhanced O
oxidation S-MANP
. O


The O
tests O
reveal O
that O
AlSi10Mg S-MATE
is O
the O
most O
susceptible O
alloy S-MATE
to O
moisture O
and O
oxygen S-MATE
pick-up O
, O
considerably O
decreasing O
the O
spreadability O
and O
relative B-PRO
density E-PRO
on O
the O
build B-MACEQ
platform E-MACEQ
. O


However O
, O
the O
results O
also O
reveal O
how O
challenging O
the O
direct O
measurement S-CHAR
of O
moisture O
levels O
in O
metal B-MATE
powders E-MATE
is O
. O


Therefore O
, O
lightweight S-CONPRI
is O
paramount.Here O
, O
a O
lightweight S-CONPRI
electromagnetic O
actuator S-MACEQ
for O
HHBs O
is O
conceived O
using O
Design B-FEAT
for I-FEAT
Additive I-FEAT
Manufacturing E-FEAT
( O
DfAM O
) O
tools S-MACEQ
, O
including O
topology B-FEAT
optimization E-FEAT
and O
free-shape O
design S-FEAT
. O


A O
prototype S-CONPRI
is O
manufactured S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
of O
alloy S-MATE
Ti-6Al-4V O
. O


The O
prototype S-CONPRI
weighs O
25 O
% O
less O
than O
the O
actuator S-MACEQ
designed O
and O
manufactured S-CONPRI
using O
traditional O
methods O
( O
i.e O
. O


CAD S-ENAT
, O
milling S-MANP
) O
and O
materials S-CONPRI
( O
i.e O
. O


Al B-MATE
alloys E-MATE
) O
. O


The O
performance S-CONPRI
of O
the O
actuator S-MACEQ
in O
service O
is O
simulated O
by O
transient S-CONPRI
modal O
mechanical B-CONPRI
analyses E-CONPRI
using O
finite B-CONPRI
element I-CONPRI
methods E-CONPRI
. O


The O
results O
show O
that O
the O
high O
strength S-PRO
of O
the O
material S-MATE
selected O
, O
combined O
with O
the O
bionic O
geometry S-CONPRI
designed S-FEAT
and O
the O
resulting O
lightweight S-CONPRI
, O
allow O
the O
actuator S-MACEQ
to O
withstand O
the O
extreme O
accelerations O
of O
the O
HHB O
( O
3000 O
g O
) O
without O
yielding O
, O
enabling O
ultra-fast O
switching O
–namely O
, O
below O
1 O
ms O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
an O
additive B-MANP
manufacturing I-MANP
process E-MANP
in O
which O
multiple O
, O
successive O
layers O
of O
metal B-MATE
powders E-MATE
are O
heated O
via O
laser S-ENAT
in O
order O
to O
build S-PARA
a O
part O
. O


Modeling S-ENAT
of O
SLM S-MANP
requires O
consideration O
of O
the O
complex O
interaction O
between O
heat B-CONPRI
transfer E-CONPRI
and O
solid O
mechanics O
. O


The O
present O
work O
describes O
the O
authors O
initial O
efforts O
to O
validate O
their O
first O
generation O
model S-CONPRI
, O
as S-MATE
described O
in O
Hodge O
et O
al S-MATE
. O


Additionally O
, O
results O
of O
various O
perturbations O
of O
the O
process B-CONPRI
parameters E-CONPRI
and O
modeling S-ENAT
strategies O
are O
discussed O
. O


Density S-PRO
, O
surface B-PRO
roughness E-PRO
and O
mechanical B-CONPRI
properties E-CONPRI
of O
printed O
AlSi10Mg S-MATE
parts O
depend O
strongly O
on O
the O
manufacturing B-MANP
process E-MANP
of O
the O
used O
powder S-MATE
. O


The O
plasma S-CONPRI
atomized S-ENAT
powder O
used O
in O
this O
study O
enables O
higher O
scanning B-PARA
speeds E-PARA
and O
thus O
a O
more O
efficient O
LPBF S-MANP
process O
than O
gas B-MANP
atomized E-MANP
powder O
. O


The O
measurement S-CHAR
of O
the O
laser S-ENAT
absorption S-CONPRI
is O
very O
sensitive O
to O
variations S-CONPRI
of O
the O
powder S-MATE
and O
reveals O
a O
clear O
correlation O
to O
the O
final O
part O
densities O
. O


The O
present O
paper O
aims O
to O
generate O
a O
deeper O
understanding O
of O
the O
influence O
of O
powder S-MATE
properties O
on O
the O
final O
parts O
manufactured S-CONPRI
by O
metal S-MATE
LPBF S-MANP
processes O
at O
constant O
parameter S-CONPRI
settings O
, O
except O
the O
hatch O
scanning B-PARA
speed E-PARA
. O


This O
issue O
was O
considered O
using O
four O
different O
AlSi10Mg S-MATE
powders.In O
addition O
to O
particle S-CONPRI
properties O
, O
such O
as S-MATE
particle O
size O
distribution S-CONPRI
and O
morphology S-CONPRI
, O
typical O
properties S-CONPRI
of O
the O
powder B-MACEQ
feedstock E-MACEQ
like O
bulk O
and O
tapped O
density S-PRO
, O
Hausner-Ratio O
, O
flowability O
and O
laser S-ENAT
absorption S-CONPRI
were O
measured O
. O


Furthermore O
, O
the O
in B-CONPRI
situ E-CONPRI
density S-PRO
of O
the O
powder S-MATE
layers O
applied O
during O
the O
LPBF S-MANP
process O
were O
analyzed O
. O


A O
comparison O
of O
the O
surface B-PARA
quality E-PARA
, O
part O
density S-PRO
and O
mechanical B-CONPRI
properties E-CONPRI
of O
AlSi10Mg S-MATE
parts O
produced O
by O
LPBF S-MANP
, O
using O
different O
particle B-CONPRI
size I-CONPRI
distributions E-CONPRI
and O
morphologies S-CONPRI
, O
has O
been O
conducted O
. O


Within O
the O
processing O
experiments O
, O
the O
laser S-ENAT
scanning O
speed O
was O
varied O
in O
order O
to O
achieve O
the O
most O
economical O
manufacturing S-MANP
of O
parts O
with O
a O
density S-PRO
> O
99.2 O
% O
.Following O
this O
comparison O
, O
it O
was O
found O
that O
the O
manufacturing B-MANP
process E-MANP
of O
the O
powder S-MATE
and O
therefore O
the O
particle S-CONPRI
morphology S-CONPRI
has O
the O
biggest O
impact S-CONPRI
on O
the O
part O
density S-PRO
and O
surface B-PARA
quality E-PARA
. O


The O
considered O
plasma S-CONPRI
atomized S-ENAT
powder O
could O
be S-MATE
processed O
at O
a O
higher O
scanning B-PARA
speed E-PARA
without O
a O
significant O
decrease O
in O
mechanical B-CONPRI
properties E-CONPRI
or O
part O
density S-PRO
. O


Generally O
, O
it O
was O
shown O
that O
higher O
densities O
of O
the O
powder S-MATE
layer S-PARA
result O
in O
higher O
part O
densities O
. O


However O
, O
the O
layer S-PARA
densities O
for O
powders S-MATE
which O
show O
almost O
the O
same O
bulk O
density S-PRO
can O
differ O
significantly O
and O
do O
not O
reach O
the O
regarding O
bulk O
density S-PRO
value O
. O


Therefore O
it O
can O
be S-MATE
stated O
that O
the O
layer S-PARA
density S-PRO
is O
not O
only O
affected O
by O
the O
bulk O
density S-PRO
. O


In O
terms O
of O
surface B-PARA
quality E-PARA
, O
the O
investigated O
plasma S-CONPRI
atomized S-ENAT
powder O
provides O
a O
significantly O
lower O
surface S-CONPRI
roughness.Moreover O
, O
it O
was O
found O
that O
the O
measurement S-CHAR
of O
the O
laser S-ENAT
absorption S-CONPRI
shows O
a O
strong O
correlation O
to O
the O
achievable O
part O
densities O
. O


In O
contrast O
to O
the O
other O
methods O
performed O
, O
it O
was O
the O
only O
measurement S-CHAR
that O
is O
very O
sensitive O
even O
to O
small O
variations S-CONPRI
of O
the O
powder S-MATE
and O
enables O
an O
unequivocal O
differentiation O
of O
the O
examined O
powders S-MATE
. O


Additive B-MANP
Manufacturing E-MANP
offers O
many O
potential O
benefits O
including O
reduced O
tooling B-CONPRI
costs E-CONPRI
and O
increased O
geometric B-CONPRI
freedom E-CONPRI
. O


However O
, O
the O
surface B-PARA
quality E-PARA
of O
the O
parts O
is O
typically O
below O
that O
of O
conventionally-processed O
materials S-CONPRI
. O


This O
paper O
evaluates O
a O
new O
chemical O
post-processing S-CONPRI
method O
to O
reduce O
the O
roughness S-PRO
of O
laser-sintered O
Nylon S-MATE
12 O
components S-MACEQ
. O


This O
process S-CONPRI
is O
called O
the O
PUSh™ O
process S-CONPRI
. O


The O
treatment O
reduced O
the O
surface B-PRO
roughness E-PRO
of O
sample S-CONPRI
parts O
from O
18 O
μm O
to O
5 O
μm O
Ra O
and O
largely O
eliminated O
roughness S-PRO
with O
length B-CHAR
scales E-CHAR
below O
500 O
μm O
. O


Treatment O
did O
not O
affect O
the O
flexural O
modulus O
, O
flexural B-PRO
strength E-PRO
, O
or O
dimensions S-FEAT
of O
3.2 O
mm S-MANP
thick O
bending S-MANP
specimens O
, O
but O
it O
did O
significantly O
impact S-CONPRI
the O
mechanical B-CONPRI
properties E-CONPRI
of O
thin O
tensile B-MACEQ
specimens E-MACEQ
that O
are O
one O
to O
eight O
layers O
thick O
. O


The O
post B-CONPRI
processing E-CONPRI
reduced O
the O
breaking O
force S-CONPRI
of O
the O
samples S-CONPRI
, O
but O
it O
increased O
the O
ultimate B-PRO
tensile I-PRO
strength E-PRO
and O
elongation S-PRO
at O
break O
. O


The O
impact S-CONPRI
was O
largest O
on O
the O
thinnest O
parts O
. O


Significant O
sample S-CONPRI
shrinkage O
( O
12–20 O
% O
) O
and O
weight B-PARA
gain E-PARA
( O
3.7–7 O
% O
) O
from O
treatment O
was O
also O
observed O
in O
the O
tensile B-MACEQ
specimens E-MACEQ
. O


The O
results O
show O
that O
the O
PUSh™ O
process S-CONPRI
dramatically O
increases O
surface S-CONPRI
smoothness S-CONPRI
and O
elongation S-PRO
at O
break O
in O
thin O
specimens O
. O


It O
decreases O
the O
surface S-CONPRI
strength S-PRO
, O
but O
effects O
are O
negligible O
in O
larger O
samples S-CONPRI
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
has O
emerged O
as S-MATE
one O
of O
the O
primary O
metal B-MANP
additive I-MANP
manufacturing E-MANP
technologies O
used O
for O
many O
applications O
in O
various O
industries S-APPL
such O
as S-MATE
medical O
and O
aerospace S-APPL
sectors O
. O


However O
, O
defects S-CONPRI
such O
as S-MATE
part O
distortion S-CONPRI
and O
delamination S-CONPRI
resulted O
from O
process-induced O
residual B-PRO
stresses E-PRO
are O
still O
one O
of O
the O
key O
challenges O
that O
hinder O
widespread O
adoptions O
of O
SLM S-MANP
. O


For O
process B-CONPRI
parameters E-CONPRI
, O
the O
laser B-CONPRI
beam E-CONPRI
scanning O
path O
will O
affect O
the O
thermomechanical S-CONPRI
behaviors O
of O
the O
build S-PARA
part O
, O
and O
thus O
, O
altering O
the O
scanning B-PARA
pattern E-PARA
may O
be S-MATE
a O
possible O
strategy O
to O
reduce O
residual B-PRO
stresses E-PRO
and O
deformations S-CONPRI
through O
influencing O
the O
heat S-CONPRI
intensity O
input O
distributions S-CONPRI
. O


In O
this O
study O
, O
a O
3D S-CONPRI
sequentially O
coupled O
finite B-CONPRI
element E-CONPRI
( O
FE S-MATE
) O
model S-CONPRI
was O
developed O
to O
investigate O
the O
thermomechanical S-CONPRI
responses O
in O
the O
SLM S-MANP
process S-CONPRI
. O


The O
model S-CONPRI
was O
applied O
to O
test O
different O
scanning B-CONPRI
strategies E-CONPRI
and O
evaluate O
their O
effects O
on O
part O
temperature S-PARA
, O
stress S-PRO
and O
deformation S-CONPRI
. O


The O
major O
results O
are O
summarized O
as S-MATE
follows O
. O


( O
1 O
) O
Among O
all O
cases O
tested O
, O
the O
out-in O
scanning B-PARA
pattern E-PARA
has O
the O
maximum O
stresses O
along O
the O
X O
and O
Y S-MATE
directions O
; O
while O
the O
45° O
inclined O
line O
scanning S-CONPRI
may O
reduce O
residual B-PRO
stresses E-PRO
in O
both O
directions O
. O


( O
2 O
) O
Large O
directional O
stress S-PRO
differences O
can O
be S-MATE
generated O
by O
the O
horizontal O
line O
scanning B-CONPRI
strategy E-CONPRI
. O


( O
3 O
) O
X O
and O
Y S-MATE
directional O
stress B-CHAR
concentrations E-CHAR
are O
shown O
around O
the O
edge O
of O
the O
deposited B-CHAR
layers E-CHAR
and O
the O
interface S-CONPRI
between O
the O
deposited B-CHAR
layers E-CHAR
and O
the O
substrate S-MATE
for O
all O
cases O
. O


( O
4 O
) O
The O
45° O
inclined O
line O
scanning S-CONPRI
case O
also O
has O
a O
smaller O
build B-PARA
direction E-PARA
deformation O
than O
other O
cases O
. O


Directed B-MANP
Energy I-MANP
Deposition E-MANP
( O
DED S-MANP
) O
was O
used O
to O
form O
a O
Stainless B-MATE
Steel E-MATE
AISI O
316 O
L O
steel S-MATE
block O
component S-MACEQ
on O
a O
Mild B-MATE
Steel E-MATE
S235JR O
substrate S-MATE
. O


Porosity S-PRO
, O
density S-PRO
, O
and O
defect S-CONPRI
were O
characterised O
at O
4 O
localities O
within O
the O
DED S-MANP
component S-MACEQ
by O
microscopy S-CHAR
and O
x-ray B-CHAR
tomography E-CHAR
. O


Three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
reconstruction S-CONPRI
of O
the O
x-ray S-CHAR
tomographic O
image S-CONPRI
sequences O
focused O
at O
select O
porosities S-PRO
is O
presented O
. O


The O
element S-MATE
composition S-CONPRI
and O
Vickers O
microhardness S-CONPRI
measurements O
were O
taken O
at O
the O
fusion S-CONPRI
lines O
and O
track O
body O
locations O
to O
characterise O
the O
differences O
in O
materials S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
at O
the O
2 O
locations O
. O


Lastly O
, O
an O
element S-MATE
mapping O
analysis O
was O
conducted O
to O
determine O
the O
solidification S-CONPRI
mode O
for O
the O
DED S-MANP
component S-MACEQ
. O


Sources O
for O
defects S-CONPRI
were O
proposed O
based O
on O
the O
characteristics O
of O
the O
porosity S-PRO
analysis O
and O
conclusions O
were O
made O
about O
the O
solidification S-CONPRI
behaviour O
of O
the O
DED S-MANP
component S-MACEQ
. O


Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
was O
applied O
in O
this O
study O
to O
produce O
a O
prototype S-CONPRI
of O
a O
miniaturized O
catalytic B-MACEQ
burner E-MACEQ
( O
CAB O
) O
, O
which O
is O
a O
key O
component S-MACEQ
of O
high-temperature O
polymer B-APPL
electrolyte I-APPL
fuel I-APPL
cells E-APPL
. O


This O
prototype S-CONPRI
was O
characterized O
by O
its O
complex O
design S-FEAT
with O
numerous O
channels O
, O
chambers O
, O
and O
thin O
walls O
. O


The O
test O
samples S-CONPRI
and O
CAB O
prototype S-CONPRI
were O
made O
of O
a O
heat-resistant O
, O
anti-corrodible O
steel S-MATE
called O
`` O
Alloy S-MATE
800H O
'' O
( O
1.4876 O
) O
, O
a O
material S-MATE
that O
poses O
problems O
for O
welding S-MANP
operations O
and O
especially O
for O
the O
LPBF S-MANP
process O
due O
to O
its O
strong O
susceptibility S-PRO
to O
hot B-CONPRI
cracking E-CONPRI
and O
spatters O
. O


The O
effects O
of O
LPBF S-MANP
parameter O
variation S-CONPRI
on O
preliminary O
test O
samples S-CONPRI
were O
investigated O
by O
nano-focus O
Computed B-CHAR
Tomography E-CHAR
( O
CT S-ENAT
) O
and O
Optical B-CHAR
microscopy E-CHAR
to O
clarify O
the O
internal B-PRO
structure E-PRO
and O
defects S-CONPRI
for O
further O
LPBF S-MANP
process O
optimization S-CONPRI
. O


Mössbauer O
spectroscopy S-CONPRI
points O
out O
that O
LPBF S-MANP
process O
does O
not O
lead S-MATE
to O
either O
local O
phase S-CONPRI
separation O
nor O
oxidation S-MANP
of O
steel S-MATE
, O
which O
is O
critical B-PRO
factor E-PRO
for O
use O
of O
CAB O
at O
high O
temperatures S-PARA
. O


The O
sufficient O
LPBF S-MANP
parameter O
sets O
were O
used O
to O
manufacture S-CONPRI
the O
CAB O
prototype S-CONPRI
, O
which O
was O
examined O
by O
micro-CT S-CHAR
and O
optics S-APPL
as S-MATE
well O
. O


The O
main O
result O
of O
the O
investigation O
is O
a O
demonstration O
of O
the O
technological O
feasibility S-CONPRI
to O
decrease O
the O
number O
and O
size O
of O
defects S-CONPRI
in O
complex O
LPBF-manufactured O
Alloy S-MATE
800H O
constructions O
without O
changes O
in O
phase B-CONPRI
composition E-CONPRI
at O
high O
temperatures S-PARA
. O


A O
multi-component O
and O
multi-phase-field O
modelling S-ENAT
approach O
, O
combined O
with O
transformation O
kinetics O
modelling S-ENAT
, O
was O
used O
to O
model B-CONPRI
microstructure E-CONPRI
evolution S-CONPRI
during O
laser S-ENAT
metal O
powder S-MATE
directed B-MANP
energy I-MANP
deposition E-MANP
of O
Alloy S-MATE
718 O
and O
subsequent O
heat B-MANP
treatments E-MANP
. O


Experimental S-CONPRI
temperature O
measurements O
were O
utilised O
to O
predict O
microstructural B-CONPRI
evolution E-CONPRI
during O
successive O
addition O
of O
layers O
. O


Segregation S-CONPRI
of O
alloying B-MATE
elements E-MATE
as O
well O
as S-MATE
formation O
of O
Laves S-CONPRI
and O
δ O
phase S-CONPRI
was O
specifically O
modelled O
. O


The O
predicted S-CONPRI
elemental O
concentrations O
were O
then O
used O
in O
transformation O
kinetics O
to O
estimate O
changes O
in O
Continuous O
Cooling S-MANP
Transformation O
( O
CCT O
) O
and O
Time O
Temperature S-PARA
Transformation O
( O
TTT O
) O
diagrams O
for O
Alloy S-MATE
718 O
. O


Modelling S-ENAT
results O
showed O
good O
agreement O
with O
experimentally O
observed O
phase B-CONPRI
evolution E-CONPRI
within O
the O
microstructure S-CONPRI
. O


The O
results O
indicate O
that O
the O
approach O
can O
be S-MATE
a O
valuable O
tool S-MACEQ
, O
both O
for O
improving O
process S-CONPRI
understanding O
and O
for O
process S-CONPRI
development O
including O
subsequent O
heat B-MANP
treatment E-MANP
. O


Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
is O
a O
widely O
used O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
technique O
. O


Recently O
, O
mechanical B-CONPRI
properties E-CONPRI
of O
plastic S-MATE
FFF S-MANP
parts O
have O
been O
enhanced O
by O
adding O
short B-MATE
carbon I-MATE
fibers E-MATE
to O
the O
thermoplastic B-MATE
polymer E-MATE
filament S-MATE
to O
form O
a O
carbon B-MATE
fiber E-MATE
filled O
( O
CFF O
) O
polymer B-MATE
composite E-MATE
. O


Unfortunately O
, O
improvements O
to O
the O
material B-CONPRI
properties E-CONPRI
of O
commercially O
available O
CFF O
filament S-MATE
are O
not O
well O
understood O
. O


This O
paper O
presents O
a O
study O
of O
CFF O
FFF S-MANP
parts O
produced O
on O
desktop B-MACEQ
3D I-MACEQ
printers E-MACEQ
using O
commercially O
available O
filament S-MATE
. O


Tensile B-CHAR
test E-CHAR
samples B-CONPRI
fabricated E-CONPRI
with O
CFF O
polymer B-MATE
composite E-MATE
and O
unfilled O
polymer S-MATE
were O
printed O
and O
then O
tested O
following O
ASTM O
D3039M O
. O


The O
filament S-MATE
considered O
here O
was O
purchased O
from O
filament S-MATE
suppliers O
and O
included O
both O
CFF O
and O
unfilled O
PLA S-MATE
, O
ABS S-MATE
, O
PETG O
and O
Amphora O
. O


Results O
for O
tensile B-PRO
strength E-PRO
and O
tensile S-PRO
modulus O
show O
that O
CFF O
coupons O
in O
general O
yield O
higher O
tensile S-PRO
modulus O
at O
all O
print S-MANP
orientations S-CONPRI
and O
higher O
tensile B-PRO
strength E-PRO
at O
0 O
° O
print S-MANP
orientation S-CONPRI
. O


The O
addition O
of O
carbon B-MATE
fiber E-MATE
was O
shown O
to O
decrease O
tensile B-PRO
strength E-PRO
for O
some O
materials S-CONPRI
when O
printed O
with O
beads S-CHAR
not O
aligned O
with O
the O
loading O
direction O
. O


Additionally O
, O
CFF O
samples S-CONPRI
are O
evaluated O
for O
fiber B-CONPRI
length E-CONPRI
distribution S-CONPRI
( O
FLD O
) O
and O
fiber S-MATE
weight O
fraction S-CONPRI
, O
where O
it O
was O
found O
that O
the O
filament S-MATE
extrusion B-MANP
process E-MANP
contributes O
very O
little O
to O
fiber S-MATE
breakage O
. O


Finally O
, O
fracture S-CONPRI
surfaces O
evaluated O
under O
SEM S-CHAR
show O
that O
voids S-CONPRI
between O
the O
beads S-CHAR
are O
reduced O
with O
CFF O
coupons O
, O
and O
poor O
interfacial B-CONPRI
bonding E-CONPRI
between O
fibers S-MATE
and O
polymer S-MATE
become O
a O
prominent O
failure B-PRO
mechanism E-PRO
. O


Three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
printing O
, O
or O
additive B-MANP
manufacturing E-MANP
, O
has O
been O
increasingly O
used O
in O
many O
fields O
, O
including O
the O
medicine S-CONPRI
, O
food O
, O
sensing S-APPL
, O
metal S-MATE
, O
automotive S-APPL
, O
and O
construction S-APPL
industries O
. O


Regardless O
of O
its O
growing O
applications O
, O
there O
are O
few O
of O
methods O
, O
guidelines O
, O
and O
specifications S-PARA
for O
measuring O
and O
quantifying O
the O
qualities O
of O
3D B-MANP
printed E-MANP
objects O
. O


In O
this O
study O
, O
for O
the O
first O
time O
, O
a O
non-contact O
, O
and O
non-destructive O
measurement S-CHAR
method O
, O
a O
3D S-CONPRI
structured O
light O
scanning S-CONPRI
system O
( O
3D-SLSS O
) O
, O
was O
employed O
for O
evaluating O
the O
printing O
qualities O
of O
clay S-MATE
objects O
with O
different O
levels O
of O
visual O
defects S-CONPRI
( O
e.g. O
, O
roughness S-PRO
and O
distortion S-CONPRI
) O
. O


3D S-CONPRI
scanned O
images S-CONPRI
of O
these O
clay S-MATE
samples O
were O
developed O
using O
3D-SLSS O
. O


Then O
, O
they O
were O
sliced O
along O
their O
sides O
( O
perpendicular O
to O
the O
base O
) O
to O
generate O
a O
number O
of O
two-dimensional S-CONPRI
( O
2D S-CONPRI
) O
plots O
, O
from O
which O
various O
parameters S-CONPRI
( O
e.g. O
, O
sample S-CONPRI
total O
height O
[ O
Htotal O
] O
, O
outer O
diameter S-CONPRI
[ O
DMouter O
] O
, O
layer B-PARA
thickness E-PARA
[ O
TL S-MATE
] O
, O
layer S-PARA
width O
, O
[ O
( O
WL O
] O
, O
surface B-PARA
angle E-PARA
[ O
Sα O
] O
, O
semi-cross-sectional O
area S-PARA
[ O
XA O
] O
, O
and O
surface B-PRO
roughness E-PRO
[ O
R O
] O
) O
were O
measured O
. O


Compared O
with O
the O
designed S-FEAT
object O
, O
the O
printed O
samples S-CONPRI
generally O
had O
reduced O
total O
height O
, O
diameter S-CONPRI
, O
and O
layer B-PARA
thickness E-PARA
; O
increased O
layer S-PARA
width O
; O
measurable O
distortion S-CONPRI
; O
and O
visible O
surface B-PRO
roughness E-PRO
. O


Many O
of O
these O
were O
largely O
because O
the O
freshly O
printed O
clay S-MATE
deformed O
under O
the O
weight S-PARA
of O
the O
layers O
above O
. O


The O
distortion S-CONPRI
angle O
and O
area S-PARA
are O
two O
necessary O
parameters S-CONPRI
for O
quantifying O
the O
degree O
of O
distortion S-CONPRI
of O
a O
printed O
sample S-CONPRI
. O


The O
diagnosed O
area S-PARA
of O
deficiency O
can O
well O
describe O
the O
overall O
qualities O
of O
the O
printed O
samples S-CONPRI
. O


Moreover O
, O
it O
can O
be S-MATE
conveniently O
extended O
to O
various O
industries S-APPL
for O
quality B-CONPRI
control E-CONPRI
of O
diverse O
3D B-MANP
printing E-MANP
products O
. O


TiB O
reinforced S-CONPRI
near O
α O
Ti-matrix O
composite S-MATE
was O
fabricated S-CONPRI
in O
this O
work O
using O
selective B-MANP
laser I-MANP
melting E-MANP
from O
a O
mixture O
of O
CrB2 O
and O
commercially O
pure O
Ti B-MATE
powders E-MATE
. O


The O
corresponding O
composites S-MATE
present O
an O
almost O
fully B-PARA
dense E-PARA
structure O
for O
suitable O
laser B-PARA
energy I-PARA
density E-PARA
conditions O
. O


The O
X-ray B-CHAR
diffraction E-CHAR
and O
microstructure S-CONPRI
analysis O
indicate O
that O
the O
TiB O
and O
β-Ti O
phase S-CONPRI
appears O
for O
parts O
obtained O
with O
a O
low O
scanning B-PARA
speed E-PARA
of O
the O
laser B-CONPRI
beam E-CONPRI
. O


The O
parts O
obtained O
at O
high O
and O
low O
scanning B-PARA
speeds E-PARA
show O
higher O
hardness S-PRO
and O
lower O
wear S-CONPRI
rate O
than O
those O
obtained O
for O
intermediate O
scanning B-PARA
speed E-PARA
which O
, O
on O
the O
contrary O
, O
show O
the O
highest O
density S-PRO
. O


The O
wear S-CONPRI
behavior O
of O
the O
as-processed O
parts O
is O
compared O
with O
that O
of O
pure O
Ti S-MATE
parts O
also O
obtained O
by O
selective B-MANP
laser I-MANP
melting E-MANP
. O


Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
is O
a O
popular O
additive B-MANP
manufacturing E-MANP
technique O
where O
molten O
polymer B-MATE
filament E-MATE
is O
applied O
in O
a O
raster B-PARA
pattern E-PARA
, O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
, O
to O
obtain O
the O
work B-MACEQ
piece E-MACEQ
. O


A O
necessary O
consequence O
of O
this O
method O
is O
a O
pronounced O
mechanical B-PRO
anisotropy E-PRO
of O
the O
product O
; O
the O
interface S-CONPRI
between O
the O
filaments S-MATE
is O
weaker O
compared O
to O
the O
filament S-MATE
itself O
. O


The O
strength S-PRO
of O
this O
interface S-CONPRI
is O
governed O
by O
the O
reptation O
theory O
which O
postulates O
a O
more O
efficient O
interpenetration O
of O
polymeric O
surfaces S-CONPRI
with O
decreasing O
polymer S-MATE
viscosity O
. O


This O
relationship O
was O
utilized O
in O
this O
work O
to O
modify O
a O
polycarbonate-acrylonitrile O
butadiene O
styrene O
polymer B-MATE
blend E-MATE
to O
produce O
FFF S-MANP
work O
pieces O
with O
less O
mechanical B-PRO
anisotropy E-PRO
, O
independent O
of O
printer S-MACEQ
settings O
. O


The O
tensile B-PRO
strength E-PRO
ratio O
of O
the O
printed O
interface S-CONPRI
to O
bulk O
tensile B-PRO
strength E-PRO
could O
be S-MATE
increased O
from O
41 O
% O
to O
95 O
% O
. O


Though O
the O
absolute O
bulk O
tensile B-PRO
strength E-PRO
decreases O
slightly O
, O
this O
method O
presents O
an O
easy O
and O
effective O
way O
to O
address O
the O
mechanical S-APPL
problems O
inherent O
in O
the O
FFF-method O
. O


The O
systematic O
occurrence O
of O
porosities S-PRO
inside O
selective B-MANP
laser I-MANP
melted E-MANP
( O
SLM S-MANP
) O
parts O
is O
a O
well-known O
phenomenon O
. O


In O
order O
to O
improve O
the O
density S-PRO
of O
SLM S-MANP
parts O
, O
it O
is O
important O
not O
only O
to O
assess O
the O
physical O
origin O
of O
the O
different O
types O
of O
porosities S-PRO
, O
but O
also O
to O
be S-MATE
able O
to O
measure O
as S-MATE
precisely O
as S-MATE
possible O
the O
porosity S-PRO
rate O
so O
that O
one O
may O
select O
the O
optimum O
manufacturing S-MANP
parameters.Considering O
316 O
L O
steel S-MATE
parts O
built O
with O
different O
input O
energies O
, O
the O
current O
paper O
aims O
to O
( O
1 O
) O
present O
the O
different O
types O
of O
porosities S-PRO
generated O
by O
SLM S-MANP
and O
their O
origins O
, O
( O
2 O
) O
compare O
different O
methods O
for O
measuring O
parts O
density S-PRO
and O
( O
3 O
) O
propose O
optimal O
procedures O
. O


After O
a O
preliminary O
optimization S-CONPRI
step O
, O
three O
methods O
were O
used O
for O
quantifying O
porosity S-PRO
rate O
: O
the O
Archimedes B-CHAR
method E-CHAR
, O
the O
helium S-MATE
pycnometry O
and O
micrographic O
observations.The O
Archimedes B-CHAR
method E-CHAR
shows O
that O
results O
depend O
on O
the O
nature O
and O
temperature S-PARA
of O
the O
fluid S-MATE
, O
but O
also O
on O
the O
sample S-CONPRI
volume O
and O
its O
surface S-CONPRI
roughness.During O
the O
micrographic O
observations O
, O
it O
has O
been O
shown O
that O
the O
results O
depend O
on O
the O
magnification S-CONPRI
used O
and O
the O
number O
of O
micrographs O
considered.A O
comparison O
of O
the O
three O
methods O
showed O
that O
the O
optimized O
Archimedes B-CHAR
method E-CHAR
and O
the O
helium S-MATE
pycnometry O
technique O
gave O
similar O
results O
, O
whereas O
optimized O
micrographic O
observations O
systematically O
underestimated O
the O
porosity S-PRO
rate.In O
a O
second O
step S-CONPRI
, O
samples S-CONPRI
were O
analyzed O
to O
illustrate O
the O
physical O
phenomena O
involved O
in O
the O
generation O
of O
porosities S-PRO
. O


It O
was O
confirmed O
that O
: O
( O
1 O
) O
low O
Volume S-CONPRI
Energy B-PARA
Density E-PARA
( O
VED O
) O
causes O
non-spherical S-CONPRI
porosities O
due O
to O
insufficient B-MATE
fusion E-MATE
, O
( O
2 O
) O
in O
intermediary O
VED O
the O
small O
amount O
of O
remaining O
blowhole S-CONPRI
porosities O
come O
from O
gas S-CONPRI
occlusion O
in O
the O
melt-pool O
and O
( O
3 O
) O
in O
excessive O
VED O
, O
cavities O
are O
formed O
due O
to O
the O
key-hole O
welding S-MANP
mode O
. O


The O
eutectic S-CONPRI
Al-33Cu O
( O
wt. O
% O
) O
alloy S-MATE
was O
processed S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
. O


Based O
on O
the O
interlamellar O
distances O
a O
local O
cooling B-PARA
rate E-PARA
can O
be S-MATE
calculated O
. O


At O
high O
laser B-PARA
powers E-PARA
the O
cooling B-PARA
rate E-PARA
is O
104 O
K/s O
, O
at O
low O
laser B-PARA
powers E-PARA
it O
is O
105 O
K/s O
. O


The O
thermal O
history O
of O
selectively O
laser-melted O
alloys S-MATE
can O
be S-MATE
explored O
. O


The O
cooling B-PARA
rates E-PARA
inherent O
to O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
were O
experimentally O
determined O
by O
processing O
the O
eutectic S-CONPRI
Al-33Cu O
( O
wt. O
% O
) O
alloy S-MATE
. O


Two O
different O
parameter S-CONPRI
sets O
yielding O
an O
identical O
volumetric O
energy B-PARA
density E-PARA
were O
employed O
to O
produce O
the O
samples S-CONPRI
. O


Based O
on O
the O
average S-CONPRI
spacing O
of O
the O
Al S-MATE
and O
CuAl2 O
lamellae S-MATE
, O
the O
cooling B-PARA
rates E-PARA
in O
different O
parts O
of O
the O
SLM S-MANP
specimens O
were O
estimated O
. O


At O
a O
high O
laser B-PARA
power E-PARA
( O
300 O
W O
) O
the O
cooling B-PARA
rate E-PARA
amounts O
to O
104 O
K/s O
and O
at O
the O
lower O
laser B-PARA
power E-PARA
( O
200 O
W O
) O
to O
105 O
K/s O
. O


The O
present O
approach O
proves O
to O
be S-MATE
useful O
for O
exploring O
the O
thermal O
history O
of O
additively B-MANP
manufactured E-MANP
metallic O
components S-MACEQ
. O


A O
3D S-CONPRI
finite O
element S-MATE
simulation O
model S-CONPRI
of O
the O
laser B-MANP
cladding E-MANP
process O
has O
been O
developed O
taking O
into O
account O
heat B-CONPRI
transfer E-CONPRI
, O
fluid B-PRO
flow E-PRO
, O
surface B-PRO
tension E-PRO
and O
free B-CONPRI
surface E-CONPRI
movement O
. O


All O
input O
parameters S-CONPRI
and O
data S-CONPRI
, O
which O
are O
independent O
of O
the O
process B-CONPRI
parameters E-CONPRI
but O
depend O
only O
on O
the O
material S-MATE
and O
machine S-MACEQ
properties O
, O
have O
been O
obtained O
from O
measurements O
. O


Thereby O
the O
melt B-MATE
pool E-MATE
and O
the O
resulting O
surface S-CONPRI
contour S-FEAT
can O
be S-MATE
simulated O
without O
compromising O
assumptions O
or O
calibration S-CONPRI
, O
because O
the O
machine B-PARA
parameters E-PARA
are O
the O
only O
variable O
input O
parameters S-CONPRI
of O
the O
model S-CONPRI
. O


Thus O
, O
the O
model S-CONPRI
can O
easily O
be S-MATE
transferred O
to O
other O
material S-MATE
combinations O
or O
other O
machines S-MACEQ
. O


For O
the O
surface S-CONPRI
contour S-FEAT
calculation O
a O
modified O
height O
function O
method O
is O
applied O
. O


The O
model S-CONPRI
surface O
follows O
this O
contour S-FEAT
as S-MATE
an O
arbitrary O
Lagrangian O
Eulerian O
( O
ALE O
) O
method O
is O
used O
allowing O
for O
mesh O
deformations S-CONPRI
. O


The O
model S-CONPRI
was O
implemented O
using O
the O
commercial O
finite B-CONPRI
element E-CONPRI
software O
COMSOL O
Multiphysics O
and O
validated O
by O
comparing O
the O
simulation S-ENAT
results O
with O
caloric O
measurements O
of O
the O
effective O
heat S-CONPRI
input O
and O
metallographic O
cross B-CONPRI
sections E-CONPRI
from O
experiments O
, O
where O
the O
nickel-base O
alloy S-MATE
MetcoClad® O
625 O
in O
powder S-MATE
form O
was O
deposited O
on O
structural O
steel S-MATE
S235JRC O
+ O
C S-MATE
and O
the O
process B-CONPRI
parameters E-CONPRI
of O
laser B-PARA
power E-PARA
, O
feed S-PARA
speed O
, O
laser B-CONPRI
beam E-CONPRI
spot O
size O
and O
powder S-MATE
mass O
flow O
were O
varied O
within O
a O
range S-PARA
of O
at O
least O
50 O
% O
of O
their O
mean O
value O
each O
. O


The O
maximum O
deviation O
of O
the O
simulation S-ENAT
results O
compared O
to O
the O
experimental B-CONPRI
data E-CONPRI
regarding O
track O
geometry S-CONPRI
is O
14 O
% O
for O
the O
parameter S-CONPRI
sets O
without O
weld S-FEAT
defects S-CONPRI
so O
that O
these O
parameter S-CONPRI
sets O
could O
be S-MATE
industrially O
applied O
, O
whereas O
the O
average S-CONPRI
deviation O
of O
track O
width O
and O
height O
is O
below O
5.1 O
% O
. O


A O
thermal B-CHAR
analysis E-CHAR
model S-CONPRI
of O
synchronous O
induction O
assisted O
laser S-ENAT
deposition S-CONPRI
is O
established O
. O


The O
effect O
of O
the O
laser-induction O
interaction O
mode O
on O
the O
thermal O
behavior O
Microstructural B-CONPRI
evolution E-CONPRI
mechanisms O
of O
synchronous O
induction O
assisted O
laser S-ENAT
deposition S-CONPRI
are O
revealed O
. O


The O
grains S-CONPRI
and O
phase S-CONPRI
can O
potentially O
be S-MATE
controlled O
separately O
by O
synchronous O
induction O
assisted O
laser S-ENAT
deposition B-MANP
process E-MANP
. O


Synchronous O
induction-assisted O
laser S-ENAT
deposition S-CONPRI
( O
SILD O
) O
can O
be S-MATE
used O
to O
address O
issues O
that O
arise O
from O
the O
extreme O
thermal O
behavior O
that O
occurs O
during O
direct B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
. O


However O
, O
the O
incorporation O
of O
induction B-MANP
heating E-MANP
simultaneously O
renders O
the O
thermal O
behavior O
during O
SILD O
more O
flexible O
and O
complicated O
. O


This O
study O
established O
a O
3-D S-CONPRI
transient O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
to O
elucidate O
the O
thermal O
behavior O
during O
SILD O
with O
a O
simplified O
inductive O
heat B-CONPRI
source E-CONPRI
. O


It O
should O
also O
be S-MATE
noted O
that O
although O
it O
was O
more O
difficult O
to O
balance O
the O
thermal O
behavior O
, O
the O
cooling B-PARA
rate E-PARA
at O
the O
β O
transus O
temperature S-PARA
of O
Ti-6Al-4 B-MATE
V E-MATE
decreased O
from O
82 O
℃/s O
to O
23 O
℃/s O
; O
further O
, O
the O
maximum O
temperature B-PARA
gradient E-PARA
in O
front O
of O
the O
solid-liquid O
interface S-CONPRI
decreased O
from O
5.8 O
× O
105 O
℃/m O
to O
4.4 O
× O
105 O
℃/m O
in O
the O
“ O
alternate O
” O
mode O
, O
which O
was O
relative O
to O
the O
“ O
without O
induction B-MANP
heating E-MANP
” O
and O
“ O
synchronous O
” O
modes O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
increasingly O
used O
for O
the O
production S-MANP
of O
functional O
parts O
. O


In O
order O
to O
ensure O
product B-CONPRI
reliability E-CONPRI
in O
challenging O
load O
cases O
and O
environments O
, O
a O
valid O
knowledge O
of O
the O
residual B-PRO
stress E-PRO
state O
is O
crucial O
. O


Since O
typical O
, O
complex O
AM S-MANP
geometries O
necessitate O
simulative O
efforts O
for O
this O
prediction S-CONPRI
, O
suitable O
validation B-CONPRI
data E-CONPRI
are O
essential O
. O


This O
study O
presents O
results O
from O
neutron B-CHAR
diffraction E-CHAR
measurements O
on O
different O
stages O
of O
a O
build-up O
of O
a O
simple S-MANP
cuboid O
structure S-CONPRI
by O
laser B-CONPRI
beam E-CONPRI
melting O
. O


The O
strain-free O
reference O
is O
obtained O
from O
measurements O
on O
small O
matchstick O
geometries S-CONPRI
cut O
from O
an O
analogously O
manufactured S-CONPRI
cuboid O
at O
the O
respective O
measurement S-CHAR
spots O
. O


By O
providing O
quasi-transient O
data S-CONPRI
of O
the O
evolution S-CONPRI
of O
residual B-PRO
stresses E-PRO
in O
both O
the O
base O
plate O
and O
the O
part O
, O
simulation S-ENAT
models O
can O
be S-MATE
investigated O
towards O
their O
structural O
validity O
. O


Results O
indicate O
that O
the O
assumption O
of O
negligible O
shear B-PRO
strains E-PRO
may O
not O
be S-MATE
justifiable O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
are O
being O
more O
frequently O
applied O
in O
several O
fields O
ranging O
from O
the O
industrial S-APPL
to O
the O
biomedical S-APPL
, O
in O
large O
part O
owing O
to O
their O
advantages O
which O
make O
them O
suitable O
for O
several O
applications O
such O
as S-MATE
scaffolds O
for O
tissue B-CONPRI
engineering E-CONPRI
, O
dental S-APPL
procedures O
, O
and O
3D B-APPL
models E-APPL
to O
improve O
surgical O
planning S-MANP
. O


Moreover O
, O
these O
processes S-CONPRI
are O
particularly O
suited O
for O
the O
fabrication S-MANP
of O
microfluidic O
devices O
and O
labs-on-a-chip O
( O
LOC O
) O
designed S-FEAT
to O
work O
with O
biological O
samples S-CONPRI
and O
chemical B-CONPRI
reaction E-CONPRI
mixtures.An O
aspect O
not O
sufficiently O
investigated O
is O
related O
to O
the O
dimensional O
verification S-CONPRI
of O
these O
devices O
. O


The O
main O
criticality O
is O
the O
texture-less O
surface S-CONPRI
that O
characterizes O
the O
AM S-MANP
products O
and O
strongly O
affects O
the O
effectiveness S-CONPRI
of O
most O
currently O
available O
3D S-CONPRI
optical O
measuring O
instruments.In O
this O
study O
, O
a O
passive O
photogrammetric O
scanning S-CONPRI
system O
has O
been O
used O
as S-MATE
a O
non-destructive O
and O
low-cost O
technique O
for O
the O
reconstruction S-CONPRI
and O
measurement S-CHAR
of O
3D B-MANP
printed E-MANP
microfluidic O
devices O
. O


Four O
devices O
, O
manufactured S-CONPRI
with O
stereolithography S-MANP
( O
SLA S-MACEQ
) O
, O
fused B-CONPRI
deposition E-CONPRI
modelling O
( O
FDM S-MANP
) O
a O
Stratasys S-APPL
trademark O
, O
also O
known O
as S-MATE
fused O
filament S-MATE
fabrication S-MANP
( O
FFF S-MANP
) O
, O
and O
Polyjet S-CONPRI
have O
been O
reconstructed O
and O
measured O
, O
and O
the O
results O
have O
been O
compared O
to O
those O
obtained O
with O
optical S-CHAR
profilometry O
that O
is O
considered O
as S-MATE
the O
gold S-MATE
standard O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
is O
a O
promising O
additive B-MANP
manufacturing E-MANP
technology O
for O
the O
production S-MANP
of O
complex O
metal S-MATE
components S-MACEQ
. O


The O
technique O
uses O
metallic B-MATE
powder E-MATE
as S-MATE
a O
starting O
material S-MATE
and O
a O
laser S-ENAT
for O
melting S-MANP
and O
building-up O
parts O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
. O


One O
crucial O
factor O
influencing O
the O
process S-CONPRI
stability O
and O
therefore O
the O
part O
quality S-CONPRI
is O
the O
shielding O
gas S-CONPRI
flow O
. O


In O
addition O
to O
the O
shielding O
properties S-CONPRI
of O
the O
inert O
atmosphere O
the O
gas S-CONPRI
flow O
is O
responsible O
for O
the O
removal O
of O
process S-CONPRI
by-products O
like O
spatter S-CHAR
and O
welding S-MANP
fumes O
originating O
from O
the O
process S-CONPRI
zone O
. O


Insufficient O
removal O
or O
inhomogeneous O
gas S-CONPRI
flow O
distribution S-CONPRI
may O
lead S-MATE
to O
increased O
interaction O
between O
laser S-ENAT
and O
process S-CONPRI
by-products O
. O


Consequences O
are O
attenuation O
of O
the O
laser S-ENAT
spot O
as S-MATE
well O
as S-MATE
redeposition O
of O
this O
by-products O
on O
surfaces S-CONPRI
which O
are O
exposed O
to O
the O
laser S-ENAT
afterwards O
. O


Furthermore O
process S-CONPRI
deviations O
are O
provoked O
by O
unfavorable O
gas S-CONPRI
flow O
conditions O
. O


Thirdly O
, O
the O
impact S-CONPRI
of O
this O
deviations O
on O
building O
surface S-CONPRI
and O
part O
quality S-CONPRI
is O
investigated O
by O
3D S-CONPRI
confocal O
microscopy S-CHAR
, O
microsections O
and O
ultrasonic O
testing S-CHAR
. O


Finally O
, O
theoretical S-CONPRI
approach O
for O
the O
formation O
of O
these O
process S-CONPRI
deviations O
and O
arising O
material S-MATE
defects S-CONPRI
is O
presented O
. O


The O
high-energy O
input O
and O
thermal O
history O
during O
additive B-MANP
manufacturing E-MANP
lead O
to O
complex O
phase S-CONPRI
transformations O
in O
titanium B-MATE
aluminide I-MATE
alloy E-MATE
. O


This O
study O
mostly O
focuses O
on O
determining O
the O
solid-state B-CONPRI
phase E-CONPRI
transformation O
mechanisms O
during O
laser S-ENAT
deposition S-CONPRI
and O
the O
failure B-PRO
mechanisms E-PRO
of O
alloys S-MATE
using O
molecular O
dynamics O
simulations S-ENAT
. O


Because O
of O
the O
directional O
temperature B-PARA
gradient E-PARA
, O
columnar B-PRO
grains E-PRO
with O
fully O
lamellar S-CONPRI
microstructures O
are O
formed O
first O
after O
solidification S-CONPRI
. O


A O
narrow O
region O
just O
below O
the O
melting S-MANP
pool O
is O
reheated O
to O
high O
temperatures S-PARA
, O
thus O
enhancing O
the O
precipitation S-CONPRI
of O
new O
equiaxed B-CONPRI
grains E-CONPRI
. O


Multiple O
thermal B-PARA
cycles E-PARA
in O
the O
α O
+ O
γ O
phase S-CONPRI
region O
promote O
the O
formation O
of O
massive O
γ O
phases O
( O
γm O
) O
at O
the O
grain B-CONPRI
boundaries E-CONPRI
. O


Finally O
, O
a O
nearly O
lamellar S-CONPRI
microstructure O
of O
alternating O
columnar O
and O
equiaxed B-CONPRI
grains E-CONPRI
with O
γm O
phases O
is O
formed O
. O


The O
deposited O
titanium B-MATE
aluminide I-MATE
alloy E-MATE
has O
good O
room O
and O
high-temperature O
( O
760 O
°C O
) O
tensile B-PRO
properties E-PRO
of O
545 O
± O
9 O
and O
471 O
± O
37 O
MPa S-CONPRI
, O
with O
elongations O
of O
1.50 O
% O
± O
0.47 O
% O
and O
1.50 O
% O
± O
0.45 O
% O
, O
respectively O
. O


The O
room O
and O
high-temperature O
samples S-CONPRI
both O
fail O
in O
the O
columnar B-PRO
grain E-PRO
region O
. O


Although O
the O
equiaxed B-CONPRI
grain E-CONPRI
regions O
contain O
several O
γm–α2 O
interfaces O
, O
the O
samples S-CONPRI
still O
fail O
in O
the O
columnar B-PRO
grain E-PRO
regions O
due O
to O
the O
increase O
in O
the O
cracking S-CONPRI
distance O
in O
the O
equiaxed O
regions O
caused O
by O
randomly O
oriented O
α2 O
+ O
γ O
lamellae S-MATE
and O
the O
comparably O
good O
plasticity S-PRO
of O
the O
γm O
phases O
. O


Multiple O
thermal B-PARA
cycles E-PARA
in O
the O
α O
+ O
γ O
phase S-CONPRI
region O
promote O
the O
formation O
of O
a O
massive O
γ O
phase S-CONPRI
( O
γm O
) O
at O
the O
grain B-CONPRI
boundaries E-CONPRI
. O


Finally O
, O
a O
nearly O
lamellar S-CONPRI
microstructure O
of O
alternating O
arrangement O
of O
columnar O
and O
equiaxed B-CONPRI
grains E-CONPRI
with O
γm O
phases O
is O
formed O
. O


Based O
on O
the O
relations O
among O
the O
orientations S-CONPRI
of O
the O
γm O
, O
γ O
, O
and O
α2 O
phases O
, O
five O
interface S-CONPRI
structure O
models O
can O
be S-MATE
established O
for O
the O
molecular O
dynamics O
simulations S-ENAT
of O
TiAl O
alloy S-MATE
fabricated O
by O
directed B-MANP
energy I-MANP
deposition E-MANP
, O
which O
can O
be S-MATE
used O
to O
accurately S-CHAR
predict O
the O
location O
of O
the O
crack O
nucleation S-CONPRI
sites O
during O
the O
tensile B-CHAR
test E-CHAR
. O


Furthermore O
, O
we O
revealed O
, O
for O
the O
first O
time O
, O
that O
the O
interface S-CONPRI
between O
α2 O
and O
γm O
is O
the O
weakest O
, O
especially O
in O
the O
case O
of O
semicoherent O
interfaces O
( O
6° O
angle O
in O
the O
[ O
1–10 O
] O
direction O
) O
, O
which O
provides O
good O
nucleation S-CONPRI
sites O
for O
cracks.Download O
: O
Download O
high-res B-CONPRI
image E-CONPRI
( O
322 O
Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM S-MANP
) O
is O
an O
increasingly O
used O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
technique O
employed O
by O
many O
industrial B-CONPRI
sectors E-CONPRI
, O
including O
the O
medical B-APPL
device E-APPL
and O
aerospace B-APPL
industries E-APPL
. O


In-situ S-CONPRI
EBM S-MANP
monitoring O
for O
quality S-CONPRI
assurance O
purposes O
has O
been O
a O
popular O
research S-CONPRI
area S-PARA
. O


Electronic O
imaging S-APPL
has O
recently O
been O
investigated O
as S-MATE
one O
of O
the O
in-situ S-CONPRI
EBM S-MANP
data S-CONPRI
collection O
methods O
, O
alongside O
thermal O
/ O
optical S-CHAR
imaging S-APPL
techniques O
. O


So O
far O
, O
the O
disseminations O
focus O
on O
the O
design S-FEAT
of O
an O
electronic O
imaging S-APPL
system O
and O
the O
ability O
to O
generate O
electronic O
images S-CONPRI
in-situ O
, O
experiments O
are O
yet O
to O
be S-MATE
carried O
out O
to O
benchmark S-MANS
one O
of O
the O
most O
important O
features O
of O
any O
imaging S-APPL
systems O
– O
spatial O
resolution S-PARA
. O


Analyses O
of O
experimental S-CONPRI
results O
indicated O
that O
the O
spatial O
resolution S-PARA
was O
of O
the O
order O
of O
0.3 O
to O
0.4 O
mm S-MANP
when O
electronic O
imaging S-APPL
was O
carried O
out O
at O
room O
temperature S-PARA
. O


It O
is O
believed O
that O
by O
disseminating O
an O
analysis O
and O
experimental S-CONPRI
method O
to O
estimate O
and O
quantify O
spatial O
resolution S-PARA
, O
this O
study O
has O
contributed O
to O
the O
on-going O
quality S-CONPRI
assessment O
research S-CONPRI
in O
the O
field O
of O
in-situ S-CONPRI
monitoring O
of O
the O
EBM S-MANP
process O
. O


The O
thermal O
history O
developed O
in O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
processes S-CONPRI
has O
been O
shown O
to O
be S-MATE
complex O
resulting O
in O
equally O
complex O
microstructures S-MATE
and O
mechanical B-CONPRI
properties E-CONPRI
. O


Three-dimensional S-CONPRI
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
was O
used O
to O
simulate O
thermal O
history O
and O
to O
predict O
the O
residual B-PRO
stress E-PRO
distribution S-CONPRI
in O
the O
as-built O
material S-MATE
. O


Computational O
thermodynamics O
was O
used O
to O
predict O
the O
micro-segregation S-CONPRI
and O
nucleation S-CONPRI
driving O
force S-CONPRI
of O
various O
phases O
in O
the O
bulk O
and O
in O
segregated O
regions O
. O


Varied O
heat-treatments O
such O
as S-MATE
simulated O
hot B-MANP
isostatic I-MANP
pressing E-MANP
, O
and O
double O
aging O
were O
applied O
. O


Their O
influence O
on O
the O
microstructure S-CONPRI
, O
micro-segregation S-CONPRI
, O
precipitate S-MATE
formation O
, O
and O
micro-hardness O
variations S-CONPRI
of O
LPBF S-MANP
alloy S-MATE
718 O
were O
investigated O
. O


Hardness S-PRO
map O
results O
showed O
heterogeneous S-CONPRI
micro-hardness O
on O
the O
xy- O
and O
xz-planes O
of O
the O
as-built O
parts O
where O
the O
bottom O
plane O
and O
center O
regions O
had O
larger O
hardness S-PRO
of O
∼315 O
HV0.5 O
while O
the O
top O
plane O
and O
contours S-FEAT
showed O
hardness S-PRO
of O
∼300 O
HV0.5 O
. O


After O
simulated O
hot B-MANP
isostatic I-MANP
pressing E-MANP
process O
( O
i.e. O
, O
without O
applied O
pressure S-CONPRI
) O
at O
1020 O
°C O
for O
4 O
h O
followed O
by O
water O
quench O
( O
HIPWQ O
) O
, O
the O
hardness S-PRO
gradient O
and O
hardness S-PRO
was O
minimized O
( O
∼210 O
HV0.5 O
) O
as S-MATE
the O
microstructure S-CONPRI
transitioned O
from O
heterogeneous S-CONPRI
columnar B-PRO
grains E-PRO
in O
the O
as-built O
condition O
to O
more O
uniform O
recrystallized S-MANP
grains S-CONPRI
. O


HIPWQ O
followed O
by O
double O
aging O
produced O
a O
homogeneous S-CONPRI
microstructure O
and O
more O
uniform O
hardness S-PRO
map O
with O
enhanced O
mechanical B-CONPRI
properties E-CONPRI
in O
LPBF S-MANP
alloy S-MATE
718 O
coupons O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
a O
promising O
manufacturing S-MANP
technique O
for O
the O
production S-MANP
of O
complex O
metallic S-MATE
components S-MACEQ
. O


One O
of O
the O
crucial O
factors O
influencing O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
final O
product O
is O
spatter S-CHAR
particles S-CONPRI
formation O
during O
the O
process S-CONPRI
. O


In O
this O
study O
, O
high- O
speed O
photography O
is O
utilized O
to O
record O
the O
formation O
mechanisms O
and O
the O
dynamic S-CONPRI
behavior O
of O
spatter S-CHAR
particles S-CONPRI
. O


An O
image S-CONPRI
processing O
analysis O
framework S-CONPRI
is O
utilized O
to O
assess O
the O
distribution S-CONPRI
of O
spatter S-CHAR
particles S-CONPRI
under O
various O
energy O
inputs O
. O


It O
is O
found O
that O
changing O
the O
laser B-ENAT
scan E-ENAT
velocity O
has O
more O
influences O
on O
spatter S-CHAR
formation O
in O
comparison O
with O
the O
energy O
input O
. O


The O
relationship O
between O
the O
numbers O
of O
created O
spatter S-CHAR
particles S-CONPRI
, O
induced O
unmelted O
regions O
and O
density S-PRO
variability O
are O
interpreted O
and O
discussed O
based O
on O
other O
observations O
, O
such O
as S-MATE
microscopic O
examination O
and O
density S-PRO
analysis O
of O
SLM S-MANP
parts O
. O


The O
obtained O
results O
could O
be S-MATE
used O
to O
enhance O
the O
current O
manufacturing B-MANP
process E-MANP
parameters O
optimization S-CONPRI
methods O
in O
SLM S-MANP
process S-CONPRI
. O


Principle O
of O
real-time O
feedback S-PARA
control O
is O
proven O
for O
ceramic S-MATE
vat O
photopolymerization S-MANP
. O


FTIR S-CHAR
spectrometry O
equipment S-MACEQ
and O
UV S-CONPRI
LED S-APPL
are O
integrated O
into O
an O
embedded O
control B-MACEQ
system E-MACEQ
. O


Control-oriented O
process B-CONPRI
model E-CONPRI
shows O
good O
agreement O
to O
experimental B-CONPRI
data E-CONPRI
. O


Feedback S-PARA
controller S-MACEQ
successfully O
compensates O
for O
a O
material S-MATE
composition S-CONPRI
disturbance O
. O


Technical O
ceramics S-MATE
for O
high-performance O
applications O
can O
be S-MATE
additively B-MANP
manufactured E-MANP
using O
vat B-MANP
photopolymerization E-MANP
technology S-CONPRI
. O


This O
technology S-CONPRI
faces O
two O
main O
challenges O
: O
increasing O
ceramic S-MATE
product O
size O
and O
improving O
product B-CONPRI
quality E-CONPRI
. O


The O
integration O
of O
process B-CONPRI
control E-CONPRI
strategies O
into O
AM S-MANP
equipment O
is O
expected O
to O
play O
a O
key O
role O
in O
tackling O
these O
challenges O
. O


This O
work O
demonstrates O
the O
feasibility S-CONPRI
of O
real-time O
and O
in-situ S-CONPRI
feedback S-PARA
control O
of O
the O
light-initiated O
polymerization S-MANP
reaction O
that O
lies O
at O
the O
core S-MACEQ
of O
vat B-MANP
photopolymerization E-MANP
technology S-CONPRI
. O


Experimental B-CONPRI
data E-CONPRI
obtained O
from O
this O
setup O
was O
used O
to O
develop O
a O
control-oriented O
process B-CONPRI
model E-CONPRI
and O
identify O
its O
parameters S-CONPRI
. O


The O
results O
show O
that O
the O
feedback S-PARA
controller S-MACEQ
successfully O
compensated O
for O
the O
material S-MATE
perturbation O
and O
reached O
the O
same O
final O
conversion O
value O
as S-MATE
the O
unperturbed O
case O
. O


This O
result O
can O
be S-MATE
considered O
a O
fundamental O
step S-CONPRI
towards O
additive B-MANP
manufacturing E-MANP
of O
defect-free O
ceramic S-MATE
parts O
using O
in-line O
process B-CONPRI
control E-CONPRI
. O


Optimization S-CONPRI
of O
single O
track O
and O
single O
layer S-PARA
is O
required O
for O
high O
final O
quality S-CONPRI
. O


Feedbacks O
between O
single O
track O
, O
single O
layer S-PARA
, O
and O
the O
3D S-CONPRI
levels O
were O
established O
. O


A O
multistep O
algorithm S-CONPRI
to O
find O
optimal O
SLM S-MANP
process B-CONPRI
parameters E-CONPRI
is O
described O
. O


The O
algorithm S-CONPRI
is O
illustrated O
for O
AISI B-MATE
420 E-MATE
stainless O
steel S-MATE
as S-MATE
an O
example O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
becoming O
a O
powerful O
additive B-MANP
manufacturing E-MANP
technology O
for O
different O
industries S-APPL
: O
automotive S-APPL
, O
medical S-APPL
, O
chemical O
, O
aerospace S-APPL
, O
etc O
. O


SLM S-MANP
could O
dramatically O
narrow O
the O
time O
frames O
to O
optimize O
production S-MANP
, O
providing O
extraordinary O
freedom O
to O
validate O
design S-FEAT
and O
to O
develop O
new O
materials S-CONPRI
. O


The O
extension O
of O
applications O
requires O
different O
materials S-CONPRI
with O
specific B-PRO
properties E-PRO
and O
therefore O
tailored O
properties S-CONPRI
of O
the O
final O
product O
. O


In O
this O
article O
, O
a O
hierarchical O
approach O
including O
mutual O
analysis O
of O
SLM S-MANP
parameters S-CONPRI
necessary O
to O
control O
the O
final O
product B-CONPRI
quality E-CONPRI
on O
every O
level O
– O
the O
track O
, O
the O
layer S-PARA
and O
the O
final O
3D B-APPL
object E-APPL
– O
is O
suggested O
and O
discussed O
. O


Numerical B-ENAT
simulation E-ENAT
allowed O
the O
estimation O
of O
temperature S-PARA
distribution S-CONPRI
during O
laser S-ENAT
melting O
and O
predicted S-CONPRI
final O
microstructures S-MATE
and O
properties S-CONPRI
of O
a O
3D S-CONPRI
SLM O
object O
. O


A O
series O
of O
single O
tracks O
, O
layers O
and O
3D B-APPL
objects E-APPL
were O
manufactured S-CONPRI
from O
AISI B-MATE
420 E-MATE
stainless O
steel S-MATE
to O
validate O
a O
proposed O
algorithm S-CONPRI
. O


The O
efficiency O
of O
the O
approach O
was O
illustrated O
by O
the O
manufacturing S-MANP
of O
fully B-PARA
dense E-PARA
samples O
from O
AISI B-MATE
420 E-MATE
stainless O
steel S-MATE
widely O
used O
in O
the O
plastics-moulding O
industry S-APPL
. O


The O
results O
show O
that O
based O
on O
the O
proposed O
systematic O
hierarchical O
approach O
, O
optimal B-PARA
process E-PARA
parameters O
can O
be S-MATE
efficiently O
established O
for O
high-quality O
SLM S-MANP
parts O
from O
metal B-MATE
powders E-MATE
. O


High O
speed O
imaging S-APPL
with O
external O
illumination O
is O
used O
to O
analyse O
defects S-CONPRI
. O


Power S-PARA
decay O
strategy O
to O
tackle O
heat B-PRO
accumulation E-PRO
in O
multiple O
layers O
is O
presented O
. O


Benchmark S-MANS
data O
of O
porosity S-PRO
, O
productivity S-CONPRI
, O
roughness S-PRO
, O
and O
microhardness S-CONPRI
is O
provided O
. O


In O
this O
work O
, O
coaxial O
laser S-ENAT
metal O
wire O
deposition S-CONPRI
( O
LMWD O
) O
process S-CONPRI
is O
studied O
, O
with O
particular O
attention O
to O
defect S-CONPRI
formation O
mechanisms O
and O
the O
establishment O
of O
stable O
processing O
conditions O
. O


The O
coaxial O
LMWD O
of O
AISI O
308 O
stainless B-MATE
steel E-MATE
wire O
was O
carried O
out O
by O
a O
multi-mode O
fiber S-MATE
laser O
delivered O
to O
an O
industrial S-APPL
coaxial O
LMWD O
deposition S-CONPRI
head O
. O


The O
continuous O
mechanical S-APPL
connection O
with O
the O
deposition S-CONPRI
region O
requires O
further O
attention O
to O
the O
process S-CONPRI
dynamics O
, O
which O
may O
alter O
the O
deposition S-CONPRI
precision O
and O
continuity O
. O


Accordingly O
, O
this O
work O
presents O
a O
systematic O
analysis O
of O
how O
the O
defects S-CONPRI
are O
formed O
at O
single O
and O
multiple O
layer S-PARA
deposition S-CONPRI
conditions O
. O


High-speed O
imaging S-APPL
is O
employed O
to O
reveal O
the O
process S-CONPRI
dynamics O
as S-MATE
a O
diagnostics O
aid O
. O


The O
process S-CONPRI
stability O
is O
determined O
initially O
at O
single O
layer S-PARA
condition O
, O
providing O
a O
correct O
match O
between O
the O
melting S-MANP
position O
and O
rate O
of O
the O
wire O
. O


At O
multiple O
layer S-PARA
deposition S-CONPRI
, O
the O
thermal O
load O
is O
managed O
to O
achieve O
high-aspect O
ratio O
components S-MACEQ
. O


At O
the O
stable O
conditions O
, O
the O
process S-CONPRI
is O
benchmarked O
for O
porosity S-PRO
, O
surface B-PRO
roughness E-PRO
, O
and O
deposition B-PARA
rates E-PARA
. O


The O
use O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
provides O
an O
opportunity O
to O
fabricate S-MANP
composite S-MATE
tooling O
molds S-MACEQ
in O
a O
rapidly O
and O
cost O
effectively O
manner O
. O


This O
work O
has O
shown O
the O
use O
of O
a O
polymer S-MATE
based O
infiltrated O
ceramics S-MATE
produced O
via O
binder B-MANP
jetting E-MANP
for O
producing O
composite S-MATE
tooling O
molds S-MACEQ
. O


Here O
, O
molds S-MACEQ
based O
on O
silica B-MATE
sand E-MATE
as S-MATE
well O
as S-MATE
zircon O
sand S-MATE
have O
been O
printed O
on O
a O
S-Max O
3D B-MACEQ
printer E-MACEQ
unit O
and O
subsequently O
impregnated O
with O
an O
epoxy S-MATE
system O
for O
yielding O
functional O
molds S-MACEQ
in O
the O
range S-PARA
of O
autoclave S-MACEQ
temperatures O
around O
150–177 O
°C O
. O


The O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
infiltrated O
3D B-MANP
printed E-MANP
materials O
have O
been O
investigated O
and O
it O
was O
observed O
that O
the O
polymer-infiltrated O
systems O
resulted O
in O
a O
compressive O
and O
flexural B-PRO
strength E-PRO
one O
order O
of O
magnitude S-PARA
higher O
than O
the O
non-infiltrated O
printed O
ceramic B-MATE
material E-MATE
. O


A O
thermal B-CHAR
analysis E-CHAR
was O
also O
performed O
on O
both O
the O
infiltrated O
and O
non-infiltrated O
printed O
samples S-CONPRI
, O
and O
it O
was O
recorded O
that O
the O
incorporation O
of O
the O
polymer S-MATE
resulted O
in O
a O
larger O
coefficient B-PRO
of I-PRO
thermal I-PRO
expansion E-PRO
on O
the O
infiltrated O
systems O
. O


Here O
, O
a O
carbon B-MATE
fiber E-MATE
reinforced O
composite S-MATE
was O
manufactured S-CONPRI
with O
the O
infiltrated O
composite S-MATE
tooling O
molds S-MACEQ
printed O
in O
the O
S-Max O
unit O
, O
and O
it O
was O
observed O
that O
the O
assembled O
molds S-MACEQ
are O
capable O
of O
producing O
a O
successful O
composite B-MATE
material E-MATE
. O


The O
present O
work O
has O
demonstrated O
that O
a O
binder B-MANP
jetting E-MANP
process O
, O
is O
a O
feasible O
technology S-CONPRI
for O
producing O
thermostable O
low O
cost O
composite S-MATE
tooling O
molds S-MACEQ
. O


In O
the O
present O
study O
, O
laser B-MANP
metal I-MANP
deposition E-MANP
( O
LMD S-MANP
) O
was O
used O
to O
produce O
compositionally O
graded O
refractory S-APPL
high-entropy O
alloys S-MATE
( O
HEAs O
) O
for O
screening O
purposes O
by O
in-situ S-CONPRI
alloying S-FEAT
of O
elemental O
powder B-MATE
blends E-MATE
. O


A O
compositional O
gradient O
from O
Ti25Zr50Nb0Ta25 O
to O
Ti25Zr0Nb50Ta25 O
is O
obtained O
by O
incrementally O
substituting O
Zr B-MATE
powder E-MATE
with O
Nb S-MATE
powder O
. O


A O
suitable O
strategy O
was O
developed O
to O
process S-CONPRI
the O
powder B-MATE
blend E-MATE
despite O
several O
challenges O
such O
as S-MATE
the O
high O
melting B-PRO
points E-PRO
of O
the O
refractory S-APPL
elements S-MATE
and O
the O
large O
differences O
in O
melting B-PRO
points E-PRO
among O
them O
. O


The O
influence O
of O
the O
LMD S-MANP
process O
on O
the O
final O
chemical B-CONPRI
composition E-CONPRI
was O
analyzed O
in O
detail O
and O
the O
LMD S-MANP
process O
was O
optimized O
to O
obtain O
a O
well-defined O
compositional O
gradient O
. O


Microstructures S-MATE
, O
textures O
, O
chemical B-CONPRI
compositions E-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
were O
characterized O
using O
SEM S-CHAR
, O
EBSD S-CHAR
, O
EDX S-CHAR
, O
and O
microhardness S-CONPRI
testing O
, O
respectively O
. O


Compositions O
between O
Ti25Zr0Nb50Ta25 O
and O
Ti25Zr25Nb25Ta25 O
were O
found O
to O
be S-MATE
single-phase O
bcc S-CONPRI
solid O
solutions O
with O
a O
coarse O
grain S-CONPRI
microstructure O
. O


Increasing O
the O
Zr S-MATE
to O
Nb S-MATE
ratio O
beyond O
the O
equiatomic O
composition S-CONPRI
results O
in O
finer O
and O
harder O
multiphase O
microstructures S-MATE
. O


The O
results O
shown O
in O
the O
present O
study O
clearly O
show O
for O
the O
first O
time O
that O
LMD S-MANP
is O
a O
suitable O
processing O
tool S-MACEQ
to O
screen O
HEAs O
over O
a O
range S-PARA
of O
chemical B-CONPRI
compositions E-CONPRI
. O


Open O
source S-APPL
3-D S-CONPRI
printer O
to O
both O
fabricate S-MANP
slot O
die S-MACEQ
and O
functionalize O
. O


Created O
a O
3-D S-CONPRI
slot O
die S-MACEQ
printing O
system O
. O


Functional O
lab-grade O
slot O
dies S-MACEQ
may O
be S-MATE
3-D S-CONPRI
printed O
. O


Semiconductor S-MATE
films O
deposited O
with O
polymer S-MATE
slot O
die S-MACEQ
down O
to O
17 O
nm O
. O


Slot O
die S-MACEQ
coating S-APPL
is O
growing O
in O
popularity O
because O
it O
is O
a O
low O
operational O
cost O
and O
easily O
scaled O
processing B-CONPRI
technique E-CONPRI
for O
depositing O
thin O
and O
uniform O
films O
rapidly O
, O
while O
minimizing O
material S-MATE
waste O
. O


The O
complex O
inner O
geometry S-CONPRI
of O
conventional O
slot O
dies S-MACEQ
require O
expensive O
machining S-MANP
that O
limits S-CONPRI
accessibility O
and O
experimentation O
. O


In O
order O
to O
overcome O
these O
issues O
this O
study O
follows O
an O
open O
hardware O
approach O
, O
which O
uses O
an O
open O
source S-APPL
3-D S-CONPRI
printer O
to O
both O
fabricate S-MANP
the O
slot O
die S-MACEQ
and O
then O
to O
functionalize O
a O
3-D S-CONPRI
slot O
die S-MACEQ
printing O
system O
. O


Polymer B-MATE
materials E-MATE
are O
tested O
and O
selected O
for O
compatibility O
with O
common O
solvents O
and O
used O
to O
fabricate S-MANP
a O
custom O
slot O
die S-MACEQ
head O
. O


This O
slot O
die S-MACEQ
is O
then O
integrated O
into O
a O
3-D S-CONPRI
printer O
augmented O
with O
a O
syringe S-MACEQ
pump O
to O
form O
an O
additive B-MANP
manufacturing E-MANP
platform O
for O
thin O
film O
semiconductor S-MATE
devices O
. O


The O
full O
design S-FEAT
of O
the O
slot O
die S-MACEQ
system O
is O
disclosed O
here O
using O
an O
open O
source S-APPL
license O
including O
software S-CONPRI
and O
operational O
protocols S-CONPRI
. O


This O
study O
demonstrates O
that O
functional O
lab-grade O
slot O
dies S-MACEQ
may O
be S-MATE
3-D S-CONPRI
printed O
using O
low-cost O
open O
source S-APPL
hardware O
methods O
A O
case B-CONPRI
study E-CONPRI
using O
NiO2 O
found O
an O
RMS O
value O
0.486 O
nm O
, O
thickness O
of O
17–49 O
nm O
, O
and O
a O
maximum O
optical S-CHAR
transmission O
of O
99.1 O
% O
, O
which O
shows O
this O
additive B-MANP
manufacturing E-MANP
approach O
to O
slot O
die S-MACEQ
depositions O
as S-MATE
well O
of O
fabrication S-MANP
is O
capable O
of O
producing O
viable O
layers O
of O
advanced O
electronic O
materials S-CONPRI
. O


Ball-milled O
Ti/TiC O
composite B-MATE
particles E-MATE
( O
TiC O
nanoparticles S-CONPRI
assembled O
on O
Ti S-MATE
microparticles O
) O
were O
designed S-FEAT
, O
prepared O
, O
and O
mixed O
with O
Al-Si-Mg O
powder S-MATE
to O
fabricate S-MANP
an O
Al-Si-Mg-Ti O
alloy S-MATE
with O
TiC O
nanoparticles S-CONPRI
( O
Al-Si-Mg-Ti/TiC O
) O
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
. O


Microstructure S-CONPRI
features O
, O
solidification S-CONPRI
behavior O
, O
and O
mechanical B-CONPRI
properties E-CONPRI
were O
investigated O
, O
and O
the O
relationship O
among O
them O
was O
established O
. O


The O
SLM-manufactured O
Al-Si-Mg-Ti/TiC O
material S-MATE
exhibited O
fine O
equiaxed-shaped O
α O
( O
Al S-MATE
) O
grains S-CONPRI
with O
nanoscale O
Si4Ti5 O
phases O
and O
Mg S-MATE
segregation O
along O
the O
grain B-CONPRI
boundaries E-CONPRI
. O


This O
structure S-CONPRI
benefited O
from O
heterogeneous B-CONPRI
nucleation E-CONPRI
as S-MATE
well O
as S-MATE
the O
grain B-CONPRI
growth E-CONPRI
restriction O
capabilities O
of O
TiC O
nanoparticles S-CONPRI
on O
α O
( O
Al S-MATE
) O
, O
fast O
diffusion S-CONPRI
of O
Ti S-MATE
in O
the O
superheated O
Al S-MATE
liquid O
, O
and O
high O
chemical O
activity O
of O
Ti S-MATE
to O
Si S-MATE
during O
solidification S-CONPRI
. O


Furthermore O
, O
Ti S-MATE
enrichment O
in O
some O
local O
areas S-PARA
of O
the O
high-temperature O
pool O
and O
the O
consequently O
intense O
Marangoni O
convection O
improved O
the O
wettability S-CONPRI
between O
TiC O
nanoparticles S-CONPRI
and O
liquid O
Al S-MATE
without O
the O
interfacial O
reaction O
. O


Consequently O
, O
the O
SLM-manufactured O
Al-Si-Mg-Ti/TiC O
showed O
a O
high O
ultimate B-PRO
tensile I-PRO
strength E-PRO
of O
up O
to O
562 O
± O
7 O
MPa S-CONPRI
and O
an O
elongation S-PRO
of O
up O
to O
8.8 O
% O
± O
1.3 O
% O
before O
fracture S-CONPRI
. O


These O
increased O
mechanical B-CONPRI
properties E-CONPRI
are O
attributed O
to O
the O
combined O
effect O
of O
grain B-CHAR
refinement E-CHAR
and O
Orowan O
and O
load-bearing S-FEAT
strengthening O
mechanisms O
. O


In O
this O
work O
, O
the O
Direct O
Ink S-MATE
Writing O
( O
DIW S-MANP
) O
technique O
was O
used O
to O
produce O
three-dimensional S-CONPRI
Ti2AlC O
ceramic S-MATE
components O
with O
high O
, O
uniform O
porosity S-PRO
. O


Suitable O
formulations O
were O
developed O
, O
with O
appropriate O
rheological B-PRO
properties E-PRO
for O
extruding S-MANP
thin O
filaments S-MATE
through O
a O
nozzle S-MACEQ
with O
a O
diameter S-CONPRI
of O
810 O
μm O
. O


The O
main O
rheological B-PRO
properties E-PRO
of O
the O
inks O
were O
investigated O
to O
evaluate O
their O
behavior O
and O
flowability O
during O
the O
printing B-MANP
process E-MANP
. O


Porous S-PRO
Ti2AlC O
lattices S-CONPRI
were O
fabricated S-CONPRI
, O
in O
selected O
conditions O
, O
with O
uniform O
pore B-PARA
size E-PARA
and O
good O
interconnectivity O
, O
and O
sintered S-MANP
at O
1400 O
°C O
in O
Ar S-ENAT
. O


Total O
porosity S-PRO
ranged O
from O
∼44 O
to O
∼63 O
vol O
% O
, O
and O
the O
mechanical B-PRO
strength E-PRO
ranged O
from O
∼43 O
to O
83 O
MPa S-CONPRI
. O


The O
influence O
of O
the O
ink S-MATE
composition S-CONPRI
and O
heat-treatment O
conditions O
on O
the O
phase B-CONPRI
composition E-CONPRI
of O
the O
3D S-CONPRI
porous O
structures O
was O
also O
evaluated O
. O


The O
high O
thermal B-PARA
gradients E-PARA
experienced O
during O
manufacture S-CONPRI
via O
selective B-MANP
laser I-MANP
melting E-MANP
commonly O
result O
in O
cracking S-CONPRI
of O
high O
γ/γ′ O
Nickel B-MATE
based I-MATE
superalloys E-MATE
. O


Such O
defects S-CONPRI
can O
not O
be S-MATE
tolerated O
in O
applications O
where O
component S-MACEQ
integrity O
is O
of O
paramount O
importance O
. O


To O
overcome O
this O
, O
many O
industrial S-APPL
practitioners O
make O
use O
of O
hot B-MANP
isostatic I-MANP
pressing E-MANP
to O
‘ O
heal O
’ O
these O
defects S-CONPRI
. O


The O
possibility O
of O
such O
defects S-CONPRI
re-opening O
during O
the O
component S-MACEQ
life O
necessitates O
optimisation O
of O
SLM S-MANP
processing O
parameters S-CONPRI
in O
order O
to O
produce O
the O
highest O
bulk O
density S-PRO
and O
integrity S-CONPRI
in O
the O
as-built O
state.In O
this O
paper O
, O
novel O
fractal O
scanning B-CONPRI
strategies E-CONPRI
based O
upon O
mathematical S-CONPRI
fill O
curves O
, O
namely O
the O
Hilbert O
and O
Peano-Gosper O
curve O
, O
are O
explored O
in O
which O
the O
use O
of O
short O
vector O
length O
scans O
, O
in O
the O
order O
of O
100 O
μm O
, O
is O
used O
as S-MATE
a O
method O
of O
reducing O
residual B-PRO
stresses E-PRO
. O


The O
effect O
on O
cracking S-CONPRI
observed O
in O
CM247LC O
superalloy O
samples S-CONPRI
was O
analysed O
using O
image S-CONPRI
processing O
, O
comparing O
the O
novel O
fractal O
scan O
strategies O
to O
more O
conventional O
‘ O
island O
’ O
scans O
. O


Scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
and O
energy B-CHAR
dispersive I-CHAR
X-ray I-CHAR
spectroscopy E-CHAR
was O
utilised O
to O
determine O
the O
cracking S-CONPRI
mechanisms.Results O
show O
that O
cracking S-CONPRI
occurs O
via O
two O
mechanisms O
, O
solidification S-CONPRI
and O
liquation O
, O
with O
a O
strong O
dependence O
on O
the O
laser B-ENAT
scan E-ENAT
vectors O
. O


Through O
the O
use O
of O
fractal O
scan O
strategies O
, O
bulk O
density S-PRO
can O
be S-MATE
increased O
by O
2 O
± O
0.7 O
% O
when O
compared O
to O
the O
‘ O
island O
’ O
scanning S-CONPRI
, O
demonstrating O
the O
potential O
of O
fractal O
scan O
strategies O
in O
the O
manufacture S-CONPRI
of O
typically O
‘ O
unweldable O
’ O
nickel S-MATE
superalloys O
. O


Porous B-FEAT
scaffolds E-FEAT
were O
studied O
for O
weight S-PARA
bearing O
biomedical B-APPL
applications E-APPL
. O


Compression S-PRO
samples O
were O
additively B-MANP
manufactured E-MANP
using O
electron B-MANP
beam I-MANP
melting E-MANP
. O


Reentrant O
and O
cubic O
Ti6Al4 O
V S-MATE
unit B-CONPRI
cell E-CONPRI
geometries S-CONPRI
were O
tested O
under O
compression S-PRO
. O


Cubic O
scaffold S-FEAT
outperformed O
the O
reentrant O
scaffold S-FEAT
at O
the O
same O
relative B-PRO
density E-PRO
. O


A O
cubic O
scaffold S-FEAT
was O
proved O
suitable O
for O
load O
bearing O
biomedical B-APPL
applications E-APPL
. O


Ti6Al4V S-MATE
porous B-FEAT
scaffolds E-FEAT
of O
two O
unit B-CONPRI
cell E-CONPRI
geometries S-CONPRI
( O
reentrant O
and O
cubic O
) O
were O
investigated O
as S-MATE
candidates O
for O
load-bearing S-FEAT
biomedical B-APPL
applications E-APPL
. O


Samples S-CONPRI
were O
fabricated S-CONPRI
using O
an O
Arcam O
A2 O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
machine S-MACEQ
and O
evaluated O
for O
geometric O
deviation O
from O
the O
original O
CAD S-ENAT
design O
using O
a O
digital O
optical S-CHAR
microscope S-MACEQ
. O


The O
mass O
and O
bounding O
volume S-CONPRI
of O
each O
sample S-CONPRI
were O
also O
measured O
to O
calculate O
the O
resulting O
relative B-PRO
density E-PRO
. O


The O
scaffolds S-FEAT
were O
loaded O
in O
compression S-PRO
in O
the O
build B-PARA
direction E-PARA
to O
determine O
the O
relative O
modulus B-PRO
of I-PRO
elasticity E-PRO
and O
ultimate O
compressive O
load O
. O


Experimental S-CONPRI
results O
were O
used O
to O
calculate O
the O
Gibson O
and O
Ashby O
relation O
parameters S-CONPRI
for O
the O
studied O
unit B-CONPRI
cell E-CONPRI
geometries S-CONPRI
. O


The O
results O
suggest O
that O
samples S-CONPRI
with O
the O
cubic O
unit B-CONPRI
cell E-CONPRI
geometries S-CONPRI
, O
with O
struts S-MACEQ
oriented O
at O
an O
angle O
of O
45° O
to O
the O
loading O
direction O
, O
exhibited O
higher O
stiffness S-PRO
than O
samples S-CONPRI
with O
the O
reentrant O
unit B-CONPRI
cell E-CONPRI
geometry S-CONPRI
at O
equivalent O
relative B-PRO
densities E-PRO
. O


A O
cubic O
scaffold S-FEAT
is O
verified O
to O
withstand O
high O
compressive O
loads O
( O
more O
than O
71 O
kN O
) O
while O
having O
an O
approximate O
pore B-PARA
size E-PARA
in O
the O
range S-PARA
of O
0.6 O
mm S-MANP
. O


The O
selective B-MANP
laser I-MANP
melting E-MANP
fabricated S-CONPRI
304L O
stainless B-MATE
steel E-MATE
exhibited O
an O
excellent O
strength–ductility O
synergy O
. O


Massive O
stacking O
faults O
and O
annealing S-MANP
twins O
formed O
in O
the O
selective B-MANP
laser I-MANP
melting E-MANP
fabricated S-CONPRI
304L O
stainless B-MATE
steel E-MATE
. O


The O
outstanding O
ductility S-PRO
is O
due O
to O
the O
activation O
of O
multiple O
deformation S-CONPRI
mechanisms O
. O


The O
microstructure S-CONPRI
, O
mechanical B-CONPRI
properties E-CONPRI
and O
deformation S-CONPRI
mechanisms O
of O
the O
304L O
stainless B-MATE
steel E-MATE
( O
SS S-MATE
) O
additively B-MANP
manufactured E-MANP
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
were O
systematically O
investigated O
. O


The O
SLM S-MANP
fabricated S-CONPRI
304L O
SS S-MATE
contains O
two O
phases O
( O
face-centered-cubic O
γ-austenite O
and O
body-centered-cubic O
δ-ferrite O
) O
and O
exhibits O
a O
hierarchical O
microstructure S-CONPRI
with O
length B-CHAR
scales E-CHAR
spanning O
several O
orders O
of O
magnitude S-PARA
. O


The O
hierarchical O
microstructure S-CONPRI
includes O
the O
melt B-MATE
pools E-MATE
and O
slightly O
elongated O
columnar B-PRO
grains E-PRO
at O
the O
micron S-FEAT
scale O
, O
cellular B-FEAT
structures E-FEAT
decorated O
with O
a O
high O
density S-PRO
of O
dislocations S-CONPRI
at O
the O
sub-micron S-FEAT
scale O
and O
oxides S-MATE
at O
the O
nanoscale O
. O


Stacking O
faults O
formed O
due O
to O
the O
residual B-PRO
stress E-PRO
in O
addition O
to O
the O
low O
stacking O
fault O
energy O
of O
the O
304L O
SS S-MATE
( O
19.2 O
mJ/m2 O
) O
while O
massive O
annealing S-MANP
twins O
were O
generated O
arising O
from O
the O
combined O
effects O
of O
residual B-PRO
stress E-PRO
and O
intrinsic O
heat B-MANP
treatment E-MANP
. O


The O
as S-MATE
built O
304L O
SS S-MATE
exhibits O
a O
significantly O
enhanced O
strength–ductility O
synergy O
compared O
to O
that O
of O
wrought S-CONPRI
and O
annealed O
counterparts O
. O


The O
enhanced O
yield B-PRO
strength E-PRO
stems O
from O
the O
hierarchically O
heterogeneous S-CONPRI
microstructure O
, O
while O
the O
outstanding O
tensile B-PRO
elongation E-PRO
is O
ascribed O
to O
the O
activation O
of O
multiple O
deformation S-CONPRI
mechanisms O
, O
involving O
the O
dislocation S-CONPRI
activities O
, O
the O
formation O
of O
stacking O
faults O
and O
mechanical S-APPL
twins O
, O
and O
the O
transformation-induced O
plasticity S-PRO
. O


Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
developing O
with O
the O
goal O
of O
fabricating S-MANP
parts O
with O
high O
performance S-CONPRI
and O
high O
efficiency O
. O


Laser B-PARA
power E-PARA
is O
the O
key O
factor O
to O
the O
efficiency O
, O
microstructure S-CONPRI
and O
performance S-CONPRI
in O
LPBF S-MANP
. O


In O
this O
work O
, O
the O
molten B-CONPRI
pool E-CONPRI
characteristics O
and O
spatter S-CHAR
behavior O
in O
LPBF S-MANP
with O
a O
high O
power S-PARA
and O
a O
wide O
process S-CONPRI
window O
( O
from O
350 O
W O
to O
1550 O
W O
) O
are O
studied O
based O
on O
high-speed O
high-resolution S-PARA
imaging O
. O


The O
results O
show O
that O
the O
molten B-CONPRI
pool E-CONPRI
characteristics O
and O
spatter S-CHAR
behavior O
depend O
on O
the O
laser S-ENAT
input O
energy O
. O


The O
average S-CONPRI
ejection O
velocity O
and O
ejection S-CONPRI
angle O
increase O
with O
the O
laser B-PARA
power E-PARA
. O


The O
droplet S-CONPRI
column O
ejection S-CONPRI
and O
large O
spatters O
are O
prone O
to O
occur O
with O
a O
high-power B-CONPRI
laser E-CONPRI
. O


Furthermore O
, O
the O
times O
at O
which O
the O
vapor O
depression O
and O
the O
protrusion O
in O
the O
molten B-CONPRI
pool E-CONPRI
first O
occur O
decrease O
dramatically O
with O
an O
increase O
in O
the O
laser S-ENAT
input O
energy O
. O


When O
the O
laser S-ENAT
mode O
and O
spot B-PARA
size E-PARA
are O
kept O
constant O
, O
the O
laser B-PARA
power E-PARA
determines O
the O
amount O
of O
time O
required O
for O
melting S-MANP
, O
the O
vapor O
depression O
and O
the O
protrusion O
in O
LPBF S-MANP
to O
occur O
, O
while O
the O
laser B-ENAT
scan E-ENAT
velocity O
determines O
whether O
the O
laser S-ENAT
dwell B-PARA
time E-PARA
is O
sufficient O
for O
these O
phenomena O
to O
form O
. O


Optimum O
distribution S-CONPRI
of O
relative B-PRO
density E-PRO
can O
enhance O
the O
bending S-MANP
stiffness O
of O
an O
architected O
cellular O
beam S-MACEQ
more O
than O
120 O
% O
. O


Optimally O
graded O
cellular O
beam S-MACEQ
samples O
are O
3D B-MANP
printed E-MANP
using O
stereolithography S-MANP
. O


Experimental S-CONPRI
bending B-CHAR
tests E-CHAR
on O
3D B-MANP
printed E-MANP
samples O
confirm O
the O
practicality O
of O
graded O
designs S-FEAT
for O
developing O
advanced O
lightweight B-MACEQ
structures E-MACEQ
. O


Periodic O
cellular B-MATE
materials E-MATE
can O
substantially O
improve O
the O
stiffness-to-weight O
ratio O
of O
structures O
. O


This O
improvement O
depends O
on O
the O
geometry S-CONPRI
of O
periodic O
cells S-APPL
. O


This O
article O
presents O
the O
idea O
of O
enhancing O
the O
bending S-MANP
stiffness O
of O
an O
architected O
cellular O
beam S-MACEQ
by O
an O
optimum O
distribution S-CONPRI
of O
relative B-PRO
density E-PRO
through O
its O
length O
and/or O
across O
its O
thickness O
. O


Detailed O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
( O
FEA O
) O
and O
experimental S-CONPRI
bending B-CHAR
tests E-CHAR
on O
specimens O
3D B-MANP
printed E-MANP
by O
stereolithography S-MANP
validate O
the O
hybrid-homogenized O
modeling S-ENAT
approach O
. O


The O
hybrid-homogenized O
model S-CONPRI
facilitates O
transforming O
the O
general O
optimization S-CONPRI
problem O
into O
a O
shape O
optimization S-CONPRI
process O
with O
the O
relative B-PRO
density E-PRO
of O
unit B-CONPRI
cells E-CONPRI
as S-MATE
design O
variables O
. O


The O
teaching-learning-based O
optimization S-CONPRI
( O
TLBO O
) O
algorithm S-CONPRI
is O
used O
to O
obtain O
the O
optimum O
relative B-PRO
density E-PRO
distribution S-CONPRI
, O
which O
maximizes O
the O
bending S-MANP
stiffness O
. O


The O
optimization S-CONPRI
results O
show O
a O
substantial O
increase O
in O
bending S-MANP
stiffness O
; O
as S-MATE
high O
as S-MATE
43 O
% O
, O
155 O
% O
, O
and O
182 O
% O
for O
a O
cellular O
beam S-MACEQ
graded O
through O
the O
length O
, O
across O
the O
thickness O
, O
and O
in O
both O
directions O
, O
respectively O
. O


It O
is O
found O
that O
varying O
the O
relative B-PRO
density E-PRO
of O
cells S-APPL
across O
the O
beam S-MACEQ
thickness O
is O
more O
effective O
than O
variation S-CONPRI
through O
the O
length O
. O


Detailed O
FEA O
and O
experimental S-CONPRI
bending B-CHAR
tests E-CHAR
corroborate O
the O
optimization S-CONPRI
findings O
and O
confirm O
the O
practicality O
of O
such O
graded O
designs S-FEAT
for O
developing O
advanced O
lightweight B-MACEQ
structures E-MACEQ
. O


Investigating O
the O
effect O
of O
cell S-APPL
architecture S-APPL
also O
reveals O
that O
optimally O
graded O
cellular O
beams O
have O
a O
potential O
to O
outperform O
uniform O
cellular O
beams O
made O
out O
of O
ideal O
unit B-CONPRI
cells E-CONPRI
( O
Voigt O
bound O
for O
elastic S-PRO
properties O
) O
by O
reaching O
bending S-MANP
stiffness-to-density O
ratios O
greater O
than O
one O
. O


The O
relatively O
simple S-MANP
graded O
cellular B-FEAT
designs E-FEAT
are O
beneficial O
in O
applications O
where O
high O
bending S-MANP
stiffness O
and O
low O
density S-PRO
are O
essential O
. O


Recent O
advances O
in O
additive B-MANP
manufacturing E-MANP
promise O
extending O
the O
presented O
grading O
strategy O
for O
polymeric O
, O
composite S-MATE
, O
and O
metallic S-MATE
3D B-MANP
printed E-MANP
cellular O
materials S-CONPRI
to O
fabricate S-MANP
high O
performance B-CONPRI
lightweight E-CONPRI
structural O
elements S-MATE
at O
a O
relatively O
low O
cost O
. O


This O
study O
investigated O
the O
effect O
of O
trace O
lanthanum S-MATE
hexaboride O
( O
LaB6 O
) O
addition O
on O
the O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
an O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
processed S-CONPRI
Ti-6Al-4V O
component S-MACEQ
. O


LaB6 O
exhibited O
a O
significant O
effect O
on O
the O
grain B-CONPRI
structure E-CONPRI
, O
phase S-CONPRI
, O
and O
texture S-FEAT
of O
the O
EBM-processed O
Ti-6Al-4V B-MATE
alloys E-MATE
. O


Although O
prior-β O
columnar B-PRO
grains E-PRO
were O
observed O
in O
both O
Ti-6Al-4V S-MATE
and O
LaB6-modified O
Ti-6Al-4V S-MATE
( O
Ti-6Al-4V-LaB6 O
) O
, O
the O
width O
of O
the O
columnar B-PRO
grains E-PRO
decreased O
significantly O
with O
LaB6 O
addition O
. O


Alternating O
acicular O
α′ O
martensite S-MATE
and O
acicular O
α O
laths O
were O
distributed O
in O
the O
Ti-6Al-4V S-MATE
, O
whereas O
refined O
lamellar S-CONPRI
α O
+ O
β O
structures O
were O
observed O
in O
the O
Ti-6Al-4V-LaB6 O
. O


We O
propose O
that O
the O
addition O
of O
LaB6 O
provided O
a O
large O
amount O
of O
heterogenous O
nucleation S-CONPRI
sites O
for O
solidification S-CONPRI
and O
α O
phase S-CONPRI
formation O
. O


Consequently O
, O
high O
tensile B-PRO
strength E-PRO
with O
considerable O
elongation S-PRO
was O
achieved O
in O
the O
EBM-processed O
Ti-6Al-4V S-MATE
modified O
by O
trace O
LaB6 O
addition O
. O


The O
purpose O
of O
this O
paper O
is O
to O
identify O
the O
key O
elements S-MATE
of O
a O
new O
hybrid O
process S-CONPRI
to O
produce O
high O
quality S-CONPRI
metal/plastic O
composites S-MATE
. O


The O
process S-CONPRI
is O
a O
combination O
of O
Fused B-CONPRI
Deposition E-CONPRI
Modelling O
( O
FDM S-MANP
) O
, O
vacuum O
forming S-MANP
and O
CNC B-MANP
machining E-MANP
. O


The O
research S-CONPRI
aims O
to O
provide O
details O
of O
the O
proposed O
hybrid O
process S-CONPRI
, O
equipment S-MACEQ
used O
, O
and O
the O
experimental S-CONPRI
results O
of O
the O
composites S-MATE
produced O
. O


The O
research S-CONPRI
has O
been O
separated O
into O
three O
study O
areas S-PARA
. O


In O
the O
first O
, O
the O
hybrid O
process S-CONPRI
has O
been O
defined O
as S-MATE
a O
whole O
whereas O
the O
second O
area S-PARA
deals O
with O
the O
breakdown O
of O
steps O
to O
produce O
the O
metal/plastic O
composites S-MATE
. O


The O
third O
area S-PARA
explains O
the O
varied O
materials S-CONPRI
used O
for O
the O
production S-MANP
and O
testing S-CHAR
of O
the O
composites S-MATE
. O


Composites S-MATE
have O
been O
made O
by O
joining S-MANP
copper S-MATE
( O
99.99 O
% O
pure O
) O
mesh O
with O
ABS S-MATE
( O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
) O
. O


Strain S-PRO
measurement S-CHAR
has O
been O
carried O
out O
on O
Cu/ABS O
sample S-CONPRI
to O
analyse O
the O
effect O
of O
metal S-MATE
mesh O
and O
to O
verify O
the O
effectiveness S-CONPRI
of O
the O
hybrid O
process S-CONPRI
. O


The O
resulting O
composites S-MATE
( O
Cu/ABS O
) O
have O
also O
been O
subjected O
to O
tensile S-PRO
loading O
with O
different O
layers O
of O
metal S-MATE
mesh O
, O
followed O
by O
microstructural B-CHAR
analysis E-CHAR
and O
comparative O
studies O
to O
serve O
as S-MATE
a O
proof O
of O
the O
methodology S-CONPRI
. O


The O
results O
show O
that O
the O
proposed O
hybrid O
process S-CONPRI
is O
very O
effective O
in O
producing O
metal/plastic O
composites S-MATE
with O
lower O
strain S-PRO
values O
compared O
to O
the O
parent O
plastic S-MATE
indicating O
a O
lower O
level O
of O
deformation S-CONPRI
due O
to O
interlocking O
of O
the O
metal S-MATE
and O
plastic S-MATE
layers O
. O


This O
effect O
has O
been O
reinforced S-CONPRI
by O
the O
tensile B-CHAR
testing E-CHAR
where O
the O
composites S-MATE
showed O
higher O
fracture S-CONPRI
load O
values O
compared O
to O
the O
parent O
plastic S-MATE
. O


Microstructural B-CHAR
analysis E-CHAR
shows O
the O
layer S-PARA
of O
metal S-MATE
mesh O
sandwiched O
between O
ABS S-MATE
layers O
indicating O
the O
existence O
of O
a O
bond O
holding O
the O
layers O
of O
metal S-MATE
and O
plastic S-MATE
together O
. O


These O
results O
demonstrate O
the O
capabilities O
and O
effectiveness S-CONPRI
of O
the O
proposed O
process S-CONPRI
that O
has O
shown O
promising O
results O
under O
tensile S-PRO
and O
static O
loading O
. O


High-mass-proportion O
TiCp/Ti6Al4V O
composites S-MATE
with O
fully B-PARA
dense E-PARA
prepared O
by O
directed B-MANP
energy I-MANP
deposition E-MANP
. O


The O
changes O
in O
microstructure S-CONPRI
and O
orientation S-CONPRI
relationship O
was O
discussed O
in O
detail O
. O


Hardness S-PRO
, O
wear B-PRO
resistance E-PRO
, O
and O
thermal B-PRO
conductivity E-PRO
increased O
, O
while O
tensile S-PRO
performance S-CONPRI
decreased O
with O
increasing O
TiCp O
content O
. O


Titanium S-MATE
matrix O
composites S-MATE
( O
TMC O
) O
have O
potential O
applications O
in O
the O
aerospace B-APPL
industry E-APPL
because O
of O
their O
excellent O
performance S-CONPRI
. O


The O
comprehensive O
performance S-CONPRI
of O
TMC O
mainly O
depends O
on O
the O
matrix O
, O
reinforcement S-PARA
and O
interface S-CONPRI
characteristics O
. O


Crack-free O
high-mass-proportion O
TiCp/Ti6Al4Vcomposites O
were O
successfully O
prepared O
by O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
. O


Meanwhile O
, O
the O
refined O
α-Ti O
in O
the O
composites S-MATE
had O
a O
relatively O
weak O
texture S-FEAT
. O


In O
addition O
, O
the O
interface S-CONPRI
between O
primary O
TiC O
and O
α-Ti O
was O
a O
semi-coherent O
interface S-CONPRI
, O
exhibiting O
a O
112-0 O
α-Ti O
// O
[ O
110 O
] O
TiC O
, O
1-100 O
α-Ti O
// O
1-11 O
TiC O
orientation S-CONPRI
relationship O
, O
which O
facilitated O
the O
heterogeneous B-CONPRI
nucleation E-CONPRI
of O
Ti S-MATE
and O
improved O
bonding S-CONPRI
of O
primary O
TiC O
with O
the O
matrix O
. O


With O
the O
increase O
in O
microhardness S-CONPRI
taking O
the O
form O
of O
a O
cubic O
function O
, O
the O
wear B-CONPRI
mechanism E-CONPRI
was O
found O
to O
transform O
from O
abrasive B-CONPRI
wear E-CONPRI
to O
slight O
delamination S-CONPRI
wear O
. O


Due O
to O
the O
fact O
that O
both O
UMT O
and O
primary O
TiC O
bonded O
well O
with O
Ti64 S-MATE
matrix O
, O
they O
shared O
partial O
friction S-CONPRI
to O
protect O
matrix O
from O
severe O
abrasion O
, O
resulting O
in O
an O
excellent O
wear B-PRO
resistance E-PRO
of O
composites S-MATE
. O


Moreover O
, O
the O
thermal B-PRO
conductivity E-PRO
of O
50 O
% O
TiCp/Ti6Al4V O
was O
9.063 O
W∙m-1∙K-1 O
, O
which O
was O
nearly O
26.5 O
% O
higher O
than O
that O
of O
Ti6Al4V S-MATE
. O


Owing O
to O
the O
premature O
cracking S-CONPRI
of O
brittle S-PRO
UMT O
and O
dendritic O
TiC O
, O
the O
tensile B-PRO
strength E-PRO
and O
elongation S-PRO
of O
the O
composite S-MATE
with O
50 O
% O
TiCp O
were O
515.5 O
MPa S-CONPRI
and O
1.83 O
% O
, O
which O
decreased O
by O
45.8 O
% O
and O
78.8 O
% O
, O
respectively O
. O


Adding O
a O
high O
proportion O
of O
TiCp O
can O
significantly O
improve O
the O
hardness S-PRO
and O
wear B-PRO
resistance E-PRO
of O
TMC O
, O
whereas O
it O
is O
detrimental O
to O
the O
tensile S-PRO
performance S-CONPRI
of O
TMC O
. O


The O
study O
have O
significant O
implications O
for O
the O
design S-FEAT
of O
novel O
TMC O
, O
particularly O
for O
the O
aerospace S-APPL
industrial O
applications O
. O


This O
paper O
presents O
the O
design S-FEAT
of O
a O
high O
speed O
, O
high B-PARA
resolution E-PARA
silicon O
based O
thermal O
imaging S-APPL
instrument O
and O
its O
application O
to O
thermally O
image S-CONPRI
the O
temperature S-PARA
distributions S-CONPRI
of O
an O
electron B-MACEQ
beam I-MACEQ
melting I-MACEQ
additive I-MACEQ
manufacturing I-MACEQ
system E-MACEQ
. O


Typically O
, O
thermal B-FEAT
images E-FEAT
are O
produced O
at O
mid O
or O
long O
wavelengths O
of O
infrared S-CONPRI
radiation O
. O


Using O
the O
shorter O
wavelengths O
that O
silicon S-MATE
focal O
plane O
arrays O
are O
sensitive O
to O
allows O
the O
use O
of O
standard S-CONPRI
windows O
in O
the O
optical S-CHAR
path O
. O


It O
also O
affords O
fewer O
modifications O
to O
the O
machine S-MACEQ
and O
enables O
us O
to O
make O
use O
of O
mature O
silicon S-MATE
camera S-MACEQ
technology O
. O


With O
this O
new O
instrument O
, O
in B-CONPRI
situ E-CONPRI
thermal O
imaging S-APPL
of O
the O
entire O
build B-PARA
area E-PARA
has O
been O
made O
possible O
at O
high O
speed O
, O
allowing O
defect S-CONPRI
detection O
and O
melt B-MATE
pool E-MATE
tracking O
. O


Melt B-MATE
pool E-MATE
tracking O
was O
used O
to O
implement O
an O
emissivity O
correction O
algorithm S-CONPRI
, O
which O
produced O
more O
accurate S-CHAR
temperatures O
of O
the O
melted S-CONPRI
areas S-PARA
of O
the O
layer S-PARA
. O


Simple S-MANP
, O
one-step O
copper S-MATE
electrodeposition O
on O
conductive O
3D B-APPL
objects E-APPL
Only O
the O
most O
conductive O
filament S-MATE
enables O
uniform O
electroplating S-MANP
. O


Electroplating S-MANP
with O
additives S-MATE
reduces O
the O
surface B-PRO
roughness E-PRO
of O
the O
print S-MANP
by O
2.4x O
. O


Electrical S-APPL
resistance O
improved O
by O
100x O
after O
one-step O
electrodeposition O
Quality S-CONPRI
factor O
of O
3D B-MANP
printed E-MANP
inductor O
is O
improved O
by O
1740x O
after O
electrodeposition O
. O


3D B-MANP
printing E-MANP
with O
electrically S-CONPRI
conductive O
filaments S-MATE
enables O
rapid B-ENAT
prototyping E-ENAT
and O
fabrication S-MANP
of O
electronics S-CONPRI
, O
but O
the O
performance S-CONPRI
of O
such O
devices O
can O
be S-MATE
limited O
by O
the O
fact O
that O
the O
most O
conductive O
thermoplastic-based O
filaments S-MATE
for O
3D B-MANP
printing E-MANP
are O
3750 O
times O
less O
conductive O
than O
copper S-MATE
. O


This O
study O
explores O
the O
use O
of O
one-step O
electrodeposition O
of O
copper S-MATE
onto O
electrically S-CONPRI
conductive O
3D B-MANP
printed E-MANP
objects O
as S-MATE
a O
way O
to O
improve O
their O
conductivity S-PRO
and O
performance S-CONPRI
. O


Comparison O
of O
three O
different O
commercially-available O
conductive O
filaments S-MATE
demonstrates O
that O
only O
the O
most O
conductive O
commercially O
available O
filament S-MATE
could O
enable O
one-step O
electrodeposition O
of O
uniform O
copper S-MATE
films O
. O


Electrodeposition O
improved O
the O
electrical B-PRO
conductivity E-PRO
and O
the O
ampacity O
of O
3D B-MANP
printed E-MANP
traces O
by O
94 O
and O
17 O
times O
respectively O
, O
compared O
to O
the O
as-printed O
object O
. O


The O
areal O
surface B-PRO
roughness E-PRO
of O
the O
objects O
was O
reduced O
from O
9.3 O
to O
6.9 O
μm O
after O
electrodeposition O
, O
and O
a O
further O
reduction S-CONPRI
in O
surface B-PRO
roughness E-PRO
to O
3.9 O
μm O
could O
be S-MATE
achieved O
through O
the O
addition O
of O
organic O
additives S-MATE
to O
the O
electrodeposition O
bath O
. O


Copper S-MATE
electrodeposition O
improved O
the O
quality S-CONPRI
factor O
of O
a O
3D B-MANP
printed E-MANP
inductor O
by O
1740 O
times O
and O
the O
gain S-PARA
of O
a O
3D B-MANP
printed E-MANP
horn O
antenna O
by O
1 O
dB O
. O


One-step O
electrodeposition O
is O
a O
fast O
and O
simple S-MANP
way O
to O
improve O
the O
conductivity S-PRO
and O
performance S-CONPRI
of O
3D B-MANP
printed E-MANP
electronic O
components S-MACEQ
. O


The O
wide O
usage O
of O
Inconel B-MATE
718 I-MATE
alloy E-MATE
is O
based O
on O
its O
fusion S-CONPRI
weldability O
and O
its O
availability O
in O
many O
different O
forms O
including O
cast S-MANP
, O
wrought S-CONPRI
and O
powder S-MATE
. O


Thus O
with O
the O
emergence O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
techniques O
for O
metals S-MATE
, O
Inconel B-MATE
718 E-MATE
is O
a O
prime O
candidate O
for O
materials S-CONPRI
to O
be S-MATE
considered O
. O


Powders S-MATE
that O
have O
been O
developed O
for O
powder B-MANP
metallurgy E-MANP
are O
readily O
available O
for O
use O
in O
various O
AM B-MANP
processes E-MANP
such O
as S-MATE
selected O
laser S-ENAT
melting O
( O
SLM S-MANP
) O
powder B-MACEQ
bed E-MACEQ
. O


While O
much O
research S-CONPRI
has O
focused O
on O
optimizing O
the O
deposition S-CONPRI
parameters O
to O
achieve O
fully O
densified S-MANP
specimens O
, O
subsequent O
heat B-MANP
treatments E-MANP
and O
their O
effect O
on O
the O
microstructure S-CONPRI
also O
need O
to O
be S-MATE
understood O
. O


This O
study O
evaluated O
the O
microstructure S-CONPRI
of O
SLM S-MANP
specimens O
of O
Inconel B-MATE
718 E-MATE
after O
various O
heat B-MANP
treatments E-MANP
and O
compared O
the O
resulting O
effect O
on O
the O
quasi-static S-CONPRI
mechanical B-CONPRI
properties E-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
has O
received O
a O
great O
deal O
of O
attention O
for O
the O
ability O
to O
produce O
three O
dimensional O
parts O
via O
laser S-ENAT
heating S-MANP
. O


One O
recently O
proposed O
method O
of O
making O
microscale S-CONPRI
AM B-MACEQ
parts E-MACEQ
is O
through O
microscale S-CONPRI
selective O
laser B-MANP
sintering E-MANP
( O
μ-SLS O
) O
where O
nanoparticles S-CONPRI
replace O
the O
traditional O
powders S-MATE
used O
in O
standard S-CONPRI
SLS B-MANP
processes E-MANP
. O


However O
, O
there O
are O
many O
challenges O
to O
understanding O
the O
physics S-CONPRI
of O
the O
process S-CONPRI
at O
nanoscale O
as S-MATE
well O
as S-MATE
with O
conducting O
experiments O
at O
that O
scale O
; O
hence O
, O
modeling S-ENAT
and O
computational O
simulations S-ENAT
are O
vital O
to O
understand O
the O
sintering S-MANP
process B-CONPRI
physics E-CONPRI
. O


At O
the O
sub-micron S-FEAT
( O
μm O
) O
level O
, O
the O
interaction O
between O
nanoparticles S-CONPRI
under O
high O
power S-PARA
laser S-ENAT
heating S-MANP
raises O
additional O
near-field O
thermal O
issues O
such O
as S-MATE
thermal O
diffusivity S-CHAR
, O
effective O
absorptivity O
, O
and O
extinction O
coefficients O
compared O
to O
larger O
scales O
. O


Thus O
, O
nanoparticle O
's O
distribution S-CONPRI
behavior O
and O
characteristic O
properties S-CONPRI
are O
very O
important O
to O
understanding O
the O
thermal B-CHAR
analysis E-CHAR
of O
nanoparticles S-CONPRI
in O
a O
μ-SLS O
process S-CONPRI
. O


This O
paper O
presents O
a O
discrete O
element S-MATE
modeling O
( O
DEM O
) O
study O
of O
how O
copper S-MATE
nanoparticles O
of O
given O
particle B-CONPRI
size I-CONPRI
distribution E-CONPRI
pack O
together O
in O
a O
μ-SLS O
powder B-MACEQ
bed E-MACEQ
. O


Initially O
, O
nanoparticles S-CONPRI
are O
distributed O
randomly O
into O
the O
bed S-MACEQ
domain O
with O
a O
random O
initial O
velocity O
vector O
and O
set S-APPL
boundary B-CONPRI
conditions E-CONPRI
. O


The O
particles S-CONPRI
are O
then O
allowed O
to O
move O
in O
discrete O
time O
steps O
until O
they O
reach O
a O
final O
steady B-CONPRI
state E-CONPRI
position O
, O
which O
creates O
the O
particle S-CONPRI
packing O
within O
the O
powder B-MACEQ
bed E-MACEQ
. O


The O
particles S-CONPRI
are O
subject O
to O
both O
gravitational O
and O
cohesive O
forces S-CONPRI
since O
cohesive O
forces S-CONPRI
become O
important O
at O
the O
nanoscale O
. O


A O
set S-APPL
of O
simulations S-ENAT
was O
performed O
for O
different O
cases O
under O
both O
Gaussian S-CONPRI
and O
log-normal O
particle B-CONPRI
size I-CONPRI
distributions E-CONPRI
with O
different O
standard B-CHAR
deviations E-CHAR
. O


In O
addition O
, O
this O
paper O
suggests O
a O
potential O
method O
to O
overcome O
the O
agglomeration O
effects O
in O
μ-SLS O
powder B-MACEQ
beds E-MACEQ
through O
the O
use O
of O
colloidal S-MATE
nanoparticle O
solutions O
that O
minimize O
the O
cohesive O
interactions O
between O
individual O
nanoparticles S-CONPRI
. O


Grain S-CONPRI
morphology O
control O
is O
a O
challenging O
issue O
for O
additive B-MANP
manufactured E-MANP
NiTi O
alloy S-MATE
, O
which O
directly O
affects O
the O
functional O
properties S-CONPRI
. O


In O
this O
work O
, O
La2O3 S-MATE
addition O
was O
applied O
to O
control O
microstructure S-CONPRI
and O
improve O
functional O
properties S-CONPRI
of O
directed O
energy O
deposited O
( O
DED S-MANP
) O
NiTi B-MATE
alloy E-MATE
. O


The O
results O
showed O
that O
the O
DEDed O
NiTi B-MATE
alloy E-MATE
mainly O
consisted O
of O
NiTi S-MATE
( O
B2 O
) O
columnar B-PRO
grains E-PRO
and O
some O
coarse O
NiTi2 O
phases O
within O
and O
at O
the O
boundaries S-FEAT
of O
NiTi S-MATE
grains S-CONPRI
. O


The O
addition O
of O
La2O3 S-MATE
led O
to O
the O
promotion O
of O
columnar-to-equiaxed O
transition S-CONPRI
and O
grain B-CHAR
refinement E-CHAR
of O
NiTi S-MATE
( O
B2 O
) O
phase S-CONPRI
. O


La2O3 S-MATE
and O
LaNi O
secondary O
phases O
can O
be S-MATE
found O
in O
the O
DEDed O
NiTi B-MATE
alloy E-MATE
with O
La2O3 S-MATE
addition O
. O


The O
La2O3 S-MATE
precipitate O
could O
act O
as S-MATE
the O
effective O
heterogeneous B-CONPRI
nucleation E-CONPRI
site O
and O
the O
NiTi2 O
or O
LaNi O
precipitates S-MATE
could O
pin O
the O
grain B-CONPRI
boundaries E-CONPRI
contributing O
to O
the O
grain B-CHAR
refinement E-CHAR
and O
the O
formation O
of O
equiaxed B-CONPRI
grains E-CONPRI
of O
NiTi S-MATE
( O
B2 O
) O
phase S-CONPRI
. O


The O
introduction O
of O
La2O3 S-MATE
could O
also O
refine O
the O
phase S-CONPRI
size O
and O
adjust O
morphology S-CONPRI
of O
NiTi2 O
phase S-CONPRI
, O
which O
was O
attributed O
to O
the O
increase O
of O
nucleation S-CONPRI
sites O
and O
more O
dispersed O
L O
( O
Ti-rich O
) O
.The O
temperatures S-PARA
and O
latent O
heat S-CONPRI
of O
phase S-CONPRI
transformation O
evidently O
increase O
with O
La2O3 S-MATE
addition O
due O
to O
the O
decrease O
in O
the O
Ni S-MATE
content O
and O
La S-MATE
dissolved O
into O
NiTi S-MATE
( O
B2 O
) O
phase S-CONPRI
. O


Improved O
superelasticity O
property S-CONPRI
was O
achieved O
after O
La2O3 S-MATE
addition O
owing O
to O
the O
promotion O
of O
grain S-CONPRI
order O
and O
yield B-PRO
strength E-PRO
of O
NiTi S-MATE
( O
B2 O
) O
phase S-CONPRI
and O
the O
reduction S-CONPRI
of O
resistance S-PRO
from O
NiTi2 O
phase S-CONPRI
for O
the O
interface S-CONPRI
movement O
. O


Mechanisms O
underlying O
the O
evolution S-CONPRI
of O
texture S-FEAT
and O
microstructure S-CONPRI
during O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
and O
their O
combined O
effects O
on O
the O
mechanical B-CONPRI
response E-CONPRI
of O
316L B-MATE
stainless I-MATE
steel E-MATE
are O
presented O
. O


Long O
columnar B-PRO
grains E-PRO
with O
a O
fiber S-MATE
texture O
< O
110 O
> O
|| O
build B-PARA
direction E-PARA
( O
BD O
) O
evolved O
in O
the O
SLM S-MANP
printed O
material S-MATE
. O


Fiber S-MATE
texture O
was O
stronger O
in O
the O
horizontal O
build S-PARA
compared O
to O
the O
vertical S-CONPRI
build S-PARA
. O


Use O
of O
bidirectional O
scanning B-CONPRI
strategy E-CONPRI
enforced O
epitaxial S-PRO
growth O
of O
grains S-CONPRI
across O
melt B-MATE
pools E-MATE
present O
within O
a O
single O
printed O
layer S-PARA
. O


< O
110 O
> O
|| O
BD O
texture S-FEAT
evolved O
as S-MATE
a O
consequence O
of O
maintaining O
the O
balance O
between O
epitaxy S-CONPRI
and O
growth O
of O
[ O
100 O
] O
along O
maximum O
thermal B-PARA
gradient E-PARA
. O


High O
dislocation B-PRO
density E-PRO
and O
not O
grain B-PRO
size E-PRO
effect O
of O
the O
ultra-fine O
cellular B-FEAT
structure E-FEAT
, O
imparted O
high O
strength S-PRO
to O
316L O
. O


Lower O
average S-CONPRI
Schmid O
factor O
and O
smaller O
effective O
grain B-PRO
size E-PRO
in O
the O
horizontal O
build S-PARA
by O
virtues O
of O
crystallographic O
and O
morphological O
textures O
, O
respectively O
, O
imparted O
higher O
yield B-PRO
strength E-PRO
than O
the O
vertical S-CONPRI
build S-PARA
. O


The O
horizontal O
build S-PARA
demonstrated O
higher O
strain B-MANP
hardening E-MANP
rate O
in O
the O
early O
stages O
of O
deformation S-CONPRI
compared O
to O
the O
vertical S-CONPRI
build S-PARA
due O
to O
higher O
crystallographic O
texture S-FEAT
dependent O
twinning S-CONPRI
. O


However O
, O
the O
higher O
rate O
of O
dislocation S-CONPRI
annihilation O
led S-APPL
to O
a O
continuous O
decline O
in O
the O
strain B-MANP
hardening E-MANP
rate O
of O
the O
horizontal O
build S-PARA
. O


In O
contrast O
, O
a O
stable O
strain B-MANP
hardening E-MANP
rate O
was O
maintained O
in O
the O
vertical S-CONPRI
build S-PARA
, O
which O
led S-APPL
to O
higher O
ductility S-PRO
than O
the O
horizontal O
build S-PARA
. O


In O
summary O
, O
the O
roles O
of O
non-equilibrium O
microstructure S-CONPRI
and O
texture S-FEAT
( O
crystallographic O
and O
morphological O
) O
in O
regulating O
mechanical B-CONPRI
properties E-CONPRI
elucidated O
here O
, O
can O
be S-MATE
utilized O
in O
designing O
additively B-MANP
manufactured E-MANP
structural O
components S-MACEQ
of O
316L B-MATE
stainless I-MATE
steel E-MATE
. O


Spatter S-CHAR
particles S-CONPRI
ejected O
from O
the O
melt B-MATE
pool E-MATE
after O
melting S-MANP
of O
316 O
L O
stainless B-MATE
steel E-MATE
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
( O
LPBF S-MANP
) O
, O
were O
found O
to O
contain O
morphologies S-CONPRI
not O
observed O
in O
as-atomized O
316 O
L O
powder S-MATE
. O


This O
spatter S-CHAR
consisted O
of O
large O
, O
spherical B-CONPRI
particles E-CONPRI
, O
highly O
dendritic O
surfaces S-CONPRI
, O
particles S-CONPRI
with O
caps O
of O
accreted O
liquid O
, O
and O
agglomerations O
of O
multiple O
individual O
particles S-CONPRI
fixed O
together O
by O
liquid O
ligaments O
. O


The O
focus O
of O
this O
study O
is O
on O
an O
additional O
, O
unique O
spatter S-CHAR
morphology S-CONPRI
consisting O
of O
larger O
, O
spherical B-CONPRI
particles E-CONPRI
with O
surface S-CONPRI
oxide S-MATE
spots O
exhibiting O
a O
wide O
distribution S-CONPRI
of O
surface S-CONPRI
configurations O
, O
including O
organized O
patterning O
. O


Spatter S-CHAR
particles S-CONPRI
with O
organized O
surface S-CONPRI
oxide S-MATE
patterns O
were O
characterized O
for O
surface S-CONPRI
and O
internal O
particle S-CONPRI
features O
using O
multiple O
imaging S-APPL
techniques O
. O


The O
following O
observations O
are O
made O
: O
1 O
) O
spots O
resided O
at O
the O
spatter S-CHAR
particle S-CONPRI
surface O
and O
did O
not O
significantly O
penetrate O
the O
interior O
, O
2 O
) O
the O
spot O
( O
s S-MATE
) O
were O
amorphous O
and O
rich O
in O
Silicon S-MATE
( O
Si S-MATE
) O
-Manganese O
( O
Mn S-MATE
) O
-Oxygen O
( O
O S-MATE
) O
, O
3 O
) O
a O
two-part O
Chromium S-MATE
( O
Cr S-MATE
) O
-O O
rich O
layer S-PARA
exists O
between O
the O
particle S-CONPRI
and O
spot O
, O
4 O
) O
Cr-O O
rich O
morphological O
features O
were O
present O
at O
the O
top O
surface S-CONPRI
of O
the O
spots O
, O
5 O
) O
the O
spatter S-CHAR
particle S-CONPRI
composition S-CONPRI
was O
consistent O
with O
316 O
L O
but O
appeared O
to O
decrease O
in O
Si S-MATE
content O
into O
the O
spatter S-CHAR
particle S-CONPRI
away O
from O
a O
spot O
, O
and O
6 O
) O
small O
Si-rich O
spherical B-CONPRI
particles E-CONPRI
existed O
within O
the O
spatter S-CHAR
particle S-CONPRI
interior O
. O


In O
this O
study O
, O
the O
fatigue S-PRO
properties O
of O
binder-jet O
3D-printed S-MANP
nickel-base O
superalloy O
625 O
were O
evaluated O
. O


Standard S-CONPRI
fatigue S-PRO
specimens O
were O
printed O
and O
sintered S-MANP
, O
then O
half O
of O
the O
samples S-CONPRI
were O
mechanically O
ground O
, O
while O
the O
other O
half O
were O
left O
in O
their O
as-sintered S-MANP
state O
. O


They O
were O
then O
characterized O
using O
micro-computed O
x-ray B-CHAR
tomography E-CHAR
, O
metallographic O
sample S-CONPRI
examination O
, O
and O
optical S-CHAR
and O
stylus S-MACEQ
profilometry O
for O
surface B-CONPRI
topography E-CONPRI
. O


The O
micro-computed B-CHAR
tomography E-CHAR
observations O
showed O
that O
density S-PRO
of O
the O
as-printed O
sample S-CONPRI
was O
∼50 O
% O
, O
while O
the O
sintered S-MANP
sample S-CONPRI
neared O
full O
densification S-MANP
( O
98.9 O
± O
0.3 O
% O
) O
upon O
sintering S-MANP
at O
1285 O
°C O
for O
4 O
h O
in O
a O
vacuum O
atmosphere O
. O


The O
metallographic O
examination O
showed O
equiaxed B-CONPRI
grains E-CONPRI
. O


The O
roughness S-PRO
of O
the O
as-sintered S-MANP
samples O
was O
significant O
with O
an O
RMS O
roughness S-PRO
of O
Rq O
= O
1.39 O
± O
0.20 O
μm O
as S-MATE
measured O
over O
a O
line-scan O
of O
5 O
mm S-MANP
, O
but O
this O
was O
reduced O
to O
Rq O
= O
0.47 O
± O
0.02 O
μm O
after O
mechanical S-APPL
grinding S-MANP
. O


All O
samples S-CONPRI
were O
tested O
to O
failure S-CONPRI
in O
fatigue S-PRO
, O
under O
fully-reversed O
tension-compression O
conditions O
. O


While O
the O
as-sintered S-MANP
samples O
showed O
poor O
fatigue S-PRO
properties O
compared O
to O
prior O
reports O
on O
cast S-MANP
and O
milled S-MANP
parts O
, O
the O
ground O
samples S-CONPRI
showed O
superior O
performance S-CONPRI
. O


Scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
observation O
was O
conducted O
on O
the O
fractured O
surfaces S-CONPRI
and O
showed O
that O
the O
samples S-CONPRI
underwent O
transgranular O
crack O
initiation O
, O
followed O
by O
intergranular O
crack B-CONPRI
growth E-CONPRI
and O
final O
failure S-CONPRI
. O


In O
the O
mechanically O
ground O
sample S-CONPRI
, O
hardness S-PRO
increased O
nearly O
two-fold O
up O
to O
75 O
μm O
beneath O
the O
sample S-CONPRI
’ O
s S-MATE
surface O
, O
and O
X-ray B-CHAR
diffraction E-CHAR
indicated O
an O
in-plane O
compressive B-PRO
stress E-PRO
, O
grain B-CHAR
refinement E-CHAR
, O
and O
micro-strain O
on O
the O
mechanically O
ground O
sample S-CONPRI
. O


The O
reduced O
roughness S-PRO
, O
surface B-MANP
hardening E-MANP
, O
and O
compressive B-PRO
stress E-PRO
resulted O
in O
increased O
fatigue B-PRO
life E-PRO
of O
the O
binder-jetted O
alloy S-MATE
625 O
. O


Every O
SLM-fabricated O
component S-MACEQ
typically O
possesses O
a O
process-specific O
microstructure S-CONPRI
that O
fundamentally O
differs O
from O
any O
conventionally O
fabricated S-CONPRI
specimen O
. O


This O
publication O
addresses O
the O
evaluation O
of O
microstructure-related O
influencing O
factors O
on O
the O
resistance S-PRO
against O
cavitation S-CONPRI
erosion O
. O


We O
exemplarily O
compared O
the O
findings O
to O
a O
cast S-MANP
and O
hot O
rolled O
reference O
sample S-CONPRI
. O


Due O
to O
careful O
adjustment O
of O
the O
process B-CONPRI
parameters E-CONPRI
, O
the O
overall O
cavitation S-CONPRI
erosion O
resistance S-PRO
of O
both O
SLM-processed O
and O
conventionally O
fabricated S-CONPRI
316L O
are O
very O
much O
alike O
in O
the O
investigated O
case O
. O


The O
incubation O
period O
of O
intact O
surface B-PARA
areas E-PARA
is O
improved O
by O
the O
greater O
hardness S-PRO
and O
yield B-PRO
strength E-PRO
of O
the O
SLM S-MANP
specimen O
, O
which O
is O
attributable O
to O
an O
increased O
dislocation B-PRO
density E-PRO
and O
a O
smaller O
grain B-PRO
size E-PRO
. O


Nevertheless O
, O
processing O
and O
powder B-MACEQ
feeding E-MACEQ
during O
SLM-fabrication O
occasionally O
results O
in O
microstructural B-CONPRI
defects E-CONPRI
, O
at O
which O
pronounced O
mass O
loss O
during O
cavitation S-CONPRI
was O
registered O
. O


X-ray S-CHAR
measurements O
of O
the O
residual B-PRO
stresses E-PRO
reveal O
the O
development O
of O
severe O
compressive B-PRO
stresses E-PRO
that O
emerge O
after O
a O
few O
seconds O
of O
cavitation S-CONPRI
. O


This O
compressive B-PRO
stress E-PRO
state O
delays O
the O
immediate O
propagation O
of O
SLM-inherent O
micro O
cracks O
. O


Moreover O
, O
investigations O
of O
the O
microstructure S-CONPRI
in O
combination O
with O
examination O
of O
the O
ongoing O
surface S-CONPRI
deformation S-CONPRI
highlighted O
the O
emergence O
of O
coarse O
grains S-CONPRI
that O
grew O
towards O
the O
temperature B-PARA
gradient E-PARA
. O


This O
effect O
leads O
to O
a O
temporarily O
high O
surface B-PRO
roughness E-PRO
, O
local B-CONPRI
stress I-CONPRI
concentrations E-CONPRI
and O
an O
increased O
probability S-CONPRI
of O
cavitation S-CONPRI
impacts O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
wherein O
a O
metal S-MATE
part O
is O
built O
in O
a O
layer-by-layer S-CONPRI
manner O
in O
a O
powder B-MACEQ
bed E-MACEQ
is O
a O
promising O
and O
versatile O
way O
for O
manufacturing S-MANP
components S-MACEQ
with O
complex B-CONPRI
geometry E-CONPRI
. O


However O
, O
components S-MACEQ
built O
by O
SLM S-MANP
suffer O
from O
substantial O
deformation S-CONPRI
of O
the O
part O
and O
residual B-PRO
stresses E-PRO
. O


Residual B-PRO
stresses E-PRO
arise O
due O
to O
temperature B-PARA
gradients E-PARA
inherent O
to O
the O
process S-CONPRI
and O
the O
accompanying O
deformation S-CONPRI
. O


It O
is O
well O
known O
that O
the O
SLM S-MANP
process B-CONPRI
parameters E-CONPRI
and O
the O
laser S-ENAT
scanning O
strategy O
have O
a O
substantial O
effect O
on O
the O
temperature S-PARA
transients O
of O
the O
part O
and O
henceforth O
on O
the O
degree O
of O
deformations S-CONPRI
and O
residual B-PRO
stresses E-PRO
. O


In O
order O
to O
provide O
a O
tool S-MACEQ
to O
investigate O
this O
relation O
, O
a O
semi-analytical O
thermal O
model S-CONPRI
of O
the O
SLM S-MANP
process S-CONPRI
is O
presented O
which O
determines O
the O
temperature S-PARA
evolution S-CONPRI
in O
a O
3D B-APPL
part E-APPL
by O
way O
of O
representing O
the O
moving O
laser S-ENAT
spot O
with O
a O
finite O
number O
of O
point O
heat B-CONPRI
sources E-CONPRI
. O


The O
solution S-CONPRI
of O
the O
thermal O
problem O
is O
constructed O
from O
the O
superposition O
of O
analytical B-CONPRI
solutions E-CONPRI
for O
point O
sources O
which O
are O
known O
in O
semi-infinite O
space O
and O
complimentary O
numerical/analytical O
fields O
to O
impose O
the O
boundary B-CONPRI
conditions E-CONPRI
. O


The O
unique O
property S-CONPRI
of O
the O
formulation O
is O
that O
numerical O
discretisation O
of O
the O
problem O
domain S-CONPRI
is O
decoupled O
from O
the O
steep O
gradients O
in O
the O
temperature S-PARA
field O
associated O
with O
localised O
laser B-PARA
heat E-PARA
input O
. O


This O
enables O
accurate S-CHAR
and O
numerically O
tractable O
simulation S-ENAT
of O
the O
process S-CONPRI
. O


The O
predictions S-CONPRI
of O
this O
semi-analytical O
model S-CONPRI
are O
validated O
by O
experiments O
and O
the O
exact O
solution S-CONPRI
known O
for O
a O
simple S-MANP
thermal O
problem O
. O


Simulations S-ENAT
for O
building O
a O
complete O
layer S-PARA
using O
two O
different O
scanning B-PARA
patterns E-PARA
and O
subsequently O
building O
of O
multiple O
layers O
with O
constant O
and O
rotating O
scanning B-PARA
patterns E-PARA
in O
successive O
layers O
are O
performed O
. O


The O
computational B-CONPRI
efficiency E-CONPRI
of O
the O
semi-analytical O
tool S-MACEQ
is O
assessed O
which O
demonstrates O
its O
potential O
to O
gain S-PARA
physical O
insight O
in O
the O
full O
SLM S-MANP
process S-CONPRI
with O
acceptable O
computational O
costs O
. O


This O
work O
investigated O
the O
processing O
of O
high O
nitrogen-alloyed O
austenitic B-MATE
stainless I-MATE
steels E-MATE
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
. O


Prior O
to O
L-PBF S-MANP
processing O
, O
the O
AISI O
316 O
L O
steel B-MATE
powder E-MATE
was O
nitrided S-MANP
at O
a O
temperature S-PARA
of O
675°C O
in O
a O
3 O
bar O
nitrogen S-MATE
atmosphere O
, O
thus O
achieving O
a O
N S-MATE
content O
of O
0.58 O
mass- O
% O
. O


By O
mixing S-CONPRI
nitrided O
316 O
L O
powder S-MATE
with O
untreated O
316 O
L O
powder S-MATE
, O
two O
different O
powder S-MATE
mixtures O
were O
obtained O
with O
0.065 O
mass- O
% O
and O
0.27 O
mass- O
% O
nitrogen S-MATE
, O
respectively O
. O


After O
nitriding S-MANP
and O
mixing S-CONPRI
, O
the O
powder S-MATE
was O
characterized O
in O
terms O
of O
its O
flow O
properties S-CONPRI
and O
chemical B-CONPRI
composition E-CONPRI
. O


The O
nitrided S-MANP
steel O
powder S-MATE
was O
then O
processed S-CONPRI
by O
L-PBF S-MANP
, O
and O
the O
microstructure S-CONPRI
as S-MATE
well O
as S-MATE
the O
chemical B-CONPRI
composition E-CONPRI
were O
investigated O
by O
means O
of O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
and O
carrier O
gas S-CONPRI
hot O
extraction O
. O


It O
was O
shown O
that O
nitriding S-MANP
of O
steel B-MATE
powders E-MATE
in O
an O
N2 S-MATE
atmosphere O
can O
be S-MATE
used O
to O
significantly O
increase O
the O
nitrogen S-MATE
content O
of O
the O
powder S-MATE
without O
impairing O
its O
flow O
properties S-CONPRI
. O


With O
increasing O
nitrogen S-MATE
content O
of O
the O
powder S-MATE
, O
the O
porosity S-PRO
within O
the O
L-PBF S-MANP
built O
specimens O
increased O
. O


However O
, O
both O
the O
yield B-PRO
strength E-PRO
and O
the O
tensile B-PRO
strength E-PRO
were O
greatly O
improved O
without O
a O
marked O
reduction S-CONPRI
in O
the O
elongation S-PRO
at O
fracture S-CONPRI
of O
the O
respective O
steels S-MATE
. O


This O
work O
shows O
that O
nitrogen-alloyed O
austenitic B-MATE
stainless I-MATE
steels E-MATE
can O
be S-MATE
processed O
by O
L-PBF S-MANP
and O
the O
mechanical B-CONPRI
properties E-CONPRI
can O
be S-MATE
improved O
. O


Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
has O
broad O
application O
prospects O
due O
to O
its O
high O
fabrication S-MANP
accuracy S-CHAR
and O
excellent O
performance S-CONPRI
, O
but O
the O
dynamic S-CONPRI
mechanical O
properties S-CONPRI
of O
LPBF S-MANP
components S-MACEQ
are O
relatively O
low O
due O
to O
defects S-CONPRI
of O
the O
melt S-CONPRI
track O
such O
as S-MATE
protrusions O
and O
depressions O
, O
whose O
generation O
mechanisms O
remain O
unclear O
. O


In O
this O
work O
, O
we O
investigate O
the O
correlation O
between O
the O
ex O
situ O
melt S-CONPRI
track O
properties S-CONPRI
and O
the O
in B-CONPRI
situ E-CONPRI
high-speed O
, O
high-resolution S-PARA
characterization O
. O


We O
correlate O
the O
protrusion O
at O
the O
starting O
position O
of O
the O
melt S-CONPRI
track O
with O
the O
droplet S-CONPRI
ejection O
behaviour O
and O
backward O
surging O
melt S-CONPRI
. O


We O
also O
reveal O
that O
the O
inclination B-FEAT
angles E-FEAT
of O
the O
depression O
walls O
are O
consistent O
with O
the O
ejection S-CONPRI
angles O
of O
the O
backward-ejected O
spatter S-CHAR
. O


Furthermore O
, O
we O
quantify O
the O
vapour O
recoil O
pressure S-CONPRI
by O
in B-CONPRI
situ E-CONPRI
characterization O
of O
the O
deflection O
of O
the O
typical O
forward-ejected O
spatter S-CHAR
. O


Our O
results O
clarify O
the O
intrinsic O
correlation O
of O
the O
melt S-CONPRI
track O
properties S-CONPRI
, O
which O
is O
important O
for O
the O
stable O
LPBF S-MANP
formation O
with O
few O
defects S-CONPRI
. O


Fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
3D B-MACEQ
printers E-MACEQ
have O
been O
largely O
limited O
to O
thermoplastics S-MATE
in O
the O
past O
but O
with O
new O
composite B-MATE
materials E-MATE
available O
on O
the O
market O
there O
are O
new O
possibilities O
for O
what O
these O
machines S-MACEQ
can O
produce O
. O


Using O
a O
conductive O
composite S-MATE
filament O
, O
electronic O
components S-MACEQ
can O
be S-MATE
manufactured O
but O
due O
to O
the O
filament S-MATE
’ O
s S-MATE
relatively O
poor O
electrical B-CONPRI
properties E-CONPRI
, O
the O
resulting O
traces O
are O
typically O
highly O
resistive O
. O


Selective O
electroplating S-MANP
on O
these O
parts O
is O
one O
approach O
to O
incorporate O
materials S-CONPRI
with O
high O
conductivity S-PRO
onto O
3D-printed S-MANP
structures O
. O


In O
this O
paper O
, O
non-conductive O
and O
conductive O
filaments S-MATE
printed O
in O
the O
same O
part O
are O
used O
to O
enable O
selective O
electroplating S-MANP
directly O
on O
regions O
defined O
by O
the O
conductive O
filament S-MATE
to O
create O
metallic B-MACEQ
parts E-MACEQ
through O
3D B-MANP
printing E-MANP
. O


This O
technique O
is O
demonstrated O
for O
the O
creation O
of O
multiple O
distinct O
conductive O
segments O
and O
to O
electroplate O
the O
same O
part O
with O
multiple O
metals S-MATE
to O
, O
for O
instance O
, O
allow O
a O
magnetic O
metal S-MATE
such O
as S-MATE
nickel O
and O
a O
highly O
conductive O
one O
such O
as S-MATE
copper O
to O
be S-MATE
incorporated O
in O
the O
same O
part O
. O


Following O
the O
characterization O
of O
the O
process S-CONPRI
, O
a O
representative O
3D B-MANP
printed E-MANP
electrical O
device O
, O
a O
selectively O
electroplated O
solenoid O
inductor S-APPL
with O
low O
frequency O
inductance O
and O
resistance S-PRO
of O
191 O
nH O
and O
18.7 O
mΩ O
respectively O
was O
manufactured S-CONPRI
using O
this O
technique O
. O


This O
is O
a O
five O
order O
of O
magnitude S-PARA
reduction O
in O
resistance S-PRO
over O
the O
original O
value O
of O
3 O
kΩ O
for O
the O
inductor S-APPL
before O
electroplating S-MANP
. O


Previous O
research S-CONPRI
on O
periodic O
lattice B-FEAT
structures E-FEAT
shows O
these O
structures O
are O
highly O
mechanically O
efficient O
with O
exceptionally O
high O
stiffness- O
and O
strength-to-weight O
ratios O
. O


Additive B-MANP
manufacturing E-MANP
technologies O
allow O
the O
construction S-APPL
slender O
member O
structures O
with O
complicated O
macroscale S-CONPRI
shapes O
. O


Structures O
with O
large O
numbers O
of O
geometric O
objects O
cause O
the O
conventional O
methods O
for O
manipulating O
, O
storing O
, O
and O
slicing S-CONPRI
the O
geometry S-CONPRI
of O
these O
parts O
via O
STL S-MANS
files S-MANS
to O
be S-MATE
highly O
inefficient O
. O


This O
work O
describes O
an O
alternate O
design B-CONPRI
process E-CONPRI
for O
slender O
member O
structures O
using O
efficient O
methods O
for O
manipulating O
, O
storing O
, O
and O
slicing S-CONPRI
the O
geometry S-CONPRI
of O
the O
part O
. O


These O
new O
methods O
, O
in O
particular O
a O
fast O
, O
efficient O
direct B-CONPRI
slicing E-CONPRI
method O
, O
enable O
printing O
slender O
member O
structures O
with O
over O
one O
hundred O
thousand O
struts S-MACEQ
. O


In O
this O
study O
, O
martensitic O
cold-work O
tool S-MACEQ
steel S-MATE
X65MoCrWV3-2 O
was O
processed S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
by O
varying O
the O
laser S-ENAT
scanning O
parameters S-CONPRI
and O
baseplate O
preheating S-MANP
temperatures O
. O


Porosity S-PRO
as S-MATE
well O
as S-MATE
crack O
density S-PRO
of O
the O
SLM-densified O
steel S-MATE
were O
determined O
by O
quantitative S-CONPRI
image B-CONPRI
analysis E-CONPRI
. O


The O
resulting O
microstructure S-CONPRI
and O
the O
associated O
local O
mechanical B-CONPRI
properties E-CONPRI
were O
characterized O
, O
and O
the O
hardness-tempering O
behavior O
of O
the O
SLM-densified O
steel S-MATE
was O
compared O
to O
the O
behavior O
of O
the O
conventionally O
manufactured S-CONPRI
X65MoCrWV3-2 O
steel S-MATE
in O
the O
cast S-MANP
and O
hot-formed O
condition O
. O


Regardless O
of O
the O
preheating S-MANP
temperature O
, O
SLM-densified O
X65MoCrWV3-2 O
possesses O
a O
porosity S-PRO
of O
less O
than O
0.5 O
vol.- O
% O
. O


The O
crack O
density S-PRO
was O
reduced O
significantly O
by O
means O
of O
a O
higher O
preheating S-MANP
temperature O
. O


The O
microstructure S-CONPRI
after O
SLM S-MANP
densification S-MANP
shows O
a O
fine O
, O
equiaxed O
cellular-dendritic O
subgrain O
structure S-CONPRI
, O
superimposed O
by O
lath- O
or O
needle-like O
martensite S-MATE
. O


The O
martensite S-MATE
morphology O
appeared O
to O
be S-MATE
finer O
at O
a O
lower O
preheating S-MANP
temperature O
, O
whereas O
the O
observed O
subgrain O
structure S-CONPRI
did O
not O
seem O
to O
be S-MATE
influenced O
by O
the O
preheating S-MANP
temperatures O
. O


Microhardness S-CONPRI
measurements O
indicated O
tempering S-MANP
effects O
in O
first O
solidified O
layers O
caused O
by O
the O
densification S-MANP
of O
subsequently O
deposited B-CHAR
layers E-CHAR
. O


Peak O
hardness S-PRO
after O
tempering S-MANP
of O
the O
SLM-densified O
steel S-MATE
was O
found O
to O
be S-MATE
higher O
compared O
to O
the O
maximum O
hardness S-PRO
in O
the O
X65MoCrWV3-2 O
steel S-MATE
in O
the O
cast S-MANP
condition O
. O


In O
order O
to O
ensure O
a O
reliable O
and O
repeatable O
additive B-MANP
manufacturing I-MANP
process E-MANP
, O
the O
material S-MATE
delivery O
rate O
in O
the O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
process S-CONPRI
requires O
in B-CONPRI
situ E-CONPRI
monitoring O
and O
control O
. O


This O
paper O
demonstrates O
acoustic B-CONPRI
emission E-CONPRI
( O
AE O
) O
sensing S-APPL
as S-MATE
a O
method O
of O
monitoring O
the O
flow O
of O
powder B-MACEQ
feedstock E-MACEQ
in O
a O
powder S-MATE
fed O
DED S-MANP
process O
. O


With O
minimal O
calibration S-CONPRI
, O
this O
signal O
closely O
correlates O
to O
the O
actual O
mass O
flow B-PARA
rate E-PARA
. O


This O
article O
describes O
the O
fabricated S-CONPRI
mass O
flow O
monitoring O
system O
, O
documents O
various O
conditions O
in O
which O
the O
actual O
flow B-PARA
rate E-PARA
deviates O
from O
its O
set S-APPL
value O
, O
and O
details O
situations O
that O
highlight O
the O
system O
’ O
s S-MATE
utility O
. O


The O
work O
presented O
here O
highlights O
the O
results O
obtained O
and O
illustrates O
that O
accurate S-CHAR
monitoring O
of O
powder S-MATE
flow O
in O
real-time O
regardless O
of O
environmental O
conditions O
within O
the O
build B-PARA
chamber E-PARA
is O
possible O
. O


Selective B-MANP
electron I-MANP
beam I-MANP
melting E-MANP
( O
SEBM S-MANP
) O
is O
a O
type O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
that O
involves O
multiple O
physical B-CONPRI
processes E-CONPRI
. O


Because O
of O
its O
unique O
process S-CONPRI
conditions O
compared O
to O
other O
AM B-MANP
processes E-MANP
, O
a O
detailed O
investigation O
into O
the O
molten B-CONPRI
pool E-CONPRI
behavior O
and O
dominant O
physics S-CONPRI
of O
SEBM S-MANP
is O
required O
. O


Fluid S-MATE
convection O
involves O
mass O
and O
heat B-CONPRI
transfer E-CONPRI
; O
therefore O
, O
fluid B-PRO
flow E-PRO
can O
have O
a O
profound O
effect O
on O
solidification S-CONPRI
conditions O
. O


In O
this O
study O
, O
computational O
thermal-fluid O
dynamics O
simulations S-ENAT
with O
multi-physical O
modeling S-ENAT
and O
proof-of-concept O
experiments O
were O
used O
to O
analyze O
the O
molten B-CONPRI
pool E-CONPRI
behavior O
and O
resultant O
thermal O
conditions O
related O
to O
solidification S-CONPRI
. O


The O
Marangoni O
effect O
of O
molten B-MATE
metal E-MATE
primarily O
determines O
fluid S-MATE
behavior O
and O
is O
a O
critical B-PRO
factor E-PRO
affecting O
the O
molten B-CONPRI
pool E-CONPRI
instability O
in O
SEBM S-MANP
of O
the O
Co–Cr–Mo O
alloy S-MATE
. O


The O
solidification B-CONPRI
parameters E-CONPRI
calculated O
from O
simulated O
data S-CONPRI
, O
especially O
the O
solidification B-PARA
rate E-PARA
, O
are O
sensitive O
to O
the O
local O
fluid B-PRO
flow E-PRO
at O
the O
solidification S-CONPRI
front O
. O


Combined O
with O
experimental S-CONPRI
analysis O
, O
the O
results O
presented O
herein O
indicate O
that O
active O
fluid S-MATE
convection O
at O
the O
solidification S-CONPRI
front O
increase O
the O
probability S-CONPRI
of O
new O
grain S-CONPRI
formation O
, O
which O
suppresses O
the O
epitaxial S-PRO
growth O
of O
columnar B-PRO
grains E-PRO
. O


The O
capability O
of O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
to O
manufacture S-CONPRI
multi-materials O
allows O
the O
fabrication S-MANP
of O
complex O
and O
multifunctional O
objects O
with O
heterogeneous S-CONPRI
material O
compositions O
and O
varying O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
material B-MANP
jetting I-MANP
AM I-MANP
process E-MANP
specifically O
has O
the O
capability O
to O
manufacture S-CONPRI
multi-material O
structures O
with O
both O
rigid O
and O
flexible O
material B-CONPRI
properties E-CONPRI
. O


Existing O
research S-CONPRI
has O
investigated O
the O
fatigue S-PRO
properties O
of O
3D B-MANP
printed E-MANP
multi-material O
specimens O
and O
shows O
that O
there O
is O
a O
weakness O
at O
multi-material B-CONPRI
interfaces E-CONPRI
. O


This O
paper O
seeks O
to O
, O
instead O
, O
investigate O
the O
effects O
of O
gradual O
material S-MATE
transitions O
on O
the O
fatigue B-PRO
life E-PRO
of O
3D B-MANP
printed E-MANP
multi-material O
specimens O
. O


In O
order O
to O
examine O
the O
fatigue B-PRO
life E-PRO
at O
the O
multi-material B-CONPRI
interface E-CONPRI
, O
stepwise O
gradients O
are O
compared O
against O
continuous O
gradients O
created O
through O
voxel-based O
design S-FEAT
. O


Results O
demonstrate O
the O
effects O
of O
different O
material B-CONPRI
gradient E-CONPRI
patterns O
and O
different O
material S-MATE
transition O
lengths O
on O
the O
fatigue B-PRO
life E-PRO
of O
multi-material S-CONPRI
specimens O
. O


In O
addition O
, O
the O
behavior O
of O
individual O
material B-MATE
composites E-MATE
is O
studied O
to O
confirm O
how O
gradient O
designs S-FEAT
based O
on O
different O
material S-MATE
compositions O
affect O
their O
material B-CONPRI
properties E-CONPRI
. O


The O
wire-based O
direct B-MANP
energy I-MANP
deposition E-MANP
of O
metallic S-MATE
lightweight S-CONPRI
materials O
such O
as S-MATE
titanium O
or O
aluminium B-MATE
alloys E-MATE
has O
recently O
received O
increasing O
attention O
in O
industry S-APPL
and O
academia O
. O


However O
, O
high-throughput O
deposition S-CONPRI
is O
mostly O
associated O
with O
process-limiting O
phenomena O
such O
as S-MATE
the O
development O
of O
high O
temperatures S-PARA
resulting O
in O
poor O
surface B-PARA
quality E-PARA
as S-MATE
well O
as S-MATE
coarse O
and O
unidirectional B-CONPRI
solidification E-CONPRI
microstructures S-MATE
. O


In O
this O
regard O
, O
laser S-ENAT
systems O
, O
which O
are O
already O
widely O
used O
in O
industrial S-APPL
processes O
, O
allow O
for O
a O
great O
variety O
in O
the O
controllability O
of O
energy O
inputs O
, O
thereby O
enabling O
the O
control O
of O
process S-CONPRI
temperatures O
and O
resulting O
microstructures S-MATE
. O


The O
subject O
of O
the O
current O
study O
is O
the O
detailed O
elucidation O
and O
evaluation O
of O
important O
features O
such O
as S-MATE
the O
development O
of O
temperature B-PARA
gradients E-PARA
, O
resulting O
cooling B-PARA
rates E-PARA
and O
thermal B-PARA
cycles E-PARA
for O
different O
laser B-CONPRI
beam E-CONPRI
irradiances O
. O


Significant O
heat B-PRO
accumulation E-PRO
and O
process S-CONPRI
instabilities O
as S-MATE
well O
as S-MATE
inhomogeneous O
thermal B-CONPRI
profiles E-CONPRI
along O
the O
length O
and O
height O
of O
the O
parts O
were O
observed O
at O
a O
high O
laser B-CONPRI
beam E-CONPRI
irradiance O
. O


In O
contrast O
, O
lower O
laser B-CONPRI
beam E-CONPRI
irradiance O
resulted O
in O
a O
more O
stable O
process S-CONPRI
with O
increased O
cooling B-PARA
rates E-PARA
, O
which O
favourably O
influenced O
the O
refinement O
of O
the O
solidification B-CONPRI
microstructure E-CONPRI
. O


Selective B-MANP
Laser I-MANP
Sintering E-MANP
( O
SLS S-MANP
) O
is O
a O
rapidly O
growing O
additive B-MANP
manufacturing I-MANP
process E-MANP
, O
because O
it O
has O
the O
capacity S-CONPRI
to O
build S-PARA
parts O
from O
a O
variety O
of O
materials S-CONPRI
. O


However O
, O
the O
dimensional B-CHAR
accuracy E-CHAR
of O
the O
fabricated S-CONPRI
parts O
in O
this O
process S-CONPRI
is O
dependent O
on O
the O
ability O
to O
control O
phenomena O
such O
as S-MATE
warpage O
and O
shrinkage S-CONPRI
. O


This O
research S-CONPRI
presents O
an O
optimization B-CONPRI
algorithm E-CONPRI
to O
find O
the O
best O
processing O
parameters S-CONPRI
for O
minimizing O
warpage S-CONPRI
. O


The O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
was O
used O
to O
simulate O
the O
sintering S-MANP
of O
a O
layer S-PARA
of O
polymer S-MATE
powder O
, O
and O
the O
warpage S-CONPRI
of O
the O
layer S-PARA
was O
calculated O
. O


The O
numerical O
model S-CONPRI
was O
verified O
through O
comparison O
with O
experimental S-CONPRI
results O
. O


A O
back-propagation O
neural B-CONPRI
network E-CONPRI
was O
used O
to O
formulate O
the O
mapping O
between O
the O
design S-FEAT
variables O
and O
the O
objective O
function O
. O


Results O
of O
40 O
simulation S-ENAT
cases O
with O
various O
input O
parameters S-CONPRI
such O
as S-MATE
scanning O
pattern S-CONPRI
and O
speed O
, O
laser B-PARA
power E-PARA
, O
surrounding O
temperature S-PARA
, O
and O
layer B-PARA
thickness E-PARA
were O
used O
to O
train O
and O
test O
the O
neutral O
network O
. O


Finally O
, O
The O
Genetic B-CONPRI
Algorithm E-CONPRI
was O
employed O
to O
optimize O
the O
objective O
function O
, O
and O
the O
influence O
of O
parameters S-CONPRI
on O
warpage S-CONPRI
was O
investigated O
. O


Insight O
into O
the O
performance S-CONPRI
of O
fibre-reinforced O
functionally B-FEAT
graded I-FEAT
lattices E-FEAT
( O
FGLs O
) O
from O
an O
experimental S-CONPRI
perspective O
. O


Effect O
of O
grading O
severity O
and O
build B-PARA
direction E-PARA
on O
the O
stiffness S-PRO
, O
energy B-CHAR
absorption E-CHAR
and O
structural O
response O
of O
FGLs O
. O


Categorization O
of O
FGLs O
with O
regards O
to O
ideally O
bending/stretching-dominated O
lattices S-CONPRI
, O
as S-MATE
proposed O
by O
Gibson-Ashby B-CONPRI
model E-CONPRI
. O


Semi-empirical O
analysis O
of O
the O
energy B-CHAR
absorption E-CHAR
and O
stiffness S-PRO
estimation O
for O
higher O
fibre S-MATE
volume O
fraction S-CONPRI
( O
Halpin-Tsai O
) O
. O


the O
scope O
for O
fine-tuning O
the O
properties S-CONPRI
of O
lattices S-CONPRI
to O
harness O
the O
potential O
for O
multi-functional O
AM-parts O
. O


Architectured O
structures O
, O
particularly O
functionally B-FEAT
graded I-FEAT
lattices E-FEAT
, O
are O
receiving O
much O
attention O
in O
both O
industry S-APPL
and O
academia O
as S-MATE
they O
facilitate O
the O
customization O
of O
the O
structural O
response O
and O
harness O
the O
potential O
for O
multi-functional O
applications O
. O


This O
work O
experimentally O
investigates S-CONPRI
how O
the O
severity O
of O
density S-PRO
and O
unit B-CONPRI
cell E-CONPRI
size O
grading O
as S-MATE
well O
as S-MATE
the O
building B-PARA
direction E-PARA
affects O
the O
stiffness S-PRO
, O
energy B-CHAR
absorption E-CHAR
and O
structural O
response O
of O
additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
short O
fibre-reinforced O
lattices S-CONPRI
with O
same O
relative B-PRO
density E-PRO
. O


Specimens O
composed O
of O
tessellated O
body-centred O
cubic O
( O
BCC S-CONPRI
) O
, O
Schwarz-P O
( O
SP O
) O
and O
Gyroid O
( O
GY O
) O
unit B-CONPRI
cells E-CONPRI
were O
tested O
under O
compression S-PRO
. O


Compared O
to O
the O
uniform O
lattices S-CONPRI
of O
equal O
density S-PRO
, O
it O
was O
found O
, O
that O
modest O
density S-PRO
grading O
has O
a O
positive O
and O
no O
effect O
on O
the O
total O
compressive O
stiffness S-PRO
of O
SP O
and O
BCC S-CONPRI
lattices O
, O
respectively O
. O


Unit B-CONPRI
cell E-CONPRI
size O
grading O
had O
no O
significant O
influence O
on O
the O
stiffness S-PRO
and O
revealed O
an O
elastomer-like O
performance S-CONPRI
as S-MATE
opposed O
to O
the O
density S-PRO
graded O
lattices S-CONPRI
of O
the O
same O
relative B-PRO
density E-PRO
, O
suggesting O
a O
foam-like O
behaviour O
. O


Density S-PRO
grading O
of O
bending-dominated O
unit B-CONPRI
cell E-CONPRI
lattices S-CONPRI
showcased O
better O
energy B-CHAR
absorption E-CHAR
capability O
for O
small O
displacements O
, O
whereas O
grading O
of O
the O
stretching-dominated O
counterparts O
is O
advantageous O
for O
large O
displacements O
when O
compared O
to O
the O
ungraded B-FEAT
lattice E-FEAT
. O


The O
severity O
of O
unit B-CONPRI
cell E-CONPRI
size O
graded O
lattices S-CONPRI
does O
not O
affect O
the O
energy B-CHAR
absorption E-CHAR
capability O
. O


Finally O
, O
a O
power-law O
approach O
was O
used O
to O
semi-empirically O
derive O
a O
formula O
that O
predicts O
the O
cumulative O
energy B-CHAR
absorption E-CHAR
as S-MATE
a O
function O
of O
the O
density B-PRO
gradient E-PRO
and O
relative B-PRO
density E-PRO
. O


The O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
lattice B-FEAT
structures E-FEAT
of O
various O
relative B-PRO
densities E-PRO
manufactured S-CONPRI
by O
Electron B-MANP
Beam I-MANP
Melting E-MANP
were O
analyzed O
. O


Special O
interest O
was O
given O
to O
the O
effect O
of O
surface B-PRO
roughness E-PRO
on O
their O
elastic S-PRO
behavior O
. O


Compression S-PRO
testing O
revealed O
that O
the O
important O
decrease O
in O
roughness S-PRO
caused O
by O
chemical O
etching S-MANP
results O
in O
an O
increase O
in O
relative O
stiffness S-PRO
, O
in O
comparison O
with O
an O
as-built O
structure S-CONPRI
of O
the O
same O
relative B-PRO
density E-PRO
. O


This O
study O
investigates S-CONPRI
the O
material S-MATE
and O
mechanical B-CONPRI
properties E-CONPRI
of O
both O
polyamide B-MATE
12 E-MATE
( O
PA12 S-MATE
) O
and O
reinforced S-CONPRI
glass B-MATE
bead E-MATE
PA12 O
composites S-MATE
, O
fabricated S-CONPRI
using O
a O
production S-MANP
scale O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
. O


The O
printing O
studies O
were O
carried O
out O
using O
the O
production S-MANP
scale O
, O
Multi B-MANP
Jet I-MANP
Fusion E-MANP
powder O
bed B-MANP
fusion E-MANP
process O
. O


The O
study O
demonstrated O
that O
the O
chemical O
functionality O
and O
the O
thermal B-CONPRI
properties E-CONPRI
of O
the O
printed O
PA S-CHAR
12 O
parts O
and O
the O
glass B-MATE
bead E-MATE
composite S-MATE
, O
were O
similar O
. O


Based O
on O
DSC S-CHAR
measurements O
, O
the O
melting B-PARA
temperature E-PARA
was O
184 O
°C O
and O
186 O
°C O
and O
the O
associated O
cooling S-MANP
cycle O
temperature S-PARA
was O
150 O
°C O
and O
146 O
°C O
for O
the O
composite S-MATE
and O
the O
PA12 S-MATE
respectively O
. O


The O
percentage O
crystallinity O
of O
the O
glass B-MATE
bead E-MATE
composite S-MATE
was O
24 O
% O
, O
compared O
with O
the O
31 O
% O
obtained O
for O
the O
PA12 S-MATE
only O
parts O
. O


Based O
on O
mechanical B-CHAR
tests E-CHAR
, O
the O
addition O
of O
glass B-MATE
beads E-MATE
increased O
the O
tensile S-PRO
and O
flexural O
modulus O
by O
85 O
% O
and O
36 O
% O
and O
lowered O
the O
tensile S-PRO
and O
flexural B-PRO
strength E-PRO
by O
39 O
% O
and O
15 O
% O
respectively O
. O


The O
effect O
of O
print S-MANP
orientation S-CONPRI
during O
the O
MJF S-MANP
process O
was O
evaluated O
based O
on O
porosity S-PRO
and O
mechanical S-APPL
performance O
. O


Using O
X-ray B-CHAR
micro I-CHAR
computed I-CHAR
tomography E-CHAR
, O
it O
was O
demonstrated O
that O
the O
porosity S-PRO
of O
the O
PA12 S-MATE
and O
composite S-MATE
parts O
were O
less O
than O
1 O
% O
. O


