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Lobzenko, I.; Mori, Hideki*; Tsuru, Tomohito
Journal of Materials Research and Technology, 40, p.3798 - 3805, 2026/01
no abstracts in English
Abe, Yosuke; Kubo, Atsushi; Ukai, Shigeharu; Tsuru, Tomohito
Journal of Nuclear Materials, 618, p.156221_1 - 156221_11, 2026/01
Understanding the stability of Cr-rich precipitates (CrRPs) is key to developing radiation-resistant ODS Fe-Cr-Al alloys. This study uses first-principles-based equilibrium Monte Carlo simulations to assess how Al content and irradiation-induced vacancies affect CrRP formation and atomic-scale structure. CrRP formation peaks at around 12 at.% Al, showing a non-monotonic trend. Higher Al levels cause segregation at CrRP-matrix interfaces and internal Al incorporation, leading to structural disorder and reduced stability. Vacancies alone have limited impact but co-segregate with Al near interfaces, potentially affecting diffusion and interfacial integrity under irradiation. These findings provide atomic-level insights for designing advanced Fe-Cr-Al alloys and guiding mesoscale modeling.
Chong, Y.*; Tsuru, Tomohito; Gholizadeh, R.*; Minor, A. M.*; Tsuji, Nobuhiro*
Acta Materialia, 301, p.121523_1 - 121523_12, 2025/12
Twinning is essential for achieving large ductility in hexagonal close-packed (HCP) titanium alloys that inherently lack independent slip systems due to an asymmetrical HCP crystal structure. Unfortunately, twinning is in principle suppressed by a trace amount of interstitial oxygen, resulting in a substantially deteriorated ductility in titanium. However, the underlying mechanism remains in dispute so far. Here, we report a systematic multiscale study on the twinning/detwinning behaviors of Ti-O alloys that provides a clear mechanistic view of how interstitial oxygen inhibits twinning. We reveal for the first time that oxygen atoms segregate to both {10
2}
2} compression twin boundaries using atom probe tomography. Combined with theoretical simulations that unravel a strong pinning effect of oxygen atoms on twin boundary due to an oxygen shuffling mechanism, we explain the distinctive migration abilities of twin boundaries in Ti-O alloys at different temperatures. The insights from our experimental and computational work provide a rationale for the design of titanium alloys with increased tolerance to variations in interstitial impurity content, with significant implications for more widespread use of this high strength, light weight material.
martensitic transformation in Ti-12Mo alloyChong, Y.*; Tsuru, Tomohito; Mitsuhara, Masatoshi*; Guo, B.*; Gholizadeh, R.*; Inoue, Koji*; Godfrey, A.*; Tsuji, Nobuhiro*
Communications Materials (Internet), 6, p.50_1 - 50_11, 2025/03
Strain-induced martensitic phase transformation (SIMT) critically affects the mechanical properties of metastable 
titanium alloys. In this study, the effects of grain size and oxygen content on SIMT in a Ti-12wt.%Mo alloy were systematically investigated. It is found that SIMT is promoted by a decrease in grain size and in oxygen content. The mechanistic origins of the anomalous grain size dependency and the acute oxygen content dependency of SIMT are discussed based on multi-scale microstructural characterization and state-of-the-art simulations. Grain refinement does not raise the energy barrier for SIMT but rather provides more nucleation sites for strain-induced martensite, thereby promoting SIMT in fine-grained Ti-12wt.%Mo alloy. In contrast, for the Ti-12wt.%Mo-0.3 wt.%O alloy, oxygen atoms substantially increase the energy barrier for SIMT, due to a change in the local configuration of oxygen atoms during the phase transformation. In addition, atom probe tomography reveals for the first time that oxygen atoms segregate at 
phase boundaries, thereby further restricting the growth of martensite.
