Yaw Wang CHAI

> Highly caliber MATERIALS SCIENTIST with a good metallurgical research background.
> Experienced in phase transformations, interfacial defects, microstructure, and crystallographic characterization in a
range of structural and functional materials;
- shape memory alloys: Ti-Nb & CuZnAl,
- thermoelectric materials: half-Heusler, -FeSi2, Mg2(Si, Sn)
- heat resistant materials: High-Cr ferritic stainless steels, Co3AlC and Ni3Al, Ti alloys
> Skilled in a wide range of microstructure and properties characterization techniques: SEM, EPMA, TEM, HRTEM, STEM-
EDS, STEM-HAADF, in-situ heating TEM, twin-jets electropolishing, focus ion beam, ion-milling, XRD, DTA, DSC, laser flash,
ZEM-3.
> Good communication and presentation skills, team player, practical approach to problem-solving, self-motivated,
positive thinker, inquisitive, and working independently.

EDUCATION

The University of Liverpool, United Kingdom

RESEARCH INTERESTS

Phase transformations in solid materials, interfacial structure analyses & crystallography, thermoelectric materials, shape memory alloys

Scopus Publications

Compositional Gradient Layered Microstructure Control for Reducing Lattice Thermal Conductivity of Mg2(Si,Sn) Thermoelectric Alloys
Feifan Zhang, Yaw Wang Chai, Yixun Wang, Yonghoon Lee, Yoshisato Kimura
Materials Transactions, 2026
Phase Stability and Thermal Expansion Properties of Additive Manufactured Super Invar Alloy
Senlin Cai, Ryota Nagashima, Yaw Wang Chai, Naoki Sakaguchi, Nobuo Nakada
Tetsu to Hagane Journal of the Iron and Steel Institute of Japan, 2025
Phase Stability and Thermal Expansion Properties of Additive Manufactured Super-invar Alloy
Senlin Cai, Ryota Nagashima, Yaw Wang Chai, Naoki Sakaguchi, Nobuo Nakada
ISIJ International, 2025
Interdiffusion of Solute Elements in the α-Fe Phase of the Fe–Cr–Mo and Fe–Cr–Si Ternary Systems
Dosung Lee, Mariko Tsuyuguchi, Manabu Watanabe, Yaw Wang Chai, Takako Yamashita, et al.
ISIJ International, 2024
Intermetallic phase precipitation and oxidation behavior of Fe–20Cr–0.5Nb–2Mo (at%) high-Cr ferritic alloy at high temperatures
Shintaro Kondo, Yaw Wang Chai, Kentaro Kanai, Lee Dosung, Manabu Watanabe, et al.
Acta Materialia, 2023
Effect of Mo addition on laves phase precipitation behavior in Fe-20%Cr-x%Nb alloys
Shin Ishikawa, Takako Yamashita, Tomohito Kiryu, Yaw Wang Chai, Yoshisato Kimura
Materials Characterization, 2022
Effect of Half-Heusler Interfacial Structure on Thermal Transport Properties of (Ti, Zr)NiSn Alloys
Mizuki Sato, Yaw Wang Chai, Yoshisato Kimura
ACS Applied Materials and Interfaces, 2021