Polymer S-MATE
and O
composite S-MATE
parts O
printed O
in O
the O
ZYX O
orientation S-CONPRI
were O
found O
to O
exhibit O
both O
the O
lowest O
porosity S-PRO
and O
highest O
mechanical B-PRO
strengths E-PRO
. O


The O
spatiotemporal O
variations S-CONPRI
of O
the O
molten B-CONPRI
pool E-CONPRI
and O
deposit O
profiles S-FEAT
during O
laser B-MANP
Directed I-MANP
Energy I-MANP
Deposition E-MANP
( O
DED S-MANP
) O
largely O
affect O
the O
formation O
of O
printing O
defects S-CONPRI
and O
the O
build S-PARA
quality O
. O


Quantitative B-CHAR
assessment E-CHAR
of O
the O
dependencies O
of O
molten B-CONPRI
pool E-CONPRI
characteristics O
on O
critical O
process S-CONPRI
variables O
is O
helpful O
to O
reveal O
the O
evolution S-CONPRI
of O
the O
depositing O
tracks O
. O


To O
this O
end O
, O
a O
novel O
3D S-CONPRI
transient O
phenomenological B-CONPRI
model E-CONPRI
was O
developed O
in O
this O
work O
to O
explore O
the O
evolution S-CONPRI
of O
the O
temperature S-PARA
and O
velocity O
fields O
and O
the O
molten B-CONPRI
pool E-CONPRI
dimensions S-FEAT
for O
both O
single-track O
and O
multi-track O
laser S-ENAT
DED S-MANP
deposits O
. O


The O
computed O
deposit O
profiles S-FEAT
showed O
that O
the O
contact S-APPL
angles O
of O
the O
single-tracks O
increased O
significantly O
with O
higher O
MUL O
intensity O
. O


The O
simulation S-ENAT
results O
showed O
that O
convex O
deposit O
profiles S-FEAT
obtained O
at O
high O
MUL O
intensity O
further O
caused O
inter-track O
voids S-CONPRI
during O
multi-track O
deposition S-CONPRI
. O


To O
compare O
the O
effect O
of O
selective B-MANP
laser I-MANP
melting E-MANP
variables O
on O
different O
mechanical B-CONPRI
properties E-CONPRI
and O
compare O
the O
results O
. O


Statistical O
analysis O
was O
used O
for O
characterising O
the O
interaction O
and O
effect O
of O
parameters S-CONPRI
on O
the O
hardness S-PRO
and O
density S-PRO
. O


Describing O
the O
governing O
phenomena O
on O
melting S-MANP
pool O
rheology S-PRO
and O
its O
effect O
on O
density S-PRO
and O
hardness S-PRO
. O


In O
this O
paper O
, O
we O
printed O
Ti-6Al-4V S-MATE
SLM S-MANP
parts O
based O
on O
Taguchi O
design B-CONPRI
of I-CONPRI
experiment E-CONPRI
and O
related O
standards S-CONPRI
to O
measure O
and O
compare O
hardness S-PRO
with O
different O
mechanical B-CONPRI
properties E-CONPRI
that O
were O
obtained O
in O
our O
previous O
research S-CONPRI
such O
as S-MATE
density O
, O
strength S-PRO
, O
elongation S-PRO
, O
and O
average S-CONPRI
surface O
. O


Then O
the O
effect O
of O
process B-CONPRI
parameters E-CONPRI
comprising O
laser B-PARA
power E-PARA
, O
scan B-PARA
speed E-PARA
, O
hatch O
space O
, O
laser S-ENAT
pattern O
angle O
coupling O
, O
along O
with O
heat B-MANP
treatment E-MANP
as S-MATE
a O
post-process S-CONPRI
, O
in O
relation O
to O
hardness S-PRO
was O
analysed O
. O


Another O
contribution O
is O
related O
to O
the O
analysis O
of O
process B-CONPRI
parameters E-CONPRI
in O
relation O
to O
hardness S-PRO
and O
explaining O
them O
by O
rheological S-PRO
phenomena O
. O


The O
results O
showed O
an O
interesting O
similarity O
between O
hardness S-PRO
and O
density S-PRO
which O
is O
highly O
related O
to O
the O
formation O
of O
the O
melting S-MANP
pool O
and O
porosities S-PRO
within O
the O
process S-CONPRI
. O


The O
layerwise O
production S-MANP
paradigm O
entailed O
in O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
offers O
the O
opportunity O
to O
acquire O
a O
wide O
range S-PARA
of O
information O
about O
the O
process S-CONPRI
stability O
and O
the O
part O
quality S-CONPRI
while O
the O
part O
is O
being O
manufactured S-CONPRI
. O


Different O
authors O
pointed O
out O
that O
high-resolution S-PARA
imaging O
of O
each O
printed O
layer S-PARA
combined O
with O
image S-CONPRI
segmentation O
methods O
can O
be S-MATE
used O
to O
detect O
powder S-MATE
recoating O
errors S-CONPRI
together O
with O
surface S-CONPRI
and O
geometrical O
defects S-CONPRI
. O


The O
paper O
presents O
the O
first O
study O
aimed O
at O
characterizing O
the O
accuracy S-CHAR
of O
in-situ B-CONPRI
contour E-CONPRI
identification O
in O
LPBF S-MANP
layerwise O
images S-CONPRI
by O
means O
of O
a O
measurement S-CHAR
system O
performance S-CONPRI
characterization O
. O


Different O
active O
contours S-FEAT
segmentation O
methods O
are O
compared O
, O
and O
the O
sources O
of O
variability S-CONPRI
of O
the O
resulting O
measurements O
are O
investigated O
in O
terms O
of O
repeatability S-CONPRI
, O
part-to-part O
and O
build-to-build O
variability S-CONPRI
. O


The O
study O
also O
analyses O
and O
compares O
the O
sensitivity S-PARA
of O
in-situ S-CONPRI
measurements O
to O
different O
lighting O
conditions O
and O
laser B-ENAT
scan E-ENAT
directions O
. O


The O
results O
show O
that O
, O
by O
combining O
appropriate O
image S-CONPRI
pre-processing O
and O
segmentation O
algorithms S-CONPRI
with O
suitable O
lighting O
configurations O
, O
a O
high O
measurement S-CHAR
repeatability O
can O
be S-MATE
achieved O
, O
i.e. O
, O
a O
pure O
error S-CONPRI
that O
is O
up O
to O
one O
order O
of O
magnitude S-PARA
lower O
than O
the O
total O
measurement S-CHAR
variability O
. O


This O
performance S-CONPRI
enables O
the O
detection O
of O
major O
geometric O
deviations O
and O
it O
paves O
the O
way O
to O
the O
design S-FEAT
of O
statistical O
in-situ S-CONPRI
quality O
monitoring O
tools S-MACEQ
that O
rely O
on O
layerwise O
image S-CONPRI
segmentation O
. O


Previous O
studies O
have O
shown O
that O
3D B-MANP
printed E-MANP
composites O
exhibit O
an O
orthotropic S-MATE
nature O
with O
inherently O
lower O
interlayer O
mechanical B-CONPRI
properties E-CONPRI
. O


This O
research S-CONPRI
work O
is O
an O
attempt O
to O
improve O
the O
interlayer O
tensile B-PRO
strength E-PRO
of O
extrusion-based O
3D B-MANP
printed E-MANP
composites O
. O


Annealing S-MANP
was O
identified O
as S-MATE
a O
suitable O
post-processing S-CONPRI
method O
and O
was O
the O
focus O
of O
this O
study O
. O


Two O
distinct O
thermoplastic B-MATE
polymers E-MATE
, O
which O
are O
common O
in O
3D B-MANP
printing E-MANP
, O
were O
selected O
to O
study O
the O
enhancement O
of O
interlayer O
tensile B-PRO
strength E-PRO
of O
composites S-MATE
by O
additive B-MANP
manufacturing E-MANP
: O
a O
) O
an O
amorphous O
polyethylene S-MATE
terephthalate-glycol O
( O
PETG O
) O
, O
and O
b S-MATE
) O
a O
semi-crystalline O
poly O
( O
lactic O
acid O
) O
( O
PLA S-MATE
) O
. O


It O
was O
determined O
that O
short B-MATE
carbon I-MATE
fiber E-MATE
reinforced S-CONPRI
composites S-MATE
have O
lower O
interlayer O
tensile B-PRO
strength E-PRO
than O
the O
corresponding O
neat O
polymers S-MATE
in O
3D B-APPL
printed I-APPL
parts E-APPL
. O


This O
reduction S-CONPRI
in O
mechanical S-APPL
performance O
was O
attributable O
to O
an O
increase O
in O
melt S-CONPRI
viscosity O
and O
the O
consequential O
slower O
interlayer O
diffusion B-CONPRI
bonding E-CONPRI
. O


However O
, O
the O
reduction S-CONPRI
in O
interlayer O
tensile B-PRO
strength E-PRO
could O
be S-MATE
recovered O
by O
post-processing S-CONPRI
when O
the O
annealing S-MANP
temperature O
was O
higher O
than O
the O
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
of O
the O
amorphous O
polymer S-MATE
. O


In O
the O
case O
of O
the O
semi-crystalline O
polymer S-MATE
, O
the O
recovery O
of O
the O
interlayer O
tensile B-PRO
strength E-PRO
was O
only O
observed O
when O
the O
annealing S-MANP
temperature O
was O
higher O
than O
the O
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
but O
lower O
than O
the O
cold-crystallization O
temperature S-PARA
. O


This O
study O
utilized O
rheological S-PRO
and O
thermal B-CHAR
analysis E-CHAR
of O
3D B-MANP
printed E-MANP
composites O
to O
provide O
a O
better O
understanding O
of O
the O
interlayer B-CONPRI
strength E-CONPRI
response O
and O
, O
therefore O
, O
overcome O
a O
mechanical S-APPL
performance O
limitation O
of O
these O
materials S-CONPRI
. O


In B-CONPRI
situ E-CONPRI
high-speed O
thermal O
monitoring O
of O
melt-pool O
during O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
. O


Probabilistic O
prediction S-CONPRI
of O
pore S-PRO
formation O
based O
on O
in B-CONPRI
situ E-CONPRI
pyrometry O
monitoring O
. O


Detection O
of O
conduction-to-keyhole O
transition S-CONPRI
using O
high-speed O
pyrometry S-CHAR
. O


Creation O
of O
pores S-PRO
and O
defects S-CONPRI
during O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
can O
lead S-MATE
to O
poor O
mechanical B-CONPRI
properties E-CONPRI
and O
thus O
must O
be S-MATE
minimized O
. O


Post-build O
inspection S-CHAR
is O
required O
to O
ensure O
the O
printed O
parts O
contain O
acceptably O
low O
defect S-CONPRI
concentrations O
. O


As S-MATE
a O
potential O
solution S-CONPRI
, O
in B-CONPRI
situ E-CONPRI
process O
monitoring O
can O
be S-MATE
used O
to O
detect O
the O
creation O
of O
defects S-CONPRI
, O
characterize O
local O
material S-MATE
behavior O
and O
predict O
expected O
component S-MACEQ
properties O
. O


However O
, O
the O
precise O
relationship O
between O
pore S-PRO
creation O
and O
in B-CONPRI
situ E-CONPRI
process O
monitoring O
still O
needs O
to O
be S-MATE
understood O
. O


In O
this O
work O
, O
high-speed O
infrared S-CONPRI
diode-based O
pyrometry S-CHAR
and O
high-speed O
optical S-CHAR
imaging S-APPL
signals O
were O
used O
to O
monitor S-CONPRI
LPBF S-MANP
printing O
of O
446 O
stainless B-MATE
steel E-MATE
316 O
L O
single O
tracks O
with O
varying O
laser B-PARA
power E-PARA
and O
velocity O
. O


Results O
indicate O
an O
increase O
in O
pyrometer O
signal O
and O
melt B-PARA
pool I-PARA
dimensions E-PARA
with O
increasing O
laser B-PARA
power E-PARA
and O
decreasing O
velocity O
in O
agreement O
with O
previous O
work O
. O


Critically O
, O
pore S-PRO
defect S-CONPRI
initiation O
as S-MATE
characterized O
by O
ex O
situ O
X-ray S-CHAR
radiography S-ENAT
was O
correlated S-CONPRI
with O
in B-CONPRI
situ E-CONPRI
thermal O
monitoring O
signals O
to O
derive O
the O
probability S-CONPRI
of O
defect S-CONPRI
creation O
. O


Our O
results O
show O
that O
, O
in O
principle O
, O
a O
probabilistic O
prediction S-CONPRI
of O
pore S-PRO
formation O
can O
be S-MATE
achieved O
based O
on O
in B-CONPRI
situ E-CONPRI
high-speed O
pyrometry S-CHAR
monitoring O
of O
the O
LPBF S-MANP
melt O
pool O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
an O
attractive O
technology S-CONPRI
, O
enabling O
the O
manufacture S-CONPRI
of O
customised O
, O
complex O
metallic S-MATE
designs S-FEAT
, O
with O
minimal O
wastage O
. O


However O
, O
uptake O
by O
industry S-APPL
is O
currently O
impeded O
by O
several O
technical O
barriers O
, O
such O
as S-MATE
the O
control O
of O
residual B-PRO
stress E-PRO
, O
which O
have O
a O
detrimental O
effect O
on O
the O
manufacturability S-CONPRI
and O
integrity S-CONPRI
of O
a O
component S-MACEQ
. O


Indirectly O
, O
these O
impose O
severe O
design S-FEAT
restrictions O
and O
reduce O
the O
reliability S-CHAR
of O
components S-MACEQ
, O
driving O
up O
costs O
. O


This O
paper O
uses O
a O
thermo-mechanical B-CONPRI
model E-CONPRI
to O
better O
understand O
the O
effect O
of O
laser B-ENAT
scan E-ENAT
strategy O
on O
the O
generation O
of O
residual B-PRO
stress E-PRO
in O
SLM S-MANP
. O


A O
complex O
interaction O
between O
transient S-CONPRI
thermal O
history O
and O
the O
build-up O
of O
residual B-PRO
stress E-PRO
has O
been O
observed O
in O
the O
two O
laser B-ENAT
scan E-ENAT
strategies O
investigated O
. O


The O
temperature B-CONPRI
gradient I-CONPRI
mechanism E-CONPRI
was O
discovered O
for O
the O
creation O
of O
residual B-PRO
stress E-PRO
. O


The O
greatest O
stress S-PRO
component S-MACEQ
was O
found O
to O
develop O
parallel O
to O
the O
scan O
vectors O
, O
creating O
an O
anisotropic S-PRO
stress O
distribution S-CONPRI
in O
the O
part O
. O


The O
stress B-PRO
distribution E-PRO
varied O
between O
laser B-ENAT
scan E-ENAT
strategies O
and O
the O
cause O
has O
been O
determined O
by O
observing O
the O
thermal O
history O
during O
scanning S-CONPRI
. O


Using O
this O
, O
proposals O
are O
suggested O
for O
designing O
laser B-ENAT
scan E-ENAT
strategies O
used O
in O
SLM S-MANP
. O


Near-net O
shape O
metal S-MATE
parts O
of O
great O
geometrical B-FEAT
complexity E-FEAT
are O
fabricated S-CONPRI
by O
the O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
( O
L-PBF S-MANP
) O
technology S-CONPRI
directly O
from O
a O
CAD B-ENAT
model E-ENAT
. O


Therefore O
, O
parts O
can O
be S-MATE
lightweight O
, O
less O
expensive O
in O
terms O
of O
material S-MATE
use O
and O
with O
shapes O
that O
may O
be S-MATE
impossible O
to O
produce O
by O
conventional O
technology S-CONPRI
. O


The O
fatigue S-PRO
behavior O
of O
L-PBF S-MANP
part O
in O
as-built O
condition O
is O
negatively O
affected O
by O
poor O
surface B-PARA
quality E-PARA
. O


Surface B-MANP
finishing E-MANP
after O
fabrication S-MANP
may O
be S-MATE
either O
unacceptably O
costly O
or O
impossible O
because O
the O
surface S-CONPRI
is O
inaccessible O
. O


Fatigue S-PRO
performance O
can O
be S-MATE
further O
reduced O
by O
the O
notch S-FEAT
effect O
due O
to O
local O
geometrical O
variations S-CONPRI
. O


Among O
the O
Al-alloys O
, O
AlSi10Mg S-MATE
is O
readily O
processed S-CONPRI
with O
L-PBF S-MANP
and O
it O
is O
of O
interest O
for O
different O
industrial S-APPL
sectors.In O
this O
contribution O
two O
aspects O
, O
that O
is O
: O
i O
) O
the O
directional O
smooth O
fatigue S-PRO
behavior O
of O
as-built O
AlSi10Mg S-MATE
, O
and O
ii O
) O
the O
notch S-FEAT
fatigue S-PRO
behavior O
with O
as-built O
surfaces S-CONPRI
are O
investigated O
. O


Eight O
sets O
of O
un-notched O
and O
notched O
miniature O
specimens O
of O
AlSi10Mg S-MATE
were O
produced O
as S-MATE
a O
single O
batch O
by O
L-PBF S-MANP
and O
tested O
in O
the O
as-build O
state O
under O
cyclic O
plane O
bending S-MANP
loading O
. O


The O
smooth O
fatigue S-PRO
behavior O
was O
determined O
as S-MATE
very O
sensitive O
to O
applied O
stress S-PRO
direction O
with O
respect O
to O
the O
build B-PARA
direction E-PARA
. O


The O
directional O
nature O
of O
the O
fatigue S-PRO
behavior O
was O
confirmed O
by O
notch S-FEAT
fatigue S-PRO
data S-CONPRI
. O


Therefore O
, O
four O
notch S-FEAT
fatigue S-PRO
factors O
that O
depend O
on O
the O
PBF S-MANP
technology O
were O
introduced O
and O
determined O
. O


The O
fatigue S-PRO
behavior O
of O
L-PBF S-MANP
AlSi10Mg S-MATE
obtained O
here O
was O
compared O
satisfactorily O
against O
recent O
data S-CONPRI
obtained O
with O
standard S-CONPRI
specimen O
geometries S-CONPRI
and O
test O
methods O
. O


The O
present O
methodology S-CONPRI
using O
mini O
specimens O
under O
cyclic O
bending S-MANP
efficiently O
determines O
the O
fatigue S-PRO
response O
of O
L-PBF S-MANP
metals O
. O


Interlayer O
bonds O
pose O
regions O
of O
weakness O
in O
structures O
produced O
via O
melt B-MANP
extrusion E-MANP
based O
polymer B-MANP
additive I-MANP
manufacturing E-MANP
. O


Bond B-CONPRI
strength E-CONPRI
was O
assessed O
both O
between O
layers O
and O
within O
layers O
as S-MATE
a O
function O
of O
print S-MANP
parameters S-CONPRI
by O
performing O
tensile B-CHAR
tests E-CHAR
on O
ABS S-MATE
coupons O
printed O
in O
two O
orientations S-CONPRI
. O


Print S-MANP
parameters S-CONPRI
considered O
were O
extruder S-MACEQ
temperature O
, O
print S-MANP
speed O
, O
and O
layer B-PARA
height E-PARA
. O


An O
IR S-CHAR
camera S-MACEQ
was O
used O
to O
track O
thermal O
history O
of O
interlayer O
bond O
lines O
during O
the O
printing B-MANP
process E-MANP
. O


Contact S-APPL
length O
between O
roads O
was O
measured O
from O
mesostructure O
optical S-CHAR
micrographs O
. O


Print S-MANP
speed O
was O
found O
to O
have O
a O
large O
impact S-CONPRI
on O
tensile B-PRO
strength E-PRO
with O
high O
speeds O
generally O
yielding O
lower O
strength S-PRO
. O


A O
plateau O
in O
tensile B-PRO
strength E-PRO
of O
22 O
MPa S-CONPRI
was O
observed O
for O
a O
normalized O
contact S-APPL
length O
greater O
than O
0.6 O
independent O
of O
print S-MANP
orientation S-CONPRI
. O


Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
is O
a O
popular O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
that O
has O
shown O
promise O
in O
fabricating S-MANP
novel O
components S-MACEQ
that O
can O
be S-MATE
utilized O
for O
a O
wide O
variety O
of O
applications O
. O


However O
, O
one O
of O
the O
main O
drawbacks O
of O
LPBF S-MANP
is O
that O
it O
produces O
large O
thermal B-PARA
gradients E-PARA
and O
fast O
cooling B-PARA
rates E-PARA
during O
the O
solidification S-CONPRI
of O
each O
layer S-PARA
, O
which O
can O
lead S-MATE
to O
large O
levels O
of O
residual S-CONPRI
stress/distortion O
, O
sometimes O
resulting O
in O
build S-PARA
failure/rejection O
. O


In O
the O
present O
work O
, O
several O
experimental S-CONPRI
techniques O
( O
x-ray B-CHAR
diffraction E-CHAR
, O
hole B-MANP
drilling E-MANP
, O
contour S-FEAT
method O
, O
and O
laser S-ENAT
line O
profilometry O
) O
were O
utilized O
to O
establish O
the O
effect O
of O
LPBF S-MANP
process O
parameters S-CONPRI
( O
scan B-PARA
speed E-PARA
, O
laser B-PARA
power E-PARA
, O
build B-PARA
height E-PARA
, O
build S-PARA
plan O
area S-PARA
, O
and O
substrate S-MATE
condition O
) O
on O
residual B-PRO
stress E-PRO
evolution S-CONPRI
and O
distortion S-CONPRI
. O


X-ray B-CHAR
diffraction E-CHAR
and O
hole-drilling O
measurements O
were O
performed O
on O
the O
surfaces S-CONPRI
of O
the O
LPBF S-MANP
deposits O
and O
substrates O
, O
while O
bulk O
residual B-PRO
stresses E-PRO
were O
measured O
using O
the O
contour S-FEAT
method O
. O


In O
addition O
, O
a O
laser S-ENAT
line O
profilometer S-MACEQ
was O
used O
to O
measure O
the O
distortion S-CONPRI
after O
fabrication S-MANP
. O


The O
results O
obtained O
by O
the O
non-destructive O
and O
destructive O
measurement S-CHAR
techniques O
suggested O
that O
process B-CONPRI
parameters E-CONPRI
greatly O
influence O
the O
development O
of O
residual B-PRO
stress E-PRO
and O
distortion S-CONPRI
throughout O
the O
LPBF S-MANP
deposit O
and O
the O
substrate S-MATE
. O


Furthermore O
, O
the O
experimental S-CONPRI
results O
in O
this O
work O
provide O
a O
valuable O
foundation O
for O
future O
modeling S-ENAT
and O
simulation S-ENAT
of O
the O
evolution S-CONPRI
of O
residual B-PRO
stress E-PRO
and O
distortion S-CONPRI
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
a O
method O
of O
laser B-MANP
powder I-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
currently O
being O
pursued O
in O
numerous O
industries S-APPL
, O
including O
space O
launch O
and O
space O
flight O
. O


In O
this O
study O
we O
performed O
an O
extensive O
parameter S-CONPRI
development O
investigation O
to O
better O
understand O
the O
effect O
of O
laser S-ENAT
parameters O
on O
surface B-PRO
roughness E-PRO
, O
density S-PRO
, O
and O
porosity S-PRO
of O
SLM S-MANP
Inconel B-MATE
718 E-MATE
parts O
. O


Laser B-PARA
energy I-PARA
density E-PARA
was O
varied O
via O
laser S-ENAT
focus O
shift O
, O
and O
the O
effects O
on O
porosity S-PRO
in O
both O
as-printed O
and O
post-HIP O
treated O
states O
were O
analyzed O
. O


Tensile B-CHAR
testing E-CHAR
was O
also O
conducted O
to O
investigate O
the O
effect O
of O
processing O
conditions O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
SLM S-MANP
718 O
. O


It O
was O
found O
that O
for O
these O
laser S-ENAT
parameters O
, O
while O
the O
material S-MATE
met O
ultimate B-PRO
tensile I-PRO
strength E-PRO
and O
yield B-PRO
strength E-PRO
requirements O
per O
AMS O
5662 O
, O
the O
strain-to-failure O
was O
reduced O
with O
negative O
focus O
shift O
due O
to O
increases O
in O
porosity S-PRO
levels O
. O


It O
was O
also O
found O
that O
while O
correlations O
were O
observed O
between O
surface B-PRO
roughness E-PRO
, O
density S-PRO
, O
and O
porosity S-PRO
within O
the O
laser S-ENAT
focus O
shift O
range S-PARA
investigated O
, O
porosity S-PRO
measurement S-CHAR
appears O
to O
be S-MATE
the O
clearest O
indicator O
of O
build S-PARA
quality O
for O
AM S-MANP
processed O
718 O
. O


Managing O
the O
dimensional B-CHAR
accuracy E-CHAR
of O
parts O
produced O
by O
the O
Electron B-MANP
Beam I-MANP
Melting E-MANP
process O
is O
a O
challenge O
. O


For O
small O
dimensions S-FEAT
, O
as S-MATE
in O
lattice B-FEAT
structures E-FEAT
( O
strut B-PARA
diameters E-PARA
) O
, O
accuracy S-CHAR
becomes O
even O
more O
important O
and O
geometric O
quality S-CONPRI
is O
linked O
to O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
dimensional O
quality S-CONPRI
of O
parts O
produced O
by O
EBM S-MANP
can O
be S-MATE
influenced O
by O
many O
process B-CONPRI
parameters E-CONPRI
. O


Simulating O
the O
process S-CONPRI
can O
help O
the O
machine S-MACEQ
user O
to O
choose O
the O
best O
process B-CONPRI
parameters E-CONPRI
and O
improve O
build S-PARA
dimensional O
accuracy S-CHAR
. O


The O
work O
presented O
here O
is O
based O
on O
a O
method O
for O
linking O
process B-CONPRI
parameters E-CONPRI
with O
beam S-MACEQ
parameters O
. O


Once O
linked O
, O
both O
sets O
of O
parameters S-CONPRI
are O
then O
integrated O
into O
a O
full O
simulation S-ENAT
of O
the O
process S-CONPRI
in O
order O
to O
make O
trajectory O
optimization S-CONPRI
possible O
. O


First O
, O
this O
paper O
explains O
how O
the O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
described O
in O
the O
literature O
can O
be S-MATE
improved O
to O
simulate O
the O
multilayer O
EBM S-MANP
process O
. O


It O
then O
describes O
how O
this O
simulation S-ENAT
is O
used O
to O
develop O
a O
method O
to O
characterize O
the O
machine S-MACEQ
beam S-MACEQ
and O
determine O
the O
link O
between O
the O
focus O
current O
and O
the O
beam B-PARA
diameter E-PARA
. O


Finally O
, O
it O
shows O
how O
this O
simulation S-ENAT
can O
be S-MATE
applied O
to O
a O
built O
shape O
( O
vertical S-CONPRI
strut S-MACEQ
) O
hence O
demonstrating O
improved O
accuracy S-CHAR
of O
the O
produced O
part O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
a O
rapidly O
expanding O
framework S-CONPRI
of O
production S-MANP
technologies O
evolving O
in O
different O
directions O
, O
following O
the O
needs O
of O
different O
industries S-APPL
. O


Among O
powder B-MANP
bed I-MANP
fusion E-MANP
technologies O
, O
one O
of O
the O
main O
branches O
of O
AM S-MANP
, O
selective B-MANP
laser I-MANP
sintering E-MANP
( O
SLS S-MANP
) O
is O
the O
second O
oldest O
one O
. O


In O
the O
last O
few O
years O
, O
a O
direct O
rival O
has O
emerged O
: O
multi B-MANP
jet I-MANP
fusion E-MANP
( O
MJF S-MANP
) O
. O


The O
purpose O
of O
this O
work O
is O
to O
compare O
these O
processes S-CONPRI
throughout O
a O
systematic O
analysis O
of O
powder S-MATE
and O
final O
parts O
made O
of O
commercially O
available O
polyamide B-MATE
12 E-MATE
( O
PA12 S-MATE
) O
. O


Differences O
have O
been O
spotted O
both O
on O
the O
molecular O
and O
powder S-MATE
scale O
, O
with O
end O
capping O
of O
the O
MJF S-MANP
feedstock S-MATE
together O
with O
different O
thermal B-CONPRI
properties E-CONPRI
of O
the O
new O
and O
recycled B-CONPRI
materials E-CONPRI
. O


On O
the O
other O
hand O
, O
flowing O
properties S-CONPRI
are O
similar O
among O
the O
two O
virgin O
and O
recycled S-CONPRI
powders S-MATE
, O
with O
only O
a O
significant O
change O
in O
the O
fraction S-CONPRI
of O
fines O
for O
SLS S-MANP
material S-MATE
. O


The O
parts O
produced O
through O
SLS S-MANP
exhibit O
higher O
Young O
's O
modulus O
but O
lower O
elongation S-PRO
at O
break O
and O
ultimate B-PRO
tensile I-PRO
strength E-PRO
if O
compared O
to O
the O
ones O
obtained O
using O
MJF S-MANP
. O


Also O
Charpy O
impact S-CONPRI
strength O
according O
to O
ISO S-MANS
179 O
has O
been O
tested O
, O
confirming O
the O
literature O
data S-CONPRI
for O
SLS S-MANP
, O
but O
also O
showing O
higher O
strength S-PRO
in O
the O
out-of-plane O
direction O
for O
un-notched O
specimens O
coming O
from O
MJF S-MANP
. O


Finally O
, O
the O
evaluation O
of O
advanced O
area S-PARA
roughness O
parameters S-CONPRI
such O
as S-MATE
surface O
roughness S-PRO
, O
skewness O
and O
kurtosis O
according O
to O
ISO S-MANS
25178 O
allows O
the O
ascertainment O
of O
subtle O
differences O
arising O
in O
parts O
with O
different O
positioning O
on O
the O
build B-MACEQ
platform E-MACEQ
, O
possibly O
due O
to O
the O
inks O
employed O
in O
the O
MJF S-MANP
process O
. O


An O
effective O
process B-CONPRI
prediction E-CONPRI
model S-CONPRI
was O
developed O
for O
additive B-MANP
manufacturing E-MANP
. O


High O
entropy O
alloy S-MATE
was O
used O
to O
test O
the O
model S-CONPRI
. O


The O
model S-CONPRI
effectively O
predicts O
energy B-PARA
density E-PARA
for O
processing O
metallic B-MATE
materials E-MATE
. O


Surface B-FEAT
structure E-FEAT
of O
power S-PARA
and O
powder B-MACEQ
bed E-MACEQ
can O
improve O
laser S-ENAT
absorptivity O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
a O
laser-based B-MANP
additive I-MANP
manufacturing E-MANP
technique O
that O
can O
fabricate S-MANP
parts O
with O
complex B-CONPRI
geometries E-CONPRI
and O
sufficient O
mechanical B-CONPRI
properties E-CONPRI
. O


However O
, O
the O
optimal O
SLM S-MANP
process S-CONPRI
windows O
of O
metallic B-MATE
materials E-MATE
are O
difficult O
to O
predict O
, O
especially O
when O
exploring O
new O
metallic B-MATE
materials E-MATE
. O


In O
this O
paper O
, O
a O
universal O
and O
simplified O
model S-CONPRI
has O
been O
proposed O
to O
predict O
the O
energy B-PARA
density E-PARA
suitable O
for O
SLM S-MANP
of O
a O
variety O
of O
metallic B-MATE
materials E-MATE
including O
Ti S-MATE
and O
Ti B-MATE
alloys E-MATE
, O
Al B-MATE
alloy E-MATE
, O
Ni-based O
superalloy O
and O
steel S-MATE
, O
on O
the O
basis O
of O
the O
relationship O
between O
energy B-CHAR
absorption E-CHAR
and O
consumption O
during O
SLM S-MANP
. O


Several O
important O
but O
easily O
overlooked O
factors O
, O
including O
the O
surface B-FEAT
structure E-FEAT
of O
metallic B-MATE
powder E-MATE
, O
porosity S-PRO
of O
powder B-MACEQ
bed E-MACEQ
, O
vaporization O
and O
heat S-CONPRI
loss O
, O
were O
considered O
to O
improve O
the O
accuracy S-CHAR
of O
the O
model S-CONPRI
. O


Results O
show O
that O
, O
to O
achieve O
near-full O
density S-PRO
parts O
, O
the O
energy B-CHAR
absorption E-CHAR
( O
Qa O
) O
by O
the O
local O
powder B-MACEQ
bed E-MACEQ
should O
be S-MATE
approximately O
3–8 O
times O
greater O
than O
the O
energy O
consumption O
( O
Qc O
) O
, O
and O
this O
finding O
applies O
to O
all O
materials S-CONPRI
investigated O
. O


The O
value O
of O
Qa/Qc O
highly O
depends O
on O
material B-CONPRI
properties E-CONPRI
, O
particularly O
laser S-ENAT
absorptivity O
, O
latent O
heat S-CONPRI
of O
melting S-MANP
and O
specific B-PRO
heat E-PRO
capacity S-CONPRI
. O


Experiments O
on O
high-entropy O
alloy S-MATE
( O
CrMnFeCoNi O
) O
and O
Hastelloy S-MATE
X O
alloy S-MATE
, O
new O
metallic B-MATE
materials E-MATE
for O
SLM S-MANP
, O
have O
been O
further O
conducted O
to O
verify O
the O
model S-CONPRI
. O


Results O
confirm O
that O
the O
model S-CONPRI
can O
predict O
suitable O
laser B-PARA
energy I-PARA
densities E-PARA
needed O
for O
processing O
the O
various O
metallic B-MATE
materials E-MATE
without O
tedious O
trial B-CONPRI
and I-CONPRI
error E-CONPRI
experiments O
. O


Therefore O
, O
medical S-APPL
additive B-MANP
manufacturing E-MANP
techniques O
are O
developed O
for O
fabrication S-MANP
of O
such O
implants S-APPL
, O
but O
currently O
do O
not O
achieve O
the O
required O
printing O
resolution S-PARA
. O


This O
is O
caused O
by O
intensive O
droplet S-CONPRI
spreading O
of O
the O
initially O
liquid O
silicone B-MATE
rubber E-MATE
on O
the O
printing O
substrate S-MATE
. O


While O
empirical S-CONPRI
optimization O
approaches O
for O
the O
droplet S-CONPRI
spreading O
are O
intensive O
in O
cost O
and O
time O
, O
we O
develop O
a O
mathematical S-CONPRI
optimization O
approach O
to O
calculate O
the O
optimal O
printing O
parameters S-CONPRI
for O
minimal O
droplet S-CONPRI
spreading O
. O


Since O
the O
viscosity S-PRO
profile S-FEAT
of O
thermal O
curing S-MANP
silicone O
rubber S-MATE
is O
the O
main O
reason O
for O
the O
droplet S-CONPRI
spreading O
, O
we O
implemented O
a O
rheology S-PRO
model S-CONPRI
for O
calculation O
of O
the O
optimal O
heat B-CONPRI
curing E-CONPRI
parameters O
. O


A O
Dual-Arrhenius O
equation O
was O
used O
to O
correlate O
the O
temperature-time-profile O
of O
the O
curing S-MANP
process O
with O
the O
curing-related O
viscosity S-PRO
rise O
and O
the O
temperature-related O
viscosity S-PRO
fall O
of O
the O
liquid O
silicone B-MATE
rubber E-MATE
. O


Two O
commonly O
used O
silicone B-MATE
rubbers E-MATE
were O
characterized O
with O
a O
rheometer O
at O
different O
isothermal S-CONPRI
and O
anisothermal O
curing S-MANP
profiles O
. O


High O
correlation O
between O
the O
calculated O
and O
the O
measured O
viscosity S-PRO
profiles S-FEAT
were O
observed O
, O
giving O
the O
ability O
to O
optimize O
the O
curing S-MANP
process O
parameters S-CONPRI
to O
the O
rheological S-PRO
behaviour O
of O
the O
used O
silicone B-MATE
rubber E-MATE
. O


Powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
is O
ideally O
suited O
to O
build S-PARA
complex O
and O
near-net-shaped O
metallic B-MACEQ
structures E-MACEQ
such O
as S-MATE
conformal O
cooling B-MACEQ
channel E-MACEQ
networks O
in O
injection O
molds S-MACEQ
. O


However O
, O
warpage S-CONPRI
occurring O
due O
to O
the O
residual B-PRO
stresses E-PRO
inherent O
to O
this O
process S-CONPRI
can O
lead S-MATE
to O
shape O
deviation O
in O
the O
internal O
channels O
and O
needs O
to O
be S-MATE
minimized O
. O


In O
this O
research S-CONPRI
, O
a O
novel O
analytical O
model S-CONPRI
based O
on O
the O
Euler-Bernoulli O
beam S-MACEQ
bending O
theory O
was O
developed O
to O
estimate O
the O
residual S-CONPRI
stress-induced O
deformation S-CONPRI
of O
internal O
channels O
printed O
horizontally O
using O
PBF S-MANP
. O


The O
proposed O
approach O
is O
thus O
expected O
to O
be S-MATE
a O
useful O
tool S-MACEQ
to O
generate O
design-for-AM O
guidelines O
for O
the O
additive B-MANP
manufacturing E-MANP
of O
overhangs S-PARA
and O
internal O
channels O
. O


Risk-averse O
areas S-PARA
such O
as S-MATE
the O
medical S-APPL
, O
aerospace S-APPL
and O
energy O
sectors O
have O
been O
somewhat O
slow O
towards O
accepting O
and O
applying O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
in O
many O
of O
their O
value O
chains O
. O


This O
is O
partly O
because O
there O
are O
still O
significant O
uncertainties O
concerning O
the O
quality S-CONPRI
of O
AM S-MANP
builds.This O
paper O
introduces O
a O
machine B-ENAT
learning I-ENAT
algorithm E-ENAT
for O
the O
automatic O
detection O
of O
faults O
in O
AM S-MANP
products O
. O


The O
approach O
is O
semi-supervised O
in O
that O
, O
during O
training O
, O
it O
is O
able O
to O
use O
data S-CONPRI
from O
both O
builds S-CHAR
where O
the O
resulting O
components S-MACEQ
were O
certified O
and O
builds S-CHAR
where O
the O
quality S-CONPRI
of O
the O
resulting O
components S-MACEQ
is O
unknown O
. O


This O
makes O
the O
approach O
cost O
efficient O
, O
particularly O
in O
scenarios O
where O
part O
certification O
is O
costly O
and O
time O
consuming.The O
study O
specifically O
analyses O
Laser S-ENAT
Powder-Bed O
Fusion S-CONPRI
( O
L-PBF S-MANP
) O
builds S-CHAR
. O


Key O
features O
are O
extracted S-CONPRI
from O
large O
sets O
of O
photodiode O
data S-CONPRI
, O
obtained O
during O
the O
building O
of O
49 O
tensile B-CHAR
test E-CHAR
bars O
. O


Ultimate B-PRO
tensile I-PRO
strength E-PRO
( O
UTS S-PRO
) O
tests O
were O
then O
used O
to O
categorise O
each O
bar O
as S-MATE
‘ O
faulty O
’ O
or O
‘ O
acceptable O
’ O
. O


As S-MATE
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
adoption O
grows O
, O
the O
demand O
for O
improved O
quality S-CONPRI
output O
product O
is O
increasing O
. O


This O
is O
evident O
in O
the O
desire O
for O
both O
increased O
repeatability S-CONPRI
and O
higher O
strength S-PRO
and O
ductility S-PRO
in O
Selective B-MANP
Laser E-MANP
Sintered O
( O
SLS® O
) O
Polymer S-MATE
parts O
. O


One O
approach O
to O
expanding O
the O
performance S-CONPRI
envelope O
for O
polymers S-MATE
in O
this O
domain S-CONPRI
is O
through O
high O
temperature S-PARA
manufacturing B-MANP
processes E-MANP
, O
supporting O
the O
use O
of O
polymers S-MATE
with O
increased O
mechanical B-PRO
strength E-PRO
, O
lighter O
weight S-PARA
, O
and O
a O
favorable O
ability O
to O
sterilize O
for O
medical B-APPL
applications E-APPL
. O


Early O
candidate O
materials S-CONPRI
that O
exhibit O
higher O
melting S-MANP
and O
glass B-CONPRI
transition I-CONPRI
temperatures E-CONPRI
include O
the O
Poly O
Ether O
Ether O
Ketone O
( O
PEEK S-MATE
) O
and O
Polyaryletherketone O
( O
PAEK O
) O
family O
of O
materials S-CONPRI
. O


This O
paper O
describes O
the O
design S-FEAT
of O
a O
laboratory S-CONPRI
SLS® O
machine S-MACEQ
for O
operation O
with O
these O
and O
other O
similar O
materials S-CONPRI
, O
emphasizing O
its O
thermal O
and O
operational O
design S-FEAT
features O
. O


Data S-CONPRI
is O
also O
provided O
from O
initial O
testing S-CHAR
of O
key O
subsystems O
during O
assembly S-MANP
and O
prior O
to O
full O
system O
operation O
. O


Because O
this O
machine S-MACEQ
is O
intended O
to O
explore O
processing O
new O
materials S-CONPRI
, O
it O
also O
incorporates O
features O
for O
improving O
the O
data S-CONPRI
collection O
, O
and O
associated O
feedback S-PARA
control O
for O
improved O
repeatability S-CONPRI
, O
and O
ultimately O
defect S-CONPRI
detection O
and O
mitigation O
during O
the O
Additive B-MANP
Manufacturing E-MANP
. O


One O
of O
the O
major O
challenges O
with O
the O
powder B-MANP
bed I-MANP
fusion I-MANP
process E-MANP
( O
PBF S-MANP
) O
and O
formation O
of O
bulk O
metallic B-MATE
glass E-MATE
( O
BMG O
) O
is O
the O
development O
of O
process B-CONPRI
parameters E-CONPRI
for O
a O
stable O
process S-CONPRI
and O
a O
defect-free O
component S-MACEQ
. O


The O
focus O
of O
this O
study O
is O
to O
predict O
formation O
of O
a O
crystalline O
phase S-CONPRI
in O
the O
glass B-MANP
forming E-MANP
alloy S-MATE
AMZ4 O
during O
PBF S-MANP
. O


The O
approach O
combines O
a O
thermal O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
for O
prediction S-CONPRI
of O
the O
temperature S-PARA
field O
and O
a O
phase B-CONPRI
model E-CONPRI
for O
prediction S-CONPRI
of O
crystallization S-CONPRI
and O
devitrification S-MANP
. O


The O
challenge O
to O
simulate O
the O
complexity S-CONPRI
of O
the O
heat B-CONPRI
source E-CONPRI
has O
been O
addressed O
by O
utilizing O
temporal O
reduction S-CONPRI
in O
a O
layer-by-layer B-CONPRI
fashion E-CONPRI
by O
a O
simplified O
heat B-CONPRI
source E-CONPRI
model O
. O


The O
heat B-CONPRI
source E-CONPRI
model O
considers O
the O
laser B-PARA
power E-PARA
, O
penetration B-PARA
depth E-PARA
and O
hatch B-PARA
spacing E-PARA
and O
is O
represented O
by O
a O
volumetric O
heat S-CONPRI
density S-PRO
equation O
in O
one O
dimension S-FEAT
. O


The O
phase B-CONPRI
model E-CONPRI
is O
developed O
and O
calibrated S-CONPRI
to O
DSC S-CHAR
measurements O
at O
varying O
heating S-MANP
rates O
. O


It O
can O
predict O
the O
formation O
of O
crystalline O
phase S-CONPRI
during O
the O
non-isothermal O
process S-CONPRI
. O


Results O
indicate O
that O
a O
critical O
location O
for O
devitrification S-MANP
is O
located O
a O
few O
layers O
beneath O
the O
top O
surface S-CONPRI
. O


Nickel B-MATE
aluminium E-MATE
bronze S-MATE
( O
NAB S-MATE
) O
is O
widely O
used O
in O
naval B-APPL
applications E-APPL
due O
to O
its O
combination O
of O
excellent O
corrosion B-CONPRI
resistance E-CONPRI
in O
sea O
water O
applications O
and O
medium O
strength S-PRO
levels O
. O


These O
alloys S-MATE
have O
complex O
microstructures S-MATE
of O
α O
and O
β O
solid B-MATE
solution E-MATE
phases O
together O
with O
different O
forms O
of O
the O
intermetallic S-MATE
κ O
phase S-CONPRI
. O


In O
this O
work O
, O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
of O
Cu-9.8Al-5.2Ni-4.6Fe-0.3 O
Mn S-MATE
( O
wt O
. O


% O
) O
NAB S-MATE
powder O
was O
optimised O
to O
produce O
dense O
NAB S-MATE
specimens O
. O


The O
as-built O
specimens O
consisted O
of O
martensitic O
microstructures S-MATE
. O


Through O
the O
application O
of O
various O
heat B-MANP
treatment E-MANP
conditions O
, O
α O
+ O
κ O
microstructures S-MATE
typical O
of O
traditional O
NAB S-MATE
alloys S-MATE
, O
were O
obtained O
and O
the O
mechanical S-APPL
and O
electrochemical S-CONPRI
properties O
were O
characterized O
. O


A O
heat B-MANP
treatment E-MANP
at O
700 O
°C O
for O
1 O
h O
on O
the O
as-built O
structure S-CONPRI
yielded O
NAB S-MATE
specimens O
with O
superior O
corrosion S-CONPRI
performance O
and O
mechanical B-CONPRI
properties E-CONPRI
than O
conventional O
wrought S-CONPRI
or O
cast S-MANP
NAB O
. O


This O
work O
shows O
that O
SLM S-MANP
of O
NAB S-MATE
alloys S-MATE
is O
possible O
and O
the O
components S-MACEQ
obtained O
exhibit O
properties S-CONPRI
at O
least O
as S-MATE
good O
as S-MATE
their O
cast S-MANP
or O
wrought S-CONPRI
counterparts O
. O


This O
opens O
up O
the O
possibility O
of O
using O
NAB S-MATE
components S-MACEQ
fabricated O
by O
SLM S-MANP
in O
engineering S-APPL
applications O
. O


Two O
batches O
of O
pre-alloyed O
Hastelloy-X O
powder S-MATE
with O
different O
Si S-MATE
, O
Mn S-MATE
and O
C S-MATE
contents O
were O
used O
to O
produce O
specimens O
by O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
. O


Two O
major O
reasons O
that O
control O
crack O
formation O
and O
propagation O
were O
considered O
: O
( O
i O
) O
internal O
strain S-PRO
accumulation O
due O
to O
the O
thermal B-PARA
cycling E-PARA
that O
is O
characteristic O
to O
SLM S-MANP
processing O
; O
( O
ii O
) O
crack O
formation O
and O
propagation O
during O
solidification S-CONPRI
. O


This O
phenomenon O
, O
known O
as S-MATE
hot O
tearing O
, O
is O
frequently O
found O
in O
conventional O
casting S-MANP
and O
is O
dependent O
on O
chemical B-CONPRI
composition E-CONPRI
. O


Using O
thermodynamic O
software S-CONPRI
simulation S-ENAT
, O
the O
temperature S-PARA
vs O
fraction S-CONPRI
of O
solid O
curves O
was O
used O
to O
determine O
hot O
tearing O
sensitivity S-PARA
as S-MATE
a O
function O
of O
Si S-MATE
, O
Mn S-MATE
and O
C S-MATE
content O
. O


It O
was O
found O
that O
low O
Si S-MATE
and O
C S-MATE
contents O
help O
in O
avoiding O
crack O
formation O
whereas O
cracking S-CONPRI
propensity O
was O
relatively O
independent O
of O
Mn S-MATE
concentration O
. O


Hence O
, O
the O
cracking S-CONPRI
mechanism O
during O
SLM S-MANP
is O
believed O
to O
be S-MATE
as S-MATE
follows O
: O
crack O
initiation O
is O
mainly O
induced O
during O
solidification S-CONPRI
and O
is O
dependent O
on O
the O
content O
of O
minor O
alloying B-MATE
elements E-MATE
such O
as S-MATE
Si O
and O
C S-MATE
, O
whereas O
crack B-CONPRI
propagation E-CONPRI
predominantly O
occurs O
during O
thermal B-PARA
cycling E-PARA
. O


If O
microstructures S-MATE
free O
of O
micro-cracks S-CONPRI
after O
solidification S-CONPRI
can O
be S-MATE
generated O
with O
optimised O
SLM S-MANP
parameters S-CONPRI
, O
these O
manufactured S-CONPRI
parts O
can O
sustain O
the O
internal O
strain S-PRO
level O
and O
, O
thus O
, O
crack O
formation O
and O
propagation O
can O
be S-MATE
avoided O
. O


Laser S-ENAT
spatter O
is O
coarser O
and O
more O
spherical S-CONPRI
than O
virgin B-MATE
powder E-MATE
. O


Condensate O
condenses O
on O
the O
surfaces S-CONPRI
of O
laser S-ENAT
spatter O
particles S-CONPRI
. O


Nano-oxide O
islands O
present O
on O
laser S-ENAT
spatter O
coalesce O
to O
form O
large O
oxide S-MATE
islands O
. O


Condensate O
is O
created O
from O
a O
large O
amount O
of O
superheat S-CONPRI
in O
the O
melt B-MATE
pool E-MATE
. O


Heat-affected O
powder S-MATE
contains O
more O
delta O
ferrite S-MATE
than O
virgin B-MATE
powder E-MATE
. O


The O
selective B-MANP
laser I-MANP
melting I-MANP
process E-MANP
, O
commonly O
referred O
to O
as S-MATE
laser O
powder-bed O
fusion S-CONPRI
( O
L-PBF S-MANP
) O
, O
is O
an O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
technique O
that O
uses O
a O
laser S-ENAT
to O
fuse S-MANP
successive O
layers O
of O
powder S-MATE
into O
near O
fully B-PARA
dense E-PARA
components S-MACEQ
. O


Due O
to O
the O
large O
energy O
input O
from O
the O
laser S-ENAT
during O
processing O
, O
vaporization O
causes O
instabilities O
in O
the O
melt B-MATE
pool E-MATE
leading O
to O
the O
formation O
of O
laser S-ENAT
spatter O
and O
condensate O
, O
collectively O
known O
as S-MATE
heat-affected O
powder S-MATE
. O


Since O
heat-affected O
powder S-MATE
settles O
into O
the O
powder B-MACEQ
bed E-MACEQ
, O
the O
properties S-CONPRI
of O
the O
unconsolidated O
powder S-MATE
may O
be S-MATE
altered O
compromising O
its O
reusability O
. O


In O
this O
study O
, O
characterization O
of O
304 O
L O
heat-affected O
powder S-MATE
was O
performed O
through O
particle S-CONPRI
size O
and O
shape O
distribution S-CONPRI
measurements O
, O
energy-dispersive O
spectroscopy S-CONPRI
, O
Raman B-CHAR
spectroscopy E-CHAR
, O
inert B-CONPRI
gas I-CONPRI
fusion E-CONPRI
, O
metallography S-CONPRI
, O
and O
x-ray B-CHAR
diffraction E-CHAR
. O


The O
results O
show O
morphological O
, O
chemical O
, O
and O
microstructural S-CONPRI
differences O
between O
the O
virgin B-MATE
powder E-MATE
and O
heat-affected O
powder S-MATE
formed O
during O
processing O
which O
aid O
in O
the O
understanding O
of O
laser S-ENAT
spatter O
and O
condensate O
that O
form O
in O
the O
L-PBF S-MANP
process O
. O


The O
impact S-CONPRI
of O
a O
rigid O
rod S-MACEQ
with O
a O
flat O
specimen O
fabricated S-CONPRI
of O
3D-printed S-MANP
materials O
was O
analyzed O
. O


An O
experimental S-CONPRI
setup O
has O
been O
designed S-FEAT
in O
order O
to O
capture O
the O
motion O
of O
the O
rod S-MACEQ
during O
the O
impact S-CONPRI
using O
a O
high-speed O
camera S-MACEQ
. O


Image S-CONPRI
processing O
algorithms S-CONPRI
were O
developed O
to O
estimate O
the O
velocity O
before O
and O
after O
the O
impact S-CONPRI
as S-MATE
well O
as S-MATE
the O
coefficient O
of O
restitution O
. O


Also O
, O
permanent O
deformations S-CONPRI
after O
the O
impact S-CONPRI
were O
scanned O
with O
an O
optical S-CHAR
profilometer O
. O


In O
this O
work O
, O
a O
theoretical S-CONPRI
formulation O
for O
the O
contact S-APPL
force O
during O
the O
impact S-CONPRI
is O
proposed O
. O


The O
impact S-CONPRI
was O
divided O
into O
two O
phases O
, O
compression S-PRO
and O
restitution O
, O
in O
which O
materials S-CONPRI
considered O
elastic–plastic O
in O
the O
first O
and O
fully O
elastic S-PRO
in O
the O
second O
one O
. O


Results O
show O
a O
good O
correlation O
between O
the O
proposed O
formulation O
for O
the O
contact S-APPL
force O
and O
the O
behavior O
of O
materials S-CONPRI
. O


The O
objective O
of O
this O
work O
is O
to O
detect O
in B-CONPRI
situ E-CONPRI
the O
occurrence O
of O
lack-of-fusion O
defects S-CONPRI
in O
titanium B-MATE
alloy E-MATE
( O
Ti-6Al-4 B-MATE
V E-MATE
) O
parts O
made O
using O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
. O


We O
use O
data S-CONPRI
from O
two O
types O
of O
in-process O
sensors S-MACEQ
, O
namely O
, O
a O
spectrometer O
and O
an O
optical S-CHAR
camera S-MACEQ
which O
are O
integrated O
into O
an O
Optomec O
MR-7 O
DED B-MACEQ
machine E-MACEQ
. O


Both O
sensors S-MACEQ
are O
focused O
on O
capturing O
the O
dynamic S-CONPRI
phenomena O
around O
the O
melt B-MATE
pool E-MATE
region O
. O


To O
detect O
lack-of-fusion O
defects S-CONPRI
, O
we O
fuse S-MANP
( O
combine O
) O
the O
data S-CONPRI
from O
the O
in-process O
sensors S-MACEQ
invoking O
the O
concept O
of O
Kronecker O
product O
of O
graphs O
. O


Subsequently O
, O
we O
use O
the O
features O
derived O
from O
the O
graph O
Kronecker O
product O
as S-MATE
inputs O
to O
a O
machine B-ENAT
learning I-ENAT
algorithm E-ENAT
to O
predict O
the O
severity O
( O
class O
or O
level O
) O
of O
average S-CONPRI
length O
of O
lack-of-fusion O
defects S-CONPRI
within O
a O
layer S-PARA
, O
which O
is O
obtained O
from O
offline O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
of O
the O
test O
parts O
. O


Accordingly O
, O
this O
work O
demonstrates O
the O
use O
of O
heterogeneous S-CONPRI
in-process O
sensing S-APPL
and O
online O
data B-CONPRI
analytics E-CONPRI
for O
in B-CONPRI
situ E-CONPRI
detection O
of O
defects S-CONPRI
in O
DED S-MANP
metal O
AM B-MANP
process E-MANP
. O


An O
extrusion-based O
additive B-MANP
manufacturing I-MANP
process E-MANP
, O
called O
the O
Ceramic S-MATE
On-Demand O
Extrusion S-MANP
( O
CODE O
) O
process S-CONPRI
, O
for O
producing O
three-dimensional S-CONPRI
ceramic S-MATE
components O
with O
near O
theoretical S-CONPRI
density S-PRO
is O
introduced O
in O
this O
paper O
. O


In O
this O
process S-CONPRI
, O
an O
aqueous O
paste O
of O
ceramic S-MATE
particles O
with O
a O
very O
low O
binder S-MATE
content O
( O
< O
1 O
vol O
% O
) O
is O
extruded S-MANP
through O
a O
moving O
nozzle S-MACEQ
at O
room O
temperature S-PARA
. O


After O
a O
layer S-PARA
is O
deposited O
, O
it O
is O
surrounded O
by O
oil S-MATE
( O
to O
a O
level O
just O
below O
the O
top O
surface S-CONPRI
of O
most O
recent O
layer S-PARA
) O
to O
preclude O
non-uniform O
evaporation S-CONPRI
from O
the O
sides O
. O


Infrared S-CONPRI
radiation O
is O
then O
used O
to O
partially O
, O
and O
uniformly O
, O
dry O
the O
just-deposited O
layer S-PARA
so O
that O
the O
yield B-PRO
stress E-PRO
of O
the O
paste O
increases O
and O
the O
part O
maintains O
its O
shape O
. O


The O
same O
procedure O
is O
repeated O
for O
every O
layer S-PARA
until O
part O
fabrication S-MANP
is O
completed O
. O


Several O
sample S-CONPRI
parts O
for O
various O
applications O
were O
produced O
using O
this O
process S-CONPRI
and O
their O
properties S-CONPRI
were O
obtained O
. O


The O
results O
indicate O
that O
the O
proposed O
method O
enables O
fabrication S-MANP
of O
large O
, O
dense O
ceramic S-MATE
parts O
with O
complex B-CONPRI
geometries E-CONPRI
. O


This O
manuscript S-CONPRI
expands O
the O
existing O
framework S-CONPRI
for O
single-material O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
printed O
dissolvable O
supports S-APPL
to O
Inconel B-MATE
718 E-MATE
( O
IN718 S-MATE
) O
. O


Prior O
work O
with O
stainless B-MATE
steel E-MATE
leveraged O
a O
sensitization O
heat B-MANP
treatment E-MANP
using O
sodium S-MATE
hexacyanoferrate O
to O
precipitate S-MATE
chromium B-MATE
carbides E-MATE
over O
the O
top O
100 O
μm O
to O
200 O
μm O
of O
material S-MATE
, O
decreasing O
the O
corrosion B-CONPRI
resistance E-CONPRI
within O
this O
top O
layer S-PARA
relative O
to O
the O
bulk O
material S-MATE
. O


The O
component S-MACEQ
is O
then O
etched O
at O
an O
anodic O
potential O
with O
a O
high O
selectivity O
toward O
the O
“ O
sensitized O
” O
surface S-CONPRI
over O
the O
base O
component S-MACEQ
material O
. O


This O
creates O
an O
etching S-MANP
process O
that O
self-terminates O
once O
the O
sensitized O
layer S-PARA
is O
removed O
. O


Additionally O
, O
the O
surface B-PRO
roughness E-PRO
of O
the O
component S-MACEQ
is O
often O
improved O
once O
the O
sensitized O
region O
is O
removed O
. O


In O
this O
work O
, O
two O
different O
sensitization O
heat S-CONPRI
schedules O
were O
investigated O
: O
750 O
°C O
for O
24 O
h O
to O
understand O
the O
impact S-CONPRI
of O
preferential O
chromium B-MATE
carbide E-MATE
precipitation O
and O
1050 O
°C O
for O
8 O
h O
to O
understand O
the O
impact S-CONPRI
of O
primary O
carbide S-MATE
precipitations O
. O


At O
1050 O
°C O
, O
the O
formation O
of O
a O
protective O
oxide S-MATE
scale O
inhibits O
material S-MATE
removal O
in O
an O
electrolyte S-APPL
of O
0.48 O
M O
HNO3 O
. O


At O
750 O
°C O
, O
70 O
μm O
of O
material S-MATE
is O
removed O
after O
quenching S-MANP
to O
avoid O
the O
precipitation S-CONPRI
of O
corrosion S-CONPRI
resistant O
oxides S-MATE
. O


This O
manuscript B-CONPRI
investigates E-CONPRI
the O
effect O
of O
targeting O
different O
carbide S-MATE
precipitation O
regimes O
and O
oxides S-MATE
to O
produce O
an O
ideal O
microstructure S-CONPRI
for O
dissolvable O
supports S-APPL
post-sensitization O
. O


To O
demonstrate O
the O
utility O
of O
the O
process S-CONPRI
, O
the O
supports S-APPL
from O
a O
mock O
IN718 S-MATE
turbine O
blade O
were O
removed O
using O
this O
process S-CONPRI
. O


One O
of O
the O
next O
avenues O
for O
Additive B-MANP
Manufacturing E-MANP
to O
develop O
is O
that O
of O
multi-material B-CONPRI
deposition E-CONPRI
in O
order O
to O
add O
functionality O
to O
the O
already O
complex B-CONPRI
geometries E-CONPRI
that O
are O
capable O
of O
being O
manufactured S-CONPRI
. O


The O
purpose O
of O
this O
study O
was O
to O
investigate O
the O
effects O
of O
solid O
surface B-PRO
tensions E-PRO
, O
σsg O
− O
σsl O
, O
on O
the O
quality S-CONPRI
of O
printed O
lines O
, O
using O
30–40 O
nm O
silver S-MATE
nanofluid O
ink S-MATE
. O


The O
solid O
surface B-PRO
tensions E-PRO
of O
silver B-MATE
ink E-MATE
on O
glass S-MATE
and O
polytetrofluoroethylene O
( O
PTFE S-MATE
) O
substrates O
were O
determined O
theoretically O
, O
knowing O
characteristics O
of O
droplet S-CONPRI
. O


Meanwhile O
, O
a O
Dimatix O
printer S-MACEQ
with O
nozzles S-MACEQ
of O
size O
of O
21.5 O
μm O
was O
used O
to O
print S-MANP
conductive O
lines O
on O
smooth O
glass S-MATE
and O
PTFE S-MATE
substrates O
. O


The O
printed O
lines O
on O
glass S-MATE
were O
observed O
to O
be S-MATE
continuous O
with O
high O
quality S-CONPRI
of O
triple O
line O
, O
which O
was O
attributed O
to O
the O
high O
solid O
surface B-PRO
tensions E-PRO
of O
silver S-MATE
nanofluid O
ink S-MATE
on O
glass S-MATE
substrates O
. O


The O
solid O
surface B-PRO
tensions E-PRO
of O
silver S-MATE
nanofluid O
ink S-MATE
were O
relatively O
low O
on O
PTFE S-MATE
, O
as S-MATE
results O
the O
printed O
lines O
were O
discontinuous O
. O


The O
solid O
surface B-PRO
tensions E-PRO
were O
introduced O
as S-MATE
a O
reliable O
criterion O
to O
predict O
the O
printability S-PARA
of O
nanofluids O
. O


The O
distribution S-CONPRI
of O
silver S-MATE
nanoparticles S-CONPRI
and O
layering O
phenomenon O
in O
silver S-MATE
nanofluid O
triple O
region O
on O
glass S-MATE
substrate O
was O
clearly O
observed O
, O
using O
environmental O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
ESEM O
) O
for O
the O
first O
time O
. O


In O
addition O
to O
disjoining O
pressure S-CONPRI
, O
the O
size O
of O
droplet S-CONPRI
and O
affinity O
of O
nanofluid O
for O
substrate S-MATE
were O
observed O
to O
have O
important O
influences O
on O
spreading O
of O
nanoparticles S-CONPRI
in O
triple O
region O
. O


Manufacturers O
struggle O
to O
produce O
low-cost O
, O
robust O
and O
intricate O
components S-MACEQ
in O
small B-PARA
batches E-PARA
. O


Additive S-MATE
processes O
like O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
inexpensively O
generate O
such O
complex B-CONPRI
geometries E-CONPRI
, O
but O
potential O
defects S-CONPRI
may O
limit S-CONPRI
these O
components S-MACEQ
’ O
viability O
in O
critical O
applications O
. O


We O
present O
a O
high-accuracy O
, O
high-throughput O
and O
low-cost O
approach O
to O
automated O
non-destructive B-CHAR
testing E-CHAR
( O
NDT S-CONPRI
) O
for O
FFF S-MANP
interlayer O
delamination S-CONPRI
. O


This O
Artificially O
Intelligent O
( O
AI O
) O
approach O
utilizes O
Flash S-MATE
Thermography O
( O
FT O
) O
data S-CONPRI
processed O
with O
Thermographic O
Signal O
Reconstruction S-CONPRI
( O
TSR O
) O
. O


A O
Deep O
Neural B-CONPRI
Network E-CONPRI
( O
DNN O
) O
attains O
95.4 O
% O
per-pixel O
accuracy S-CHAR
when O
differentiating O
four O
delamination S-CONPRI
severities O
5 O
mm S-MANP
below O
the O
surface S-CONPRI
in O
PolyLactic B-MATE
Acid E-MATE
( O
PLA S-MATE
) O
widgets O
, O
and O
98.6 O
% O
accuracy S-CHAR
in O
differentiating O
acceptable O
from O
unacceptable O
states O
for O
the O
same O
components S-MACEQ
. O


Automation S-CONPRI
supports O
time- O
and O
cost-efficient O
inspection S-CHAR
for O
delamination B-CONPRI
defects E-CONPRI
in O
100 O
% O
of O
widgets O
, O
supporting O
FFF S-MANP
's O
use O
in O
critical O
and O
lot-size O
one O
applications O
. O


To O
identify O
the O
dominant O
contributing O
factor O
in O
the O
anomalously O
high O
strength S-PRO
of O
Al–Si-based O
alloys S-MATE
fabricated O
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
, O
microstructural S-CONPRI
characteristics O
of O
a O
SLM-built O
Al–10Si–0.3 O
Mg B-MATE
alloy E-MATE
( O
AlSi10Mg S-MATE
) O
and O
their O
changes O
upon O
annealing S-MANP
at O
elevated O
temperatures S-PARA
were O
investigated O
. O


The O
as-built O
AlSi10Mg B-MATE
alloy E-MATE
exhibits O
a O
peculiar O
microstructure S-CONPRI
comprising O
of O
a O
number O
of O
columnar O
α-Al O
( O
fcc S-CONPRI
) O
phase S-CONPRI
with O
concentrated O
Si S-MATE
in O
solution S-CONPRI
. O


At O
elevated O
temperatures S-PARA
, O
a O
number O
of O
Si S-MATE
phase S-CONPRI
( O
diamond S-MATE
structure O
) O
precipitates S-MATE
consumed O
the O
solute O
Si S-MATE
in O
the O
columnar O
α-Al O
phase S-CONPRI
, O
but O
the O
microstructure S-CONPRI
of O
the O
α-Al O
matrix O
changed O
slightly O
. O


After O
annealing S-MANP
at O
elevated O
temperatures S-PARA
, O
the O
tensile B-PRO
strength E-PRO
of O
the O
as-built O
AlSi10Mg B-MATE
alloy E-MATE
substantially O
decreased O
accompanied O
by O
a O
reduction S-CONPRI
in O
the O
strain B-MANP
hardening E-MANP
rate O
. O


The O
supersaturated O
solid B-MATE
solution E-MATE
of O
the O
α-Al O
phase S-CONPRI
containing O
numerous O
nano-sized O
particles S-CONPRI
enhanced O
the O
strain B-MANP
hardening E-MANP
, O
resulting O
in O
the O
anomalous O
strengthening S-MANP
of O
the O
SLM-built O
AlSi10Mg B-MATE
alloy E-MATE
. O


The O
microstructural S-CONPRI
features O
were O
formed O
due O
to O
rapid B-MANP
solidification E-MANP
at O
an O
extremely O
high O
cooling B-PARA
rate E-PARA
in O
the O
SLM S-MANP
process S-CONPRI
, O
which O
provides O
important O
insights O
into O
controlling O
the O
strength S-PRO
of O
Al–Si-based O
alloys S-MATE
fabricated O
by O
SLM S-MANP
. O


The O
parametric O
design S-FEAT
of O
graded O
porous B-FEAT
scaffold E-FEAT
based O
on O
TMPS O
surfaces S-CONPRI
was O
realized O
. O


The O
mechanical S-APPL
performance O
of O
SLM S-MANP
scaffolds S-FEAT
was O
altered O
by O
tuning O
graded O
structures O
. O


Graded O
structure S-CONPRI
played O
a O
key O
role O
in O
influencing O
deformation S-CONPRI
behavior O
of O
scaffolds S-FEAT
. O


Optimized O
heat B-MANP
treatment E-MANP
conditions O
improved O
mechanical B-CONPRI
properties E-CONPRI
of O
SLM S-MANP
scaffolds S-FEAT
. O


The O
rapid O
development O
of O
additive B-MANP
manufacturing E-MANP
technology O
makes O
it O
possible O
to O
fabricate S-MANP
parts O
with O
complex O
inner O
structures O
, O
especially O
for O
functionally B-CONPRI
graded E-CONPRI
scaffolds O
( O
FGS O
) O
in O
the O
field O
of O
bone S-BIOP
tissue O
engineering S-APPL
. O


The O
parametric O
design S-FEAT
of O
FGS O
is O
of O
great O
significance O
to O
the O
in-depth O
study O
of O
the O
effects O
of O
structural O
parameters S-CONPRI
of O
porous S-PRO
bone B-BIOP
scaffolds E-BIOP
on O
their O
mechanical B-CONPRI
properties E-CONPRI
and O
rehabilitation O
of O
patients O
. O


The O
present O
study O
proposed O
a O
parametric O
design S-FEAT
method O
for O
FGS O
using O
a O
triply B-CONPRI
periodic I-CONPRI
minimal I-CONPRI
surface E-CONPRI
( O
TPMS O
) O
. O


Uniform O
and O
functionally B-CONPRI
graded E-CONPRI
samples O
were O
fabricated S-CONPRI
using O
selective B-MANP
laser I-MANP
melting E-MANP
of O
Ti-6Al-4V B-MATE
powder E-MATE
. O


The O
FGSs O
successfully O
realized O
flexible O
control O
of O
structural O
parameters S-CONPRI
and O
showed O
comparable O
mechanical B-CONPRI
properties E-CONPRI
and O
permeability S-PRO
with O
natural O
bone S-BIOP
tissue O
. O


Furthermore O
, O
heat B-MANP
treatment E-MANP
was O
verified O
to O
be S-MATE
an O
effective O
way O
to O
improve O
the O
ductility S-PRO
of O
TPMS-FGS O
. O


The O
deformation S-CONPRI
process O
and O
principal O
strain S-PRO
distribution S-CONPRI
of O
the O
FGSs O
were O
elucidated O
using O
a O
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
method O
. O


The O
FGSs O
proposed O
in O
the O
present O
study O
showed O
great O
potential O
in O
orthopedic O
implant S-APPL
or O
bone-substituting O
biomaterials S-MATE
. O


Processing O
of O
Ti6Al4V S-MATE
and O
SS410 O
as S-MATE
a O
bimetallic O
joint S-CONPRI
using O
laser-based O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
system O
. O


Niobium S-MATE
( O
Nb S-MATE
) O
was O
used O
as S-MATE
a O
bond O
layer S-PARA
between O
the O
two O
immiscible O
base-materials O
. O


The O
bimetallic O
joint S-CONPRI
showed O
improved O
bond B-CONPRI
strength E-CONPRI
, O
both O
under O
compression S-PRO
and O
shear O
loading O
. O


Proof-of-concept O
part O
demonstrated O
the O
application O
of O
the O
bimetallic O
joint S-CONPRI
by O
welding S-MANP
base B-MATE
metals E-MATE
, O
end-to-end O
, O
to O
the O
joint S-CONPRI
. O


Bimetallic O
structures O
provide O
a O
unique O
solution S-CONPRI
to O
achieve O
site-specific O
functionalities O
and O
enhanced-property O
capabilities O
in O
engineering S-APPL
systems O
but O
suffer O
from O
bonding S-CONPRI
compatibility O
issues O
. O


Materials S-CONPRI
such O
as S-MATE
titanium O
alloy S-MATE
( O
Ti6Al4 O
V S-MATE
) O
and O
stainless B-MATE
steel E-MATE
( O
SS410 O
) O
have O
distinct O
attractive O
properties S-CONPRI
but O
are O
impossible O
to O
reliably O
weld S-FEAT
together O
using O
traditional O
processes S-CONPRI
. O


To O
this O
end O
, O
a O
laser-based O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
system O
was O
used O
to O
fabricate S-MANP
bimetallic O
joint S-CONPRI
of O
Ti6Al4 O
V S-MATE
and O
SS410 O
keeping O
niobium S-MATE
( O
Nb S-MATE
) O
as S-MATE
a O
diffusion S-CONPRI
barrier B-APPL
layer E-APPL
. O


Both O
shear O
and O
compression B-CHAR
tests E-CHAR
were O
used O
to O
characterize O
the O
joint S-CONPRI
’ O
s S-MATE
strength O
, O
and O
compared O
with O
the O
base O
materials S-CONPRI
. O


The O
bimetallic-joint O
shear O
and O
compressive O
yield B-PRO
strengths E-PRO
were O
419 O
± O
3 O
MPa S-CONPRI
( O
∼114 O
% O
of O
SS410 O
) O
and O
560 O
± O
4 O
MPa S-CONPRI
( O
∼169 O
% O
of O
SS410 O
) O
, O
respectively O
. O


The O
increase O
in O
interfacial O
shear O
and O
compressive O
yield B-PRO
strengths E-PRO
over O
the O
base O
material S-MATE
indicates O
strong O
metallurgical B-CONPRI
bonding E-CONPRI
between O
the O
base O
materials S-CONPRI
and O
the O
interlayer O
, O
Nb S-MATE
. O


Proof-of-concept O
part O
for O
direct O
application O
of O
the O
bimetallic O
joint S-CONPRI
was O
demonstrated O
by O
welding S-MANP
base B-MATE
metals E-MATE
, O
end-to-end O
, O
to O
the O
joint S-CONPRI
. O


The O
interfacial O
microstructures S-MATE
, O
elemental O
diffusion S-CONPRI
and O
phases O
, O
including O
failure B-PRO
modes E-PRO
were O
examined O
using O
secondary O
and O
backscatter O
electron O
imaging S-APPL
, O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
and O
energy B-CHAR
dispersive I-CHAR
spectroscopy E-CHAR
( O
EDS S-CHAR
) O
. O


The O
bimetallic-joint O
interfaces O
were O
free O
from O
brittle S-PRO
intermetallic O
compounds O
such O
as S-MATE
FeTi O
and O
Fe2Ti O
that O
are O
generally O
responsible O
for O
weak O
bond B-CONPRI
strength E-CONPRI
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
widely O
gaining O
popularity O
as S-MATE
an O
alternative O
manufacturing S-MANP
technique O
for O
complex O
and O
customized O
parts O
. O


SLM S-MANP
is O
a O
near B-MANP
net I-MANP
shape E-MANP
process O
with O
minimal O
post B-CONPRI
processing E-CONPRI
machining S-MANP
required O
dependent O
upon O
final O
application O
. O


The O
fact O
that O
SLM S-MANP
produces O
little O
waste O
and O
enables O
more O
optimal O
designs S-FEAT
also O
raises O
opportunities O
for O
environmental O
advantages O
. O


The O
use O
of O
aluminium S-MATE
( O
Al S-MATE
) O
alloys S-MATE
in O
SLM S-MANP
is O
still O
quite O
limited O
due O
to O
difficulties O
in O
processing O
that O
result O
in O
parts O
with O
high O
degrees B-CHAR
of I-CHAR
porosity E-CHAR
. O


However O
, O
Al B-MATE
alloys E-MATE
are O
favoured O
in O
many O
high-end O
applications O
for O
their O
exceptional O
strength S-PRO
and O
stiffness B-PRO
to I-PRO
weight I-PRO
ratio E-PRO
meaning O
that O
they O
are O
extensively O
used O
in O
the O
automotive S-APPL
and O
aerospace B-APPL
industries E-APPL
. O


This O
study O
investigates S-CONPRI
the O
windows O
of O
parameters S-CONPRI
required O
to O
produce O
high O
density S-PRO
parts O
from O
AlSi10Mg B-MATE
alloy E-MATE
using O
selective B-MANP
laser I-MANP
melting E-MANP
. O


Modelling S-ENAT
the O
thermal O
behaviour O
of O
the O
melt B-MATE
pool E-MATE
produced O
in O
Laser S-ENAT
Powder-Bed O
Fusion S-CONPRI
( O
L-PBF S-MANP
) O
processes S-CONPRI
is O
not O
an O
easy O
task O
, O
as S-MATE
many O
complex O
non-linear O
thermal O
phenomena O
are O
involved O
. O


An O
effective O
way O
to O
make O
the O
computational O
cost O
of O
these O
analyses O
affordable O
is O
to O
model S-CONPRI
powder O
and O
molten B-MATE
metal E-MATE
as S-MATE
continuous O
media O
, O
wherein O
all O
the O
heat B-CONPRI
transfer E-CONPRI
modes O
occurring O
in O
the O
liquid O
are O
simulated O
as S-MATE
lumped O
fictitious O
heat B-CONPRI
conduction E-CONPRI
. O


The O
augmentation O
factor O
used O
to O
enhance O
the O
thermal B-PRO
conductivity E-PRO
of O
the O
liquid O
is O
in O
general O
calibrated S-CONPRI
through O
experimental S-CONPRI
estimations O
of O
the O
melt B-MATE
pool E-MATE
size O
. O


The O
present O
work O
is O
aimed O
at O
devising O
a O
robust O
method O
for O
the O
calibration S-CONPRI
of O
such O
thermal O
parameters S-CONPRI
. O


A O
specific O
point O
of O
novelty O
of O
the O
present O
paper O
is O
the O
definition O
of O
a O
method O
to O
correlate O
surface B-PRO
roughness E-PRO
and O
numerically O
predicted B-CONPRI
melting E-CONPRI
pool O
size O
. O


This O
strategy O
is O
able O
to O
predict O
with O
good O
accuracy S-CHAR
the O
roughness S-PRO
of O
L-PBF S-MANP
fabricated S-CONPRI
parts O
and O
could O
pave O
the O
way O
for O
calibration S-CONPRI
strategies O
based O
on O
roughness S-PRO
measurements O
. O


For O
this O
purpose O
, O
a O
3-factor O
, O
3-level O
Design B-CONPRI
of I-CONPRI
Experiment E-CONPRI
( O
DoE O
) O
has O
been O
carried O
out O
to O
investigate O
melting S-MANP
pool O
size O
and O
roughness S-PRO
by O
changing O
the O
machine S-MACEQ
process O
parameters S-CONPRI
: O
laser B-PARA
power E-PARA
, O
hatch B-PARA
distance E-PARA
, O
time O
exposure S-CONPRI
. O


In O
this O
way O
, O
the O
calibration S-CONPRI
of O
the O
thermal B-CONPRI
properties E-CONPRI
is O
made O
less O
sensitive O
to O
the O
large O
uncertainty O
usually O
affecting O
the O
melt B-MATE
pool E-MATE
size O
measurements O
and O
the O
range S-PARA
of O
applicability O
of O
the O
thermal O
model S-CONPRI
is O
explored O
over O
a O
broad O
spectrum O
of O
L-PBF S-MANP
process O
parameters S-CONPRI
. O


Anisotropic S-PRO
and O
isotropic S-PRO
enhanced O
thermal B-PRO
conductivity E-PRO
approaches O
are O
applied O
in O
combination O
with O
a O
laser B-MACEQ
source E-MACEQ
modelled O
either O
as S-MATE
a O
2D S-CONPRI
or O
3D S-CONPRI
heat O
source S-APPL
, O
respectively O
. O


The O
latter O
approach O
proved O
to O
be S-MATE
more O
accurate S-CHAR
and O
robust O
against O
experimental S-CONPRI
uncertainties O
. O


Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
, O
one O
of O
the O
most O
popular O
processes S-CONPRI
of O
3D B-MANP
printing E-MANP
, O
offers O
flexibility B-CONPRI
in I-CONPRI
manufacturing E-CONPRI
and O
introduces O
anisotropic S-PRO
properties O
to O
the O
final O
parts O
. O


With O
the O
use O
of O
Curvilinear O
Variable O
Stiffness S-PRO
( O
CVS O
) O
3D B-ENAT
printing I-ENAT
technology E-ENAT
, O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
manufactured B-CONPRI
products E-CONPRI
can O
be S-MATE
further O
improved O
and O
optimized O
. O


In O
this O
work O
, O
we O
demonstrate O
how O
CVS O
design S-FEAT
can O
improve O
open-hole O
tensile B-PRO
strength E-PRO
and O
failure S-CONPRI
strain O
of O
the O
manufactured S-CONPRI
specimens O
per O
ASTM O
D5766 O
. O


In O
addition O
, O
the O
ratio O
of O
the O
specimen O
width O
to O
the O
hole O
diameter S-CONPRI
is O
considered O
as S-MATE
a O
design S-FEAT
parameter O
and O
investigated O
. O


It O
is O
found O
that O
CVS O
design S-FEAT
improves O
the O
failure S-CONPRI
strength O
by O
38.0 O
% O
for O
a O
larger O
hole O
diameter B-CONPRI
configuration E-CONPRI
( O
from O
48.0 O
MPa S-CONPRI
to O
66.2 O
MPa S-CONPRI
) O
, O
while O
the O
improvement O
in O
failure S-CONPRI
strain O
( O
from O
0.0125 O
mm/mm O
to O
0.0130 O
mm/mm O
) O
is O
limited O
to O
only O
4.0 O
% O
. O


On O
the O
other O
hand O
, O
for O
a O
smaller O
hole O
diameter S-CONPRI
case O
, O
a O
substantial O
improvement O
of O
52.5 O
% O
in O
failure S-CONPRI
strain O
is O
obtained O
with O
the O
use O
of O
CVS O
design S-FEAT
( O
from O
0.0141 O
mm/mm O
to O
0.0215 O
mm/mm O
) O
, O
while O
16.7 O
% O
improvement O
in O
failure S-CONPRI
stress O
( O
76.0 O
MPa S-CONPRI
to O
88.6 O
MPa S-CONPRI
) O
is O
less O
pronounced O
. O


During O
part O
fabrication S-MANP
by O
laser S-ENAT
powder-bed O
fusion S-CONPRI
( O
L-PBF S-MANP
) O
, O
an O
Additive B-MANP
Manufacturing I-MANP
process E-MANP
, O
a O
large O
amount O
of O
energy O
is O
input O
from O
the O
laser S-ENAT
into O
the O
melt B-MATE
pool E-MATE
, O
causing O
generation O
of O
spatter S-CHAR
and O
condensate O
, O
both O
of O
which O
have O
the O
potential O
to O
settle O
in O
the O
surrounding O
powder-bed O
compromising O
its O
reusability O
. O


In O
this O
study O
, O
AISI B-MATE
304 E-MATE
L O
stainless B-MATE
steel E-MATE
powder S-MATE
is O
subjected O
to O
seven O
reuses O
in O
the O
L-PBF S-MANP
process O
to O
assess O
the O
changes O
in O
powder S-MATE
properties O
that O
occur O
as S-MATE
a O
result O
of O
successive O
recycling S-CONPRI
. O


The O
powder S-MATE
was O
characterized O
morphologically O
by O
particle S-CONPRI
size O
and O
shape O
distribution S-CONPRI
measurements O
, O
chemically O
through O
inert B-CONPRI
gas I-CONPRI
fusion E-CONPRI
for O
evaluation O
of O
oxygen S-MATE
content O
, O
and O
microstructurally O
by O
X-ray B-CHAR
diffraction E-CHAR
for O
phase S-CONPRI
identification O
. O


The O
evolution S-CONPRI
in O
powder S-MATE
properties O
was O
used O
to O
explain O
observed O
performance S-CONPRI
differences O
obtained O
by O
the O
Hausner O
ratio O
and O
a O
Revolution O
Powder S-MATE
Analyzer O
for O
quantifying O
flowability O
. O


The O
results O
show O
that O
recycled S-CONPRI
powder S-MATE
coarsens O
and O
becomes O
more O
spherical S-CONPRI
, O
accrues O
oxygen S-MATE
, O
and O
accumulates O
delta O
ferrite S-MATE
as S-MATE
it O
is O
reused O
. O


Due O
to O
the O
change O
in O
powder S-MATE
morphology S-CONPRI
, O
recycled S-CONPRI
powder S-MATE
exhibited O
improved O
flowability O
in O
comparison O
to O
the O
virgin B-MATE
powder E-MATE
. O


The O
energy O
per O
layer S-PARA
was O
found O
to O
be S-MATE
critical O
factor O
to O
print S-MANP
fully B-PARA
dense E-PARA
AlSi12 S-MATE
samples O
using O
SLM S-MANP
process S-CONPRI
. O


The O
printing O
area S-PARA
along O
the O
build B-PARA
direction E-PARA
varies O
when O
a O
sample S-CONPRI
is O
built O
in O
different O
orientations S-CONPRI
. O


The O
anisotropy S-PRO
of O
SLM-built O
samples S-CONPRI
corresponds O
to O
the O
variable O
energy O
per O
layer S-PARA
and O
printing O
area S-PARA
. O


Fully B-PARA
dense E-PARA
SLM-built O
AlSi12 S-MATE
samples O
were O
printed O
by O
using O
energy O
per O
layer S-PARA
in O
an O
optimum O
range S-PARA
. O


The O
anisotropy S-PRO
in O
the O
tensile B-PRO
properties E-PRO
of O
AlSi12 S-MATE
alloy S-MATE
fabricated O
using O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
additive B-MANP
manufacturing I-MANP
process E-MANP
was O
investigated O
. O


The O
tensile S-PRO
samples S-CONPRI
were O
printed O
in O
three O
different O
orientations S-CONPRI
, O
horizontal O
( O
H O
- O
0° O
) O
, O
inclined O
( O
I O
- O
45° O
) O
, O
and O
vertical S-CONPRI
( O
V S-MATE
- O
90° O
) O
, O
and O
found O
to O
exhibit O
yield B-PRO
strength E-PRO
between O
225 O
MPa S-CONPRI
and O
263 O
MPa S-CONPRI
, O
tensile B-PRO
strength E-PRO
between O
260 O
MPa S-CONPRI
and O
365 O
MPa S-CONPRI
, O
and O
ductility S-PRO
between O
1 O
and O
4 O
% O
, O
showing O
distinct O
fracture S-CONPRI
patterns O
. O


It O
was O
established O
that O
the O
build B-PARA
orientation E-PARA
had O
insignificant O
effect O
on O
the O
microstructural S-CONPRI
characteristics O
of O
the O
SLM-printed O
samples S-CONPRI
, O
while O
XRD S-CHAR
phase S-CONPRI
analysis O
showed O
variations S-CONPRI
in O
the O
Al S-MATE
( O
111 O
) O
and O
Al S-MATE
( O
200 O
) O
peak O
intensities O
. O


Consequently O
, O
the O
anisotropy S-PRO
in O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
SLM-printed O
AlSi12 S-MATE
samples O
was O
attributed O
to O
the O
differences O
in O
their O
relative B-PRO
density E-PRO
. O


Although O
the O
energy B-PARA
density E-PARA
was O
kept O
constant O
when O
printing O
the O
samples S-CONPRI
along O
different O
orientations S-CONPRI
, O
the O
“ O
energy O
per O
layer S-PARA
” O
was O
found O
to O
be S-MATE
different O
owing O
to O
the O
variation S-CONPRI
in O
the O
printing O
area S-PARA
along O
the O
build B-PARA
direction E-PARA
. O


Further O
investigation O
on O
the O
effect O
of O
printing O
area S-PARA
, O
and O
correspondingly O
energy O
per O
layer S-PARA
, O
on O
the O
relative B-PRO
density E-PRO
was O
carried O
out O
. O


It O
was O
found O
that O
energy O
per O
layer S-PARA
in O
the O
range S-PARA
of O
504–895 O
J O
yielded O
≥99.8 O
% O
relatively O
dense O
AlSi12 S-MATE
SLM-printed O
samples S-CONPRI
. O


This O
study O
puts O
forth O
a O
new O
idea O
that O
the O
density S-PRO
of O
the O
SLM-printed O
samples S-CONPRI
could O
be S-MATE
controlled O
using O
energy O
per O
layer S-PARA
as S-MATE
an O
input O
process B-CONPRI
parameter E-CONPRI
. O


Polyvinylidene O
fluoride O
( O
PVDF O
) O
is O
a O
polymer S-MATE
prized O
for O
its O
unique O
material B-CONPRI
properties E-CONPRI
, O
including O
a O
high O
resistance S-PRO
to O
corrosive S-PRO
acids O
such O
as S-MATE
HCL O
and O
HF S-MATE
and O
its O
piezoelectric O
potential O
based O
on O
the O
proper O
microstructure S-CONPRI
arrangement O
. O


In O
this O
work O
, O
the O
effects O
of O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
routine O
parameters S-CONPRI
on O
printed O
PVDF O
film O
properties S-CONPRI
were O
investigated O
using O
a O
variety O
of O
experimental S-CONPRI
methods O
. O


The O
influence O
of O
in-fill O
angle O
( O
0° O
, O
45° O
, O
and O
90° O
) O
on O
the O
effective O
Young O
’ O
s S-MATE
Modulus O
, O
Poisson O
’ O
s S-MATE
ratio O
, O
and O
yield B-PRO
strength E-PRO
were O
evaluated O
using O
tensile B-CHAR
testing E-CHAR
and O
a O
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
( O
DIC S-CONPRI
) O
analysis O
. O


The O
phase S-CONPRI
content O
, O
in O
particular O
the O
β-phase O
amount O
, O
within O
the O
semi-crystalline O
PVDF O
films O
was O
determined O
as S-MATE
a O
function O
of O
processing O
parameters S-CONPRI
using O
the O
FTIR S-CHAR
method O
. O


Considered O
parameters S-CONPRI
included O
the O
extrusion S-MANP
temperature O
, O
horizontal O
speed O
, O
in-situ S-CONPRI
applied O
hot B-MACEQ
end E-MACEQ
voltage O
, O
and O
bed S-MACEQ
material O
. O


Results O
showed O
that O
higher O
β-phase O
content O
was O
associated O
with O
lower O
extrusion S-MANP
temperatures O
, O
faster O
extrusion B-PARA
rates E-PARA
, O
and O
higher O
hot B-MACEQ
end E-MACEQ
voltages O
. O


New O
advancements O
in O
3D B-MANP
printing E-MANP
enable O
manufacturing S-MANP
a O
solid O
part O
with O
spatially O
controlled O
and O
varying O
material B-CONPRI
properties E-CONPRI
; O
this O
research S-CONPRI
seeks O
to O
establish O
techniques O
for O
finding O
optimal O
designs S-FEAT
that O
use O
this O
new O
technology S-CONPRI
for O
the O
greatest O
structural O
benefit O
. O


We O
describe O
the O
use O
of O
a O
sequential O
quadratic O
programming O
based O
optimization S-CONPRI
solver O
to O
find O
an O
optimal O
distribution S-CONPRI
of O
material B-CONPRI
properties E-CONPRI
that O
minimize O
strain S-PRO
energy O
gradients O
, O
as S-MATE
calculated O
using O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
. O


This O
design S-FEAT
method O
is O
applied O
to O
the O
case O
of O
a O
flat O
thin O
plate O
with O
a O
hole O
, O
and O
has O
been O
proven O
to O
successfully O
reduce O
strain S-PRO
energy O
gradients O
and O
therefore O
stress B-CHAR
concentrations E-CHAR
. O


The O
optimally O
designed S-FEAT
plates O
are O
3D B-MANP
printed E-MANP
using O
a O
novel O
technology S-CONPRI
that O
uses O
vat B-MANP
polymerization E-MANP
technology S-CONPRI
. O


The O
computational B-ENAT
model E-ENAT
is O
validated O
with O
experiments O
. O


Enabling O
design S-FEAT
engineers O
to O
customize O
material B-CONPRI
properties E-CONPRI
around O
geometric O
discontinuities O
will O
provide O
greater O
flexibility S-PRO
in O
reducing O
stress B-CHAR
concentrations E-CHAR
without O
modifying O
geometry S-CONPRI
or O
adding O
additional O
supports S-APPL
. O


Laser B-MANP
Engineered I-MANP
Net I-MANP
Shaping E-MANP
( O
LENS S-MANP
) O
is O
an O
additive B-MANP
manufacturing E-MANP
technique O
that O
belongs O
to O
the O
ASTM O
standardized O
directed B-MANP
energy I-MANP
deposition E-MANP
category O
. O


To O
date O
, O
very O
limited O
work O
has O
been O
conducted O
towards O
understanding O
the O
fatigue B-CONPRI
crack I-CONPRI
growth E-CONPRI
behavior O
of O
LENS S-MANP
fabricated S-CONPRI
materials O
, O
which O
hinders O
the O
widespread O
adoption O
of O
this O
technology S-CONPRI
for O
high-integrity O
structural O
applications O
. O


In O
this O
study O
, O
the O
propagation O
of O
a O
20 O
μm O
initial O
crack O
in O
LENS S-MANP
fabricated S-CONPRI
Ti-6Al-4V O
was O
captured O
in-situ S-CONPRI
, O
using O
high-energy O
synchrotron S-ENAT
x-ray O
microtomography O
. O


Fatigue B-CONPRI
crack I-CONPRI
growth E-CONPRI
( O
FCG O
) O
data S-CONPRI
were O
then O
determined O
from O
2D S-CONPRI
and O
3D S-CONPRI
tomography O
reconstructions O
, O
as S-MATE
well O
as S-MATE
from O
fracture S-CONPRI
surface O
striation S-FEAT
measurements O
using O
SEM S-CHAR
. O


The O
observed O
agreement O
demonstrates O
that O
x-ray B-CHAR
microtomography E-CHAR
and O
fractographic B-CHAR
analysis E-CHAR
using O
SEM S-CHAR
can O
be S-MATE
successfully O
combined O
to O
study O
the O
propagation O
behavior O
of O
fatigue S-PRO
cracks O
. O


A O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
of O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
( O
LPBF S-MANP
) O
process S-CONPRI
applied O
to O
metallic B-MATE
alloys E-MATE
at O
a O
mesoscopic O
scale O
is O
presented O
. O


This O
Level-Set O
model S-CONPRI
allows O
to O
follow O
melt B-MATE
pool E-MATE
evolution S-CONPRI
and O
track O
development O
during O
building O
. O


A O
volume S-CONPRI
heat B-CONPRI
source E-CONPRI
model O
is O
used O
for O
laser/powder O
interaction O
considering O
the O
material S-MATE
absorption S-CONPRI
coefficients O
, O
while O
a O
surface S-CONPRI
heat B-CONPRI
source E-CONPRI
is O
used O
to O
consider O
the O
high O
laser B-CONPRI
energy E-CONPRI
absorption S-CONPRI
by O
dense O
metal B-MATE
alloys E-MATE
. O


Shrinkage S-CONPRI
during O
consolidation S-CONPRI
from O
powder S-MATE
to O
dense O
material S-MATE
is O
modelled O
by O
a O
compressible O
Newtonian O
constitutive O
law O
. O


An O
automatic O
remeshing S-CONPRI
strategy O
is O
also O
used O
to O
provide O
a O
good O
compromise O
between O
accuracy S-CHAR
and O
computing O
time O
. O


Different O
cases O
are O
investigated O
to O
demonstrate O
the O
influence O
of O
the O
vaporisation O
phenomena O
, O
of O
material B-CONPRI
properties E-CONPRI
and O
of O
laser B-ENAT
scan E-ENAT
strategy O
on O
bead B-CONPRI
morphology E-CONPRI
. O


Due O
to O
the O
layer-based O
nature O
of O
the O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
process S-CONPRI
, O
part O
surfaces S-CONPRI
oriented O
in O
space O
at O
varying O
angles O
with O
respect O
to O
the O
build B-PARA
direction E-PARA
are O
differently O
affected O
by O
a O
wide O
array O
of O
manufacturing-induced O
phenomena O
( O
staircase O
effects O
, O
spatter S-CHAR
, O
particles S-CONPRI
, O
etc O
. O


For O
assessing O
surface B-CONPRI
topography E-CONPRI
of O
PBF S-MANP
surfaces O
most O
researchers O
have O
looked O
at O
surface B-FEAT
texture E-FEAT
parameters S-CONPRI
( O
profile S-FEAT
- O
ISO S-MANS
4287 O
and O
areal O
- O
ISO S-MANS
25178−2 O
) O
. O


Texture S-FEAT
parameters S-CONPRI
provide O
useful O
summaries O
of O
surface-wide O
properties S-CONPRI
, O
but O
do O
not O
allow O
the O
analysis O
to O
focus O
on O
specific O
topographic O
formations O
of O
interest O
. O


In O
this O
work O
, O
the O
topography S-CHAR
of O
electron B-CONPRI
beam E-CONPRI
powder O
bed B-MANP
fusion E-MANP
( O
EBPBF O
) O
surfaces S-CONPRI
as S-MATE
a O
function O
of O
orientation S-CONPRI
with O
respect O
to O
the O
build B-PARA
direction E-PARA
was O
investigated O
using O
a O
combined O
approach O
consisting O
of O
both O
texture S-FEAT
parameters S-CONPRI
and O
feature-based O
characterisation O
. O


A O
custom-designed O
test O
part O
featuring O
surfaces S-CONPRI
at O
different O
orientations S-CONPRI
was O
measured O
with O
a O
focus O
variation S-CONPRI
instrument O
. O


A O
feature-based O
characterisation O
pipeline O
was O
implemented O
for O
the O
identification O
, O
isolation O
and O
geometrical O
characterisation O
of O
spatter S-CHAR
formations O
and O
particles S-CONPRI
present O
on O
the O
as-built O
surfaces S-CONPRI
. O


The O
surfaces S-CONPRI
deprived O
of O
the O
identified O
features O
were O
then O
characterised O
by O
means O
of O
conventional O
ISO S-MANS
25178−2 O
texture S-FEAT
parameters S-CONPRI
. O


The O
results O
confirm O
that O
combining O
feature-based O
characterisation O
with O
conventional O
analysis O
through O
texture S-FEAT
parameters S-CONPRI
creates O
new O
perspectives O
for O
looking O
at O
EBPBF O
surfaces S-CONPRI
, O
thus O
better O
supporting O
future O
research S-CONPRI
endeavours O
aimed O
at O
achieving O
a O
more O
comprehensive O
insight O
on O
the O
nature O
of O
EBPBF O
surfaces S-CONPRI
. O


For O
the O
first O
time O
quantitative S-CONPRI
results O
are O
provided O
on O
number O
, O
shape O
and O
localisation O
of O
spatter S-CHAR
and O
other O
particles S-CONPRI
in O
EBPBF O
surfaces S-CONPRI
as S-MATE
a O
function O
of O
build B-PARA
orientation E-PARA
, O
and O
texture S-FEAT
parameters S-CONPRI
are O
provided O
that O
describe O
the O
fabricated S-CONPRI
surfaces O
in O
a O
more O
reliable O
way O
as S-MATE
particles O
and O
spatter S-CHAR
formations O
have O
been O
removed O
. O


Unimodal O
powder S-MATE
samples O
were O
used O
in O
the O
laser B-MANP
sintering E-MANP
process O
. O


Different O
powder B-MATE
particle E-MATE
size O
and O
laser B-ENAT
scan E-ENAT
speeds O
were O
used O
. O


Microphotography O
, O
bulk O
density S-PRO
and O
tensile B-PRO
strength E-PRO
of O
artefact O
were O
measured O
. O


Neck O
size O
and O
strength S-PRO
were O
estimated O
with O
the O
Rumpf O
model S-CONPRI
for O
the O
strength S-PRO
of O
powder B-MATE
aggregates E-MATE
. O


Sintering S-MANP
temperatures O
were O
estimated O
with O
the O
Frenkel O
model S-CONPRI
for O
the O
effect O
of O
time O
on O
the O
sintering S-MANP
process S-CONPRI
. O


Selective B-MANP
Laser I-MANP
Sintering E-MANP
( O
SLS S-MANP
) O
of O
ceramic B-MATE
powders E-MATE
is O
studied O
in O
order O
to O
understand O
how O
the O
initial O
material B-CONPRI
properties E-CONPRI
and O
the O
process S-CONPRI
conditions O
affect O
the O
degree O
of O
sintering/melting O
and O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
sintered S-MANP
material S-MATE
. O


Unimodal O
powder S-MATE
samples O
of O
different O
narrow O
particle B-CONPRI
size I-CONPRI
distributions E-CONPRI
between O
16 O
and O
184 O
μm O
were O
sintered S-MANP
with O
a O
40 O
W O
CO2 S-MATE
laser O
, O
using O
laser B-ENAT
scan E-ENAT
speeds O
of O
either O
50 O
or O
100 O
mm S-MANP
s−1 O
and O
, O
in O
both O
cases O
, O
a O
scanning S-CONPRI
energy O
of O
160 O
J O
m−1 O
. O


The O
sintered S-MANP
material S-MATE
was O
studied O
by O
means O
of O
optical S-CHAR
and O
SEM S-CHAR
microphotography O
and O
characterized O
in O
terms O
of O
bulk O
density S-PRO
and O
tensile B-PRO
strength E-PRO
. O


The O
Rumpf O
approach O
to O
relate O
interparticle O
forces S-CONPRI
to O
the O
strength S-PRO
of O
powder S-MATE
agglomerates O
was O
used O
in O
this O
work O
to O
estimate O
the O
average S-CONPRI
strength O
of O
the O
sintered S-MANP
interparticle O
contacts S-APPL
starting O
from O
the O
tensile B-PRO
strength E-PRO
of O
specimens O
. O


In O
turn O
, O
the O
average S-CONPRI
strength O
of O
the O
neck O
contact S-APPL
was O
used O
to O
estimate O
the O
size O
of O
the O
neck O
of O
fused S-CONPRI
material O
between O
two O
sintered S-MANP
particles S-CONPRI
. O


These O
data S-CONPRI
coupled O
with O
the O
Frenkel O
model S-CONPRI
for O
particle S-CONPRI
sintering O
allowed O
an O
estimate O
of O
the O
sintering S-MANP
temperature O
for O
the O
different O
experimental S-CONPRI
conditions O
tested O
. O


The O
temperatures S-PARA
found O
are O
consistent O
with O
the O
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
of O
the O
material S-MATE
used O
. O


The O
effect O
of O
particle S-CONPRI
size O
and O
scanning B-PARA
speed E-PARA
is O
assessed O
and O
discussed O
. O


The O
Z O
axis O
table O
motion O
errors S-CONPRI
and O
laser S-ENAT
positioning O
errors S-CONPRI
an O
EOSINT O
M280 O
were O
evaluated O
using O
a O
set S-APPL
of O
standard S-CONPRI
metrology S-CONPRI
techniques O
and O
instrumentation O
. O


While O
the O
linear O
displacement O
error S-CONPRI
of O
the O
table O
is O
quite O
low O
( O
4.5 O
μm O
) O
, O
straightness S-CONPRI
, O
yaw O
and O
pitch O
errors S-CONPRI
on O
the O
other O
hand O
were O
significantly O
higher O
and O
may O
contribute O
from O
20 O
to O
30 O
microns O
of O
form O
and O
orientation S-CONPRI
tolerances O
over O
a O
large O
size O
build.The O
performance S-CONPRI
of O
the O
laser S-ENAT
positioning O
system O
was O
much O
worse O
. O


A O
designed S-FEAT
artifact O
was O
produced O
, O
and O
used O
to O
evaluate O
the O
laser S-ENAT
performance O
against O
a O
set S-APPL
of O
tolerance B-FEAT
controls E-FEAT
extracted S-CONPRI
from O
the O
ASME O
Y14.5-2009 O
Standard S-CONPRI
. O


The O
largest O
tolerance B-PARA
magnitude E-PARA
( O
239 O
μm O
) O
was O
calculated O
as S-MATE
the O
combined O
effect O
of O
location O
, O
orientation S-CONPRI
, O
size O
and O
form O
errors S-CONPRI
in O
the O
trace O
of O
a O
large O
quadrifolium O
etched O
over O
the O
working O
area S-PARA
of O
the O
laser S-ENAT
. O


The O
errors S-CONPRI
measured O
in O
this O
research S-CONPRI
are O
substantial O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
was O
utilized O
to O
fabricate S-MANP
Sc O
and O
Zr S-MATE
modified O
Al-Mg B-MATE
alloy E-MATE
. O


Different O
precipitation S-CONPRI
behavior O
between O
various O
scan B-PARA
speeds E-PARA
are O
characterized O
by O
SEM S-CHAR
and O
TEM S-CHAR
. O


Significant O
improvement O
of O
hardness S-PRO
is O
evaluated O
and O
explained O
under O
a O
relative O
low O
scan B-PARA
speed E-PARA
. O


Relationships O
between O
scan B-PARA
speed E-PARA
, O
precipitate S-MATE
distribution S-CONPRI
, O
and O
the O
resultant O
mechanical B-CONPRI
properties E-CONPRI
are O
elucidated O
. O


The O
interest O
of O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
Al-based O
alloys S-MATE
for O
lightweight S-CONPRI
applications O
, O
especially O
the O
rare O
earth O
element S-MATE
Sc O
modified O
Al-Mg B-MATE
alloy E-MATE
, O
is O
increasing O
. O


In O
this O
work O
, O
high-performance O
Al-Mg-Sc-Zr O
alloy S-MATE
was O
successfully O
fabricated S-CONPRI
by O
SLM S-MANP
. O


The O
phase S-CONPRI
identification O
, O
densification S-MANP
behavior O
, O
precipitate S-MATE
distribution S-CONPRI
and O
mechnical O
properties S-CONPRI
of O
the O
as-fabricated O
parts O
at O
a O
wide O
range S-PARA
of O
processing O
parameters S-CONPRI
were O
carefully O
characterized O
. O


Meanwhile O
, O
the O
evolution S-CONPRI
of O
nanoprecipitation O
behavior O
under O
various O
scan B-PARA
speeds E-PARA
is O
revealed O
and O
TEM S-CHAR
analysis O
of O
precipitates S-MATE
shows O
that O
a O
small O
amount O
of O
spherical S-CONPRI
nanoprecipitates O
Al3 O
( O
Sc O
, O
Zr S-MATE
) O
were O
embedded O
at O
the O
bottom O
of O
the O
molten B-CONPRI
pool E-CONPRI
using O
a O
low O
scan B-PARA
speed E-PARA
. O


While O
no O
precipitates S-MATE
were O
found O
in O
the O
matrix O
using O
a O
relatively O
high O
scan B-PARA
speed E-PARA
due O
to O
the O
combined O
effects O
of O
the O
variation S-CONPRI
of O
Marangoni O
convection O
vector O
, O
ultrashort O
lifetime O
of O
liquid O
and O
the O
rapid O
cooling B-PARA
rate E-PARA
. O


An O
increased O
hardness S-PRO
and O
a O
reduced O
wear S-CONPRI
rate O
of O
94 O
HV0.2 O
and O
1.74 O
× O
10−4 O
mm3N-1 O
m-1 O
were O
resultantly O
obtained O
respectively O
as S-MATE
a O
much O
lower O
scan B-PARA
speed E-PARA
was O
applied O
. O


A O
relationship O
between O
the O
processing O
parameters S-CONPRI
, O
the O
surface B-PRO
tension E-PRO
, O
the O
convection O
flow O
, O
the O
precipitation S-CONPRI
distribution S-CONPRI
and O
the O
resultant O
mechanical B-CONPRI
properties E-CONPRI
has O
been O
well O
established O
, O
demonstrating O
that O
the O
high-performance O
of O
SLM-processed O
Al-Mg-Sc-Zr O
alloy S-MATE
could O
be S-MATE
tailored O
by O
controlling O
the O
distribution S-CONPRI
of O
nanoprecipitates O
. O


Continuous O
carbon B-MATE
nanotube E-MATE
( O
CNT S-MATE
) O
yarn B-MATE
filaments E-MATE
can O
be S-MATE
employed O
as S-MATE
an O
inherently O
multifunctional O
feedstock S-MATE
for O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
. O


With O
this O
material S-MATE
, O
it O
becomes O
possible O
to O
use O
a O
single O
material S-MATE
to O
impart O
multiple O
functionalities O
in O
components S-MACEQ
and O
take O
advantage O
of O
the O
tailorability O
offered O
by O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
over O
conventional O
fabrication S-MANP
techniques O
. O


Some O
of O
the O
challenges O
associated O
with O
coupling O
this O
emerging O
material S-MATE
with O
advanced O
processing O
are O
addressed O
here O
through O
the O
fabrication S-MANP
and O
characterization O
of O
additively B-MANP
manufactured E-MANP
functional O
objects O
. O


Continuous O
CNT S-MATE
yarn O
reinforced S-CONPRI
Ultem® O
specimens O
are O
characterized O
to O
determine O
their O
mechanical S-APPL
and O
electrical B-CONPRI
properties E-CONPRI
. O


The O
potential O
to O
produce O
net B-MANP
shape E-MANP
fabricated S-CONPRI
multifunctional O
components S-MACEQ
is O
demonstrated O
by O
additively O
manufacturing S-MANP
a O
quadcopter O
frame O
using O
Ultem® O
and O
continuous O
CNT S-MATE
yarn O
reinforced S-CONPRI
Ultem® O
, O
where O
the O
CNT S-MATE
yarn O
reinforcement S-PARA
was O
designed S-FEAT
to O
also O
act O
as S-MATE
the O
electrical S-APPL
conductors S-MATE
carrying O
current O
to O
the O
motors O
. O


A O
computational O
modeling S-ENAT
approach O
to O
simulate O
residual B-PRO
stress E-PRO
formation O
during O
the O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
process S-CONPRI
within O
the O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
for O
Inconel B-MATE
718 E-MATE
is O
presented O
in O
this O
paper O
. O


The O
EBM S-MANP
process O
has O
demonstrated O
a O
high O
potential O
to O
fabricate S-MANP
components S-MACEQ
with O
complex B-CONPRI
geometries E-CONPRI
, O
but O
the O
resulting O
components S-MACEQ
are O
influenced O
by O
the O
thermal B-PARA
cycles E-PARA
observed O
during O
the O
manufacturing B-MANP
process E-MANP
. O


When O
processing O
nickel B-MATE
based I-MATE
superalloys E-MATE
, O
very O
high O
temperatures S-PARA
( O
approx O
. O


1000 O
°C O
) O
are O
observed O
in O
the O
powder B-MACEQ
bed E-MACEQ
, O
base O
plate O
, O
and O
build S-PARA
. O


These O
high O
temperatures S-PARA
, O
when O
combined O
with O
substrate S-MATE
adherence O
, O
can O
result O
in O
warping S-CONPRI
of O
the O
base O
plate O
and O
affect O
the O
final O
component S-MACEQ
by O
causing O
defects S-CONPRI
. O


It O
is O
important O
to O
have O
an O
understanding O
of O
the O
thermo-mechanical S-CONPRI
response O
of O
the O
entire O
system O
, O
that O
is O
, O
its O
mechanical S-APPL
behavior O
towards O
thermal B-CONPRI
loading E-CONPRI
occurring O
during O
the O
EBM S-MANP
process O
prior O
to O
manufacturing S-MANP
a O
component S-MACEQ
. O


Therefore O
, O
computational B-ENAT
models E-ENAT
to O
predict O
the O
response O
of O
the O
system O
during O
the O
EBM S-MANP
process O
will O
aid O
in O
eliminating O
the O
undesired O
process S-CONPRI
conditions O
, O
a O
priori O
, O
in O
order O
to O
fabricate S-MANP
the O
optimum O
component S-MACEQ
. O


Such O
a O
comprehensive O
computational O
modeling S-ENAT
approach O
is O
demonstrated O
to O
analyze O
warping S-CONPRI
of O
the O
base O
plate O
, O
stress S-PRO
and O
plastic S-MATE
strain O
accumulation O
within O
the O
material S-MATE
, O
and O
thermal B-PARA
cycles E-PARA
in O
the O
system O
during O
different O
stages O
of O
the O
EBM S-MANP
process O
. O


Parts O
made O
by O
fused B-MANP
filament I-MANP
fabrication E-MANP
differ O
in O
their O
mechanical B-CONPRI
properties E-CONPRI
from O
the O
parent O
material S-MATE
. O


To O
investigate O
the O
effect O
of O
the O
manufacturing B-MANP
process E-MANP
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
3D-printed B-APPL
parts E-APPL
, O
a O
series O
of O
experiments O
including O
Dynamic B-CONPRI
Mechanical I-CONPRI
Analysis E-CONPRI
( O
DMA S-CONPRI
) O
and O
ultrasonic O
wave O
propagation O
were O
conducted O
. O


For O
this O
purpose O
, O
printed O
parts O
were O
made O
from O
custom O
ABS S-MATE
filament O
and O
were O
printed O
using O
a O
rectangular O
bead S-CHAR
shape O
to O
minimize O
porosity S-PRO
. O


The O
main O
properties S-CONPRI
investigated O
included O
the O
elastic S-PRO
, O
loss O
and O
storage O
moduli O
, O
and O
the O
material S-MATE
loss O
tangent O
( O
tan O
δ O
) O
. O


Results O
indicate O
that O
the O
elastic B-PRO
modulus E-PRO
of O
the O
printed O
material S-MATE
was O
somewhat O
lower O
than O
that O
of O
the O
parent O
material S-MATE
, O
about O
2 O
GPa S-PRO
for O
frequencies O
0.1 O
Hz–100 O
Hz O
. O


Droplet S-CONPRI
jetting O
behavior O
largely O
determines O
the O
final O
drop O
deposition B-CHAR
quality E-CHAR
in O
the O
inkjet B-MANP
printing I-MANP
process E-MANP
. O


Forming S-MANP
such O
behavior O
is O
governed O
by O
the O
fluid B-PRO
flow E-PRO
pattern O
. O


Therefore O
, O
a O
measurement S-CHAR
of O
the O
flow B-CONPRI
pattern E-CONPRI
is O
of O
great O
importance O
for O
improving O
the O
printing O
quality S-CONPRI
of O
the O
inkjet B-MANP
printing I-MANP
process E-MANP
. O


Most O
of O
the O
current O
works O
use O
static O
images S-CONPRI
for O
the O
study O
of O
the O
drop O
evolution S-CONPRI
process O
. O


The O
problem O
of O
the O
static O
images S-CONPRI
is O
that O
the O
images S-CONPRI
can O
not O
recognize O
the O
motion O
information O
( O
i.e. O
, O
temporal O
transformation O
) O
of O
the O
droplet S-CONPRI
. O


Thus O
the O
information O
of O
the O
jetting S-MANP
process O
in O
the O
temporal O
domain S-CONPRI
will O
be S-MATE
lost O
. O


Instead O
of O
using O
the O
images S-CONPRI
, O
this O
paper O
takes O
the O
video O
data S-CONPRI
as S-MATE
the O
study O
subject O
to O
investigate O
the O
droplet S-CONPRI
evolution O
behavior O
in O
the O
inkjet B-MANP
printing I-MANP
process E-MANP
. O


Compared O
to O
most O
of O
the O
current O
learning O
approaches O
conducted O
in O
a O
supervised/semi-supervised O
manner O
for O
manufacturing B-MANP
process E-MANP
data S-CONPRI
, O
we O
propose O
an O
unsupervised O
learning O
method O
for O
studying O
the O
flow B-CONPRI
pattern E-CONPRI
of O
the O
droplet S-CONPRI
, O
which O
does O
not O
require O
well-defined O
ground-truth O
labels O
. O


Regarding O
the O
spatial O
and O
temporal O
transformation O
of O
the O
droplet S-CONPRI
in O
video O
data S-CONPRI
, O
we O
apply O
a O
deep O
recurrent O
neural B-CONPRI
network E-CONPRI
( O
DRNN O
) O
to O
implement O
the O
proposed O
unsupervised O
learning O
. O


Experimental S-CONPRI
results O
demonstrate O
that O
the O
proposed O
method O
can O
learn O
latent O
representations O
of O
the O
droplet S-CONPRI
jetting O
process S-CONPRI
video O
data S-CONPRI
, O
which O
is O
very O
useful O
for O
the O
prediction S-CONPRI
of O
the O
droplet S-CONPRI
behavior O
. O


Furthermore O
, O
through O
latent O
space O
decoding O
, O
the O
learned O
representations O
can O
infer O
the O
droplet S-CONPRI
forming O
stimulus O
parameters S-CONPRI
such O
as S-MATE
material O
properties S-CONPRI
, O
which O
would O
be S-MATE
very O
helpful O
for O
further O
understanding O
of O
the O
process S-CONPRI
dynamics O
and O
achieving O
real-time O
in-situ S-CONPRI
droplet S-CONPRI
deposition B-CHAR
quality E-CHAR
monitoring O
and O
control O
. O


The O
surface S-CONPRI
of O
SLMed S-MANP
composite S-MATE
shows O
low O
roughness S-PRO
and O
high O
homogeneity O
. O


A O
phase S-CONPRI
transition O
from O
bcc S-CONPRI
martensite O
to O
fcc S-CONPRI
austensite O
appears O
with O
the O
addition O
of O
WC S-MATE
. O


Metallurgical B-CONPRI
bonding E-CONPRI
between O
reinforcement S-PARA
and O
matrix O
is O
realized O
. O


Tensile S-PRO
behavior O
of O
SLMed S-MANP
composite S-MATE
is O
different O
from O
that O
of O
SLMed S-MANP
maraging B-MATE
steel E-MATE
. O


In O
this O
work O
, O
tungsten B-MATE
carbide E-MATE
( O
WC S-MATE
) O
reinforced S-CONPRI
maraging B-MATE
steel E-MATE
matrix O
composites S-MATE
were O
in-situ S-CONPRI
manufactured O
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
from O
powder S-MATE
mixture O
. O


The O
SLM S-MANP
processed S-CONPRI
samples O
presented O
high O
relative B-PRO
density E-PRO
( O
over O
99 O
% O
) O
with O
a O
homogenous O
distribution S-CONPRI
of O
WC S-MATE
. O


The O
as-fabricated O
surface B-PARA
quality E-PARA
of O
SLM S-MANP
processed S-CONPRI
samples O
was O
improved O
significantly O
by O
the O
addition O
of O
WC S-MATE
. O


Focused O
ion S-CONPRI
beam S-MACEQ
and O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
were O
employed O
to O
characterize O
the O
interfacial O
properties S-CONPRI
between O
tungsten B-MATE
carbide E-MATE
and O
steel S-MATE
matrix O
. O


The O
elemental B-CHAR
analysis E-CHAR
indicates O
that O
metallurgical B-CONPRI
bonding E-CONPRI
appears O
at O
interfacial O
region O
due O
to O
the O
diffusion S-CONPRI
. O


Tensile S-PRO
behavior O
of O
SLM S-MANP
processed S-CONPRI
maraging B-MATE
steel E-MATE
was O
different O
from O
their O
composite S-MATE
with O
several O
WC S-MATE
contents O
. O


To O
understand O
the O
fundamentals O
of O
microstructure S-CONPRI
formation O
in O
an O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
additive-manufacturing O
process S-CONPRI
, O
which O
is O
classified O
as S-MATE
a O
type O
of O
electron B-CONPRI
beam E-CONPRI
powder O
bed B-MANP
fusion E-MANP
( O
EB-PBF O
) O
in O
ISO562910/ASTM-F42 O
, O
single O
bead S-CHAR
experiments O
were O
conducted O
by O
using O
an O
electron B-CONPRI
beam E-CONPRI
to O
scan O
an O
IN718 S-MATE
plate O
, O
using O
various O
combinations O
of O
power S-PARA
and O
scan B-PARA
speed E-PARA
, O
focusing O
on O
the O
relationship O
between O
( O
i O
) O
the O
beam S-MACEQ
irradiation O
level O
, O
( O
ii O
) O
the O
melt B-MATE
pool E-MATE
geometry S-CONPRI
, O
and O
( O
iii O
) O
the O
solidification B-CONPRI
microstructure E-CONPRI
. O


The O
width O
and O
depth O
of O
the O
melt B-MATE
pool E-MATE
increases O
almost O
linearly O
with O
the O
line O
energy O
. O


Elongated O
grains S-CONPRI
, O
which O
are O
generally O
called O
“ O
columnar B-PRO
grains E-PRO
” O
were O
observed O
in O
almost O
the O
entire O
cross-section O
of O
the O
beads S-CHAR
regardless O
of O
the O
process B-CONPRI
parameters E-CONPRI
. O


Temporal O
evolution S-CONPRI
of O
the O
temperature S-PARA
distribution S-CONPRI
for O
the O
single O
bead S-CHAR
experiments O
was O
simulated O
by O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
( O
FEA O
) O
with O
thermal O
conduction O
and O
recoalescence O
taken O
into O
account O
. O


The O
surface S-CONPRI
heat B-CONPRI
source E-CONPRI
model O
used O
in O
the O
simulation S-ENAT
was O
modified O
to O
cause O
the O
geometry S-CONPRI
of O
the O
simulated O
melt B-MATE
pool E-MATE
to O
align O
with O
that O
which O
was O
observed O
experimentally O
. O


The O
distributions S-CONPRI
of O
the O
temperature B-PARA
gradient E-PARA
( O
G O
) O
and O
solidification B-PARA
rate E-PARA
( O
R O
) O
on O
the O
solidification B-CONPRI
interface E-CONPRI
were O
evaluated O
from O
the O
simulation S-ENAT
results O
. O


The O
distributions S-CONPRI
of O
the O
microstructures S-MATE
were O
constructed O
from O
the O
distributions S-CONPRI
of O
G O
and O
R O
, O
as S-MATE
obtained O
from O
a O
solidification S-CONPRI
map O
in O
the O
literature O
. O


Contrary O
to O
the O
experimental S-CONPRI
observations O
, O
the O
constructed O
microstructure S-CONPRI
consisted O
mostly O
of O
equiaxed O
and O
mixed O
grains S-CONPRI
. O


While O
the O
volumetric O
energy B-PARA
density E-PARA
is O
commonly O
used O
to O
qualify O
a O
process B-CONPRI
parameter E-CONPRI
set O
, O
and O
to O
quantify O
its O
influence O
on O
the O
microstructure S-CONPRI
and O
performance S-CONPRI
of O
additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
materials S-CONPRI
and O
components S-MACEQ
, O
it O
has O
been O
already O
shown O
that O
this O
description O
is O
by O
no O
means O
exhaustive O
. O


In O
this O
work O
, O
new O
aspects O
of O
the O
optimization S-CONPRI
of O
the O
selective B-MANP
laser I-MANP
melting I-MANP
process E-MANP
are O
investigated O
for O
AM S-MANP
Ti-6Al-4V O
. O


We O
focus O
on O
the O
amount O
of O
near-surface O
residual B-PRO
stress E-PRO
( O
RS O
) O
, O
often O
blamed O
for O
the O
failure S-CONPRI
of O
components S-MACEQ
, O
and O
on O
the O
porosity S-PRO
characteristics O
( O
amount O
and O
spatial B-CHAR
distribution E-CHAR
) O
. O


First O
, O
using O
synchrotron S-ENAT
x-ray O
diffraction S-CHAR
we O
show O
that O
higher O
RS O
in O
the O
subsurface O
region O
is O
generated O
if O
a O
lower O
energy B-PARA
density E-PARA
is O
used O
. O


Second O
, O
we O
show O
that O
laser S-ENAT
de-focusing O
and O
sample S-CONPRI
positioning O
inside O
the O
build B-PARA
chamber E-PARA
also O
play O
an O
eminent O
role O
, O
and O
we O
quantify O
this O
influence O
. O


In O
parallel O
, O
using O
X-ray B-CHAR
Computed I-CHAR
Tomography E-CHAR
, O
we O
observe O
that O
porosity S-PRO
is O
mainly O
concentrated O
in O
the O
contour S-FEAT
region O
, O
except O
in O
the O
case O
where O
the O
laser S-ENAT
speed O
is O
small O
. O


3D-printed S-MANP
Ti-6Al-4V O
components S-MACEQ
have O
great O
potential O
in O
the O
aerospace S-APPL
and O
biomedical B-APPL
industries E-APPL
. O


However O
, O
their O
wide O
application O
is O
limited O
by O
some O
inherent O
disadvantages O
, O
such O
as S-MATE
poor O
surface B-FEAT
finish E-FEAT
and O
high O
porosity S-PRO
. O


In O
this O
study O
, O
an O
innovative O
method O
, O
electrically-assisted O
ultrasonic O
nanocrystal O
surface B-MANP
modification E-MANP
( O
EA-UNSM O
) O
was O
introduced O
to O
process S-CONPRI
3D-printed S-MANP
Ti-6Al-4V O
samples S-CONPRI
. O


The O
effect O
of O
EA-UNSM O
on O
surface B-FEAT
finish E-FEAT
, O
microstructure S-CONPRI
, O
porosity S-PRO
and O
in-depth O
hardness S-PRO
was O
investigated O
. O


Compared O
with O
the O
conventional O
UNSM O
process S-CONPRI
, O
smoother O
surfaces S-CONPRI
and O
lower O
subsurface O
porosities S-PRO
were O
obtained O
after O
EA-UNSM O
. O


Numerical O
modelling S-ENAT
showed O
that O
localized O
heating S-MANP
occurs O
near O
the O
pores S-PRO
in O
3D-printed S-MANP
Ti-6Al-4V O
subjected O
to O
electric O
current O
. O


This O
localized O
heating S-MANP
could O
potentially O
facilitate O
pore S-PRO
closure O
under O
ultrasonic O
striking O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
technology S-CONPRI
is O
a O
layer-wise O
powder-based B-MANP
additive I-MANP
manufacturing E-MANP
method O
capable O
of O
building O
3D S-CONPRI
components O
from O
their O
CAD B-ENAT
models E-ENAT
. O


This O
approach O
offers O
enormous O
benefits O
for O
generating O
objects O
with O
geometrical B-FEAT
complexity E-FEAT
. O


However O
, O
due O
to O
the O
layer-wise O
nature O
of O
the O
process S-CONPRI
, O
surface B-PRO
roughness E-PRO
is O
formed O
between O
layers O
, O
thus O
influenced O
by O
layer B-PARA
thickness E-PARA
and O
other O
processing O
parameters S-CONPRI
. O


In O
this O
study O
, O
systematic O
research S-CONPRI
has O
been O
carried O
out O
to O
study O
the O
influence O
of O
processing O
parameters S-CONPRI
on O
surface B-PRO
roughness E-PRO
in O
Hastelloy S-MATE
X O
alloy S-MATE
. O


All O
samples S-CONPRI
were O
manufactured S-CONPRI
using O
an O
EOSINT O
M O
280 O
machine S-MACEQ
. O


Laser B-PARA
power E-PARA
, O
scan B-PARA
speed E-PARA
, O
layer B-PARA
thickness E-PARA
and O
sloping O
angle O
of O
a O
surface S-CONPRI
were O
systematically O
varied O
to O
understand O
their O
effects O
on O
surface B-PRO
roughness E-PRO
. O


The O
arithmetic O
average S-CONPRI
roughness O
, O
Ra O
, O
was O
measured O
using O
a O
surface B-PRO
roughness E-PRO
tester O
, O
and O
optimum O
conditions O
for O
achieving O
the O
lowest O
roughness S-PRO
for O
both O
up-skin O
surfaces S-CONPRI
and O
down-skin O
surfaces S-CONPRI
have O
been O
obtained O
. O


The O
formation O
mechanism S-CONPRI
for O
the O
roughness S-PRO
on O
these O
two O
types O
of O
surfaces S-CONPRI
has O
been O
studied O
. O


Computer B-CONPRI
simulation E-CONPRI
was O
also O
used O
to O
understand O
thermal B-CONPRI
profiles E-CONPRI
at O
those O
two O
surfaces S-CONPRI
and O
their O
resultant O
influence O
on O
surface B-PRO
roughness E-PRO
. O


Contour S-FEAT
scan O
and O
skywriting O
scan O
strategies O
were O
found O
to O
be S-MATE
helpful O
for O
reducing O
the O
surface B-PRO
roughness E-PRO
. O


Selective B-MANP
laser I-MANP
sintering E-MANP
( O
SLS S-MANP
) O
is O
a O
promising O
additive B-MANP
manufacturing E-MANP
technique O
, O
where O
powder B-MATE
particles E-MATE
are O
fused S-CONPRI
together O
under O
the O
influence O
of O
a O
laser B-CONPRI
beam E-CONPRI
. O


To O
obtain O
good O
material B-CONPRI
properties E-CONPRI
in O
the O
final O
product O
, O
the O
powder B-MATE
particles E-MATE
need O
to O
form O
a O
homogeneous S-CONPRI
melt O
during O
the O
fabrication S-MANP
process O
. O


On O
the O
other O
hand O
, O
you O
want O
the O
process S-CONPRI
to O
be S-MATE
as S-MATE
fast O
as S-MATE
possible O
. O


We O
developed O
a O
computational B-ENAT
model E-ENAT
based O
on O
the O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
to O
study O
the O
material S-MATE
and O
process B-CONPRI
parameters E-CONPRI
concerning O
the O
melt B-CONPRI
flow E-CONPRI
of O
the O
powder B-MATE
particles E-MATE
. O


In O
this O
work O
, O
we O
restrict O
ourselves O
to O
varying O
the O
temperature-dependent O
viscosity S-PRO
, O
the O
process B-CONPRI
parameters E-CONPRI
, O
and O
the O
convective O
heat B-CONPRI
transfer E-CONPRI
coefficient O
of O
the O
sintering S-MANP
of O
two O
polymer S-MATE
( O
polyamide B-MATE
12 E-MATE
) O
particles S-CONPRI
. O


The O
simulations S-ENAT
allow O
for O
a O
quantitative S-CONPRI
analysis O
of O
the O
influence O
of O
the O
different O
material S-MATE
and O
processing O
parameters S-CONPRI
. O


From O
the O
simulations S-ENAT
follows O
that O
an O
optimal O
sintering S-MANP
process S-CONPRI
has O
a O
low O
ambient O
temperature S-PARA
, O
a O
narrow O
beam S-MACEQ
width O
with O
enough O
power S-PARA
to O
heat S-CONPRI
the O
particles S-CONPRI
only O
a O
few O
degrees O
above O
the O
melting B-PARA
temperature E-PARA
, O
and O
a O
polymer S-MATE
of O
which O
the O
viscosity S-PRO
decreases O
significantly O
within O
these O
few O
degrees O
. O


Laser B-MANP
Engineered I-MANP
Net I-MANP
Shaping E-MANP
( O
LENS™ O
) O
was O
utilized O
to O
create O
novel O
silica S-MATE
( O
SiO2 S-MATE
) O
coatings S-APPL
onto O
commercially-pure O
titanium S-MATE
( O
Cp-Ti O
) O
. O


It O
was O
hypothesized O
that O
if O
silica S-MATE
could O
be S-MATE
deposited O
as S-MATE
a O
coating S-APPL
via O
laser S-ENAT
surface O
engineering S-APPL
, O
high O
hardness S-PRO
and O
wear B-PRO
resistance E-PRO
could O
be S-MATE
added O
to O
existing O
Cp-Ti O
material S-MATE
. O


Post-deposition O
heat-treatments O
in O
the O
form O
of O
laser S-ENAT
passes O
( O
LP O
) O
and O
a O
furnace S-MACEQ
residual-stress O
relief O
were O
completed O
on O
the O
coatings S-APPL
and O
mechanical/material O
properties S-CONPRI
were O
subsequently O
evaluated O
. O


Titanium B-MATE
silicide E-MATE
( O
Ti5Si3 O
) O
formation O
and O
related O
dendritic O
microstructures S-MATE
were O
identified O
throughout O
the O
coating S-APPL
by O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
, O
energy B-CHAR
dispersive I-CHAR
spectroscopy E-CHAR
( O
EDS S-CHAR
) O
, O
scanning S-CONPRI
electron O
microscopic O
( O
SEM S-CHAR
) O
analysis O
, O
and O
appeared O
more O
ordered O
after O
stress-relief O
heat B-MANP
treatment E-MANP
. O


High O
hardness S-PRO
values O
of O
approximately O
1500 O
HV O
were O
measured O
at O
the O
coating S-APPL
’ O
s S-MATE
topmost O
surface S-CONPRI
while O
specific O
wear S-CONPRI
rates O
showed O
a O
maximum O
98 O
% O
reduction S-CONPRI
from O
346.2 O
× O
10−6 O
mm3/N-m O
in O
the O
Cp-Ti O
substrate S-MATE
to O
7.1 O
× O
10−6 O
mm3/N-m O
in O
the O
heat S-CONPRI
treated O
1 O
LP O
coating S-APPL
. O


In B-CONPRI
situ E-CONPRI
tribofilm O
formation O
was O
observed O
during O
wear S-CONPRI
, O
which O
indicated O
self-healing O
properties S-CONPRI
from O
the O
material S-MATE
and O
likely O
aided O
further O
in O
wear B-CONPRI
reduction E-CONPRI
. O


Our O
results O
show O
that O
silica B-MATE
coating E-MATE
on O
titanium S-MATE
via O
laser S-ENAT
surface O
engineering S-APPL
could O
be S-MATE
used O
as S-MATE
a O
suitable O
manufacturing S-MANP
practice O
to O
create O
hard O
, O
Ti5Si3-reinforced O
ceramic B-MATE
coatings E-MATE
with O
high O
wear B-PRO
resistance E-PRO
and O
self-healing O
properties S-CONPRI
for O
applications O
ranging O
from O
biomedical S-APPL
to O
aerospace S-APPL
. O


To O
increase O
the O
mechanical B-PRO
strength E-PRO
of O
Zircaloy-4 S-MATE
cladding S-MANP
at O
high O
temperatures S-PARA
, O
partial O
oxide S-MATE
dispersion-strengthened O
( O
ODS O
) O
treatment O
of O
the O
cladding S-MANP
tube O
surface S-CONPRI
was O
achieved O
by O
using O
laser B-CONPRI
processing E-CONPRI
technology O
. O


The O
microstructural S-CONPRI
characteristics O
and O
stability S-PRO
of O
the O
ODS O
layer S-PARA
formed O
on O
the O
Zircaloy-4 S-MATE
cladding S-MANP
surface O
were O
analyzed O
at O
temperatures S-PARA
up O
to O
1000 O
°C O
. O


Ring O
tensile S-PRO
and O
loss-of-coolant O
accident O
( O
LOCA O
) O
simulation S-ENAT
tests O
were O
performed O
to O
evaluate O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
surface S-CONPRI
ODS O
treated O
Zircaloy-4 S-MATE
cladding S-MANP
tube O
. O


The O
formation O
and O
uniform O
distribution S-CONPRI
of O
Y2O3 O
particles S-CONPRI
formed O
in O
the O
Zr S-MATE
matrix O
were O
identified O
, O
and O
the O
stability S-PRO
of O
the O
particles S-CONPRI
was O
confirmed O
up O
to O
1000 O
°C O
. O


When O
compared O
to O
the O
reference O
Zircaloy-4 S-MATE
cladding S-MANP
tube O
, O
the O
surface S-CONPRI
ODS O
treated O
Zircaloy-4 S-MATE
cladding S-MANP
tube O
showed O
improved O
mechanical B-CONPRI
properties E-CONPRI
at O
both O
room O
temperature S-PARA
and O
500 O
°C O
, O
as S-MATE
well O
as S-MATE
under O
LOCA O
simulation S-ENAT
conditions O
. O


Material B-MANP
extrusion E-MANP
is O
an O
Additive B-MANP
Manufacturing I-MANP
process E-MANP
able O
to O
fabricate S-MANP
a O
physical O
object O
directly O
from O
a O
virtual B-ENAT
model E-ENAT
using O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
deposition S-CONPRI
of O
a O
thermoplastic B-MATE
filament E-MATE
extruded S-MANP
by O
a O
nozzle S-MACEQ
. O


The O
fabrication S-MANP
of O
functional B-CONPRI
components E-CONPRI
implies O
the O
need O
for O
the O
assembly S-MANP
with O
other O
parts O
with O
different O
properties S-CONPRI
in O
terms O
of O
material S-MATE
and O
surface B-PARA
quality E-PARA
. O


One O
of O
the O
most O
used O
assembly S-MANP
method O
involving O
plastic S-MATE
materials S-CONPRI
is O
the O
interference B-CONPRI
fit E-CONPRI
. O


It O
consists O
of O
fastening O
elements S-MATE
in O
which O
the O
two O
parts O
are O
pushed O
together O
, O
by O
means O
of O
a O
fit S-CONPRI
force O
, O
and O
no O
other O
fastener S-MACEQ
is O
necessary O
. O


It O
requires O
the O
accurate S-CHAR
design O
of O
the O
interference O
, O
typically O
carried O
out O
by O
the O
designers O
through O
diagrams O
and O
theoretical S-CONPRI
formulations O
supplied O
by O
the O
material S-MATE
manufacturers O
. O


At O
present O
no O
theory O
has O
been O
provided O
for O
material B-MANP
extrusion E-MANP
parts O
due O
to O
the O
anisotropic S-PRO
behavior O
: O
the O
mesostructure O
, O
the O
surface B-PRO
roughness E-PRO
and O
the O
dimensional O
deviations O
mainly O
depend O
upon O
the O
build S-PARA
orientation.In O
this O
work O
the O
effects O
of O
the O
surface B-CHAR
morphology E-CHAR
and O
the O
interference O
grade O
on O
the O
assembly S-MANP
and O
disassembly S-CONPRI
forces O
in O
an O
interference B-CONPRI
fit E-CONPRI
joint O
are O
investigated O
. O


For O
the O
purpose O
, O
a O
design B-CONPRI
of I-CONPRI
experiment E-CONPRI
with O
a O
factorial O
plan O
has O
been O
carried O
out O
. O


Through O
this O
model S-CONPRI
it O
is O
possible O
to O
know O
in O
advance O
the O
force S-CONPRI
necessary O
to O
assemble O
a O
material B-MANP
extrusion E-MANP
part O
with O
an O
assigned O
interference O
grade O
. O


Fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
enables O
production S-MANP
of O
3D B-APPL
objects E-APPL
over O
a O
range S-PARA
of O
material S-MATE
compositions O
at O
low-cost O
relative O
to O
traditional B-MANP
manufacturing E-MANP
approaches O
. O


To O
date O
, O
a O
limited O
but O
growing O
number O
of O
materials S-CONPRI
are O
able O
to O
be S-MATE
used O
with O
FFF S-MANP
, O
however O
many O
applications O
exist O
where O
specific O
mechanical S-APPL
, O
thermal O
, O
or O
chemical O
properties S-CONPRI
are O
needed O
that O
can O
not O
currently O
be S-MATE
met O
with O
the O
available O
feedstock S-MATE
selection O
. O


Therefore O
, O
a O
need O
exists O
to O
tune O
these O
materials S-CONPRI
for O
specific O
chemical O
or O
mechanical B-CONPRI
properties E-CONPRI
. O


One O
common O
formulation O
strategy O
to O
address O
these O
demanding O
design S-FEAT
parameters O
is O
to O
develop O
composites S-MATE
or O
polymer B-MATE
blend E-MATE
filaments S-MATE
. O


This O
mixing S-CONPRI
occurs O
via O
software-controlled O
rotating O
hardware O
in O
the O
chamber O
of O
an O
extruder S-MACEQ
’ O
s S-MATE
hot-end O
. O


The O
efficiency O
of O
mixing S-CONPRI
within O
the O
printed O
layers O
has O
been O
characterized O
in O
detail O
as S-MATE
a O
function O
of O
the O
rotational O
speed O
and O
geometry S-CONPRI
of O
the O
blending S-MANP
hardware O
. O


These O
parameters S-CONPRI
were O
exploited O
to O
program O
the O
ratio O
and O
distribution S-CONPRI
of O
thermoplastic-based O
filaments S-MATE
blended O
within O
printed O
extrudate S-MATE
. O


Example O
printed O
specimens O
were O
produced O
with O
thermoplastic B-MATE
polyurethane E-MATE
( O
TPU O
) O
elastomer S-MATE
blended O
with O
rigid O
polylactic B-MATE
acid E-MATE
( O
PLA S-MATE
) O
and O
Nylon S-MATE
blended O
with O
PLA S-MATE
. O


In O
addition O
, O
a O
conductive O
carbon B-MATE
nanotube E-MATE
( O
CNT S-MATE
) O
-PLA O
composite S-MATE
was O
blended O
as S-MATE
a O
function O
of O
mixer O
geometry S-CONPRI
and O
input O
feed S-PARA
ratios O
with O
non-conductive O
PLA S-MATE
and O
resistance S-PRO
values O
were O
measured O
across O
the O
resulting O
printed O
specimens O
. O


SLM S-MANP
fabricated S-CONPRI
Al-Mg-Sc-Zr O
alloy S-MATE
showed O
a O
heterogeneous B-CONPRI
grain I-CONPRI
structure E-CONPRI
. O


A O
good O
strength-ductility O
synergy O
was O
achieved O
in O
SLMed S-MANP
Al-Mg-Sc-Zr O
alloy S-MATE
. O


Strain S-PRO
partitioning O
among O
heterogeneous B-CONPRI
grain I-CONPRI
structure E-CONPRI
provided O
additional O
back O
stress S-PRO
hardening S-MANP
. O


In O
this O
work O
, O
a O
Sc/Zr O
modified O
Al-Mg B-MATE
alloy E-MATE
was O
processed S-CONPRI
by O
both O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
and O
directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
. O


Due O
to O
different O
precipitation S-CONPRI
behavior O
of O
primary O
Al3 O
( O
Sc O
, O
Zr S-MATE
) O
-L12 O
nucleation S-CONPRI
sites O
, O
a O
heterogeneous B-CONPRI
grain I-CONPRI
structure E-CONPRI
was O
formed O
in O
SLMed S-MANP
sample S-CONPRI
, O
which O
consisted O
of O
ultrafine O
equiaxed B-CONPRI
grains E-CONPRI
bands O
and O
columnar B-PRO
grains E-PRO
domains O
, O
while O
a O
fully O
equiaxed B-CONPRI
grain E-CONPRI
structure O
was O
obtained O
in O
DEDed O
sample S-CONPRI
. O


Tensile S-PRO
results O
showed O
that O
the O
as S-MATE
built O
SLMed S-MANP
sample S-CONPRI
had O
a O
good O
combination O
of O
strength S-PRO
and O
ductility S-PRO
. O


The O
yield B-PRO
strength E-PRO
of O
SLMed S-MANP
sample S-CONPRI
( O
335 O
± O
4 O
MPa S-CONPRI
) O
was O
about O
2.8 O
times O
that O
of O
DEDed O
sample S-CONPRI
( O
118 O
± O
3 O
MPa S-CONPRI
) O
, O
however O
, O
the O
ductility S-PRO
in O
uniform B-PARA
elongation E-PARA
( O
23.6 O
± O
1.9 O
% O
) O
was O
still O
comparable O
to O
that O
of O
DEDed O
sample S-CONPRI
( O
23.8 O
± O
2.6 O
% O
) O
. O


Based O
on O
the O
relationship O
between O
the O
heterogeneous B-CONPRI
grain I-CONPRI
structure E-CONPRI
and O
strain B-MANP
hardening E-MANP
behavior O
, O
the O
strength-ductility O
synergy O
mechanism S-CONPRI
of O
the O
SLMed S-MANP
Al-Mg-Sc-Zr O
alloy S-MATE
was O
discussed O
. O


Stress S-PRO
partitioning O
tests O
showed O
that O
the O
contribution O
of O
back O
stress S-PRO
hardening S-MANP
to O
flow B-PRO
stress E-PRO
was O
higher O
in O
SLMed S-MANP
sample S-CONPRI
than O
DEDed O
sample S-CONPRI
, O
while O
effective O
stress S-PRO
hardening S-MANP
showed O
an O
opposite O
trend S-CONPRI
. O


Despite O
the O
overall O
strain B-MANP
hardening E-MANP
ability O
of O
SLMed S-MANP
sample S-CONPRI
was O
limited O
by O
the O
high O
dynamic S-CONPRI
recovery O
rate O
of O
ultrafine O
equiaxed B-CONPRI
grains E-CONPRI
, O
additional O
back O
stress S-PRO
hardening S-MANP
, O
which O
was O
caused O
by O
strain S-PRO
partitioning O
between O
equiaxed B-CONPRI
grains E-CONPRI
bands O
and O
columnar B-PRO
grains E-PRO
domains O
, O
improved O
its O
strain B-MANP
hardening E-MANP
ability O
and O
resulted O
in O
the O
good O
combination O
of O
strength S-PRO
and O
ductility S-PRO
. O


Silicone B-MATE
elastomers E-MATE
are O
of O
commercial O
interest O
in O
a O
number O
of O
areas S-PARA
because O
of O
their O
distinctive O
properties S-CONPRI
. O


Current O
3D-printing S-MANP
( O
additive B-MANP
manufacturing E-MANP
) O
technologies S-CONPRI
for O
silicones S-MATE
mainly O
rely O
on O
the O
extrusion S-MANP
of O
high-viscosity O
pre-elastomer O
inks O
of O
one O
or O
two O
parts O
. O


Some O
of O
the O
challenges O
presented O
by O
high O
viscosity S-PRO
materials S-CONPRI
, O
for O
instance O
, O
difficulties O
in O
mixing S-CONPRI
and O
changing O
inks O
to O
create O
devices O
from O
more O
than O
one O
type O
of O
silicone S-MATE
, O
could O
be S-MATE
overcome O
by O
use O
of O
lower O
viscosity S-PRO
inks O
. O


Here O
we O
describe O
a O
family O
of O
rapidly O
curing S-MANP
( O
shape O
holding O
within O
< O
2 O
s S-MATE
, O
full O
cure S-CONPRI
in O
< O
20 O
s S-MATE
) O
, O
readily O
mixed O
, O
low-viscosity O
silicone B-MATE
inks E-MATE
using O
a O
combination O
of O
chain-extender O
, O
cross-linker O
, O
base O
polymer S-MATE
and O
photoinduced O
thiol-ene O
click O
chemistry S-CONPRI
. O


A O
key O
advantage O
of O
low O
viscosity S-PRO
is O
the O
facility O
to O
mix O
or O
change O
ink S-MATE
constituents O
, O
which O
facilitates O
changing O
inks O
, O
and O
the O
properties S-CONPRI
of O
the O
resulting O
cured S-MANP
materials O
. O


Microfluidic O
printheads O
and O
pneumatic O
control B-MACEQ
systems E-MACEQ
that O
switch O
rapidly O
between O
multiple O
inks O
, O
and O
then O
cure S-CONPRI
them O
using O
a O
UV B-CONPRI
exposure E-CONPRI
system O
, O
are O
also O
described O
. O


The O
combination O
of O
fast O
curing S-MANP
inks O
, O
and O
the O
printhead O
that O
extrudes O
and O
then O
cures O
them O
, O
allows O
3D S-CONPRI
extrusion O
printing O
of O
low-viscosity O
silicone B-MATE
materials E-MATE
without O
the O
use O
of O
supporting O
material S-MATE
. O


The O
ability O
to O
print S-MANP
overhanging B-CONPRI
structures E-CONPRI
, O
discrete O
and O
continuous O
structures O
, O
as S-MATE
well O
as S-MATE
multimaterial O
structures O
using O
a O
single O
nozzle S-MACEQ
is O
demonstrated O
. O


The O
technology S-CONPRI
described O
here O
is O
scalable O
to O
produce O
higher B-PARA
resolution E-PARA
, O
multimaterial O
silicone S-MATE
structures O
that O
should O
find O
application O
in O
rapid B-ENAT
prototyping E-ENAT
and O
mold S-MACEQ
making O
. O


Continuous O
direct B-MANP
metal I-MANP
deposition E-MANP
in O
Z O
direction O
is O
carried O
out O
successfully O
. O


Superior O
austenite/ferrite O
dual O
phase B-CONPRI
microstructure E-CONPRI
is O
formed O
. O


Thin O
316L B-MATE
stainless I-MATE
steel E-MATE
rods O
were O
fabricated S-CONPRI
by O
continuous O
directed B-MANP
energy I-MANP
deposition E-MANP
in O
Z O
direction O
. O


The O
process B-CONPRI
parameters E-CONPRI
( O
laser B-PARA
power E-PARA
, O
scan O
velocity O
, O
and O
powder B-MACEQ
feeding E-MACEQ
rate O
) O
were O
carefully O
selected O
to O
obtain O
a O
stable O
deposition B-MANP
process E-MANP
and O
the O
effects O
of O
powder B-MACEQ
feeding E-MACEQ
rate O
and O
scan O
velocity O
were O
studied O
. O


A O
preliminary O
study O
on O
microstructure S-CONPRI
and O
tensile B-PRO
properties E-PRO
of O
the O
specimens O
was O
carried O
out O
. O


Results O
indicated O
that O
the O
specimen O
showed O
superior O
austenite/ferrite O
( O
γ/δ O
) O
dual O
phase B-CONPRI
microstructure E-CONPRI
, O
high O
strength S-PRO
( O
608.24 O
MPa S-CONPRI
) O
, O
and O
good O
plastic B-PRO
deformation E-PRO
capacity S-CONPRI
( O
65.08 O
% O
shrinkage S-CONPRI
rate O
) O
when O
setting O
the O
laser B-PARA
power E-PARA
at O
45.2 O
W O
, O
powder B-MACEQ
feeding E-MACEQ
rate O
at O
2.81 O
g/min O
, O
and O
scan O
velocity O
at O
0.5 O
mm/s O
. O


The O
technique O
reported O
in O
this O
paper O
is O
expected O
to O
lay S-CONPRI
the O
foundation O
for O
the O
deposition S-CONPRI
of O
wire O
or O
frame O
structures O
more O
efficiently O
than O
traditional O
layer-by-layer S-CONPRI
directed B-MANP
energy I-MANP
deposition E-MANP
. O


Thermal B-CONPRI
modeling E-CONPRI
of O
additive B-MANP
manufacturing I-MANP
processes E-MANP
such O
as S-MATE
laser O
powder B-MANP
bed I-MANP
fusion E-MANP
is O
able O
to O
calculate O
a O
thermal O
history O
of O
a O
build S-PARA
. O


This O
simulated O
thermal O
history O
can O
in O
turn O
be S-MATE
used O
as S-MATE
an O
input O
to O
further O
simulate O
temperature S-PARA
related O
characteristics O
such O
as S-MATE
residual O
stress S-PRO
, O
distortion S-CONPRI
, O
microstructure S-CONPRI
, O
lack O
of O
fusion S-CONPRI
porosity O
, O
and O
hot O
spots O
. O


In O
order O
to O
estimate O
the O
heat S-CONPRI
loss O
to O
the O
powder B-MACEQ
bed E-MACEQ
during O
the O
process S-CONPRI
, O
convective O
heat B-CONPRI
transfer E-CONPRI
is O
widely O
used O
as S-MATE
thermal O
boundary B-CONPRI
condition E-CONPRI
in O
finite B-CONPRI
element E-CONPRI
modeling O
of O
laser S-ENAT
powder O
fusion S-CONPRI
processes O
. O


However O
, O
this O
convection O
coefficient O
is O
usually O
selected O
based O
on O
empirical S-CONPRI
estimation O
or O
model S-CONPRI
tuning O
. O


In O
this O
work O
, O
FEA O
models O
of O
the O
part O
and O
surrounding O
powder S-MATE
are O
used O
as S-MATE
a O
reference O
to O
determine O
the O
surface S-CONPRI
convection O
BC O
's O
for O
modeling S-ENAT
the O
part O
only O
. O


Seven O
types O
of O
commonly O
used O
AM B-MATE
materials E-MATE
with O
a O
wide O
range S-PARA
of O
thermal B-PRO
conductivities E-PRO
were O
studied O
for O
better O
testing S-CHAR
of O
the O
conductivity S-PRO
dependency O
of O
the O
convection O
coefficient O
. O


The O
convection O
coefficient O
values O
, O
which O
predict O
similar O
thermal O
history O
as S-MATE
the O
powder S-MATE
model S-CONPRI
, O
are O
found O
to O
be S-MATE
a O
function O
of O
thermal B-PRO
conductivity E-PRO
of O
the O
deposited O
material S-MATE
and O
the O
cross-sectional O
thickness O
of O
the O
part O
feature S-FEAT
. O


A O
new O
thickness O
dependent O
convection O
boundary B-CONPRI
condition E-CONPRI
is O
proposed O
and O
found O
to O
be S-MATE
capable O
of O
predicting O
much O
closer O
thermal O
history O
to O
the O
powder S-MATE
model S-CONPRI
. O


These O
newly O
developed O
boundary B-CONPRI
conditions E-CONPRI
improve O
the O
peak O
temperature S-PARA
prediction S-CONPRI
accuracy S-CHAR
by O
36 O
% O
while O
running O
in O
1/4th O
of O
the O
time O
as S-MATE
the O
powder S-MATE
model S-CONPRI
. O


The O
computed B-CHAR
tomography E-CHAR
( O
CT S-ENAT
) O
evaluation O
of O
the O
material B-MANP
extrusion E-MANP
( O
MEX O
) O
of O
a O
short B-MATE
carbon I-MATE
fiber E-MATE
( O
SCF O
) O
Nylon-12 O
filament S-MATE
and O
part O
is O
presented O
. O


CT S-ENAT
, O
a O
non-destructive B-CHAR
testing E-CHAR
method O
, O
was O
used O
to O
quantify O
the O
internal B-PRO
structure E-PRO
of O
specimens O
into O
three O
phases O
: O
pore S-PRO
, O
Nylon S-MATE
, O
and O
SCF O
. O


The O
intensity O
histograms O
from O
the O
CT S-ENAT
data O
were O
fit S-CONPRI
using O
a O
mixed O
skew-Gaussian O
distribution S-CONPRI
( O
MSGD O
) O
algorithm S-CONPRI
to O
segment O
the O
CT S-ENAT
image O
into O
phases O
. O


Thresholded O
images S-CONPRI
were O
used O
to O
isolate O
pores S-PRO
in O
the O
CT S-ENAT
image O
to O
determine O
pore S-PRO
volume O
and O
distribution S-CONPRI
within O
both O
the O
MEX O
SCF O
filament S-MATE
and O
part O
. O


The O
phase S-CONPRI
volume O
percentages O
of O
the O
MEX O
SCF O
filament S-MATE
were O
found O
to O
be S-MATE
1.6 O
% O
pore S-PRO
, O
62.2 O
% O
Nylon S-MATE
, O
and O
36.2 O
% O
SCF O
. O


The O
volume S-CONPRI
of O
most O
pores S-PRO
within O
the O
filament S-MATE
were O
found O
to O
be S-MATE
under O
100 O
μm3 O
. O


The O
highest O
frequency O
of O
pores S-PRO
was O
located O
near O
the O
outside O
of O
the O
filament S-MATE
, O
but O
the O
large O
pores S-PRO
were O
located O
near O
the O
center O
of O
the O
filament S-MATE
. O


This O
result O
indicates O
that O
the O
thermoplastic B-MANP
filament I-MANP
extrusion I-MANP
process E-MANP
likely O
entraps O
large O
bubbles O
in O
the O
center O
of O
filament S-MATE
or O
causes O
large O
thermal B-PARA
gradients E-PARA
and O
residual B-PRO
stresses E-PRO
that O
induce O
voids S-CONPRI
during O
post-extrusion O
cooling S-MANP
. O


MSGD O
analysis O
of O
sections O
of O
the O
MEX O
SCF O
part O
estimated O
phase S-CONPRI
volume O
percentages O
to O
be S-MATE
9.8 O
% O
pore S-PRO
, O
59.6 O
% O
Nylon S-MATE
, O
and O
30.9 O
% O
SCF O
. O


For O
the O
MEX O
SCF O
part O
, O
the O
average S-CONPRI
pore O
area S-PARA
was O
found O
to O
be S-MATE
highest O
( O
> O
250 O
μm2 O
) O
at O
the O
bottom O
of O
the O
layer S-PARA
and O
smallest O
( O
< O
100 O
μm2 O
) O
at O
the O
top O
of O
the O
layer S-PARA
, O
which O
could O
be S-MATE
explained O
by O
a O
large O
temperature B-PARA
gradient E-PARA
between O
and O
contractile O
thermal B-PRO
stresses E-PRO
inside O
the O
layer S-PARA
that O
cause O
the O
thermoplastic S-MATE
to O
shrink S-FEAT
into O
a O
smaller O
volume S-CONPRI
allowing O
the O
voids S-CONPRI
to O
grow O
during O
deposition S-CONPRI
. O


A O
qualitative S-CONPRI
analysis O
of O
fiber B-FEAT
orientation E-FEAT
conducted O
on O
the O
SCF O
filament S-MATE
indicated O
that O
the O
SCFs O
maintain O
their O
orientation S-CONPRI
from O
filament S-MATE
to O
part O
except O
in O
the O
intersection O
zone O
of O
rasters O
. O


In O
the O
quest O
to O
achieve O
functional O
3D B-APPL
printed I-APPL
parts E-APPL
with O
open O
source S-APPL
machines S-MACEQ
and O
tools S-MACEQ
it O
is O
required O
to O
study O
all O
the O
error S-CONPRI
sources O
. O


Flow O
control O
is O
a O
major O
contributor O
to O
accuracy S-CHAR
of O
parts O
manufactured S-CONPRI
additively O
with O
material B-MANP
extrusion E-MANP
and O
a O
precise O
filament S-MATE
feed S-PARA
rate O
is O
therefore O
essential O
. O


Filament S-MATE
slippage O
is O
measured O
in O
this O
work O
. O


The O
speed O
difference O
between O
filament S-MATE
feed S-PARA
gear O
speed O
and O
filament S-MATE
speed O
is O
measured O
with O
a O
cost O
effective O
, O
automated O
setup O
, O
using O
a O
low O
cost O
USB O
microscope S-MACEQ
video O
camera S-MACEQ
and O
image S-CONPRI
processing O
. O


The O
filament S-MATE
width O
is O
also O
measured O
simultaneously O
, O
allowing O
for O
real O
time O
volumetric O
flow B-PARA
rate E-PARA
estimation O
. O


Extrusion S-MANP
temperature O
and O
feed S-PARA
rate O
are O
found O
to O
influence O
the O
amount O
of O
slippage O
. O


Proof O
of O
concept O
closed B-CONPRI
loop I-CONPRI
control E-CONPRI
of O
the O
extruder S-MACEQ
is O
also O
implemented O
and O
reduces O
the O
amount O
of O
slippage O
considerably O
. O


In O
this O
paper O
we O
present O
the O
results O
of O
a O
study O
on O
the O
impact S-CONPRI
of O
a O
thin O
reflective O
film O
between O
the O
substrate S-MATE
and O
photoresin O
on O
the O
two-photon O
polymerization S-MANP
procedure O
. O


We O
have O
proposed O
a O
model S-CONPRI
for O
the O
elementary O
polymerization S-MANP
volume O
( O
voxel S-CONPRI
) O
formation O
for O
the O
introduced O
case O
and O
carried O
out O
simulations S-ENAT
to O
examine O
the O
influence O
of O
the O
refractive O
indexes O
relation O
, O
layer B-PARA
thickness E-PARA
, O
roughness S-PRO
, O
and O
polymerization S-MANP
depth O
on O
the O
polymerization S-MANP
performance S-CONPRI
. O


The O
experiments O
on O
fabrication S-MANP
of O
2D S-CONPRI
and O
2.5D O
structures O
have O
shown O
the O
benefit O
of O
the O
proposed O
configuration S-CONPRI
for O
the O
substrate/photoresin O
interface S-CONPRI
localization O
as S-MATE
well O
as S-MATE
for O
the O
distortion-free O
fabrication S-MANP
. O


Directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
is O
a O
promising O
technique O
for O
cladding S-MANP
and O
repair O
due O
to O
its O
ability O
to O
deposit O
molten B-MATE
metal E-MATE
onto O
existing O
surfaces S-CONPRI
. O


To O
date O
, O
much O
still O
needs O
to O
be S-MATE
understood O
regarding O
the O
microstructure B-CONPRI
evolution E-CONPRI
during O
DED S-MANP
. O


The O
work O
herein O
seeks O
to O
reveal O
the O
effect O
of O
build B-PARA
height E-PARA
on O
mechanical B-CONPRI
properties E-CONPRI
and O
corrosion S-CONPRI
for O
austenitic B-MATE
stainless I-MATE
steel E-MATE
316L O
. O


A O
large O
316L O
block O
was O
fabricated S-CONPRI
via O
DED S-MANP
and O
horizontal O
tensile B-MACEQ
specimens E-MACEQ
were O
taken O
from O
every O
3 O
mm S-MANP
along O
the O
build B-PARA
height E-PARA
in O
order O
to O
assess O
the O
effect O
of O
build B-PARA
height E-PARA
on O
the O
mechanical B-CONPRI
response E-CONPRI
. O


Electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
mapping O
was O
also O
conducted O
on O
sections O
taken O
from O
the O
bottom O
, O
middle O
and O
top O
heights O
of O
the O
build S-PARA
, O
to O
assess O
the O
microstructural B-CONPRI
evolution E-CONPRI
. O


Cyclic O
polarisation O
testing S-CHAR
was O
performed O
on O
sections O
from O
the O
build S-PARA
to O
assess O
the O
pitting S-CONPRI
potential O
and O
re-passivation O
as S-MATE
a O
function O
of O
build B-PARA
height E-PARA
. O


Parameters S-CONPRI
for O
selective B-MANP
laser I-MANP
melting E-MANP
of O
Zr59.3Cu28.8Al10.4Nb1.5 O
( O
trade O
name O
AMZ4 O
) O
, O
allowing O
crack-free O
bulk O
metallic B-MATE
glass E-MATE
with O
low O
porosity S-PRO
, O
have O
been O
developed O
. O


The O
phase S-CONPRI
formation O
was O
found O
to O
be S-MATE
strongly O
influenced O
by O
the O
heating S-MANP
power O
of O
the O
laser S-ENAT
. O


X-ray S-CHAR
amorphous O
samples S-CONPRI
were O
obtained O
with O
laser B-PARA
power E-PARA
at O
and O
below O
75 O
W. O
The O
as-processed O
bulk O
metallic B-MATE
glass E-MATE
was O
found O
to O
devitrify O
by O
a O
two-stage O
crystallization S-CONPRI
process O
within O
which O
the O
presence O
of O
oxygen S-MATE
was O
concluded O
to O
play O
an O
essential O
role O
. O


At O
laser B-PARA
powers E-PARA
above O
75 O
W O
, O
the O
observed O
crystallites S-MATE
were O
found O
to O
be S-MATE
a O
cubic O
phase S-CONPRI
( O
Cu2Zr4O O
) O
. O


The O
hardness S-PRO
and O
Young O
’ O
s S-MATE
modulus O
in O
the O
as-processed O
samples S-CONPRI
was O
found O
to O
increase O
marginally O
with O
increased O
fraction S-CONPRI
of O
the O
crystalline O
phase S-CONPRI
. O


Large-scale O
printing B-ENAT
technology E-ENAT
is O
proposed O
for O
non-metallic O
lightning O
protection O
. O


The O
printing B-MANP
process E-MANP
integrates O
continuous B-MATE
carbon I-MATE
fiber E-MATE
and O
E-Beam O
irradiation S-MANP
curing S-MANP
. O


Low-energy O
E-Beam O
is O
applied O
for O
fast O
and O
low-temperature O
curing S-MANP
adequacy O
of O
print S-MANP
. O


Regarding O
impregnation S-MANP
of O
epoxy S-MATE
, O
the O
fiber S-MATE
content O
of O
this O
printing O
reached O
58 O
wt O
% O
. O


Continuous B-MATE
fiber E-MATE
mesh O
provides O
comparative O
protection O
as S-MATE
commercial O
copper S-MATE
mesh O
. O


