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

https://doi.org/10.1016/j.commatsci.2022.111987

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

https://doi.org/10.1016/j.commatsci.2022.111450

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

https://doi.org/10.1016/j.commatsci.2021.110865

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

https://doi.org/10.1007/s10853-019-03716-0

Effects of stacking fault energies on formation of irradiation-induced defects at various temperatures in face-centred cubic metals

Nakanishi, Daiki*; Kawabata, Tomoya*; Doihara, Kohei*; Okita, Taira*; Itakura, Mitsuhiro; Suzuki, Katsuyuki*

Philosophical Magazine, 98(33), p.3034 - 3047, 2018/09

https://doi.org/10.1080/14786435.2018.1515507

By using the six sets of interatomic potentials for face-centredcubic metals that differ in the stacking fault energy (SFE) while most of the other material parameters are kept almost identical, we conducted molecular dynamics simulations to evaluate the effects of SFE on the defect formation process through collision cascades. The ratio of glissile SIA clusters tends to decrease with increasing SFE. This is because perfect loops, the edges of which split into two partial dislocations with stacking fault structures between them in most cases, prefer to form at lower SFEs. The enhanced formation of glissile SIA clusters at lower SFEs can also be observed even at increased temperature.

Atomic simulations to evaluate effects of stacking fault energy on interactions between edge dislocation and spherical void in face-centred cubic metals

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

Philosophical Magazine, 98(22), p.2061 - 2076, 2018/05

https://doi.org/10.1080/14786435.2018.1472401

In this study, molecular dynamics simulations were performed to elucidate the effects of stacking fault energy (SFE) on the physical interactions between an edge dislocation and a spherical void in the crystal structure of face-centred cubic metals at various temperatures and for different void sizes. Four different types of interaction morphologies were observed, in which (1) two partial dislocations detached from the void separately, and the maximum stress corresponded to the detachment of the trailing partial; (2) two partial dislocations detached from the void separately, and the maximum stress corresponded to the detachment of the leading partial; (3) the partial dislocations detached from the void almost simultaneously without jog formation; and (4) the partial dislocations detached from the void almost simultaneously with jog formation. With an increase in void size or SFE, the interaction morphology changed in the above-mentioned order. It was observed that the magnitude of the critical resolved shear stress (CRSS) and its dependence on the SFE were determined by these interaction morphologies. The value of the CRSS in the case of interaction morphology (1) is almost equal to an analytical one based on the linear elasticity by employing the Burgers vector of a single partial dislocation. The maximum value of the CRSS is also obtained by the analytical model with the Burgers vector of the two partial dislocations.

The Effect of stacking fault energy on interactions between an edge dislocation and a spherical void by molecular dynamics simulations

Asari, Keisuke*; Hetland, O. S.*; Fujita, Satoshi*; Itakura, Mitsuhiro; Okita, Taira*

Journal of Nuclear Materials, 442(1), p.360 - 364, 2013/11

https://doi.org/10.1016/j.jnucmat.2013.05.076

Molecular dynamics simulations were conducted using a set of six interatomic potentials for FCC metals that differed only in stacking fault energy (SFE), to clarify the effect of SFE on interactions between a dissociated edge dislocation and a void. There are two different types of interaction mechanism: separate depinning of the individual partial dislocations and almost simultaneous depinning of the combined partial dislocations. The interaction mechanism depends on both the SFE and void size, and changes the absolute value of the critical resolved shear stress (CRSS) and its dependence on the SFE. In the separate depinning case, the CRSS is relatively low and is almost independent of the SFE, while in the simultaneous case, the CRSS is increases with SFE. The void size for which the change in interaction mechanism occurs increases with decreasing SFE.

Study for the SCC degradation incorporating dose rate effects, 1

Okita, Taira*; Koshiishi, Masato*; Hashimoto, Tsuneyuki*; Tanaka, Shigeaki*; Kodama, Mitsuhiro*; Kondo, Keietsu; Tsukada, Takashi

no journal, , 

no abstracts in English

Development of an EAM potential for Fe-Cr-Ni alloys

Itakura, Mitsuhiro; Miyashiro, Satoshi*; Okita, Taira*; Yamaguchi, Masatake; Okuda, Hiroshi*

no journal, , 

An embedded atom method (EAM) type interatomic potential for Fe-Cr-Ni alloys is presented. The potential is fitted to reproduce the density functional theory (DFT) calculation results of bulk properties in the FCC structure, such as lattice constant and elastic constants, based on the DFT results of randomly generated 60 atomic configurations. We show that the magnetic ordering of the periodicity (2a, 0, 0) in stabilizes the FCC lattice structure at zero temperature. To obtain the bulk properties of the stable FCC structure, all the elements are treated as non-magnetic in the DFT calculations. The validity of this non-magnetic treatment will also be discussed.

First-princilpes study of solute elements in Zirconium

Itakura, Mitsuhiro; Okita, Taira*

no journal, , 

Time to hydride precipitation in Zircaloy fuel cladding determines the lifetime of the fuel cladding of nuclear reactors. For the design of a new reactor with increased irradiation to transmute TRU elements and reduce waste, the effect of irradiation on the hydride formation must be evaluated. We carried out ab-initio calculations of interaction between solute iron atoms and self-interstitial Zr atoms to deduce the fundamental parameters for the modeling of irradiation effect. The results are indispensable for the design of the new reactor.