SUMMER 2019VOL. 8 NO. 2

POWDERMETALLURGYREVIEW

POWDER METALLURGY IN INDIA
AUTOMOTIVE APPLICATIONS FOR PM
SPARK PLASMA SINTERING
Published by Inovar Communications Ltd

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India’s growing Powder
Metallurgy market
Having attended the APMA Conference this year in Pune,
India, it was evident that the Indian Powder Metallurgy
market is thriving, reporting continued growth that is
mirroring the state of the country’s expanding automotive
sector.
The country’s PM structural part makers are not justsubsidiaries of leading global PM companies, butalso include many locally established enterprises. As
the market grows, investment in these companies is
continuing, with many reporting facility expansions.
Not content with meeting the needs of the growing local
market, a number of the larger PM part manufacturers
are also seeking to attract new overseas customers.
Reporting from within the industry, Kadambari Gopinath,offers a unique insight into the region, considers the stateof its automotive market and identifies the key players in
the country’s PM structural parts industry.
There are, of course, many applications in theautomotive sector for the use of Powder Metallurgy. The
process offers numerous advantages over alternative
manufacturing routes, from cost savings to novel designs
and unique material properties. Much of this innovation
has been recognised through industry awards over theyears and in this issue, we present award winning PM
structural parts from the automotive sector.

Paul Whittaker
Editor, Powder Metallurgy Review

Subscriptions
Powder Metallurgy Review is published on aquarterly basis. It is available as a free electronic
publication or as a paid print subscription. The
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Design and production
Inovar Communications Ltd.
ISSN 2050-9693 (Print edition)
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This magazine is also available for freedownload from www.pm-review.com© 2017 Inovar Communications Ltd

Cover image

ABS sensor rings are justone of the many automotive
components suited to
Powder Metallurgy (Courtesy
Sintercom India)

Summer 2019

Powder Metallurgy Review

3

GLO

N

S
D
E
E

D
OW

ER ME
T
A
L
About Kymera International:

41

POWDERMETALLURGYREVIEW

55

61

72

89

in this issue
57

The Powder Metallurgy market in India:
Potential for continued growth as auto
industry advances
India produced a total of 31 million vehicles lastyear, including passenger and commercial vehicles as well as three and two-wheelers, making
it the fourth largest automotive manufacturer
in the world. The domestic market for sinteredcomponents is growing at a CAGR of 22%, withmany businesses reporting further investment
and new product lines. In this review, Kadambari
Gopinath, reports on the current state of India’s
automotive market and provides an insight into
the country’s growing PM industry.

SEE US AT

With nine manufacturing sites in seven countries,
Kymera International is a global leading producer
and distributor of powders, pastes and granules ofaluminum, aluminum alloys, copper, copper oxide,
bronze, brass, tin and several specialty alloys.

© 2019 Kymera International

OR YOUR P
SF

A
B

L
U
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T
S
I ON
L

Summer 201971

89

Spark Plasma Sintering: Method, systems,
applications and industrialisation
For around thirty years, Spark Plasma Sintering(SPS) has been of great interest to the Powder
Metallurgy industry and academia alike, forboth product manufacturing and advanced
material research and development. Today, anumber of components made using SPS are
already in production, with the process movingfrom the R&D stage to practical industrial use.
In this article, Dr Masao Tokita, of NJS Co.,
Ltd., introduces the latest in SPS technology,
discusses the development of the production
systems and highlights a number of industrial
applications.

Award winning automotive applications
showcase potential of PM

POWDERMET2019
regular features

Powder Metallurgy can be used to produce awide range of automotive components. The
technology offers numerous advantages overother metal working processes, from reduced
manufacturing costs to improved properties
and unique material characteristics. Over
recent years, many of these parts have been therecipient of industry awards, and in this article,
6
Industry news
Dr David Whittaker highlights a number of the
105
Events guide
TECHNICAL PROGRAM
winning parts to showcase the potential for PM in
Held with the co-locatedconference
AMPM2019, Additive Manufacturing
the automotive
sector.
106
Advertisers’ index

June 23–26, 2019 • Sheraton Grand • Phoenix, Arizona

International204/206
Conference
BOOTH
on Powder Metallurgy& Particulate Materials

www.kymerainternational.com
20
1
9with Powder Metallurgy, POWDERMET2019 attendees will have access toover 200 technical presentations from worldwide experts on the latest
research and development.
© 2019 Inovar Communications Ltd
Summer 2019

Powder Metallurgy Review

5Spark plasma sintering| contents page | news | events | advertisers’ index | email |International exhibition and conference
on the next generation of manufacturing technologies

Spark Plasma Sintering:
Method, systems, applications
and industrialisation

Frankfurt, Germany, 19 – 22 November 2019
formnext.com

The entire world of additive manufacturing
For around thirty years, Spark Plasma Sintering (SPS) has been of great interest to
the Powder Metallurgy industry and academia alike, for both product manufacturing
and advanced material research and development. Today in Japan, a number ofcomponents made using SPS are already in production, with the process movingfrom the R&D stage to practical industrial use. In this article, Dr Masao Tokita, of
NJS Co., Ltd., introduces the latest in SPS technology, discusses the development of
SPS systems and highlights a number of industrial applications.

Design and software

R&D
Metrology

Materials

Post-processing
Services

Manufacturing solutions
Pre-processing

Additive manufacturing surrounds a whole world of processes.
Instead of a world tour you only need one ticket – for Formnext!

Where ideas take shape.

