Modeling radiation induced segregation in Ni–Cr model alloys from first principles

Highlights: ► We have assembled the first ab initio-based RIS model for Ni–Cr alloys. ► The parameters are too sensitive to be determined via ab initio alone. ► Some fitting to experimental RIS data is necessary to produce an accurate model. ► The best fit model suggests a RIS mechanism that is contrary to previous models. - Abstract: In this paper, a rate theory model is employed to study radiation induced segregation (RIS) in Ni–Cr model alloys. In contrast with similar previous models, model parameters have been obtained from first principles via density functional theory (DFT) calculation. Qualitative model behavior is compared and contrasted with the physical mechanisms that underlie conventional RIS models, and the effects of Cr–Cr interstitial trapping and defect sink bias are investigated. It is concluded that: (1) the parameters required in this RIS model are too sensitive to be rigorously determined by present DFT approaches alone, and fitting to experimental RIS data is necessary to produce an accurate model. (2) In contrast with the emphasis of previous RIS models, the best fit DFT-based RIS model suggests that under radiation, the interstitial flux should drive Cr strongly toward enrichment near defect sinks, while the vacancy flux should drive Cr strongly toward depletion, and that the vacancy effect should be slightly stronger resulting in moderate Cr depletion. (3) The effects on RIS of Cr–Cr interstitial trapping and biased defect sinks are relatively small compared with the effects associated with variations in the species dependent diffusivities.