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Journal Articles

Machine learning molecular dynamics simulations for evaluation of high-temperature properties of nuclear fuel materials

Kobayashi, Keita; Nakamura, Hiroki; Itakura, Mitsuhiro; Machida, Masahiko; Okumura, Masahiko

Materia, 62(3), p.175 - 181, 2023/03

no abstracts in English

Journal Articles

Improved mechanical properties of Co-free high-entropy Cantor alloy; A First-principles study

Lobzenko, I.; Wei, D.*; Itakura, Mitsuhiro; Shiihara, Yoshinori*; Tsuru, Tomohito

Results in Materials (Internet), 17, p.100364_1 - 100364_7, 2023/03

High-entropy alloys (HEAs) have received attention for their excellent mechanical and thermodynamic properties. A recent study revealed that Co-free face-centered cubic HEAs carried a potential to improve strength and ductility, which is of high importance for nuclear materials. Here, we implemented first-principles calculations to explore the fundamental mechanism of improving mechanical properties in Co-free HEA. We found that the local lattice distortion of Co-free HEA is more significant than that of the well-known Cantor alloy. In addition, the short-range order formation in Co-free HEA caused highly fluctuated stacking fault energy. Thus, the significant local lattice distortion and the non-uniform solid solution states composed of low- and high-stacking fault regions contribute to improving strength and ductility.

Journal Articles

Long-timescale transformations of self-interstitial atom clusters of Cu using the SEAKMC method; The Effect of setting an activation energy threshold for saddle point searches

Hayakawa, Sho*; Yamamoto, Yojiro*; Okita, Taira*; Itakura, Mitsuhiro; Suzuki, Katsuyuki*

Computational Materials Science, 218, p.111987_1 - 111987_10, 2023/02

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

Journal Articles

Molecular dynamics simulation to elucidate effects of spatial geometry on interactions between an edge dislocation and rigid, impenetrable precipitate in Cu

Tsugawa, Kiyoto*; Hayakawa, Sho*; Okita, Taira*; Aichi, Masaatsu*; Itakura, Mitsuhiro; Suzuki, Katsuyuki*

Computational Materials Science, 215, p.111806_1 - 111806_8, 2022/12

 Times Cited Count:1 Percentile:41.57(Materials Science, Multidisciplinary)

Journal Articles

Molecular dynamics simulations to quantify the interaction of a rigid and impenetrable precipitate with an edge dislocation in Cu

Tsugawa, Kiyoto*; Hayakawa, Sho*; Iwase, Yuki*; Okita, Taira*; Suzuki, Katsuyuki*; Itakura, Mitsuhiro; Aichi, Masaatsu*

Computational Materials Science, 210, p.111450_1 - 111450_9, 2022/07

 Times Cited Count:5 Percentile:81.96(Materials Science, Multidisciplinary)

Journal Articles

Atomistic weak interaction criterion for the specificity of liquid metal embrittlement

Yamaguchi, Masatake; Tsuru, Tomohito; Itakura, Mitsuhiro; Abe, Eiji*

Scientific Reports (Internet), 12(1), p.10886_1 - 10886_7, 2022/07

 Times Cited Count:0 Percentile:0(Multidisciplinary Sciences)

no abstracts in English

Journal Articles

Machine learning molecular dynamics simulations toward exploration of high-temperature properties of nuclear fuel materials; Case study of thorium dioxide

Kobayashi, Keita; Okumura, Masahiko; Nakamura, Hiroki; Itakura, Mitsuhiro; Machida, Masahiko; Cooper, M. W. D.*

Scientific Reports (Internet), 12(1), p.9808_1 - 9808_11, 2022/06

 Times Cited Count:1 Percentile:41.57(Multidisciplinary Sciences)

no abstracts in English

Journal Articles

Modeling changes in the second harmonic generation of ultrasonic waves having wavelengths beyond the length scale of conventional molecular dynamics

Mori, Sho*; Matsuda, Nayuta*; Okita, Taira*; Aichi, Masaatsu*; Itakura, Mitsuhiro; Suzuki, Katsuyuki*

Materialia, 21, p.101371_1 - 101371_6, 2022/03

Journal Articles

Dislocation core structure and motion in pure titanium and titanium alloys; A First-principles study

Tsuru, Tomohito; Itakura, Mitsuhiro; Yamaguchi, Masatake; Watanabe, Chihiro*; Miura, Hiromi*

Computational Materials Science, 203, p.111081_1 - 111081_9, 2022/02

 Times Cited Count:6 Percentile:59.59(Materials Science, Multidisciplinary)

The deformation mode of some titanium (Ti) alloys differs from that of pure Ti due to the presence of alloying elements in $$alpha$$-phase. Herein, we investigated all possible slip modes in pure Ti and the effects of Al and V solutes as typical additive elements on the dislocation motion in $$alpha$$-Ti alloys using density functional theory (DFT) calculations. The stacking fault (SF) energies in possible slip planes indicated that both Al and V solutes reduce the SF energy in the basal plane and, in contrast, the Al solute increases the SF energy particularly in the prismatic plane. DFT calculations were subsequently performed to simulate dislocation core structures. The energy landscape of the transition between all possible dislocation core structures and the barriers for dislocation glide in various slip planes clarified the nature of dislocation motion in pure Ti. (i) the energy of prismatic core is higher than most stable pyramidal core, and thereby dislocations need to overcome the energy barrier of the cross-slip (22.8 meV/b) when they move in the prismatic plane, (ii) the energy difference between the prismatic and basal cores is larger (127 meV/b), that indicates the basal slip does not activate, (iii) however, the Peierls barrier for motion in the basal plane is not as high (16 meV/b). Direct calculations for the dislocation core around solutes revealed that both Al and V solutes facilitate dislocation motion in the basal plane by reducing the energy difference between the prismatic and basal cores. The effect of solutes characterizes the difference in the deformation mode of pure Ti and $$alpha$$-Ti alloys.