The microstructure of the half-Heusler phase separation in half-Heusler (HH) MNiSn(M = Ti, Zr) intermetallic compounds has been investigated systematically in this study. Scanning electron microscopy observations from a range of (Tix, Zr1-x)NiSn have revealed the HH single phase at high temperature formed into many HH domains of various HH compositions with different Ti/Zr concentration ratios when x > 0.1. The formation of Ti-rich and Zr-rich HH domains with rather large size (up to several hundred μm in diameter) is thought to originate from a combination of the liquid solidification process and followed by an HH phase decomposition process within a miscibility gap between the TiNiSn and ZrNiSn HH phases. We have noticed that in addition to the mass and size difference based phonon scattering, sharp interfaces between the Ti-rich and Zr-rich HH domains containing high density of misfit dislocations could provide additional phonon scattering centers and reduced thermal conductivity of the alloys. Moreover, the cyclic heat treatment process at temperatures near the HH phase-decomposition's critical temperature could modify the HH domains' microstructure to become more diffuse, coherent with a more comprehensive length scale, and globular shape. These diffuse and coherent Ti-rich HH1/Zr-rich HH2 interfaces can provide an additional enhancement of phonon scattering and thereby result in a more considerable reduction of thermal conductivity than those of relatively less diffuse ones. We anticipate a similar approach of using cyclic heat treatment to modify the microstructure and consequently lead to further enhancement of phonon scattering can also apply to many other thermoelectric alloy systems possessing a miscibility gap.
Disconnections and Laves (C14) precipitation in high-Cr ferritic stainless steels
Yaw Wang Chai, Ko Kato, Chieri Yabu, Shin Ishikawa, Yoshisato Kimura
Acta Materialia, 2020
Even though it is widely accepted that the Laves phase is a promising strengthener for chromium-containing stainless steels, there is little information available on its microstructural evolution and growth. Therefore, in this study, we analysed the behaviour of Laves (C14) precipitates in high-Cr ferritic stainless steel, Fe-20Cr-2Mo-0.5Nb (at%), annealed at 1073 K for different time periods. A high density of (Fe,Cr)2(Mo,Nb) precipitates was formed in the α matrix during annealing. Morphological evolution in the Laves phase followed the sequence of spheroidal → faceted ellipsoidal → faceted needle-like → faceted plate-like. The Laves phase is related to the α matrix by two sets of orientation relationships, viz. OR-1: [ 1 ¯ 1 ¯ 2 ] α / [ 1 2 ¯ 10 ] L , [ 111 ] α / [ 0 1 ¯ 10 ] L , and ( 1 ¯ 10 ) α / ( 000 1 ¯ ) L and OR-2: [ 1 1 ¯ 0 ] α / [ 0001 ] L , [ 113 ] α / [ 1 ¯ 1 ¯ 20 ] L , and ( 3 ¯ 3 ¯ 2 ) α / ( 1 1 ¯ 00 ) L . The habit plane of the Laves phase was found to deviate slightly from the ( 3 ¯ 3 ¯ 2 ) α / ( 1 1 ¯ 00 ) L plane. Interfacial defects, namely disconnections (bD, h) and super disconnections (mbD, mh), observed experimentally along the habit plane, were consistent with theoretical results based on OR-2 as the reference coordinate frame. The Burgers vector bD exhibited