Introduction of vacancy drag effect to first-principles-based rate theory model for irradiation-induced grain-boundary phosphorus segregation

In order to examine the vacancy drag effect on phosphorus segregation at grain-boundaries, we estimated partial diffusion coefficients by kinetic Monte Carlo simulations considering atomic transitions for all the binding states of a phosphorus atom and a vacancy, and incorporated them into a rate theory model to simulate grain-boundary phosphorus coverage in neutron-irradiated reactor pressure vessel steels. As a result, it was confirmed that phosphorus atoms are transported to grain-boundaries by the vacancy drag effect. We found that the vacancy drag effect occurs even when only the first-nearest-neighbor binding states are considered, though it does not occur if the partial diffusion coefficients are obtained through the expression derived by theoretical analysis [Ebihara, et al., J. Nucl. Mater. 414 (2011) 328–335]. In addition, we found that grain-boundary phosphorus segregation is suppressed by the vacancy mechanism of phosphorus transport regardless of the vacancy drag effect.