Wind-turbine O
blades O
are O
more O
vulnerable O
to O
lightning O
strikes O
as S-MATE
they O
lack O
a O
protection O
system O
for O
large-scale O
glass B-MATE
fiber E-MATE
reinforced O
polymer S-MATE
( O
GFRP O
) O
composite B-CONPRI
structures E-CONPRI
. O


A O
low-energy O
electron B-CONPRI
beam E-CONPRI
( O
EB O
) O
cured S-MANP
printing O
process S-CONPRI
for O
fabricating S-MANP
a O
continuous O
carbon S-MATE
fiber-reinforced O
thermoset O
resin S-MATE
as S-MATE
a O
non-metallic O
lightning O
protection O
mesh O
on O
a O
GFRP O
composite S-MATE
surface O
was O
carried O
out O
in O
this O
study O
. O


During O
the O
proposed O
process S-CONPRI
, O
a O
continuous B-MATE
carbon I-MATE
fiber E-MATE
mesh O
was O
printed O
through O
a O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
that O
integrates O
the O
rapid O
curing S-MANP
of O
an O
epoxy S-MATE
resin O
with O
low-energy O
EB O
irradiation S-MANP
. O


The O
printing B-MANP
process E-MANP
was O
analyzed O
and O
optimized O
by O
examining O
the O
correlation O
between O
the O
EB O
exposure S-CONPRI
dose O
and O
the O
printing O
height O
. O


Results O
from O
artificial O
lightning O
strikes O
showed O
that O
the O
printed O
carbon B-MATE
fiber E-MATE
mesh O
prevented O
damage S-PRO
, O
and O
the O
structure S-CONPRI
remained O
relatively O
intact O
with O
residual S-CONPRI
strength O
reaching O
90.1 O
% O
at O
100 O
kA O
maximum O
peak O
current O
. O


The O
protection O
mechanism S-CONPRI
was O
investigated O
using O
a O
high-speed O
camera S-MACEQ
, O
which O
revealed O
that O
the O
carbon B-MATE
fiber E-MATE
mesh O
spreads O
the O
striking O
current O
outside O
the O
laminate S-CONPRI
instead O
of O
penetrating O
inside O
. O


In O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
products O
are O
built O
by O
melting S-MANP
layers O
of O
metal B-MATE
powder E-MATE
successively O
. O


Optimal B-PARA
process E-PARA
parameters O
are O
usually O
obtained O
by O
scanning S-CONPRI
single O
vectors O
and O
subsequently O
determining O
which O
settings O
lead S-MATE
to O
a O
good O
compromise O
between O
product O
density S-PRO
and O
build B-PARA
speed E-PARA
. O


This O
paper O
proposes O
a O
model S-CONPRI
that O
describes O
the O
effects O
occurring O
when O
scanning S-CONPRI
single O
vectors O
. O


Energy B-CHAR
absorption E-CHAR
and O
heat B-CONPRI
conduction E-CONPRI
are O
modeled O
to O
determine O
the O
temperature S-PARA
distribution S-CONPRI
and O
melt B-MATE
pool E-MATE
characteristics O
for O
different O
laser B-PARA
powers E-PARA
, O
scan B-PARA
speeds E-PARA
and O
layer B-PARA
thicknesses E-PARA
. O


The O
model S-CONPRI
shows O
good O
agreement O
with O
experimentally O
obtained O
scan O
vectors O
and O
can O
therefore O
be S-MATE
used O
to O
predict O
SLM S-MANP
process B-CONPRI
parameters E-CONPRI
. O


This O
research B-CONPRI
investigates E-CONPRI
the O
microstructure S-CONPRI
, O
mechanical S-APPL
, O
residual B-PRO
stress E-PRO
and O
tribological B-CONPRI
properties E-CONPRI
of O
as-printed O
Inconel B-MATE
718 E-MATE
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
. O


The O
microstructure S-CONPRI
exhibits O
a O
hierarchical B-FEAT
structure E-FEAT
composed O
of O
melt B-CONPRI
pool I-CONPRI
boundaries E-CONPRI
and O
directionally B-MANP
solidified E-MANP
columnar O
thin O
dendrites S-BIOP
. O


No O
significant O
size O
of O
defects S-CONPRI
or O
undesirable O
phases O
such O
as S-MATE
Laves O
phases O
or O
macrosegregation S-CONPRI
was O
found O
in O
the O
microstructure S-CONPRI
. O


The O
Vickers O
microhardness S-CONPRI
results O
did O
not O
show O
any O
significant O
differences O
in O
hardness S-PRO
value O
across O
the O
tracks O
and O
layers O
of O
melt B-CONPRI
pool I-CONPRI
boundaries E-CONPRI
. O


The O
hot O
tribological S-CONPRI
behaviour O
of O
the O
alloy S-MATE
was O
investigated O
for O
the O
range S-PARA
of O
temperatures S-PARA
( O
28 O
°C O
, O
400 O
°C O
, O
500 O
°C O
and O
600 O
°C O
) O
in O
a O
high O
temperature S-PARA
pin O
( O
Inconel B-MATE
718 E-MATE
) O
on O
disc O
( O
EN31 O
steel S-MATE
) O
set S-APPL
up O
. O


The O
worn O
surface S-CONPRI
and O
loose O
wear S-CONPRI
debris O
were O
analysed O
with O
the O
aid O
of O
SEM/EDS O
and O
XRD S-CHAR
analysis O
. O


The O
wear S-CONPRI
loss O
and O
friction S-CONPRI
coefficient O
increase O
with O
the O
test O
temperature S-PARA
. O


The O
friction S-CONPRI
results O
show O
the O
running-in-period O
and O
steady-state-period O
for O
the O
high O
temperature S-PARA
cases O
. O


The O
abrasion O
wear S-CONPRI
is O
predominant O
at O
28 O
°C O
. O


In O
contrast O
, O
delamination S-CONPRI
wear O
and O
oxidation S-MANP
wear O
are O
dominant O
for O
high O
temperature S-PARA
cases O
. O


The O
observation O
of O
high O
friction S-CONPRI
and O
wear S-CONPRI
loss O
with O
the O
test O
temperature S-PARA
is O
attributed O
to O
the O
increased O
intensity O
of O
delamination S-CONPRI
wear O
and O
oxidation S-MANP
rate O
of O
non-lubricative O
NiO S-MATE
. O


The O
wear S-CONPRI
debris O
size O
increases O
with O
the O
test O
temperature S-PARA
and O
the O
shape O
has O
undergone O
changes O
from O
short O
angular O
to O
long O
angular O
sheets S-MATE
. O


Single-pass O
depositions O
of O
columnar O
René O
142 O
on O
investment O
cast S-MANP
single-crystal O
( O
SX O
) O
René O
N5 O
substrates O
having O
[ O
100 O
] O
and O
[ O
001 O
] O
primary O
dendrite S-BIOP
growth O
directions O
were O
obtained O
through O
scanning S-CONPRI
laser S-ENAT
epitaxy S-CONPRI
( O
SLE O
) O
, O
a O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
-based O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
. O


The O
microstructure S-CONPRI
and O
the O
microhardness S-CONPRI
properties O
of O
the O
René O
142 O
deposits O
were O
investigated O
through O
high-resolution S-PARA
optical O
microscopy S-CHAR
( O
HR-OM O
) O
, O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
, O
energy B-CHAR
dispersive I-CHAR
x-ray I-CHAR
spectroscopy E-CHAR
( O
EDS S-CHAR
) O
, O
x-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
, O
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
( O
EBSD S-CHAR
) O
, O
and O
micro-hardness O
measurements O
. O


SEM S-CHAR
investigations O
demonstrated O
that O
the O
primary O
γ/γ′ O
precipitates S-MATE
in O
the O
deposit O
region O
were O
90 O
% O
finer O
in O
size O
compared O
to O
the O
substrate S-MATE
. O


Microhardness S-CONPRI
measurements O
showed O
an O
increase O
in O
the O
hardness S-PRO
values O
by O
∼10 O
% O
in O
the O
deposit O
region O
compared O
to O
the O
cast S-MANP
substrate O
. O


The O
results O
showed O
that O
the O
SLE O
process S-CONPRI
has O
tremendous O
potential O
in O
producing O
epitaxial S-PRO
deposits O
of O
nickel-based B-MATE
superalloys E-MATE
and O
, O
therefore O
, O
the O
findings O
reported O
in O
this O
work O
can O
pave O
ways O
to O
fabricate S-MANP
components S-MACEQ
with O
dissimilar-chemistry O
high-γ′ O
nickel-based B-MATE
superalloys E-MATE
using O
an O
LPBF-based O
AM B-MANP
process E-MANP
. O


Neutron B-CHAR
diffraction E-CHAR
study O
of O
poly-crystalline O
bulk O
samples S-CONPRI
of O
Ti-6Al-4V S-MATE
, O
prepared O
using O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
and O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
, O
and O
of O
their O
ingredient O
powders S-MATE
, O
is O
reported O
. O


Both O
the O
SLM S-MANP
and O
EBM S-MANP
samples O
do O
not O
contain O
the O
macro- O
and O
micro-strain O
, O
found O
in O
the O
ingredient O
powder B-MATE
particles E-MATE
. O


In O
addition O
, O
the O
micro-structure O
of O
the O
EBM S-MANP
sample O
is O
found O
free O
of O
preferential O
orientation S-CONPRI
, O
whereas O
in O
the O
SLM S-MANP
sample S-CONPRI
significant O
preference O
towards O
the O
hexagonal S-FEAT
basal B-CONPRI
plane E-CONPRI
is O
found O
. O


Hot-rolled O
Inconel B-MATE
718 E-MATE
showed O
superior O
creep S-PRO
performance O
to O
LPBF S-MANP
Inconel B-MATE
718 E-MATE
. O


HIPing O
worsened O
creep S-PRO
life O
and O
HT O
improved O
creep S-PRO
life O
of O
LPBF S-MANP
Inconel B-MATE
718 E-MATE
. O


Intergranular O
precipitation S-CONPRI
in O
the O
HIP S-MANP
’ O
d O
samples S-CONPRI
explained O
worse O
creep S-PRO
performance O
. O


Hot-rolled O
samples S-CONPRI
avoided O
intergranular O
fracture S-CONPRI
. O


In O
this O
study O
, O
the O
creep S-PRO
performance O
of O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
manufactured O
Inconel B-MATE
718 E-MATE
specimens O
is O
studied O
in O
detail O
and O
compared O
with O
conventional O
hot-rolled O
specimens O
alongside O
as-built O
then O
heat-treated S-MANP
and O
as-built O
then O
hot-isostatic O
pressed S-MANP
specimens O
. O


Hot-rolled O
specimens O
showed O
the O
best O
creep S-PRO
resistance O
, O
while O
the O
hot-isostatic O
pressed S-MANP
specimens O
yielded O
the O
worst O
performance S-CONPRI
, O
inferior O
to O
the O
as-built O
condition O
. O


Creep S-PRO
testing O
of O
all O
samples S-CONPRI
showed O
increased O
secondary O
creep S-PRO
rate O
was O
consistently O
correlated S-CONPRI
with O
a O
reduced O
life O
. O


Fractography S-CHAR
revealed O
intergranular O
fracture S-CONPRI
was O
the O
primary O
failure B-PRO
mode E-PRO
for O
all O
as-built O
samples S-CONPRI
. O


Preferential O
intergranular O
precipitation S-CONPRI
in O
the O
case O
of O
the O
hot-isostatic O
pressed S-MANP
specimens O
during O
hot-isostatic O
pressing S-MANP
extensive O
intergranular O
cracking S-CONPRI
as S-MATE
the O
primary O
failure B-PRO
mechanism E-PRO
. O


Heat-treated S-MANP
specimens O
possessed O
only O
sparse O
intergranular O
precipitates S-MATE
, O
thereby O
explaining O
an O
improved O
creep S-PRO
lifetime O
. O


The O
hot-rolled O
specimens O
, O
having O
smallest O
grain B-PRO
size E-PRO
, O
showed O
the O
least O
extensive O
cracking S-CONPRI
, O
particularly O
in O
locations O
of O
finest O
grains S-CONPRI
, O
explaining O
avoidance O
of O
intergranular O
fracture S-CONPRI
as S-MATE
a O
key O
creep S-PRO
mechanism O
, O
thereby O
explaining O
the O
ductile B-PRO
creep E-PRO
fracture O
surfaces S-CONPRI
in O
the O
case O
of O
the O
hot-rolled O
samples S-CONPRI
. O


The O
build-up O
of O
residual B-PRO
stresses E-PRO
in O
a O
part O
during O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
provides O
a O
significant O
limitation O
to O
the O
adoption O
of O
this O
process S-CONPRI
. O


These O
residuals S-CONPRI
stresses O
may O
cause O
a O
part O
to O
fail O
during O
a O
build S-PARA
or O
fall O
outside O
the O
specified O
tolerances S-PARA
after O
fabrication S-MANP
. O


In O
the O
present O
work O
a O
thermomechanical B-CONPRI
model E-CONPRI
is O
used O
to O
simulate O
the O
build S-PARA
process O
and O
calculate O
the O
residual B-PRO
stress E-PRO
state O
for O
Ti–6Al–4V O
specimens O
built O
with O
continuous O
and O
island O
scan O
strategies O
. O


A O
material S-MATE
model O
is O
developed O
to O
naturally O
capture O
the O
strain-rate O
dependence O
and O
annealing S-MANP
behavior O
of O
Ti–6Al–4V O
at O
elevated O
temperatures S-PARA
. O


Results O
from O
the O
thermomechanical S-CONPRI
simulations S-ENAT
showed O
good O
agreement O
with O
synchrotron S-ENAT
X-ray O
diffraction S-CHAR
measurements O
used O
to O
determine O
the O
residual S-CONPRI
elastic S-PRO
strains O
in O
these O
parts O
. O


However O
, O
the O
experimental S-CONPRI
measurements O
showed O
higher O
residual S-CONPRI
strains O
for O
the O
specimen O
built O
with O
an O
island O
scan O
strategy O
; O
a O
trend S-CONPRI
not O
fully O
captured O
by O
the O
simulations S-ENAT
. O


Parameter S-CONPRI
studies O
were O
performed O
to O
fully O
understand O
the O
advantages O
and O
limitations O
of O
the O
current O
simulation S-ENAT
methodology S-CONPRI
. O


Using O
defocus O
can O
lead S-MATE
to O
a O
stable O
SLM S-MANP
process S-CONPRI
with O
high O
build B-CHAR
rates E-CHAR
. O


Melt B-MATE
pool E-MATE
morphology O
can O
be S-MATE
predicted O
by O
normalized O
enthalpy O
and O
Rosenthal B-CONPRI
equation E-CONPRI
Melt B-PARA
pool I-PARA
depth E-PARA
is O
more O
influenced O
by O
defocusing O
than O
its O
width O
. O


Despite O
its O
many O
benefits O
, O
Selective B-MANP
Laser I-MANP
Melting E-MANP
's O
( O
SLM S-MANP
) O
relatively O
low O
productivity S-CONPRI
compared O
to O
deposition-based O
additive B-MANP
manufacturing E-MANP
techniques O
is O
a O
major O
drawback O
. O


Increasing O
the O
laser B-PARA
beam I-PARA
diameter E-PARA
improves O
SLM S-MANP
's O
build B-CHAR
rate E-CHAR
, O
but O
causes O
loss O
of O
precision S-CHAR
. O


The O
aim O
of O
this O
study O
is O
to O
investigate O
laser B-CONPRI
beam E-CONPRI
focus O
shift O
, O
or O
“ O
defocus O
” O
, O
using O
a O
dynamic S-CONPRI
focusing O
unit O
, O
in O
order O
to O
increase O
the O
laser B-PARA
spot I-PARA
size E-PARA
. O


When O
applied O
to O
the O
SLM S-MANP
process S-CONPRI
, O
focus O
shift O
can O
be S-MATE
integrated O
into O
a O
“ O
hull-core O
” O
strategy O
. O


This O
involves O
scanning S-CONPRI
the O
core S-MACEQ
with O
a O
high O
productivity S-CONPRI
parameter S-CONPRI
set O
using O
defocus O
while O
enabling O
return O
to O
the O
focused O
smaller O
spot B-PARA
size E-PARA
position O
for O
hull O
scanning S-CONPRI
. O


To O
assess O
the O
process S-CONPRI
stability O
, O
single O
line O
scans O
were O
made O
from O
316L B-MATE
stainless I-MATE
steel I-MATE
powder E-MATE
. O


The O
consolidated O
melt B-MATE
pool E-MATE
morphology O
was O
analyzed O
and O
correlated S-CONPRI
with O
the O
process B-CONPRI
parameters E-CONPRI
comprising O
laser B-PARA
power E-PARA
, O
scanning B-PARA
speed E-PARA
and O
defocus O
distance O
. O


In O
order O
to O
link O
the O
melt B-MATE
pool E-MATE
morphology O
with O
the O
heat S-CONPRI
input O
, O
Volumetric O
Energy B-PARA
Density E-PARA
, O
Normalized O
Enthalpy O
and O
Rosenthal B-CONPRI
equation E-CONPRI
were O
considered O
. O


The O
suitability O
of O
using O
the O
Normalized O
Enthalpy O
as S-MATE
a O
design S-FEAT
parameter O
to O
predict O
the O
melt B-PARA
pool I-PARA
depth E-PARA
and O
Rosenthal B-CONPRI
equation E-CONPRI
to O
predict O
its O
width O
was O
highlighted O
. O


This O
study O
shows O
that O
within O
a O
single O
laser S-ENAT
setup O
, O
implementing O
defocus O
can O
lead S-MATE
to O
a O
potential O
productivity S-CONPRI
increase O
by O
840 O
% O
, O
i.e O
. O


New O
generation O
of O
selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
machines S-MACEQ
are O
evolving O
towards O
higher O
power S-PARA
lasers O
as S-MATE
well O
as S-MATE
multi O
laser S-ENAT
systems O
in O
order O
to O
increase O
the O
productivity S-CONPRI
. O


The O
increase O
in O
laser B-PARA
power E-PARA
and O
the O
modification O
of O
the O
laser B-PARA
power E-PARA
distribution S-CONPRI
leads O
to O
microstructural S-CONPRI
and O
mechanical B-CONPRI
property E-CONPRI
variations O
that O
are O
still O
not O
well O
understood.This O
work O
aims O
at O
better O
understanding O
the O
interaction O
of O
a O
1 O
kW O
top-hat O
power S-PARA
distribution S-CONPRI
laser O
on O
a O
well O
know O
material S-MATE
, O
316 O
L O
stainless B-MATE
steel E-MATE
. O


The O
influence O
of O
texture S-FEAT
and O
microstructure S-CONPRI
on O
relative B-PRO
density E-PRO
and O
crack O
density S-PRO
, O
when O
varying O
scan O
rotation O
, O
was O
evaluated O
. O


The O
high O
power S-PARA
( O
HP O
) O
laser S-ENAT
and O
low O
power S-PARA
( O
LP O
) O
laser S-ENAT
were O
compared O
with O
respect O
to O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
. O


HP O
leads O
to O
an O
increase O
in O
morphological O
and O
crystallographic O
texture S-FEAT
together O
with O
a O
coarsening O
of O
the O
cell S-APPL
structure O
in O
contrast O
to O
the O
more O
random O
and O
finer O
cells S-APPL
found O
in O
LP O
processed B-CONPRI
material E-CONPRI
. O


Hot B-MANP
isostatic I-MANP
pressing E-MANP
was O
applied O
as S-MATE
a O
post-process S-CONPRI
treatment O
in O
order O
to O
close O
remaining O
pores S-PRO
and O
cracks O
. O


This O
helped O
in O
achieving O
higher O
elongations O
for O
LP O
and O
HP O
processed B-CONPRI
materials E-CONPRI
, O
while O
competitive O
mechanical B-CONPRI
properties E-CONPRI
to O
the O
316 O
L O
material S-MATE
specifications O
were O
obtained O
in O
both O
cases O
. O


Laser B-MANP
sintering E-MANP
( O
LS O
) O
of O
polymer B-MATE
materials E-MATE
is O
a O
process S-CONPRI
that O
has O
been O
developed O
over O
the O
last O
two O
decades O
and O
has O
been O
applied O
in O
industries S-APPL
ranging O
from O
aerospace S-APPL
to O
sporting O
goods O
. O


However O
, O
one O
of O
the O
current O
major O
limitations O
of O
the O
process S-CONPRI
is O
the O
restricted O
range S-PARA
of O
usable O
materials S-CONPRI
. O


Various B-MATE
material E-MATE
characteristics O
have O
been O
proposed O
as S-MATE
being O
important O
to O
optimise O
the O
laser B-MANP
sintering E-MANP
process O
, O
key O
aspects O
of O
which O
have O
been O
combined O
in O
this O
work O
to O
develop O
an O
understanding O
of O
the O
most O
crucial O
requirements O
for O
LS O
process S-CONPRI
design S-FEAT
and O
materials S-CONPRI
selection O
. O


Using O
the O
favourable O
characteristics O
of O
polyamide-12 O
( O
the O
most O
often O
used O
material S-MATE
for O
laser B-MANP
sintering E-MANP
) O
as S-MATE
a O
benchmark S-MANS
, O
a O
previously O
un-sintered O
thermoplastic B-MATE
elastomer E-MATE
material S-MATE
was O
identified O
as S-MATE
being O
suitable O
for O
the O
LS O
process S-CONPRI
, O
through O
a O
combination O
of O
information O
from O
Differential O
Scanning S-CONPRI
Calorimetry O
( O
DSC S-CHAR
) O
, O
hot O
stage O
microscopy S-CHAR
( O
HSM O
) O
and O
knowledge O
of O
viscosity S-PRO
data S-CONPRI
. O


Subsequent O
laser B-MANP
sintering E-MANP
builds S-CHAR
confirmed O
the O
viability O
of O
this O
new O
material S-MATE
, O
and O
tensile B-CHAR
test E-CHAR
results O
were O
favourable O
when O
compared O
with O
materials S-CONPRI
that O
are O
currently O
commercially O
available O
, O
thereby O
demonstrating O
the O
efficacy O
of O
the O
chosen O
selection O
process S-CONPRI
. O


Selective B-MANP
laser I-MANP
melting E-MANP
is O
already O
established O
as S-MATE
a O
commercial O
production S-MANP
technique O
. O


In-situ S-CONPRI
process O
monitoring O
is O
a O
promising O
means O
to O
accommodate O
this O
issue O
, O
but O
quantitative S-CONPRI
correlations O
between O
monitoring O
signals O
and O
actual O
part O
defects S-CONPRI
have O
been O
lacking O
. O


In O
this O
paper O
, O
results O
are O
presented O
that O
have O
been O
obtained O
with O
an O
off-axis O
melt B-MATE
pool E-MATE
monitoring O
system O
on O
a O
3D B-APPL
Systems E-APPL
ProX O
DMP O
320 O
using O
Ti-6Al-4 B-MATE
V E-MATE
ELI O
. O


The O
focus O
is O
on O
the O
development O
of O
a O
method O
for O
predicting O
the O
presence O
and O
location O
of O
lack O
of O
fusion S-CONPRI
porosities O
as S-MATE
they O
can O
have O
a O
large O
impact S-CONPRI
on O
part O
quality S-CONPRI
and O
are O
not O
always O
easily O
detected O
post-build O
. O


The O
processed S-CONPRI
signals O
from O
the O
monitoring O
system O
are O
shown O
to O
have O
a O
high O
degree O
of O
correlation O
with O
the O
presence O
of O
lack O
of O
fusion S-CONPRI
porosities O
as S-MATE
measured O
by O
CT S-ENAT
scans O
. O


A O
prediction S-CONPRI
sensitivity O
of O
90 O
% O
for O
lack O
of O
fusion S-CONPRI
events O
in O
the O
range S-PARA
of O
pores S-PRO
having O
a O
volume S-CONPRI
greater O
than O
0.001 O
mm3 O
, O
roughly O
equivalent O
to O
160 O
μm O
in O
diameter S-CONPRI
, O
was O
obtained O
. O


Relationships O
between O
prior O
beta O
grain B-PRO
size E-PRO
in O
solidified O
Ti-6Al-4V S-MATE
and O
melting S-MANP
process O
parameters S-CONPRI
in O
the O
Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM S-MANP
) O
process S-CONPRI
are O
investigated O
. O


Samples S-CONPRI
are O
built O
by O
varying O
a O
machine-dependent O
proprietary O
speed O
function O
to O
cover O
the O
process S-CONPRI
space O
. O


Optical B-CHAR
microscopy E-CHAR
is O
used O
to O
measure O
prior O
beta O
grain S-CONPRI
widths O
and O
assess O
the O
number O
of O
prior O
beta O
grains S-CONPRI
present O
in O
a O
melt B-MATE
pool E-MATE
in O
the O
raster O
region O
of O
the O
build S-PARA
. O


Despite O
the O
complicated O
evolution S-CONPRI
of O
beta O
grain B-PRO
sizes E-PRO
, O
the O
beta O
grain S-CONPRI
width O
scales O
with O
melt B-MATE
pool E-MATE
width O
. O


The O
resulting O
understanding O
of O
the O
relationship O
between O
primary O
machine S-MACEQ
variables O
and O
prior O
beta O
grain S-CONPRI
widths O
is O
a O
key O
step S-CONPRI
toward O
enabling O
the O
location O
specific O
control O
of O
as-built O
microstructure S-CONPRI
in O
the O
EBM S-MANP
process O
. O


The O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
process S-CONPRI
is O
used O
throughout O
the O
world O
. O


This O
process S-CONPRI
is O
based O
on O
the O
continuous O
( O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
) O
surfacing O
of O
metallic B-MATE
powder E-MATE
which O
is O
fused S-CONPRI
by O
laser S-ENAT
or O
high-power O
electron B-CONPRI
beam E-CONPRI
. O


In O
this O
paper O
is O
presented O
studies O
of O
the O
structure S-CONPRI
of O
a O
nickel B-MATE
alloy E-MATE
( O
EP718 O
) O
component S-MACEQ
formed O
using O
the O
SLM S-MANP
process S-CONPRI
, O
and O
the O
effects O
of O
heat B-MANP
treatment E-MANP
and O
hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
samples B-CONPRI
manufactured E-CONPRI
by O
SLM S-MANP
technology O
. O


Mechanical B-CHAR
tests E-CHAR
have O
shown O
that O
components S-MACEQ
formed O
using O
SLM S-MANP
exhibit O
a O
low O
level O
of O
strength S-PRO
but O
with O
a O
high O
degree O
of O
plasticity S-PRO
. O


Subsequent O
heat B-MANP
treatment E-MANP
led O
to O
an O
increase O
in O
strength S-PRO
and O
a O
corresponding O
reduction S-CONPRI
in O
plasticity S-PRO
owing O
to O
the O
formation O
of O
reinforcing O
particles S-CONPRI
of O
molybdenum S-MATE
silicides O
and O
an O
incomplete O
relaxation O
, O
with O
low O
grain B-CONPRI
growth E-CONPRI
. O


However O
, O
a O
combination O
of O
SLM S-MANP
+ O
HIP S-MANP
+ O
heat B-MANP
treatment E-MANP
resulted O
in O
optimum O
levels O
of O
strength S-PRO
and O
plasticity S-PRO
in O
comparison O
with O
other O
samples S-CONPRI
. O


In O
this O
work O
, O
3D S-CONPRI
cubic O
test O
specimens O
were O
manufactured S-CONPRI
by O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
from O
commercially O
available O
Ni/Fe-based O
superalloy O
powder S-MATE
, O
and O
were O
further O
subjected O
to O
heat B-MANP
treatment E-MANP
. O


The O
evolution S-CONPRI
of O
their O
microstructure S-CONPRI
, O
phase B-CONPRI
composition E-CONPRI
and O
microhardness S-CONPRI
were O
analysed O
in O
relation O
to O
the O
applied O
heat-treatment O
procedure.Parametric O
study O
of O
the O
SLM S-MANP
process S-CONPRI
allows O
determination O
of O
a O
suitable O
parametric O
set S-APPL
for O
obtaining O
of O
3D B-APPL
objects E-APPL
from O
the O
Ni/Fe-based O
single-crystal O
superalloy O
Thymonel-2 O
, O
with O
the O
resulting O
porosity S-PRO
of O
0.35 O
% O
.The O
manufactured B-CONPRI
3D E-CONPRI
specimens O
were O
subjected O
to O
three O
different O
heat-treatment O
procedures O
. O


The O
microstructure S-CONPRI
and O
the O
phase B-CONPRI
composition E-CONPRI
of O
the O
as-manufactured O
and O
the O
heat-treated S-MANP
samples O
were O
analysed O
in O
order O
to O
study O
the O
microstructure-microhardness O
correlation O
of O
Thymonel-2.XRD O
analysis O
of O
the O
as-manufactured O
samples S-CONPRI
reveals O
the O
presence O
of O
the O
fcc S-CONPRI
γ- O
( O
Fe S-MATE
, O
Ni S-MATE
) O
phase S-CONPRI
only O
. O


The O
literature O
reports O
a O
considerable O
amount O
of O
γ′ O
phase S-CONPRI
in O
Ni/Fe-based O
superalloys S-MATE
processed S-CONPRI
by O
conventional O
metallurgy S-CONPRI
. O


The O
absence O
of O
the O
γ′ O
can O
be S-MATE
explained O
by O
extremely O
high O
cooling B-PARA
rates E-PARA
during O
SLM S-MANP
which O
prevents O
precipitation S-CONPRI
. O


Post B-MANP
heat-treatment E-MANP
of O
the O
specimens O
leads O
to O
significant O
changes O
in O
microstructure S-CONPRI
and O
the O
resulting O
30–90 O
% O
increase O
in O
microhardness.Recommendations O
on O
SLM S-MANP
strategy O
and O
post B-MANP
heat-treatment E-MANP
of O
Thymonel-2 O
are O
provided O
. O


This O
work O
presents O
a O
novel O
modeling S-ENAT
framework S-CONPRI
combining O
computational B-CHAR
fluid I-CHAR
dynamics E-CHAR
( O
CFD S-APPL
) O
and O
cellular O
automata O
( O
CA S-MATE
) O
, O
to O
predict O
the O
solidification B-CONPRI
microstructure E-CONPRI
evolution S-CONPRI
of O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
fabricated S-CONPRI
316 O
L O
stainless B-MATE
steel E-MATE
. O


A O
CA S-MATE
model O
is O
developed O
which O
is O
based O
on O
the O
modified O
decentered O
square O
method O
to O
improve O
computational B-CONPRI
efficiency E-CONPRI
. O


Using O
this O
framework S-CONPRI
, O
the O
fluid S-MATE
dynamics O
of O
the O
melt B-MATE
pool E-MATE
flow O
in O
the O
laser S-ENAT
melting O
process S-CONPRI
is O
found O
to O
be S-MATE
mainly O
driven O
by O
the O
competing O
Marangoni O
force S-CONPRI
and O
the O
recoil O
pressure S-CONPRI
on O
the O
liquid B-MATE
metal E-MATE
surface O
. O


Evaporation S-CONPRI
occurs O
at O
the O
front O
end O
of O
the O
laser S-ENAT
spot O
. O


The O
initial O
high O
temperature S-PARA
occurs O
in O
the O
center O
of O
the O
laser S-ENAT
spot O
. O


However O
, O
due O
to O
Marangoni O
force S-CONPRI
, O
which O
drives O
high-temperature O
liquid O
flowing O
to O
low-temperature O
region O
, O
the O
highest O
temperature S-PARA
region O
shifts O
to O
the O
front O
side O
of O
the O
laser S-ENAT
spot O
where O
evaporation S-CONPRI
occurs O
. O


Additionally O
, O
the O
recoil O
pressure S-CONPRI
pushes O
the O
liquid B-MATE
metal E-MATE
downward O
to O
form O
a O
depression O
zone O
. O


The O
simulated O
melt B-PARA
pool I-PARA
depths E-PARA
are O
compared O
well O
with O
the O
experimental B-CONPRI
data E-CONPRI
. O


Additionally O
, O
the O
simulated O
solidification B-CONPRI
microstructure E-CONPRI
using O
the O
CA S-MATE
model O
is O
in O
a O
good O
agreement O
with O
the O
experimental S-CONPRI
observation O
. O


The O
simulations S-ENAT
show O
that O
higher O
scan B-PARA
speeds E-PARA
result O
in O
smaller O
melt B-PARA
pool I-PARA
depth E-PARA
, O
and O
lack-of-fusion O
pores S-PRO
can O
be S-MATE
formed O
. O


Higher O
laser B-ENAT
scan E-ENAT
speed O
also O
leads O
to O
finer O
grain B-PRO
size E-PRO
, O
larger O
laser-grain O
angle O
, O
and O
higher O
columnar B-PRO
grain E-PRO
contents O
, O
which O
are O
consistent O
with O
experimental S-CONPRI
observations O
. O


This O
model S-CONPRI
can O
be S-MATE
potentially O
used O
as S-MATE
a O
tool S-MACEQ
to O
optimize O
the O
metal B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
process O
, O
through O
generating O
desired O
microstructure S-CONPRI
and O
resultant O
material B-CONPRI
properties E-CONPRI
. O


We O
report O
our O
efforts O
toward O
3D B-MANP
printing E-MANP
of O
polyether O
ether O
ketone O
( O
PEEK S-MATE
) O
at O
room O
temperature S-PARA
by O
direct-ink O
write O
technology S-CONPRI
. O


The O
room-temperature O
extrusion S-MANP
printing O
method O
was O
enabled O
by O
a O
unique O
formulation O
comprised O
of O
commercial O
PEEK S-MATE
powder O
, O
soluble S-CONPRI
epoxy-functionalized O
PEEK S-MATE
( O
ePEEK O
) O
, O
and O
fenchone O
. O


This O
combination O
formed O
a O
Bingham O
plastic S-MATE
that O
could O
be S-MATE
extruded O
using O
a O
readily O
available O
direct-ink O
write O
printer S-MACEQ
. O


The O
initial O
green B-CONPRI
body E-CONPRI
specimens O
were O
strong O
enough O
to O
be S-MATE
manipulated O
manually O
after O
drying S-MANP
. O


After O
printing O
, O
thermal O
processing O
at O
230 O
°C O
resulted O
in O
crosslinking O
of O
the O
ePEEK O
components S-MACEQ
to O
form O
a O
stabilizing O
network O
throughout O
the O
specimen O
, O
which O
helped O
to O
preclude O
distortion S-CONPRI
and O
cracking S-CONPRI
upon O
sintering S-MANP
. O


The O
final O
parts O
were O
found O
to O
have O
excellent O
thermal B-PRO
stability E-PRO
and O
solvent O
resistance S-PRO
. O


The O
Tg S-CHAR
of O
the O
product O
specimens O
was O
found O
to O
be S-MATE
158 O
°C O
, O
which O
is O
13 O
°C O
higher O
than O
commercial O
PEEK S-MATE
as S-MATE
measured O
by O
DSC S-CHAR
. O


Moreover O
, O
the O
thermal B-MANP
decomposition E-MANP
temperature S-PARA
was O
found O
to O
be S-MATE
528 O
°C O
, O
which O
compares O
well O
against O
commercial O
molded O
PEEK S-MATE
samples O
. O


Chemical B-PRO
resistance E-PRO
in O
trifluoroacetic O
acid O
and O
8 O
common O
organic O
solvents O
, O
including O
CH2Cl2 O
and O
toluene O
, O
were O
also O
investigated O
and O
no O
signs O
of O
degradation S-CONPRI
or O
weight S-PARA
changes O
were O
observed O
from O
parts O
submerged O
for O
1 O
week O
in O
each O
solvent O
. O


Test O
specimens O
also O
displayed O
desirable O
mechanical B-CONPRI
properties E-CONPRI
, O
such O
as S-MATE
a O
Young O
’ O
s S-MATE
modulus O
of O
2.5 O
GPa S-PRO
, O
which O
corresponds O
to O
63 O
% O
of O
that O
of O
commercial O
PEEK S-MATE
( O
reported O
to O
be S-MATE
4.0 O
GPa S-PRO
) O
. O


Due O
to O
the O
relative O
youth O
of O
metallic B-MATE
powder E-MATE
bed S-MACEQ
additive B-MANP
manufacturing E-MANP
technologies O
and O
difficulties O
with O
monitoring O
the O
process S-CONPRI
in B-CONPRI
situ E-CONPRI
, O
there O
is O
little O
consensus O
in O
the O
user O
community O
on O
how O
to O
optimize O
user O
variable O
parameters S-CONPRI
to O
ensure O
the O
highest O
quality S-CONPRI
and O
most O
cost O
effective O
build S-PARA
. O


Temperature S-PARA
distribution S-CONPRI
is O
the O
critical B-PRO
factor E-PRO
that O
dictates O
melting S-MANP
, O
microstructure S-CONPRI
and O
eventually O
the O
final O
part O
quality S-CONPRI
. O


Monitoring O
or O
measuring O
the O
temperature S-PARA
during O
the O
process S-CONPRI
is O
extremely O
difficult O
due O
to O
the O
ultra-high O
speeds O
and O
microscale S-CONPRI
size O
of O
the O
laser S-ENAT
or O
electron B-CONPRI
beam E-CONPRI
. O


Therefore O
, O
other O
tools S-MACEQ
such O
as S-MATE
finite O
element S-MATE
modeling O
can O
be S-MATE
utilized O
to O
optimize O
these O
processes S-CONPRI
and O
predict O
the O
behavior O
of O
the O
system O
for O
different O
materials S-CONPRI
. O


This O
research S-CONPRI
presents O
transient S-CONPRI
, O
dynamic S-CONPRI
finite O
element S-MATE
model O
of O
the O
build S-PARA
process O
for O
both O
laser S-ENAT
and O
electron B-MANP
beam I-MANP
melting E-MANP
techniques O
. O


The O
model S-CONPRI
includes O
melting S-MANP
and O
solidification S-CONPRI
of O
the O
powder S-MATE
as S-MATE
well O
as S-MATE
different O
thermal O
aspects O
such O
as S-MATE
conduction O
and O
radiation S-MANP
. O


Diffusivity S-CHAR
of O
the O
powder S-MATE
is O
modeled O
and O
phase S-CONPRI
change O
is O
modeled O
such O
that O
latent B-CONPRI
heat I-CONPRI
of I-CONPRI
fusion E-CONPRI
is O
considered O
. O


Melt B-MATE
pool E-MATE
geometry S-CONPRI
and O
temperature S-PARA
distribution S-CONPRI
was O
obtained O
for O
different O
heat B-CONPRI
sources E-CONPRI
and O
different O
materials S-CONPRI
such O
as S-MATE
Ti6Al4V O
, O
Stainless B-MATE
Steel E-MATE
316 O
, O
and O
7075 O
Aluminum S-MATE
powders O
. O


It O
was O
determined O
that O
heat B-PRO
accumulation E-PRO
is O
most O
consolidated O
within O
titanium B-MATE
powder E-MATE
beds O
, O
with O
steel S-MATE
being O
the O
second O
most O
consolidated O
, O
and O
aluminum S-MATE
powder O
beds O
having O
the O
most O
heat B-CONPRI
dissipation E-CONPRI
. O


As S-MATE
a O
result O
, O
titanium S-MATE
was O
seen O
to O
exhibit O
the O
highest O
local O
temperatures S-PARA
and O
largest O
melt B-MATE
pools E-MATE
, O
followed O
by O
steel S-MATE
and O
aluminum S-MATE
in O
decreasing O
order O
. O


Naturally O
, O
laser S-ENAT
models O
showed O
smaller O
melt B-MATE
pool E-MATE
sizes O
and O
depths O
due O
to O
lower O
power S-PARA
. O


The O
beam S-MACEQ
speed O
and O
power S-PARA
used O
for O
Ti S-MATE
were O
found O
inadequate O
for O
creating O
a O
sustained O
and O
continuous O
melting S-MANP
of O
Al S-MATE
and O
Steel S-MATE
. O


Therefore O
, O
adjustments O
were O
made O
to O
these O
parameters S-CONPRI
and O
presented O
in O
this O
research S-CONPRI
. O


An O
effective O
liquid O
conductivity S-PRO
approach O
has O
been O
developed O
to O
describe O
the O
convective O
transport S-CHAR
modes O
existing O
within O
the O
melt B-MATE
pool E-MATE
in O
powder B-MANP
bed I-MANP
additive I-MANP
manufacturing E-MANP
processes O
. O


A O
first B-CHAR
principles E-CHAR
approach O
is O
introduced O
to O
derive O
an O
effective O
conductive O
transport S-CHAR
mode O
that O
encompasses O
conduction O
and O
advection O
within O
the O
melt B-MATE
pool E-MATE
. O


A O
modified O
Bond O
number O
was O
calculated O
by O
comparing O
surface B-PRO
tension E-PRO
forces S-CONPRI
with O
viscous B-CONPRI
forces E-CONPRI
within O
the O
melt B-MATE
pool E-MATE
region O
. O


It O
was O
determined O
, O
due O
to O
the O
small O
size O
scale O
of O
melt B-MATE
pools E-MATE
in O
powder B-MACEQ
bed E-MACEQ
processes O
, O
that O
the O
surface B-PRO
tension E-PRO
gradient O
driven O
flow O
, O
or O
the O
Marangoni O
effect O
, O
is O
the O
dominant O
mass O
transport S-CHAR
phenomenon O
within O
the O
melt B-MATE
pool E-MATE
. O


Validation S-CONPRI
was O
conducted O
by O
comparing O
simulation S-ENAT
melt B-MATE
pool E-MATE
widths O
and O
depths O
against O
experimental S-CONPRI
measurements O
for O
Inconel B-MATE
718 E-MATE
built O
at O
beam S-MACEQ
powers O
of O
150 O
W O
, O
200 O
W O
and O
300 O
W O
and O
a O
scan B-PARA
speed E-PARA
of O
200 O
mm/s O
. O


By O
introducing O
the O
effective O
liquid O
conductivity S-PRO
, O
simulated O
melt B-MATE
pool E-MATE
widths O
were O
up O
to O
50 O
% O
closer O
to O
experimental S-CONPRI
widths O
and O
simulated O
melt B-PARA
pool I-PARA
depths E-PARA
were O
up O
to O
80 O
% O
closer O
to O
experimental S-CONPRI
measurements O
. O


Analytic O
temperature S-PARA
profiles S-FEAT
and O
melt B-PARA
pool I-PARA
dimensions E-PARA
are O
compared O
between O
Ti6Al4V S-MATE
, O
Stainless B-MATE
Steel E-MATE
316L O
, O
Aluminum B-MATE
7075 E-MATE
and O
Inconel B-MATE
718 E-MATE
built O
with O
similar O
process B-CONPRI
parameters E-CONPRI
, O
while O
including O
effective O
liquid O
conductivity S-PRO
. O


The O
reasons O
for O
differences O
in O
temperature S-PARA
and O
melt B-MATE
pool E-MATE
geometry S-CONPRI
are O
discussed O
. O


Experimental S-CONPRI
measurements O
are O
a O
critical O
component S-MACEQ
of O
model S-CONPRI
development O
, O
as S-MATE
they O
are O
needed O
to O
validate O
the O
accuracy S-CHAR
of O
the O
model S-CONPRI
predictions O
. O


Currently O
, O
there O
is O
a O
deficiency O
in O
the O
availability O
of O
experimental B-CONPRI
data E-CONPRI
for O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
made O
parts O
. O


Here O
, O
two O
experimental S-CONPRI
builds S-CHAR
of O
cylindrical S-CONPRI
geometry O
, O
one O
using O
a O
rotating O
scan B-PARA
pattern E-PARA
and O
the O
other O
using O
a O
constant O
scan B-PARA
pattern E-PARA
, O
are O
designed S-FEAT
to O
provide O
post-build O
distortion S-CONPRI
measurements O
. O


Measurements O
show O
that O
for O
these O
cylindrical S-CONPRI
thin O
wall O
builds S-CHAR
, O
there O
is O
no O
discernable S-CONPRI
effect O
on O
distortion S-CONPRI
from O
using O
the O
rotating O
versus O
constant O
scan B-PARA
patterns E-PARA
. O


Project O
Pan O
finite B-CONPRI
element E-CONPRI
modeling O
software S-CONPRI
is O
used O
to O
model S-CONPRI
each O
of O
the O
experimental S-CONPRI
builds S-CHAR
. O


The O
simulation S-ENAT
results O
show O
good O
agreement O
with O
experimental S-CONPRI
measurements O
of O
post-build O
deformation S-CONPRI
, O
within O
a O
12 O
% O
percent O
error S-CONPRI
as S-MATE
compared O
to O
experimental S-CONPRI
measurements O
. O


Using O
the O
FE S-MATE
model O
, O
the O
effect O
of O
a O
flexible O
versus O
a O
rigid O
substrate S-MATE
on O
distortion S-CONPRI
profile O
is O
examined O
. O


The O
FE S-MATE
model O
is O
validated O
against O
in B-CONPRI
situ E-CONPRI
experimental S-CONPRI
measurements O
of O
substrate S-MATE
distortion S-CONPRI
. O


The O
simulated O
results O
are O
used O
to O
study O
stress S-PRO
and O
distortion S-CONPRI
evolution O
during O
the O
build S-PARA
process O
. O


Internal B-PRO
stresses E-PRO
calculated O
by O
the O
model S-CONPRI
throughout O
the O
part O
are O
used O
in O
explaining O
the O
final O
part O
distortion S-CONPRI
. O


The O
combination O
of O
experimental S-CONPRI
and O
simulation S-ENAT
results O
from O
this O
study O
show O
that O
the O
distortion S-CONPRI
of O
the O
top O
layer S-PARA
is O
relatively O
small O
( O
less O
than O
30 O
% O
) O
throughout O
the O
duration O
of O
the O
build S-PARA
process O
compared O
to O
the O
peak O
distortion S-CONPRI
, O
which O
occurs O
several O
layers O
below O
the O
most O
recently O
deposited B-CHAR
layer E-CHAR
. O


Designing O
metallic S-MATE
cellular B-FEAT
structures E-FEAT
with O
triply B-CONPRI
periodic I-CONPRI
minimal I-CONPRI
surface E-CONPRI
( O
TPMS O
) O
sheet S-MATE
cores S-MACEQ
is O
a O
novel O
approach O
for O
lightweight S-CONPRI
and O
multi-functional O
structural O
applications O
. O


Different O
from O
current O
honeycombs O
and O
lattices S-CONPRI
, O
TPMS O
sheet S-MATE
structures O
are O
composed O
of O
continuous O
and O
smooth O
shells O
, O
allowing O
for O
large O
surface B-PARA
areas E-PARA
and O
continuous O
internal O
channels O
. O


In O
this O
paper O
, O
we O
investigate O
the O
mechanical B-CONPRI
properties E-CONPRI
and O
energy B-CHAR
absorption E-CHAR
abilities O
of O
three O
types O
of O
TPMS O
sheet S-MATE
structures O
( O
Primitive O
, O
Diamond S-MATE
, O
and O
Gyroid O
) O
fabricated S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
with O
316 O
L O
stainless B-MATE
steel E-MATE
under O
compression S-PRO
loading O
and O
classify O
their O
failure B-PRO
mechanisms E-PRO
and O
printing O
accuracy S-CHAR
with O
the O
help O
of O
numerical O
analysis O
. O


Experimental S-CONPRI
results O
reveal O
the O
superior O
stiffness S-PRO
, O
plateau O
stress S-PRO
and O
energy B-CHAR
absorption E-CHAR
ability O
of O
TPMS O
sheet S-MATE
structures O
compared O
to O
body-centred O
cubic O
lattices S-CONPRI
, O
with O
Diamond-type O
sheet S-MATE
structures O
performing O
best O
. O


Nonlinear O
finite B-CONPRI
element E-CONPRI
simulation O
results O
also O
show O
that O
Diamond S-MATE
and O
Gyroid O
sheet S-MATE
structures O
display O
relatively O
uniform O
stress B-PRO
distributions E-PRO
across O
all O
lattice S-CONPRI
cells S-APPL
under O
compression S-PRO
, O
leading O
to O
stable O
collapse O
mechanisms O
and O
desired O
energy B-CHAR
absorption E-CHAR
performance O
. O


Parts O
manufactured S-CONPRI
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
contain O
significant O
residual B-PRO
stress E-PRO
. O


This O
stress S-PRO
causes O
failures O
during O
the O
build S-PARA
process O
, O
distorts O
parts O
and O
limits S-CONPRI
in-service O
performance S-CONPRI
. O


A O
pragmatic O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
of O
the O
build S-PARA
process O
is O
introduced O
here O
to O
predict O
residual B-PRO
stress E-PRO
in O
a O
computationally O
efficient O
manner O
. O


The O
part O
is O
divided O
into O
coarse O
sections O
which O
activate O
at O
the O
melting B-PARA
temperature E-PARA
in O
an O
order O
that O
imitates O
the O
build S-PARA
process O
. O


Temperature S-PARA
and O
stress S-PRO
in O
the O
part O
are O
calculated O
using O
a O
sequentially O
coupled O
thermomechanical S-CONPRI
analysis O
with O
temperature S-PARA
dependent O
material B-CONPRI
properties E-CONPRI
. O


The O
model S-CONPRI
is O
validated O
against O
two O
sets O
of O
experimental S-CONPRI
measurements O
: O
the O
first O
from O
a O
bridge S-APPL
component O
made O
from O
316L B-MATE
stainless I-MATE
steel E-MATE
and O
the O
second O
from O
a O
cuboidal O
component S-MACEQ
made O
from O
Inconel B-MATE
718 E-MATE
. O


For O
the O
bridge S-APPL
component O
the O
simulated O
distortion S-CONPRI
is O
within O
5 O
% O
of O
the O
experimental S-CONPRI
measurement O
when O
modelled O
with O
a O
section O
height O
of O
0.8 O
mm S-MANP
. O


This O
is O
16 O
times O
larger O
than O
the O
50 O
μm O
layer B-PARA
height E-PARA
in O
the O
experimental S-CONPRI
part O
. O


For O
the O
cuboid O
component S-MACEQ
the O
simulated O
distortion S-CONPRI
is O
within O
10 O
% O
of O
experimental S-CONPRI
measurement O
with O
a O
section O
height O
10 O
times O
larger O
than O
the O
experiment S-CONPRI
layer O
height O
. O


These O
results O
show O
that O
simulation S-ENAT
of O
every O
layer S-PARA
in O
the O
build S-PARA
process O
is O
not O
required O
to O
obtain O
accurate S-CHAR
results O
, O
reducing O
computational O
effort O
and O
enabling O
the O
prediction S-CONPRI
of O
residual B-PRO
stress E-PRO
in O
larger O
components S-MACEQ
. O


A O
mesoscale S-CONPRI
multi-physics O
model S-CONPRI
is O
developed O
to O
simulate O
rapid B-MANP
solidification E-MANP
. O


Solute O
transport S-CHAR
, O
phase S-CONPRI
transition O
, O
heat B-CONPRI
transfer E-CONPRI
, O
latent O
heat S-CONPRI
, O
and O
melt B-CONPRI
flow E-CONPRI
are O
modeled O
. O


Powder B-MANP
bed I-MANP
fusion E-MANP
is O
a O
recently O
developed O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technique O
for O
alloys S-MATE
, O
which O
builds S-CHAR
parts O
by O
selectively O
melting S-MANP
metallic O
powders S-MATE
with O
a O
high-energy O
laser S-ENAT
or O
electron B-CONPRI
beam E-CONPRI
. O


Nevertheless O
, O
there O
is O
still O
a O
lack O
of O
fundamental O
understanding O
of O
the O
rapid B-CONPRI
solidification I-CONPRI
process E-CONPRI
for O
better O
quality B-CONPRI
control E-CONPRI
. O


To O
simulate O
the O
microstructure B-CONPRI
evolution E-CONPRI
of O
alloys S-MATE
during O
the O
rapid B-MANP
solidification E-MANP
, O
in O
this O
research S-CONPRI
, O
a O
mesoscale S-CONPRI
multi-physics O
model S-CONPRI
is O
developed O
to O
simultaneously O
consider O
solute O
transport S-CHAR
, O
phase S-CONPRI
transition O
, O
heat B-CONPRI
transfer E-CONPRI
, O
latent O
heat S-CONPRI
, O
and O
melt B-CONPRI
flow E-CONPRI
. O


In O
this O
model S-CONPRI
, O
the O
phase-field O
method O
simulates O
the O
dendrite S-BIOP
growth O
of O
alloys S-MATE
, O
whereas O
the O
thermal O
lattice S-CONPRI
Boltzmann O
method O
models O
heat B-CONPRI
transfer E-CONPRI
and O
fluid B-PRO
flow E-PRO
. O


The O
simulation S-ENAT
results O
of O
Ti-6Al-4V S-MATE
show O
that O
the O
consideration O
of O
latent O
heat S-CONPRI
is O
necessary O
because O
it O
reveals O
the O
details O
of O
the O
formation O
of O
secondary O
arms O
and O
provides O
more O
realistic O
kinetics O
of O
dendrite S-BIOP
growth O
. O


The O
proposed O
multi-physics O
simulation S-ENAT
model S-CONPRI
provides O
new O
insights O
into O
the O
complex O
solidification B-MANP
process E-MANP
in O
AM S-MANP
. O


Relationship O
between O
laser B-PARA
energy I-PARA
density E-PARA
and O
thermal B-CONPRI
expansion E-CONPRI
was O
explained O
. O


Critical O
laser B-PARA
energy I-PARA
density E-PARA
exists O
for O
each O
material S-MATE
. O


Void S-CONPRI
formation O
and O
alloying B-MATE
element E-MATE
vaporization O
occurred O
during O
selective B-MANP
laser I-MANP
melting E-MANP
of O
Ni- O
and O
Fe-based O
alloys S-MATE
. O


Magnetic O
properties S-CONPRI
and O
thermal B-PRO
expansion I-PRO
coefficients E-PRO
of O
parts O
produced O
were O
quantified O
. O


Process S-CONPRI
window O
was O
determined O
for O
Invar S-MATE
36 O
and O
stainless B-MATE
steel E-MATE
316 O
L O
based O
on O
stable O
melting S-MANP
. O


This O
paper O
presents O
an O
experimental S-CONPRI
study O
on O
the O
metallurgical S-APPL
issues O
associated O
with O
selective B-MANP
laser I-MANP
melting E-MANP
of O
Invar S-MATE
36 O
and O
stainless B-MATE
steel E-MATE
316 O
L O
and O
the O
resulting O
coefficient B-PRO
of I-PRO
thermal I-PRO
expansion E-PRO
. O


Invar S-MATE
36 O
has O
been O
used O
in O
aircraft O
control B-MACEQ
systems E-MACEQ
, O
electronic O
devices O
, O
optical S-CHAR
instruments O
, O
and O
medical S-APPL
instruments O
that O
are O
exposed O
to O
significant O
temperature S-PARA
changes O
. O


Stainless B-MATE
steel E-MATE
316 O
L O
is O
commonly O
used O
for O
applications O
that O
require O
high O
corrosion B-CONPRI
resistance E-CONPRI
in O
the O
aerospace S-APPL
, O
medical S-APPL
, O
and O
nuclear O
industries S-APPL
. O


Both O
Invar S-MATE
36 O
and O
stainless B-MATE
steel E-MATE
316 O
L O
are O
weldable O
austenitic S-MATE
face-centered O
cubic O
crystal B-PRO
structures E-PRO
, O
but O
stainless B-MATE
steel E-MATE
316 O
L O
may O
experience O
chromium S-MATE
evaporation O
and O
Invar S-MATE
36 O
may O
experience O
weld S-FEAT
cracking S-CONPRI
during O
the O
welding S-MANP
process S-CONPRI
. O


Various O
laser S-ENAT
process O
parameters S-CONPRI
were O
tested O
based O
on O
a O
full O
factorial B-CONPRI
design E-CONPRI
of O
experiments O
. O


The O
microstructure S-CONPRI
, O
material S-MATE
composition S-CONPRI
, O
coefficient B-PRO
of I-PRO
thermal I-PRO
expansion E-PRO
, O
and O
magnetic O
dipole O
moment O
were O
measured O
for O
both O
materials S-CONPRI
. O


It O
was O
found O
that O
there O
exists O
a O
critical O
laser B-PARA
energy I-PARA
density E-PARA
for O
each O
material S-MATE
, O
EC O
, O
for O
which O
selective B-MANP
laser I-MANP
melting I-MANP
process E-MANP
is O
optimal O
for O
material B-CONPRI
properties E-CONPRI
. O


The O
critical O
laser B-PARA
energy I-PARA
density E-PARA
provides O
enough O
energy O
to O
induce O
stable O
melting S-MANP
, O
homogeneous S-CONPRI
microstructure O
and O
chemical B-CONPRI
composition E-CONPRI
, O
resulting O
in O
thermal B-CONPRI
expansion E-CONPRI
and O
magnetic O
properties S-CONPRI
in O
line O
with O
that O
expected O
for O
the O
wrought B-MATE
material E-MATE
. O


Below O
the O
critical O
energy O
, O
a O
lack O
of O
fusion S-CONPRI
due O
to O
insufficient O
melt S-CONPRI
tracks O
and O
discontinuous O
beads S-CHAR
was O
observed O
. O


The O
melt S-CONPRI
track O
was O
also O
unstable O
above O
the O
critical O
energy O
due O
to O
vaporization O
and O
microsegregation S-CONPRI
of O
alloying B-MATE
elements E-MATE
. O


Both O
cases O
can O
generate O
stress S-PRO
risers S-MACEQ
and O
part O
flaws S-CONPRI
during O
manufacturing S-MANP
. O


These O
flaws S-CONPRI
could O
be S-MATE
avoided O
by O
finding O
the O
critical O
laser B-CONPRI
energy E-CONPRI
needed O
for O
each O
material S-MATE
. O


The O
critical O
laser B-PARA
energy I-PARA
density E-PARA
was O
determined O
to O
be S-MATE
86.8 O
J/mm3 O
for O
Invar S-MATE
36 O
and O
104.2 O
J/mm3 O
for O
stainless B-MATE
steel E-MATE
316 O
L. O
The O
present O
study O
investigated O
the O
effects O
of O
set S-APPL
radius O
of O
curvature O
and O
fiber B-MATE
bundle E-MATE
size O
on O
the O
precision S-CHAR
of O
the O
radius O
of O
curvature O
during O
continuous B-MATE
carbon I-MATE
fiber E-MATE
three-dimensional O
( O
3D S-CONPRI
) O
printing O
. O


First O
, O
individual O
circles O
with O
various O
radii O
using O
various O
sizes O
of O
fiber B-MATE
bundles E-MATE
were O
printed O
with O
a O
3D B-MACEQ
printer E-MACEQ
. O


It O
was O
demonstrated O
that O
with O
a O
larger O
fiber B-MATE
bundle E-MATE
size O
or O
a O
smaller O
set S-APPL
radius O
, O
the O
printed O
radius O
would O
be S-MATE
lower O
than O
the O
set S-APPL
value O
. O


Equiatomic O
CoCrFeMnNi O
HEA O
was O
successfully O
fabricated S-CONPRI
by O
SLM S-MANP
. O


The O
XRD S-CHAR
profiles S-FEAT
of O
the O
SLM-CoCrFeMnNi O
HEA O
were O
refined O
by O
the O
Rietveld O
program O
. O


The O
effect O
of O
the O
peak O
load O
on O
the O
creep S-PRO
deformation O
was O
investigated O
by O
nanoindentation S-CHAR
with O
a O
Berkovich B-CHAR
indenter E-CHAR
. O


The O
creep S-PRO
was O
mainly O
dominated O
by O
deformation S-CONPRI
controlled O
by O
dislocation B-CONPRI
motion E-CONPRI
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
was O
used O
to O
fabricate S-MANP
an O
equiatomic O
CoCrFeMnNi O
high-entropy O
alloy S-MATE
( O
HEA O
) O
. O


The O
SLM-fabricated O
CoCrFeMnNi O
HEA O
samples S-CONPRI
were O
studied O
with O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
, O
field-emission O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
FESEM S-CHAR
) O
, O
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
( O
EBSD S-CHAR
) O
and O
nanoindentation S-CHAR
techniques O
to O
characterize O
the O
microstructure S-CONPRI
and O
creep B-PRO
behavior E-PRO
. O


It O
was O
found O
that O
the O
HEA O
comprised O
a O
single O
face-centered O
cubic O
( O
fcc S-CONPRI
) O
structure S-CONPRI
. O


Due O
to O
the O
fast O
solidification S-CONPRI
and O
high O
temperature B-PARA
gradients E-PARA
of O
the O
molten B-CONPRI
pool E-CONPRI
during O
the O
SLM S-MANP
process S-CONPRI
, O
the O
microstructure S-CONPRI
comprised O
cellular O
subgrains S-CONPRI
with O
grain B-CONPRI
boundary E-CONPRI
angles O
lower O
than O
5° O
. O


Moreover O
, O
the O
effect O
of O
the O
peak O
holding O
load O
on O
the O
nanoindentation S-CHAR
creep S-PRO
deformation O
of O
the O
SLM-fabricated O
HEA O
was O
investigated O
using O
a O
Berkovich B-CHAR
indenter E-CHAR
. O


The O
results O
of O
this O
study O
indicated O
that O
the O
creep S-PRO
was O
mainly O
dominated O
by O
deformation S-CONPRI
controlled O
by O
dislocation B-CONPRI
motion E-CONPRI
. O


Spatter S-CHAR
distribution S-CONPRI
on O
AlSi10Mg S-MATE
powder O
bed S-MACEQ
was O
quantified O
in O
terms O
of O
mass O
, O
size O
and O
processed B-CONPRI
images E-CONPRI
. O


Established O
vision O
methodology S-CONPRI
showed O
moderate O
positive O
relationship O
with O
quantified O
mass O
of O
spatter S-CHAR
. O


Spatter S-CHAR
mass O
and O
size O
distributions S-CONPRI
could O
serve O
as S-MATE
ground O
truth O
validation B-CONPRI
data E-CONPRI
for O
future O
simulation S-ENAT
studies O
. O


Exponential O
decay O
in O
the O
Stk O
number O
with O
respect O
to O
the O
distance O
travelled O
by O
the O
spatter S-CHAR
particles S-CONPRI
. O


In O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
, O
inert B-CONPRI
gas E-CONPRI
is O
pumped O
into O
the O
chamber O
to O
eliminate O
the O
deleterious O
by-products O
, O
which O
includes O
spatter S-CHAR
. O


Despite O
this O
, O
traces O
of O
spatter S-CHAR
on O
the O
powder B-MACEQ
bed E-MACEQ
have O
always O
been O
observed O
. O


Earlier O
research S-CONPRI
mainly O
focussed O
on O
the O
formation O
and O
characterization O
of O
spatter S-CHAR
particles S-CONPRI
that O
were O
freshly O
ejected O
from O
the O
melt B-MATE
pool E-MATE
. O


However O
, O
in O
this O
study O
, O
the O
quantification O
of O
the O
spatter S-CHAR
distribution S-CONPRI
on O
the O
powder B-MACEQ
bed E-MACEQ
was O
performed O
, O
following O
their O
transport S-CHAR
by O
the O
inert B-CONPRI
gas E-CONPRI
flow O
which O
was O
varied O
at O
two O
gas S-CONPRI
pump O
settings O
( O
60 O
and O
67 O
% O
) O
. O


Image S-CONPRI
processing O
for O
spatter S-CHAR
detection O
based O
on O
contrast O
was O
first O
conducted O
. O


The O
sieved O
out O
spatter S-CHAR
particles S-CONPRI
were O
quantified O
by O
precision S-CHAR
weighing O
of O
mass O
. O


Optical B-CHAR
microscopy E-CHAR
was O
then O
utilised O
for O
size O
determination O
. O


The O
majority O
of O
spatter S-CHAR
particles S-CONPRI
were O
originally O
distributed O
along O
the O
−x O
direction O
, O
as S-MATE
observed O
from O
the O
top O
down O
images S-CONPRI
taken O
. O


However O
, O
increasing O
the O
gas S-CONPRI
flow O
velocity O
did O
not O
correspond O
to O
a O
lesser O
mass O
distribution S-CONPRI
. O


Computations O
on O
the O
Stk O
number O
revealed O
that O
at O
the O
gas S-CONPRI
pump O
setting O
of O
67 O
% O
, O
spatter S-CHAR
particles S-CONPRI
of O
greater O
size O
were O
deposited O
earlier O
on O
the O
powder B-MACEQ
bed E-MACEQ
, O
suggesting O
that O
increasing O
the O
gas S-CONPRI
flow O
velocity O
to O
a O
large O
extent O
would O
increase O
the O
likelihood O
of O
powder B-MACEQ
bed E-MACEQ
contamination O
. O


The O
forward O
extrapolation O
of O
the O
exponential O
Stk O
number O
trendlines O
also O
elucidated O
the O
reason O
for O
the O
limitations O
on O
the O
width O
of O
the O
powder B-MACEQ
bed E-MACEQ
in O
machines S-MACEQ
designed S-FEAT
by O
SLM S-MANP
Solutions O
. O


Bulk O
high O
strength S-PRO
and O
thermally O
stable O
Al85Nd8Ni5Co2 O
samples S-CONPRI
have O
been O
prepared O
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
. O


The O
alloy S-MATE
shows O
a O
composite-like O
microstructure S-CONPRI
consisting O
of O
submicron-sized O
stable O
intermetallic S-MATE
phases O
dispersed O
in O
an O
Al S-MATE
matrix O
, O
which O
leads O
to O
high O
compressive B-PRO
strength E-PRO
( O
1–0.5 O
GPa S-PRO
) O
at O
elevated O
temperatures S-PARA
( O
303–573 O
K S-MATE
) O
. O


These O
results O
indicate O
that O
SLM S-MANP
is O
an O
effective O
alternative O
to O
conventional O
routes O
for O
producing O
dense O
, O
thermally O
stable O
and O
near O
net O
shaped O
components S-MACEQ
from O
high O
strength S-PRO
Al-based O
alloys S-MATE
. O


In O
this O
study O
, O
novel O
biomedical S-APPL
Co29Cr9W3Cu O
samples S-CONPRI
were O
fabricated S-CONPRI
using O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
technology S-CONPRI
. O


In O
order O
to O
better O
understand O
the O
formation O
of O
the O
lattice B-CONPRI
defects E-CONPRI
during O
the O
melting S-MANP
process O
, O
and O
the O
tensile S-PRO
deformation S-CONPRI
mechanism O
of O
the O
SLM-produced O
Co29Cr9W3Cu O
samples S-CONPRI
, O
the O
microstructures S-MATE
of O
the O
samples S-CONPRI
before O
and O
after O
tensile S-PRO
deformation S-CONPRI
were O
observed O
using O
a O
scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
( O
SEM S-CHAR
) O
, O
a O
transmission B-CHAR
electron I-CHAR
microscope E-CHAR
( O
TEM S-CHAR
) O
, O
and O
an O
electron O
back-scattered O
diffraction S-CHAR
( O
EBSD S-CHAR
) O
, O
respectively O
. O


The O
SEM S-CHAR
morphology S-CONPRI
indicated O
that O
the O
non-equilibrium O
structure S-CONPRI
of O
the O
SLM-produced O
Co29Cr9W3Cu O
samples S-CONPRI
contained O
cellular O
and O
columnar O
subgrains S-CONPRI
. O


The O
TEM S-CHAR
observation O
and O
EBSD S-CHAR
analysis O
showed O
that O
the O
accumulated O
residual B-PRO
stress E-PRO
during O
the O
SLM S-MANP
process S-CONPRI
predominated O
in O
the O
overlapping O
regions O
between O
the O
adjacent O
scanning S-CONPRI
tracks O
, O
which O
consequently O
induced O
a O
larger O
number O
of O
the O
lattice B-CONPRI
defects E-CONPRI
, O
such O
as S-MATE
dislocations O
and O
overlapping O
stacking O
faults O
. O


The O
analysis O
of O
the O
tensile S-PRO
deformation S-CONPRI
revealed O
that O
the O
main O
plastic B-PRO
deformation E-PRO
was O
caused O
by O
the O
strain-induced O
martensitic O
transformation O
effect O
in O
the O
SLM-produced O
Co29Cr9W3Cu O
samples S-CONPRI
. O


Alumina/aluminum O
titanate O
composites S-MATE
were O
prepared O
using O
directed O
laser S-ENAT
deposition S-CONPRI
. O


Scanning B-PARA
speed E-PARA
has O
a O
significant O
effect O
on O
the O
microstructure S-CONPRI
and O
macro S-FEAT
features O
. O


Microstructure S-CONPRI
and O
macro S-FEAT
defects S-CONPRI
are O
responsible O
for O
the O
trend S-CONPRI
of O
properties S-CONPRI
. O


Optimal O
forming S-MANP
quality O
was O
achieved O
at O
the O
medium-speed O
scanning B-CONPRI
process E-CONPRI
window O
. O


Directed B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
has O
developed O
rapidly O
in O
recent O
years O
as S-MATE
a O
new O
material-structure O
integration O
manufacturing B-MANP
technology E-MANP
for O
preparing O
melt-growth O
ceramics S-MATE
. O


However O
, O
the O
influence O
of O
process S-CONPRI
conditions O
on O
the O
forming S-MANP
quality O
has O
not O
been O
systematically O
studied O
. O


Alumina/aluminum O
titanate O
composite B-MATE
ceramics E-MATE
were O
directly O
prepared O
using O
DED S-MANP
technology O
with O
an O
extensive O
process S-CONPRI
window O
. O


The O
effects O
of O
the O
scanning B-PARA
speed E-PARA
on O
the O
typical O
defects S-CONPRI
, O
microstructure S-CONPRI
, O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
prepared O
samples S-CONPRI
were O
systematically O
investigated O
, O
and O
the O
optimized O
process B-CONPRI
parameters E-CONPRI
were O
determined O
. O


Results O
show O
that O
the O
scanning B-PARA
speed E-PARA
has O
a O
significant O
effect O
on O
the O
macroscopic B-CONPRI
defects E-CONPRI
, O
such O
as S-MATE
cracks O
and O
pores S-PRO
, O
microstructure S-CONPRI
characteristics O
, O
such O
as S-MATE
grain O
morphology S-CONPRI
and O
size O
, O
and O
mechanical B-CONPRI
properties E-CONPRI
, O
such O
as S-MATE
flexural O
strength S-PRO
. O


Slow-speed O
scanning S-CONPRI
achieved O
a O
longer O
retention O
time O
of O
the O
liquid O
molten B-CONPRI
pool E-CONPRI
, O
which O
was O
beneficial O
to O
pore S-PRO
suppression O
. O


Rapid O
scanning S-CONPRI
reduced O
the O
temperature B-PARA
gradient E-PARA
at O
the O
bottom O
of O
the O
molten B-CONPRI
pool E-CONPRI
to O
obtain O
crack-free O
samples S-CONPRI
. O


The O
directional O
growth O
tendency O
of O
α-Al2O3 O
cellular O
dendrites S-BIOP
that O
were O
discretely O
distributed O
in O
the O
Al6Ti2O13 O
matrix O
phase S-CONPRI
weakened O
, O
and O
the O
secondary B-MATE
dendrites E-MATE
gradually O
developed O
by O
increasing O
the O
scanning B-PARA
speed E-PARA
. O


This O
phenomenon O
was O
attributed O
to O
the O
change O
of O
the O
heat-dissipation O
direction O
and O
the O
solidification B-PARA
rate E-PARA
of O
solid/liquid O
interface S-CONPRI
caused O
by O
the O
scanning B-PARA
speed E-PARA
. O


Moreover O
, O
the O
fracture S-CONPRI
toughness O
of O
the O
prepared O
samples S-CONPRI
gradually O
increased O
as S-MATE
the O
scanning B-PARA
speed E-PARA
increased O
, O
while O
the O
flexural B-PRO
strength E-PRO
showed O
a O
parabolic O
law O
behavior O
. O


The O
trend S-CONPRI
of O
the O
properties S-CONPRI
was O
due O
to O
microstructure S-CONPRI
refinement O
and O
macroscopic B-CONPRI
defects E-CONPRI
. O


Generally O
, O
the O
optimal O
forming S-MANP
quality O
was O
achieved O
at O
a O
scanning B-PARA
speed E-PARA
of O
300-500 O
mm/min O
. O


Within O
this O
process S-CONPRI
window O
, O
the O
sample S-CONPRI
had O
up O
to O
98 O
% O
densification S-MANP
, O
1640 O
Hv O
hardness S-PRO
, O
3.75 O
MPa S-CONPRI
m1/2 O
fracture S-CONPRI
toughness O
, O
and O
212 O
MPa S-CONPRI
flexural B-PRO
strength E-PRO
. O


In-situ S-CONPRI
uniaxial O
tensile B-CHAR
tests E-CHAR
coupled O
with O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
( O
XCT O
) O
were O
carried O
out O
on O
a O
Cu-4.3Sn O
alloy S-MATE
fabricated O
by O
selective B-MANP
laser I-MANP
melting E-MANP
. O


XCT O
models O
were O
constructed O
to O
enable O
step-by-step O
visualization O
of O
pore S-PRO
growth O
during O
deformation S-CONPRI
. O


Evolution S-CONPRI
of O
pores S-PRO
( O
mean O
diameter S-CONPRI
, O
density S-PRO
, O
volume B-PARA
fraction E-PARA
and O
sphericity O
) O
was O
quantified O
as S-MATE
a O
function O
of O
plastic S-MATE
strain O
. O


Results O
show O
that O
macroscopic S-CONPRI
instability O
begins O
once O
the O
largest O
internal O
pores S-PRO
reach O
the O
surface S-CONPRI
. O


Also O
, O
accelerated O
growth O
and O
coalescence O
of O
the O
largest O
50 O
pores S-PRO
leads O
to O
rapid O
localization O
of O
strain S-PRO
followed O
by O
fracture S-CONPRI
. O


Pore S-PRO
growth O
was O
modeled O
using O
the O
Rice-Tracey O
( O
RT S-MANP
) O
and O
Huang O
models O
for O
different O
populations O
of O
pores S-PRO
and O
the O
parameters S-CONPRI
were O
optimized O
. O


The O
RT S-MANP
and O
Huang O
constants O
were O
found O
to O
depend O
on O
the O
initial O
mean O
pore S-PRO
diameter S-CONPRI
. O


With O
increasing O
industrial S-APPL
interest O
and O
significance O
of O
the O
selective B-MANP
laser I-MANP
melting E-MANP
the O
importance O
for O
profound O
process S-CONPRI
knowledge O
increases O
so O
that O
new O
materials S-CONPRI
can O
be S-MATE
qualified O
faster O
. O


Therefore O
a O
3D S-CONPRI
numerical O
model S-CONPRI
for O
the O
selective B-MANP
laser I-MANP
melting I-MANP
process E-MANP
is O
presented O
that O
allows O
a O
detailed O
look O
into O
the O
process S-CONPRI
dynamics O
at O
comparably O
low O
calculation O
effort O
. O


It O
combines O
a O
finite O
difference O
method O
with O
a O
combined O
level O
set S-APPL
volume O
of O
fluid S-MATE
method O
for O
the O
simulation S-ENAT
of O
the O
process S-CONPRI
and O
starts O
with O
a O
homogenized S-MANP
powder O
bed S-MACEQ
in O
its O
initial O
configuration S-CONPRI
. O


The O
model S-CONPRI
uses O
a O
comprehensive O
representation O
of O
various O
physical O
effects O
like O
dynamic S-CONPRI
laser O
power S-PARA
absorption S-CONPRI
, O
buoyancy O
effect O
, O
Marangoni O
effect O
, O
capillary B-CONPRI
effect E-CONPRI
, O
evaporation S-CONPRI
, O
recoil O
pressure S-CONPRI
and O
temperature S-PARA
dependent O
material B-CONPRI
properties E-CONPRI
. O


It O
is O
validated O
for O
different O
process B-CONPRI
parameters E-CONPRI
using O
cubic O
samples S-CONPRI
of O
stainless B-MATE
steel E-MATE
316L O
and O
nickel-based O
superalloy O
IN738LC S-MATE
. O


The O
results O
show O
the O
significance O
of O
evaporation S-CONPRI
and O
its O
related O
recoil O
pressure S-CONPRI
for O
a O
feasible O
prediction S-CONPRI
of O
the O
melt B-MATE
pool E-MATE
dynamics O
. O


Furthermore O
a O
possible O
way O
to O
reduce O
the O
times O
and O
costs O
for O
material S-MATE
qualification O
by O
using O
the O
simulation S-ENAT
model S-CONPRI
to O
predict O
possible O
process B-CONPRI
parameters E-CONPRI
and O
therefore O
to O
reduce O
the O
necessary O
experimental S-CONPRI
effort O
for O
material S-MATE
qualification O
to O
a O
minimum O
is O
shown O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
is O
an O
increasingly O
attractive O
technology S-CONPRI
for O
the O
manufacture S-CONPRI
of O
complex O
and O
low O
volume/high O
value O
metal S-MATE
parts O
. O


However O
, O
the O
inevitable O
residual B-PRO
stresses E-PRO
that O
are O
generated O
can O
lead S-MATE
to O
defects S-CONPRI
or O
build B-CHAR
failure E-CHAR
. O


Due O
to O
the O
complexity S-CONPRI
of O
this O
process S-CONPRI
, O
efficient O
and O
accurate S-CHAR
prediction O
of O
residual B-PRO
stress E-PRO
in O
large O
components S-MACEQ
remains O
challenging O
. O


For O
the O
development O
of O
predictive B-CONPRI
models E-CONPRI
of O
residual B-PRO
stress E-PRO
, O
knowledge O
on O
their O
generation O
is O
needed O
. O


This O
study O
investigates S-CONPRI
the O
geometrical O
effect O
of O
scan O
strategy O
on O
residual B-PRO
stress E-PRO
development O
. O


It O
was O
shown O
that O
the O
laser B-ENAT
scan E-ENAT
strategy O
becomes O
less O
important O
for O
scan O
vector O
length O
beyond O
3 O
mm S-MANP
. O


Together O
, O
these O
findings O
, O
provide O
a O
route O
towards O
optimising O
scan O
strategies O
at O
the O
meso-scale O
, O
and O
additionally O
, O
developing O
a O
model B-CONPRI
abstraction E-CONPRI
for O
predicting O
residual B-PRO
stress E-PRO
based O
on O
scan O
vectors O
alone O
. O


Fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
, O
sometimes O
called O
material B-MANP
extrusion E-MANP
( O
ME O
) O
offers O
an O
alternative O
option O
to O
traditional O
polymer S-MATE
manufacturing S-MANP
techniques O
to O
allow O
the O
fabrication S-MANP
of O
objects O
without O
the O
need O
of O
a O
mold S-MACEQ
or O
template S-MACEQ
. O


However O
, O
these O
parts O
are O
limited O
in O
the O
degree O
to O
which O
the O
welding B-FEAT
interface E-FEAT
is O
eliminated O
post O
deposition S-CONPRI
, O
resulting O
in O
a O
decrease O
in O
the O
interlaminar O
fracture S-CONPRI
toughness O
relative O
to O
the O
bulk O
material S-MATE
. O


Here O
reptation O
theory O
under O
nonisothermal O
conditions O
is O
utilized O
to O
predict O
the O
development O
of O
healing O
over O
time O
, O
from O
the O
rheological S-PRO
and O
thermal B-CONPRI
properties E-CONPRI
of O
Acrylonitrile-Butadiene-Styrene O
( O
ABS S-MATE
) O
. O


ABS S-MATE
is O
rheologically O
complex O
and O
acts O
as S-MATE
a O
gel S-MATE
and O
as S-MATE
such O
considerations O
had O
to O
be S-MATE
made O
for O
the O
relaxation O
time O
of O
the O
matrix O
which O
is O
important O
in O
predicting O
the O
degree O
of O
interfacial O
healing O
. O


The O
nonsiothermal O
healing O
model S-CONPRI
developed O
is O
then O
successfully O
compared O
to O
experimental S-CONPRI
interlaminar O
fracture S-CONPRI
experiments O
at O
variable O
printing O
temperatures S-PARA
, O
allowing O
future O
optimization S-CONPRI
of O
the O
process S-CONPRI
to O
make O
stronger O
parts O
. O


Modeling S-ENAT
of O
mechanical S-APPL
behavior O
for O
the O
material-jet O
printed O
polymers S-MATE
including O
composites S-MATE
. O


Validation S-CONPRI
of O
the O
material S-MATE
models O
was O
conducted O
. O


A O
desired O
strain S-PRO
field O
can O
be S-MATE
created O
by O
locally O
tuning O
the O
printed O
material S-MATE
distribution S-CONPRI
. O


The O
goal O
of O
this O
work O
is O
to O
validate O
the O
material S-MATE
models O
for O
parts O
created O
with O
a O
Material B-MANP
Jetting E-MANP
3-dimensional O
printer S-MACEQ
through O
the O
comparison O
of O
Finite B-CONPRI
Element I-CONPRI
Analysis E-CONPRI
( O
FEA O
) O
simulations S-ENAT
and O
physical O
tests O
. O


The O
strain S-PRO
maps O
generated O
by O
a O
video O
extensometer O
for O
multi-material S-CONPRI
samples O
are O
compared O
to O
the O
FEA O
results O
based O
on O
our O
material S-MATE
models O
. O


Two O
base O
materials S-CONPRI
( O
ABS-like O
and O
rubber-like O
) O
and O
their O
composites S-MATE
are O
co-printed O
in O
the O
graded O
tensile B-CHAR
test E-CHAR
samples S-CONPRI
. O


The O
simulations S-ENAT
were O
conducted O
utilizing O
previously O
fitted O
material S-MATE
models O
, O
a O
two-parameter O
Mooney-Rivlin O
model S-CONPRI
for O
the O
elastic S-PRO
materials O
( O
Tango O
Black+ O
, O
DM95 O
, O
and O
DM60 O
) O
and O
a O
bilinear O
model S-CONPRI
for O
the O
rigid O
material S-MATE
( O
Vero O
White+ O
) O
. O


The O
results O
show O
that O
the O
simulation S-ENAT
results O
based O
on O
our O
material S-MATE
models O
can O
predict O
the O
deformation S-CONPRI
behaviors O
of O
the O
multi-material S-CONPRI
samples O
during O
a O
uniaxial O
tensile B-CHAR
test E-CHAR
. O


Our O
simulation S-ENAT
results O
are O
able O
to O
predict O
the O
maximum O
strain S-PRO
in O
the O
matrix O
material S-MATE
( O
TB+ O
) O
within O
5 O
% O
error S-CONPRI
. O


Both O
global O
deformation S-CONPRI
pattern O
and O
local O
strain S-PRO
level O
confirm O
the O
validity O
of O
the O
simulated O
material S-MATE
models O
. O


Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
of O
a O
high B-MATE
strength I-MATE
low I-MATE
alloy I-MATE
steel E-MATE
HY100 O
is O
considered O
in O
the O
present O
investigation O
. O


The O
current O
work O
describes O
( O
i O
) O
optimization S-CONPRI
of O
SLM S-MANP
process B-CONPRI
parameters E-CONPRI
for O
producing O
fully B-PARA
dense E-PARA
parts O
in O
HY100 O
steel S-MATE
and O
( O
ii O
) O
the O
effects O
of O
post-processing B-CONPRI
heat E-CONPRI
treatment O
on O
the O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
. O


Samples S-CONPRI
have O
been O
fabricated S-CONPRI
by O
SLM S-MANP
using O
different O
combinations O
of O
laser B-PARA
power E-PARA
, O
laser B-ENAT
scan E-ENAT
speed O
, O
and O
hatch B-PARA
spacing E-PARA
. O


Fully B-PARA
dense E-PARA
samples O
were O
achieved O
at O
an O
energy B-PARA
density E-PARA
of O
65 O
J/mm3 O
. O


Microstructures S-MATE
of O
the O
as-built O
and O
heat S-CONPRI
treated O
samples S-CONPRI
were O
investigated O
using O
optical S-CHAR
and O
scanning B-MACEQ
electron I-MACEQ
microscopes E-MACEQ
, O
X-ray B-CHAR
diffraction E-CHAR
, O
and O
electron O
backscattered O
diffraction S-CHAR
techniques O
. O


The O
as-built O
parts O
are O
unsuitable O
for O
direct O
application O
due O
to O
untempered O
, O
hard O
and O
brittle S-PRO
martensite O
microstructure S-CONPRI
. O


The O
as-built O
parts O
were O
subjected O
to O
post-processing B-CONPRI
heat E-CONPRI
treatments O
( O
“ O
direct O
temper S-MANP
” O
and O
“ O
quench O
and O
temper S-MANP
” O
) O
. O


The O
direct O
tempered S-MANP
samples S-CONPRI
exhibited O
higher O
yield B-PRO
strength E-PRO
and O
ultimate B-PRO
strength E-PRO
than O
the O
quench O
and O
temper S-MANP
ones O
. O


Noticeable O
amounts O
of O
anisotropy S-PRO
with O
respect O
to O
the O
build B-PARA
orientation E-PARA
, O
especially O
in O
tensile B-PRO
elongation E-PRO
, O
were O
observed O
in O
the O
direct O
tempered S-MANP
samples S-CONPRI
due O
to O
in-homogenous O
microstructure S-CONPRI
. O


Quench O
and O
temper S-MANP
treatment O
of O
the O
parts O
resulted O
in O
recrystallized S-MANP
grains S-CONPRI
with O
uniform O
microstructure S-CONPRI
. O


The O
current O
investigation O
shows O
that O
quench O
and O
temper S-MANP
at O
650 O
°C O
is O
an O
optimum O
post B-CONPRI
processing E-CONPRI
treatment O
for O
HY100 O
SLM S-MANP
parts O
as S-MATE
it O
manifests O
desired O
strength S-PRO
with O
good O
tensile B-PRO
elongation E-PRO
. O


Surface S-CONPRI
pore S-PRO
defects S-CONPRI
are O
always O
formed O
during O
directed B-MANP
energy I-MANP
deposition I-MANP
processes E-MANP
, O
which O
may O
stem O
from O
entrapped O
gas S-CONPRI
bubbles O
. O


Such O
defects S-CONPRI
have O
detrimental O
effects O
on O
the O
build S-PARA
quality O
and O
performance S-CONPRI
of O
safety-critical O
metal S-MATE
parts O
. O


Despite O
previous O
experimental S-CONPRI
and O
theoretical S-CONPRI
studies O
devoted O
to O
this O
subject O
, O
direct O
observations O
of O
the O
dynamic S-CONPRI
behavior O
of O
gas S-CONPRI
bubbles O
and O
elucidation O
of O
how O
they O
form O
surface S-CONPRI
pore S-PRO
defects S-CONPRI
have O
not O
yet O
been O
achieved O
. O


In O
this O
work O
, O
the O
relationships O
between O
surface S-CONPRI
pore S-PRO
defects S-CONPRI
and O
the O
bubbles O
originating O
on O
the O
melt B-MATE
pool E-MATE
surface O
were O
carefully O
studied O
using O
high-speed O
photography O
at O
up O
to O
20,000 O
frames O
per O
second O
. O


The O
appearance O
of O
surface S-CONPRI
pores S-PRO
was O
a O
result O
of O
dynamic S-CONPRI
competition O
between O
bubble O
explosion O
and O
solidification S-CONPRI
of O
the O
surrounding O
melt S-CONPRI
, O
where O
the O
final O
location O
of O
the O
surface S-CONPRI
pores S-PRO
is O
determined O
by O
the O
melt S-CONPRI
convection O
and O
the O
boundary S-FEAT
motion O
of O
the O
melt B-MATE
pool E-MATE
. O


In O
the O
case O
of O
single-track O
deposition S-CONPRI
, O
complex O
thermocapillary O
convection O
drives O
gas S-CONPRI
bubble O
diffusion S-CONPRI
, O
and O
pore S-PRO
defects S-CONPRI
cluster O
along O
the O
lateral O
edge O
. O


In O
the O
case O
of O
multi-track O
deposition S-CONPRI
, O
surface S-CONPRI
pore S-PRO
defects S-CONPRI
were O
more O
likely O
to O
occur O
on O
the O
last O
track O
due O
to O
the O
gravity-driven O
flow O
effect O
that O
is O
determined O
by O
the O
track O
path O
and O
overlap S-CONPRI
. O


Metal-filled O
polymers S-MATE
containing O
micro-powders O
of O
highly O
conductive O
metals S-MATE
can O
serve O
as S-MATE
a O
starting O
material S-MATE
to O
fabricate S-MANP
complex O
metal S-MATE
structures O
using O
economic O
filament S-MATE
extrusion-based O
3D B-MANP
printing E-MANP
and O
molding S-MANP
methods O
. O


We O
report O
our O
measurements O
of O
the O
thermal B-PRO
conductivity E-PRO
of O
copper S-MATE
samples O
prepared O
using O
these O
methods O
before O
and O
after O
a O
thermal B-MANP
treatment E-MANP
process S-CONPRI
. O


Sintering S-MANP
the O
samples S-CONPRI
at O
980 O
℃ O
leads O
to O
an O
order O
of O
magnitude S-PARA
improvement O
in O
thermal B-PRO
conductivity E-PRO
when O
compared O
with O
as-printed O
or O
as-molded O
samples S-CONPRI
. O


Thermal B-PRO
conductivity E-PRO
values O
of O
approximately O
30 O
W/mK O
are O
achieved O
using O
commercially O
available O
polymer-copper O
composite S-MATE
filaments O
with O
a O
copper S-MATE
volume O
fraction S-CONPRI
of O
0.4 O
. O


Over-sintering O
the O
samples S-CONPRI
at O
1080 O
℃ O
further O
enhances O
the O
thermal B-PRO
conductivity E-PRO
by O
more O
than O
two O
folds O
, O
but O
it O
leads O
to O
uncontrolled O
shrinkage S-CONPRI
of O
the O
samples S-CONPRI
. O


The O
measured O
thermal B-PRO
conductivities E-PRO
show O
a O
modest O
decrease O
with O
increasing O
temperatures S-PARA
due O
to O
increased O
electron-phonon O
scattering O
rates O
. O


The O
experimental B-CONPRI
data E-CONPRI
agree O
well O
with O
the O
thermal B-PRO
conductivity E-PRO
models O
previously O
reported O
for O
sintered S-MANP
porous B-MATE
metal E-MATE
samples O
. O


The O
measured O
electrical B-PRO
conductivity E-PRO
, O
Young O
’ O
s S-MATE
modulus O
and O
yield B-PRO
strength E-PRO
of O
the O
present O
sintered S-MANP
samples S-CONPRI
are O
also O
reported O
. O


The O
Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM S-MANP
) O
technology S-CONPRI
enables O
the O
manufacturing S-MANP
of O
new O
designs S-FEAT
and O
sophisticated O
geometries S-CONPRI
. O


The O
process S-CONPRI
is O
particularly O
well O
suited O
for O
the O
fabrication S-MANP
of O
lattice B-FEAT
structures E-FEAT
. O


A O
standard S-CONPRI
methodology S-CONPRI
is O
presented O
in O
order O
to O
predict O
the O
mechanical B-CONPRI
response E-CONPRI
of O
lattice B-FEAT
structures E-FEAT
fabricated S-CONPRI
by O
EBM S-MANP
. O


The O
inner O
and O
outer O
structure S-CONPRI
of O
single O
struts S-MACEQ
produced O
by O
EBM S-MANP
was O
characterized O
using O
X-ray B-CHAR
tomography E-CHAR
. O


Struts S-MACEQ
with O
a O
1 O
mm S-MANP
diameter S-CONPRI
and O
different O
orientations S-CONPRI
respect O
to O
the O
build B-PARA
direction E-PARA
were O
analyzed O
. O


The O
geometry S-CONPRI
discrepancies O
between O
the O
designed S-FEAT
and O
the O
fabricated S-CONPRI
strut O
were O
highlighted O
. O


Two O
effects O
were O
identified O
: O
( O
i O
) O
The O
produced O
struts S-MACEQ
are O
generally O
thinner O
than O
the O
designed S-FEAT
ones O
, O
( O
ii O
) O
Within O
the O
produced O
struts S-MACEQ
, O
loads O
are O
not O
transmitted O
by O
the O
entire O
geometry S-CONPRI
. O


The O
elastic S-PRO
response O
of O
the O
strut S-MACEQ
was O
assumed O
to O
be S-MATE
represented O
by O
a O
circular O
cylinder O
with O
an O
equivalent O
diameter S-CONPRI
. O


The O
first O
one O
is O
the O
diameter S-CONPRI
of O
an O
inscribed O
cylinder O
whereas O
the O
second O
one O
is O
the O
result O
of O
a O
numerical B-ENAT
simulation E-ENAT
based O
on O
the O
3D B-CONPRI
image E-CONPRI
of O
the O
strut S-MACEQ
characterized O
by O
X-ray B-CHAR
tomography E-CHAR
. O


The O
methodology S-CONPRI
was O
then O
applied O
to O
an O
octet-truss O
lattice B-FEAT
structure E-FEAT
. O


The O
mechanical S-APPL
equivalent O
diameter S-CONPRI
obtained O
by O
numerical B-ENAT
simulation E-ENAT
on O
a O
3D B-CONPRI
image E-CONPRI
of O
the O
strut S-MACEQ
allows O
to O
simulate O
the O
“ O
true O
” O
properties S-CONPRI
of O
the O
lattice B-FEAT
structure E-FEAT
by O
taking O
into O
account O
the O
manufacturing B-CONPRI
constraints E-CONPRI
of O
the O
EBM S-MANP
process O
. O


We O
have O
investigated O
the O
spatial B-CHAR
distribution E-CHAR
of O
microstructures S-MATE
of O
a O
Co-Cr-Mo O
alloy S-MATE
rod O
fabricated S-CONPRI
by O
Electron B-MANP
Beam I-MANP
Melting E-MANP
( O
EBM S-MANP
) O
method O
along O
built O
height O
. O


The O
topside O
of O
the O
rod S-MACEQ
is O
rich O
in O
γ-fcc O
phase S-CONPRI
and O
consists O
of O
fine O
grains S-CONPRI
with O
high O
local O
distortion S-CONPRI
density S-PRO
. O


The O
bottom O
part O
has O
an O
ε-hcp O
single O
phase S-CONPRI
and O
consists O
of O
relatively O
coarser O
grains S-CONPRI
with O
low O
local O
distortion S-CONPRI
density S-PRO
. O


The O
mean O
grain B-PRO
size E-PRO
increases O
from O
56 O
μm O
( O
at O
the O
top O
of O
the O
rod S-MACEQ
) O
to O
159 O
μm O
( O
at O
the O
bottom O
) O
, O
and O
is O
accompanied O
by O
a O
decrease O
in O
the O
γ-fcc O
phase B-CONPRI
fraction E-CONPRI
. O


As S-MATE
a O
result O
, O
the O
hardness S-PRO
of O
the O
samples S-CONPRI
, O
as S-MATE
well O
as S-MATE
the O
area S-PARA
fraction O
of O
precipitates S-MATE
formed O
in O
the O
samples S-CONPRI
, O
increases O
gradually O
from O
top O
to O
bottom O
of O
the O
rod S-MACEQ
, O
while O
corrosion B-CONPRI
resistance E-CONPRI
is O
uniformly O
high O
throughout O
the O
rod S-MACEQ
almost O
independently O
of O
the O
location O
. O


The O
mechanism S-CONPRI
behind O
the O
formation O
of O
phase S-CONPRI
distribution S-CONPRI
is O
discussed O
in O
terms O
of O
thermodynamic O
phase S-CONPRI
stability O
and O
kinetics O
of O
phase S-CONPRI
transformation O
accompanying O
the O
thermal O
history O
during O
the O
post-solidification O
process S-CONPRI
. O


To O
increase O
the O
productivity S-CONPRI
of O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
( O
LPBF S-MANP
) O
, O
a O
hull-bulk O
strategy O
can O
be S-MATE
implemented O
. O


This O
approach O
consists O
in O
using O
a O
high O
layer B-PARA
thickness E-PARA
in O
the O
core S-MACEQ
of O
the O
part O
, O
hence O
reducing O
the O
build B-PARA
time E-PARA
, O
and O
a O
low O
layer B-PARA
thickness E-PARA
in O
the O
skin O
, O
to O
maintain O
a O
high O
accuracy S-CHAR
and O
good O
surface B-FEAT
finish E-FEAT
. O


The O
present O
study O
investigated O
to O
what O
extent O
this O
strategy O
affected O
the O
surface B-PRO
roughness E-PRO
, O
relative B-PRO
density E-PRO
, O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
Ti-6Al-4 B-MATE
V E-MATE
parts O
. O


Ti-6Al-4 B-MATE
V E-MATE
specimens O
were O
built O
using O
two O
distinct O
sets O
of O
process B-CONPRI
parameters E-CONPRI
, O
one O
optimized O
for O
a O
90 O
μm-layer O
thickness O
in O
the O
bulk O
and O
the O
other O
for O
a O
30 O
μm-layer O
thickness O
in O
the O
hull O
. O


In O
addition O
to O
surface B-PRO
roughness E-PRO
and O
relative B-PRO
density E-PRO
measurements O
, O
a O
thorough O
microstructure S-CONPRI
analysis O
was O
done O
using O
both O
optical B-CHAR
microscopy E-CHAR
and O
SEM S-CHAR
. O


Additionally O
, O
EBSD S-CHAR
measurements O
and O
numerical O
reconstruction S-CONPRI
of O
the O
parent O
β O
grains S-CONPRI
were O
performed O
to O
evaluate O
the O
mesostructure O
and O
texture S-FEAT
evolution S-CONPRI
from O
hull O
to O
bulk O
. O


Microhardness S-CONPRI
measurements O
and O
tensile B-CHAR
tests E-CHAR
were O
done O
to O
assess O
the O
effect O
of O
the O
hull-bulk O
strategy O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
present O
study O
demonstrated O
the O
possibility O
of O
using O
the O
hull-bulk O
strategy O
to O
build S-PARA
high-quality O
Ti-6Al-4 B-MATE
V E-MATE
parts O
, O
without O
impacting O
their O
tensile B-PRO
properties E-PRO
, O
hence O
increasing O
the O
productivity S-CONPRI
of O
the O
process S-CONPRI
by O
a O
geometry-dependent O
factor O
, O
typically O
ranging O
between O
25 O
% O
and O
100 O
% O
. O


In O
Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
, O
metal B-MATE
powders E-MATE
, O
sensitive O
to O
humidity O
and O
oxygen S-MATE
, O
like O
AlSi10Mg S-MATE
or O
Ti-6Al-4 B-MATE
V E-MATE
are O
used O
as S-MATE
starting O
material S-MATE
. O


Titanium-based O
materials S-CONPRI
are O
influenced O
by O
oxygen S-MATE
and O
nitrogen S-MATE
due O
to O
the O
formation O
of O
oxides S-MATE
and O
nitrides S-MATE
, O
respectively O
. O


During O
this O
research S-CONPRI
, O
the O
oxygen S-MATE
concentration O
in O
the O
build B-PARA
chamber E-PARA
was O
controlled O
from O
2 O
ppm O
to O
1000 O
ppm O
using O
an O
external O
measurement S-CHAR
device O
. O


Built O
Ti-6Al-4 B-MATE
V E-MATE
specimens O
were O
evaluated O
regarding O
their O
microstructure S-CONPRI
, O
hardness S-PRO
, O
tensile B-PRO
strength E-PRO
, O
notch S-FEAT
toughness O
, O
chemical B-CONPRI
composition E-CONPRI
and O
porosity S-PRO
, O
demonstrating O
the O
importance O
of O
a O
stable O
atmospheric O
control O
. O


It O
could O
be S-MATE
shown O
that O
an O
increased O
oxygen S-MATE
concentration O
in O
the O
shielding O
gas S-CONPRI
atmosphere O
leads O
to O
an O
increase O
of O
the O
ultimate B-PRO
tensile I-PRO
strength E-PRO
by O
30 O
MPa S-CONPRI
and O
an O
increased O
( O
188.3 O
ppm O
) O
oxygen S-MATE
concentration O
in O
the O
bulk O
material S-MATE
. O


These O
results O
were O
compared O
to O
hot O
isostatic O
pressed S-MANP
( O
HIPed O
) O
samples S-CONPRI
to O
prevent O
the O
influence O
of O
porosity S-PRO
. O


In O
addition O
, O
the O
fatigue S-PRO
behavior O
was O
investigated O
, O
revealing O
increasingly O
resistant O
samples S-CONPRI
when O
oxygen S-MATE
levels O
in O
the O
atmosphere O
are O
lower O
. O


A O
concept O
of O
body O
heat B-CONPRI
flux E-CONPRI
has O
been O
developed O
to O
predict O
part O
distortion S-CONPRI
. O


Powder-liquid-solid O
material S-MATE
state O
transition S-CONPRI
was O
simulated O
via O
user O
subroutine O
. O


Large O
tensile B-PRO
residual I-PRO
stress E-PRO
occurs O
on O
the O
top O
layer S-PARA
of O
the O
part O
. O


Part O
distortion S-CONPRI
was O
predicted S-CONPRI
with O
reasonable O
accuracy S-CHAR
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
a O
promising O
technology S-CONPRI
to O
manufacture S-CONPRI
functional O
( O
end-use O
) O
metal S-MATE
parts O
with O
complex B-CONPRI
geometry E-CONPRI
directly O
from O
CAD S-ENAT
data O
. O


The O
process S-CONPRI
induced O
high O
tensile B-PRO
residual I-PRO
stress E-PRO
and O
part O
distortion S-CONPRI
due O
to O
the O
non-uniform O
heat S-CONPRI
input O
during O
a O
SLM S-MANP
process S-CONPRI
would O
detrimentally O
affect O
the O
part O
performance S-CONPRI
. O


However O
, O
it O
is O
extremely O
challenging O
to O
predict O
distortion S-CONPRI
of O
a O
practical O
SLMed S-MANP
part O
if O
each O
single O
track O
is O
taken O
into O
account O
by O
using O
the O
conventional O
modeling S-ENAT
methods O
The O
complex O
multiphysics O
phenomenon O
such O
as S-MATE
fluid O
flow O
in O
the O
melt B-MATE
pool E-MATE
, O
phase S-CONPRI
transformation O
during O
cooling S-MANP
, O
and O
resulted O
anisotropic S-PRO
properties O
further O
complicate O
this O
issue O
. O


In O
this O
study O
, O
a O
temperature-thread O
multiscale B-CONPRI
modeling E-CONPRI
approach O
has O
been O
developed O
to O
effectively O
predict O
residual B-PRO
stress E-PRO
and O
part O
distortion S-CONPRI
of O
a O
twin O
cantilever S-FEAT
. O


An O
equivalent O
body O
heat B-CONPRI
flux E-CONPRI
has O
been O
proposed O
from O
the O
microscale S-CONPRI
laser B-ENAT
scan E-ENAT
model O
and O
imported O
as S-MATE
the O
“ O
temperature-thread O
” O
to O
the O
subsequent O
mesoscale S-CONPRI
layer S-PARA
hatch O
model S-CONPRI
. O


The O
hatched O
layer S-PARA
is O
then O
heated O
up O
by O
the O
equivalent O
body O
heat B-CONPRI
flux E-CONPRI
and O
used O
as S-MATE
a O
basic O
unit O
to O
build S-PARA
up O
the O
macroscale S-CONPRI
part O
in O
a O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
fashion S-CONPRI
. O


The O
thermal O
history O
and O
residual B-PRO
stress E-PRO
fields O
of O
the O
twin O
cantilever S-FEAT
during O
the O
SLM S-MANP
process S-CONPRI
were O
simulated O
. O


The O
predicted S-CONPRI
cantilever S-FEAT
distortion O
agrees O
with O
the O
measured O
data S-CONPRI
with O
a O
reasonable O
accuracy S-CHAR
. O


Open O
cellular B-FEAT
structures E-FEAT
fabricated O
in O
Ti6Al4V S-MATE
using O
the O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
process S-CONPRI
have O
been O
proposed O
for O
tissue O
scaffolds S-FEAT
and O
low O
stiffness S-PRO
implants S-APPL
that O
approximate O
the O
properties S-CONPRI
of O
bone S-BIOP
. O


The O
properties S-CONPRI
of O
these O
structures O
, O
regardless O
of O
cell S-APPL
geometry O
, O
have O
often O
been O
determined O
through O
compressive O
testing S-CHAR
, O
and O
very O
few O
of O
these O
studies O
have O
investigated O
the O
flexural O
properties S-CONPRI
. O


For O
certain O
types O
of O
implants S-APPL
that O
are O
designed S-FEAT
to O
fill O
very O
large O
segmental O
defects S-CONPRI
in O
appendicular O
bones O
, O
such O
as S-MATE
those O
used O
in O
limb O
sparing O
, O
compression S-PRO
testing O
does O
not O
provide O
the O
necessary O
insight O
into O
the O
complex O
loading O
states O
typical O
of O
bending S-MANP
. O


In O
this O
study O
, O
EBM-fabricated O
Ti6Al4V S-MATE
prismatic S-CONPRI
bars O
, O
populated O
with O
rhombic O
dodecahedron O
unit B-CONPRI
cells E-CONPRI
of O
various O
sizes O
and O
relative B-PRO
densities E-PRO
, O
were O
subjected O
to O
four-point O
flexure B-CHAR
tests E-CHAR
. O


While O
the O
results O
generally O
follow O
the O
power S-PARA
scaling O
models O
of O
Gibson O
and O
Ashby O
, O
the O
use O
of O
these O
models O
as S-MATE
a O
design S-FEAT
tool O
is O
limited O
by O
machine S-MACEQ
resolution O
, O
particularly O
when O
producing O
structures O
with O
small O
pore B-PARA
sizes E-PARA
required O
for O
bone B-CONPRI
ingrowth E-CONPRI
. O


The O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
process S-CONPRI
can O
produce O
parts O
with O
complex O
internal B-FEAT
geometries E-FEAT
that O
can O
not O
be S-MATE
easily O
manufactured S-CONPRI
using O
a O
material B-CONPRI
removal I-CONPRI
process E-CONPRI
. O


However O
, O
owing O
to O
the O
different O
heat B-CONPRI
transfer E-CONPRI
efficiencies O
of O
a O
laser S-ENAT
melting O
process S-CONPRI
, O
the O
optimal B-PARA
process E-PARA
parameters O
are O
limited O
to O
a O
small O
range S-PARA
. O


This O
study O
used O
galvanometric O
scanner O
technology S-CONPRI
and O
a O
diffractive O
optical B-APPL
element E-APPL
( O
DOE O
) O
to O
build S-PARA
an O
experimental S-CONPRI
multi-spot O
LPBF S-MANP
system O
. O


An O
adjustable O
multi-spot O
method O
was O
used O
to O
modulate O
the O
temperature S-PARA
field O
on O
the O
powder B-MACEQ
bed E-MACEQ
and O
enhance O
the O
processing O
quality S-CONPRI
and O
throughput S-CHAR
. O


The O
results O
from O
the O
synchronized O
three-spot O
method O
using O
different O
scanning B-CONPRI
strategies E-CONPRI
improved O
the O
layer S-PARA
surface O
roughness S-PRO
Ra O
by O
3.2 O
μm O
. O


Moreover O
, O
the O
scanning B-PARA
time E-PARA
was O
decreased O
by O
38.1 O
% O
of O
the O
single-spot O
method O
. O


It O
has O
been O
shown O
that O
quality S-CONPRI
of O
components S-MACEQ
built O
using O
selective B-MANP
laser I-MANP
sintering E-MANP
( O
SLS S-MANP
) O
are O
strongly O
affected O
by O
the O
thermal O
history O
of O
the O
building B-CHAR
process E-CHAR
. O


Temperature S-PARA
variations O
of O
a O
few O
degrees O
across O
the O
powder S-MATE
surface O
can O
alter O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
components S-MACEQ
and O
render O
them O
unsuitable O
for O
their O
intended O
purpose O
. O


Therefore O
, O
to O
improve O
the O
quality S-CONPRI
of O
SLS S-MANP
components S-MACEQ
and O
ease O
their O
adoption O
into O
the O
marketplace O
, O
temperature S-PARA
fluctuation O
issues O
must O
be S-MATE
addressed O
. O


Some O
success O
has O
been O
demonstrated O
in O
the O
past O
at O
reducing O
temperature S-PARA
non-uniformity O
by O
improving O
the O
heater O
system O
that O
pre-heats O
the O
polymer S-MATE
powder O
prior O
to O
sintering S-MANP
with O
the O
laser S-ENAT
. O


This O
paper O
will O
cover O
a O
complimentary O
approach O
of O
actively O
controlling O
laser S-ENAT
fluence O
on O
the O
powder S-MATE
surface O
based O
on O
infrared S-CONPRI
temperature O
measurements O
. O


By O
controlling O
the O
amount O
of O
energy O
input O
by O
the O
laser S-ENAT
, O
a O
high O
level O
of O
control O
over O
the O
final O
part O
temperature S-PARA
can O
be S-MATE
achieved O
and O
uniformity O
can O
be S-MATE
improved O
. O


This O
paper O
will O
cover O
development O
of O
the O
feed-forward O
control B-MACEQ
system E-MACEQ
and O
will O
present O
results O
showing O
that O
for O
constant O
cross-section O
specimens O
, O
a O
45 O
% O
improvement O
in O
ultimate O
flexural B-PRO
strength E-PRO
standard O
deviation O
was O
achieved O
. O


In O
the O
selective B-MANP
laser I-MANP
sintering E-MANP
of O
polymers S-MATE
, O
the O
most O
widely O
used O
powders S-MATE
are O
based O
on O
polyamide B-MATE
12 E-MATE
( O
PA12 S-MATE
) O
, O
which O
is O
a O
semi-crystalline O
polymer S-MATE
. O


Because O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
printed O
parts O
depend O
largely O
on O
the O
microstructure S-CONPRI
, O
knowledge O
on O
the O
crystalline O
architecture S-APPL
is O
important O
. O


We O
developed O
a O
numerical O
model S-CONPRI
based O
on O
the O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
to O
solve O
the O
flow O
, O
temperature S-PARA
and O
crystallization S-CONPRI
kinetics O
of O
PA12 S-MATE
powder O
during O
sintering S-MANP
using O
two O
different O
geometries S-CONPRI
. O


Our O
results O
show O
that O
the O
temperature S-PARA
plays O
a O
crucial O
role O
in O
the O
crystallization S-CONPRI
kinetics O
and O
that O
simplified O
0D O
calculations O
can O
be S-MATE
used O
to O
study O
the O
crystallization S-CONPRI
kinetics O
if O
the O
temperature S-PARA
behavior O
in O
time O
at O
a O
certain O
location O
is O
known O
. O


With O
our O
choice O
of O
initial O
and O
boundary B-CONPRI
conditions E-CONPRI
, O
we O
found O
primarily O
crystals O
of O
the O
α′-phase O
. O


A O
model S-CONPRI
for O
predicting O
the O
thermal O
response O
of O
Inconel® O
718 O
during O
laser S-ENAT
powder-bed O
fusion S-CONPRI
processing O
( O
LPBF S-MANP
) O
is O
developed O
. O


The O
approach O
includes O
the O
pre-placed O
powder S-MATE
layer S-PARA
in O
the O
analysis O
by O
initially O
assigning O
powder S-MATE
properties O
to O
the O
top O
layer S-PARA
of O
elements S-MATE
before O
restoring O
the O
solid O
properties S-CONPRI
as S-MATE
the O
heat B-CONPRI
source E-CONPRI
traverses O
the O
layer S-PARA
. O


Different O
linear O
heat S-CONPRI
inputs O
are O
examined O
by O
varying O
both O
laser B-PARA
power E-PARA
and O
scan B-PARA
speed E-PARA
. O


The O
effectiveness S-CONPRI
of O
the O
model S-CONPRI
is O
demonstrated O
by O
comparing O
the O
predicted S-CONPRI
temperatures O
to O
in B-CONPRI
situ E-CONPRI
experimental S-CONPRI
thermocouple O
data S-CONPRI
gathered O
during O
LPBF S-MANP
processing O
. O


The O
simulated O
temperatures S-PARA
accurately S-CHAR
capture O
the O
measured O
peak O
temperatures S-PARA
( O
within O
11 O
% O
error S-CONPRI
) O
and O
temperature S-PARA
trends O
. O


The O
effect O
of O
neglecting O
the O
pre-placed O
powder S-MATE
layer S-PARA
in O
the O
simulations S-ENAT
is O
also O
investigated O
demonstrating O
that O
conduction O
into O
the O
powder B-MATE
material E-MATE
should O
be S-MATE
accounted O
for O
in O
LPBF S-MANP
analyses O
. O


The O
simulation S-ENAT
neglecting O
the O
powder S-MATE
predicts O
temperatures S-PARA
more O
than O
30 O
% O
higher O
than O
the O
simulation S-ENAT
including O
the O
powder S-MATE
. O


Four O
stages O
were O
designed S-FEAT
to O
evaluate O
the O
surface B-CHAR
morphologies E-CHAR
of O
Ti6Al4V S-MATE
SLM S-MANP
parts O
. O


The O
stages O
focused O
laser B-PARA
power E-PARA
, O
scanning B-PARA
speed E-PARA
, O
hatch B-PARA
spacing E-PARA
and O
rescanning O
effects O
. O


Processing O
parameters S-CONPRI
significantly O
influenced O
vertical S-CONPRI
and O
top O
surface S-CONPRI
properties S-CONPRI
. O


The O
microcracks S-CONPRI
were O
noticed O
at O
the O
interfaces O
of O
adhered O
particles S-CONPRI
and O
melt B-MATE
pool E-MATE
. O


Viscosity S-PRO
and O
cooling B-PARA
rate E-PARA
are O
the O
key O
factors O
to O
regulate O
the O
surface B-CHAR
morphology E-CHAR
. O


The O
surface B-CHAR
morphology E-CHAR
of O
a O
product O
plays O
a O
crucial O
role O
under O
mechanical B-CONPRI
loading E-CONPRI
and O
chemical O
environment O
. O


Surfaces S-CONPRI
of O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
products O
often O
contain O
high O
roughness S-PRO
, O
which O
varies O
in O
different O
planes O
as S-MATE
well O
. O


The O
authors O
have O
explored O
the O
surface S-CONPRI
characteristics O
of O
the O
SLM S-MANP
samples S-CONPRI
that O
are O
influenced O
by O
different O
combinations O
of O
laser B-CONPRI
processing E-CONPRI
parameters O
. O


The O
considered O
processing O
parameters S-CONPRI
were O
Energy B-PARA
Density E-PARA
( O
ED S-CHAR
) O
and O
its O
technological O
parameters S-CONPRI
namely O
laser B-PARA
power E-PARA
, O
scanning B-PARA
speed E-PARA
and O
hatch B-PARA
spacing E-PARA
. O


Additionally O
, O
a O
comparison O
study O
has O
been O
executed O
by O
rescanning O
effects O
considering O
melting S-MANP
with O
low O
ED S-CHAR
and O
, O
thereafter O
, O
rescanning O
by O
the O
best O
possible O
laser B-CONPRI
processing E-CONPRI
parameters O
. O


The O
results O
evidently O
showed O
that O
the O
surface B-CHAR
morphologies E-CHAR
differ O
significantly O
due O
to O
different O
laser B-CONPRI
processing E-CONPRI
parameters O
. O


Eventually O
, O
the O
thermal O
and O
physical O
behavior O
of O
materials S-CONPRI
, O
such O
as S-MATE
the O
viscosity S-PRO
of O
the O
melt B-MATE
pool E-MATE
, O
thermal O
and O
physical O
stability S-PRO
of O
the O
melt B-MATE
pool E-MATE
, O
solidification B-CONPRI
time E-CONPRI
, O
cooling S-MANP
time O
, O
shrinkage S-CONPRI
, O
capillary B-CONPRI
effect E-CONPRI
, O
surface B-PRO
tension E-PRO
, O
balling O
effect O
, O
and O
the O
amount O
of O
melting S-MANP
of O
a O
powder B-MATE
particle E-MATE
, O
influenced O
the O
surface S-CONPRI
properties S-CONPRI
of O
the O
samples S-CONPRI
, O
along O
with O
unpredictability O
. O


The O
results O
showed O
an O
interesting O
correlation O
between O
the O
processing O
parameters S-CONPRI
and O
the O
occurrence O
of O
microcracks S-CONPRI
on O
the O
vertical S-CONPRI
walls O
of O
the O
specimens O
caused O
by O
the O
partially O
melted S-CONPRI
adhered O
powder B-MATE
particles E-MATE
. O


Acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
specimens O
fabricated S-CONPRI
by O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
were O
post O
treated O
by O
acetone S-MATE
, O
ethyl O
acetate O
and O
their O
mixed O
vapour O
. O


The O
effect O
of O
different O
chemical O
vapour O
, O
exposure S-CONPRI
time O
and O
building B-PARA
orientation E-PARA
on O
the O
surface B-PRO
roughness E-PRO
, O
tensile B-PRO
strength E-PRO
, O
dimension S-FEAT
and O
weight S-PARA
stability S-PRO
of O
the O
ABS S-MATE
specimens O
were O
investigated O
before O
and O
after O
treatment O
. O


The O
results O
demonstrated O
that O
all O
chemical O
vapours O
were O
capable O
of O
improving O
the O
surface S-CONPRI
coarseness O
of O
ABS S-MATE
specimens O
. O


The O
tensile B-PRO
strength E-PRO
of O
specimens O
treated O
with O
the O
acetone S-MATE
or O
the O
mixed O
vapour O
decreased O
with O
increasing O
the O
exposure S-CONPRI
time O
. O


The O
weight S-PARA
of O
specimens O
after O
treatment O
increased O
with O
prolonging O
the O
exposure S-CONPRI
time O
due O
to O
the O
absorption S-CONPRI
of O
the O
chemical O
vapours O
. O


In O
this O
work O
, O
polyphenylene O
sulfide O
( O
PPS O
) O
was O
reinforced S-CONPRI
with O
a O
thermotropic B-MATE
liquid I-MATE
crystalline I-MATE
polymer E-MATE
( O
TLCP O
) O
to O
generate O
composite S-MATE
filaments O
for O
use O
in O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
. O


Because O
of O
non-overlapping O
processing O
temperatures S-PARA
, O
rheology S-PRO
enabled O
taking O
the O
advantage O
of O
the O
dual O
extrusion S-MANP
technology O
, O
which O
generated O
nearly O
continuously O
reinforced S-CONPRI
filaments S-MATE
that O
exhibited O
a O
tensile B-PRO
strength E-PRO
and O
modulus O
of O
155.0 O
± O
24.2 O
MPa S-CONPRI
and O
40.4 O
± O
7.5 O
GPa S-PRO
, O
respectively O
. O


On O
printing O
using O
these O
filaments S-MATE
, O
the O
maximum O
tensile B-PRO
strength E-PRO
and O
modulus O
obtained O
were O
108.5 O
± O
19.4 O
MPa S-CONPRI
and O
25.9 O
± O
1.1 O
GPa S-PRO
, O
respectively O
, O
higher O
than O
the O
properties S-CONPRI
reported O
on O
using O
short B-MATE
fiber I-MATE
composites E-MATE
. O


Moreover O
, O
the O
tensile B-PRO
strength E-PRO
was O
lower O
, O
and O
the O
tensile S-PRO
modulus O
was O
higher O
in O
comparison O
with O
the O
reported O
use O
of O
continuous B-MATE
fibers E-MATE
. O


Additionally O
, O
the O
tensile B-PRO
properties E-PRO
in O
the O
print S-MANP
direction O
were O
higher O
than O
those O
of O
compression S-PRO
molded O
samples S-CONPRI
. O


The O
nearly O
continuous O
reinforcement S-PARA
did O
not O
restrict O
the O
mobility O
of O
the O
printer S-MACEQ
, O
unlike O
the O
reported O
performance S-CONPRI
of O
the O
continuously O
reinforced S-CONPRI
carbon B-MATE
fiber E-MATE
thermoplastics O
in O
FFF S-MANP
. O


This O
work O
aims O
to O
investigate O
the O
influence O
of O
the O
orientation S-CONPRI
and O
microtexture O
of O
columnar B-PRO
grains E-PRO
on O
the O
fatigue B-CONPRI
crack I-CONPRI
growth E-CONPRI
of O
a O
Ti-6.5Al-2Zr-Mo-V B-MATE
titanium I-MATE
alloy E-MATE
fabricated S-CONPRI
by O
directed B-MANP
energy I-MANP
deposition E-MANP
. O


In O
this O
paper O
, O
the O
fatigue B-PARA
crack I-PARA
growth I-PARA
rate E-PARA
test O
in O
three O
sampling S-CONPRI
directions O
in O
a O
directed O
energy O
deposited O
Ti-6.5Al-2Zr-Mo-V B-MATE
titanium I-MATE
alloy E-MATE
using O
compact S-MANP
specimens O
was O
carried O
out O
. O


The O
crack O
length O
was O
measured O
visually O
, O
and O
the O
fatigue B-PARA
crack I-PARA
growth I-PARA
rate E-PARA
of O
the O
stable O
crack B-CONPRI
growth E-CONPRI
stage O
was O
obtained O
. O


During O
the O
test O
, O
the O
influence O
of O
the O
microstructure S-CONPRI
on O
the O
crack B-CONPRI
growth E-CONPRI
was O
directly O
observed O
. O


In O
addition O
, O
the O
complete O
crack O
front O
shape O
was O
indicated O
on O
the O
fracture S-CONPRI
surface O
by O
the O
marker O
load O
technique O
, O
and O
the O
crack B-CONPRI
growth E-CONPRI
behavior O
was O
obtained O
. O


An O
optical B-CHAR
microscopy E-CHAR
, O
a O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
and O
a O
laser S-ENAT
confocal O
microscopy S-CHAR
were O
used O
to O
observe O
and O
clarify O
the O
influence O
of O
the O
columnar B-CONPRI
grain I-CONPRI
boundary E-CONPRI
on O
the O
crack B-CONPRI
growth E-CONPRI
behavior O
and O
the O
interaction O
between O
the O
crack O
front O
and O
microstructure S-CONPRI
. O


The O
results O
show O
that O
the O
fatigue B-PARA
crack I-PARA
growth I-PARA
rate E-PARA
in O
the O
three O
sampling S-CONPRI
directions O
is O
different O
in O
the O
low O
ΔK O
region O
; O
the O
columnar B-CONPRI
grain I-CONPRI
boundary E-CONPRI
has O
no O
significant O
effect O
on O
the O
fatigue B-CONPRI
crack I-CONPRI
growth E-CONPRI
behavior O
, O
but O
the O
columnar B-PRO
grain E-PRO
itself O
has O
an O
effect O
on O
the O
fatigue B-CONPRI
crack I-CONPRI
growth E-CONPRI
behavior O
, O
which O
is O
indicated O
by O
the O
irregularity O
of O
the O
crack O
front O
shape O
in O
different O
columnar B-PRO
grains E-PRO
. O


Microhardness S-CONPRI
testing O
and O
electron O
backscattered O
diffraction S-CHAR
were O
used O
to O
explain O
the O
above O
phenomena O
based O
on O
static O
and O
orientation S-CONPRI
characteristics O
. O


It O
was O
found O
that O
the O
microtexture O
and O
orientation S-CONPRI
of O
the O
columnar B-PRO
grains E-PRO
are O
responsible O
for O
differences O
in O
the O
crack B-CONPRI
growth E-CONPRI
rates O
, O
and O
the O
orientation S-CONPRI
of O
the O
columnar B-PRO
grains E-PRO
also O
determines O
the O
extent O
of O
the O
difference O
. O


Multi-scale O
microstructure S-CONPRI
of O
a O
laser S-ENAT
3D-printed S-MANP
Ni-based O
superalloy O
was O
examined O
. O


Elements S-MATE
and O
precipitates S-MATE
heterogeneously S-CONPRI
distribute O
at O
the O
cellular O
scale O
. O


Cell S-APPL
boundaries S-FEAT
are O
characterized O
as S-MATE
low O
angle O
grain B-CONPRI
boundaries E-CONPRI
. O


The O
heterogeneous S-CONPRI
microstructure O
of O
a O
laser S-ENAT
3D B-MANP
printed E-MANP
Ni-based O
superalloy O
was O
examined O
at O
multiple O
length B-CHAR
scales E-CHAR
. O


The O
crystal O
grains S-CONPRI
grow O
in O
epitaxy S-CONPRI
with O
the O
substrate S-MATE
under O
the O
large O
temperature B-PARA
gradient E-PARA
and O
high O
cooling B-PARA
rate E-PARA
. O


The O
cell S-APPL
boundaries S-FEAT
, O
decorated O
with O
γ/γ′ O
eutectics O
, O
μ-phase O
precipitates S-MATE
and O
high O
density S-PRO
of O
dislocations S-CONPRI
, O
show O
enrichment O
of O
γ′ O
forming S-MANP
elements S-MATE
and O
low-angle O
misorientations O
. O


Dislocations S-CONPRI
trapped O
in O
the O
intra-cellular O
regions O
are O
characterized O
as S-MATE
statistically O
stored O
dislocations S-CONPRI
with O
no O
detectable O
contribution O
to O
lattice S-CONPRI
curvature O
, O
and O
are O
the O
results O
of O
the O
interaction O
between O
dislocations S-CONPRI
and O
γ′ O
precipitates S-MATE
. O


Unlike O
conventional O
powder B-MANP
metallurgy E-MANP
techniques O
, O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
characterised O
by O
its O
fully O
melting S-MANP
process O
and O
very O
high O
heating S-MANP
and O
cooling B-PARA
rates E-PARA
and O
little O
has O
been O
known O
about O
the O
influence O
of O
powder S-MATE
surface O
state O
on O
the O
SLM S-MANP
process S-CONPRI
. O


In O
this O
study O
, O
the O
influence O
of O
low O
temperature S-PARA
powder S-MATE
drying S-MANP
on O
the O
surface S-CONPRI
chemistry S-CONPRI
of O
Al-12Si O
powder S-MATE
and O
its O
subsequent O
effect O
on O
SLM S-MANP
was O
investigated O
in O
detail O
by O
means O
of O
an O
in-depth O
X-ray B-CHAR
photoelectron I-CHAR
spectroscopy E-CHAR
. O


An O
enhanced O
densification S-MANP
( O
relative B-PRO
density E-PRO
≥99 O
% O
) O
was O
achieved O
in O
the O
dried S-MANP
Al-12Si O
powder S-MATE
compared O
to O
the O
as-received O
powder S-MATE
. O


This O
has O
been O
attributed O
to O
the O
modification O
of O
powder S-MATE
surface O
by O
removing O
a O
moisture O
skin O
during O
the O
drying S-MANP
process O
, O
which O
prevents O
the O
formation O
of O
deleterious O
oxide S-MATE
and O
hydroxide S-MATE
during O
SLM S-MANP
. O


This O
study O
provides O
important O
information O
for O
achieving O
high O
relative B-PRO
density E-PRO
in O
SLM S-MANP
fabricated S-CONPRI
metal O
components S-MACEQ
from O
a O
powder S-MATE
drying S-MANP
aspect O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
processed S-CONPRI
stainless O
steel S-MATE
usually O
exhibits O
an O
inhomogeneous O
microstructure S-CONPRI
in O
the O
as-built O
condition O
. O


The O
effect O
of O
powder S-MATE
chemical B-CONPRI
composition E-CONPRI
on O
the O
microstructural B-CONPRI
evolution E-CONPRI
of O
SLM S-MANP
processed S-CONPRI
17-4 O
PH S-CONPRI
in O
the O
as-built O
condition O
was O
studied O
. O


A O
path O
to O
achieve O
a O
fully O
martensitic O
17-4 O
PH S-CONPRI
component S-MACEQ
in O
the O
as-built O
condition O
by O
fine-tuning O
the O
alloy S-MATE
composition O
without O
any O
post-built O
heat B-MANP
treatments E-MANP
was O
demonstrated O
. O


The O
as-built O
17-4 O
PH S-CONPRI
phase O
transformation O
from O
δ O
ferrite S-MATE
to O
austenite S-MATE
( O
γ O
) O
and O
subsequently O
to O
martensite S-MATE
( O
α O
’ O
) O
was O
governed O
by O
the O
concentrations O
of O
ferrite S-MATE
and O
austenite S-MATE
stabilizing O
elements S-MATE
as S-MATE
represented O
by O
a O
chromium S-MATE
to O
nickel S-MATE
equivalent O
( O
Creq/Nieq O
) O
value O
. O


Electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
( O
EBSD S-CHAR
) O
analysis O
revealed O
that O
increase O
in O
the O
WRC-1992 O
equations O
based O
Creq/Nieq O
value O
to O
≥ O
2.65 O
resulted O
in O
coarse O
δ O
ferrite S-MATE
grains O
with O
a O
< O
100 O
> O
preferential O
crystal B-PRO
orientation E-PRO
along O
the O
build B-PARA
direction E-PARA
. O


Epitaxial S-PRO
growth O
of O
semi-circular O
and O
columnar O
δ O
ferrite S-MATE
grains O
accompanied O
by O
a O
marginal O
volume B-PARA
fraction E-PARA
of O
retained B-MATE
austenite E-MATE
and O
transformed O
martensitic O
phases O
was O
observed O
. O


Retained B-MATE
austenite E-MATE
and O
transformed O
martensitic O
phases O
exhibited O
a O
fine O
grain B-CONPRI
structure E-CONPRI
preferentially O
along O
the O
coarse O
ferrite S-MATE
grain O
boundaries S-FEAT
. O


EBSD S-CHAR
phase O
composition S-CONPRI
analysis O
along O
with O
thermodynamic O
equilibrium S-CONPRI
modeling O
implies O
that O
a O
lower O
Creq/Nieq O
value O
promotes O
martensite S-MATE
formation O
resulting O
in O
a O
less O
retained O
δ O
ferrite S-MATE
in O
the O
as-built O
condition O
. O


The O
microstructure S-CONPRI
of O
as-deposited O
LAMed O
300 O
M O
steel S-MATE
is O
different O
from O
that O
of O
forgings O
. O


Heat B-PRO
accumulation E-PRO
affects O
the O
as-deposited O
microstructure S-CONPRI
of O
LAMed O
300 O
M O
steel S-MATE
. O


After O
heat B-MANP
treatment E-MANP
, O
the O
microstructure S-CONPRI
of O
LAMed O
300 O
M O
steel S-MATE
is O
refined O
and O
uniform O
. O


After O
heat B-MANP
treatment E-MANP
, O
the O
impact S-CONPRI
toughness O
of O
LAMed O
300 O
M O
steel S-MATE
significantly O
improved O
. O


The O
crack B-CONPRI
propagation E-CONPRI
mechanism O
of O
LAMed O
300 O
M O
steel S-MATE
is O
revealed O
by O
EBSD S-CHAR
. O


Direct B-CONPRI
manufacturing E-CONPRI
techniques O
, O
such O
as S-MATE
directed O
energy O
deposition S-CONPRI
( O
DED S-MANP
) O
, O
are O
able O
to O
produce O
complex O
components S-MACEQ
efficiently O
. O


In O
this O
study O
, O
microstructure B-CONPRI
evolution E-CONPRI
and O
impact S-CONPRI
toughness O
of O
DED S-MANP
300M O
ultra-high O
strength S-PRO
steel S-MATE
are O
investigated O
. O


The O
results O
show O
that O
the O
microstructure S-CONPRI
of O
the O
as-deposited O
DED S-MANP
300M O
ultra-high O
strength S-PRO
steel S-MATE
is O
mainly O
composed O
of O
martensite S-MATE
and O
some O
blocky O
bainite S-MATE
. O


The O
micro-segregation S-CONPRI
of O
elements S-MATE
is O
observed O
within O
the O
interdendritic O
area S-PARA
. O


After O
heat B-MANP
treatment E-MANP
, O
the O
microstructure S-CONPRI
becomes O
uniform O
and O
consists O
of O
martensite S-MATE
and O
lower O
bainite S-MATE
. O


The O
impact S-CONPRI
toughness O
of O
the O
as-deposited O
DED S-MANP
300M O
ultra-high O
strength S-PRO
steel S-MATE
is O
9 O
J/cm2 O
, O
while O
it O
is O
significantly O
increased O
to O
25 O
J/cm2 O
after O
heat B-MANP
treatment E-MANP
. O


Furthermore O
, O
it O
is O
observed O
that O
the O
fracture S-CONPRI
mode O
of O
the O
as-deposited O
sample S-CONPRI
is O
quasi-cleavage O
fracture S-CONPRI
. O


During O
the O
process S-CONPRI
of O
propagation O
, O
the O
main O
cracks O
would O
go S-MATE
across O
the O
martensite S-MATE
packet O
and O
deflect O
in O
the O
another O
one O
, O
and O
secondary O
cracks O
also O
deflected O
in O
the O
high-angle O
grain B-CONPRI
boundaries E-CONPRI
. O


By O
contrast O
, O
the O
fracture S-CONPRI
mode O
of O
heat-treated B-MANP
DED E-MANP
300 O
M O
steel S-MATE
is O
ductile B-CONPRI
fracture E-CONPRI
. O


CP-Ti O
was O
used O
to O
produce O
SLM S-MANP
RAIs O
for O
immediate O
implantation S-MANP
. O


Inclination B-FEAT
angle E-FEAT
affects O
Sa O
by O
determining O
the O
powders S-MATE
melted S-CONPRI
in O
stairs O
. O


Dental S-APPL
implant O
with O
a O
consistent O
Sa O
was O
produced O
with O
gradient O
parameters S-CONPRI
. O


Vivo O
experiment S-CONPRI
showed O
good O
osteogenesis O
with O
the O
SLM S-MANP
RAIs O
in O
experimental S-CONPRI
dogs O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
a O
promising O
technology S-CONPRI
for O
use O
in O
“ O
immediate O
implantation S-MANP
” O
to O
quickly O
fabricate S-MANP
customized O
dental S-APPL
implants O
. O


However O
, O
the O
implant S-APPL
surface O
produced O
using O
SLM S-MANP
has O
a O
high O
and O
inconsistent O
surface B-PRO
roughness E-PRO
, O
which O
greatly O
affects O
early O
cell S-APPL
behaviors O
and O
osseointegration S-PRO
. O


In O
this O
work O
, O
samples S-CONPRI
were O
produced O
with O
different O
border O
process B-CONPRI
parameters E-CONPRI
and O
inclination B-FEAT
angles E-FEAT
. O


The O
surface B-PRO
roughness E-PRO
and O
morphology S-CONPRI
of O
the O
side O
surfaces S-CONPRI
were O
measured O
and O
studied O
. O


The O
results O
indicate O
that O
a O
large O
offset S-CONPRI
value O
increases O
surface B-PRO
roughness E-PRO
due O
to O
an O
insufficient O
energy O
input O
, O
while O
a O
small O
offset S-CONPRI
increases O
surface B-PRO
roughness E-PRO
due O
to O
an O
intensified O
Marangoni O
convection O
. O


Different O
inclination B-FEAT
angles E-FEAT
affect O
surface B-PRO
roughness E-PRO
due O
to O
stair O
effects O
and O
the O
heat-affected O
zone O
. O


Based O
on O
the O
above O
results O
, O
a O
dental S-APPL
implant O
was O
fabricated S-CONPRI
using O
gradient O
processing O
. O


Compared O
with O
the O
implant S-APPL
fabricated S-CONPRI
with O
a O
single O
parameter S-CONPRI
process O
, O
the O
implant S-APPL
processed O
with O
gradient O
parameters S-CONPRI
had O
a O
low O
and O
consistent O
surface B-PRO
roughness E-PRO
. O


An O
energy O
balance O
that O
describes O
the O
transfer O
of O
energy O
is O
proposed O
for O
the O
laser-based O
directed B-MANP
energy I-MANP
deposition I-MANP
process E-MANP
. O


The O
partitioning O
of O
laser B-CONPRI
energy E-CONPRI
was O
experimentally O
measured O
and O
accurately S-CHAR
validated O
using O
a O
special O
process S-CONPRI
calorimeter O
for O
Ti-6Al-4V S-MATE
and O
Inconel S-MATE
625™ O
alloys S-MATE
. O


The O
total O
energy O
provided O
by O
the O
laser S-ENAT
was O
partitioned O
as S-MATE
: O
the O
energy O
directly O
absorbed O
by O
the O
substrate S-MATE
, O
the O
energy O
absorbed O
by O
the O
powder S-MATE
stream O
and O
deposited O
onto O
the O
substrate S-MATE
, O
the O
energy O
reflected O
from O
the O
substrate S-MATE
surface O
, O
and O
the O
energy O
reflected O
or O
absorbed O
and O
lost O
from O
the O
powder S-MATE
stream O
. O


Titanium B-MATE
alloy E-MATE
Ti-6Al-4V S-MATE
showed O
higher O
overall O
or O
bulk O
absorption S-CONPRI
than O
the O
Inconel S-MATE
625™ O
alloy S-MATE
. O


Processing O
with O
powder S-MATE
resulted O
in O
lower O
laser B-CONPRI
energy E-CONPRI
absorption S-CONPRI
within O
the O
substrate S-MATE
than O
without O
powder S-MATE
, O
due O
to O
the O
“ O
shadowing O
” O
effect O
of O
the O
powder S-MATE
stream O
within O
the O
beam S-MACEQ
and O
loss O
of O
energy O
representing O
unfused O
powder S-MATE
. O


During O
processing O
at O
a O
laser B-PARA
power E-PARA
of O
approximately O
1 O
kW O
the O
total O
energy O
absorbed O
during O
the O
deposition B-MANP
process E-MANP
was O
found O
to O
be S-MATE
42 O
% O
for O
the O
Ti-6Al-4V B-MATE
alloy E-MATE
and O
37 O
% O
for O
the O
Inconel S-MATE
625™ O
alloy S-MATE
. O


Under O
these O
conditions O
14 O
% O
of O
the O
total O
energy O
was O
lost O
by O
the O
Ti-6Al-4V S-MATE
unfused O
powder S-MATE
; O
whereas O
only O
11 O
% O
was O
lost O
by O
the O
Inconel S-MATE
625™ O
powder S-MATE
. O


Cold O
gas B-CONPRI
dynamic E-CONPRI
spray O
is O
a O
cold O
spray O
technique O
for O
obtaining O
solid-state S-CONPRI
surface O
coating S-APPL
. O


Several O
materials S-CONPRI
such O
as S-MATE
metal O
, O
metal B-MATE
alloys E-MATE
, O
composite B-MATE
materials E-MATE
, O
and O
polymer S-MATE
have O
been O
deposited O
successfully O
through O
cold O
spray O
onto O
a O
substrate B-MATE
material E-MATE
. O


A O
number O
of O
industrial S-APPL
applications O
for O
cold O
spray O
have O
been O
developed O
worldwide O
in O
the O
field O
of O
aerospace S-APPL
, O
energy O
, O
automobile S-APPL
, O
biotechnology O
, O
and O
military S-APPL
applications O
. O


In O
the O
current O
study O
, O
effects O
of O
various O
processing O
parameter S-CONPRI
such O
as S-MATE
impact O
velocity O
, O
substrate S-MATE
preheating S-MANP
temperature O
, O
a O
combination O
of O
different O
materials S-CONPRI
and O
coefficient B-PRO
of I-PRO
friction E-PRO
were O
used O
to O
describe O
the O
impact S-CONPRI
behaviour O
of O
ductile S-PRO
materials O
( O
copper S-MATE
, O
Cu S-MATE
, O
and O
aluminium S-MATE
, O
Al S-MATE
) O
after O
deposition S-CONPRI
to O
find O
a O
way O
of O
addressing O
high-strain-rate O
dynamic S-CONPRI
problems O
. O


The O
parameters S-CONPRI
were O
also O
used O
to O
verify O
the O
deposition B-MANP
process E-MANP
for O
the O
modelling S-ENAT
of O
cold O
gas B-CONPRI
dynamic E-CONPRI
spray O
( O
CGDS O
) O
by O
the O
Lagrangian O
approach O
of O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
. O


The O
results O
of O
the O
analysis O
( O
simulation S-ENAT
) O
and O
that O
of O
the O
published O
experimental S-CONPRI
results O
in O
the O
literature O
correlated S-CONPRI
well O
. O


The O
understanding O
of O
the O
impact S-CONPRI
behaviour O
using O
different O
parameters S-CONPRI
was O
evident O
by O
the O
analysis O
of O
temperature S-PARA
and O
equivalent O
plastic S-MATE
strain O
( O
PEEQ O
) O
. O


It O
was O
discovered O
that O
the O
deposition B-MANP
process E-MANP
and O
deformation S-CONPRI
are O
largely O
affected O
by O
particle S-CONPRI
material S-MATE
as S-MATE
compared O
to O
the O
substrate S-MATE
. O


A O
lower O
restitution O
coefficient O
was O
obtained O
when O
different O
materials S-CONPRI
of O
varying O
properties S-CONPRI
were O
combined O
compared O
to O
the O
combination O
of O
the O
same O
material S-MATE
. O


Also O
, O
the O
parameters S-CONPRI
under O
investigation O
do O
not O
affect O
the O
CGDS O
process S-CONPRI
individually O
, O
as S-MATE
their O
effects O
are O
interrelated O
. O


A O
β O
titanium B-MATE
alloy E-MATE
, O
Ti-10V-2Fe-3Al O
, O
was O
selectively O
laser S-ENAT
melted O
under O
a O
modulated O
pulsed B-MANP
laser E-MANP
mode O
with O
different O
processing O
conditions O
. O


The O
as-fabricated O
samples S-CONPRI
were O
examined O
using O
a O
range S-PARA
of O
characterization O
techniques O
and O
properties S-CONPRI
evaluated O
through O
tensile B-CHAR
testing E-CHAR
. O


It O
is O
shown O
that O
with O
a O
small O
powder S-MATE
layer B-PARA
thickness E-PARA
( O
30 O
μm O
) O
, O
a O
low O
laser B-PARA
power E-PARA
and O
a O
short O
exposure S-CONPRI
time O
( O
i.e. O
, O
low O
energy B-PARA
density E-PARA
) O
led S-APPL
to O
development O
of O
fine O
β O
columnar B-PRO
grains E-PRO
and O
widespread O
cell S-APPL
structures O
whereas O
increased O
laser B-PARA
power E-PARA
and O
exposure S-CONPRI
time O
( O
i.e. O
, O
high O
energy B-PARA
density E-PARA
) O
resulted O
in O
pronounced O
grain B-CONPRI
growth E-CONPRI
, O
increased O
texture S-FEAT
and O
significantly O
decreased O
cell S-APPL
structures O
. O


Increasing O
powder S-MATE
layer B-PARA
thickness E-PARA
effectively O
promoted O
the O
columnar-to-equiaxed O
grain S-CONPRI
transition O
( O
CET O
) O
, O
leading O
to O
a O
greatly O
reduced O
texture S-FEAT
and O
a O
hybrid O
microstructure S-CONPRI
which O
consists O
of O
small O
and O
chunky O
equiaxed B-CONPRI
grains E-CONPRI
together O
with O
a O
small O
number O
of O
large O
columnar B-PRO
grains E-PRO
. O


Athermal O
ω O
precipitates S-MATE
were O
observed O
in O
all O
the O
as-fabricated O
samples S-CONPRI
. O


In O
the O
samples S-CONPRI
made O
with O
high O
energy B-PARA
densities E-PARA
, O
α O
laths O
which O
tend O
to O
constitute O
a O
grid-like O
structure S-CONPRI
were O
observed O
. O


The O
samples S-CONPRI
with O
the O
finest O
columnar B-PRO
grains E-PRO
show O
both O
high O
strengths S-PRO
and O
good O
ductility S-PRO
thanks O
to O
full O
plastic B-PRO
deformation E-PRO
through O
both O
slipping O
and O
twinning S-CONPRI
. O


The O
samples S-CONPRI
with O
the O
hybrid O
grain B-CONPRI
structure E-CONPRI
, O
however O
, O
exhibits O
a O
highly O
limited O
or O
no O
ductility S-PRO
due O
to O
intergranular O
fracturing O
. O


The O
α-containing O
samples S-CONPRI
which O
also O
have O
coarse O
grains S-CONPRI
all O
failed O
in O
a O
cleavage O
fracture S-CONPRI
mode O
and O
exhibited O
almost O
no O
ductility S-PRO
. O


Transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
study O
reveals O
that O
the O
α-demarcated O
grid O
structure S-CONPRI
tended O
to O
confine O
plastic B-PRO
deformation E-PRO
within O
the O
β O
matrix O
and O
suppress O
the O
macroscopic S-CONPRI
plastic O
deformation S-CONPRI
throughout O
the O
samples S-CONPRI
. O


3-D S-CONPRI
printing O
shows O
great O
potential O
in O
laboratories S-CONPRI
for O
making O
customized O
labware O
and O
reaction O
vessels O
. O


In O
addition O
, O
affordable O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
-based O
3-D S-CONPRI
printing O
has O
successfully O
produced O
high-quality O
and O
affordable O
scientific O
equipment S-MACEQ
, O
focusing O
on O
tools S-MACEQ
without O
strict O
chemical O
compatibility O
limitations O
. O


As S-MATE
the O
additives S-MATE
and O
colorants S-MATE
used O
in O
3-D S-CONPRI
printing O
filaments S-MATE
are O
proprietary O
, O
their O
compatibility O
with O
common O
chemicals O
is O
unknown O
, O
which O
has O
prevented O
their O
widespread O
use O
in O
laboratory S-CONPRI
chemical O
processing O
. O


The O
results O
provide O
data S-CONPRI
on O
materials S-CONPRI
unavailable O
in O
the O
literature O
and O
the O
chemical O
properties S-CONPRI
of O
3-D S-CONPRI
printable O
plastics S-MATE
that O
were O
, O
are O
in O
line O
with O
literature O
. O


Overall O
, O
many O
3-D S-CONPRI
printable O
plastics S-MATE
are O
compatible O
with O
concentrated O
solutions O
. O


Polypropylene S-MATE
emerged O
as S-MATE
a O
promising O
3-D S-CONPRI
printable O
material S-MATE
for O
semiconductor S-MATE
processing O
due O
to O
its O
tolerance S-PARA
of O
strongly O
oxidizing O
acids O
, O
such O
as S-MATE
nitric O
and O
sulfuric O
acids O
. O


In O
addition O
, O
3-D S-CONPRI
printed O
custom O
tools S-MACEQ
were O
demonstrated O
for O
a O
range S-PARA
of O
wet O
processing O
applications O
. O


The O
results O
show O
that O
3-D S-CONPRI
printed O
plastics S-MATE
are O
potential O
materials S-CONPRI
for O
bespoke O
chemically O
resistant O
labware O
at O
less O
than O
10 O
% O
of O
the O
cost O
of O
such O
purchased O
tools S-MACEQ
. O


However O
, O
further O
studies O
are O
required O
to O
ascertain O
if O
such O
materials S-CONPRI
are O
fully O
compatible O
with O
clean B-CONPRI
room E-CONPRI
processing O
. O


Large O
pulsed O
electron B-CONPRI
beam E-CONPRI
irradiation O
was O
proposed O
as S-MATE
the O
new O
post-treatment S-MANP
of O
the O
selective B-MANP
laser I-MANP
melting I-MANP
process E-MANP
. O


LPEB O
irradiation S-MANP
can O
remove O
the O
partially O
melted S-CONPRI
particles O
and O
fill O
the O
cracks O
and O
void S-CONPRI
on O
the O
SLM-MS O
. O


There O
is O
the O
significant O
reduction S-CONPRI
of O
the O
surface B-PRO
roughness E-PRO
and O
the O
bcc S-CONPRI
α-martensite O
phase S-CONPRI
on O
the O
SLM-MS O
. O


Corrosion S-CONPRI
testing O
revealed O
that O
there O
is O
a O
moderate O
improvement O
in O
corrosion B-CONPRI
resistance E-CONPRI
after O
LPEB O
irradiation S-MANP
. O


The O
present O
work O
aimed O
to O
decrease O
the O
surface B-PRO
roughness E-PRO
of O
maraging B-MATE
steel E-MATE
( O
MS O
) O
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
using O
large O
pulsed O
electron-beam O
( O
LPEB O
) O
irradiation S-MANP
as S-MATE
a O
post-treatment S-MANP
. O


The O
MS O
samples S-CONPRI
were O
fabricated S-CONPRI
using O
different O
combinations O
of O
laser B-PARA
power E-PARA
, O
scanning B-PARA
speed E-PARA
, O
hatch B-PARA
distance E-PARA
, O
and O
build S-PARA
angle O
. O


The O
morphological O
features O
, O
surface B-PRO
roughness E-PRO
, O
phase S-CONPRI
content O
, O
and O
corrosion B-CONPRI
resistance E-CONPRI
of O
the O
MS O
samples S-CONPRI
in O
their O
as-fabricated O
( O
ASF O
) O
state O
were O
compared O
after O
LPEB O
irradiation S-MANP
. O


The O
ASF O
SLM-MS O
samples S-CONPRI
exhibit O
the O
presence O
of O
partially O
melted S-CONPRI
particles O
that O
spread S-CONPRI
over O
the O
entire O
surface S-CONPRI
and O
many O
cracks O
in O
both O
the O
longitudinal O
and O
transverse O
directions O
. O


Post-treatment S-MANP
by O
LPEB O
irradiation S-MANP
removed O
the O
partially O
melted S-CONPRI
particles O
, O
while O
reflow O
of O
the O
molten O
mass O
filled O
the O
cracks O
and O
voids S-CONPRI
and O
facilitated O
the O
formation O
of O
a O
uniform O
surface S-CONPRI
with O
a O
bright O
metallic S-MATE
finish O
. O


Body-centered O
cubic O
α-martensite O
was O
the O
predominant O
phase S-CONPRI
for O
the O
ASF O
SLM-MS O
samples S-CONPRI
, O
along O
with O
a O
small O
fraction S-CONPRI
face-centered O
cubic O
γ-austenite O
phase S-CONPRI
. O


After O
LPEB O
irradiation S-MANP
, O
the O
martensite S-MATE
was O
reverted O
to O
the O
austenite B-CHAR
phase E-CHAR
. O


The O
corrosion B-CONPRI
resistance E-CONPRI
of O
the O
LPEB-irradiated O
samples S-CONPRI
was O
moderately O
better O
than O
that O
of O
the O
ASF O
SLM-MS O
samples S-CONPRI
. O


The O
uniform O
surface B-CHAR
morphology E-CHAR
, O
removal O
of O
partially O
melted S-CONPRI
particles O
, O
absence O
of O
pores S-PRO
and O
cracks O
, O
decrease O
in O
Sa O
, O
and O
moderate O
improvement O
in O
corrosion B-CONPRI
resistance E-CONPRI
suggests O
that O
LPEB O
irradiation S-MANP
can O
be S-MATE
used O
as S-MATE
a O
post-treatment S-MANP
for O
SLM-MS O
samples S-CONPRI
. O


The O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
process S-CONPRI
produces O
complex O
microstructures S-MATE
and O
specific O
defects S-CONPRI
. O


To O
build S-PARA
structural O
components S-MACEQ
with O
an O
acceptable O
mechanical B-PRO
integrity E-PRO
, O
optimization S-CONPRI
of O
the O
processing O
parameters S-CONPRI
is O
required O
. O


In O
addition O
, O
the O
evolution S-CONPRI
of O
defects S-CONPRI
under O
service O
conditions O
should O
be S-MATE
investigated O
. O


In O
this O
study O
, O
the O
nickel-based B-MATE
alloy E-MATE
718 O
was O
studied O
in O
the O
as-built O
metallurgical S-APPL
state O
. O


Laser B-CONPRI
processing E-CONPRI
parameters O
such O
as S-MATE
the O
laser B-PARA
power E-PARA
, O
scanning B-PARA
speed E-PARA
, O
and O
hatch B-PARA
spacing E-PARA
were O
modified O
to O
evaluate O
their O
effects O
on O
the O
porosity S-PRO
, O
microstructure S-CONPRI
, O
and O
mechanical B-CONPRI
properties E-CONPRI
at O
high O
temperatures S-PARA
. O


The O
porosity S-PRO
and O
pore S-PRO
shape O
were O
evaluated O
using O
relative B-PRO
density E-PRO
measurements O
and O
image B-CONPRI
analysis E-CONPRI
. O


Moreover O
, O
the O
effects O
of O
the O
microstructure S-CONPRI
and O
defects S-CONPRI
on O
the O
tensile B-PRO
properties E-PRO
and O
damaging O
processes S-CONPRI
at O
650 O
°C O
were O
investigated O
in O
air O
. O


The O
results O
revealed O
that O
the O
loading O
direction O
is O
critical O
to O
the O
mechanical B-PRO
integrity E-PRO
of O
the O
alloy S-MATE
, O
due O
to O
the O
specific O
orientation S-CONPRI
of O
the O
microstructural S-CONPRI
interfaces O
and O
defects S-CONPRI
. O


A O
tensile B-CHAR
test E-CHAR
was O
conducted O
in O
vacuum O
at O
650 O
°C O
and O
2.10−4 O
s−1 O
, O
and O
the O
results O
indicated O
that O
damage S-PRO
processes O
were O
not O
affected O
by O
oxidation S-MANP
when O
the O
experiments O
were O
carried O
out O
in O
air O
. O


Microrobotic O
prototypes S-CONPRI
for O
water O
cleaning S-MANP
are O
produced O
combining O
stereolithography B-MANP
3D I-MANP
printing E-MANP
and O
wet O
metallization S-MANP
. O


Different O
metallic S-MATE
layers O
are O
deposited O
on O
3D B-APPL
printed I-APPL
parts E-APPL
using O
both O
electroless O
and O
electrolytic B-CONPRI
deposition E-CONPRI
to O
impart O
required O
functionalities O
. O


In O
particular O
, O
by O
exploiting O
the O
flexibility S-PRO
and O
versatility O
of O
electrolytic O
codeposition O
, O
pollutants O
photodegradation O
and O
bacteria O
killing O
are O
for O
the O
first O
time O
combined O
on O
the O
same O
device O
by O
coating S-APPL
it O
with O
a O
composite S-MATE
nanocoating O
containing O
titania S-MATE
nanoparticles S-CONPRI
in O
a O
silver S-MATE
matrix O
. O


The O
microstructure S-CONPRI
of O
the O
microrobots O
thus O
obtained O
is O
fully O
characterized O
and O
they O
are O
successfully O
actuated O
by O
applying O
rotating O
magnetic B-CONPRI
fields E-CONPRI
. O


This O
paper O
presents O
the O
results O
of O
numerical B-ENAT
simulations E-ENAT
and O
experimental S-CONPRI
tests O
on O
AlSi10Mg S-MATE
samples O
, O
having O
thin O
cylindrical S-CONPRI
channels O
built O
in O
the O
horizontal O
direction O
, O
using O
selective B-MANP
laser I-MANP
melting E-MANP
technology O
. O


The O
thermal O
state O
of O
the O
samples S-CONPRI
with O
channels O
of O
varying O
diameters O
is O
investigated O
by O
employing O
a O
simplified O
part-scale O
transient B-CONPRI
model E-CONPRI
that O
takes O
into O
consideration O
the O
overmelting O
effects O
through O
the O
change O
of O
the O
materials S-CONPRI
properties O
related O
with O
phase S-CONPRI
transition O
effects O
in O
the O
melted S-CONPRI
area S-PARA
of O
the O
sample S-CONPRI
. O


Comparison O
of O
simulation S-ENAT
results O
and O
computing O
tomography O
of O
experimental S-CONPRI
samples O
reveal O
that O
the O
final O
cross B-CONPRI
section E-CONPRI
geometry O
of O
thin O
channels O
can O
be S-MATE
predicted O
and O
evaluated O
by O
the O
proposed O
model S-CONPRI
. O


Namely O
, O
it O
is O
found O
that O
the O
unsupported O
down-skin O
area S-PARA
of O
the O
channels O
is O
processed S-CONPRI
with O
formation O
of O
protrusions O
due O
to O
presence O
of O
the O
low O
conductive O
powder B-MACEQ
bed E-MACEQ
under O
the O
melted S-CONPRI
metal O
layer S-PARA
. O


This O
powder S-MATE
area S-PARA
overheated O
during O
laser S-ENAT
action O
and O
melted S-CONPRI
together O
with O
desirable O
solid O
region O
of O
the O
model S-CONPRI
. O


Overmelting O
effects O
lead S-MATE
to O
the O
total O
closing O
of O
the O
channels O
with O
diameter S-CONPRI
less O
than O
200 O
μm O
, O
partial O
closing O
of O
the O
channels O
of O
diameters O
0.2-1 O
mm S-MANP
, O
and O
distortion S-CONPRI
of O
the O
cross B-CONPRI
section E-CONPRI
of O
larger O
channels O
. O


Possible O
approaches O
of O
adjusting O
the O
geometry S-CONPRI
of O
a O
channel S-APPL
are O
studied O
, O
considering O
the O
teardrop O
and O
enlarged O
shapes O
of O
the O
cross B-CONPRI
sections E-CONPRI
, O
which O
could O
help O
obtain O
a O
predefined O
cylindrical S-CONPRI
shape O
of O
the O
channels O
. O


A O
quasi-2D O
model S-CONPRI
of O
Micro-Selective O
Laser S-ENAT
Melting O
( O
μ-SLM O
) O
process S-CONPRI
using O
molecular O
dynamics O
is O
developed O
to O
investigate O
the O
localized O
melting S-MANP
and O
solidification S-CONPRI
of O
a O
randomly-distributed O
Aluminum S-MATE
nano-powder O
bed S-MACEQ
. O


One O
of O
the O
biggest O
challenges O
in O
modeling S-ENAT
the O
μ-SLM O
process S-CONPRI
is O
the O
computational O
treatment O
of O
the O
formation O
and O
growth O
of O
crystal O
nuclei S-CONPRI
in O
the O
meltpool S-CHAR
. O


The O
present O
work O
overcomes O
this O
challenge O
using O
molecular O
dynamics O
simulation S-ENAT
because O
of O
its O
capability O
to O
explicitly O
model S-CONPRI
the O
nucleation S-CONPRI
and O
growth O
of O
grains S-CONPRI
inside O
the O
meltpool S-CHAR
. O


The O
localized O
heating S-MANP
and O
rapid B-MANP
solidification E-MANP
of O
meltpool S-CHAR
is O
simulated O
by O
the O
direct O
control O
of O
the O
temperature S-PARA
in O
the O
meltpool S-CHAR
both O
spatially O
and O
temporally O
. O


The O
rapid B-MANP
solidification E-MANP
in O
the O
meltpool S-CHAR
reveals O
the O
cooling B-PARA
rate E-PARA
dependent O
homogeneous B-CONPRI
nucleation E-CONPRI
of O
equiaxed B-CONPRI
grains E-CONPRI
at O
the O
center O
of O
the O
meltpool S-CHAR
. O


Additionally O
, O
the O
epitaxial S-PRO
grain O
growth O
from O
the O
adjacent O
laser S-ENAT
tracks O
, O
previous O
layers O
, O
and O
partially O
melted S-CONPRI
nano-powders O
into O
the O
solidifying O
meltpool S-CHAR
is O
observed O
along O
the O
highest O
heat S-CONPRI
flow O
directions O
. O


The O
growth O
of O
the O
long O
columnar B-PRO
grains E-PRO
into O
the O
top O
layer S-PARA
is O
inhibited O
if O
the O
penetration B-PARA
depth E-PARA
during O
the O
remelting O
of O
a O
previous O
layer S-PARA
is O
less O
than O
the O
depth O
of O
the O
equiaxed B-CONPRI
grains E-CONPRI
. O


Long O
columnar B-PRO
grains E-PRO
that O
spread S-CONPRI
across O
three O
layers O
, O
equiaxed B-CONPRI
grains E-CONPRI
, O
nano-pores O
, O
twin O
boundaries S-FEAT
, O
and O
stacking O
faults O
are O
observed O
in O
the O
final O
solidified O
nanostructure O
obtained O
after O
ten O
passes O
of O
the O
laser B-CONPRI
beam E-CONPRI
on O
three O
layers O
of O
Aluminum S-MATE
nano-powder O
particles S-CONPRI
. O


Hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
of O
the O
final O
solidified O
nanostructure O
is O
employed O
to O
eliminate O
the O
nano-pores O
, O
which O
act O
as S-MATE
sources O
of O
crack O
initiation O
during O
tensile S-PRO
loading O
. O


This O
work O
examines O
the O
use O
of O
dual-material S-CONPRI
fused O
filament S-MATE
fabrication S-MANP
for O
3D B-MANP
printing E-MANP
electronic O
components S-MACEQ
and O
circuits O
with O
conductive O
thermoplastic B-MATE
filaments E-MATE
. O


The O
resistivity S-PRO
of O
traces O
printed O
from O
conductive O
thermoplastic B-MATE
filaments E-MATE
made O
with O
carbon-black O
, O
graphene S-MATE
, O
and O
copper S-MATE
as S-MATE
conductive O
fillers O
was O
found O
to O
be S-MATE
12 O
, O
0.78 O
, O
and O
0.014 O
Ω O
cm O
, O
respectively O
, O
enabling O
the O
creation O
of O
resistors S-MACEQ
with O
values O
spanning O
3 O
orders O
of O
magnitude S-PARA
. O


The O
carbon B-MATE
black E-MATE
and O
graphene B-MATE
filaments E-MATE
were O
brittle S-PRO
and O
fractured O
easily O
, O
but O
the O
copper-based O
filament S-MATE
could O
be S-MATE
bent O
at O
least O
500 O
times O
with O
little O
change O
in O
its O
resistance S-PRO
. O


Impedance B-CHAR
measurements E-CHAR
made O
on O
the O
thermoplastic B-MATE
filaments E-MATE
demonstrate O
that O
the O
copper-based O
filament S-MATE
had O
an O
impedance O
similar O
to O
a O
copper S-MATE
PCB O
trace O
at O
frequencies O
greater O
than O
1 O
MHz O
. O


Dual O
material S-MATE
3D B-MANP
printing E-MANP
was O
used O
to O
fabricate S-MANP
a O
variety O
of O
inductors O
and O
capacitors S-APPL
with O
properties S-CONPRI
that O
could O
be S-MATE
predictably O
tuned O
by O
modifying O
either O
the O
geometry S-CONPRI
of O
the O
components S-MACEQ
, O
or O
the O
materials S-CONPRI
used O
to O
fabricate S-MANP
the O
components S-MACEQ
. O


These O
resistors S-MACEQ
, O
capacitors S-APPL
, O
and O
inductors O
were O
combined O
to O
create O
a O
fully O
3D B-MANP
printed E-MANP
high-pass O
filter S-APPL
with O
properties S-CONPRI
comparable O
to O
its O
conventional O
counterparts O
. O


The O
relatively O
low O
impedance O
of O
the O
copper-based O
filament S-MATE
enabled O
its O
use O
for O
3D B-MANP
printing E-MANP
of O
a O
receiver O
coil O
for O
wireless O
power S-PARA
transfer O
. O