an edge component b y D (0.1539 nm) parallel to Y / [ 113 ] α / [ 1 ¯ 1 ¯ 20 ] L and a small normal component b z D (0.0747 nm) perpendicular to the terraces; meanwhile, the overlap step height h = d ( 1 1 ¯ 00 ) L . The morphological evolution of Laves precipitates was described based on the lateral motion of disconnections and super disconnections on { 3 ¯ 3 ¯ 2 } α / { 1 1 ¯ 00 } L terraces in the 〈 113 〉 α / 〈 1 ¯ 1 ¯ 20 〉 direction. Arrays of the disconnections (bD, h) were found to be capable of accommodating the misfit strain on { 3 ¯ 3 ¯ 2 } α / { 1 1 ¯ 00 } L terraces.
Reduced Thermal Conductivity of Mg2(Si, Sn) Solid Solutions by a Gradient Composition Layered Microstructure
Zhifang Zhou, Yaw Wang Chai, Yu Ikuta, Yonghoon Lee, Yuanhua Lin, et al.
ACS Applied Materials and Interfaces, 2020
Solid solutioning of Mg2(Si, Sn) has been a promising approach in reducing thermal conductivity and leads to improvement of thermoelectric performance. In addition to the Mg2(Si, Sn) solid solutions, we have noticed layered structure with gradient composition, which is formed by non-equilibrium solidification and peritectic reaction process, can provide further reduction of thermal conductivity of the Mg2(Si, Sn) solid solutions. All the layers of the layered structure have the same face centered cubic (FCC)-based structure but varying Sn/Si concentration ratios in each layer. The interfaces between the layers are semi-coherent reticulating with different numbers of misfit dislocations. Such interfacial structure brings large numbers of phonon scattering sources, resulting in the further reduction of thermal conductivity in the Mg2(Si, Sn) solid solutions. Consequently, the undoped Mg2Si0.75Sn0.25 containing higher density of the layered structure has relatively lower thermal conductivity, 1.9 W m -1 K -1 at 523 K than Mg2Si0.25Sn0.75 with much lower density of the layered structure, 2.3 W m -1 K -1 at 523 K.
Nanoscale hierarchical structure of twins in nanograins embedded with twins and the strengthening effect
Haochun Tang, Tso-Fu Mark Chang, Yaw-Wang Chai, Chun-Yi Chen, Takashi Nagoshi, et al.
Metals, 2019
Hierarchical structures of 20 nm grains embedded with twins are realized in electrodeposited Au–Cu alloys. The electrodeposition method allows refinement of the average grain size to 20 nm order, and the alloying stabilizes the nanoscale grain structure. Au–Cu alloys are face-centered cubic (FCC) metals with low stacking fault energy that favors formation of growth twins. Due to the hierarchical structure, the Hall–Petch relationship is still observed when the crystalline size (average twin space) is refined to sub 10 nm region. The yield strength reaches 1.50 GPa in an electrodeposited Au–Cu alloy composed of 16.6 ± 1.1 nm grains and the average twin spacing at 4.7 nm.
Stabilizing austenite via a core-shell structure in the medium Mn steels