Offical event hashtag #formnext

It is widely recognised that the Spark
Plasma Sintering (SPS) method isan advanced processing technology,
used to produce a homogeneous,
highly-dense, nanostructuralsintered compact, as well as in
Functionally Graded Materials(FGMs), fine ceramics, composite
materials, wear-resistant materials,
thermo-electric semiconductors andbiomaterials. Originating in Japan,
the technology, also referred to as apressure-assisted pulse energisingprocess, Field-Assisted Sintering
Technology (FAST), Electric Current
Activated/assisted Sintering (ECAS)
or Pulsed Electric Current Sintering(PECS), is today finding new applications in many global regions.
As of January 2019, over five
hundred SPS systems are installedin Japan alone, located in universities, technical colleges, national
institutes and private companies foruse in both the R&D and manufacturing sectors. It is estimated thataround one thousand SPS systems
are currently installed globally,© 2019 Inovar Communications Ltd

including those found in Europe, theUSA, Russia, China, Korea and others.
SPS technology is seen as apromising technology for innovative
processing in the field of advanced
new materials fabrication in the 21st

century [1-3]. Today’s fifth generation SPS systems are capable ofproducing parts of increasing size,
offering improved functionality,
reproducibility, productivity and costeffectiveness.

Fig. 1 Spark Plasma Sintering (SPS) can be used to produce a variety ofcomponents, from FGMs to porous filters

Summer 2019

Powder Metallurgy Review

89Large• Customised SPS systems• Cost effective• High reliability

2010~

5 Generation
SPS Processth• Sinter Land Inc.

Size effect2001~

4th Generation
SPS Process

1989~

1962~

3rd Generation:

1st Generation:
Spark Sintering

Spark Plasma
Sintering• JAPAX Inc.

• Sumitomo Coal
Mining Co., Ltd.

1986

2nd Generation:
Plasma ActivatedSintering (PAS)• IJR Inc (Inoue JAPAX
Research Inc)

Small
Low

• Sumitimo/SPSS• 4 Processes• 5 Basic production systems• Industrialisation,
expanding applications• High & low-pressure system• Large DC pulsed current• Homogeneity/high density• High repeatability• Low-pressure system• Small DC pulsed current

Shape effect: Functionality, reproducibility, productivity

High

Fig. 2 Historical progress of the Spark Plasma Sintering method and technology

A story of continual
innovation
Initial studies, dating back to around1910 in Germany, report a process
where an electric energising technique was applied to consolidatea powder material. In the USA, a
few years later in 1933, G F Tayler
patented the first resistance sintering

method for sheet metals [4]. These
processes are considered as theorigin of the Hot Pressing (HP) technique, where a high-frequency induction heating method is applied.
It was in the 1960s that a methodof Spark Sintering (SS) was developedby Dr Kiyoshi Inoue of JAPAX Inc.,
Japan [5, 6]. As shown in Fig. 2, thisis now referred to as a first genera-

Conventional reaction sintering
Reaction
sintering
Pressurelesssintering

Thermal plasma sintering(conventional)

Atmosphericsintering

Sintering
Methods

Self-propagating hightemperature synthesis (SHS)

Vac. Air, Ar/N2
inert gas

Solidcompaction

Microwave, Milliwave sintering
Hot Pressing (HP)
Spark Plasma Sintering (SPS)
Ultra high-pressure sintering

Pressurised
sintering

Hot Isostatic Pressing (HIP)
Gas
compaction

High pressure gas reaction
sintering

Fig. 3 Typical classification of sintering methods

90

Powder Metallurgy Review

Summer 2019tion SPS system. The process was
further developed by Inoue, resulting
in a second generation techniqueknown as Plasma-Activated Sintering(PAS) released in 1986. Thereafter,in 1989, the Spark Plasma Sintering
method was introduced by Sumitomo
Coal Mining Co., Ltd, Japan [7], being
recognised as the third generationof large DC pulse applied sintering
techniques.
Ongoing R&D for the implementation of SPS methods and systems
was initiated to design practical
hardware and software for industrial
applications. The development ofsmall- to medium-sized box-type
experimental use SPS systems
for new materials preparation,and single-head open-type limited
production systems, followed. From2001 to 2009, as the fourth-generation technology developed to accommodate for product manufacturing,
five basic styles of SPS production
systems emerged to suit medium- to
mass-production scales [8]. In addition to sintering, SPS technology also
found application in solid phase diffusion bonding and joining [9], surface
modification (treatment) [10] and asynthesis technique, for example, of asingle-crystal fabrication.

© 2019 Inovar Communications Ltd

Spark plasma sintering| contents page | news | events | advertisers’ index | email |After 2010, the progress of SPS
technology was such that new,advanced SPS systems are now seen
as being fifth-generation machines.
Customised SPS apparatus, alongwith more practical manufacturing
applications, offer high reliability andreduced production costs.
A further interesting technology,
derived from the ongoing development of SPS, is the emergence ofFlash Sintering and Flash-SPS, acategory of Electric Current Activated/assisted Sintering [3,11]. Still
under research, Flash Sintering could
prove an innovative future technology.

