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3(111) symmetrical tilt grain boundary in 
-ironEbihara, Kenichi; Suzudo, Tomoaki
Modelling and Simulation in Materials Science and Engineering, 26(6), p.065005_1 - 065005_10, 2018/09
Times Cited Count：4 Percentile：20.17(Materials Science, Multidisciplinary)Irradiation-induced grain boundary phosphorus segregation is an important factor for estimating the embrittlement of nuclear reactor pressure vessel steels, but the physical process of phosphorus migration to grain boundaries is still unclear. We numerically studied phosphorus migration toward 3(111) symmetrical tilt grain boundary in -iron using molecular dynamics. We found that, in the vicinity of the grain boundary within 
1 nm distance, an iron-phosphorus mixed dumbbell and an octahedral interstitial phosphorus atom push a self-interstitial atom into the grain boundary, and the phosphorus atom becomes a substitutional atom. A phosphorus vacancy complex in the region also becomes dissociated, and the vacancy is absorbed in the grain boundary without dragging phosphorus. The results claim that a novel view of the segregation process is required.
-ironEbihara, Kenichi; Suzudo, Tomoaki; Yamaguchi, Masatake
no journal, ,
It is desired that segregation of phosphorus(P), which is known to to cause GB embrittlement in neutron-irradiated reactor pressure vessel steels, to grain-boundary is estimated for various irradiation conditions. In order to evaluate GB P segregation using the first-principles-based rate theory model, we evaluated the diffusion coefficient(DC) for mixed interstitial dumbbell(MID) in -iron using the first-principles-based kinetic Monte Carlo(kMC) simulation, and compared it with those both for octahedral interstitial P(octP) atoms and for the vacancy(V) migration mode. As results, it was confirmed that DCs of MIDs and octP atoms are much larger than that of V migration mode. In addition, by applying the model incorporating the evaluated DCs to simulation of GB P segregation, it was found that the model needs to be modified. Furthermore, we will describe the investigation of the process of GB P segregation using molecular dynamics simulation.
Ebihara, Kenichi; Suzudo, Tomoaki; Yamaguchi, Masatake
no journal, ,
Phosphorus is known as an element which causes the ductile-brittle transition in reactor pressure vessel steels. In the migration simulation of phosphorus grain-boundary segregation using molecular dynamics, a mixed dumbbell, an interstitial P atom, and a vacancy-phosphorus complex cannot reach a grain-boundary directly. It was found that the cause of the phenomena is explained by thermal fluctuation of the grain-boundary and the energy stability of the defects. It indicates the modification of the conventional idea of the process for grain boundary segregation.
-ironEbihara, Kenichi; Suzudo, Tomoaki
no journal, ,
Grain boundary (GB) phosphorus (P) segregation is one factor for understanding embrittlement of reactor pressure vessel steels due to aging. Thus, the rate theory model for estimating GB P segregation by irradiation has been developed. In this study, for elucidating the segregation mechanism of P atoms to GBs, the P migration to a GB was simulated by molecular dynamics (MD), and the result of MD simulations was verified by the first-principles calculation. As a result, in the region near GB, a vacancy or a self-interstitial atom which migrates along with a P atom was absorbed by the GB and the P atom became substitutional. This phenomenon was confirmed by the first-principles calculation in the case of the mixed-interstitial dumbbell. This presentation is based on the paper [Modelling and Simulation in Materials Science and Engineering 26(2018) 065005].