Xinhao Wan, Geng Liu, Ran Ding, Nobuo Nakada, Yaw-Wang Chai, et al.
Scripta Materialia, 2019
Effects of Si on Phase Stability and Precipitation Behavior of C14 Laves Phase (Fe,Cr)2(Nb,Mo) in High Cr αfe-base Alloys
Yoshisato Kimura, Ko Kato, Yaw Wang Chai
MRS Advances, 2019
Thermoelectric properties of nearly single-phase ¢-FeSi2 alloys fabricated by gas-atomized powder sintering
Yoshisato Kimura, Masashi Yamada, Yaw Wang Chai
Materials Transactions, 2019
Evaluation of Microstructure Formation and Phase Equilibria for Thermoelectric β-FeSi2 Composite Alloys
Yoshisato Kimura, Hiroaki Otani, Ayaka Mori, Yaw-Wang Chai
MRS Advances, 2017
The effect of an isoelectronic Ti-Zr substitution on Heusler nanoprecipitation and the thermoelectric properties of a (Ti0.2,Zr0.8)Ni1.1Sn half-Heusler alloy
Yaw Wang Chai, Toshinori Oniki, Takahiro Kenjo, Yoshisato Kimura
Journal of Alloys and Compounds, 2016
Microstructure and thermoelectric properties of a ZrNi1.1Sn half-Heusler alloy
Yaw Wang Chai, Toshinori Oniki, Yoshisato Kimura
Acta Materialia, 2015
Ordered Structures and Thermoelectric Properties of MNiSn (M = Ti, Zr, Hf)-Based Half-Heusler Compounds Affected by Close Relationship with Heusler Compounds
Yoshisato Kimura, Yaw-Wang Chai
JOM, 2015
Solid solution behavior and thermoelectric properties of half-heusler (Zrx, Nb1-x)(Niy, Co1-y)Sn alloy
Kentaro Yoshioka, Yaw Wang Chai, Yoshisato Kimura
Nippon Kinzoku Gakkaishi Journal of the Japan Institute of Metals, 2015
Fabrication of β-FeSi2-based thermoelectric composite alloys by oxidation and reduction reactions during sintering of eutectoid si and iron oxide powder
Yoshisato Kimura, Koichiro Takeno, Ayaka Mori, Yaw-Wang Chai
Nippon Kinzoku Gakkaishi Journal of the Japan Institute of Metals, 2015
Thermoelectric properties control of half-Heusler compounds by lattice defects and interfaces introduced based on the close relationship with Heusler compounds
Yoshisato Kimura, Yaw-Wang Chai, Toshinori Oniki, Takahiko Itagaki, Shinya Otani
Materials Research Society Symposium Proceedings, 2015
Intrinsic point defects in thermoelectric half-Heusler alloys
Yaw Wang Chai, Kentaro Yoshioka, Yoshisato Kimura
Scripta Materialia, 2014
Microstructure evolution of nanoprecipitates in half-Heusler TiNiSn alloys
Yaw Wang Chai, Yoshisato Kimura
Acta Materialia, 2013
Effect of interstitial carbon atoms on phase stability and mechanical properties of E21 (L12) Ni3AlC1-x single crystals
Yoshisato Kimura, Masato Kawakita, Hiroyasu Yuyama, Yaw-Wang Chai
Materials Research Society Symposium Proceedings, 2013
Nanosized precipitates in half-Heusler TiNiSn alloy
Yaw Wang Chai, Yoshisato Kimura
Applied Physics Letters, 2012
Effect of vacancy-site occupation in half-Heusler compound ZrNiSn on phase stability and thermoelectric properties
Yoshisato Kimura, Toshiyasu Tanoguchi, Yasuhiro Sakai, Yaw-Wang Chai, Yoshinao Mishima
Materials Research Society Symposium Proceedings, 2011

