A theory of radiation-induced segregation in concentrated alloys

Abstract

A new and simple theory for radiation-induced segregation in concentrated alloys is presented. The coupling between defect fluxes and atom fluxes is accounted for by the concept of preferential migration of vacancies and interstitials via A-atoms or B-atoms in a binary A-B alloy. Similarly, atom fluxes are partitioned into those occurring via vacancies and via interstitials. This approach permits expression of the defect fluxes and atom fluxes in terms of partial diffusivity coeffi- cients and concentration gradients of defects and alloy components. The time and space dependence of the defect concen- trations and composition of a binary alloy is described by a set of three coupled partial differential equations containing four partial diffusivity coefficients, i.e., those of A-atoms and B-atoms diffusing via vacancies and via interstitials. The set of differential equations has been integrated for some model binary alloys with complete miscibility, utilizing the geometry of a thin foil. The sample calculations are in good qualitative agreement with the general features of radiation-induced segregation as deduced from experiments. The temperature, dose and dose-rate dependencies of segregation in concentrated alloys are found to be similar to those predicted by the Johnson-Lam model for dilute alloys.