The Spark Plasma Sintering
process
The Spark Plasma Sintering process
enables sintering and sinter-bonding,at low temperatures and at highspeed. The technique, a form ofpressurised sintering as seen in
Fig. 3, involves the application of ahigh-energy, low-voltage electricalcurrent, believed to result in a ‘spark
plasma’ phenomenon in the powder.
Although the precise mechanism of
the spark plasma remains unclear,many years of research by manydifferent material researchers has
resulted in a number of theories[12-16].
One of the most accepted explanations is based around the illustrationin Fig. 4 where, once compacted
and still under pressure, an on-off
DC pulse voltage, at high current, isapplied to the powder using a special
pulse generator. It is understood thatthe electrical discharge results in ahigh-temperature spark plasma, up
to several thousand degrees centigrade, generated momentarily at theinitial stage of energising. This forms
uniformly throughout the compact
and the generated heat fuses, purifies and activates the surface of thepowder particles (Fig. 5).
The initial stage of the pulse energising results in a discharge between
the powder particles and between
the powder and the graphite diewall surface (Fig. 6). When sparking
occurs, a high-temperature sput-© 2019 Inovar Communications LtdP
Oil pressure/AC servo motor/
pneumatic system

Upper electrode

Powder

Upper
punch

Thermocouple
and/or Digitalradiation
thermometer

Die
Lower
punch

Controller/computing

Temperature
Pressure
Current-voltage
VacuumLongitudinal displacement

Vacuumchamber
Lower electrodeP

Fig. 4 Basic theory of the SPS process
Electric current

Particle

Sintering die(inside wall)| contents page | news | events | advertisers’ index | email |On-off DC pulse
generator

Spark plasma sintering

Joule
heat

Discharge

Fig. 5 ON-OFF DC pulsed current path and pulsed current flow through powder
particles

Fig. 6 The sintering stage in a graphite mould and vacuum chamber

Summer 2019

Powder Metallurgy Review

91Spark plasma sintering

Pulse voltage| contents page | news | events | advertisers’ index | email |Phenomenon
Generation of spark plasma

Effects
Surface activation• Evaporation, melting &purification

ON

High-speed diffusion,
high-speed material transfer

Generation of spark
impact pressure• Local stress and sputtering

Efficient heating, plastic
deformation promotion

Generation of Joule heat
• Local high-temperature
generation

Action of electric field• High-speed ion migration

Efficient generation ofpulse voltage and current
OFF

Thermal diffusion• Heat transfer from hightemperature generating point

Practical advantage
Low-temperature, short-timesintering
Sintering of hard-to-sintermaterial (without catalyst),
bonding of dissimilarmaterials

High-density energy supply

Short-time sintering

Dispersed movementof discharge point

Uniform sintering - short time

Quick cooling ofintergranular bonding
Quick cooling ofintergranular bonding

Sintering of amorphousmaterials
Sintering of metastablephase
Low-temperature sintering

Fig. 7 Effects of ON-OFF DC pulse energising
tering effect is generated by spark
plasma and spark impact pressure.
This works to eliminate adsorptive
gases and oxide films and impurities
existing on the surface of the powder
particles. The action of the electromagnetic field enhances high-speed
diffusion due to the electro-migration
effects of ions.
A Joule heating stage, causedby the passage of electric current
through the powder whilst undermechanical pressure, further assistsin the SPS process. The intense joule
heating effect can often result in
localised high-temperature generation, and therefore leads to localised
vaporisation or cleaning of powder
surfaces. Such a phenomenon
ensures a favourable path for current
flow. Further effects of the on-off
pulse DC voltage are shown in moredetail in Fig. 7.

Configuration of an SPS
systemFig. 8 This medium-sized 5th Generation SPS system produced by SinterLand Inc, Japan, offers high-precision process control and short cycle times.
Systems such as this can be used with multiple materials and offer wide
temperature ranges (Courtesy Sinter Land)

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Spark plasma sintering| contents page | news | events | advertisers’ index | email |The configuration of a typical SPS
system consists of a compacting
press with a vertical, single-axis pressurisation mechanism, incorporating
specially designed punch electrodes
made from graphite. The system can© 2019 Inovar Communications Ltd

Fig. 9 World’s largest semi-tunnel type automatic SPS production system has three vacuum chambers, 6 MN press witha pallet-type special conveyer, and inverter-type 40,000 A DC pulse generator (Courtesy Sinter Land)

incorporate a water-cooled vacuum
chamber, a vacuum/air/argon-gas
atmosphere control mechanism, a
special DC-pulsed power generator,
Z-axis position measuring andcontrol unit, temperature measuring
and control units, an applied pressure display unit, a data analysing
unit and various safety interlock
devices. A typical 5th Generation
medium-sized system can be seen in
Fig. 8. This model is ideally suited to
R&D work, as well as prototype andproduct manufacture.
Production-scale SPS systems
Custom built SPS systems are alsoavailable today, as well as large
production-based machines such as
the example seen in Fig. 9. The moveto production-scale SPS systems
requires consideration of manyfactors. The cost and developmentof optimum systems will depend on
production strategies, including therequired cycle time, technologies
to support scale expansion, massproduction, automation and numerical control systems. There is also thedevelopment of process technologies
for high functionality, reproducibility,
uniformity and structural control. In
addition, pre- and post-processes for
manufacturing must be considered.

© 2019 Inovar Communications Ltd

In order to meet different productivity levels, there are typically five
options to consider. These include:
multi-head, batch, tunnel, rotary andshuttle-type SPS systems. In addition to these, scaling-up process,automatic handling and powder
stacking equipment for materials
and process optimisation have also
been developed [17].