Shimizu, Kazuyuki*; Toda, Hiroyuki*; Hirayama, Kyosuke*; Fujihara, Hiro*; Tsuru, Tomohito; Yamaguchi, Masatake; Sasaki, Taisuke*; Uesugi, Masayuki*; Takeuchi, Akihisa*
International Journal of Hydrogen Energy, 109, p.1421 - 1436, 2025/03
Times Cited Count：3 Percentile：83.00(Chemistry, Physical)Our preceding investigation revealed that multiple hydrogen traps at coherent interfaces of MgZn
precipitates initiated spontaneous interface decohesion, causing hydrogen-induced quasicleavage cracking in Al-Zn-Mg alloys. Herein, we performed a quantitative and systematic investigation to discern the mechanisms by which hydrogen trapped at coherent/semi-coherent interfaces of precipitates could influence macroscopic hydrogen embrittlement by modulating the coherent interface of MgZn through aging. To explore this hydrogen embrittlement phenomenon based on hydrogen trapping at the precipitate interface, we determined the hydrogen trapping energy of the semi-coherent MgZn interface via first-principles calculations (0.56 eV/atom). Hydrogen partitioning of all hydrogen trapping sites, including vacancies, grain boundaries, and coherent and semi-coherent MgZn interfaces, revealed that in overaged alloys, over 90% of the hydrogen was sequestered at semi-coherent interfaces. Owing to the inherent characteristics of the MgZn interface, the hydrogen sequestered at the semi-coherent interface decreased the interfacial cohesive energy, causing semispontaneous decohesion of the interface and quasicleavage fracture in the Al-Zn-Mg alloys. These results implied that intergranular fracture was not directly induced by hydrogen trapped at grain boundaries but rather by the decohesion of precipitate interfaces along grain boundaries.
Abe, Yosuke; Tsuru, Tomohito; Fujita, Yohei*; Otomo, Masahide*; Sasaki, Taisuke*; Yamashita, Shinichiro; Okubo, Nariaki; Ukai, Shigeharu
Journal of Nuclear Materials, 606, p.155606_1 - 155606_12, 2025/02
Times Cited Count：2 Percentile：91.88(Materials Science, Multidisciplinary)We investigated the effect of Al addition on the formation of 
phase in Fe-Cr-Al model alloys by thermal aging. The Vickers hardness tests and a machine learning model indicate that the formation of the phase is promoted by low Al additions and suppressed by high Al additions. First-principles calculations, which indicate that Cr-Al-vacancy pairs are more stable than Cr-Cr pairs and that including Al atoms during phase nucleation may be energetically advantageous. On the other hand, the formation of Al-Al pairs was very unstable. The formation of Al-Al pairs near the interface can be avoided when the amount of Al addition is small. However, it is inevitable when the amount of Al addition is significant, leading to the instability of the phase.
(Mg
Si)-phase in Al-Mg-Si-Ag alloyAhmed, A.*; Uttarasak, K.*; Tsuchiya, Taiki*; Lee, S.*; Nishimura, Katsuhiko*; Nunomura, Norio*; Ikeno, Susumu*; Malik, A.*; Shimizu, Kazuyuki*; Hirayama, Kyosuke*; et al.
Materials Today Communications (Internet), 43, p.111835_1 - 111835_10, 2025/02
Yamaguchi, Masatake; Ebihara, Kenichi; Itakura, Mitsuhiro; Tsuru, Tomohito
Scripta Materialia, 255, p.116366_1 - 116366_5, 2025/01
Times Cited Count：3 Percentile：48.49(Nanoscience & Nanotechnology)Reduction of grain boundary cohesive energy by hydrogen has been considered as one of the candidate causes of grain boundary fracture in steels and aluminum alloys. Recently, the effects of grain boundary segregation elements have been investigated by first-principles calculations, but there are few studies that quantitatively estimate the grain boundary cohesive energy. In this study, we describe a quantitative evaluation method using first-principles calculation results and show some examples of experimental calculations.
Shimizu, Kazuyuki*; Nishimura, Katsuhiko*; Matsuda, Kenji*; Nunomura, Norio*; Namiki, Takahiro*; Tsuchiya, Taiki*; Akamaru, Satoshi*; Lee, S.*; Tsuru, Tomohito; Higemoto, Wataru; et al.
