A defect-based model of radiation-induced segregation to free surfaces in binary alloys

Abstract

A defect-based model of radiation-induced segregation in binary solid solutions is presented. The model consists of a set of reaction–diffusion equations governing the space and time evolution of vacancies, dumbbell interstitials and lattice atoms under irradiation. Irradiation, the mechanism driving evolution, is represented by stochastic and spatially-resolved defect generation events. A key feature of the model presented here is that the role of boundaries as defect sinks is ensured by a set of defect–boundary reaction boundary conditions. Defining defect–boundary interactions in this way makes it possible to capture both segregation and boundary motion simultaneously. The model is tested with Cu–Au solid solution. Enrichment of Cu and depletion of Au has been observed near the boundaries, in agreement with experimental observations. For a particular dose rate, the amount of segregation after a given period of irradiation has been found to be highest at an intermediate temperature. At lower temperatures, maximum segregation is observed by lowering the dose rates, and vice versa. The activation barrier for the defect–surface reactions plays a significant role in segregation near the boundaries. A slight increase in the sample size is also noticed during the simulations due to rapid migration of interstitials to the surface.