Development of pulse generators
Presently, there are two basic types ofDC pulse generator for SPS apparatus, thyristor-type and invertor-type
power supply. Fig. 10 shows examplesof typical on-off pulse waveforms anddifferent pulse width and ratio. The
waveform, max./min. on-time/off-time
pulse width, peak current, frequency,
duty factor settings, control system

ON-time: 30 ms OFF-time: 10 ms

ON-time: 10 ms OFF-time: 30 ms

Fig. 10 Typical wave form of a thyristor-type pulse generator (ON-OFF ratio in 50 Hz)

Summer 2019

Powder Metallurgy Review

93Spark plasma sintering| contents page | news | events | advertisers’ index | email |Classification

Materials for SPS processing

MetalsFe, Cu, Al, Au, Ag, Ni, Cr, Mo, Sn, Ti, W, Be, C

Ceramics

OxidesAl2O3,Mulite, ZrO2, MgO,SiO2, TiO2, HfO2

CarbidesSiC, B4C, TaC, TiC, WC, ZrC, VC

Nitrides

Si3N4, TaN, TiN, AlN, ZrN, VN

Borides

TiB2, HfB2, LaB6, ZrB2, VB2, MgB2

Fluorides

LiF, CaF2, MgF2

Virtually any metal possible

Al2O3+Ti, ZrO2+stainless steel, Al2O3+stainless steel
WC+Co, WC+Ni, TiC+TiN+Ni, BN+Fe,
TiAl, MoSi2, Si3Zr5, NiAl

Intermetallic compounds

NbCo, Nb3Al, LaBaCuSO4, Sm2Co17

Other materials

Organic materials (polyimide, etc.), FRM, FRC, CNT composite materials

Table 1 Suitable materials for SPS process
2400

Hardness HV(1000)

2300

Al2O3

2200
2100
2000
1900
1800
0

Pure nano-SiC
Powder particle size: 30 nm
R.D: 99.4%
mHV: 2380
Diameter: 20 mm
Grain size after SPS: 100 nm

No binder
Binder addition
PLS

HP

HIP

SPS

Sintering method
Fig. 11 Nano-SiC compact by SPS and Al2O3 HV hardness distribution behaviour
sintered by various methods

SPS

HP Sintering

◎
◎
◎
◎

×
×
×
×

Temperature rise time

Fast

Slow

Holding time

Short

Long

○
◎
◎
○
◎

○
△
△
△
△

Temperature gradient sintering
Grain boundary controlled sintering
Fine crystalline structure controlled sintering
Temperature rise rate
Sintering time

Homogeneous sintering
Expandability
Productivity
Investment in equipment
Running cost(◎ excellent | ○ good | △ fair | × difficult)

Table 2 Comparison of the characteristics of SPS and HP sintering

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Powder Metallurgy Review

Summer 2019

field effect, such as an electro-migration, and preferential orientation of
crystalline structure [18].

Load
A: Material A
B: Material B

Comparing traditionalsintering processes to Spark
Plasma Sintering

Si3N4+Ni, Al2O3+Ni, ZrO2+Ni
Cermets

Spark plasma sintering| contents page | news | events | advertisers’ index | email |and energy consumption vary between
each system. Each pulse generator
has its own advantages and should bechosen based on the desired purpose
and usage of the SPS system.
The majority of SPS systems
installed in universities, national institutes and private companies employ
the thyristor-type pulse generator, due
to a rich reference database on SPS
and higher reliability of power supply
hardware. The invertor type, with a
Pulse Width Modulation (PWM) control,
offers a lower power consumption
and a more compact size, which could
make it a more attractive option foreconomical low-cost production. The
development of pulse generators isstill ongoing.

Materials
The SPS process is suited to a numberof materials, including conductive
and non-conductive powders. An
example of suitable materials for SPS
is provided in Table 1; these include
metals, ceramics, cermets, intermetallic compounds and others.
When using non-conductive
materials, where no sparking occurs
between powder particles, it is considered that the effect of on-off DC pulse
current still exists, energising particles, which results in an enhancementof the sinterability and densification
rate of the material. The large pulsed
energy generates an electro-magnetic© 2019 Inovar Communications Ltd

The method of applying heat directly
to the compact results in extremely
high heating and cooling rates, andis therefore capable of reducing
sintering time from hours to minutes.
Compared with conventional sintering,
the SPS method has demonstrated
superior material properties, as it
can offer a structure tailoring effect,
minimise grain growth, enhanceelectro-migration and provide a strong
preferential orientation effect.
A comparison of various sintering
techniques and the resulting HV
Vickers hardness is shown in Fig. 11
for an Al2O3 example. The results indicate that SPS offers hardness equal
to and greater than processing by HIP
or conventional hot press sintering. A
comparison of specific characteristicsof the SPS method, against conventional Hot Press (HP) sintering, isshown in Table 2.
As a sintering technique, SPS has
drawn considerable attention as one
the newest rapid sintering methods.
The novel process also benefits fromlow power consumption of between
1/5 and 1/3 that of conventionalsintering techniques, such as pressureless sintering, hot press sinteringand Hot Isostatic Pressing (HIP).

(a)

(b)

(c)

PowderDC Pulse Power

Load

Fig. 13 A typical fabrication process for FGMs by Spark Plasma Sintering

Examples of SPS processapplications
Functionally Graded Materials
Functionally Graded Materials(FGMs), often referred to as having‘dream’ properties, are advanced
materials characterised by agradual variation in compositionand structure, resulting in changes
to the properties of the component.
The original concept of FGMs was
proposed in 1984 by material scientists in Japan during an aerospaceresearch project.

