[SY-B1] Computational study of phosphorous migration to grain-boundary in alpha-iron
Phosphorus(P) causes Grain-boundary(GB) embrittlement that is considered as one factor of ductile-brittle transition in reactor pressure vessel steels. While the prediction of GB P segregation is desired, the detailed process of P segregation to GB is still unclear. We studied the process of P segregation to GB by simulating the migration of a mixed interstitial dumbbell, an octahedral interstitial P atom and a P-vacancy complex using a molecular dynamics method. As a result, it was found that the P atom of them becomes a substitutional atom before they reach the GB. The self-interstitial atom (SIA) or vacancy of them was absorbed by the GB. This phenomenon was also confirmed partially by first-principles calculations. In addition, it was found that the P atom left behind approaches the GB by successively interacting with an SIA or a vacancy coming to its nearest neighbor site. We think that the conventional understanding of GB P segregation should be revised.