Journal Articles

Construction of machine-learning Zr interatomic potentials for identifying the formation process of c-type dislocation loops

Okita, Taira*; Terayama, Satoshi*; Tsugawa, Kiyoto*; Kobayashi, Keita; Okumura, Masahiko; Itakura, Mitsuhiro; Suzuki, Katsuyuki*

Computational Materials Science, 202, p.110865_1 - 110865_9, 2022/02

 Times Cited Count:5 Percentile:52.96(Materials Science, Multidisciplinary)

Journal Articles

Molecular dynamic simulations evaluating the effect of the stacking fault energy on defect formations in face-centered cubic metals subjected to high-energy particle irradiation

Terayama, Satoshi*; Iwase, Yuki*; Hayakawa, Sho*; Okita, Taira*; Itakura, Mitsuhiro; Suzuki, Katsuyuki*

Computational Materials Science, 195, p.110479_1 - 110479_12, 2021/07

 Times Cited Count:6 Percentile:52.96(Materials Science, Multidisciplinary)

Journal Articles

Self-learning hybrid Monte Carlo method for isothermal-isobaric ensemble; Application to liquid silica

Kobayashi, Keita; Nagai, Yuki; Itakura, Mitsuhiro; Shiga, Motoyuki

Journal of Chemical Physics, 155(3), p.034106_1 - 034106_9, 2021/07

 Times Cited Count:4 Percentile:42.16(Chemistry, Physical)

no abstracts in English

Journal Articles

Hydrogen-trapping energy in screw and edge dislocations in aluminum; First-principles calculations

Yamaguchi, Masatake; Itakura, Mitsuhiro; Tsuru, Tomohito; Ebihara, Kenichi

Materials Transactions, 62(5), p.582 - 589, 2021/05

 Times Cited Count:7 Percentile:70.25(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Machine learning potentials for tobermorite minerals

Kobayashi, Keita; Nakamura, Hiroki; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Okumura, Masahiko

Computational Materials Science, 188, p.110173_1 - 110173_14, 2021/02

 Times Cited Count:10 Percentile:76.74(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Density functional theory study of solute cluster growth processes in Mg-Y-Zn LPSO alloys

Itakura, Mitsuhiro; Yamaguchi, Masatake; Egusa, Daisuke*; Abe, Eiji*

Acta Materialia, 203, p.116491_1 - 116491_9, 2021/01

 Times Cited Count:19 Percentile:93.84(Materials Science, Multidisciplinary)

Solute cluster in LPSO alloys plays a key role in their idiosyncratic plastic behavior such as kink formation and kink strengthening. Identifying the atomistic details of the cluster structure is a prerequisite for any atomistic modeling of LPSO alloys aiming for their improved strength and ductility, but there have been uncertainty about interstitial atom in the cluster. While density functional theory calculations have shown that inclusion of interstitial atom is energetically favorable, it has been unclear how the extra atom is provided, how much of the cluster have interstitial atoms, and what kind of element they are. In the present work we use density functional theory calculations to investigate the growth process of the solute cluster, specifically that of Mg-Y-Zn LPSO alloy, to determine the precise atomistic structure of solute cluster. We show that a pair of an interstitial atom and a vacancy is spontaneously created when a certain number of solute atoms are absorbed into the cluster, and all the full-grown cluster should include interstitial atom. We also show that interstitial atom is either Mg or Y atom, while Zn interstitial atom is extremely rare. These knowledge greatly simplifies atomistic modeling of solute clusters in Mg-Y-Zn alloy. Owing to the vacancies emitted from the cluster, vacancy density should be over-saturated in regions where solute clusters are growing, and the increased vacancy density accelerates cluster growth.

JAEA Reports

Status of study of long-term assessment of transport of radioactive contaminants in the environment of Fukushima (FY2018) (Translated document)

Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.

JAEA-Research 2020-007, 249 Pages, 2020/10


The accident of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, Japan Atomic Energy Agency (JAEA) has been conducting "Long-term Assessment of Transport of Radioactive Contaminants in the Environment of Fukushima" concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.

Journal Articles

Hydrogen trapping in Mg$$_2$$Si and Al$$_7$$FeCu$$_2$$ intermetallic compounds in aluminum alloy; First-principles calculations

Yamaguchi, 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:7 Percentile:52.49(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Hydrogen-accelerated spontaneous microcracking in high-strength aluminium alloys

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:19 Percentile:78.86(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.

Journal Articles

Anomalous solution softening by unique energy balance mediated by kink mechanism in tungsten-rhenium 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:2 Percentile:16.57(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.

Journal Articles

Screw dislocation-spherical void interactions in fcc metals and their dependence on stacking fault energy

Hayakawa, Sho*; Doihara, Kohei*; Okita, Taira*; Itakura, Mitsuhiro; Aichi, Masaatsu*; Suzuki, Katsuyuki*

Journal of Materials Science, 54(17), p.11509 - 11525, 2019/09

 Times Cited Count:11 Percentile:48.78(Materials Science, Multidisciplinary)

217 (Records 1-20 displayed on this page)