(d)

Examples of bulk FGM compactsa) ZrO2/stainless steel,b) ZrO2/Ni, c) Cu/stainless steel,d) Al/Polyimide and e) Al2O3/Ti

Examples of bulk FGM
compacts, produced by Spark
Plasma Sintering, are demonstrated in Fig. 12. Seen from theleft, (a) ZrO2(3Y)/stainless steel
compact with six interlayers, (b)ZrO2(3Y)/nickel compact with seveninterlayers, (c) copper/stainlesssteel compact with five interlayers,(d) aluminium/polyimide compact
with three interlayers and, on theright, (e) Al2O3/titanium compact
with three interlayers. The SPS
process resulted in full-density
sintered compacts, with no microcracks detected.

(e)Enlarged cross-sectionof Al/Polyimide FGM

ZrO2(3Y)/410L stainless steel
6 layers (left) and 21 layers

Fig. 12 Typical examples of bulk FGMs

© 2019 Inovar Communications Ltd

Summer 2019

Powder Metallurgy Review

95

| contents page | news | events | advertisers’ index | email |Utilising a temperature gradientsintering technique of SPS, theprocess has successfully createda wide range of bulk FGMs withmultiple layers, including various
systems of ZrO2/stainless steel, ZrO2/
TiAl, ZrO2/Ni, Al2O3/stainless steel,Al2O3/Ti, Al2O3/Ti-6Al-4V, WC/stainless steel, WC/Co, WC/Ni, Cu/stainless steel, SiO2glass/stainless steel,
Al/polyimide resin, Cu/phenol resin
and Cu/polyimide resin materials,
etc. [19-22].
Fig. 13 shows a schematic illustration of an SPS temperature gradientdie assembly and an example ofmulti-layered ZrO2(3Y)/stainless steel
FGMs compact, which contains a 3
mol.% yttrium partially stabilised
zirconia (PSZ) powder, a 410L stainless steel powder and mixed powdersof the two as intermediate layers witha different volume fraction. The FGM
powders were stacked in a graphite
temperature-gradient die of 20 mm
internal diameter. The stainless steel
powder has an average particle sizeof 9 μm while the PSZ powder is of
granulated particles with an average
particle size of 50 μm (its crystalline
size is 350 Å). The sintering pressures used were 20–40 MPa, SPS
temperatures of 1243–1293 K, witha temperature rise rate of 50 K/min
measured near the stainless steel
layer [20, 21].

Horn-tip tool for an ultrasonichomogeniser
Ultrasonic homogenisers act
through the rapid vibration of atitanium probe, or horn, transmitting
ultrasonic energy to the sample. The
vibration causes homogenisation
directly through the ultrasonic forces
as well as through cavitation, where
the rapid formation and collapse of
bubbles occurs as a result of thevacuum formed when the probe
retracts. Conventional titanium
horn-tips, although chemicallystable and mechanically easy to
produce to the desired shape, resultin low wear resistance, can lead tocontamination and have a short life
span. Alternative options, such asbrazed ZrO2 plates on a Ti body, canresult in weakness at the brazed
layer. Monolithic ceramic horn-tips
have good hardness, but are brittle
and can result in a short life span.
The FGM horn-tip shown in
Fig. 14 is based on the optimised
sintering conditions of Al2O3/
Ti-Ti, with a five layered ZrO2/Ti/
Ti-6Al-4V alloy FGM developed forthe structure. The ceramic-metalmaterial achieved a hardnessof HV 1364 and, due to the thehigh hardness at the surface,offered greatly improved corrosion
resistance during the cavitation
process. A sintering temperatureof 1573 K, at a pressure of 30
MPa, resulted in the lowest 17
mg wear amount following a 50 hhomogenising operation test.
The life span of the new horn-tip
has proved to be around eight-to-tentimes greater than conventional
options, without cracking, peelingor breakage. It is expected that
remarkably less contamination will
present a highly reliable production
process, and the available largesized horn-tip encourages higher
output power oscillation with muchbetter productivity.
Sputtering target fabrication
With the SPS process, highly-dense
sintered products can be fabricatedat a much lower temperatures andwith shorter heating up and holding
times, compared with hot pressingand HIPing. Thus, sputtering target
materials are another application
field for SPS that can provide positive
results. Indeed, several companies
have developed a profitable businessusing SPS in this way.
Fig. 15 shows a typical example
of a large-sized metallic sputteringtarget with a diameter of 350 mm
produced by a large-size SPS
system. When producing this part by
SPS, productivity was approximately
seven-to-eight times higher thanconventional sintering of HP and HIP

ZrO2 100%
ZrO2 70% - Ti 30%
ZrO2 50% - Ti 50%
ZrO2 20% - Ti 80%

Oscillator

Ti-6Al-4V 100%

Horn Tip

Oscillator
Converter
Horn Tool / Tip (from Ti alloy to FGMs)

Fig. 14 Ultrasonic homogeniser and ZrO2/Ti alloy system FGM horn tip tool (manufactured by Mitsui Electric Co.,Ltd,
Japan)

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Spark plasma sintering| contents page | news | events | advertisers’ index | email |Comparison of Sintering time
9
8
7
6

time

Spark plasma sintering

5
4
3
2
1
0

SPS Sintering temperature: 1373-1473 K
Relative density: 99-100% Material: Ru

SPS

HP/HIP

Axis Title

Materials example: CrB2, CrB, SiC, SiO2, Ta2O5, ITO, BaTiO3, PbTiO3, TiN,
TiAl, Ti-Al-Si, TiTa, Mg2Si, Ru, RuCo, NiCr, others

Fig. 15 Example of Ø350 mm large-size metallic sputtering target material

Material: Al2O3
R.D: 98-99%
Dimensions: Ø 300 x 10 mmMaterial: Al2O3
R.D: 99-100%
Dimensions: Ø 200 x 10 mmMaterial: pure WC (no additives)
R.D: 99-100%
Dimensions: Ø 100 x 16 mm

