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-iron; A Molecular dynamics studySuzudo, Tomoaki; Ebihara, Kenichi; Tsuru, Tomohito
AIP Advances (Internet), 10(11), p.115209_1 - 115209_8, 2020/11
The mechanism of their brittle fracture of BCC metals is not fully understood. In this study, we conduct a series of three-dimensional molecular dynamics simulations of cleavage fracture of -iron. In particular, we focus on mode-I loading starting from curved crack fronts. In the simulations, brittle fractures are observed at cleavages on the {100} plane, while the initial cracks become blunted on other planes as a result of dislocation emissions. Our modeling results agreed with a common experimental observation, that is, {100} is the preferential cleavage plane in bcc transition metals.
Toda, Hiroyuki*; Tsuru, Tomohito; Yamaguchi, Masatake; Matsuda, Kenji*; Shimizu, Kazuyuki*; Hirayama, Kyosuke*
Kagaku, 75(10), p.48 - 53, 2020/10
Highly-concentrated precipitations play therefore dominant role in mechanical properties and hydrogen embrittlement of aluminum alloys. It has been considered that the coherent interface between matrix and precipitation does not contribute to the crack initiation and embrittlement due to its coherency. Here, we discovered the origin of unprecedented quasi-cleavage fracture mode. Hydrogen partitioning at various defect sites is investigated comprehensively combined with experiment, theory and first-principles calculations. We demonstrate that despite low excess free volume, the aluminum--precipitation interface is more preferable trap site than void and grain boundary. The cohesivity of the interface deteriorates significantly with increasing occupancy while hydrogen atoms are trapped stably up to extremely high occupancy equivalent to spontaneous cleavage.
Si and Al
FeCu intermetallic compounds in aluminum alloy; First-principles calculationsYamaguchi, Masatake; Tsuru, Tomohito; Ebihara, Kenichi; Itakura, Mitsuhiro; Matsuda, Kenji*; Shimizu, Kazuyuki*; Toda, Hiroyuki*
Materials Transactions, 61(10), p.1907 - 1911, 2020/10
Times Cited Count：0no abstracts in English
Bendo, A.*; Matsuda, Kenji*; Nishimura, Katsuhiko*; Nunomura, Norio*; Tsuchiya, Taiki*; Lee, S.*; Marioara, C. D.*; Tsuru, Tomohito; Yamaguchi, Masatake; Shimizu, Kazuyuki*; et al.
Materials Science and Technology, 36(15), p.1621 - 1627, 2020/09
Metastable phases in aluminum alloys are the primary nano-scale precipitates which have the biggest contribution to the increase in the tangible mechanical properties. The continuous increase in hardness in the 7xxx aluminum alloys is associated with the phase transformation from clusters or GP-zones to the metastable 
phase. The transformation which is structural and compositional should occur following the path of the lowest activation energy. This work is an attempt to gain insight into how the structural transformation may occur based on the shortest route of diffusion for the eventual structure to result in that of phase. However, for the compositional transformation to occur, the proposed mechanism may not stand, since it is a prerequisite for the atoms to be at very precise positions in the aluminum lattice, at the very beginning of structural transformation, which may completely differ from that of the GP-zones atomic arrangements.
Tsuru, Tomohito; Shimizu, Kazuyuki*; Yamaguchi, Masatake; Itakura, Mitsuhiro; Ebihara, Kenichi; Bendo, A.*; Matsuda, Kenji*; Toda, Hiroyuki*
Scientific Reports (Internet), 10, p.1998_1 - 1998_8, 2020/04
Times Cited Count：3 Percentile：17.34(Multidisciplinary Sciences)Age-hardening has been one and only process to achieve high strength aluminum alloys since unlike iron and titanium, pure aluminum does not have other solid phases during heat treatment. Highly-concentrated precipitations play therefore dominant role in mechanical properties and hydrogen embrittlement of aluminium alloys. It has been considered that the coherent interface between matrix and precipitation does not contribute to the crack initiation and embrittlement due to its coherency. Here, we discovered the origin of unprecedented quasi-cleavage fracture mode. Hydrogen partitioning at various defect sites is investigated comprehensively combined with experiment, theory and first-principles calculations. We demonstrate that despite low excess free volume, the aluminum-precipitation interface is more preferable trap site than void and grain boundary. The cohesivity of the interface deteriorates significantly with increasing occupancy while hydrogen atoms are trapped stably up to extremely high occupancy equivalent to spontaneous cleavage.