RECENT SCHOLAR PUBLICATIONS

Compositional Gradient Layered Microstructure Control for Reducing Lattice Thermal Conductivity of Mg2 (Si, Sn) Thermoelectric Alloys
F Zhang, YW Chai, Y Wang, Y Lee, Y Kimura
MATERIALS TRANSACTIONS 67 (5), 842-853 , 2026
2026
Influence of elastic energy on the microstructure of nano TiNi2Sn precipitates within a Half-Heusler TiNiSn matrix
M Shmulevitsh, Y Gelbstein, YW Chai, RZ Shneck
Acta Materialia 296, 121243 , 2025
2025
Phase stability and thermal expansion properties of additive manufactured super-invar alloy
S Cai, R Nagashima, YW Chai, N Sakaguchi, N Nakada
ISIJ International 65 (8), 1201-1208 , 2025
2025
Citations: 3
Interdiffusion of solute elements in the α-Fe phase of the Fe–Cr–Mo and Fe–Cr–Si ternary systems
D Lee, M Tsuyuguchi, M Watanabe, YW Chai, T Yamashita, S Ishikawa, ...
ISIJ International 64 (5), 826-835 , 2024
2024
Citations: 1
Intermetallic precipitation and oxidation behavior of a Fe–20Cr–0.5 Nb–2Mo (at%) high-Cr ferritic alloy
YAWW CHAI, YW Chai, S Kondo, K Kanai, D Lee
(No Title) , 2024
2024
Intermetallic phase precipitation and oxidation behavior of Fe–20Cr–0.5 Nb–2Mo (at%) high-Cr ferritic alloy at high temperatures
S Kondo, YW Chai, K Kanai, L Dosung, M Watanabe, S Ishikawa, ...
Acta Materialia 246, 118677 , 2023
2023
Citations: 22
Solid-phase reaction and microstructure formation in Fe-Nb and Fe-Mo binary diffusion couples
D Lee, M Tsuyuguchi, M Watanabe, YAWW CHAI, YW Chai
(No Title) , 2023
2023
Effect of doping and heat-treatment process on the full-Heusler microstructure and thermoelectric properties of half-Heusler alloys
YAWW CHAI, YW Chai, Y KIMURA
(No Title) , 2023
2023
Effect of Mo addition on laves phase precipitation behavior in Fe-20% Cr-x% Nb alloys
S Ishikawa, T Yamashita, T Kiryu, YW Chai, Y Kimura
Materials Characterization 190, 112077 , 2022
2022
Citations: 18
Disconnections and Laves (C14) precipitation in a high-Cr Fe-based alloy
YAWW CHAI, YW Chai
(No Title) , 2022
2022
Evaluation of NP type conversion mechanism in thermoelectric Zr (Ni, X) Sn (X= Ir, Co) by first-principles calculation
YA CHEN, YA Chen, M Watanabe, Y Gohda, Y KIMURA, YAWW CHAI, ...
(No Title) , 2022
2022
Precipitation of Intermetallic Phases and Mutual Effects with High Temperature Oxidation in the Fe-Cr-Nb-Mo Ferrite Alloys
Y KIMURA, M WATANABE, YW CHAI
ふぇらむ 27 (7), 457-466 , 2022
2022
Effect of half-heusler interfacial structure on thermal transport properties of (Ti, Zr) NiSn alloys
M Sato, YW Chai, Y Kimura
ACS applied materials & interfaces 13 (21), 25503-25512 , 2021
2021
Citations: 18
Disconnections and Laves (C14) precipitation in high-Cr ferritic stainless steels
YW Chai, K Kato, C Yabu, S Ishikawa, Y Kimura
Acta Materialia 198, 230-241 , 2020
2020
Citations: 54
Reduced Thermal Conductivity of Mg 2 (Si, Sn) Solid Solutions by a Gradient Composition Layered Microstructure
Z Zhou, YW Chai, Y Ikuta, Y Lee, Y Lin, Y Kimura
ACS Applied Materials & Interfaces 12 (17), 19547-19552 , 2020
2020
Citations: 24
Multiscale microstructure engineering and the development of high performance, environmental friendly, low cost and thermally stable half-Heusler thermoelectric materials
YW Chai, Y Kimura
Impact 2020 (1), 65-67 , 2020
2020
Citations: 1
Nanoscale hierarchical structure of twins in nanograins embedded with twins and the strengthening effect
H Tang, TFM Chang, YW Chai, CY Chen, T Nagoshi, D Yamane, H Ito, ...
Metals 9 (9), 987 , 2019
2019
Citations: 13
Stabilizing austenite via a core-shell structure in the medium Mn steels
X Wan, G Liu, R Ding, N Nakada, YW Chai, Z Yang, C Zhang, H Chen
Scripta Materialia 166, 68-72 , 2019
2019
Citations: 73
Thermoelectric properties of nearly single-phase β-FeSi2 alloys fabricated by gas-atomized powder sintering
Y Kimura, M Yamada, YW Chai
MATERIALS TRANSACTIONS 60 (5), 652-661 , 2019
2019
Citations: 9
Effects of Si on phase stability and precipitation behavior of C14 laves phase (Fe, Cr) 2 (Nb, Mo) in high Cr αFe-base alloys
Y Kimura, K Kato, YW Chai
MRS Advances 4 (25-26), 1477-1483 , 2019
2019
Citations: 12