Material: SiC (with additives)
R.D: 99-100%
Dimensions: Ø 150 x 12 mm

Fig. 16 Example of large-size ceramics by SPS

processes. Also, due to the obtained
finer grain size of the SPS sputteringtarget materials, superior sputtering
performances can result where, forexample, no splashing phenomenon
occurs in the coating process.
Large-sized oxide (Al2O3, ZrO2,
SiO2), carbide (WC, SiC, B4C), nitride(Si3N4) and boride (TiB2) ceramicmaterials have also been fabricatedhomogenously with finer grain size
and almost full density. The samples
shown in Fig. 16 were investigated by
SEM and it was observed that almost
no residual micro pores and no
cracks were present in the sinteredcompacts.
Pure WC (tungsten carbide)
aspheric glass lens mould
The growing demand for in-vehicle
camera systems for monitoringroad conditions, as well as generalsurveillance and security cameras,
has greatly increased the need for© 2019 Inovar Communications Ltd

the cost-effective production of highperformance aspherical glass lenses
used in the digital cameras. To meetthis need, SPS has been utilised in
the production of moulds used toform the aspherical glass lenses. The
mould consists of three pieces; anupper punch, lower punch and sleeve
die part. Fig. 17 shows examples ofsuch moulds used commercially inthe optics industry, which are madefrom a binderless pure-tungsten
carbide (WC single phase, HV 2600)
material.
The SPS moulds were homogenously consolidated in nanostructured fine grain size material.
By using an ultra-fine grinding
machine, a superior mirror surface
finish, with a roughness of Ra 2-6
nm, can be obtained. The advantages of SPS pure WC are that noFig. 17 Examples of pure WC Aspheric glass lens mould materials

Summer 2019

Powder Metallurgy Review

97Spark plasma sintering

Material: Al2O3 Length: 60mm
Outer dia. (Tapered):30/15mm
Inner dia. (Straight):6mm| contents page | news | events | advertisers’ index | email |Generalcommercial
products

SPS sinterednozzleAdvantage of SPS
sintered nozzle

Vickers hardness (HV)

900 - 1100

2100 - 2200

High hardness

Relative density (%)

91

100

High density

SurfaceRough

Mirroredsurface

Mirror finishedsurface by near-net
shapeLifetime

One day

Ten days

Ten times longer
lifetime

Fig. 18 Comparison of SPSed nozzle and other commercial productadditives are used in the solid-phasesintering and a finer grain size aswell as higher oxidation resistance isachieved, compared to conventionallyproduced binderless WC materials.
By running a 10 h oxidisation test in
an atmospheric furnace at 973 K,
a 30-60% better oxidisation rate involume (g/cm3) was demonstrated.
Complex near-net shape forming of
Al2O3 blasting nozzle
An example of an Al2O3 ceramic
nozzle, used in sand-blasting apparatus, is shown in Fig. 18. Comparative testing between a conventionally
manufactured nozzle and one madeusing SPS process, was undertaken in real-time blast operating
conditions. The SPSed Al2O3 nozzle
achieved ten times longer life span
than a conventionally sintered one
produced in an atmospheric pressureless sintering furnace.
The SPS nozzle is produced
without post processing and has
Vickers hardness of HV 2100-2200,

compared to a conventional nozzle
with HV 900-1100. Produced to nearnet shape accuracy, a Ra 0.64 μm
surface roughness was obtained.
Emerging super-plasticity and highspecific strength of aluminium-Si
alloy materials
The SPS process can be used toachieve nanostructured densehigh-silicon/aluminium alloys. The
rapidly solidified Al-Si powder, of
average particle size 120-150 μm,
silicon content 12–17% or higher
and nanocrystalline structure,
was successfully consolidated into
Ø 60–120 mm x 40–60 mm cylindricalcompacts with between 600–800 nm
grain size as shown in the TEM
micrograph in Fig. 19. The sinteredcompacts, with relative densityof almost 100%, were obtained attemperatures of 723–773 K, appliedpressures of 100–150 MPa and heatup and holding time of 20 min. Whenthe Ø 60 mm x 40 mm nanostructure
SPSed bulk body was formed into

Rapidlysolidifiedpowder
powder Powder
Powderconsolidation
Rapidlysolidified
Powderconsolidation
Rapidly solidified
consolidation
bySPS
SPS
preparedby
SPS
prepared
powder prepared by
by
by
water
atomizingbywateratomizingwater
atomisationa three dimensional shape for an
automotive engine piston component, by a high-speed forging pressmachine, it was demonstrated toprovide full forming for lengths of
75 mm within 15–20 seconds per
stroke with the strain rate of 10-2S-1
or higher. The results indicate thephenomenon of ‘super-plasticity’occurred, improving the ductility andelongation of the sintered compact.
The tensile strength was 350 MPa
and it was approximately 1.5 times
stronger than a conventionally forgedcomponent. This Al-Si alloy withnanostructural material is expected
to find wide applications in various
electric appliances, electronics andautomotive components [23].
Porous materials prepared by SPS
The fabrication of both metallic andceramic porous structures is anotherapplication where SPS could offer
advantages over existing sintering
methods. In this example, the puretitanium and ZrO2(3Y) bead struc-

Superplastic
plasticforming
formingSuperplastic
formingSuper
byforging
ForgingpressmachinebyForgingpressmachinepressmachineforautomotive
Automotivecomponent
component
for
Automotive
component
for

TEMTEMmicrographofTEM
micrographof
micrographof
SPSed compact
compact
SPSed
SPSed compact

1μm
1μm

Fig. 19 Appearance of Super-plasticity on automotive component

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Spark plasma sintering| contents page | news | events | advertisers’ index | email |tures seen in Fig. 20 are formed byapplying a low sintering pressurein the range of 0–5MPa, demonstrating that it is possible to obtainhigh porosity with higher bonding
strength at the neck portion.
Potential commercial applications for this process include
materials for a bio-reactor, filters,
artificial bone joints, vent corematerials for a plastic moulding
die, electric and hybrid-electricvehicle applications, solid oxide
fuel cell (SOFC) batteries, thermoelectric semi-conductors, heatspreaders for thermal conductive
components and others.