Tsuru, Tomohito
Keikinzoku, 70(2), p.73 - 81, 2020/02
Elements strategy becomes important to investigate alternative materials of rare metals. I have dedicated to establish a new approach based on computational methods. In the present paper, I propose two approaches based on first-principles and theory of dislocations. These methods are introduced to magnesium alloys.
Tsuru, Tomohito; Wakeda, Masato*; Suzudo, Tomoaki; Itakura, Mitsuhiro; Ogata, Shigenobu*
Journal of Applied Physics, 127(2), p.025101_1 - 025101_9, 2020/01
Times Cited Count：0 Percentile：100(Physics, Applied)We explored softening/strengthening behavior in various solute in W matrix by density functional theory (DFT) calculations combined with solid solution model. As a result of DFT calculations for various solute, a clear trend was observed in the interaction energy between a solute and a screw dislocation, which has predominant influence on solid solution behavior. The predictions based on the solid solution model with DFT can reasonably reproduce the complicated softening/strengthening as a function of temperature and solute concentration. We conclude that this specific balance is the origin of macroscopic solid solution softening.
Bendo, A.*; Matsuda, Kenji*; Lervik, A.*; Tsuru, Tomohito; Nishimura, Katsuhiko*; Nunomura, Norio*; Holmestad, R.*; Marioara, C. D.*; Shimizu, Kazuyuki*; Toda, Hiroyuki*; et al.
Materials Characterization, 158, p.109958_1 - 109958_7, 2019/12
Times Cited Count：3 Percentile：62.48(Materials Science, Multidisciplinary)Characterization of precipitates in Al-Zn-Mg alloys, using a combination of electron diffraction, bright field transmission electron microscopy and atomic scale scanning transmission electron microscopy imaging revealed the presence of an unreported 
orientation relationship between the -MgZn phase and the Al lattice with the following orientation relationship (0001) 
(120)
and (
) (001), plate on (120). The precipitate interfaces were observed and analyzed along two projections 90
to one-another. The precipitate coarsening was through the common thickening ledge mechanism. The ledges were significantly stepped along one lateral direction. An interface relaxation model using density functional theory was carried out to explain the precipitate behavior.
Tsuru, Tomohito; Itakura, Mitsuhiro; Yuge, Koretaka*; Aoyagi, Yoshiteru*; Shimokawa, Tomotsugu*; Kubo, Momoji*; Ogata, Shigenobu*
Proceedings of 4th International Symposium on Atomistic and Multiscale Modeling of Mechanics and Multiphysics (ISAM-4) (Internet), p.59 - 62, 2019/08
High entropy alloys (HEAs) are chemically complex single- or multi-phase alloys with crystal structures. There are no major components but five or more elements are included with near equiatomic fraction. In such a situation, deformation behavior can no longer be described by conventional solid solution strengthening model. Some HEAs, indeed, show higher strengthening behavior and anomalous slip. However, the mechanisms of these features have yet to be understood. In the present study, we investigate the core structure of dislocations in BCC-HEAs using density functional theory (DFT) calculations. We found that core structure of a screw dislocation is identified as is the case with common BCC metals. On the other hand, dislocation motion should be different from pure BCC metals because of chemical and configurational disorder around dislocation core. We confirmed the specific feature of dislocation motion in HEAs by two-dimensional Peierls potential surface.
Yang, P.-J.*; Li, Q.-J.*; Tsuru, Tomohito; Ogata, Shigenobu*; Zhang, J.-W.*; Sheng, H.-W.*; Shan, Z.-W.*; Sha, G.*; Han, W.-Z.*; Li, J.*; et al.
