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3(111) and 5(0-13) grain boundaries of 
-ironEbihara, Kenichi; Suzudo, Tomoaki
Metals, 12(4), p.662_1 - 662_10, 2022/04
Times Cited Count：2 Percentile：30.25(Materials Science, Multidisciplinary)Phosphorus atoms in steels accumulate at grain boundaries via thermal and/or irradiation effects and induce grain boundary embrittlement. Quantitative prediction of phosphorus segregation at grain boundaries under various temperature and irradiation conditions is therefore essential for preventing embrittlement. To develop a model of grain boundary phosphorus segregation in -iron, we studied the migration of a phosphorus atom in two types of symmetrical tilt grain boundaries (3[1-10](111) and 5[100](0-13) grain boundaries) using molecular dynamics simulations with an embedded atom method potential. The results revealed that, in the 3 grain boundary, phosphorus atoms migrate three-dimensionally mainly in the form of interstitial atoms, whereas in the 5 grain boundary, these atoms migrate one-dimensionally mainly via vacancy-atom exchanges. Moreover, de-trapping of phosphorus atoms and vacancies was investigated.
-Iron Using First-Principles-Based Kinetic Monte CarloEbihara, Kenichi; Suzudo, Tomoaki; Yamaguchi, Masatake
Materials Transactions, 58(1), p.26 - 32, 2017/01
Times Cited Count：8 Percentile：38.12(Materials Science, Multidisciplinary)In order to evaluate grain boundary (GB) phosphorous (P) segregation in nuclear reactor pressure vessel steels under irradiation, the rate-theory model based on first-principles calculations is developed. In this study, we evaluated the diffusion coefficient of the mixed interstitial dumbbell of a P atom and an iron(Fe) atom using a kinetic Monte Carlo (kMC) simulation based on first-principles calculations. The evaluated diffusion coefficient was almost the same with the diffusion coefficient of P atoms which migrate via octahedral interstitial sites, and was much faster than that for P transport by vacancies. Furthermore, from the simulation of the irradiation induced GB P segregation using the model which was modified to include P atoms of octahedral interstitial sites, it was found that the boundary condition at GB is not valid for P atoms of octahedral interstitial sites
Ebihara, Kenichi; Suzudo, Tomoaki; Yamaguchi, Masatake; Nishiyama, Yutaka
no journal, ,
Since grain-boundary (GB) embrittlement by phosphorus (P) under irradiation is a crucial problem in steels, it is necessary to evaluate irradiation-induced P GB segregation in order to secure the integrity of nuclear structural materials. Recently, partial diffusion coefficients including the vacancy (V) drag effect, which are obtained by the kinetic Monte Carlo method incorporating the barrier energy estimated by the first-principles calculation, are built into the diffusion rate model, and the model is applied to the evaluation of the P GB segregation. Since the amount of V is affected by temperature, we evaluated the P GB segregation by the model. As a result, although the model could not simulate the increase of P GB segregation in the high temperature region which is shown by the McLean's diffusion model, the model incorporating the process of capturing and releasing P at GB simulated the increase. Hence, such a process is significant for simulating the temperature dependence.
iron using kinetic Monte Carlo based on first-principles calculationEbihara, Kenichi; Suzudo, Tomoaki; Yamaguchi, Masatake
no journal, ,
no abstracts in English
Ebihara, Kenichi; Suzudo, Tomoaki; Yamaguchi, Masatake
no journal, ,
Phosphorus (P) atoms bring about grain boundary (GB) embrittlement in steel materials and can influence the rise of ductile-brittle transition temperature in reactor pressure vessel steels. Thus, a rate theory model for analyzing irradiation-induced GB P segregation is developed based on the atomistic processes. So far, we have incorporated the trapping process to the model based on the result of molecular dynamics (MD) simulations. However, the conventional model is used for the trapping process. In this study, we simulated the migration of a P atom in a GB. In addition, based on the consideration of the MD results, we modified the de-trapping model and applied the rate theory model to the temperature dependence of irradiation-induced GB P segregation. It was found that P atoms migrate through a gap in the GB region. In the calculated GB P segregation, the GB P coverage increased at T 
600
C and that the increase depended on the GB P segregation energy.