Ti beads

ZrO2(3Y)beads

beads
TiTi beads

ZrO
ZrO
2(3Y)beads
2(3Y) beads

neck by
Ti Ti
Neck
bySPS
SPS

Pre-heating stage

Sintering stage

Cooling Cooling/Air introduction s

Neckstage
SPS
Fine-WC/Co hard alloy FGMs for Vacuum
Fig.exhausting
20 Ti
Examplesofby
porousmaterial
Sintering stage Cooling Cooling/Air introduction stage
Pre-heatingstage
die & mould and wear-resistantmaterials industries
Inletexhausting stage
VacuumOutletAs a typical high-wear resistantPre-heating
Sintering
Coolingcooling/air
introduction
material, WC/Co or WC/Ni systemInlet
Vacuum exhausting
Outletcemented carbides are now widelyused in various press-stamping
Inlet
Outletdies and cutting tools for industrial applications. Although thefabrication of WC/Co hard alloys
usually takes many hours, with thedevelopment of new automated
SPS systems, it is proving possible
2 pieces and 20 min/cycle
to sinter such materials in a
10 times continuous operation
significantly shorter period, taking
advantage of the characteristics
inherent in SPS rapid sintering
technology.
Table 3 highlights the typicalmechanical properties of SPS fineWC system hard alloy products.
Fig. 21 shows the production
machine’s system configuration
and an outside view of the fullyFig. 21 System configuration and outside view of tunnel-type SPS and largeautomated five-stage chambersize 100×70 mm WC/Co cemented carbide hard-alloy compacts fabricated in
type continuous SPS system. Using
10 times continuous operation
this full tunnel automated systemand optimised conditions, large
square-shaped WC/Co cemented
Transverse
Product
Co
WC pdr.
FractureDensity Hardness rupture
carbide hard alloys, with dimencode
content grain size
toughness
3
g/cm
mHV
strengthsions of 70 mm × 100 mm × 5-20
name
wt.%
μm
K1C
MPa
mm, were homogeneously fabriTC-05
<2
<0.5
15.2
2350
2300
6.2
cated in a shorter sintering time
TC-10
<4
<0.5
15.0
2150
2640
6.5
and with a finer grain size thanconventional sintering methods.
TC-20
<6
<0.5
14.8
2050
2940
7.3
The fine-WC/Co hard alloys
M78
0
<0.2
15.4
2600
1500
5.1
obtained by SPS show higher hardWC100
0
<0.08
15.6
2700
1470
5.6
ness, transverse rupture strength
NC100
0
<0.5
15.4
2570
1180
5.4
and fracture toughness, than thoseobtained by conventional methods.
Table 3 Typical mechanical properties of Fine WC/Co hard alloys by SPS© 2019 Inovar Communications Ltd

Summer 2019

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99

2500

| contents page | news | events | advertisers’ index | email |WC 3.5 μm/Co 14%

1500

WC 5 μm/Co 20%

7 5

2000

WC0.5μm-6%Co

8

WC 0.5 μm/Co 6%

WC5.0μm-20%Co

20

Micro vichkers hardness (mVH)

Spark plasma sintering

WC9.0μm-20%Co

1000
500
0

WC 9 μm/Co 20%
0

5
10
15
20
Distance from surface (mm)500-580 GPa was attained under
SPS temperature of 1473–1523 K.
To achieve series production, in thisexample continuous SPS operation
through multiple work shifts per
day resulted in the simultaneous
fabrication of 15–20 plates perbatch.

WC3.5μm-14%Co

25

Fig. 22 Large-size WC/Co FGM fabricated by SPS (100 mm × 100 mm × 40 mm) and profiles of micro-hardness on Co
content graded cemented carbide by SPS

WC/Co and WC/Co/Ni FGMs forindustrial applications
In the first example, a WC/Co FGM
block, compositionally graded bycobalt content and measuring 100
× 100 × 40 mm, was produced using
SPS within an hour (Fig. 22) [32,33]. The FGM was then machinedby numerically-controlled wire-

cut electrical discharge machine
to remove smaller pieces of thematerial. As shown in Fig. 23, thesmaller piece of WC/Co FGM wasground to form the specified profiles.
The fine WC/Co FGM hard alloy
demonstrated high hardness in the
top layer and higher strength andfracture toughness in the bottom

Fig. 23 Example of press stamping die and punch made of WC/Co FGMs forelectronic component

Fig. 24 Weldable WC/Ni FGMs tile and the FGMs screw product for the
extruding machine

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die set, the FGM sample achieved
an approximately three and a half to
ten times longer life time comparedwith conventional commercial WC/Co
cemented carbides.
In a further project, a weldable WC/Ni FGMs screw, used in
an extruding machine, was also
produced using the SPS process (Fig.
24). The working life proved to be overthree times longer than that of theconventional screw, resulting in morethan 3000 h service compared toaround a typical 800 h in the conventional screw. This FGM screw has
proved a successful example of SPS
manufacturing and has now beenin operation for a number of years
at Japan’s Hokkaido Electric Power
company [24].