International Journal of Hydrogen Energy, 95, p.292 - 299, 2024/12
Times Cited Count：1 Percentile：10.70(Chemistry, Physical)Zero-field muon spin relaxation experiments were conducted on Al-0.06%Mn, Al-0.06%Cr, Al-0.02%Fe, and Al-0.02%Ni alloys (at.%) across the temperature ranging from 5 to 300 K. The temperature-dependent variations of the dipole field widths (
) elucidated four distinct peaks for the prepared alloys. Atomic configurations of the muon trapping sites corresponding to the observed peaks below 200 K were meticulously characterized utilizing first-principles calculations for the trapping energies of hydrogen in proximity to a solute and solute-vacancy pair. This comprehensive analysis facilitated the establishment of a linear correlation between the muon peak temperature and the hydrogen trapping energy. However, significant deviations from this linear relationship were observed for the fourth peaks above 200 K in Al-Mn, Al-Cr, Al-Fe, and Al-Ni alloys. This discrepancy can be interpreted by considering the disparate distribution functions of muon and hydrogen within the tetrahedral site, wherein two of the four Al atoms are substituted by the solute element and vacancy (solute-vacancy pair).
Shoji, Mizuki*; Kurihara, Kensuke*; Lobzenko, I.; Tsuru, Tomohito; Serizawa, Ai*
Keikinzoku, 74(12), p.535 - 545, 2024/12
While Plate-like Guinier-Preston (GP) zones are formed during aging process in Al-Cu alloys, spherical nanocluster formation occurs in the early stage of aging in Al-Mg-Si alloys. Unlike well-known GP (I) zone in Al-Cu, there is no specific configurations within the nanocluster. However, the solute concentration and local configuration should play decisive role in subsequent formation of precipitations. In the present study, the first-principles calculations were performed to investigate the factors determining the stable shape during the formation process of GP zones and clusters in Al-Cu and Al-Mg-Si alloys. As a result of formation energy of three-body bonds, the Cu-Cu-Cu triplet with the bond angle of 90deg was the most stable. Monte Carlo simulations with newly developed machine-learning potential were then performed, and consequently the segregation of Cu atom formed with bond angle of 90deg are observed more frequently. In contrast, three-body triplet in Al-Mg-Si alloy was most stable without any specific directional anisotropy, when the bond angle was 60deg, resulting in the formation of spherical nanoclusters. These results suggest that the intrinsic feature of the stability of local bonding dominates the shape of GP zones and nanoclusters, in which planar- or spherical-like cluster is formed.
Tsuru, Tomohito; Han, S.*; Chen, Z.*; Lobzenko, I.; Inui, Haruyuki*
Materia, 63(10), p.695 - 702, 2024/10
VNbMoTaW, a typical high-entropy alloy with the BCC phase, is composed of metals with high melting points, and is called a reflectory high-entropy alloy. TiZrNbTaHf, which are also known as typical high-entropy alloys with the BCC phase, are also single phase and have a melting point 500 
C lower than that of VNbMoTaW, but are known to exhibit excellent ductility at low temperatures below room temperature. Understanding what properties govern the mechanical properties is essential for designing alloys such as high-temperature resistant alloys with excellent high-temperature strength and low-temperature ductility. Given that both VNbMoTaW and TiZrNbTaHf are single-phase alloys, the key lies in the relationship between the constituent elements and the properties underlying the deformation, such as dislocations. This paper presents the results of the differences in mechanical properties of these two refractory high-entropy alloys, using experimental, theoretical, and computer simulations to investigate the key factors controlling ductility and strength.
Yano, Rei*; Tanaka, Masaki*; Yamasaki, Shigeto*; Morikawa, Tatsuya*; Tsuru, Tomohito
Materials Transactions, 65(10), p.1260 - 1267, 2024/10
Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)Impact tests and tensile tests were conducted between 77K and 450K in order to elucidate the temperature dependence of absorbed-impact energy, yield stress, effective shear stress, activation volume, and activation enthalpy. The impact-absorbed energy decreased with decreasing test temperature, however, this alloy did not undergo low-temperature embrittlement although it has a bcc structure. Tensile tests showed changes in both the work-hardening rate and the temperature dependence of yield stress at approximately 120 K. This suggests a change in the mechanism behind the plastic deformation at the temperature. The temperature dependence of the activation enthalpy for dislocation glide suggests that double-kink nucleation of a screw dislocation is the dominant mechanism for the dislocation glide from 150K to 200 K, while the interaction between a dislocation and solute atoms dominantly controls the dislocation glide above 200 K. Superelasticity appears in stress-strain curves tested below 120 K, suggesting that the yielding is governed by transformation-induced plasticity below 120 K. The enhanced toughness at low temperatures in these alloys is discussed from the viewpoint of dislocation shielding theory.