Acta Materialia, 168, p.331 - 342, 2019/04
Times Cited Count：11 Percentile：6.69(Materials Science, Multidisciplinary)Body-centred-cubic metallic materials, such as niobium (Nb) and other refractory metals, are prone to embrittlement due to low levels of oxygen solutes. The mechanisms responsible for the oxygen-induced rampant hardening and damage are unclear. Here we illustrate that screw dislocations moving through a random repulsive force field imposed by impurity oxygen interstitials readily form cross-kinks and emit excess vacancies in Nb. The vacancies bind strongly with oxygen and screw dislocation in a three-body fashion, rendering dislocation motion difficult and hence pronounced dislocation storage and hardening. This leads to unusually high strain hardening rates and fast breeding of nano-cavities that underlie damage and failure.
hydrogen partitioning controlToda, Hiroyuki*; Yamaguchi, Masatake; Matsuda, Kenji*; Shimizu, Kazuyuki*; Hirayama, Kyosuke*; Su, H.*; Fujiwara, Hiro*; Ebihara, Kenichi; Itakura, Mitsuhiro; Tsuru, Tomohito; et al.
Tetsu To Hagane, 105(2), p.240 - 253, 2019/02
Times Cited Count：0 Percentile：100(Metallurgy & Metallurgical Engineering)no abstracts in English
Yamaguchi, Masatake; Ebihara, Kenichi; Itakura, Mitsuhiro; Tsuru, Tomohito; Matsuda, Kenji*; Toda, Hiroyuki*
Computational Materials Science, 156, p.368 - 375, 2019/01
Times Cited Count：7 Percentile：24.94(Materials Science, Multidisciplinary)The segregation of multiple hydrogen atoms along aluminum (Al) grain boundaries (GBs) and fracture surfaces (FSs) was investigated through first-principles calculations considering the characteristics of GBs. The results indicate that hydrogen segregation is difficult along low-energy GBs. The segregation energy of multiple hydrogen atoms along GBs and FSs and the cohesive energy was obtained for three types of high-energy Al GBs. With increasing hydrogen segregation along the GBs, the cohesive energy of the GB decreases and approaches zero with no decrease in GB segregation energy. The GB cohesive energy decreases in parallel with the volume expansion of the region of low electron density along the GB.
Yamaguchi, Masatake; Tsuru, Tomohito; Ebihara, Kenichi; Itakura, Mitsuhiro
Keikinzoku, 68(11), p.588 - 595, 2018/11
no abstracts in English
Ebihara, Kenichi; Yamaguchi, Masatake; Tsuru, Tomohito; Itakura, Mitsuhiro
Keikinzoku, 68(11), p.596 - 602, 2018/11
Hydrogen embrittlement (HE) is considered as one cause of stress corrosion cracking. HE is a serious problem in the development of high strength aluminum alloy as with steels. For understanding HE, it is inevitable to know hydrogen trapping states in the alloys and it can be identified using thermal desorption spectrometry of H. In this study, we numerically simulated thermal desorption spectra of hydrogen in aluminum for a cylindrical and a plate specimens and interpreted the desorption peaks included in them on the basis of the trap site concentration and the trap energy. As a result, we found that the peak at the lowest-temperature side can result from grain boundaries and confirmed that the reported interpretation for other peaks is reasonable. We also obtained the result showing the possibility that the trap site concentration of defects changes during heating the specimens. This result may give a suggestion for the interpretation of temperature desorption spectra of steels.
Bendo, A.*; Matsuda, Kenji*; Lee, S.*; Nishimura, Katsuhiko*; Toda, Hiroyuki*; Shimizu, Kazuyuki*; Tsuru, Tomohito; Yamaguchi, Masatake
Materialia, 3, p.50 - 56, 2018/11
Tsuru, Tomohito; Suzudo, Tomoaki
Nuclear Materials and Energy (Internet), 16, p.221 - 225, 2018/08
Changes in mechanical properties due to transmutation products (Re and Os) in W alloys is a central issue for plasma-facing materials in fusion reactors. We implemented density function theory calculations to investigate the effect of Re, Os, and other 5d solutes on dislocation core structure and motion associated with plastic deformation. Ir, Pt, Au, and Hg solutes show strong attractive interactions with screw dislocations, causing solution strengthening by the pinning mechanism. On the other hand, Hf, Ta, and Re cause softening by facilitating dislocation motion around solutes. This prediction corresponds well with the experimental observation of softening behavior in W-Re alloys.