We O
also O
demonstrate O
the O
ability O
to O
embed O
and O
connect O
surface S-CONPRI
mounted O
components S-MACEQ
in O
3D B-MANP
printed E-MANP
objects O
with O
a O
low-cost O
( O
$ O
1000 O
in O
parts O
) O
, O
open O
source S-APPL
dual-material S-CONPRI
3D B-MACEQ
printer E-MACEQ
. O


This O
work O
thus O
demonstrates O
the O
potential O
for O
FFF B-MANP
3D I-MANP
printing E-MANP
to O
create O
complex O
, O
three-dimensional S-CONPRI
circuits O
composed O
of O
either O
embedded O
or O
fully-printed O
electronic O
components S-MACEQ
. O


The O
aim O
of O
the O
present O
study O
is O
to O
utilize O
fractographic O
methods O
employing O
scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
( O
SEM S-CHAR
) O
images S-CONPRI
to O
investigate O
the O
effects O
of O
build B-PARA
direction E-PARA
and O
orientation S-CONPRI
on O
the O
mechanical B-CONPRI
response E-CONPRI
and O
failure B-PRO
mechanism E-PRO
for O
Acrylonitrile–Butadiene–Styrene O
( O
ABS S-MATE
) O
specimens O
fabricated S-CONPRI
by O
fused S-CONPRI
deposited O
modeling S-ENAT
( O
FDM S-MANP
) O
. O


The O
material S-MATE
characterized O
here O
is O
ABS-M30 O
manufactured S-CONPRI
by O
Stratasys S-APPL
, O
Inc. O
Measurements O
of O
tensile B-PRO
strength E-PRO
, O
elongation-at-break O
and O
tensile S-PRO
modulus O
measurements O
along O
with O
the O
failure S-CONPRI
surfaces O
were O
characterized O
on O
a O
range S-PARA
of O
specimens O
at O
different O
build B-PARA
direction E-PARA
and O
raster B-PARA
orientation E-PARA
: O
±45° O
, O
0° O
, O
0/90° O
, O
and O
90° O
. O


The O
analysis O
of O
mechanical B-CHAR
testing E-CHAR
of O
the O
tensile B-MACEQ
specimens E-MACEQ
until O
failure S-CONPRI
will O
contribute O
to O
advances O
in O
creating O
stronger O
and O
more O
robust O
structure S-CONPRI
for O
various O
applications O
. O


Parameters S-CONPRI
, O
such O
as S-MATE
build O
direction O
and O
raster B-PARA
orientation E-PARA
, O
can O
be S-MATE
interdependent O
and O
exhibit O
varying O
effects O
on O
the O
properties S-CONPRI
of O
the O
ABS S-MATE
specimens O
. O


The O
ABS-M30 O
specimens O
were O
found O
to O
exhibit O
anisotropy S-PRO
in O
the O
mechanical B-CONPRI
response E-CONPRI
when O
exposed O
to O
axial O
tensile S-PRO
loading O
. O


The O
stress-strain O
data S-CONPRI
was O
characterized O
by O
a O
monotonic O
increase O
with O
an O
abrupt O
failure S-CONPRI
signifying O
brittle B-CONPRI
fracture E-CONPRI
. O


In O
certain O
combinations O
of O
build B-PARA
direction E-PARA
and O
raster B-PARA
orientation E-PARA
tensile O
failure S-CONPRI
was O
preceded O
by O
slight O
softening O
. O


The O
tensile B-PRO
strength E-PRO
and O
modulus O
, O
and O
elongation-at-break O
were O
found O
to O
be S-MATE
highly O
dependent O
upon O
the O
raster B-PARA
orientation E-PARA
and O
build B-PARA
direction E-PARA
. O


The O
relationship O
between O
the O
mechanical B-CONPRI
properties E-CONPRI
and O
failure S-CONPRI
was O
established O
by O
fractographic B-CHAR
analysis E-CHAR
. O


The O
fractographic B-CHAR
analysis E-CHAR
offers O
insight O
and O
provides O
valuable O
experimental B-CONPRI
data E-CONPRI
for O
the O
purpose O
of O
building O
structures O
in O
orientations S-CONPRI
tailored O
to O
their O
exemplified O
strength S-PRO
. O


Other O
examples O
are O
shown O
where O
artifacts O
of O
the O
FDM B-MANP
fabrication E-MANP
process O
act O
to O
enhance O
tensile B-PRO
strength E-PRO
when O
configured O
properly O
with O
respect O
to O
the O
load O
. O


The O
study O
also O
presents O
a O
systematic O
scheme O
employing O
analogs O
to O
traditional O
fiber-reinforced O
polymer B-MATE
composites E-MATE
for O
the O
designation O
of O
build B-PARA
orientation E-PARA
and O
raster B-PARA
orientation E-PARA
parameters S-CONPRI
. O


The O
dissolution O
kinetics O
of O
Laves B-CONPRI
phase E-CONPRI
has O
been O
analyzed O
. O


The O
mechanical B-CONPRI
properties E-CONPRI
of O
Inconel B-MATE
718 E-MATE
are O
closely O
related O
to O
the O
morphology S-CONPRI
and O
size O
of O
the O
Laves B-CONPRI
phase E-CONPRI
, O
which O
must O
be S-MATE
quantitatively O
controlled O
to O
change O
the O
effect O
of O
the O
Laves B-CONPRI
phase E-CONPRI
from O
deleterious O
to O
beneficial O
. O


In O
this O
study O
, O
post-heat O
treatment O
was O
used O
to O
regulate O
the O
morphology S-CONPRI
and O
size O
of O
the O
Laves B-CONPRI
phase E-CONPRI
in O
Inconel B-MATE
718 E-MATE
fabricated S-CONPRI
using O
laser B-MANP
directed I-MANP
energy I-MANP
deposition E-MANP
, O
and O
the O
dissolution O
behavior O
of O
the O
Laves B-CONPRI
phase E-CONPRI
during O
solution B-MANP
heat I-MANP
treatment E-MANP
was O
investigated O
. O


The O
results O
indicated O
that O
the O
sharp O
corners O
and O
grooves O
of O
the O
Laves B-CONPRI
phase E-CONPRI
preferentially O
dissolved O
, O
causing O
the O
morphology S-CONPRI
of O
the O
Laves B-CONPRI
phase E-CONPRI
to O
change O
from O
a O
long-striped O
to O
granular O
shape O
during O
dissolution O
. O


The O
dissolution O
kinetics O
of O
the O
Laves B-CONPRI
phase E-CONPRI
were O
also O
investigated O
using O
the O
Johnson–Mehl–Avrami–Kolmogorov O
and O
Singh–Flemings O
models O
. O


The O
initial O
stage O
of O
dissolution O
was O
controlled O
by O
both O
the O
long-range O
diffusion S-CONPRI
of O
Nb S-MATE
and O
the O
interfacial O
reaction O
. O


Directed B-MANP
Energy I-MANP
Deposition E-MANP
was O
used O
to O
process S-CONPRI
316 O
L O
in O
different O
atmosphere O
modes O
. O


A O
slightly O
higher O
oxide S-MATE
content O
was O
detected O
in O
samples S-CONPRI
built O
using O
shielding O
gas S-CONPRI
. O


The O
mechanical B-CONPRI
properties E-CONPRI
in O
both O
conditions O
were O
extremely O
high O
. O


Samples S-CONPRI
built O
in O
controlled O
atmosphere O
had O
slightly O
higher O
yield B-PRO
strength E-PRO
. O


A O
correlation O
between O
tensile B-PRO
properties E-PRO
and O
oxide S-MATE
content O
is O
reported O
. O


Laser-Directed O
Energy O
Deposition S-CONPRI
was O
used O
to O
produce O
AISI O
316L B-MATE
stainless I-MATE
steel E-MATE
samples O
. O


The O
effect O
of O
the O
protective O
atmosphere O
on O
the O
microstructure S-CONPRI
and O
mechanical S-APPL
performance O
of O
AISI O
316L O
deposited O
parts O
was O
investigated O
by O
building O
samples S-CONPRI
using O
a O
simple S-MANP
nitrogen S-MATE
shielding O
gas S-CONPRI
or O
using O
a O
nitrogen-filled O
build B-PARA
chamber E-PARA
. O


The O
effect O
of O
the O
different O
processing O
conditions O
on O
the O
microstructure S-CONPRI
was O
evaluated O
by O
X-ray B-CHAR
analysis E-CHAR
, O
optical S-CHAR
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
. O


Only O
slight O
differences O
in O
the O
cellular O
dendrites S-BIOP
morphology O
of O
samples S-CONPRI
built O
under O
different O
protective O
atmosphere O
conditions O
were O
observed O
. O


However O
, O
the O
presence O
of O
oxides S-MATE
was O
monitored O
too O
: O
the O
oxides S-MATE
composition S-CONPRI
and O
area S-PARA
fraction O
were O
analysed O
and O
compared O
by O
image B-CONPRI
analyses E-CONPRI
, O
and O
it O
was O
demonstrated O
that O
the O
protective O
atmosphere O
mainly O
affects O
the O
oxides S-MATE
dimensions S-FEAT
. O


The O
effect O
of O
the O
oxides S-MATE
and O
nitrogen S-MATE
pick-up O
on O
the O
mechanical S-APPL
performance O
of O
the O
samples S-CONPRI
was O
evaluated O
by O
tensile B-CHAR
tests E-CHAR
. O


The O
results O
revealed O
that O
the O
nitrogen-filled O
build B-PARA
chamber E-PARA
allowed O
the O
achievement O
of O
slightly O
higher O
tensile B-PRO
strength E-PRO
and O
elongation S-PRO
with O
respect O
to O
the O
other O
processing O
conditions O
as S-MATE
a O
consequence O
of O
the O
reduced O
size O
of O
the O
oxide B-MATE
inclusions E-MATE
. O


Currently O
, O
the O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
process S-CONPRI
can O
not O
offer O
a O
reproducible O
and O
predefined O
quality S-CONPRI
of O
the O
processed S-CONPRI
parts O
. O


Recent O
research S-CONPRI
on O
process B-CONPRI
monitoring E-CONPRI
focuses O
strongly O
on O
integrated O
optical B-CHAR
measurement E-CHAR
technology O
. O


Besides O
optical S-CHAR
sensors O
, O
acoustic O
sensors S-MACEQ
also O
seem O
promising O
. O


Previous O
studies O
have O
shown O
the O
potential O
of O
analyzing O
structure-borne O
and O
air-borne O
acoustic B-CONPRI
emissions E-CONPRI
in O
laser B-MANP
welding E-MANP
. O


Only O
a O
few O
works O
evaluate O
the O
potential O
that O
lies O
in O
the O
L-PBF S-MANP
process.This O
work O
shows O
how O
the O
approach O
to O
structure-borne O
acoustic O
process B-CONPRI
monitoring E-CONPRI
can O
be S-MATE
elaborated O
by O
correlating O
acoustic O
signals O
to O
statistical O
values O
indicating O
part O
quality S-CONPRI
. O


Density B-CHAR
measurements E-CHAR
according O
to O
Archimedes O
’ O
principle O
are O
used O
to O
label O
the O
layer-based O
acoustic O
data S-CONPRI
and O
to O
measure O
the O
quality S-CONPRI
. O


The O
data S-CONPRI
set O
is O
then O
treated O
as S-MATE
a O
classification S-CONPRI
problem O
while O
investigating O
the O
applicability O
of O
existing O
artificial B-ENAT
neural I-ENAT
network E-ENAT
algorithms S-CONPRI
, O
such O
as S-MATE
the O
TensorFlow O
in O
the O
Python O
language O
, O
to O
match O
acoustic O
data S-CONPRI
with O
density B-CHAR
measurements E-CHAR
. O


Heat B-MANP
treatment E-MANP
of O
Scandium O
and O
Zirconium S-MATE
modified O
AlMg O
alloys S-MATE
processed O
by O
Selective B-MANP
Laser I-MANP
Melting E-MANP
leads O
to O
precipitation S-CONPRI
of O
coherent O
Al3Sc O
particles S-CONPRI
. O


The O
number O
density S-PRO
of O
coherent O
Al3Sc O
particles S-CONPRI
in O
heat S-CONPRI
treated O
condition O
reaches O
5.2 O
× O
1023 O
m−3 O
. O


Coherently O
precipitated O
Al3Sc O
particles S-CONPRI
are O
< O
5 O
nm O
in O
diameter S-CONPRI
. O


Grain B-CONPRI
boundary E-CONPRI
particles O
stabilize O
the O
microstructure S-CONPRI
against O
grain B-CONPRI
growth E-CONPRI
during O
heat B-MANP
treatment E-MANP
. O


Sc- O
Zr-modified O
Al-Mg B-MATE
alloy E-MATE
, O
processed S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
, O
offers O
excellent O
properties S-CONPRI
in O
the O
as S-MATE
processed O
condition O
, O
due O
to O
the O
formation O
of O
a O
desirable O
microstructure S-CONPRI
. O


As S-MATE
in O
conventional O
processing O
, O
such O
alloys S-MATE
are O
age O
hardenable O
, O
thereby O
precipitating O
a O
high O
fraction S-CONPRI
of O
finely O
dispersed O
coherent O
Al3 O
( O
Scx O
Zr1-x O
) O
intermetallics S-MATE
, O
which O
serve O
for O
the O
improvement O
of O
the O
mechanical B-PRO
strength E-PRO
. O


Electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
measurements O
and O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
were O
used O
to O
determine O
the O
effects O
of O
heat B-MANP
treatment E-MANP
and O
HIP S-MANP
on O
the O
microstructures S-MATE
of O
SLM S-MANP
processed S-CONPRI
specimens O
. O


In O
addition O
, O
the O
chemistry S-CONPRI
and O
number O
density S-PRO
of O
Al3Sc O
particles S-CONPRI
was O
analysed O
by O
atom B-CHAR
probe I-CHAR
tomography E-CHAR
. O


The O
results O
show O
that O
the O
bi-modal O
grain B-PRO
size E-PRO
distribution S-CONPRI
observed O
in O
the O
as-processed O
condition O
can O
be S-MATE
maintained O
even O
after O
a O
heat B-MANP
treatment E-MANP
, O
due O
to O
a O
high O
density S-PRO
of O
intragranular O
Al3 O
( O
ScxZr1-x O
) O
precipitates S-MATE
, O
and O
various O
other O
particles S-CONPRI
pinning O
the O
grain B-CONPRI
boundaries E-CONPRI
. O


A O
HIP S-MANP
post-processing O
can O
lead S-MATE
to O
grain B-CONPRI
growth E-CONPRI
in O
certain O
coarser O
grained O
areas S-PARA
, O
probably O
due O
to O
a O
local O
imbalance O
between O
driving O
and O
dragging O
forces S-CONPRI
, O
hence O
higher O
defect S-CONPRI
density O
and O
fewer O
pinning O
precipitates S-MATE
. O


Applying O
a O
heat B-MANP
treatment E-MANP
results O
in O
an O
increase O
of O
the O
density S-PRO
of O
≤5 O
nm O
sized O
intragranular O
Al3 O
( O
Scx O
Zr1-x O
) O
particles S-CONPRI
by O
a O
factor O
of O
4–6 O
, O
reaching O
3·1023 O
m−3 O
to O
5·1023 O
m−3 O
. O


Shrinkage S-CONPRI
stress O
occur O
perpendicular O
to O
boundaries S-FEAT
of O
primary O
columnar B-PRO
grains E-PRO
. O


This O
stress S-PRO
forms O
immobile O
dislocation S-CONPRI
networks O
that O
hinder O
dislocation S-CONPRI
movement O
. O


Recrystallization S-CONPRI
during O
annealing S-MANP
at O
≥1373 O
K S-MATE
eliminates O
the O
dislocation S-CONPRI
network O
. O


Networks O
of O
connected O
deformation S-CONPRI
and O
annealing S-MANP
twins O
block O
dislocation S-CONPRI
movement O
. O


Dislocation S-CONPRI
walls O
were O
found O
near O
grain B-CONPRI
boundaries E-CONPRI
. O


To O
widen O
the O
applications O
of O
FeCoCrNi O
high-entropy O
alloys S-MATE
( O
HEAs O
) O
fabricated S-CONPRI
via O
selective B-MANP
laser I-MANP
melting E-MANP
, O
their O
mechanical B-CONPRI
properties E-CONPRI
must O
be S-MATE
improved O
, O
and O
annealing S-MANP
plays O
an O
important O
role O
in O
this O
regard O
. O


In O
this O
study O
, O
the O
microstructure S-CONPRI
, O
residual B-PRO
stress E-PRO
, O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
as-printed O
specimen O
and O
specimens O
annealed O
at O
773–1573 O
K S-MATE
for O
2 O
h O
were O
compared O
. O


As S-MATE
the O
annealing S-MANP
temperature O
increased O
, O
the O
specimen O
structure S-CONPRI
recrystallized S-MANP
from O
all O
columnar B-PRO
grains E-PRO
to O
equiaxial O
grains S-CONPRI
containing O
numerous O
annealing S-MANP
twins O
. O


The O
dislocation S-CONPRI
network O
, O
which O
formed O
during O
the O
solidification B-MANP
process E-MANP
under O
considerable O
shrinkage S-CONPRI
strain O
, O
decomposed O
into O
dislocations S-CONPRI
. O


The O
residual B-PRO
stress E-PRO
, O
yield B-PRO
strength E-PRO
, O
and O
hardness S-PRO
decreased O
, O
while O
the O
plasticity S-PRO
and O
impact S-CONPRI
toughness O
increased O
. O


During O
the O
deformation S-CONPRI
of O
as-printed O
and O
low-temperature-annealed O
specimens O
, O
the O
dislocation S-CONPRI
network O
remained O
unchanged O
and O
provided O
resistance S-PRO
to O
the O
dislocations S-CONPRI
moving O
within O
it O
, O
thus O
strengthening S-MANP
the O
specimen O
. O


The O
tensile B-PRO
strength E-PRO
remained O
largely O
unchanged O
owing O
to O
the O
reduction S-CONPRI
in O
the O
residual B-PRO
stress E-PRO
during O
low-temperature O
annealing S-MANP
, O
as S-MATE
well O
as S-MATE
the O
formation O
of O
the O
twinning S-CONPRI
network O
and O
dislocation S-CONPRI
wall O
under O
large O
deformation S-CONPRI
upon O
high-temperature O
annealing S-MANP
. O


Meanwhile O
, O
the O
ductility S-PRO
greatly O
increased O
, O
thus O
increasing O
the O
potential O
for O
industrial S-APPL
application O
of O
HEAs O
. O


First-time O
fabrication S-MANP
of O
FCC S-CONPRI
+ O
BCC S-CONPRI
dual-phase O
high-entropy O
alloys S-MATE
( O
DP-HEAs O
) O
by O
SLM S-MANP
. O


New O
alloy S-MATE
design O
strategy O
for O
attaining O
strong O
, O
yet O
ductile S-PRO
DP-HEAs O
suitable O
for O
rapid B-MANP
solidification E-MANP
. O


Deformation S-CONPRI
nano-twins O
, O
stacking O
faults O
and O
strain-activated O
B2-to-FCC O
phase S-CONPRI
transition O
are O
discovered O
in O
BCC S-CONPRI
phase O
. O


The O
deformation S-CONPRI
mechanisms O
of O
the O
FCC S-CONPRI
and O
B2 O
phases O
are O
uncovered O
. O


Preparing O
dual-phase O
high-entropy O
alloys S-MATE
( O
DP-HEAs O
) O
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
has O
never O
been O
achieved O
owing O
to O
high O
crack O
susceptibility S-PRO
induced O
by O
rapid B-MANP
solidification E-MANP
. O


Here O
we O
design S-FEAT
and O
fabricate S-MANP
new O
face-centered O
cubic O
( O
FCC S-CONPRI
) O
and O
body-centered O
cubic O
( O
BCC S-CONPRI
) O
DP-HEAs O
based O
on O
BCC S-CONPRI
AlCrCuFeNi O
HEA O
using O
SLM S-MANP
. O


Results O
show O
that O
the O
addition O
of O
Ni S-MATE
facilitates O
the O
columnar-to-near-equiaxed O
transition S-CONPRI
and O
improves O
the O
formability S-PRO
of O
the O
as-built O
AlCrCuFeNix O
( O
2.0 O
≤ O
x O
≤ O
3.0 O
) O
HEAs O
. O


Especially O
, O
the O
as-built O
AlCrCuFeNi3.0 O
HEA O
exhibits O
modulated O
nano-sized O
lamellar S-CONPRI
or O
cellular O
dual-phase O
structures O
and O
possesses O
the O
best O
combination O
of O
ultimate B-PRO
tensile I-PRO
strength E-PRO
( O
∼ O
957 O
MPa S-CONPRI
) O
and O
ductility S-PRO
( O
∼ O
14.3 O
% O
) O
. O


Post-deformation O
research S-CONPRI
reveals O
that O
the O
FCC S-CONPRI
phase O
is O
deformed S-MANP
through O
planar O
dislocation S-CONPRI
slip O
with O
{ O
111 O
} O
< O
110 O
> O
slip O
systems O
, O
and O
stacking O
faults O
( O
SFs O
) O
. O


Strain-activated O
B2-to-FCC O
phase S-CONPRI
transition O
occurs O
in O
the O
B2 O
phase S-CONPRI
. O


The O
uncovered O
synergy O
of O
various O
deformation S-CONPRI
modes O
and O
the O
underlying O
back O
stress S-PRO
strengthening S-MANP
induced O
by O
heterogeneous S-CONPRI
microstructures O
contribute O
to O
the O
high O
ultimate B-PRO
tensile I-PRO
strength E-PRO
and O
good O
ductility S-PRO
of O
the O
as-built O
AlCrCuFeNi3.0 O
HEA O
. O


3D B-MANP
printing E-MANP
of O
flexible O
conductive O
nanocomposites O
were O
investigated O
. O


Conductivity S-PRO
was O
found O
largely O
independent O
of O
process S-CONPRI
temperatures O
. O


Anisotropy S-PRO
in O
conductivity S-PRO
was O
observed O
up O
to O
an O
order O
of O
magnitude S-PARA
. O


Soft O
actuators S-MACEQ
with O
built-in O
touch O
sensors S-MACEQ
was O
successfully O
printed O
. O


Soft O
actuators S-MACEQ
with O
built-in O
piezoresistive O
sensing S-APPL
was O
demonstrated O
. O


With O
applications O
in O
flexible O
electronics S-CONPRI
and O
soft B-APPL
robotics E-APPL
, O
the O
ability O
to O
fabricate S-MANP
elastic S-PRO
functional O
materials S-CONPRI
with O
complex B-CONPRI
geometries E-CONPRI
has O
become O
highly O
desirable O
. O


In O
this O
work O
, O
flexible O
thermoplastic S-MATE
polyurethane/multiwalled O
carbon B-MATE
nanotube E-MATE
( O
TPU-MWCNT O
) O
composites S-MATE
were O
printed O
using O
multi-material S-CONPRI
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
to O
study O
their O
feasibility S-CONPRI
towards O
built-in O
sensing S-APPL
capabilities O
in O
soft B-APPL
robotics E-APPL
. O


The O
microstructure S-CONPRI
, O
electrical B-PRO
conductivity E-PRO
, O
capacitive O
sensing S-APPL
, O
and O
piezoresistive O
sensing S-APPL
of O
the O
printed O
samples S-CONPRI
were O
investigated O
. O


MWCNT O
content O
, O
print S-MANP
orientation S-CONPRI
, O
and O
layer B-PARA
height E-PARA
was O
found O
to O
be S-MATE
the O
most O
influential O
parameters S-CONPRI
on O
the O
electrical B-CONPRI
properties E-CONPRI
while O
the O
nozzle S-MACEQ
and O
bed S-MACEQ
temperatures O
showed O
insignificant O
impacts O
. O


Overall O
, O
the O
in-line O
and O
through-line O
conductivities O
were O
one O
order O
of O
magnitude S-PARA
higher O
than O
the O
through-layer O
conductivity S-PRO
. O


A O
soft O
pneumatic O
actuator S-MACEQ
was O
then O
designed S-FEAT
and O
printed O
out O
of O
TPU-MWCNT O
using O
the O
optimized O
process S-CONPRI
conditions O
. O


The O
built-in O
capacitive O
and O
piezoresistive O
sensing S-APPL
capabilities O
of O
the O
printed O
actuators S-MACEQ
were O
successfully O
demonstrated O
upon O
gripping O
contact S-APPL
and O
actuation O
at O
three O
different O
pressure S-CONPRI
levels O
. O


This O
work O
unveils O
the O
potential O
of O
integrating O
a O
variety O
of O
feedback S-PARA
sensors O
in O
robotic O
actuators S-MACEQ
through O
FFF S-MANP
process O
. O


In O
this O
study O
, O
commercially O
pure O
titanium S-MATE
( O
CP-Ti O
) O
parts O
were O
successfully O
fabricated S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
using O
cost-effective O
hydride-dehydride O
( O
HDH O
) O
Ti B-MATE
powders E-MATE
for O
the O
first O
time O
modified O
by O
jet O
milling S-MANP
. O


Jet O
milling S-MANP
effectively O
improves O
the O
particle-shape O
sphericity O
, O
suppresses O
the O
impurity S-PRO
pick-up O
, O
and O
produces O
localized O
plastic B-PRO
deformation E-PRO
. O


The O
oxide S-MATE
layer S-PARA
in O
the O
powder S-MATE
surface O
is O
determined O
with O
the O
thickness O
of O
∼8 O
nm O
and O
TiO O
being O
the O
predominant O
phase S-CONPRI
before O
and O
after O
jet O
milling S-MANP
. O


The O
SLM-made O
( O
SLMed S-MANP
) O
CP-Ti O
achieves O
dominant O
martensitic O
α O
’ O
phase S-CONPRI
with O
the O
fracture S-CONPRI
tensile O
strength S-PRO
up O
to O
731.5 O
± O
5.7 O
MPa S-CONPRI
and O
elongation S-PRO
of O
20.5 O
± O
1.1 O
% O
, O
comparable O
with O
those O
using O
expensive O
atomized S-ENAT
powders O
. O


Contrary O
to O
the O
conventional O
metallurgical S-APPL
mechanism S-CONPRI
for O
Ti S-MATE
which O
suffers O
the O
cost-performance O
dilemma O
, O
this O
work O
presents O
SLMed S-MANP
CP-Ti O
with O
excellent O
synergy O
of O
strength S-PRO
and O
ductility S-PRO
while O
using O
the O
cost-affordable O
HDH O
Ti B-MATE
powders E-MATE
. O


In O
this O
work O
the O
tensile S-PRO
behaviour O
of O
selective B-MANP
laser I-MANP
melted E-MANP
( O
SLMed S-MANP
) O
aluminium B-MATE
alloy E-MATE
A357 O
in O
the O
as-fabricated O
and O
heat-treated S-MANP
states O
is O
explained O
using O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
, O
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
( O
EBSD S-CHAR
) O
, O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
TEM S-CHAR
) O
, O
and O
transmission S-CHAR
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
( O
t-EBSD O
) O
. O


The O
as-built O
sample S-CONPRI
has O
an O
ultrafine O
microstructure S-CONPRI
, O
with O
high O
residual B-PRO
stresses E-PRO
and O
non-equilibrium O
solid O
solute O
concentration O
of O
Si S-MATE
in O
the O
supersaturated O
Al S-MATE
matrix O
. O


Consequently O
, O
the O
tensile B-PRO
properties E-PRO
of O
the O
SLMed S-MANP
Al B-MATE
alloy E-MATE
A357 O
are O
comparable O
or O
better O
than O
traditional O
cast S-MANP
counterparts O
. O


The O
Al S-MATE
grains O
in O
the O
SLMed S-MANP
alloy S-MATE
consist O
of O
sub-micron S-FEAT
sized O
Al S-MATE
cells O
, O
and O
both O
high O
angle O
and O
low O
angle O
boundaries S-FEAT
are O
initially O
occupied O
by O
eutectic S-CONPRI
nano-sized O
Si S-MATE
particles S-CONPRI
, O
which O
are O
beneficial O
for O
strength S-PRO
but O
detrimental O
for O
ductility S-PRO
. O


With O
subsequent O
solution B-MANP
heat I-MANP
treatment E-MANP
, O
the O
Si S-MATE
particles S-CONPRI
on O
the O
low O
angle O
cell S-APPL
boundaries S-FEAT
( O
LACBs O
) O
dissolve O
while O
those O
at O
the O
high O
angle O
grain B-CONPRI
boundaries E-CONPRI
( O
HAGBs O
) O
coarsen O
. O


Simultaneously O
internal B-PRO
stresses E-PRO
decrease O
, O
as S-MATE
does O
solute O
content O
in O
the O
matrix O
. O


The O
evolution S-CONPRI
of O
these O
microstructural S-CONPRI
features O
explains O
the O
improved O
tensile B-PRO
ductility E-PRO
( O
at O
its O
maximum O
> O
23 O
% O
) O
and O
reduced O
tensile B-PRO
strength E-PRO
for O
the O
heat S-CONPRI
treated O
SLMed S-MANP
aluminium B-MATE
alloy E-MATE
A357 O
samples S-CONPRI
. O


Correlations O
between O
microstructures S-MATE
and O
corrosion B-CONPRI
resistances E-CONPRI
of O
SLMed S-MANP
Inconel B-MATE
718 I-MATE
alloy E-MATE
are O
studied O
. O


Platelet-shape O
δ O
phases O
are O
discovered O
after O
solution B-MANP
annealing I-MANP
treatment E-MANP
. O


Corrosion S-CONPRI
micro-batteries O
cause O
the O
formation O
of O
pits O
or O
cracks O
at O
secondary O
phase B-CONPRI
boundaries E-CONPRI
. O


Corrosion S-CONPRI
mechanism O
of O
SLMed S-MANP
Inconel B-MATE
718 I-MATE
alloy E-MATE
is O
revealed O
. O


The O
microstructures S-MATE
and O
corrosion B-CONPRI
resistances E-CONPRI
of O
Inconel B-MATE
718 I-MATE
alloy E-MATE
prepared O
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
, O
SLM S-MANP
following O
various O
heat B-MANP
treatments E-MANP
, O
and O
conventional O
rolling S-MANP
are O
studied O
. O


Results O
show O
that O
only O
Nb S-MATE
element S-MATE
is O
enriched O
in O
interdendritic O
regions O
while O
Fe S-MATE
element S-MATE
is O
abundant O
in O
dendritic O
trunks O
for O
the O
as-built O
Inconel B-MATE
718 I-MATE
alloy E-MATE
. O


After O
solution B-MANP
annealing I-MANP
treatment E-MANP
, O
incomplete O
recrystallization S-CONPRI
is O
observed O
and O
distortion S-CONPRI
energy O
is O
released O
. O


Increasing O
the O
solution S-CONPRI
annealing S-MANP
temperature O
from O
980 O
°C O
to O
1020 O
°C O
( O
ST1∼ST3 O
) O
, O
the O
morphologies S-CONPRI
of O
δ O
phases O
turn O
from O
needle-like O
into O
short O
platelet O
shape O
, O
which O
reduces O
the O
anodic O
current O
density S-PRO
and O
improves O
the O
corrosion B-CONPRI
resistance E-CONPRI
compared O
to O
other O
heat-treated S-MANP
samples O
in O
3.5 O
wt O
% O
NaCl S-MATE
solution O
. O


Corrosion S-CONPRI
morphology O
observation O
shows O
that O
obvious O
cracking S-CONPRI
of O
surface S-CONPRI
passive O
film O
occurs O
for O
the O
SLM S-MANP
, O
solution S-CONPRI
annealing S-MANP
plus O
double O
aging O
( O
SA O
) O
and O
rolled O
samples S-CONPRI
, O
while O
corrosion S-CONPRI
pits O
and O
micro-cracks S-CONPRI
appear O
at O
the O
δ O
phase B-CONPRI
boundaries E-CONPRI
of O
solution-annealed O
( O
ST1∼ST3 O
) O
samples S-CONPRI
. O


The O
surface S-CONPRI
passive O
film O
is O
smooth O
for O
the O
rolled O
sample S-CONPRI
. O


The O
corrosion B-CONPRI
resistance E-CONPRI
of O
samples S-CONPRI
obtained O
by O
different O
processes S-CONPRI
follows O
in O
the O
order O
of O
rolled O
> O
ST3 O
> O
ST2 O
> O
ST1 O
> O
SA O
> O
SLM S-MANP
. O


The O
high O
interface S-CONPRI
energy O
and O
lattice S-CONPRI
misfit O
may O
provide O
driving O
forces S-CONPRI
for O
the O
preferential O
dissolution O
of O
γ O
matrix O
rather O
than O
second O
phases O
. O


The O
inferior O
corrosion B-CONPRI
resistance E-CONPRI
of O
the O
as-built O
Inconel B-MATE
718 I-MATE
alloy E-MATE
can O
be S-MATE
significantly O
improved O
through O
solution B-MANP
annealing I-MANP
treatment E-MANP
at O
1020 O
°C O
. O


The O
increase O
of O
molecular O
weight S-PARA
of O
partcake O
powder S-MATE
could O
be S-MATE
traced O
back O
to O
a O
linear O
chain O
growth O
/ O
post O
condensation O
reaction O
with O
GPC O
analysis O
. O


The O
influence O
of O
build B-PARA
time E-PARA
in O
selective B-MANP
laser I-MANP
sintering E-MANP
on O
molecular O
changes O
of O
polyamide B-MATE
12 E-MATE
powder O
is O
more O
significant O
than O
the O
effect O
of O
build S-PARA
temperature O
. O


With O
increasing O
molecular O
weight S-PARA
, O
the O
chain O
mobility O
is O
reduced O
and O
the O
crystallization S-CONPRI
temperature O
shifts O
to O
lower O
temperatures S-PARA
. O


This O
broadens O
the O
processing O
window O
, O
but O
higher O
molecular O
weights O
go S-MATE
along O
with O
a O
higher O
viscosity S-PRO
, O
which O
is O
not O
favorable O
for O
SLS B-MANP
process E-MANP
. O


The O
material B-CONPRI
aging E-CONPRI
in O
selective B-MANP
laser I-MANP
sintering E-MANP
SLS O
of O
polyamide B-MATE
12 E-MATE
is O
one O
challenge O
, O
which O
has O
to O
be S-MATE
overcome O
for O
implementation O
of O
this O
technique O
in O
serial O
production S-MANP
. O


High O
temperatures S-PARA
and O
along O
going O
processing O
times O
lead S-MATE
to O
chemical O
and O
physical O
aging O
effects O
of O
the O
supporting O
partcake O
material S-MATE
. O


The O
investigations O
in O
this O
study O
aims O
at O
the O
influence O
of O
processing O
time O
and O
temperature S-PARA
on O
molecular O
changes O
and O
thermal B-CONPRI
properties E-CONPRI
of O
polyamide B-MATE
12 E-MATE
partcake O
material S-MATE
in O
selective B-MANP
laser I-MANP
sintering E-MANP
. O


The O
focus O
of O
the O
investigations O
lays O
on O
the O
global O
heat B-CONPRI
exposure E-CONPRI
of O
the O
of O
the O
bulk O
material S-MATE
und O
thus O
on O
global O
material S-MATE
changes O
. O


Gel S-MATE
permeation O
chromatography O
analysis O
was O
used O
to O
determine O
the O
molecular O
weight S-PARA
distribution S-CONPRI
and O
changes O
of O
polymer S-MATE
structure O
. O


With O
increasing O
build B-PARA
time E-PARA
and O
build B-PARA
chamber E-PARA
temperature O
the O
average S-CONPRI
molecular O
weight S-PARA
is O
rising O
, O
whereby O
the O
influence O
of O
build B-PARA
time E-PARA
is O
more O
significant O
. O


The O
rise O
of O
chain O
length O
leads O
to O
a O
reduction S-CONPRI
of O
crystallization S-CONPRI
temperature O
, O
which O
was O
detected O
by O
DSC S-CHAR
. O


This O
work O
investigated O
the O
superelastic O
response O
of O
the O
low-modulus O
porous S-PRO
β O
type O
Ti-35Nb-2Ta-3Zr O
scaffolds S-FEAT
with O
different O
pore B-PARA
dimensions E-PARA
fabricated S-CONPRI
by O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
. O


The O
superelastic O
behavior O
was O
enhanced O
with O
increasing O
the O
pore B-PARA
size E-PARA
and O
stress-induced O
phase S-CONPRI
transformation O
, O
which O
correspondingly O
led S-APPL
to O
stress-induced O
α O
'' O
[ O
110 O
] O
-type O
I O
twin O
martensitic O
transformation O
and O
ω O
formation O
adjacent O
to O
β O
matrix/twins O
. O


The O
resultant O
interstitial O
compound O
phase S-CONPRI
structure O
facilitated O
the O
β O
→ O
α O
'' O
and O
β O
→ O
ω O
transition S-CONPRI
, O
which O
was O
triggered O
by O
interfacial O
stress/strain O
concentration O
and O
high-density O
dislocations S-CONPRI
. O


Substantial O
high-angle O
grain B-CONPRI
boundaries E-CONPRI
( O
HAGBs O
) O
accumulated O
high-intensity O
Schimd O
factor O
and O
crystallographic O
texture S-FEAT
after O
being O
deformed S-MANP
. O


Moreover O
, O
a O
lower O
Young O
’ O
s S-MATE
modulus O
was O
obtained O
when O
the O
pore B-PARA
size E-PARA
and O
stress S-PRO
increased O
. O


A O
vision-based O
inspection S-CHAR
system O
based O
on O
three O
digital O
cameras O
is O
proposed O
for O
measuring O
the O
cladding S-MANP
height O
in O
the O
Direct B-MANP
Energy I-MANP
Deposition E-MANP
( O
DED S-MANP
) O
process S-CONPRI
. O


To O
improve O
the O
accuracy S-CHAR
of O
the O
cladding S-MANP
height O
measurements O
, O
an O
image S-CONPRI
processing O
technique O
is O
applied O
to O
remove O
the O
undesirable O
zone O
from O
the O
binary S-CONPRI
image O
. O


Furthermore O
, O
since O
the O
unit O
length O
in O
the O
captured O
images S-CONPRI
is O
different O
to O
that O
in O
the O
world O
coordinate S-PARA
framework O
, O
a O
calibration S-CONPRI
bar O
method O
is O
designed S-FEAT
to O
transform O
the O
pixel O
value O
to O
the O
real O
size O
. O


An O
image-processing O
technique O
is O
then O
employed O
to O
isolate O
the O
laser S-ENAT
nozzle O
and O
melt B-MATE
pool E-MATE
in O
the O
captured O
images S-CONPRI
. O


Finally O
, O
the O
cladding S-MANP
height O
is O
estimated O
based O
on O
the O
distance O
between O
the O
tip O
of O
the O
laser S-ENAT
nozzle O
and O
the O
centroid O
of O
the O
melt B-MATE
pool E-MATE
. O


The O
validity O
of O
the O
proposed O
approach O
is O
demonstrated O
by O
comparing O
the O
inspection S-CHAR
results O
for O
the O
cladding S-MANP
height O
of O
a O
horseshoe O
component S-MACEQ
with O
the O
measurements O
obtained O
using O
a O
3-D S-CONPRI
scanner O
. O


The O
maximum O
estimation O
error S-CONPRI
is O
found O
to O
be S-MATE
just O
4.2 O
% O
Overall O
, O
the O
results O
confirm O
that O
the O
proposed O
trinocular O
vision-based O
system O
provides O
a O
rapid O
, O
convenient O
and O
accurate S-CHAR
means O
of O
determining O
the O
cladding S-MANP
height O
in O
the O
DED S-MANP
process O
. O


The O
aim O
of O
this O
study O
is O
to O
promote O
the O
magnetic O
shielding O
characteristics O
of O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
processed S-CONPRI
NiFeMo O
alloy S-MATE
. O


This O
was O
achieved O
via O
controlling O
the O
crystallographic O
texture S-FEAT
of O
the O
builds S-CHAR
to O
increase O
the O
grain S-CONPRI
population O
along O
the O
easy O
axis O
of O
magnetisation O
, O
as S-MATE
well O
as S-MATE
the O
use O
of O
post-process S-CONPRI
hydrogen O
heat B-MANP
treatment E-MANP
( O
HT O
) O
and O
hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
processes S-CONPRI
. O


The O
as-fabricated O
microstructure S-CONPRI
typically O
demonstrates O
weak O
magnetic O
properties S-CONPRI
due O
to O
the O
alignment O
of O
the O
crystallographic O
orientation/spin O
order O
along O
the O
[ O
100 O
] O
hard O
axis O
of O
magnetisation O
, O
which O
is O
parallel O
to O
the O
build B-PARA
direction E-PARA
since O
it O
is O
also O
the O
preferred O
growth O
direction O
during O
solidification S-CONPRI
in O
cubic O
materials S-CONPRI
. O


The O
improved O
ferromagnetism S-PRO
following O
HIP S-MANP
+ O
HT O
was O
due O
to O
several O
combined O
effects O
, O
including O
stress S-PRO
relief O
, O
consolidation S-CONPRI
of O
gas S-CONPRI
pores O
, O
recrystallisation O
, O
and O
grain B-CONPRI
growth E-CONPRI
. O


The O
post-processing S-CONPRI
sequence O
( O
HT O
+ O
HIP S-MANP
vs. O
HIP S-MANP
+ O
HT O
) O
appeared O
to O
affect O
the O
resulting O
magnetic O
characteristics O
. O


Finally O
, O
the O
tensile B-PRO
properties E-PRO
for O
the O
builds S-CHAR
were O
characterised O
to O
ensure O
that O
both O
functional O
and O
mechanical B-CONPRI
behaviours E-CONPRI
would O
achieve O
the O
required O
performance S-CONPRI
. O


Usually O
the O
process B-CONPRI
gas E-CONPRI
flow B-PARA
rates E-PARA
and O
the O
process B-CONPRI
gas E-CONPRI
types O
are O
not O
regarded O
as S-MATE
the O
primary O
process B-CONPRI
parameters E-CONPRI
of O
the O
laser B-MANP
cladding E-MANP
process O
. O


Herein O
it O
is O
shown O
, O
how O
the O
melt B-MATE
pool E-MATE
surface O
oxidation S-MANP
can O
be S-MATE
significantly O
reduced O
by O
the O
change O
of O
the O
carrier O
gas S-CONPRI
type O
, O
by O
a O
reduced O
carrier O
gas B-PARA
flow I-PARA
rate E-PARA
and O
by O
minor O
changes O
in O
the O
powder S-MATE
nozzle S-MACEQ
design S-FEAT
. O


A O
simulation S-ENAT
model S-CONPRI
for O
the O
gas S-CONPRI
flow O
and O
the O
powder B-MATE
particle E-MATE
flow O
between O
the O
powder S-MATE
nozzle S-MACEQ
and O
the O
melt B-MATE
pool E-MATE
surface O
has O
been O
developed O
, O
which O
reveals O
the O
volume S-CONPRI
percentage O
of O
different O
gas S-CONPRI
types O
and O
so O
the O
quality S-CONPRI
of O
the O
shield O
gas S-CONPRI
atmosphere O
. O


Additionally O
, O
the O
powder B-MATE
particle E-MATE
distribution S-CONPRI
and O
the O
attenuation O
of O
the O
laser B-CONPRI
beam E-CONPRI
by O
the O
powder B-MATE
particles E-MATE
can O
be S-MATE
simulated O
. O


The O
simulation S-ENAT
results O
are O
confirmed O
by O
experimental S-CONPRI
measurements O
of O
the O
powder B-MATE
particle E-MATE
density B-PRO
distribution E-PRO
in O
the O
working O
plane O
, O
by O
measurements O
of O
the O
oxygen S-MATE
volume O
percentage O
at O
the O
workpiece S-CONPRI
surface S-CONPRI
, O
by O
high-speed O
camera S-MACEQ
images O
of O
the O
melt B-MATE
pool E-MATE
surface O
and O
by O
absorptivity O
measurements O
, O
which O
show O
the O
effect O
of O
oxidation S-MANP
on O
the O
process S-CONPRI
. O


TiB O
precipitates S-MATE
were O
significantly O
refined O
in O
the O
EB-PBF-built O
Ti-6242S-1.0B O
alloy S-MATE
compared O
with O
forged O
alloys S-MATE
. O


Finer O
oxides S-MATE
contributed O
to O
the O
formation O
of O
more O
compact S-MANP
oxidation O
layers O
in O
the O
EB-PBF-built O
alloy S-MATE
than O
as-forged O
alloy S-MATE
. O


Evaporation S-CONPRI
of O
B2O3 S-MATE
from O
coarse O
TiB O
particles S-CONPRI
destabilized O
the O
oxidation S-MANP
layer S-PARA
in O
the O
as-forged O
alloy S-MATE
. O


Evaporation S-CONPRI
of O
B2O3 S-MATE
from O
fine O
TiB O
particles S-CONPRI
did O
not O
destabilize O
the O
oxidation S-MANP
layer S-PARA
in O
the O
EB-PBF-built O
alloy S-MATE
. O


EB-PBF-built O
Ti-6242S-1.0B O
alloy S-MATE
was O
more O
resistant O
to O
oxidation S-MANP
than O
the O
as-forged O
alloy S-MATE
. O


Refined O
TiB O
precipitates S-MATE
significantly O
enhance O
the O
oxidation B-PRO
resistance E-PRO
of O
Ti-6Al-2Sn-4Zr-2Mo-0.1Si-1.0B O
alloy S-MATE
fabricated O
by O
electron B-CONPRI
beam E-CONPRI
powder O
bed B-MANP
fusion E-MANP
( O
EB-PBF O
) O
. O


Refined O
TiB O
precipitates S-MATE
in O
the O
EB-PBF-built O
alloy S-MATE
enable O
finer O
oxide S-MATE
formation O
than O
the O
larger O
precipitates S-MATE
in O
the O
forged O
alloy S-MATE
, O
and O
the O
resulting O
oxidation S-MANP
layers O
are O
more O
compact S-MANP
. O


Evaporation S-CONPRI
of O
scattered O
B2O3 S-MATE
generated O
by O
the O
refined O
TiB O
precipitates S-MATE
in O
the O
EB-PBF-built O
alloy S-MATE
do O
not O
significantly O
accelerate O
detachment O
of O
the O
oxidation S-MANP
layer S-PARA
from O
the O
substrate S-MATE
. O


However O
, O
collective O
evaporation S-CONPRI
of O
B2O3 S-MATE
generated O
by O
larger O
TiB O
precipitates S-MATE
in O
the O
forged O
alloy S-MATE
accelerate O
detachment O
. O


The O
oxidation S-MANP
layer S-PARA
on O
the O
EB-PBF-fabricated O
alloy S-MATE
was O
more O
stable O
, O
preventing O
further O
oxidation S-MANP
and O
improving O
oxidation B-PRO
resistance E-PRO
. O


We O
report O
on O
the O
development O
of O
a O
miniaturized O
device O
for O
operando O
X-ray B-CHAR
diffraction E-CHAR
during O
laser S-ENAT
3D B-MANP
printing E-MANP
. O


We O
describe O
the O
design B-CONPRI
considerations E-CONPRI
, O
details O
on O
the O
setup O
and O
the O
implementation O
at O
two O
different O
beamlines O
of O
the O
Swiss O
Light B-MACEQ
Source E-MACEQ
. O


Its O
capabilities O
are O
demonstrated O
by O
ex O
situ O
printing O
of O
complex B-PRO
shapes E-PRO
and O
operando O
X-ray B-CHAR
diffraction E-CHAR
experiments O
using O
Ti-6Al-4V B-MATE
powder E-MATE
. O


It O
is O
shown O
that O
the O
beamline O
characteristics O
have O
an O
important O
influence O
on O
the O
X-ray S-CHAR
footprints O
of O
the O
microstructural B-CONPRI
evolution E-CONPRI
during O
3D B-MANP
printing E-MANP
. O


From O
the O
intensity O
of O
the O
diffraction S-CHAR
peaks O
, O
the O
evolution S-CONPRI
of O
the O
different O
phases O
can O
be S-MATE
followed O
during O
printing O
. O


Furthermore O
, O
the O
diffuse O
scattering O
signal O
provides O
information O
on O
the O
precise O
location O
of O
the O
laser B-CONPRI
beam E-CONPRI
on O
the O
sample S-CONPRI
and O
the O
scanning S-CONPRI
head O
settling O
time O
. O


Some O
AM B-MANP
processes E-MANP
such O
as S-MATE
directed O
energy O
deposition S-CONPRI
( O
DED S-MANP
) O
have O
typical O
powder S-MATE
usage O
efficiencies O
ranging O
between O
40 O
and O
80 O
% O
. O


Since O
, O
for O
a O
given O
alloy S-MATE
, O
powder S-MATE
cost O
is O
proportional O
to O
its O
purity O
, O
choosing O
a O
less O
expensive O
powder S-MATE
or O
reusing O
powders S-MATE
is O
interesting O
for O
economical O
and O
environmental O
reasons O
. O


The O
work O
summarized O
below O
studied O
the O
effect O
of O
oxygen S-MATE
content O
in O
Ti6Al4V B-MATE
powders E-MATE
on O
mechanical B-CONPRI
properties E-CONPRI
of O
AM B-MACEQ
parts E-MACEQ
fabricated O
by O
DED S-MANP
. O


Three O
different O
powders S-MATE
with O
increasing O
oxygen S-MATE
content O
were O
used O
to O
produce O
specimens O
and O
characterize O
its O
effect O
on O
microstructure S-CONPRI
and O
tensile B-PRO
properties E-PRO
before O
and O
after O
heat B-MANP
treatment E-MANP
. O


Only O
coarsening O
of O
the O
particle B-CONPRI
size I-CONPRI
distribution E-CONPRI
and O
the O
presence O
of O
fragmented O
particles S-CONPRI
was O
observed O
for O
the O
recycled S-CONPRI
powder S-MATE
. O


Comparing O
the O
chemistry S-CONPRI
of O
parts O
vs O
that O
of O
powder B-MACEQ
feedstock E-MACEQ
it O
was O
determined O
that O
for O
all O
the O
tests O
, O
the O
Al S-MATE
content O
was O
slightly O
lower O
in O
the O
parts O
and O
that O
no O
significant O
loss O
of O
vanadium S-MATE
was O
noted O
when O
printing O
with O
new O
( O
fresh O
) O
powders S-MATE
. O


On O
the O
other O
hand O
, O
V S-MATE
loss O
was O
significant O
in O
parts O
made O
with O
recycled S-CONPRI
powders S-MATE
, O
although O
still O
leaving O
them O
within O
acceptable O
chemistry S-CONPRI
to O
respect O
their O
original O
grade O
5 O
classification S-CONPRI
. O


The O
build S-PARA
quality O
of O
laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
( O
PBF S-MANP
) O
components S-MACEQ
largely O
depends O
on O
printing O
issues O
such O
as S-MATE
inter-track O
voids S-CONPRI
and O
undesired O
microstructure S-CONPRI
. O


In O
this O
work O
, O
a O
comprehensive O
phenomenological B-CONPRI
model E-CONPRI
was O
developed O
to O
compute O
the O
complex O
transport S-CHAR
phenomena O
during O
laser S-ENAT
PBF O
of O
Ti-6Al-4V S-MATE
. O


The O
transient S-CONPRI
temperature S-PARA
and O
velocity O
fields O
during O
single-track O
and O
multi-track O
laser S-ENAT
PBF O
were O
computed O
considering O
the O
melting S-MANP
and O
solidification S-CONPRI
of O
the O
powder B-MACEQ
feedstocks E-MACEQ
. O


Critical O
metallurgical S-APPL
variables O
including O
the O
molten B-CONPRI
pool E-CONPRI
characteristics O
and O
thermal B-PARA
cycles E-PARA
were O
obtained O
. O


The O
model S-CONPRI
was O
validated O
by O
comparing O
the O
computed O
results O
against O
corresponding O
experimental B-CONPRI
data E-CONPRI
. O


The O
formation O
and O
evolution S-CONPRI
of O
inter-track O
voids S-CONPRI
in O
different O
heat S-CONPRI
input O
conditions O
were O
studied O
. O


The O
first O
type O
appeared O
in O
irregular O
elongated O
shapes O
and O
was O
caused O
by O
the O
incomplete O
melting S-MANP
of O
the O
powder B-MACEQ
feedstocks E-MACEQ
. O


Cooling B-PARA
rates E-PARA
were O
obtained O
to O
interpret O
the O
metallurgical S-APPL
conditions O
for O
the O
solid-state B-CONPRI
phase E-CONPRI
transformations O
. O


The O
novel O
findings O
from O
this O
research S-CONPRI
are O
helpful O
to O
the O
understanding O
of O
the O
formation O
and O
mitigation O
of O
inter-track O
voids S-CONPRI
, O
and O
the O
assessment O
of O
phase S-CONPRI
transformations O
during O
laser S-ENAT
PBF O
of O
titanium B-MATE
alloys E-MATE
. O


The O
fracture S-CONPRI
toughness O
( O
K1c O
) O
and O
fatigue B-PARA
crack I-PARA
growth I-PARA
rate E-PARA
( O
FCGR O
) O
properties S-CONPRI
of O
selective B-MANP
laser I-MANP
melted E-MANP
( O
SLM S-MANP
) O
specimens O
produced O
from O
grade O
5 O
Ti6Al4V B-MATE
powder I-MATE
metal E-MATE
has O
been O
investigated O
. O


Three O
specimen O
orientations S-CONPRI
relative O
to O
the O
build B-PARA
direction E-PARA
as S-MATE
well O
as S-MATE
two O
different O
post-build O
heat B-MANP
treatments E-MANP
were O
considered O
. O


Specimens O
and O
test O
procedures O
were O
designed S-FEAT
in O
accordance O
with O
ASTM O
E399 O
and O
ASTM O
E647 O
standard S-CONPRI
. O


The O
results O
show O
that O
there O
is O
a O
strong O
influence O
of O
post-build O
processing O
( O
heat S-CONPRI
treated O
versus O
‘ O
as S-MATE
built O
’ O
) O
as S-MATE
well O
as S-MATE
specimen O
orientation S-CONPRI
on O
the O
dynamic S-CONPRI
behaviour O
of O
SLM S-MANP
produced O
Ti6Al4V S-MATE
. O


The O
greatest O
improvement O
in O
properties S-CONPRI
after O
heat B-MANP
treatment E-MANP
was O
demonstrated O
when O
the O
fracture S-CONPRI
plane O
is O
perpendicular O
to O
the O
SLM S-MANP
build B-PARA
direction E-PARA
. O


This O
behaviour O
is O
attributed O
to O
the O
higher O
anticipated O
influence O
of O
tensile B-PRO
residual I-PRO
stress E-PRO
for O
this O
orientation S-CONPRI
. O


The O
transformation O
of O
the O
initial O
rapidly B-MANP
solidified E-MANP
microstructure S-CONPRI
during O
heat B-MANP
treatment E-MANP
has O
a O
smaller O
beneficial O
effect O
on O
improving O
mechanical B-CONPRI
properties E-CONPRI
. O


3D-printed S-MANP
PLA/Ti O
scaffolds S-FEAT
with O
tailored O
porosity S-PRO
and O
pore B-PARA
size E-PARA
were O
fabricated S-CONPRI
via O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
. O


Thermal B-CONPRI
properties E-CONPRI
of O
PLA/Ti O
filaments S-MATE
were O
changed O
by O
the O
addition O
of O
Ti S-MATE
. O


5–10 O
vol O
% O
of O
Ti S-MATE
enhanced O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
3D-printed S-MANP
PLA/Ti O
scaffolds S-FEAT
. O


In O
vitro O
assays O
showed O
good O
cell S-APPL
responses O
in O
PLA/Ti O
scaffolds S-FEAT
. O


3D-printed S-MANP
PLA/Ti O
scaffolds S-FEAT
have O
potential O
as S-MATE
bone O
substitutes O
for O
tissue B-CONPRI
engineering E-CONPRI
. O


Ideal O
bone S-BIOP
substitutes O
should O
ensure O
good O
integration O
with O
bone S-BIOP
tissue O
and O
are O
therefore O
required O
to O
exhibit O
good O
mechanical S-APPL
stability O
and O
biocompatibility S-PRO
. O


Consequently O
, O
the O
high O
elastic B-PRO
modulus E-PRO
( O
similar O
to O
that O
of O
bone S-BIOP
) O
, O
thermoplasticity O
, O
and O
biocompatibility S-PRO
of O
poly O
( O
lactic O
acid O
) O
( O
PLA S-MATE
) O
make O
it O
well O
suited O
for O
the O
fabrication S-MANP
of O
such O
substitutes O
by O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
-based O
3D B-MANP
printing E-MANP
. O


However O
, O
the O
demands O
of O
present-day O
applications O
require O
the O
mechanical S-APPL
and O
biological O
properties S-CONPRI
of O
PLA S-MATE
to O
be S-MATE
further O
improved O
. O


Herein O
, O
we O
fabricated S-CONPRI
PLA/Ti O
composite S-MATE
scaffolds O
by O
FFF-based O
3D B-MANP
printing E-MANP
and O
used O
thermogravimetric B-CHAR
analysis E-CHAR
to O
confirm O
the O
homogenous O
dispersion S-CONPRI
of O
Ti S-MATE
particles S-CONPRI
in O
the O
PLA S-MATE
matrix O
at O
loadings O
of O
5–20 O
vol O
% O
. O


Notably O
, O
the O
thermal B-PRO
stability E-PRO
of O
these O
composites S-MATE
and O
the O
crystallization S-CONPRI
temperature/crystallinity O
degree O
of O
PLA S-MATE
therein O
decreased O
with O
increasing O
Ti S-MATE
content O
, O
while O
the O
corresponding O
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
and O
melting B-PARA
temperature E-PARA
concomitantly O
increased O
. O


The O
compressive O
and O
tensile B-PRO
strengths E-PRO
of O
PLA/Ti O
composites S-MATE
increased O
with O
Ti S-MATE
increasing O
loading O
until O
it O
reached O
10 O
vol O
% O
and O
were O
within O
the O
range S-PARA
of O
real O
bone S-BIOP
values O
, O
while O
the O
impact S-CONPRI
strengths O
of O
the O
above O
composites S-MATE
significantly O
exceeded O
that O
of O
pure O
PLA S-MATE
. O


The O
incorporation O
of O
Ti S-MATE
resulted O
in O
enhanced O
in O
vitro O
biocompatibility S-PRO
, O
promoting O
the O
initial O
attachment O
, O
proliferation O
, O
and O
differentiation O
of O
pre-osteoblast O
cells S-APPL
, O
which O
allowed O
us O
to O
conclude O
that O
the O
prepared O
PLA/Ti O
composite S-MATE
scaffolds O
with O
enhanced O
mechanical S-APPL
and O
biological O
properties S-CONPRI
are O
promising O
candidates O
for O
bone S-BIOP
tissue O
engineering S-APPL
applications O
. O


Effect O
of O
laser S-ENAT
conditions O
on O
selectively O
laser S-ENAT
melted O
maraging B-MATE
steel E-MATE
was O
studied O
. O


Volumetric O
energy B-PARA
density E-PARA
could O
not O
always O
clarify O
the O
change O
in O
relative B-PRO
density E-PRO
. O


Deposited O
energy B-PARA
density E-PARA
could O
clarify O
the O
change O
in O
relative B-PRO
density E-PRO
. O


This O
study O
provides O
an O
important O
insight O
for O
selectively O
laser S-ENAT
melted O
materials S-CONPRI
. O


In O
this O
study O
, O
the O
effects O
of O
laser B-PARA
power E-PARA
and O
scan B-PARA
speed E-PARA
on O
the O
relative B-PRO
density E-PRO
, O
melt B-PARA
pool I-PARA
depth E-PARA
, O
and O
Vickers B-PRO
hardness E-PRO
of O
selectively O
laser S-ENAT
melted O
( O
SLM S-MANP
) O
maraging B-MATE
steel E-MATE
were O
systematically O
investigated O
. O


The O
change O
in O
these O
structural O
parameters S-CONPRI
and O
hardness S-PRO
could O
not O
always O
be S-MATE
clarified O
by O
the O
volumetric O
energy B-PARA
density E-PARA
, O
which O
is O
widely O
used O
in O
the O
SLM S-MANP
processes S-CONPRI
. O


The O
deposited O
energy B-PARA
density E-PARA
, O
wherein O
the O
thermal O
diffusion S-CONPRI
length O
is O
used O
as S-MATE
a O
heat-distributed O
depth O
, O
can O
express O
the O
change O
in O
these O
structural O
parameters S-CONPRI
and O
the O
hardness S-PRO
with O
one O
curve O
. O


To O
clarify O
the O
effect O
of O
the O
laser S-ENAT
parameters O
, O
the O
deposited O
energy O
should O
be S-MATE
used O
instead O
of O
the O
volumetric O
energy B-PARA
density E-PARA
. O


Thus O
, O
this O
study O
provides O
a O
new O
insight O
on O
the O
selection O
of O
the O
laser S-ENAT
condition O
for O
SLM-fabricated O
materials S-CONPRI
. O


This O
work O
presents O
a O
comprehensive O
study O
on O
the O
influence O
of O
three O
different O
processing O
technologies S-CONPRI
( O
Selective B-MANP
Laser I-MANP
Melting E-MANP
, O
Hot B-MANP
Pressing E-MANP
and O
conventional O
casting S-MANP
) O
on O
the O
microstructure S-CONPRI
, O
mechanical S-APPL
and O
wear S-CONPRI
behavior O
of O
an O
austenitic S-MATE
316L B-MATE
Stainless I-MATE
Steel E-MATE
. O


A O
correlation O
between O
the O
processing O
technologies S-CONPRI
, O
the O
obtained O
microstructure S-CONPRI
and O
the O
mechanical S-APPL
and O
wear S-CONPRI
behavior O
was O
achieved O
. O


The O
results O
showed O
that O
the O
highest O
mechanical B-CONPRI
properties E-CONPRI
and O
tribological B-CONPRI
performance E-CONPRI
were O
obtained O
for O
316L O
SS S-MATE
specimens O
produced O
by O
Selective B-MANP
Laser I-MANP
Melting E-MANP
, O
when O
compared O
to O
Hot B-MANP
Pressing E-MANP
and O
conventional O
casting S-MANP
. O


The O
high O
wear S-CONPRI
and O
mechanical S-APPL
performance O
of O
316L B-MATE
Stainless I-MATE
Steel E-MATE
fabricated O
by O
Selective B-MANP
Laser I-MANP
Melting E-MANP
are O
mainly O
due O
to O
the O
finer B-FEAT
microstructure E-FEAT
, O
induced O
by O
the O
process S-CONPRI
. O


In O
this O
sense O
, O
Selective B-MANP
Laser I-MANP
Melting E-MANP
seems O
a O
promising O
method O
to O
fabricate S-MANP
customized O
316L O
SS S-MATE
implants S-APPL
with O
improved O
mechanical S-APPL
and O
wear B-CONPRI
performance E-CONPRI
. O


This O
original O
work O
proposes O
to O
investigate O
the O
transposition O
of O
crystallography S-MANP
rules O
to O
cubic O
lattice S-CONPRI
architectured O
materials S-CONPRI
to O
generate O
new O
3D S-CONPRI
porous O
structures O
. O


The O
application O
of O
symmetry O
operations O
provides O
a O
complete O
and O
convenient O
way O
to O
configure O
the O
lattice S-CONPRI
architecture S-APPL
with O
only O
two O
parameters S-CONPRI
. O


New O
lattice B-FEAT
structures E-FEAT
were O
created O
by O
slipping O
from O
the O
conventional O
Bravais O
lattice S-CONPRI
toward O
non-compact O
complex B-CONPRI
structures E-CONPRI
. O


The O
resulting O
stiffness S-PRO
of O
the O
porous B-MATE
materials E-MATE
was O
thoroughly O
evaluated O
for O
all O
the O
combinations O
of O
architecture S-APPL
parameters O
. O


This O
exhaustive O
study O
revealed O
attractive O
structures O
having O
high O
specific B-PRO
stiffness E-PRO
, O
up O
to O
twice O
as S-MATE
large O
as S-MATE
the O
usual O
octet-truss O
for O
a O
given O
relative B-PRO
density E-PRO
. O


It O
results O
in O
a O
relationship O
between O
effective O
Young B-PRO
modulus E-PRO
and O
relative B-PRO
density E-PRO
for O
any O
lattice B-FEAT
structure E-FEAT
. O


The O
collection O
of O
the O
elastic S-PRO
properties O
for O
all O
the O
cubic B-FEAT
structures E-FEAT
into O
3D S-CONPRI
maps O
provides O
a O
convenient O
tool S-MACEQ
for O
lattice S-CONPRI
materials O
design S-FEAT
, O
for O
research S-CONPRI
, O
and O
for O
mechanical B-APPL
engineering E-APPL
. O


The O
resulting O
mechanical B-CONPRI
properties E-CONPRI
are O
highly O
variable O
according O
to O
architecture S-APPL
, O
and O
can O
be S-MATE
easily O
tailored O
for O
specific O
applications O
using O
the O
simple S-MANP
yet O
powerful O
formalism O
developed O
in O
this O
work O
. O


A O
volumetric O
, O
mini O
extruder S-MACEQ
for O
pellets S-CONPRI
or O
granules S-CONPRI
of O
recycled S-CONPRI
plastic S-MATE
that O
can O
be S-MATE
used O
in O
a O
RepRap B-MACEQ
FDM I-MACEQ
3D I-MACEQ
printer E-MACEQ
for O
rapid B-ENAT
prototyping E-ENAT
is O
discussed O
. O


The O
steer O
Auger S-MACEQ
portion O
is O
added O
to O
increase O
the O
pressure S-CONPRI
inside O
a O
helix O
stator O
container O
of O
n-lobes O
as S-MATE
a O
helical O
rotor O
is O
turned O
. O


A O
novel O
, O
alternative O
multi-layer O
Moineau-based O
pump O
−easier O
to O
build S-PARA
, O
implement O
and O
clean– O
is O
also O
introduced O
to O
extrude S-MANP
a O
quantity O
of O
viscous O
material S-MATE
in O
vertical S-CONPRI
direction O
. O


In O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
PBF-LB O
) O
, O
material S-MATE
is O
continuously O
ejected O
from O
the O
melt B-MATE
pool E-MATE
, O
commonly O
called O
spatter S-CHAR
, O
and O
is O
distributed O
throughout O
the O
build B-PARA
chamber E-PARA
. O


There O
is O
a O
lack O
of O
understanding O
of O
the O
nature O
of O
this O
spatter S-CHAR
and O
the O
effect O
it O
may O
have O
on O
the O
integrity S-CONPRI
of O
the O
final O
part O
and O
the O
quality S-CONPRI
of O
any O
recycled S-CONPRI
powder S-MATE
. O


This O
work O
reports O
a O
detailed O
investigation O
of O
spatter S-CHAR
metallurgy S-CONPRI
for O
Inconel B-MATE
718 E-MATE
. O


It O
is O
seen O
that O
the O
spatter S-CHAR
created O
during O
processing O
produces O
powder S-MATE
that O
is O
significantly O
different O
to O
the O
virgin O
material S-MATE
, O
with O
particles S-CONPRI
up O
to O
6 O
times O
larger O
. O


Oxidation S-MANP
, O
predominantly O
in O
the O
form O
of O
spots O
or O
films O
of O
Al2O3 S-MATE
and O
TiO2 S-MATE
was O
observed O
on O
the O
surface S-CONPRI
of O
some O
of O
the O
spatter S-CHAR
particles S-CONPRI
. O


It O
is O
established O
that O
this O
oxide S-MATE
formation O
occurs O
at O
the O
melt B-MATE
pool E-MATE
surface O
before O
ejection S-CONPRI
of O
the O
spatter S-CHAR
from O
the O
melt B-MATE
pool E-MATE
, O
and O
also O
that O
this O
issue O
is O
generic O
to O
PBF-LB O
process S-CONPRI
and O
certain O
alloys S-MATE
. O


The O
characteristics O
of O
different O
types O
of O
spatter S-CHAR
are O
identified O
and O
are O
linked O
to O
spatter S-CHAR
generation O
mechanisms O
. O


The O
vaporisation O
of O
material S-MATE
during O
processing O
produces O
clusters O
of O
nano S-FEAT
particles O
whose O
composition S-CONPRI
indicate O
a O
preferential O
vaporisation O
of O
Cr S-MATE
from O
the O
bulk O
. O


The O
results O
of O
this O
study O
highlight O
that O
oxidation S-MANP
and O
issues O
presented O
by O
spatter S-CHAR
particles S-CONPRI
dissimilar O
from O
the O
virgin O
material S-MATE
are O
unavoidable O
and O
greater O
consideration O
is O
needed O
for O
the O
generation O
and O
effect O
of O
spatter S-CHAR
on O
part O
and O
powder S-MATE
quality O
. O


The O
paper O
describes O
a O
new O
approach O
in O
controlling O
and O
tailoring O
residual B-PRO
stress E-PRO
profile S-FEAT
of O
parts O
made O
by O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
. O


SLM S-MANP
parts O
are O
well O
known O
for O
the O
high O
tensile B-PRO
stresses E-PRO
in O
the O
as S-MATE
– O
built O
state O
in O
the O
surface S-CONPRI
or O
subsurface O
region O
. O


These O
stresses O
have O
a O
detrimental O
effect O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
and O
especially O
on O
the O
fatigue B-PRO
life E-PRO
. O


Laser S-ENAT
Shock O
Peening S-MANP
( O
LSP O
) O
as S-MATE
a O
surface B-MANP
treatment E-MANP
method O
was O
applied O
on O
SLM S-MANP
parts O
and O
residual B-PRO
stress E-PRO
measurements O
with O
the O
hole O
– O
drilling S-MANP
method O
were O
performed O
. O


Two O
different O
grades O
of O
stainless B-MATE
steel E-MATE
were O
used O
: O
a O
martensitic O
15-5 O
precipitation S-CONPRI
hardenable O
PH1 O
and O
an O
austenitic S-MATE
316L O
. O


Different O
LSP O
parameters S-CONPRI
were O
used O
, O
varying O
laser B-CONPRI
energy E-CONPRI
, O
shot O
overlap S-CONPRI
, O
laser B-PARA
spot I-PARA
size E-PARA
and O
treatments O
with O
and O
without O
an O
ablative O
medium O
. O


For O
both O
materials S-CONPRI
the O
as-built O
( O
AB S-MATE
) O
residual B-PRO
stress E-PRO
state O
was O
changed O
to O
a O
more O
beneficial O
compressive O
state O
. O


The O
value O
and O
the O
depth O
of O
the O
compressive B-PRO
stress E-PRO
was O
analyzed O
and O
showed O
a O
clear O
dependence O
on O
the O
LSP O
processing O
parameters S-CONPRI
. O


The O
use O
of O
LSP O
during O
the O
building O
phase S-CONPRI
of O
SLM S-MANP
as S-MATE
a O
“ O
3D S-CONPRI
LSP O
” O
method O
would O
possibly O
give O
the O
advantage O
of O
further O
increasing O
the O
depth O
and O
volume S-CONPRI
of O
compressive O
residual B-PRO
stresses E-PRO
, O
and O
selectively O
treating O
key O
areas S-PARA
of O
the O
part O
, O
thereby O
further O
increasing O
fatigue B-PRO
life E-PRO
. O


Template-free O
3D B-MANP
printing E-MANP
of O
electronic O
devices O
has O
the O
potential O
to O
broaden O
electronics S-CONPRI
integration O
to O
include O
complex O
integrated O
form O
factors O
, O
but O
success O
requires O
precise O
, O
adaptive B-CONPRI
control E-CONPRI
over O
materials B-CHAR
processing E-CHAR
. O


The O
development O
of O
such O
manufacturing B-MANP
technologies E-MANP
requires O
exploration O
of O
new O
combinations O
of O
ink S-MATE
sets O
, O
printing O
techniques O
, O
and O
automation S-CONPRI
strategies O
. O


A O
closed-loop O
feedback S-PARA
system O
that O
links O
deposition S-CONPRI
parameters O
with O
characterization O
was O
necessary O
to O
maintain O
μm-precision O
deposition S-CONPRI
for O
over O
20 O
h O
without O
human O
involvement O
. O


This O
closed-loop B-MACEQ
control E-MACEQ
scheme O
enabled O
3D B-MANP
printing E-MANP
of O
both O
single- O
and O
double-layer O
high-voltage O
capacitors S-APPL
with O
capacitances O
as S-MATE
large O
as S-MATE
314 O
pF O
( O
at O
1 O
kHz O
) O
and O
breakdown O
voltages O
over O
1000 O
V S-MATE
, O
which O
is O
significant O
step S-CONPRI
towards O
repeatable O
template-free O
, O
3D B-MANP
printing E-MANP
of O
electronics S-CONPRI
for O
rapid B-ENAT
prototyping E-ENAT
of O
multifunctional O
devices O
. O


The O
precise B-CONPRI
control E-CONPRI
over O
low O
minimum O
feature B-FEAT
dimension E-FEAT
, O
high O
breakdown O
voltage O
, O
and O
long O
print S-MANP
duration O
enables O
the O
exploration O
of O
a O
broader O
range S-PARA
of O
printed B-CONPRI
electronics E-CONPRI
application O
than O
conventional O
3D B-MANP
printing E-MANP
techniques O
. O


Three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
printing O
can O
be S-MATE
a O
promising O
tool S-MACEQ
in O
tissue B-CONPRI
engineering E-CONPRI
applications O
for O
generating O
tissue-specific O
3D S-CONPRI
architecture O
. O


The O
3D B-MANP
printing E-MANP
process O
, O
including O
computer-aided B-ENAT
design E-ENAT
( O
CAD S-ENAT
) O
, O
can O
be S-MATE
combined O
with O
the O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
( O
FEM S-CONPRI
) O
to O
design S-FEAT
and O
fabricate S-MANP
3D S-CONPRI
tissue O
architecture S-APPL
with O
designated O
mechanical B-CONPRI
properties E-CONPRI
. O


In O
this O
study O
, O
we O
generated O
four O
types O
of O
3D S-CONPRI
CAD O
models O
to O
print S-MANP
tissue-engineered O
scaffolds S-FEAT
with O
different O
inner O
geometries S-CONPRI
( O
lattice S-CONPRI
, O
wavy O
, O
hexagonal S-FEAT
, O
and O
shifted O
microstructures S-MATE
) O
and O
analyzed O
them O
by O
FEM S-CONPRI
to O
predict O
their O
mechanical S-APPL
behaviors O
. O


For O
the O
validity O
of O
computational O
simulations S-ENAT
by O
FEM S-CONPRI
, O
we O
measured O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
3D B-MANP
printed E-MANP
scaffolds O
. O


Results O
showed O
that O
the O
theoretical S-CONPRI
compressive O
elastic B-PRO
moduli E-PRO
of O
the O
designed S-FEAT
constructs O
were O
23.3 O
, O
56.5 O
, O
67.5 O
, O
and O
1.8 O
MPa S-CONPRI
, O
and O
the O
experimental S-CONPRI
compressive O
elastic B-PRO
moduli E-PRO
were O
23.6 O
± O
0.6 O
, O
45.1 O
± O
1.4 O
, O
56.7 O
± O
1.7 O
, O
and O
1.6 O
± O
0.2 O
MPa S-CONPRI
for O
lattice S-CONPRI
, O
wavy O
, O
hexagonal S-FEAT
, O
and O
shifted O
microstructures S-MATE
, O
respectively O
, O
while O
maintaining O
the O
same O
construct O
dimension S-FEAT
and O
porosity S-PRO
. O


In O
addition O
, O
van O
der O
Waals O
hyperelastic O
material S-MATE
model O
was O
successfully O
utilized O
to O
predict O
the O
nonlinear O
mechanical S-APPL
behavior O
of O
the O
printed O
scaffolds S-FEAT
with O
different O
inner O
geometries S-CONPRI
. O


These O
findings O
indicated O
that O
the O
CAD-based O
FEM S-CONPRI
prediction O
could O
be S-MATE
used O
for O
designing O
tissue-specific O
constructs O
to O
mimic S-MACEQ
the O
mechanical B-CONPRI
properties E-CONPRI
of O
targeted O
tissues O
or O
organs O
. O


The O
optical S-CHAR
penetration O
depth O
of O
the O
laser B-CONPRI
beam E-CONPRI
into O
the O
powder B-MACEQ
bed E-MACEQ
is O
taken O
into O
account O
in O
this O
model S-CONPRI
. O


The O
convective O
heat B-CONPRI
flux E-CONPRI
dominate O
the O
heat S-CONPRI
tranfer O
in O
the O
molten B-CONPRI
pool E-CONPRI
, O
and O
further O
decides O
the O
shape O
of O
molten B-CONPRI
pool E-CONPRI
. O


Heat B-PRO
accumulation E-PRO
can O
significantly O
change O
the O
size O
of O
the O
molten B-CONPRI
pool E-CONPRI
, O
but O
has O
little O
effect O
on O
the O
molten B-CONPRI
pool E-CONPRI
shape O
. O


A O
physical B-CONPRI
model E-CONPRI
coupled O
with O
heat B-CONPRI
transfer E-CONPRI
and O
fluid B-PRO
flow E-PRO
was O
developed O
to O
investigate O
the O
thermofluid O
field O
of O
molten B-CONPRI
pool E-CONPRI
and O
its O
effects O
on O
SLM S-MANP
process S-CONPRI
of O
Inconel B-MATE
718 I-MATE
alloy E-MATE
, O
in O
which O
a O
heat B-CONPRI
source E-CONPRI
considering O
the O
porous S-PRO
properties O
of O
powder B-MACEQ
bed E-MACEQ
and O
its O
reflection S-CHAR
to O
laser B-CONPRI
beam E-CONPRI
is O
used O
. O


The O
simulation S-ENAT
results O
showed O
that O
surface B-PRO
tension E-PRO
caused O
by O
temperature B-PARA
gradient E-PARA
on O
the O
surface S-CONPRI
of O
molten B-CONPRI
pool E-CONPRI
drives O
to O
Marangoni O
convection O
, O
which O
makes O
fluid B-PRO
flow E-PRO
state O
mainly O
an O
outward O
convection O
during O
SLM S-MANP
process S-CONPRI
. O


Marangoni O
convection O
includes O
convective O
and O
conductive O
heat B-CONPRI
flux E-CONPRI
, O
both O
of O
them O
have O
effects O
of O
on O
molten B-CONPRI
pool E-CONPRI
shape O
, O
but O
the O
effect O
of O
convective O
heat B-CONPRI
flux E-CONPRI
is O
dominant O
because O
its O
magnitude S-PARA
is O
one O
order O
larger O
than O
that O
of O
conductive O
heat B-CONPRI
flux E-CONPRI
. O


The O
convective O
heat B-CONPRI
flux E-CONPRI
accelerates O
the O
flow B-PARA
rate E-PARA
of O
the O
molten B-MATE
metal E-MATE
, O
benefits O
to O
heat B-CONPRI
dissipation E-CONPRI
. O


The O
convective O
heat B-CONPRI
flux E-CONPRI
makes O
the O
molten B-CONPRI
pool E-CONPRI
wider O
, O
while O
the O
conductive O
heat B-CONPRI
flux E-CONPRI
makes O
comparably O
the O
molten B-CONPRI
pool E-CONPRI
deeper O
and O
wider O
. O


Furthermore O
, O
heat B-PRO
accumulation E-PRO
caused O
by O
multiple O
scanning S-CONPRI
increases O
convection O
and O
conduction O
heat B-CONPRI
flux E-CONPRI
resulting O
in O
the O
increase O
of O
the O
width O
and O
depth O
of O
the O
molten B-CONPRI
pool E-CONPRI
, O
but O
no O
change O
of O
dominant O
role O
of O
convective O
heat B-CONPRI
flux E-CONPRI
to O
the O
shape O
of O
the O
molten B-CONPRI
pool E-CONPRI
. O


A O
staircase O
Inconel B-MATE
718 E-MATE
block O
was O
fabricated S-CONPRI
to O
investigate O
the O
effects O
of O
the O
thermal B-PARA
cycles E-PARA
on O
the O
microstructure B-CONPRI
evolution E-CONPRI
in O
the O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
part O
using O
optical S-CHAR
scope O
( O
OM S-CHAR
) O
, O
scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
( O
SEM S-CHAR
) O
, O
and O
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
( O
EBSD S-CHAR
) O
. O


The O
laser B-CONPRI
beam E-CONPRI
scanning O
strategy O
was O
clearly O
shown O
in O
the O
part O
under O
OM S-CHAR
, O
including O
laser S-ENAT
scanning O
pattern S-CONPRI
and O
hatch B-PARA
spacing E-PARA
. O


The O
Y-plane O
( O
side O
surface S-CONPRI
) O
was O
characterized O
by O
elongated O
colonies O
of O
cellular O
dendrites S-BIOP
with O
an O
average S-CONPRI
cell O
spacing O
of O
0.511 O
∼ O
0.845 O
μm O
. O


In O
addition O
, O
Laves B-CONPRI
phase E-CONPRI
was O
observed O
in O
the O
inter-layers O
and O
inter-cellular O
regions O
. O


Under O
the O
continuing O
effects O
of O
the O
thermal B-PARA
cycles E-PARA
, O
the O
fraction S-CONPRI
of O
the O
Laves-phase O
showed O
a O
significant O
drop O
with O
their O
morphology S-CONPRI
changing O
from O
coarse O
and O
interconnected O
particles S-CONPRI
to O
discrete O
Laves B-CONPRI
phase E-CONPRI
. O


This O
is O
attributed O
to O
the O
reheating O
process S-CONPRI
as S-MATE
Laves O
phase S-CONPRI
can O
be S-MATE
dissolved O
at O
a O
proper O
heat B-MANP
treatment E-MANP
. O


In O
terms O
of O
the O
width O
of O
the O
cellular O
dendrites S-BIOP
, O
the O
longer O
the O
thermal B-PARA
cycle E-PARA
period O
is O
, O
the O
coarser O
the O
elongated O
grains S-CONPRI
are O
. O


With O
the O
repeating O
thermal B-PARA
cycle E-PARA
period O
elongating O
, O
the O
maximum O
intensity O
of O
the O
texture S-FEAT
, O
together O
with O
the O
fraction S-CONPRI
of O
larger O
grains S-CONPRI
and O
the O
high O
misorientation O
angles O
, O
increased O
. O


Moreover O
, O
the O
area S-PARA
fraction O
of O
the O
porosity S-PRO
was O
below O
0.2 O
% O
, O
with O
no O
remarkable O
effects O
found O
from O
the O
thermal B-PARA
cycles E-PARA
and O
the O
build B-PARA
height E-PARA
. O


Simulations S-ENAT
capable O
of O
predicting O
the O
complex O
thermal O
behavior O
which O
occurs O
in O
a O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
process S-CONPRI
would O
help O
design S-FEAT
and O
manufacturing S-MANP
engineers O
build S-PARA
more O
optimum O
designs S-FEAT
in O
a O
reliable O
manner O
. O


A O
multiscale O
feed S-PARA
forward O
adaptive O
refinement O
and O
de-refinement O
( O
FFD-AMRD O
) O
finite B-CONPRI
element E-CONPRI
framework O
has O
been O
developed O
in O
response O
to O
this O
need O
. O


Support B-FEAT
structures E-FEAT
fabricated S-CONPRI
during O
SLM S-MANP
to O
overcome O
residual B-PRO
stress E-PRO
induced O
part O
distortion S-CONPRI
are O
a O
key O
part O
of O
the O
process S-CONPRI
, O
and O
a O
representation O
of O
these O
support B-FEAT
structures E-FEAT
in O
a O
finite B-CONPRI
element E-CONPRI
framework O
must O
be S-MATE
considered O
. O


If O
support B-FEAT
structures E-FEAT
could O
be S-MATE
designed O
with O
minimal O
material S-MATE
usage O
while O
still O
maintaining O
an O
ability O
to O
withstand O
the O
residual B-PRO
stresses E-PRO
generated O
during O
the O
part O
fabrication S-MANP
, O
this O
would O
significantly O
impact S-CONPRI
industrial O
use O
of O
SLM S-MANP
. O


In O
this O
work O
, O
the O
effective O
thermal B-CONPRI
properties E-CONPRI
of O
support B-FEAT
structures E-FEAT
are O
represented O
using O
thermal O
homogenization S-MANP
. O


The O
effective O
thermal B-CONPRI
properties E-CONPRI
of O
the O
support B-FEAT
structures E-FEAT
have O
been O
found O
to O
be S-MATE
a O
function O
of O
their O
geometry S-CONPRI
, O
anisotropy S-PRO
and O
constituent O
independent O
thermal B-CONPRI
properties E-CONPRI
. O


The O
objective O
of O
this O
work O
is O
to O
derive O
effective O
thermal B-CONPRI
property E-CONPRI
functions O
which O
could O
be S-MATE
directly O
incorporated O
in O
the O
FFD-AMRD O
framework S-CONPRI
mentioned O
above O
to O
enhance O
computational B-PARA
speed E-PARA
. O


Polymer B-MANP
Laser I-MANP
Sintering E-MANP
( O
LS O
) O
is O
a O
well-known O
Additive B-MANP
Manufacturing I-MANP
process E-MANP
, O
capable O
of O
producing O
highly O
complex B-CONPRI
geometries E-CONPRI
with O
little O
or O
no O
cost O
penalty O
. O


However O
, O
the O
restricted O
range S-PARA
of O
materials S-CONPRI
currently O
available O
for O
this O
process S-CONPRI
has O
limited O
its O
applications O
. O


Whilst O
it O
is O
common O
to O
modify O
the O
properties S-CONPRI
of O
standard S-CONPRI
LS O
polymers S-MATE
with O
the O
inclusion S-MATE
of O
fillers O
e.g O
. O


nanoclays O
, O
achieving O
effective O
dispersions O
can O
be S-MATE
difficult O
. O


The O
work O
presented O
here O
investigates S-CONPRI
the O
use O
of O
plasma S-CONPRI
treatment O
as S-MATE
a O
method O
of O
enhancing O
dispersion S-CONPRI
with O
an O
expectation O
of O
improving O
consistency S-CONPRI
and O
surface B-PARA
quality E-PARA
of O
laser S-ENAT
sintered O
nanocomposite O
parts O
. O


To O
enable O
the O
preparation O
of O
polyamide B-MATE
12 E-MATE
nanocomposite O
powder S-MATE
for O
applications O
in O
LS O
, O
plasma S-CONPRI
surface O
modification O
using O
Low O
Pressure S-CONPRI
Air O
Plasma S-CONPRI
Treatment O
was O
carried O
out O
on O
two O
nanoclays O
: O
Cloisite O
30B O
( O
C30B O
) O
and O
Nanomer O
I.34TCN O
( O
I.34TCN O
) O
. O


Plasma S-CONPRI
treatment O
strongly O
reduced O
the O
aggregation O
of O
the O
nanoclay O
( O
C30B O
and O
I.34TCN O
) O
particles S-CONPRI
, O
and O
powders S-MATE
displayed O
higher O
decomposition S-PRO
temperatures O
than O
those O
without O
plasma S-CONPRI
treatment O
. O


LS O
parts O
from O
neat O
polyamide B-MATE
12 E-MATE
, O
untreated O
I.34TCN O
and O
plasma S-CONPRI
treated O
I.34TCN O
composites S-MATE
were O
successfully O
produced O
with O
different O
complex B-PRO
shapes E-PRO
. O


The O
presence O
of O
well O
dispersed O
plasma S-CONPRI
treated O
nanoclays O
was O
observed O
and O
found O
to O
be S-MATE
essential O
for O
an O
improved O
surface B-PARA
quality E-PARA
of O
LS O
fabricated S-CONPRI
which O
was O
achieved O
only O
for O
plasma S-CONPRI
treated O
I.34TCN O
. O


Likewise O
, O
some O
mechanical B-CONPRI
properties E-CONPRI
could O
be S-MATE
improved O
above O
that O
of O
PA12 S-MATE
by O
incorporation O
of O
treated O
I.34TCN O
. O


For O
example O
, O
the O
elastic B-PRO
modulus E-PRO
of O
plasma S-CONPRI
treated O
composites S-MATE
was O
higher O
than O
that O
of O
polyamide B-MATE
12 E-MATE
and O
the O
untreated O
composite S-MATE
. O


In O
the O
case O
of O
the O
ultimate O
strain S-PRO
, O
the O
plasma S-CONPRI
treated O
composite S-MATE
performed O
better O
than O
untreated O
and O
results O
had O
a O
reduced O
variation S-CONPRI
between O
samples S-CONPRI
. O


This O
illustrates O
the O
feasibility S-CONPRI
of O
the O
use O
of O
plasma S-CONPRI
treatments O
on O
nanoclays O
to O
improve O
the O
properties S-CONPRI
of O
LS O
parts O
, O
even O
though O
further O
studies O
will O
be S-MATE
required O
to O
exploit O
the O
full O
potential O
. O


Accuracy S-CHAR
in O
dental B-MACEQ
prosthesis E-MACEQ
plays O
a O
significant O
role O
. O


Surgical O
guides O
are O
widely O
used O
for O
accurate S-CHAR
positioning O
of O
dental S-APPL
implants O
. O


Designing O
of O
guides O
using O
modern O
software S-CONPRI
is O
useful O
in O
achieving O
precision S-CHAR
; O
however O
, O
translation O
of O
these O
images S-CONPRI
into O
actual O
fabricated S-CONPRI
parts O
can O
be S-MATE
achieved O
using O
Three-dimensional S-CONPRI
( O
3-D S-CONPRI
) O
printing O
. O


Conventionally O
, O
guides O
were O
fabricated S-CONPRI
using O
vacuum O
forming S-MANP
technique O
which O
leads O
to O
several O
dimensional O
inaccuracies O
. O


Computed B-CHAR
Tomography E-CHAR
( O
CT S-ENAT
) O
images S-CONPRI
of O
patients O
with O
missing O
teeth O
are O
modeled O
to O
design S-FEAT
surgical O
guide O
using O
Computer B-ENAT
Aided I-ENAT
Design E-ENAT
( O
CAD S-ENAT
) O
/ O
Computer B-ENAT
Aided I-ENAT
Manufacturing E-ENAT
( O
CAM S-ENAT
) O
software S-CONPRI
which O
is O
then O
combined O
with O
surface S-CONPRI
scan O
files S-MANS
in O
Standard B-MANS
Tessellation I-MANS
Language E-MANS
( O
STL S-MANS
) O
formats O
to O
design S-FEAT
the O
guide O
. O


In O
this O
work O
, O
surgical O
guides O
have O
been O
3-D S-CONPRI
printed O
using O
different O
technologies S-CONPRI
like O
Material B-MANP
Jetting E-MANP
technology O
( O
MJT O
) O
, O
Vat B-MANP
photopolymerization E-MANP
( O
VP O
) O
and O
Material B-MANP
extrusion E-MANP
( O
ME O
) O
. O


Depth O
, O
diameter S-CONPRI
, O
Area S-PARA
and O
Volume S-CONPRI
of O
the O
printed O
guides O
have O
been O
calculated O
using O
vernier B-MACEQ
caliper E-MACEQ
and O
scan O
measurements O
. O


These O
dimensions S-FEAT
have O
then O
been O
compared O
with O
the O
dimensions S-FEAT
obtained O
from O
software S-CONPRI
modeled O
images S-CONPRI
. O


Least O
error S-CONPRI
has O
been O
found O
for O
the O
guides O
fabricated S-CONPRI
using O
MJT O
. O


The O
experimental S-CONPRI
work O
in O
this O
paper O
, O
hence O
, O
suggests O
MJT O
be S-MATE
the O
most O
preferred O
printing O
technique O
due O
to O
its O
superior O
accuracy S-CHAR
for O
printing O
dental B-MACEQ
prosthesis E-MACEQ
like O
aligners O
, O
implants S-APPL
, O
and O
crowns O
, O
etc O
. O


Four O
distinct O
TPU O
grades O
are O
analyzed O
for O
the O
use O
in O
laser B-MANP
sintering E-MANP
. O


Clear O
links O
between O
material B-CONPRI
properties E-CONPRI
and O
sintering S-MANP
behavior O
are O
established O
. O


Guidelines O
for O
future O
selection O
of O
TPU O
grades O
for O
laser B-MANP
sintering E-MANP
are O
deduced O
. O


As S-MATE
laser O
sintering S-MANP
is O
increasingly O
being O
used O
for O
the O
production S-MANP
of O
actual O
end-use O
parts O
, O
there O
is O
considerable O
interest O
in O
developing O
materials S-CONPRI
that O
would O
enable O
new O
applications O
for O
this O
technique O
. O


Considering O
their O
properties S-CONPRI
and O
current O
applications O
, O
elastomeric O
polymers S-MATE
such O
as S-MATE
thermoplastic O
polyurethanes S-MATE
( O
TPU O
) O
have O
a O
very O
high O
potential O
in O
this O
regard O
. O


This O
study O
investigates S-CONPRI
the O
material B-CONPRI
properties E-CONPRI
that O
are O
involved O
in O
TPU O
sintering S-MANP
through O
the O
analysis O
of O
four O
distinct O
TPU O
grades O
. O


Examined O
parameters S-CONPRI
include O
powder S-MATE
flow O
, O
rheology S-PRO
of O
the O
melt S-CONPRI
and O
shrinkage S-CONPRI
and O
hardening S-MANP
behavior O
. O


It O
is O
found O
that O
, O
even O
though O
the O
particle S-CONPRI
morphology S-CONPRI
is O
not O
optimum O
, O
smooth O
and O
dense O
powder S-MATE
layers O
can O
be S-MATE
deposited O
for O
the O
investigated O
powders S-MATE
. O


Low O
melt S-CONPRI
viscosity O
and O
low O
shrinkage S-CONPRI
upon O
hardening S-MANP
further O
enable O
these O
materials S-CONPRI
to O
be S-MATE
easily O
processed S-CONPRI
into O
functional O
parts O
. O


Remaining O
issues O
, O
however O
, O
are O
part O
porosity S-PRO
and O
material S-MATE
degradation S-CONPRI
. O


The O
findings O
in O
this O
study O
provide O
clear O
links O
between O
material B-CONPRI
properties E-CONPRI
and O
behavior O
during O
laser B-MANP
sintering E-MANP
, O
and O
result O
in O
guidelines O
for O
future O
selection O
of O
TPU O
grades O
. O


Support B-FEAT
structures E-FEAT
are O
critical O
to O
the O
successful O
printing O
of O
the O
overhang S-PARA
structures O
in O
selective B-MANP
laser I-MANP
melting E-MANP
. O


The O
heat B-CONPRI
transfer E-CONPRI
performance O
of O
support B-FEAT
structures E-FEAT
has O
significant O
influence O
on O
the O
temperature S-PARA
distribution S-CONPRI
and O
cooling B-PARA
rate E-PARA
within O
the O
overhang S-PARA
structures O
which O
in O
turn O
determine O
the O
microstructure S-CONPRI
and O
residual B-PRO
stress E-PRO
. O


In O
the O
present O
study O
, O
functionally B-CONPRI
graded E-CONPRI
support O
structures O
have O
been O
proposed O
and O
their O
thermal O
performance S-CONPRI
has O
been O
numerically O
investigated O
, O
with O
the O
consideration O
of O
different O
materials S-CONPRI
, O
cooling S-MANP
times O
and O
gradedness O
values O
. O


It O
has O
been O
found O
that O
functionally B-CONPRI
graded E-CONPRI
support O
structures O
can O
maintain O
a O
higher O
temperature S-PARA
level O
than O
the O
conventional O
uniform O
support B-FEAT
structure E-FEAT
at O
the O
bottom O
of O
overhang S-PARA
, O
which O
is O
equivalent O
to O
an O
extra O
pre-heating O
effect O
. O


The O
temperature S-PARA
fluctuation O
and O
cooling B-PARA
rate E-PARA
at O
the O
bottom O
of O
overhang S-PARA
can O
also O
be S-MATE
reduced O
by O
adopting O
the O
functionally B-CONPRI
graded E-CONPRI
support O
structures O
. O


Topology-optimized O
structure S-CONPRI
has O
ultrahigh O
normalized O
fatigue B-PRO
life E-PRO
of O
0.65 O
at O
106 O
cycles O
and O
low O
density S-PRO
. O


Topology-optimized O
structure S-CONPRI
increases O
fatigue B-PRO
life E-PRO
by O
reducing O
stress B-CHAR
concentration E-CHAR
. O


Twinning S-CONPRI
formed O
in O
porous S-PRO
CP-Ti O
samples S-CONPRI
enhances O
plasticity S-PRO
and O
fatigue S-PRO
properties O
. O


The O
fatigue S-PRO
properties O
are O
critical O
considerations O
for O
porous S-PRO
structures O
, O
and O
most O
of O
the O
existing O
porous B-MATE
materials E-MATE
have O
unsatisfactory O
performances O
due O
to O
a O
lack O
of O
structural B-CONPRI
optimization E-CONPRI
. O


This O
work O
shows O
that O
a O
topology-optimized O
structure B-CONPRI
fabricated E-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
using O
commercial-purity O
titanium S-MATE
( O
CP-Ti O
) O
exhibits O
excellent O
fatigue S-PRO
properties O
with O
an O
ultra-high O
normalized O
fatigue B-PRO
life E-PRO
of O
∼0.65 O
at O
106 O
cycles O
and O
at O
a O
low O
density S-PRO
of O
1.3 O
g/cm3 O
. O


The O
main O
factors O
affecting O
fatigue S-PRO
, O
i.e. O
, O
material B-CONPRI
properties E-CONPRI
and O
a O
porous S-PRO
structure O
were O
studied O
. O


Both O
the O
factors O
can O
affect O
the O
fatigue S-PRO
crack O
initiation O
time O
, O
thereby O
affecting O
the O
fatigue B-PRO
life E-PRO
. O


Because O
of O
twinning S-CONPRI
that O
occurred O
during O
the O
fatigue S-PRO
process O
, O
the O
porous S-PRO
CP-Ti O
samples S-CONPRI
exhibit O
a O
high O
plasticity S-PRO
. O


In O
addition O
, O
the O
fatigue S-PRO
crack B-CONPRI
propagation I-CONPRI
rate E-CONPRI
is O
significantly O
reduced O
because O
of O
the O
high O
plasticity S-PRO
of O
the O
CP-Ti O
material S-MATE
and O
the O
occurrence O
of O
fatigue S-PRO
crack O
deflection O
. O


Microstructure B-CONPRI
evolution E-CONPRI
in O
the O
molten B-CONPRI
pool E-CONPRI
of O
SLM-processed O
parts O
was O
disclosed O
. O


Variation S-CONPRI
of O
microhardness S-CONPRI
with O
local O
zone O
within O
the O
molten B-CONPRI
pool E-CONPRI
were O
measured O
. O


Thermal O
behavior O
within O
the O
molten B-CONPRI
pool E-CONPRI
was O
quantitatively S-CONPRI
analyzed O
. O


Relationship O
among O
microstructure S-CONPRI
, O
properties S-CONPRI
and O
thermal O
behavior O
was O
discussed O
. O


This O
work O
presented O
a O
comprehensive O
study O
of O
microstructural B-CONPRI
evolution E-CONPRI
, O
microhardness S-CONPRI
and O
quantitative S-CONPRI
thermodynamic O
analysis O
within O
the O
molten B-CONPRI
pool E-CONPRI
during O
Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
of O
Inconel B-MATE
718 E-MATE
parts O
. O


Microstructures S-MATE
and O
corresponding O
microhardness S-CONPRI
of O
different O
zones O
within O
the O
molten B-CONPRI
pool E-CONPRI
experienced O
the O
following O
evolution S-CONPRI
: O
fine O
cellular O
dendrites S-BIOP
or O
equiaxed B-CONPRI
grains E-CONPRI
on O
the O
top O
surface S-CONPRI
( O
387HV O
) O
; O
columnar B-MATE
dendrites E-MATE
with O
single O
direction O
of O
grain B-CONPRI
growth E-CONPRI
at O
the O
bottom O
( O
337HV O
) O
; O
columnar B-MATE
dendrites E-MATE
with O
multiple O
directions O
of O
grain B-CONPRI
growth E-CONPRI
at O
the O
edge O
of O
the O
molten B-CONPRI
pool E-CONPRI
( O
340HV-350HV O
) O
; O
microstructures S-MATE
between O
cellular O
and O
columnar B-PRO
grains E-PRO
around O
the O
center O
of O
the O
molten B-CONPRI
pool E-CONPRI
( O
363HV O
) O
. O


The O
impact S-CONPRI
of O
Gaussian-distributed O
laser B-CONPRI
energy E-CONPRI
and O
relatively O
weak O
thermal B-PRO
conductivity E-PRO
and O
convection O
of O
Inconel B-MATE
718 E-MATE
contributed O
to O
the O
variation S-CONPRI
of O
temperature B-PARA
gradient E-PARA
at O
different O
zones O
within O
the O
molten B-CONPRI
pool E-CONPRI
. O


The O
formation O
of O
different O
kinds O
of O
microstructures S-MATE
in O
the O
molten B-CONPRI
pool E-CONPRI
was O
controlled O
by O
the O
temperature B-PARA
gradient E-PARA
( O
which O
determined O
the O
direction O
of O
grain B-CONPRI
growth E-CONPRI
) O
and O
the O
cooling B-PARA
rate E-PARA
( O
which O
determined O
the O
size O
of O
grain B-CONPRI
growth E-CONPRI
) O
. O


The O
variation S-CONPRI
of O
microhardness S-CONPRI
within O
the O
molten B-CONPRI
pool E-CONPRI
was O
ascribed O
to O
the O
number O
of O
grain B-CONPRI
boundaries E-CONPRI
and O
the O
stress S-PRO
characteristics O
of O
different O
kinds O
of O
microstructures S-MATE
under O
mechanical S-APPL
load O
. O


The O
zones O
with O
fine O
cellular B-CONPRI
grains E-CONPRI
had O
elevated O
mechanical S-APPL
performance O
due O
to O
the O
superior O
capability O
to O
endure O
the O
load O
. O


This O
work O
hopefully O
provides O
scientific O
and O
theoretical S-CONPRI
support S-APPL
for O
SLM-processed O
Inconel B-MATE
718 E-MATE
parts O
with O
favorable O
properties S-CONPRI
. O


With O
a O
view O
to O
developing O
a O
highly O
biocompatible S-PRO
and O
highly O
reliable O
material S-MATE
for O
artificial O
hip S-MANP
joints O
, O
cellular O
lattice B-FEAT
structures E-FEAT
with O
high O
strength S-PRO
and O
low O
Young O
’ O
s S-MATE
modulus O
( O
E O
) O
were O
designed S-FEAT
using O
computational O
shape O
optimization S-CONPRI
. O


These O
structures O
were O
fabricated S-CONPRI
from O
a O
biomedical S-APPL
Co-Cr-Mo O
alloy S-MATE
via O
electron B-MANP
beam I-MANP
melting E-MANP
. O


As S-MATE
a O
starting O
point O
for O
shape O
optimization S-CONPRI
, O
inverse O
body-centered-cubic O
( O
iBCC O
) O
-based O
structures O
with O
different O
porosities S-PRO
and O
aspects O
were O
fabricated S-CONPRI
. O


The O
strength S-PRO
tended O
to O
increase O
with O
increasing O
E. O
Then O
, O
the O
structures O
were O
re-designed O
using O
shape O
optimization S-CONPRI
based O
on O
the O
traction O
method O
, O
targeting O
a O
simultaneous O
increase O
in O
yield B-PRO
strength E-PRO
with O
retention O
of O
the O
low O
E. O
The O
shapes O
were O
optimized O
through O
minimization O
of O
the O
maximum O
local O
von B-PRO
Mises I-PRO
stress E-PRO
and O
control O
of O
E O
to O
3/2 O
or O
2/3 O
of O
the O
original O
value O
, O
while O
maintaining O
constant O
porosity S-PRO
. O


The O
re-designed O
cellular B-FEAT
structures E-FEAT
were O
fabricated S-CONPRI
and O
subjected O
to O
mechanical B-CHAR
testing E-CHAR
. O


The O
E O
values O
of O
the O
porous S-PRO
structures O
were O
comparable O
to O
the O
design S-FEAT
values O
, O
but O
the O
strength S-PRO
of O
the O
cellular O
lattice S-CONPRI
with O
E O
= O
2/3 O
( O
design S-FEAT
value O
) O
was O
lower O
than O
expected O
. O


This O
discrepancy O
was O
attributed O
to O
inhomogeneities O
in O
the O
microstructures S-MATE
and O
their O
impact S-CONPRI
on O
the O
lattice S-CONPRI
mechanical O
properties S-CONPRI
. O


Thus O
, O
shape O
optimization S-CONPRI
considering O
crystal B-PRO
orientation E-PRO
is O
a O
significant O
challenge O
for O
future O
research S-CONPRI
, O
but O
this O
approach O
has O
considerable O
potential O
. O


A O
3D S-CONPRI
finite O
element S-MATE
modelling O
of O
the O
SLM S-MANP
process S-CONPRI
at O
the O
track O
scale O
is O
considered O
. O


Heat B-CONPRI
transfer E-CONPRI
and O
fluid B-PRO
flow E-PRO
are O
simulated O
for O
different O
material S-MATE
and O
process S-CONPRI
conditions O
. O


Scan B-PARA
speed E-PARA
, O
laser S-ENAT
interaction O
and O
Marangoni O
effect O
have O
a O
clear O
impact S-CONPRI
on O
track O
shape O
. O


The O
present O
study O
is O
based O
on O
a O
formerly O
developed O
3D S-CONPRI
finite O
element S-MATE
modelling O
of O
the O
selective B-MANP
laser I-MANP
melting I-MANP
process E-MANP
( O
SLM S-MANP
) O
at O
the O
track O
scale O
. O


This O
numerical O
model S-CONPRI
is O
used O
to O
assess O
the O
impact S-CONPRI
of O
two O
phenomena O
on O
the O
shape O
of O
the O
elementary O
track O
resulting O
from O
SLM S-MANP
processing O
: O
laser S-ENAT
interaction O
on O
one O
hand O
, O
and O
Marangoni O
effect O
on O
the O
other O
hand O
. O


As S-MATE
regards O
laser S-ENAT
interaction O
, O
it O
is O
modelled O
by O
a O
Beer-Lambert O
type O
heat B-CONPRI
source E-CONPRI
, O
in O
which O
lateral O
scattering O
and O
material S-MATE
absorption S-CONPRI
are O
considered O
through O
two O
characteristic O
parameters S-CONPRI
. O


The O
impact S-CONPRI
of O
these O
parameters S-CONPRI
is O
shown O
in O
terms O
of O
width O
and O
depth O
of O
melted S-CONPRI
zone O
. O


The O
Marangoni O
effect O
caused O
by O
tangential O
gradients O
of O
surface B-PRO
tension E-PRO
is O
modelled O
to O
simulate O
the O
fluid S-MATE
dynamics O
in O
the O
melt B-MATE
pool E-MATE
. O


The O
resulting O
convection O
flow O
is O
demonstrated O
with O
surface B-PRO
tension E-PRO
values O
either O
increasing O
or O
decreasing O
with O
temperature S-PARA
. O


The O
influence O
of O
energy O
distribution S-CONPRI
, O
surface B-PRO
tension E-PRO
effects O
, O
as S-MATE
well O
as S-MATE
laser O
scanning B-PARA
speed E-PARA
on O
temperature S-PARA
distribution S-CONPRI
and O
melt B-MATE
pool E-MATE
geometry S-CONPRI
is O
investigated O
. O


The O
stability S-PRO
and O
regularity O
of O
the O
solidified O
track O
are O
a O
direct O
output O
of O
the O
simulations S-ENAT
, O
and O
their O
variations S-CONPRI
with O
material S-MATE
and O
process S-CONPRI
conditions O
are O
discussed O
. O


A O
three-dimensional S-CONPRI
finite B-CONPRI
element I-CONPRI
model E-CONPRI
is O
developed O
to O
allow O
for O
the O
prediction S-CONPRI
of O
temperature S-PARA
, O
residual B-PRO
stress E-PRO
, O
and O
distortion S-CONPRI
in O
multi-layer O
Laser S-ENAT
Powder-Bed O
Fusion S-CONPRI
builds S-CHAR
. O


Undesirable O
residual B-PRO
stress E-PRO
and O
distortion S-CONPRI
caused O
by O
thermal B-PARA
gradients E-PARA
are O
a O
common O
source S-APPL
of O
failure S-CONPRI
in O
AM S-MANP
builds O
. O


A O
non-linear O
thermoelastoplastic O
model S-CONPRI
is O
combined O
with O
an O
element S-MATE
coarsening O
strategy O
in O
order O
to O
simulate O
the O
thermal O
and O
mechanical B-CONPRI
response E-CONPRI
of O
a O
significant O
volume S-CONPRI
of O
deposited O
material S-MATE
( O
38 O
layers O
and O
91 O
mm3 O
) O
. O


It O
is O
found O
that O
newly O
deposited B-CHAR
layers E-CHAR
experience O
the O
greatest O
amount O
of O
tensile B-PRO
stress E-PRO
, O
while O
layers O
beneath O
are O
forced O
into O
compressive B-PRO
stress E-PRO
. O


The O
residual B-PRO
stress E-PRO
evolution S-CONPRI
drives O
the O
mechanical B-CONPRI
response E-CONPRI
of O
the O
workpiece S-CONPRI
. O


The O
model S-CONPRI
is O
validated O
by O
comparing O
the O
predicted S-CONPRI
in B-CONPRI
situ E-CONPRI
and O
post O
process B-CONPRI
distortion E-CONPRI
to O
experimental S-CONPRI
measurements O
taken O
on O
the O
same O
geometry S-CONPRI
. O


The O
model B-CONPRI
accurately E-CONPRI
predicts O
the O
distortion S-CONPRI
of O
the O
workpiece S-CONPRI
( O
5 O
% O
error S-CONPRI
) O
. O


This O
paper O
presents O
the O
first O
report O
on O
the O
development O
of O
weak-textured O
microstructures S-MATE
and O
resulting O
reduced O
in-plane O
anisotropy S-PRO
of O
mechanical B-CONPRI
properties E-CONPRI
in O
commercially O
pure O
titanium S-MATE
( O
CP-Ti O
) O
fabricated S-CONPRI
by O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
. O


The O
as-built O
specimens O
exhibited O
fine O
grain B-CONPRI
structures E-CONPRI
with O
weakened O
crystallographic O
textures O
. O


The O
β O
→ O
α′ O
martensitic O
transformation O
after O
solidification S-CONPRI
was O
responsible O
for O
the O
weak O
textures O
as S-MATE
well O
as S-MATE
the O
relatively O
high O
strength S-PRO
. O


The O
results O
suggest O
that O
it O
is O
possible O
to O
use O
EBM S-MANP
to O
produce O
isotropic S-PRO
CP-Ti O
components S-MACEQ
, O
which O
can O
not O
be S-MATE
obtained O
by O
conventional O
processes S-CONPRI
. O


In O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
the O
surface S-CONPRI
layer S-PARA
temperature O
is O
continually O
changing O
throughout O
the O
build S-PARA
process O
. O


Variations S-CONPRI
in O
part O
geometry S-CONPRI
, O
scanned O
cross-section O
and O
number O
of O
parts O
all O
influence O
the O
thermal O
field O
within O
a O
build S-PARA
. O


Process B-CONPRI
parameters E-CONPRI
do O
not O
take O
these O
variations S-CONPRI
into O
account O
and O
this O
can O
result O
in O
increased O
porosity S-PRO
and O
differences O
in O
local O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
, O
undermining O
confidence O
in O
the O
structural B-PRO
integrity E-PRO
of O
a O
part O
. O


In O
this O
paper O
a O
wide-field O
in B-CONPRI
situ E-CONPRI
infra-red O
imaging S-APPL
system O
is O
developed O
and O
calibrated S-CONPRI
to O
enable O
measurement S-CHAR
of O
both O
solid O
and O
powder S-MATE
surface O
temperatures S-PARA
across O
the O
full O
powder B-MACEQ
bed E-MACEQ
. O


The O
influence O
of O
inter-layer O
cooling S-MANP
time O
is O
investigated O
using O
a O
build S-PARA
scenario O
with O
cylindrical S-CONPRI
components S-MACEQ
of O
differing O
heights O
. O


In B-CONPRI
situ E-CONPRI
surface O
temperature S-PARA
data S-CONPRI
are O
acquired O
throughout O
the O
build S-PARA
process O
and O
are O
compared O
to O
results O
from O
porosity S-PRO
, O
microstructure S-CONPRI
and O
mechanical B-CONPRI
property E-CONPRI
investigations O
. O


Changes O
in O
surface S-CONPRI
temperature O
of O
up O
to O
200 O
°C O
are O
attributed O
to O
variation S-CONPRI
in O
inter-layer O
cooling S-MANP
time O
and O
this O
is O
found O
to O
correlate O
with O
density S-PRO
and O
grain B-CONPRI
structure E-CONPRI
changes O
in O
the O
part O
. O


This O
work O
shows O
that O
these O
changes O
are O
significant O
and O
must O
be S-MATE
accounted O
for O
to O
improve O
the O
consistency S-CONPRI
and O
structural B-PRO
integrity E-PRO
of O
LPBF S-MANP
components S-MACEQ
. O


A O
three-dimensional B-ENAT
model E-ENAT
was O
developed O
for O
studying O
thermal O
behavior O
during O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
of O
commercially O
pure O
titanium S-MATE
( O
CP O
Ti S-MATE
) O
powder S-MATE
. O


The O
effects O
of O
scan B-PARA
speed E-PARA
and O
laser B-PARA
power E-PARA
on O
SLM S-MANP
thermal O
behavior O
were O
investigated O
. O


The O
results O
showed O
that O
the O
average S-CONPRI
temperature O
of O
the O
powder B-MACEQ
bed E-MACEQ
gradually O
increased O
during O
the O
SLM S-MANP
process S-CONPRI
, O
caused O
by O
a O
heat B-PRO
accumulation E-PRO
effect O
. O


The O
maximum O
molten B-CONPRI
pool E-CONPRI
temperature O
( O
2248 O
°C O
) O
and O
liquid O
lifetime O
( O
1.47 O
ms O
) O
were O
obtained O
for O
a O
successful O
SLM S-MANP
process S-CONPRI
for O
a O
laser B-PARA
power E-PARA
of O
150 O
W O
and O
a O
laser B-ENAT
scan E-ENAT
speed O
of O
100 O
mm/s O
. O


The O
temperature B-PARA
gradient E-PARA
in O
the O
molten B-CONPRI
pool E-CONPRI
increased O
slightly O
( O
from O
1.03 O
× O
104 O
to O
1.07 O
× O
104 O
°C/mm O
in O
the O
direction O
perpendicular O
to O
the O
scanning S-CONPRI
path O
; O
from O
1.21 O
× O
104 O
to O
1.28 O
× O
104 O
°C/mm O
in O
the O
thickness O
direction O
) O
when O
the O
scan B-PARA
speed E-PARA
was O
increased O
from O
50 O
to O
200 O
mm/s O
, O
but O
increased O
significantly O
( O
from O
1.29 O
× O
104 O
to O
8.24 O
× O
104 O
°C/mm O
in O
the O
direction O
perpendicular O
to O
the O
scanning S-CONPRI
path O
; O
from O
1.53 O
× O
104 O
to O
9.84 O
× O
104 O
°C/mm O
in O
the O
thickness O
direction O
) O
when O
the O
laser B-PARA
power E-PARA
was O
increased O
from O
100 O
to O
200 O
W. O
The O
width O
and O
depth O
of O
the O
molten B-CONPRI
pool E-CONPRI
decreased O
( O
width O
from O
137.1 O
to O
93.8 O
μm O
, O
depth O
from O
64.2 O
to O
38.5 O
μm O
) O
when O
the O
scan B-PARA
speed E-PARA
was O
increased O
from O
50 O
to O
200 O
mm/s O
, O
but O
increased O
( O
width O
from O
71.2 O
to O
141.4 O
μm O
, O
depth O
from O
32.7 O
to O
67.3 O
μm O
) O
when O
the O
laser B-PARA
power E-PARA
was O
increased O
from O
100 O
to O
200 O
W. O
Experimental S-CONPRI
SLM O
of O
CP O
Ti B-MATE
powder E-MATE
was O
carried O
out O
under O
different O
laser B-CONPRI
processing E-CONPRI
conditions O
and O
the O
microstructure S-CONPRI
of O
SLM-produced O
parts O
was O
investigated O
to O
demonstrate O
the O
reliability S-CHAR
of O
the O
physical B-CONPRI
model E-CONPRI
and O
simulation S-ENAT
results O
. O


Rational O
design B-CONPRI
of I-CONPRI
experiment E-CONPRI
is O
employed O
to O
optimize O
the O
contour S-FEAT
parameters O
to O
improve O
surface B-FEAT
finish E-FEAT
of O
inclined O
surfaces S-CONPRI
. O


A O
significant O
variance O
in O
surface B-PRO
roughness E-PRO
is O
found O
among O
samples S-CONPRI
made O
at O
opposite O
corners O
on O
the O
build B-MACEQ
platform E-MACEQ
. O


The O
recoating O
process S-CONPRI
sorts O
powder S-MATE
by O
size O
, O
smaller O
particles S-CONPRI
settle O
within O
a O
short O
distance O
from O
start O
position O
of O
recoater O
. O


Large O
particles S-CONPRI
ejected O
from O
melt B-MATE
pool E-MATE
can O
not O
be S-MATE
completely O
removed O
by O
inert B-CONPRI
gas E-CONPRI
flow O
and O
affect O
subsequent O
SLM S-MANP
process S-CONPRI
. O


At O
a O
given O
position O
, O
inclined O
surface S-CONPRI
build S-PARA
up O
and O
away O
from O
the O
centre O
of O
the O
build B-MACEQ
platform E-MACEQ
has O
higher O
surface B-PRO
roughness E-PRO
. O


A O
rational O
design B-CONPRI
of I-CONPRI
experiments E-CONPRI
was O
employed O
to O
evaluate O
the O
correlation O
between O
scan O
parameters S-CONPRI
and O
the O
resulting O
surface B-PRO
roughness E-PRO
of O
Selective B-MANP
Laser I-MANP
Melted E-MANP
Ti-6Al-4V O
components S-MACEQ
. O


There O
is O
a O
statistically O
significant O
difference O
in O
surface B-PRO
roughness E-PRO
values O
from O
specimens O
built O
with O
identical O
laser S-ENAT
exposure S-CONPRI
parameters O
but O
located O
at O
different O
positions O
on O
the O
build B-MACEQ
platform E-MACEQ
. O


We O
hypothesise O
that O
this O
is O
a O
consequence O
of O
changing O
powder B-MATE
particle E-MATE
size O
distributions S-CONPRI
across O
the O
powder B-MACEQ
bed E-MACEQ
resulting O
from O
the O
combined O
actions O
of O
the O
recoater O
arm O
and O
gas S-CONPRI
flow O
. O


We O
further O
hypothesise O
that O
orientation S-CONPRI
of O
a O
part O
and O
the O
projected O
shape O
of O
the O
incident O
laser B-CONPRI
beam E-CONPRI
play O
a O
part O
in O
surface B-PRO
roughness E-PRO
variation O
at O
any O
given O
location O
. O


We O
found O
that O
during O
the O
powder S-MATE
re-coating O
process S-CONPRI
, O
fine O
particles S-CONPRI
tend O
to O
settle O
within O
a O
short O
distance O
from O
the O
re-coater O
starting O
position O
, O
accompanied O
by O
higher O
variability S-CONPRI
of O
local O
powder S-MATE
size O
distribution S-CONPRI
. O


Spatter S-CHAR
material S-MATE
was O
found O
to O
be S-MATE
distributed O
across O
the O
powder B-MACEQ
bed E-MACEQ
by O
the O
gas S-CONPRI
flow O
. O


However O
, O
once O
at O
any O
given O
location O
the O
surface B-PRO
roughness E-PRO
of O
inclined O
surfaces S-CONPRI
is O
affected O
by O
the O
orientation S-CONPRI
of O
the O
surface S-CONPRI
to O
the O
centre O
of O
the O
build B-MACEQ
platform E-MACEQ
at O
which O
the O
laser B-CONPRI
beam E-CONPRI
originates O
. O


Each O
of O
these O
factors O
affects O
the O
surface B-PRO
roughness E-PRO
and O
has O
implications O
for O
the O
order O
in O
which O
parts O
are O
built O
in O
Selective B-MANP
Laser I-MANP
Melting E-MANP
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
one O
of O
the O
most O
commonly O
used O
metallic S-MATE
component S-MACEQ
3D B-MANP
printing E-MANP
techniques O
. O


In O
a O
previous O
investigation O
of O
multiple O
materials S-CONPRI
SLM O
reported O
by O
The O
University O
of O
Manchester O
, O
high O
porosities S-PRO
and O
cracks O
were O
found O
in O
the O
regions O
where O
the O
powder S-MATE
was O
deposited O
via O
an O
ultrasonic O
powder S-MATE
dispenser O
. O


The O
low O
powder S-MATE
packing O
density S-PRO
was O
identified O
as S-MATE
a O
critical O
reason O
for O
this O
. O


In O
this O
paper O
, O
we O
report O
a O
new O
method O
to O
compress O
the O
ultrasonically O
deposited O
powder S-MATE
layer S-PARA
in O
order O
to O
increase O
the O
powder S-MATE
packing O
density S-PRO
. O


The O
effects O
of O
powder S-MATE
deposition S-CONPRI
velocity O
, O
powder S-MATE
track O
overlap S-CONPRI
distance O
and O
powder S-MATE
compression S-PRO
force O
on O
the O
deposited O
powder S-MATE
characteristics O
were O
investigated O
. O


The O
microstructure S-CONPRI
, O
tensile B-PRO
strengths E-PRO
, O
and O
porosity S-PRO
of O
the O
laser-fused O
samples S-CONPRI
were O
analyzed O
. O


The O
results O
indicated O
that O
powder S-MATE
compression S-PRO
could O
reduce O
porosity S-PRO
and O
component S-MACEQ
distortion O
and O
increase O
the O
mechanical B-PRO
strength E-PRO
of O
the O
printed O
parts O
. O


Heterogeneous S-CONPRI
materials O
used O
in O
biomedical S-APPL
, O
structural O
and O
electronics S-CONPRI
applications O
contain O
a O
high O
fraction S-CONPRI
of O
solids O
( O
> O
60 O
vol. O
% O
) O
and O
exhibit O
extremely O
high O
viscosities O
( O
μ O
> O
1000 O
Pa S-CHAR
s O
) O
, O
which O
hinders O
their O
3D B-MANP
printing E-MANP
using O
existing O
technologies S-CONPRI
. O


This O
study O
shows O
that O
inducing O
high-amplitude O
ultrasonic B-PARA
vibrations E-PARA
within O
a O
nozzle S-MACEQ
imparts O
sufficient O
inertial O
forces S-CONPRI
to O
these O
materials S-CONPRI
to O
drastically O
reduce O
effective O
wall O
friction S-CONPRI
and O
flow B-PRO
stresses E-PRO
, O
enabling O
their O
3D B-MANP
printing E-MANP
with O
moderate O
back O
pressures S-CONPRI
( O
< O
1 O
MPa S-CONPRI
) O
at O
high O
rates O
and O
with O
precise O
flow O
control O
. O


This O
effect O
is O
utilized O
to O
demonstrate O
the O
printing O
of O
a O
commercial O
polymer B-MATE
clay E-MATE
, O
an O
aluminum-polymer O
composite S-MATE
and O
a O
stiffened O
fondant O
with O
viscosities O
up O
to O
14,000 O
Pa·s O
with O
minimal O
residual S-CONPRI
porosity S-PRO
at O
rates O
comparable O
to O
thermoplastic S-MATE
extrusion S-MANP
. O


This O
new O
method O
can O
significantly O
extend O
the O
type O
of O
materials S-CONPRI
that O
can O
be S-MATE
printed O
to O
produce O
functional O
parts O
without O
relying O
on O
special O
shear/thermal O
thinning O
formulations O
or O
solvents O
to O
lower O
viscosity S-PRO
of O
the O
plasticizing O
component S-MACEQ
. O


The O
high O
yield B-PRO
strength E-PRO
of O
the O
printed O
material S-MATE
also O
allows O
freeform B-CONPRI
3D E-CONPRI
fabrication S-MANP
with O
minimal O
need O
for O
supports S-APPL
. O


A O
self-healing O
and O
recyclable S-CONPRI
polyurethane S-MATE
based O
on O
dynamic S-CONPRI
halogenated O
bisphenol O
carbamate O
bonds O
was O
developed O
. O


The O
dynamic S-CONPRI
crosslinked O
polyurethane S-MATE
powders O
was O
developed O
for O
selective B-MANP
laser I-MANP
sintering E-MANP
for O
the O
first O
time O
. O


The O
introduction O
of O
dynamic S-CONPRI
bonds O
enhances O
interface S-CONPRI
interaction O
and O
Z-direction S-FEAT
mechanical B-PRO
strength E-PRO
of O
printed O
products O
. O


Selective B-MANP
laser I-MANP
sintering E-MANP
( O
SLS S-MANP
) O
is O
one O
of O
the O
mainstream O
3D B-ENAT
printing I-ENAT
technologies E-ENAT
. O


A O
major O
challenge O
for O
SLS S-MANP
technology O
is O
the O
lack O
of O
novel O
polymer S-MATE
powder O
materials S-CONPRI
with O
improved O
Z-direction S-FEAT
strength S-PRO
. O


Herein O
, O
a O
dynamic S-CONPRI
polymer O
was O
utilized O
to O
solve O
the O
challenge O
of O
SLS S-MANP
. O


The O
obtained O
dynamic S-CONPRI
polyurethane O
exhibited O
excellent O
mechanical B-PRO
strength E-PRO
and O
self-healing O
efficiency O
, O
in O
addition O
to O
SLS S-MANP
processing O
ability O
. O


A O
small O
molecule O
model S-CONPRI
study O
confirmed O
the O
dynamic S-CONPRI
reversible O
characteristics O
of O
the O
chlorinated O
bisphenol O
carbamate O
, O
which O
dissociates O
into O
isocyanate O
and O
hydroxyl O
at O
120 O
°C O
and O
reforms O
at O
80 O
°C O
, O
as S-MATE
confirmed O
by O
NMR S-CHAR
and O
FT-IR S-CHAR
. O


SLS S-MANP
3D B-MANP
printing E-MANP
using O
the O
self-made O
healable O
PBP-PU O
powders S-MATE
was O
successfully O
realized O
. O


The O
interface S-CONPRI
interaction O
between O
the O
adjacent O
SLS S-MANP
layers O
can O
be S-MATE
significantly O
improved O
via O
dynamic S-CONPRI
chemical O
bond O
linking O
instead O
of O
traditional O
physical O
entanglement O
, O
which O
leads O
to O
an O
improved O
Z-direction S-FEAT
mechanical B-PRO
strength E-PRO
. O


The O
SLS B-MANP
processed E-MANP
PBP-PU O
sample S-CONPRI
exhibits O
an O
X-axis O
tensile B-PRO
strengths E-PRO
of O
∼23 O
MPa S-CONPRI
and O
an O
elongation S-PRO
at O
break O
of O
∼600 O
% O
. O


The O
Z-axis S-CONPRI
tensile B-PRO
strength E-PRO
is O
∼88 O
% O
of O
X-axis O
’ O
s S-MATE
, O
much O
higher O
than O
that O
of O
control O
TPU O
sample S-CONPRI
( O
∼56 O
% O
) O
. O


High O
porosity S-PRO
and O
interconnected O
pore B-PARA
size E-PARA
are O
crucial O
factors O
for O
bone B-BIOP
scaffolds E-BIOP
. O


However O
, O
since O
porosity S-PRO
is O
inversely O
related O
to O
strength S-PRO
, O
the O
microstructure S-CONPRI
must O
be S-MATE
optimized O
to O
achieve O
bone B-BIOP
scaffolds E-BIOP
suitable O
for O
load-bearing S-FEAT
applications O
. O


The O
powder B-MANP
bed I-MANP
3D I-MANP
printing I-MANP
method E-MANP
can O
fabricate S-MANP
the O
highly O
porous S-PRO
parts O
possessing O
the O
desired O
properties S-CONPRI
using O
micron-sized O
ceramic B-MATE
powders E-MATE
( O
> O
30 O
μm O
) O
and O
polymeric B-MATE
ink E-MATE
, O
however O
, O
low O
sinterability S-PRO
and O
, O
consequently O
, O
low O
strength S-PRO
is O
still O
a O
problem O
. O


In O
this O
study O
, O
nano-scale B-MATE
powders E-MATE
are O
granulated O
and O
printed O
by O
a O
special O
3D B-MANP
printing E-MANP
method O
called O
‘ O
solvent B-CONPRI
jetting E-CONPRI
on O
granulated O
feedstock S-MATE
containing O
binder S-MATE
’ O
to O
achieve O
an O
interconnected O
macropore B-CONPRI
structure E-CONPRI
with O
high O
strength S-PRO
. O


The O
advantages O
of O
this O
method O
, O
aside O
from O
the O
above O
mentioned O
, O
include O
obtaining O
controllable O
porosity S-PRO
, O
high O
strut S-MACEQ
density S-PRO
, O
wide B-CONPRI
neck I-CONPRI
formation E-CONPRI
, O
and O
small O
grain B-PRO
size E-PRO
; O
all O
of O
which O
are O
beneficial O
to O
mechanical B-PRO
strength E-PRO
. O


Using O
this O
method O
, O
a O
purely O
ceramic S-MATE
sample O
with O
30 O
% O
porosity S-PRO
and O
compressive B-PRO
strength E-PRO
of O
113.1 O
MPa S-CONPRI
was O
obtained O
. O


Furthermore O
, O
a O
bone B-MACEQ
scaffold I-MACEQ
prototype E-MACEQ
with O
total O
porosity S-PRO
of O
nearly O
50 O
% O
and O
mechanical B-PRO
strength E-PRO
of O
30.2 O
MPa S-CONPRI
was O
fabricated S-CONPRI
. O


These O
procedures O
and O
results O
are O
described O
and O
compared O
to O
another O
solvent B-CONPRI
jetting E-CONPRI
method O
which O
uses O
micron-sized B-MATE
powders E-MATE
. O


The O
use O
of O
porous S-PRO
cellular B-FEAT
structures E-FEAT
in O
bone S-BIOP
tissue O
engineering S-APPL
can O
provide O
mechanical S-APPL
and O
biological O
environments O
closer O
to O
the O
host B-BIOP
bone E-BIOP
. O


However O
, O
poor O
internal O
architectural O
designs S-FEAT
may O
lead S-MATE
to O
catastrophic O
failure S-CONPRI
. O


In O
this O
work O
, O
192 O
open-porous O
cellular B-FEAT
structures E-FEAT
were O
fabricated S-CONPRI
using O
3D B-MANP
printing E-MANP
( O
3DP S-MANP
) O
techniques O
. O


It O
was O
found O
that O
the O
pillar O
octahedral O
shape O
has O
not O
only O
greater O
stiffness S-PRO
and O
strength S-PRO
under O
compression S-PRO
, O
shear O
and O
torsion O
but O
increased O
rate O
of O
pre-osteoblastic O
cell S-APPL
proliferation O
. O


We O
believe O
bone B-APPL
implants E-APPL
can O
be S-MATE
fabricated O
using O
3DP S-MANP
techniques O
and O
their O
mechanical S-APPL
and O
biological O
performance S-CONPRI
can O
be S-MATE
tailored O
by O
modifying O
the O
internal B-PRO
architectures E-PRO
. O


Vat B-MANP
photopolymerization E-MANP
is O
used O
for O
printing O
very O
precise O
and O
accurate S-CHAR
parts O
from O
photopolymer B-MATE
resins E-MATE
. O


Conventional O
3D-printers O
based O
on O
vat B-MANP
photopolymerization E-MANP
are O
curing S-MANP
resins O
with O
low O
viscosity S-PRO
at O
or O
slightly O
above O
room O
temperature S-PARA
. O


The O
newly O
developed O
Hot O
Lithography S-CONPRI
provides O
vat B-MANP
photopolymerization E-MANP
where O
the O
resin S-MATE
is O
heated O
and O
cured S-MANP
at O
elevated O
temperatures S-PARA
. O


This O
study O
presents O
the O
influence O
of O
printing O
temperature S-PARA
( O
23 O
°C O
and O
70 O
°C O
) O
on O
the O
properties S-CONPRI
of O
a O
printed O
dimethacrylate O
resin S-MATE
. O


Specimens O
were O
printed O
in O
XYZ O
and O
ZXY O
orientation S-CONPRI
. O


The O
resulting O
tensile B-PRO
properties E-PRO
were O
tested O
, O
dynamic B-CONPRI
mechanical I-CONPRI
analysis E-CONPRI
was O
carried O
out O
and O
the O
double-bond O
conversion O
was O
analyzed O
. O


Therefore O
, O
the O
exposure S-CONPRI
time O
was O
reduced O
from O
50 O
s S-MATE
to O
30 O
s S-MATE
to O
reach O
similar O
curing B-PARA
depth E-PARA
. O


Higher O
printing O
temperature S-PARA
provided O
higher O
double-bond O
conversion O
, O
tensile B-PRO
strength E-PRO
and O
modulus O
of O
the O
green B-PRO
parts E-PRO
. O


However O
, O
printing O
temperature S-PARA
did O
not O
affect O
the O
properties S-CONPRI
after O
post-curing O
in O
XYZ O
orientation S-CONPRI
. O


Post-cured O
tensile B-MACEQ
specimens E-MACEQ
in O
ZXY O
orientation S-CONPRI
had O
higher O
tensile B-PRO
strength E-PRO
when O
printed O
at O
23 O
°C O
, O
because O
higher O
over-polymerization O
led S-APPL
to O
a O
smoother O
surface S-CONPRI
of O
the O
specimens O
. O


Overall O
, O
higher O
printing O
temperatures S-PARA
lowered O
the O
viscosity S-PRO
of O
the O
resin S-MATE
, O
reduced O
the O
printing O
time O
and O
provided O
better O
mechanical B-CONPRI
properties E-CONPRI
of O
green B-PRO
parts E-PRO
while O
post-cured O
properties S-CONPRI
were O
mostly O
not O
affected O
. O


In O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
, O
melt B-MATE
pool E-MATE
dynamics O
and O
stability S-PRO
are O
driven O
by O
the O
temperature S-PARA
field O
in O
the O
melt B-MATE
pool E-MATE
. O


If O
the O
temperature S-PARA
field O
is O
unfavourable O
defects S-CONPRI
are O
likely O
to O
form O
. O


The O
localised O
and O
rapid O
heating S-MANP
and O
cooling S-MANP
in O
the O
process S-CONPRI
presents O
a O
challenge O
for O
the O
experimental S-CONPRI
methods O
used O
to O
measure O
temperature S-PARA
. O


As S-MATE
a O
result O
, O
understanding O
of O
these O
process S-CONPRI
fundamentals O
is O
limited O
. O


In O
this O
paper O
a O
method O
is O
developed O
that O
uses O
coaxial O
imaging S-APPL
with O
high-speed O
cameras O
to O
give O
both O
the O
spatial O
and O
temporal O
resolution S-PARA
necessary O
to O
resolve O
the O
surface S-CONPRI
temperature O
of O
the O
melt B-MATE
pool E-MATE
. O


A O
two O
wavelength S-CONPRI
imaging S-APPL
setup O
is O
used O
to O
account O
for O
changes O
in O
emissivity O
. O


Temperature S-PARA
fields O
are O
captured O
at O
100 O
kHz O
with O
a O
resolution S-PARA
of O
20 O
μm O
during O
the O
processing O
of O
a O
simple S-MANP
Ti6Al4V O
component S-MACEQ
. O


Thermal B-PARA
gradients E-PARA
in O
the O
range S-PARA
5–20 O
K/μm O
and O
cooling B-PARA
rates E-PARA
in O
range S-PARA
1–40 O
K/μs O
are O
measured O
. O


The O
results O
presented O
give O
new O
insight O
into O
the O
effect O
of O
parameters S-CONPRI
, O
geometry S-CONPRI
and O
scan O
path O
on O
the O
melt B-MATE
pool E-MATE
temperature O
and O
cooling B-PARA
rates E-PARA
. O


The O
method O
developed O
here O
provides O
a O
new O
tool S-MACEQ
to O
assist O
in O
optimising O
scan O
strategies O
and O
parameters S-CONPRI
, O
identifying O
the O
causes O
of O
defect S-CONPRI
prone O
locations O
and O
controlling O
cooling B-PARA
rates E-PARA
for O
local O
microstructure S-CONPRI
development O
. O


In O
laser B-MANP
directed I-MANP
energy I-MANP
deposition E-MANP
( O
L-DED O
) O
processes S-CONPRI
, O
by O
applying O
a O
converged O
powder S-MATE
stream O
, O
relatively O
high O
laser B-PARA
power E-PARA
and O
larger O
laser S-ENAT
spot O
, O
the O
powder S-MATE
utilisation O
efficiency O
and O
processing O
speed O
can O
be S-MATE
increased O
. O


In O
this O
paper O
, O
a O
three-dimensional S-CONPRI
numerical O
model S-CONPRI
is O
established O
to O
study O
the O
mass O
transport S-CHAR
and O
heat B-CONPRI
transfer E-CONPRI
in O
the O
melt B-MATE
pools E-MATE
in O
high B-PARA
deposition I-PARA
rate E-PARA
( O
HDR O
) O
L-DED O
of O
316L B-MATE
stainless I-MATE
steel E-MATE
. O


The O
Volume B-CONPRI
of I-CONPRI
Fluid E-CONPRI
( O
VOF S-CONPRI
) O
method O
is O
employed O
to O
track O
the O
melt B-MATE
pool E-MATE
free B-CONPRI
surfaces E-CONPRI
, O
and O
enthalpy-porosity O
method O
is O
used O
to O
model S-CONPRI
the O
solid-liquid O
phase S-CONPRI
change O
. O


A O
discrete O
powder S-MATE
source O
model S-CONPRI
is O
developed O
by O
considering O
the O
non-uniform O
powder S-MATE
feed S-PARA
rate O
distribution S-CONPRI
. O


Different O
from O
conventional O
L-DED O
processes S-CONPRI
, O
the O
impact S-CONPRI
of O
higher O
mass O
addition O
on O
the O
melt B-MATE
pool E-MATE
fluid B-PRO
flow E-PRO
and O
temperature S-PARA
distribution S-CONPRI
is O
significant O
. O


With O
the O
extracted S-CONPRI
temperature O
distribution S-CONPRI
and O
geometry S-CONPRI
at O
the O
solidification S-CONPRI
front O
, O
the O
solidification S-CONPRI
conditions O
are O
also O
calculated O
, O
as S-MATE
well O
as S-MATE
the O
primary O
dendrite S-BIOP
arm O
spacing O
( O
PDAS O
) O
of O
the O
solidified O
tracks O
. O


Due O
to O
the O
high O
laser B-CONPRI
energy E-CONPRI
input O
, O
the O
temperature B-PARA
gradient E-PARA
is O
lower O
, O
and O
coarser O
microstructures S-MATE
are O
formed O
compared O
with O
conventional O
L-DED O
. O


A O
single-photon O
absorption B-CONPRI
3D E-CONPRI
stereolithographic O
methodology S-CONPRI
is O
presented O
. O


Meso-scale O
architectures O
can O
be S-MATE
achieved O
with O
5 O
μm O
resolution S-PARA
along O
( O
x O
, O
y S-MATE
, O
z O
) O
. O


Process B-CONPRI
parameters E-CONPRI
( O
e.g O
. O


exposure S-CONPRI
, O
slicing S-CONPRI
) O
adaptable O
to O
each O
region O
of O
the O
3D S-CONPRI
design O
. O


3D B-MANP
printing E-MANP
of O
highly O
complex O
porous S-PRO
architectures O
featuring O
overhanging O
units O
. O


The O
realization O
of O
2D S-CONPRI
and O
3D S-CONPRI
meso-scale O
architectures O
is O
an O
area S-PARA
of O
research S-CONPRI
involving O
a O
wide O
range S-PARA
of O
disciplines O
ranging O
from O
materials S-CONPRI
science O
, O
microelectronics S-CONPRI
, O
phononics O
, O
microfluidics S-CONPRI
to O
biomedicine S-APPL
requiring O
millimeter O
to O
centimeter-sized O
objects O
embedding O
micrometric O
features O
. O


In O
the O
recent O
years O
, O
several O
technologies S-CONPRI
have O
been O
employed O
to O
provide O
optimal O
features O
in O
terms O
of O
object O
size O
flexibility S-PRO
, O
printing O
resolution S-PARA
, O
large O
materials S-CONPRI
library O
and O
fabrication S-MANP
speed O
. O


In O
this O
work O
, O
we O
report O
a O
fully O
customizable O
single-photon O
absorption B-CONPRI
3D E-CONPRI
fabrication O
methodology S-CONPRI
based O
on O
direct O
laser S-ENAT
fabrication S-MANP
. O


To O
validate O
this O
approach O
and O
highlight O
the O
versatility O
of O
the O
setup O
, O
we O
have O
fabricated S-CONPRI
a O
comprehensive O
ensemble O
of O
2D S-CONPRI
and O
3D S-CONPRI
designs O
with O
potential O
applications O
in O
biomimetics S-CONPRI
, O
3D S-CONPRI
scaffolding O
and O
microfluidics S-CONPRI
. O


The O
high O
degree O
of O
tunability O
of O
the O
reported O
fabrication S-MANP
system O
allows O
tailoring O
the O
laser B-PARA
power E-PARA
, O
slicing S-CONPRI
and O
fabrication S-MANP
speed O
for O
each O
single O
area S-PARA
of O
the O
design S-FEAT
. O


These O
unique O
features O
enable O
a O
rapid B-ENAT
prototyping E-ENAT
of O
millimeter O
to O
centimeter-sized O
objects O
involving O
3D S-CONPRI
architectures O
with O
true O
freestanding O
subunits O
and O
micrometric O
feature S-FEAT
reproducibility O
. O


This O
study O
focuses O
on O
the O
microstructure B-CONPRI
evolution E-CONPRI
induced O
by O
eutectic S-CONPRI
WC-W2C O
inoculants O
during O
the O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
of O
IN718 S-MATE
. O


The O
as-built O
microstructure S-CONPRI
observed O
using O
an O
electron O
microscope S-MACEQ
indicates O
that O
grain S-CONPRI
nucleation O
occurred O
on O
the O
surface S-CONPRI
of O
inoculants O
and O
that O
the O
diffusion S-CONPRI
layer O
between O
inoculants O
and O
IN718 S-MATE
composed O
of O
a O
mixture O
of O
IN718 S-MATE
and O
inoculants O
. O


After O
the O
post O
heat B-MANP
treatment E-MANP
of O
the O
as-built O
SLM S-MANP
specimens O
, O
more O
grains S-CONPRI
nucleated O
around O
the O
inoculants O
, O
and O
Nb-rich O
precipitates S-MATE
were O
formed O
along O
the O
grain B-CONPRI
boundaries E-CONPRI
. O


With O
an O
increase O
in O
the O
post B-MANP
heat-treatment E-MANP
temperature O
, O
the O
microstructure B-CONPRI
evolution E-CONPRI
became O
more O
pronounced O
. O


To O
elucidate O
the O
underlying O
mechanism S-CONPRI
, O
both O
theoretical S-CONPRI
and O
experimental S-CONPRI
analyses O
were O
performed O
. O


In O
summary O
, O
eutectic S-CONPRI
WC-W2C O
inoculants O
could O
provide O
heterogeneous B-CONPRI
nucleation E-CONPRI
sites O
for O
grain S-CONPRI
formation O
owing O
to O
the O
low O
wetting O
angle O
and O
the O
semi-coherent O
interface S-CONPRI
with O
the O
matrix O
. O


Theoretical S-CONPRI
analysis O
suggests O
that O
the O
difference O
in O
the O
thermal B-PRO
expansion I-PRO
coefficient E-PRO
between O
inoculants O
and O
IN718 S-MATE
did O
not O
provide O
a O
significant O
amount O
of O
residual B-PRO
stress E-PRO
. O


Thus O
, O
it O
can O
be S-MATE
concluded O
that O
heterogeneous B-CONPRI
nucleation E-CONPRI
is O
the O
primary O
mechanism S-CONPRI
by O
which O
inoculants O
can O
influence O
the O
microstructure S-CONPRI
in O
the O
present O
study O
. O


This O
paper O
presents O
an O
integrated O
physics-based O
and O
statistical O
modeling S-ENAT
approach O
to O
predict O
temperature S-PARA
field O
and O
meltpool S-CHAR
geometry S-CONPRI
in O
multi-track O
processing O
of O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
of O
nickel S-MATE
625 O
alloy S-MATE
. O


Multi-track O
laser B-CONPRI
processing E-CONPRI
of O
powder B-MATE
material E-MATE
using O
L-PBF S-MANP
process O
has O
been O
studied O
using O
2-D O
finite B-CONPRI
element E-CONPRI
simulations O
to O
calculate O
temperature S-PARA
fields O
along O
the O
scan O
and O
hatch O
directions O
for O
three O
consecutive O
tracks O
for O
a O
moving O
laser B-PARA
heat E-PARA
source O
to O
understand O
the O
heating S-MANP
and O
melting S-MANP
process O
. O


Based O
on O
the O
predicted S-CONPRI
temperature O
fields O
, O
width O
, O
depth O
and O
shape O
of O
the O
meltpool S-CHAR
is O
determined O
. O


Designed S-FEAT
experiments O
on O
L-PBF S-MANP
of O
nickel B-MATE
alloy E-MATE
625 O
powder B-MATE
material E-MATE
are O
conducted O
to O
measure O
the O
relative B-PRO
density E-PRO
and O
meltpool S-CHAR
geometry S-CONPRI
. O


Experimental S-CONPRI
work O
is O
reported O
on O
the O
measured O
density S-PRO
of O
built O
coupons O
and O
meltpool S-CHAR
size O
. O


Statistically-based O
predictive B-CONPRI
models E-CONPRI
using O
response O
surface S-CONPRI
regression S-CONPRI
for O
relative B-PRO
density E-PRO
, O
meltpool S-CHAR
geometry S-CONPRI
, O
peak O
temperature S-PARA
, O
and O
time O
above O
melting B-PRO
point E-PRO
are O
developed O
and O
multi-objective O
optimization S-CONPRI
studies O
are O
conducted O
by O
using O
genetic B-CONPRI
algorithm E-CONPRI
and O
swarm O
intelligence O
. O


A O
fragile S-CONPRI
and O
non-thixotropic B-PRO
biocompatible E-PRO
low B-MATE
molecular I-MATE
weight I-MATE
gel E-MATE
is O
printed O
in O
3D B-CONPRI
structures E-CONPRI
by O
a O
solvent B-CONPRI
exchange E-CONPRI
process S-CONPRI
. O


The O
3D B-MANP
printing E-MANP
process O
is O
based O
on O
the O
continuous O
extrusion S-MANP
of O
a O
solution S-CONPRI
of O
a O
small O
amphiphile S-MATE
molecule O
, O
N-heptyl-d-galactonamide S-MATE
, O
in O
dimethylsulfoxide S-MATE
, O
that O
forms O
a O
gel S-MATE
in O
contact S-APPL
with O
water O
. O


The O
diffusion S-CONPRI
of O
water O
in O
the O
dimethylsulfoxide S-MATE
/ O
N-heptyl-d-galactonamide S-MATE
solution O
triggers O
the O
self-assembly S-CONPRI
of O
the O
molecule O
into O
supramolecular B-MATE
fibers E-MATE
and O
the O
setting O
of O
the O
ink S-MATE
. O


The O
conditions O
for O
getting O
a O
well-defined O
pattern S-CONPRI
and O
the O
dimensions S-FEAT
of O
the O
constructs O
have O
been O
determined O
. O


The O
resulting O
constructs O
can O
be S-MATE
easily O
dissolved O
, O
orienting O
its O
application O
as S-MATE
a O
sacrificial B-MATE
ink E-MATE
or O
a O
temporary O
support S-APPL
. O


This O
method O
opens O
the O
way O
to O
the O
injection O
and O
the O
3D B-MANP
printing E-MANP
of O
other O
fragile S-CONPRI
and O
non-thixotropic S-PRO
supramolecular O
hydrogels S-MATE
. O


Biofabrication S-MANP
is O
the O
process S-CONPRI
of O
transforming O
materials S-CONPRI
into O
systems O
that O
reproduce O
biological B-FEAT
structure E-FEAT
and O
function O
. O


Previous O
attempts O
to O
create O
biomimetic S-CONPRI
systems O
have O
often O
used O
single O
materials S-CONPRI
shaped O
into O
limited O
configurations O
that O
do O
not O
mimic S-MACEQ
the O
heterogeneous S-CONPRI
structure O
and O
properties S-CONPRI
of O
many O
biological B-MATE
tissues E-MATE
. O


The O
printer S-MACEQ
was O
used O
to O
fabricate S-MANP
a O
range S-PARA
of O
composite B-MATE
materials E-MATE
containing O
varying O
blends S-MATE
of O
a O
tough O
alginate/poly O
( O
acrylamide O
) O
ionic O
covalent O
entanglement O
hydrogel S-MATE
and O
an O
acrylated O
urethane S-MATE
based O
UV-curable O
adhesive S-MATE
material O
. O


The O
hard O
adhesive S-MATE
material O
acted O
as S-MATE
particulate O
reinforcement S-PARA
within O
the O
matrix O
of O
composites S-MATE
printed O
with O
a O
large O
hydrogel S-MATE
volume O
fraction S-CONPRI
. O


The O
composite B-MATE
materials E-MATE
were O
characterized O
mechanically O
and O
their O
performance S-CONPRI
could O
be S-MATE
modeled O
with O
standard S-CONPRI
composite S-MATE
theory O
. O


The O
platform S-MACEQ
of O
a O
3D B-MACEQ
printer E-MACEQ
allowed O
these O
composite B-MATE
materials E-MATE
to O
be S-MATE
fabricated O
directly O
with O
a O
smooth O
and O
continuous O
gradient O
of O
modulus O
between O
the O
soft O
hydrogel S-MATE
and O
harder O
acrylated O
urethane B-MATE
material E-MATE
, O
which O
may O
be S-MATE
useful O
in O
the O
development O
of O
bio-inspired B-FEAT
structures E-FEAT
such O
as S-MATE
artificial O
tendons O
. O


This O
work O
investigated O
the O
utility O
of O
three O
piezoelectric O
inkjet S-MANP
printers O
as S-MATE
energetic O
material S-MATE
deposition S-CONPRI
systems O
, O
focusing O
on O
the O
ability O
of O
each O
system O
to O
achieve O
the O
seamless O
integration O
of O
energetic O
material S-MATE
into O
small-scale O
electronic O
devices O
. O


Aluminum S-MATE
copper O
( O
II O
) O
oxide S-MATE
nanothermite O
was O
deposited O
using O
the O
three O
deposition S-CONPRI
systems O
. O


The O
printers S-MACEQ
were O
evaluated O
based O
on O
their O
robustness S-PRO
to O
energetic O
ink S-MATE
solids O
loading O
, O
drop O
formation O
reliability S-CHAR
, O
drop O
quality B-CONPRI
degradation E-CONPRI
over O
time O
, O
and O
the O
energetic O
performance S-CONPRI
of O
the O
deposited O
material S-MATE
. O


These O
metrics O
correlate O
to O
the O
feasibility S-CONPRI
of O
a O
deposition S-CONPRI
system O
to O
successfully O
achieve O
high O
sample S-CONPRI
throughput O
while O
maintaining O
the O
energetic O
performance S-CONPRI
of O
the O
printed O
material S-MATE
. O


After O
initial O
system O
testing S-CHAR
, O
the O
PipeJet O
P9 O
500 O
μm O
pipe O
was O
used O
to O
demonstrate O
the O
successful O
deposition S-CONPRI
of O
nanothermite O
in O
varying O
geometric O
patterns O
with O
micrometer S-MACEQ
precision O
. O


Popular O
3D B-MANP
printing E-MANP
techniques O
such O
as S-MATE
fused O
deposition S-CONPRI
modelling O
( O
FDM S-MANP
) O
and O
stereolithography S-MANP
( O
SLA S-MACEQ
) O
have O
certain O
limitations O
and O
challenges O
. O


Although O
printing O
multi-material S-CONPRI
functional O
parts O
combining O
smart O
and O
conventional O
materials S-CONPRI
is O
a O
promising O
area S-PARA
, O
existing O
printers S-MACEQ
are O
not O
ideally O
suited O
to O
this O
, O
with O
FDM B-MACEQ
printers E-MACEQ
typically O
requiring O
high O
operating O
temperatures S-PARA
and O
SLA S-MACEQ
using O
a O
tank O
containing O
one O
single O
material S-MATE
. O


Common O
3D B-MACEQ
printers E-MACEQ
also O
require O
the O
deposition S-CONPRI
of O
additional O
“ O
support S-APPL
” O
material S-MATE
to O
hold O
the O
shape O
of O
an O
object O
when O
printing O
overhang S-PARA
structures O
. O


The O
concept O
of O
adding O
additional O
rotational O
axes O
to O
the O
system O
to O
eliminate O
this O
problem O
has O
shown O
promising O
results O
, O
but O
such O
systems O
still O
lack O
the O
capability O
to O
print S-MANP
complex B-CONPRI
structures E-CONPRI
without O
supports S-APPL
. O


To O
overcome O
these O
limitations O
there O
is O
a O
need O
to O
develop O
a O
new O
3D B-MANP
printing E-MANP
techniques O
that O
combine O
the O
strengths S-PRO
of O
existing O
methods O
. O


A O
photopolymer S-MATE
extrusion S-MANP
3D B-MANP
printing E-MANP
technique O
, O
which O
combines O
the O
strengths S-PRO
of O
FDM S-MANP
and O
UV S-CONPRI
assisted O
3D B-ENAT
printing I-ENAT
technology E-ENAT
is O
demonstrated O
in O
this O
paper O
. O


By O
using O
photopolymer S-MATE
extrusion S-MANP
in O
combination O
with O
two O
additional O
rotational O
axes O
, O
the O
printer S-MACEQ
developed O
in O
this O
work O
not O
only O
allows O
the O
traditional O
layer S-PARA
upon O
layer S-PARA
printing O
, O
but O
is O
also O
capable O
of O
free O
form O
printing O
. O


Fumed O
silica S-MATE
is O
used O
as S-MATE
a O
filler O
in O
order O
to O
control O
the O
material S-MATE
viscosity O
for O
proper O
extrusion S-MANP
and O
curing S-MANP
. O


Mechanical B-CHAR
tests E-CHAR
were O
conducted O
on O
objects O
printed O
using O
different O
concentrations O
of O
filler O
in O
the O
photopolymer S-MATE
to O
understand O
its O
effect O
and O
determine O
the O
range S-PARA
of O
suitable O
filler O
concentration O
. O


Multilayer O
HSS S-MATE
alloys S-MATE
have O
been O
produced O
by O
laser B-MANP
cladding E-MANP
and O
characterized O
in O
terms O
of O
their O
microstructural B-CONPRI
evolution E-CONPRI
, O
hardness S-PRO
, O
stress S-PRO
state O
and O
tensile B-PRO
properties E-PRO
. O


Massive O
martensitic O
transformation O
during O
cladding S-MANP
of O
HSS S-MATE
alloys S-MATE
, O
resulted O
in O
the O
compressive O
state O
of O
clads O
and O
suppressed O
the O
cracking S-CONPRI
. O


Re-heating O
during O
laser B-MANP
cladding E-MANP
of O
thick O
multilayer O
coatings S-APPL
of O
an O
Fe-Cr-Mo-W-V O
alloy S-MATE
had O
a O
detrimental O
effect O
on O
the O
hardness S-PRO
of O
intermediate O
layers O
. O


Addition O
of O
Co S-MATE
in O
LC1 O
at O
the O
expense O
of O
Fe S-MATE
( O
Fe−x-Cr-Mo-W-V-Cox O
) O
significantly O
increased O
the O
overall O
coating S-APPL
hardness O
by O
strengthen O
the O
matrix O
. O


Tensile B-CHAR
testing E-CHAR
results O
showed O
a O
strong O
adherence O
of O
thick O
multilayer O
coatings S-APPL
with O
the O
substrate S-MATE
. O


Two O
high B-MATE
speed I-MATE
steel E-MATE
( O
HSS S-MATE
) O
alloys S-MATE
were O
laser S-ENAT
cladded O
on O
42CrMo4 O
steel S-MATE
cylindrical S-CONPRI
substrate O
by O
using O
a O
4 O
kW O
Nd B-MATE
: I-MATE
YAG E-MATE
laser B-MACEQ
source E-MACEQ
. O


After O
optimization S-CONPRI
of O
the O
laser S-ENAT
material O
processing O
parameters S-CONPRI
for O
single O
layers O
, O
multilayered O
clads O
were O
produced O
. O


Microstructural B-CHAR
characterization E-CHAR
of O
the O
laser S-ENAT
deposits O
constitutes O
studies O
of O
the O
carbides S-MATE
and O
matrix O
, O
which O
was O
done O
by O
using O
Scanning B-CHAR
Electron I-CHAR
Microscopy E-CHAR
( O
SEM S-CHAR
) O
, O
Energy B-CHAR
Dispersive I-CHAR
Spectroscopy E-CHAR
( O
EDS S-CHAR
) O
, O
Electron O
Backscattered O
Diffraction S-CHAR
( O
EBSD S-CHAR
) O
and O
High B-CHAR
Resolution I-CHAR
Transmission I-CHAR
Electron I-CHAR
Microscopy E-CHAR
( O
HRTEM S-CHAR
) O
.The O
strengthening B-CONPRI
mechanism E-CONPRI
of O
LC1 O
( O
Fe-Cr-Mo-W-V O
) O
was O
comprised O
of O
a O
martensitic O
matrix O
and O
retained B-MATE
austenite E-MATE
along O
with O
networks O
of O
VC S-MATE
and O
Mo2C O
eutectic S-CONPRI
carbides S-MATE
. O


Cr S-MATE
enriched O
fine O
carbides S-MATE
( O
Cr7C3 O
and O
Cr23C6 O
) O
were O
embedded O
within O
the O
matrix O
. O


During O
laser B-MANP
cladding E-MANP
of O
the O
multilayer O
deposits O
, O
cladding S-MANP
of O
subsequent O
layers O
had O
a O
detrimental O
effect O
on O
the O
hardness S-PRO
of O
previously O
cladded O
layers O
, O
which O
was O
due O
to O
tempering S-MANP
of O
existing O
lath O
martensite S-MATE
. O


To O
overcome O
the O
hardness S-PRO
drop O
, O
a O
new O
alloy S-MATE
LC2 O
( O
Febal−x-Cr-Mo-W-V-Cox O
) O
was O
blended O
by O
addition O
of O
3–5 O
% O
of O
Co S-MATE
in O
LC1 O
. O


The O
addition O
of O
Co S-MATE
resulted O
in O
an O
overall O
increase O
in O
hardness S-PRO
and O
a O
reduction S-CONPRI
in O
the O
hardness S-PRO
drop O
during O
sequential O
layer S-PARA
cladding S-MANP
; O
the O
latter O
was O
due O
to O
the O
presence O
of O
Co S-MATE
in O
the O
solid B-MATE
solution E-MATE
with O
Fe.HRTEM O
was O
performed O
to O
characterize O
the O
nanometer-sized O
precipitates S-MATE
evolved O
during O
the O
re-heating O
. O


These O
carbides S-MATE
were O
either O
enriched O
with O
V S-MATE
and O
W O
or O
formed O
from O
a O
complex O
combination O
of O
V S-MATE
, O
Mo S-MATE
, O
W O
and O
Cr S-MATE
with O
lattice S-CONPRI
spacings O
of O
0.15 O
nm O
to O
0.26 O
nm O
. O


An O
urgent O
need O
in O
the O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
process S-CONPRI
is O
to O
efficiently O
remove O
emissions O
from O
or O
around O
the O
moving O
melt B-MATE
pool E-MATE
since O
the O
powder B-MACEQ
bed E-MACEQ
contamination O
by O
spatter S-CHAR
can O
potentially O
damage S-PRO
fabricated O
part O
quality S-CONPRI
. O


The O
objective O
of O
this O
study O
is O
to O
propose O
new O
designs S-FEAT
of O
the O
gas S-CONPRI
flow O
system O
in O
the O
build B-PARA
chamber E-PARA
to O
enhance O
the O
removability O
of O
spatter S-CHAR
. O


Specifically O
, O
a O
Computational B-CHAR
Fluid I-CHAR
Dynamics E-CHAR
( O
CFD S-APPL
) O
model S-CONPRI
for O
the O
LPBF S-MANP
gas S-CONPRI
flow O
system O
has O
been O
developed O
to O
simulate O
the O
complicated O
flow O
behavior O
inside O
the O
build B-PARA
chamber E-PARA
. O


The O
movement O
of O
spatter S-CHAR
has O
been O
calculated O
by O
the O
Discrete O
Phase B-CONPRI
Model E-CONPRI
( O
DPM O
) O
. O


The O
fully O
coupled O
CFD-DPM O
fluid-particle O
interaction O
method O
has O
been O
applied O
to O
capture O
the O
influence O
of O
gas S-CONPRI
flow O
on O
solid O
particles S-CONPRI
accurately S-CHAR
. O


Additionally O
, O
an O
analytical O
expression O
is O
utilized O
to O
obtain O
the O
threshold O
velocity O
of O
inert B-CONPRI
gas E-CONPRI
flow O
upon O
the O
powder B-MACEQ
bed E-MACEQ
. O


The O
spatter S-CHAR
distribution S-CONPRI
in O
a O
generic O
gas S-CONPRI
chamber O
design S-FEAT
was O
studied O
. O


It O
was O
found O
that O
the O
Coanda O
effect O
, O
a O
gas S-CONPRI
flow O
downward O
tendency O
toward O
the O
substrate S-MATE
, O
can O
have O
a O
significant O
impact S-CONPRI
on O
the O
spatter S-CHAR
removal O
process S-CONPRI
. O


With O
the O
proposed O
new O
designs S-FEAT
, O
the O
Coanda O
effect O
is O
minimized O
, O
and O
most O
of O
the O
spatters O
can O
be S-MATE
removed O
from O
the O
build S-PARA
region O
without O
blowing S-MANP
up O
powder B-MACEQ
bed E-MACEQ
particles S-CONPRI
. O


Polymer B-MANP
extrusion E-MANP
three O
dimensional O
( O
3D S-CONPRI
) O
printing O
, O
such O
as S-MATE
fused O
deposition B-CONPRI
modeling E-CONPRI
( O
FDM S-MANP
) O
, O
has O
recently O
garnered O
attention O
due O
to O
its O
inherent O
process S-CONPRI
flexibility S-PRO
and O
rapid B-ENAT
prototyping E-ENAT
capability O
. O