Diamond dicing blades for cutting
tool industry
The manufacture of diamond dicing
blades, for use in the cutting tool
and wear-resistant materials
industry, is a further example of
how the SPS process can offer
distinct advantages. As shown in Fig.
25, metal bonded dicing blades of
100/150 mm diameter and 0.35/0.4
mm thickness can be produced witha flatness level within ± 20 μm andminimal residual stresses. Obtaining
such flatness by SPS eliminatesa grinding process. The sintered
WC/Co plate has relative density
99-100% and a Young’s modulus© 2019 Inovar Communications Ltd

Spark plasma sintering| contents page | news | events | advertisers’ index | email |Other Industrial Applications
Although not discussed in thisarticle, research into the use of SPS
in other categories of materials
includes MMC/FRC/FRM composites, thermoelectric semiconductorsof SiGe, Bi2Te3, FeSi2, CoSb3, MnSi2,
Mg2Si systems for clean energy
generation, Nd-Fe-B, Sm2Co17 andferrite for magnetic materials,
MgB2 superconducting materials[25], BaTiO3 [26], PbTiO3 dielectricmaterials, shape memory alloys,
solid cell materials, glassy metals,
optically functional materials andnanocrystalline materials [27]. All
could be promising candidates forindustrial SPS applications [28].
Applications for SPS 3D forming
methods and titanium/hydroxyapatite (HAP) for biomedical applications could also move from the
R&D/prototype level into practicaluse in the near future [29,30].

Summary & outlook
In this article, the history andfundamentals of SPS, as well as thewider availability of SPS systems
and related industrial applications have been discussed. Typicaladvantages of SPS processing areindicated in the synthesis of FGMs,
nanocrystalline materials and wearresistant hard materials. Due to theversatility of SPS, the remarkable
and rapid growth in the number ofpresented papers and patents inthe last decade should be noted,
resulting from a new, worldwide
adoption of SPS technology in boththe scientific community and theindustrial sector.
SPS features an electricalenergy concentration at areas
where current flows easily. In© 2019 Inovar Communications Ltd

Sintering Powder
Material(or Green body)Multi
Layers:n=5 ~ 20
possible

GraphiteSpacerOuter DiameterØ 100/150 mm

Inner DiameterØ 40/60 mm

Thickness

0.35/0.40 mm

SPS sintering temp.

1473 ~ 1523 K

Sintering Pressure

40 ~ 50 MPa

Relative Density

99 ~ 100%

Young Modules

500 ~ 580 GPa

Flatness<± 20 μm

Fig. 25 WC/Co sintered very thin plate with diamond of Dicing Bladeterms of the high energy density ofdynamic sintering, further study ofthese characteristics will lead tothe successful advancement andexpansion of SPS applications forcommercial production. The SPS
process has the potential to becomea major manufacturing tool in theautomotive, electronics, mould& die, tooling, clean energy andaerospace industries, to name justa few, with opportunities in both
high-value added, small scale andmass-production markets.

Author
Masao TOKITA (Ph.D)
Head of SPS R&D Center
Senior Managing Director
NJS Co.,Ltd.
301 Office Shinyokohama,2-14-8, Shinyokohama,Kouhoku-ku, Yokohama,
Kanagawa, 222-0033,
Japan
website: www.njs-japan.co.jp
email: tokita@njs-japan.co.jp

References[1] M. Tokita, “Development ofAdvanced Spark Plasma Sintering(SPS) Systems and Its Industrial
Applications”, Ceramic Transaction
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M. Ohyanagi, “The effect of electricfield and pressure on the synthesis
and consolidation of materials: A
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method”, J. Material Science, 41(2006)763-777[3] S. Grasso, Y. Sakka and G. Maizza,“Electric current activated/assisted
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Patent No. 1, 896.854 (1933)[5] K. Inoue, “Electric Discharge
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3,241,956(1966) ( Ser. No. 247,387
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Spark plasma sintering| contents page | news | events | advertisers’ index | email |Connecting Global Competence[6] K. Inoue, “Apparatus for electrically sintering discrete bodies”,
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Under this motto ceramitec launches a brandnew format in 2019: ceramitec conference.
Ceramitec conference covers the need to[27] U.Anselmi-Tamburini, J.E. Garay,
Z.A. Munir, “Fast low-temperature
consolidation of bulk nanometricceramic materials”, Scripta Materialia, 54(2006)823-828

present current and future ceramic solutions
to the following applying industries:∙ Automotive[28] Y. Makino, K. Mizuuchi, M. Tokita,
Y. Agari, M. Kawahara and K. Inoue,”
Synthesis of new structural and functional materials by SPS processing”,
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Plasma Sintering (SPS) method forthe fabrication on an industrial scaleof Functionally Graded Materials”,
Advances in Science and Technology
Vol. 63 (2010)322-331

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[30] M. Tokita, “Development of ZrO2/
Ti alloy FGMs Horn tip tool for Ultrasonic Homogenizer by Spark Plasma
Sintering (SPS) method”, proceedingsof ISFGMs2018 15th International
symposium on Functionally Graded
Materials, Kitakyushu, Japan (Aug.
2018) O-17/1-6

Sintering”, Proc. NEDO Int. Sympo.
on Functionally Graded Materials,
Tokyo, Japan, (1999) 67-74

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