Tsuru, Tomohito; Mayama, Tsuyoshi*
Keikinzoku, 74(9), p.442 - 450, 2024/09
Magnesium (Mg) alloys have a wide range of expanding applications as structural materials and biomaterials. On the other hand, there is room for improvement in mechanical properties and corrosion resistance, and there are many issues related to structural design and prediction of deformation behavior due to their remarkable plastic anisotropy, and material development based on material/process design is still actively conducted. In this paper, as computational materials science research into the mechanical properties of Mg alloys, we introduce a method for non-empirical evaluation of the effect of alloying on mechanical properties using first-principles calculations, and an analysis method for polycrystalline behavior and non-uniform deformation using the crystal plasticity finite element method, together with specific analysis examples.
Tsuru, Tomohito
Materials Transactions, 65(9), p.988 - 994, 2024/09
Times Cited Count：1 Percentile：19.07(Materials Science, Multidisciplinary)Some high-entropy alloys (HEAs) with the face-centered cubic (FCC) structure have an excellent strength-ductility balance. While unique deformation modes such as fine twinning patterns other than dislocation glide contribute to the mechanical properties, it has not understood what fundamental properties and features of HEAs cause such unique deformation. In the present study, fundamental properties responsible for the excellent mechanical properties of CoCrFeNiMn and its subsystems were explored comprehensively by the first-principles calculations. The local lattice distortion reaches almost 2% of the Burger vector, which contributes to improving strength in HEAs. Furthermore, the stacking fault energy (SFE) was significantly low in random solid solution, while it increases around some domains where the short-range order (SRO) is formed. The increase in the SFE is caused by the disturbance of the chemical SRO and the spin order due to the SF formation. Our calculations suggest that low and high SFE domains distributed in a solid solution region unique to HEAs lead to successive activation of various deformation modes (Plaston), which achieves excellent strength-ductility balance.
Kiyohara, Shin*; Tsuru, Tomohito; Kumagai, Yu*
Science and Technology of Advanced Materials, 25(1), p.2393567_1 - 2393567_9, 2024/09
Times Cited Count：1 Percentile：14.17(Materials Science, Multidisciplinary)While ceramic materials are widely used in our society, their understanding of the plasticity is not fully understood. MgO is one of the prototypical ceramics, extensively investigated experimentally and theoretically. However, there is still controversy over whether edge or screw dislocations glide more easily. In this study, we directly model the atomic structures of the dislocation cores in MgO based on the first-principles calculations and estimate the Peierls stresses. Our results reveal that the screw dislocation on the primary slip system exhibits a smaller Peierls stress than the edge dislocation. The tendency is not consistent with metals, but rather with TiN, suggesting a characteristic inherent to ceramics.
Somekawa, Hidetoshi*; Tsuru, Tomohito; Naito, Kimiyoshi*; Singh, A.*
Scripta Materialia, 249, p.116173_1 - 116173_6, 2024/08
Times Cited Count：3 Percentile：58.91(Nanoscience & Nanotechnology)The segregated 
twin boundaries play a role in obstruction of dislocation slips. Thus, they contribute to increase in hardness. Internal friction tests reveal that, irrespective of the solute elements, induced twin boundaries are effective in enhancing damping capacity, owing to their reversible motion, i.e., growth and shrinkage. In contrast, by comparison of the loss factor of specimens with/without twin boundary segregation, segregation leads to a decrease in damping capacity. The energy barrier required for twin boundary sliding to occur is closely related to the loss factor.
-phase in Al-Mg-Si alloys during aging treatmentAhmed, A.*; Uttarasak, K.*; Tsuchiya, Taiki*; Lee, S.*; Nishimura, Katsuhiko*; Nunomura, Norio*; Shimizu, Kazuyuki*; Hirayama, Kyosuke*; Toda, Hiroyuki*; Yamaguchi, Masatake; et al.