Specifically O
, O
the O
addition O
of O
electrical S-APPL
components S-MACEQ
and O
interconnects O
into O
a O
3D B-MANP
printing E-MANP
build O
sequence O
has O
received O
heavy O
interest O
for O
space O
applications O
. O


However O
, O
the O
addition O
of O
these O
components S-MACEQ
, O
along O
with O
the O
thermal O
load O
associated O
with O
space-based O
applications O
, O
may O
prove O
problematic O
for O
typical O
thermally O
insulating S-CONPRI
3D B-MANP
printed E-MANP
polymer O
structures O
. O


The O
work O
presented O
here O
addresses O
thermally O
conductive O
polymer B-MATE
matrix I-MATE
composites E-MATE
( O
specifically O
, O
graphite S-MATE
, O
carbon B-MATE
fiber E-MATE
, O
and O
silver S-MATE
in O
an O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
polymer O
matrix O
) O
to O
identify O
the O
effect O
of O
composite S-MATE
geometry O
and O
print S-MANP
direction O
on O
thermal O
anisotropic S-PRO
properties O
. O


The O
work O
also O
examines O
the O
effect O
of O
these O
composites S-MATE
on O
print B-CONPRI
quality E-CONPRI
, O
mechanical S-APPL
tensile O
properties S-CONPRI
, O
fracture S-CONPRI
plane O
analysis O
, O
micrograph O
imaging S-APPL
, O
and O
cube S-CONPRI
satellite O
thermal B-CHAR
analysis E-CHAR
. O


The O
thermal B-PRO
conductivity E-PRO
of O
3D B-MANP
printed E-MANP
material O
systems O
in O
this O
work O
may O
enable O
the O
production S-MANP
of O
thermally O
stable O
3D B-MANP
printed E-MANP
structures O
, O
supports S-APPL
, O
and O
devices O
. O


Key O
results O
of O
this O
work O
include O
anisotropic S-PRO
thermal O
conductivity S-PRO
for O
3D B-MANP
printed E-MANP
structures O
related O
to O
print S-MANP
direction O
and O
filler O
morphology S-CONPRI
meaning O
that O
thermal B-PRO
conductivity E-PRO
can O
be S-MATE
controlled O
through O
a O
combination O
of O
print S-MANP
raster O
direction O
and O
material S-MATE
design S-FEAT
. O


When O
the O
materials S-CONPRI
analyzed O
in O
this O
work O
are O
incorporated O
with O
other O
active O
cooling S-MANP
systems O
, O
space-based O
3D B-MANP
printed E-MANP
applications O
can O
then O
be S-MATE
designed O
to O
incorporate O
increasing O
thermal O
loads O
, O
opening O
a O
new O
door O
to O
producing O
space-ready O
3D B-MANP
printed E-MANP
structures O
. O


Inverse O
process S-CONPRI
embedded B-MANP
3D I-MANP
printing E-MANP
multi O
internal O
surfaces S-CONPRI
hydrogel S-MATE
and O
application O
in O
anatomical O
organ O
model S-CONPRI
. O


Inverse O
process-based O
printing O
strategies O
can O
speed O
up O
3D B-MANP
printing E-MANP
and O
increase O
efficiency O
. O


Prepolymer S-MATE
has O
high O
transparency O
, O
and O
has O
shear B-CONPRI
thinning E-CONPRI
behavior O
and O
yield B-PRO
stress E-PRO
characteristics O
. O


The O
most O
current O
3D B-MANP
printing E-MANP
method O
involves O
the O
combination O
of O
additional O
processes S-CONPRI
, O
such O
as S-MATE
casting O
and O
demolding S-CONPRI
, O
to O
produce O
an O
organ O
model S-CONPRI
. O


This O
method O
requires O
professionals O
to O
invest O
a O
considerable O
amount O
of O
time O
in O
editing O
the O
model S-CONPRI
and O
post-processing S-CONPRI
activities O
. O


In O
this O
work O
, O
embedded B-MANP
three-dimensional I-MANP
printing E-MANP
( O
EMB3D S-MANP
) O
is O
performed O
in O
a O
transparent S-CONPRI
and O
photocrosslinkable S-FEAT
support O
medium O
. O


Based O
on O
a O
photo-curable S-FEAT
hydrogel S-MATE
precursor O
with O
yield B-PRO
stress E-PRO
behavior O
, O
a O
new O
EMB3D S-MANP
printing O
strategy O
is O
developed O
, O
which O
could O
be S-MATE
considered O
as S-MATE
an O
inverse O
process S-CONPRI
. O


During O
printing O
, O
a O
closed O
shell S-MACEQ
is O
formed O
with O
a O
release O
ink S-MATE
using O
a O
capillary B-MACEQ
needle E-MACEQ
. O


After O
printing O
, O
the O
support S-APPL
medium O
is O
photocrosslinked S-FEAT
to O
a O
solid O
part O
, O
and O
the O
object O
is O
peeled O
off O
along O
with O
the O
closed O
shell S-MACEQ
. O


The O
stated O
approach O
makes O
it O
possible O
to O
produce O
transparent S-CONPRI
and O
elastic S-PRO
solid O
objects O
with O
multi-internal O
surfaces S-CONPRI
. O


Moreover O
, O
it O
can O
be S-MATE
applied O
in O
providing O
a O
soft O
, O
dissectible S-CONPRI
, O
accurate S-CHAR
, O
and O
highly O
interactive O
model S-CONPRI
for O
medical S-APPL
doctors O
to O
facilitate O
surgical B-CONPRI
processes E-CONPRI
. O


A O
geometry-based O
model S-CONPRI
for O
predicting O
lack-of-fusion O
porosity S-PRO
is O
presented O
. O


The O
model S-CONPRI
relies O
on O
melt B-PARA
pool I-PARA
dimension E-PARA
, O
hatch B-PARA
spacing E-PARA
and O
layer B-PARA
thickness E-PARA
. O


Porosity S-PRO
( O
or O
density S-PRO
) O
predicted S-CONPRI
with O
the O
model S-CONPRI
agrees O
well O
with O
reported O
literature O
data S-CONPRI
. O


A O
geometry-based O
simulation S-ENAT
is O
used O
to O
predict O
porosity S-PRO
caused O
by O
insufficient O
overlap S-CONPRI
of O
melt B-MATE
pools E-MATE
( O
lack O
of O
fusion S-CONPRI
) O
in O
powder B-MANP
bed I-MANP
fusion E-MANP
. O


The O
inputs O
into O
the O
simulation S-ENAT
are O
hatch B-PARA
spacing E-PARA
, O
layer B-PARA
thickness E-PARA
, O
and O
melt-pool O
cross-sectional O
area S-PARA
. O


Melt-pool O
areas S-PARA
used O
in O
the O
simulations S-ENAT
can O
be S-MATE
obtained O
from O
experiments O
, O
or O
estimated O
with O
the O
analytical O
Rosenthal B-CONPRI
equation E-CONPRI
. O


The O
necessary O
material S-MATE
constants O
, O
including O
absorptivity O
for O
laser-based O
melting S-MANP
, O
have O
been O
collated O
for O
alloy B-MATE
steels E-MATE
, O
aluminum B-MATE
alloys E-MATE
and O
titanium B-MATE
alloys E-MATE
. O


Comparison O
with O
several O
data S-CONPRI
sets O
from O
the O
literature O
shows O
that O
the O
simulations S-ENAT
correctly O
predict O
process S-CONPRI
conditions O
at O
which O
lack-of-fusion O
porosity S-PRO
becomes O
apparent O
, O
as S-MATE
well O
as S-MATE
the O
rate O
at O
which O
porosity S-PRO
increases O
with O
changes O
in O
process S-CONPRI
conditions O
such O
as S-MATE
beam O
speed O
, O
layer B-PARA
thickness E-PARA
and O
hatch B-PARA
spacing E-PARA
. O


To O
fabricate S-MANP
highly O
complex B-CONPRI
structures E-CONPRI
, O
sacrificial O
support B-MATE
material E-MATE
is O
usually O
needed O
. O


However O
, O
traditional O
petroleum-based S-MATE
support O
materials S-CONPRI
are O
un-sustainable S-CONPRI
, O
non-recyclable S-CONPRI
, O
and O
difficult O
to O
be S-MATE
completely O
removed O
from O
the O
target O
structure S-CONPRI
after O
3D B-CONPRI
processing E-CONPRI
. O


Instead O
, O
cellulose B-MATE
nanocrystals E-MATE
( O
CNC S-ENAT
) O
gel S-MATE
could O
serves O
as S-MATE
an O
interesting O
3D B-MANP
printing E-MANP
support O
material S-MATE
due O
to O
its O
sustainability S-CONPRI
, O
renewability S-CONPRI
, O
and O
potential O
recyclability S-CONPRI
. O


Since O
CNCs S-MATE
are O
highly O
dispersible O
in O
water O
as S-MATE
nanoparticles O
and O
are O
also O
not O
UV S-CONPRI
sensitive O
, O
it O
has O
less O
absorption S-CONPRI
or O
bondability S-CONPRI
with O
other O
UV B-MATE
curable I-MATE
polymer E-MATE
matrices O
. O


This O
allows O
them O
to O
be S-MATE
completely O
washed O
out O
by O
water O
, O
which O
offers O
a O
green O
and O
efficient O
method O
to O
remove O
the O
CNC S-ENAT
support O
material S-MATE
during O
post B-CONPRI
processing E-CONPRI
. O


In O
addition O
, O
with O
increasing O
needs O
for O
more O
intricate O
structures O
, O
combining O
different O
3D B-MANP
printing E-MANP
strategies O
into O
a O
hybrid B-MANP
3D I-MANP
printing E-MANP
platform O
can O
be S-MATE
highly O
beneficial O
. O


In O
this O
work O
, O
a O
multi-materials-multi-methods S-CONPRI
( O
M4 S-MANP
) O
printer S-MACEQ
with O
dual O
direct-ink-write S-MANP
( O
DIW S-MANP
) O
and O
DIW-inkjet B-MANP
printing E-MANP
capability O
was O
used O
to O
fabricate S-MANP
various O
complex B-CONPRI
structures E-CONPRI
while O
using O
CNC S-ENAT
as S-MATE
support O
material S-MATE
. O


After O
3D B-MANP
printing E-MANP
, O
water O
was O
used O
to O
remove O
the O
CNC S-ENAT
support O
structure S-CONPRI
. O


Even O
in O
a O
highly O
confined O
environment O
, O
such O
as S-MATE
the O
inside O
of O
a O
balloon O
structure S-CONPRI
, O
CNC S-ENAT
support O
material S-MATE
was O
still O
easily O
removed O
. O


The O
potential O
of O
using O
sustainable S-CONPRI
CNC S-ENAT
support O
material S-MATE
and O
M4 S-MANP
hybrid B-MANP
3D I-MANP
printing E-MANP
strategies O
to O
fabricate S-MANP
different O
complex B-CONPRI
structures E-CONPRI
was O
demonstrated O
. O


Since O
CNC B-MATE
gel E-MATE
is O
derived O
from O
forestry O
products O
and O
is O
entirely O
water O
based O
, O
the O
3D B-MANP
printing E-MANP
process O
was O
also O
made O
more O
environmentally O
friendly O
, O
sustainable S-CONPRI
, O
and O
potentially O
recyclable S-CONPRI
. O


Composite B-MATE
coatings E-MATE
of O
titanium S-MATE
reinforced S-CONPRI
separately O
with O
hydroxyapatite S-MATE
( O
HAp O
) O
and O
bioglass O
( O
BG O
) O
were O
deposited O
on O
titanium B-MATE
substrate E-MATE
using O
Laser B-MANP
Engineered I-MANP
Net I-MANP
Shaping E-MANP
( O
LENS™ O
) O
. O


The O
microstructure S-CONPRI
, O
phase S-CONPRI
constituents O
, O
in O
vitro O
electrochemical S-CONPRI
, O
tribological S-CONPRI
and O
biological O
properties S-CONPRI
of O
these O
composite B-MATE
coatings E-MATE
deposited O
using O
different O
laser B-PARA
powers E-PARA
was O
studied O
. O


The O
composite B-MATE
coatings E-MATE
showed O
several O
reaction O
products O
such O
as S-MATE
Ca2P2O7 O
, O
CaTiO3 O
, O
Na2Ca2Si3O9 O
due O
to O
high O
temperature S-PARA
interaction O
of O
HAp O
and O
BG O
with O
Ti S-MATE
. O


The O
average S-CONPRI
top O
surface S-CONPRI
hardness S-PRO
of O
the O
Ti B-MATE
substrate E-MATE
was O
148 O
± O
5 O
HV O
and O
that O
of O
the O
composite B-MATE
coatings E-MATE
was O
between O
720 O
and O
740 O
HV O
. O


As S-MATE
a O
result O
, O
the O
composite B-MATE
coatings E-MATE
exhibited O
significant O
increase O
in O
the O
in O
vitro O
wear B-PRO
resistance E-PRO
. O


The O
incorporation O
of O
HAp O
and O
BG O
in O
Ti S-MATE
increased O
the O
corrosion S-CONPRI
current O
, O
possibly O
due O
to O
the O
presence O
of O
residual B-PRO
stresses E-PRO
, O
but O
shifted O
the O
corrosion S-CONPRI
potential O
towards O
noble O
direction O
due O
bioactive O
reinforcements O
. O


In O
vitro O
proliferation O
of O
mouse O
embryonic O
fibroblast S-BIOP
cells S-APPL
( O
NIH3T3 O
) O
was O
found O
to O
be S-MATE
more O
on O
composite B-MATE
coatings E-MATE
than O
on O
titanium B-MATE
substrate E-MATE
demonstrating O
their O
superior O
cell-materials O
interactions O
. O


One-photon O
or O
two O
photon O
absorption S-CONPRI
by O
dye O
molecules O
in O
photopolymers S-MATE
enable O
direct O
2D S-CONPRI
& O
3D S-CONPRI
lithography O
of O
micro/nano O
structures O
with O
high O
spatial O
resolution S-PARA
and O
can O
be S-MATE
used O
effectively O
in O
fabricating S-MANP
artificially O
structured O
nanomaterials S-MATE
. O


Complex O
2D B-FEAT
patterns E-FEAT
and O
3D S-CONPRI
meshes O
were O
fabricated S-CONPRI
with O
sub-micron S-FEAT
resolution S-PARA
, O
in O
commercially O
available O
liquid O
photopolymer S-MATE
to O
show O
the O
impact/versatility O
of O
this O
technique O
. O


Pure O
Al S-MATE
with O
high O
laser S-ENAT
reflectivity O
is O
essentially O
incompatible O
with O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
. O


The O
retention O
of O
a O
large O
number O
of O
unmelted O
particles S-CONPRI
leads O
to O
inferior O
geometrical O
quality S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
printed O
pure O
Al S-MATE
parts O
. O


In O
the O
present O
study O
, O
we O
propose O
decorating O
Al S-MATE
with O
a O
small O
amount O
of O
high O
laser S-ENAT
absorbing O
Co S-MATE
nanoparticles O
on O
the O
surface S-CONPRI
of O
Al S-MATE
powders O
to O
reduce O
laser S-ENAT
reflectivity O
and O
improve O
printability S-PARA
. O


The O
near O
homogenous O
dispersion S-CONPRI
of O
Co S-MATE
slightly O
modified O
the O
surface S-CONPRI
chemical B-CONPRI
composition E-CONPRI
and O
roughened O
the O
powder S-MATE
surface O
. O


This O
approach O
completely O
melted S-CONPRI
the O
particles S-CONPRI
and O
eliminated O
the O
internal O
pores S-PRO
, O
thereby O
favorably O
tuning O
the O
geometrical O
dimensions S-FEAT
. O


Additionally O
, O
the O
introduction O
of O
Co S-MATE
provided O
solid B-MATE
solution E-MATE
strengthening O
and O
precipitation B-MANP
hardening E-MANP
via O
dispersion S-CONPRI
of O
second-phase O
Al9Co2 O
with O
a O
coherent O
interfacial O
relationship O
with O
the O
Al S-MATE
matrix O
. O


The O
tensile B-PRO
properties E-PRO
of O
printed O
Al S-MATE
parts O
were O
comparable O
to O
commercial O
medium-strength O
Al B-MATE
alloys E-MATE
at O
an O
optimal O
Co-content O
of O
0.5 O
wt. O
% O
. O


Addition O
of O
Nb S-MATE
and O
Mo S-MATE
improved O
the O
UTS S-PRO
and O
elongation S-PRO
of O
L-PBF S-MANP
420 B-MATE
stainless I-MATE
steel E-MATE
. O


Nanoscale O
NbC O
precipitated O
in O
the O
presence O
of O
Nb S-MATE
and O
Mo S-MATE
. O


Tempering S-MANP
of O
martensites O
and O
NbC O
correlated S-CONPRI
with O
improved O
mechanical B-CONPRI
properties E-CONPRI
. O


Mechanical S-APPL
and O
corrosion B-PRO
properties E-PRO
of O
L-PBF S-MANP
specimens O
were O
superior O
to O
wrought S-CONPRI
420 B-MATE
stainless I-MATE
steel E-MATE
. O


Niobium S-MATE
( O
Nb S-MATE
) O
and O
molybdenum S-MATE
( O
Mo S-MATE
) O
are O
conventionally O
added O
to O
stainless B-MATE
steels E-MATE
to O
improve O
their O
mechanical S-APPL
and O
corrosion B-PRO
properties E-PRO
. O


However O
, O
the O
effects O
of O
Nb S-MATE
and O
Mo S-MATE
addition O
on O
the O
processing O
and O
properties S-CONPRI
in O
laser-powder O
bed B-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
have O
not O
been O
well O
investigated O
, O
especially O
in O
the O
context O
of O
420 B-MATE
stainless I-MATE
steel E-MATE
. O


In O
this O
study O
, O
420 B-MATE
stainless I-MATE
steel E-MATE
pre-alloyed O
with O
Nb S-MATE
( O
1.2 O
wt. O
% O
) O
and O
Mo S-MATE
( O
0.57 O
wt. O
% O
) O
was O
processed S-CONPRI
by O
L-PBF S-MANP
and O
characterized O
in O
terms O
of O
its O
physical O
, O
mechanical S-APPL
and O
corrosion B-PRO
properties E-PRO
as S-MATE
well O
as S-MATE
microstructure O
. O


The O
addition O
of O
Nb S-MATE
and O
Mo S-MATE
did O
not O
significantly O
affect O
the O
densification S-MANP
of O
420 B-MATE
stainless I-MATE
steel E-MATE
when O
printed O
over O
an O
energy O
range S-PARA
of O
28–75 O
J/mm3 O
and O
a O
maximum O
density S-PRO
of O
99.3 O
± O
0.02 O
% O
theoretical S-CONPRI
at O
63 O
J/mm3 O
was O
achieved O
. O


In O
mechanical B-CHAR
tests E-CHAR
, O
L-PBF S-MANP
420 B-MATE
stainless I-MATE
steel E-MATE
specimens O
exhibited O
higher O
mechanical B-CONPRI
properties E-CONPRI
in O
the O
presence O
of O
Nb S-MATE
and O
Mo S-MATE
. O


After O
heat B-MANP
treatment E-MANP
, O
the O
UTS S-PRO
of O
420 B-MATE
stainless I-MATE
steel E-MATE
with O
Nb S-MATE
and O
Mo S-MATE
improved O
to O
1750 O
± O
30 O
MPa S-CONPRI
and O
elongation S-PRO
to O
9.0 O
± O
0.2 O
% O
, O
much O
higher O
than O
previously O
reported O
properties S-CONPRI
achieved O
in O
L-PBF S-MANP
and O
exceeding O
wrought S-CONPRI
420 B-MATE
stainless I-MATE
steel E-MATE
. O


The O
tempering S-MANP
of O
martensite S-MATE
phases O
as S-MATE
well O
as S-MATE
the O
presence O
of O
nanoscale O
NbC O
were O
found O
to O
correlate O
with O
improved O
mechanical B-CONPRI
properties E-CONPRI
. O


In O
electrochemical B-CHAR
tests E-CHAR
, O
420 B-MATE
stainless I-MATE
steel E-MATE
exhibited O
slightly O
better O
corrosion B-PRO
properties E-PRO
with O
the O
addition O
of O
Nb S-MATE
and O
Mo S-MATE
. O


Bagasse S-MATE
CNF O
inks O
are O
produced O
for O
3D B-MANP
printing E-MANP
by O
direct-ink-writing B-MANP
technology E-MANP
. O


The O
CNF S-MATE
were O
found O
not O
to O
have O
a O
cytotoxic S-CONPRI
potential O
. O


Alginate S-MATE
and O
Ca2+ S-MATE
caused O
significant O
structural O
changes O
to O
the O
3D B-MANP
printed E-MANP
grid O
constructs O
. O


Ca2+ S-MATE
crosslinked O
constructs O
offer O
potential O
for O
personalized O
wound B-MACEQ
dressing I-MACEQ
devices E-MACEQ
. O


Sugarcane B-MATE
bagasse E-MATE
, O
an O
abundant O
residue S-MATE
, O
is O
usually O
burned O
as S-MATE
an O
energy O
source S-APPL
. O


However O
, O
provided O
that O
appropriate O
and O
sustainable S-CONPRI
pulping O
and O
fractionation O
processes S-CONPRI
are O
applied O
, O
bagasse S-MATE
can O
be S-MATE
utilized O
as S-MATE
a O
main O
source S-APPL
of O
cellulose B-MATE
nanofibrils E-MATE
( O
CNF S-MATE
) O
. O


We O
explored O
in O
this O
study O
the O
production S-MANP
of O
CNF B-MATE
inks E-MATE
for O
3D B-MANP
printing E-MANP
by O
direct-ink-writing B-MANP
technology E-MANP
. O


The O
CNF S-MATE
were O
tested O
against O
L929 B-MATE
fibroblasts E-MATE
cell S-APPL
line O
and O
we O
confirmed O
that O
the O
CNF S-MATE
from O
soda B-MATE
bagasse I-MATE
fibers E-MATE
were O
found O
not O
to O
have O
a O
cytotoxic S-CONPRI
potential O
. O


Additionally O
, O
we O
demonstrated O
that O
the O
alginate S-MATE
and O
Ca2+ S-MATE
caused O
significant O
dimensional O
changes O
to O
the O
3D B-CONPRI
printed I-CONPRI
constructs E-CONPRI
. O


The O
CNF-alginate S-MATE
grids O
exhibited O
a O
lateral B-CONPRI
expansion E-CONPRI
after O
printing O
and O
then O
shrank O
due O
to O
the O
cross-linking S-CONPRI
with O
the O
Ca2+ S-MATE
. O


The O
release O
of O
Ca2+ S-MATE
from O
the O
CNF S-MATE
and O
CNF-alginate S-MATE
constructs O
was O
quantified O
thus O
providing O
more O
insight O
about O
the O
CNF S-MATE
as S-MATE
carrier O
for O
Ca2+ S-MATE
. O


This O
, O
combined O
with O
3D B-MANP
printing E-MANP
, O
offers O
potential O
for O
personalized O
wound B-MACEQ
dressing I-MACEQ
devices E-MACEQ
, O
i.e O
. O


Herein O
, O
we O
developed O
a O
direct-write O
printing B-MANP
process E-MANP
capable O
of O
producing O
versatile O
biomimetic S-CONPRI
patterns O
with O
aligned O
neurites O
using O
multiple O
cell S-APPL
types O
. O


After O
two O
weeks O
of O
differentiation O
, O
aligned O
neurites O
were O
induced O
by O
the O
contractile O
force S-CONPRI
of O
the O
printed O
cells S-APPL
. O


Finally O
, O
we O
demonstrated O
the O
usefulness O
of O
the O
printing B-MANP
process E-MANP
by O
fabricating S-MANP
a O
Y-shaped O
branch O
and O
six-layered O
pattern S-CONPRI
. O


The O
six-layered O
pattern S-CONPRI
mimicking O
cerebral O
cortex O
tissue O
was O
produced O
by O
precise O
printing O
of O
two O
different O
colored O
cells S-APPL
. O


These O
results O
indicate O
that O
versatile O
biomimetic S-CONPRI
neural O
constructs O
composed O
of O
multiple O
cell S-APPL
types O
can O
be S-MATE
produced O
by O
our O
new O
direct-write O
printing B-MANP
process E-MANP
. O


Electrets S-MATE
have O
been O
increasingly O
investigated O
for O
their O
high O
piezoelectric B-PRO
sensitivity E-PRO
for O
sensing S-APPL
and O
energy B-CONPRI
harvesting E-CONPRI
applications O
, O
but O
fabricating S-MANP
complex O
3D B-CONPRI
structures E-CONPRI
for O
optimum O
performance S-CONPRI
has O
remained O
challenging O
. O


3D B-MANP
printing E-MANP
capabilities O
have O
likewise O
become O
a O
mature O
manufacturing B-MANP
technology E-MANP
widely O
used O
for O
end-user O
customization O
and O
rapid B-ENAT
prototyping E-ENAT
, O
but O
limitations O
on O
materials S-CONPRI
and O
geometries S-CONPRI
have O
complicated O
the O
incorporation O
of O
electroactive B-CONPRI
structures E-CONPRI
. O


In O
this O
paper O
, O
the O
first O
completely O
3D B-MANP
printed E-MANP
porous O
piezoelectret S-CONPRI
is O
demonstrated O
. O


These O
samples S-CONPRI
were O
structured O
using O
standard S-CONPRI
infill S-PARA
patterns O
commonly O
used O
in O
3D B-MANP
printing E-MANP
, O
allowing O
easy O
incorporation O
with O
current O
3D B-ENAT
printing I-ENAT
technology E-ENAT
. O


Pores S-PRO
generated O
by O
fused-filament B-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
are O
characterized O
, O
charged O
, O
and O
the O
resultant O
piezoelectret S-CONPRI
activity O
measured O
. O


Analytical O
electromechanical B-CONPRI
models E-CONPRI
are O
used O
to O
understand O
and O
compare O
the O
measured O
charge B-PARA
density E-PARA
and O
piezoelectric B-CONPRI
coefficients E-CONPRI
. O


The O
piezoelectric B-CONPRI
coefficient E-CONPRI
is O
found O
to O
increase O
strongly O
with O
decreasing O
infill B-PARA
percentages E-PARA
. O


An O
average S-CONPRI
piezoelectric O
d33 O
coefficient O
of O
87 O
pC S-MATE
N−1 O
is O
achieved O
for O
5 O
% O
infill S-PARA
samples O
and O
is O
found O
to O
be S-MATE
stable O
for O
a O
period O
of O
at O
least O
2 O
weeks O
, O
competitive O
with O
many O
other O
state-of-the-art S-CONPRI
single-pore O
piezoelectretic B-MATE
materials E-MATE
. O


These O
results O
provide O
a O
first O
step S-CONPRI
in O
using O
3D B-MANP
printing E-MANP
techniques O
to O
optimize O
and O
integrate O
piezoelectrets S-MATE
into O
parts O
, O
allowing O
a O
useful O
new O
electroactive B-CONPRI
functionality E-CONPRI
for O
additive B-MANP
manufacturing E-MANP
. O


Three-dimensionally S-CONPRI
( O
3D S-CONPRI
) O
printed O
flexible O
piezoresistive B-MACEQ
composite I-MACEQ
sensors E-MACEQ
have O
provided O
valuable O
solutions O
for O
the O
personalized O
therapeutic S-CONPRI
development O
due O
to O
their O
promising O
capability O
in O
biomonitoring B-APPL
applications E-APPL
. O


Silicone B-MATE
rubber E-MATE
( O
SR S-MATE
) O
matrix O
is O
an O
important O
candidate O
to O
enable O
flexibility S-PRO
to O
the O
3D B-MANP
printed E-MANP
devices O
. O


However O
, O
3D B-MANP
printing E-MANP
of O
silicone B-MATE
inks E-MATE
blended O
with O
conductive O
fillers O
is O
limited O
due O
to O
the O
high O
viscosity S-PRO
, O
long O
curing B-PARA
time E-PARA
, O
and O
high O
percolation B-PARA
threshold E-PARA
. O


In O
the O
present O
study O
, O
a O
novel O
high-speed O
material B-MANP
jetting E-MANP
( O
MJ S-MANP
) O
3D B-MANP
printing E-MANP
of O
high-viscosity O
conductive O
inks O
based O
on O
the O
mixture O
of O
a O
UV S-CONPRI
crosslinkable O
silicone B-MATE
rubber E-MATE
and O
milled B-MATE
carbon I-MATE
fibers E-MATE
( O
MCF S-MATE
) O
is O
demonstrated O
. O


The O
MCF S-MATE
content O
was O
optimized O
for O
printability S-PARA
, O
UV B-PRO
curability E-PRO
, O
and O
electrical B-PRO
conductivity E-PRO
. O


The O
sensors S-MACEQ
( O
with O
30 O
wt O
. O


% O
MCF S-MATE
content O
) O
show O
high O
flexibility S-PRO
and O
foldability S-PRO
as S-MATE
well O
as S-MATE
a O
high O
resistance B-PRO
sensitivity E-PRO
to O
sever O
bending B-CHAR
tests E-CHAR
. O


The O
stretchability S-FEAT
of O
3D B-MANP
printed E-MANP
sensors O
was O
further O
improved O
by O
sandwiching S-CONPRI
the O
MCF/SR S-MATE
sensing O
layer S-PARA
between O
the O
SR S-MATE
layers O
. O


The O
electromechanical S-CONPRI
evaluation O
of O
the O
sandwiched B-MACEQ
MCF/SR I-MACEQ
sensors E-MACEQ
( O
S-MCF/SR S-MACEQ
) O
confirmed O
the O
high O
piezoresistive B-PRO
sensitivity E-PRO
of O
sensors S-MACEQ
( O
gauge B-PRO
factor E-PRO
in O
order O
of O
∼400 O
) O
. O


Finally O
, O
the O
3D B-MANP
printed E-MANP
sensors O
were O
employed O
for O
monitoring O
human B-CONPRI
joint I-CONPRI
motions E-CONPRI
to O
demonstrate O
the O
potential O
application O
in O
monitoring O
biosignals S-CONPRI
. O


Polymer S-MATE
bonding S-CONPRI
of O
gas-atomized B-MATE
lightweight I-MATE
permanent I-MATE
magnet E-MATE
MnAlC O
particles S-CONPRI
. O


Optimized O
particle S-CONPRI
size O
leads O
to O
flexible O
filament S-MATE
with O
high O
filling B-PARA
factor E-PARA
( O
80 O
wt O
% O
) O
. O


Extrusion S-MANP
of O
continuous O
permanent B-MATE
magnet I-MATE
MnAlC I-MATE
filaments E-MATE
( O
length O
over O
10 O
m O
) O
. O


No O
deterioration O
of O
permanent B-CONPRI
magnet I-CONPRI
properties E-CONPRI
of O
MnAlC B-MATE
particles E-MATE
along O
processing O
. O


3D-printed S-MANP
permanent O
magnet S-APPL
objects O
avoiding O
the O
use O
of O
critical O
raw B-MATE
materials E-MATE
. O


Additive B-MANP
manufacturing E-MANP
is O
an O
attractive O
technology S-CONPRI
for O
many O
high-tech O
sectors O
such O
as S-MATE
energy O
, O
automotive S-APPL
and O
aerospace S-APPL
because O
of O
the O
freedom O
in O
designing O
and O
high O
performance S-CONPRI
of O
the O
fabricated S-CONPRI
objects O
. O


In O
the O
field O
of O
permanent B-MATE
magnets E-MATE
there O
is O
an O
increasing O
interest O
for O
applying O
this O
technology S-CONPRI
. O


However O
, O
key O
points O
need O
to O
be S-MATE
faced O
for O
obtaining O
products O
with O
non-deteriorated B-CONPRI
magnetic I-CONPRI
properties E-CONPRI
. O


Herein O
, O
we O
report O
on O
the O
preparation O
of O
MnAlC-based B-MACEQ
flexible I-MACEQ
filament E-MACEQ
with O
permanent B-CONPRI
magnet I-CONPRI
properties E-CONPRI
and O
a O
high O
filling B-PARA
factor E-PARA
of O
80 O
wt O
% O
resulting O
from O
an O
optimum O
fine-to-coarse O
particle S-CONPRI
ratio O
( O
25/75 O
) O
, O
which O
has O
been O
successfully O
used O
for O
3D-printing S-MANP
magnetic O
objects O
. O


Particles S-CONPRI
of O
MnAlC S-MATE
–rare O
earth-free O
permanent O
magnet– O
have O
been O
produced O
in O
nearly O
spherical S-CONPRI
shape O
with O
mean O
sizes O
of O
16 O
and O
30 O
μm O
by O
gas B-MANP
atomization E-MANP
. O


This O
has O
allowed O
for O
the O
fabrication S-MANP
of O
a O
permanent B-MATE
magnet I-MATE
composite E-MATE
, O
MnAlC/ABS S-MATE
, O
with O
a O
large O
concentration O
of O
MnAlC B-MATE
particles E-MATE
. O


The O
methodology S-CONPRI
here O
used O
has O
made O
possible O
the O
preparation O
of O
composite S-MATE
, O
filament S-MATE
and O
3D-printed S-MANP
objects O
with O
no O
degradation S-CONPRI
of O
the O
permanent B-CONPRI
magnet I-CONPRI
properties E-CONPRI
. O


The O
reported O
results O
open O
a O
new O
route O
to O
advance O
in O
the O
application O
of O
3D-printing S-MANP
to O
fabricate S-MANP
permanent O
magnet S-APPL
elements S-MATE
with O
a O
high O
filling B-PARA
factor E-PARA
for O
technological O
applications O
. O


We O
introduce O
an O
algorithm S-CONPRI
to O
generate O
tool B-CONPRI
paths E-CONPRI
using O
G2/G3-codes O
. O


The O
algorithms S-CONPRI
reduce O
time O
and O
cost O
while O
they O
enhance O
the O
quality S-CONPRI
of O
printed O
objects O
. O


Extrusion-based O
printing O
frequently O
requires O
a O
hollowing O
step S-CONPRI
to O
remove O
material S-MATE
from O
inside O
of O
artifacts O
and O
subsequently O
reduce O
the O
amount O
of O
material S-MATE
, O
printing O
time O
, O
product O
weight S-PARA
, O
energy O
consumption O
, O
and O
ultimately O
, O
the O
cost O
. O


In O
addition O
to O
reducing O
stress B-CHAR
concentration E-CHAR
through O
their O
inherently O
smooth B-FEAT
boundaries E-FEAT
, O
these O
spheroids O
require O
no O
additional O
support B-FEAT
structure E-FEAT
, O
when O
properly O
designed S-FEAT
. O


Here O
, O
spheroids O
are O
arranged O
by O
the O
Voronoi O
diagram O
of O
3D S-CONPRI
ellipsoids O
and O
the O
tool B-CONPRI
path E-CONPRI
, O
including O
circular O
printing O
motions O
, O
is O
produced O
using O
the O
Voronoi O
diagram O
of O
circular O
2D S-CONPRI
disks O
. O


The O
proposed O
algorithms S-CONPRI
are O
implemented O
as S-MATE
the O
HollowTron O
webserver O
and O
are O
freely O
available O
from O
Voronoi O
Diagram O
Research S-CONPRI
Center O
. O


3D B-MANP
printing E-MANP
allows O
rapid B-MANP
fabrication E-MANP
of O
complex O
objects O
from O
digital O
designs S-FEAT
. O


One O
3D-printing S-MANP
process O
, O
direct B-ENAT
laser I-ENAT
writing E-ENAT
, O
polymerises S-CONPRI
a O
light-sensitive B-MATE
material E-MATE
by O
steering S-PARA
a O
focused B-CONPRI
laser I-CONPRI
beam E-CONPRI
through O
the O
shape O
of O
the O
object O
to O
be S-MATE
created O
. O


The O
highest-resolution S-PARA
direct B-MANP
laser I-MANP
writing I-MANP
systems E-MANP
use O
a O
femtosecond B-CONPRI
laser E-CONPRI
, O
steered O
using O
mechanised O
stages O
or O
galvanometer-controlled B-MACEQ
mirrors E-MACEQ
, O
to O
effect O
two-photon B-ENAT
polymerisation E-ENAT
. O


Here O
we O
report O
a O
new O
high-resolution S-PARA
direct B-MANP
laser I-MANP
writing I-MANP
system E-MANP
that O
employs O
a O
resonant O
mirror B-MACEQ
scanner E-MACEQ
to O
achieve O
a O
significant O
increase O
in O
printing B-PARA
speed E-PARA
over O
current O
methods O
while O
maintaining O
resolution S-PARA
on O
the O
order O
of O
a O
micron S-FEAT
. O


This O
printer S-MACEQ
is O
based O
on O
a O
software S-CONPRI
modification O
to O
a O
commercially O
available O
resonant-scanning O
two-photon B-MACEQ
microscope E-MACEQ
. O


We O
demonstrate O
the O
complete O
process B-ENAT
chain E-ENAT
from O
hardware O
configuration S-CONPRI
and O
control O
software S-CONPRI
to O
the O
printing O
of O
objects O
of O
approximately O
400 O
× O
400 O
× O
350 O
μm O
, O
and O
validate O
performance S-CONPRI
with O
objective O
benchmarks O
. O


Released O
under O
an O
open-source S-CONPRI
license O
, O
this O
work O
makes O
micron-scale S-FEAT
3D B-MANP
printing E-MANP
available O
at O
little O
or O
no O
cost O
to O
the O
large O
community O
of O
two-photon B-MACEQ
microscope E-MACEQ
users O
, O
and O
paves O
the O
way O
toward O
widespread O
availability O
of O
precision-printed O
devices O
. O


The O
introduction O
of O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
printing O
in O
the O
pharmaceutical S-APPL
arena O
has O
caused O
a O
major O
shift O
towards O
the O
advancement O
of O
modern B-CONPRI
medicines E-CONPRI
, O
including O
drug O
products O
with O
different O
configurations O
and O
complex B-CONPRI
geometries E-CONPRI
. O


Otherwise O
challenging O
to O
create O
via O
conventional O
pharmaceutical B-CONPRI
techniques E-CONPRI
, O
3D B-ENAT
printing I-ENAT
technologies E-ENAT
have O
been O
explored O
for O
the O
fabrication S-MANP
of O
multi-drug B-CONPRI
loaded I-CONPRI
dosage E-CONPRI
forms O
to O
reduce O
pill B-CONPRI
burden E-CONPRI
and O
improve O
patient B-CONPRI
adherence E-CONPRI
. O


In O
this O
study O
, O
stereolithography S-MANP
( O
SLA S-MACEQ
) O
, O
a O
vat B-MANP
polymerisation E-MANP
technique O
, O
was O
used O
to O
manufacture S-CONPRI
a O
multi-layer O
3D B-MANP
printed E-MANP
oral O
dosage O
form O
( O
polyprintlet S-MATE
) O
incorporating O
four O
antihypertensive B-MATE
drugs E-MATE
including O
irbesartan S-MATE
, O
atenolol S-MATE
, O
hydrochlorothiazide S-MATE
and O
amlodipine S-MATE
. O


Although O
successful O
in O
its O
fabrication S-MANP
, O
for O
the O
first O
time O
, O
we O
report O
an O
unexpected O
chemical B-CONPRI
reaction E-CONPRI
between O
a O
photopolymer S-MATE
and O
drug O
. O


Fourier B-ENAT
Transform I-ENAT
Infrared E-ENAT
( O
FTIR S-CHAR
) O
spectroscopy S-CONPRI
and O
Nuclear B-CONPRI
Magnetic I-CONPRI
Resonance E-CONPRI
( O
NMR S-CHAR
) O
spectroscopy S-CONPRI
confirmed O
the O
occurrence O
of O
a O
Michael B-CONPRI
addition I-CONPRI
reaction E-CONPRI
between O
the O
diacrylate S-MATE
group O
of O
the O
photoreactive B-MATE
monomer E-MATE
and O
the O
primary B-MATE
amine E-MATE
group O
of O
amlodipine S-MATE
. O


The O
study O
herein O
demonstrates O
the O
importance O
of O
careful O
selection O
of O
photocurable B-MATE
resins E-MATE
for O
the O
manufacture S-CONPRI
of O
drug-loaded B-CONPRI
oral I-CONPRI
dosage E-CONPRI
forms O
via O
SLA S-MACEQ
3D B-ENAT
printing I-ENAT
technology E-ENAT
. O


Photopolymerization-based S-CONPRI
3D B-MANP
printing E-MANP
has O
emerged O
as S-MATE
a O
promising O
technique O
to O
fabricate B-CONPRI
3D I-CONPRI
structures E-CONPRI
. O


However O
, O
during O
the O
printing B-MANP
process E-MANP
, O
polymerized B-MATE
materials E-MATE
such O
as S-MATE
hydrogels O
often O
become O
highly O
light-scattering S-CONPRI
, O
thus O
perturbing B-CONPRI
incident I-CONPRI
light I-CONPRI
distribution E-CONPRI
and O
thereby O
deteriorating O
the O
final O
print B-PARA
resolution E-PARA
. O


To O
overcome O
this O
scattering-induced O
resolution B-CONPRI
deterioration E-CONPRI
, O
we O
developed O
a O
novel O
method O
termed O
flashing B-MANP
photopolymerization E-MANP
( O
FPP S-MANP
) O
. O


Our O
FPP S-MANP
approach O
is O
informed O
by O
the O
fundamental O
kinetics O
of O
photopolymerization S-MANP
reactions O
, O
where O
light B-CONPRI
exposure E-CONPRI
is O
delivered O
in O
millisecond-scale S-CONPRI
‘ O
flashes O
’ O
, O
as S-MATE
opposed O
to O
continuous B-CONPRI
light I-CONPRI
exposure E-CONPRI
. O


During O
the O
period O
of O
flash B-CONPRI
exposure E-CONPRI
, O
the O
prepolymer B-MATE
material E-MATE
negligibly O
scatters O
light O
. O


The O
material S-MATE
then O
polymerizes S-CONPRI
and O
opacifies S-CONPRI
in O
absence O
of O
light O
, O
therefore O
the O
exposure B-CONPRI
pattern E-CONPRI
is O
not O
perturbed O
by O
scattering O
. O


Compared O
to O
the O
conventional O
use O
of O
a O
continuous B-CONPRI
wave E-CONPRI
( O
CW S-CONPRI
) O
light B-MACEQ
source E-MACEQ
, O
the O
FPP S-MANP
fabrication B-PARA
resolution E-PARA
is O
improved O
. O


FPP S-MANP
also O
shows O
little O
dependency O
on O
the O
exposure S-CONPRI
, O
thus O
minimizing O
trial-and-error S-CONPRI
type O
optimization S-CONPRI
. O


Using O
FPP S-MANP
, O
we O
demonstrate O
its O
use O
in O
generating O
high-fidelity S-CONPRI
3D B-CONPRI
printed I-CONPRI
constructs E-CONPRI
. O


Material S-MATE
based O
actuation O
with O
metallic B-MATE
fibers E-MATE
, O
for O
example O
shape B-MATE
memory I-MATE
alloys E-MATE
( O
SMA O
) O
is O
gaining O
popularity O
to O
replace O
the O
conventional O
bulky O
actuators S-MACEQ
used O
for O
shape O
morphing O
in O
aerospace S-APPL
sectors O
. O


However O
, O
Joule O
heating S-MANP
arising O
from O
electrical S-APPL
actuation O
of O
SMA O
affects O
the O
interfacial B-CONPRI
bonding E-CONPRI
between O
the O
SMA O
and O
the O
composite S-MATE
matrix O
and O
thus O
reduces O
the O
life O
span O
of O
the O
structure S-CONPRI
. O


Insulating S-CONPRI
the O
SMA O
from O
the O
composite S-MATE
matrix O
will O
tremendously O
increase O
the O
service B-CONPRI
life E-CONPRI
of O
these O
reconfigurable O
structures O
. O


Three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
printing O
of O
functional O
elements S-MATE
during O
the O
fabrication S-MANP
phase O
of O
the O
composite B-CONPRI
structures E-CONPRI
permits O
the O
flexibility S-PRO
to O
form O
complex O
shaped O
reconfigurable O
lightweight S-CONPRI
aerospace B-MACEQ
components E-MACEQ
. O


Here O
, O
we O
present O
a O
novel O
technique O
to O
embed O
polymer S-MATE
encapsulated S-CONPRI
functional O
elements S-MATE
into O
structural O
composites S-MATE
. O


We O
use O
the O
direct-write O
( O
DW O
) O
technique O
to O
coat O
SMA O
with O
a O
polymer S-MATE
solution O
while O
simultaneously O
printing O
them O
onto O
carbon B-MATE
fiber E-MATE
prepreg O
. O


We O
develop O
high O
performance S-CONPRI
polymeric O
inks O
- O
polyetherimide O
and O
polycarbonate S-MATE
- O
compatible O
with O
the O
DW O
technique O
, O
the O
coating S-APPL
, O
as S-MATE
well O
as S-MATE
the O
composite S-MATE
. O


In O
addition O
to O
SMA O
, O
the O
technique O
can O
also O
be S-MATE
easily O
extended O
to O
embed O
various O
kinds O
of O
other O
functional O
fibers S-MATE
into O
composites S-MATE
, O
in O
any O
shape O
or O
form O
. O


Additionally O
, O
we O
also O
demonstrate O
the O
application O
of O
this O
technique O
to O
integrate O
SMA O
with O
polymeric O
structures O
towards O
actuators S-MACEQ
for O
robotics S-APPL
grippers O
or O
surgical B-MACEQ
tools E-MACEQ
. O


The O
emergence O
of O
smart O
technologies S-CONPRI
is O
spurring O
the O
development O
of O
a O
wider O
range S-PARA
of O
applications O
for O
stretchable S-FEAT
and O
conformable S-CONPRI
sensors O
, O
as S-MATE
the O
design B-CONPRI
flexibility E-CONPRI
offered O
by O
additive B-MANP
manufacturing E-MANP
may O
enable O
the O
production S-MANP
of O
sensors S-MACEQ
that O
are O
superior O
to O
those O
produced O
by O
conventional B-MANP
manufacturing E-MANP
techniques O
. O


In O
this O
work O
, O
a O
multi-material B-MANP
3D I-MANP
printing E-MANP
system O
with O
three O
extrusion B-MACEQ
heads E-MACEQ
was O
developed O
to O
fabricate S-MANP
a O
stretchable S-FEAT
, O
soft B-MACEQ
pressure I-MACEQ
sensor E-MACEQ
built O
using O
an O
ionic B-MATE
liquid E-MATE
( O
IL S-MATE
) O
–based O
pressure-sensitive B-CONPRI
layer E-CONPRI
that O
was O
sandwiched O
between O
carbon B-MATE
nanotube E-MATE
( O
CNT S-MATE
) O
–based O
stretchable S-FEAT
electrodes S-MACEQ
and O
encapsulated S-CONPRI
within O
stretchable S-FEAT
top O
and O
bottom O
insulating B-CONPRI
layers E-CONPRI
. O


The O
sensor S-MACEQ
materials S-CONPRI
were O
modified O
in O
order O
to O
achieve O
3D B-CONPRI
printable I-CONPRI
characteristics E-CONPRI
. O


The O
capability O
of O
the O
system O
was O
tested O
by O
printing O
structures O
made O
from O
three O
materials S-CONPRI
and O
a O
multilayer B-MACEQ
sensor E-MACEQ
via O
an O
extrusion-based B-MANP
direct-print I-MANP
process E-MANP
. O


Multi-material B-MANP
3D I-MANP
printing E-MANP
of O
the O
sensor S-MACEQ
was O
successfully O
realized O
, O
as S-MATE
the O
sensing S-APPL
material S-MATE
retained O
its O
functionality O
once O
the O
printing B-MANP
process E-MANP
was O
complete O
. O


Silicone-based B-MATE
materials E-MATE
are O
commonly O
used O
in O
medical B-APPL
applications E-APPL
such O
as S-MATE
pre-surgery O
models O
or O
implants S-APPL
, O
leading O
to O
interesting O
biomimetic S-CONPRI
mechanical O
properties S-CONPRI
. O


Emergence O
of O
3D B-MANP
printing E-MANP
and O
particularly O
liquid B-MANP
deposition I-MANP
modelling E-MANP
( O
LDM S-MANP
) O
has O
shown O
that O
specific O
rheological S-PRO
behaviors O
, O
particularly O
yield B-PRO
stress E-PRO
characters O
, O
were O
required O
to O
achieve O
efficient O
LDM S-MANP
. O


Unfortunately O
, O
standard S-CONPRI
silicone S-MATE
formulations O
seldom O
present O
such O
behaviors O
and O
are O
then O
proved O
to O
have O
low O
applicability O
in O
LDM-based S-MANP
3D S-CONPRI
printing.In O
the O
present O
study O
, O
polyethylene B-MATE
glycol E-MATE
of O
different O
lengths O
were O
added O
as S-MATE
yield O
stress S-PRO
agents O
in O
a O
bi-component B-MATE
silicone E-MATE
and O
were O
demonstrated O
to O
operate O
a O
drastic O
improvement O
of O
the O
material S-MATE
rheological O
behaviors O
, O
without O
significant O
impact S-CONPRI
on O
the O
final O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
material S-MATE
. O


An O
interesting O
relationship O
was O
demonstrated O
between O
dynamic S-CONPRI
yield O
stress S-PRO
values O
and O
reachable O
3D B-FEAT
geometries E-FEAT
( O
the O
higher O
σys O
, O
the O
more O
complex O
the O
3D B-MANP
printed E-MANP
shape O
can O
be S-MATE
) O
but O
the O
study O
also O
revealed O
that O
it O
is O
not O
the O
only O
key O
factor O
to O
ensure O
the O
printability S-PARA
of O
viscoelastic S-PRO
materials S-CONPRI
when O
highly O
complex B-CONPRI
geometries E-CONPRI
are O
seek O
; O
tack O
and O
melt B-PRO
strength E-PRO
have O
also O
to O
be S-MATE
investigated O
. O


To O
improve O
the O
formability S-PRO
and O
properties S-CONPRI
of O
calcia S-MATE
( O
CaO S-MATE
) O
based O
ceramic B-MACEQ
core E-MACEQ
, O
the O
binder-jet B-MANP
3D-printing E-MANP
was O
performed O
to O
fabricate S-MANP
porous O
CaO/caicium B-MATE
zirconate E-MATE
( O
CaZrO3 S-MATE
) O
ceramic B-MACEQ
core E-MACEQ
composites O
with O
two O
nanozirconia S-MATE
addition O
methods O
. O


The O
effects O
of O
the O
nanozirconia S-MATE
addition O
method O
and O
additive S-MATE
amount O
on O
the O
properties S-CONPRI
of O
the O
3D-printed S-MANP
CaO/CaZrO3 O
bodies O
were O
investigated O
. O


The O
dimensional B-CHAR
accuracy E-CHAR
, O
surface B-PRO
roughness E-PRO
, O
relative B-PRO
density E-PRO
, O
bending B-PRO
strength E-PRO
, O
and O
hydration O
resistance S-PRO
of O
CaO/CaZrO3 S-MATE
bodies O
printed O
with O
a O
nanozirconia S-MATE
suspension O
binder S-MATE
for O
deposition S-CONPRI
in O
the O
CaO S-MATE
powder O
layer S-PARA
were O
better O
than O
those O
of O
CaO/CaZrO3 S-MATE
bodies O
printed O
in O
the O
traditional O
manner O
of O
directly O
mixing S-CONPRI
nanozirconia O
in O
the O
CaO S-MATE
powder O
. O


Application O
of O
the O
nanozirconia S-MATE
suspension O
uniformly O
capped O
nanozirconia S-MATE
particles O
on O
the O
surfaces S-CONPRI
of O
the O
CaO S-MATE
particles O
and O
filled O
the O
pores S-PRO
of O
the O
CaO S-MATE
powder O
layer S-PARA
, O
which O
afforded O
denser O
and O
more O
uniform O
green B-CONPRI
bodies E-CONPRI
. O


After O
sintering S-MANP
at O
1500 O
°C O
, O
the O
ZrO2 S-MATE
formed O
thicker O
and O
denser O
CaZrO3 S-MATE
layers O
with O
the O
CaO S-MATE
over O
the O
CaO S-MATE
grain O
surfaces S-CONPRI
, O
which O
improved O
the O
strength S-PRO
and O
hydration O
resistance S-PRO
of O
the O
sintered S-MANP
CaO/CaZrO3 S-MATE
ceramic O
core S-MACEQ
bodies O
, O
and O
certainly O
reduced O
their O
collapsibility S-CONPRI
. O


A O
3D S-CONPRI
numerical O
model S-CONPRI
is O
developed O
to O
study O
the O
flow O
mechanism S-CONPRI
with O
rotation O
nozzle S-MACEQ
at O
the O
corner O
under O
various O
conditions O
during O
the O
extrusion S-MANP
and O
deposition B-MANP
process E-MANP
; O
Material S-MATE
rheological O
properties S-CONPRI
have O
little O
effects O
on O
material S-MATE
distribution S-CONPRI
ratio O
at O
corners O
, O
while O
process B-CONPRI
parameters E-CONPRI
affect O
material S-MATE
distribution S-CONPRI
ratio O
significantly O
; O
Increasing O
corner O
radius O
and O
relative O
nozzle S-MACEQ
travel O
speed O
while O
decreasing O
nozzle S-MACEQ
aspect B-FEAT
ratio E-FEAT
are O
beneficial O
to O
suppressing O
uneven O
mass O
distribution S-CONPRI
at O
corners O
; O
When O
conducting O
corner O
printing O
with O
rotational O
rectangular O
nozzle S-MACEQ
, O
a O
greater O
amount O
of O
material S-MATE
is O
deposited O
inside O
the O
filament S-MATE
and O
hence O
tearing O
and O
skewing O
will O
occur O
on O
the O
surface S-CONPRI
of O
the O
printed O
filament S-MATE
. O


With O
the O
aim O
of O
maintaining O
the O
surface B-FEAT
finish E-FEAT
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
printed O
filament S-MATE
, O
a O
3D S-CONPRI
numerical O
model S-CONPRI
is O
developed O
to O
study O
the O
flow O
mechanism S-CONPRI
at O
a O
corner O
under O
various O
conditions O
during O
the O
extrusion S-MANP
and O
deposition B-MANP
processes E-MANP
with O
rotational O
nozzle S-MACEQ
. O


After O
experimental S-CONPRI
validation O
, O
the O
numerical O
model S-CONPRI
is O
employed O
to O
study O
the O
material S-MATE
flow O
mechanism S-CONPRI
under O
various O
conditions O
. O


The O
results O
indicate O
that O
the O
rheological B-PRO
properties E-PRO
have O
little O
effect O
on O
the O
mass O
distribution S-CONPRI
ratio O
. O


However O
, O
a O
high O
relative O
nozzle S-MACEQ
travel O
speed O
, O
larger O
corner O
radii O
and O
lower O
nozzle S-MACEQ
aspect B-FEAT
ratio E-FEAT
is O
a O
promising O
route O
in O
obtaining O
a O
uniform O
material S-MATE
distribution S-CONPRI
ratio O
. O


The O
interlinking O
of O
process B-CONPRI
parameters E-CONPRI
affects O
the O
material S-MATE
distribution S-CONPRI
ratio O
significantly O
as S-MATE
well O
. O


Furthermore O
, O
the O
importance O
of O
the O
factors O
that O
affect O
the O
mass O
distribution S-CONPRI
was O
determined O
quantitatively S-CONPRI
. O


Fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
is O
a O
3D B-MANP
printing E-MANP
technique O
which O
allows O
layer-by-layer S-CONPRI
build-up O
of O
a O
part O
by O
the O
deposition S-CONPRI
of O
thermoplastic B-MATE
material E-MATE
through O
a O
nozzle S-MACEQ
. O


The O
technique O
allows O
for O
complex B-PRO
shapes E-PRO
to O
be S-MATE
made O
with O
a O
degree B-CONPRI
of I-CONPRI
design I-CONPRI
freedom E-CONPRI
unachievable O
with O
traditional B-MANP
manufacturing E-MANP
methods O
. O


However O
, O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
thermoplastic B-MATE
materials E-MATE
used O
are O
low O
compared O
to O
common O
engineering B-MATE
materials E-MATE
. O


In O
this O
work O
, O
composite S-MATE
3D B-MANP
printing E-MANP
feedstocks O
for O
FFF S-MANP
are O
investigated O
, O
wherein O
carbon B-MATE
fibres E-MATE
are O
embedded O
into O
a O
thermoplastic B-MATE
matrix E-MATE
to O
increase O
strength S-PRO
and O
stiffness S-PRO
. O


First O
, O
the O
key O
processing O
parameters S-CONPRI
for O
FFF S-MANP
are O
reviewed O
, O
showing O
how O
fibres S-MATE
alter O
the O
printing B-CONPRI
dynamics E-CONPRI
by O
changing O
the O
viscosity S-PRO
and O
the O
thermal B-CONPRI
profile E-CONPRI
of O
the O
printed O
material S-MATE
. O


The O
state-of-the-art S-CONPRI
in O
composite S-MATE
3D B-MANP
printing E-MANP
is O
presented O
, O
showing O
a O
distinction O
between O
short B-MATE
fibre I-MATE
feedstocks E-MATE
versus O
continuous B-MATE
fibre I-MATE
feedstocks E-MATE
. O


An O
experimental S-CONPRI
study O
was O
performed O
to O
benchmark S-MANS
these O
two O
methods O
. O


It O
is O
found O
that O
printing O
of O
continuous B-MATE
carbon I-MATE
fibres E-MATE
using O
the O
MarkOne B-MACEQ
printer E-MACEQ
gives O
significant O
increases O
in O
performance S-CONPRI
over O
unreinforced B-MATE
thermoplastics E-MATE
, O
with O
mechanical B-CONPRI
properties E-CONPRI
in O
the O
same O
order O
of O
magnitude S-PARA
of O
typical O
unidirectional B-MATE
epoxy I-MATE
matrix I-MATE
composites E-MATE
. O


The O
method O
, O
however O
, O
is O
limited O
in O
design B-CONPRI
freedom E-CONPRI
as S-MATE
the O
brittle S-PRO
continuous O
carbon B-MATE
fibres E-MATE
can O
not O
be S-MATE
deposited O
freely O
through O
small O
steering B-PARA
radii E-PARA
and O
sharp B-FEAT
angles E-FEAT
. O


Filaments S-MATE
with O
embedded O
short O
carbon B-MATE
microfibres E-MATE
( O
∼100 O
μm O
) O
show O
better O
print B-CONPRI
capabilities E-CONPRI
and O
are O
suitable O
for O
use O
with O
standard S-CONPRI
printing O
methods O
, O
but O
only O
offer O
a O
slight O
increase O
in O
mechanical B-CONPRI
properties E-CONPRI
over O
the O
pure O
thermoplastic B-PRO
properties E-PRO
. O


It O
is O
hypothesized O
that O
increasing O
the O
fibre B-CONPRI
length E-CONPRI
in O
short O
fibre B-MATE
filament E-MATE
is O
expected O
to O
lead S-MATE
to O
increased O
mechanical B-CONPRI
properties E-CONPRI
, O
potentially O
approaching O
those O
of O
continuous B-MATE
fibre I-MATE
composites E-MATE
, O
whilst O
keeping O
the O
high O
degree B-CONPRI
of I-CONPRI
design I-CONPRI
freedom E-CONPRI
of O
the O
FFF S-MANP
process O
. O


Water-soluble B-MATE
glass E-MATE
patterned O
by O
3D B-MANP
printing E-MANP
is O
a O
versatile B-MACEQ
tool E-MACEQ
for O
tissue B-CONPRI
engineering E-CONPRI
and O
microfluidics S-CONPRI
. O


Glasses S-MATE
can O
be S-MATE
patterned O
layer-by-layer S-CONPRI
as S-MATE
in O
conventional O
fused B-MANP
deposition I-MANP
modeling E-MANP
but O
also O
along O
3D S-CONPRI
, O
“ O
freeform S-CONPRI
” O
paths O
. O


In O
the O
latter O
approach O
, O
extruding S-MANP
heated O
material S-MATE
through O
a O
nozzle S-MACEQ
translating O
in O
3D B-CONPRI
space E-CONPRI
allows O
for O
fabrication S-MANP
of O
sparse O
, O
freestanding B-CONPRI
networks E-CONPRI
of O
cylindrical B-CONPRI
filaments E-CONPRI
. O


These O
freeform B-CONPRI
structures E-CONPRI
are O
suitable O
for O
sacrificial B-MANP
molding E-MANP
with O
a O
variety O
of O
media O
, O
leaving O
complex O
microchannel B-CONPRI
networks E-CONPRI
. O


However O
, O
3D B-MANP
printing E-MANP
carbohydrate O
glass S-MATE
in O
this O
way O
presents O
several O
unique O
challenges O
: O
1 O
) O
the O
material S-MATE
must O
resist O
degradation S-CONPRI
and O
crystallization S-CONPRI
during O
printing O
, O
2 O
) O
the O
glass S-MATE
must O
be S-MATE
hot O
enough O
to O
flow B-CONPRI
freely E-CONPRI
during O
extrusion S-MANP
and O
fuse S-MANP
to O
the O
printed B-CONPRI
construct E-CONPRI
, O
while O
cooling B-CONPRI
rapidly E-CONPRI
to O
retain O
its O
shape O
upon O
exiting O
the O
nozzle S-MACEQ
, O
3 O
) O
the O
extruder S-MACEQ
needs O
to O
apply O
high O
pressure S-CONPRI
, O
with O
rapid O
stop O
and O
start O
times O
and O
4 O
) O
the O
net O
force S-CONPRI
that O
acts O
on O
the O
filament S-MATE
during O
extrusion S-MANP
must O
be S-MATE
minimized O
so O
that O
the O
filament S-MATE
shape O
is O
predictable S-CONPRI
, O
i.e. O
, O
coincides O
with O
the O
path O
taken O
by O
the O
nozzle S-MACEQ
. O


First O
, O
we O
review O
the O
properties S-CONPRI
of O
commercially O
available O
carbohydrate B-MATE
glasses E-MATE
and O
provide O
a O
guide O
for O
processing O
isomalt S-MATE
, O
our O
material S-MATE
of O
choice O
, O
to O
achieve O
the O
best O
printing B-CONPRI
performance E-CONPRI
. O


A O
pressure-controlled S-CONPRI
, O
piston-driven B-MACEQ
extruder E-MACEQ
is O
then O
described O
which O
allows O
for O
rapid O
responses O
and O
precise B-CONPRI
control E-CONPRI
over O
the O
material B-PARA
flow I-PARA
rate E-PARA
. O


We O
then O
analyze O
the O
heat B-CONPRI
transfer E-CONPRI
within O
the O
filament S-MATE
and O
the O
forces S-CONPRI
that O
contribute O
to O
the O
filament S-MATE
’ O
s S-MATE
final O
shape O
. O


We O
find O
that O
the O
dominant B-CONPRI
force E-CONPRI
is O
due O
to O
the O
radial B-CONPRI
flow E-CONPRI
of O
the O
molten B-MATE
glass E-MATE
as S-MATE
it O
exits O
the O
nozzle S-MACEQ
. O


This O
analysis O
is O
validated O
on O
a O
purpose-built O
isomalt S-MATE
3D B-MACEQ
printer E-MACEQ
, O
which O
we O
utilize O
to O
characterize O
relationships O
between O
extrusion B-PARA
pressure E-PARA
, O
translation B-PARA
speed E-PARA
, O
filament B-PARA
diameter E-PARA
, O
and O
viscous B-CONPRI
force E-CONPRI
. O


The O
insights O
of O
the O
physics S-CONPRI
of O
the O
printing B-MANP
process E-MANP
enable O
fabrication S-MANP
of O
intricate B-CONPRI
freeform I-CONPRI
prints E-CONPRI
as S-MATE
well O
as S-MATE
layer-by-layer O
designs S-FEAT
. O


The O
practical O
and O
theoretical S-CONPRI
considerations O
should O
facilitate O
adoption O
of O
additive B-MANP
manufacturing E-MANP
of O
carbohydrate B-MATE
glasses E-MATE
with O
applications O
to O
a O
wide O
variety O
of O
fields O
, O
including O
tissue B-CONPRI
engineering E-CONPRI
and O
microfluidics S-CONPRI
. O


Multi-material B-MANP
3D I-MANP
printing E-MANP
with O
several O
mechanically O
distinct O
materials S-CONPRI
at O
once O
has O
expanded O
the O
potential O
applications O
for O
additive B-MANP
manufacturing E-MANP
technology O
. O


Fewer O
material S-MATE
options O
exist O
, O
however O
, O
for O
additive B-MANP
systems E-MANP
that O
employ O
vat B-MANP
photopolymerization E-MANP
( O
such O
as S-MATE
stereolithography O
, O
SLA S-MACEQ
, O
and O
digital B-MANP
light I-MANP
projection E-MANP
, O
DLP S-MANP
, O
3D B-MACEQ
printers E-MACEQ
) O
, O
which O
are O
more O
commonly O
used O
for O
advanced B-CONPRI
engineering I-CONPRI
prototypes E-CONPRI
and O
manufacturing S-MANP
. O


Those O
material S-MATE
selections O
that O
do O
exist O
are O
limited O
in O
their O
capacity S-CONPRI
for O
fusion S-CONPRI
due O
to O
disparate O
chemical O
and O
physical B-PRO
properties E-PRO
, O
limiting O
the O
potential O
mechanical S-APPL
range O
for O
multi-material B-MATE
printed I-MATE
composites E-MATE
. O


Here O
, O
we O
present O
an O
ethylene B-MATE
glycol I-MATE
phenyl I-MATE
ether I-MATE
acrylate E-MATE
( O
EGPEA S-MATE
) O
-based O
formulation O
for O
a O
polymer B-MATE
resin E-MATE
yielding O
a O
range S-PARA
of O
elastic B-PRO
moduli E-PRO
between O
0.6 O
MPa S-CONPRI
and O
31 O
MPa S-CONPRI
simply O
by O
altering O
the O
ratio O
of O
monomer S-MATE
and O
crosslinker B-MATE
feedstocks E-MATE
in O
the O
formulation O
. O


This O
simple S-MANP
chemistry S-CONPRI
is O
also O
well O
suited O
to O
form O
seamless B-CONPRI
adhesions E-CONPRI
between O
mechanically B-CONPRI
dissimilar I-CONPRI
formulations E-CONPRI
, O
making O
it O
a O
promising O
candidate O
for O
multi-material B-MANP
DLP I-MANP
3D I-MANP
printing E-MANP
. O


Preliminary O
tests O
with O
these O
polymer S-MATE
formulations O
indicate O
that O
variability S-CONPRI
due O
to O
molecular B-CONPRI
differences E-CONPRI
between O
hard O
and O
soft O
formulations O
is O
less O
than O
3 O
% O
of O
the O
prescribed O
model B-CONPRI
dimensions E-CONPRI
, O
comparable O
to O
existing O
commercial O
DLP S-MANP
and O
SLA S-MACEQ
resins S-MATE
, O
with O
unique O
advantages O
of O
a O
wide O
range S-PARA
of O
elastomer B-PRO
stiffness E-PRO
and O
seamless B-CONPRI
fusion E-CONPRI
for O
3D B-MANP
printing E-MANP
of O
structurally O
detailed O
and O
mechanically O
heterogeneous B-MATE
composites E-MATE
. O


We O
introduce O
a O
novel O
divide-and-conquer O
approach O
for O
3D B-MANP
printing E-MANP
, O
which O
provides O
automatic O
decomposition S-PRO
and O
configuration S-CONPRI
of O
an O
input O
object O
into O
print-ready O
components S-MACEQ
. O


Our O
method O
improves O
3D B-MANP
printing E-MANP
by O
reducing O
material S-MATE
consumption O
, O
decreasing O
printing O
time O
, O
and O
improving O
fidelity O
of O
printed O
models O
. O


Then O
the O
configuration S-CONPRI
phase O
provides O
a O
robust O
algorithm S-CONPRI
to O
pack O
the O
components S-MACEQ
for O
an O
efficient O
print S-MANP
job O
. O


Our O
results O
show O
that O
the O
framework S-CONPRI
can O
reduce O
print S-MANP
time O
by O
up O
to O
65 O
% O
( O
fused B-MANP
deposition I-MANP
modeling E-MANP
, O
or O
FDM S-MANP
) O
and O
36 O
% O
( O
stereolithography S-MANP
, O
or O
SLA S-MACEQ
) O
on O
average S-CONPRI
and O
diminish O
material S-MATE
consumption O
by O
up O
to O
35 O
% O
( O
FDM S-MANP
) O
and O
10 O
% O
( O
SLA S-MACEQ
) O
on O
consumer O
printers S-MACEQ
, O
while O
also O
providing O
more O
accurate S-CHAR
objects O
. O


Conventional O
3D B-MANP
printing E-MANP
approaches O
are O
restricted O
to O
building B-MATE
up I-MATE
material E-MATE
in O
a O
layer-by-layer S-CONPRI
format O
, O
which O
is O
more O
appropriately O
considered O
“ O
2.5-D O
” O
printing O
. O


The O
layered B-CONPRI
structure E-CONPRI
inherently O
results O
in O
significant O
mechanical B-PRO
anisotropy E-PRO
in O
printed O
parts O
, O
causing O
the O
tensile B-PRO
strength E-PRO
in O
the O
build B-PARA
direction E-PARA
( O
z-axis S-CONPRI
) O
to O
be S-MATE
only O
a O
fraction S-CONPRI
of O
the O
in-plane B-PRO
strength E-PRO
– O
a O
decrease O
of O
50–75 O
% O
is O
common O
. O


In O
this O
study O
, O
a O
novel O
“ O
z-pinning S-ENAT
” O
approach O
is O
described O
that O
allows O
continuous O
material S-MATE
to O
be S-MATE
deposited O
across O
multiple O
layers O
within O
the O
volume S-CONPRI
of O
the O
part O
. O


The O
z-pinning S-ENAT
process S-CONPRI
is O
demonstrated O
using O
a O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
printer S-MACEQ
for O
polylactic B-MATE
acid E-MATE
( O
PLA S-MATE
) O
and O
carbon B-MATE
fiber I-MATE
reinforced I-MATE
PLA E-MATE
. O


For O
both O
materials S-CONPRI
, O
z-pinning S-ENAT
increased O
the O
tensile B-PRO
strength E-PRO
and O
toughness S-PRO
in O
the O
z-direction S-FEAT
by O
more O
than O
a O
factor O
of O
3.5 O
. O


Direct O
comparisons O
to O
tensile B-PRO
strength E-PRO
in O
the O
x-axis O
showed O
a O
significant O
decrease O
in O
mechanical B-PRO
anisotropy E-PRO
as S-MATE
the O
volume S-CONPRI
of O
the O
pin O
was O
increased O
relative O
to O
the O
void S-CONPRI
in O
the O
rectilinear B-CONPRI
grid I-CONPRI
structure E-CONPRI
. O


In O
fact O
, O
the O
PLA S-MATE
sample O
with O
the O
largest O
pin O
volume S-CONPRI
demonstrated O
mechanically O
isotropic S-PRO
properties O
within O
the O
statistical O
uncertainty O
of O
the O
tests O
. O


Tensile B-CHAR
test E-CHAR
results O
were O
also O
analyzed O
relative O
to O
the O
functional O
area S-PARA
resisting O
deformation S-CONPRI
for O
each O
sample S-CONPRI
. O


Digital B-MANP
light I-MANP
processing I-MANP
3D I-MANP
printing E-MANP
method O
was O
used O
to O
fabricate S-MANP
conductive O
parts O
. O


MWCNTs O
were O
used O
with O
photocurable B-MATE
resin E-MATE
to O
form O
conductive O
ink S-MATE
for O
3D B-MANP
printing E-MANP
. O


Complicated O
3D S-CONPRI
conductive O
structures O
were O
demonstrated O
. O


These O
structures O
can O
be S-MATE
used O
as S-MATE
capacitive O
sensors S-MACEQ
and O
shape O
memory O
composites S-MATE
. O


3D B-MANP
printing E-MANP
has O
gained O
significant O
research S-CONPRI
interest O
recently O
for O
directly O
manufacturing S-MANP
3D S-CONPRI
components O
and O
structures O
for O
use O
in O
a O
variety O
of O
applications O
. O


In O
this O
paper O
, O
a O
digital B-MANP
light I-MANP
processing E-MANP
( O
DLP® O
) O
based O
3D B-MANP
printing E-MANP
technique O
was O
explored O
to O
manufacture B-CONPRI
electrically E-CONPRI
conductive O
objects O
of O
polymer S-MATE
nanocomposites O
. O


Here O
, O
the O
ink S-MATE
was O
made O
of O
a O
mixture O
of O
photocurable B-MATE
resin E-MATE
with O
multi-walled O
carbon B-MATE
nanotubes E-MATE
( O
MWCNTs O
) O
. O


The O
concentrations O
of O
MWCNT O
as S-MATE
well O
as S-MATE
the O
printing O
parameters S-CONPRI
were O
investigated O
to O
yield O
optimal O
conductivity S-PRO
and O
printing O
quality S-CONPRI
. O


We O
found O
that O
0.3 O
wt O
% O
loading O
of O
MWCNT O
in O
the O
resin S-MATE
matrix O
can O
provide O
the O
maximum O
electrical B-PRO
conductivity E-PRO
of O
0.027S/m O
under O
the O
resin S-MATE
viscosity O
limit S-CONPRI
that O
allows O
high O
printing O
quality S-CONPRI
. O


With O
electric O
conductivity S-PRO
, O
the O
printed O
MWCNT O
nanocomposites O
can O
be S-MATE
used O
as S-MATE
smart O
materials S-CONPRI
and O
structures O
with O
strain S-PRO
sensitivity S-PARA
and O
shape B-PRO
memory I-PRO
effect E-PRO
. O


We O
demonstrate O
that O
the O
printed B-MACEQ
conductive E-MACEQ
complex B-CONPRI
structures E-CONPRI
as S-MATE
hollow O
capacitive O
sensor S-MACEQ
, O
electrically S-CONPRI
activated O
shape O
memory O
composites S-MATE
, O
stretchable S-FEAT
circuits O
, O
showing O
the O
versatility O
of O
DLP® O
3D B-MANP
printing E-MANP
for O
conductive B-FEAT
complex I-FEAT
structures E-FEAT
. O


In O
addition O
, O
mechanical B-CHAR
tests E-CHAR
showed O
that O
the O
addition O
of O
MWCNT O
could O
slightly O
increase O
the O
modulus O
and O
ultimate O
tensile B-PRO
stress E-PRO
while O
decreasing O
slightly O
the O
ultimate O
stretch O
, O
indicating O
that O
the O
new O
functionality O
is O
not O
obtained O
at O
the O
price O
of O
sacrificing O
mechanical B-CONPRI
properties E-CONPRI
. O


3D B-ENAT
printing I-ENAT
technology E-ENAT
has O
revolutionized O
the O
field O
of O
machinery O
, O
aerospace S-APPL
, O
and O
electronics S-CONPRI
. O


To O
address O
the O
shortcomings O
of O
previous O
studies O
on O
improving O
the O
poor O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
resin S-MATE
used O
in O
3D B-MACEQ
printers E-MACEQ
, O
this O
study O
presents O
a O
technology S-CONPRI
for O
fabricating S-MANP
short O
fibres S-MATE
or O
a O
continuous O
fibre-composite O
material S-MATE
using O
stereolithography B-MANP
3D I-MANP
printing E-MANP
. O


Glass S-MATE
powder O
and O
fibreglass O
fabric O
were O
used O
as S-MATE
the O
discontinuous O
and O
continuous O
fibre S-MATE
reinforcement O
of O
light-cured O
resin B-MATE
material E-MATE
. O


The O
tensile B-PRO
strength E-PRO
and O
Young O
’ O
s S-MATE
modulus O
showed O
a O
marked O
increase O
: O
these O
were O
7.2 O
and O
11.5 O
times O
higher O
than O
those O
of O
the O
resin S-MATE
specimen O
, O
respectively O
. O


The O
3D B-MANP
printing E-MANP
of O
fiber-reinforced O
soft O
composites S-MATE
( O
FrSCs O
) O
is O
a O
hybrid O
process S-CONPRI
that O
combines O
conventional O
inkjet-based O
3D B-MANP
printing E-MANP
with O
the O
directed O
deposition S-CONPRI
of O
electrospun O
polymer B-MATE
fiber E-MATE
mats S-MATE
. O


This O
paper O
investigates S-CONPRI
the O
spreading O
characteristics O
of O
droplets S-CONPRI
when O
deposited O
on O
fibrous S-PRO
substrates O
, O
under O
conditions O
relevant O
to O
3D B-MANP
printing E-MANP
of O
aligned O
FrSCs O
. O


High-speed O
imaging S-APPL
is O
used O
to O
study O
the O
characteristic O
time-scales O
and O
the O
spreading O
behavior O
of O
the O
droplets S-CONPRI
. O


The O
single O
droplet S-CONPRI
impingement O
studies O
on O
stationary O
substrates O
reveal O
that O
the O
presence O
of O
fibers S-MATE
promotes O
droplet S-CONPRI
spreading O
along O
the O
length O
of O
the O
fibers S-MATE
. O


Occasional O
surface S-CONPRI
energy O
variations S-CONPRI
in O
the O
fiber S-MATE
mats O
in O
the O
form O
of O
voids S-CONPRI
and O
fiber B-MATE
bundles E-MATE
are O
also O
seen O
to O
affect O
the O
droplet S-CONPRI
shape O
and O
the O
characteristic O
spreading O
times O
. O


In O
the O
case O
of O
a O
moving O
substrate S-MATE
, O
the O
droplets S-CONPRI
are O
seen O
to O
spread S-CONPRI
the O
most O
during O
in-line O
printing O
, O
i.e. O
, O
when O
the O
direction O
of O
the O
printing O
velocity O
coincides O
with O
the O
direction O
of O
fiber B-FEAT
alignment E-FEAT
. O


They O
spread S-CONPRI
the O
least O
during O
orthogonal O
printing O
, O
i.e. O
, O
when O
the O
direction O
of O
the O
printing O
velocity O
is O
perpendicular O
to O
the O
direction O
of O
fiber B-FEAT
alignment E-FEAT
. O


The O
findings O
of O
the O
high-speed O
imaging S-APPL
studies O
have O
been O
confirmed O
by O
3D B-MANP
printing E-MANP
comparable O
artifacts O
using O
UV S-CONPRI
curable O
inks O
. O


These O
studies O
indicate O
that O
for O
a O
given O
fiber S-MATE
mat O
and O
UV S-CONPRI
curable O
ink S-MATE
combination O
, O
the O
choice O
of O
the O
in-line O
or O
orthogonal O
printing O
strategy O
has O
implications O
for O
the O
overall O
printing O
time O
, O
fiber S-MATE
content O
, O
edge O
resolution S-PARA
and O
surface B-PARA
quality E-PARA
of O
the O
3D B-MANP
printed E-MANP
FrSC O
part O
. O


Multi-material S-CONPRI
extrusion S-MANP
in O
3D B-MANP
printing E-MANP
is O
gaining O
attention O
due O
to O
a O
wide O
range S-PARA
of O
possibilities O
that O
it O
provides O
, O
specially O
driven O
by O
the O
commercial O
availability O
of O
a O
large O
variety O
of O
non-conventional O
filament S-MATE
materials O
. O


With O
this O
in O
mind O
, O
this O
paper O
addresses O
the O
mechanical S-APPL
performance O
of O
multi-material S-CONPRI
printed O
objects O
, O
specially O
focused O
on O
the O
interface S-CONPRI
zone O
generated O
between O
the O
different O
materials S-CONPRI
at O
their O
geometrical O
boundaries S-FEAT
. O


Tensile B-CHAR
test E-CHAR
specimens O
were O
designed S-FEAT
and O
printed O
in O
three O
types O
: O
( O
A O
) O
a O
single-material O
specimen O
printed O
by O
a O
single O
extrusion B-MACEQ
head E-MACEQ
; O
( O
B S-MATE
) O
a O
single-material O
but O
multi-section O
specimen O
printed O
in O
a O
zebra-crossing O
structure S-CONPRI
by O
two O
extrusion B-MACEQ
heads E-MACEQ
; O
and O
( O
C S-MATE
) O
a O
multi-material S-CONPRI
specimen O
printed O
with O
two O
materials S-CONPRI
in O
a O
zebra-crossing O
pattern S-CONPRI
. O


The O
materials S-CONPRI
considered O
were O
PLA S-MATE
, O
TPU O
and O
PET O
. O


The O
comparison O
of O
the O
mechanical S-APPL
performance O
between O
Type-A O
and O
-B O
specimens O
demonstrated O
the O
negative O
influence O
of O
the O
presence O
of O
a O
geometrical O
boundary S-FEAT
interface O
between O
the O
same O
material S-MATE
. O


The O
methodology S-CONPRI
proposed O
to O
assess O
the O
quality S-CONPRI
of O
the O
pairs O
of O
materials S-CONPRI
selected O
is O
innovative O
, O
and O
enabled O
to O
depict O
the O
importance O
of O
the O
boundary S-FEAT
design O
in O
multi-material B-MANP
printing E-MANP
techniques O
. O


The O
aim O
of O
the O
present O
work O
was O
to O
develop O
a O
pilot O
scale O
process S-CONPRI
to O
produce O
drug-loaded O
filaments S-MATE
for O
3D B-MANP
printing E-MANP
of O
oral O
solid O
dose O
forms O
by O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
. O


Using O
hot O
melt B-MANP
extrusion E-MANP
, O
a O
viable O
operating O
space O
and O
understanding O
of O
processing O
limits S-CONPRI
were O
established O
using O
a O
hydrophilic O
polymer S-MATE
( O
hydroxypropyl O
methylcellulose O
( O
HPMC O
) O
– O
Affinisol™ O
LV15 O
) O
. O


From O
the O
process S-CONPRI
development O
work O
, O
challenges O
in O
achieving O
a O
pilot O
scale O
process S-CONPRI
for O
filament S-MATE
production O
for O
pharmaceutical S-APPL
applications O
have O
been O
highlighted O
. O


3D B-MANP
printing E-MANP
trials O
across O
the O
range S-PARA
of O
compositions O
demonstrated O
limitations O
concerning O
the O
ability O
to O
print S-MANP
successfully O
across O
all O
compositions O
. O


Results O
from O
characterisation O
techniques O
including O
thermal O
and O
mechanical B-CHAR
testing E-CHAR
when O
applied O
to O
the O
formulated O
filaments S-MATE
indicated O
that O
these O
techniques O
are O
a O
useful O
predictive O
measure O
for O
assessing O
the O
ability O
to O
print S-MANP
a O
given O
formulation O
via O
filament S-MATE
methods O
. O


However O
, O
fabrication S-MANP
methods O
using O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
bioprinters O
are O
limited O
by O
the O
simple S-MANP
nozzle-based O
extrusion S-MANP
or O
uncontrollability O
of O
photo-reactive O
systems O
. O


Hence O
, O
most O
studies O
on O
inducing O
topographical O
cues O
were O
focused O
on O
two-dimensional S-CONPRI
( O
2D S-CONPRI
) O
surface B-FEAT
structures E-FEAT
and O
based O
on O
imprinting O
and O
soft-lithography O
processes S-CONPRI
. O


Although O
2D S-CONPRI
patterned O
surfaces S-CONPRI
provide O
outstanding O
insight O
into O
optimal O
patterned O
architectures O
by O
facilitating O
the O
analysis O
of O
various O
myoblast O
responses O
, O
it O
can O
be S-MATE
difficult O
to O
achieve O
complex O
3D B-CONPRI
structures E-CONPRI
with O
microscale S-CONPRI
topographical O
cues O
. O


For O
this O
reason O
, O
we O
propose O
a O
new O
strategy O
for O
obtaining O
topographical O
cues O
in O
3D B-MANP
printed E-MANP
synthetic O
biopolymers S-MATE
for O
regenerating O
muscle O
tissue O
. O


A O
uniaxially O
aligned O
pattern S-CONPRI
was O
obtained O
on O
the O
struts S-MACEQ
of O
the O
matrix O
composed O
of O
poly O
( O
ε-caprolactone O
) O
( O
PCL S-MATE
) O
or O
poly O
( O
lactic-co-glycolic O
acid O
) O
( O
PLGA S-MATE
) O
, O
by O
taking O
advantage O
of O
the O
immiscible O
rheological B-PRO
properties E-PRO
and O
flow-induced O
force S-CONPRI
in O
the O
dispersed O
pluronic O
F-127 O
phase S-CONPRI
( O
sacrificial O
material S-MATE
) O
and O
matrix O
materials S-CONPRI
. O


Stereolithography S-MANP
is O
a O
3D B-MANP
printing E-MANP
technique O
in O
which O
a O
liquid O
monomer S-MATE
is O
photopolymerized O
to O
produce O
a O
solid O
object O
. O


Photoinitiators O
can O
absorb O
UV S-CONPRI
or O
( O
less O
often O
) O
visible O
light O
, O
producing O
radicals O
for O
direct O
decomposition S-PRO
or O
hydrogen O
abstraction S-CONPRI
. O


In O
fact O
, O
vegetable O
oils S-MATE
contain O
unsaturations O
, O
and O
thus O
, O
they O
can O
be S-MATE
exploited O
as S-MATE
monomers O
. O


In O
particular O
, O
linseed O
oil S-MATE
, O
tung O
oil S-MATE
or O
edible O
oils S-MATE
( O
soybean O
, O
sunflower O
or O
corn O
) O
could O
be S-MATE
good O
candidates O
as S-MATE
raw O
materials S-CONPRI
. O


Unfortunately O
, O
the O
photoinduced O
radical O
polymerization S-MANP
of O
these O
oils S-MATE
either O
does O
not O
occur O
or O
is O
too O
slow O
for O
3D B-MANP
printing E-MANP
applications O
. O


For O
this O
reason O
, O
the O
oils S-MATE
were O
modified O
as S-MATE
epoxides O
. O


Epoxides O
are O
monomers O
that O
are O
more O
reactive O
than O
natural O
oils S-MATE
, O
and O
they O
can O
be S-MATE
polymerized O
via O
a O
cationic O
mechanism S-CONPRI
. O


The O
aim O
of O
this O
work O
was O
to O
exploit O
visible O
light O
generated O
by O
a O
common O
digital O
projector S-MACEQ
( O
like O
those O
used O
in O
classrooms O
) O
as S-MATE
a O
light B-MACEQ
source E-MACEQ
. O


Vegetable O
oil S-MATE
epoxides O
, O
together O
with O
curcumin O
and O
visible O
light O
could O
replace O
acrylates O
from O
3D S-CONPRI
printing.Download O
: O
Download O
high-res B-CONPRI
image E-CONPRI
( O
82 O
Challenging O
to O
3-D S-CONPRI
print O
functional O
parts O
with O
known O
mechanical B-CONPRI
properties E-CONPRI
. O


Using O
variable O
open O
source S-APPL
3-D S-CONPRI
printers O
for O
a O
wide O
range S-PARA
of O
materials S-CONPRI
. O


Tested O
tensile B-PRO
strength E-PRO
following O
ASTM O
D638 O
for O
fused B-MANP
filament I-MANP
fabrication E-MANP
. O


Tensile B-PRO
strength E-PRO
of O
a O
3-D S-CONPRI
printed O
specimen O
depends O
largely O
on O
the O
mass O
. O


2 O
step B-CONPRI
process E-CONPRI
developed O
to O
screen O
3-D S-CONPRI
prints O
for O
mechanical B-CONPRI
functionality E-CONPRI
. O


3D B-MANP
printing E-MANP
functional O
parts O
with O
known O
mechanical B-CONPRI
properties E-CONPRI
is O
challenging O
using O
variable O
open O
source S-APPL
3D B-MACEQ
printers E-MACEQ
. O


This O
study O
investigates S-CONPRI
the O
mechanical B-CONPRI
properties E-CONPRI
of O
3D B-APPL
printed I-APPL
parts E-APPL
using O
a O
commercial O
open-source S-CONPRI
3D B-MACEQ
printer E-MACEQ
for O
a O
wide O
range S-PARA
of O
materials S-CONPRI
. O


The O
samples S-CONPRI
are O
tested O
for O
tensile B-PRO
strength E-PRO
following O
ASTM O
D638 O
. O


The O
results O
are O
presented O
and O
conclusions O
are O
drawn O
about O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
various O
fused B-MANP
filament I-MANP
fabrication E-MANP
materials O
. O


The O
study O
demonstrates O
that O
the O
tensile B-PRO
strength E-PRO
of O
a O
3D B-MANP
printed E-MANP
specimen O
depends O
largely O
on O
the O
mass O
of O
the O
specimen O
, O
for O
all O
materials S-CONPRI
. O


Thus O
, O
to O
solve O
the O
challenge O
of O
unknown O
print B-CONPRI
quality E-CONPRI
on O
mechanical B-CONPRI
properties E-CONPRI
of O
a O
3D B-APPL
printed I-APPL
part E-APPL
a O
two O
step B-CONPRI
process E-CONPRI
is O
proposed O
, O
which O
has O
a O
reasonably O
high O
expectation O
that O
a O
part O
will O
have O
tensile B-PRO
strengths E-PRO
described O
in O
this O
study O
for O
a O
given O
material S-MATE
. O


This O
mass O
is O
compared O
to O
the O
theoretical S-CONPRI
value O
using O
densities O
for O
the O
material S-MATE
and O
the O
volume S-CONPRI
of O
the O
object O
. O


This O
two O
step B-CONPRI
process E-CONPRI
provides O
a O
means O
to O
assist O
low-cost O
open-source S-CONPRI
3D B-MACEQ
printers E-MACEQ
expand O
the O
range S-PARA
of O
object O
production S-MANP
to O
functional O
parts O
. O


Novel O
blend S-MATE
feedstocks O
developed O
using O
recycled S-CONPRI
plastic S-MATE
materials S-CONPRI
. O


Blend S-MATE
composition O
and O
processing O
conditions O
optimized O
for O
morphology/interfacial O
adhesion S-PRO
. O


Blend S-MATE
perform O
on O
par O
with O
commercial O
HIPS B-MATE
filaments E-MATE
. O


Recycled S-CONPRI
polymer B-MATE
blends E-MATE
are O
valid O
feedstocks S-MATE
for O
AM S-MANP
and O
could O
be S-MATE
used O
for O
manufacturing S-MANP
in O
remote O
environments O
. O


Consumer-grade O
plastics S-MATE
can O
be S-MATE
considered O
a O
low-cost O
and O
sustainable S-CONPRI
feedstock S-MATE
for O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
additive B-MANP
manufacturing I-MANP
processes E-MANP
. O


Such O
materials S-CONPRI
are O
excellent O
candidates O
for O
distributed O
manufacturing S-MANP
, O
in O
which O
parts O
are O
printed O
from O
local O
materials S-CONPRI
at O
the O
point O
of O
need O
. O


Most O
plastic S-MATE
waste O
streams O
contain O
a O
mixture O
of O
polymers S-MATE
, O
such O
as S-MATE
water O
bottles O
and O
caps O
comprised O
of O
polyethylene B-MATE
terephthalate E-MATE
( O
PET O
) O
and O
polypropylene S-MATE
( O
PP O
) O
, O
and O
complete O
separation O
is O
rarely O
implemented O
. O


In O
this O
work O
, O
blends S-MATE
of O
waste O
PET O
, O
PP O
and O
polystyrene S-MATE
( O
PS O
) O
were O
processed S-CONPRI
into O
filaments S-MATE
for O
3D B-MANP
printing E-MANP
. O


The O
effect O
of O
blend S-MATE
composition O
and O
styrene O
ethylene O
butylene O
styrene O
( O
SEBS O
) O
compatibilizer O
on O
the O
resulting O
mechanical S-APPL
and O
thermal B-CONPRI
properties E-CONPRI
were O
probed O
. O


Recycled S-CONPRI
PET O
had O
the O
highest O
tensile B-PRO
strength E-PRO
at O
35 O
± O
8 O
MPa S-CONPRI
. O


Blends S-MATE
of O
PP/PET O
compatibilized O
with O
SEBS O
and O
maleic O
anhydride O
functionalized O
SEBS O
had O
tensile B-PRO
strengths E-PRO
of O
23 O
± O
1 O
MPa S-CONPRI
and O
24 O
± O
1 O
MPa S-CONPRI
, O
respectively O
. O


The O
non-compatibilized O
PP/PS O
blend S-MATE
had O
a O
tensile B-PRO
strength E-PRO
of O
22 O
± O
1 O
MPa S-CONPRI
. O


PP/PS O
blends S-MATE
exhibited O
reduced O
tensile B-PRO
strength E-PRO
to O
ca S-MATE
. O


Elongation S-PRO
to O
failure S-CONPRI
was O
generally O
improved O
for O
the O
blended O
materials S-CONPRI
compared O
to O
neat O
recycled S-CONPRI
PET O
and O
PS O
. O


The O
glass S-MATE
transition O
was O
shifted O
to O
higher O
temperatures S-PARA
for O
all O
of O
the O
blends S-MATE
except O
the O
50–50 O
wt O
. O


% O
PP/PET O
blend S-MATE
. O


% O
PP/PET O
blend S-MATE
with O
SEBS-maleic O
anhydride O
. O


Solvent O
extraction O
of O
the O
dispersed O
phase S-CONPRI
revealed O
polypropylene S-MATE
was O
the O
matrix O
phase S-CONPRI
in O
both O
the O
50–50 O
wt O
. O


% O
PP/PET O
and O
PP/PS O
blends S-MATE
. O


Porous S-PRO
tricalcium O
phosphate S-MATE
( O
TCP O
) O
scaffolds S-FEAT
are O
becoming O
more O
and O
more O
important O
for O
treating O
musculoskeletal O
diseases O
. O


With O
the O
maturation O
of O
3D B-MANP
printing E-MANP
( O
3DP S-MANP
) O
technology S-CONPRI
in O
the O
past O
two O
decades O
, O
porous S-PRO
TCP O
scaffolds S-FEAT
can O
also O
be S-MATE
easily O
prepared O
with O
complex O
design S-FEAT
and O
high O
dimensional B-CHAR
accuracy E-CHAR
. O


However O
, O
the O
mechanical S-APPL
and O
biological O
properties S-CONPRI
of O
porous S-PRO
TCP O
scaffolds S-FEAT
prepared O
by O
3D B-MANP
printing E-MANP
still O
need O
improvements O
. O


In O
this O
study O
, O
novel O
3D B-MANP
printed E-MANP
TCP O
and O
MgO/ZnO-TCP O
scaffolds S-FEAT
were O
prepared O
by O
an O
binder-jet O
3D B-MACEQ
printer E-MACEQ
. O


Scaffolds S-FEAT
had O
a O
dense O
core S-MACEQ
and O
porous S-PRO
surface O
feature S-FEAT
with O
a O
designed S-FEAT
pore O
size O
of O
500 O
μm O
and O
a O
designed S-FEAT
porosity O
of O
18 O
% O
. O


After O
printing O
, O
scaffolds S-FEAT
were O
sintered S-MANP
in O
a O
muffle O
furnace S-MACEQ
at O
1250 O
°C O
. O


The O
presence O
of O
MgO S-MATE
and O
ZnO O
increased O
the O
surface B-PARA
area E-PARA
of O
TCP O
from O
1.18 O
± O
0.01 O
m2/g O
to O
2.65 O
± O
0.02 O
m2/g O
, O
the O
bulk O
density S-PRO
from O
37.89 O
± O
0.83 O
% O
to O
50.82 O
± O
1.10 O
% O
, O
and O
the O
compressive B-PRO
strength E-PRO
from O
17.94 O
± O
1.65 O
MPa S-CONPRI
to O
27.46 O
± O
2.63 O
MPa S-CONPRI
. O


Enhanced O
osteoblast S-BIOP
proliferation O
was O
shown O
in O
doped O
3D B-MANP
printed E-MANP
TCP O
scaffolds S-FEAT
compared O
to O
the O
pure O
3DP S-MANP
TCP O
. O


In O
addition O
, O
the O
use O
of O
3D B-MANP
printing E-MANP
as O
well O
as S-MATE
dense O
core S-MACEQ
and O
porous S-PRO
surface O
design S-FEAT
enhanced O
the O
surface B-PRO
roughness E-PRO
and O
osteoblast S-BIOP
proliferation O
of O
TCP B-BIOP
scaffolds E-BIOP
. O


This O
novel O
3D B-MANP
printed E-MANP
MgO/ZnO-TCP O
scaffold S-FEAT
shows O
enhanced O
mechanical S-APPL
and O
biological O
properties S-CONPRI
, O
which O
is O
promising O
for O
orthopedic O
and O
dental B-APPL
applications E-APPL
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
which O
is O
also O
referred O
to O
as S-MATE
3D B-MANP
printing E-MANP
, O
is O
a O
class O
of O
manufacturing S-MANP
techniques O
that O
fabricate S-MANP
three O
dimensional O
( O
3D S-CONPRI
) O
objects O
by O
accumulating O
materials S-CONPRI
. O


Constrained O
surface S-CONPRI
based O
stereolithography S-MANP
is O
one O
of O
the O
most O
widely O
used O
AM B-MANP
techniques E-MANP
. O


In O
the O
process S-CONPRI
, O
a O
thin O
layer S-PARA
of O
liquid O
photosensitive B-MATE
resin E-MATE
is O
constrained O
between O
a O
constrained O
surface S-CONPRI
and O
the O
platform S-MACEQ
or O
part O
. O


The O
light O
penetrates O
the O
transparent S-CONPRI
constrained O
surface S-CONPRI
and O
cures O
that O
layer S-PARA
of O
liquid O
polymer S-MATE
. O


Then O
the O
platform S-MACEQ
is O
moved O
up O
to O
separate O
the O
newly O
cured B-CONPRI
layer E-CONPRI
to O
let O
new O
liquid O
resin S-MATE
fill O
into O
the O
gap O
and O
get O
cured S-MANP
. O


The O
separation O
of O
newly O
cured B-CONPRI
layer E-CONPRI
from O
the O
constrained O
surface S-CONPRI
is O
a O
grand O
challenge O
that O
limits S-CONPRI
the O
printable O
size O
and O
printing B-PARA
speed E-PARA
in O
this O
manufacturing S-MANP
technique O
. O


Numerous O
experimental S-CONPRI
works O
have O
been O
performed O
to O
understand O
how O
to O
reduce O
the O
separation B-CONPRI
force E-CONPRI
in O
the O
process S-CONPRI
. O


In O
this O
paper O
we O
study O
a O
new O
design S-FEAT
of O
constrained O
surface S-CONPRI
with O
radial O
groove O
texture S-FEAT
that O
significantly O
influences O
the O
effectiveness S-CONPRI
of O
reduction S-CONPRI
of O
the O
separation B-CONPRI
force E-CONPRI
and O
hence O
the O
manufacturing S-MANP
capability O
via O
theoretical S-CONPRI
modeling S-ENAT
. O


The O
proposed O
model S-CONPRI
is O
validated O
with O
numerical B-ENAT
simulations E-ENAT
demonstrating O
an O
excellent O
agreement O
. O


We O
demonstrate O
the O
possibility O
of O
drastic O
reduction S-CONPRI
of O
the O
separation B-CONPRI
force E-CONPRI
( O
up O
to O
112 O
% O
) O
via O
surface B-MANP
texturing E-MANP
of O
the O
permeable O
window O
for O
continuous O
3D B-MANP
printing E-MANP
. O


A O
novel O
large-scale O
3D B-MACEQ
printer E-MACEQ
is O
introduced O
. O


A O
full O
scaffolding S-ENAT
solution O
allows O
any O
3D B-FEAT
geometry E-FEAT
to O
be S-MATE
printed O
. O


Part O
geometry B-CONPRI
errors E-CONPRI
are O
detected O
and O
corrected O
using O
geometric O
feedback S-PARA
. O


Although O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
now O
a O
well-established O
industry S-APPL
, O
very O
few O
large-scale O
AM S-MANP
systems O
have O
been O
developed O
. O


Here O
, O
a O
large-scale O
3D B-MACEQ
printer E-MACEQ
is O
introduced O
, O
which O
uses O
a O
six-degree-of-freedom O
cable-suspended O
robot S-MACEQ
for O
positioning O
, O
with O
polyurethane B-MATE
foam E-MATE
as S-MATE
the O
object O
material S-MATE
and O
shaving S-MANP
foam S-MATE
as S-MATE
the O
support B-MATE
material E-MATE
. O


Cable-positioning O
systems O
provide O
large O
ranges O
of O
motion O
and O
cables O
can O
be S-MATE
compactly O
wound O
on O
spools O
, O
making O
them O
less O
expensive O
, O
much O
lighter O
, O
more O
transportable O
, O
and O
more O
easily O
reconfigurable O
, O
compared O
to O
the O
gantry-type O
positioning B-ENAT
systems E-ENAT
traditionally O
used O
in O
3D B-MANP
printing E-MANP
. O


The O
3D S-CONPRI
foam O
printer S-MACEQ
performance S-CONPRI
is O
demonstrated O
through O
the O
construction S-APPL
of O
a O
2.16-m-high O
statue O
of O
Sir O
Wilfrid O
Laurier O
, O
the O
seventh O
Prime O
Minister O
of O
Canada O
, O
at O
an O
accuracy S-CHAR
of O
approximately O
1 O
cm O
, O
which O
requires O
38 O
h O
of O
printing O
time O
. O


The O
system O
advantages O
and O
drawbacks O
are O
then O
discussed O
, O
and O
novel O
features O
such O
as S-MATE
unique O
support S-APPL
techniques O
and O
geometric O
feedback S-PARA
are O
highlighted O
. O


PA/ABS O
blend S-MATE
optimized O
formulation O
improved O
bead-bead O
adhesion S-PRO
in O
3-D S-CONPRI
printing O
. O


Anisotropy S-PRO
ratio O
( O
z O
property/x O
property S-CONPRI
) O
indicator O
of O
bead-bead O
adhesion S-PRO
. O


Small-scale O
printing O
can O
provide O
test O
case O
for O
large-scale O
printed O
material B-CONPRI
properties E-CONPRI
. O


SMA O
was O
an O
effective O
compatiblizer O
for O
PA/ABS O
blends S-MATE
at O
printed O
interface S-CONPRI
. O


For O
additive B-MANP
manufacturing E-MANP
interfacial O
adhesion S-PRO
( O
bead-bead O
) O
remains O
an O
important O
issue O
affecting O
uniformity O
of O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
present O
work O
examined O
the O
role O
a O
compatibilizer O
would O
play O
when O
used O
in O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
printing O
. O


Both O
small O
and O
large-scale O
3-D S-CONPRI
component O
properties S-CONPRI
were O
examined O
. O


The O
mechanical B-CONPRI
property E-CONPRI
anisotropy S-PRO
ratio O
, O
an O
indication O
of O
bead-bead O
adhesive S-MATE
strength O
( O
defined O
as S-MATE
a O
property S-CONPRI
measured O
along O
the O
z O
axis O
versus O
the O
x O
axis O
) O
is O
representative O
of O
adhesive S-MATE
strength O
. O


Large-scale O
( O
big O
area S-PARA
additive B-MANP
manufacturing E-MANP
, O
BAAM O
) O
tests O
( O
flexural O
properties S-CONPRI
) O
showed O
62 O
% O
improvement O
in O
the O
anisotropy S-PRO
ratio O
for O
modulus O
, O
77 O
% O
improvement O
in O
the O
anisotropy S-PRO
ratio O
of O
the O
strength S-PRO
, O
56 O
% O
improvement O
in O
the O
anisotropy S-PRO
ratio O
of O
elongation S-PRO
at O
break O
, O
and O
55 O
% O
improvement O
of O
the O
anisotropy S-PRO
ratio O
of O
the O
Charpy O
impact S-CONPRI
strength O
over O
the O
control O
PA S-CHAR
values O
. O


Thus O
, O
use O
of O
compatibilized O
polymer B-MATE
blends E-MATE
can O
provide O
customized O
materials S-CONPRI
without O
the O
need O
for O
new O
chemistry S-CONPRI
. O


Addition O
of O
maleic O
anhydride-compatibilized O
ABS S-MATE
improved O
PA S-CHAR
blend S-MATE
bead-bead O
adhesion S-PRO
. O


The O
thixotropic S-PRO
ink S-MATE
is O
able O
to O
maintain O
the O
shape O
after O
direct O
printing O
. O


MNPs O
interact O
with O
polymer S-MATE
network O
and O
alter O
its O
physicochemical O
properties S-CONPRI
. O


Nanofiller O
renders O
the O
3D-printed S-MANP
hydrogel O
magnetic O
. O


3D-printed S-MANP
objects O
can O
be S-MATE
remotely O
actuated O
via O
magnetic B-CONPRI
fields E-CONPRI
. O


Magnetic O
hydrogels S-MATE
have O
a O
myriad O
of O
promising O
applications O
including O
soft O
electronics S-CONPRI
, O
flexible O
robotics S-APPL
, O
biomedical S-APPL
devices O
, O
and O
wastewater B-APPL
treatment E-APPL
. O


However O
, O
their O
potential O
is O
limited O
by O
conventional O
fabrication S-MANP
methods O
which O
impede O
creating O
convoluted O
geometries S-CONPRI
. O


3D B-MANP
printing E-MANP
may O
replace O
traditional O
fabrication S-MANP
techniques O
as S-MATE
it O
has O
an O
ability O
to O
fabricate S-MANP
complex B-PRO
shapes E-PRO
using O
a O
wide O
variety O
of O
materials S-CONPRI
. O


A O
new O
3D B-MANP
printing E-MANP
ink O
, O
a O
bionanocomposite O
based O
on O
alginate S-MATE
, O
methylcellulose O
and O
magnetic O
nanoparticles S-CONPRI
( O
MNPs O
) O
was O
used O
to O
print S-MANP
pre-designed O
high-quality O
3D B-CONPRI
structures E-CONPRI
. O


Three-dimensional S-CONPRI
hydrogel S-MATE
constructs O
had O
good O
mechanical S-APPL
stability O
and O
exhibited O
responsiveness O
to O
an O
applied O
magnetic B-CONPRI
field E-CONPRI
. O


Inclusion S-MATE
of O
the O
MNPs O
within O
the O
hydrogel S-MATE
and O
its O
precursor S-MATE
( O
ink S-MATE
) O
influenced O
their O
rheological B-PRO
properties E-PRO
- O
and O
mechanical S-APPL
stability O
. O


MNPs O
were O
found O
to O
play O
dual O
roles O
: O
( O
1 O
) O
as S-MATE
a O
nanofiller O
that O
interacts O
with O
polymer S-MATE
backbone O
and O
alters O
its O
physicochemical O
properties S-CONPRI
, O
and O
( O
2 O
) O
as S-MATE
a O
function O
provider O
that O
renders O
a O
bionanocomposite O
magnetic O
. O


The O
magnetic O
ink S-MATE
allows O
for O
the O
fabrication S-MANP
of O
multi-material B-FEAT
structures E-FEAT
such O
as S-MATE
hydrogels O
with O
a O
magnetic O
nanoparticle O
gradient O
. O


3D-printed S-MANP
objects O
can O
be S-MATE
remotely O
actuated O
via O
magnetic B-CONPRI
fields E-CONPRI
. O


Reactive O
magnesium B-MATE
oxide E-MATE
cement S-MATE
( O
RMC S-CHAR
) O
is O
gaining O
increasing O
attention O
as S-MATE
a O
sustainable S-CONPRI
construction S-APPL
material O
due O
to O
its O
significantly O
low O
carbon B-CONPRI
footprint E-CONPRI
during O
the O
production S-MANP
as S-MATE
well O
as S-MATE
the O
operational O
phase S-CONPRI
compared O
to O
the O
conventional O
Portland O
cement S-MATE
. O


Whereas O
several O
studies O
have O
demonstrated O
the O
potential O
of O
RMC S-CHAR
as S-MATE
a O
suitable O
and O
environment-friendly O
construction S-APPL
material O
, O
this O
study O
reports O
that O
RMC S-CHAR
can O
be S-MATE
shaped O
into O
complex B-CONPRI
structures E-CONPRI
via O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
printing B-ENAT
technology E-ENAT
. O


By O
adding O
suitable O
additives S-MATE
and O
only O
3 O
wt O
. O


% O
of O
caustic O
magnesium B-MATE
oxide E-MATE
to O
the O
commercially O
available O
RMC S-CHAR
, O
appropriate O
rheology S-PRO
and O
buildability O
were O
achieved O
that O
enabled O
smooth O
3D B-MANP
printing E-MANP
of O
complex B-CONPRI
structures E-CONPRI
with O
precise O
shape O
retention O
. O


Moreover O
, O
the O
3D B-MANP
printed E-MANP
RMC O
exhibited O
higher O
densification S-MANP
and O
nearly O
twofold O
the O
compressive B-PRO
strength E-PRO
as S-MATE
compared O
to O
its O
cast S-MANP
counterpart O
. O


Therefore O
, O
this O
work O
demonstrates O
the O
potential O
of O
RMC S-CHAR
as S-MATE
a O
3D S-CONPRI
printable O
construction S-APPL
material O
for O
sustainable S-CONPRI
and O
modern O
architecture S-APPL
. O


Achievement O
of O
optimized O
lateral O
and O
vertical S-CONPRI
resolution S-PARA
is O
a O
key O
factor O
to O
obtaining O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
structural O
details O
fabricated S-CONPRI
through O
digital B-MANP
light I-MANP
processing E-MANP
( O
DLP S-MANP
) O
-based O
3D B-ENAT
printing I-ENAT
technologies E-ENAT
which O
exploit O
digitalized O
ultraviolet S-CONPRI
( O
UV S-CONPRI
) O
or O
near-UV O
light O
to O
trigger O
localized O
photopolymerization B-MANP
forming E-MANP
solid O
patterns O
from O
liquid O
polymer B-MATE
resins E-MATE
. O


Many O
efforts O
have O
been O
made O
to O
optimize O
printing O
resolution S-PARA
through O
improving O
the O
optical S-CHAR
systems O
. O


However O
, O
researchers O
have O
paid O
comparatively O
little O
attention O
to O
understand O
the O
influences O
of O
polymer S-MATE
formulation O
on O
the O
printing O
resolution S-PARA
and O
surface B-PARA
quality E-PARA
. O


Here O
, O
we O
report O
an O
investigation O
on O
the O
effects O
of O
in-house O
formulated O
( O
meth O
) O
acrylate-based O
photopolymer S-MATE
constituent O
types O
and O
concentrations O
on O
the O
resolution S-PARA
and O
quality S-CONPRI
of O
structures O
printed O
on O
a O
bottom-exposure O
DLP-based O
3D B-MANP
printing E-MANP
system O
. O


We O
examined O
a O
wide O
variety O
of O
resin S-MATE
formulations O
to O
determine O
optimal O
formulations O
that O
yield O
best O
printing O
resolution S-PARA
and O
surface B-PARA
quality E-PARA
over O
a O
reasonably O
broad O
range S-PARA
of O
mechanical B-CONPRI
properties E-CONPRI
. O


We O
demonstrated O
the O
controlled O
fabrication S-MANP
of O
sub-pixel O
conical O
and O
aspherical O
smooth O
features O
, O
whereby O
the O
shape O
and O
dimensions S-FEAT
could O
be S-MATE
prescribed O
with O
the O
resin S-MATE
formulation O
and O
process B-CONPRI
parameters E-CONPRI
. O


Such O
features O
hold O
promising O
implications O
in O
micro-optic O
and O
microfluidic O
fabrication S-MANP
using O
the O
DLP-based O
3D B-MANP
printing E-MANP
technique O
. O


Use O
of O
this O
solution S-CONPRI
minimized O
the O
‘ O
stair-stepping O
’ O
effect O
in O
components S-MACEQ
printed O
in O
a O
layer-by-layer S-CONPRI
manner O
. O


Taken O
together O
, O
the O
present O
findings O
provide O
a O
basis O
for O
optimized O
photopolymer B-MATE
resin E-MATE
formulations O
that O
retain O
maximum O
vertical S-CONPRI
and O
lateral O
resolutions O
and O
minimal O
surface B-PRO
roughness E-PRO
and O
layering O
artifacts O
for O
a O
versatile O
range S-PARA
of O
mechanical S-APPL
and O
rheological B-PRO
properties E-PRO
suited O
to O
novel O
applications O
in O
3D B-MANP
printing E-MANP
of O
smooth O
free-form O
solids O
, O
micro-optics O
, O
and O
direct O
fabrication S-MANP
of O
microfluidic O
platforms O
with O
functional O
surfaces S-CONPRI
. O


The O
optimization S-CONPRI
of O
slurry S-MATE
compositions O
and O
processing O
parameters S-CONPRI
has O
significant O
potential O
for O
layered O
extrusion S-MANP
forming O
, O
a O
novel O
slurry-based O
additive B-MANP
manufacturing E-MANP
method O
. O


The O
optimal O
slurry S-MATE
composition S-CONPRI
was O
composed O
of O
50vol. O
% O
Al2O3 S-MATE
loading O
, O
1.5wt. O
% O
acetic O
acid O
as S-MATE
dispersant O
and O
2wt. O
% O
methylcellulose O
solution S-CONPRI
as S-MATE
binder O
. O


The O
processing O
parameters S-CONPRI
including O
layer B-PARA
height E-PARA
, O
print S-MANP
speed O
and O
nozzle B-CONPRI
diameter E-CONPRI
significantly O
influenced O
the O
fabrication S-MANP
quality O
. O


The O
orthogonal O
experiment S-CONPRI
showed O
that O
the O
print S-MANP
speed O
of O
15mm/s O
, O
nozzle B-CONPRI
diameter E-CONPRI
of O
0.40mm O
and O
layer B-PARA
height E-PARA
set O
as S-MATE
70 O
% O
of O
nozzle B-CONPRI
diameter E-CONPRI
was O
the O
optimized O
processing O
conditions O
. O


The O
lattice B-FEAT
structure E-FEAT
constructed O
under O
the O
optimized O
conditions O
exhibited O
uniform O
and O
well-shaped O
morphology S-CONPRI
before O
and O
after O
sintering S-MANP
. O


The O
solid-infilled O
ceramic S-MATE
specimen O
prepared O
via O
optimized O
parameters S-CONPRI
exhibited O
uniform O
structure S-CONPRI
and O
the O
surface B-PRO
roughness E-PRO
was O
0.75μm O
, O
which O
greatly O
improved O
the O
surface B-PARA
quality E-PARA
. O


Current O
3D B-MANP
printing E-MANP
capabilities O
onboard O
the O
International O
Space O
Station O
( O
ISS O
) O
are O
classified O
as S-MATE
experimental O
payloads O
. O


As S-MATE
payloads O
the O
products O
of O
these O
printers S-MACEQ
are O
returned O
to O
the O
ground O
for O
testing S-CHAR
and O
analysis O
. O


However O
, O
it O
has O
long O
been O
thought O
that O
3D B-MANP
printing E-MANP
must O
one O
day O
become O
a O
tool S-MACEQ
of O
space O
operations O
much O
like O
the O
electrical S-APPL
diagnostic O
equipment S-MACEQ
, O
and O
the O
soldering S-MANP
iron S-MATE
. O


This O
paper O
explores O
a O
case B-CONPRI
study E-CONPRI
in O
the O
use O
of O
one O
of O
the O
payload O
3D B-MACEQ
printers E-MACEQ
to O
manufacture S-CONPRI
a O
device O
to O
be S-MATE
used O
by O
the O
crew O
as S-MATE
part O
of O
nominal O
ISS O
Operations O
. O


The O
path O
from O
concept O
development O
through O
onboard O
printing O
and O
crew O
inspection S-CHAR
will O
be S-MATE
described O
. O


The O
lessons O
learned O
from O
this O
process S-CONPRI
are O
reviewed O
as S-MATE
constructive O
feedback S-PARA
on O
how O
existing O
processes S-CONPRI
can O
be S-MATE
expanded O
to O
enable O
this O
capability O
in O
the O
future O
. O


This O
experience O
will O
be S-MATE
carried O
forward O
into O
the O
development O
of O
a O
new O
process S-CONPRI
which O
will O
open O
the O
door O
for O
future O
use O
of O
3D B-MANP
printing E-MANP
onboard O
the O
ISS O
. O


Continuous O
fiber–reinforced O
thermosetting B-MATE
polymer E-MATE
composites S-MATE
( O
CFRTPCs O
) O
were O
prepared O
via O
three–dimensional O
( O
3D S-CONPRI
) O
printing O
. O


Typical O
process B-CONPRI
parameters E-CONPRI
were O
systematically O
investigated O
over O
a O
wide O
range S-PARA
. O


3D B-MANP
printed E-MANP
CFRTPC O
samples S-CONPRI
exhibited O
maximum O
flexural B-PRO
strength E-PRO
and O
modulus O
of O
952.89 O
MPa S-CONPRI
and O
74.05 O
GPa S-PRO
, O
respectively O
. O


Mechanical S-APPL
performance O
of O
the O
optimized O
process S-CONPRI
has O
increased O
nearly O
an O
order O
of O
magnitude S-PARA
than O
the O
previous O
reports O
. O


Advanced B-MATE
composite E-MATE
structures O
can O
be S-MATE
3D B-MANP
printed E-MANP
for O
potential O
applications O
in O
the O
future O
research S-CONPRI
. O


Continuous O
fiber-reinforced O
thermosetting B-MATE
polymer E-MATE
composites S-MATE
( O
CFRTPCs O
) O
were O
prepared O
via O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
printing O
in O
this O
study O
. O


The O
entire O
process S-CONPRI
was O
divided O
into O
impregnation S-MANP
, O
printing O
, O
and O
curing S-MANP
stages O
. O


The O
impregnation S-MANP
stage O
ensured O
a O
tightly O
bonded O
interface S-CONPRI
and O
uniform O
distribution S-CONPRI
of O
fibers S-MATE
and O
resin S-MATE
. O


The O
printing O
stage O
solved O
the O
great O
conveying O
resistance S-PRO
and O
poor O
adhesion S-PRO
caused O
by O
the O
addition O
of O
continuous B-MATE
fibers E-MATE
. O


The O
curing S-MANP
stage O
aimed O
to O
preserve O
the O
shapes O
of O
the O
pre-formed O
samples S-CONPRI
and O
completed O
the O
polymerization S-MANP
and O
crosslinking O
reactions O
. O


An O
investigation O
into O
the O
experimental B-CONPRI
design E-CONPRI
focused O
on O
optimizing O
the O
parameters S-CONPRI
of O
the O
manufacturing B-MANP
process E-MANP
, O
wherein O
printing B-PARA
speed E-PARA
, O
printing O
space O
, O
printing O
thickness O
, O
curing S-MANP
pressure O
, O
and O
curing S-MANP
temperature O
were O
selected O
as S-MATE
target O
variables O
. O


Finally O
, O
3D B-MANP
printed E-MANP
CFRTPC O
samples S-CONPRI
with O
58 O
wt. O
% O
fiber S-MATE
content O
exhibited O
maximum O
flexural B-PRO
strength E-PRO
and O
modulus O
of O
952.89 O
MPa S-CONPRI
and O
74.05 O
GPa S-PRO
, O
respectively O
. O


Moreover O
, O
complex O
CFRTPC O
components S-MACEQ
were O
fabricated S-CONPRI
to O
demonstrate O
the O
feasibility S-CONPRI
and O
generality O
of O
the O
proposed O
technique O
. O


These O
results O
may O
broaden O
the O
potential O
use O
of O
3D B-MANP
printed E-MANP
CFRTPCs O
in O
aerospace S-APPL
, O
defense O
, O
and O
automotive S-APPL
applications O
. O


A O
hybrid O
multi-objective O
optimization S-CONPRI
approach O
is O
proposed O
to O
optimize O
the O
printed O
line O
quality S-CONPRI
. O


The O
inherent O
contradiction O
is O
analyzed O
by O
a O
statistical O
response B-CONPRI
surface I-CONPRI
methodology E-CONPRI
. O


The O
robust O
3D S-CONPRI
optimal O
Pareto S-CONPRI
front O
is O
identified O
based O
on O
statistical O
uncertainty O
and O
a O
genetic B-CONPRI
algorithm E-CONPRI
. O


Aerosol O
jet O
printing O
( O
AJP O
) O
is O
an O
emerging O
3-dimensional O
( O
3D S-CONPRI
) O
printing B-ENAT
technology E-ENAT
to O
fabricate S-MANP
customized O
and O
conformal O
microelectronic O
components S-MACEQ
on O
various O
flexible O
substrates O
. O


Although O
the O
AJP O
technology S-CONPRI
has O
the O
capability O
of O
depositing O
fine O
features O
, O
the O
inherent O
contradiction O
between O
the O
printed O
line O
thickness O
and O
line O
edge O
roughness S-PRO
has O
a O
great O
impact S-CONPRI
on O
the O
printed O
line O
quality S-CONPRI
. O


The O
proposed O
approach O
consists O
of O
a O
central O
composite S-MATE
design O
( O
CCD O
) O
, O
a O
response B-CONPRI
surface I-CONPRI
methodology E-CONPRI
, O
a O
desirability O
function O
approach O
and O
a O
non-dominated O
sorting O
genetic B-CONPRI
algorithm E-CONPRI
III O
( O
NSGA-III O
) O
. O


In O
the O
proposed O
approach O
, O
the O
response B-CONPRI
surface I-CONPRI
methodology E-CONPRI
is O
combined O
with O
the O
CCD O
to O
investigate O
and O
quantify O
the O
correlations O
between O
the O
printed O
line O
features O
and O
the O
key O
process B-CONPRI
parameters E-CONPRI
. O


And O
the O
conflicting O
relationship O
between O
the O
printed O
line O
edge O
roughness S-PRO
and O
line O
thickness O
is O
identified O
by O
the O
CCD O
derived O
response O
surface B-ENAT
models E-ENAT
( O
RSMs O
) O
. O


The O
experimental S-CONPRI
results O
demonstrate O
that O
the O
proposed O
hybrid O
multi-objective O
optimization S-CONPRI
approach O
is O
beneficial O
to O
minimize O
the O
conflict O
between O
the O
printed O
line O
features O
, O
hence O
the O
lines O
can O
be S-MATE
produced O
with O
low O
line O
edge O
roughness S-PRO
and O
sufficient O
line O
thickness O
. O


Different O
from O
a O
traditional O
trial-and-error S-CONPRI
method O
in O
AJP O
, O
the O
proposed O
printing O
quality B-CONPRI
optimization E-CONPRI
approach O
is O
developed O
based O
on O
the O
principles O
of O
statistical O
modeling S-ENAT
, O
analysis O
of O
variance O
and O
global O
optimization S-CONPRI
. O


Therefore O
, O
the O
proposed O
printing O
quality B-CONPRI
optimization E-CONPRI
approach O
is O
more O
efficient O
and O
systematic O
. O


Moreover O
, O
the O
data-driven O
based O
characteristic O
makes O
the O
proposed O
approach O
applicable O
to O
other O
multi-objective O
optimization S-CONPRI
researches O
in O
additive B-MANP
manufacturing E-MANP
technologies O
. O


We O
explore O
elastic S-PRO
wave O
focusing O
and O
enhanced O
energy B-CONPRI
harvesting E-CONPRI
by O
means O
of O
a O
3D-printed S-MANP
Gradient-Index O
Phononic O
Crystal O
Lens S-MANP
( O
GRIN-PCL O
) O
bonded O
on O
a O
metallic S-MATE
host O
structure S-CONPRI
. O


The O
lens S-MANP
layer S-PARA
is O
fabricated S-CONPRI
by O
3D B-MANP
printing E-MANP
a O
rectangular O
array O
of O
cylindrical S-CONPRI
nylon O
stubs O
with O
varying O
heights O
. O


The O
stub O
heights O
are O
designed S-FEAT
to O
obtain O
a O
hyperbolic O
secant O
distribution S-CONPRI
of O
the O
refractive O
index O
to O
achieve O
the O
required O
phase S-CONPRI
velocity O
variation S-CONPRI
in O
space O
, O
hence O
the O
gradient-index O
lens S-MANP
behavior O
. O


Finite B-CONPRI
element E-CONPRI
simulations O
are O
performed O
on O
composite S-MATE
unit O
cells S-APPL
with O
various O
stub O
heights O
to O
obtain O
the O
lowest O
antisymmetric O
mode O
Lamb O
wave O
band O
diagrams O
, O
yielding O
a O
correlation O
between O
the O
stub O
height O
and O
refractive O
index O
. O


The O
elastic S-PRO
wave O
focusing O
performance S-CONPRI
of O
lenses O
with O
different O
design S-FEAT
parameters O
( O
gradient O
coefficient O
and O
aperture O
size O
) O
is O
simulated O
numerically O
under O
plane O
wave O
excitation S-CHAR
. O


It O
is O
observed O
that O
the O
focal O
points O
of O
the O
wider O
aperture O
lens S-MANP
designs S-FEAT
have O
better O
consistency S-CONPRI
with O
the O
analytical O
beam S-MACEQ
trajectory O
results O
. O


Experiments O
are O
conducted O
using O
a O
PA2200 O
nylon S-MATE
lens S-MANP
bonded O
to O
an O
aluminum S-MATE
plate O
to O
demonstrate O
wave O
focusing O
and O
enhanced O
energy B-CONPRI
harvesting E-CONPRI
within O
the O
3D-printed S-MANP
GRIN-PCL O
domain S-CONPRI
. O


The O
results O
show O
that O
3D B-MANP
printing E-MANP
can O
provide O
a O
simple S-MANP
and O
practical O
method O
for O
implementing O
phononic O
crystal O
concepts O
with O
minimal O
modification O
of O
the O
host O
structure S-CONPRI
. O


The O
spatial O
orientation S-CONPRI
of O
an O
object O
on O
a O
3D B-MANP
printing E-MANP
plate O
is O
a O
significant O
contributor O
to O
its O
printing O
time O
. O


Thus O
, O
the O
speed O
of O
the O
3D B-MANP
printing E-MANP
processes O
can O
generally O
be S-MATE
increased O
by O
using O
time-efficient O
object O
orientations S-CONPRI
. O


This O
paper O
presents O
a O
novel O
method O
for O
speeding-up O
printing B-MANP
processes E-MANP
that O
employs O
maximally O
efficient O
orientations S-CONPRI
. O


This O
method O
finds O
an O
orientation S-CONPRI
for O
the O
object O
that O
minimizes O
the O
number O
of O
disconnected O
components S-MACEQ
and O
the O
distance O
between O
the O
disconnected O
components S-MACEQ
that O
remain O
, O
thereby O
minimizing O
the O
time O
needed O
for O
the O
printer S-MACEQ
head O
to O
traverse O
empty O
areas S-PARA
. O


The O
method O
also O
considers O
the O
height O
of O
the O
printed O
object O
, O
its O
trapped O
volume S-CONPRI
, O
and O
the O
number O
of O
connected O
components S-MACEQ
in O
each O
layer S-PARA
. O


Our O
novel O
algorithm S-CONPRI
considers O
all O
four O
criteria O
, O
each O
weighted O
according O
to O
printer-specific O
and O
experimentally-obtained O
parameters S-CONPRI
. O


Preliminary O
trials O
demonstrate O
that O
this O
methodology S-CONPRI
can O
decrease O
printing O
times O
on O
fused B-CONPRI
deposition E-CONPRI
printers O
to O
45 O
% O
of O
that O
of O
current O
state O
of O
the O
art S-APPL
algorithms S-CONPRI
. O


Waveguides O
are O
important O
optical B-APPL
elements E-APPL
for O
sensing S-APPL
, O
illumination O
, O
artistic O
displays O
, O
integrated O
optical S-CHAR
circuits O
, O
as S-MATE
well O
as S-MATE
teaching O
aids O
for O
demonstrating O
important O
optical S-CHAR
phenomena O
. O


However O
, O
despite O
the O
high O
demand O
, O
most O
optical S-CHAR
materials S-CONPRI
are O
difficult O
to O
fabricate S-MANP
into O
desired O
shapes O
using O
state-of-the-art S-CONPRI
manufacturing B-MANP
technologies E-MANP
. O


This O
paper O
presents O
a O
novel O
method O
for O
3D B-MANP
printing E-MANP
customizable O
optics S-APPL
with O
a O
soft O
and O
stretchable S-FEAT
( O
over O
100 O
% O
elastic S-PRO
strains O
) O
thermoplastic B-MATE
polymer E-MATE
. O


To O
showcase O
the O
versatility O
of O
this O
approach O
, O
several O
applications O
were O
demonstrated O
, O
including O
unique O
artistic O
illumination O
, O
caustic O
patterns O
, O
beam S-MACEQ
splitter O
and O
combiner O
on O
both O
planar O
and O
3D S-CONPRI
conformal O
surfaces S-CONPRI
, O
and O
optical B-MACEQ
encoder E-MACEQ
. O


The O
simplicity O
of O
the O
fabrication S-MANP
process O
, O
low-cost O
, O
excellent O
optical B-PRO
properties E-PRO
, O
and O
flexibility S-PRO
provide O
an O
attractive O
pathway O
for O
fabricating S-MANP
integrated O
optical S-CHAR
devices O
and O
new O
opportunities O
for O
controlling O
light O
. O


( O
c S-MATE
) O
As-printed O
waveguide O
splitter O
and O
combiner O
circuit O
on O
a O
3D B-MANP
printed E-MANP
dome O
surface S-CONPRI
, O
and O
( O
d O
) O
Top O
view O
of O
lighted O
circuited O
. O


( O
e O
) O
Pattern S-CONPRI
of O
our O
group O
name O
“ O
AM3 O
Lab O
” O
on O
a O
black O
paper O
substrate S-MATE
, O
and O
( O
f S-MANP
) O
Lighted O
with O
different O
LEDs.Download O
: O
Download O
high-res B-CONPRI
image E-CONPRI
( O
296 O
Inkjet B-MANP
printing E-MANP
has O
been O
used O
as S-MATE
an O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
method O
to O
fabricate S-MANP
three-dimensional O
( O
3D S-CONPRI
) O
structures O
. O


However O
, O
a O
lack O
of O
materials S-CONPRI
suitable O
for O
inkjet B-MANP
printing E-MANP
poses O
one O
of O
the O
key O
challenges O
that O
impedes O
industry S-APPL
from O
fully O
adopting O
this O
technology S-CONPRI
. O


Consequently O
, O
many O
industry S-APPL
sectors O
are O
required O
to O
spend O
significant O
time O
and O
resources O
on O
formulating O
new O
materials S-CONPRI
for O
an O
AM B-MANP
process E-MANP
, O
instead O
of O
focusing O
on O
product B-CONPRI
development E-CONPRI
. O


To O
achieve O
the O
spatially O
controlled O
deposition S-CONPRI
of O
a O
printed O
voxel S-CONPRI
in O
a O
predictable S-CONPRI
and O
repeatable O
fashion S-CONPRI
, O
a O
combination O
of O
the O
physical B-PRO
properties E-PRO
of O
the O
‘ O
ink S-MATE
’ O
material S-MATE
, O
print B-MACEQ
head E-MACEQ
design S-FEAT
, O
and O
processing O
parameters S-CONPRI
is O
associated O
. O


Use O
of O
a O
liquid O
handler O
containing O
multi-pipette O
heads O
, O
to O
rapidly O
prepare O
inkjet S-MANP
formulations O
in O
a O
micro-array O
format O
, O
and O
subsequently O
measure O
the O
viscosity S-PRO
and O
surface B-PRO
tension E-PRO
for O
each O
in O
a O
high-throughput O
manner O
is O
reported O
. O


The O
throughput S-CHAR
is O
96 O
formulations O
per O
13.1 O
working O
hours O
, O
including O
sample S-CONPRI
preparation O
and O
subsequent O
printability S-PARA
determination O
. O


The O
HTS O
technique O
was O
validated O
by O
comparison O
with O
conventional O
viscosity S-PRO
and O
surface B-PRO
tension E-PRO
measurements O
, O
as S-MATE
well O
as S-MATE
the O
observation O
of O
droplet S-CONPRI
ejection O
during O
inkjet B-MANP
printing I-MANP
processes E-MANP
. O


Using O
this O
approach O
, O
a O
library O
of O
96 O
acrylate/methacrylate O
materials S-CONPRI
was O
screened O
to O
identify O
the O
printability S-PARA
of O
each O
formulation O
at O
different O
processing O
temperatures S-PARA
. O


The O
methodology S-CONPRI
and O
the O
material S-MATE
database S-ENAT
established O
using O
this O
HTS O
technique O
will O
allow O
academic O
and O
industrial S-APPL
users O
to O
rapidly O
select O
the O
most O
ideal O
formulation O
to O
deliver O
printability S-PARA
and O
a O
predicted S-CONPRI
processing O
window O
for O
a O
chosen O
application O
. O


Controlling O
cooling S-MANP
airflow O
is O
feasible O
in O
FFF S-MANP
process O
for O
enhancing O
performance S-CONPRI
. O


Cooling S-MANP
airflow O
has O
opposite O
influence O
on O
geometric O
quality S-CONPRI
and O
mechanical B-PRO
strength E-PRO
. O


Void S-CONPRI
and O
crystallinity O
of O
printed O
PLA S-MATE
model S-CONPRI
are O
influenced O
by O
the O
airflow O
cooling S-MANP
. O


The O
dimensional O
quality S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
a O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
-printed O
3D B-APPL
model E-APPL
are O
influenced O
by O
several O
process B-CONPRI
parameters E-CONPRI
. O


A O
forced-air O
cooling S-MANP
system O
that O
moves O
along O
with O
the O
print B-MACEQ
head E-MACEQ
was O
designed S-FEAT
and O
installed O
on O
a O
commercial O
3D S-CONPRI
FFF O
printer S-MACEQ
to O
control O
the O
cooling S-MANP
of O
the O
printed O
model S-CONPRI
. O


The O
quality S-CONPRI
of O
the O
printed O
polylactide O
( O
PLA S-MATE
) O
model S-CONPRI
, O
including O
the O
dimensions S-FEAT
and O
mechanical B-CONPRI
properties E-CONPRI
, O
was O
investigated O
for O
different O
cooling S-MANP
air O
velocities O
. O


It O
was O
found O
that O
the O
cooling S-MANP
air O
velocity O
had O
different O
influences O
on O
the O
dimensional O
quality S-CONPRI
and O
mechanical B-PRO
strength E-PRO
of O
the O
printed O
model S-CONPRI
. O


More O
specifically O
, O
higher O
cooling S-MANP
speeds O
generated O
better O
geometric O
accuracy S-CHAR
but O
lower O
mechanical B-PRO
strength E-PRO
. O


With O
the O
highest O
and O
lowest O
cooling S-MANP
air O
speeds O
of O
5 O
m/s O
and O
0 O
m/s O
, O
respectively O
, O
the O
tensile B-PRO
strengths E-PRO
of O
the O
printed O
models O
differed O
by O
4-fold O
. O


In O
order O
to O
determine O
a O
suitable O
cooling S-MANP
air O
velocity O
setting O
for O
each O
specific O
printing O
material S-MATE
, O
a O
design S-FEAT
model O
was O
proposed O
. O


The O
determined O
printing O
parameters S-CONPRI
were O
employed O
in O
the O
fabrication S-MANP
of O
a O
Rubik O
’ O
s S-MATE
cube S-CONPRI
, O
as S-MATE
an O
example O
. O


The O
assembled O
cube S-CONPRI
demonstrated O
satisfactory O
performance S-CONPRI
both O
in O
the O
dimensional O
quality S-CONPRI
and O
in O
the O
mechanical S-APPL
function O
. O


Therefore O
, O
the O
cooling S-MANP
air O
velocity O
can O
be S-MATE
employed O
as S-MATE
an O
additional O
control O
parameter S-CONPRI
in O
3D B-MANP
printing E-MANP
for O
a O
specified O
model S-CONPRI
. O


Material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
is O
widely O
used O
for O
porous B-FEAT
scaffolds E-FEAT
in O
which O
polymer B-MATE
filaments E-MATE
are O
extruded S-MANP
in O
the O
form O
of O
log-pile O
structures O
. O


These O
structures O
are O
typically O
designed S-FEAT
with O
the O
assumption O
that O
filaments S-MATE
have O
a O
continuous O
cylindrical S-CONPRI
profile O
. O


However O
, O
as S-MATE
a O
filament S-MATE
is O
extruded S-MANP
, O
it O
interacts O
with O
previously O
printed O
filaments S-MATE
( O
e.g O
. O


on O
lower O
3D B-MANP
printed E-MANP
layers O
) O
and O
its O
geometry S-CONPRI
varies O
from O
the O
cylindrical S-CONPRI
form O
. O


No O
models O
currently O
exist O
that O
can O
predict O
this O
critical O
variation S-CONPRI
, O
which O
impacts O
filament S-MATE
geometry O
, O
pore B-PARA
size E-PARA
and O
mechanical B-CONPRI
properties E-CONPRI
. O


Therefore O
, O
expensive O
time-consuming O
trial-and-error S-CONPRI
approaches O
to O
scaffold S-FEAT
design S-FEAT
are O
currently O
necessary O
. O


Multiphysics O
models O
for O
material B-MANP
extrusion E-MANP
are O
extremely O
computationally-demanding O
and O
not O
feasible O
for O
the O
size-scales O
involved O
in O
scaffold S-FEAT
structures.This O
paper O
presents O
a O
new O
computationally-efficient O
method O
, O
called O
the O
VOLume S-CONPRI
COnserving O
model S-CONPRI
for O
3D B-MANP
printing E-MANP
( O
VOLCO O
) O
. O


The O
VOLCO O
model S-CONPRI
simulates O
material B-MANP
extrusion E-MANP
during O
manufacturing S-MANP
and O
generates O
a O
voxelised O
3D-geometry-model O
of O
the O
predicted B-CONPRI
microarchitecture E-CONPRI
. O


The O
extrusion-deposition O
process S-CONPRI
is O
simulated O
in O
3D S-CONPRI
as O
a O
filament S-MATE
that O
elongates O
in O
the O
direction O
that O
the O
print-head O
travels O
. O


For O
each O
simulation S-ENAT
step O
in O
the O
model S-CONPRI
, O
a O
set S-APPL
volume O
of O
new O
material S-MATE
is O
simulated O
at O
the O
end O
of O
the O
filament S-MATE
. O


When O
previously O
3D B-MANP
printed E-MANP
filaments O
obstruct O
the O
deposition S-CONPRI
of O
this O
new O
material S-MATE
, O
it O
is O
deposited O
into O
the O
nearest O
neighbouring O
voxels S-CONPRI
according O
to O
a O
minimum O
distance O
criterion O
. O


This O
leads O
to O
filament S-MATE
spreading O
and O
widening.Experimental O
validation S-CONPRI
demonstrates O
the O
ability O
of O
VOLCO O
to O
simulate O
the O
geometry S-CONPRI
of O
3D B-MANP
printed E-MANP
filaments O
. O


In O
addition O
, O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
( O
FEA O
) O
simulations S-ENAT
utilising O
3D-geometry-models O
generated O
by O
VOLCO O
demonstrate O
its O
value O
and O
applicability O
for O
predicting O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
presented O
method O
enables O
structures O
to O
be S-MATE
validated O
and O
optimised O
prior O
to O
manufacture S-CONPRI
. O


Potential O
future O
adaptations O
of O
the O
model S-CONPRI
and O
integration O
into O
3D B-MANP
printing E-MANP
software O
are O
discussed O
. O


A O
new O
stitching O
algorithm S-CONPRI
that O
self-adapts O
to O
the O
object O
geometry S-CONPRI
is O
introduced O
. O


For O
slender O
objects O
, O
printing O
time O
can O
be S-MATE
reduced O
by O
25 O
% O
with O
the O
new O
algorithm S-CONPRI
. O


An O
inevitable O
trade-off O
between O
resolution S-PARA
and O
total O
size O
exists O
when O
3D B-MANP
printing E-MANP
objects O
. O


While O
it O
is O
capable O
of O
reaching O
a O
sub-micron S-FEAT
feature B-PARA
size E-PARA
, O
it O
needs O
to O
combine O
a O
high O
precision S-CHAR
movement O
mechanism S-CONPRI
with O
a O
lower O
precision S-CHAR
one O
when O
writing O
centimetric O
size O
objects O
. O


As S-MATE
is O
demonstrated O
on O
a O
winding S-CONPRI
microfluidic O
channel S-APPL
, O
this O
can O
lead S-MATE
to O
substantial O
manufacturing S-MANP
time O
gains O
of O
up O
to O
25 O
% O
. O


In O
this O
paper O
, O
a O
non-conventional O
way O
of O
additive B-MANP
manufacturing E-MANP
, O
curved-layered O
printing O
, O
has O
been O
applied O
to O
large-scale O
construction S-APPL
process O
. O


Despite O
the O
number O
of O
research S-CONPRI
works O
on O
Curved O
Layered O
Fused B-CONPRI
Deposition E-CONPRI
Modelling O
( O
CLFDM O
) O
over O
the O
last O
decade O
, O
few O
practical O
applications O
have O
been O
reported O
. O


The O
method O
was O
evaluated O
with O
the O
3D S-CONPRI
Concrete O
Printing B-MANP
process E-MANP
developed O
at O
Loughborough O
University O
. O


The O
evaluation O
of O
the O
method O
including O
the O
results O
of O
simulation S-ENAT
and O
printing O
revealed O
three O
principal O
benefits O
compared O
with O
existing O
flat-layered O
printing O
paths O
, O
which O
are O
particularly O
beneficial O
to O
large-scale O
AM B-MANP
techniques E-MANP
: O
( O
i O
) O
better O
surface B-PARA
quality E-PARA
, O
( O
ii O
) O
shorter O
printing O
time O
and O
( O
iii O
) O
higher O
surface S-CONPRI
strengths S-PRO
. O


Despite O
the O
enormous O
potential O
of O
additive B-MANP
manufacturing E-MANP
in O
fabricating S-MANP
three-dimensional O
battery S-APPL
electrodes O
, O
the O
structures O
realized O
through O
this O
technology S-CONPRI
are O
mainly O
limited O
to O
the O
interdigitated O
geometries S-CONPRI
due O
to O
the O
nature O
of O
the O
manufacturing B-MANP
process E-MANP
. O


This O
work O
reports O
a O
major O
advance O
in O
3D S-CONPRI
batteries O
, O
where O
highly O
complex O
and O
controlled O
3D S-CONPRI
electrode O
architectures O
with O
a O
lattice B-FEAT
structure E-FEAT
and O
a O
hierarchical O
porosity S-PRO
are O
realized O
by O
3D B-MANP
printing E-MANP
. O


Microlattice O
electrodes S-MACEQ
with O
porous S-PRO
solid O
truss S-MACEQ
members O
( O
Ag O
) O
are O
fabricated S-CONPRI
by O
Aerosol O
Jet O
3D B-MANP
printing E-MANP
that O
leads O
to O
an O
unprecedented O
improvement O
in O
the O
battery S-APPL
performance O
such O
as S-MATE
400 O
% O
increase O
in O
specific O
capacity S-CONPRI
, O
100 O
% O
increase O
in O
areal O
capacity S-CONPRI
, O
and O
a O
high O
electrode S-MACEQ
volume O
utilization O
when O
compared O
to O
a O
thin O
solid O
Ag O
block O
electrode S-MACEQ
. O


Further O
, O
the O
microlattice O
electrodes S-MACEQ
retain O
their O
morphologies S-CONPRI
after O
40 O
electrochemical S-CONPRI
cycles O
, O
demonstrating O
their O
mechanical S-APPL
robustness O
. O


These O
results O
indicate O
that O
the O
3D S-CONPRI
microlattice O
structure S-CONPRI
with O
a O
hierarchical O
porosity S-PRO
enhances O
the O
electrolyte S-APPL
transport O
through O
the O
electrode S-MACEQ
volume O
, O
increases O
the O
available O
surface B-PARA
area E-PARA
for O
electrochemical S-CONPRI
reaction O
, O
and O
relieves O
the O
intercalation-induced O
stress S-PRO
; O
leading O
to O
an O
extremely O
robust O
high O
capacity S-CONPRI
battery S-APPL
system O
. O


Results O
presented O
in O
this O
work O
can O
lead S-MATE
to O
new O
avenues O
for O
improving O
the O
performance S-CONPRI
of O
a O
wide O
range S-PARA
of O
electrochemical S-CONPRI
energy O
storage O
systems O
. O


Pores S-PRO
are O
common O
defects S-CONPRI
in O
the O
process S-CONPRI
of O
directed O
laser S-ENAT
deposition S-CONPRI
( O
DLD O
) O
which O
not O
only O
greatly O
reduce O
the O
fracture S-CONPRI
toughness O
of O
ceramic B-MATE
materials E-MATE
, O
but O
also O
lead S-MATE
to O
the O
failure S-CONPRI
of O
shaped O
parts O
. O


In O
this O
paper O
, O
the O
formation O
mechanism S-CONPRI
of O
pores S-PRO
was O
analyzed O
and O
the O
effects O
of O
laser B-PARA
power E-PARA
, O
feeding O
rate O
, O
scanning B-PARA
speed E-PARA
and O
ultrasonic O
power S-PARA
on O
pores S-PRO
were O
investigated O
. O


Transmission B-CHAR
electron I-CHAR
microscope E-CHAR
, O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
observation O
and O
X-ray B-CHAR
diffraction I-CHAR
analysis E-CHAR
were O
carried O
out O
for O
sample S-CONPRI
microstructure S-CONPRI
and O
phase B-CONPRI
composition E-CONPRI
respectively O
. O


The O
relative B-PRO
density E-PRO
of O
samples S-CONPRI
was O
measured O
by O
the O
progressive O
focused O
ion S-CONPRI
beam S-MACEQ
and O
the O
porosity S-PRO
was O
calculated O
by O
image S-CONPRI
processing O
software B-CONPRI
Image E-CONPRI
. O


The O
results O
show O
that O
the O
pores S-PRO
are O
divided O
into O
gas S-CONPRI
holes O
and O
shrinkage S-CONPRI
cavities O
. O


The O
appearance O
of O
circular O
gas S-CONPRI
holes O
with O
smooth O
inner O
walls O
are O
caused O
by O
the O
feeding O
method O
by O
gas S-CONPRI
forced O
blowing S-MANP
, O
the O
gas S-CONPRI
mixed O
with O
powder S-MATE
itself O
, O
and O
the O
gas S-CONPRI
in O
the O
molten B-CONPRI
pool E-CONPRI
formed O
by O
gasification O
of O
low-melting O
impurities S-PRO
and O
alumina/zirconia O
during O
laser B-CONPRI
processing E-CONPRI
. O


The O
gas S-CONPRI
holes O
are O
evenly O
distributed O
in O
the O
cross-section O
of O
the O
thin-walled O
specimen O
parallel O
to O
the O
scanning B-PARA
speed E-PARA
. O


As S-MATE
the O
temperature S-PARA
changes O
drastically O
, O
the O
material S-MATE
around O
the O
melt S-CONPRI
solidifies O
first O
, O
the O
melt S-CONPRI
will O
be S-MATE
attached O
to O
the O
solidified O
material S-MATE
to O
shrink S-FEAT
, O
so O
that O
the O
melt S-CONPRI
can O
not O
be S-MATE
filled O
as S-MATE
a O
solid O
and O
finally O
the O
shrinkage S-CONPRI
cavities O
are O
formed O
. O


Generally O
the O
shrinkage S-CONPRI
cavities O
are O
irregular O
and O
the O
pore S-PRO
wall O
is O
relatively O
rough O
, O
mainly O
concentrated O
on O
the O
top O
of O
thin-walled O
samples S-CONPRI
. O


The O
laser B-PARA
power E-PARA
has O
the O
greatest O
influence O
on O
the O
pores S-PRO
, O
which O
has O
the O
greatest O
effect O
on O
the O
porosity S-PRO
but O
little O
effect O
on O
the O
shrinkage S-CONPRI
cavities O
. O


When O
the O
ultrasonic O
power S-PARA
is O
180 O
W O
, O
the O
porosity S-PRO
reaches O
a O
minimum O
of O
0.1±0.05 O
% O
and O
the O
relative B-PRO
density E-PRO
is O
99.9±0.1 O
% O
. O


Traditional O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
bioprinting S-APPL
techniques O
of O
reactive B-MATE
materials E-MATE
usually O
include O
a O
mixing S-CONPRI
step O
of O
reactive O
agents O
prior O
to O
deposition S-CONPRI
, O
leading O
to O
potential O
changes O
in O
the O
rheological S-PRO
and O
biocompatibility S-PRO
properties O
of O
the O
resulting O
ink S-MATE
. O


During O
intersecting O
jets O
printing O
, O
reactive B-MATE
materials E-MATE
are O
dispensed O
separately O
, O
colliding O
and O
mixing S-CONPRI
with O
each O
other O
in O
air O
before O
landing O
on O
a O
previously O
deposited B-CHAR
layer E-CHAR
. O


While O
this O
enables O
reactive B-MATE
material E-MATE
printing O
using O
a O
printing-then-mixing O
approach O
, O
the O
resulting O
excess O
fluid S-MATE
may O
compromise O
the O
printing O
quality S-CONPRI
and O
accuracy S-CHAR
. O


This O
study O
aims O
to O
improve O
the O
performance S-CONPRI
of O
intersecting O
jets–based O
reactive B-MATE
material E-MATE
printing O
by O
introducing O
a O
stainless-steel O
wire O
mesh O
and O
fibrous S-PRO
tissue O
paper–based O
liquid-absorbing O
system O
, O
which O
functions O
as S-MATE
a O
method O
to O
remove O
the O
excess O
resultant O
liquid O
from O
the O
printing O
zone O
. O


By O
selecting O
a O
proper O
wire O
mesh O
, O
the O
proposed O
liquid-absorbing O
system O
can O
absorb O
up O
to O
65–90 O
% O
of O
the O
excess O
liquid O
( O
water O
herein O
) O
resulting O
from O
printing O
aqueous O
reactive O
sodium S-MATE
alginate S-MATE
and O
calcium S-MATE
chloride O
inks O
, O
which O
are O
selected O
as S-MATE
model O
materials S-CONPRI
in O
this O
study O
. O


By O
controlling O
the O
tilt B-FEAT
angles E-FEAT
of O
intersecting O
jets O
, O
the O
incident O
angle O
of O
post-collision O
droplets S-CONPRI
is O
desirable O
to O
be S-MATE
less O
than O
14° O
to O
avoid O
droplet S-CONPRI
bouncing O
on O
the O
top O
of O
a O
previously O
deposited B-CHAR
layer E-CHAR
during O
3D B-MANP
bioprinting E-MANP
. O


Using O
the O
liquid-absorbing O
system O
, O
different O
3D B-CONPRI
structures E-CONPRI
have O
been O
successfully O
printed O
using O
intersecting O
jets O
printing O
. O


For O
tubular S-FEAT
alginate S-MATE
constructs O
printed O
in O
air O
from O
sodium S-MATE
alginate S-MATE
and O
calcium S-MATE
chloride O
inks O
, O
a O
2.5 O
height-diameter O
ratio O
can O
be S-MATE
achieved O
. O


The O
proposed O
printing B-ENAT
technology E-ENAT
does O
not O
influence O
the O
post-printing O
cell B-CHAR
viability E-CHAR
while O
printing O
3T3 O
cells S-APPL
, O
demonstrating O
its O
promising O
potential O
for O
bioprinting S-APPL
applications O
. O


Methodology S-CONPRI
and O
challenges O
of O
3D B-MANP
printing E-MANP
repairs O
outlined O
. O


Repeatable O
geopolymer O
temperature S-PARA
sensor S-MACEQ
presented O
. O


Adhesion S-PRO
strength O
between O
printed O
patch O
and O
concrete S-MATE
substrate O
0.6 O
MPa S-CONPRI
. O


This O
paper O
addresses O
this O
issue O
by O
outlining O
, O
for O
the O
first O
time O
a O
3D S-CONPRI
printable O
temperature S-PARA
sensing S-APPL
repair O
for O
concrete S-MATE
. O


The O
multifunctional O
material S-MATE
used O
in O
this O
study O
is O
a O
geopolymer O
: O
a O
durable O
alternative O
to O
ordinary O
Portland O
cement S-MATE
repairs O
, O
which O
can O
be S-MATE
electrically O
interrogated O
to O
act O
as S-MATE
a O
sensor S-MACEQ
. O


In O
this O
paper O
, O
we O
outline O
the O
material S-MATE
and O
3D B-MANP
printing E-MANP
process O
development O
, O
and O
demonstrate O
3D B-MANP
printed E-MANP
repair O
patches O
with O
a O
temperature S-PARA
sensing S-APPL
precision S-CHAR
of O
0.1 O
°C O
, O
a O
long-term O
sensing S-APPL
repeatability S-CONPRI
of O
0.3 O
°C O
, O
a O
compressive B-PRO
strength E-PRO
of O
24 O
MPa S-CONPRI
, O
and O
an O
adhesion S-PRO
strength O
to O
concrete S-MATE
of O
0.6 O
MPa S-CONPRI
. O


The O
work O
demonstrates O
the O
feasibility S-CONPRI
of O
using O
additive B-MANP
manufacturing E-MANP
as O
a O
new O
means O
of O
applying O
repairs O
to O
concrete S-MATE
substrates O
, O
and O
provides O
one O
clear O
pathway O
to O
removing O
some O
of O
the O
barriers O
to O
the O
field O
deployment O
of O
multifunctional O
materials S-CONPRI
in O
a O
civil O
engineering S-APPL
context O
. O


The O
process S-CONPRI
shown O
here O
could O
enhance O
the O
design S-FEAT
versatility O
of O
self-sensing O
repairs O
, O
unlock O
remote O
deployment O
, O
and O
de-cost O
and O
de-risk O
actions O
that O
prolong O
the O
lifespan O
and O
performance S-CONPRI
of O
existing O
concrete S-MATE
structures O
. O


Brittle S-PRO
polymers O
suffer O
from O
the O
lack O
of O
stretchability S-FEAT
, O
which O
limits S-CONPRI
their O
application O
when O
large O
deformation S-CONPRI
is O
required O
. O


To O
address O
this O
limitation O
, O
we O
investigate O
the O
stretchability S-FEAT
of O
a O
set S-APPL
of O
cellular B-MATE
materials E-MATE
with O
conventional O
and O
novel O
cell S-APPL
architectures O
through O
3D B-MANP
printing E-MANP
, O
experimental S-CONPRI
testing O
, O
and O
computational O
simulation S-ENAT
. O


The O
presence O
of O
sharp O
corners O
restricts O
the O
stretchability S-FEAT
of O
the O
honeycomb S-CONPRI
and O
arrowhead O
cellular O
architectures O
. O


A O
new O
class O
of O
accordion-like O
cellular O
architecture S-APPL
with O
sinusoidal O
struts S-MACEQ
is O
designed S-FEAT
to O
enhance O
the O
planar O
stretchability S-FEAT
of O
cellular O
solids O
. O


These O
accordion-like O
sinusoidal O
architectures O
exhibit O
an O
enhancement O
in O
the O
stretchability S-FEAT
of O
the O
cellular B-MATE
materials E-MATE
even O
for O
those O
samples B-CONPRI
fabricated E-CONPRI
from O
brittle S-PRO
polymers O
. O


The O
manufacturability S-CONPRI
of O
the O
proposed O
architectures O
is O
demonstrated O
utilizing O
SLA S-MACEQ
and O
FDM B-MANP
additive I-MANP
manufacturing I-MANP
techniques E-MANP
. O


We O
customize O
the O
3D B-MANP
printing E-MANP
settings O
to O
fabricate S-MANP
specimens O
with O
tailored O
architectures O
for O
experimental S-CONPRI
testing O
. O


Comparing O
the O
stress-strain O
curves O
obtained O
by O
experimental S-CONPRI
testing O
on O
the O
3D B-MANP
printed E-MANP
samples O
with O
numerical B-ENAT
simulation E-ENAT
confirms O
that O
the O
failure S-CONPRI
strains O
for O
sinusoidal O
architectures O
can O
be S-MATE
as S-MATE
high O
as S-MATE
20 O
times O
that O
of O
conventional O
honeycombs O
without O
compromising O
the O
energy B-CHAR
absorption E-CHAR
efficiency O
of O
the O
cellular B-MATE
materials E-MATE
. O


The O
stress-strain O
curves O
for O
3D B-MANP
printed E-MANP
samples O
fabricated S-CONPRI
from O
flexible O
polymers S-MATE
are O
presented O
to O
show O
that O
energy O
dissipation O
in O
a O
hysteresis B-CHAR
loop E-CHAR
also O
can O
be S-MATE
enhanced O
by O
exploiting O
the O
accordion-like O
sinusoidal O
architectural O
designs S-FEAT
. O


The O
sinusoidal O
struts S-MACEQ
in O
accordion-like O
cellular O
architectures O
offer O
a O
design S-FEAT
route O
to O
extend O
the O
material B-CONPRI
property E-CONPRI
chart O
to O
achieve O
ultrahigh O
stretchability S-FEAT
in O
lightweight B-CONPRI
3D E-CONPRI
printable O
brittle S-PRO
and O
flexible O
polymers S-MATE
for O
applications O
that O
require O
combined O
stretchability S-FEAT
, O
lightweighting S-PRO
, O
and O
energy B-CHAR
absorption E-CHAR
such O
as S-MATE
soft O
robotics S-APPL
, O
stretchable B-MACEQ
electronics E-MACEQ
, O
and O
wearable O
protection O
shields O
. O


In O
additive S-MATE
construction O
, O
ambitious O
goals O
to O
fabricate S-MANP
a O
concrete S-MATE
building O
in O
less O
than O
24 O
h O
are O
attempted O
. O


This O
analysis O
included O
a O
study O
of O
the O
variation S-CONPRI
in O
comprehensive O
layer S-PARA
print O
times O
, O
expected O
trends S-CONPRI
and O
forecasting O
for O
what O
is O
expected O
in O
future O
prints O
of O
similar O
types O
. O


Furthermore O
, O
the O
study O
included O
a O
determination O
and O
comparison O
of O
print S-MANP
time O
, O
elapsed O
time O
and O
construction S-APPL
time O
, O
as S-MATE
well O
as S-MATE
a O
look O
at O
the O
effect O
of O
environmental O
conditions O
on O
the O
delay O
events O
. O


Upon O
finishing S-MANP
, O
the O
analysis O
concluded O
that O
the O
3D B-MANP
printed E-MANP
building O
was O
completed O
in O
14-hours O
of O
print S-MANP
time O
, O
31.2-hours O
elapsed O
time O
, O
or O
a O
total O
of O
5 O
days O
of O
construction S-APPL
time O
. O


Anisotropy S-PRO
of O
mechanical B-CONPRI
properties E-CONPRI
and O
support B-MATE
material E-MATE
removing O
are O
the O
two O
main O
problems O
when O
fabricating S-MANP
3D S-CONPRI
lattice O
structures O
by O
integrated O
printing O
via O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technology S-CONPRI
. O


Aiming O
at O
these O
two O
problems O
, O
a O
snap-fit S-FEAT
method O
is O
introduced O
into O
PolyJet S-CONPRI
technology O
to O
fabricate S-MANP
polymer O
lattice B-FEAT
structures E-FEAT
with O
four O
typical O
configurations O
, O
namely O
BCC S-CONPRI
, O
BCC-Z O
, O
FCC S-CONPRI
and O
octet O
. O


Uniaxial O
compression B-CHAR
tests E-CHAR
indicate O
that O
both O
the O
strengths S-PRO
and O
energy B-CHAR
absorptions E-CHAR
of O
the O
four O
kinds O
of O
snap-fitted O
lattices S-CONPRI
are O
increased O
by O
over O
100 O
% O
compared O
to O
the O
integrated O
counterparts O
. O


The O
effect O
of O
strut B-PARA
thickness E-PARA
on O
compressive O
responses O
of O
the O
snap-fitted O
and O
integrated O
lattices S-CONPRI
is O
investigated O
. O


With O
the O
decrease O
of O
strut B-PARA
thickness E-PARA
, O
the O
advantage O
in O
the O
strength S-PRO
of O
the O
snap-fitted O
lattices S-CONPRI
becomes O
more O
obvious O
compared O
to O
the O
integrated O
counterparts O
. O


Ideal O
maximum O
strength S-PRO
models O
based O
on O
yield O
, O
elastic B-PRO
buckling E-PRO
and O
inelastic O
buckling S-PRO
are O
developed O
and O
are O
able O
to O
predict O
the O
compressive O
peak O
strengths S-PRO
of O
the O
snap-fitted O
PolyJet B-CONPRI
lattices E-CONPRI
. O


This O
study O
opens O
up O
an O
avenue O
for O
the O
fabrication S-MANP
of O
large O
scale O
3D B-MANP
printed E-MANP
lattice O
structures O
with O
optimal O
mechanical B-CONPRI
properties E-CONPRI
and O
without O
support B-MATE
material E-MATE
removing O
problem O
. O


This O
paper O
aims O
to O
study O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
mixed O
isotropic B-MATE
carbon I-MATE
fiber E-MATE
3D B-MANP
printed E-MANP
composites O
and O
further O
investigates S-CONPRI
the O
influence O
of O
hot O
press S-MACEQ
on O
the O
[ O
0°/45°/90° O
] O
2 O
fiber S-MATE
angles O
composite S-MATE
with O
varying O
temperature S-PARA
, O
pressure S-CONPRI
and O
time O
. O


Tensile B-CHAR
tests E-CHAR
, O
autoclave S-MACEQ
treatment O
and O
microstructural B-CHAR
observation E-CHAR
were O
utilized O
to O
characterize O
the O
composites S-MATE
. O


Results O
revealed O
that O
the O
[ O
0°/45°/90° O
] O
2 O
performed O
the O
highest O
tensile B-PRO
strength E-PRO
of O
79 O
MPa S-CONPRI
and O
modulus O
of O
3.51 O
GPa S-PRO
, O
compared O
to O
[ O
30°/45°/60° O
] O
2 O
and O
[ O
15°/45°/75° O
] O
2 O
. O


This O
is O
due O
to O
the O
fibers S-MATE
along O
the O
tensile S-PRO
axis O
angle O
that O
bears O
maximum O
load O
in O
longitudinal O
direction O
. O


At O
200 O
°C O
temperature S-PARA
, O
the O
hot B-MANP
pressed E-MANP
composites S-MATE
presented O
the O
highest O
tensile B-PRO
strength E-PRO
of O
98 O
MPa S-CONPRI
and O
modulus O
of O
3.93 O
GPa S-PRO
than O
non-hot O
pressed S-MANP
. O


Increased O
temperature S-PARA
caused O
better O
interface S-CONPRI
wettability O
between O
fibers S-MATE
and O
matrix O
. O