MOST CITED SCHOLAR PUBLICATIONS

Self-accommodation in Ti–Nb shape memory alloys
YW Chai, HY Kim, H Hosoda, S Miyazaki
Acta materialia 57 (14), 4054-4064 , 2009
2009
Citations: 228
Interfacial defects in Ti–Nb shape memory alloys
YW Chai, HY Kim, H Hosoda, S Miyazaki
Acta Materialia 56 (13), 3088-3097 , 2008
2008
Citations: 127
Topological modelling of martensitic transformations
RC Pond, X Ma, YW Chai, JP Hirth
Dislocations in solids 13, 225-261 , 2007
2007
Citations: 84
Nanosized precipitates in half-Heusler TiNiSn alloy
Y Wang Chai, Y Kimura
Applied Physics Letters 100 (3) , 2012
2012
Citations: 80
Microstructure evolution of nanoprecipitates in half-Heusler TiNiSn alloys
YW Chai, Y Kimura
Acta materialia 61 (18), 6684-6697 , 2013
2013
Citations: 78
Stabilizing austenite via a core-shell structure in the medium Mn steels
X Wan, G Liu, R Ding, N Nakada, YW Chai, Z Yang, C Zhang, H Chen
Scripta Materialia 166, 68-72 , 2019
2019
Citations: 73
Microstructure and thermoelectric properties of a ZrNi1. 1Sn half-Heusler alloy
YW Chai, T Oniki, Y Kimura
Acta Materialia 85, 290-300 , 2015
2015
Citations: 64
Ordered structures and thermoelectric properties of MNiSn (M= Ti, Zr, Hf)-based half-Heusler compounds affected by close relationship with Heusler compounds
Y Kimura, YW Chai
Jom 67 (1), 233-245 , 2015
2015
Citations: 60
Disconnections and Laves (C14) precipitation in high-Cr ferritic stainless steels
YW Chai, K Kato, C Yabu, S Ishikawa, Y Kimura
Acta Materialia 198, 230-241 , 2020
2020
Citations: 54
The effect of an isoelectronic Ti–Zr substitution on Heusler nanoprecipitation and the thermoelectric properties of a (Ti0. 2, Zr0. 8) Ni1. 1Sn half-Heusler alloy
YW Chai, T Oniki, T Kenjo, Y Kimura
Journal of Alloys and Compounds 662, 566-577 , 2016
2016
Citations: 42
Intrinsic point defects in thermoelectric half-Heusler alloys
YW Chai, K Yoshioka, Y Kimura
Scripta Materialia 83, 13-16 , 2014
2014
Citations: 32
Reduced Thermal Conductivity of Mg 2 (Si, Sn) Solid Solutions by a Gradient Composition Layered Microstructure
Z Zhou, YW Chai, Y Ikuta, Y Lee, Y Lin, Y Kimura
ACS Applied Materials & Interfaces 12 (17), 19547-19552 , 2020
2020
Citations: 24
Intermetallic phase precipitation and oxidation behavior of Fe–20Cr–0.5 Nb–2Mo (at%) high-Cr ferritic alloy at high temperatures
S Kondo, YW Chai, K Kanai, L Dosung, M Watanabe, S Ishikawa, ...
Acta Materialia 246, 118677 , 2023
2023
Citations: 22
Improvements in honeycomb abradable seals
DJ Potter, YW Chai, GJ Tatlock
Materials at High Temperatures 26 (2), 127-135 , 2009
2009
Citations: 19
Effect of Mo addition on laves phase precipitation behavior in Fe-20% Cr-x% Nb alloys
S Ishikawa, T Yamashita, T Kiryu, YW Chai, Y Kimura
Materials Characterization 190, 112077 , 2022
2022
Citations: 18
Effect of half-heusler interfacial structure on thermal transport properties of (Ti, Zr) NiSn alloys
M Sato, YW Chai, Y Kimura
ACS applied materials & interfaces 13 (21), 25503-25512 , 2021
2021
Citations: 18
Nanoscale hierarchical structure of twins in nanograins embedded with twins and the strengthening effect
H Tang, TFM Chang, YW Chai, CY Chen, T Nagoshi, D Yamane, H Ito, ...
Metals 9 (9), 987 , 2019
2019
Citations: 13
Effects of Si on phase stability and precipitation behavior of C14 laves phase (Fe, Cr) 2 (Nb, Mo) in high Cr αFe-base alloys
Y Kimura, K Kato, YW Chai
MRS Advances 4 (25-26), 1477-1483 , 2019
2019
Citations: 12
Thermoelectric performance of Half-Heusler TiNiSn alloys fabricated by solid-liquid reaction sintering
Y Kimura, C Asami, YW Chai, Y Mishima
Materials Science Forum 654, 2795-2798 , 2010
2010
Citations: 10
Thermoelectric properties of nearly single-phase β-FeSi2 alloys fabricated by gas-atomized powder sintering
Y Kimura, M Yamada, YW Chai
MATERIALS TRANSACTIONS 60 (5), 652-661 , 2019
2019
Citations: 9