Journal of Alloys and Compounds, 988, p.174234_1 - 174234_9, 2024/06
Times Cited Count：12 Percentile：93.13(Chemistry, Physical)This study aims to clarify the growth process of the-phase in Al-Mg-Si alloys from the point of view of morphology evolution. For this research, the -phase orientation relationship, shape, growth process, misfit value, and interfacial condition between the -phase and Al matrix were investigated using high-resolution transmission electron microscopy (HR-TEM), focus ion beam (FIB), and optical microscope (OM). Results include the identification of {111} facets at the edges of the -phase, as well as the proposal of two new three-dimensional shapes for the -phase. We purposed the morphology evolution during the growth process of MgSi crystal and calculated the misfit to understand the unstable (111) facet has a higher misfit value as compared to the (001) and (011) facets. Our observations provide how they influence the behavior of MgSi crystals.
MnShimizu, Kazuyuki*; Nishimura, Katsuhiko*; Matsuda, Kenji*; Akamaru, Satoshi*; Nunomura, Norio*; Namiki, Takahiro*; Tsuchiya, Taiki*; Lee, S.*; Higemoto, Wataru; Tsuru, Tomohito; et al.
Scripta Materialia, 245, p.116051_1 - 116051_6, 2024/05
Times Cited Count：2 Percentile：35.25(Nanoscience & Nanotechnology)Hydrogen at the mass ppm level causes hydrogen embrittlement in metallic materials, but it is extremely difficult to experimentally elucidate the hydrogen trapping sites. We have taken advantage of the fact that positive muons can act as light isotopes of hydrogen to study the trapping state of hydrogen in matter. Zero-field muon spin relaxation experiments and the density functional theory (DFT) calculations for hydrogen trapping energy are carried out for AlMn. The DFT calculations for hydrogen in AlMn have found four possible trapping sites in which the hydrogen trapping energies are 0.168 (site 1), 0.312 (site 2), 0.364 (site 3), and 0.495 (site 4) in the unit of eV/atom. Temperature variations of the deduced dipole field width () indicated step-like changes at temperatures, 94, 193, and 236 K. Considering their site densities, the observed change temperatures are interpreted by trapping muons at sites 1, 3, and 4.
-FeSuzudo, Tomoaki; Ebihara, Kenichi; Tsuru, Tomohito; Mori, Hideki*
Journal of Applied Physics, 135(7), p.075102_1 - 075102_7, 2024/02
Times Cited Count：3 Percentile：49.85(Physics, Applied)Fracture of body centred cubic (bcc) metals and alloys below the ductile-to-brittle transition temperature is brittle. This is theoretically explained by the notion that the critical stress intensity factor of a given crack front for brittle fracture is smaller than that for plastic deformation; hence, brittle fracture is chosen over plastic deformation. Although this view is true from a macroscopic point of view, such brittle fracture is always accompanied by small-scale plastic deformation in the vicinity of the crack tip, i.e. crack tip plasticity. This short paper investigates the origin of this plasticity using atomistic modeling with a recently developed machine-learning interatomic potential of -Fe. The computational results identified the precursor of crack tip plasticity, i.e. the group of activated atoms dynamically nucleated by fast crack propagation.
Somekawa, Hidetoshi*; Tsuru, Tomohito; Singh, A.*
Materials Science & Engineering A, 893, p.146066_1 - 146066_8, 2024/02
Times Cited Count：3 Percentile：58.91(Nanoscience & Nanotechnology)The effect of p-block elements (Ga, Ge and In) addition on grain boundary structures and room temperature mechanical responses was investigated on extruded Mg binary alloys with fine-grained structures. Grain boundary segregation was confirmed in the Mg-Ga and Mg-In alloys, whereas the Mg-Ge alloy did not show such microstructures associated with solubility. Grain boundary segregation affected the plastic deformation of the Mg-Ga and Mg-In alloys. In particular, the Mg-In alloy had a large strain rate dependency and exhibited good deformability at low strain rate regimens. First-principles calculations indicated that p-block elements produce a bond-weakening effect at grain boundaries, and atomistic distances at grain boundaries varies according to the element. Solute atom which brings about both bond-weakening and bond-expansion effects to Mg atoms is effective in enhancing the contribution of grain boundary sliding in deformation.