Suzudo, Tomoaki; Tsuru, Tomohito; Hasegawa, Akira*
Journal of Nuclear Materials, 505, p.15 - 21, 2018/07
Times Cited Count：3 Percentile：55.45(Materials Science, Multidisciplinary)Tungsten (W) is considered as a promising candidate for plasma-facing materials for future nuclear fusion devices, and selecting optimal alloying constituents is a critical issue to improve radiation resistance of the W alloys as well as to improve their mechanical properties. We conducted in the current study a series of first-principles calculations for investigating solvent-solute mixed dumbbells in W crystals. The results suggested that titanium (Ti), vanadium (V), and chromium (Cr) are favorable as solutes for W alloys from irradiation-effect perspectives because these elements are expected to promote vacancy-interstitial recombination without causing radiation-induced precipitation that reduces ductility of irradiated materials.
Tsuru, Tomohito; Somekawa, Hidetoshi*; Chrzan, D. C.*
Acta Materialia, 151, p.78 - 86, 2018/06
Times Cited Count：19 Percentile：6.61(Materials Science, Multidisciplinary)We investigated the effect of solute elements on interfacial segregation and fracture in Mg alloys by experiments and first-principles density functional theory calculations in conjunction with interfacial fracture mechanics. Based on the assumption of brittle fracture in Mg alloys, the interfacial separation caused by segregated solutes in Mg can be efficiently described by the energy-based criterion of fracture, which is in good agreement with the fracture toughness obtained by experimental tests of Mg-M binary alloys. The electronic interaction, that is, the change in the electronic state between the interface and surface, mainly influences the ideal work of separation regardless of the type of interface. We found that IIIB (
) and IVB (
) solutes, such as Zr, show distinctive hybridization between the p band of Mg and the d band of the solute, which characterizes the strong fracture toughness of Zr-doped Mg alloys in both the calculations and experiments.
precipitate in Al-Mg-Zn alloysTsuru, Tomohito; Yamaguchi, Masatake; Ebihara, Kenichi; Itakura, Mitsuhiro; Shiihara, Yoshinori*; Matsuda, Kenji*; Toda, Hiroyuki*
Computational Materials Science, 148, p.301 - 306, 2018/06
Times Cited Count：16 Percentile：20.85(Materials Science, Multidisciplinary)Hydrogen embrittlement susceptibility of high strength 7xxx series Al alloys has been recognized as the critical issues in the practical use of Al alloys. Focusing on the interface between MgZn precipitates and an Al matrix, which is considered as one of the important segregation sites in these alloys, we investigated the stable -MgZn-Al interface, and the possible hydrogen trap sites in MgZn and at the -MgZn-Al interface via first-principles calculation. Most of the interstitial sites inside the MgZn crystal were not possible trap sites because their energy is relatively higher than that of other trap sites. The trap energy of the most favorable site at the -MgZn-Al is approximately -0.3 eV/H, which is more stable that of the interstitial site at the grain boundary. The interface between MgZn and Al is likely to be a possible trap site in Al alloys.
Somekawa, Hidetoshi*; Tsuru, Tomohito
Materials Science & Engineering A, 708, p.267 - 273, 2017/12
Times Cited Count：14 Percentile：20.43(Nanoscience & Nanotechnology)The effect of alloying elements on grain boundary sliding was systematically investigated using several binary magnesium alloys via both experimental and numerical methods. The alloying element clearly affected damping properties related to grain boundary sliding, as measured by nanoindentation tests. The properties, such as damping capacity and strain rate sensitivity, apparently depended on grain boundary characteristics, i.e., the grain boundary energy. By increasing and decreasing the grain boundary energy, the alloying element was found to play a role in enhancing and suppressing grain boundary sliding, respectively. First-principles calculations revealed that lithium element had a weak bonding to magnesium due to a few operation of electric orbit. On the other hand, rare-earth elements exhibited relatively strong bonding to magnesium, because of electron interactions with the first nearest neighbor site, and tended to prevent grain boundary sliding.
