Statistical derivation of basic equations of diffusional kinetics in alloys with application to the description of diffusion of carbon in austenite

Abstract

Basic equations of diffusional kinetics in alloys are statistically derived using the master equation approach. To describe diffusional transformations in substitution alloys, we derive the “quasi-equilibrium” kinetic equation that generalizes its earlier versions by taking possible “interaction renormalization” effects into account. For the interstitial alloys Me-X, we derive an explicit expression for the diffusivity D of an interstitial atom X. This expression notably differs from those used in previous phenomenological treatments. This microscopic expression for D is applied to describe the diffusion of carbon in austenite based on some simple models of carbon-carbon interaction. The results obtained enable us to make certain conclusions about the real form of these interactions and about the scale of the “transition state entropy” for diffusion of carbon in austenite.