Nanotechnologies / Materials
Automotive, Medical & healthcare

Achieving near-isotropic high tensile performance in additively
manufactured Ti through interstitial solute influences
Joining and Welding Research InstituteSpecially Appointed Assistant Professor Ammarueda Issariyapat

https://researchmap.jp/ammarueda?lang=en

Professor Junko Umeda							https://researchmap.jp/umeda?lang=en▍

100 μm

An economical titanium additive manufacturing material, enhanced with nitrogen, has achieved impressive strength, ductility,and isotropic, making it a compelling alternative to costly Ti-6Al-

N: 0.69%, O: 0.10%NSEM

N-rich shell I
N-rich shell II

Intensity
Max.

10 μm

N-depleted core III
10 μm

Min.

Figure 1. The modification of Ti powder via gas-solid interactions process at an elevated temperature presents aFigure 1. The modification of Ti powder via gas-solid interactions process at an
method that affords two noteworthy advantages. Firstly, it maintains the exceptional flowability of the feedstock.
elevatedtemperaturepresents
methodofthat
affords
noteworthy
Secondly,
it ensures
the potential forthe even adistribution
N following
thetwofabrication
process.advantag-es. Firstly, it maintains the exceptional flowability of the feedstock. Secondly, itensures the potential for the even distribution of N following the fabrication process.

TS = 709.33 MPa (+78%)
EL = 26.72% (+48%)

TS = 398.44 MPa
EL = 18.03%

N = 0.01 wt%

TS = 975.99 MPa (+145%)
EL = 21.71% (+20%)

0001
0001
0001
0001
N = 0.02 wt%
N = 0.04 wt%
N = 0.09 wt%
N = 0.31 wt%

0001
Grain
structure
evolution bysoluteelement

Primary β grain boundaries
NN

Liquid Ti

Laser
N atomh = 60 μm

Significance of the research and Future perspective

N2Constant temperature

Scan direction
Z(BD)
YX

L

Wβ2000Wβ1500 a-2 b-2 β(a-3)(b-3)α+β1000
882500

(b-2)

(a-2)

2500

α

Large martensite

a-3 b-3

N (wt.%)

1

BD

The widely used Ti-6Al-4V alloy, prominent in aircraft and biomaterial applications, is primarily reliant on rare metals. However,concerns regarding the supply of rare metals and the potential for
price volatility due to international circumstances have prompted
the need for novel titanium alloy designs that are independent ofrare elements. In response, novel titanium alloy designs based onelemental strategies have emerged, advocating the use of abundant and cost-effective elements like oxygen, nitrogen, carbon,and iron. Notably, these elements, typically deemed impurities
affecting titanium’s ductility, have predefined limits under JIS/ASTM
standards. In the context of metal AM, a unique challenge arises
in which crystal grains tend to elongate during rapid solidification,
causing pronounced mechanical anisotropy. To address thesechallenges, our research pioneers a cost-effective, rare metal-freetitanium alloy emphasizing mechanical functionality. By using structured Ti-(N) powder, we have successfully developed a novel titanium material, boasting remarkable strength and ductility, utilizing
the solid solution characteristics of nitrogen components. Notably,in the ultra-fast solidification process of AM, nitrogen not only impedes the growth of α-Ti grains but also fosters the nucleation of ametastable martensitic phase with random crystal orientation. This
results in the formation of fine crystal grains and reduces mechanical anisotropy. As a result, we have achieved a rare metal-freetitanium alloy, while outperforming the conventional Ti-6Al-4V alloy
through the sole addition of nitrogen. This achievement opens newhorizons for advanced applications across various industries.

N2

HT at 800 °C
smooth surface

Cooling stage
N2

Temperature (°C)

▍ Background & Results

FurnaceTi powder

Overlap zone
~30 μmIn our pursuit of innovative AM materials, we have developed arare metal-free titanium alloy recognized for its remarkable specificstrength, high ductility, and biocompatibility, while emphasizing
cost-efficiency. Key challenges like the costly Ti powder containing
rare metals such as vanadium and mechanical property dependence on layering direction drove us to develop a Ti-(N) powder
with a Core-Shell structure, incorporating cost-effective nitrogen forsolid solution strengthening. This material, used in titanium additive
manufacturing, attains outstanding strength and ductility throughcrystal structure refinement and orientation control via nitrogensolid solution atoms, ensuring isotropic mechanical properties.
These findings unveil exciting possibilities for diverse industry applications, establishing this alloy as a rare metal-free, mechanicallysuperior alternative to conventional Ti-6Al-4V alloys.

4V alloy. This development offers economic advantages and shows
promise across diverse industries. Especially in resource-limited
Japan, this advancement positions us as a leader in the titaniummaterials industry. This strategic transition reduces dependence onrare metals, mitigating geopolitical risks, and fosters technologies
for regenerating and recycling raw materials, aligning with the circular economy. We are committed to actively promoting initiatives
related to this noble undertaking.

Melted zone
~ 30-60 μm

Nanotechnologies / Materials

Abstract

Refined martensite

Wβ: primary β grain width

Figure 2. The transformation of grain structure resulting from an increase in N concentration, elucidating
Figure2. Thetransformationof grain
structure
resultingfrom an increase
throughthe utilizationof 3D
IPF mappings for α-Ti,complementedby schematic
representations
that depict themicrostructuralchanges occurringelucidating
during the rapidthroughsolidification
process.
in N concentration,
theutilization of 3D IPF mappings

for α-Ti, complemented by schematic representations that depict the microstructural changes occurring during the rapid solidification process.

P a t e n t
Issariyapat, Ammarueda; Umeda, Junko; Kondoh, Katsuyoshi et al. Development of core–shell-structured Ti-(N) powders for additive manufacturing andcomparison of tensile properties of the additively manufactured and spark-plasma-sintered Ti-N alloys. Advanced Powder Technology, 2021, 32, 23792389. doi: 10.1016/j.apt.2021.05.023
Kondoh, Katsuyoshi; Issariyapat, Ammarueda; Umeda, Junko et al. Selective laser-melted titanium materials with nitrogen solid solutions for balanced
T r e a t i s e strength and ductility. Materials Science and Engineering: A, 2020, 790, 139641. doi: 10.1016/j.msea.2020.139641
Issariyapat, Ammarueda; Umeda, Junko; Kondoh, Katsuyoshi et al. Refined grain formation behavior and strengthening mechanism of α-titanium withnitrogen fabricated by selective laser melting. Additive Manufacturing, 2020, 36, 101537. doi: 10.1016/j.addma.2020.101537
Issariyapat, Ammarueda; Umeda, Junko; Kondoh, Katsuyoshi et al. Solute-induced near-isotropic performance of laser powder bed fusion manufactured
pure titanium. Additive Manufacturing, 2022, 56, 102907. doi: 10.1016/j.addma.2022.102907
URL http://www.jwri.osaka-u.ac.jp/~dpt6/index_en.html
K e y w o r d titanium (Ti), nitrogen (N), tensile properties, additive manufacturing (AM)