At O
200 O
kPa O
pressure S-CONPRI
, O
the O
hot B-MANP
pressed E-MANP
composites S-MATE
showed O
the O
highest O
tensile B-PRO
strength E-PRO
of O
100 O
MPa S-CONPRI
and O
modulus O
of O
4.06 O
GPa S-PRO
than O
non-hot O
pressed S-MANP
. O


Further O
increased O
pressure S-CONPRI
resulted O
in O
lower O
tensile B-PRO
strength E-PRO
and O
modulus O
, O
as S-MATE
the O
material S-MATE
became O
stiffer O
pushing O
more O
matrix O
material S-MATE
to O
side O
leaving O
numerous O
fibers S-MATE
unbounded O
by O
the O
matrix O
. O


For O
30 O
min O
withholding O
time O
, O
the O
hot B-MANP
pressed E-MANP
composites S-MATE
indicated O
the O
highest O
tensile B-PRO
strength E-PRO
of O
106 O
MPa S-CONPRI
and O
modulus O
of O
4.27 O
GPa S-PRO
than O
non-hot O
pressed S-MANP
. O


Increased O
time O
caused O
strongest O
interface B-CONPRI
bonding E-CONPRI
by O
removing O
the O
air O
gaps O
induced O
during O
printing O
between O
fibers S-MATE
and O
matrix O
. O


Results O
revealed O
that O
hot O
press S-MACEQ
significantly O
improved O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
carbon B-MATE
fiber E-MATE
3D B-MANP
printed E-MANP
composites O
. O


To O
realize O
the O
full O
potential O
of O
3D B-ENAT
Printing I-ENAT
technology E-ENAT
in O
the O
design S-FEAT
of O
materials S-CONPRI
and O
structures O
, O
it O
is O
indispensable O
to O
characterize O
and O
predict O
the O
mechanical B-CONPRI
response E-CONPRI
of O
3D B-MANP
Printing E-MANP
materials O
to O
external B-CONPRI
stimuli E-CONPRI
. O


This O
study O
is O
focused O
on O
hyperelastic O
strain S-PRO
measurements O
and O
constitutive O
parameters S-CONPRI
identification O
of O
3D B-MANP
printed E-MANP
soft O
polymers S-MATE
undergoing O
uniaxial O
deformation S-CONPRI
. O


A O
simple S-MANP
method O
using O
an O
optical S-CHAR
camera S-MACEQ
in O
conjunction O
with O
an O
image S-CONPRI
processing O
tool S-MACEQ
is O
proposed O
to O
accurately S-CHAR
measure O
the O
average S-CONPRI
strain O
experienced O
by O
rubbery O
polymers S-MATE
during O
a O
tensile B-CHAR
test E-CHAR
. O


The O
potential O
of O
the O
method O
is O
demonstrated O
through O
tensile B-CHAR
tests E-CHAR
of O
3D B-MANP
printed E-MANP
soft O
polymer S-MATE
by O
accurately S-CHAR
determining O
the O
stress–strain O
response O
and O
the O
Poisson O
's O
ratio O
without O
using O
extensometers O
. O


Influence O
of O
printing O
direction O
on O
the O
anisotropic S-PRO
behavior O
of O
3D B-MANP
printed E-MANP
polymer O
is O
investigated O
by O
applying O
the O
proposed O
test O
method O
to O
specimens O
printed O
in O
two O
different O
directions O
. O


The O
Neo-Hookean O
constitutive O
parameters S-CONPRI
of O
the O
soft O
polymer S-MATE
are O
determined O
from O
the O
experimentally O
obtained O
stress–strain O
data S-CONPRI
. O


Moreover O
, O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
( O
FEA O
) O
of O
the O
soft O
polymer S-MATE
is O
performed O
to O
show O
that O
the O
constitutive O
parameters S-CONPRI
determined O
can O
predict O
the O
mechanical B-CONPRI
response E-CONPRI
of O
the O
tested O
polymer S-MATE
accurately S-CHAR
if O
used O
in O
commercial O
FEA O
packages O
. O


The O
additive B-MANP
manufacturing E-MANP
of O
structural O
composites S-MATE
is O
a O
disruptive O
technology S-CONPRI
currently O
limited O
by O
its O
moderate O
mechanical B-CONPRI
properties E-CONPRI
. O


Continuous O
fibre S-MATE
reinforcements O
have O
recently O
been O
developed O
to O
create O
high O
performance S-CONPRI
composites S-MATE
and O
open O
up O
encouraging O
prospects O
. O


In O
addition O
, O
to O
apply O
these O
materials S-CONPRI
to O
engineering S-APPL
applications O
, O
it O
is O
of O
high O
importance O
to O
evaluate O
the O
effect O
of O
environmental O
conditions O
on O
their O
mechanical S-APPL
performances O
, O
particularly O
when O
moisture-sensitive O
polymer S-MATE
is O
used O
( O
PolyAmide S-MATE
PA S-CHAR
for O
instance O
) O
which O
is O
currently O
lacking O
in O
the O
literature.This O
present O
article O
aims O
to O
investigate O
in O
more O
detail O
the O
relationship O
between O
the O
process S-CONPRI
, O
the O
mechanical B-CONPRI
behaviour E-CONPRI
and O
the O
induced O
properties S-CONPRI
of O
continuous O
carbon S-MATE
and O
glass B-MATE
fibres E-MATE
reinforced O
with O
a O
polyamide S-MATE
matrix O
manufactured S-CONPRI
using O
a O
commercial O
3D B-MACEQ
printer E-MACEQ
. O


In O
addition O
, O
their O
hygromechanical O
behaviour O
linked O
to O
moisture O
effect O
is O
investigated O
through O
sorption O
, O
hygroexpansion O
and O
mechanical B-CONPRI
properties E-CONPRI
characterization O
on O
a O
wide O
range S-PARA
of O
relative O
humidity O
( O
10–98 O
% O
Relative O
Humidity O
RH S-MATE
) O
.The O
printing B-MANP
process E-MANP
induces O
an O
original O
microstructure S-CONPRI
with O
multiscale O
singularities O
( O
intra/inter O
beads S-CHAR
porosity O
and O
filament S-MATE
loop O
) O
. O


Longitudinal O
tensile S-PRO
performance S-CONPRI
shows O
that O
the O
reinforcing O
mechanism S-CONPRI
is O
typical O
of O
composite S-MATE
laminates O
for O
glass S-MATE
and O
carbon S-MATE
. O


However O
, O
the O
rather O
poor O
transverse O
properties S-CONPRI
are O
not O
well O
fitted O
by O
the O
Rule B-CONPRI
Of I-CONPRI
Mixture E-CONPRI
( O
ROM O
) O
, O
thus O
underlining O
the O
specificity O
of O
the O
printing-induced O
microstructure S-CONPRI
and O
an O
anisotropic S-PRO
behaviour O
in O
the O
material.Non-negligible O
( O
5–6 O
% O
) O
moisture O
uptake O
is O
observed O
at O
98 O
% O
RH S-MATE
, O
as S-MATE
well O
as S-MATE
orthotropic O
hygroscopic S-PRO
expansion O
of O
PA/carbon O
and O
PA/glass O
composites S-MATE
. O


The O
consequences O
of O
various O
moisture O
contents O
on O
mechanical B-CONPRI
properties E-CONPRI
are O
studied O
, O
showing O
a O
reduction S-CONPRI
of O
PA/carbon O
stiffness S-PRO
and O
strength S-PRO
of O
25 O
and O
18 O
% O
in O
the O
longitudinal O
direction O
and O
45 O
and O
70 O
% O
in O
the O
transverse O
direction O
. O


For O
PA/glass O
composites S-MATE
, O
we O
obtain O
a O
reduction S-CONPRI
in O
strength S-PRO
of O
25 O
% O
in O
the O
longitudinal O
direction O
, O
along O
with O
a O
80 O
% O
reduction S-CONPRI
of O
stiffness S-PRO
and O
45 O
% O
in O
strength S-PRO
in O
the O
transverse O
direction O
. O


Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
is O
one O
of O
the O
most O
popular O
3D B-MANP
printing E-MANP
processes O
that O
can O
be S-MATE
used O
to O
manufacture S-CONPRI
flexible O
parts O
. O


In O
this O
work O
, O
we O
investigate O
the O
impact S-CONPRI
of O
stacking O
sequence O
, O
slit O
size O
, O
and O
thickness O
on O
the O
tensile B-PRO
properties E-PRO
of O
3D B-MANP
printed E-MANP
flexible O
kirigami O
specimens O
. O


In O
addition O
, O
we O
demonstrate O
how O
the O
transition S-CONPRI
phenomenon O
and O
out-of-plane O
deformation S-CONPRI
can O
significantly O
improve O
percent O
elongation S-PRO
at O
their O
breaking O
point O
. O


Considering O
the O
deformed B-PRO
shape E-PRO
during O
testing S-CHAR
, O
specimens O
with O
a O
combination O
of O
layers O
printed O
along O
and O
transverse O
to O
their O
length O
showed O
the O
highest O
tensile S-PRO
break O
strength S-PRO
and O
the O
percent O
break O
elongation S-PRO
( O
2.43 O
MPa S-CONPRI
and O
183 O
% O
, O
respectively O
) O
. O


It O
is O
also O
determined O
that O
the O
occurrence O
of O
the O
transition S-CONPRI
phenomenon O
depends O
on O
the O
specimen O
’ O
s S-MATE
thickness O
, O
and O
was O
observed O
for O
the O
1 O
mm S-MANP
and O
1.5 O
mm S-MANP
thick O
samples S-CONPRI
. O


The O
heating S-MANP
of O
a O
polymer S-MATE
in O
a O
liquefier O
of O
a O
material B-MANP
extrusion I-MANP
3D I-MANP
printer E-MANP
is O
numerically O
studied O
. O


The O
polymer S-MATE
is O
taken O
as S-MATE
a O
generalized O
Newtonian B-CONPRI
fluid E-CONPRI
with O
a O
dynamical O
viscosity S-PRO
function O
of O
shear O
rate O
and O
temperature S-PARA
. O


The O
system O
of O
equations O
is O
solved O
using O
a O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
. O


The O
boundary B-CONPRI
conditions E-CONPRI
are O
adapted O
by O
comparison O
with O
the O
previous O
work O
of O
Peng O
et O
al S-MATE
. O


[ O
5 O
] O
showing O
that O
the O
thermal O
contact S-APPL
between O
the O
polymer S-MATE
and O
the O
liquefier O
is O
very O
well O
established O
. O


The O
limiting O
printing O
conditions O
are O
studied O
by O
determining O
the O
length O
over O
which O
the O
polymer S-MATE
temperature O
is O
below O
the O
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
. O


This O
provides O
a O
simple S-MANP
relation O
for O
the O
inlet S-MACEQ
velocity O
as S-MATE
a O
function O
of O
the O
working O
parameters S-CONPRI
and O
the O
polymer S-MATE
properties O
. O


The O
use O
of O
3D B-ENAT
printing I-ENAT
technologies E-ENAT
enhanced O
with O
component S-MACEQ
placement O
and O
electrical S-APPL
interconnect O
deposition S-CONPRI
enables O
electronic O
systems O
with O
freedom O
in O
fabrication S-MANP
and O
complex O
embedded O
circuitry O
. O


However O
, O
with O
more O
electrical S-APPL
functionality O
being O
integrated O
, O
new O
material S-MATE
requirements O
become O
increasingly O
important O
. O


This O
paper O
introduces O
a O
novel O
approach O
for O
processing O
adhesives S-MATE
with O
an O
extrusion-based O
UV-assisted O
3D S-CONPRI
dispensing O
process S-CONPRI
. O


A O
specimen O
study O
revealed O
promising O
results O
for O
three O
out O
of O
six O
adhesives S-MATE
( O
denoted O
as S-MATE
A O
, O
D O
, O
E O
) O
, O
for O
which O
an O
extensive O
anisotropy S-PRO
evaluation O
was O
performed O
: O
The O
relationship O
between O
the O
layered O
construction S-APPL
strategy O
and O
the O
material B-CONPRI
properties E-CONPRI
of O
the O
printed O
parts O
was O
characterized O
by O
micrograph O
analysis O
, O
tensile B-CHAR
testing E-CHAR
along O
with O
fracture S-CONPRI
analysis O
and O
laser S-ENAT
flash S-MATE
analysis O
. O


An O
exemplary O
study O
for O
one O
adhesive S-MATE
via O
tensile B-CHAR
testing E-CHAR
showed O
no O
significant O
difference O
between O
three O
printing O
orientations S-CONPRI
. O


However O
, O
different O
construction S-APPL
strategies O
influenced O
the O
degree O
of O
anisotropy S-PRO
. O


In O
addition O
, O
the O
evaluation O
of O
thermal O
anisotropy S-PRO
revealed O
a O
link O
between O
the O
thermal B-PRO
conductivity E-PRO
and O
the O
rate O
of O
the O
UV-curing O
for O
A O
and O
D. O
For O
material S-MATE
E O
, O
no O
significant O
difference O
was O
measured O
. O


The O
work O
presented O
in O
this O
article O
shows O
that O
dual-curing O
adhesives S-MATE
, O
in O
particular O
epoxy S-MATE
systems O
, O
are O
promising O
choices O
for O
additive B-MANP
manufacturing E-MANP
: O
It O
was O
possible O
to O
print S-MANP
fine O
geometries S-CONPRI
with O
good O
material B-CONPRI
properties E-CONPRI
and O
low O
anisotropy S-PRO
. O


The O
findings O
serve O
to O
derive O
first O
design B-CONPRI
rules E-CONPRI
and O
provide O
a O
basis O
for O
further O
studies O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
more O
commonly O
referred O
to O
as S-MATE
3D B-MANP
printing E-MANP
, O
is O
revolutionizing O
the O
manufacturing S-MANP
industry S-APPL
. O


With O
any O
new O
technology S-CONPRI
comes O
new O
rules O
and O
guidelines O
for O
the O
optimal O
use O
of O
said O
technology S-CONPRI
. O


Big O
Area S-PARA
Additive B-MANP
Manufacturing E-MANP
( O
BAAM O
) O
, O
developed O
by O
Cincinnati O
Incorporated O
and O
Oak O
Ridge O
National O
Laboratory S-CONPRI
’ O
s S-MATE
Manufacturing S-MANP
Demonstration O
Facility O
, O
requires O
a O
host O
of O
new O
design S-FEAT
parameters O
compared O
to O
small-scale O
3D B-MANP
printing E-MANP
to O
create O
large-scale O
parts O
. O


However O
, O
BAAM O
also O
creates O
new O
possibilities O
in O
material S-MATE
testing O
and O
various O
applications O
in O
the O
manufacturing S-MANP
industry S-APPL
. O


Most O
of O
the O
design S-FEAT
constraints O
of O
small-scale O
polymer S-MATE
3D B-MACEQ
printers E-MACEQ
still O
apply O
to O
BAAM O
. O


Beyond O
those O
constraints O
, O
new O
rules O
and O
limitations O
exist O
because O
BAAM O
’ O
s S-MATE
large-scale O
system O
significantly O
changes O
the O
thermal B-CONPRI
properties E-CONPRI
associated O
with O
small-scale O
AM S-MANP
. O


This O
work O
details O
both O
physical O
and O
software-related O
design B-CONPRI
considerations E-CONPRI
for O
additive B-MANP
manufacturing E-MANP
. O


After O
reading O
this O
guide O
, O
one O
will O
have O
a O
better O
understanding O
of O
slicing S-CONPRI
software O
’ O
s S-MATE
capabilities O
and O
limitations O
, O
different O
physical O
characteristics O
of O
design S-FEAT
and O
how O
to O
apply O
them O
appropriately O
for O
AM S-MANP
, O
and O
how O
to O
take O
the O
inherent O
nature O
of O
AM S-MANP
into O
consideration O
during O
the O
design B-CONPRI
process E-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
is O
considered O
a O
promising O
technology S-CONPRI
for O
many O
applications O
, O
such O
as S-MATE
in O
the O
construction S-APPL
industry O
. O


However O
, O
the O
size O
of O
a O
design S-FEAT
is O
constrained O
by O
the O
chamber O
volume S-CONPRI
of O
the O
3D B-MACEQ
printer E-MACEQ
, O
and O
large-scale O
additive B-MANP
manufacturing E-MANP
technology O
with O
flexible O
equipment S-MACEQ
is O
still O
unproven O
. O


This O
paper O
proposes O
a O
large-scale O
3D B-MANP
printing E-MANP
system O
composed O
of O
multiple O
robots S-MACEQ
working O
in O
collaboration O
. O


For O
this O
flexible O
and O
extensible O
3D B-MANP
printing E-MANP
system O
, O
the O
influences O
of O
the O
multi-robot O
layout S-CONPRI
on O
the O
maximum O
reachable O
area S-PARA
and O
the O
geometry S-CONPRI
adaptability O
are O
discussed O
. O


Furthermore O
, O
a O
printer S-MACEQ
task O
optimized O
scheduling O
algorithm S-CONPRI
based O
on O
efficiency O
egalitarianism O
is O
proposed O
in O
this O
paper O
, O
and O
a O
robot S-MACEQ
interference O
avoidance O
strategy O
is O
designed S-FEAT
by O
dividing O
the O
printing O
layer S-PARA
into O
several O
safe O
areas S-PARA
and O
interference O
areas S-PARA
. O


Poly O
( O
lactic O
acid O
) O
( O
PLA S-MATE
) O
and O
PLA S-MATE
grafted O
cellulose S-MATE
nanofibers O
( O
PLA-g-CNFs O
) O
mixture O
were O
extruded S-MANP
into O
filaments S-MATE
, O
and O
subsequently O
3D B-MANP
printed E-MANP
into O
composites S-MATE
. O


As-3D O
printed O
composites S-MATE
were O
then O
thermally O
annealed O
at O
a O
temperature S-PARA
above O
PLA S-MATE
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
( O
Tg S-CHAR
) O
. O


Dynamic B-CONPRI
mechanical I-CONPRI
analysis E-CONPRI
, O
including O
temperature S-PARA
ramp O
, O
frequency O
sweep O
, O
and O
creep S-PRO
for O
annealed O
composites S-MATE
, O
confirmed O
the O
enhanced O
responses O
to O
various O
viscoelastic S-PRO
factors O
. O


Such O
enhancements O
were O
ascribed O
to O
the O
presence O
of O
PLA S-MATE
crystalline O
regions O
containing O
both O
ɑ O
and O
ɑʹ O
phases O
, O
which O
were O
induced O
and O
developed O
through O
the O
annealing B-MANP
treatment E-MANP
. O


After O
3-point O
bending B-CHAR
test E-CHAR
at O
70 O
°C O
, O
unannealed O
composites S-MATE
were O
partially O
damaged O
, O
while O
annealed O
composites S-MATE
preserved O
the O
originally O
well-integrated O
layer S-PARA
structures O
. O


Experimental S-CONPRI
creep S-PRO
and O
recovery O
data S-CONPRI
essentially O
fitted O
to O
the O
Burger O
’ O
s S-MATE
model S-CONPRI
and O
Weibull O
’ O
s S-MATE
distribution S-CONPRI
function O
, O
respectively O
. O


The O
calculated O
parameters S-CONPRI
( O
e.g. O
, O
moduli O
) O
from O
numerical O
fitting O
curves O
demonstrated O
the O
synergetic O
effect O
of O
PLA-g-CNFs O
and O
annealing B-MANP
treatment E-MANP
on O
the O
enahncement O
of O
flexural O
properties S-CONPRI
for O
3D B-MANP
printed E-MANP
PLA O
composites S-MATE
. O


Patient-specific O
tissue-mimicking O
phantoms O
have O
a O
wide O
range S-PARA
of O
biomedical B-APPL
applications E-APPL
including O
validation S-CONPRI
of O
computational B-ENAT
models E-ENAT
and O
imaging S-APPL
techniques O
, O
medical B-APPL
device E-APPL
testing O
, O
surgery S-APPL
planning S-MANP
, O
medical S-APPL
education O
, O
doctor-patient O
interaction O
, O
etc O
. O


Although O
3D B-ENAT
printing I-ENAT
technologies E-ENAT
have O
demonstrated O
great O
potential O
in O
fabricating S-MANP
patient-specific O
phantoms O
, O
current O
3D B-MANP
printed E-MANP
phantoms O
are O
usually O
only O
geometrically O
accurate S-CHAR
. O


Mechanical B-CONPRI
properties E-CONPRI
of O
soft O
tissues O
can O
merely O
be S-MATE
mimicked O
at O
small O
strain S-PRO
situations O
, O
such O
as S-MATE
ultrasonic O
induced O
vibration O
. O


Under O
large O
deformation S-CONPRI
, O
the O
soft O
tissues O
and O
the O
3D B-MANP
printed E-MANP
phantoms O
behave O
differently O
. O


The O
essential O
barrier O
is O
the O
inherent O
difference O
in O
the O
stress-strain O
curves O
of O
soft O
tissues O
and O
3D S-CONPRI
printable O
polymers S-MATE
. O


This O
study O
investigated O
the O
feasibility S-CONPRI
of O
mimicking O
the O
strain-stiffening O
behavior O
of O
soft O
tissues O
using O
dual-material S-CONPRI
3D B-MANP
printed E-MANP
metamaterials O
with O
micro-structured O
reinforcement S-PARA
embedded O
in O
soft O
polymeric O
matrix O
. O


Three O
types O
of O
metamaterials S-MATE
were O
designed S-FEAT
and O
tested O
: O
sinusoidal O
wave O
, O
double O
helix O
, O
and O
interlocking O
chains O
. O


Even O
though O
the O
two O
base O
materials S-CONPRI
were O
strain-softening O
polymers S-MATE
, O
both O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
and O
uniaxial O
tension B-CHAR
tests E-CHAR
indicated O
that O
two O
of O
those O
dual-material S-CONPRI
designs S-FEAT
were O
able O
to O
exhibit O
strain-stiffening O
effects O
as S-MATE
a O
metamaterial S-MATE
. O


The O
effects O
of O
the O
design S-FEAT
parameters O
on O
the O
mechanical S-APPL
behavior O
of O
the O
metamaterials S-MATE
were O
also O
demonstrated O
. O


The O
results O
suggested O
that O
the O
fabrication S-MANP
of O
patient-specific O
tissue-mimicking O
phantoms O
with O
both O
geometrical O
and O
mechanical S-APPL
accuracies O
is O
possible O
with O
dual-material S-CONPRI
3D B-MANP
printed E-MANP
metamaterials O
. O


Direct O
ink S-MATE
writing O
with O
acoustophoresis O
is O
used O
to O
write O
tailored O
composite S-MATE
filaments O
. O


Nozzle S-MACEQ
rotational O
asymmetry O
and O
printer S-MACEQ
calibration S-CONPRI
influence O
direction O
dependence O
. O


Yield B-PRO
stress E-PRO
fluid S-MATE
support O
geometry S-CONPRI
influences O
direction O
dependence O
. O


Direct O
ink S-MATE
writing O
enables O
deposition S-CONPRI
of O
multiphase O
filaments S-MATE
with O
designed S-FEAT
microstructures O
. O


Using O
acoustophoresis O
, O
we O
establish O
a O
narrow O
distribution S-CONPRI
of O
microparticles O
at O
the O
center O
of O
a O
direct-write O
nozzle S-MACEQ
. O


The O
distribution S-CONPRI
shifts O
and O
widens O
after O
deposition S-CONPRI
depending O
on O
the O
printing O
direction O
. O


We O
use O
particle S-CONPRI
image S-CONPRI
velocimetry O
and O
digital O
image B-CONPRI
analysis E-CONPRI
to O
identify O
flows O
transverse O
to O
the O
printing O
direction O
and O
characterize O
particle S-CONPRI
distributions S-CONPRI
in O
the O
printed O
filament S-MATE
. O


Sources O
of O
direction-dependent O
effects O
include O
square O
nozzles S-MACEQ
, O
co-deposition O
of O
support B-MATE
material E-MATE
, O
a O
rotationally O
asymmetric O
microstructure S-CONPRI
established O
in O
the O
nozzle S-MACEQ
, O
and O
speed O
inaccuracies O
that O
occur O
in O
3-axis O
gantries O
. O


We O
propose O
an O
analytical O
model S-CONPRI
for O
predicting O
print S-MANP
direction-dependent O
flows O
and O
particle S-CONPRI
distributions S-CONPRI
as S-MATE
a O
function O
of O
anisotropy S-PRO
of O
the O
particle S-CONPRI
distribution S-CONPRI
in O
the O
nozzle S-MACEQ
, O
a O
disturbed O
zone O
near O
the O
nozzle S-MACEQ
, O
fluid S-MATE
reshaping O
of O
the O
print S-MANP
bead S-CHAR
, O
uniform O
rotation O
of O
the O
print S-MANP
bead S-CHAR
, O
calibration S-CONPRI
of O
the O
ink S-MATE
and O
support S-APPL
nozzle S-MACEQ
positions O
, O
and O
3D B-MACEQ
printer E-MACEQ
motor O
error S-CONPRI
. O


Using O
the O
model S-CONPRI
, O
we O
propose O
strategies O
for O
controlling O
direction O
dependent O
microstructures S-MATE
in O
direct O
ink S-MATE
writing O
. O


The O
analytical O
model S-CONPRI
can O
be S-MATE
easily O
adapted O
to O
similar O
direct-write O
applications O
to O
diagnose O
sources O
of O
direction O
dependent O
microstructures S-MATE
. O


Freeform B-CONPRI
3D E-CONPRI
printing O
combined O
with O
sacrificial B-MANP
molding E-MANP
promises O
to O
lead S-MATE
advances O
in O
production S-MANP
of O
highly O
complex O
tubular S-FEAT
systems O
for O
biomedical B-APPL
applications E-APPL
. O


Here O
we O
leverage O
a O
purpose-built O
isomalt S-MATE
3D B-MACEQ
printer E-MACEQ
to O
generate O
complex O
channel S-APPL
geometries O
in O
hydrogels S-MATE
which O
would O
be S-MATE
inaccessible O
with O
other O
techniques O
. O


To O
control O
the O
dissolution O
of O
the O
scaffold S-FEAT
, O
we O
propose O
an O
enabling O
technology S-CONPRI
consisting O
of O
an O
automated O
nebulizer O
coating S-APPL
system O
which O
applies O
octadecane O
to O
isomalt S-MATE
scaffolds O
. O


Octadecane O
, O
a O
saturated O
hydrocarbon O
, O
protects O
the O
rigid O
mold S-MACEQ
from O
dissolution O
and O
provides O
ample O
time O
for O
gels O
to O
set S-APPL
around O
the O
sacrificial O
structure S-CONPRI
. O


With O
a O
simplified O
model S-CONPRI
of O
the O
nebulizer O
system O
, O
the O
robotic O
motion O
was O
optimized O
for O
uniform O
coating S-APPL
. O


Using O
a O
combination O
of O
stimulated O
Raman B-CHAR
scattering E-CHAR
( O
SRS O
) O
microscopy S-CHAR
and O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
, O
the O
coating S-APPL
was O
characterized O
to O
assess O
surface B-PRO
roughness E-PRO
and O
consistency S-CONPRI
. O


Colorimetric O
measurements O
of O
dissolution O
rates O
allowed O
optimization S-CONPRI
of O
sprayer O
parameters S-CONPRI
, O
yielding O
a O
decrease O
in O
dissolution O
rates O
by O
at O
least O
4 O
orders O
of O
magnitude S-PARA
. O


Spontaneous O
Raman B-CHAR
scattering E-CHAR
microspectroscopy O
and O
white O
light O
microscopy S-CHAR
indicate O
cleared O
channels O
are O
free O
of O
octadecane O
following O
gentle O
flushing O
. O


The O
capabilities O
of O
the O
workflow S-CONPRI
are O
highlighted O
with O
several O
complex O
channel S-APPL
architectures O
including O
helices O
, O
blind O
channels O
, O
and O
multiple O
independent O
channels O
within O
polyacrylamide O
hydrogels S-MATE
of O
varying O
stiffnesses O
. O


This O
study O
is O
an O
investigation O
on O
the O
size O
dependence O
of O
strength S-PRO
of O
a O
3D B-MANP
printed E-MANP
acrylic O
polymer S-MATE
. O


3D B-MANP
printed E-MANP
beams O
are O
used O
in O
three-point O
bend O
fracture S-CONPRI
experiments O
. O


Three O
print S-MANP
modes O
of O
the O
PolyJet S-CONPRI
process O
are O
used O
to O
manufacture S-CONPRI
beams O
of O
dimensions S-FEAT
commonly O
considered O
in O
3D B-MANP
printed E-MANP
structures O
( O
1–5 O
mm S-MANP
) O
. O


It O
is O
found O
that O
for O
that O
range S-PARA
of O
dimensions S-FEAT
, O
the O
fracture S-CONPRI
response O
is O
in O
the O
nonlinear O
size-strength O
domain S-CONPRI
and O
specimens O
neither O
follow O
the O
limiting O
linear O
elastic S-PRO
fracture O
mechanics O
nor O
the O
strength S-PRO
criterion O
. O


Consequently O
, O
strength S-PRO
and O
toughness S-PRO
are O
size O
dependent O
. O


Moreover O
, O
a O
strong O
interaction O
between O
specimen O
dimensions S-FEAT
and O
print B-PARA
layer E-PARA
thickness O
was O
found O
. O


A O
size O
threshold O
exists O
below O
which O
there O
appears O
to O
be S-MATE
an O
interaction O
between O
specimen O
dimensions S-FEAT
and O
print B-PARA
layer E-PARA
thickness O
, O
and O
for O
specimens O
of O
dimension S-FEAT
below O
that O
threshold O
exhibit O
a O
declining O
strength S-PRO
with O
size O
. O


From O
the O
present O
experiments O
, O
the O
size O
threshold O
is O
estimated O
to O
be S-MATE
50 O
times O
the O
print B-PARA
layer E-PARA
thickness O
. O


The O
finding O
of O
a O
maximum O
strength S-PRO
relative O
to O
geometric O
dimensions S-FEAT
should O
be S-MATE
accounted O
for O
in O
designing O
with O
3D B-MANP
printed E-MANP
materials O
. O


In O
conventional O
additive B-MANP
manufacturing E-MANP
, O
most O
processes S-CONPRI
for O
creating O
the O
layers O
of O
a O
part O
are O
performed O
on O
a O
horizontal O
plane O
. O


In O
contrast O
, O
a O
conformal O
additive B-MANP
manufacturing I-MANP
process E-MANP
has O
been O
suggested O
in O
order O
to O
build S-PARA
a O
real O
3D B-CONPRI
structure E-CONPRI
on O
a O
freeform S-CONPRI
surface O
using O
a O
direct-print O
process S-CONPRI
based O
on O
material B-MANP
extrusion E-MANP
. O


A O
new O
algorithm S-CONPRI
was O
developed O
that O
is O
able O
to O
use O
the O
standard S-CONPRI
3D B-MANP
printing E-MANP
file O
format O
that O
includes O
both O
a O
3D B-APPL
model E-APPL
to O
be S-MATE
printed O
and O
a O
3D B-APPL
model E-APPL
of O
a O
freeform S-CONPRI
substrate O
along O
with O
the O
desired O
printing O
parameters S-CONPRI
as S-MATE
input O
, O
and O
it O
returns O
G-code S-ENAT
instructions O
for O
the O
3D B-MANP
printing E-MANP
process O
as S-MATE
output O
. O


A O
slicing S-CONPRI
surface O
was O
generated O
to O
slice S-CONPRI
the O
3D B-APPL
model E-APPL
by O
offsetting O
the O
surface S-CONPRI
of O
a O
freeform S-CONPRI
substrate O
model S-CONPRI
by O
a O
discrete O
amount O
( O
i.e. O
, O
layer B-PARA
thickness E-PARA
) O
for O
each O
layer S-PARA
. O


The O
perimeters O
of O
each O
layer S-PARA
( O
including O
the O
internal O
features O
) O
were O
extracted S-CONPRI
based O
on O
the O
intersections O
between O
the O
slicing S-CONPRI
surface O
and O
the O
3D B-APPL
model E-APPL
, O
and O
infill S-PARA
toolpaths O
were O
created O
by O
projecting O
2D B-FEAT
patterns E-FEAT
reflecting O
the O
features O
to O
be S-MATE
printed O
with O
a O
desired O
fill O
factor O
( O
in O
the O
x–y O
plane O
) O
onto O
the O
slicing S-CONPRI
surface O
to O
create O
3D S-CONPRI
patterns O
. O


Several O
3D B-APPL
models E-APPL
were O
sliced O
and O
printed O
on O
a O
freeform S-CONPRI
surface O
to O
validate O
the O
developed O
algorithm S-CONPRI
. O


A O
laser B-MANP
enhanced I-MANP
direct I-MANP
print I-MANP
additive I-MANP
manufacturing E-MANP
process O
is O
proposed O
for O
3D B-MANP
printing E-MANP
optical O
interconnects O
An O
optical S-CHAR
interconnect O
is O
directly O
printed O
on O
a O
circuit O
board O
for O
the O
first O
time O
using O
this O
process S-CONPRI
Transmitted O
optical S-CHAR
power O
of O
the O
3D B-MANP
printed E-MANP
optical O
fiber S-MATE
interconnects O
is O
63 O
% O
of O
that O
of O
a O
commercial O
fiber S-MATE
in O
these O
preliminary O
prototypes S-CONPRI
Processing O
conditions O
are O
established O
using O
fluid B-PRO
flow E-PRO
and O
heat B-CONPRI
transfer E-CONPRI
modeling O
Integrated O
photonics O
have O
many O
compelling O
advantages O
for O
computing O
and O
communication O
applications O
, O
including O
in O
high-speed O
and O
extremely O
wide O
bandwidth O
operations O
. O


Current O
systems O
are O
typically O
hybrid O
assemblies O
of O
packaged O
photonic O
devices O
where O
printed B-MACEQ
circuit I-MACEQ
boards E-MACEQ
often O
serve O
to O
route O
electrical S-APPL
signals O
and O
power S-PARA
, O
and O
in O
some O
cases O
, O
have O
runs O
of O
optical S-CHAR
fibers S-MATE
. O


We O
present O
a O
flexible O
, O
low O
cost O
assembly S-MANP
method O
of O
optical S-CHAR
interconnects O
for O
photonic O
systems O
that O
could O
enable O
higher O
transmission S-CHAR
rates O
, O
lower O
power S-PARA
requirements O
, O
improved O
signal O
integrity S-CONPRI
and O
timing O
, O
less O
heat S-CONPRI
generation O
, O
and O
improved O
security O
of O
communication O
signals O
. O


The O
new O
process S-CONPRI
is O
based O
on O
laser B-MANP
enhanced I-MANP
direct I-MANP
print I-MANP
additive I-MANP
manufacturing E-MANP
( O
LE-DPAM S-MANP
) O
that O
combines O
fused B-MANP
deposition I-MANP
modeling E-MANP
( O
FDM S-MANP
) O
of O
plastic S-MATE
, O
micro-dispensing O
of O
rubber-like O
materials S-CONPRI
, O
and O
picosecond O
laser S-ENAT
subtraction O
. O


The O
process S-CONPRI
is O
demonstrated O
by O
fabricating S-MANP
few-mode O
and O
multi-mode O
optical S-CHAR
fibers S-MATE
in O
a O
controlled O
manner O
such O
that O
compact S-MANP
, O
3-dimensional O
optical S-CHAR
interconnects O
can O
be S-MATE
printed O
along O
non-lineal O
paths O
. O


We O
have O
produced O
working O
optical S-CHAR
interconnects O
with O
fiber S-MATE
core S-MACEQ
diameters O
from O
70-μm O
to O
as S-MATE
small O
as S-MATE
12-μm O
. O


Our O
results O
demonstrate O
surface B-PRO
roughness E-PRO
of O
less O
than O
100 O
nm O
, O
and O
optical S-CHAR
transmitted O
power S-PARA
of O
63 O
% O
that O
of O
a O
commercial O
fiber S-MATE
, O
for O
proof O
of O
concept O
devices O
. O


The O
LE-DPAM S-MANP
approach O
could O
lead S-MATE
to O
large O
scale O
integrated O
photonic O
computing O
devices O
that O
would O
replace O
our O
current O
generation O
of O
servers O
, O
computers S-ENAT
, O
and O
phones O
. O


In O
this O
paper O
, O
we O
investigated O
the O
process S-CONPRI
variable O
effects O
on O
the O
damage S-PRO
and O
deformational O
behavior O
of O
fused B-MANP
deposition I-MANP
modeling E-MANP
( O
FDM S-MANP
) O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
-printed O
specimens O
by O
performing O
tensile B-CHAR
tests E-CHAR
and O
inverse O
identification O
analyses O
. O


A O
characterization O
of O
the O
effects O
of O
different O
parametric O
variations S-CONPRI
of O
3D-printed S-MANP
specimens O
on O
fracture S-CONPRI
properties O
are O
a O
matter O
of O
considerable O
significance O
that O
are O
often O
overlooked O
. O


By O
combining O
the O
infill S-PARA
density S-PRO
and O
the O
layer B-PARA
thickness E-PARA
options O
that O
are O
available O
in O
the O
3D B-MACEQ
printer E-MACEQ
machine O
, O
six O
groups O
with O
different O
structural O
configurations O
can O
be S-MATE
obtained O
. O


The O
data S-CONPRI
and O
images S-CONPRI
obtained O
from O
experiments O
are O
employed O
to O
investigate O
the O
failure B-PRO
mechanism E-PRO
of O
3D-printed S-MANP
specimens O
and O
demonstrate O
the O
relationship O
that O
exists O
between O
structural O
variations S-CONPRI
and O
fracture S-CONPRI
mechanical O
properties S-CONPRI
. O


On O
the O
basis O
of O
experimental S-CONPRI
results O
, O
a O
Gurson-type O
porous B-PRO
plasticity E-PRO
model S-CONPRI
was O
used O
within O
a O
3D S-CONPRI
continuum O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
to O
characterize O
the O
process–damage O
parameter S-CONPRI
relationship O
through O
an O
inverse O
identification O
process S-CONPRI
. O


A O
PDMS O
contacting O
layer S-PARA
with O
nano-scaled O
pillars O
and O
an O
oxygen-permeable B-MATE
membrane E-MATE
were O
bonded O
together O
as S-MATE
the O
composite S-MATE
functional O
release O
film O
of O
rapid O
stereolithography S-MANP
. O


Optical S-CHAR
simulations O
demonstrated O
that O
the O
nano-texture O
would O
not O
influence O
the O
curing S-MANP
effect O
of O
the O
resin S-MATE
. O


Nowadays O
, O
along O
with O
the O
demand O
for O
new O
technologies S-CONPRI
and O
new O
materials S-CONPRI
, O
a O
revolution O
in O
3D B-ENAT
printing I-ENAT
technology E-ENAT
is O
emerging O
. O


In O
recent O
years O
, O
stereolithography B-MANP
3D I-MANP
printing E-MANP
has O
been O
widely O
used O
in O
both O
academia O
and O
industry S-APPL
, O
due O
to O
its O
fast O
forming S-MANP
speed O
, O
high O
precision S-CHAR
, O
and O
low-cost O
advantages O
. O


The O
continuous B-MANP
liquid I-MANP
interface I-MANP
production E-MANP
technology O
has O
made O
the O
printing B-PARA
speed E-PARA
even O
faster O
. O


However O
, O
the O
process S-CONPRI
of O
resin S-MATE
refilling O
constrains O
the O
printing B-PARA
speed E-PARA
and O
the O
printing O
capabilities O
of O
such O
technologies S-CONPRI
, O
since O
only O
hollow O
structures O
can O
be S-MATE
fabricated O
. O


In O
this O
study O
, O
a O
nano-textured O
hydrophobic O
PDMS O
contacting O
layer S-PARA
and O
an O
oxygen-permeable B-MATE
membrane E-MATE
were O
bonded O
together O
as S-MATE
the O
functional O
release O
film O
. O


The O
oxygen S-MATE
inhibition O
layer S-PARA
was O
successfully O
maintained O
by O
the O
molecular O
oxygen S-MATE
permeated O
through O
the O
composite S-MATE
release O
film O
, O
achieving O
rapid O
stereolithography S-MANP
, O
and O
key O
factors O
that O
affecting O
resin S-MATE
refilling O
are O
selectively O
studied O
by O
the O
orthogonal O
experiment S-CONPRI
. O


Additionally O
, O
optical S-CHAR
simulations O
also O
demonstrated O
that O
the O
nano-texture O
would O
not O
influence O
the O
curing S-MANP
effect O
of O
the O
resin S-MATE
. O


This O
work O
proposed O
a O
promising O
strategy O
for O
rapid O
stereolithography S-MANP
of O
3D B-APPL
models E-APPL
containing O
larger O
cross-sectional O
areas S-PARA
. O


A O
nano-textured O
PDMS O
contacting O
layer S-PARA
and O
an O
oxygen-permeable B-MATE
membrane E-MATE
were O
bonded O
together O
as S-MATE
the O
printing O
substrate S-MATE
, O
providing O
high O
oxygen S-MATE
permeability O
to O
form O
an O
oxygen S-MATE
inhibition O
layer S-PARA
. O


The O
introduction O
of O
the O
nano-texture O
on O
PDMS O
not O
only O
increased O
the O
refilling O
speed O
of O
the O
resin S-MATE
by O
two O
times O
and O
reduced O
the O
printing O
time O
by O
nearly O
25 O
% O
, O
and O
the O
printing O
reliability S-CHAR
of O
larger O
cross-sectional O
areas S-PARA
was O
remarkably O
improved.Download O
: O
Download O
high-res B-CONPRI
image E-CONPRI
( O
272 O
Fracture S-CONPRI
, O
the O
breakdown O
of O
materials S-CONPRI
as S-MATE
cracks O
advance O
, O
is O
one O
of O
the O
most O
intriguing O
materials S-CONPRI
phenomena O
; O
it O
can O
happen O
even O
to O
very O
tough O
biological B-MATE
tissues E-MATE
including O
tendons O
, O
skin O
, O
bone S-BIOP
and O
teeth O
, O
materials S-CONPRI
whose O
critical O
physiological O
functions O
can O
be S-MATE
compromised O
by O
structural O
irregularities O
. O


It O
has O
been O
suggested O
that O
creating O
composites S-MATE
by O
mixing B-CONPRI
heterogeneous E-CONPRI
constituents O
of O
contrasting O
material B-CONPRI
properties E-CONPRI
can O
yield O
designs S-FEAT
that O
can O
better O
adapt O
to O
stress B-CHAR
concentration E-CHAR
, O
leading O
to O
synthetic B-MATE
materials E-MATE
with O
higher O
toughness S-PRO
than O
their O
constituents O
. O


Here O
, O
an O
optimization B-CONPRI
algorithm E-CONPRI
is O
used O
to O
assess O
material S-MATE
fracture B-PRO
resistance E-PRO
in O
the O
presence O
of O
a O
crack O
. O


The O
analysis O
is O
further O
extended O
through O
experiments O
that O
involve O
the O
use O
of O
additive B-MANP
manufacturing E-MANP
. O


Optimal O
solutions O
are O
composed O
solely O
of O
soft O
and O
stiff O
material B-MATE
elements E-MATE
, O
and O
are O
compared O
to O
various O
benchmarks O
. O


Multi-material S-CONPRI
three-dimensional-printing O
( O
3D-printing S-MANP
) O
is O
used O
to O
create O
material S-MATE
samples O
. O


Experimental S-CONPRI
results O
and O
mechanical B-CHAR
testing E-CHAR
show O
that O
an O
algorithmic O
design S-FEAT
coupled O
with O
3D-printing S-MANP
technology O
can O
generate O
morphologies S-CONPRI
of O
composites S-MATE
more O
than O
20 O
times O
tougher O
than O
the O
stiffest O
base O
material S-MATE
, O
and O
more O
than O
twice O
as S-MATE
strong O
as S-MATE
the O
strongest O
base O
material S-MATE
. O


Direct O
comparison O
of O
strain S-PRO
fields O
around O
cracks O
shows O
excellent O
agreement O
between O
simulation S-ENAT
and O
experiment S-CONPRI
. O


The O
results O
suggest O
that O
the O
systematic O
use O
of O
microstructure S-CONPRI
optimization O
to O
generate O
enhanced O
fracture B-PRO
resistance E-PRO
constitutes O
a O
new O
materials S-CONPRI
design S-FEAT
paradigm O
. O


Three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
printed O
highly O
conductive O
graphene-based O
nanocomposites O
have O
led S-APPL
to O
a O
paradigm O
shift O
in O
the O
development O
of O
flexible O
electronics S-CONPRI
as S-MATE
well O
as S-MATE
customized O
therapeutic S-CONPRI
devices O
. O


This O
article O
addresses O
the O
deployment O
and O
characterization O
of O
a O
piezoelectric-pneumatic O
material-jetting O
( O
PPMJ O
) O
additive B-MANP
manufacturing I-MANP
process E-MANP
to O
print S-MANP
graphene-based O
nanocomposites O
with O
3D B-CONPRI
structures E-CONPRI
. O


Here O
, O
development O
of O
a O
graphene-silicone O
ink S-MATE
, O
so-called O
MJ-3DG O
, O
with O
a O
high O
content O
of O
graphene S-MATE
( O
70 O
wt O
% O
) O
and O
its O
adoption O
for O
the O
PPMJ O
process S-CONPRI
to O
3D B-MANP
print E-MANP
a O
highly O
conductive O
graphene-silicone O
structure S-CONPRI
is O
demonstrated O
. O


The O
robust O
3D B-MANP
printed E-MANP
structure O
from O
MJ-3DG O
ink S-MATE
with O
the O
surface B-PRO
roughness E-PRO
around O
2.99 O
( O
µm O
) O
has O
the O
resistivity S-PRO
as S-MATE
low O
as S-MATE
0.41 O
( O
Ω.cm O
) O
. O


This O
low O
resistivity S-PRO
is O
fairly O
comparable O
with O
the O
previously O
reported O
extrusion-based O
3D-printed S-MANP
graphene O
structures O
that O
are O
the O
highest O
among O
all O
the O
carbon-based O
3D-printed S-MANP
structures O
reported O
to O
date O
. O


Furthermore O
, O
in O
contrast O
to O
the O
extrusion-based B-MACEQ
systems E-MACEQ
, O
the O
high O
process S-CONPRI
speed O
( O
up O
to O
500 O
mm/s O
) O
and O
the O
drop-on-demand O
nature O
of O
PPMJ O
provide O
internal O
design B-CONPRI
flexibility E-CONPRI
for O
3D B-MANP
printed E-MANP
structures O
and O
make O
the O
development O
of O
smart O
graphene-based O
electronic O
and O
biomonitoring O
devices O
possible O
. O


Owing O
to O
the O
lack O
of O
optimization S-CONPRI
, O
the O
dimensional B-CHAR
accuracy E-CHAR
of O
low-cost O
3D B-MACEQ
printers E-MACEQ
is O
quite O
limited O
. O


In O
order O
to O
enhance O
the O
performances O
of O
a O
Prusa O
i3 O
3D B-MACEQ
printer E-MACEQ
, O
an O
optimization S-CONPRI
challenge O
was O
assigned O
to O
the O
students O
of O
the O
Specializing O
Master O
in O
Industrial S-APPL
Automation S-CONPRI
of O
the O
Politecnico O
di O
Torino O
. O


The O
enhancements O
were O
applied O
to O
four O
printers S-MACEQ
by O
manufacturing S-MANP
new O
self-replicated O
parts O
by O
means O
of O
the O
same O
3D B-MACEQ
printers E-MACEQ
. O


The O
benchmarking O
involved O
the O
fabrication S-MANP
of O
replicas O
of O
an O
innovative O
reference O
artifact O
by O
means O
of O
the O
modified O
printers S-MACEQ
. O


A O
coordinate B-MACEQ
measuring I-MACEQ
machine E-MACEQ
( O
CMM S-MACEQ
) O
was O
then O
used O
to O
inspect O
the O
dimensions S-FEAT
of O
the O
replicas O
. O


Measures O
were O
used O
to O
compare O
the O
performances O
of O
the O
four O
optimized O
printers S-MACEQ
in O
terms O
of O
dimensional B-CHAR
accuracy E-CHAR
using O
ISO S-MANS
IT O
grades O
. O


The O
form O
errors S-CONPRI
of O
the O
geometrical B-FEAT
features E-FEAT
of O
the O
replicas O
were O
also O
evaluated O
according O
to O
the O
GD S-MATE
& O
T O
system O
. O


The O
benchmarking O
results O
show O
that O
the O
most O
effective O
modifications O
to O
the O
original O
printer S-MACEQ
were O
those O
related O
to O
the O
improvement O
of O
the O
structure S-CONPRI
stiffness S-PRO
and O
chatter O
reduction S-CONPRI
. O


Extrusion-based O
3D B-MANP
printing E-MANP
of O
photo-curable S-FEAT
hydrogel S-MATE
materials O
can O
be S-MATE
used O
for O
the O
generation O
of O
complex O
objects O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
without O
the O
need O
for O
molds S-MACEQ
. O


Photo-curing O
often O
is O
the O
final O
step S-CONPRI
of O
the O
3D B-MANP
printing E-MANP
process O
, O
fixing O
the O
shape O
of O
the O
generated O
object O
. O


However O
, O
the O
fabricated S-CONPRI
objects O
have O
to O
support S-APPL
themselves O
before O
curing S-MANP
, O
limiting O
the O
size O
of O
the O
objects O
. O


In O
this O
contribution O
, O
intermediate O
curing S-MANP
after O
completing O
each O
individual O
layer S-PARA
with O
poly O
( O
ethylene O
glycol O
) O
diacrylate S-MATE
as S-MATE
a O
radically O
curing S-MANP
hydrogel O
system O
was O
investigated O
compared O
with O
single O
curing S-MANP
of O
the O
whole O
structure S-CONPRI
after O
complete O
layered O
deposition S-CONPRI
, O
and O
its O
effect O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
and O
achievable O
object O
size O
was O
assessed O
. O


Defect-free O
hydrogel S-MATE
samples O
for O
mechanical B-CHAR
testing E-CHAR
were O
obtained O
with O
an O
optimized O
washing/swelling O
protocol S-CONPRI
. O


It O
was O
found O
that O
hydrogel S-MATE
objects O
cured S-MANP
after O
completion O
without O
intermediate O
curing S-MANP
steps O
had O
the O
highest O
fracture S-CONPRI
stresses O
and O
compression S-PRO
at O
break O
with O
32.5 O
N S-MATE
cm−2 O
and O
44 O
% O
, O
respectively O
. O


With O
increasing O
intermediate O
curing B-PARA
time E-PARA
, O
both O
the O
fracture S-CONPRI
stress O
and O
the O
compression S-PRO
at O
break O
decreased O
down O
to O
7.8 O
N S-MATE
cm−2 O
and O
26 O
% O
, O
respectively O
, O
for O
5 O
s S-MATE
intermediate O
curing S-MANP
. O


Long O
intermediate O
curing B-PARA
times E-PARA
between O
the O
layers O
lead S-MATE
to O
preferred O
crack O
formation O
parallel O
to O
the O
layers O
due O
to O
decreased O
chemical O
bonding S-CONPRI
. O


However O
, O
the O
formation O
of O
higher O
hydrogel S-MATE
objects O
than O
enabled O
by O
the O
yield B-PRO
stress E-PRO
of O
the O
hydrogel S-MATE
was O
only O
possible O
with O
intermediate O
curing S-MANP
due O
to O
the O
better O
self-support O
of O
partially O
cured S-MANP
objects O
. O


The O
effect O
of O
printing B-PARA
speed E-PARA
on O
quality S-CONPRI
of O
parts O
fabricated S-CONPRI
via O
Binder B-MANP
Jetting E-MANP
process O
is O
experimentally O
evaluated O
. O


The O
dimensional B-CHAR
accuracy E-CHAR
of O
printed O
samples S-CONPRI
reduces O
linearly O
with O
increasing O
printing B-PARA
speed E-PARA
due O
to O
the O
enhanced O
spreading O
of O
droplets S-CONPRI
under O
more O
significant O
inertia O
forces S-CONPRI
. O


Saturation O
level O
of O
printed O
features O
is O
also O
linearly O
influenced O
by O
the O
printing B-PARA
speed E-PARA
, O
which O
can O
be S-MATE
attributed O
to O
increase O
of O
dimensional O
inaccuracy O
. O


Binder B-MANP
Jetting E-MANP
Process O
is O
an O
Additive B-MANP
Manufacturing E-MANP
technique O
( O
AM S-MANP
) O
in O
which O
a O
liquid B-MATE
binder E-MATE
is O
employed O
for O
establishing O
the O
initial O
strength S-PRO
and O
fabricating S-MANP
the O
geometry S-CONPRI
of O
components S-MACEQ
. O


In O
this O
process S-CONPRI
, O
the O
delivery O
of O
the O
binding O
agent O
is O
accomplished O
through O
a O
drop-on-demand O
( O
DOD S-MANP
) O
printhead O
by O
deposition S-CONPRI
of O
picoliter-sized O
droplets S-CONPRI
of O
the O
liquid B-MATE
binder E-MATE
. O


The O
velocity O
of O
the O
droplets S-CONPRI
impinging O
the O
powder B-MACEQ
bed E-MACEQ
surface O
might O
have O
significant O
effect O
on O
droplet S-CONPRI
spreading O
and O
absorption S-CONPRI
dynamics O
, O
which O
can O
be S-MATE
manifested O
in O
quality S-CONPRI
and O
integrity S-CONPRI
of O
the O
fabricated S-CONPRI
parts O
. O


In O
the O
present O
study O
, O
the O
effect O
of O
the O
printing B-PARA
speed E-PARA
on O
dimensional B-CHAR
accuracy E-CHAR
and O
equilibrium S-CONPRI
saturation O
level O
of O
printed O
samples S-CONPRI
is O
experimentally O
investigated O
and O
the O
observed O
trends S-CONPRI
are O
discussed O
in O
detail O
. O


Big O
Area S-PARA
Additive B-MANP
Manufacturing E-MANP
( O
BAAM O
) O
is O
a O
large O
format O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
. O


However O
, O
at O
this O
scale O
, O
lack O
of O
high O
print B-PARA
resolution E-PARA
and O
extruder S-MACEQ
flowrate O
control O
lead S-MATE
to O
potentially O
significant O
geometric O
deviations O
in O
the O
printed O
part O
. O


Multi-resolution O
printing O
, O
extrusion S-MANP
diversion O
, O
and O
feedforward O
extruder S-MACEQ
control O
are O
examined O
herein O
. O


These O
methods O
were O
all O
found O
to O
be S-MATE
effective O
in O
mitigating O
phenomena O
detrimental O
to O
geometric O
part O
quality S-CONPRI
on O
the O
BAAM O
process S-CONPRI
. O


A O
space O
frame O
lattice S-CONPRI
and O
shell S-MACEQ
finite B-CONPRI
element I-CONPRI
model E-CONPRI
was O
created O
to O
predict O
the O
linearly O
elastic S-PRO
response O
of O
test O
coupons O
made O
with O
a O
modified O
polyetherimide O
( O
PEI O
) O
material S-MATE
. O


This O
approach O
was O
employed O
because O
it O
provides O
an O
efficient O
procedure O
to O
design S-FEAT
and O
optimize O
3D B-APPL
printed I-APPL
parts E-APPL
. O


The O
modeled O
coupons O
were O
3D B-MANP
printed E-MANP
by O
extrusion S-MANP
of O
molten O
thermoplastic B-MATE
polymer E-MATE
. O


The O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
was O
verified O
by O
comparing O
the O
predicted S-CONPRI
values O
of O
elastic B-PRO
modulus E-PRO
, O
shear B-PRO
modulus E-PRO
, O
and O
Poisson O
’ O
s S-MATE
ratio O
in O
two O
material S-MATE
directions O
with O
the O
corresponding O
values O
obtained O
from O
quasi-static S-CONPRI
mechanical S-APPL
experiments O
. O


The O
values O
obtained O
for O
the O
moduli O
and O
the O
Poisson O
’ O
s S-MATE
ratios O
from O
the O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
matched O
closely O
with O
those O
obtained O
from O
the O
experiments O
. O


Material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
( O
MEAM O
) O
, O
also O
known O
as S-MATE
three-dimensional O
( O
3D S-CONPRI
) O
printing O
, O
is O
a O
popular O
additive B-MANP
manufacturing E-MANP
technique O
suitable O
for O
producing O
3D S-CONPRI
shapes O
using O
thermoplastic B-MATE
materials E-MATE
. O


The O
majority O
of O
companies S-APPL
that O
design S-FEAT
and O
test O
3D B-MANP
printing E-MANP
machines O
work O
with O
thermoplastic S-MATE
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
and O
polylactic B-MATE
acid E-MATE
( O
PLA S-MATE
) O
filaments S-MATE
. O


It O
is O
, O
however O
, O
crucial O
to O
utilize O
different O
types O
of O
filaments S-MATE
for O
a O
broader O
range S-PARA
of O
applications O
with O
different O
mechanical B-CONPRI
property E-CONPRI
requirements O
. O


MEAM O
techniques O
may O
be S-MATE
used O
for O
the O
production S-MANP
of O
SMP-based O
parts O
, O
allowing O
for O
smart B-FEAT
structures E-FEAT
to O
be S-MATE
created O
in O
a O
wide O
variety O
of O
geometries S-CONPRI
. O


In O
this O
work O
, O
a O
commercial O
3D-printer O
was O
used O
to O
produce O
3D B-MANP
printed E-MANP
polyurethane-based O
SMP O
specimens O
. O


Mechanical S-APPL
and O
thermomechanical S-CONPRI
testing S-CHAR
was O
conducted O
to O
study O
the O
effects O
of O
testing S-CHAR
temperatures S-PARA
and O
annealing S-MANP
heat O
treatments O
on O
the O
tensile S-PRO
and O
shape O
memory O
properties S-CONPRI
of O
the O
samples S-CONPRI
. O


3D B-MANP
printing E-MANP
was O
shown O
to O
be S-MATE
a O
suitable O
technique O
for O
producing O
SMP O
parts O
capable O
of O
retaining O
good O
shape O
memory O
characteristics O
. O


Different O
annealing S-MANP
heat O
treatments O
and O
test O
temperatures S-PARA
were O
found O
to O
have O
considerable O
effects O
on O
the O
SMP O
specimen O
properties S-CONPRI
. O


In O
particular O
, O
annealing S-MANP
the O
specimens O
at O
85 O
°C O
for O
2 O
h O
helped O
to O
improve O
the O
rate O
of O
shape O
recovery O
and O
the O
consistency S-CONPRI
of O
mechanical B-CHAR
test E-CHAR
results O
. O


A O
systematic O
approach O
on O
the O
numerical B-ENAT
simulation E-ENAT
of O
electrified O
jet O
printing O
is O
studied O
. O


The O
Volume B-CONPRI
of I-CONPRI
Fluid E-CONPRI
( O
VOF S-CONPRI
) O
method O
which O
suits O
for O
modeling S-ENAT
multiphase O
flows O
with O
a O
continuous O
interface S-CONPRI
is O
used O
. O


The O
surface B-PRO
tension E-PRO
force S-CONPRI
is O
calculated O
with O
the O
Continuum B-CONPRI
Surface I-CONPRI
Force E-CONPRI
( O
CSF S-CONPRI
) O
method O
and O
the O
electric O
forces S-CONPRI
are O
added O
to O
the O
momentum O
equation O
by O
taking O
the O
divergence O
of O
the O
Maxwell O
stress S-PRO
tensor O
. O


Employing O
these O
dimensionless O
numbers O
, O
the O
number O
of O
effective O
parameters S-CONPRI
is O
reduced O
, O
and O
a O
relative O
comparison O
of O
the O
importance O
of O
competing O
forces S-CONPRI
on O
the O
process S-CONPRI
becomes O
possible O
. O


In O
this O
study O
, O
an O
elastoplastic O
constitutive O
model S-CONPRI
is O
developed O
to O
implement O
a O
quantitative S-CONPRI
description O
of O
the O
mechanical S-APPL
behavior O
of O
materials B-CONPRI
fabricated E-CONPRI
by O
stereolithography S-MANP
( O
SLA S-MACEQ
) O
. O


Considering O
the O
characteristics O
of O
the O
SLA S-MACEQ
printing B-MANP
process E-MANP
and O
the O
influence O
of O
the O
printing O
angle O
and O
layer B-PARA
thickness E-PARA
, O
the O
transversely O
isotropic B-PRO
elastic E-PRO
model O
and O
the O
Hill O
anisotropic S-PRO
yield O
model S-CONPRI
are O
used O
to O
describe O
the O
mechanical S-APPL
behavior O
of O
SLA-printed O
materials S-CONPRI
. O


In O
the O
analysis O
of O
the O
elasticity S-PRO
and O
strength S-PRO
of O
SLA-printed O
materials S-CONPRI
, O
equations O
to O
predict O
the O
elastic B-PRO
modulus E-PRO
and O
ultimate B-PRO
tensile I-PRO
strength E-PRO
are O
derived O
. O


Uniaxial O
tensile B-CHAR
tests E-CHAR
are O
carried O
out O
to O
obtain O
the O
elastic B-PRO
modulus E-PRO
and O
ultimate B-PRO
tensile I-PRO
strength E-PRO
of O
the O
standard S-CONPRI
SLA-printed O
materials S-CONPRI
under O
different O
printing O
angles O
and O
layer B-PARA
thicknesses E-PARA
. O


The O
parameters S-CONPRI
of O
the O
constitutive O
model S-CONPRI
are O
employed O
in O
ABAQUS S-ENAT
to O
simulate O
the O
mechanical S-APPL
behavior O
of O
a O
cellular B-FEAT
structure E-FEAT
and O
compare O
it O
with O
the O
experimental S-CONPRI
results O
. O


The O
results O
demonstrate O
that O
the O
elastoplastic O
constitutive O
model S-CONPRI
developed O
in O
this O
study O
can O
effectively O
describe O
the O
mechanical S-APPL
behavior O
of O
SLA-printed O
materials S-CONPRI
. O


Transparent B-CONPRI
materials E-CONPRI
for O
fused B-MANP
filament I-MANP
fabrication E-MANP
printers O
are O
widely O
available O
and O
may O
be S-MATE
useful O
for O
constructing O
3D B-MANP
printed E-MANP
devices O
with O
applications O
in O
UV/VIS O
spectroscopy S-CONPRI
. O


In O
this O
study O
, O
colourless O
polylactic B-MATE
acid E-MATE
, O
HD O
Glass S-MATE
and O
T-Glase O
were O
evaluated O
as S-MATE
construction O
materials S-CONPRI
for O
biochemical O
sensors S-MACEQ
, O
which O
contain O
immobilised O
enzymes O
, O
for O
analysis O
by O
UV/VIS O
spectrophotometry O
. O


Experiments O
were O
conducted O
on O
both O
the O
native O
3D B-MANP
print E-MANP
and O
after O
coating S-APPL
with O
XTC-3D® O
, O
a O
transparent S-CONPRI
epoxy S-MATE
resin O
used O
to O
improve O
optical S-CHAR
transparency O
of O
3D B-MANP
prints E-MANP
. O


Individual O
enzymes O
were O
immobilised O
within O
the O
3D B-MANP
prints E-MANP
by O
coupling O
the O
enzymes O
to O
tosyl-activated O
magnetic O
beads S-CHAR
and O
attracted O
to O
the O
print S-MANP
surface O
by O
magnets S-APPL
embedded O
in O
the O
3D B-MANP
print E-MANP
. O


A O
transparent S-CONPRI
3D B-MANP
printed E-MANP
device O
was O
demonstrated O
using O
enzymatic O
assays O
of O
lactose O
and O
glucose O
. O


Further O
studies O
showed O
that O
enzyme O
assays O
performed O
in O
these O
3D B-MANP
printed E-MANP
devices O
are O
reproducible O
, O
accurate S-CHAR
and O
of O
comparable O
sensitivity S-PARA
to O
the O
same O
assays O
performed O
in O
polystyrene S-MATE
cuvettes O
. O


Additive B-MANP
manufacturing E-MANP
is O
now O
considered O
as S-MATE
a O
new O
paradigm O
that O
is O
foreseen O
to O
improve O
progress O
in O
many O
fields O
. O


The O
field O
of O
tissue B-CONPRI
engineering E-CONPRI
has O
been O
facing S-MANP
the O
need O
for O
tissue O
vascularization S-CONPRI
when O
producing O
thick O
tissues O
. O


The O
use O
of O
sugar B-MATE
glass E-MATE
as S-MATE
a O
fugitive O
ink S-MATE
to O
produce O
vascular O
networks O
through O
rapid O
casting S-MANP
may O
offer O
the O
key O
to O
vascularization S-CONPRI
of O
thick O
tissues O
produced O
by O
tissue B-CONPRI
engineering E-CONPRI
. O


Here O
, O
a O
3D B-MACEQ
printer I-MACEQ
head E-MACEQ
capable O
of O
producing O
complex B-CONPRI
structures E-CONPRI
out O
of O
sugar B-MATE
glass E-MATE
is O
presented O
. O


This O
printer S-MACEQ
head O
uses O
a O
motorized O
heated O
syringe S-MACEQ
fitted O
with O
a O
custom O
made O
nozzle S-MACEQ
. O


The O
printer S-MACEQ
head O
was O
adapted O
to O
be S-MATE
mounted O
on O
a O
commercially O
available O
3D B-MACEQ
printer E-MACEQ
. O


A O
mathematical S-CONPRI
model O
was O
derived O
to O
predict O
the O
diameter S-CONPRI
of O
the O
filaments S-MATE
based O
on O
the O
printer S-MACEQ
head O
feed S-PARA
rate O
and O
extrusion B-PARA
rate E-PARA
. O


Using O
a O
1 O
mm S-MANP
diameter S-CONPRI
nozzle O
, O
the O
printer S-MACEQ
accurately S-CHAR
produced O
filaments S-MATE
ranging O
from O
0.3 O
mm S-MANP
to O
3.2 O
mm S-MANP
in O
diameter S-CONPRI
. O


One O
of O
the O
main O
advantages O
of O
this O
manufacturing S-MANP
method O
is O
the O
self-supporting S-FEAT
behaviour O
of O
sugar B-MATE
glass E-MATE
that O
allows O
the O
production S-MANP
of O
long O
, O
horizontal O
, O
curved O
, O
as S-MATE
well O
as S-MATE
overhanging O
filaments S-MATE
needed O
to O
produce O
complex O
vascular O
networks O
. O


Finally O
, O
to O
establish O
a O
proof O
of O
concept O
, O
polydimethylsiloxane S-MATE
was O
used O
as S-MATE
the O
gel S-MATE
matrix O
during O
the O
rapid O
casting S-MANP
to O
produce O
various O
“ O
vascularized O
” O
constructs O
that O
were O
successfully O
perfused O
, O
which O
suggests O
that O
this O
new O
fabrication S-MANP
method O
can O
be S-MATE
used O
in O
a O
number O
of O
tissue B-CONPRI
engineering E-CONPRI
applications O
, O
including O
the O
vascularization S-CONPRI
of O
thick O
tissues O
. O


3D S-CONPRI
printable O
zwitterionic O
nanoclay O
hydrogel S-MATE
with O
self-supporting S-FEAT
abilities O
. O


Printing B-PARA
speed E-PARA
had O
a O
considerable O
effect O
on O
the O
material S-MATE
’ O
s S-MATE
tensile O
properties S-CONPRI
. O


Increased O
aging O
time O
of O
the O
pre-gels O
significantly O
reduced O
strain S-PRO
at O
failure S-CONPRI
. O


Excellent O
recovery O
of O
compressed O
hydrogels S-MATE
when O
left O
for O
24 O
h O
at O
room O
temperature S-PARA
. O


A O
UV-curable O
nanoclay-zwitterionic O
hydrogel S-MATE
is O
synthesised O
and O
evaluated O
though O
rheological S-PRO
and O
mechanical B-CHAR
testing E-CHAR
. O


Compression S-PRO
and O
tensile S-PRO
samples S-CONPRI
are O
printed O
and O
compared O
to O
cast S-MANP
samples O
. O


The O
pre-gel O
aging O
time O
showed O
that O
an O
increased O
time O
resulted O
in O
a O
lower O
strain S-PRO
at O
failure S-CONPRI
for O
both O
cast S-MANP
and O
extruded S-MANP
samples O
. O


Furthermore O
, O
the O
compressed O
samples S-CONPRI
display O
self-healing O
abilities O
at O
room O
temperature S-PARA
and O
almost O
completely O
returns O
to O
its O
original O
state O
before O
compression S-PRO
occurred O
. O


Net-shape O
98 O
% O
dense O
objects O
have O
been O
fabricated S-CONPRI
from O
a O
rapidly B-MANP
solidified E-MANP
ferrous O
powder S-MATE
using O
binder S-MATE
jet O
3D B-MANP
printing E-MANP
and O
molten O
bronze S-MATE
infiltration O
. O


X-ray B-CHAR
diffraction E-CHAR
, O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
, O
and O
differential O
thermal B-CHAR
analysis E-CHAR
were O
used O
to O
characterize O
the O
structural O
evolution S-CONPRI
of O
the O
powder B-MACEQ
feedstock E-MACEQ
during O
an O
infiltration S-CONPRI
heating S-MANP
cycle O
. O


Microindentation O
and O
bend B-CHAR
tests E-CHAR
were O
performed O
on O
the O
infiltrated O
material S-MATE
to O
evaluate O
its O
mechanical B-CONPRI
properties E-CONPRI
. O


It O
was O
found O
that O
infiltration S-CONPRI
improved O
the O
strength S-PRO
of O
the O
sintered S-MANP
preforms O
by O
eliminating O
the O
stress B-CHAR
concentration E-CHAR
points O
at O
interparticle O
necks O
. O


We O
have O
printed O
microscale S-CONPRI
3-dimensional O
tissue O
scaffolds S-FEAT
using O
cellulose B-MATE
acetate E-MATE
( O
CA S-MATE
) O
for O
the O
first O
time O
and O
produced O
a O
range S-PARA
of O
pore B-PARA
sizes E-PARA
ranging O
from O
99 O
to O
608 O
μm O
that O
are O
potentially O
favorable O
for O
tissue B-CONPRI
engineering E-CONPRI
. O


In O
the O
process S-CONPRI
we O
have O
elucidated O
some O
of O
the O
formulation-fabrication-morphology O
relationships O
which O
enabled O
advancements O
in O
ink S-MATE
development O
, O
optimization S-CONPRI
of O
fabrication S-MANP
parameters O
, O
and O
morphological O
control O
. O


We O
believe O
this O
study O
will O
increase O
the O
knowledge O
base O
for O
additive B-MANP
manufacturing E-MANP
of O
CA S-MATE
and O
enable O
further O
research S-CONPRI
into O
the O
use O
of O
3D-printed S-MANP
CA O
for O
tissue B-CONPRI
engineering E-CONPRI
applications O
. O


Also O
, O
our O
findings O
on O
printing O
optimization S-CONPRI
may O
provide O
some O
practical O
principles O
and O
methodologies O
that O
are O
applicable O
for O
the O
ink S-MATE
development O
using O
other O
biomaterials S-MATE
. O


Anisotropy S-PRO
in O
dielectric S-MACEQ
properties O
can O
have O
deleterious O
effects O
in O
structures O
intended O
for O
use O
in O
high-field O
environments O
. O


We O
show O
that O
dielectric S-MACEQ
anisotropy S-PRO
is O
introduced O
into O
parts O
fabricated S-CONPRI
using O
additive B-MANP
manufacturing E-MANP
techniques O
based O
on O
the O
orientation S-CONPRI
in O
which O
the O
part O
is O
printed O
. O


Dielectric B-PRO
strength E-PRO
testing O
data S-CONPRI
, O
based O
on O
the O
ASTM O
D149 O
standard S-CONPRI
, O
are O
presented O
for O
samples B-CONPRI
fabricated E-CONPRI
using O
the O
polymer S-MATE
jetting S-MANP
( O
PolyJet S-CONPRI
) O
, O
stereolithography S-MANP
( O
SLA S-MACEQ
) O
, O
fused B-MANP
deposition I-MANP
modeling E-MANP
( O
FDM S-MANP
) O
, O
and O
selective B-MANP
laser I-MANP
sintering E-MANP
( O
SLS S-MANP
) O
additive B-MANP
manufacturing E-MANP
techniques O
. O


Each O
printing O
technique O
was O
found O
to O
introduce O
anisotropic S-PRO
dielectric O
properties S-CONPRI
within O
the O
sample S-CONPRI
coupons O
that O
were O
a O
function O
of O
the O
original O
orientation S-CONPRI
in O
which O
the O
part O
was O
printed O
, O
and O
the O
direction O
of O
structural O
susceptibility S-PRO
was O
found O
to O
be S-MATE
print-method O
dependent O
. O


Differences O
in O
dielectric B-PRO
strength E-PRO
for O
coupons O
printed O
in O
different O
orientations S-CONPRI
were O
found O
to O
exceed O
70 O
% O
for O
some O
combinations O
of O
printing O
technique O
and O
polymer S-MATE
. O


Overall O
, O
test O
coupons O
printed O
with O
stereolithography S-MANP
( O
SLA S-MACEQ
) O
were O
found O
to O
exhibit O
the O
lowest O
degree O
of O
dielectric B-PRO
strength I-PRO
anisotropy E-PRO
between O
print S-MANP
orientations S-CONPRI
. O


Dielectric S-MACEQ
failure O
mechanisms O
are O
discussed O
. O


Effect O
of O
deposition S-CONPRI
velocity O
on O
the O
width O
, O
continuity O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
printed O
mortar O
. O


The O
pumping O
flow B-PARA
rate E-PARA
influences O
the O
printed O
mortar O
specimens O
. O


Mechanical B-PRO
strength E-PRO
of O
multi-layered O
printed O
specimens O
in O
the O
presence/absence O
of O
glass B-MATE
fibre E-MATE
, O
compared O
with O
moulded S-MACEQ
mortar O
. O


An O
adaptable O
industrial B-MACEQ
robot E-MACEQ
end-effector O
orientation S-CONPRI
and O
velocity O
control O
approach O
for O
versatile O
novel O
form O
fabrication S-MANP
. O


Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
are O
widely O
used O
in O
various O
fields O
of O
industry S-APPL
and O
research S-CONPRI
. O


Continual O
research S-CONPRI
has O
enabled O
AM B-MANP
technologies E-MANP
to O
be S-MATE
considered O
as S-MATE
a O
feasible O
substitute O
for O
certain O
applications O
in O
the O
construction S-APPL
industry O
, O
particularly O
given O
the O
advances O
in O
the O
use O
of O
glass B-MATE
fibre E-MATE
reinforced O
mortar O
. O


An O
investigation O
of O
the O
resulting O
mechanical B-CONPRI
properties E-CONPRI
of O
various O
mortar O
mixes O
extruded S-MANP
using O
a O
robotic B-MACEQ
arm E-MACEQ
is O
presented O
. O


The O
nozzle S-MACEQ
paths O
were O
projected O
via O
‘ O
spline O
’ O
interpolation S-CONPRI
to O
obtain O
the O
desired O
trajectory O
and O
deposition S-CONPRI
velocity O
in O
the O
reference O
frame O
of O
the O
manipulator S-MACEQ
. O


In O
this O
study O
, O
the O
mixes O
consist O
of O
ordinary O
Portland O
cement S-MATE
, O
fine O
sand S-MATE
, O
chopped O
glass B-MATE
fibres E-MATE
( O
6 O
mm S-MANP
) O
and O
chemical O
admixtures O
, O
which O
are O
used O
to O
print S-MANP
prismatic- O
and O
cubic-shaped O
specimens O
. O


Mechanical B-PRO
strength E-PRO
tests O
were O
performed O
on O
the O
printed O
specimens O
to O
evaluate O
the O
behaviour O
of O
the O
materials S-CONPRI
in O
the O
presence O
and O
absence O
of O
glass B-MATE
fibre E-MATE
. O


Robot S-MACEQ
end-effector O
velocity O
tests O
were O
performed O
to O
examine O
the O
printability S-PARA
and O
extrudability O
of O
the O
mortar O
mixes O
. O


The O
results O
show O
that O
printed O
specimens O
with O
glass B-MATE
fibre E-MATE
have O
enhanced O
compressive B-PRO
strength E-PRO
compared O
with O
specimens O
without O
glass B-MATE
fibre E-MATE
. O


Blends S-MATE
of O
raco-PP O
and O
amorphous O
PP O
show O
best O
3D B-MANP
printing E-MANP
performances O
. O


Tailored O
polypropylene S-MATE
features O
enhanced O
interlayer O
bonding S-CONPRI
quality O
and O
reduced O
warpage S-CONPRI
. O


3D B-MANP
printed E-MANP
frog O
with O
PP O
as S-MATE
test O
sample S-CONPRI
demonstrates O
outstanding O
part O
performance S-CONPRI
. O


This O
paper O
reports O
on O
the O
optimization S-CONPRI
of O
polypropylene S-MATE
( O
PP O
) O
feedstock B-MATE
material E-MATE
towards O
extrusion-based O
additive B-MANP
manufacturing E-MANP
. O


To O
achieve O
this O
, O
two O
commercially O
available O
grades O
of O
polypropylene/ethylene O
random O
copolymers S-MATE
( O
raco O
PP O
) O
were O
modified O
, O
aiming O
to O
reduce O
warp O
deformation S-CONPRI
caused O
by O
shrinkage S-CONPRI
and O
at O
the O
same O
time O
reduce O
the O
anisotropic S-PRO
property O
by O
improving O
the O
interlayer O
bonding S-CONPRI
quality O
of O
3D B-APPL
printed I-APPL
parts E-APPL
processed O
by O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
. O


A O
β-nucleating O
agent O
, O
several O
amorphous O
polypropylenes S-MATE
( O
aPP O
) O
and O
one O
linear O
low-density O
polyethylene S-MATE
( O
LLDPE O
) O
were O
selected O
as S-MATE
additive S-MATE
or O
blending S-MANP
component O
with O
the O
goal O
to O
reduce O
shrinkage S-CONPRI
. O


The O
polypropylene B-MATE
feedstock E-MATE
material S-MATE
optimization O
was O
conducted O
by O
a O
combination O
of O
a O
lab-scale O
filament S-MATE
rod O
processing O
method O
and O
utilizing O
printed O
square O
tubes O
to O
optimize O
printing B-CONPRI
performance E-CONPRI
. O


The O
achieved O
results O
demonstrate O
that O
the O
crystallization S-CONPRI
behavior O
and O
E-modulus O
of O
polypropylene S-MATE
play O
significant O
roles O
for O
warp O
deformation S-CONPRI
in O
extrusion-based O
3D B-APPL
printed I-APPL
parts E-APPL
. O


The O
investigated O
polymer B-MATE
blend E-MATE
of O
raco O
PP O
and O
LLDPE O
shows O
no O
significant O
contribution O
to O
reduce O
warpage S-CONPRI
and O
impairs O
also O
the O
interlayer O
bonding S-CONPRI
. O


With O
two O
aPP O
grades O
warp O
deformation S-CONPRI
could O
be S-MATE
drastically O
reduced O
. O


In O
addition O
, O
the O
interlayer O
bonding S-CONPRI
quality O
is O
remarkably O
enhanced O
in O
these O
blends S-MATE
in O
spite O
of O
slight O
decreases O
in O
stiffness S-PRO
and O
strength S-PRO
. O


In O
conclusion O
, O
the O
optimized O
PP O
feedstock B-MATE
material E-MATE
features O
less O
warp O
deformation S-CONPRI
, O
high O
stiffness S-PRO
, O
and O
most O
importantly O
, O
outstanding O
interlayer O
bonding S-CONPRI
qualities O
. O


This O
paper O
investigates S-CONPRI
the O
effect O
of O
interlayer O
cooling S-MANP
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
structures O
that O
are O
3D B-MANP
printed E-MANP
using O
fusion S-CONPRI
based O
material B-MANP
extrusion E-MANP
. O


Two O
different O
types O
of O
samples S-CONPRI
were O
prepared O
, O
one O
designed S-FEAT
to O
measure O
the O
compressive B-PRO
strength E-PRO
of O
the O
structural O
material S-MATE
, O
and O
the O
other O
designed S-FEAT
to O
measure O
the O
shear B-PRO
strength E-PRO
of O
the O
structural O
material S-MATE
. O


As S-MATE
the O
wait O
time O
in O
between O
layers O
was O
increased O
, O
the O
effective O
yield B-PRO
strength E-PRO
was O
decreased O
for O
both O
types O
of O
samples S-CONPRI
. O


Temperature S-PARA
data S-CONPRI
was O
collected O
from O
the O
top O
layer S-PARA
of O
the O
structures O
after O
each O
successive O
layer S-PARA
deposition S-CONPRI
. O


This O
data S-CONPRI
revealed O
significant O
cooling S-MANP
over O
the O
wait O
times O
being O
considered O
. O


These O
trends S-CONPRI
prove O
that O
additional O
care O
needs O
to O
be S-MATE
taken O
when O
selecting O
the O
print S-MANP
settings O
for O
structural B-CONPRI
components E-CONPRI
that O
are O
manufactured S-CONPRI
using O
fused B-MANP
filament I-MANP
fabrication E-MANP
. O


This O
study O
shows O
that O
printing B-MANP
processes E-MANP
that O
require O
additional O
time O
( O
i.e O
. O


larger O
parts O
, O
finer O
geometries S-CONPRI
, O
etc O
. O


) O
will O
inherently O
lead S-MATE
to O
a O
reduction S-CONPRI
in O
the O
mechanical B-PRO
strength E-PRO
of O
the O
printed O
structure S-CONPRI
. O


To O
improve O
printing O
fidelity O
, O
reducing O
the O
slice S-CONPRI
thickness O
to O
eliminate O
the O
staircase O
effect O
is O
of O
great O
importance O
for O
digital B-MANP
light I-MANP
processing E-MANP
( O
DLP S-MANP
) O
technology S-CONPRI
. O


However O
, O
using O
a O
thinner O
slice S-CONPRI
printing O
model S-CONPRI
leads O
to O
a O
longer O
total O
printing O
time O
in O
the O
conventional O
DLP S-MANP
approach O
, O
which O
significantly O
reduces O
printing O
efficiency O
. O


In O
this O
work O
, O
a O
tunable O
pre-curing O
DLP S-MANP
approach O
was O
developed O
where O
the O
relationship O
between O
the O
forming S-MANP
layer O
thickness O
and O
ultraviolet S-CONPRI
( O
UV S-CONPRI
) O
exposure S-CONPRI
time O
is O
theoretically O
analyzed O
, O
and O
the O
curing S-MANP
process O
of O
photo-curable S-FEAT
solutions O
is O
divided O
into O
two O
sub-processes O
: O
pre-curing O
and O
further O
curing S-MANP
. O


In O
the O
pre-curing O
process S-CONPRI
, O
the O
photo-curable S-FEAT
solution O
is O
initially O
pre-cured O
and O
kept O
at O
the O
pre-gelled O
state O
due O
to O
continuous O
UV B-CONPRI
exposure E-CONPRI
during O
subsequent O
DLP S-MANP
printing O
. O


Then O
, O
the O
pre-cured O
photo-curable S-FEAT
solution O
is O
quickly O
cured S-MANP
to O
form O
a O
designed S-FEAT
thickness O
in O
each O
printing O
cycle O
. O


Also O
, O
the O
UV S-CONPRI
absorbing O
agent O
is O
added O
to O
the O
photo-curable S-FEAT
hydrogel S-MATE
solutions O
to O
regulate O
the O
pre-curing O
process S-CONPRI
. O


Using O
a O
10 O
μm O
slice S-CONPRI
for O
DLP S-MANP
printing O
, O
the O
total O
printing O
time O
of O
the O
tunable O
pre-curing O
DLP S-MANP
is O
approximately O
5.6 O
% O
of O
the O
conventional O
DLP S-MANP
, O
and O
the O
staircase O
effect O
on O
the O
surface S-CONPRI
is O
significantly O
eliminated O
using O
10 O
μm O
slice S-CONPRI
tunable O
pre-curing O
DLP S-MANP
approach O
, O
which O
leads O
to O
a O
better O
printing O
fidelity O
. O


Moreover O
, O
the O
reduction S-CONPRI
of O
UV B-CONPRI
exposure E-CONPRI
time O
and O
slice S-CONPRI
thickness O
is O
beneficial O
for O
cell B-CHAR
viability E-CHAR
during O
DLP S-MANP
bioprinting S-APPL
of O
thick O
bulk O
structures O
, O
which O
is O
demonstrated O
by O
the O
printing O
of O
PC12 O
cell-laden O
gelatin O
methacrylate O
( O
GelMA O
) O
bioinks O
. O


Using O
the O
tunable O
pre-curing O
DLP S-MANP
approach O
, O
the O
PC12 O
cells S-APPL
achieved O
higher O
cell B-CHAR
viability E-CHAR
( O
90.2 O
± O
6.1 O
% O
) O
and O
better O
cell S-APPL
morphology O
than O
the O
conventional O
DLP S-MANP
approach O
( O
54.5 O
± O
4.8 O
% O
) O
. O


The O
tunable O
pre-curing O
DLP S-MANP
approach O
provides O
a O
promising O
alternative O
to O
extend O
the O
application O
of O
DLP S-MANP
printing O
greatly O
. O


This O
paper O
proposes O
an O
electromagnetic O
based O
planar O
pressure S-CONPRI
sensor O
using O
a O
substrate S-MATE
integrated O
waveguide O
( O
SIW O
) O
. O


The O
proposed O
pressure S-CONPRI
sensor O
is O
inspired O
by O
a O
rectangular O
SIW O
cavity O
and O
is O
additively B-MANP
manufactured E-MANP
using O
3D B-MANP
printed E-MANP
dielectric O
material S-MATE
with O
inkjet S-MANP
printed O
conductive O
pattern S-CONPRI
. O


We O
inserted O
meshed O
material S-MATE
at O
the O
SIW O
centre O
, O
to O
facilitate O
soft O
pressing S-MANP
, O
and O
simplify O
producing O
frequency O
shifts O
due O
to O
capacitive O
coupling O
perturbation O
from O
different O
pressure S-CONPRI
levels O
. O


This O
paper O
investigates S-CONPRI
the O
bending S-MANP
behaviors O
of O
a O
bi-material O
structure S-CONPRI
( O
BMS O
) O
using O
both O
experimental S-CONPRI
and O
numerical O
methods O
The O
BMS O
is O
a O
composite B-MATE
material E-MATE
built O
by O
a O
3D-printed S-MANP
, O
open-cellular O
brittle S-PRO
plaster O
structure S-CONPRI
filled O
with O
a O
silicone B-MATE
elastomer E-MATE
. O


The O
composition S-CONPRI
and O
configuration S-CONPRI
of O
the O
two O
materials S-CONPRI
determine O
the O
overall O
mechanical B-CONPRI
properties E-CONPRI
. O


Four-point O
bending B-CHAR
test E-CHAR
results O
show O
a O
non-linear O
elastic S-PRO
property O
, O
enhanced O
strength S-PRO
and O
toughness S-PRO
of O
BMS O
samples S-CONPRI
compared O
to O
either O
material S-MATE
phase O
alone O
. O


Such O
behavior O
is O
believed O
to O
be S-MATE
a O
result O
of O
delayed O
microcrack O
propagation O
in O
the O
brittle S-PRO
phase O
and O
a O
hardening S-MANP
effect O
of O
elastomer S-MATE
. O


In O
the O
numerical O
study O
, O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
( O
FEA O
) O
is O
employed O
to O
verify O
these O
hypotheses O
. O


The O
FEA O
incorporates O
a O
brittle S-PRO
cracking O
material S-MATE
model O
for O
the O
plaster O
and O
a O
hyperelastic O
model S-CONPRI
for O
the O
silicone S-MATE
. O


The O
brittle S-PRO
cracking O
model S-CONPRI
enables O
the O
estimation O
of O
element S-MATE
degradation S-CONPRI
as S-MATE
a O
result O
of O
crack O
development O
and O
thus O
eliminates O
the O
need O
for O
the O
extremely O
refined O
mesh O
. O


Simulation S-ENAT
result O
confirms O
the O
non-linear O
elastic S-PRO
transition O
and O
crack-induced O
material S-MATE
degradation S-CONPRI
and O
visualizes O
the O
silicone S-MATE
strengthening O
mechanism S-CONPRI
that O
can O
avoid O
rapid O
structural O
rupture O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
rapidly O
becoming O
one O
of O
the O
most O
popular O
manufacturing S-MANP
techniques O
for O
short O
run O
part O
production S-MANP
and O
rapid B-ENAT
prototyping E-ENAT
. O


AM S-MANP
encompasses O
a O
range S-PARA
of O
technologies S-CONPRI
, O
including O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
process S-CONPRI
. O


The O
purpose O
of O
this O
paper O
is O
to O
evaluate O
and O
benchmark S-MANS
the O
mechanical S-APPL
performance O
of O
polyamide B-MATE
12 E-MATE
( O
PA12 S-MATE
) O
parts O
, O
fabricated S-CONPRI
using O
a O
production S-MANP
scale O
powder B-MANP
bed I-MANP
fusion E-MANP
printing O
process S-CONPRI
( O
HP O
Multi B-MANP
Jet I-MANP
Fusion E-MANP
printing O
process S-CONPRI
) O
. O


This O
system O
has O
a O
build B-PARA
volume E-PARA
is O
380 O
× O
254 O
× O
350 O
mm S-MANP
. O


The O
printed O
polymer S-MATE
parts O
were O
examined O
to O
determine O
their O
hydrophobicity O
, O
morphology S-CONPRI
, O
porosity S-PRO
and O
roughness S-PRO
. O


Chemical O
and O
thermal B-CONPRI
properties E-CONPRI
of O
the O
PA12 S-MATE
parts O
were O
also O
evaluated O
using O
attenuated O
total O
reflection S-CHAR
infrared S-CONPRI
spectroscopy O
( O
ATR O
FT-IR S-CHAR
) O
, O
x-ray B-CHAR
photoelectron I-CHAR
spectroscopy E-CHAR
( O
XPS S-CHAR
) O
and O
differential O
scanning S-CONPRI
calorimetry O
( O
DSC S-CHAR
) O
. O


The O
study O
highlights O
the O
influence O
of O
build B-PARA
orientation E-PARA
on O
the O
tensile S-PRO
( O
ISO S-MANS
527-1:2012 O
) O
and O
flexural O
( O
ISO S-MANS
178:2010 O
) O
properties S-CONPRI
. O


In O
terms O
of O
tensile B-PRO
strength E-PRO
, O
the O
parts O
exhibited O
isotropic S-PRO
behaviour O
with O
a O
maximum O
tensile B-PRO
strength E-PRO
of O
49 O
MPa S-CONPRI
. O


In O
terms O
of O
flexural O
testing S-CHAR
, O
the O
build B-PARA
orientations E-PARA
had O
a O
significant O
effect O
on O
the O
strength S-PRO
of O
the O
printed O
part O
. O


The O
Z O
orientation S-CONPRI
exhibited O
a O
40 O
% O
higher O
flexural B-PRO
strength E-PRO
, O
when O
compared O
to O
that O
of O
the O
X O
orientation S-CONPRI
. O


The O
maximum O
flexural B-PRO
strength E-PRO
observed O
was O
70 O
MPa S-CONPRI
. O


The O
results O
of O
this O
rapid O
, O
production S-MANP
scale O
AM S-MANP
study O
are O
compared O
with O
previous O
studies O
that O
detail O
the O
mechanical S-APPL
performance O
of O
PA12 S-MATE
, O
fabricated S-CONPRI
using O
PBF S-MANP
processes O
, O
such O
as S-MATE
selective O
laser B-MANP
sintering E-MANP
. O


Fab O
labs O
, O
which O
offer O
small-scale O
distributed O
digital B-MANP
fabrication E-MANP
, O
are O
forming S-MANP
a O
Green O
Fab O
Lab O
Network O
, O
which O
embraces O
concepts O
of O
an O
open O
source S-APPL
symbiotic O
economy O
and O
circular O
economy O
patterns O
. O


With O
the O
use O
of O
industrial S-APPL
3D B-MACEQ
printers E-MACEQ
capable O
of O
fused S-CONPRI
particle O
fabrication/ O
fused S-CONPRI
granular O
fabrication S-MANP
( O
FPF/FGF O
) O
printing O
directly O
from O
waste O
plastic S-MATE
streams O
, O
green O
fab O
labs O
could O
act O
as S-MATE
defacto O
recycling S-CONPRI
centers O
for O
converting O
waste O
plastics S-MATE
into O
valuable O
products O
for O
their O
communities O
. O


Thus O
, O
in O
this O
study O
the O
Gigabot O
X O
, O
an O
open O
source S-APPL
industrial S-APPL
3D B-MACEQ
printer E-MACEQ
, O
which O
has O
been O
shown O
to O
be S-MATE
amenable O
to O
a O
wide O
array O
of O
recyclables O
for O
FPF/FGF O
3D B-MANP
printing E-MANP
, O
is O
used O
to O
evaluate O
this O
economic O
potential O
. O


An O
economic O
life B-CONPRI
cycle E-CONPRI
analysis O
of O
the O
technology S-CONPRI
is O
completed O
comprised O
of O
three O
cases O
studies O
using O
FPF O
for O
large O
sporting O
equipment S-MACEQ
products O
. O


Sensitivities S-PARA
are O
run O
on O
the O
electricity O
costs O
for O
operation O
, O
materials S-CONPRI
costs O
from O
various O
feed S-PARA
stocks O
and O
the O
capacity S-CONPRI
factors O
of O
the O
3D B-MACEQ
printers E-MACEQ
. O


The O
results O
showed O
that O
FPF/FGF O
3D B-MANP
printing E-MANP
is O
capable O
of O
energy O
efficient O
production S-MANP
of O
a O
wide O
range S-PARA
of O
large O
high-value O
sporting O
goods O
products O
. O


For O
the O
case B-CONPRI
study E-CONPRI
products O
analyzed O
even O
the O
lowest O
capacity S-CONPRI
factor O
( O
starting O
only O
one O
print S-MANP
per O
week O
) O
represented O
a O
profit O
when O
comparing O
to O
high-end O
value O
products O
. O


For O
some O
products O
the O
profit O
potential O
and O
return B-CONPRI
on I-CONPRI
investment E-CONPRI
was O
substantial O
( O
e.g O
. O


The O
results O
clearly O
show O
that O
open O
source S-APPL
industrial S-APPL
FPF/FGF O
3D B-MACEQ
printers E-MACEQ
have O
significant O
economic O
potential O
when O
used O
as S-MATE
a O
distributed O
recycling/manufacturing O
system O
using O
recyclable S-CONPRI
feed S-PARA
stocks O
in O
the O
green O
fab O
lab O
context O
. O


It O
is O
well-known O
that O
the O
effective O
mechanical B-CONPRI
properties E-CONPRI
of O
cellular B-FEAT
structures E-FEAT
can O
be S-MATE
tuned O
by O
varying O
its O
relative B-PRO
density E-PRO
. O


With O
the O
advancement O
of O
3D B-MANP
printing E-MANP
, O
variable-density O
cellular B-FEAT
structures E-FEAT
can O
be S-MATE
fabricated O
with O
high O
precision S-CHAR
using O
this O
emerging O
manufacturing B-MANP
technology E-MANP
. O


Taking O
advantage O
of O
this O
unique O
ability O
to O
fabricate S-MANP
variable-density O
cellular B-FEAT
structure E-FEAT
, O
an O
efficient O
homogenization-based O
topology B-FEAT
optimization E-FEAT
method O
for O
natural O
frequency O
optimization S-CONPRI
is O
presented O
in O
this O
work O
. O


The O
method O
is O
demonstrated O
using O
a O
cantilevered O
plate O
with O
a O
honeycomb B-FEAT
structure E-FEAT
and O
is O
validated O
by O
detailed O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
and O
experiment S-CONPRI
. O


It O
is O
shown O
that O
the O
optimal O
design S-FEAT
can O
be S-MATE
fabricated O
by O
3D B-MANP
printing E-MANP
and O
shows O
significant O
enhancement O
in O
natural O
frequency O
and O
reduction S-CONPRI
in O
weight S-PARA
. O


Among O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
, O
binder B-MANP
jetting E-MANP
( O
BJ S-MANP
) O
produces O
workpieces O
that O
could O
be S-MATE
used O
in O
a O
great O
variety O
of O
applications O
, O
such O
as S-MATE
decorative O
parts O
, O
prototypes S-CONPRI
, O
foundry S-MANP
molds O
, O
bone B-APPL
implants E-APPL
, O
and O
others O
. O


This O
technique O
includes O
the O
powder S-MATE
deposition S-CONPRI
to O
form O
the O
layers O
, O
binder S-MATE
application O
, O
and O
post-processing S-CONPRI
to O
enhance O
mechanical B-CONPRI
properties E-CONPRI
. O


Fibers S-MATE
can O
be S-MATE
mixed O
with O
traditional O
raw B-MATE
material E-MATE
powder S-MATE
in O
order O
to O
produce O
composite S-MATE
parts O
that O
are O
stronger O
. O


Sisal O
fibers S-MATE
are O
considered O
to O
be S-MATE
a O
promising O
reinforcement S-PARA
in O
composites S-MATE
because O
of O
their O
low O
cost O
, O
high O
strength S-PRO
, O
and O
lack O
of O
risk O
to O
human O
health O
. O


In O
Brazil O
, O
sisal O
fibers S-MATE
are O
abundant O
and O
there O
has O
been O
no O
previous O
study O
on O
the O
application O
of O
this O
fiber S-MATE
in O
binder B-MANP
jetting E-MANP
. O


This O
article O
proposes O
the O
production S-MANP
of O
gypsum–sisal O
fiber S-MATE
parts O
using O
BJ S-MANP
and O
the O
analysis O
of O
the O
effects O
of O
some O
manufacturing S-MANP
parameters O
, O
such O
as S-MATE
the O
presence O
of O
fiber S-MATE
, O
printing O
orientation S-CONPRI
, O
and O
post-processing S-CONPRI
. O


A O
material S-MATE
characterization O
is O
performed O
on O
raw B-MATE
materials E-MATE
and O
printed O
parts O
in O
the O
form O
of O
thermogravimetric B-CHAR
analysis E-CHAR
( O
TGA S-CHAR
) O
, O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
, O
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
. O


A O
complete O
24 O
factorial B-CONPRI
design E-CONPRI
for O
analysis O
of O
variance O
was O
performed O
to O
evaluate O
the O
mechanical B-PRO
strength E-PRO
and O
porosity S-PRO
of O
the O
manufactured S-CONPRI
parts O
. O


It O
was O
observed O
that O
the O
fibers S-MATE
had O
a O
positive O
influence O
on O
the O
mechanical B-PRO
strength E-PRO
of O
the O
infiltrated O
parts O
, O
but O
a O
loss O
of O
strength S-PRO
was O
verified O
on O
the O
green B-PRO
parts E-PRO
. O


The O
reason O
for O
a O
loss O
of O
mechanical B-PRO
strength E-PRO
correlated S-CONPRI
with O
the O
increase O
in O
porosity S-PRO
caused O
by O
the O
fiber S-MATE
during O
the O
printing B-MANP
process E-MANP
; O
however O
, O
this O
increased O
porosity S-PRO
contributed O
to O
a O
more O
efficient O
infiltration S-CONPRI
post-processing O
. O


We O
experimentally O
and O
numerically O
investigate O
elastic S-PRO
wave O
propagation O
in O
a O
class O
of O
lightweight S-CONPRI
architected O
materials S-CONPRI
composed O
of O
hollow O
spheres O
and O
binders S-MATE
. O


Elastic S-PRO
wave O
transmission S-CHAR
tests O
demonstrate O
the O
existence O
of O
vibration O
mitigation O
capability O
in O
the O
proposed O
architected O
foams O
, O
which O
is O
validated O
against O
the O
numerically O
predicted S-CONPRI
phononic O
band O
gap O
. O


We O
further O
describe O
that O
the O
phononic O
band O
gap O
properties S-CONPRI
can O
be S-MATE
significantly O
altered O
through O
changing O
hollow O
sphere O
thickness O
and O
binder S-MATE
size O
in O
the O
architected O
foams O
. O


At O
the O
threshold O
stiffness S-PRO
contrast O
of O
50 O
, O
the O
proposed O
architected O
foam S-MATE
requires O
only O
a O
volume B-PARA
fraction E-PARA
of O
10.8 O
% O
while O
exhibiting O
an O
omnidirectional O
band O
gap O
size O
exceeding O
130 O
% O
. O


The O
proposed O
design S-FEAT
paradigm O
and O
physical O
mechanisms O
are O
robust O
and O
applicable O
to O
architected O
foams O
with O
other O
topologies S-CONPRI
, O
thus O
providing O
new O
opportunities O
to O
design S-FEAT
phononic O
metamaterials S-MATE
for O
low-frequency O
vibration O
control O
. O


Additive B-MANP
manufacturing E-MANP
of O
polymer S-MATE
derived O
ceramics S-MATE
with O
fused B-MANP
filament I-MANP
fabrication E-MANP
. O


Producing O
ceramics S-MATE
with O
hollow O
struts S-MACEQ
by O
surface S-CONPRI
coating S-APPL
with O
preceramic O
polymers S-MATE
. O


Creating O
a O
multi-level O
porous S-PRO
system O
with O
stable O
geometry S-CONPRI
. O


All O
3-D S-CONPRI
printing O
materials S-CONPRI
produced O
ceramics S-MATE
skins O
of O
less O
than O
100 O
microns O
. O


A O
promising O
method O
for O
obtaining O
ceramic S-MATE
components O
with O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
to O
use O
a O
two-step O
process S-CONPRI
of O
first O
printing O
the O
artifact O
in O
polymer S-MATE
and O
then O
converting O
it O
to O
ceramic S-MATE
using O
pyrolysis S-MANP
to O
form O
polymer S-MATE
derived O
ceramics S-MATE
( O
PDCs O
) O
. O


AM S-MANP
of O
ceramic S-MATE
components O
using O
PDCs O
has O
been O
demonstrated O
with O
a O
number O
of O
high-cost O
techniques O
, O
but O
data S-CONPRI
is O
lacking O
for O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
-based O
3-D S-CONPRI
printing O
. O


This O
study O
investigates S-CONPRI
the O
potential O
of O
lower-cost O
, O
more O
widespread O
and O
accessible O
FFF-based O
3-D S-CONPRI
printing O
of O
PDCs O
. O


Low-cost O
FFF S-MANP
machines O
have O
a O
resolution S-PARA
limit S-CONPRI
set O
by O
the O
nozzle S-MACEQ
width O
, O
which O
is O
inferior O
to O
the O
resolutions O
obtained O
with O
expensive O
stereolithography S-MANP
or O
selective B-MANP
laser I-MANP
sintering E-MANP
AM S-MANP
systems O
. O


However O
, O
to O
match O
the O
performance S-CONPRI
a O
partial O
PDC O
conversion O
is O
used O
here O
, O
where O
only O
the O
outer O
surface S-CONPRI
of O
the O
printed O
polymer S-MATE
frame O
is O
converted O
to O
ceramic S-MATE
. O


Here O
the O
FFF-based O
3-D S-CONPRI
printed O
sample S-CONPRI
is O
coated S-APPL
with O
a O
preceramic O
polymer S-MATE
and O
then O
it O
is O
converted O
into O
the O
corresponding O
PDC O
sample S-CONPRI
with O
a O
high O
temperature S-PARA
pyrolysis S-MANP
process S-CONPRI
. O


A O
screening O
experiment S-CONPRI
is O
performed O
on O
commercial O
filaments S-MATE
to O
obtain O
ceramic S-MATE
3-D S-CONPRI
prints O
by O
surface S-CONPRI
coating S-APPL
both O
hard O
thermoplastics S-MATE
: O
poly O
lactic O
acid O
( O
PLA S-MATE
) O
, O
polycarbonate S-MATE
( O
PC S-MATE
) O
, O
nylon B-MATE
alloys E-MATE
, O
polypropylene S-MATE
( O
PP O
) O
, O
polyethylene B-MATE
terephthalate E-MATE
glycol O
( O
PETG O
) O
, O
polyethylene B-MATE
terephthalate E-MATE
( O
PET O
) O
, O
and O
co-polyesters O
; O
and O
flexible O
materials S-CONPRI
including O
: O
flexible O
PLA S-MATE
, O
thermoplastic B-MATE
elastomer E-MATE
and O
thermoplastic B-MATE
polyurethane I-MATE
filaments E-MATE
. O


Mass O
and O
volume S-CONPRI
changes O
were O
quantified O
for O
the O
soaking O
and O
pyrolysis S-MANP
steps O
to O
form O
a O
hollow O
ceramic S-MATE
skin O
. O


All O
3-D S-CONPRI
printing O
materials S-CONPRI
extruded S-MANP
at O
250 O
microns O
successfully O
produced O
hollow O
ceramics S-MATE
skins O
of O
less O
than O
100 O
microns O
. O


The O
novel O
results O
developed O
here O
can O
be S-MATE
used O
to O
choose O
FFF-based O
polymers S-MATE
to O
use O
for O
PDC O
processing O
on O
a O
wide O
range S-PARA
of O
applications O
such O
as S-MATE
heat O
exchangers O
, O
heat B-MACEQ
sinks E-MACEQ
, O
scaffoldings O
for O
bone B-CONPRI
tissue I-CONPRI
growth E-CONPRI
, O
chemical/ O
gas S-CONPRI
filters S-APPL
and O
custom O
scientific O
hardware O
. O


Additive B-MANP
manufacturing E-MANP
via O
3-D S-CONPRI
printing O
technologies S-CONPRI
have O
become O
a O
frontier O
in O
materials S-CONPRI
research O
, O
including O
its O
application O
in O
the O
development O
and O
recycling S-CONPRI
of O
permanent B-MATE
magnets E-MATE
. O


This O
work O
addresses O
the O
opportunity O
to O
integrate O
magnetic B-CONPRI
field E-CONPRI
sources O
into O
3-D S-CONPRI
printing O
process S-CONPRI
in O
order O
to O
enable O
printing O
, O
alignment O
of O
anisotropic S-PRO
permanent O
magnets S-APPL
or O
magnetizing O
of O
magnetic O
filler O
materials S-CONPRI
, O
without O
requiring O
further O
processing O
. O


A O
non-axisymmetric O
electromagnet-type O
field O
source S-APPL
architecture S-APPL
was O
designed S-FEAT
, O
modelled O
, O
constructed O
, O
installed O
to O
a O
fused S-CONPRI
filament S-MATE
commercial O
3-D S-CONPRI
printer O
, O
and O
tested O
. O


The O
testing S-CHAR
was O
performed O
by O
applying O
magnetic B-CONPRI
field E-CONPRI
while O
printing O
composite S-MATE
anisotropic S-PRO
Nd-Fe-B O
+ O
Sm-Fe-N O
powders S-MATE
bonded O
in O
Nylon12 O
( O
65 O
vol. O
% O
) O
and O
recycled S-CONPRI
Sm-Co O
powder S-MATE
bonded O
in O
PLA S-MATE
( O
15 O
vol. O
% O
) O
. O


Magnetic B-CHAR
characterization E-CHAR
indicated O
that O
the O
degree-of-alignment O
of O
the O
magnet S-APPL
powders O
increased O
both O
with O
alignment O
field O
strength S-PRO
( O
controlled O
by O
the O
electric O
current O
applied O
to O
the O
magnetizing O
system O
) O
and O
the O
printing O
temperature S-PARA
. O


Both O
coercivity O
and O
remanence O
were O
found O
to O
be S-MATE
strongly O
dependent O
on O
the O
degree-of-alignment O
, O
except O
for O
printing O
performed O
below O
but O
near O
the O
Curie B-PARA
temperature E-PARA
of O
Nd-Fe-B O
( O
310 O
° O
C S-MATE
) O
. O


The O
variations S-CONPRI
in O
coercivity O
were O
consistent O
with O
previous O
observations O
in O
bonded O
magnet S-APPL
materials O
. O


This O
work O
verifies O
that O
integration O
of O
magnetic B-CONPRI
field E-CONPRI
sources O
into O
3-D S-CONPRI
printing O
processes S-CONPRI
will O
result O
in O
magnetic O
alignment O
of O
particles S-CONPRI
while O
ensuring O
that O
other O
advantages O
of O
3-D S-CONPRI
printing O
are O
retained O
. O


Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
is O
the O
most O
popular O
additive B-MANP
manufacturing E-MANP
method O
because O
of O
its O
numerous O
capabilities O
and O
relatively O
low O
cost O
. O


This O
comes O
with O
a O
trade O
off O
as S-MATE
FFF O
printed O
parts O
are O
typically O
weak O
in O
the O
layer S-PARA
deposition B-PARA
direction E-PARA
due O
to O
insufficient O
interlayer O
bonding S-CONPRI
. O


This O
research S-CONPRI
adopts O
the O
method O
of O
cold O
plasma S-CONPRI
treatment O
and O
investigates S-CONPRI
the O
potential O
enhancement O
of O
interlayer O
bonding S-CONPRI
by O
altering O
the O
printed O
surface S-CONPRI
prior O
to O
the O
deposition S-CONPRI
of O
the O
next O
layer S-PARA
. O


Polylactic B-MATE
acid E-MATE
( O
PLA S-MATE
) O
is O
used O
as S-MATE
the O
printing O
material S-MATE
, O
due O
to O
its O
ubiquity O
in O
industry S-APPL
. O


The O
bonding B-PRO
strength E-PRO
is O
measured O
by O
the O
shear O
bond B-CONPRI
strength E-CONPRI
test O
. O


The O
results O
show O
that O
bond B-CONPRI
strength E-CONPRI
improved O
over O
100 O
% O
with O
30 O
s S-MATE
of O
treatment O
and O
over O
50 O
% O
with O
300 O
s S-MATE
of O
treatment O
. O


This O
indicates O
that O
wettability S-CONPRI
may O
not O
be S-MATE
the O
dominant O
mechanism S-CONPRI
for O
enhanced O
bonding S-CONPRI
after O
treatment O
. O


Using O
3D B-MANP
printed E-MANP
, O
patient-specific O
medical S-APPL
phantoms O
has O
become O
increasingly O
popular O
for O
use O
in O
biomedical B-APPL
applications E-APPL
including O
medical B-APPL
device E-APPL
testing O
, O
medical S-APPL
education O
, O
and O
surgical O
planning S-MANP
, O
etc O
. O


To O
overcome O
the O
inherent O
differences O
in O
mechanical B-CONPRI
properties E-CONPRI
between O
biological B-MATE
tissues E-MATE
and O
printable O
polymers S-MATE
, O
metamaterials S-MATE
are O
being O
introduced O
to O
mimic S-MACEQ
the O
mechanical B-CONPRI
response E-CONPRI
of O
the O
biological B-MATE
tissues E-MATE
. O


However O
, O
the O
existing O
trial-and-error S-CONPRI
approaches O
for O
finding O
the O
geometric O
parameters S-CONPRI
of O
the O
metamaterial S-MATE
result O
in O
time-consuming O
trials O
, O
which O
can O
not O
meet O
the O
urgent O
needs O
for O
medical B-APPL
applications E-APPL
. O


We O
addressed O
this O
issue O
by O
proposing O
an O
optimization-based O
statistical O
approach O
with O
an O
easy-to-evaluate O
surrogate O
model S-CONPRI
to O
guide O
the O
design B-CONPRI
process E-CONPRI
and O
reduce O
the O
design S-FEAT
time O
. O


In O
this O
paper O
, O
several O
validation S-CONPRI
tests O
were O
reported O
, O
including O
a O
biomedical B-APPL
application E-APPL
of O
mimicking O
the O
mechanical B-CONPRI
response E-CONPRI
of O
human O
articular O
cartilage O
. O


The O
proposed O
approach O
achieves O
excellent O
accuracy S-CHAR
both O
visually O
and O
quantitatively S-CONPRI
. O


This O
data-driven O
approach O
demonstrates O
efficacy O
and O
flexibility S-PRO
in O
building O
the O
surrogate O
model S-CONPRI
even O
when O
no O
obvious O
physical O
trends S-CONPRI
can O
be S-MATE
extracted O
. O


With O
the O
proposed O
statistical O
approach O
, O
we O
can O
efficiently O
design S-FEAT
the O
metamaterial S-MATE
and O
3D-print O
mechanically O
accurate S-CHAR
phantoms O
for O
sophisticated O
engineering S-APPL
applications O
. O


Cartilage O
regeneration S-CONPRI
is O
challenging O
because O
of O
the O
poor O
intrinsic O
self-repair O
capacity S-CONPRI
of O
avascular O
tissue O
. O


Three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
bioprinting S-APPL
has O
gained O
significant O
attention O
in O
the O
field O
of O
tissue B-CONPRI
engineering E-CONPRI
and O
is O
a O
promising O
technology S-CONPRI
to O
overcome O
current O
difficulties O
in O
cartilage O
regeneration S-CONPRI
. O


Although O
bioink O
is O
an O
essential O
component S-MACEQ
of O
bioprinting S-APPL
technology O
, O
several O
challenges O
remain O
in O
satisfying O
different O
requirements O
for O
ideal O
bioink O
, O
including O
biocompatibility S-PRO
and O
printability S-PARA
based O
on O
specific O
biological O
requirements O
. O


Gelatin O
and O
hyaluronic O
acid O
( O
HA O
) O
have O
been O
shown O
to O
be S-MATE
ideal O
biomimetic S-CONPRI
hydrogel O
sources O
for O
cartilage O
regeneration S-CONPRI
. O


However O
, O
controlling O
their O
structure S-CONPRI
, O
mechanical B-CONPRI
properties E-CONPRI
, O
biocompatibility S-PRO
, O
and O
degradation B-CHAR
rate E-CHAR
for O
cartilage O
repair O
remains O
a O
challenge O
. O


Here O
, O
we O
show O
a O
photocurable O
bioink O
created O
by O
hybridization O
of O
gelatin O
methacryloyl O
( O
GelMA O
) O
and O
glycidyl-methacrylated O
HA O
( O
GMHA O
) O
for O
material B-MANP
extrusion I-MANP
3D I-MANP
bioprinting E-MANP
in O
cartilage O
regeneration S-CONPRI
. O


GelMA O
and O
GMHA O
were O
mixed O
in O
various O
ratios O
, O
and O
the O
mixture O
of O
7 O
% O
GelMA O
and O
5 O
% O
GMHA O
bioink O
( O
G7H5 O
) O
demonstrated O
the O
most O
reliable O
mechanical B-CONPRI
properties E-CONPRI
, O
rheological B-PRO
properties E-PRO
, O
and O
printability S-PARA
. O


This O
bioink O
also O
provided O
an O
excellent O
microenvironment O
for O
chondrogenesis O
of O
tonsil-derived O
mesenchymal B-MATE
stem I-MATE
cells E-MATE
( O
TMSCs O
) O
in O
vitro O
and O
in O
vivo O
. O


In O
summary O
, O
this O
study O
presents O
the O
ideal O
formulation O
of O
GelMA/GMHA O
hybrid O
bioink O
to O
generate O
a O
well-suited O
photocurable O
bioink O
for O
cartilage O
regeneration S-CONPRI
of O
TMSCs O
using O
a O
material B-MANP
extrusion E-MANP
bioprinter S-MACEQ
, O
and O
could O
be S-MATE
applied O
to O
cartilage O
tissue B-CONPRI
engineering E-CONPRI
. O


Fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
is O
one O
of O
the O
most O
popular O
additive B-MANP
manufacturing I-MANP
processes E-MANP
. O


However O
, O
structural O
applications O
of O
FFF S-MANP
are O
still O
limited O
by O
unwanted O
variations S-CONPRI
in O
mechanical B-PRO
strength E-PRO
and O
structural O
dimensions S-FEAT
of O
printed O
parts O
. O


The O
samples S-CONPRI
were O
prepared O
by O
a O
low-cost O
open-source S-CONPRI
FFF B-MACEQ
3D I-MACEQ
printer E-MACEQ
, O
and O
full O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
geometrical O
characterizations O
were O
performed O
on O
them O
using O
X-ray B-CHAR
micro I-CHAR
computed I-CHAR
tomography E-CHAR
( O
micro-CT S-CHAR
) O
. O


The O
results O
showed O
significant O
geometry S-CONPRI
variation O
depending O
on O
different O
printing O
conditions O
, O
including O
print S-MANP
speed O
, O
layer B-PARA
height E-PARA
, O
and O
nozzle S-MACEQ
temperature O
. O


Based O
on O
the O
results O
, O
we O
demonstrated O
the O
effects O
of O
reducing O
layer B-PARA
height E-PARA
and O
increasing O
nozzle S-MACEQ
temperature O
as S-MATE
well O
as S-MATE
compensating O
material B-MANP
extrusion E-MANP
rate O
to O
improve O
geometric O
precision S-CHAR
with O
minimum O
0.8 O
% O
deviation O
. O


Moreover O
, O
uniaxial O
tensile S-PRO
and O
Mode O
III O
tear O
tests O
results O
showed O
that O
there O
are O
linear O
relations O
between O
bonding S-CONPRI
zone O
geometry S-CONPRI
and O
bonding B-PRO
strength E-PRO
. O


In O
addition O
, O
from O
the O
3D B-FEAT
geometry E-FEAT
of O
the O
resulting O
printed O
part O
, O
we O
could O
estimate O
the O
Young O
’ O
s S-MATE
modulus O
in O
the O
extrudate S-MATE
stacking O
direction O
using O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
, O
which O
showed O
good O
agreement O
with O
the O
measured O
value O
. O


Our O
experimental B-CONPRI
data E-CONPRI
may O
also O
serve O
as S-MATE
benchmark O
data S-CONPRI
for O
future O
multi-physics O
simulation S-ENAT
models O
. O


The O
process B-ENAT
simulation E-ENAT
tool O
Additive3D O
has O
been O
developed O
in O
Abaqus© O
2017 O
to O
model S-CONPRI
the O
Extrusion S-MANP
Deposition S-CONPRI
Additive B-MANP
Manufacturing E-MANP
( O
EDAM O
) O
process S-CONPRI
for O
fiber-reinforced O
thermoplastic B-MATE
composites E-MATE
. O


This O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
method O
encompasses O
material S-MATE
deposition B-MANP
processes E-MANP
where O
geometries S-CONPRI
are O
constructed O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
and O
the O
resulting O
layer S-PARA
properties O
are O
highly O
anisotropic.The O
goal O
is O
to O
predict O
final O
deformed B-PRO
shapes E-PRO
and O
residual B-PRO
stresses E-PRO
of O
printed O
geometries S-CONPRI
due O
to O
the O
printing B-MANP
process E-MANP
and O
the O
material S-MATE
anisotropy S-PRO
. O


The O
resulting O
design S-FEAT
tool O
allows O
to O
assess O
the O
outcomes O
of O
the O
printing B-MANP
process E-MANP
based O
on O
the O
part O
geometry S-CONPRI
, O
the O
printing O
material S-MATE
and O
the O
position O
control O
parameters.Material O
properties S-CONPRI
were O
characterized O
, O
and O
validation S-CONPRI
experiments O
, O
without O
additional O
calibration S-CONPRI
, O
show O
an O
excellent O
agreement O
between O
modeled O
and O
measured O
part O
deformation S-CONPRI
states O
with O
relative O
deviations O
below O
7 O
% O
. O


Due O
to O
the O
physics-based O
nature O
of O
the O
developed O
simulation S-ENAT
tools O
, O
the O
simulations S-ENAT
can O
be S-MATE
extended O
to O
account O
for O
different O
part O
scales O
, O
printing O
materials S-CONPRI
and O
printing O
histories O
. O


Binder S-MATE
jet O
printing O
is O
one O
additive B-MANP
manufacturing E-MANP
technique O
utilized O
in O
today O
’ O
s S-MATE
industry S-APPL
that O
uses O
an O
adhesive S-MATE
to O
bind S-MANP
powders O
together O
selectively O
in O
a O
bed S-MACEQ
. O


Post-printing O
processes S-CONPRI
are O
necessary O
for O
binder S-MATE
jet O
printed O
parts O
to O
increase O
key O
properties S-CONPRI
in O
materials S-CONPRI
such O
as S-MATE
density O
, O
but O
the O
full O
effects O
of O
this O
post-processing S-CONPRI
are O
not O
yet O
well O
understood O
. O


This O
study O
aims O
to O
enhance O
the O
understanding O
of O
how O
the O
process S-CONPRI
of O
sintering S-MANP
can O
affect O
the O
density S-PRO
evolution O
of O
a O
Ti-6Al-4 B-MATE
V E-MATE
binder S-MATE
jet O
printed O
part O
. O


Results O
show O
that O
the O
density S-PRO
is O
lower O
at O
the O
edges O
of O
the O
part O
and O
higher O
in O
regions O
of O
significant O
topological O
curvature O
, O
likely O
due O
to O
variations S-CONPRI
originating O
from O
the O
printing B-MANP
process E-MANP
that O
are O
propagated O
. O


These O
printing B-MANP
process E-MANP
effects O
can O
be S-MATE
due O
to O
binder- O
or O
powder-related O
occurrences O
, O
which O
are O
described O
in O
relation O
to O
the O
obtained O
results O
. O


Binder S-MATE
effects O
include O
high-velocity O
impact S-CONPRI
, O
particle S-CONPRI
disruption O
, O
and O
excessive O
spreading O
. O


Powder S-MATE
effects O
include O
printhead O
and O
recoater O
speed O
, O
satellite O
particles S-CONPRI
, O
and O
changing O
pressure S-CONPRI
throughout O
the O
powder B-MACEQ
bed E-MACEQ
. O


These O
factors O
affected O
the O
coordination O
number O
of O
particles S-CONPRI
in O
the O
green B-PRO
part E-PRO
, O
and O
caused O
sintering S-MANP
to O
progress O
more O
slowly O
in O
certain O
areas S-PARA
. O


In O
large O
area S-PARA
pellet O
extrusion S-MANP
additive B-MANP
manufacturing E-MANP
, O
the O
temperature S-PARA
of O
the O
substrate S-MATE
just O
before O
the O
deposition S-CONPRI
of O
a O
new O
subsequent O
layer S-PARA
affects O
the O
overall O
structure S-CONPRI
of O
the O
part O
. O


Warping S-CONPRI
and O
cracking S-CONPRI
occur O
if O
the O
substrate S-MATE
temperature O
is O
below O
a O
material-specific O
threshold O
, O
and O
deformation S-CONPRI
and O
deposition S-CONPRI
adhesion S-PRO
failure O
occur O
if O
the O
substrate S-MATE
temperature O
is O
above O
a O
different O
threshold O
. O


Currently O
, O
Big O
Area S-PARA
Additive B-MANP
Manufacturing E-MANP
( O
BAAM O
) O
machine S-MACEQ
users O
mitigate O
this O
problem O
by O
trial B-CONPRI
and I-CONPRI
error E-CONPRI
, O
which O
is O
costly O
and O
may O
result O
in O
decreased O
mechanical B-CONPRI
properties E-CONPRI
, O
monetary O
losses O
and O
time O
inefficiencies O
. O


Through O
thermal O
imaging S-APPL
, O
the O
range S-PARA
of O
temperatures S-PARA
present O
during O
the O
printing O
of O
a O
20 O
wt O
. O


% O
carbon B-MATE
fiber E-MATE
reinforced O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS-20CF O
) O
single-bead O
vertical S-CONPRI
wall O
via O
the O
BAAM O
machine S-MACEQ
was O
measured O
. O


Compression B-CHAR
tests E-CHAR
were O
performed O
to O
understand O
the O
material S-MATE
behavior O
at O
those O
temperatures S-PARA
. O


Optical S-CHAR
imaging S-APPL
was O
performed O
to O
identify O
a O
relationship O
between O
porosity S-PRO
in O
the O
printed O
bead S-CHAR
and O
plateau O
regions O
in O
the O
compression S-PRO
curves O
at O
temperatures S-PARA
of O
170 O
°C O
and O
below O
. O


From O
the O
thermal O
imaging S-APPL
and O
compressive O
testing S-CHAR
, O
it O
was O
concluded O
that O
if O
the O
substrate S-MATE
temperature O
is O
above O
200 O
°C O
, O
it O
will O
not O
be S-MATE
able O
to O
withstand O
the O
load O
exerted O
by O
the O
deposition S-CONPRI
of O
a O
new O
layer S-PARA
without O
experiencing O
deformation S-CONPRI
. O


This O
behavior O
was O
attributed O
to O
the O
experimentally O
obtained O
low O
compressive B-PRO
strength E-PRO
of O
ABS-20CF O
observed O
at O
temperatures S-PARA
above O
200 O
°C O
. O


Taking O
advantage O
of O
an O
extended O
design S-FEAT
and O
manufacturing S-MANP
space O
for O
composites S-MATE
, O
the O
technology S-CONPRI
of O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
of O
continuous O
fibre-reinforced O
thermoplastics S-MATE
shows O
great O
potential O
for O
the O
production S-MANP
of O
the O
next O
generation O
of O
lightweight S-CONPRI
structural O
parts O
. O


This O
process S-CONPRI
still O
has O
room O
for O
development O
. O


Moreover O
, O
knowledge O
of O
the O
mechanical B-CONPRI
behaviour E-CONPRI
of O
the O
resulting O
3D B-MANP
printed E-MANP
composites O
is O
still O
limited O
. O


In O
this O
work O
, O
the O
intra- O
and O
inter-laminar O
behaviours O
of O
carbon S-MATE
fibre/polyamide O
printed O
laminates S-CONPRI
were O
extensively O
characterised O
to O
determine O
ply O
elastic S-PRO
and O
strength B-PRO
properties E-PRO
, O
as S-MATE
well O
as S-MATE
interface O
strength S-PRO
and O
fracture S-CONPRI
characteristics O
. O


Moreover O
, O
the O
effects O
of O
eventual O
production S-MANP
defects S-CONPRI
on O
these O
properties S-CONPRI
were O
analysed O
, O
putting O
in O
evidence O
some O
of O
the O
present O
shortcomings O
of O
the O
FFF S-MANP
process O
. O


Such O
defects S-CONPRI
include O
non-homogeneous O
fibre S-MATE
distribution S-CONPRI
, O
large O
amounts O
of O
intra- O
and O
interlaminar O
voids S-CONPRI
, O
and O
weak O
interlayer O
bonding S-CONPRI
, O
which O
are O
likely O
to O
be S-MATE
due O
to O
insufficient O
thermo-mechanical B-CONPRI
consolidation E-CONPRI
of O
the O
material S-MATE
during O
the O
FFF S-MANP
process O
, O
and O
have O
significant O
influence O
on O
the O
matrix-dominated O
mechanical B-CONPRI
properties E-CONPRI
. O


As S-MATE
a O
result O
, O
the O
transverse O
and O
interlaminar O
properties S-CONPRI
were O
found O
to O
be S-MATE
lower O
than O
those O
obtained O
through O
hot O
compression S-PRO
moulding O
of O
carbon S-MATE
fibre/polyamide O
laminates S-CONPRI
. O


Besides O
highlighting O
possible O
process S-CONPRI
improvements O
, O
the O
mechanical S-APPL
characterisation O
carried O
out O
in O
this O
work O
promises O
a O
significant O
contribution O
to O
the O
abilities O
of O
designing O
and O
simulating O
general O
3D B-MANP
printed E-MANP
composite O
parts O
. O


The O
most O
common O
method O
for O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
of O
polymers S-MATE
is O
melt B-MANP
extrusion E-MANP
, O
which O
normally O
requires O
several O
pre-processing O
steps O
to O
compound O
and O
extrude S-MANP
filament O
feedstock S-MATE
, O
resulting O
in O
an O
overall O
long O
melt S-CONPRI
residency O
time O
. O


Consequently O
a O
typical O
melt S-CONPRI
extrusion-based O
AM B-MANP
process E-MANP
is O
time/cost O
consuming O
, O
and O
limited O
in O
the O
availability B-CONPRI
of I-CONPRI
materials E-CONPRI
that O
can O
be S-MATE
processed O
. O


Polyvinyl O
alcohol O
( O
PVOH O
) O
is O
one O
of O
the O
heat-sensitive O
polymers S-MATE
demonstrating O
a O
thermal B-MANP
decomposition E-MANP
temperature S-PARA
overlapping O
its O
processing O
window O
. O


This O
study O
proposed O
to O
use O
a O
pellet-fed O
material B-MANP
extrusion E-MANP
technique O
to O
directly O
process S-CONPRI
PVOH O
granules S-CONPRI
without O
the O
necessity O
of O
using O
any O
pre-processing O
steps O
. O


The O
approach O
essentially O
combined O
compounding O
, O
extrusion S-MANP
and O
AM S-MANP
, O
allowing O
multi-material B-MANP
printing E-MANP
with O
minimum O
exposure S-CONPRI
to O
heat S-CONPRI
during O
the O
process S-CONPRI
. O


The O
processing O
parameters S-CONPRI
were O
determined O
via O
thermal O
and O
rheological S-PRO
characterisation O
of O
PVOH O
. O


Effects O
of O
processing O
temperature S-PARA
and O
time O
on O
the O
thermal B-MANP
decomposition E-MANP
of O
PVOH O
were O
demonstrated O
, O
which O
further O
affected O
the O
tensile B-PRO
properties E-PRO
and O
solubility S-PRO
. O


The O
pellet-fed O
material B-MANP
extrusion E-MANP
technology O
demonstrated O
good O
3D S-CONPRI
printability O
, O
multi-material B-MANP
printing E-MANP
capability O
, O
and O
great O
versatility O
in O
processing O
polymer B-MATE
melts E-MATE
. O


In O
this O
paper O
, O
we O
investigate O
the O
print S-MANP
orientation S-CONPRI
effects O
on O
the O
macrostructure O
, O
the O
mechanical S-APPL
and O
thermal B-CONPRI
properties E-CONPRI
, O
and O
the O
strain S-PRO
field O
behavior O
of O
ULTEM® O
9085 O
using O
a O
Stratasys S-APPL
Fused B-MANP
deposition I-MANP
modeling E-MANP
( O
FDM S-MANP
) O
400 O
Printer S-MACEQ
. O


The O
tensile B-PRO
strength E-PRO
, O
failure S-CONPRI
strain O
, O
Poisson O
’ O
s S-MATE
ratio O
, O
coefficient B-PRO
of I-PRO
thermal I-PRO
expansion E-PRO
and O
modulus O
were O
all O
shown O
to O
vary O
significantly O
depending O
on O
the O
build B-PARA
orientation E-PARA
of O
identical O
dogbones O
. O


FDM S-MANP
parts O
ranged O
in O
strength S-PRO
from O
46 O
to O
85 O
% O
of O
strengths S-PRO
attainable O
from O
comparable O
injection-molded O
parts O
. O


The O
coefficient O
of O
variation S-CONPRI
( O
CV O
) O
increased O
from O
2 O
to O
13 O
% O
as S-MATE
the O
primary O
layer S-PARA
orientation O
deviated O
from O
the O
primary O
load O
direction O
. O


CAT O
scan O
and O
SEM S-CHAR
were O
employed O
to O
relate O
the O
corresponding O
macrostructure O
to O
the O
mechanical B-CONPRI
response E-CONPRI
of O
the O
material S-MATE
along O
the O
parts O
’ O
3-primary O
directions O
, O
using O
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
( O
DIC S-CONPRI
) O
. O


The O
fracture S-CONPRI
surfaces O
of O
these O
parts O
further O
suggest O
that O
3D S-CONPRI
FDM O
materials S-CONPRI
behave O
more O
like O
laminated O
composite B-CONPRI
structures E-CONPRI
than O
isotropic S-PRO
cast S-MANP
resins O
and O
therefore O
design S-FEAT
allowables O
should O
reflect O
actual O
part O
build S-PARA
configurations O
. O


One O
of O
the O
main O
benefits O
of O
material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
, O
also O
known O
as S-MATE
fused O
filament S-MATE
fabrication S-MANP
( O
FFF S-MANP
) O
or O
3D B-MANP
printing E-MANP
, O
is O
the O
flexibility S-PRO
in O
terms O
of O
printing O
materials S-CONPRI
. O


Locally O
reinforced S-CONPRI
components S-MACEQ
can O
be S-MATE
easily O
produced O
by O
selectively O
combining O
reinforced S-CONPRI
with O
unfilled O
tough O
thermoplastics S-MATE
. O


However O
, O
such O
multi-material S-CONPRI
composites S-MATE
usually O
lack O
sufficient O
weld B-PRO
strength E-PRO
in O
order O
to O
be S-MATE
able O
to O
withstand O
operation O
loads O
. O


The O
present O
study O
attempts O
to O
close O
this O
gap O
by O
characterising O
the O
cohesion O
between O
the O
strands O
of O
two O
materials S-CONPRI
with O
different O
stiffness S-PRO
, O
namely O
neat O
PLA S-MATE
and O
short O
carbon B-MATE
fibre E-MATE
reinforced O
PLA S-MATE
( O
CF-PLA O
) O
, O
produced O
by O
FFF S-MANP
using O
advanced O
fracture S-CONPRI
mechanical O
techniques O
. O


The O
full O
set S-APPL
of O
engineering S-APPL
constants O
of O
both O
materials S-CONPRI
were O
obtained O
under O
the O
assumption O
of O
transverse O
isotropy O
from O
tensile B-CHAR
tests E-CHAR
in O
combination O
with O
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
. O


Both O
tests O
were O
in O
good O
correlation O
with O
each O
other O
and O
revealed O
that O
the O
interlayer O
PLA/CF-PLA O
bonding S-CONPRI
was O
at O
least O
as S-MATE
tough O
as S-MATE
the O
interlayer O
CF-PLA/CF-PLA O
bonding S-CONPRI
. O


In O
this O
work O
, O
systematic O
studies O
were O
carried O
out O
on O
SLS S-MANP
( O
selective B-MANP
laser I-MANP
sintering E-MANP
) O
printed O
samples S-CONPRI
, O
with O
two O
different O
geometries S-CONPRI
, O
standard S-CONPRI
test O
samples S-CONPRI
dumb-bells O
( O
dog O
bones O
) O
and O
tubes O
( O
Ø O
30 O
mm S-MANP
and O
150 O
mm S-MANP
long O
) O
, O
consisting O
of O
two O
different O
materials S-CONPRI
, O
viz O
. O


PA12 S-MATE
( O
polyamide S-MATE
) O
with O
and O
without O
the O
addition O
of O
carbon B-MATE
fibres E-MATE
( O
CFs O
) O
. O


These O
samples S-CONPRI
were O
tested O
according O
to O
their O
respective O
ISO B-MANS
standards E-MANS
. O


The O
standard S-CONPRI
test O
samples S-CONPRI
exhibited O
relatively O
small O
differences O
with O
regards O
to O
printing O
directions O
when O
PA12 S-MATE
was O
used O
alone O
. O


Their O
tensile B-PRO
strengths E-PRO
( O
σm O
) O
were O
approx O
. O


75 O
% O
–80 O
% O
of O
the O
injection-moulded O
sample S-CONPRI
. O


The O
addition O
of O
carbon B-MATE
fibres E-MATE
significantly O
enhanced O
the O
tensile B-PRO
strengths E-PRO
, O
namely O
50 O
% O
greater O
for O
the O
vertically O
printed O
test O
sample S-CONPRI
and O
more O
than O
100 O
% O
greater O
for O
the O
horizontally O
printed O
samples S-CONPRI
, O
compared O
to O
the O
respective O
objects O
consisting O
of O
PA12 S-MATE
alone O
. O


The O
strong O
difference O
in O
printing O
directions O
can O
be S-MATE
attributed O
to O
the O
orientation S-CONPRI
of O
the O
carbon B-MATE
fibres E-MATE
. O


Mechanical B-CHAR
tests E-CHAR
on O
the O
SLS S-MANP
printed O
tubes O
confirmed O
the O
trends S-CONPRI
that O
were O
found O
in O
the O
standard S-CONPRI
test O
samples S-CONPRI
. O


Porosity S-PRO
and O
pore S-PRO
structure O
inside O
the O
SLS S-MANP
printed O
tubes O
were O
studied O
by O
combining O
optical B-CHAR
microscopy E-CHAR
and O
X-ray B-CHAR
microtomography E-CHAR
with O
image B-CONPRI
analysis E-CONPRI
. O


It O
was O
found O
that O
porosity S-PRO
was O
a O
general O
phenomenon O
inside O
the O
SLS S-MANP
printed O
samples S-CONPRI
. O


Nevertheless O
, O
there O
were O
significant O
differences O
in O
porosity S-PRO
, O
which O
probably O
depended O
on O
the O
properties S-CONPRI
of O
the O
materials S-CONPRI
used O
, O
both O
with O
and O
without O
carbon B-MATE
fibres E-MATE
, O
thus O
causing O
significant O
differences O
in O
light O
absorption S-CONPRI
and O
heat B-PRO
conductivity E-PRO
. O


The O
printed O
samples S-CONPRI
made O
of O
PA12 S-MATE
alone O
possessed O
quite O
a O
high O
level O
of O
porosity S-PRO
( O
4.7 O
% O
) O
, O
of O
which O
the O
size O
of O
the O
biggest O
pore S-PRO
was O
hundreds O
of O
microns O
. O


The O
twenty O
biggest O
pores S-PRO
with O
an O
average S-CONPRI
size O
of O
75*104 O
μ O
m3 O
accounted O
for O
43 O
% O
of O
the O
total O
porosity S-PRO
. O


However O
, O
the O
porosity S-PRO
of O
the O
printed O
samples S-CONPRI
made O
from O
PA12 S-MATE
+ O
CF O
was O
only O
0.68 O
% O
, O
with O
the O
biggest O
pore S-PRO
being O
only O
tens O
of O
microns O
. O


The O
corresponding O
average S-CONPRI
pore O
size O
of O
the O
20 O
biggest O
pores S-PRO
was O
72*103 O
μ O
m3 O
, O
which O
was O
one O
order O
of O
magnitude S-PARA
smaller O
than O
the O
printed O
samples S-CONPRI
made O
from O
PA12 S-MATE
alone O
. O


Pores S-PRO
inside O
the O
SLS S-MANP
printed O
samples S-CONPRI
were O
probably O
responsible O
for O
a O
spread S-CONPRI
in O
the O
mechanical B-CONPRI
properties E-CONPRI
measured O
, O
e.g O
. O


tensile B-PRO
strengths E-PRO
, O
tensile S-PRO
( O
Young O
’ O
s S-MATE
) O
modulus O
, O
strain S-PRO
at O
break O
, O
etc O
. O


The O
ratios O
of O
their O
standard B-CHAR
deviations E-CHAR
to O
their O
corresponding O
mean O
values O
in O
the O
standard S-CONPRI
test O
samples S-CONPRI
could O
probably O
be S-MATE
used O
as S-MATE
an O
indicator O
of O
porosity S-PRO
, O
i.e O
. O


An O
integrated O
wearable O
3-D S-CONPRI
printable O
microfluidic O
pump O
was O
developed O
, O
which O
uses O
a O
novel O
actuation O
process S-CONPRI
. O


Fused B-CONPRI
deposition E-CONPRI
manufacture O
3-D S-CONPRI
printing O
was O
used O
as S-MATE
a O
means O
to O
accurately S-CHAR
produce O
this O
device O
. O


This O
resulted O
in O
the O
fabrication S-MANP
of O
high O
precision S-CHAR
integrated O
parts O
made O
from O
poly-lactic-acid O
bioplastic O
. O


By O
integrating O
an O
electro-magnetically O
actuated O
closed O
diffuser O
nozzle S-MACEQ
pump O
configuration S-CONPRI
a O
micro-fabricated O
microfluidic O
pump O
has O
been O
produced O
. O


Biofluids O
have O
been O
driven O
through O
the O
device O
by O
actuating O
a O
composite S-MATE
polydimethylsiloxane O
diaphragm O
actuated O
polymeric O
microstructure S-CONPRI
diaphragm O
membrane O
using O
electromagnetic B-CONPRI
force E-CONPRI
. O


This O
composite S-MATE
diaphragm O
was O
made O
by O
suspending O
10 O
μm O
iron S-MATE
particles O
in O
the O
polydimethylsiloxane S-MATE
at O
concentrations O
of O
30 O
% O
, O
40 O
% O
and O
50 O
% O
. O


It O
is O
shown O
that O
this O
device O
acts O
as S-MATE
an O
effective O
electromagnetic B-CONPRI
force E-CONPRI
actuated O
a O
pump O
. O


The O
integration O
of O
3D B-MANP
printed E-MANP
devices O
to O
form O
a O
micropump O
is O
proven O
through O
practical O
testing S-CHAR
which O
demonstrate O
a O
controllable O
flow B-PARA
rate E-PARA
was O
generated O
. O


The O
Bladder O
Assisted O
Composite B-MANP
Manufacturing E-MANP
( O
BACM O
) O
technique O
allows O
fabrication S-MANP
of O
complex O
hollow O
composite S-MATE
geometries O
. O


However O
, O
traditional O
bladder O
manufacturing S-MANP
methods O
require O
multiple O
steps O
and O
a O
master O
geometry S-CONPRI
which O
increases O
the O
cost O
and O
the O
manufacturing S-MANP
time O
. O


Hence O
, O
additively B-MANP
manufactured E-MANP
bladders O
are O
presented O
as S-MATE
an O
alternative O
solution S-CONPRI
to O
bladders O
manufactured S-CONPRI
through O
traditional O
methods O
. O


The O
use O
of O
printed O
bladders O
is O
demonstrated O
by O
consolidating O
and O
curing S-MANP
a O
composite S-MATE
part O
made O
out O
of O
an O
aerospace S-APPL
grade O
composite S-MATE
prepreg O
material S-MATE
, O
IM7/8552 O
. O


Bladders O
are O
additively B-MANP
manufactured E-MANP
using O
the O
Fused B-MANP
Deposition I-MANP
Modeling E-MANP
( O
FDM S-MANP
) O
technique O
with O
Thermoplastic B-MATE
Polyurethane E-MATE
( O
TPU O
) O
. O


Based O
on O
the O
results O
of O
a O
thermomechanical S-CONPRI
investigation O
of O
the O
TPU O
, O
a O
two-step O
curing S-MANP
cycle O
for O
manufacturing S-MANP
a O
composite S-MATE
part O
with O
IM7/8552 O
prepreg S-MATE
was O
designed S-FEAT
. O


The O
part B-CONPRI
consolidation E-CONPRI
achieved O
with O
this O
method O
was O
characterized O
by O
measuring O
void S-CONPRI
content O
and O
comparing O
it O
to O
the O
void S-CONPRI
content O
in O
a O
sample S-CONPRI
cured S-MANP
in O
a O
standard S-CONPRI
autoclave S-MACEQ
process O
. O


The O
low O
void S-CONPRI
content O
achieved O
with O
the O
BACM O
method O
demonstrated O
the O
potential O
of O
this O
technology S-CONPRI
for O
providing O
bladders O
for O
short O
production B-PARA
runs E-PARA
or O
prototyping S-CONPRI
. O


As S-MATE
more O
manufacturing B-MANP
processes E-MANP
and O
research S-CONPRI
institutions O
adopt O
customized O
manufacturing S-MANP
as S-MATE
a O
key O
element S-MATE
in O
their O
design S-FEAT
strategies O
and O
finished O
products O
, O
the O
resulting O
mechanical B-CONPRI
properties E-CONPRI
of O
parts O
produced O
through O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
must O
be S-MATE
characterized O
and O
understood O
. O


In O
polymer B-MANP
extrusion E-MANP
( O
PE S-MANP
) O
, O
the O
most O
recently O
extruded S-MANP
polymer O
filament S-MATE
must O
bond O
to O
the O
previously O
extruded S-MANP
filament O
via O
polymer B-CONPRI
diffusion E-CONPRI
to O
form O
a O
“ O
weld S-FEAT
” O
. O


The O
strength S-PRO
of O
the O
weld B-PARA
limits E-PARA
the O
performance S-CONPRI
of O
the O
manufactured S-CONPRI
part O
and O
is O
controlled O
through O
processing O
conditions O
. O


Understanding O
the O
role O
of O
processing O
conditions O
, O
specifically O
extruder S-MACEQ
velocity O
and O
extruder S-MACEQ
temperature O
, O
on O
the O
overall O
strength S-PRO
of O
the O
weld S-FEAT
will O
allow O
optimization S-CONPRI
of O
PE-AM S-MATE
parts O
. O


Here O
, O
the O
fracture S-CONPRI
toughness O
of O
a O
single O
weld S-FEAT
is O
determined O
through O
a O
facile O
“ O
trouser O
tear O
” O
Mode B-CONPRI
III I-CONPRI
fracture E-CONPRI
experiment S-CONPRI
. O


The O
actual O
weld B-PARA
thickness E-PARA
is O
observed O
directly O
by O
optical B-CHAR
microscopy E-CHAR
( O
OM S-CHAR
) O
characterization O
of O
cross B-CONPRI
sections E-CONPRI
of O
PE-AM S-MATE
samples O
. O


Representative O
data S-CONPRI
of O
weld B-PRO
strength E-PRO
as S-MATE
a O
function O
of O
printing O
parameters S-CONPRI
on O
a O
commercial O
3D B-MACEQ
printer E-MACEQ
demonstrates O
the O
robustness S-PRO
of O
the O
method O
. O


Digital B-MANP
light I-MANP
processing E-MANP
technology O
( O
DLP S-MANP
) O
is O
an O
effective O
additive B-MANP
manufacturing E-MANP
method O
to O
fabricate S-MANP
ceramic S-MATE
components O
with O
high O
precision S-CHAR
and O
complicated O
structure S-CONPRI
. O


Here O
, O
a O
novel O
strategy O
to O
prepare O
chopped O
carbon B-MATE
fibers E-MATE
( O
Cf O
) O
/SiC O
ceramic B-FEAT
composites E-FEAT
through O
stereolithography S-MANP
Cf O
combined O
with O
liquid O
silicon S-MATE
infiltration S-CONPRI
is O
presented O
. O


The O
3D-architectured O
bodies O
possessed O
high O
printing O
stableness O
and O
accuracy S-CHAR
with O
the O
forming S-MANP
deviation O
of O
less O
than O
5 O
% O
. O


Moreover O
, O
the O
tightly O
bonded O
adjacent O
layers O
can O
contribute O
to O
the O
synergistic O
effect O
from O
curing S-MANP
adhesion S-PRO
of O
photosensitive B-MATE
resin E-MATE
and O
crisscrossed O
pinning O
of O
chopped O
carbon B-MATE
fibers E-MATE
. O


As-prepared O
components S-MACEQ
after O
liquid O
silicon S-MATE
infiltration S-CONPRI
were O
dense O
and O
exhibited O
maximum O
flexural B-PRO
strength E-PRO
of O
262.6 O
MPa S-CONPRI
. O


This O
strategy O
demonstrates O
a O
promising O
prospect O
and O
tantalizing O
possibility O
to O
fabricate S-MANP
SiC O
ceramic B-FEAT
composites E-FEAT
with O
complex B-PRO
shapes E-PRO
and O
structures O
. O


Successful O
3D B-MANP
printing E-MANP
of O
metatsable O
high O
entropy O
alloy S-MATE
Fe40Mn20Co20Cr15Si5 O
( O
CS-HEA O
) O
is O
acheived O
. O


CS-HEA O
demonstrated O
Excellent O
printability S-PARA
due O
to O
very O
low O
defect S-CONPRI
denisty O
. O


High O
entropy O
alloys S-MATE
( O
HEAs O
) O
have O
attracted O
scientific O
interest O
due O
to O
their O
good O
mechanical B-CONPRI
properties E-CONPRI
and O
failure S-CONPRI
resistance O
, O
whereas O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
has O
emerged O
as S-MATE
a O
powerful O
yet O
flexible O
processing O
route O
for O
advanced O
materials S-CONPRI
. O


However O
, O
limitations O
inherent O
in O
both O
these O
fields O
include O
HEAs O
display O
inferior O
mechanical B-CONPRI
properties E-CONPRI
in O
as S-MATE
cast O
condition O
; O
and O
AM S-MANP
demands O
expansion O
of O
printable O
alloys S-MATE
. O


dominated O
microstructure S-CONPRI
after O
laser B-MANP
powder I-MANP
bed I-MANP
fusion I-MANP
additive I-MANP
manufacturing E-MANP
has O
been O
evaluated O
. O


As-printed O
CS-HEA O
showed O
higher O
strength S-PRO
due O
to O
high O
work O
hardenability S-PRO
, O
whereas O
substantial O
uniform O
ductility S-PRO
is O
associated O
with O
a O
combination O
of O
transformation O
and O
twinning S-CONPRI
induced O
plasticity S-PRO
during O
deformation S-CONPRI
. O


Additionally O
, O
very O
low O
volume S-CONPRI
percent O
of O
voids S-CONPRI
( O
∼0.1 O
% O
) O
along O
with O
high O
strength-ductility O
shows O
excellent O
printability S-PARA
of O
the O
CS-HEA O
using O
laser-based B-MANP
additive I-MANP
manufacturing E-MANP
. O


Izod O
impact B-CHAR
test E-CHAR
specimens O
were O
fabricated S-CONPRI
via O
a O
desktop B-FEAT
grade E-FEAT
material O
extrusion S-MANP
3D B-MACEQ
printer E-MACEQ
process O
using O
ABS S-MATE
in O
four O
build B-PARA
orientations E-PARA
. O


The O
3D B-MANP
printed E-MANP
impact O
test O
specimens O
were O
examined O
in O
order O
to O
compare O
the O
effect O
of O
stress S-PRO
concentrator O
fabrication S-MANP
on O
impact B-CHAR
test E-CHAR
data S-CONPRI
where O
two O
methods O
were O
used O
to O
fabricate S-MANP
the O
stress S-PRO
concentrating O
notch S-FEAT
: O
( O
1 O
) O
printing O
the O
stress S-PRO
concentrator O
; O
and O
( O
2 O
) O
machining S-MANP
the O
stress S-PRO
concentrator O
where O
the O
dimensions S-FEAT
of O
the O
notch S-FEAT
matched O
those O
specified O
in O
the O
ASTM O
standard S-CONPRI
D256-10 O
. O


In O
both O
test O
cases O
, O
sensitivity S-PARA
to O
build B-PARA
orientation E-PARA
was O
also O
observed O
. O


The O
sample S-CONPRI
sets O
with O
printed O
stress S-PRO
concentrators O
were O
found O
to O
be S-MATE
statistically O
similar O
to O
their O
counterparts O
with O
milled S-MANP
stress O
concentrators O
. O


The O
experiment S-CONPRI
was O
repeated O
again O
on O
a O
commercial B-FEAT
grade E-FEAT
material O
extrusion S-MANP
3D B-MACEQ
printer E-MACEQ
using O
ABS S-MATE
, O
PC S-MATE
, O
PC-ABS O
, O
and O
Ultem O
9085 O
and O
differences O
in O
impact B-CHAR
test E-CHAR
results O
were O
observed O
most O
notably O
when O
Ultem O
9085 O
was O
tested O
. O


Scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
was O
utilized O
to O
perform O
fractograpy O
on O
impact B-CHAR
test E-CHAR
specimens O
to O
explore O
the O
effect O
of O
stress S-PRO
concentrator O
fabrication S-MANP
on O
the O
fracture S-CONPRI
surface O
morphology S-CONPRI
of O
the O
failed O
specimens O
. O


The O
work O
here O
demonstrates O
the O
need O
for O
materials S-CONPRI
testing O
standards S-CONPRI
that O
are O
specific O
to O
additive B-MANP
manufacturing E-MANP
technologies O
; O
as S-MATE
well O
as S-MATE
concluding O
that O
all-printed O
impact B-CHAR
test E-CHAR
specimens O
may O
offer O
the O
best O
representation O
of O
the O
impact S-CONPRI
characteristics O
of O
3D B-MANP
printed E-MANP
structures O
. O


In O
recent O
years O
3D B-MANP
printing E-MANP
has O
gained O
popularity O
amongst O
industry S-APPL
professionals O
and O
hobbyists O
alike O
, O
with O
many O
new O
types O
of O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
apparatus O
types O
becoming O
available O
on O
the O
market O
. O


A O
massively O
overlooked O
component S-MACEQ
of O
FFF S-MANP
is O
the O
requirement O
for O
a O
simple S-MANP
method O
to O
calculate O
the O
geometries S-CONPRI
of O
polymer S-MATE
depositions O
extruded S-MANP
during O
the O
FFF S-MANP
process O
. O


Manufacturers O
have O
so O
far O
achieved O
adequate O
methods O
to O
calculate O
tool-paths O
through O
so O
called O
slicer S-ENAT
software O
packages O
which O
calculate O
the O
required O
velocities O
of O
extrusion S-MANP
from O
prior O
knowledge O
and O
data S-CONPRI
. O


Presented O
here O
is O
a O
method O
for O
obtaining O
a O
series O
of O
equations O
for O
predicting O
height O
, O
width O
and O
cross-sectional O
area S-PARA
values O
for O
given O
processing O
parameters S-CONPRI
within O
the O
FFF S-MANP
process O
for O
initial O
laydown O
on O
to O
a O
glass S-MATE
surface O
. O


This O
work O
investigates S-CONPRI
the O
evolution S-CONPRI
of O
the O
tensile S-PRO
and O
structural O
properties S-CONPRI
of O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
, O
formed O
polymers S-MATE
under O
gamma O
irradiation S-MANP
. O


Commercial O
off-the-shelf O
print S-MANP
filaments S-MATE
of O
Poly O
( O
lactic O
acid O
) O
( O
PLA S-MATE
) O
, O
Thermoplastic B-MATE
polyurethane E-MATE
( O
TPU O
) O
, O
Chlorinated O
polyethylene B-MATE
elastomer E-MATE
( O
CPE O
) O
, O
Nylon S-MATE
, O
Acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
and O
Polycarbonate S-MATE
( O
PC S-MATE
) O
were O
exposed O
to O
gamma-ray O
doses O
of O
up O
to O
5.3 O
MGy O
. O


The O
suitability O
of O
FFF-formed O
components S-MACEQ
made O
from O
these O
materials S-CONPRI
for O
use O
in O
radiation S-MANP
environments O
is O
evaluated O
by O
considering O
their O
structural O
properties S-CONPRI
. O


We O
identify O
clear O
trends S-CONPRI
in O
the O
structural O
properties S-CONPRI
of O
all O
the O
materials S-CONPRI
tested O
and O
correlate O
them O
with O
changes O
in O
the O
chemical O
structure S-CONPRI
. O


We O
find O
that O
Nylon S-MATE
shows O
the O
best O
performance S-CONPRI
under O
these O
conditions O
, O
with O
no O
change O
in O
ultimate B-PRO
tensile I-PRO
strength E-PRO
and O
an O
increase O
in O
stiffness S-PRO
. O


However O
, O
some O
of O
our O
findings O
suggest O
that O
the O
effect O
of O
additives S-MATE
to O
this O
type O
of O
filament S-MATE
may O
result O
in O
potentially O
undesirable O
adhesive S-MATE
properties O
. O


The O
organic O
polymer B-MATE
PLA E-MATE
was O
notably O
more O
radiation-sensitive O
than O
the O
other O
materials S-CONPRI
tested O
, O
showing O
50 O
% O
decrease O
in O
Young O
’ O
s S-MATE
Modulus O
and O
ultimate B-PRO
tensile I-PRO
strength E-PRO
at O
order O
of O
magnitude S-PARA
lower O
radiation S-MANP
dose O
. O


A O
mechanism S-CONPRI
is O
proposed O
whereby O
FFF-processed O
components S-MACEQ
would O
have O
substantially O
different O
radiation S-MANP
tolerances O
than O
bulk O
material S-MATE
. O


In O
this O
article O
, O
we O
report O
the O
synthesis O
of O
a O
series O
of O
multi-branched O
benzylidene O
( O
BI S-MATE
) O
ketone-based O
photo-initiators O
for O
two-photon B-ENAT
polymerisation E-ENAT
based O
3D S-CONPRI
printing/additive O
manufacturing S-MANP
. O


The O
successful O
fabrication S-MANP
of O
complex O
3D B-CONPRI
structures E-CONPRI
at O
high O
writing O
speeds O
( O
up O
to O
100 O
mm/s O
) O
indicated O
that O
the O
four-branched O
initiator O
4-BI O
could O
potentially O
increase O
the O
fabrication S-MANP
efficiency O
and O
hence O
become O
a O
promising O
initiator O
for O
two-photon B-ENAT
polymerisation E-ENAT
. O


A O
path B-CONPRI
planning I-CONPRI
methodology E-CONPRI
is O
proposed O
for O
FFF S-MANP
based O
on O
stress S-PRO
orientations S-CONPRI
. O


Specimens O
created O
with O
the O
stress-based O
path O
exhibit O
better O
mechanical B-CONPRI
properties E-CONPRI
. O


Anisotropy S-PRO
of O
tool-paths O
leads O
to O
stress S-PRO
redistribution O
of O
stress S-PRO
components S-MACEQ
. O


Different O
tool-paths O
are O
broken O
with O
variable O
fracture S-CONPRI
processes O
and O
surfaces S-CONPRI
. O


Tool-path S-PARA
planning S-MANP
has O
a O
considerable O
impact S-CONPRI
on O
the O
quality S-CONPRI
of O
components S-MACEQ
printed O
by O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
. O


This O
research S-CONPRI
proposes O
a O
path O
generation O
strategy O
based O
on O
the O
orientations S-CONPRI
of O
the O
maximum O
principal B-PRO
stresses E-PRO
. O


According O
to O
stress S-PRO
calculations O
from O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
( O
FEA O
) O
of O
the O
components S-MACEQ
, O
tool-paths O
, O
which O
are O
programmed O
as S-MATE
parallel O
to O
the O
maximum O
principal B-PRO
stress E-PRO
directions O
, O
are O
constructed O
with O
the O
depth-first O
search O
( O
DFS O
) O
method O
and O
a O
connection O
criterion O
. O


The O
Dijkstra O
algorithm S-CONPRI
is O
engaged O
to O
reduce O
the O
nozzle S-MACEQ
jump O
distance O
and O
shorten O
the O
production S-MANP
time O
. O


Stretching O
tests O
of O
different O
specimens O
printed O
with O
the O
developed O
path O
generation O
algorithms S-CONPRI
demonstrate O
that O
the O
model S-CONPRI
with O
the O
stress-based O
path O
has O
better O
mechanical S-APPL
performance O
. O


The O
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
( O
DIC S-CONPRI
) O
method O
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
SEM S-CHAR
) O
are O
employed O
to O
observe O
the O
fracture S-CONPRI
processes O
and O
fracture S-CONPRI
surfaces O
, O
respectively O
. O


Corresponding O
results O
of O
DIC S-CONPRI
and O
SEM S-CHAR
reveal O
that O
different O
path O
filling O
forms O
exhibit O
variable O
failure S-CONPRI
patterns O
because O
of O
filament S-MATE
anisotropy S-PRO
. O


The O
filling O
fraction S-CONPRI
is O
calculated O
and O
indicates O
that O
the O
deposition B-CHAR
quality E-CHAR
of O
the O
advanced O
path O
is O
not O
compromised O
. O


This O
work O
provides O
a O
synthesis O
methodology S-CONPRI
for O
improving O
the O
mechanical S-APPL
performance O
of O
3D B-MANP
printing E-MANP
products O
. O


In O
the O
context O
of O
the O
large O
format O
additive B-MANP
manufacturing E-MANP
in O
ambient O
conditions O
, O
extrusion S-MANP
materials O
need O
to O
be S-MATE
thermally O
stable O
, O
thus O
short O
fiber-reinforced O
composites S-MATE
have O
been O
developed O
to O
tailor O
the O
thermal O
behavior O
. O


However O
, O
lack O
of O
public O
knowledge O
in O
material B-CONPRI
properties E-CONPRI
and O
dataset O
lead S-MATE
to O
improper O
processing O
; O
yielding O
degradation S-CONPRI
of O
materials S-CONPRI
during O
trial O
& O
error S-CONPRI
operations O
which O
not O
only O
increase O
cost O
but O
also O
reduce O
the O
quality S-CONPRI
of O
printed O
parts O
. O


This O
research S-CONPRI
investigated O
neat O
and O
composite B-MATE
ABS E-MATE
filled O
with O
short B-MATE
carbon I-MATE
fiber E-MATE
( O
ABS/CF O
) O
and O
glass B-MATE
fiber E-MATE
( O
ABS/GF O
) O
using O
thermophysical O
and O
thermomechanical S-CONPRI
characterization O
techniques O
to O
generate O
dataset O
and O
knowledge O
that O
can O
be S-MATE
used O
to O
process B-CONPRI
materials E-CONPRI
without O
degrading O
the O
properties S-CONPRI
as S-MATE
well O
as S-MATE
achieving O
the O
quality S-CONPRI
parts O
in O
future O
. O


Thermogravimetric B-CHAR
analysis E-CHAR
was O
performed O
to O
study O
the O
degradation S-CONPRI
behavior O
. O


Differential O
scanning S-CONPRI
calorimetry O
( O
DSC S-CHAR
) O
analyzed O
the O
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
( O
Tg S-CHAR
) O
and O
specific B-PRO
heat E-PRO
to O
understand O
the O
heat B-CONPRI
dissipation E-CONPRI
of O
neat O
and O
composite B-MATE
materials E-MATE
. O


While O
the O
Tg S-CHAR
measured O
in O
DSC S-CHAR
was O
not O
significantly O
different O
, O
the O
dynamic B-CONPRI
mechanical I-CONPRI
analysis E-CONPRI
showed O
that O
Tg S-CHAR
in O
ABS/CF O
was O
increased O
due O
to O
the O
impeded O
polymer S-MATE
chain O
mobility O
. O


The O
thermomechanical S-CONPRI
analysis O
described O
the O
deformation S-CONPRI
behavior O
before O
and O
after O
the O
transition S-CONPRI
temperature S-PARA
which O
suggested O
that O
ABS/CF O
has O
the O
highest O
thermal B-PRO
stability E-PRO
to O
retain O
the O
shape O
at O
elevated O
temperature S-PARA
followed O
by O
ABS/GF O
and O
neat O
ABS S-MATE
. O


The O
findings O
of O
this O
article O
can O
be S-MATE
used O
during O
the O
modeling S-ENAT
of O
pellet-fed O
large O
format O
AM S-MANP
and O
developing O
empirical S-CONPRI
process O
parameters S-CONPRI
. O


The O
use O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
rapidly O
expanding O
in O
many O
industries S-APPL
mostly O
because O
of O
the O
flexibility S-PRO
to O
manufacture S-CONPRI
complex B-CONPRI
geometries E-CONPRI
. O


Recently O
, O
a O
family O
of O
technologies S-CONPRI
that O
produce O
fiber S-MATE
reinforced O
components S-MACEQ
has O
been O
introduced O
, O
widening O
the O
options O
available O
to O
designers O
. O


AM S-MANP
fiber O
reinforced S-CONPRI
composites S-MATE
are O
characterized O
by O
the O
fact O
that O
process S-CONPRI
related O
parameters S-CONPRI
such O
as S-MATE
the O
amount O
of O
reinforcement S-PARA
fiber S-MATE
, O
or O
printing O
architecture S-APPL
, O
significantly O
affect O
the O
tensile B-PRO
properties E-PRO
of O
final O
parts O
. O


To O
find O
optimal B-FEAT
structures E-FEAT
using O
new O
AM B-MANP
technologies E-MANP
, O
guidelines O
for O
the O
design S-FEAT
of O
3D B-MANP
printed E-MANP
composite O
parts O
are O
needed O
. O


This O
paper O
presents O
an O
evaluation O
of O
the O
effects O
that O
different O
geometric O
parameters S-CONPRI
have O
on O
the O
tensile B-PRO
properties E-PRO
of O
3D B-MANP
printed E-MANP
composites O
manufactured S-CONPRI
by O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
out O
of O
continuous O
and O
chopped O
carbon B-MATE
fiber E-MATE
reinforcement O
. O


Parameters S-CONPRI
such O
as S-MATE
infill O
density S-PRO
and O
infill S-PARA
patterns O
of O
chopped O
composite B-MATE
material E-MATE
, O
as S-MATE
well O
as S-MATE
fiber O
volume B-PARA
fraction E-PARA
and O
printing O
architecture S-APPL
of O
continuous B-MATE
fiber I-MATE
reinforcement E-MATE
( O
CFR O
) O
composites S-MATE
are O
varied O
. O


The O
effect O
of O
the O
location O
of O
the O
initial O
deposit O
point O
of O
reinforcement S-PARA
fibers S-MATE
on O
the O
tensile B-PRO
properties E-PRO
of O
the O
test O
specimens O
is O
studied O
. O


Also O
, O
the O
effect O
that O
the O
fiber S-MATE
deposition S-CONPRI
pattern O
has O
on O
tensile S-PRO
performance S-CONPRI
is O
quantified O
. O


Considering O
the O
geometric O
parameters S-CONPRI
that O
were O
studied O
, O
a O
variation S-CONPRI
of O
the O
Rule B-CONPRI
of I-CONPRI
Mixtures E-CONPRI
( O
ROM O
) O
that O
provides O
a O
way O
to O
estimate O
the O
elastic B-PRO
modulus E-PRO
of O
a O
3D B-MANP
printed E-MANP
composite O
is O
proposed O
. O


Findings O
may O
be S-MATE
used O
by O
designers O
to O
define O
the O
best O
construction S-APPL
parameters O
for O
3D B-MANP
printed E-MANP
composite O
parts O
. O


The O
application O
space O
for O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
printing O
, O
such O
as S-MATE
fused O
filament S-MATE
fabrication S-MANP
( O
FFF S-MANP
) O
, O
has O
grown O
significantly O
through O
the O
use O
of O
high-performance O
composite B-MATE
materials E-MATE
. O


While O
the O
mechanical S-APPL
, O
thermal O
, O
optical S-CHAR
, O
and O
electrical B-CONPRI
properties E-CONPRI
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
polymer B-MATE
composites E-MATE
are O
being O
actively O
studied O
, O
the O
magnetic O
properties S-CONPRI
of O
AM B-MACEQ
parts E-MACEQ
have O
seen O
much O
less O
attention O
. O


Prior O
research S-CONPRI
has O
shown O
that O
the O
structural O
print S-MANP
settings O
for O
FFF S-MANP
influence O
the O
magnetic O
properties S-CONPRI
of O
the O
printed O
part O
( O
Bollig O
et O
al. O
, O
2017 O
) O
. O


However O
, O
the O
structural B-CONPRI
hierarchy E-CONPRI
present O
in O
the O
FFF S-MANP
process O
complicates O
a O
simple S-MANP
analysis O
of O
how O
these O
magnetic O
differences O
arise O
. O


Here O
, O
a O
magnetic O
filament S-MATE
consisting O
of O
polylactic B-MATE
acid E-MATE
( O
PLA S-MATE
) O
polymer S-MATE
and O
40 O
wt. O
% O
iron S-MATE
was O
used O
to O
print S-MANP
a O
variety O
of O
samples S-CONPRI
to O
investigate O
how O
the O
macroscopic S-CONPRI
sample O
shape O
and O
the O
mesoscopic O
infill S-PARA
orientation O
and O
infill B-PARA
percentage E-PARA
affects O
the O
magnetic O
properties S-CONPRI
. O


The O
array O
of O
samples S-CONPRI
systematically O
covered O
different O
aspect B-FEAT
ratios E-FEAT
( O
length O
: O
width O
) O
, O
edge O
contours S-FEAT
( O
rectangular O
vs. O
ellipsoidal O
) O
, O
two O
infill S-PARA
orientations O
( O
long O
axis O
alignment O
vs. O
short O
axis O
alignment O
) O
, O
and O
varying O
infill B-PARA
percentages E-PARA
. O


The O
key O
results O
show O
that O
the O
highest O
magnetic B-CHAR
susceptibility E-CHAR
was O
seen O
for O
magnetic B-CONPRI
fields E-CONPRI
applied O
parallel O
to O
the O
infill S-PARA
orientation O
. O


The O
macroscopic B-CONPRI
geometry E-CONPRI
increased O
the O
magnetic B-CHAR
susceptibility E-CHAR
parallel O
to O
the O
long O
axis O
of O
the O
sample S-CONPRI
. O


Lastly O
, O
certain O
factors O
, O
such O
as S-MATE
edge O
contours S-FEAT
and O
infill B-PARA
percentage E-PARA
, O
only O
affected O
the O
magnetic B-CHAR
susceptibility E-CHAR
when O
the O
magnetic B-CONPRI
field E-CONPRI
was O
applied O
transverse O
to O
the O
infill S-PARA
orientation O
, O
but O
had O
no O
effect O
when O
field O
was O
applied O
along O
the O
infill S-PARA
direction O
. O


Elucidating O
how O
the O
part O
shape O
, O
infill S-PARA
orientation O
, O
and O
infill B-PARA
percentage E-PARA
affects O
the O
magnetic O
properties S-CONPRI
of O
AM B-MACEQ
parts E-MACEQ
will O
help O
the O
community O
better O
understand O
how O
an O
FFF S-MANP
process O
can O
be S-MATE
utilized O
to O
make O
optimal O
magnetic O
components S-MACEQ
, O
such O
as S-MATE
transformer O
cores S-MACEQ
, O
electric O
motors O
, O
and O
electromagnetic O
interference O
shielding O
. O


The O
interface S-CONPRI
between O
layers O
has O
bulk-material O
strength S-PRO
. O


Filament-scale O
grooves O
reduce O
load-bearing S-FEAT
capacity S-CONPRI
at O
the O
interface S-CONPRI
. O


Toughness S-PRO
and O
strain-at-fracture O
are O
higher O
in O
the O
direction O
of O
extruded S-MANP
filaments O
. O


Aspect B-FEAT
ratio E-FEAT
has O
an O
important O
effect O
on O
load-bearing S-FEAT
capacity S-CONPRI
. O


Strain-localisation O
is O
a O
predominant O
cause O
of O
fracture S-CONPRI
, O
based O
on O
simulation S-ENAT
. O


This O
study O
demonstrates O
that O
the O
interface S-CONPRI
between O
layers O
in O
3D-printed S-MANP
polylactide O
has O
strength S-PRO
of O
the O
bulk O
filament S-MATE
. O


Specially O
designed S-FEAT
3D-printed S-MANP
tensile O
specimens O
were O
developed O
to O
test O
mechanical B-CONPRI
properties E-CONPRI
in O
the O
direction O
of O
the O
extruded S-MANP
filament O
( O
F S-MANP
specimens O
) O
, O
representing O
bulk O
material B-CONPRI
properties E-CONPRI
, O
and O
normal O
to O
the O
interface S-CONPRI
between O
3D-printed S-MANP
layers O
( O
Z O
specimens O
) O
. O


A O
wide O
range S-PARA
of O
cross-sectional O
aspect B-FEAT
ratios E-FEAT
for O
extruded-filament O
geometries S-CONPRI
were O
considered O
by O
printing O
with O
five O
different O
LHs O
and O
five O
different O
EFWs O
. O


Both O
F S-MANP
and O
Z O
specimens O
demonstrated O
bulk O
material B-PRO
strength E-PRO
. O


In O
contrast O
, O
strain-at-fracture O
, O
specific O
load-bearing S-FEAT
capacity S-CONPRI
, O
and O
toughness S-PRO
were O
found O
to O
be S-MATE
lower O
in O
Z O
specimens O
due O
to O
the O
presence O
of O
filament-scale O
geometric O
features O
( O
grooves O
between O
extruded S-MANP
filaments O
) O
. O


The O
different O
trends S-CONPRI
for O
strength S-PRO
as S-MATE
compared O
to O
other O
mechanical B-CONPRI
properties E-CONPRI
were O
evaluated O
with O
finite-element O
analysis O
. O


It O
was O
found O
that O
anisotropy S-PRO
was O
caused O
by O
the O
extruded-filament O
geometry S-CONPRI
and O
localised O
strain S-PRO
( O
as S-MATE
opposed O
to O
assumed O
incomplete O
bonding S-CONPRI
of O
the O
polymer S-MATE
across O
the O
interlayer O
interface S-CONPRI
) O
. O


Additionally O
, O
effects O
of O
variation S-CONPRI
in O
print S-MANP
speed O
and O
layer S-PARA
time O
were O
studied O
and O
found O
to O
have O
no O
influence O
on O
interlayer O
bond B-CONPRI
strength E-CONPRI
. O


The O
relevance O
of O
the O
results O
to O
other O
materials S-CONPRI
, O
toolpath S-PARA
design S-FEAT
, O
industrial S-APPL
applications O
, O
and O
future O
research S-CONPRI
is O
discussed O
. O


Multi-photon O
polymerization S-MANP
, O
like O
the O
so-called O
direct B-ENAT
laser I-ENAT
writing E-ENAT
( O
DLW O
) O
technique O
allows O
for O
flexible O
additive B-MANP
manufacturing E-MANP
of O
three-dimensional S-CONPRI
ultra-precise O
structures O
on O
the O
micro- S-CHAR
and O
nanoscale O
. O


A O
possible O
application O
for O
DLW O
is O
the O
manufacturing S-MANP
of O
measurement B-CONPRI
standards E-CONPRI
for O
calibration S-CONPRI
procedures O
of O
optical B-CHAR
measurement E-CHAR
instruments O
. O


This O
requires O
flexible O
and O
high O
precision S-CHAR
manufacturing S-MANP
of O
individualized O
geometries S-CONPRI
with O
high O
quality S-CONPRI
surfaces O
. O


However O
, O
many O
of O
the O
process B-CONPRI
parameters E-CONPRI
in O
DLW O
have O
to O
be S-MATE
selected O
based O
on O
experience O
and O
previous O
knowledge.In O
this O
article O
, O
the O
influence O
of O
DLW O
process B-CONPRI
parameters E-CONPRI
on O
the O
micro-geometry O
and O
surface B-PRO
roughness E-PRO
produced O
are O
systematically O
studied O
, O
and O
optimized O
in O
terms O
of O
printing B-PARA
speed E-PARA
and O
manufacturing S-MANP
accuracy S-CHAR
. O


Resulting O
microstructures S-MATE
are O
being O
evaluated O
with O
different O
measurement S-CHAR
techniques O
, O
i.e. O
, O
a O
stylus S-MACEQ
instrument O
, O
SEM S-CHAR
and O
AFM O
. O


Based O
on O
optimized O
process B-CONPRI
parameters E-CONPRI
, O
a O
new O
measurement B-CONPRI
standard E-CONPRI
for O
the O
novel O
interferometric O
measurement S-CHAR
instrument O
Ellipso-Height-Topometer O
is O
manufactured S-CONPRI
and O
examined O
as S-MATE
a O
case B-CONPRI
study E-CONPRI
. O


As S-MATE
a O
result O
, O
it O
can O
be S-MATE
shown O
, O
that O
DLW O
is O
able O
to O
manufacture S-CONPRI
ultra-precise O
micro O
geometries S-CONPRI
in O
a O
very O
flexible O
and O
very O
fast O
way O
and O
satisfies O
the O
tolerances S-PARA
for O
manufacturing S-MANP
of O
the O
designed S-FEAT
measurement O
standard S-CONPRI
. O


The O
spreading O
of O
molten O
polymer S-MATE
between O
the O
moving O
printing B-MACEQ
head E-MACEQ
and O
the O
substrate S-MATE
in O
extrusion S-MANP
additive B-MANP
manufacturing E-MANP
is O
studied O
. O


Finite B-CONPRI
element E-CONPRI
computation S-CONPRI
and O
an O
analytical O
model S-CONPRI
have O
been O
used O
. O


The O
hypotheses O
of O
the O
analytical O
model S-CONPRI
are O
qualitatively O
justified O
by O
the O
results O
of O
the O
numerical O
computation S-CONPRI
. O


The O
analytical O
calculation O
is O
a O
powerful O
tool S-MACEQ
to O
rapidly O
evaluate O
the O
relationships O
between O
processing O
parameters S-CONPRI
( O
extrusion B-PARA
rate E-PARA
, O
printing B-MACEQ
head E-MACEQ
velocity O
, O
gap O
between O
the O
printing B-MACEQ
head E-MACEQ
and O
the O
substrate S-MATE
) O
and O
some O
characteristics O
of O
the O
deposition S-CONPRI
( O
dimensions S-FEAT
of O
the O
deposited O
filament S-MATE
, O
pressure S-CONPRI
at O
the O
printing B-MACEQ
head E-MACEQ
nozzle S-MACEQ
, O
separating O
force S-CONPRI
between O
substrate S-MATE
and O
printing B-MACEQ
head E-MACEQ
) O
. O


An O
isothermal S-CONPRI
hypothesis O
is O
discussed O
. O


The O
viscous O
non-Newtonian O
behavior O
is O
accounted O
for O
through O
an O
approximate O
shear B-CONPRI
thinning E-CONPRI
power S-PARA
law O
model S-CONPRI
. O


A O
printing O
processing O
window O
is O
defined O
following O
several O
requirements O
: O
a O
continuous O
deposit O
, O
without O
spreading O
in O
front O
of O
the O
printing B-MACEQ
head E-MACEQ
, O
maximum O
and O
minimum O
spreading O
pressures S-CONPRI
, O
an O
upper-limit O
for O
the O
separating O
force S-CONPRI
between O
head O
and O
substrate S-MATE
. O


A O
heated O
build S-PARA
environment O
in O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
used O
to O
promote O
layer S-PARA
bonding S-CONPRI
in O
printed O
parts O
and O
reduce O
the O
difference O
in O
temperature S-PARA
between O
the O
extrusion S-MANP
and O
environment O
decreasing O
the O
shrinkage S-CONPRI
, O
residual B-PRO
stresses E-PRO
, O
and O
part O
deformation S-CONPRI
. O


A O
build S-PARA
environment O
capable O
of O
maintaining O
a O
high-temperature O
( O
> O
200 O
°C O
) O
is O
often O
required O
to O
enable O
high-quality O
FFF S-MANP
printing O
of O
high-glass-transition O
, O
high-performance O
polymers S-MATE
such O
as S-MATE
nylon O
, O
PPSF O
, O
and O
ULTEM O
. O


Industrial-scale O
AM S-MANP
systems O
are O
capable O
of O
printing O
such O
polymers S-MATE
, O
as S-MATE
they O
offer O
a O
controlled O
, O
high-temperature O
printing O
environment O
; O
however O
, O
the O
machine S-MACEQ
cost O
often O
exceeds O
> O
$ O
100,000 O
. O


Many O
of O
these O
printers S-MACEQ
use O
bed S-MACEQ
heating O
rather O
than O
controlled O
environment O
heating S-MANP
, O
which O
can O
lead S-MATE
to O
inhomogeneous O
heat B-CONPRI
transfer E-CONPRI
and O
inconsistent O
properties S-CONPRI
. O


The O
key O
barrier O
to O
offering O
high-temperature O
environments O
for O
desktop-scale O
FFF S-MANP
systems O
in O
a O
cost-effective O
manner O
is O
that O
the O
electrical S-APPL
components S-MACEQ
must O
be S-MATE
compatible O
with O
, O
protected O
from O
, O
or O
removed O
from O
environments O
exceeding O
100 O
°C.To O
enable O
desktop-scale O
FFF S-MANP
printing O
of O
high-performance O
polymers S-MATE
at O
a O
low O
cost O
and O
high O
quality S-CONPRI
, O
the O
authors O
present O
a O
novel O
inverted O
FFF S-MANP
system O
design S-FEAT
that O
provides O
a O
build S-PARA
environment O
of O
up O
to O
400 O
°C O
. O


The O
inverted O
configuration S-CONPRI
effectively O
isolates O
the O
system O
electronics S-CONPRI
from O
the O
heated O
build S-PARA
environment O
, O
which O
allows O
for O
the O
use O
of O
inexpensive O
components S-MACEQ
. O


In O
this O
paper O
, O
the O
authors O
verify O
the O
inverted O
design S-FEAT
concept O
analytically O
via O
a O
computational B-CHAR
fluid I-CHAR
dynamics E-CHAR
model O
. O


The O
concept O
is O
then O
experimentally B-CONPRI
validated E-CONPRI
via O
a O
comparison O
of O
the O
strength S-PRO
of O
PPSF O
components S-MACEQ
printed O
on O
the O
inverted O
desktop-scale O
FFF S-MANP
system O
. O


Additively B-MANP
manufactured E-MANP
parts O
made O
with O
polymer B-MANP
extrusion E-MANP
techniques O
can O
be S-MATE
50–75 O
% O
weaker O
in O
the O
z-direction S-FEAT
( O
across O
layers O
) O
than O
in O
the O
x- O
and O
y-directions O
. O


This O
is O
particularly O
a O
challenge O
when O
printing O
large-scale O
parts O
, O
such O
as S-MATE
with O
the O
Big O
Area S-PARA
Additive B-MANP
Manufacturing E-MANP
( O
BAAM O
) O
system O
, O
because O
layer S-PARA
times O
can O
exceed O
several O
minutes O
. O


The O
current O
work O
presents O
a O
method O
for O
controlling O
the O
temperature S-PARA
of O
the O
substrate B-MATE
material E-MATE
on O
the O
BAAM O
just O
prior O
to O
deposition S-CONPRI
using O
infrared S-CONPRI
heating S-MANP
lamps O
. O


Long O
layer S-PARA
times O
were O
also O
simulated O
by O
actively O
cooling S-MANP
the O
material S-MATE
following O
deposition S-CONPRI
of O
each O
layer S-PARA
. O


The O
effect O
of O
substrate S-MATE
temperature O
on O
the O
z-direction S-FEAT
mechanical B-CONPRI
properties E-CONPRI
of O
20 O
% O
carbon B-MATE
fiber E-MATE
reinforced O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
was O
measured O
for O
an O
initial O
temperature S-PARA
ranging O
from O
50 O
°C O
to O
150 O
°C O
and O
a O
preheated O
temperature S-PARA
ranging O
from O
150 O
°C O
to O
220 O
°C O
. O


Infrared S-CONPRI
preheating O
proved O
to O
be S-MATE
very O
effective O
when O
applied O
to O
substrates O
that O
had O
cooled O
considerably O
, O
almost O
doubling O
the O
tensile B-PRO
strength E-PRO
and O
increasing O
the O
fracture S-CONPRI
toughness O
by O
a O
factor O
of O
7x O
. O


Poly-l-lactic O
acid O
( O
PLLA O
) O
is O
a O
bioresorbable O
polymer S-MATE
used O
in O
a O
variety O
of O
biomedical B-APPL
applications E-APPL
. O


Many O
3D B-MACEQ
printers E-MACEQ
employ O
the O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
approach O
with O
the O
ubiquitous O
low-cost O
poly-lactic O
acid O
( O
PLA S-MATE
) O
fiber S-MATE
. O


However O
, O
use O
of O
the O
FFF S-MANP
approach O
to O
fabricate S-MANP
scaffolds O
with O
medical S-APPL
grade O
PLLA O
polymer S-MATE
remains O
largely O
unexplored O
. O


In O
this O
study O
, O
high O
molecular O
weight S-PARA
PL-32 O
pellets S-CONPRI
were O
extruded S-MANP
into O
∼1.7 O
mm S-MANP
diameter S-CONPRI
PLLA O
fiber S-MATE
. O


Melt S-CONPRI
rheometric O
data S-CONPRI
of O
the O
PLLA O
polymer S-MATE
was O
analyzed O
and O
demonstrated O
pseudo-plastic O
behavior O
with O
a O
flow O
index O
of O
n S-MATE
= O
0.465 O
( O
< O
1 O
) O
. O


Differential O
scanning S-CONPRI
calorimetry O
( O
DSC S-CHAR
) O
was O
conducted O
using O
samples S-CONPRI
from O
the O
extruded S-MANP
fiber O
to O
obtain O
thermal B-CONPRI
properties E-CONPRI
. O


DSC S-CHAR
of O
the O
3D B-MANP
printed E-MANP
struts O
was O
also O
analyzed O
to O
assess O
changes O
in O
thermal B-CONPRI
properties E-CONPRI
due O
to O
FFF S-MANP
. O


The O
DSC S-CHAR
and O
rheometric O
analysis O
results O
were O
subsequently O
used O
to O
define O
appropriate O
FFF S-MANP
process O
parameters S-CONPRI
. O


Constant O
porosity S-PRO
scaffolds O
were O
FFF S-MANP
3D B-MANP
printed E-MANP
with O
4 O
distinct O
laydown O
patterns O
; O
0/90° O
rectilinear O
( O
control O
) O
, O
45/135° O
rectilinear O
, O
Archimedean O
chords O
, O
and O
honeycomb S-CONPRI
using O
the O
in-house O
developed O
custom O
multi-modality O
3D S-CONPRI
bioprinter O
( O
CMMB O
) O
. O


The O
effect O
of O
laydown O
pattern S-CONPRI
on O
scaffold S-FEAT
bulk O
erosion O
( O
weight S-PARA
loss O
) O
was O
studied O
by O
immersion O
in O
phosphate-buffered O
saline O
( O
PBS S-MATE
) O
over O
a O
6-month O
period O
and O
measured O
monthly O
. O


Cross-sectional O
scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
( O
SEM S-CHAR
) O
images S-CONPRI
of O
the O
6-month O
degraded O
scaffolds S-FEAT
showed O
noticeable O
structural O
deterioration O
. O


The O
study O
demonstrates O
successful O
processing O
of O
PLLA O
fiber S-MATE
from O
PL-32 O
pellets S-CONPRI
and O
FFF-based O
3D B-MANP
printing E-MANP
of O
bioresorbable O
scaffolds S-FEAT
with O
pre-defined O
laydown O
patterns O
using O
medical S-APPL
grade O
PLLA O
polymer S-MATE
which O
could O
prove O
beneficial O
in O
biomedical B-APPL
applications E-APPL
. O


Filament S-MATE
printed O
GO S-MATE
structures O
are O
mechanically O
stable O
by O
rapid O
freezing O
in O
liquid O
nitrogen S-MATE
and O
lyiophilization O
. O


Thermally O
reduced O
GO S-MATE
( O
rGO S-MATE
) O
structures O
are O
rapidly O
infiltrated O
with O
a O
preceramic O
polymer S-MATE
under O
vacuum O
conditions O
. O


The O
composite B-CONPRI
structure E-CONPRI
perfectly O
replicates O
the O
printed O
GO S-MATE
structure O
. O


The O
hybrid B-MATE
composite E-MATE
structure O
( O
rGO/SiCN O
) O
shows O
high O
strength S-PRO
and O
electrical B-PRO
conductivity E-PRO
. O


Steady O
graphene B-MATE
oxide E-MATE
( O
GO S-MATE
) O
scaffolds S-FEAT
created O
by O
direct O
ink S-MATE
writing O
are O
used O
to O
develop O
a O
silicon S-MATE
carbonitride O
( O
SiCN O
) O
-graphene O
oxide S-MATE
hybrid O
material S-MATE
through O
a O
preceramic O
polymer S-MATE
route O
. O


For O
achieving O
mechanically O
stable O
GO S-MATE
scaffolds O
, O
the O
drying S-MANP
method O
is O
critical O
as S-MATE
the O
ink S-MATE
contains O
about O
5 O
wt. O
% O
of O
GO S-MATE
, O
10 O
wt. O
% O
of O
polyelectrolytes O
and O
85 O
wt. O
% O
of O
water O
. O


The O
liquid O
preceramic O
polymer S-MATE
( O
polysilazane O
type O
) O
quickly O
infiltrates O
the O
3D S-CONPRI
scaffolds O
, O
under O
vacuum O
conditions O
, O
entirely O
covering O
the O
GO S-MATE
network O
creating O
a O
replica O
of O
the O
original O
scaffold S-FEAT
. O


The O
hybrid O
cellular B-FEAT
structure E-FEAT
-once O
thermally B-MANP
treated E-MANP
for O
GO S-MATE
reduction O
and O
ceramic S-MATE
conversion- O
consists O
of O
a O
network O
of O
reduced O
GO S-MATE
( O
∼10 O
wt. O
% O
) O
embedded O
in O
an O
amorphous O
SiCN O
matrix O
following O
the O
designed S-FEAT
architecture S-APPL
. O


The O
3D S-CONPRI
hybrid O
structures O
show O
notable O
electrical B-PRO
conductivity E-PRO
( O
890 O
S S-MATE
m−1 O
at O
room O
temperature S-PARA
) O
, O
thermal B-PRO
stability E-PRO
and O
considerable O
strength S-PRO
, O
about O
20 O
times O
higher O
than O
the O
single O
GO S-MATE
scaffold O
. O


Single-operation O
, O
hybrid-AM O
fabrication S-MANP
of O
form-factor O
free O
supercapacitors O
. O


As-printed O
gravimetric O
EDLC O
electrode S-MACEQ
capacitance O
of O
116.4 O
±0.6 O
F S-MANP
g−1 O
at O
10 O
mV O
s−1 O
. O


Detailed O
insight O
into O
FFF S-MANP
and O
DIW S-MANP
processing O
parameters S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
may O
offer O
a O
flexible O
, O
cost-effective O
approach O
to O
address O
conventional B-MANP
manufacturing E-MANP
limitations O
, O
such O
as S-MATE
time-consuming O
, O
high O
work-in-progress O
, O
multi-step O
assembly S-MANP
. O


In O
principle O
AM S-MANP
can O
also O
allow O
more O
novel O
geometric O
or O
even O
bespoke O
designs S-FEAT
of O
structural O
and O
functional O
products O
. O


However O
, O
in O
terms O
of O
energy B-APPL
storage E-APPL
devices O
such O
as S-MATE
batteries O
and O
supercapacitors O
, O
the O
benefits O
of O
AM S-MANP
have O
not O
yet O
been O
explored O
to O
any O
significant O
extent O
. O


In O
this O
paper O
, O
a O
hybrid-AM O
system O
, O
combining O
low-cost O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
and O
direct O
ink S-MATE
writing O
( O
DIW S-MANP
) O
techniques O
, O
has O
been O
designed S-FEAT
to O
fabricate S-MANP
supercapacitors O
( O
electro-chemical O
double O
layer S-PARA
capacitors S-APPL
, O
EDLCs O
) O
in O
a O
single O
, O
automated O
operation O
. O


The O
inherent O
flexibility S-PRO
of O
the O
AM B-MANP
process E-MANP
provided O
an O
opportunity O
to O
address O
restrictions O
in O
geometric O
form O
factor O
associated O
with O
conventional O
planar O
supercapacitor S-APPL
manufacturing B-MANP
approaches E-MANP
. O


Functioning O
, O
ring-shaped O
EDLC O
devices O
were O
manufactured S-CONPRI
in O
a O
single O
, O
multi-material S-CONPRI
operation O
comprising O
symmetric O
activated O
carbon S-MATE
electrodes O
in O
a O
1Μ O
potassium O
hydroxide S-MATE
( O
KOH O
) O
electrolyte S-APPL
hydrogel O
. O


The O
work O
aims O
to O
accelerate O
progress O
towards O
monolithic S-PRO
integration O
of O
energy B-APPL
storage E-APPL
devices O
in O
product O
manufacture S-CONPRI
, O
offering O
an O
alternative O
fabrication S-MANP
process O
for O
applications O
with O
irregular O
volume/shape O
and O
mass-customization O
requirements O
. O


A O
novel O
method O
to O
quantify O
the O
pore B-PARA
size E-PARA
distribution S-CONPRI
and O
porosity S-PRO
was O
proposed O
. O


New O
method O
exhibits O
high O
precision S-CHAR
, O
information O
and O
repeatability S-CONPRI
but O
low O
cost O
. O


Electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
is O
a O
representative O
powder-bed O
fusion S-CONPRI
additive B-MANP
manufacturing E-MANP
technology O
, O
which O
is O
suitable O
for O
producing O
near-net-shape S-MANP
metallic S-MATE
components S-MACEQ
with O
complex B-CONPRI
geometries E-CONPRI
and O
near-full O
densities O
. O


However O
, O
various O
types O
of O
pores S-PRO
are O
usually O
present O
in O
the O
additively B-MANP
manufactured E-MANP
components O
. O


These O
pores S-PRO
may O
affect O
mechanical B-CONPRI
properties E-CONPRI
, O
particularly O
the O
fatigue S-PRO
properties O
. O


Therefore O
, O
inspection S-CHAR
of O
size O
, O
quantity O
and O
distribution S-CONPRI
of O
pores S-PRO
is O
critical O
for O
the O
process B-CONPRI
control E-CONPRI
and O
assessment O
of O
additively B-MANP
manufactured E-MANP
components O
. O


Here O
, O
we O
propose O
a O
method O
to O
quantify O
the O
pore B-PARA
size E-PARA
distribution S-CONPRI
and O
porosity S-PRO
of O
additively B-MANP
manufactured E-MANP
components O
by O
utilizing O
scanning B-CHAR
optical I-CHAR
microscopy E-CHAR
. O


The O
advantages O
and O
limitations O
of O
the O
developed O
method O
are O
discussed O
based O
on O
the O
comparison O
study O
between O
Archimedes B-CHAR
method E-CHAR
, O
conventional O
optical B-CHAR
microscopy E-CHAR
and O
x-ray B-CHAR
computed I-CHAR
tomography E-CHAR
. O


This O
provides O
a O
new O
metrology S-CONPRI
for O
measurement S-CHAR
of O
not O
only O
pores S-PRO
but O
also O
micro-cracks S-CONPRI
, O
which O
are O
the O
common O
defects S-CONPRI
in O
additively B-MANP
manufactured E-MANP
components O
. O


Four-dimensional O
( O
4D S-CONPRI
) O
printing O
has O
great O
potential O
for O
fabricating S-MANP
patient-specific O
, O
stimuli-responsive O
3D B-CONPRI
structures E-CONPRI
for O
the O
medical S-APPL
sector O
. O


Porous S-PRO
Shape O
memory O
polymers S-MATE
have O
high O
volumetric O
expansion O
and O
enhanced O
biological O
activity O
, O
which O
make O
them O
as S-MATE
ideal O
candidates O
for O
implant S-APPL
materials O
through O
minimally O
invasive O
surgical O
procedures O
. O


In O
this O
paper O
, O
the O
porous S-PRO
SMPU O
was O
fabricated S-CONPRI
by O
combining O
extrusion S-MANP
, O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
and O
salt S-MATE
leaching S-MANP
. O


The O
filament S-MATE
for O
FFF S-MANP
was O
produced O
by O
extruding S-MANP
the O
mixture O
of O
SMPU O
, O
NaCl S-MATE
, O
and O
Tungsten S-MATE
at O
the O
desired O
composition S-CONPRI
. O


The O
3D B-MANP
printed E-MANP
and O
salt S-MATE
leached O
porous S-PRO
SMPU O
was O
observed O
to O
have O
the O
porosity S-PRO
in O
the O
range S-PARA
of O
32.7–36 O
% O
and O
pore B-PARA
sizes E-PARA
of O
< O
250 O
μm O
with O
anthe O
interconnected O
network O
. O


The O
feasibility S-CONPRI
of O
combining O
fused B-MANP
filament I-MANP
fabrication E-MANP
and O
salt S-MATE
leaching S-MANP
technique O
was O
established O
for O
fabricating S-MANP
the O
radiopaque O
porous S-PRO
SMPU O
having O
the O
required O
characteristics O
for O
embolization O
, O
which O
can O
be S-MATE
explored O
by O
the O
Interventional O
Radiologist O
. O


Limitations O
for O
the O
current O
clinical O
treatment O
strategies O
for O
breast O
reconstruction S-CONPRI
have O
prompted O
researchers O
and O
bioengineers O
to O
develop O
unique O
techniques O
based O
on O
tissue B-CONPRI
engineering E-CONPRI
and O
regenerative O
medicine S-CONPRI
( O
TE S-MATE
& O
RM O
) O
principles O
. O


Recently O
, O
scaffold-guided O
soft O
TE S-MATE
has O
emerged O
as S-MATE
a O
promising O
approach O
due O
to O
its O
potential O
to O
modulate O
the O
process S-CONPRI
of O
tissue O
regeneration S-CONPRI
. O


Herein O
, O
we O
utilized O
additive S-MATE
biomanufacturing O
( O
ABM O
) O
to O
develop O
an O
original O
design-based O
concept O
for O
scaffolds S-FEAT
which O
can O
be S-MATE
applied O
in O
TE-based O
breast O
reconstruction S-CONPRI
procedures O
. O


The O
scaffold S-FEAT
design S-FEAT
addresses O
biomechanical S-APPL
and O
biological O
requirements O
for O
medium O
to O
large-volume O
regeneration S-CONPRI
with O
the O
potential O
of O
customization O
. O


The O
model S-CONPRI
is O
composed O
of O
two O
independent O
structural B-CONPRI
components E-CONPRI
. O


The O
external O
structure S-CONPRI
provides O
biomechanical S-APPL
stability O
to O
minimize O
load O
transduction O
to O
the O
newly O
formed O
tissue O
while O
the O
internal B-PRO
structure E-PRO
provides O
a O
large O
pore S-PRO
and O
fully O
interconnected O
pore S-PRO
architecture S-APPL
to O
facilitate O
tissue O
regeneration S-CONPRI
. O


A O
methodology S-CONPRI
was O
established O
to O
design S-FEAT
, O
optimize O
and O
3D B-MANP
print E-MANP
the O
external O
structure S-CONPRI
with O
customized O
biomechanical B-PRO
properties E-PRO
. O


The O
internal B-PRO
structure E-PRO
was O
also O
designed S-FEAT
and O
printed O
with O
a O
gradient O
of O
pore B-PARA
size E-PARA
and O
a O
channel S-APPL
structure O
to O
facilitate O
lipoaspirated O
fat O
delivery O
and O
entrapment O
. O


A O
fused S-CONPRI
filament S-MATE
fabrication-based O
printing O
strategy O
was O
employed O
to O
print S-MANP
two O
structures O
as S-MATE
a O
monolithic S-PRO
breast O
implant S-APPL
. O


Numerical B-ENAT
simulations E-ENAT
of O
material S-MATE
deposition S-CONPRI
at O
corners O
in O
material B-MANP
extrusion I-MANP
AM E-MANP
. O


Toolpath S-PARA
smoothing O
and O
over-extrusion O
affect O
the O
corner O
rounding O
and O
swelling S-CONPRI
. O


An O
optimal O
amount O
of O
toolpath S-PARA
smoothing O
improves O
the O
quality S-CONPRI
of O
the O
corner O
. O


A O
uniform O
track O
width O
is O
obtained O
with O
a O
proportional O
extrusion B-PARA
rate E-PARA
. O


The O
material S-MATE
deposition S-CONPRI
along O
a O
toolpath S-PARA
with O
a O
sharp O
corner O
is O
simulated O
with O
a O
computational B-CHAR
fluid I-CHAR
dynamics E-CHAR
model O
. O


We O
investigate O
the O
effects O
of O
smoothing O
the O
toolpath S-PARA
and O
material S-MATE
over-extrusion O
on O
the O
corner O
rounding O
and O
the O
corner O
swelling S-CONPRI
, O
for O
90° O
and O
30° O
turns O
. O


The O
toolpath S-PARA
motion O
is O
controlled O
with O
trapezoidal O
velocity O
profiles S-FEAT
constrained O
by O
a O
maximal O
acceleration O
. O


The O
toolpath S-PARA
smoothing O
of O
the O
corner O
is O
parametrized O
by O
a O
blending S-MANP
acceleration O
factor O
. O


Analytical B-CONPRI
solutions E-CONPRI
for O
the O
deviation O
of O
the O
smoothed O
toolpath S-PARA
from O
the O
trajectory O
of O
the O
sharp O
corner O
, O
as S-MATE
well O
as S-MATE
the O
additional O
printing O
time O
required O
by O
the O
deceleration O
and O
acceleration O
phases O
in O
the O
vicinity O
of O
the O
turn O
are O
provided O
. O


Moreover O
, O
several O
scenarios O
with O
different O
blending S-MANP
acceleration O
factors O
are O
simulated O
, O
for O
the O
cases O
of O
a O
constant O
extrusion B-PARA
rate E-PARA
and O
an O
extrusion B-PARA
rate E-PARA
proportional O
to O
the O
printing B-MACEQ
head E-MACEQ
speed O
. O


The O
constant O
extrusion B-PARA
rate E-PARA
causes O
material S-MATE
over-extrusion O
during O
the O
deceleration O
and O
acceleration O
phases O
of O
the O
printing B-MACEQ
head E-MACEQ
. O


However O
, O
the O
toolpath S-PARA
smoothing O
reduces O
the O
corner O
swelling S-CONPRI
. O


A O
uniform O
road O
width O
is O
obtained O
with O
the O
proportional O
extrusion B-PARA
rate E-PARA
. O


Proper O
support S-APPL
geometry S-CONPRI
design S-FEAT
is O
critical O
for O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
techniques O
to O
be S-MATE
successful O
, O
particularly O
for O
material S-MATE
deposition S-CONPRI
AM B-MANP
techniques E-MANP
, O
such O
as S-MATE
fused O
deposition B-CONPRI
modeling E-CONPRI
( O
FDM S-MANP
) O
. O


Many O
methods O
have O
been O
proposed O
for O
support S-APPL
geometry S-CONPRI
generation O
, O
mostly O
geared O
toward O
FDM S-MANP
and O
most O
often O
with O
the O
objective O
of O
minimizing O
support-material O
use O
and O
part-construction O
time O
. O


Here O
, O
two O
new O
support S-APPL
geometry B-CONPRI
algorithms E-CONPRI
are O
proposed O
, O
which O
are O
particularly O
suitable O
for O
weak O
support B-MATE
materials E-MATE
: O
the O
shell S-MACEQ
technique O
, O
whereby O
the O
primary O
support B-MATE
material E-MATE
would O
collapse O
under O
its O
own O
weight S-PARA
and O
thus O
a O
second O
support B-MATE
material E-MATE
is O
used O
to O
create O
a O
containment O
shell S-MACEQ
; O
the O
film O
technique O
, O
whereby O
a O
second O
support B-MATE
material E-MATE
is O
deposited O
as S-MATE
a O
thin O
film O
between O
the O
part O
and O
the O
primary O
support B-MATE
material E-MATE
. O


The O
proposed O
techniques O
also O
facilitate O
support B-MATE
material E-MATE
removal O
, O
a O
laborious O
manual O
step S-CONPRI
for O
many O
AM B-MANP
processes E-MANP
. O


Both O
techniques O
are O
demonstrated O
through O
the O
construction S-APPL
of O
parts O
using O
an O
experimental S-CONPRI
large-scale O
3D S-CONPRI
foam O
printer S-MACEQ
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
a O
promising O
approach O
for O
fabricating S-MANP
structures O
to O
serve O
as S-MATE
bone O
substitutes O
, O
or O
as S-MATE
biomaterial O
components S-MACEQ
in O
biphasic O
implants S-APPL
for O
repair O
of O
osteochondral O
defects S-CONPRI
. O


In O
this O
study O
, O
the O
three B-MANP
dimensional I-MANP
printing E-MANP
( O
3DP S-MANP
) O
AM B-MANP
process E-MANP
was O
investigated O
to O
determine O
the O
effect O
of O
powder S-MATE
layer S-PARA
orientation O
on O
mechanical S-APPL
and O
structural O
properties S-CONPRI
of O
fabricated S-CONPRI
parts O
. O


Five O
types O
of O
standard S-CONPRI
cylindrical S-CONPRI
parts O
were O
manufactured S-CONPRI
via O
AM S-MANP
with O
0° O
, O
30° O
, O
45° O
, O
60° O
and O
90° O
stacking O
layer S-PARA
orientations O
relative O
to O
the O
vertical S-CONPRI
z-axis O
of O
the O
print S-MANP
bed S-MACEQ
, O
using O
amorphous O
calcium S-MATE
polyphosphate O
( O
CPP O
) O
powder S-MATE
of O
irregular O
particle S-CONPRI
shape O
, O
average B-FEAT
aspect I-FEAT
ratio E-FEAT
≈1.70 O
and O
particle S-CONPRI
size O
between O
75 O
and O
150 O
μm O
. O


It O
was O
concluded O
that O
layer S-PARA
orientation O
had O
an O
effect O
on O
porosity S-PRO
and O
compressive B-PRO
strength E-PRO
, O
based O
on O
induced O
powder B-MATE
particle E-MATE
orientation S-CONPRI
in O
the O
green B-PRO
part E-PRO
during O
powder S-MATE
layering O
. O


The O
resulting O
bulk B-PRO
porosity E-PRO
values O
ranged O
between O
30.0 O
± O
2.4 O
% O
and O
38.2 O
± O
2.7 O
% O
, O
while O
the O
compressive B-PRO
strength E-PRO
ranged O
between O
13.50 O
± O
1.95 O
MPa S-CONPRI
and O
45.13 O
± O
6.82 O
MPa S-CONPRI
. O


The O
orientation S-CONPRI
with O
the O
highest O
compressive B-PRO
strength E-PRO
was O
90° O
, O
while O
orientations S-CONPRI
with O
the O
weakest O
compressive B-PRO
strength E-PRO
were O
0° O
and O
45° O
. O


The O
stacking O
layer S-PARA
orientation O
which O
results O
in O
the O
highest O
strength S-PRO
performance S-CONPRI
along O
a O
preferred O
loading O
orientation S-CONPRI
can O
be S-MATE
implemented O
to O
further O
optimize O
mechanical B-PRO
strength E-PRO
of O
constructs O
along O
the O
maximum O
loading O
direction O
. O


Recent O
efforts O
in O
the O
bone S-BIOP
and O
tissue B-CONPRI
engineering E-CONPRI
field O
have O
been O
made O
to O
create O
resorbable O
bone B-BIOP
scaffolds E-BIOP
that O
mimic S-MACEQ
the O
structure S-CONPRI
and O
function O
of O
natural O
bone S-BIOP
. O


While O
enhancing O
mechanical B-PRO
strength E-PRO
through O
increased O
ceramics S-MATE
loading O
has O
been O
shown O
for O
sintered S-MANP
parts O
, O
few O
studies O
have O
reported O
that O
the O
crosslinked O
polymer S-MATE
provides O
strength S-PRO
for O
the O
composite S-MATE
parts O
without O
post B-CONPRI
processing E-CONPRI
. O


The O
objective O
of O
this O
study O
is O
to O
assess O
the O
effect O
of O
amylose O
content O
on O
the O
mechanical S-APPL
and O
physical B-PRO
properties E-PRO
of O
starch-hydroxyapatite O
( O
HA O
) O
composite S-MATE
scaffolds O
for O
bone S-BIOP
and O
tissue B-CONPRI
engineering E-CONPRI
applications O
. O


Starch-HA O
composite S-MATE
scaffolds O
utilizing O
corn O
, O
potato O
, O
and O
cassava O
sources O
of O
gelatinized O
starch S-BIOP
were O
fabricated S-CONPRI
through O
the O
utilization O
of O
a O
self-designed O
and O
built O
solid O
freeform S-CONPRI
fabricator O
( O
SFF O
) O
. O


It O
was O
hypothesized O
that O
the O
mechanical B-PRO
strength E-PRO
of O
the O
starch-HA O
scaffolds S-FEAT
would O
increase O
with O
increasing O
amylose O
content O
based O
on O
the O
botanical O
source S-APPL
and O
weight S-PARA
percentage O
added O
. O


Overall O
, O
compressive B-PRO
strengths E-PRO
of O
scaffolds S-FEAT
were O
achieved O
up O
to O
12.49 O
± O
0.22 O
MPa S-CONPRI
, O
through O
the O
implementation O
of O
5.46 O
wt O
% O
corn O
starch S-BIOP
with O
a O
total O
amylose O
content O
of O
1.37 O
% O
. O


The O
authors O
propose O
a O
reinforcement S-PARA
mechanism S-CONPRI
through O
a O
matrix O
of O
gelled O
starch S-BIOP
particles S-CONPRI
and O
interlocking O
of O
hydroxyl-rich O
amylose O
with O
hydroxyapatite S-MATE
through O
hydrogen B-CONPRI
bonding E-CONPRI
. O


XRD S-CHAR
, O
FTIR S-CHAR
, O
and O
FESEM S-CHAR
were O
utilized O
to O
further O
characterize O
these O
scaffold S-FEAT
structures O
, O
ultimately O
elucidating O
amylose O
as S-MATE
a O
biologically O
relevant O
reinforcement S-PARA
phase S-CONPRI
of O
resorbable O
bone B-BIOP
scaffolds E-BIOP
. O


Significant O
efforts O
have O
been O
made O
to O
treat O
bone S-BIOP
disorders O
through O
the O
development O
of O
composite S-MATE
scaffolds O
utilizing O
calcium B-MATE
phosphate E-MATE
( O
CaP O
) O
using O
additive B-MANP
manufacturing E-MANP
techniques O
. O


However O
, O
the O
incorporation O
of O
natural O
polymers S-MATE
with O
CaP O
during O
3D B-MANP
printing E-MANP
is O
difficult O
and O
remains O
a O
formidable O
challenge O
in O
bone S-BIOP
and O
tissue B-CONPRI
engineering E-CONPRI
applications O
. O


The O
objective O
of O
this O
study O
is O
to O
understand O
the O
use O
of O
a O
natural O
polymer B-MATE
binder E-MATE
system O
in O
ceramic B-FEAT
composite E-FEAT
scaffolds O
using O
a O
ceramic S-MATE
slurry-based O
solid O
freeform S-CONPRI
fabricator O
( O
SFF O
) O
. O


This O
was O
achieved O
through O
the O
utilization O
of O
naturally O
sourced O
gelatinized O
starch S-BIOP
with O
hydroxyapatite S-MATE
( O
HA O
) O
ceramic S-MATE
in O
order O
to O
obtain O
high O
mechanical B-PRO
strength E-PRO
and O
enhanced O
biological O
properties S-CONPRI
of O
the O
green B-PRO
part E-PRO
without O
the O
need O
for O
cross-linking S-CONPRI
or O
post B-CONPRI
processing E-CONPRI
. O


The O
parametric O
effects O
of O
solids O
loading O
, O
polycaprolactone O
( O
PCL S-MATE
) O
polymer S-MATE
addition O
, O
and O
designed S-FEAT
porosity O
on O
starch-HA O
composite S-MATE
scaffolds O
were O
measured O
via O
mechanical B-PRO
strength E-PRO
, O
microstructure S-CONPRI
, O
and O
in O
vitro O
biocompatibility S-PRO
utilizing O
human O
osteoblast B-BIOP
cells E-BIOP
. O


It O
was O
hypothesized O
that O
starch S-BIOP
incorporation O
would O
improve O
the O
mechanical B-PRO
strength E-PRO
of O
the O
scaffolds S-FEAT
and O
increase O
proliferation O
of O
osteoblast B-BIOP
cells E-BIOP
in O
vitro O
. O


Starch S-BIOP
loading O
was O
shown O
to O
improve O
mechanical B-PRO
strength E-PRO
from O
4.07 O
± O
0.66 O
MPa S-CONPRI
to O
10.35 O
± O
1.10 O
MPa S-CONPRI
, O
more O
closely O
resembling O
the O
mechanical B-PRO
strength E-PRO
of O
cancellous B-BIOP
bone E-BIOP
. O


Based O
on O
these O
results O
, O
a O
reinforcing O
mechanism S-CONPRI
of O
gelatinized O
starch S-BIOP
based O
on O
interparticle O
and O
apatite S-MATE
crystal O
interlocking O
is O
proposed O
. O


Morphological B-CHAR
characterization E-CHAR
utilizing O
FESEM S-CHAR
and O
MTT O
cell B-CHAR
viability E-CHAR
assay O
showed O
enhanced O
osteoblast B-BIOP
cell E-BIOP
proliferation O
in O
the O
presence O
of O
starch S-BIOP
and O
PCL S-MATE
. O


Overall O
, O
the O
utilization O
of O
starch S-BIOP
as S-MATE
a O
natural O
binder S-MATE
system O
in O
SFF O
scaffolds S-FEAT
was O
found O
to O
improve O
both O
compressive B-PRO
strength E-PRO
and O
in O
vitro O
biocompatibility S-PRO
. O


a O
) O
Ceramic S-MATE
slurry O
preparation O
of O
starch S-BIOP
and O
hydroxyapaitite O
( O
HA O
) O
utilized O
for O
fabrication S-MANP
of O
bone B-BIOP
scaffolds E-BIOP
without O
the O
need O
for O
post B-CONPRI
processing E-CONPRI
. O


b S-MATE
) O
Schematic O
of O
Solid O
Freeform S-CONPRI
Fabricator O
. O


c S-MATE
) O
Representation O
of O
scaffold B-CONPRI
model E-CONPRI
utilizing O
solid O
works O
file S-MANS
and O
CURA O
program O
and O
final O
scaffold S-FEAT
prints O
d O
) O
in O
vitro O
cell S-APPL
work O
regarding O
the O
proliferation O
of O
osteoblast B-BIOP
cells E-BIOP
utilizing O
starch S-BIOP
based O
composite S-MATE
HA O
scaffolds S-FEAT
, O
ultimately O
acquiring O
sufficient O
mechanical B-PRO
integrity E-PRO
and O
enhanced O
biactivity O
to O
be S-MATE
utilized O
in O
bone S-BIOP
repair.Download O
: O
Download O
high-res B-CONPRI
image E-CONPRI
( O
217 O
Bonding S-CONPRI
in O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
remains O
a O
key O
challenge O
in O
improving O
part O
properties S-CONPRI
. O


For O
thermally O
driven O
AM S-MANP
methods O
, O
such O
as S-MATE
material O
extrusion B-MANP
AM E-MANP
( O
MatEx O
) O
, O
temperature S-PARA
governs O
bonding S-CONPRI
. O


Experimental S-CONPRI
measurements O
of O
temperature S-PARA
are O
limited O
in O
their O
ability O
to O
probe S-MACEQ
many O
points O
in O
space O
and O
time O
during O
a O
process S-CONPRI
without O
disturbing O
the O
temperature S-PARA
profiles S-FEAT
being O
measured O
. O


These O
limitations O
may O
be S-MATE
overcome O
with O
computational B-ENAT
methods E-ENAT
; O
however O
, O
computing O
power S-PARA
considerations O
confined O
simulations S-ENAT
to O
one O
or O
two O
dimensions S-FEAT
until O
recently O
. O


Additionally O
, O
most O
existing O
models O
have O
had O
only O
limited O
ability O
to O
modify O
geometry S-CONPRI
or O
process B-CONPRI
parameters E-CONPRI
. O


In O
this O
work O
, O
an O
adaptable O
FEA O
model S-CONPRI
capable O
of O
simulating O
heat B-CONPRI
transfer E-CONPRI
in O
3D S-CONPRI
and O
at O
sufficiently O
small O
time B-FEAT
scales E-FEAT
to O
capture O
the O
rapid O
cooling S-MANP
in O
AM S-MANP
is O
presented O
. O


Cooling S-MANP
trends O
from O
simulation S-ENAT
are O
shown O
to O
be S-MATE
in O
agreement O
with O
experimental B-CONPRI
data E-CONPRI
. O


Temperature S-PARA
profiles S-FEAT
are O
collapsed O
to O
equivalent O
time O
at O
a O
reference O
temperature S-PARA
and O
predict O
little O
variation S-CONPRI
in O
bonding S-CONPRI
along O
the O
z-axis S-CONPRI
of O
a O
part O
or O
with O
changes O
in O
print S-MANP
speed O
. O


A O
previously O
unreported O
peak O
in O
cooling B-PARA
rates E-PARA
for O
print S-MANP
speeds O
between O
10 O
and O
30 O
mm/s O
is O
shown O
. O


Uniformity O
in O
equivalent O
time O
at O
Tg S-CHAR
suggests O
weld B-PRO
strength E-PRO
will O
not O
vary O
with O
print S-MANP
speed O
; O
however O
, O
high O
cooling B-PARA
rates E-PARA
for O
common O
print S-MANP
speeds O
may O
lead S-MATE
to O
greater O
residual B-PRO
stresses E-PRO
and O
reduced O
mechanical B-CONPRI
properties E-CONPRI
. O


Demonstrates O
PBF S-MANP
printing O
of O
high-performance O
polymer S-MATE
, O
PPS O
, O
on O
standard S-CONPRI
printer S-MACEQ
. O


Evaluates O
the O
universality O
of O
print S-MANP
parameter S-CONPRI
selection O
methods O
for O
non-polyamides O
. O


XY O
plane O
printed O
dogbones O
show O
failure S-CONPRI
at O
61.8 O
± O
4.0 O
MPa S-CONPRI
and O
3.27 O
± O
0.22 O
% O
. O


In O
this O
paper O
, O
the O
authors O
present O
evidence O
of O
printing O
poly O
( O
phenylene O
sulfide O
) O
( O
PPS O
) O
, O
a O
high-performance O
polymer S-MATE
, O
via O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
using O
a O
bed S-MACEQ
temperature O
of O
230 O
°C O
, O
which O
is O
significantly O
below O
both O
its O
observed O
melting B-PARA
temperature E-PARA
( O
Tm O
˜ O
285 O
°C O
) O
and O
its O
observed O
onset O
temperature S-PARA
of O
crystallization S-CONPRI
( O
Tc O
˜ O
255 O
°C O
) O
. O


This O
contradicts O
existing O
material S-MATE
screening O
guidelines O
for O
PBF S-MANP
, O
which O
suggest O
maintaining O
bed S-MACEQ
temperature O
above O
the O
observed O
onset O
of O
crystallization S-CONPRI
. O


Existing O
methods O
for O
theoretically O
determining O
processing O
bounds O
were O
used O
to O
predict O
a O
range S-PARA
of O
energy B-PARA
densities E-PARA
at O
which O
PPS O
can O
be S-MATE
printed O
. O


One O
combination O
of O
process B-CONPRI
parameter E-CONPRI
values O
was O
selected O
based O
on O
machine S-MACEQ
constraints O
imposed O
by O
typical O
PBF B-MACEQ
machines E-MACEQ
not O
designed S-FEAT
to O
print S-MANP
high-temperature O
polymers S-MATE
and O
used O
to O
fabricate S-MANP
multilayer O
, O
complex O
parts O
. O


The O
presented O
process B-CONPRI
parameters E-CONPRI
result O
in O
final O
part O
density S-PRO
upwards O
of O
1.18 O
g/cm3 O
and O
ultimate B-PRO
tensile I-PRO
strength E-PRO
and O
elongation S-PRO
of O
62 O
MPa S-CONPRI
and O
3.3 O
% O
, O
respectively O
. O


Hypotheses O
on O
the O
generalizability O
of O
low-temperature O
PBF S-MANP
printing O
of O
high-performance O
polymers S-MATE
, O
and O
steps O
towards O
updating O
materials S-CONPRI
and O
process B-CONPRI
parameter E-CONPRI
selection O
guidelines O
for O
PBF S-MANP
, O
are O
also O
presented O
. O


We O
demonstrate O
a O
novel O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
nozzle S-MACEQ
design S-FEAT
to O
enable O
measurements O
of O
in-situ S-CONPRI
conditions O
inside O
FFF S-MANP
nozzles O
, O
which O
is O
critical O
to O
ensuring O
that O
the O
polymer B-MATE
extrudate E-MATE
is O
flowing O
at O
appropriate O
temperature S-PARA
and O
flow B-PARA
rate E-PARA
during O
the O
part O
build S-PARA
process O
. O


Testing S-CHAR
was O
performed O
with O
ABS S-MATE
filament O
using O
a O
modified O
Monoprice O
Maker O
Select O
3D B-MACEQ
printer E-MACEQ
. O


In-situ S-CONPRI
measurements O
using O
the O
printer S-MACEQ
’ O
s S-MATE
default O
temperature S-PARA
control O
settings O
showed O
an O
11 O
°C O
decrease O
in O
temperature S-PARA
and O
significant O
fluctuation O
in O
pressure S-CONPRI
during O
printing O
as S-MATE
well O
as S-MATE
fluctuations O
while O
idle O
of O
± O
2 O
°C O
and O
±14 O
kPa O
. O


These O
deviations O
were O
eliminated O
at O
lower O
flow B-PARA
rates E-PARA
with O
a O
properly O
calibrated S-CONPRI
proportional–integral–derivative O
( O
PID O
) O
system O
. O


At O
the O
highest O
tested O
flow B-PARA
rates E-PARA
, O
decreases O
in O
melt S-CONPRI
temperature O
as S-MATE
high O
as S-MATE
6.5 O
°C O
were O
observed O
, O
even O
with O
a O
properly O
calibrated S-CONPRI
PID O
, O
providing O
critical O
insight O
into O
the O
significance O
of O
flow B-PARA
rate E-PARA
and O
PID O
calibration S-CONPRI
on O
actual O
polymer B-MATE
melt E-MATE
temperature O
inside O
the O
FFF S-MANP
nozzle O
. O


Pressure S-CONPRI
readings O
ranging O
from O
140 O
to O
6900 O
kPa O
were O
measured O
over O
a O
range S-PARA
of O
filament S-MATE
feed S-PARA
rates O
and O
corresponding O
extrusion S-MANP
flow O
rates O
. O


In-situ S-CONPRI
pressure O
measurements O
were O
higher O
than O
theoretical B-CONPRI
predictions E-CONPRI
using O
a O
power-law O
fluid S-MATE
model O
, O
suggesting O
that O
the O
assumptions O
used O
for O
theoretical S-CONPRI
calculations O
may O
not O
be S-MATE
completely O
capturing O
the O
dynamics O
in O
the O
FFF S-MANP
liquefier O
. O


Our O
nozzle S-MACEQ
prototype O
succeeded O
in O
measuring O
the O
internal O
conditions O
of O
FFF S-MANP
nozzles O
, O
thereby O
providing O
a O
number O
of O
important O
insights O
into O
the O
printing B-MANP
process E-MANP
which O
are O
vital O
for O
monitoring O
and O
improving O
FFF S-MANP
printed O
parts O
. O


Increasing O
void S-CONPRI
size O
in O
printed O
objects O
through O
FFF S-MANP
negatively O
affects O
strength S-PRO
Novel O
method O
of O
FFF S-MANP
proposed O
to O
reduce O
the O
void S-CONPRI
size O
Novel O
method O
reduces O
cross-sectional O
void S-CONPRI
surface B-PARA
area E-PARA
by O
18.0 O
% O
Novel O
method O
improves O
density S-PRO
by O
6.5 O
% O
per O
mm S-MANP
increase O
in O
nozzle S-MACEQ
size O
Novel O
method O
improves O
max O
. O


shear B-PRO
stress E-PRO
by O
7.2 O
% O
per O
mm S-MANP
increase O
in O
nozzle S-MACEQ
size O
Additive B-MANP
manufacturing E-MANP
techniques O
, O
such O
as S-MATE
Fused O
Filament S-MATE
Fabrication S-MANP
( O
FFF S-MANP
) O
, O
are O
rapidly O
revolutionising O
the O
manufacturing S-MANP
and O
mining O
sectors O
. O


Firstly O
, O
an O
alternative O
method O
of O
filament S-MATE
positioning O
in O
material B-MANP
extrusion E-MANP
is O
proposed O
, O
referred O
to O
as S-MATE
the O
‘ O
offset S-CONPRI
method O
’ O
, O
which O
aims O
to O
reduce O
the O
volume S-CONPRI
of O
empty O
cavities O
between O
deposited O
material S-MATE
. O


Then O
the O
shear B-PRO
properties E-PRO
, O
density S-PRO
properties O
, O
and O
cross-sectional O
void S-CONPRI
surface B-PARA
area E-PARA
are O
compared O
to O
structures O
printed O
using O
the O
aligned O
printing O
method O
. O


Experimental S-CONPRI
results O
on O
solid O
printed O
( O
no O
infill S-PARA
) O
samples S-CONPRI
, O
through O
four O
different- O
sized O
nozzles S-MACEQ
, O
have O
shown O
the O
newly O
proposed O
method O
produces O
a O
6.5 O
% O
increase O
in O
density S-PRO
and O
a O
7.2 O
% O
improvement O
in O
maximum O
in-plane O
shear B-PRO
stress E-PRO
per O
millimetre O
increase O
in O
nozzle S-MACEQ
size O
, O
compared O
with O
the O
aligned O
method O
of O
FFF S-MANP
. O


The O
offset S-CONPRI
method O
was O
found O
to O
produce O
a O
material S-MATE
with O
increased O
interlayer O
contact S-APPL
, O
compared O
to O
the O
aligned O
method O
, O
which O
results O
in O
a O
higher O
fictitious O
shear B-PRO
stress E-PRO
modulus O
. O


The O
effect O
of O
the O
increased O
interlayer O
contact S-APPL
on O
the O
fictitious O
shear B-PRO
modulus E-PRO
and O
real O
shear B-PRO
stress E-PRO
was O
investigated O
using O
a O
FEM S-CONPRI
analysis O
of O
the O
unit B-CONPRI
cells E-CONPRI
. O


In O
short O
, O
using O
the O
same O
feedstock B-MATE
material E-MATE
, O
the O
offset S-CONPRI
method O
produces O
a O
stiffer O
material S-MATE
with O
a O
higher O
fictitious O
shear B-PRO
strength E-PRO
than O
the O
aligned O
method O
of O
FFF S-MANP
printing O
. O


This O
study O
focuses O
on O
the O
characterization O
of O
additive B-MANP
manufacturing E-MANP
technology O
based O
on O
composite S-MATE
filament O
fabrication S-MANP
( O
CFF O
) O
. O


CFF O
utilizes O
a O
similar O
method O
of O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
printing O
as S-MATE
fused O
filament S-MATE
fabrication S-MANP
but O
is O
also O
capable O
of O
reinforcing O
parts O
with O
layers O
of O
various O
continuous B-MATE
fibers E-MATE
into O
a O
polymer S-MATE
matrix O
. O


Due O
to O
the O
orthotropic S-MATE
characteristics O
of O
additive B-MANP
manufacturing E-MANP
based O
on O
fused B-MANP
filament I-MANP
fabrication E-MANP
, O
3D B-APPL
printed I-APPL
parts E-APPL
may O
present O
different O
mechanical S-APPL
behavior O
under O
different O
orientations S-CONPRI
of O
stress S-PRO
. O


Furthermore O
, O
technologies S-CONPRI
such O
as S-MATE
CFF O
allow O
a O
range S-PARA
of O
configurations O
to O
fabricate S-MANP
and O
reinforce O
the O
parts O
. O


In O
this O
study O
, O
mechanical S-APPL
characterization O
of O
polyamide S-MATE
6 O
( O
PA6 O
) O
reinforced S-CONPRI
with O
carbon B-MATE
fiber E-MATE
was O
conducted O
by O
design B-CONPRI
of I-CONPRI
experiment E-CONPRI
as S-MATE
a O
statistical B-CONPRI
method E-CONPRI
, O
to O
investigate O
the O
effect O
of O
reinforcement S-PARA
pattern S-CONPRI
, O
reinforcement S-PARA
distribution S-CONPRI
, O
print S-MANP
orientation S-CONPRI
and O
percentage O
of O
fiber S-MATE
on O
compressive O
and O
flexural O
mechanical B-CONPRI
properties E-CONPRI
. O


CFF B-MANP
technology E-MANP
3D B-MANP
print E-MANP
stronger O
parts O
than O
conventional O
additive B-MANP
manufacturing E-MANP
technologies O
. O


Maximized O
compressive O
response O
was O
achieved O
with O
a O
0.2444 O
Carbon B-MATE
Fiber E-MATE
volume O
ratio O
, O
concentric O
and O
equidistant O
reinforcement S-PARA
configuration S-CONPRI
, O
resulting O
in O
a O
compressive O
modulus O
of O
2.102 O
GPa S-PRO
and O
a O
stress S-PRO
at O
proportional B-PARA
limit E-PARA
of O
53.3 O
MPa S-CONPRI
. O


Maximized O
flexural O
response O
was O
achieved O
with O
0.4893 O
Carbon B-MATE
Fiber E-MATE
volume O
ratio O
, O
concentric O
reinforcement S-PARA
and O
perpendicular O
to O
the O
applied O
force S-CONPRI
, O
resulting O
in O
a O
flexural O
modulus O
of O
14.17 O
GPa S-PRO
and O
a O
proportional B-PARA
limit E-PARA
of O
231.1 O
MPa S-CONPRI
. O


This O
study O
presents O
development O
of O
a O
test O
method O
for O
characterization O
of O
interlayer O
, O
mode-I O
fracture S-CONPRI
toughness O
of O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
materials S-CONPRI
using O
a O
modified O
double O
cantilever B-MACEQ
beam E-MACEQ
( O
DCB O
) O
test O
. O


This O
test O
consists O
of O
DCB O
specimen O
fabricated S-CONPRI
from O
using O
unidirectional S-CONPRI
FFF S-MANP
layers O
, O
an O
8 O
μm O
Kapton O
starter O
crack O
inserted O
in O
the O
midplane S-CONPRI
during O
the O
printing B-MANP
process E-MANP
, O
and O
reinforcing O
glass/epoxy O
doublers O
to O
prevent O
DCB O
arm O
failure S-CONPRI
during O
loading O
. O


DCB O
specimens O
are O
manufactured S-CONPRI
with O
a O
commercially O
available O
3D B-MACEQ
printer E-MACEQ
using O
unreinforced O
Acrylonitrile B-MATE
Butadiene I-MATE
Styrene E-MATE
( O
ABS S-MATE
) O
and O
chopped O
carbon-fiber-reinforced O
ABS S-MATE
( O
CF-ABS O
) O
filaments S-MATE
. O


To O
examine O
the O
effect O
of O
the O
FFF S-MANP
printing O
process S-CONPRI
on O
fracture S-CONPRI
toughness O
, O
additional O
ABS S-MATE
and O
CF-ABS O
specimens O
are O
hot-press O
molded O
using O
the O
filament S-MATE
material O
, O
and O
tested O
with O
the O
single O
end O
notch S-FEAT
bend O
( O
SENB O
) O
specimen O
configuration S-CONPRI
. O


The O
fracture S-CONPRI
toughness O
data S-CONPRI
from O
DCB O
and O
SENB O
tests O
reveal O
that O
the O
FFF S-MANP
process O
significantly O
lowers O
the O
mode-I O
fracture S-CONPRI
toughness O
of O
ABS S-MATE
and O
CF-ABS O
. O


For O
both O
materials S-CONPRI
, O
in B-CONPRI
situ E-CONPRI
thermal O
imaging S-APPL
and O
post-mortem O
fractography S-CHAR
shows O
, O
respectively O
, O
rapid O
cool-down O
of O
the O
rasters O
during O
filament S-MATE
deposition S-CONPRI
and O
presence O
of O
voids S-CONPRI
between O
adjacent O
raster O
roads O
; O
both O
of O
which O
serve O
to O
reduce O
fracture S-CONPRI
toughness O
. O


For O
CF-ABS O
specimens O
, O
fracture S-CONPRI
toughness O
is O
further O
reduced O
by O
inclusion S-MATE
of O
poorly O
wetted O
chopped O
carbon B-MATE
fibers E-MATE
. O


Although O
this O
study O
did O
not O
attempt O
to O
optimize O
the O
fracture S-CONPRI
performance O
of O
FFF S-MANP
specimens O
, O
the O
results O
demonstrate O
that O
the O
proposed O
methodology S-CONPRI
is O
suitable O
for O
design S-FEAT
and O
optimization S-CONPRI
of O
FFF S-MANP
processes O
for O
improved O
interlayer O
fracture S-CONPRI
performance O
. O


Polyimides S-MATE
are O
a O
group O
of O
high O
performance S-CONPRI
thermal O
stable O
dielectric S-MACEQ
materials O
used O
in O
diverse O
applications O
. O


In O
this O
article O
, O
we O
synthesized O
and O
developed O
a O
high-performance O
polyimide O
precursor B-MATE
ink E-MATE
for O
a O
Material B-MANP
Jetting E-MANP
( O
MJ S-MANP
) O
process S-CONPRI
. O


The O
proposed O
ink S-MATE
formulation O
was O
shown O
to O
form O
a O
uniform O
and O
dense O
polyimide O
film O
through O
reactive O
MJ S-MANP
utilising O
real-time O
thermo-imidisation O
process S-CONPRI
. O


By O
means O
of O
selectively O
depositing O
4 O
μm O
thick O
patches O
at O
the O
cross-over O
points O
of O
two O
circuit O
patterns O
, O
a O
traditional O
double-sided O
printed B-MACEQ
circuit I-MACEQ
board E-MACEQ
( O
PCB O
) O
can O
be S-MATE
printed O
on O
one O
side O
, O
providing O
the O
user O
with O
higher O
design B-CONPRI
freedom E-CONPRI
to O
achieve O
a O
more O
compact S-MANP
high O
performance S-CONPRI
PCB O
structure S-CONPRI
. O


This O
study O
presents O
development O
of O
a O
test O
method O
for O
characterization O
of O
interlayer O
, O
mode-I O
fracture S-CONPRI
toughness O
of O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
materials S-CONPRI
using O
a O
modified O
double O
cantilever B-MACEQ
beam E-MACEQ
( O
DCB O
) O
test O
. O


This O
test O
consists O
of O
DCB O
specimen O
fabricated S-CONPRI
from O
using O
unidirectional S-CONPRI
FFF S-MANP
layers O
, O
an O
8 O
μm O
Kapton O
starter O
crack O
inserted O
in O
the O
midplane S-CONPRI
during O
the O
printing B-MANP
process E-MANP
, O
and O
reinforcing O
glass/epoxy O
doublers O
to O
prevent O
DCB O
arm O
failure S-CONPRI
during O
loading O
. O


DCB O
specimens O
are O
manufactured S-CONPRI
with O
a O
commercially O
available O
3D B-MACEQ
printer E-MACEQ
using O
unreinforced O
Acrylonitrile B-MATE
Butadiene I-MATE
Styrene E-MATE
( O
ABS S-MATE
) O
and O
chopped O
carbon-fiber-reinforced O
ABS S-MATE
( O
CF-ABS O
) O
filaments S-MATE
. O


To O
examine O
the O
effect O
of O
the O
FFF S-MANP
printing O
process S-CONPRI
on O
fracture S-CONPRI
toughness O
, O
additional O
ABS S-MATE
and O
CF-ABS O
specimens O
are O
hot-press O
molded O
using O
the O
filament S-MATE
material O
, O
and O
tested O
with O
the O
single O
end O
notch S-FEAT
bend O
( O
SENB O
) O
specimen O
configuration S-CONPRI
. O


The O
fracture S-CONPRI
toughness O
data S-CONPRI
from O
DCB O
and O
SENB O
tests O
reveal O
that O
the O
FFF S-MANP
process O
significantly O
lowers O
the O
mode-I O
fracture S-CONPRI
toughness O
of O
ABS S-MATE
and O
CF-ABS O
. O


For O
both O
materials S-CONPRI
, O
in B-CONPRI
situ E-CONPRI
thermal O
imaging S-APPL
and O
post-mortem O
fractography S-CHAR
shows O
, O
respectively O
, O
rapid O
cool-down O
of O
the O
rasters O
during O
filament S-MATE
deposition S-CONPRI
and O
presence O
of O
voids S-CONPRI
between O
adjacent O
raster O
roads O
; O
both O
of O
which O
serve O
to O
reduce O
fracture S-CONPRI
toughness O
. O


For O
CF-ABS O
specimens O
, O
fracture S-CONPRI
toughness O
is O
further O
reduced O
by O
inclusion S-MATE
of O
poorly O
wetted O
chopped O
carbon B-MATE
fibers E-MATE
. O


Although O
this O
study O
did O
not O
attempt O
to O
optimize O
the O
fracture S-CONPRI
performance O
of O
FFF S-MANP
specimens O
, O
the O
results O
demonstrate O
that O
the O
proposed O
methodology S-CONPRI
is O
suitable O
for O
design S-FEAT
and O
optimization S-CONPRI
of O
FFF S-MANP
processes O
for O
improved O
interlayer O
fracture S-CONPRI
performance O
. O


This O
paper O
presents O
an O
end-to-end O
design B-CONPRI
process E-CONPRI
for O
compliance O
minimization-based O
topological B-FEAT
optimization E-FEAT
of O
cellular B-FEAT
structures E-FEAT
through O
to O
the O
realization O
of O
a O
final O
printed O
product O
. O


Homogenization S-MANP
is O
used O
to O
derive O
properties S-CONPRI
representative O
of O
these O
structures O
through O
direct O
numerical B-ENAT
simulation E-ENAT
of O
unit B-CONPRI
cell E-CONPRI
models O
. O


The O
resulting O
homogenized S-MANP
properties O
are O
then O
used O
assuming O
uniform O
distribution S-CONPRI
of O
the O
cellular B-FEAT
structure E-FEAT
to O
compute O
the O
macroscale S-CONPRI
structure O
. O


Results O
are O
presented O
that O
illustrate O
the O
fine-scale O
stresses O
developed O
in O
the O
macroscale S-CONPRI
optimized O
part O
as S-MATE
well O
as S-MATE
the O
effect O
that O
fine-scale O
structure S-CONPRI
has O
on O
the O
optimized O
topology S-CONPRI
. O


Quite O
fine O
cellular B-FEAT
structures E-FEAT
are O
shown O
to O
be S-MATE
possible O
using O
this O
method O
. O


Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
is O
the O
most O
widely O
available O
Additive B-MANP
Manufacturing E-MANP
technology O
. O


Offering O
the O
possibility O
of O
producing O
complex B-CONPRI
geometries E-CONPRI
in O
a O
compressed O
product B-CONPRI
development E-CONPRI
cycle O
and O
in O
a O
plethora O
of O
materials S-CONPRI
, O
it O
comes O
as S-MATE
no O
surprise O
that O
FFF S-MANP
is O
attractive O
to O
multiple O
industries S-APPL
, O
including O
the O
automotive S-APPL
and O
aerospace S-APPL
segments O
. O


However O
, O
the O
high O
anisotropy S-PRO
of O
parts O
developed O
through O
this O
technique O
implies O
that O
failure S-CONPRI
prediction O
is O
extremely O
difficult O
-a O
requirement O
that O
must O
be S-MATE
satisfied O
to O
guarantee O
the O
safety S-CONPRI
of O
the O
final O
user O
. O


This O
work O
applies O
a O
criterion O
that O
incorporates O
stress S-PRO
interactions O
to O
define O
a O
3D S-CONPRI
failure O
envelope O
that O
could O
prove O
an O
invaluable O
tool S-MACEQ
in O
formalizing O
the O
embrace O
of O
FFF S-MANP
in O
industry S-APPL
. O


Tensile S-PRO
, O
compressive O
and O
torsion B-CHAR
tests E-CHAR
were O
executed O
on O
coupons O
developed O
in O
a O
traditional O
FFF S-MANP
printer O
, O
as S-MATE
well O
as S-MATE
a O
customized O
, O
6-axis O
robotic O
printer S-MACEQ
necessary O
to O
produce O
specimens O
in O
out O
of O
ordinary O
orientations S-CONPRI
. O


These O
tests O
were O
used O
to O
calculate O
the O
parameters S-CONPRI
of O
the O
mathematical S-CONPRI
function O
that O
describe O
the O
failure S-CONPRI
envelope O
. O


Mechanical B-CHAR
tests E-CHAR
clearly O
showed O
significant O
difference O
between O
tensile S-PRO
, O
compressive O
and O
shear B-PRO
strengths E-PRO
. O


The O
calculated O
envelope O
shows O
strong O
interactions O
between O
axial O
loads O
, O
and O
a O
considerable O
interaction O
between O
shear B-PRO
stresses E-PRO
and O
loads O
applied O
in O
directions O
parallel O
and O
perpendicular O
to O
the O
beads S-CHAR
. O


A O
new O
class O
of O
high-performance O
resins S-MATE
are O
available O
for O
additive B-MANP
manufacturing E-MANP
with O
the O
introduction O
of O
Digital B-MANP
Light I-MANP
Synthesis E-MANP
( O
DLS S-MANP
) O
technology S-CONPRI
. O


In O
combination O
with O
Continuous B-MANP
Liquid I-MANP
Interface I-MANP
Production E-MANP
( O
CLIP S-MANP
) O
, O
DLS S-MANP
uses O
ultraviolet B-CONPRI
light E-CONPRI
and O
oxygen S-MATE
to O
continuously O
grow O
objects O
from O
a O
pool O
of O
resin S-MATE
instead O
of O
printing O
them O
layer-by-layer S-CONPRI
, O
subsequently O
increasing O
the O
printing B-PARA
speed E-PARA
and O
the O
mechanical S-APPL
performance O
. O


For O
many O
DLS S-MANP
resin O
systems O
, O
a O
secondary O
thermal O
curing S-MANP
step O
is O
required O
in O
order O
to O
reach O
the O
final O
material B-CONPRI
properties E-CONPRI
after O
printing O
. O


This O
step S-CONPRI
is O
a O
major O
limiting O
factor O
in O
the O
production S-MANP
time O
of O
the O
DLS S-MANP
process O
, O
as S-MATE
materials O
may O
require O
several O
hours O
of O
thermal O
post O
curing S-MANP
. O


The O
aim O
of O
this O
study O
is O
to O
optimize O
this O
secondary O
curing S-MANP
cycle O
for O
the O
epoxy-based O
resin S-MATE
EPX O
82 O
by O
reducing O
the O
thermal O
curing B-PARA
time E-PARA
while O
avoiding O
a O
negative O
influence O
on O
the O
final O
mechanical B-CONPRI
properties E-CONPRI
. O


Differential O
scanning S-CONPRI
calorimetry O
( O
DSC S-CHAR
) O
was O
used O
with O
different O
heating S-MANP
rates O
and O
a O
chemical B-CONPRI
reaction E-CONPRI
model O
was O
developed O
. O


The O
Di O
Benedetto O
relationship O
was O
used O
to O
include O
diffusion S-CONPRI
control O
for O
high O
degrees O
of O
cure S-CONPRI
. O


Powder B-MANP
Bed I-MANP
Fusion E-MANP
( O
PBF S-MANP
) O
is O
a O
range S-PARA
of O
advanced O
manufacturing B-MANP
technologies E-MANP
that O
can O
fabricate S-MANP
three-dimensional O
assets O
directly O
from O
CAD S-ENAT
data O
, O
on O
a O
successive O
layer-by-layer S-CONPRI
strategy O
by O
using O
thermal B-CONPRI
energy E-CONPRI
, O
typically O
from O
a O
laser B-MACEQ
source E-MACEQ
, O
to O
irradiate O
and O
fuse S-MANP
particles O
within O
a O
powder S-MATE
bed.The O
aim O
of O
this O
paper O
was O
to O
investigate O
the O
application O
of O
this O
advanced O
manufacturing S-MANP
technique O
to O
process S-CONPRI
ceramic S-MATE
multicomponent O
materials S-CONPRI
into O
3D S-CONPRI
layered O
structures O
. O


The O
materials S-CONPRI
used O
matched O
those O
found O
on O
the O
Lunar O
and O
Martian O
surfaces S-CONPRI
. O


The O
indigenous O
extra-terrestrial O
Lunar O
and O
Martian O
materials S-CONPRI
could O
potentially O
be S-MATE
used O
for O
manufacturing S-MANP
physical O
assets O
onsite O
( O
i.e. O
, O
off-world O
) O
on O
future O
planetary O
exploration O
missions O
and O
could O
cover O
a O
range S-PARA
of O
potential O
applications O
including O
: O
infrastructure O
, O
radiation S-MANP
shielding O
, O
thermal O
storage O
, O
etc.Two O
different O
simulants O
of O
the O
mineralogical O
and O
basic O
properties S-CONPRI
of O
Lunar O
and O
Martian O
indigenous O
materials S-CONPRI
were O
used O
for O
the O
purpose O
of O
this O
study O
and O
processed S-CONPRI
with O
commercially O
available O
laser B-MANP
additive I-MANP
manufacturing E-MANP
equipment S-MACEQ
. O


The O
results O
of O
the O
laser B-CONPRI
processing E-CONPRI
were O
investigated O
and O
quantified O
through O
mechanical S-APPL
hardness S-PRO
testing O
, O
optical S-CHAR
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
, O
X-ray S-CHAR
fluorescence S-CHAR
spectroscopy O
, O
thermo-gravimetric O
analysis O
, O
spectrometry O
, O
and O
finally O
X-ray S-CHAR
diffraction.The O
research S-CONPRI
resulted O
in O
the O
identification O
of O
a O
range S-PARA
of O
process B-CONPRI
parameters E-CONPRI
that O
resulted O
in O
the O
successful O
manufacture S-CONPRI
of O
three-dimensional S-CONPRI
components S-MACEQ
from O
Lunar O
and O
Martian O
ceramic S-MATE
multicomponent O
simulant O
materials S-CONPRI
. O


The O
feasibility S-CONPRI
of O
using O
thermal O
based O
additive B-MANP
manufacturing E-MANP
with O
multi-component O
ceramic B-MATE
materials E-MATE
has O
therefore O
been O
established O
, O
which O
represents O
a O
potential O
solution S-CONPRI
to O
off-world O
bulk O
structure B-CONPRI
manufacture E-CONPRI
for O
future O
human O
space O
exploration O
. O


This O
study O
investigates S-CONPRI
the O
moisture O
absorption S-CONPRI
characteristics O
of O
the O
ULTEM® O
9085 O
filament S-MATE
and O
how O
the O
uptake O
concentration O
affects O
the O
quality S-CONPRI
of O
material B-MANP
extrusion E-MANP
manufactured B-CONPRI
3-D E-CONPRI
parts O
. O


The O
rate O
of O
transport S-CHAR
was O
modeled O
by O
Fickian O
diffusion S-CONPRI
and O
diffusion S-CONPRI
coefficients O
were O
obtained O
for O
various O
exposure S-CONPRI
conditions O
. O


Moduli O
, O
strain S-PRO
to O
failure S-CONPRI
and O
ultimate B-PRO
strength E-PRO
were O
evaluated O
in O
the O
XY O
( O
flat O
horizontal O
) O
and O
ZX O
( O
vertical S-CONPRI
) O
direction O
relative O
to O
the O
build B-MACEQ
plate E-MACEQ
orientation O
. O


Image B-CONPRI
analyses E-CONPRI
of O
cross-sections S-CONPRI
as S-MATE
well O
as S-MATE
their O
corresponding O
fracture S-CONPRI
surfaces O
were O
evaluated O
for O
consolidation S-CONPRI
, O
porosity S-PRO
distribution S-CONPRI
and O
failure S-CONPRI
behavior O
. O


Mechanical B-CHAR
test E-CHAR
data S-CONPRI
showed O
a O
significant O
decrease O
in O
tensile B-PRO
strength E-PRO
( O
> O
60 O
% O
) O
and O
failure S-CONPRI
strain O
( O
> O
50 O
% O
) O
over O
the O
range S-PARA
of O
filament S-MATE
moisture O
levels O
investigated O
. O


A O
decrease O
in O
failure S-CONPRI
strain O
of O
41 O
% O
was O
observed O
with O
moisture O
levels O
as S-MATE
low O
as S-MATE
0.16 O
% O
. O


This O
degradation S-CONPRI
was O
especially O
sensitive O
in O
parts O
printed O
in O
the O
vertical S-CONPRI
direction O
, O
which O
resulted O
in O
an O
ultimate O
failure S-CONPRI
strain O
of O
only O
1 O
% O
. O


The O
changes O
in O
mechanical S-APPL
performance O
are O
believed O
to O
be S-MATE
due O
to O
a O
combination O
of O
entrapped O
volatiles O
resulting O
in O
increased O
porosity S-PRO
at O
higher O
moisture O
levels O
as S-MATE
well O
as S-MATE
moisture O
induced O
pseudo-crosslinking O
at O
lower O
concentrations O
. O


Optical S-CHAR
micrographs O
showed O
that O
specimens O
with O
0.16 O
% O
moisture O
or O
greater O
were O
filled O
with O
observable O
porosity S-PRO
and O
increased O
surface B-PRO
roughness E-PRO
. O


The O
rheological S-PRO
behavior O
of O
extruded S-MANP
material O
indicated O
plasticization O
as S-MATE
evidenced O
by O
melt B-PARA
flow I-PARA
index E-PARA
measurements O
and O
changes O
in O
the O
flow O
characteristics O
of O
moisture-exposed O
extrudate S-MATE
. O


DMA B-CONPRI
data E-CONPRI
show O
a O
distinct O
decrease O
in O
Tg S-CHAR
with O
increased O
moisture O
content O
, O
which O
is O
consistent O
with O
plasticization O
. O


The O
absorption S-CONPRI
characteristics O
at O
room O
temperature S-PARA
lab O
conditions O
indicate O
that O
the O
material S-MATE
will O
reach O
an O
unacceptable O
level O
within O
one O
hour O
of O
room-temperature O
exposure S-CONPRI
. O


This O
investigation O
emphasized O
the O
need O
for O
awareness O
of O
the O
moisture O
sensitivities S-PARA
of O
ULTEM® O
9085 O
when O
manufacturing S-MANP
high-quality O
material B-MANP
extrusion E-MANP
processed O
structures O
. O


Stereolithography S-MANP
( O
SL S-MANP
) O
is O
an O
additive B-MANP
manufacturing E-MANP
technique O
that O
uses O
light O
to O
cure S-CONPRI
liquid O
resins S-MATE
into O
thin O
layers O
and O
fabricate S-MANP
3-dimensional O
objects O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
. O


SL S-MANP
is O
of O
high O
interest O
for O
small-volume O
manufacturing S-MANP
and O
rapid B-ENAT
prototyping E-ENAT
because O
of O
its O
ability O
to O
relatively O
quickly O
create O
objects O
with O
intricate O
100 O
μm O
or O
smaller O
features O
. O


However O
, O
widespread O
adoption O
of O
SL S-MANP
faces O
a O
number O
of O
obstacles O
including O
unsuitable O
thermomechanical B-CONPRI
properties E-CONPRI
, O
anisotropic S-PRO
properties O
, O
and O
limited O
resolution S-PARA
and O
fidelity O
. O


In O
this O
work O
, O
we O
incorporate O
a O
reversible O
addition-fragmentation O
chain O
transfer O
( O
RAFT S-MACEQ
) O
agent O
into O
a O
glassy O
acrylate O
formulation O
to O
modify O
mechanical B-CONPRI
properties E-CONPRI
and O
improve O
resolution S-PARA
of O
objects O
printed O
using O
digital B-MANP
light I-MANP
processing E-MANP
( O
DLP S-MANP
) O
SL S-MANP
. O


Incorporating O
a O
small O
amount O
of O
a O
trithiocarbonate O
RAFT S-MACEQ
agent O
into O
the O
formulation O
leads O
to O
increased O
elongation S-PRO
and O
toughness S-PRO
accompanied O
by O
a O
small O
decrease O
in O
tensile S-PRO
modulus O
. O


To O
determine O
anisotropic S-PRO
properties O
of O
DLP S-MANP
SL O
, O
samples S-CONPRI
were O
printed O
in O
“ O
horizontal O
” O
or O
“ O
vertical S-CONPRI
” O
directions O
, O
where O
the O
long O
axis O
of O
the O
sample S-CONPRI
was O
printed O
in O
the O
x-axis O
or O
z-axis S-CONPRI
, O
respectively O
. O


RAFT S-MACEQ
samples O
printed O
in O
a O
vertical B-CONPRI
orientation E-CONPRI
exhibit O
a O
higher O
modulus O
than O
non-RAFT O
controls O
prior O
to O
post-cure O
in O
addition O
to O
a O
similar O
modulus O
with O
increased O
toughness S-PRO
upon O
UV S-CONPRI
post-cure O
due O
to O
the O
living/controlled O
nature O
of O
RAFT S-MACEQ
polymerization S-MANP
. O


Furthermore O
, O
incorporating O
a O
RAFT S-MACEQ
agent O
into O
the O
formulation O
allows O
significantly O
higher O
fidelity O
printing O
of O
a O
broad O
range S-PARA
of O
positive O
and O
negative O
features O
as S-MATE
small O
as S-MATE
100 O
μm O
. O


The O
RAFT S-MACEQ
formulation O
allows O
objects O
to O
be S-MATE
printed O
with O
significantly O
better O
fidelity O
than O
non-RAFT O
formulations O
, O
even O
when O
a O
radical O
scavenger O
is O
incorporated O
to O
mimic S-MACEQ
reaction O
rates O
observed O
from O
the O
RAFT S-MACEQ
formulation O
. O


Additionally O
, O
the O
RAFT S-MACEQ
agent O
significantly O
increases O
the O
critical O
energy O
parameter S-CONPRI
determined O
from O
the O
SL S-MANP
working O
curve O
, O
indicating O
an O
increase O
in O
gel B-PRO
point E-PRO
conversion O
. O


This O
work O
demonstrates O
the O
benefits O
of O
using O
controlled/living O
polymerization S-MANP
in O
a O
highly O
cross-linked O
acrylate O
system O
to O
improve O
toughness S-PRO
, O
modify O
anisotropic S-PRO
properties O
, O
and O
print S-MANP
high-fidelity S-CONPRI
features O
with O
enhanced O
properties S-CONPRI
in O
3D B-MANP
printed E-MANP
materials O
. O


Support B-FEAT
structures E-FEAT
and O
materials S-CONPRI
are O
indispensable O
components S-MACEQ
in O
many O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
systems O
in O
order O
to O
fabricate S-MANP
complex O
3D B-CONPRI
structures E-CONPRI
. O


For O
inkjet-based O
AM B-MANP
techniques E-MANP
( O
known O
as S-MATE
Material O
Jetting S-MANP
) O
, O
there O
is O
a O
paucity O
of O
studies O
on O
specific O
inks O
for O
fabricating S-MANP
such O
support B-FEAT
structures E-FEAT
. O


This O
limits S-CONPRI
the O
potential O
of O
fabricating S-MANP
complex O
3D B-APPL
objects E-APPL
containing O
overhanging B-CONPRI
structures E-CONPRI
. O


In O
this O
paper O
, O
we O
investigate O
the O
use O
of O
Tripropylene O
Glycol O
Diacrylated O
( O
TPGDA O
) O
to O
prepare O
a O
thermally O
stable O
ink S-MATE
with O
reliable O
printability S-PARA
to O
produce O
removable O
support B-FEAT
structures E-FEAT
in O
an O
experimental S-CONPRI
Material O
Jetting S-MANP
system O
. O


The O
addition O
of O
TGME O
to O
the O
TPGDA O
was O
found O
to O
considerably O
reduce O
the O
modulus O
of O
the O
photocured O
structure S-CONPRI
from O
575 O
MPa S-CONPRI
down O
to O
27 O
MPa S-CONPRI
by O
forming S-MANP
micro-pores O
in O
the O
cured S-MANP
structure O
. O


The O
cured S-MANP
support O
structure S-CONPRI
was O
shown O
to O
be S-MATE
easily O
removed O
following O
the O
fabrication S-MANP
process O
. O


During O
TG-IR O
tests O
the O
T5 O
% O
temperature S-PARA
of O
the O
support B-FEAT
structure E-FEAT
was O
above O
150 O
°C O
whilst O
the O
majority O
of O
decomposition S-PRO
happened O
around O
400 O
°C O
. O


Specimens O
containing O
overhanging B-CONPRI
structures E-CONPRI
( O
gate-like O
structure S-CONPRI
, O
propeller O
structure S-CONPRI
) O
were O
successfully O
manufactured S-CONPRI
to O
highlight O
the O
viability O
of O
the O
ink S-MATE
as S-MATE
a O
support B-MATE
material E-MATE
. O


The O
potential O
of O
topology B-FEAT
optimization E-FEAT
to O
amplify O
the O
benefits O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
by O
fully O
exploiting O
the O
vast O
design B-CONPRI
space E-CONPRI
that O
AM S-MANP
allows O
, O
is O
widely O
recognized O
. O


However O
, O
existing O
topology B-FEAT
optimization E-FEAT
approaches O
do O
not O
consider O
AM-specific O
limitations O
during O
the O
design B-CONPRI
process E-CONPRI
, O
resulting O
in O
designs S-FEAT
that O
are O
not O
self-supporting S-FEAT
. O


This O
leads O
to O
additional O
effort O
and O
costs O
in O
post-processing S-CONPRI
and O
use O
of O
sacrificial O
support B-FEAT
structures E-FEAT
. O


To O
overcome O
this O
difficulty O
, O
this O
paper O
presents O
a O
topology B-FEAT
optimization E-FEAT
formulation O
that O
includes O
a O
simplified O
AM S-MANP
fabrication O
model S-CONPRI
implemented O
as S-MATE
a O
layerwise O
filtering O
procedure O
. O


Unprintable O
geometries S-CONPRI
are O
effectively O
excluded O
from O
the O
design B-CONPRI
space E-CONPRI
, O
resulting O
in O
fully O
self-supporting S-FEAT
optimized O
designs S-FEAT
. O


The O
procedure O
is O
demonstrated O
on O
numerical O
examples O
involving O
compliance O
minimization O
, O
eigenfrequency O
maximization O
and O
compliant B-CONPRI
mechanism E-CONPRI
design O
. O


Despite O
the O
applied O
restrictions O
, O
in O
suitable O
orientations S-CONPRI
fully O
printable O
AM-restrained O
designs S-FEAT
matched O
the O
performance S-CONPRI
of O
reference O
designs S-FEAT
obtained O
by O
conventional O
topology B-FEAT
optimization E-FEAT
. O


To O
enable O
the O
advancement O
of O
large-scale O
additive B-MANP
manufacturing I-MANP
processes E-MANP
, O
it O
is O
necessary O
to O
establish O
and O
standardize O
methodologies O
to O
characterize O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
printed O
test O
coupons O
. O


Due O
to O
the O
large O
size O
of O
the O
print S-MANP
beads S-CHAR
, O
conventional O
test O
standards S-CONPRI
are O
inadequate O
. O


The O
focus O
of O
this O
study O
was O
to O
determine O
the O
feasibility S-CONPRI
of O
using O
Digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
( O
DIC S-CONPRI
) O
technology S-CONPRI
as S-MATE
a O
key O
enabler O
for O
robust O
data S-CONPRI
collection O
of O
strain S-PRO
measurements O
of O
large O
3D B-APPL
printed I-APPL
parts E-APPL
. O


) O
glass S-MATE
filled O
ABS S-MATE
test O
coupons O
for O
adequate O
contrast O
. O


Through O
this O
technique O
, O
Poisson O
's O
ratio O
and O
elastic B-PRO
modulus E-PRO
were O
measured O
and O
stress B-CONPRI
strain I-CONPRI
curves E-CONPRI
were O
generated O
. O


The O
data S-CONPRI
produced O
by O
DIC B-CONPRI
correlated E-CONPRI
well O
with O
failure S-CONPRI
analysis O
performed O
on O
spent O
test O
coupons O
. O


Additionally O
, O
fracture S-CONPRI
surface O
analysis O
of O
the O
specimens O
revealed O
poor O
adhesion S-PRO
among O
the O
ABS B-MATE
matrix E-MATE
and O
glass B-MATE
fibers E-MATE
. O


This O
matrix/fiber O
debonding O
demonstrated O
the O
need O
for O
improved O
printing O
parameters S-CONPRI
to O
maximize O
tensile B-PRO
strength E-PRO
. O


Finally O
, O
critical O
length O
analysis O
of O
the O
fibers S-MATE
revealed O
them O
to O
be S-MATE
dimensionally O
inadequate O
. O


In O
this O
work O
, O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
was O
reinforced S-CONPRI
with O
a O
thermotropic B-MATE
liquid I-MATE
crystalline I-MATE
polymer E-MATE
( O
TLCP O
) O
for O
use O
in O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
. O


As S-MATE
ABS S-MATE
and O
the O
selected O
TLCP O
do O
not O
exhibit O
overlapping O
processing O
temperatures S-PARA
, O
the O
composite S-MATE
filaments O
were O
generated O
using O
a O
dual O
extrusion S-MANP
technology O
which O
allows O
processing O
of O
such O
matrix-TLCP O
combinations O
. O


The O
40.0 O
wt. O
% O
TLCP/ABS O
filaments S-MATE
exhibited O
a O
tensile B-PRO
strength E-PRO
and O
modulus O
of O
169.2 O
± O
4.0 O
MPa S-CONPRI
and O
39.9 O
± O
3.7 O
GPa S-PRO
, O
respectively O
, O
due O
to O
a O
nearly O
continuous O
reinforcement S-PARA
of O
the O
filament S-MATE
. O


The O
postprocessing S-CONPRI
of O
the O
filaments S-MATE
in O
FFF S-MANP
was O
carried O
out O
below O
the O
melting B-PARA
temperature E-PARA
of O
the O
TLCP O
, O
which O
allowed O
the O
printer S-MACEQ
to O
take O
sharp O
turns O
despite O
having O
nearly O
continuous O
reinforcement S-PARA
. O


On O
printing O
with O
the O
40.0 O
wt. O
% O
TLCP/ABS O
filaments S-MATE
, O
the O
tensile B-PRO
strength E-PRO
and O
modulus O
in O
the O
print S-MANP
direction O
were O
74.9 O
± O
2.4 O
MPa S-CONPRI
and O
16.5 O
± O
0.8 O
GPa S-PRO
, O
respectively O
. O


The O
compression S-PRO
molded O
specimens O
exhibited O
a O
tensile B-PRO
strength E-PRO
and O
modulus O
of O
79.6 O
± O
4.4 O
MPa S-CONPRI
and O
12.3 O
± O
1.2 O
GPa S-PRO
, O
respectively O
, O
whereas O
the O
injection O
molded O
specimens O
exhibited O
51.3 O
± O
3.0 O
MPa S-CONPRI
and O
4.5 O
± O
0.1 O
GPa S-PRO
, O
respectively O
. O


Moisture O
absorption S-CONPRI
degrades O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
polymeric O
parts O
that O
are O
3D-printed S-MANP
by O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
. O


This O
limitation O
is O
particularly O
significant O
for O
short O
fiber-reinforced O
polymers S-MATE
because O
the O
mechanical S-APPL
enhancement O
obtained O
by O
the O
fiber B-FEAT
reinforcement E-FEAT
can O
be S-MATE
compromised O
by O
the O
plasticizing O
effect O
introduced O
by O
water O
absorption S-CONPRI
. O


Therefore O
, O
the O
present O
work O
investigates S-CONPRI
the O
effects O
of O
two O
different O
coatings S-APPL
, O
a O
UV B-CONPRI
cured E-CONPRI
acrylate O
resin S-MATE
and O
an O
acrylic S-MATE
varnish O
, O
on O
the O
moisture O
absorption S-CONPRI
of O
FFF B-MANP
3D-printed E-MANP
samples O
consisting O
of O
polyamide S-MATE
reinforced O
by O
short B-MATE
carbon I-MATE
fibers E-MATE
. O


The O
coating S-APPL
effects O
were O
evaluated O
by O
conducting O
tensile B-CHAR
tests E-CHAR
to O
compare O
the O
Young O
’ O
s S-MATE
modulus O
, O
yield B-PRO
stress E-PRO
, O
and O
ultimate O
stress S-PRO
of O
the O
coated S-APPL
and O
uncoated O
specimens O
. O


The O
results O
demonstrated O
a O
significant O
reduction S-CONPRI
of O
CI S-MATE
and O
OP O
with O
both O
the O
acrylic S-MATE
and O
UV S-CONPRI
resin B-MATE
coatings E-MATE
, O
as S-MATE
well O
as S-MATE
considerable O
enhancements O
of O
these O
samples S-CONPRI
’ O
mechanical B-CONPRI
properties E-CONPRI
. O


Stress-strain O
curves O
evidenced O
a O
strain S-PRO
reduction S-CONPRI
after O
water O
immersion O
, O
which O
can O
be S-MATE
ascribed O
to O
a O
greater O
stability S-PRO
against O
different O
moisture O
conditions O
. O


These O
findings O
indicate O
the O
significant O
potential O
of O
the O
proposed O
coating S-APPL
processes O
to O
extend O
the O
use O
of O
FFF B-MANP
3D-printed E-MANP
composite B-MATE
materials E-MATE
to O
a O
broader O
range S-PARA
of O
applications O
. O


In O
this O
paper O
, O
the O
effects O
of O
part O
build B-PARA
directions E-PARA
or O
raster B-PARA
orientations E-PARA
have O
been O
studied O
on O
the O
strain-life O
fatigue S-PRO
parameters O
of O
a O
wide O
range S-PARA
of O
3D B-MANP
printed E-MANP
plastic O
materials S-CONPRI
. O


These O
materials S-CONPRI
have O
been O
manufactured S-CONPRI
through O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
, O
also O
known O
under O
its O
trademarked O
name O
Fused B-MANP
Deposition I-MANP
Modeling E-MANP
( O
FDM S-MANP
) O
. O


To O
do O
so O
, O
precise O
analyses O
of O
fatigue S-PRO
data S-CONPRI
with O
the O
Ramberg-Osgood O
form O
of O
stress-strain O
curves O
were O
utilized O
through O
a O
strain-based O
approach O
to O
fatigue S-PRO
. O


Materials S-CONPRI
considered O
in O
this O
study O
were O
Ultem O
9085 O
, O
Polycarbonate S-MATE
( O
PC S-MATE
) O
, O
and O
Polylactic B-MATE
Acid E-MATE
( O
PLA S-MATE
) O
. O


Additive B-MANP
manufactured E-MANP
plastic O
parts O
that O
are O
FDM-processed O
exhibited O
large O
anisotropy S-PRO
of O
strain-life O
fatigue S-PRO
parameters O
. O


Hence O
, O
the O
upper O
and O
lower O
bounds O
for O
fatigue B-PRO
life E-PRO
prediction O
were O
introduced O
based O
on O
the O
strongest O
and O
weakest O
part O
build B-PARA
directions E-PARA
or O
raster B-PARA
orientations E-PARA
of O
3D B-MANP
printed E-MANP
materials O
. O


For O
all O
materials S-CONPRI
studied O
in O
the O
present O
paper O
, O
fill O
densities O
, O
which O
seem O
to O
have O
significant O
impact S-CONPRI
on O
fatigue B-PRO
strength E-PRO
of O
3D B-APPL
printed I-APPL
parts E-APPL
, O
have O
been O
selected O
based O
on O
the O
maximum O
fatigue B-PRO
strength E-PRO
of O
each O
part O
. O


Results O
showed O
that O
, O
in O
some O
build B-PARA
orientations E-PARA
, O
the O
transition S-CONPRI
fatigue B-PRO
life E-PRO
does O
not O
exist O
. O


In O
other O
orientations S-CONPRI
, O
in O
which O
the O
plastic S-MATE
strain O
components S-MACEQ
are O
high O
enough O
, O
transition S-CONPRI
fatigue B-PRO
lives E-PRO
vary O
roughly O
between O
20–400 O
cycles O
. O


This O
means O
that O
if O
the O
part O
design S-FEAT
in O
very O
low O
cycle O
fatigue S-PRO
regime O
is O
of O
interest O
, O
plastic S-MATE
strains O
and O
more O
complicated O
plasticity S-PRO
analysis O
are O
needed O
. O


Results O
show O
that O
the O
load O
ratio O
has O
no O
major O
impact S-CONPRI
on O
the O
fatigue S-PRO
parameters O
of O
3D B-MANP
printed E-MANP
PC O
parts O
. O


In O
addition O
, O
changing O
in O
the O
loading O
type O
from O
tensile B-PRO
fatigue E-PRO
to O
rotating O
bending S-MANP
fatigue O
can O
significantly O
impact S-CONPRI
the O
fatigue B-PRO
strength E-PRO
coefficient O
of O
3D B-MANP
printed E-MANP
PLA O
specimens O
however O
, O
it O
does O
not O
noticeably O
alter O
the O
fatigue B-PRO
strength E-PRO
exponents O
. O


Material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
utilizes O
a O
thermoplastic B-MATE
polymer E-MATE
in O
the O
form O
of O
a O
solid O
filament S-MATE
as S-MATE
a O
built O
material S-MATE
. O


The O
polymer B-MATE
melts E-MATE
inside O
the O
hot-end O
channel S-APPL
and O
flows O
under O
the O
pressure S-CONPRI
generated O
by O
the O
filament S-MATE
feeding O
force S-CONPRI
. O


The O
flow O
of O
polymer S-MATE
through O
the O
hot-end O
is O
not O
fully O
understood O
yet O
, O
as S-MATE
it O
involves O
many O
complex O
phenomena O
, O
such O
as S-MATE
phase O
transition S-CONPRI
, O
shear O
rate O
and O
temperature S-PARA
dependent O
viscosity S-PRO
, O
as S-MATE
well O
as S-MATE
viscoelastic O
effects O
. O


In O
this O
paper O
, O
we O
investigate O
experimentally O
the O
filament S-MATE
feeding O
force S-CONPRI
, O
as S-MATE
a O
function O
of O
the O
feeding O
rate O
, O
for O
different O
materials S-CONPRI
( O
PLA S-MATE
and O
ABS S-MATE
) O
, O
liquefier O
temperatures S-PARA
, O
nozzle B-CONPRI
diameters E-CONPRI
, O
and O
lengths O
of O
the O
liquefier O
. O


Increasing O
the O
liquefier O
length O
and O
liquefier O
temperature S-PARA
are O
found O
to O
extend O
the O
linear O
extrusion S-MANP
regime O
. O


A O
model S-CONPRI
solely O
based O
on O
heat B-CONPRI
transfer E-CONPRI
considerations O
is O
proposed O
to O
estimate O
the O
maximum O
feeding O
rate O
before O
the O
extrusion S-MANP
becomes O
unstable O
. O


The O
modelling S-ENAT
results O
agree O
well O
with O
the O
measurements O
. O


The O
model S-CONPRI
can O
be S-MATE
used O
to O
select O
the O
hot-end O
design S-FEAT
as S-MATE
well O
as S-MATE
appropriate O
printing O
parameters S-CONPRI
. O


This O
paper O
details O
a O
novel O
study O
and O
manufacturing B-MANP
approach E-MANP
of O
fiber B-FEAT
alignment E-FEAT
in O
flexible O
hybrid O
carbon B-MATE
fiber E-MATE
composites O
using O
Material B-MANP
extrusion E-MANP
. O


Varying O
carbon B-MATE
fiber E-MATE
volume O
fractions O
from O
0 O
to O
4 O
vol O
% O
was O
melt S-CONPRI
blended O
with O
a O
masterbatch O
of O
TPU O
+ O
10 O
wt O
% O
MWCNT O
followed O
by O
extrusion S-MANP
. O


The O
final O
extrudate S-MATE
was O
then O
filament S-MATE
wound O
onto O
a O
spool S-MACEQ
and O
two O
different O
filament S-MATE
layout O
orientations S-CONPRI
, O
0° O
and O
45° O
, O
were O
printed O
to O
compare O
their O
mechanical B-CONPRI
properties E-CONPRI
to O
validate O
the O
effect O
of O
fiber B-FEAT
alignment E-FEAT
during O
the O
printing B-MANP
process E-MANP
for O
these O
flexible O
fiber B-MATE
composites E-MATE
. O


The O
0° O
printed O
composites S-MATE
exhibited O
up O
to O
34 O
% O
improvement O
in O
stiffness S-PRO
as S-MATE
compared O
to O
the O
45° O
composite S-MATE
. O


To O
validate O
this O
fiber B-FEAT
orientation E-FEAT
, O
the O
flexible O
composite S-MATE
was O
textured O
using O
fiber-debonding O
and O
pullout O
phenomenon O
and O
the O
surfaces S-CONPRI
were O
visually O
and O
quantifiably O
characterized O
using O
SEM S-CHAR
images S-CONPRI
and O
surface B-PRO
roughness E-PRO
respectively O
. O


To O
further O
elucidate O
the O
fiber B-FEAT
alignment E-FEAT
as S-MATE
indicated O
by O
the O
surface B-PRO
roughness E-PRO
, O
a O
water O
contact S-APPL
angle O
hydrophobicity O
test O
was O
conducted O
to O
prove O
that O
the O
0° O
printed O
composite S-MATE
showed O
higher O
contact S-APPL
angle O
as S-MATE
compared O
with O
the O
45° O
orientation S-CONPRI
, O
confirming O
greater O
entrapment O
due O
to O
fiber B-FEAT
alignment E-FEAT
at O
the O
surface S-CONPRI
. O


These O
composites S-MATE
are O
expected O
to O
find O
future O
potential O
in O
high O
strength S-PRO
and O
surface B-MANP
texturing E-MANP
applications O
. O


Conventional O
material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
is O
capable O
of O
building O
complex B-CONPRI
structures E-CONPRI
. O


Overhanging B-FEAT
features E-FEAT
require O
the O
use O
of O
support B-FEAT
structures E-FEAT
. O


Printing O
the O
support B-FEAT
structure E-FEAT
requires O
additional O
time O
and O
material S-MATE
. O


Conventional O
processes S-CONPRI
need O
time O
to O
remove O
support B-MATE
material E-MATE
and O
may O
lead S-MATE
to O
degraded O
surface B-FEAT
finish E-FEAT
. O


The O
use O
of O
support B-FEAT
structures E-FEAT
can O
be S-MATE
avoided O
by O
dynamically O
reorienting O
the O
build-platform O
. O


This O
paper O
presents O
a O
novel O
approach O
to O
build S-PARA
accurate S-CHAR
thin O
shell S-MACEQ
parts O
using O
supportless O
extrusion-based O
additive B-MANP
manufacturing E-MANP
. O


We O
describe O
the O
layer S-PARA
slicing O
algorithm S-CONPRI
, O
the O
tool-path S-PARA
planning S-MANP
algorithm S-CONPRI
, O
and O
the O
neural O
network-based O
compensated O
trajectory O
generation O
scheme O
to O
use O
a O
3 O
degree O
of O
freedom O
build-platform O
and O
a O
3 O
degree O
of O
freedom O
extrusion S-MANP
tool O
to O
build S-PARA
accurate S-CHAR
thin O
shell S-MACEQ
parts O
using O
two O
manipulators S-MACEQ
. O


Such O
thin O
shell S-MACEQ
parts O
can O
not O
be S-MATE
built O
without O
supports S-APPL
by O
previous O
supportless O
AM B-MANP
processes E-MANP
. O


We O
illustrate O
the O
usefulness O
of O
our O
algorithms S-CONPRI
by O
building O
several O
thin O
shell S-MACEQ
parts O
. O


Material B-MANP
extrusion E-MANP
( O
MEX O
) O
is O
a O
well O
established O
production S-MANP
method O
in O
additive B-MANP
manufacturing E-MANP
. O


However O
, O
internal O
residual S-CONPRI
strains O
are O
accumulated O
during O
the O
layer-by-layer S-CONPRI
fabrication S-MANP
process O
. O


They O
bring O
about O
shape O
distortions O
and O
a O
degradation S-CONPRI
of O
mechanical B-CONPRI
properties E-CONPRI
. O


In O
this O
paper O
, O
an O
in-situ S-CONPRI
distributed O
measurement S-CHAR
of O
residual S-CONPRI
strains O
in O
MEX O
fabricated S-CONPRI
thermoplastic O
specimens O
is O
achieved O
for O
the O
first O
time O
. O


This O
innovative O
measuring O
system O
consists O
of O
an O
Optical S-CHAR
Backscatter O
Reflectometry O
( O
OBR O
) O
interrogation O
unit O
connected O
to O
a O
distributed O
fiber S-MATE
optic O
strain S-PRO
sensor S-MACEQ
which O
is O
embedded O
during O
the O
MEX O
process S-CONPRI
. O


The O
characteristic O
residual S-CONPRI
strain O
distribution S-CONPRI
inside O
3D B-MANP
printed E-MANP
components O
is O
revealed O
and O
numerically O
validated O
. O


The O
main O
mechanisms O
of O
residual S-CONPRI
strain O
creation O
and O
the O
sensing S-APPL
principles O
of O
in-situ S-CONPRI
OBR O
are O
described O
. O


A O
minimum O
measuring O
range S-PARA
of O
4 O
mm S-MANP
and O
a O
spatial O
resolution S-PARA
of O
0.15 O
mm S-MANP
were O
experimentally O
demonstrated O
. O


The O
potential O
of O
in-situ S-CONPRI
OBR O
technology S-CONPRI
for O
detecting O
invisible O
manufacturing S-MANP
defects S-CONPRI
was O
shown O
by O
a O
trial O
experiment S-CONPRI
. O


To O
aid O
in O
the O
transition S-CONPRI
of O
3D B-APPL
printed I-APPL
parts E-APPL
from O
prototypes S-CONPRI
to O
functional O
products O
it O
is O
necessary O
to O
investigate O
the O
mechanical B-PRO
anisotropy E-PRO
induced O
by O
the O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
process S-CONPRI
. O


Since O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
an O
FFF S-MANP
part O
are O
most O
greatly O
affected O
by O
the O
bead S-CHAR
orientation O
and O
printed O
density S-PRO
, O
or O
solidity O
ratio O
, O
techniques O
to O
precisely O
control O
these O
variables O
are O
required O
. O


An O
open O
source S-APPL
Python O
program O
, O
SciSlice O
, O
was O
developed O
to O
create O
the O
desired O
tool S-MACEQ
paths/layer O
orientations S-CONPRI
and O
convert O
them O
into O
machine S-MACEQ
commands O
( O
e.g O
. O


G-Code S-ENAT
) O
. O


SciSlice O
was O
then O
used O
to O
develop O
tool B-CONPRI
paths E-CONPRI
which O
either O
directly O
printed O
tensile B-MACEQ
specimens E-MACEQ
or O
printed O
sheets S-MATE
from O
which O
specimens O
could O
be S-MATE
water-jet O
cut O
. O


The O
effects O
of O
proper O
bed S-MACEQ
leveling O
and O
feed S-PARA
wheel O
adjustment O
are O
noted O
and O
a O
careful O
analysis O
of O
both O
bead S-CHAR
orientation O
and O
solidity O
ratio O
are O
presented O
. O


Finally O
, O
it O
is O
shown O
that O
with O
proper O
bead S-CHAR
orientation O
, O
low O
layer B-PARA
heights E-PARA
, O
and O
a O
maximum O
solidity O
ratio O
, O
tensile B-PRO
strengths E-PRO
within O
3 O
% O
of O
injection O
molded O
parts O
are O
achievable O
. O


In O
this O
paper O
the O
authors O
present O
a O
novel O
design S-FEAT
tool O
for O
realizing O
dielectric S-MACEQ
structures O
with O
spatially O
varying O
electromagnetic O
properties S-CONPRI
via O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
. O


To O
create O
tool B-CONPRI
paths E-CONPRI
ideal O
for O
AM B-MANP
processes E-MANP
, O
space-filling O
curves O
were O
utilized O
. O


Using O
fused B-MANP
deposition I-MANP
modeling E-MANP
( O
FDM S-MANP
) O
, O
spatially O
varying O
structures O
were O
printed O
that O
produced O
a O
spatially O
varying O
relative O
permittivity O
. O


Furthermore O
, O
the O
authors O
verified O
that O
this O
design S-FEAT
tool O
can O
be S-MATE
applied O
to O
practical O
structures O
by O
designing O
, O
printing O
and O
testing S-CHAR
a O
gradient O
index O
flat O
lens S-MANP
. O


Strain-rate O
dependence O
is O
anisotropic S-PRO
in O
Material B-MANP
Extrusion I-MANP
Additive I-MANP
Manufacturing E-MANP
. O


Strain-rate O
dependence O
in O
ME-AM S-MANP
is O
different O
from O
compression S-PRO
molded O
products O
. O


Ree-Eyring O
flow O
rule O
can O
adequately O
describe O
the O
yield O
kinetics O
of O
ME-AM S-MANP
components S-MACEQ
. O


Compression S-PRO
molded O
samples S-CONPRI
show O
brittle S-PRO
stress-strain O
behavior O
. O


Several O
ME-AM S-MANP
samples O
show O
semi-ductile O
stress-strain O
behavior O
. O


The O
strain-rate O
dependence O
of O
the O
yield B-PRO
stress E-PRO
for O
Material B-MANP
Extrusion I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
ME-AM S-MANP
) O
polylactide O
samples S-CONPRI
was O
investigated O
. O


Apparent O
densities O
of O
the O
ME-AM S-MANP
processed O
tensile B-CHAR
test E-CHAR
specimens O
were O
measured O
and O
taken O
into O
account O
in O
order O
to O
study O
the O
effects O
of O
the O
ME-AM S-MANP
processing O
step S-CONPRI
on O
the O
material S-MATE
behavior O
. O


Three O
different O
printing O
parameters S-CONPRI
were O
changed O
to O
investigate O
their O
influence O
on O
mechanical B-CONPRI
properties E-CONPRI
, O
i.e O
. O


infill S-PARA
velocity O
, O
infill S-PARA
orientation O
angle O
, O
and O
bed S-MACEQ
temperature O
. O


Additionally O
, O
compression S-PRO
molded O
test O
samples S-CONPRI
were O
manufactured S-CONPRI
in O
order O
to O
determine O
bulk O
properties S-CONPRI
, O
which O
have O
been O
compared O
to O
the O
ME-AM S-MANP
sample O
sets O
. O


Anisotropy S-PRO
was O
detected O
in O
the O
strain-rate O
dependence O
of O
the O
yield B-PRO
stresses E-PRO
. O


The O
Ree-Eyring O
modification O
of O
the O
Eyring O
flow O
rule O
is O
able O
to O
accurately S-CHAR
describe O
the O
strain-rate O
dependence O
of O
the O
yield B-PRO
stresses E-PRO
, O
taking O
two O
molecular O
deformation S-CONPRI
processes O
into O
account O
to O
describe O
the O
yield O
kinetics O
. O


The O
results O
from O
this O
paper O
further O
show O
a O
change O
from O
a O
brittle S-PRO
behavior O
in O
case O
of O
compression S-PRO
molded O
samples S-CONPRI
to O
a O
semi-ductile O
behavior O
for O
some O
of O
the O
ME-AM S-MANP
sample O
sets O
. O


This O
change O
is O
attributed O
to O
the O
processing O
phase S-CONPRI
and O
stresses O
the O
importance O
that O
the O
temperature S-PARA
profile S-FEAT
( O
initial O
fast O
cooling S-MANP
combined O
with O
successive O
heating S-MANP
cycles O
) O
and O
the O
strain S-PRO
profile S-FEAT
during O
ME-AM S-MANP
processing O
have O
on O
the O
resulting O
mechanical B-CONPRI
properties E-CONPRI
. O


Both O
these O
profiles S-FEAT
are O
significantly O
different O
from O
the O
thermo-mechanical S-CONPRI
history O
that O
material B-MATE
elements E-MATE
experience O
during O
conventional O
processing O
methods O
, O
e.g O
. O


injection O
or O
compression B-MANP
molding E-MANP
. O


This O
paper O
can O
be S-MATE
seen O
as S-MATE
initial O
work O
that O
can O
help O
to O
further O
develop O
predictive O
numerical O
tools S-MACEQ
for O
Material B-MANP
Extrusion I-MANP
Additive I-MANP
Manufacturing E-MANP
, O
as S-MATE
well O
as S-MATE
for O
the O
design S-FEAT
of O
structural B-CONPRI
components E-CONPRI
. O


This O
study O
investigates S-CONPRI
the O
suitability O
of O
direct O
write O
( O
DW O
) O
technology S-CONPRI
for O
the O
fabrication S-MANP
of O
high-resolution S-PARA
wear O
sensors S-MACEQ
. O


The O
sintered S-MANP
lines O
exhibited O
an O
electrical B-CHAR
resistivity E-CHAR
of O
5.29 O
× O
10−8 O
Ω O
m O
( O
about O
three O
times O
bulk O
silver S-MATE
resistivity S-PRO
reported O
in O
the O
literature O
) O
with O
a O
standard B-CHAR
deviation E-CHAR
of O
3.68 O
× O
10-9 O
Ω O
m O
( O
ca S-MATE
. O


7 O
% O
variation S-CONPRI
) O
. O


To O
determine O
the O
conditions O
needed O
to O
consistently O
create O
fine O
conductive O
lines O
, O
we O
simulated O
the O
volumetric O
flow B-PARA
rate E-PARA
and O
analyzed O
the O
effects O
on O
line O
geometry S-CONPRI
of O
several O
printing O
parameters S-CONPRI
including O
valve O
opening O
, O
dispensing O
gap O
, O
and O
substrate S-MATE
translation O
speed O
. O


Our O
results O
indicate O
decreasing O
the O
valve O
opening O
, O
decreasing O
the O
dispensing O
gap O
, O
and/or O
increasing O
the O
translation B-PARA
speed E-PARA
of O
the O
substrate S-MATE
reduces O
the O
resultant O
printing O
flow B-PARA
rate E-PARA
and O
cross-sectional O
area S-PARA
of O
DW O
lines O
. O


Comprehensive O
mechanical B-CHAR
tests E-CHAR
are O
carried O
out O
on O
two O
new O
PolyJet S-CONPRI
elastomers S-MATE
. O


The O
stress-strain O
response O
of O
PolyJet S-CONPRI
elastomers S-MATE
is O
highly O
sensitive O
to O
strain B-CONPRI
rate E-CONPRI
. O


A O
visco-hyperelastic O
material S-MATE
model O
captures O
the O
strain B-PRO
rate I-PRO
sensitivity E-PRO
of O
the O
elastomers S-MATE
. O


The O
elastomers S-MATE
fully O
recover O
after O
20 O
s S-MATE
after O
repeated O
cyclic B-PRO
loading E-PRO
. O


Anisotropy S-PRO
in O
the O
elastomers S-MATE
is O
dependent O
on O
strain S-PRO
and O
strain B-CONPRI
rate E-CONPRI
. O


Material B-MANP
jetting E-MANP
, O
particularly O
PolyJet S-CONPRI
technology O
, O
is O
an O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
which O
has O
introduced O
novel O
flexible O
elastomers S-MATE
used O
in O
bio-inspired S-CONPRI
soft O
robots S-MACEQ
, O
compliant O
structures O
and O
dampers O
. O


Finite B-CONPRI
Element I-CONPRI
Analysis E-CONPRI
( O
FEA O
) O
is O
a O
key O
tool S-MACEQ
for O
the O
development O
of O
such O
applications O
, O
which O
requires O
comprehensive O
material S-MATE
characterisation O
utilising O
advanced O
material S-MATE
models O
. O


However O
, O
in O
contrast O
to O
conventional O
rubbers S-MATE
, O
PolyJet S-CONPRI
elastomers S-MATE
have O
been O
less O
explored O
leading O
to O
a O
few O
material S-MATE
models O
with O
various O
limitations O
in O
fidelity O
. O


Therefore O
, O
one O
aim O
of O
this O
study O
was O
to O
characterise O
the O
mechanical B-CONPRI
response E-CONPRI
of O
the O
latest O
PolyJet S-CONPRI
elastomers S-MATE
, O
Agilus30 O
( O
A30 O
) O
and O
Tango+ O
( O
T+ O
) O
, O
under O
large O
strain S-PRO
tension-compression O
and O
time-dependent O
high-frequency/relaxation O
loadings O
. O


Another O
aim O
was O
to O
calibrate O
a O
visco-hyperelastic O
material S-MATE
model O
to O
accurately S-CHAR
predict O
these O
responses O
. O


Tensile S-PRO
, O
compressive O
, O
cyclic O
, O
dynamic B-CONPRI
mechanical I-CONPRI
analysis E-CONPRI
( O
DMA S-CONPRI
) O
and O
stress B-CONPRI
relaxation E-CONPRI
tests O
were O
carried O
out O
on O
pristine O
A30 O
and O
T+ O
samples S-CONPRI
. O


Quasi-static S-CONPRI
tension-compression O
tests O
were O
used O
to O
calibrate O
a O
3-term O
Ogden O
hyperelastic O
model S-CONPRI
. O


Stress B-CONPRI
relaxation E-CONPRI
and O
DMA S-CONPRI
results O
were O
combined O
to O
determine O
the O
constants O
of O
a O
5-term O
Prony O
series O
across O
a O
large O
window O
of O
relaxation O
time O
( O
10 O
μs–100 O
s S-MATE
) O
. O


A O
numerical O
time-stepping O
scheme O
was O
employed O
to O
predict O
the O
visco-hyperelastic O
response O
of O
the O
3D-printed S-MANP
elastomers O
at O
large O
strains O
and O
different O
strain B-CONPRI
rates E-CONPRI
. O


In O
addition O
, O
the O
anisotropy S-PRO
in O
the O
elastomers S-MATE
, O
which O
stemmed O
from O
build B-PARA
orientation E-PARA
, O
was O
explored O
. O


Highly O
nonlinear O
stress-strain O
relationships O
were O
observed O
in O
both O
elastomers S-MATE
, O
with O
a O
strong O
dependency O
on O
strain B-CONPRI
rate E-CONPRI
. O


Relaxation O
tests O
revealed O
that O
A30 O
and O
T+ O
elastomers S-MATE
relax O
to O
50 O
% O
and O
70 O
% O
of O
their O
peak O
stress S-PRO
values O
respectively O
in O
less O
than O
20 O
s. O
The O
effect O
of O
orientation S-CONPRI
on O
the O
loading O
response O
was O
most O
pronounced O
with O
prints O
along O
the O
Z-direction S-FEAT
, O
particularly O
at O
large O
strains O
and O
lower O
strain B-CONPRI
rates E-CONPRI
. O


Moreover O
, O
the O
visco-hyperelastic O
material S-MATE
model O
accurately S-CHAR
predicted O
the O
large O
strain S-PRO
and O
time-dependent O
behaviour O
of O
both O
elastomers S-MATE
. O


Our O
findings O
will O
allow O
for O
the O
development O
of O
more O
accurate S-CHAR
computational O
models O
of O
3D-printed S-MANP
elastomers O
, O
which O
can O
be S-MATE
utilised O
for O
computer-aided B-ENAT
design E-ENAT
in O
novel O
applications O
requiring O
flexible O
or O
rate-sensitive O
AM B-MATE
materials E-MATE
. O


Measures O
thermal B-PRO
conductivity E-PRO
of O
additively B-MANP
manufactured E-MANP
components O
. O


Demonstrates O
significant O
direction-dependence O
of O
thermal B-PRO
conductivity E-PRO
. O


Demonstrates O
significant O
effect O
of O
process B-CONPRI
parameters E-CONPRI
. O


Results O
may O
be S-MATE
helpful O
in O
design S-FEAT
of O
3D-printed S-MANP
heat O
transfer O
components S-MACEQ
. O


Additive B-MANP
manufacturing E-MANP
, O
or O
3D B-MANP
printing E-MANP
, O
is O
an O
exciting O
manufacturing S-MANP
technique O
based O
on O
layer-by-layer S-CONPRI
build-up O
as S-MATE
opposed O
to O
the O
subtractive S-MANP
approach O
in O
most O
traditional O
machining S-MANP
processes O
. O


Specifically O
, O
in O
polymer-based O
additive B-MANP
manufacturing I-MANP
processes E-MANP
, O
filaments S-MATE
of O
a O
polymer S-MATE
are O
dispensed O
from O
a O
rastering O
extruder S-MACEQ
to O
define O
each O
layer S-PARA
. O


Due O
to O
the O
directional O
nature O
of O
this O
process S-CONPRI
, O
it O
is O
of O
interest O
to O
determine O
whether O
thermal O
transport S-CHAR
properties S-CONPRI
of O
the O
built O
part O
are O
direction O
dependent O
. O


Such O
an O
understanding O
is O
critical O
for O
accurate S-CHAR
design O
of O
components S-MACEQ
that O
serve O
a O
thermal O
function O
. O


This O
paper O
reports O
measurement S-CHAR
of O
thermal B-PRO
conductivity E-PRO
of O
additively B-MANP
manufactured E-MANP
polymer O
samples S-CONPRI
in O
the O
filament S-MATE
rastering O
direction O
and O
in O
the O
build B-PARA
direction E-PARA
. O


Samples S-CONPRI
are O
designed S-FEAT
and O
built O
in O
order O
to O
force S-CONPRI
heat O
flow O
only O
in O
one O
direction O
during O
thermal B-CONPRI
property E-CONPRI
measurement S-CHAR
. O


Experimental B-CONPRI
data E-CONPRI
indicate O
significant O
anisotropy S-PRO
in O
thermal B-PRO
conductivity E-PRO
, O
with O
the O
value O
in O
the O
build B-PARA
direction E-PARA
being O
much O
lower O
than O
in O
the O
raster O
direction O
. O


Both O
thermal B-PRO
conductivities E-PRO
are O
found O
to O
depend O
strongly O
on O
the O
air O
gap O
between O
adjacent O
filaments S-MATE
. O


A O
theoretical S-CONPRI
thermal O
conduction O
model S-CONPRI
is O
found O
to O
be S-MATE
in O
good O
agreement O
with O
experimental B-CONPRI
data E-CONPRI
. O


Cross B-CONPRI
section E-CONPRI
images O
of O
samples S-CONPRI
confirm O
the O
strong O
effect O
of O
the O
gap O
on O
the O
microstructure S-CONPRI
, O
and O
hence O
on O
thermal B-CONPRI
properties E-CONPRI
. O


Results O
from O
this O
paper O
provide O
a O
key O
insight O
into O
the O
anisotropic S-PRO
nature O
of O
thermal O
conduction O
in O
additively B-MANP
manufactured E-MANP
components O
, O
and O
establish O
the O
presence O
of O
significant O
inter-layer O
thermal O
contact S-APPL
resistance O
. O


These O
results O
may O
be S-MATE
helpful O
in O
the O
fundamental O
understanding O
of O
heat B-CONPRI
transfer E-CONPRI
in O
3D-printed S-MANP
components O
, O
as S-MATE
well O
as S-MATE
in O
accurate S-CHAR
design O
and O
fabrication S-MANP
of O
heat B-CONPRI
transfer E-CONPRI
components S-MACEQ
through O
3D B-MANP
printing E-MANP
. O


A O
computational B-CHAR
fluid I-CHAR
dynamics E-CHAR
model O
is O
used O
to O
predict O
the O
mesostructure O
formed O
by O
the O
successive O
deposition S-CONPRI
of O
parallel O
strands O
in O
material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
. O


The O
numerical O
model S-CONPRI
simulates O
the O
extrusion S-MANP
of O
the O
material S-MATE
onto O
the O
substrate S-MATE
. O


The O
simulated O
mesostructures O
are O
compared O
to O
optical S-CHAR
micrographs O
of O
the O
mesostructures O
of O
3D-printed S-MANP
samples O
, O
and O
the O
predictions S-CONPRI
agree O
well O
with O
the O
experiments O
. O


In O
addition O
, O
the O
influence O
of O
the O
layer B-PARA
thickness E-PARA
, O
the O
strand-to-strand O
distance O
, O
and O
the O
deposition B-CONPRI
configuration E-CONPRI
( O
with O
aligned O
or O
skewed O
layers O
) O
on O
the O
formation O
of O
the O
mesostructure O
is O
investigated O
. O


The O
simulations S-ENAT
provide O
detailed O
information O
about O
the O
porosity S-PRO
, O
the O
inter- O
and O
intra-layer O
bond O
line O
densities O
, O
and O
the O
surface B-PRO
roughness E-PRO
of O
the O
mesostructures O
, O
which O
potentially O
can O
be S-MATE
used O
in O
a O
model-based O
slicing S-CONPRI
software O
. O


Lithography-based O
Additive B-MANP
Manufacturing E-MANP
Technologies O
( O
L-AMT O
) O
exploit O
the O
curing S-MANP
of O
photosensitive O
materials S-CONPRI
upon O
light B-CONPRI
exposure E-CONPRI
. O


We O
developed O
a O
hybrid O
exposure S-CONPRI
concept O
. O


This O
system O
is O
able O
to O
overcome O
the O
challenge O
of O
providing O
good O
surface B-PARA
qualities E-PARA
and O
excellent O
feature S-FEAT
resolution O
as S-MATE
well O
as S-MATE
a O
throughput S-CHAR
similar O
to O
dynamic S-CONPRI
mask-based O
L-AMT O
systems O
by O
combining O
two O
light B-MACEQ
sources E-MACEQ
. O


A O
Digital B-MANP
Light I-MANP
Processing E-MANP
( O
DLP® O
) O
Light O
Engine O
( O
LE O
) O
with O
a O
building O
area S-PARA
of O
144 O
x O
90 O
mm² O
offers O
a O
pixelsize O
of O
56 O
μm O
. O


In O
order O
to O
further O
improve O
the O
achievable O
resolution S-PARA
, O
a O
continuous O
laser-exposed O
contour S-FEAT
line O
( O
spot B-PARA
size E-PARA
20 O
μm O
) O
on O
the O
outside O
of O
the O
projected O
envelope O
can O
be S-MATE
written O
with O
an O
additional O
scanning S-CONPRI
laser-system O
. O


The O
matching O
of O
the O
DLP® O
projection O
mask S-CONPRI
and O
the O
laser-contour O
is O
crucial O
for O
accurate S-CHAR
printing O
. O


Therefore O
a O
calibration S-CONPRI
tool O
was O
developed O
, O
which O
facilitates O
the O
alignment O
of O
the O
two O
light B-MACEQ
sources E-MACEQ
. O


A O
dichroic O
coated S-APPL
mirror O
enables O
a O
perpendicular O
alignment O
of O
the O
DLP® O
light O
beam S-MACEQ
and O
the O
laser B-CONPRI
beam E-CONPRI
. O


In O
this O
paper O
, O
we O
formulate O
the O
generation O
of O
support B-FEAT
structures E-FEAT
for O
additive B-MANP
manufacturing E-MANP
as O
a O
topology B-FEAT
optimization E-FEAT
problem O
. O


Compared O
with O
usual O
geometric O
considerations O
based O
support B-FEAT
structure E-FEAT
design S-FEAT
, O
this O
formulation O
affords O
mechanistic O
meaning O
to O
the O
computed O
support B-FEAT
structures E-FEAT
. O


Moreover O
, O
our O
study O
reveals O
that O
the O
topology B-FEAT
optimization E-FEAT
formulation O
generally O
leads O
to O
self-supporting B-FEAT
designs E-FEAT
without O
extraneous O
self-supporting S-FEAT
constraints O
. O


The O
resulting O
support B-FEAT
structures E-FEAT
have O
been O
3D B-MANP
printed E-MANP
, O
demonstrating O
that O
the O
computed O
designs S-FEAT
can O
successfully O
be S-MATE
used O
as S-MATE
supports O
. O


To O
better O
understand O
the O
impact S-CONPRI
of O
complex B-CONPRI
structure E-CONPRI
on O
mechanical B-CONPRI
properties E-CONPRI
in O
additively B-MANP
manufactured E-MANP
ceramics O
, O
truss S-MACEQ
structures O
were O
3D B-MANP
printed E-MANP
in O
preceramic O
polymer S-MATE
and O
mechanically O
evaluated O
in O
the O
pyrolyzed O
SiOC O
state O
. O


Specimens O
were O
printed O
using O
digital B-MANP
light I-MANP
processing E-MANP
with O
a O
siloxane O
polymer B-MATE
resin E-MATE
blend S-MATE
. O


Four O
different O
designs S-FEAT
were O
printed O
: O
two O
bending-dominant O
Kelvin O
cell S-APPL
structures O
, O
a O
stretching-dominant O
octet B-CONPRI
structure E-CONPRI
, O
and O
a O
mixture O
of O
the O
two O
with O
geometries S-CONPRI
chosen O
for O
equivalent O
stiffness S-PRO
. O


Mechanical S-APPL
characterization O
was O
done O
at O
multiple O
length B-CHAR
scales E-CHAR
: O
uniaxial O
compression S-PRO
to O
evaluate O
the O
entire O
truss S-MACEQ
structure S-CONPRI
, O
and O
three-point O
flexure S-MACEQ
to O
assess O
individual O
beam S-MACEQ
elements O
. O


After O
pyrolysis S-MANP
, O
it O
was O
found O
that O
truss S-MACEQ
designs S-FEAT
exhibited O
different O
shrinkages O
at O
the O
beam S-MACEQ
element O
scale O
despite O
being O
composed O
of O
the O
same O
preceramic O
polymer S-MATE
and O
exhibiting O
isotropic S-PRO
shrinkage O
at O
the O
macro-truss O
scale O
. O


This O
manner O
of O
nonuniform O
shrinkage S-CONPRI
has O
rarely O
, O
if O
ever O
been O
reported O
, O
as S-MATE
it O
is O
standard S-CONPRI
practice O
in O
additive B-MANP
manufacturing E-MANP
to O
report O
only O
bulk O
linear O
shrinkage S-CONPRI
. O


In O
uniaxial O
compression S-PRO
, O
Kelvin O
structures O
with O
thicker O
beams O
exhibited O
the O
highest O
strength S-PRO
of O
10 O
MPa S-CONPRI
, O
and O
octet B-CONPRI
structures E-CONPRI
exhibited O
the O
lowest O
strength S-PRO
of O
3.8 O
MPa S-CONPRI
. O


In O
beam S-MACEQ
element O
flexure S-MACEQ
however O
, O
the O
octet O
beams O
had O
the O
highest O
strength S-PRO
, O
1.9 O
GPa S-PRO
, O
four O
times O
stronger O
than O
the O
Kelvin O
beam S-MACEQ
elements O
and O
500 O
times O
stronger O
than O
the O
octet O
bulk O
structure S-CONPRI
. O


Achieving O
better O
control O
in O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
relies O
on O
a O
molecular O
understanding O
of O
how O
thermoplastic S-MATE
printing O
materials S-CONPRI
behave O
during O
the O
printing B-MANP
process E-MANP
. O


For O
semi-crystalline O
polymers S-MATE
, O
the O
ultimate O
crystal O
morphology S-CONPRI
and O
how O
it O
develops O
during O
cooling S-MANP
is O
crucial O
to O
determining O
part O
properties S-CONPRI
. O


Here O
crystallisation O
kinetics O
are O
added O
to O
a O
previously-developed O
model S-CONPRI
, O
which O
contains O
a O
molecularly-aware O
constitutive O
equation O
to O
describe O
polymer S-MATE
stretch O
and O
orientation S-CONPRI
during O
typical O
non-isothermal O
FFF S-MANP
flow O
, O
and O
conditions O
under O
which O
flow-enhanced O
nucleation S-CONPRI
occurs O
due O
to O
residual S-CONPRI
stretch O
are O
revealed O
. O


Flow-enhanced O
nucleation S-CONPRI
leads O
to O
accelerated O
crystallisation O
times O
at O
the O
surface S-CONPRI
of O
a O
deposited O
filament S-MATE
, O
whilst O
the O
bulk O
of O
the O
filament S-MATE
is O
governed O
by O
slower O
quiescent O
kinetics O
. O


The O
predicted S-CONPRI
time O
to O
10 O
% O
crystallinity O
, O
t10 O
, O
is O
in O
quantitative S-CONPRI
agreement O
with O
in-situ S-CONPRI
Raman O
spectroscopy S-CONPRI
measurements O
of O
polycaprolactone O
( O
PCL S-MATE
) O
. O


The O
model S-CONPRI
highlights O
important O
features O
not O
captured O
by O
a O
single O
measurement S-CHAR
of O
t10 O
. O


In O
particular O
, O
the O
crystal O
morphology S-CONPRI
varies O
cross-sectionally O
, O
with O
smaller O
spherulites O
forming S-MANP
in O
an O
outer O
skin O
layer S-PARA
, O
explaining O
features O
observed O
in O
full O
transient S-CONPRI
crystallisation O
measurements O
. O


Finally O
, O
exploitation O
of O
flow-enhanced O
crystallisation O
is O
proposed O
as S-MATE
a O
mechanism S-CONPRI
to O
increase O
weld B-PRO
strength E-PRO
at O
the O
interface S-CONPRI
between O
deposited O
filaments S-MATE
. O


In O
nature O
, O
mesoscopic O
or O
microscopic O
cellular B-FEAT
structures E-FEAT
like O
trabecular B-MATE
bone E-MATE
, O
wood S-MATE
, O
shell S-MACEQ
, O
and O
sea O
urchin O
, O
can O
have O
high O
load-carrying O
capacity S-CONPRI
. O


These O
cellular B-FEAT
structures E-FEAT
with O
diverse O
shapes O
, O
forms O
and O
designs S-FEAT
can O
be S-MATE
mainly O
classified O
into O
open O
and O
closed O
cell S-APPL
cellular O
structures O
. O


It O
is O
difficult O
to O
replicate O
these O
natural O
complex O
lattice B-FEAT
structures E-FEAT
with O
traditional B-MANP
manufacturing E-MANP
, O
but O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technology S-CONPRI
development O
has O
allowed O
engineers O
and O
scientists O
to O
mimic S-MACEQ
these O
natural O
structures O
. O


Fabricating S-MANP
close O
cell S-APPL
lattice O
structures O
is O
still O
considered O
difficult O
due O
to O
the O
support B-FEAT
structure E-FEAT
within O
the O
lattices S-CONPRI
. O


This O
paper O
evaluates O
a O
novel O
way O
of O
fabricating S-MANP
a O
close O
cell S-APPL
lattice O
structure S-CONPRI
with O
a O
material B-MANP
extrusion E-MANP
process O
. O


The O
design S-FEAT
eliminates O
the O
need O
for O
support B-FEAT
structures E-FEAT
and O
the O
subsequent O
post-processing S-CONPRI
required O
to O
remove O
them O
. O


A O
shell-shaped O
close O
cell S-APPL
lattice O
structure S-CONPRI
bio-mimicking O
a O
sea O
urchin O
shape O
was O
introduced O
for O
the O
load-bearing S-FEAT
structure O
application O
. O


The O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
proposed O
structure S-CONPRI
, O
including O
stiffness S-PRO
, O
deformation S-CONPRI
behavior O
and O
energy B-CHAR
absorption E-CHAR
, O
were O
compared O
with O
those O
of O
benchmarked O
honeycomb S-CONPRI
and O
open O
cell S-APPL
sea O
urchin O
( O
SU O
) O
lattice B-FEAT
structures E-FEAT
of O
the O
same O
density S-PRO
. O


SU O
lattice B-FEAT
structures E-FEAT
and O
honeycomb S-CONPRI
periodic O
lattice B-FEAT
structures E-FEAT
with O
varied O
sizes O
but O
the O
same O
morphology S-CONPRI
and O
fixed O
density S-PRO
were O
designed S-FEAT
and O
printed O
in O
polylactic B-MATE
acid I-MATE
material E-MATE
( O
PLA S-MATE
) O
. O


Their O
physical O
characteristics O
, O
deformation S-CONPRI
behavior O
, O
and O
compressive O
properties S-CONPRI
were O
investigated O
experimentally O
and O
via O
finite B-CONPRI
element I-CONPRI
analysis E-CONPRI
. O


The O
effect O
of O
the O
unit B-CONPRI
cell E-CONPRI
size O
on O
mechanical B-CONPRI
properties E-CONPRI
was O
studied O
and O
discussed O
, O
and O
the O
rankings O
of O
better O
performances O
were O
drawn O
. O


A O
possible O
application O
of O
the O
closed O
cell S-APPL
is O
for O
fabricating S-MANP
the O
load O
bearing O
structure S-CONPRI
; O
it O
can O
also O
be S-MATE
encapsulated O
within O
a O
fluid S-MATE
to O
impart O
strength S-PRO
and O
damping O
characteristics O
. O


An O
anisotropic S-PRO
cohesive O
zone O
model S-CONPRI
with O
XFEM O
is O
developed O
to O
capture O
fracture S-CONPRI
in O
additively B-MANP
manufactured E-MANP
polymer O
materials S-CONPRI
. O


The O
XFEM O
is O
able O
to O
model S-CONPRI
crack B-CONPRI
propagations E-CONPRI
in O
3D B-MANP
printed E-MANP
materials O
without O
knowing O
a O
priori O
the O
crack O
path O
. O


Parametric O
studies O
show O
that O
the O
competition O
between O
inter-layer O
failure S-CONPRI
and O
max O
principal B-PRO
stress E-PRO
failure S-CONPRI
largely O
affects O
the O
kinked O
cracks O
. O


The O
fracture S-CONPRI
of O
additively B-MANP
manufactured E-MANP
polymer O
materials S-CONPRI
with O
various O
layer S-PARA
orientations O
is O
studied O
using O
the O
extended O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
( O
XFEM O
) O
in O
an O
anisotropic S-PRO
cohesive O
zone O
model S-CONPRI
( O
CZM O
) O
. O


The O
single O
edge O
notched O
bending S-MANP
( O
SENB O
) O
specimens O
made O
of O
acrylonitrile-butadiene-styrene O
( O
ABS S-MATE
) O
materials S-CONPRI
through O
fused B-MANP
filament I-MANP
fabrications E-MANP
with O
various O
crack O
tip/layer O
orientations S-CONPRI
are O
considered O
. O


The O
XFEM O
coupled O
with O
anisotropic S-PRO
CZM O
is O
employed O
to O
model S-CONPRI
the O
brittle B-CONPRI
fracture E-CONPRI
( O
fracture S-CONPRI
between O
layers O
) O
, O
ductile B-CONPRI
fracture E-CONPRI
( O
fracture S-CONPRI
through O
layers O
) O
, O
as S-MATE
well O
as S-MATE
kinked O
fracture S-CONPRI
behaviors O
of O
ABS S-MATE
specimens O
printed O
with O
vertical S-CONPRI
, O
horizontal O
, O
and O
oblique O
layer S-PARA
orientations O
, O
respectively O
. O


Both O
elastic S-PRO
and O
elastoplastic O
fracture S-CONPRI
models O
, O
coupled O
with O
linear O
or O
exponential O
traction-separation O
laws O
, O
are O
developed O
for O
the O
inter-layer O
and O
cross-layer O
fracture S-CONPRI
, O
respectively O
. O


For O
mixed O
inter-/cross- O
layer S-PARA
fracture S-CONPRI
, O
an O
anisotropic S-PRO
cohesive O
zone O
model S-CONPRI
is O
developed O
to O
predict O
the O
kinked O
crack B-CONPRI
propagations E-CONPRI
. O


Two O
crack O
initiation O
and O
evolution S-CONPRI
criteria O
are O
defined O
to O
include O
both O
crack B-CONPRI
propagation E-CONPRI
between O
layers O
( O
weak O
plane O
failure S-CONPRI
) O
and O
crack O
penetration S-CONPRI
through O
layers O
( O
maximum B-CONPRI
principal I-CONPRI
stress I-CONPRI
failure E-CONPRI
) O
that O
jointly O
determine O
the O
zig-zag O
crack B-CONPRI
growth E-CONPRI
paths O
. O


The O
anisotropic S-PRO
cohesive O
zone O
model S-CONPRI
with O
XFEM O
developed O
in O
this O
study O
is O
able O
to O
capture O
different O
fracture S-CONPRI
behaviors O
of O
additively B-MANP
manufactured E-MANP
ABS S-MATE
samples O
with O
different O
layer S-PARA
orientations O
. O


A O
conformal O
, O
compliant O
and O
multi-layer O
tactile O
sensor S-MACEQ
was O
built O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
using O
a O
hybrid B-CONPRI
manufacturing E-CONPRI
process O
including O
conformal O
Direct-Print O
( O
DP O
) O
technology S-CONPRI
and O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
soft O
molding S-MANP
process O
with O
a O
developed O
piezoresistive O
polymer/nanocomposite O
. O


A O
multi-layer O
conformal O
skin O
structure S-CONPRI
of O
the O
sensor S-MACEQ
was O
created O
using O
the O
soft O
molding S-MANP
process O
along O
with O
a O
highly O
flexible O
rubber B-MATE
material E-MATE
. O


Two O
layers O
of O
sensing S-APPL
elements S-MATE
were O
designed S-FEAT
, O
where O
the O
sensing S-APPL
elements S-MATE
in O
the O
lower O
sensing S-APPL
layer S-PARA
were O
orthogonally O
placed O
against O
those O
in O
the O
upper O
sensing S-APPL
layer S-PARA
so O
that O
the O
sensing S-APPL
elements S-MATE
in O
two O
layers O
could O
cross O
each O
other O
with O
an O
insulating B-CONPRI
layer E-CONPRI
between O
them O
. O


A O
conformal O
printing O
algorithm S-CONPRI
was O
developed O
to O
advance O
the O
capability O
of O
DP O
technology S-CONPRI
. O


Thus O
, O
all O
the O
sensing S-APPL
elements S-MATE
were O
printed O
uniformly O
within O
the O
conformal O
skin O
structure S-CONPRI
. O


Several O
experiments O
on O
position O
detection O
were O
performed O
to O
evaluate O
the O
performance S-CONPRI
of O
the O
fabricated S-CONPRI
conformal O
sensor S-MACEQ
. O


The O
results O
showed O
that O
the O
sensor S-MACEQ
can O
detect O
locations O
of O
external O
forces S-CONPRI
applied O
on O
the O
sensor S-MACEQ
surface O
due O
to O
the O
multiple O
layers O
of O
sensing S-APPL
elements S-MATE
. O


It O
is O
concluded O
that O
the O
suggested O
manufacturing S-MANP
methods O
and O
developed O
materials S-CONPRI
are O
promising O
tools S-MACEQ
to O
develop O
conformal O
, O
compliant O
tactile O
sensors S-MACEQ
. O


Microstereolithography S-MANP
( O
MSL O
) O
has O
been O
employed O
to O
create O
3D S-CONPRI
microstructures O
for O
a O
wide O
range S-PARA
of O
applications O
. O


Despite O
the O
many O
advantages O
of O
using O
this O
process S-CONPRI
, O
there O
are O
still O
several O
drawbacks O
such O
as S-MATE
the O
need O
to O
use O
a O
large O
amount O
of O
a O
material S-MATE
compared O
to O
the O
volume S-CONPRI
of O
the O
microstructure S-CONPRI
to O
be S-MATE
built O
, O
oxygen S-MATE
inhibition O
, O
and O
difficulty O
in O
processing O
highly O
viscous O
photopolymers S-MATE
. O


To O
minimize O
the O
amount O
of O
material S-MATE
required O
, O
the O
use O
of O
a O
liquid O
bridge S-APPL
has O
been O
suggested O
as S-MATE
a O
modification O
to O
the O
existing O
microstereolithography S-MANP
process O
. O


A O
liquid O
bridge S-APPL
can O
be S-MATE
easily O
found O
in O
nature O
after O
a O
rainfall O
. O


Basically O
, O
a O
bridge S-APPL
can O
be S-MATE
formed O
between O
two O
solid O
bodies O
, O
where O
surface B-PRO
tension E-PRO
can O
sustain O
a O
liquid O
bridge S-APPL
against O
a O
gravitational O
force S-CONPRI
, O
which O
tends O
to O
destroy O
it O
. O


With O
this O
natural O
phenomenon O
, O
a O
photopolymer S-MATE
can O
be S-MATE
intentionally O
formed O
between O
two O
substrates O
: O
a O
transparent S-CONPRI
substrate S-MATE
with O
a O
low O
surface S-CONPRI
energy O
can O
be S-MATE
used O
as S-MATE
a O
top O
substrate S-MATE
, O
while O
another O
substrate S-MATE
with O
a O
higher O
surface S-CONPRI
energy O
can O
be S-MATE
used O
to O
hold O
the O
fabricated S-CONPRI
structure O
together O
. O


This O
process S-CONPRI
, O
called O
liquid O
bridge S-APPL
microstereolithography O
( O
LBMSL O
) O
, O
is O
advantageous O
since O
it O
uses O
a O
relatively O
small O
amount O
of O
a O
material S-MATE
, O
removes O
oxygen S-MATE
inhibition O
due O
to O
the O
constraint O
of O
the O
material S-MATE
surface O
, O
and O
offers O
the O
possibility O
of O
utilizing O
a O
highly O
viscous O
material S-MATE
. O


In O
this O
study O
, O
a O
mathematical S-CONPRI
model O
was O
taken O
to O
simulate O
a O
liquid O
bridge S-APPL
with O
a O
certain O
volume S-CONPRI
and O
height O
. O


Adhesion S-PRO
tests O
were O
accomplished O
to O
ensure O
the O
fabricated S-CONPRI
layer O
detaches O
from O
the O
top O
substrate S-MATE
while O
the O
fabricated S-CONPRI
structure O
remains O
attached O
to O
the O
bottom O
structure S-CONPRI
. O


Finally O
, O
various O
3D S-CONPRI
microstructures O
were O
fabricated S-CONPRI
by O
LBMSL O
; O
these O
fabricated S-CONPRI
microstructures O
provide O
compelling O
evidence O
that O
LBMSL O
is O
advantageous O
over O
the O
existing O
process S-CONPRI
for O
MSL O
. O


The O
paper O
presents O
a O
method O
to O
optimize O
build B-PARA
orientation E-PARA
and O
topological O
layout S-CONPRI
simultaneously O
in O
density-based O
topology B-FEAT
optimization E-FEAT
for O
additive B-MANP
manufacturing E-MANP
. O


Support B-FEAT
structures E-FEAT
are O
required O
in O
additive B-MANP
manufacturing E-MANP
of O
parts O
of O
complex B-PRO
shape E-PRO
. O


To O
eliminate O
or O
reduce O
support B-FEAT
structures E-FEAT
during O
the O
additive S-MATE
processes O
, O
we O
constrain O
the O
lower O
bound O
of O
the O
overhang B-PARA
angle E-PARA
of O
the O
optimized O
design S-FEAT
. O


In O
this O
method O
, O
the O
build B-PARA
orientation E-PARA
and O
the O
density B-PRO
field E-PRO
used O
to O
represent O
the O
part O
are O
simultaneously O
optimized O
to O
satisfy O
the O
overhang B-PARA
angle E-PARA
constraints O
for O
part O
self-support O
. O


The O
first O
directional O
gradient O
based O
global O
constraint O
controls O
the O
overhang B-PARA
angle E-PARA
of O
the O
solid/void O
interface S-CONPRI
inside O
the O
design S-FEAT
domain O
to O
eliminate O
the O
internal O
supports S-APPL
. O


The O
second O
density-based O
global O
constraint O
controls O
the O
angle O
of O
the O
design S-FEAT
domain O
boundary S-FEAT
to O
reduce O
the O
external O
supports S-APPL
. O


Numerical O
examples O
on O
both O
2D S-CONPRI
and O
3D S-CONPRI
linear O
elastic S-PRO
problems O
are O
presented O
to O
demonstrate O
the O
validity O
and O
efficiency O
of O
the O
proposed O
formulations O
in O
the O
build B-PARA
orientation E-PARA
optimization O
and O
in O
the O
overhang B-PARA
angle E-PARA
control O
. O


As S-MATE
the O
application O
space O
for O
large-scale O
3D B-MANP
printed E-MANP
components O
continues O
to O
grow O
, O
it O
is O
necessary O
to O
identify O
appropriate O
processing O
conditions O
for O
high-performance O
thermoplastics S-MATE
on O
large O
format O
Additive B-MANP
Manufacturing E-MANP
( O
LFAM O
) O
systems O
. O


This O
study O
compares O
the O
rheological S-PRO
behavior O
of O
a O
high-performance O
thermoplastic S-MATE
, O
polyphenylsulfone O
( O
PPSU O
) O
, O
with O
that O
of O
a O
commonly O
used O
low-temperature O
polymer S-MATE
, O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
, O
to O
identify O
suitable O
processing O
conditions O
for O
large O
format O
AM S-MANP
systems O
. O


The O
linear O
viscoelastic B-PRO
properties E-PRO
( O
complex O
viscosity S-PRO
, O
storage O
modulus O
, O
loss O
modulus O
, O
and O
tan O
delta O
) O
of O
these O
materials S-CONPRI
are O
evaluated O
as S-MATE
a O
function O
of O
temperature S-PARA
, O
angular O
frequency O
, O
and O
carbon B-MATE
fiber E-MATE
content O
. O


The O
addition O
of O
20–35 O
% O
by O
weight S-PARA
of O
carbon B-MATE
fiber E-MATE
increased O
the O
shear B-CONPRI
thinning E-CONPRI
effect O
of O
both O
thermoplastics S-MATE
, O
showing O
a O
potential O
variation S-CONPRI
of O
2–3 O
x O
over O
the O
range S-PARA
of O
expected O
LFAM O
extrusion S-MANP
shear O
rates O
( O
10–100 O
s−1 O
) O
. O


Sustainable S-CONPRI
and O
environmentally O
friendly O
process S-CONPRI
for O
spherical S-CONPRI
poly O
( O
L-lactide O
) O
( O
PLLA O
) O
particles S-CONPRI
for O
Additive B-MANP
Manufacturing E-MANP
. O


PLLA O
microspheres S-CONPRI
produced O
by O
liquid-liquid O
phase S-CONPRI
separation O
and O
precipitation S-CONPRI
using O
triacetin O
as S-MATE
solvent O
. O


Particle S-CONPRI
characterization O
with O
respect O
to O
processability O
in O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
of O
polymers S-MATE
. O


Narrowly O
distributed O
, O
spherical S-CONPRI
PLLA O
powders S-MATE
show O
excellent O
flowability O
. O


Manufacturing S-MANP
and O
mechanical S-APPL
characterization O
of O
3D B-MANP
printed E-MANP
tensile O
test O
bars O
and O
complex O
porous S-PRO
gyroid O
specimens O
. O


In O
this O
work O
, O
the O
development O
and O
processing O
behavior O
of O
poly O
( O
L-lactide O
) O
( O
PLLA O
) O
particles S-CONPRI
for O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
of O
polymers S-MATE
obtained O
via O
a O
green O
and O
sustainable B-CONPRI
process E-CONPRI
route O
are O
thoroughly O
studied O
. O


Liquid-liquid O
phase S-CONPRI
separation O
and O
precipitation S-CONPRI
from O
triacetin O
, O
a O
non-toxic O
solvent O
, O
are O
applied O
for O
the O
production S-MANP
of O
highly O
spherical S-CONPRI
PLLA O
particles S-CONPRI
of O
excellent O
flowability O
. O


Starting O
from O
the O
measured O
cloud-point O
diagram O
of O
the O
PLLA-triacetin O
system O
, O
appropriate O
temperature S-PARA
profiles S-FEAT
for O
the O
precipitation S-CONPRI
process O
are O
derived O
. O


The O
effect O
of O
process B-CONPRI
parameters E-CONPRI
on O
the O
product O
properties S-CONPRI
is O
addressed O
in O
detail O
; O
the O
PLLA O
particles S-CONPRI
are O
characterized O
regarding O
their O
size O
distribution S-CONPRI
and O
morphology S-CONPRI
. O


Furthermore O
, O
material B-CONPRI
properties E-CONPRI
including O
thermal O
behavior O
( O
c.f O
. O


processing O
window O
for O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
) O
and O
powder S-MATE
flowability O
are O
assessed O
. O


The O
spherical S-CONPRI
PLLA O
particles S-CONPRI
of O
narrow O
size O
distribution S-CONPRI
display O
a O
wide O
sintering S-MANP
window O
of O
59 O
K S-MATE
and O
an O
excellent O
flowability O
due O
to O
the O
intrinsic O
surface B-PRO
roughness E-PRO
of O
the O
particles S-CONPRI
. O


Thus O
, O
tensile B-CHAR
test E-CHAR
bars O
and O
complex O
porous S-PRO
gyroid O
specimens O
were O
successfully O
manufactured S-CONPRI
via O
PBF S-MANP
without O
the O
need O
for O
any O
additional O
surface S-CONPRI
functionalization O
of O
the O
particles S-CONPRI
with O
flow O
agents O
. O


The O
high O
potential O
of O
the O
newly O
developed O
PLLA O
powders S-MATE
produced O
via O
an O
environmentally O
friendly O
approach O
omitting O
the O
use O
of O
halogenated O
or O
toxic O
solvents O
, O
as S-MATE
well O
as S-MATE
flowing O
aids O
, O
is O
demonstrated O
by O
mechanical B-CHAR
testing E-CHAR
of O
the O
printed O
specimens O
. O


Composite S-MATE
textiles O
have O
found O
widespread O
use O
and O
advantages O
in O
various O
industries S-APPL
and O
applications O
. O


The O
constant O
demand O
for O
high-quality O
products O
and O
services O
requires O
companies S-APPL
to O
minimize O
their O
manufacturing B-CONPRI
costs E-CONPRI
and O
delivery O
time O
in O
order O
to O
compete O
with O
general O
and O
niche O
marketplaces O
. O


Creation O
of O
molding S-MANP
and O
tooling S-CONPRI
options O
for O
advanced B-MATE
composites E-MATE
encompasses O
a O
large O
portion O
of O
fabrication B-PARA
time E-PARA
, O
making O
it O
a O
costly O
process S-CONPRI
and O
a O
restraining O
factor O
. O


This O
research S-CONPRI
discusses O
a O
preliminary O
investigation O
into O
the O
use O
and O
control O
of O
soluble S-CONPRI
polymer S-MATE
compounds O
and O
additive B-MANP
manufacturing E-MANP
to O
fabricate S-MANP
sacrificial O
molds S-MACEQ
. O


These O
molds S-MACEQ
suffer O
from O
dimensional O
errors S-CONPRI
due O
to O
several O
factors O
, O
which O
have O
also O
been O
characterized O
. O


The O
basic O
soluble S-CONPRI
mold S-MACEQ
of O
a O
composite S-MATE
is O
3D B-MANP
printed E-MANP
to O
meet O
the O
desired O
dimensions S-FEAT
and O
geometry S-CONPRI
of O
holistic O
structures O
or O
spliced O
components S-MACEQ
. O


The O
time O
taken O
to O
dissolve O
the O
mold S-MACEQ
depends O
on O
the O
rate O
of O
agitation S-CONPRI
of O
the O
solvent O
. O


This O
process S-CONPRI
is O
steered O
towards O
enabling O
the O
implantation S-MANP
of O
optoelectronic O
devices O
within O
the O
composite S-MATE
to O
provide O
a O
sensing S-APPL
capability O
for O
structural O
health O
monitoring O
. O


The O
shape O
deviation O
of O
the O
3D B-MANP
printed E-MANP
mold O
is O
also O
studied O
and O
compared O
to O
its O
original O
dimensions S-FEAT
to O
optimize O
the O
dimensional O
quality S-CONPRI
to O
produce O
dimensionally O
accurate S-CHAR
parts O
of O
up O
to O
0.02 O
% O
error S-CONPRI
. O


In O
order O
to O
use O
selective B-MANP
laser I-MANP
sintering E-MANP
to O
manufacture S-CONPRI
structural O
parts O
for O
automotive S-APPL
and O
aerospace S-APPL
applications O
, O
the O
failure S-CONPRI
conditions O
of O
such O
a O
component S-MACEQ
must O
be S-MATE
understood O
and O
predicted S-CONPRI
. O


A O
3D S-CONPRI
failure O
criterion O
for O
anisotropic S-PRO
materials O
that O
incorporates O
stress S-PRO
interactions O
is O
implemented O
to O
predict O
failure S-CONPRI
of O
selective B-MANP
laser E-MANP
sintered O
parts O
manufactured S-CONPRI
using O
polyamide B-MATE
12 E-MATE
powder O
. O


Special O
test O
specimens O
that O
capture O
tensile S-PRO
, O
compressive O
and O
shear B-PRO
strengths E-PRO
, O
as S-MATE
single O
or O
combined O
loads O
, O
were O
designed S-FEAT
, O
manufactured S-CONPRI
and O
tested O
. O


Results O
show O
that O
significant O
differences O
exist O
between O
tensile S-PRO
and O
compressive B-PRO
strengths E-PRO
, O
and O
that O
failure S-CONPRI
of O
additive B-APPL
manufactured I-APPL
parts E-APPL
is O
strongly O
influenced O
by O
the O
interaction O
between O
stresses O
. O


The O
test O
data S-CONPRI
shows O
an O
excellent O
fit S-CONPRI
with O
a O
tensor S-CONPRI
based O
failure S-CONPRI
criterion O
that O
includes O
interaction O
strength S-PRO
tensor O
components S-MACEQ
, O
thus O
being O
able O
to O
capture O
the O
strength S-PRO
behavior O
of O
SLS S-MANP
printed O
components S-MACEQ
under O
complex O
loading O
conditions O
. O


Vat B-MANP
photopolymerization E-MANP
( O
VP O
) O
of O
silicone S-MATE
can O
produce O
better O
finish O
and O
higher B-PARA
resolution E-PARA
than O
the O
conventional O
extrusion-based O
method O
. O


One O
challenge O
in O
the O
current O
bottom-up O
VP O
processes S-CONPRI
is O
the O
separation O
that O
forms O
between O
the O
cured S-MANP
part O
and O
vat S-MACEQ
at O
each O
layer S-PARA
. O


Oxygen-inhibition O
is O
commonly O
adopted O
as S-MATE
a O
solution S-CONPRI
( O
i.e O
. O


LOPP O
is O
achieved O
by O
a O
low-absorbance O
wavelength S-CONPRI
and O
a O
gradient O
light O
beam S-MACEQ
. O


The O
first O
experiment S-CONPRI
measured O
the O
effect O
of O
beam S-MACEQ
power O
; O
the O
second O
experiment S-CONPRI
measured O
the O
effect O
of O
scanning B-PARA
speed E-PARA
. O


The O
curing S-MANP
speed O
of O
385 O
nm O
at O
the O
same O
power S-PARA
level O
was O
10 O
times O
slower O
than O
375 O
nm O
, O
but O
could O
be S-MATE
scaled O
up O
non-linearly O
by O
the O
beam S-MACEQ
power O
. O


A O
tripled O
light O
power S-PARA
of O
385 O
nm O
can O
accelerate O
the O
process S-CONPRI
by O
a O
factor O
of O
7 O
and O
be S-MATE
comparable O
to O
that O
of O
375 O
nm O
. O


Thus O
, O
this O
study O
confirms O
the O
feasibility S-CONPRI
of O
an O
optically O
created O
dead O
zone O
and O
also O
uncovers O
the O
necessity O
of O
high-power O
light B-MACEQ
source E-MACEQ
for O
this O
application O
. O


Fused B-CONPRI
deposition E-CONPRI
modelling O
( O
FDM S-MANP
) O
is O
a O
well-known O
additive B-MANP
manufacturing E-MANP
technique O
, O
which O
can O
transfer O
digital O
three-dimensional S-CONPRI
( O
3D S-CONPRI
) O
models O
into O
functional B-CONPRI
components E-CONPRI
directly O
. O


Despite O
many O
advantages O
FDM S-MANP
can O
offer O
, O
poor O
surface B-CHAR
accuracy E-CHAR
of O
fabricated S-CONPRI
objects O
has O
always O
been O
a O
big O
issue O
that O
attracts O
increasing O
attention O
. O


To O
study O
the O
influence O
on O
the O
surface B-FEAT
profiles E-FEAT
imposed O
by O
various O
process B-CONPRI
parameters E-CONPRI
effectively O
as S-MATE
well O
as S-MATE
quantitatively O
, O
the O
mathematical S-CONPRI
model O
of O
the O
surface B-FEAT
profile E-FEAT
need O
to O
be S-MATE
developed O
. O


In O
this O
work O
, O
a O
new O
surface B-FEAT
profile E-FEAT
model S-CONPRI
is O
developed O
to O
characterize O
the O
surface B-FEAT
profile E-FEAT
of O
FDM S-MANP
fabricated S-CONPRI
parts O
. O


The O
process B-CONPRI
parameters E-CONPRI
are O
classified O
into O
two O
groups O
( O
i.e O
. O


pre-process O
parameters S-CONPRI
and O
fabrication S-MANP
process O
parameters S-CONPRI
) O
to O
investigate O
the O
impacts O
on O
surface B-CHAR
characterization E-CHAR
. O


Corresponding O
experiments O
are O
conducted O
using O
an O
FDM S-MANP
machine O
to O
make O
comparison O
with O
the O
predicted S-CONPRI
values O
and O
to O
validate O
the O
reliability S-CHAR
and O
effectiveness S-CONPRI
of O
the O
proposed O
surface B-ENAT
models E-ENAT
. O


Both O
the O
experimental S-CONPRI
results O
and O
theoretical S-CONPRI
values O
indicate O
that O
the O
surface B-CHAR
accuracy E-CHAR
of O
the O
top O
surface S-CONPRI
is O
mainly O
determined O
by O
the O
ratio O
between O
molten O
paste O
flowrate O
and O
the O
nozzle S-MACEQ
feedrate O
under O
specified O
layer B-PARA
thickness E-PARA
and O
path O
spacing O
. O


On O
the O
other O
hand O
, O
the O
surface B-PARA
quality E-PARA
of O
the O
side O
surface S-CONPRI
is O
primarily O
affected O
by O
the O
layer B-PARA
thickness E-PARA
and O
the O
stratification O
angle O
of O
the O
surface S-CONPRI
. O


At O
the O
same O
time O
, O
some O
optimization S-CONPRI
approaches O
for O
the O
surface S-CONPRI
improvement O
are O
presented O
: O
appropriate O
ratio O
between O
paste O
flowrate O
and O
fabrication S-MANP
speed O
are O
required O
for O
desirable O
top O
surface S-CONPRI
and O
thinner O
layer B-PARA
thickness E-PARA
can O
, O
to O
some O
extent O
, O
alleviate O
the O
staircase O
effect O
out O
of O
the O
slicing S-CONPRI
procedure O
and O
the O
stratification O
angle O
of O
the O
side O
surface S-CONPRI
should O
be S-MATE
confined O
to O
a O
range S-PARA
to O
avoid O
large O
geometric O
errors S-CONPRI
. O


In O
this O
study O
, O
an O
in B-CONPRI
situ E-CONPRI
bioprinting-based O
methodological O
workflow S-CONPRI
is O
advanced O
to O
directly O
fabricate S-MANP
a O
custom O
engineered O
skin O
graft O
onto O
a O
skin O
burn O
phantom O
. O


To O
illustrate O
this O
modular S-CONPRI
approach O
, O
a O
burn O
phantom O
is O
first O
created O
by O
mold S-MACEQ
casting S-MANP
gelatin-alginate O
hydrogel S-MATE
material O
to O
simulate O
a O
burn O
wound O
bed S-MACEQ
with O
arbitrary O
2D S-CONPRI
shape O
and O
uniform O
depth O
. O


The O
cast S-MANP
hydrogel O
phantom O
is O
then O
placed O
on O
the O
printer B-MACEQ
platform E-MACEQ
to O
host O
the O
to-be-printed O
skin O
graft O
. O


This O
is O
followed O
by O
implementing O
a O
contour B-CONPRI
calibration E-CONPRI
process O
based O
on O
fiducial O
markers O
to O
yield O
the O
real O
dimension S-FEAT
and O
pose O
of O
the O
burn O
phantom O
. O


A O
new O
directed O
toolpath S-PARA
generation O
algorithm S-CONPRI
is O
detailed O
to O
generate O
a O
burn-specific O
toolpath S-PARA
for O
the O
microextrusion-based O
bioprinting S-APPL
process O
. O


Based O
on O
this O
method O
, O
the O
bioprinted O
cell-laden O
gelatin-alginate O
hydrogel B-MATE
filaments E-MATE
are O
precisely O
arranged O
in O
a O
meshed O
pattern S-CONPRI
that O
is O
bound O
by O
the O
burn O
phantom O
contour S-FEAT
. O


Internal B-FEAT
geometries E-FEAT
defined O
by O
the O
filament S-MATE
and O
pore S-PRO
dimensional O
characteristics O
of O
the O
printed B-CONPRI
construct E-CONPRI
design S-FEAT
can O
be S-MATE
controlled O
to O
promote O
cell B-CHAR
viability E-CHAR
, O
proliferation O
, O
and O
nutrient O
delivery O
. O


Printed O
cell-laden O
multi-layered O
constructs O
are O
evaluated O
for O
single O
filament S-MATE
and O
pore S-PRO
dimensional O
precision S-CHAR
, O
alignment O
of O
filaments S-MATE
between O
layers O
, O
and O
positional O
accuracy S-CHAR
of O
the O
filaments S-MATE
within O
the O
extracted B-CONPRI
contour E-CONPRI
. O


Finally O
, O
a O
24-hour O
time O
course O
incubation O
study O
reveals O
that O
the O
printed B-CONPRI
constructs E-CONPRI
preserve O
their O
structural O
properties S-CONPRI
while O
cells S-APPL
proliferate O
and O
maintain O
their O
spatial O
positioning O
. O


X-ray S-CHAR
interferometry S-CONPRI
provides O
a O
dark-field O
image S-CONPRI
, O
essentially O
a O
small-angle O
X-ray S-CHAR
scattering O
image S-CONPRI
, O
of O
the O
voids S-CONPRI
and O
print S-MANP
defects S-CONPRI
in O
an O
additively B-MANP
manufactured E-MANP
polymer O
object O
. O


The O
samples S-CONPRI
studied O
included O
Stanford O
Bunnies O
, O
fabricated S-CONPRI
from O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
and O
polylactic B-MATE
acid E-MATE
( O
PLA S-MATE
) O
, O
and O
a O
quadratic O
test O
object O
fabricated S-CONPRI
from O
PLA S-MATE
. O


The O
dark-field O
projection O
images S-CONPRI
show O
orientation-dependent O
X-ray S-CHAR
scattering O
which O
is O
due O
to O
anisotropic S-PRO
voids O
and O
gaps O
at O
the O
filament-to-filament O
interface S-CONPRI
in O
these O
fused B-MANP
deposition I-MANP
modeling E-MANP
additive B-MANP
manufacturing E-MANP
objects O
. O


SEM S-CHAR
corroborates O
the O
existence O
of O
gaps O
between O
filaments.The O
absorption S-CONPRI
and O
dark-field O
volumes O
are O
used O
to O
correlate O
printhead O
trajectory O
with O
print S-MANP
defect S-CONPRI
density O
. O


There O
is O
a O
slight O
increase O
in O
X-ray S-CHAR
scattering O
, O
hence O
print S-MANP
defect S-CONPRI
density O
, O
at O
regions O
with O
high O
curvature.Two O
X-ray S-CHAR
interferometry S-CONPRI
techniques O
were O
used O
: O
stepped-grating O
and O
single-shot O
. O


As S-MATE
currently O
developed O
, O
stepped-grating O
has O
the O
larger O
field-of-view—examination O
of O
an O
entire O
test O
object—whilst O
single-shot O
has O
the O
potential O
for O
real-time O
, O
in B-CONPRI
situ E-CONPRI
measurement O
of O
the O
printing B-MANP
process E-MANP
within O
1 O
mm S-MANP
of O
the O
printhead O
. O


Efficient O
generation O
of O
freeform S-CONPRI
TPMS O
porous B-FEAT
scaffolds E-FEAT
. O


Hierarchical O
scaffold S-FEAT
construction S-APPL
based O
on O
fractal O
sheet S-MATE
TPMSs O
. O


Porosity S-PRO
distribution S-CONPRI
manipulation O
according O
to O
CT S-ENAT
images O
. O


The O
external O
geometry S-CONPRI
design S-FEAT
and O
manipulation O
of O
internal O
porosity S-PRO
distribution S-CONPRI
according O
to O
the O
actual O
application O
demands O
are O
the O
main O
challenges O
of O
scaffold S-FEAT
generation O
; O
moreover O
, O
computational B-CONPRI
efficiency E-CONPRI
is O
a O
key O
factor O
that O
should O
be S-MATE
considered O
. O


This O
paper O
proposes O
efficient O
generation O
strategies O
for O
constructing O
internal O
porous S-PRO
architectures O
by O
using O
triply B-CONPRI
periodic I-CONPRI
minimal I-CONPRI
surfaces E-CONPRI
( O
TPMSs O
) O
and O
external O
freeform S-CONPRI
shapes O
through O
T-spline O
surfaces S-CONPRI
. O


After O
discretizing O
the O
geometries S-CONPRI
as S-MATE
slicing O
contours S-FEAT
, O
TPMSs O
can O
be S-MATE
efficiently O
extracted S-CONPRI
using O
the O
intersection-interpolation O
method O
in O
2D S-CONPRI
space O
, O
and O
then O
be S-MATE
offset O
as S-MATE
infill O
areas S-PARA
of O
sheet S-MATE
solids O
. O


Based O
on O
the O
proposed O
fractal O
sheet S-MATE
TPMSs O
, O
hierarchical O
scaffolds S-FEAT
are O
further O
generated O
using O
the O
refined O
constrained O
Delaunay O
triangulation O
method O
to O
construct O
multiscale O
pores S-PRO
. O


The O
porosity S-PRO
features O
can O
be S-MATE
conveniently O
controlled O
in O
2D S-CONPRI
space O
according O
to O
the O
actual O
computed B-CHAR
tomography E-CHAR
images O
. O


Eventually O
, O
the O
resulting O
infill B-PARA
areas E-PARA
can O
be S-MATE
directly O
fabricated S-CONPRI
as S-MATE
scaffolds O
by O
additive B-MANP
manufacturing E-MANP
technology O
. O


Several O
experimental S-CONPRI
instances O
validate O
the O
effectiveness S-CONPRI
and O
efficiency O
of O
the O
proposed O
strategies O
. O


Additive B-MANP
manufacturing E-MANP
allows O
design B-CONPRI
freedom E-CONPRI
and O
reduces O
the O
cost O
to O
manufacture S-CONPRI
a O
complex O
form O
. O


Prefabrication O
can O
be S-MATE
more O
time-efficient O
than O
additive B-MANP
manufacturing E-MANP
. O


Schedule O
shortening O
is O
not O
the O
main O
advantage O
of O
Additive B-MANP
manufacturing E-MANP
in O
construction S-APPL
. O


A O
breakeven O
point O
should O
be S-MATE
determined O
to O
choose O
the O
manufacturing S-MANP
method O
that O
suits O
best O
the O
need O
. O


The O
objective O
of O
this O
paper O
is O
to O
present O
a O
reflection S-CHAR
on O
the O
use O
of O
Additive B-MANP
manufacturing E-MANP
in O
construction S-APPL
. O


In O
this O
research S-CONPRI
examples O
from O
manufacturing S-MANP
industries S-APPL
are O
presented O
. O


Some O
Advantages O
of O
additive B-MANP
manufacturing E-MANP
in O
industry S-APPL
were O
identified O
. O


Relevant O
cases O
used O
to O
promote O
AM S-MANP
for O
construction S-APPL
are O
: O
building O
rate O
improvement O
and O
schedules O
shortening O
. O


Firstly O
, O
a O
comparison O
between O
construction S-APPL
and O
manufacturing S-MANP
industry S-APPL
was O
presented O
. O


Secondly O
, O
Design S-FEAT
and O
Building O
rate O
for O
construction S-APPL
were O
studied O
using O
data S-CONPRI
from O
a O
French O
construction S-APPL
company S-APPL
. O


Finally O
a O
comparison O
was O
made O
between O
conventional O
processes S-CONPRI
and O
Additive B-MANP
manufacturing E-MANP
. O


Conventional O
processes S-CONPRI
included O
prefabrication O
and O
casting S-MANP
on O
site O
. O


Results O
showed O
that O
pre-casting O
may O
be S-MATE
faster O
than O
AM S-MANP
in O
some O
cases O
. O


Time O
saving O
is O
not O
necessary O
the O
best O
advantage O
from O
applying O
additive B-MANP
manufacturing E-MANP
to O
construction S-APPL
. O


Leveraging O
the O
technology S-CONPRI
's O
unique O
ability O
to O
selectively O
place O
multiple O
materials S-CONPRI
throughout O
a O
part O
volume S-CONPRI
, O
the O
authors O
demonstrate O
a O
new O
approach O
for O
the O
fabrication S-MANP
of O
a O
new O
physical O
security O
feature S-FEAT
for O
additively B-MANP
manufactured E-MANP
parts O
. O


Specifically O
, O
the O
authors O
create O
photopolymer S-MATE
suspensions O
featuring O
quantum O
dots O
– O
a O
nanoparticle O
that O
absorbs O
ultraviolet B-CONPRI
light E-CONPRI
and O
emits O
light O
in O
the O
visible O
spectrum O
– O
that O
are O
then O
embedded O
into O
objects O
created O
by O
PolyJet B-MANP
material I-MANP
jetting E-MANP
. O


While O
the O
quantum O
dots O
appear O
ordered O
at O
the O
macroscale S-CONPRI
, O
their O
stochastic S-CONPRI
arrangement O
at O
the O
microscale S-CONPRI
( O
via O
the O
inkjetted O
droplet S-CONPRI
) O
provide O
the O
randomness O
necessary O
to O
serve O
as S-MATE
the O
key O
element S-MATE
of O
a O
Physical O
Unclonable O
Function O
, O
essentially O
transforming O
the O
3D B-MANP
printed E-MANP
object O
itself O
as S-MATE
an O
anti-counterfeiting O
system O
. O


In O
this O
work O
the O
authors O
explore O
the O
effects O
of O
quantum O
dot O
loading O
on O
optical S-CHAR
signatures O
of O
the O
nanoparticles S-CONPRI
in O
the O
photopolymer S-MATE
matrix O
. O


Quantum O
dot O
loadings O
as S-MATE
low O
as S-MATE
5 O
× O
10−3 O
wt. O
% O
can O
be S-MATE
detected O
inside O
the O
object O
with O
a O
fluorescent O
microscope S-MACEQ
, O
while O
this O
same O
concentration O
is O
invisible O
to O
the O
naked O
eye O
. O


By O
adjusting O
the O
magnification S-CONPRI
of O
the O
fluorescent O
microscope S-MACEQ
, O
we O
demonstrate O
the O
feasibility S-CONPRI
of O
a O
new O
paradigm O
for O
three-dimensional S-CONPRI
security O
patterns O
. O


The O
adaptation O
of O
inkjet S-MANP
technology O
for O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
enabled O
the O
highest O
standards S-CONPRI
of O
print S-MANP
speed O
and O
print B-PARA
resolution E-PARA
in O
the O
industry S-APPL
. O


However O
, O
inkjet S-MANP
printheads O
impose O
strict O
limitations O
on O
ink S-MATE
properties O
. O


Ink S-MATE
compositions O
ex O
volatility O
, O
rehydration O
, O
surface B-PRO
tension E-PRO
, O
chemical B-PRO
stability E-PRO
, O
abrasiveness O
, O
and O
electrical B-CONPRI
properties E-CONPRI
that O
deviate O
from O
printhead O
specifications S-PARA
shorten O
its O
service B-CONPRI
life E-CONPRI
. O


Frequent O
and O
complex O
maintenance O
procedures O
are O
necessary O
, O
but O
replacement O
is O
the O
only O
solution S-CONPRI
to O
declining O
print B-CONPRI
quality E-CONPRI
, O
accruing O
heavy O
maintenance O
costs O
. O


This O
is O
especially O
limiting O
for O
AM S-MANP
as O
part O
quality S-CONPRI
and O
properties S-CONPRI
are O
closely O
dependent O
on O
ink S-MATE
composition S-CONPRI
. O


We O
propose O
an O
ink S-MATE
deposition S-CONPRI
system O
designed S-FEAT
for O
robustness S-PRO
by O
implementing O
modular S-CONPRI
and O
dedicated O
components S-MACEQ
. O


The O
system O
deposits O
ink S-MATE
in O
a O
continuous O
jet O
. O


We O
find O
optimal B-PARA
process E-PARA
parameters O
and O
evaluate O
system O
performance S-CONPRI
in O
comparison O
to O
inkjet S-MANP
and O
material B-MANP
extrusion E-MANP
( O
ME O
) O
. O


The O
system O
produces O
line O
widths O
between O
0.3-0.5mm O
, O
indicating O
print B-PARA
resolution E-PARA
capabilities O
are O
comparable O
to O
commercial O
ME O
systems O
. O


Sandwich B-FEAT
structures E-FEAT
are O
extensively O
used O
in O
aviation O
industries S-APPL
to O
reduce O
the O
overall O
weight S-PARA
of O
the O
system O
. O


Although O
the O
mechanical S-APPL
behavior O
of O
these O
structures O
has O
been O
widely O
studied O
, O
the O
performance S-CONPRI
of O
core S-MACEQ
shape O
in O
vibration O
response O
has O
been O
minimally O
explored O
. O


This O
study O
focuses O
on O
understanding O
the O
various O
influences O
of O
sandwich B-FEAT
structures E-FEAT
considering O
the O
following O
parameters S-CONPRI
: O
( O
i O
) O
nature O
of O
core S-MACEQ
shape O
, O
( O
ii O
) O
number O
of O
infill S-PARA
shapes O
, O
and O
( O
iii O
) O
orientation S-CONPRI
of O
cores S-MACEQ
, O
which O
affect O
the O
dynamic S-CONPRI
behavior O
of O
sandwich B-FEAT
structures E-FEAT
. O


Nine O
sandwich B-FEAT
structures E-FEAT
comprising O
three O
different O
core S-MACEQ
shapes O
, O
hexagon O
, O
triangle O
, O
and O
square O
shapes O
, O
in O
three O
different O
orientations S-CONPRI
, O
namely O
0° O
, O
45° O
, O
and O
90° O
, O
were O
considered O
for O
the O
present O
study O
. O


These O
structures O
in O
the O
beginning O
were O
put O
by O
modal O
analysis O
using O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
( O
FEM S-CONPRI
) O
. O


All O
the O
nine O
structures O
were O
printed O
using O
the O
fused B-CONPRI
deposition E-CONPRI
method O
to O
validate O
the O
FEM S-CONPRI
findings O
, O
while O
the O
DEWE O
soft O
data B-MACEQ
acquisition I-MACEQ
system E-MACEQ
was O
used O
to O
estimate O
the O
modal O
parameters S-CONPRI
( O
i O
) O
natural O
frequency O
and O
( O
ii O
) O
damping O
ratio O
. O


This O
study O
demonstrates O
that O
although O
the O
square O
core S-MACEQ
orientated O
at O
0° O
exhibited O
superior O
stiffness S-PRO
in O
bending S-MANP
loads O
, O
the O
hexagonal S-FEAT
core S-MACEQ
orientated O
at O
0° O
displayed O
an O
admirable O
combination O
of O
both O
stiffness S-PRO
and O
damping O
properties S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
shows O
an O
intrinsic O
compatibility O
with O
building O
in O
extra-terrestrial O
colonization O
. O


The O
use O
of O
raw B-MATE
materials E-MATE
found O
in B-CONPRI
situ E-CONPRI
can O
drastically O
reduce O
the O
complexity S-CONPRI
of O
the O
material S-MATE
supply O
chain O
. O


Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
( O
LPBF S-MANP
) O
is O
a O
flexible O
option O
for O
producing O
components S-MACEQ
starting O
from O
powder B-MACEQ
feedstock E-MACEQ
. O


This O
work O
addresses O
the O
processability O
of O
lunar O
highlands O
regolith O
simulant O
NU-LHT-2 O
M O
by O
Laser B-MANP
Powder I-MANP
Bed I-MANP
Fusion E-MANP
on O
an O
open O
prototypal O
system O
. O


The O
investigation O
into O
the O
influence O
of O
process B-CONPRI
parameters E-CONPRI
and O
different O
base O
plate O
materials S-CONPRI
( O
carbon B-MATE
steel E-MATE
, O
self-supporting S-FEAT
deposition S-CONPRI
and O
refractory S-APPL
clay S-MATE
) O
was O
enabled O
by O
the O
in-house O
developed O
LPBF S-MANP
machine O
. O


The O
process B-CONPRI
feasibility E-CONPRI
window O
for O
multi-layer O
deposition S-CONPRI
was O
determined O
on O
the O
refractory S-APPL
clay S-MATE
base O
plate O
which O
ensured O
stable O
deposition S-CONPRI
. O


Finally O
, O
process B-CONPRI
parameters E-CONPRI
were O
studied O
to O
produce O
multi-layer O
cubical O
samples S-CONPRI
which O
were O
further O
analysed O
for O
their O
mechanical B-CONPRI
properties E-CONPRI
. O


Specimens O
presented O
compressive O
yield B-PRO
stress E-PRO
values O
in O
excess O
of O
31.4 O
MPa S-CONPRI
and O
micro O
hardness S-PRO
values O
in O
excess O
of O
680 O
HV O
, O
showing O
the O
potential O
of O
the O
technology S-CONPRI
for O
the O
deposition S-CONPRI
of O
lunar O
regolith O
components S-MACEQ
. O


Carbon B-MATE
fiber E-MATE
reinforced O
polymer S-MATE
( O
CFRP O
) O
composite S-MATE
is O
known O
for O
its O
high O
stiffness-to-weight O
ratio O
and O
hence O
is O
of O
great O
interest O
in O
several O
engineering S-APPL
fields O
such O
as S-MATE
aerospace S-APPL
, O
automotive S-APPL
, O
defense O
, O
etc O
. O


However O
, O
such O
a O
composite S-MATE
is O
not O
suitable O
for O
energy O
dissipation O
as S-MATE
failure O
occurs O
with O
very O
little O
or O
no O
plastic B-PRO
deformation E-PRO
. O


Herein O
, O
we O
present O
an O
extendable O
multi-material S-CONPRI
projection O
microstereolithography S-MANP
process O
capable O
of O
producing O
carbon-fiber-reinforced O
cellular B-MATE
materials E-MATE
that O
achieve O
simultaneously O
high O
specific B-PRO
stiffness E-PRO
and O
damping O
coefficient O
. O


Inspired O
by O
the O
upper O
bounds O
of O
stiffness-loss O
coefficient O
in O
a O
two-phase O
composite S-MATE
, O
we O
designed S-FEAT
and O
additively B-MANP
manufactured E-MANP
CFRP O
microlattices O
with O
soft O
phases O
architected O
into O
selected O
stiff-phase O
struts S-MACEQ
. O


Our O
results O
, O
confirmed O
by O
experimental S-CONPRI
and O
analytical O
calculations O
, O
revealed O
that O
the O
damping O
performance S-CONPRI
can O
be S-MATE
significantly O
enhanced O
by O
the O
addition O
of O
only O
a O
small O
fraction S-CONPRI
of O
the O
soft O
phase S-CONPRI
. O


The O
presented O
design S-FEAT
and O
additive B-MANP
manufacturing E-MANP
strategy O
allow O
for O
optimizing O
mutually O
exclusive O
properties S-CONPRI
. O


As S-MATE
a O
result O
, O
these O
CFRP O
microlattices O
achieved O
high O
specific B-PRO
stiffness E-PRO
comparable O
to O
commercial O
CFRP O
, O
technical O
ceramics S-MATE
, O
and O
composites S-MATE
, O
while O
being O
dissipative O
like O
elastomers S-MATE
. O


This O
paper O
presents O
an O
experimental S-CONPRI
approach O
to O
investigate O
the O
effects O
of O
variation S-CONPRI
in O
the O
process B-CONPRI
parameter E-CONPRI
settings O
, O
found O
commonly O
in O
most O
fused B-CONPRI
deposition E-CONPRI
modelling O
printers S-MACEQ
, O
on O
the O
geometrical O
properties S-CONPRI
of O
the O
printed O
parts O
. O


A O
benchmark S-MANS
component O
was O
designed S-FEAT
to O
include O
simple S-MANP
geometric O
features O
which O
allows O
for O
measurement S-CHAR
for O
both O
dimensional B-CHAR
accuracy E-CHAR
and O
geometric O
characteristics O
. O


Taguchi O
’ O
s S-MATE
design B-CONPRI
of I-CONPRI
experiment E-CONPRI
statistical O
approach O
was O
used O
to O
establish O
the O
relationship O
between O
varying O
process B-CONPRI
parameter E-CONPRI
settings O
on O
the O
geometrical O
properties S-CONPRI
of O
the O
benchmark S-MANS
component O
. O


The O
critical O
process B-CONPRI
parameters E-CONPRI
affecting O
both O
the O
dimensional B-CHAR
accuracy E-CHAR
and O
geometric O
characteristics O
are O
identified O
and O
the O
theoretical S-CONPRI
optimum O
print S-MANP
settings O
were O
found O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
a O
key O
enabler O
for O
architectured O
lattice S-CONPRI
materials O
, O
because O
of O
the O
geometric O
complexity S-CONPRI
of O
parts O
that O
can O
be S-MATE
produced O
. O


Recent O
advancements O
in O
AM S-MANP
have O
enabled O
rapid O
production S-MANP
speeds O
, O
high O
spatial O
resolution S-PARA
, O
and O
a O
variety O
of O
engineering S-APPL
polymers O
. O


An O
open O
question O
remains O
whether O
production S-MANP
grade O
AM S-MANP
can O
accurately S-CHAR
and O
repeatably O
produce O
lattice S-CONPRI
parts O
. O


This O
study O
presents O
design S-FEAT
, O
production S-MANP
, O
and O
mechanical B-CONPRI
property E-CONPRI
testing O
of O
hexagonal S-FEAT
lattice O
parts O
manufactured S-CONPRI
using O
continuous B-MANP
liquid I-MANP
interface I-MANP
production E-MANP
( O
CLIP S-MANP
) O
based O
AM S-MANP
. O


We O
printed O
and O
tested O
84 O
parts O
, O
in O
three O
polymer B-MATE
materials E-MATE
having O
relative B-PRO
density E-PRO
ranging O
from O
0.06 O
to O
0.23 O
. O


Lattice S-CONPRI
wall O
structures O
were O
reliably O
printed O
when O
truss S-MACEQ
aspect B-FEAT
ratio E-FEAT
was O
in O
the O
range S-PARA
5 O
to O
20 O
and O
wall B-FEAT
thicknesses E-FEAT
were O
0.35 O
or O
0.5 O
mm S-MANP
. O


The O
printed O
lattice S-CONPRI
parts O
, O
each O
comprising O
hundreds O
of O
slender O
walls O
, O
were O
measured O
using O
high B-PARA
resolution E-PARA
optical O
scanning S-CONPRI
. O


The O
images S-CONPRI
were O
analyzed O
to O
evaluate O
the O
difference O
between O
the O
printed O
parts O
and O
their O
designs S-FEAT
, O
and O
the O
effect O
of O
geometric O
deviations O
on O
the O
mechanical S-APPL
behavior O
. O


The O
measured O
elastic B-PRO
moduli E-PRO
of O
the O
printed O
parts O
are O
close O
to O
the O
values O
expected O
from O
the O
materials S-CONPRI
specifications O
. O


The O
measured O
strength S-PRO
of O
the O
printed O
parts O
deviates O
by O
7 O
% O
from O
the O
behavior O
predicted S-CONPRI
from O
the O
scanned O
geometry S-CONPRI
. O


The O
failure B-PRO
mode E-PRO
of O
the O
printed O
structures O
depends O
upon O
the O
material S-MATE
and O
part O
geometry S-CONPRI
. O


To O
our O
knowledge O
, O
this O
is O
the O
largest O
study O
on O
the O
accuracy S-CHAR
and O
performance S-CONPRI
of O
AM S-MANP
lattice O
parts O
, O
and O
the O
first O
study O
of O
its O
type O
for O
lattice S-CONPRI
parts O
made O
using O
CLIP S-MANP
. O


Over O
the O
past O
two O
decades O
, O
additive B-MANP
manufacturing E-MANP
has O
opened O
a O
new O
window O
of O
opportunities O
in O
fabricating S-MANP
complex O
porous S-PRO
matrix O
structures O
such O
as S-MATE
cellular O
solids O
. O


Several O
factors O
including O
design S-FEAT
, O
material S-MATE
and O
process B-CONPRI
parameters E-CONPRI
can O
selectively O
be S-MATE
varied O
to O
tailor O
the O
porous S-PRO
properties O
of O
products O
based O
on O
the O
intended O
application O
. O


This O
article O
addresses O
the O
effect O
of O
variable O
throughout O
layer B-PARA
thickness E-PARA
configuration S-CONPRI
in O
the O
binder-jet O
additive B-MANP
manufacturing E-MANP
of O
titanium S-MATE
structures O
for O
orthopedic O
applications O
. O


Two O
layer B-PARA
thicknesses E-PARA
of O
80 O
and O
150 O
μm O
are O
selectively O
controlled O
inside O
of O
each O
titanium S-MATE
sample S-CONPRI
with O
four O
different O
configurations O
. O


Several O
studies O
were O
performed O
, O
including O
shrinkage S-CONPRI
analysis O
, O
porosity S-PRO
measurements O
, O
and O
mechanical S-APPL
compression B-CHAR
tests E-CHAR
to O
quantify O
the O
effect O
of O
layer B-PARA
thickness E-PARA
on O
part O
quality S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
results O
of O
the O
porosity S-PRO
measurement S-CHAR
revealed O
that O
there O
is O
about O
5 O
% O
variation S-CONPRI
among O
the O
samples S-CONPRI
with O
different O
layer B-PARA
thickness E-PARA
configuration S-CONPRI
. O


Bulk B-PRO
porosity E-PRO
values O
obtained O
from O
micro O
computed B-CHAR
tomography E-CHAR
( O
μCT O
) O
scan O
data S-CONPRI
placed O
the O
bulk B-PRO
porosity E-PRO
of O
the O
samples S-CONPRI
combining O
more O
than O
one O
layer B-PARA
thickness E-PARA
, O
in O
between O
of O
the O
results O
for O
control O
specimens O
, O
which O
were O
manufactured S-CONPRI
by O
applying O
a O
single O
layer B-PARA
thickness E-PARA
throughout O
the O
samples S-CONPRI
. O


Mechanical B-CONPRI
properties E-CONPRI
did O
not O
show O
any O
significant O
variation S-CONPRI
, O
which O
is O
attributed O
to O
the O
low O
range S-PARA
of O
the O
porosity S-PRO
deviation O
( O
less O
than O
5 O
% O
) O
. O


The O
highest O
Young O
’ O
s S-MATE
modulus O
of O
3.50 O
± O
0.4 O
GPa S-PRO
and O
yield B-PRO
stress E-PRO
of O
175 O
± O
25 O
MPa S-CONPRI
were O
obtained O
from O
analysis O
of O
the O
data S-CONPRI
achieved O
from O
the O
compression B-CHAR
test E-CHAR
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
techniques O
provide O
significant O
advantages O
over O
conventional O
subtractive B-MANP
manufacturing E-MANP
techniques O
in O
terms O
of O
the O
wide O
range S-PARA
of O
part O
geometry S-CONPRI
that O
can O
be S-MATE
obtained O
. O


Powder S-MATE
delivery O
is O
a O
process S-CONPRI
that O
occurs O
thousands O
of O
times O
during O
the O
AM S-MANP
build O
process S-CONPRI
, O
consequently O
assessment O
of O
delivery O
quality S-CONPRI
would O
be S-MATE
advantageous O
in O
the O
process S-CONPRI
in O
order O
to O
provide O
feedback S-PARA
for O
process B-CONPRI
control E-CONPRI
. O


This O
paper O
presents O
an O
in-situ S-CONPRI
quantitative O
inspection S-CHAR
technique O
for O
assessing O
the O
whole O
of O
the O
powder B-MACEQ
bed E-MACEQ
post O
raking O
, O
by O
using O
fringe O
projection O
profilometry O
. O


In O
order O
to O
increase O
accuracy S-CHAR
and O
traceability O
of O
the O
inspection S-CHAR
technique O
, O
an O
accepted O
fringe O
projection O
method O
, O
is O
enhanced O
using O
a O
novel O
surface S-CONPRI
fitting O
algorithm S-CONPRI
employed O
to O
reduce O
the O
influence O
of O
phase B-CONPRI
error E-CONPRI
and O
random O
noise O
during O
calibration S-CONPRI
. O


A O
simulation S-ENAT
was O
conducted O
to O
verify O
the O
accuracy S-CHAR
of O
the O
proposed O
system O
calibration S-CONPRI
. O


The O
proposed O
in-situ S-CONPRI
inspection O
technique O
has O
been O
applied O
in O
an O
Electron B-CONPRI
Beam E-CONPRI
Powder O
Bed B-MANP
Fusion E-MANP
( O
PBF-EB O
) O
machine S-MACEQ
, O
also O
known O
as S-MATE
Electron O
Beam S-MACEQ
Melting O
( O
EBM S-MANP
) O
. O


Some O
examples O
of O
melting S-MANP
edge O
swelling S-CONPRI
and O
excessive O
powder S-MATE
delivery O
due O
to O
rake O
damage S-PRO
during O
a O
real O
part O
build S-PARA
are O
used O
to O
demonstrate O
the O
system O
capability O
on O
the O
actual O
EBM S-MANP
machine O
. O


Experimental S-CONPRI
results O
demonstrate O
that O
powder S-MATE
defects S-CONPRI
can O
be S-MATE
efficiently O
inspected O
and O
the O
results O
used O
as S-MATE
feedback O
information O
in O
a O
build S-PARA
process O
. O


The O
Big O
Area S-PARA
Additive B-MANP
Manufacturing E-MANP
( O
BAAM O
) O
system O
can O
print S-MANP
structures O
on O
the O
order O
of O
several O
meters O
at O
high O
extrusion B-PARA
rates E-PARA
, O
thereby O
having O
the O
potential O
to O
significantly O
impact S-CONPRI
automotive S-APPL
, O
aerospace S-APPL
and O
energy O
sectors O
. O


The O
functional O
use O
of O
such O
parts O
, O
however O
, O
may O
be S-MATE
limited O
by O
mechanical B-PRO
anisotropy E-PRO
, O
in O
which O
the O
strength S-PRO
of O
printed O
parts O
across O
successive O
layers O
in O
the O
build B-PARA
direction E-PARA
( O
z-direction S-FEAT
) O
can O
be S-MATE
significantly O
lower O
than O
the O
corresponding O
in-plane B-PRO
strength E-PRO
( O
x-y O
directions O
) O
. O


This O
has O
been O
primarily O
attributed O
to O
poor O
bonding S-CONPRI
between O
printed O
layers O
since O
the O
lower O
layers O
cool O
below O
the O
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
( O
Tg S-CHAR
) O
before O
the O
next O
layer S-PARA
is O
deposited O
. O


Therefore O
, O
the O
potential O
of O
using O
infrared S-CONPRI
heating S-MANP
is O
considered O
for O
increasing O
the O
surface S-CONPRI
temperature O
of O
the O
printed O
layer S-PARA
just O
prior O
to O
deposition S-CONPRI
of O
new O
material S-MATE
to O
improve O
the O
interlayer B-CONPRI
strength E-CONPRI
of O
the O
components S-MACEQ
. O


This O
study O
found O
significant O
improvements O
in O
bond B-CONPRI
strength E-CONPRI
for O
the O
deposition S-CONPRI
of O
acrylonitrile B-MATE
butadiene I-MATE
styrene E-MATE
( O
ABS S-MATE
) O
reinforced S-CONPRI
with O
20 O
% O
chopped O
carbon B-MATE
fiber E-MATE
when O
the O
surface S-CONPRI
temperature O
of O
the O
substrate B-MATE
material E-MATE
was O
increased O
from O
below O
Tg S-CHAR
to O
close O
to O
or O
above O
Tg S-CHAR
using O
infrared S-CONPRI
heating S-MANP
. O


The O
use O
of O
Magnetic O
Resonance O
Imaging S-APPL
( O
MRI O
) O
for O
monitoring O
, O
studying O
and O
performing O
output O
quality S-CONPRI
measurements O
of O
the O
acrylate-based O
polymeric O
patterns O
manufactured S-CONPRI
using O
stereolithography S-MANP
( O
SL S-MANP
) O
was O
introduced O
in O
this O
work O
. O


The O
effects O
of O
build B-PARA
parameters E-PARA
and O
humid O
environment O
on O
sample S-CONPRI
homogeneity O
, O
distribution S-CONPRI
of O
crosslink O
density S-PRO
, O
stability S-PRO
and O
defect S-CONPRI
formation O
were O
examined O
. O


The O
spatial O
resolution S-PARA
of O
the O
method O
was O
found O
to O
be S-MATE
sufficient O
to O
identify O
patterns O
according O
to O
the O
build B-PARA
parameters E-PARA
used O
and O
to O
detect O
specific O
hatch-predicted O
crosslink O
density S-PRO
variations O
. O


Qualitative S-CONPRI
information O
obtained O
using O
MRI O
visualisation O
was O
supplemented O
by O
quantitative B-CHAR
measurements E-CHAR
of O
Nuclear B-CONPRI
Magnetic I-CONPRI
Resonance E-CONPRI
( O
NMR S-CHAR
) O
relaxation O
times O
and O
1H O
NMR S-CHAR
spectra O
. O


NMR S-CHAR
spectroscopy O
confirmed O
the O
identity O
of O
the O
chemical B-CONPRI
composition E-CONPRI
among O
the O
patterns O
and O
showed O
that O
the O
crosslink O
density S-PRO
variation O
observed O
via O
spatially O
resolved O
T2-profiles O
stems O
from O
the O
difference O
of O
the O
build B-PARA
parameters E-PARA
. O


Different O
types O
of O
defects S-CONPRI
in O
the O
samples S-CONPRI
were O
observed O
and O
classified O
; O
some O
defects S-CONPRI
originated O
from O
local O
matrix O
continuity O
failures O
( O
partially O
cured S-MANP
resin O
trapping O
within O
the O
polymer S-MATE
or O
bubbles O
formation O
) O
, O
while O
other O
defects S-CONPRI
were O
found O
in O
the O
form O
of O
bulk O
layering O
. O


MRI O
visualisation O
coupled O
with O
relaxometry O
and O
1H O
spectroscopy S-CONPRI
of O
patterns O
during O
their O
interaction O
with O
humidity O
allowed O
tracking O
water O
distribution S-CONPRI
inside O
the O
sample S-CONPRI
and O
observing O
effects O
of O
swelling S-CONPRI
, O
fracturing O
and O
chemical O
decomposition S-PRO
. O


As S-MATE
a O
result O
, O
the O
approach O
presented O
in O
this O
work O
improves O
the O
output O
quality B-CONPRI
control E-CONPRI
and O
current O
testing S-CHAR
techniques O
, O
provides O
insight O
how O
physical B-PRO
properties E-PRO
of O
the O
3D B-APPL
parts E-APPL
are O
affected O
by O
different O
technical O
parameters S-CONPRI
, O
and O
eventually O
can O
help O
the O
use O
of O
SL S-MANP
technologies O
for O
a O
variety O
of O
applications O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
evolving O
from O
rapid B-ENAT
prototyping E-ENAT
to O
production S-MANP
of O
structural B-CONPRI
components E-CONPRI
. O


The O
widespread O
application O
of O
AM S-MANP
demands O
a O
high O
level O
of O
mechanical S-APPL
performance O
from O
these O
components S-MACEQ
, O
and O
it O
is O
therefore O
essential O
to O
improve O
feedstock B-MATE
material E-MATE
in O
order O
to O
meet O
these O
mechanical S-APPL
expectations O
. O


However O
, O
compared O
to O
traditional B-MANP
manufacturing E-MANP
techniques O
, O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
AM B-MATE
materials E-MATE
and O
their O
resulting O
components S-MACEQ
are O
not O
well O
understood O
. O


In O
this O
study O
, O
we O
investigated O
the O
processability O
, O
microstructure S-CONPRI
, O
and O
mechanical S-APPL
performance O
of O
twin-screw O
compounded O
short B-MATE
carbon I-MATE
fiber I-MATE
reinforced I-MATE
polyphenylene I-MATE
sulfide E-MATE
( O
PPS O
) O
pellets S-CONPRI
as S-MATE
a O
feedstock B-MATE
material E-MATE
for O
big O
area S-PARA
AM S-MANP
( O
BAAM O
) O
. O


The O
performance S-CONPRI
of O
the O
AM S-MANP
components O
was O
compared O
to O
that O
of O
traditional O
processing O
methods O
, O
namely O
injection B-MANP
molding E-MANP
( O
IM O
) O
and O
extrusion-compression O
molding S-MANP
( O
ECM S-MANP
) O
. O


It O
was O
found O
that O
the O
AM S-MANP
composites O
exhibited O
118 O
% O
lower O
tensile B-PRO
strength E-PRO
and O
55 O
% O
lower O
tensile S-PRO
modulus O
when O
compared O
to O
traditional O
injection B-MANP
molding E-MANP
composite S-MATE
specimens O
; O
however O
, O
AM S-MANP
composites O
exhibited O
comparable O
properties S-CONPRI
to O
ECM S-MANP
composites S-MATE
. O


This O
response O
was O
attributed O
to O
highly O
aligned O
fibers S-MATE
in O
IM O
and O
AM S-MANP
samples O
. O


However O
, O
the O
AM S-MANP
composites O
contained O
porosity S-PRO
( O
15.5 O
% O
volume S-CONPRI
) O
, O
which O
reduced O
their O
mechanical B-CONPRI
properties E-CONPRI
in O
comparison O
to O
ECM S-MANP
composites S-MATE
. O


The O
IM O
process S-CONPRI
showed O
the O
maximum O
amount O
of O
fiber S-MATE
attrition O
with O
minimum O
porosity S-PRO
( O
0.007 O
% O
volume S-CONPRI
) O
, O
while O
the O
ECM S-MANP
process O
exhibited O
the O
least O
fiber S-MATE
attrition O
with O
4.3 O
% O
volume S-CONPRI
porosity S-PRO
. O


Composite B-MANP
manufacturing E-MANP
processes O
adapted O
for O
assisted-additive O
manufacturing S-MANP
( O
AM S-MANP
) O
have O
recently O
been O
proposed O
. O


Extrusion-based O
AM S-MANP
utilizes O
shear-driven O
alignment O
in O
producing O
printed O
structures O
where O
polymers S-MATE
and O
fibers S-MATE
naturally O
align O
parallel O
to O
the O
material S-MATE
flow O
. O


Convergent O
flow O
geometries S-CONPRI
become O
the O
dominant O
processing O
route O
for O
thermoplastic-melts O
and O
thermoset O
polymer B-MANP
extrusions E-MANP
. O


For O
rotational O
fibers S-MATE
, O
the O
phenomenon O
known O
as S-MATE
Jeffrey O
orbits O
poses O
issues O
during O
extrusion S-MANP
through O
a O
convergent O
channel S-APPL
, O
resulting O
in O
a O
randomized O
fiber S-MATE
architecture S-APPL
. O


Methods O
of O
minimizing O
Jeffrey O
orbits O
include O
the O
application O
of O
an O
additional O
external O
force S-CONPRI
such O
as S-MATE
a O
magnetic B-CONPRI
field E-CONPRI
to O
arrest O
or O
counteract O
the O
rotation O
. O


This O
work O
explores O
a O
combination O
of O
magnetic O
forces S-CONPRI
in O
conjunction O
with O
adjusted O
channel S-APPL
geometries O
using O
theory O
and O
experimental S-CONPRI
observations O
. O


The O
findings O
suggest O
the O
ability O
to O
alter O
fiber B-FEAT
orientation E-FEAT
in O
flow O
in O
a O
300 O
cP O
viscosity S-PRO
matrix O
by O
modifying O
the O
extrusion S-MANP
channel S-APPL
geometry O
. O


Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
has O
largely O
relieved O
the O
design B-CONPRI
freedom E-CONPRI
of O
functional O
parts O
. O


Topology B-FEAT
optimization E-FEAT
has O
been O
widely O
used O
to O
design S-FEAT
lightweight O
structures O
fabricated S-CONPRI
by O
AM S-MANP
. O


In O
this O
paper O
, O
a O
general O
design S-FEAT
method O
is O
proposed O
to O
design S-FEAT
solid O
lattice S-CONPRI
hybrid O
structures O
. O


An O
optimization B-CONPRI
algorithm E-CONPRI
is O
used O
in O
this O
method O
that O
can O
generate O
a O
functionally B-CONPRI
graded E-CONPRI
heterogeneous O
lattice B-FEAT
structure E-FEAT
connecting O
the O
solid O
part O
. O


The O
manufacturability S-CONPRI
can O
be S-MATE
improved O
due O
to O
the O
lattice B-FEAT
structure E-FEAT
supporting O
the O
overhangs S-PARA
. O


A O
hybrid O
element S-MATE
model O
is O
used O
to O
simulate O
the O
mechanical S-APPL
performance O
and O
optimize O
the O
material S-MATE
distribution S-CONPRI
of O
the O
lattice B-FEAT
structure E-FEAT
. O


To O
validate O
the O
design S-FEAT
theory O
and O
the O
advantage O
of O
the O
hybrid O
structure S-CONPRI
, O
a O
three-point B-CHAR
bending E-CHAR
beam S-MACEQ
is O
designed S-FEAT
by O
the O
proposed O
method O
and O
the O
existing O
methods O
. O


Both O
the O
simulation S-ENAT
result O
and O
the O
experimental S-CONPRI
result O
show O
that O
the O
hybrid O
structure S-CONPRI
has O
a O
higher O
stiffness S-PRO
, O
yield B-PRO
strength E-PRO
, O
and O
critical O
buckling B-CHAR
load E-CHAR
than O
the O
pure O
solid O
structure S-CONPRI
and O
the O
pure O
lattice B-FEAT
structure E-FEAT
. O


Advancements O
in O
distributed O
recycling S-CONPRI
technologies O
now O
allow O
for O
on-demand O
reconstitution O
of O
traditionally O
neglected O
MRE O
pouch O
waste O
into O
useful O
appliances O
via O
material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
. O


In O
this O
work O
, O
we O
demonstrate O
recycling S-CONPRI
of O
MRE O
pouch O
materials S-CONPRI
through O
a O
combined O
compounding O
, O
filament S-MATE
extrusion S-MANP
, O
and O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
additive B-MANP
manufacturing E-MANP
protocol O
. O


Mechanical B-CONPRI
properties E-CONPRI
and O
barrier O
properties S-CONPRI
of O
additively B-MANP
manufactured E-MANP
structures O
were O
evaluated O
through O
tensile B-CHAR
testing E-CHAR
and O
water O
vapor O
transmission S-CHAR
testing S-CHAR
, O
respectively O
, O
and O
found O
to O
be S-MATE
comparable O
to O
the O
native O
pouch O
materials S-CONPRI
. O


Differential O
Scanning S-CONPRI
Calorimetry O
and O
Thermogravimetric B-CHAR
Analysis E-CHAR
of O
the O
extruded S-MANP
filament O
and O
printed O
materials S-CONPRI
were O
contrasted O
with O
native O
pouch O
materials S-CONPRI
, O
showing O
minimal O
effects O
of O
the O
manufacturing B-MANP
process E-MANP
on O
critical O
thermal O
transitions O
in O
the O
polymer S-MATE
. O


To O
reduce O
the O
lead B-PARA
time E-PARA
, O
polymer S-MATE
fuel O
tanks O
could O
be S-MATE
toollessly O
produced O
using O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
. O


Detailed O
knowledge O
of O
the O
performance S-CONPRI
of O
AM S-MANP
polymers O
is O
essential O
for O
the O
design S-FEAT
and O
development O
of O
such O
components S-MACEQ
. O


In O
instrumented O
static O
( O
0.01 O
mm/s O
) O
and O
dynamic S-CONPRI
( O
2.5 O
m/s O
) O
three-point B-CHAR
bending E-CHAR
and O
puncture O
tests O
, O
the O
impact S-CONPRI
behaviors O
of O
polyamide S-MATE
and O
methacrylate-based O
photopolymer S-MATE
test O
specimens O
were O
compared O
. O


The O
polyamide S-MATE
test O
specimens O
were O
produced O
by O
laser B-MANP
sintering E-MANP
and O
multijet O
fusion S-CONPRI
, O
and O
the O
photopolymer S-MATE
test O
specimens O
were O
produced O
by O
a O
hot O
lithography S-CONPRI
process O
. O


Fractography S-CHAR
was O
performed O
using O
stereo O
light O
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
to O
investigate O
the O
fracture S-CONPRI
surface O
morphology S-CONPRI
. O


The O
test O
results O
were O
used O
to O
analyze O
the O
relationships O
among O
the O
surface B-PRO
roughness E-PRO
, O
shear B-PRO
modulus E-PRO
, O
and O
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
. O


The O
AM S-MANP
polymers O
revealed O
comparable O
force–displacement O
behaviors O
in O
a O
static O
three-point B-CHAR
bending I-CHAR
test E-CHAR
, O
but O
their O
impact S-CONPRI
behaviors O
differed O
greatly O
. O


The O
obtained O
results O
highlight O
that O
the O
impact S-CONPRI
performance O
of O
AM S-MANP
polymers O
is O
an O
essential O
design S-FEAT
variable O
for O
fluid-containing O
parts O
. O


This O
investigation O
focuses O
on O
geometric O
parameters S-CONPRI
of O
nozzles S-MACEQ
used O
in O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
. O


They O
are O
mainly O
responsible O
for O
the O
extrusion S-MANP
force O
. O


Typical O
nozzles S-MACEQ
are O
made O
of O
brass S-MATE
and O
feature S-FEAT
a O
decrease O
in O
diameter S-CONPRI
from O
an O
entry O
channel S-APPL
to O
a O
capillary O
with O
a O
conical O
section O
in O
between O
. O


Commercially O
available O
and O
custom O
nozzles S-MACEQ
with O
various O
of O
these O
parameters S-CONPRI
were O
investigated O
on O
a O
test O
stand O
using O
Polylactic B-MATE
Acid E-MATE
( O
PLA S-MATE
) O
filament S-MATE
. O


All O
nozzles S-MACEQ
exhibit O
a O
common O
behavior O
. O


The O
extrusion S-MANP
force O
rises O
linearly O
with O
increasing O
filament S-MATE
feed S-PARA
velocity O
. O


Here O
, O
unmolten O
plastic S-MATE
reaches O
the O
nozzle S-MACEQ
. O


This O
characteristic O
is O
dependent O
on O
extrusion S-MANP
temperature O
and O
geometric O
parameters S-CONPRI
of O
the O
nozzles S-MACEQ
. O


Different O
capillary O
lengths O
were O
used O
to O
determine O
the O
entry O
pressure S-CONPRI
loss O
at O
different O
filament S-MATE
feed S-PARA
velocities O
. O


The O
material S-MATE
and O
coating S-APPL
of O
the O
nozzles S-MACEQ
had O
no O
significant O
influence O
on O
extrusion S-MANP
force O
. O


A O
higher O
thermal O
mass O
, O
two O
conical O
sections O
or O
two O
entry O
channels O
have O
a O
positive O
effect O
on O
extrusion S-MANP
forces O
and O
maximum O
filament S-MATE
feed S-PARA
velocities O
, O
thus O
maximal O
build B-CHAR
rate E-CHAR
. O


Multi-material B-MANP
additive I-MANP
manufacturing E-MANP
enables O
high-performance O
heterogeneous S-CONPRI
design S-FEAT
at O
the O
mesoscale S-CONPRI
, O
through O
which O
bulk O
parts O
can O
be S-MATE
engineered O
to O
adapt O
to O
complex O
loading O
conditions O
. O


The O
optimization S-CONPRI
of O
multi-material S-CONPRI
parts O
relies O
on O
accurate S-CHAR
forward O
prediction S-CONPRI
, O
which O
is O
challenging O
to O
achieve O
owing O
to O
the O
complex O
processing O
conditions O
in O
additive B-MANP
manufacturing E-MANP
and O
the O
resultant O
uncertainties O
in O
material B-CONPRI
properties E-CONPRI
. O


To O
address O
these O
limitations O
, O
here O
we O
present O
a O
new O
model B-CONPRI
calibration E-CONPRI
and O
model S-CONPRI
selection O
framework S-CONPRI
based O
on O
the O
high O
dimensional O
, O
local-scale O
deformation B-CONPRI
data E-CONPRI
. O


By O
matching O
the O
pixel-level O
deformation B-CONPRI
data E-CONPRI
from O
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
experiments O
and O
constitutive O
modeling S-ENAT
, O
the O
presented O
framework S-CONPRI
enables O
more O
accurate S-CHAR
prediction O
and O
significant O
reduction S-CONPRI
of O
the O
prediction S-CONPRI
uncertainties O
, O
as S-MATE
compared O
to O
the O
single O
material S-MATE
calibration S-CONPRI
approach O
that O
is O
widely O
used O
in O
additive B-MANP
manufacturing E-MANP
. O


In O
turn O
, O
this O
enables O
quantitative S-CONPRI
comparison O
of O
the O
candidate O
models O
, O
so O
the O
most O
accurate S-CHAR
and O
computationally O
efficient O
constitutive O
model S-CONPRI
can O
be S-MATE
selected O
for O
forward O
prediction S-CONPRI
in O
heterogeneous S-CONPRI
material O
design S-FEAT
. O


The O
advantages O
of O
the O
framework S-CONPRI
are O
demonstrated O
using O
a O
multi-polymer O
system O
manufactured S-CONPRI
by O
dual-extrusion O
additive B-MANP
manufacturing E-MANP
, O
which O
consists O
of O
two O
constituent O
materials S-CONPRI
with O
dramatically O
different O
deformation S-CONPRI
behaviors O
. O


Despite O
the O
potential O
benefits O
of O
photopolymerization-based S-CONPRI
additive B-MANP
manufacturing E-MANP
, O
photochemical S-MATE
reactions O
in O
free-radical O
polymerization S-MANP
rarely O
proceed O
to O
completion O
, O
leading O
to O
the O
accumulation O
of O
residual S-CONPRI
monomer S-MATE
in O
polymer S-MATE
networks O
. O


In O
the O
absence O
of O
residual S-CONPRI
methyl O
methacrylate O
, O
other O
potentially O
toxic O
acrylic S-MATE
esters O
were O
observed O
thus O
emphasizing O
the O
need O
to O
thoroughly O
scrutinize O
additively B-MANP
manufactured E-MANP
dental O
devices O
prior O
to O
their O
use O
. O


In O
the O
long O
term O
, O
standards S-CONPRI
for O
medical B-APPL
devices E-APPL
in O
dentistry S-APPL
could O
be S-MATE
revised O
to O
reflect O
the O
current O
trends S-CONPRI
in O
biomaterials S-MATE
and O
precursors O
they O
are O
generated O
from O
. O


The O
tensile B-PRO
strength E-PRO
and O
strain S-PRO
properties S-CONPRI
as S-MATE
well O
as S-MATE
failure O
modes O
in O
silicone S-MATE
dumbbell O
specimens O
fabricated S-CONPRI
by O
extrusion-based O
additive B-MANP
manufacturing E-MANP
are O
investigated O
. O


Effects O
of O
process B-CONPRI
parameters E-CONPRI
, O
specifically O
the O
infill S-PARA
direction O
( O
0° O
, O
±45° O
, O
and O
90° O
relative O
to O
the O
tensile S-PRO
direction O
) O
and O
adjacent O
line O
spacing O
on O
the O
void S-CONPRI
formation O
and O
ultimate B-PRO
tensile I-PRO
strength E-PRO
are O
studied O
and O
compared O
to O
the O
baseline O
of O
stamped O
silicone S-MATE
specimens O
. O


The O
additive B-MANP
manufactured E-MANP
specimens O
with O
±45° O
and O
90° O
infill S-PARA
direction O
and O
either O
the O
minimal O
or O
small O
void S-CONPRI
extrusion S-MANP
configuration S-CONPRI
had O
the O
strongest O
ultimate B-PRO
tensile I-PRO
strength E-PRO
( O
average S-CONPRI
ranged O
from O
1.44 O
to O
1.51 O
MPa S-CONPRI
) O
. O


This O
strength S-PRO
is O
close O
to O
that O
of O
the O
sheet S-MATE
stamped O
specimens O
which O
have O
an O
average S-CONPRI
ultimate O
tensile B-PRO
strength E-PRO
of O
1.63 O
MPa S-CONPRI
. O


As S-MATE
the O
void S-CONPRI
size O
became O
larger O
and O
more O
elongated O
in O
shape O
, O
the O
average S-CONPRI
ultimate O
tensile B-PRO
strength E-PRO
significantly O
reduced O
to O
1.15 O
and O
0.90 O
MPa S-CONPRI
for O
specimens O
with O
±45° O
and O
90° O
infill S-PARA
direction O
, O
respectively O
. O


Counterintuitively O
, O
specimens O
with O
0° O
infill S-PARA
direction O
were O
consistently O
the O
worst O
performing O
due O
to O
the O
tangency O
voids S-CONPRI
and O
poor O
edge O
surface B-FEAT
finish E-FEAT
resulting O
from O
the O
toolpath S-PARA
. O


We O
show O
that O
, O
to O
maximize O
ultimate B-PRO
tensile I-PRO
strength E-PRO
of O
silicone S-MATE
parts O
made O
by O
extrusion-based O
additive B-MANP
manufacturing E-MANP
, O
it O
is O
important O
to O
select O
process B-CONPRI
parameters E-CONPRI
which O
minimize O
the O
elongated O
voids S-CONPRI
, O
infill S-PARA
tangency O
voids S-CONPRI
, O
and O
surface S-CONPRI
edges O
. O


If O
these O
conditions O
can O
be S-MATE
achieved O
, O
the O
infill S-PARA
direction O
does O
not O
play O
a O
significant O
role O
in O
tensile B-PRO
strength E-PRO
of O
the O
tensile B-MACEQ
specimen E-MACEQ
. O


As S-MATE
part O
of O
a O
larger O
study O
on O
the O
laser B-MANP
sintering E-MANP
( O
LS O
) O
of O
nano-composite O
structures O
for O
biomedical B-APPL
applications E-APPL
, O
a O
wet O
mixing S-CONPRI
method O
was O
used O
to O
coat O
Polyamide B-MATE
12 E-MATE
( O
PA12 S-MATE
) O
particles S-CONPRI
with O
nano-hydroxyapatite O
( O
nHA O
) O
. O


The O
addition O
of O
nHA O
significantly O
affected O
powder S-MATE
processability O
due O
to O
laser S-ENAT
absorption S-CONPRI
and O
heat B-CONPRI
transfer E-CONPRI
effects O
which O
led S-APPL
to O
part O
warping S-CONPRI
. O


Nano-composites O
containing O
0.5–1.5 O
wt O
% O
nHA O
were O
successfully O
produced O
and O
tensile B-CHAR
testing E-CHAR
showed O
that O
0.5 O
wt O
% O
nHA O
provided O
the O
greatest O
reinforcement S-PARA
with O
a O
20 O
% O
and O
15 O
% O
increase O
in O
modulus O
and O
strength S-PRO
respectively O
. O


However O
, O
the O
elongation S-PRO
at O
break O
had O
significantly O
declined O
which O
was O
likely O
due O
to O
the O
formation O
of O
nHA O
aggregates S-MATE
at O
the O
sintering S-MANP
borders O
following O
the O
processing O
of O
the O
coated S-APPL
powders O
despite O
being O
initially O
well O
dispersed O
on O
the O
particle S-CONPRI
surface O
. O


An O
intelligent O
optimization S-CONPRI
system O
is O
proposed O
to O
establish O
quantitative S-CONPRI
relationships O
between O
process B-CONPRI
parameters E-CONPRI
and O
multiple O
optimization S-CONPRI
objectives O
, O
including O
mechanical B-CONPRI
properties E-CONPRI
, O
productivity S-CONPRI
, O
energy O
efficiency O
, O
etc O
. O


Contour S-FEAT
maps O
of O
operation O
window O
, O
productivity S-CONPRI
and O
energy O
efficiency O
can O
be S-MATE
developed O
to O
predict O
optimal O
parameters S-CONPRI
by O
considering O
the O
constraints O
of O
mechanical B-CONPRI
properties E-CONPRI
and O
material S-MATE
degradation S-CONPRI
. O


Using O
a O
facile O
data-driven O
approach O
, O
the O
relationships O
between O
process B-CONPRI
parameters E-CONPRI
and O
optimization S-CONPRI
objectives O
can O
be S-MATE
utilized O
in O
the O
process B-CONPRI
optimization E-CONPRI
and O
material S-MATE
selection O
. O


Powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
represents O
a O
class O
of O
additive B-MANP
manufacturing I-MANP
processes E-MANP
with O
the O
unique O
advantage O
of O
being O
able O
to O
fabricate S-MANP
functional O
products O
with O
complex O
three-dimensional B-CONPRI
geometries E-CONPRI
. O


PBF S-MANP
has O
been O
broadly O
applied O
in O
highly O
value-added O
industries S-APPL
, O
including O
the O
biomedical S-APPL
device O
and O
aerospace B-APPL
industries E-APPL
. O


However O
, O
it O
is O
challenging O
to O
construct O
a O
comprehensive O
knowledgebase O
to O
guide O
material S-MATE
selection O
and O
process B-CONPRI
optimization E-CONPRI
decisions O
to O
satisfy O
the O
product O
standards S-CONPRI
of O
various O
industries S-APPL
based O
on O
a O
poor O
understanding O
of O
process-structure-property/performance O
relationships O
for O
each O
type O
of O
thermoplastic S-MATE
. O


In O
this O
paper O
, O
an O
intelligent O
optimization S-CONPRI
system O
is O
proposed O
to O
establish O
quantitative S-CONPRI
relationships O
between O
process B-CONPRI
parameters E-CONPRI
and O
multiple O
optimization S-CONPRI
objectives O
, O
including O
mechanical B-CONPRI
properties E-CONPRI
, O
productivity S-CONPRI
, O
energy O
efficiency O
, O
and O
degree O
of O
material S-MATE
degradation S-CONPRI
. O


Polyurethane S-MATE
is O
considered O
as S-MATE
a O
representative O
thermoplastic S-MATE
because O
it O
is O
sensitive O
to O
thermal-induced O
degradation S-CONPRI
and O
has O
a O
relatively O
narrow O
process S-CONPRI
window O
. O


Material S-MATE
and O
powder S-MATE
properties O
as S-MATE
functions O
of O
temperature S-PARA
are O
investigated O
using O
systematic O
material S-MATE
screening O
. O


Numerical O
models O
are O
created O
to O
analyze O
the O
interactions O
between O
laser B-CONPRI
beams E-CONPRI
and O
polymeric O
powders S-MATE
by O
considering O
the O
effects O
of O
chamber O
thermal O
conditions O
, O
laser S-ENAT
parameters O
, O
temperature-dependent O
properties S-CONPRI
, O
and O
phase S-CONPRI
transitions O
of O
polymers S-MATE
, O
as S-MATE
well O
as S-MATE
laser O
beam S-MACEQ
characteristics O
. O


The O
theoretically O
predicted S-CONPRI
features O
of O
melting S-MANP
pools O
are O
validated O
experimentally O
and O
then O
utilized O
to O
develop O
quantitative S-CONPRI
relationships O
between O
process B-CONPRI
parameters E-CONPRI
and O
multiple O
optimization S-CONPRI
objectives O
. O


The O
established O
relationships O
can O
guide O
process B-CONPRI
parameter E-CONPRI
optimization S-CONPRI
and O
material S-MATE
selection O
decisions O
for O
polymer S-MATE
PBF S-MANP
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
emerging O
as S-MATE
a O
promising O
technology S-CONPRI
to O
fabricate S-MANP
cost-effective O
, O
customized O
functional O
parts O
. O


Designing O
such O
functional O
, O
i.e. O
, O
load O
bearing O
, O
parts O
can O
be S-MATE
challenging O
and O
time O
consuming O
where O
the O
goal O
is O
to O
balance O
performance S-CONPRI
and O
material S-MATE
usage O
. O


Topology B-FEAT
optimization E-FEAT
( O
TO O
) O
is O
a O
powerful O
design S-FEAT
method O
which O
can O
complement O
AM S-MANP
by O
automating O
the O
design B-CONPRI
process E-CONPRI
. O


However O
, O
for O
TO O
to O
be S-MATE
a O
useful O
methodology S-CONPRI
, O
the O
underlying O
mathematical S-CONPRI
model O
must O
be S-MATE
carefully O
constructed O
. O


Specifically O
, O
it O
is O
well O
established O
that O
parts O
fabricated S-CONPRI
through O
some O
AM B-MANP
technologies E-MANP
, O
such O
as S-MATE
fused O
deposition B-CONPRI
modeling E-CONPRI
( O
FDM S-MANP
) O
, O
exhibit O
behavioral O
anisotropicity O
. O


This O
induced O
anisotropy S-PRO
can O
have O
a O
negative O
impact S-CONPRI
on O
functionality O
of O
the O
part O
, O
and O
must O
be S-MATE
considered O
. O


In O
the O
present O
work O
, O
a O
strength-based O
topology B-FEAT
optimization E-FEAT
method O
for O
structures O
with O
anisotropic S-PRO
materials O
is O
presented O
. O


More O
specifically O
, O
we O
propose O
a O
new O
topological B-CONPRI
sensitivity E-CONPRI
formulation O
based O
on O
strength S-PRO
ratio O
of O
non-homogeneous O
failure S-CONPRI
criteria O
, O
such O
as S-MATE
Tsai-Wu O
. O


The O
rapid O
transition S-CONPRI
of O
the O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
from O
small O
scale O
prototype S-CONPRI
models O
to O
large O
scale O
polymer S-MATE
deposition S-CONPRI
has O
been O
driven O
, O
in O
part O
, O
by O
the O
addition O
of O
short B-MATE
carbon I-MATE
fibers E-MATE
to O
the O
polymer B-MATE
feedstock E-MATE
. O


The O
addition O
of O
short B-MATE
carbon I-MATE
fibers E-MATE
improves O
both O
the O
mechanical S-APPL
and O
thermal B-CONPRI
properties E-CONPRI
of O
the O
printed O
beads S-CHAR
. O


The O
improvements O
to O
the O
anisotropic S-PRO
mechanical O
and O
thermal B-CONPRI
properties E-CONPRI
of O
the O
polymer B-MATE
feedstock E-MATE
are O
dependent O
on O
the O
spatially O
varying O
orientation S-CONPRI
of O
short B-MATE
carbon I-MATE
fibers E-MATE
which O
is O
itself O
a O
function O
of O
the O
velocity O
gradients O
in O
the O
flow O
field O
throughout O
the O
nozzle S-MACEQ
and O
in O
the O
extrudate S-MATE
during O
deposition S-CONPRI
flow O
. O


This O
paper O
presents O
a O
computational O
approach O
for O
simulating O
the O
deposition S-CONPRI
flow O
that O
occurs O
in O
the O
Large O
Area S-PARA
Additive B-MANP
Manufacturing E-MANP
( O
LAAM O
) O
process S-CONPRI
and O
the O
effects O
on O
the O
final O
short B-MATE
fiber E-MATE
orientation S-CONPRI
state O
in O
the O
deposited O
polymer S-MATE
bead S-CHAR
and O
the O
resulting O
bead S-CHAR
mechanical O
and O
thermal B-CONPRI
properties E-CONPRI
. O


The O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
is O
used O
to O
evaluate O
Stokes O
flow O
for O
a O
two-dimensional S-CONPRI
planar O
flow O
field O
within O
a O
Strangpresse O
Model S-CONPRI
19 O
LAAM O
polymer S-MATE
deposition S-CONPRI
nozzle O
. O


A O
shape O
optimization S-CONPRI
method O
is O
employed O
to O
compute O
the O
shape O
of O
the O
polymer B-MATE
melt E-MATE
flow O
free B-CONPRI
surface E-CONPRI
below O
the O
nozzle S-MACEQ
exit O
as S-MATE
the O
bead S-CHAR
is O
deposited O
on O
a O
moving O
print S-MANP
platform S-MACEQ
. O


Three O
nozzle S-MACEQ
configurations O
are O
considered O
in O
this O
study O
. O


Fiber B-FEAT
orientation E-FEAT
tensors O
are O
calculated O
throughout O
the O
fluid S-MATE
domain S-CONPRI
using O
the O
Folgar-Tucker O
fiber S-MATE
interaction O
model S-CONPRI
. O


The O
effective O
bulk O
mechanical B-CONPRI
properties E-CONPRI
, O
specifically O
the O
longitudinal O
and O
transverse O
moduli O
, O
and O
the O
coefficient B-PRO
of I-PRO
thermal I-PRO
expansion E-PRO
, O
are O
also O
calculated O
for O
the O
deposited B-CHAR
bead E-CHAR
based O
on O
the O
spatially O
varying O
fiber B-FEAT
orientation E-FEAT
tensors O
. O


Fiber B-FEAT
orientation E-FEAT
is O
found O
to O
be S-MATE
highly O
aligned O
along O
the O
deposition B-PARA
direction E-PARA
of O
the O
resulting O
bead S-CHAR
and O
the O
computed O
properties S-CONPRI
through O
the O
thickness O
of O
the O
bead S-CHAR
are O
found O
to O
be S-MATE
affected O
by O
nozzle S-MACEQ
height O
during O
deposition S-CONPRI
. O


Significant O
improvements O
to O
the O
throughput S-CHAR
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
are O
essential O
to O
their O
cost-effectiveness O
and O
competitiveness O
with O
traditional O
processing O
routes O
. O


Moreover O
, O
high-throughput O
AM B-MANP
processes E-MANP
, O
in O
combination O
with O
the O
geometric O
versatility O
of O
AM S-MANP
, O
will O
enable O
entirely O
new O
workflows S-CONPRI
for O
product B-FEAT
design E-FEAT
and O
customization O
. O


We O
present O
the O
design S-FEAT
and O
validation S-CONPRI
of O
a O
desktop-scale O
extrusion B-MANP
AM E-MANP
system O
that O
achieves O
a O
much O
greater O
build B-CHAR
rate E-CHAR
than O
benchmarked O
commercial O
systems O
. O


This O
system O
, O
which O
we O
call O
‘ O
FastFFF O
’ O
, O
is O
motivated O
by O
our O
recent O
analysis O
of O
the O
rate-limiting O
mechanisms O
to O
conventional O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
technology S-CONPRI
. O


The O
FastFFF O
system O
mutually O
overcomes O
these O
limits S-CONPRI
, O
using O
a O
nut-feed O
extruder S-MACEQ
, O
laser-heated O
polymer S-MATE
liquefier O
, O
and O
servo-driven O
parallel O
gantry O
system O
to O
achieve O
high O
extrusion S-MANP
force O
, O
rapid O
filament S-MATE
heating O
, O
and O
fast O
gantry O
motion O
, O
respectively O
. O


The O
extrusion S-MANP
and O
heating S-MANP
mechanisms O
are O
contained O
in O
a O
compact S-MANP
printhead O
that O
receives O
a O
threaded O
filament S-MATE
and O
augments O
conduction O
heat B-CONPRI
transfer E-CONPRI
with O
a O
fiber-coupled O
diode S-APPL
laser O
. O


The O
prototype S-CONPRI
system O
achieves O
a O
volumetric O
build B-CHAR
rate E-CHAR
of O
127 O
cm3/hr O
, O
which O
is O
approximately O
7-fold O
greater O
than O
commercial O
desktop O
FFF S-MANP
systems O
, O
at O
comparable O
resolution S-PARA
; O
the O
maximum O
extrusion B-PARA
rate E-PARA
of O
the O
printhead O
is O
∼14-fold O
greater O
( O
282 O
cm3/hr O
) O
than O
our O
benchmarks O
. O


The O
performance B-CONPRI
limits E-CONPRI
of O
the O
printhead O
and O
motion O
systems O
are O
characterized O
, O
and O
the O
tradeoffs O
between O
build B-CHAR
rate E-CHAR
and O
resolution S-PARA
are O
assessed O
and O
discussed O
. O


High-speed O
desktop O
AM S-MANP
raises O
the O
possibility O
of O
new O
use O
cases O
and O
business B-APPL
models E-APPL
for O
AM S-MANP
, O
where O
handheld O
parts O
are O
built O
in O
minutes O
rather O
than O
hours O
. O


Adaptation O
of O
this O
technology S-CONPRI
to O
print S-MANP
high-temperature O
thermoplastics S-MATE
and O
composite B-MATE
materials E-MATE
, O
which O
require O
high O
extrusion S-MANP
forces O
, O
is O
also O
of O
interest O
. O


The O
driver O
for O
this O
research S-CONPRI
is O
the O
development O
of O
multi-material B-MANP
additive I-MANP
manufacturing E-MANP
processes O
that O
provide O
the O
potential O
for O
multi-functional O
parts O
to O
be S-MATE
manufactured O
in O
a O
single O
operation O
. O


In O
order O
to O
exploit O
the O
potential O
benefits O
of O
this O
emergent O
technology S-CONPRI
, O
new O
design S-FEAT
, O
analysis O
and O
optimization S-CONPRI
methods O
are O
needed O
. O


This O
paper O
presents O
a O
method O
that O
enables O
in O
the O
optimization S-CONPRI
of O
a O
multifunctional O
part O
by O
coupling O
both O
the O
system O
and O
structural B-FEAT
design E-FEAT
aspects O
. O


This O
is O
achieved O
by O
incorporating O
the O
effects O
of O
a O
system O
, O
comprised O
of O
a O
number O
of O
connected O
functional B-CONPRI
components E-CONPRI
, O
on O
the O
structural O
response O
of O
a O
part O
within O
a O
structural O
topology B-FEAT
optimization E-FEAT
procedure O
. O


The O
potential O
of O
the O
proposed O
method O
is O
demonstrated O
by O
performing O
a O
coupled O
optimization S-CONPRI
on O
a O
cantilever S-FEAT
plate O
with O
integrated O
components S-MACEQ
and O
circuitry O
. O


Biocompatible S-PRO
and O
biodegradable O
poly O
( O
lactic O
acid O
) O
( O
PLA S-MATE
) O
and O
hydroxyapatite S-MATE
( O
HAP O
) O
are O
widely O
used O
for O
bone S-BIOP
repair O
. O


In O
this O
study O
, O
microspheres S-CONPRI
consisting O
of O
poly O
( O
lactic O
acid O
) O
( O
PLA S-MATE
) O
and O
nano-hydroxyapatite O
( O
nano-HAP O
) O
were O
synthesized O
by O
emulsion S-MATE
solvent O
evaporation S-CONPRI
and O
were O
then O
used O
to O
fabricate S-MANP
layered O
parts O
using O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
. O


The O
effect O
of O
various O
parameters S-CONPRI
of O
the O
emulsion S-MATE
solvent O
evaporation S-CONPRI
technique O
on O
the O
size O
and O
morphology S-CONPRI
of O
the O
resulting O
PLA/nano-HAP O
microspheres S-CONPRI
was O
examined O
. O


We O
also O
evaluated O
how O
L-PBF S-MANP
parameters O
affected O
the O
physicochemical O
and O
biological O
properties S-CONPRI
of O
the O
fabricated S-CONPRI
parts O
. O


Nano-HAP O
was O
uniformly O
incorporated O
into O
PLA S-MATE
microspheres S-CONPRI
. O


Incorporation O
of O
HAP O
particles S-CONPRI
triggered O
pore S-PRO
formation O
on O
the O
microsphere O
surface S-CONPRI
. O


Layered O
parts O
fabricated S-CONPRI
by O
L-PBF S-MANP
using O
these O
composite S-MATE
microspheres O
as S-MATE
a O
material S-MATE
source O
showed O
good O
biocompatibility S-PRO
and O
osteogenesis O
. O


A O
10 O
wt O
% O
of O
nano-HAP O
content O
in O
the O
layered O
part O
could O
effectively O
facilitate O
osteogenic O
differentiation O
of O
rat O
mesenchymal B-MATE
stem I-MATE
cells E-MATE
( O
rMSCs O
) O
. O


Thus O
, O
L-PBF S-MANP
is O
a O
promising O
technology S-CONPRI
that O
can O
be S-MATE
used O
for O
manufacturing S-MANP
bone-repair O
implants S-APPL
consisting O
of O
PLA/nano-HAP O
composites S-MATE
materials O
. O


In O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
, O
part O
and O
process S-CONPRI
attributes O
are O
often O
optimized O
with O
build S-PARA
orientation/tool-path O
direction O
. O


Both O
of O
them O
may O
alter O
the O
layer S-PARA
topology O
and O
tool-path S-PARA
pattern S-CONPRI
which O
implicitly O
affect O
the O
part O
and O
process S-CONPRI
attributes O
. O


However O
, O
optimizing O
either O
build B-PARA
orientation E-PARA
or O
tool-path S-PARA
direction O
independently O
undermines O
the O
hierarchical O
relationship O
in O
the O
AM B-MANP
process E-MANP
plan O
and O
may O
produce O
a O
sub-optimal O
solution S-CONPRI
. O


In O
this O
paper O
, O
an O
integrated O
framework S-CONPRI
is O
proposed O
to O
quantify O
their O
combined O
effect O
on O
the O
part O
and O
process S-CONPRI
attributes O
by O
analyzing O
the O
generated O
geometry S-CONPRI
. O


The O
proposed O
methodology S-CONPRI
is O
designed S-FEAT
on O
the O
basis O
of O
the O
layer S-PARA
geometries S-CONPRI
to O
ensure O
manufacturability S-CONPRI
and O
minimize O
fabrication S-MANP
complexity S-CONPRI
in O
AM B-MANP
processes E-MANP
. O


Both O
build B-PARA
orientation E-PARA
and O
tool-path/deposition O
direction O
are O
concurrently O
optimized O
using O
a O
Genetic B-CONPRI
Algorithm E-CONPRI
( O
GA S-MATE
) O
. O


Multi B-MANP
Jet I-MANP
Fusion E-MANP
process O
. O


Modelling S-ENAT
the O
capillarity O
effect O
in O
Multi B-MANP
Jet I-MANP
Fusion E-MANP
technology O
. O


Multi B-MANP
Jet I-MANP
Fusion E-MANP
is O
a O
powder-based B-MANP
Additive I-MANP
Manufacturing E-MANP
technology O
patented O
by O
Hewlett-Packard O
Inc O
. O


It O
is O
characterised O
by O
the O
use O
of O
lamps O
instead O
of O
lasers O
to O
heat S-CONPRI
and O
melt S-CONPRI
polymers O
and O
by O
fusing S-CONPRI
and O
detailing O
agents O
that O
are O
jetted O
on O
the O
polymeric O
particles S-CONPRI
to O
modify O
and O
to O
control O
their O
heat B-PRO
absorption E-PRO
and O
thus O
selectively O
melt S-CONPRI
them O
. O


The O
high O
production S-MANP
rate O
and O
excellent O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
manufactured S-CONPRI
parts O
, O
even O
in O
comparison O
with O
Laser B-MANP
Sintering E-MANP
, O
together O
with O
the O
overall O
product B-CONPRI
quality E-CONPRI
make O
this O
technology S-CONPRI
effective O
for O
a O
production S-MANP
of O
small O
series O
of O
end-parts O
rather O
than O
functional O
prototypes.In O
the O
present O
paper O
, O
the O
so-called O
capillarity O
effect O
is O
investigated O
. O


A O
benchmark S-MANS
geometry O
was O
designed S-FEAT
to O
be S-MATE
affected O
by O
the O
capillarity O
effect O
and O
then O
manufactured S-CONPRI
by O
the O
MJF S-MANP
process O
. O


Values O
of O
the O
contact S-APPL
angle O
and O
of O
the O
characteristic O
length O
of O
the O
capillary O
, O
which O
are O
necessary O
to O
implement O
the O
analytical O
model S-CONPRI
, O
were O
obtained O
by O
experimental S-CONPRI
measurements O
made O
on O
the O
benchmark S-MANS
geometry.As O
a O
result O
the O
capillarity O
effect O
showed O
a O
dependence O
on O
the O
border O
edge O
orientation S-CONPRI
. O


The O
comparison O
between O
calculated O
shapes O
of O
the O
plane O
affected O
by O
the O
capillarity O
effect O
through O
the O
analytical O
model S-CONPRI
was O
in O
accordance O
with O
the O
experimental S-CONPRI
measurements O
thus O
allowing O
a O
reliable O
prediction S-CONPRI
to O
be S-MATE
made O
. O


Experiment S-CONPRI
to O
identify O
influence O
factors O
of O
nozzle S-MACEQ
clogging O
. O


Identification O
of O
reasons O
causing O
clogging O
of O
sphere-filled O
polycarbonate S-MATE
. O


Model S-CONPRI
for O
the O
occurrence O
of O
nozzle S-MACEQ
clogging O
. O


Mathematical S-CONPRI
viscosity O
model S-CONPRI
to O
approximate O
printability S-PARA
of O
materials S-CONPRI
. O


Fused B-MANP
filament I-MANP
fabrication E-MANP
with O
reinforced S-CONPRI
or O
filled O
polymers S-MATE
provides O
improved O
material B-CONPRI
properties E-CONPRI
compared O
to O
ordinary O
feedstock S-MATE
. O


A O
current O
limitation O
of O
these O
materials S-CONPRI
is O
the O
occurrence O
of O
nozzle S-MACEQ
clogging O
at O
higher O
filler O
contents O
. O


In O
this O
work O
, O
an O
experiment S-CONPRI
is O
designed S-FEAT
to O
identify O
the O
factors O
causing O
nozzle S-MACEQ
clogging O
. O


Glass S-MATE
sphere-filled O
polycarbonate S-MATE
is O
investigated O
by O
varying O
nozzle S-MACEQ
and O
filler O
diameters O
, O
the O
resin S-MATE
viscosity O
, O
the O
filler O
content O
, O
and O
the O
extrusion B-PARA
pressure E-PARA
. O


Based O
on O
these O
results O
, O
a O
model S-CONPRI
for O
the O
clogging O
of O
sphere-filled O
polymers S-MATE
is O
proposed O
. O


Last O
, O
a O
mathematical S-CONPRI
model O
is O
derived O
, O
which O
approximates O
the O
printability S-PARA
of O
filled O
polymers S-MATE
without O
the O
preparation O
of O
composites S-MATE
. O


This O
model S-CONPRI
is O
based O
on O
the O
nozzle S-MACEQ
geometry S-CONPRI
, O
the O
filler O
type O
and O
content O
, O
the O
resin S-MATE
viscosity O
, O
and O
the O
printer S-MACEQ
’ O
s S-MATE
maximum O
extrusion S-MANP
force O
. O


In O
this O
study O
, O
we O
propose O
a O
tool-path S-PARA
generation O
approach O
for O
material S-MATE
extrusion-based O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
that O
considers O
the O
machining S-MANP
efficiency O
and O
fabrication S-MANP
precision O
, O
which O
are O
inherent O
drawbacks O
of O
general O
AM B-MANP
techniques E-MANP
compared O
with O
conventional B-MANP
manufacturing E-MANP
methods O
. O


These O
three O
modules O
interact O
to O
affect O
the O
efficiency O
and O
precision S-CHAR
of O
AM S-MANP
significantly O
. O


In O
order O
to O
find O
an O
optimal O
inclination S-FEAT
, O
we O
first O
analyze O
the O
impacts O
on O
the O
fabrication S-MANP
efficiency O
and O
manufacturing S-MANP
accuracy S-CHAR
with O
different O
inclinations S-FEAT
. O


A O
comparatively O
accurate S-CHAR
building O
time O
model S-CONPRI
is O
developed O
subsequently O
to O
obtain O
the O
optimal O
tool-path S-PARA
inclination S-FEAT
, O
but O
without O
compromising O
the O
machining S-MANP
precision O
, O
based O
on O
the O
analysis O
of O
a O
geometrical O
accuracy S-CHAR
model O
. O


The O
proposed O
approach O
employs O
different O
inclinations S-FEAT
in O
distinct O
layers O
according O
to O
specific O
manufacturing S-MANP
scenarios O
and O
technological O
requirements O
. O


Fused B-MANP
deposition I-MANP
modeling E-MANP
( O
FDM S-MANP
) O
is O
shown O
to O
be S-MATE
a O
future-oriented O
technology S-CONPRI
. O


In O
this O
study O
, O
short-term O
creep S-PRO
deformation O
of O
PC-ABS O
parts O
created O
by O
FDM S-MANP
under O
different O
fabrication S-MANP
conditions O
was O
investigated O
using O
a O
recently O
innovative O
class O
of O
experimental B-CONPRI
design E-CONPRI
− O
definitive O
screening O
design S-FEAT
( O
DSD O
) O
− O
along O
with O
graphical O
analysis O
. O


Short-term O
creep S-PRO
experiments O
were O
conducted O
at O
prescribed O
combinations O
of O
FDM S-MANP
operating O
conditions O
, O
namely O
layer B-PARA
thickness E-PARA
, O
air O
gap O
, O
raster O
angle O
, O
build B-PARA
orientation E-PARA
, O
road O
width O
and O
number O
of O
contours S-FEAT
, O
as S-MATE
per O
DSD O
matrix O
. O


The O
results O
have O
shown O
that O
layer B-PARA
thickness E-PARA
, O
number O
of O
contours S-FEAT
, O
raster O
angle O
and O
build B-PARA
orientation E-PARA
have O
a O
major O
effect O
on O
the O
creep S-PRO
rate O
of O
the O
parts O
. O


However O
, O
road O
width O
and O
air O
gap O
have O
least O
impact S-CONPRI
on O
the O
creep S-PRO
rate O
of O
FDM S-MANP
processed O
prototypes S-CONPRI
. O


We O
present O
the O
design S-FEAT
and O
characterisation O
of O
a O
high-speed O
sintering S-MANP
additive B-MANP
manufacturing E-MANP
benchmarking O
artefact O
following O
a O
design-for-metrology O
approach O
. O


In O
an O
important O
improvement O
over O
conventional O
approaches O
, O
the O
specifications S-PARA
and O
operating O
principles O
of O
the O
instruments O
that O
would O
be S-MATE
used O
to O
measure O
the O
manufactured S-CONPRI
artefact O
were O
taken O
into O
account O
during O
its O
design B-CONPRI
process E-CONPRI
. O


With O
the O
design-for-metrology O
methodology S-CONPRI
, O
we O
aim O
to O
improve O
and O
facilitate O
measurements O
on O
parts O
produced O
using O
additive B-MANP
manufacturing E-MANP
. O


The O
benchmarking O
artefact O
has O
a O
number O
of O
geometrical B-FEAT
features E-FEAT
, O
including O
sphericity O
, O
cylindricity S-CONPRI
, O
coaxiality O
and O
minimum B-PARA
feature I-PARA
size E-PARA
, O
all O
of O
which O
are O
measured O
using O
contact S-APPL
, O
optical S-CHAR
and O
X-ray B-CHAR
computed I-CHAR
tomography E-CHAR
coordinate S-PARA
measuring O
systems O
. O


The O
results O
highlight O
the O
differences O
between O
the O
measuring O
methods O
, O
and O
the O
need O
to O
establish O
a O
specification S-PARA
standards O
and O
guidance O
for O
the O
dimensional O
assessment O
of O
additive B-MANP
manufacturing E-MANP
parts O
. O


Low O
molecular O
weight S-PARA
gelators O
can O
facilitate O
direct O
writing O
of O
epoxy S-MATE
resin O
. O


Low O
viscosity S-PRO
ink S-MATE
preparation O
. O


Processing-enabled O
manipulation O
of O
matrix O
morphology S-CONPRI
. O


Cured S-MANP
epoxy O
resin S-MATE
kinetically O
traps O
low O
molecular O
weight S-PARA
gelator O
. O


Direct O
writing O
a O
thermosetting O
resin S-MATE
typically O
requires O
a O
rheological S-PRO
modifier O
or O
peripheral O
reaction O
rate-modulating O
equipment S-MACEQ
to O
enable O
shape B-CONPRI
fidelity E-CONPRI
during O
parts O
fabrication S-MANP
. O


These O
low O
molecular O
weight S-PARA
gelators O
( O
LMWG S-CONPRI
) O
are O
thermally B-MANP
activated E-MANP
to O
produce O
sufficient O
yield B-PRO
stress E-PRO
for O
self-supporting S-FEAT
, O
reactive O
, O
physical O
gels O
. O


Physical O
gelation O
occurs O
by O
assembly S-MANP
of O
the O
LMWG S-CONPRI
into O
supramolecular B-CONPRI
morphologies E-CONPRI
that O
vary O
by O
mode O
of O
processing O
. O


Flow O
of O
the O
form-stable O
epoxy S-MATE
resin O
is O
induced O
by O
yielding O
of O
the O
physical O
gel S-MATE
structure O
. O


When O
the O
physical O
gel S-MATE
is O
cured S-MANP
at O
temperatures S-PARA
below O
the O
melt S-CONPRI
transition O
of O
the O
organic O
gelator O
, O
the O
network O
structure S-CONPRI
likely O
kinetically O
traps O
the O
organic O
gelator O
in O
a O
metastable S-PRO
state O
. O


Recrystallization S-CONPRI
of O
the O
kinetically O
trapped O
organic O
gelator O
is O
impeded O
when O
the O
network O
is O
post-cured O
above O
the O
melt S-CONPRI
transition O
temperature S-PARA
of O
the O
organic O
gelator O
. O


The O
use O
of O
low O
molecular O
weight S-PARA
agents O
that O
physically O
gel S-MATE
by O
thermal O
activation O
, O
generates O
low O
viscosity S-PRO
solution S-CONPRI
processability O
and O
suggests O
that O
this O
platform S-MACEQ
may O
be S-MATE
suitable O
for O
high O
solids O
loading O
applications O
amenable O
to O
direct O
writing O
. O


The O
effect O
on O
fatigue S-PRO
resistance O
of O
additively B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
AlSi10Mg S-MATE
specimens O
fabricated S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
following O
surface B-MANP
treatment E-MANP
by O
shot-peening O
was O
investigated O
. O


Specimen O
surface S-CONPRI
was O
shot-peened O
with O
either O
steel S-MATE
or O
ceramic S-MATE
balls O
. O


Nano-indentation O
measurements O
revealed O
that O
shot-peening O
caused O
surface B-MANP
hardening E-MANP
, O
with O
the O
hardness S-PRO
profile O
from O
the O
surface S-CONPRI
to O
the O
interior O
of O
the O
bulk O
disappearing O
50 O
μm O
below O
the O
surface S-CONPRI
. O


Surfaces S-CONPRI
polished O
before O
shot-peening O
or O
following O
removal O
of O
about O
25–30 O
μm O
from O
the O
surface S-CONPRI
after O
shot-peening O
by O
either O
mechanical S-APPL
or O
electrolytic O
polishing S-MANP
showed O
improved O
fatigue S-PRO
resistance O
and O
fatigue S-PRO
limit O
. O


The O
fracture S-CONPRI
area S-PARA
of O
AM-SLM O
AlSi10Mg S-MATE
specimens O
before O
and O
after O
shot-peening O
displayed O
a O
ductile B-CONPRI
fracture E-CONPRI
with O
relatively O
deep O
dimples O
. O


In O
contrast O
to O
AM S-MANP
specimens O
, O
the O
final O
fracture S-CONPRI
area S-PARA
of O
die-cast O
samples S-CONPRI
exhibited O
a O
brittle B-CONPRI
fracture E-CONPRI
surface O
, O
containing O
numerous O
cleavage O
facets S-CONPRI
and O
micro-cracks S-CONPRI
. O


The O
extrusion-based O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
of O
moisture-cured O
silicone B-MATE
elastomer E-MATE
with O
minimal O
voids S-CONPRI
and O
high O
strength S-PRO
, O
elongation S-PRO
, O
and O
fatigue B-PRO
life E-PRO
is O
presented O
. O


Due O
to O
the O
soft O
nature O
and O
extended O
cure S-CONPRI
time O
of O
moisture-cured O
silicone S-MATE
, O
AM S-MANP
is O
technically O
challenging O
. O


This O
compression S-PRO
is O
exploited O
to O
prevent O
void S-CONPRI
formation O
in O
silicone S-MATE
AM S-MANP
. O


This O
research S-CONPRI
aims O
to O
explore O
process B-CONPRI
parameters E-CONPRI
for O
voidless O
silicone S-MATE
AM S-MANP
of O
solid O
and O
thin-wall O
structures O
for O
pneumatic O
actuators S-MACEQ
. O


Experiments O
were O
performed O
to O
study O
effects O
of O
flowrate O
, O
layer B-PARA
height E-PARA
, O
and O
distance O
between O
adjacent O
silicone S-MATE
lines O
on O
the O
solid O
and O
thin-wall O
vertical S-CONPRI
layer S-PARA
deformation S-CONPRI
and O
void S-CONPRI
generation O
. O


The O
results O
were O
then O
applied O
in O
AM S-MANP
of O
two O
thin-walled O
hollow O
silicone S-MATE
pneumatic O
parts O
: O
the O
sphere-like O
balloons O
and O
finger O
pneumatic O
actuators S-MACEQ
. O


The O
sphere-like O
balloons O
exhibited O
diametric O
expansion O
between O
152 O
and O
207 O
% O
with O
burst O
stress S-PRO
between O
1.46 O
and O
2.55 O
MPa S-CONPRI
( O
which O
is O
comparable O
to O
the O
base O
material B-CONPRI
properties E-CONPRI
) O
while O
the O
pneumatic O
finger O
actuators S-MACEQ
were O
able O
to O
fully O
articulate O
over O
30,000 O
cycles O
before O
failure S-CONPRI
. O


Fiber S-MATE
trajectory O
of O
composite B-CONPRI
structures E-CONPRI
is O
optimized O
for O
Additive B-MANP
manufacturing E-MANP
. O


The O
stiffness S-PRO
and O
strength S-PRO
were O
simultaneously O
improved O
by O
the O
proposed O
method O
. O


A O
methodology S-CONPRI
of O
fiber S-MATE
trajectory O
optimization S-CONPRI
is O
proposed O
for O
Additive B-MANP
Manufacturing E-MANP
of O
composites S-MATE
. O


The O
present O
method O
aligns O
fiber S-MATE
with O
a O
physically-determined O
load O
path O
to O
simultaneously O
increase O
the O
stiffness S-PRO
and O
strength S-PRO
of O
the O
composite B-CONPRI
structures E-CONPRI
. O


In O
the O
case O
of O
open-hole O
panel O
, O
the O
deformation S-CONPRI
and O
the O
failure S-CONPRI
index O
were O
decreased O
by O
8 O
% O
and O
55 O
% O
compared O
to O
those O
obtained O
by O
the O
unidirectional B-CONPRI
structure E-CONPRI
. O


In O
the O
case O
of O
PAF O
, O
the O
decrease O
in O
failure S-CONPRI
index O
was O
76 O
% O
, O
but O
the O
reduction S-CONPRI
of O
deformation S-CONPRI
was O
not O
significant O
( O
6 O
% O
) O
. O


The O
present O
method O
also O
identified O
the O
structural O
members O
that O
did O
not O
contribute O
to O
strength S-PRO
and O
rigidity O
, O
which O
in O
turn O
realized O
the O
appropriate O
weight S-PARA
savings O
and O
increased O
the O
specific B-PRO
strength E-PRO
and O
specific B-PRO
stiffness E-PRO
. O


Microstructures S-MATE
with O
spatially-varying O
properties S-CONPRI
such O
as S-MATE
trabecular O
bone S-BIOP
are O
widely O
seen O
in O
nature O
. O


These O
functionally B-MATE
graded I-MATE
materials E-MATE
possess O
smoothly O
changing O
microstructural S-CONPRI
topologies O
that O
enable O
excellent O
micro O
and O
macroscale S-CONPRI
performance O
. O


The O
fabrication S-MANP
of O
such O
microstructural B-CONPRI
materials E-CONPRI
is O
now O
enabled O
by O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
. O


A O
challenging O
aspect O
in O
the O
computational O
design S-FEAT
of O
such O
materials S-CONPRI
is O
ensuring O
compatibility O
between O
adjacent O
microstructures S-MATE
. O


Existing O
works O
address O
this O
problem O
by O
ensuring O
geometric O
connectivity O
between O
adjacent O
microstructural S-CONPRI
unit O
cells S-APPL
. O


In O
this O
paper O
, O
we O
aim O
to O
find O
the O
optimal O
connectivity O
between O
topology S-CONPRI
optimized O
microstructures S-MATE
. O


Recognizing O
the O
fact O
that O
the O
optimality O
of O
connectivity O
can O
be S-MATE
evaluated O
by O
the O
resulting O
physical B-PRO
properties E-PRO
of O
the O
assemblies O
, O
we O
propose O
to O
consider O
the O
assembly S-MANP
of O
adjacent O
cells S-APPL
together O
with O
the O
optimization S-CONPRI
of O
individual O
cells S-APPL
. O


In O
particular O
, O
our O
method O
simultaneously O
optimizes O
the O
physical B-PRO
properties E-PRO
of O
the O
individual O
cells S-APPL
as S-MATE
well O
as S-MATE
those O
of O
neighbouring O
pairs O
, O
to O
ensure O
material S-MATE
connectivity O
and O
smoothly O
varying O
physical B-PRO
properties E-PRO
. O


We O
demonstrate O
the O
application O
of O
our O
method O
in O
the O
design S-FEAT
of O
functionally B-MATE
graded I-MATE
materials E-MATE
for O
implant S-APPL
design S-FEAT
( O
including O
an O
implant S-APPL
prototype O
made O
by O
AM S-MANP
) O
, O
and O
in O
the O
multiscale O
optimization S-CONPRI
of O
structures O
. O


An O
analytical O
model S-CONPRI
was O
created O
to O
illustrate O
the O
powder S-MATE
stream O
distribution S-CONPRI
under O
the O
four-jet O
nozzles S-MACEQ
in O
direct B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
. O


Weight S-PARA
measurement S-CHAR
method O
was O
used O
to O
validate O
the O
powder S-MATE
flow O
distributions S-CONPRI
at O
different O
positions O
under O
the O
nozzle S-MACEQ
. O


Analyzed O
the O
effects O
of O
the O
input O
variables O
on O
the O
powder S-MATE
stream O
distribution S-CONPRI
. O


Estimated O
the O
powder S-MATE
deposition S-CONPRI
efficiency O
( O
PDE O
) O
based O
on O
the O
simulation S-ENAT
results O
. O


As S-MATE
an O
important O
factor O
during O
direct B-MANP
energy I-MANP
deposition E-MANP
( O
DED S-MANP
) O
additive B-MANP
manufacturing I-MANP
process E-MANP
, O
powder S-MATE
stream O
distribution S-CONPRI
will O
not O
only O
affect O
the O
deposition B-PARA
rate E-PARA
, O
but O
also O
the O
powder-gas O
and O
power-powder O
interactions O
, O
and O
thus O
the O
consequent O
quality S-CONPRI
and O
property S-CONPRI
of O
the O
fabricated S-CONPRI
part O
. O


This O
paper O
created O
an O
analytical O
model S-CONPRI
to O
illustrate O
the O
powder S-MATE
stream O
distribution S-CONPRI
under O
the O
four-jet O
nozzles S-MACEQ
in O
the O
DED S-MANP
. O


To O
validate O
the O
proposed O
model S-CONPRI
, O
weight S-PARA
measurement S-CHAR
method O
was O
used O
to O
track O
the O
powder S-MATE
stream O
distributions S-CONPRI
at O
different O
positions O
under O
the O
nozzle S-MACEQ
. O


Additionally O
, O
the O
effects O
of O
the O
input O
variables O
, O
including O
powder B-PARA
flow I-PARA
rate E-PARA
, O
gas B-PARA
flow I-PARA
rate E-PARA
and O
particle S-CONPRI
size O
, O
on O
the O
powder S-MATE
stream O
distribution S-CONPRI
were O
also O
analyzed O
. O


The O
results O
suggest O
a O
relatively O
good O
agreement O
between O
the O
modelling S-ENAT
and O
experimental S-CONPRI
measurements O
. O


At O
the O
end O
, O
the O
powder S-MATE
deposition S-CONPRI
efficiency O
( O
PDE O
) O
was O
estimated O
based O
on O
the O
simulation S-ENAT
results O
. O


The O
influence O
of O
build B-PARA
orientation E-PARA
, O
layer B-PARA
thickness E-PARA
, O
strain B-CONPRI
rate E-CONPRI
and O
size B-CONPRI
effect E-CONPRI
on O
the O
Young O
’ O
s S-MATE
modulus O
, O
ultimate B-PRO
tensile I-PRO
strength E-PRO
and O
fracture S-CONPRI
strains O
in O
vat B-MANP
photopolymerization E-MANP
based O
additively B-MANP
manufactured E-MANP
specimens O
is O
investigated O
. O


Mechanical B-CHAR
testing E-CHAR
and O
subsequent O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
tests O
on O
additively B-MANP
manufactured E-MANP
specimens O
are O
conducted O
. O


Anisotropy S-PRO
in O
mechanical S-APPL
behavior O
is O
only O
observed O
in O
specimens O
fabricated S-CONPRI
in O
different O
planes O
. O


An O
increase O
in O
layer B-PARA
thickness E-PARA
and O
decrease O
in O
strain B-CONPRI
rate E-CONPRI
resulted O
in O
lower O
strength S-PRO
, O
stiffness S-PRO
and O
higher O
fracture S-CONPRI
strains O
. O


No O
significant O
size B-CONPRI
effect E-CONPRI
on O
strength S-PRO
and O
failure S-CONPRI
strains O
is O
observed O
. O


Cure S-CONPRI
kinetics O
is O
found O
to O
have O
significant O
influence O
on O
mechanical B-CONPRI
properties E-CONPRI
of O
additively B-MANP
manufactured E-MANP
specimens O
. O


Warping S-CONPRI
and O
delamination S-CONPRI
in O
material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
( O
MatEx O
) O
parts O
are O
well O
documented O
and O
irreversible O
thermal O
strain S-PRO
( O
ITε O
) O
has O
also O
recently O
been O
reported O
. O


As S-MATE
parts O
are O
built O
up O
as S-MATE
a O
collection O
of O
roads O
, O
they O
are O
analogous O
to O
fiber B-MATE
reinforced I-MATE
composites E-MATE
. O


However O
, O
the O
lack O
of O
bonding S-CONPRI
between O
the O
matrix O
, O
air O
, O
and O
the O
reinforcing B-APPL
phase E-APPL
, O
polymer S-MATE
roads O
, O
necessitates O
the O
development O
of O
a O
micromechanical O
model S-CONPRI
for O
these O
parts O
. O


In O
this O
work O
, O
a O
micromechanical O
model S-CONPRI
for O
MatEx O
parts O
is O
developed O
to O
describe O
bulk O
part O
behavior O
that O
incorporates O
void B-CONPRI
fraction E-CONPRI
, O
road O
morphology S-CONPRI
, O
and O
bonding S-CONPRI
between O
and O
within O
layers O
. O


Combining O
stress S-PRO
accumulation O
within O
roads O
with O
the O
micromechanical O
model S-CONPRI
successfully O
predicted S-CONPRI
ITε O
and O
provided O
a O
rationale O
for O
ITε O
dependence O
on O
both O
layer B-PARA
thickness E-PARA
and O
raster O
angle O
. O


Additionally O
, O
the O
micromechanical O
model S-CONPRI
developed O
can O
be S-MATE
used O
to O
explain O
bonding S-CONPRI
limitations O
in O
MatEx O
based O
on O
road O
and O
bond O
geometry S-CONPRI
. O


Material S-MATE
anisotropy S-PRO
model O
formulation O
for O
the O
full O
three O
dimensional O
space O
. O


Efficient O
optimization S-CONPRI
of O
lattice B-FEAT
structures E-FEAT
with O
respect O
to O
material S-MATE
anisotropy S-PRO
. O


Effects O
of O
the O
material S-MATE
anisotropy S-PRO
on O
lightweight B-CONPRI
lattice E-CONPRI
structures O
. O


Finding O
the O
optimized O
build B-PARA
orientation E-PARA
with O
respect O
to O
the O
material S-MATE
anisotropy S-PRO
. O


Large O
increase O
in O
accuracy S-CHAR
, O
hence O
, O
safety S-CONPRI
compared O
to O
conventional O
approaches O
. O


The O
build B-PARA
orientation E-PARA
is O
one O
the O
most O
influential O
factors O
on O
material B-CONPRI
properties E-CONPRI
in O
additively B-MANP
manufactured E-MANP
parts O
. O


Advanced O
applications O
, O
such O
as S-MATE
lattice O
structures O
optimized O
for O
lightweight S-CONPRI
, O
often O
rely O
on O
small O
safety S-CONPRI
margins O
and O
are O
, O
hence O
, O
particularly O
affected O
, O
but O
research S-CONPRI
has O
not O
gone O
far O
beyond O
the O
pure O
empirical S-CONPRI
characterization O
. O


The O
focus O
of O
this O
paper O
is O
to O
investigate O
in O
detail O
the O
influence O
of O
anisotropy S-PRO
induced O
through O
fabrication S-MANP
on O
the O
mechanical S-APPL
performance O
and O
build B-PARA
orientation E-PARA
of O
whole O
structures O
when O
subject O
to O
optimization S-CONPRI
. O


First O
, O
a O
material B-CONPRI
property E-CONPRI
model O
for O
both O
compression S-PRO
and O
tension O
states O
is O
formulated O
. O


Then O
, O
the O
Generalized O
Optimality O
Criteria O
method O
is O
extended O
for O
fixed O
topology B-CONPRI
lattice E-CONPRI
structures O
with O
respect O
to O
constraints O
in O
displacement O
, O
stress S-PRO
, O
and O
Euler O
buckling S-PRO
. O


The O
two O
latter O
are O
formulated O
as S-MATE
local O
constraints O
that O
are O
handled O
in O
combination O
with O
Fully-Stressed O
Design S-FEAT
recursion O
. O


The O
results O
reveal O
significant O
safety S-CONPRI
threads O
likely O
leading O
to O
premature O
failure S-CONPRI
when O
using O
properties S-CONPRI
from O
one-directional O
tests O
, O
as S-MATE
is O
so O
far O
the O
case O
, O
rather O
than O
the O
full O
anisotropy S-PRO
model O
developed O
herein O
. O


If O
used O
inversely O
, O
the O
algorithm S-CONPRI
yields O
the O
optimal O
orientation S-CONPRI
of O
a O
structure S-CONPRI
on O
the O
build B-MACEQ
platform E-MACEQ
, O
allowing O
further O
weight S-PARA
reduction S-CONPRI
while O
maintaining O
the O
mechanical B-CONPRI
properties E-CONPRI
. O


Selective B-MANP
Laser I-MANP
Melting E-MANP
( O
SLM S-MANP
) O
facilitates O
the O
formation O
of O
complex O
, O
stochastic S-CONPRI
or O
non-stochastic O
, O
metallic S-MATE
cellular B-FEAT
structures E-FEAT
. O


There O
is O
a O
high O
level O
of O
interest O
in O
these O
structures O
recently O
, O
particularly O
due O
to O
their O
high O
strength B-PRO
to I-PRO
weight I-PRO
ratios E-PRO
and O
osteoconductive S-PRO
properties O
. O


While O
the O
ability O
to O
in-situ S-CONPRI
monitor O
the O
SLM S-MANP
process S-CONPRI
is O
of O
key O
importance O
for O
future O
quality B-CONPRI
control E-CONPRI
methods.In O
this O
work O
lattice B-FEAT
structures E-FEAT
were O
fabricated S-CONPRI
, O
using O
the O
single O
exposure S-CONPRI
scanning O
strategy O
, O
on O
a O
Renishaw O
500M O
SLM S-MANP
machine S-MACEQ
. O


The O
build S-PARA
process O
was O
also O
monitored O
using O
a O
co-axial O
in-situ S-CONPRI
process O
monitoring O
system.It O
was O
found O
that O
by O
increasing O
the O
energy O
input O
, O
through O
increasing O
the O
laser B-PARA
power E-PARA
and/or O
exposure S-CONPRI
time O
, O
the O
lattice S-CONPRI
strut O
diameters O
, O
within O
the O
1.5 O
mm S-MANP
diamond S-MATE
unit O
cells S-APPL
, O
increased O
from O
119 O
to O
293 O
μm O
, O
resulting O
in O
the O
major O
pore S-PRO
diameter S-CONPRI
decreasing O
from O
1106 O
to O
932 O
μm O
. O


The O
effect O
of O
systematically O
altering O
the O
laser B-CONPRI
beam E-CONPRI
spot O
size O
on O
the O
cellular B-FEAT
structures E-FEAT
was O
also O
evaluated O
. O


It O
was O
observed O
that O
by O
doubling O
the O
laser B-CONPRI
beam E-CONPRI
spot O
size O
, O
that O
there O
was O
a O
17 O
% O
reduction S-CONPRI
in O
strut B-PARA
diameter E-PARA
and O
a O
22 O
% O
reduction S-CONPRI
in O
mechanical B-PRO
strength E-PRO
of O
the O
structures O
. O


It O
was O
also O
observed O
that O
at O
constant O
energy O
input O
levels O
, O
the O
lattice B-FEAT
structures E-FEAT
created O
using O
a O
focused O
laser S-ENAT
exhibited O
an O
81 O
% O
lower O
mechanical B-PRO
strength E-PRO
than O
the O
structures O
created O
using O
a O
de-focused O
laser S-ENAT
. O


Thus O
, O
demonstrating O
that O
the O
mode O
of O
energy O
input O
is O
critical O
to O
achieving O
the O
desired O
strength S-PRO
in O
these O
structures.Based O
on O
the O
outputs O
from O
the O
in-situ S-CONPRI
monitoring O
system O
, O
a O
broadly O
linear O
correlation O
was O
obtained O
between O
the O
laser S-ENAT
input O
energy O
, O
the O
associated O
process B-CONPRI
monitoring E-CONPRI
data S-CONPRI
generated O
and O
the O
mechanical B-PRO
strength E-PRO
of O
the O
lattice B-FEAT
structures E-FEAT
. O


Elevated O
heat-treatment O
temperatures S-PARA
increased O
mechanical B-CONPRI
properties E-CONPRI
. O


Long O
heat-treatment O
times O
decreased O
ductility S-PRO
and O
Young O
’ O
s S-MATE
modulus O
. O


All O
elevated O
temperature S-PARA
heat-treatments O
yielded O
similar O
percent O
crystallinity O
. O


Increasing O
print S-MANP
and O
heat-treatment O
temperature S-PARA
increased O
inter-road O
bonding S-CONPRI
. O


Post-processing S-CONPRI
heat-treatments O
increased O
mechanical B-CONPRI
properties E-CONPRI
of O
printed O
parts O
. O


Material B-MANP
extrusion I-MANP
additive I-MANP
manufacturing E-MANP
( O
MEAM O
) O
and O
other O
additive B-MANP
manufacturing E-MANP
methods O
provide O
part O
design S-FEAT
options O
that O
would O
be S-MATE
difficult O
or O
impossible O
to O
realize O
with O
conventional B-MANP
manufacturing E-MANP
methods O
. O


However O
, O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
parts O
produced O
with O
MEAM O
are O
lower O
than O
bulk O
material B-CONPRI
properties E-CONPRI
because O
of O
the O
interfaces O
between O
roads O
and O
layers O
inherent O
to O
the O
additive S-MATE
build O
technique O
of O
MEAM O
. O


The O
effects O
of O
material S-MATE
dependent O
MEAM O
process B-CONPRI
parameters E-CONPRI
on O
the O
interlayer O
bonding S-CONPRI
and O
percent O
crystallinity O
of O
MEAM O
parts O
fabricated S-CONPRI
with O
polyphenylene O
sulfide O
( O
PPS O
) O
were O
examined O
in O
this O
study O
using O
a O
design B-CONPRI
of I-CONPRI
experiments E-CONPRI
technique O
known O
as S-MATE
the O
Taguchi B-CONPRI
method E-CONPRI
. O


The O
MEAM O
parameters S-CONPRI
studied O
were O
print S-MANP
temperature O
, O
heat-treatment O
time O
, O
and O
heat-treatment O
temperature S-PARA
. O


Heat-treatment O
temperature S-PARA
was O
shown O
to O
be S-MATE
the O
most O
influential O
parameter S-CONPRI
on O
all O
the O
studied O
properties S-CONPRI
. O


Utilizing O
heat-treatments O
on O
MEAM O
parts O
increased O
the O
ultimate B-PRO
tensile I-PRO
strength E-PRO
( O
UTS S-PRO
) O
from O
52 O
% O
of O
the O
PPS O
film O
UTS S-PRO
to O
80 O
% O
. O


The O
study O
showed O
that O
utilizing O
post-processing S-CONPRI
heat-treatments O
on O
MEAM O
parts O
could O
improve O
the O
interlayer O
bonding S-CONPRI
in O
these O
parts O
. O


Ultra O
High O
Molecular O
Weight S-PARA
Polyethylene S-MATE
( O
UHMWPE O
) O
is O
a O
semi-crystalline O
polymer S-MATE
that O
has O
remarkable O
properties S-CONPRI
of O
high O
mechanical B-CONPRI
properties E-CONPRI
, O
excellent O
wear B-PRO
resistance E-PRO
, O
low O
friction S-CONPRI
and O
chemical B-PRO
resistance E-PRO
, O
and O
it O
is O
found O
in O
many O
applications O
such O
sporting O
goods O
, O
medical S-APPL
artificial B-APPL
joints E-APPL
, O
bullet O
proof O
jackets O
and O
armours O
, O
ropes O
and O
fishing O
lines O
[ O
1 O
] O
. O


UHMWPE O
parts O
can O
not O
be S-MATE
produced O
easily O
by O
many O
conventional O
processes S-CONPRI
because O
of O
its O
very O
high O
melt S-CONPRI
viscosity O
resulting O
from O
its O
very O
long O
chains O
[ O
2 O
] O
. O


Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
is O
moving O
from O
being O
an O
industrial S-APPL
rapid O
prototyping B-CONPRI
process E-CONPRI
to O
becoming O
a O
mainstream O
manufacturing B-MANP
process E-MANP
in O
a O
wide O
range S-PARA
of O
applications O
. O


Laser B-MANP
sintering E-MANP
of O
polymers S-MATE
is O
one O
of O
the O
AM B-MANP
techniques E-MANP
that O
is O
most O
promising O
process S-CONPRI
owing O
to O
its O
ability O
to O
produce O
parts O
with O
complex B-CONPRI
geometries E-CONPRI
, O
accurate S-CHAR
dimensions O
, O
and O
good O
mechanical B-PRO
strength E-PRO
[ O
3 O
] O
. O


This O
paper O
reports O
attempts O
to O
laser-sinter O
UHMWPE O
and O
assesses O
the O
effects O
of O
laser B-PARA
energy I-PARA
density E-PARA
on O
the O
flexural O
properties S-CONPRI
of O
the O
sintered S-MANP
parts O
. O


The O
properties S-CONPRI
of O
the O
UHMWPE O
sintered S-MANP
parts O
were O
evaluated O
by O
performing O
flexural O
three B-CONPRI
point I-CONPRI
bending E-CONPRI
tests O
and O
were O
compared O
in O
terms O
of O
flexural B-PRO
strength E-PRO
, O
flexural O
modulus O
and O
ductility S-PRO
( O
deflection O
) O
. O


Part O
dimensions S-FEAT
and O
relative B-PRO
density E-PRO
were O
evaluated O
in O
order O
to O
optimise O
the O
laser B-MANP
sintering E-MANP
parameters O
. O


Thermal B-CHAR
analysis E-CHAR
of O
samples S-CONPRI
was O
made O
by O
differential O
scanning S-CONPRI
calorimetry O
( O
DSC S-CHAR
) O
for O
the O
virgin B-MATE
powder E-MATE
. O


Results O
show O
that O
flexural B-PRO
strength E-PRO
, O
modulus O
and O
ductility S-PRO
are O
influenced O
by O
laser B-PARA
energy I-PARA
density E-PARA
and O
flexural B-PRO
strength E-PRO
and O
modulus O
of O
1.37 O
MPa S-CONPRI
and O
32.12 O
MPa S-CONPRI
respectively O
are O
still O
achievable O
at O
a O
lower O
laser B-PARA
energy I-PARA
density E-PARA
of O
0.016 O
J/mm2 O
( O
Laser B-PARA
power E-PARA
of O
6 O
W O
) O
. O


Part O
dimensions S-FEAT
and O
bulk O
density S-PRO
are O
also O
influenced O
by O
laser B-PARA
energy I-PARA
density E-PARA
. O


γ-Fe O
phase S-CONPRI
increase O
with O
the O
increasing O
SS316L O
content O
. O


The O
increase O
of O
SS316L O
content O
improves O
general O
and O
pitting B-CONPRI
corrosion E-CONPRI
resistance O
. O


Graded O
material S-MATE
with O
SS316L O
content O
≥50 O
wt. O
% O
still O
has O
relatively O
high O
microhardness S-CONPRI
. O


Graded O
material S-MATE
with O
SS316L O
content O
≥50 O
wt. O
% O
has O
lower O
pitting S-CONPRI
susceptibility O
. O


Composition-graded O
materials S-CONPRI
could O
be S-MATE
designed O
to O
rapidly O
establish O
the O
structure-property O
with O
high-throughput O
methods O
. O


In O
this O
study O
, O
stainless B-MATE
steel E-MATE
316L O
( O
SS316L O
) O
- O
431 O
( O
SS431 O
) O
graded O
material S-MATE
with O
the O
SS316L O
content O
ranging O
from O
0 O
to O
100 O
wt. O
% O
was O
fabricated S-CONPRI
by O
directed B-MANP
energy I-MANP
deposition I-MANP
additive I-MANP
manufacturing E-MANP
. O


Composition S-CONPRI
, O
phase S-CONPRI
constitution O
, O
microstructure S-CONPRI
and O
corrosion B-PRO
behavior E-PRO
of O
the O
graded O
material S-MATE
were O
characterized O
by O
laser-induced O
breakdown O
spectroscopy S-CONPRI
( O
LIBS O
) O
, O
micro-beam O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
, O
scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
( O
SEM S-CHAR
) O
and O
high-throughput O
local O
electrochemical S-CONPRI
techniques O
respectively O
. O


Accordingly O
, O
the O
dominant O
microstructure S-CONPRI
varies O
from O
equiaxed O
dendrites S-BIOP
to O
a O
mixture O
of O
dendritic O
and O
cellular B-FEAT
structures E-FEAT
. O


As S-MATE
the O
content O
of O
SS316L O
increases O
, O
the O
reduced O
carbides S-MATE
at O
grain B-CONPRI
boundaries E-CONPRI
and O
the O
increasing O
compactness O
of O
passive O
film O
improve O
the O
general O
and O
pitting B-CONPRI
corrosion E-CONPRI
resistance O
of O
the O
material S-MATE
. O


Such O
a O
high-throughput O
screening O
process S-CONPRI
allows O
one O
to O
reliably O
select O
the O
constituents O
with O
the O
presence O
of O
SS316L O
over O
50 O
wt. O
% O
as S-MATE
a O
potential O
component S-MACEQ
under O
the O
requirement O
of O
high O
corrosion B-CONPRI
resistance E-CONPRI
and O
wear B-PRO
resistance E-PRO
. O


Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
is O
an O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
method O
that O
relies O
on O
the O
thermal O
extrusion S-MANP
of O
a O
thermoplastic B-MATE
feedstock E-MATE
from O
a O
mobile O
deposition S-CONPRI
head O
. O


Conventional O
FFF S-MANP
constructs O
components S-MACEQ
from O
stacks O
of O
individual O
extruded S-MANP
layers O
using O
tool B-CONPRI
paths E-CONPRI
with O
fixed O
z-values O
in O
each O
individual O
layer S-PARA
. O


Consequently O
, O
the O
manufactured S-CONPRI
components S-MACEQ
often O
contain O
inherent O
weaknesses O
in O
the O
z-axis S-CONPRI
due O
to O
the O
relatively O
weak O
thermal O
fusion B-CONPRI
bonding E-CONPRI
that O
occurs O
between O
individual O
layers O
, O
as S-MATE
well O
as S-MATE
poor O
surface B-FEAT
finish E-FEAT
in O
shallow O
sloped O
contours S-FEAT
. O


This O
study O
demonstrates O
the O
use O
of O
Curved O
Layer S-PARA
FFF S-MANP
( O
CLFFF O
) O
tool B-CONPRI
paths E-CONPRI
in O
tandem O
with O
a O
commercially O
available O
parallel O
, O
or O
delta O
, O
style O
FFF S-MANP
system O
to O
allow O
the O
deposition S-CONPRI
head O
to O
follow O
the O
topology S-CONPRI
of O
the O
component S-MACEQ
. O


By O
incorporating O
a O
delta O
robot S-MACEQ
and O
CLFFF O
tool B-CONPRI
paths E-CONPRI
in O
this O
way O
, O
improvements O
in O
the O
surface B-FEAT
finish E-FEAT
of O
the O
manufactured S-CONPRI
parts O
has O
been O
observed O
, O
and O
time O
costs O
associated O
with O
Cartesian O
robot S-MACEQ
based O
CLFFF O
manufacturing S-MANP
have O
been O
notably O
reduced O
. O


Furthermore O
, O
employing O
a O
delta O
robot S-MACEQ
provides O
additional O
flexibility S-PRO
to O
CLFFF O
manufacturing S-MANP
and O
increases O
the O
feasibility S-CONPRI
of O
its O
application O
for O
advanced O
manufacturing S-MANP
. O


The O
study O
has O
also O
demonstrated O
a O
viable O
approach O
to O
multi-material S-CONPRI
FFF S-MANP
by O
decoupling O
support B-FEAT
structure E-FEAT
and O
part O
manufacture S-CONPRI
into O
regions O
of O
CLFFF O
and O
static O
z O
tool S-MACEQ
pathing O
in O
an O
appropriate O
fashion S-CONPRI
. O


Reducing O
the O
relative O
quality S-CONPRI
of O
lattice S-CONPRI
materials O
is O
a O
key O
factor O
in O
expanding O
their O
scope O
of O
application O
. O


Experimental S-CONPRI
samples O
of O
Ti6Al4V S-MATE
, O
including O
both O
VPOS O
and O
a O
body-centered O
cubic O
( O
BCC S-CONPRI
) O
octahedral O
model S-CONPRI
, O
are O
prepared O
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
. O


The O
influence O
of O
pose O
( O
θ O
) O
on O
the O
relative B-PRO
density E-PRO
of O
the O
lattice B-FEAT
structures E-FEAT
is O
evaluated O
analytically O
. O


The O
mechanical B-CONPRI
response E-CONPRI
and O
specific B-CONPRI
energy I-CONPRI
absorption E-CONPRI
( O
SEA O
) O
of O
these O
structures O
under O
compression S-PRO
are O
investigated O
. O


Compared O
with O
the O
experimental B-CONPRI
BCC E-CONPRI
data S-CONPRI
, O
the O
relative B-PRO
density E-PRO
of O
the O
VPOS O
samples S-CONPRI
is O
reduced O
, O
and O
their O
SEA O
values O
are O
improved O
. O


The O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
VPOSs O
in O
the O
z O
and O
y S-MATE
directions O
are O
optimized O
when O
θ=43° O
. O


When O
θ O
= O
10° O
, O
the O
z-direction S-FEAT
SEA O
is O
maximum O
( O
∼2.4 O
times O
the O
BCC S-CONPRI
value O
) O
. O


Among O
the O
various O
Ti6Al4V S-MATE
octahedral O
lattice B-FEAT
structures E-FEAT
, O
the O
structure S-CONPRI
with O
θ O
= O
43° O
exhibits O
the O
best O
mechanical B-CONPRI
properties E-CONPRI
at O
unit O
density S-PRO
. O


This O
study O
demonstrates O
that O
the O
performance S-CONPRI
of O
lattice B-FEAT
structures E-FEAT
can O
be S-MATE
improved O
to O
different O
degrees O
by O
varying O
the O
unit B-CONPRI
cell E-CONPRI
pose O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
has O
gone O
through O
major O
developments O
in O
the O
past O
decade O
, O
enabling O
the O
rapid O
manufacture S-CONPRI
of O
complex B-CONPRI
geometries E-CONPRI
from O
traditional O
engineering B-MATE
materials E-MATE
. O


This O
study O
aims O
to O
facilitate O
the O
development O
and O
additive B-MANP
manufacturing E-MANP
of O
a O
new O
generation O
of O
fast O
and O
simple S-MANP
digital O
components S-MACEQ
with O
integrated O
magnetic O
shape O
memory O
( O
MSM O
) O
alloy S-MATE
sections O
that O
can O
be S-MATE
actuated O
by O
an O
external O
magnetic B-CONPRI
field E-CONPRI
. O


Here O
, O
we O
employ O
a O
systematic O
design B-CONPRI
of I-CONPRI
experiments E-CONPRI
( O
DoE O
) O
approach O
for O
investigating O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
of O
a O
Ni-Mn-Ga O
based O
MSM O
alloy S-MATE
. O


The O
effects O
of O
the O
applied O
process B-CONPRI
parameters E-CONPRI
on O
the O
chemical B-CONPRI
composition E-CONPRI
and O
relative B-PRO
density E-PRO
are O
determined O
, O
and O
detailed O
investigations O
are O
conducted O
on O
the O
microstructural S-CONPRI
properties O
of O
the O
as-deposited O
material S-MATE
obtained O
using O
optimized O
parameters S-CONPRI
. O


The O
results O
show O
that O
although O
the O
L-PBF S-MANP
of O
Ni-Mn-Ga O
is O
characterized O
by O
an O
ever-present O
loss O
of O
Mn S-MATE
, O
deposition S-CONPRI
of O
Ni-Mn-Ga O
with O
a O
high O
relative B-PRO
density E-PRO
of O
98.3 O
% O
and O
a O
minimal O
loss O
of O
Mn S-MATE
at O
∼1.1 O
at. O
% O
is O
feasible O
. O


However O
, O
combined O
measurements O
by O
the O
low-field O
ac O
magnetic B-CHAR
susceptibility E-CHAR
method O
( O
LFMS O
) O
and O
DSC S-CHAR
revealed O
that O
the O
phase S-CONPRI
transformation O
of O
the O
as-deposited O
material S-MATE
from O
martensite S-MATE
to O
austenite S-MATE
, O
and O
vice O
versa O
, O
was O
broad O
and O
occurred O
in O
a O
paramagnetic O
state O
. O


Inspection S-CHAR
by O
SEM S-CHAR
revealed O
a O
layered O
microstructure S-CONPRI
with O
a O
stripe-like O
surface S-CONPRI
relief O
that O
originated O
from O
the O
presence O
of O
martensitic O
twins O
within O
the O
sample S-CONPRI
. O


Overall O
, O
L-PBF S-MANP
shows O
high O
potential O
for O
the O
production S-MANP
of O
functional O
Ni-Mn-Ga O
based O
MSM O
alloys S-MATE
. O


Fabricated S-CONPRI
Schwarz O
P S-MATE
unit O
cell-based O
scaffolds S-FEAT
underwent O
geometrical O
transformations O
in O
the O
form O
of O
shrinkage S-CONPRI
. O


Computational O
effective O
modulus O
of O
the O
original O
Schwarz O
P S-MATE
unit O
cell S-APPL
under-estimated O
the O
experimental S-CONPRI
modulus O
by O
86.05 O
% O
. O


Computational O
effective O
modulus O
of O
the O
reconstructed O
unit B-CONPRI
cell E-CONPRI
over-estimated O
the O
experimental S-CONPRI
modulus O
by O
6.94 O
% O
. O


Micromechanical O
analysis O
was O
able O
to O
accommodate O
geometrical O
transformations O
of O
the O
Schwarz O
P S-MATE
unit O
cell S-APPL
. O


Schwarz O
P S-MATE
unit O
cell-based O
tissue O
scaffolds S-FEAT
comprised O
of O
poly O
( O
D O
, O
L-lactide-co- O
ε O
-caprolactone O
) O
( O
PLCL O
) O
fabricated S-CONPRI
via O
the O
additive B-MANP
manufacturing E-MANP
technique O
, O
two-photon B-ENAT
polymerisation E-ENAT
( O
2PP O
) O
were O
found O
to O
undergo O
geometrical O
transformations O
from O
the O
original O
input O
design S-FEAT
. O


A O
Schwarz O
P S-MATE
unit O
cell S-APPL
surface O
geometry S-CONPRI
CAD B-ENAT
model E-ENAT
was O
reconstructed O
to O
take O
into O
account O
the O
geometrical O
transformations O
through O
CAD S-ENAT
modeling O
techniques O
using O
measurements O
obtained O
from O
an O
image-based O
averaging O
technique O
before O
its O
implementation O
for O
micromechanical O
analysis O
. O


Effective O
modulus O
results O
obtained O
from O
computational O
mechanical S-APPL
characterization O
via O
micromechanical O
analysis O
of O
the O
reconstructed O
unit B-CONPRI
cell E-CONPRI
assigned O
with O
the O
same O
material S-MATE
model O
making O
up O
the O
fabricated S-CONPRI
scaffolds O
demonstrated O
excellent O
agreement O
with O
a O
small O
margin O
of O
error S-CONPRI
at O
6.94 O
% O
from O
the O
experimental S-CONPRI
mean O
modulus O
( O
0.69 O
± O
0.29 O
MPa S-CONPRI
) O
. O


The O
inter-relationships O
between O
different O
dimensional O
parameters S-CONPRI
making O
up O
the O
Schwarz O
P S-MATE
architecture S-APPL
and O
resulting O
effective O
modulus O
are O
also O
assessed O
and O
discussed O
. O


With O
the O
ability O
to O
accommodate O
the O
geometrical O
transformations O
, O
maintain O
efficiency O
in O
terms O
of O
time O
and O
computational O
resources O
, O
micromechanical O
analysis O
has O
the O
potential O
to O
be S-MATE
implemented O
in O
tissue O
scaffolds S-FEAT
with O
a O
periodic O
microstructure S-CONPRI
as S-MATE
well O
as S-MATE
other O
structures O
outside O
the O
field O
of O
tissue B-CONPRI
engineering E-CONPRI
in O
general O
. O


Nanoparticle-enhanced B-MATE
Al I-MATE
7075 E-MATE
can O
be S-MATE
used O
to O
make O
crack-free B-CONPRI
welds E-CONPRI
, O
overlays S-FEAT
, O
and O
multi-layer O
parts O
via O
arc B-MANP
welding E-MANP
. O


Hardness S-PRO
of O
deposited O
nanoparticle-enhanced B-MATE
Al I-MATE
7075 E-MATE
weld O
material S-MATE
return O
to O
that O
of O
parent O
alloy S-MATE
after O
T73 B-MANP
heat I-MANP
treatment E-MANP
. O


Post-weld O
T73 B-MANP
heat I-MANP
treatment E-MANP
of O
nanoparticle-enhanced B-MATE
Al I-MATE
7075 E-MATE
results O
in O
tensile B-PRO
properties E-PRO
indiscernible O
from O
parent O
alloy S-MATE
. O


Aluminum B-MATE
alloy I-MATE
7075 E-MATE
( O
Al B-MATE
7075 E-MATE
) O
with O
a O
T73 B-MANP
heat I-MANP
treatment E-MANP
is O
commonly O
used O
in O
aerospace S-APPL
applications O
due O
to O
exceptional O
specific B-PRO
strength E-PRO
properties S-CONPRI
. O


Challenges O
with O
manufacturing S-MANP
the O
material S-MATE
from O
the O
melt S-CONPRI
has O
previously O
limited O
the O
processing O
of O
Al B-MATE
7075 E-MATE
via O
welding S-MANP
, O
casting S-MANP
, O
and O
additive B-MANP
manufacturing E-MANP
. O


Recent O
research S-CONPRI
has O
shown O
the O
capabilities O
of O
nanoparticle B-MATE
additives E-MATE
to O
control O
the O
solidification S-CONPRI
behavior O
of O
high-strength O
aluminum B-MATE
alloys E-MATE
, O
showcasing O
the O
first O
Al B-MATE
7075 E-MATE
components O
processed S-CONPRI
via O
casting S-MANP
, O
welding S-MANP
, O
and O
AM S-MANP
. O


In O
this O
work O
, O
the O
properties S-CONPRI
of O
nanoparticle-enhanced B-MATE
aluminum I-MATE
7075 E-MATE
are O
investigated O
on O
welded B-MACEQ
parts E-MACEQ
, O
overlays S-FEAT
and O
through O
wire-based B-MANP
additive I-MANP
manufacturing E-MANP
. O


The O
hardness S-PRO
and O
tensile B-PRO
strength E-PRO
of O
the O
deposited O
materials S-CONPRI
were O
measured O
in O
the O
as-welded O
and O
T73 B-MANP
heat-treated E-MANP
conditions O
showing O
that O
the O
properties S-CONPRI
of O
Al B-MATE
7075 I-MATE
T73 E-MATE
can O
be S-MATE
recovered O
in O
welded S-MANP
and O
layer-deposited O
parts O
. O


The O
work O
shows O
that O
Al B-MATE
7075 E-MATE
now O
has O
the O
potential O
to O
be S-MATE
conventionally O
welded S-MANP
or O
additively B-MANP
manufactured E-MANP
from O
wire O
into O
high-strength O
, O
crack-free B-CONPRI
parts E-CONPRI
. O


The O
dissimilar O
resistance B-MANP
spot I-MANP
welding E-MANP
of O
additively B-MATE
manufactured I-MATE
steel E-MATE
to O
conventional B-MATE
automotive I-MATE
steel E-MATE
has O
attracted O
significant O
attention O
from O
automotive S-APPL
manufacturer O
. O


However O
, O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
dissimilar O
spot B-FEAT
welds E-FEAT
could O
be S-MATE
affected O
by O
the O
printed O
properties S-CONPRI
of O
additively B-MATE
manufactured I-MATE
steels E-MATE
, O
limiting O
the O
further O
application O
of O
3D B-MANP
printing E-MANP
process O
in O
auto-body B-MANP
assembly I-MANP
line E-MANP
. O


This O
paper O
proposed O
an O
approach O
to O
improve O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
spot-welded B-PRO
joints E-PRO
of O
additive B-MATE
manufactured I-MATE
steels E-MATE
by O
the O
design S-FEAT
of O
binder B-MANP
jetting E-MANP
printed O
steels S-MATE
with O
the O
addition O
of O
nanoparticles S-CONPRI
. O


Cu-Sn B-MATE
nanoparticles E-MATE
have O
been O
injected O
to O
the O
stainless B-MATE
steel E-MATE
via O
binder B-MANP
jetting E-MANP
process O
, O
aiming O
to O
fill O
the O
voids S-CONPRI
between O
steel S-MATE
particles S-CONPRI
and O
reduce O
the O
microstructure B-CONPRI
heterogeneity E-CONPRI
in O
the O
spot B-FEAT
welds E-FEAT
. O


The O
microstructure B-CONPRI
evolution E-CONPRI
, O
sintering S-MANP
behavior O
of O
nanoparticles S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
resistance B-MANP
spot I-MANP
welded E-MANP
stainless O
steel S-MATE
were O
characterized O
and O
analyzed O
. O


The O
sintering S-MANP
behavior O
of O
Cu-Sn B-MATE
nanoparticles E-MATE
during O
welding S-MANP
process S-CONPRI
attributes O
to O
the O
formation O
of O
transition S-CONPRI
zone O
with O
homogenous O
microstructure S-CONPRI
, O
resulting O
to O
the O
improvement O
of O
hardness S-PRO
property O
and O
lap-shear B-PRO
strength E-PRO
of O
spot-welded B-PRO
joints E-PRO
. O


Compared O
to O
the O
spot B-FEAT
welds E-FEAT
of O
selective B-MANP
laser I-MANP
melting E-MANP
printed O
stainless B-MATE
steels E-MATE
, O
the O
resistance B-MANP
spot I-MANP
welded E-MANP
stainless O
steel S-MATE
via O
binder B-MANP
jetting E-MANP
process O
shows O
better O
mechanical B-CONPRI
properties E-CONPRI
with O
48 O
% O
increase O
of O
energy B-CHAR
absorption E-CHAR
and O
19 O
% O
increase O
of O
peak O
load O
. O


Additively B-MANP
manufactured E-MANP
plates O
are O
successfully O
joined O
using O
FSW S-MANP
for O
the O
first O
time O
. O


Weld B-CONPRI
microstructure E-CONPRI
consists O
of O
( O
α O
+ O
β O
) O
phase S-CONPRI
and O
very O
fine O
equiaxed O
α O
grain S-CONPRI
with O
a O
refined O
β O
phase S-CONPRI
at O
the O
grain B-CONPRI
boundary E-CONPRI
. O


The O
tensile B-PRO
strength E-PRO
of O
the O
FSW S-MANP
is O
nearly O
equal O
to O
the O
base O
material S-MATE
at O
a O
relatively O
higher O
tool B-PARA
rotation I-PARA
speed E-PARA
. O


Significant O
tool B-CONPRI
wear E-CONPRI
is O
observed O
at O
lower O
tool B-PARA
rotation I-PARA
speeds E-PARA
, O
resulting O
in O
lower O
weld B-PRO
strength E-PRO
. O


Additive B-MANP
manufacturing E-MANP
of O
titanium B-MATE
alloy I-MATE
Ti-6Al-4 I-MATE
V E-MATE
has O
significantly O
increased O
over O
the O
past O
few O
years O
, O
primarily O
due O
to O
its O
broad O
application O
over O
the O
conventional B-MANP
manufacturing E-MANP
process O
for O
complex O
and O
near B-MANP
net I-MANP
shape E-MANP
production O
. O


We O
study O
the O
feasibility S-CONPRI
of O
friction B-MANP
stir I-MANP
welding E-MANP
of O
Ti-6Al-4 B-MATE
V E-MATE
plates O
made O
by O
electron B-MANP
beam I-MANP
melting E-MANP
, O
performing O
both O
microstructural S-CONPRI
and O
mechanical B-CONPRI
analysis E-CONPRI
. O


Microstructures S-MATE
for O
all O
the O
welds S-FEAT
reveal O
lamellar S-CONPRI
( O
α O
+ O
β O
) O
phase S-CONPRI
and O
very O
fine O
equiaxed O
α O
grain S-CONPRI
with O
the O
prior O
β O
phase S-CONPRI
at O
grain B-CONPRI
boundaries E-CONPRI
in O
the O
stirred O
zone O
. O


Microhardness S-CONPRI
at O
different O
depths O
of O
the O
joint S-CONPRI
is O
measured O
and O
the O
strength S-PRO
of O
the O
joint S-CONPRI
is O
determined O
using O
a O
tensile B-CHAR
test E-CHAR
. O


The O
results O
obtained O
prove O
the O
feasibility S-CONPRI
of O
the O
process S-CONPRI
and O
provide O
the O
necessary O
processing O
conditions O
. O


The O
Additive B-MANP
manufacturing E-MANP
technologies O
familiarize O
many O
innovative O
and O
monetary O
gains O
when O
compared O
to O
conservative O
subtractive B-MANP
manufacturing E-MANP
methods O
in O
rapid B-ENAT
prototyping E-ENAT
( O
RP S-ENAT
) O
and O
small O
production B-CHAR
capacity E-CHAR
. O


In O
other O
exceedingly O
industrialized O
fields O
including O
aerospace S-APPL
, O
automobile S-APPL
, O
and O
bio-medical B-APPL
industries E-APPL
, O
additive B-MANP
manufacturing E-MANP
has O
turned O
out O
to O
be S-MATE
a O
subject O
of O
high O
interest O
. O


Nowadays O
, O
Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
of O
Titanium B-MATE
alloys E-MATE
has O
grown O
into O
an O
imperative O
field O
of O
study O
. O


The O
foremost O
prominence O
of O
Titanium B-MATE
alloys E-MATE
is O
excellent O
strength B-PRO
to I-PRO
weight I-PRO
ratio E-PRO
, O
high O
weathering B-PRO
resistance E-PRO
, O
and O
admirable O
characteristics O
involving O
high O
tensile B-PRO
strength E-PRO
and O
toughness S-PRO
with O
comparatively O
low O
electrical S-APPL
and O
thermal B-PRO
conductivity E-PRO
. O


The O
manufacturing S-MANP
of O
Titanium S-MATE
through O
AM B-MANP
technology E-MANP
is O
marginally O
expensive O
and O
durable O
as S-MATE
it O
enables O
to O
create O
freedom O
in O
design S-FEAT
community O
to O
fabricate S-MANP
user O
defined O
and O
complex B-CONPRI
structures E-CONPRI
which O
is O
hard O
to O
produce O
through O
other O
conventional B-MANP
manufacturing E-MANP
methods O
. O


The O
Ti-6Al-4V B-MATE
alloy E-MATE
is O
popularly O
known O
as S-MATE
the O
“ O
work O
horse O
” O
of O
titanium S-MATE
is O
comprehensively O
used O
in O
aerospace S-APPL
and O
biomedical B-APPL
industries E-APPL
. O


At O
present O
, O
several O
studies O
have O
focused O
on O
hybrid B-CONPRI
manufacturing E-CONPRI
and O
enhancing O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
Ti-6Al-4V S-MATE
with O
additive B-MANP
manufacturing E-MANP
techniques O
. O


In O
this O
research S-CONPRI
work O
, O
a O
short O
review O
on O
additive B-MANP
manufacturing E-MANP
of O
Ti-6Al-4V B-MATE
alloys E-MATE
has O
been O
investigated O
to O
define O
its O
mechanical S-APPL
and O
metallurgical S-APPL
properties O
in O
both O
as-built O
and O
heat S-CONPRI
treated O
conditions O
. O


Using O
tungsten B-MANP
inert I-MANP
gas I-MANP
welding E-MANP
, O
a O
simple S-MANP
technique O
to O
additively O
construct O
single-channel O
multilayer O
Ti B-MATE
alloy E-MATE
( O
Ti-6Al-4V S-MATE
) O
was O
developed O
. O


In O
the O
manufacturing B-MANP
process E-MANP
, O
the O
flow B-PARA
rate E-PARA
of O
nitrogen S-MATE
is O
used O
to O
control O
the O
microstructure S-CONPRI
and O
composition S-CONPRI
of O
each O
individual O
layer S-PARA
. O


The O
use O
of O
nitrogen S-MATE
leads O
to O
the O
formation O
of O
TiN S-MATE
particles S-CONPRI
, O
whose O
amount O
increases O
with O
the O
flow B-PARA
rate E-PARA
of O
nitrogen S-MATE
. O


There O
is O
no O
significant O
difference O
in O
the O
elastic B-PRO
moduli E-PRO
among O
individual O
layers O
. O


Increasing O
the O
flow B-PARA
rate E-PARA
of O
nitrogen S-MATE
results O
in O
an O
increase O
in O
the O
compression B-PRO
strength E-PRO
of O
the O
individual O
layers O
and O
a O
decrease O
in O
the O
ductility S-PRO
of O
individual O
layers O
. O


The O
Vickers B-PRO
hardness E-PRO
increases O
gradually O
from O
300 O
to O
400 O
HV O
for O
the O
base B-MATE
metal E-MATE
to O
∼1000 O
HV O
for O
the O
top O
layer S-PARA
of O
the O
Ti B-MATE
alloy E-MATE
, O
and O
the O
compressive B-PRO
strength E-PRO
of O
the O
Ti B-MATE
alloy E-MATE
reaches O
1.92 O
GPa S-PRO
at O
a O
1.5 O
L/min O
nitrogen B-PARA
flow I-PARA
rate E-PARA
. O


The O
technique O
developed O
in O
this O
work O
provides O
a O
feasible O
route O
to O
additively O
construct O
single-channel O
multilayer O
structures O
with O
spatial B-CHAR
distributions E-CHAR
of O
the O
composition S-CONPRI
and O
microstructures S-MATE
. O


Direct O
observation O
of O
pore S-PRO
formation O
dynamics O
during O
LPBF S-MANP
additive B-MANP
manufacturing E-MANP
. O


Revealed O
three O
new O
pore S-PRO
formation O
mechanisms O
. O


Reconfirmed O
three O
previously O
studied O
pore S-PRO
formation O
mechanisms O
Laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
( O
LPBF S-MANP
) O
is O
a O
3D B-ENAT
printing I-ENAT
technology E-ENAT
that O
can O
print S-MANP
parts O
with O
complex B-CONPRI
geometries E-CONPRI
that O
are O
unachievable O
by O
conventional B-MANP
manufacturing E-MANP
technologies O
. O


However O
, O
pores S-PRO
formed O
during O
the O
printing B-MANP
process E-MANP
impair O
the O
mechanical S-APPL
performance O
of O
the O
printed O
parts O
, O
severely O
hindering O
their O
widespread O
application O
. O


Here O
, O
we O
report O
six O
pore S-PRO
formation O
mechanisms O
that O
were O
observed O
during O
the O
LPBF S-MANP
process O
. O


Our O
results O
reconfirm O
three O
pore S-PRO
formation O
mechanisms O
- O
keyhole O
induced O
pores S-PRO
, O
pore S-PRO
formation O
from O
feedstock S-MATE
powder O
and O
pore S-PRO
formation O
along O
the O
melting B-CONPRI
boundary E-CONPRI
during O
laser S-ENAT
melting O
from O
vaporization O
of O
a O
volatile O
substance S-CONPRI
or O
an O
expansion O
of O
a O
tiny O
trapped O
gas S-CONPRI
. O


We O
also O
observe O
three O
new O
pore S-PRO
formation O
mechanisms O
: O
( O
1 O
) O
pore S-PRO
trapped O
by O
surface S-CONPRI
fluctuation O
, O
( O
2 O
) O
pore S-PRO
formation O
due O
to O
depression O
zone O
fluctuation O
when O
the O
depression O
zone O
is O
shallow O
and O
( O
3 O
) O
pore S-PRO
formation O
from O
a O
crack O
. O


The O
results O
presented O
here O
provide O
direct O
evidence O
and O
insight O
into O
pore S-PRO
formation O
mechanisms O
during O
the O
LPBF S-MANP
process O
, O
which O
may O
guide O
the O
development O
of O
pore S-PRO
elimination/mitigation O
approaches O
. O


Since O
certain O
laser B-CONPRI
processing E-CONPRI
conditions O
studied O
here O
are O
similar O
to O
the O
situations O
in O
high O
energy B-PARA
density E-PARA
laser O
welding S-MANP
, O
the O
results O
presented O
here O
also O
have O
implications O
for O
laser B-MANP
welding E-MANP
. O


The O
processes S-CONPRI
of O
ultrasonic B-MANP
spot I-MANP
welding E-MANP
and O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
are O
modelled O
by O
approximating O
the O
weld S-FEAT
interface S-CONPRI
as S-MATE
rough O
metallic S-MATE
surfaces O
in O
sliding O
contact S-APPL
. O


It O
is O
assumed O
that O
bonding S-CONPRI
is O
due O
to O
athermal B-CONPRI
plastic I-CONPRI
deformation E-CONPRI
of O
surface B-CONPRI
asperities E-CONPRI
and O
the O
associated O
growth O
of O
metallic S-MATE
junctions S-APPL
along O
the O
weld S-FEAT
interface S-CONPRI
. O


To O
link O
the O
process S-CONPRI
variables O
and O
the O
extent O
of O
junction S-APPL
growth O
, O
an O
expression O
for O
the O
real O
contact S-APPL
area S-PARA
at O
the O
weld S-FEAT
interface S-CONPRI
is O
combined O
with O
process-specific O
frictional O
heating S-MANP
models O
developed O
here O
. O


The O
resulting O
framework S-CONPRI
is O
validated O
by O
comparing O
its O
predictions S-CONPRI
of O
the O
weld B-PRO
strength E-PRO
with O
data S-CONPRI
from O
the O
ultrasonic B-MANP
welding E-MANP
literature O
. O


The O
close O
agreement O
between O
the O
framework S-CONPRI
's O
predictions S-CONPRI
and O
the O
experimental B-CONPRI
data E-CONPRI
demonstrates O
that O
the O
surface B-CONPRI
asperities E-CONPRI
soften O
due O
to O
frictional O
heating S-MANP
, O
while O
acoustic B-CONPRI
softening I-CONPRI
effects E-CONPRI
are O
insignificant O
. O


The O
junction S-APPL
growth O
model S-CONPRI
is O
used O
to O
identify O
parameter S-CONPRI
sets O
for O
ultrasonic B-MANP
spot I-MANP
welding E-MANP
and O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
that O
maximize O
the O
weld B-PRO
strength E-PRO
while O
simultaneously O
minimizing O
the O
thermal O
excursion O
at O
the O
weld S-FEAT
interface S-CONPRI
. O


It O
is O
found O
that O
in O
ultrasonic B-MANP
spot I-MANP
welding E-MANP
, O
certain O
processing O
conditions O
can O
cause O
interfacial B-CONPRI
melting E-CONPRI
, O
although O
melting S-MANP
is O
not O
required O
to O
form O
strong O
bonds O
. O


It O
is O
also O
shown O
that O
in O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
, O
the O
deposition B-PARA
rate E-PARA
is O
highest O
when O
the O
positions O
of O
the O
peak O
temperature S-PARA
and O
complete O
interfacial B-CONPRI
bonding E-CONPRI
coincide O
underneath O
the O
sonotrode S-MACEQ
. O


If O
the O
position O
of O
complete O
interfacial B-CONPRI
bonding E-CONPRI
leads O
the O
position O
of O
the O
peak O
temperature S-PARA
, O
there O
is O
excessive O
heating S-MANP
of O
the O
build S-PARA
, O
and O
the O
sonotrode S-MACEQ
velocity O
can O
be S-MATE
increased O
without O
degrading O
bond B-CONPRI
quality E-CONPRI
. O


Although O
Additive B-MANP
Manufacturing E-MANP
implementation O
is O
rapidly O
growing O
, O
industrial B-CONPRI
sectors E-CONPRI
are O
demanding O
an O
increase O
of O
manufactured S-CONPRI
part O
size O
which O
most O
extended O
processes S-CONPRI
, O
such O
as S-MATE
Selective O
Laser S-ENAT
Melting O
( O
SLM S-MANP
) O
or O
Laser B-MANP
Metal I-MANP
Deposition E-MANP
( O
LMD S-MANP
) O
, O
are O
not O
able O
to O
offer O
. O


In O
this O
sense O
, O
Wire-Arc B-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
offers O
high B-PARA
deposition I-PARA
rates E-PARA
and O
quality S-CONPRI
without O
size O
limits S-CONPRI
, O
becoming O
the O
best O
alternative O
for O
additive B-MANP
manufacturing E-MANP
of O
medium-large O
size O
parts O
with O
high O
mechanical S-APPL
requirements O
such O
as S-MATE
structural O
parts O
in O
the O
aeronautical S-APPL
industry.WAAM O
technology S-CONPRI
adds O
material S-MATE
in O
form O
of O
wire O
using O
an O
arc B-MANP
welding E-MANP
process O
in O
order O
to O
melt S-CONPRI
both O
the O
wire O
and O
the O
substrate S-MATE
. O


There O
are O
three O
welding S-MANP
processes S-CONPRI
that O
are O
mainly O
used O
in O
WAAM S-MANP
: O
Plasma B-MANP
Arc I-MANP
Welding E-MANP
( O
PAW S-MANP
) O
, O
Gas B-MANP
Tungsten I-MANP
Arc I-MANP
Welding E-MANP
( O
GTAW S-MANP
or O
TIG S-MANP
) O
and O
Gas B-MANP
Metal I-MANP
Arc I-MANP
Welding E-MANP
( O
GMAW S-MANP
or O
MIG S-MANP
) O
. O


This O
paper O
studies O
these O
processes S-CONPRI
regarding O
on O
their O
capabilities O
for O
additive B-MANP
manufacturing E-MANP
and O
compares O
the O
mechanical B-CONPRI
properties E-CONPRI
obtained O
by O
the O
different O
welding S-MANP
technologies S-CONPRI
applied O
in O
WAAM S-MANP
. O


Obtained O
results O
show O
the O
applicability O
of O
the O
technology S-CONPRI
as S-MATE
an O
alternative O
of O
traditional O
metallic S-MATE
preforms O
manufacturing B-MANP
processes E-MANP
, O
such O
as S-MATE
casting O
or O
forging S-MANP
. O


A O
weak B-CONPRI
coupling I-CONPRI
modeling I-CONPRI
method E-CONPRI
is O
developed O
for O
arc B-MANP
welding E-MANP
based O
additive B-MANP
manufacturing E-MANP
. O


This O
weak B-CONPRI
coupling I-CONPRI
modeling I-CONPRI
method E-CONPRI
is O
capable O
of O
simulating O
the O
complex O
heat B-CONPRI
and I-CONPRI
mass I-CONPRI
transfer E-CONPRI
effectively O
and O
efficiently O
. O


In O
arc B-MANP
welding E-MANP
based O
additive B-MANP
manufacturing E-MANP
, O
the O
surface B-CONPRI
topographies E-CONPRI
of O
deposited B-CHAR
layer E-CHAR
are O
more O
complex O
than O
conventional B-MANP
welding E-MANP
, O
therefore O
, O
the O
distribution S-CONPRI
of O
the O
electromagnetic B-CONPRI
force E-CONPRI
in O
molten B-CONPRI
pool E-CONPRI
, O
arc B-PARA
pressure E-PARA
, O
plasma S-CONPRI
shear O
stress S-PRO
and O
heat B-CONPRI
flux E-CONPRI
on O
molten B-CONPRI
pool E-CONPRI
surface O
are O
not O
the O
same O
as S-MATE
the O
conventional B-MANP
welding E-MANP
. O


A O
three-dimensional S-CONPRI
weak O
coupling O
modeling S-ENAT
method O
of O
the O
arc S-CONPRI
and O
metal B-CONPRI
transport E-CONPRI
is O
developed O
to O
simulate O
the O
arc S-CONPRI
, O
molten B-CONPRI
pool E-CONPRI
dynamic S-CONPRI
and O
droplet S-CONPRI
impingement O
in O
arc B-MANP
welding E-MANP
based O
additive B-MANP
manufacturing E-MANP
. O


In O
the O
arc S-CONPRI
model O
, O
the O
molten B-CONPRI
pool E-CONPRI
is O
simplified O
to O
be S-MATE
solid O
state O
on O
the O
basis O
of O
experimentally O
observed O
results O
. O


The O
arc S-CONPRI
is O
simulated O
firstly O
, O
and O
then O
the O
electromagnetic B-CONPRI
force E-CONPRI
, O
arc B-PARA
pressure E-PARA
, O
plasma S-CONPRI
shear O
stress S-PRO
and O
heat B-CONPRI
flux E-CONPRI
are O
extracted S-CONPRI
and O
transmitted O
to O
metal B-CONPRI
transport E-CONPRI
model O
. O


The O
volume B-CONPRI
of I-CONPRI
fluid E-CONPRI
( O
VOF S-CONPRI
) O
method O
is O
employed O
to O
track O
free B-CONPRI
surface E-CONPRI
of O
molten B-CONPRI
pool E-CONPRI
and O
droplet S-CONPRI
, O
and O
the O
continuum B-CONPRI
surface I-CONPRI
force E-CONPRI
( O
CSF S-CONPRI
) O
method O
is O
applied O
to O
transform O
all O
the O
surface B-CONPRI
forces E-CONPRI
on O
free B-CONPRI
surface E-CONPRI
as S-MATE
localized O
body B-CONPRI
forces E-CONPRI
. O


This O
weak B-CONPRI
coupling I-CONPRI
model E-CONPRI
has O
better O
accuracy S-CHAR
than O
empirical S-CONPRI
model O
and O
decreases O
computational O
consumption O
. O


The O
molten B-CONPRI
pool E-CONPRI
morphology O
and O
cross-sectional O
profile S-FEAT
of O
simulated O
results O
accord O
well O
with O
experimental S-CONPRI
results O
in O
both O
single-bead O
deposition S-CONPRI
and O
overlapping O
deposition S-CONPRI
, O
which O
indicates O
that O
this O
weak B-CONPRI
coupling I-CONPRI
modeling I-CONPRI
method E-CONPRI
is O
capable O
of O
simulating O
the O
complex O
heat B-CONPRI
and I-CONPRI
mass I-CONPRI
transfer E-CONPRI
phenomena O
in O
arc B-MANP
welding E-MANP
based O
additive B-MANP
manufacturing E-MANP
. O


Laser B-MANP
additive I-MANP
manufacturing E-MANP
is O
an O
advanced O
, O
very O
perspective O
technology S-CONPRI
with O
potentially O
wide O
industrial S-APPL
applications O
, O
one O
of O
them O
being O
an O
improvement O
of O
durability S-PRO
of O
forms O
and O
dies S-MACEQ
. O


The O
aim O
is O
to O
improve O
surface S-CONPRI
properties S-CONPRI
like O
wear B-PRO
resistance E-PRO
using O
special O
layers O
of O
powder S-MATE
sintered O
or O
remelted O
by O
laser B-CONPRI
beam E-CONPRI
. O


At O
present O
, O
dies S-MACEQ
are O
manufactured S-CONPRI
by O
machining S-MANP
with O
following O
bulk B-MANP
heat I-MANP
treatment E-MANP
, O
which O
is O
an O
expensive O
process S-CONPRI
. O


Concerning O
repairs O
of O
dies S-MACEQ
, O
they O
are O
usually O
performed O
manually O
, O
using O
arc S-CONPRI
or O
plasma B-MANP
welding E-MANP
with O
numerous O
difficulties O
and O
disadvantages O
in O
comparison O
with O
promising O
and O
advanced O
laser S-ENAT
overlaying O
. O


The O
paper O
contains O
results O
of O
a O
comprehensive O
evaluation O
of O
several O
types O
of O
hard O
overlayed O
powder S-MATE
of O
H13 B-MATE
tool I-MATE
steel E-MATE
on O
a O
S355 B-MATE
structural I-MATE
steel E-MATE
using O
laser B-CONPRI
beam E-CONPRI
. O