Diffusion in substitutionally disordered B2 intermetallics

In this paper, a comprehensive diffusion kinetics theory is formulated to describe seamlessly tracer and chemical diffusion in antistructurally disordered B2 intermetallics showing positive and negative deviations from stoichiometry. The theory is based around unit processes consisting of six-jump cycles that can be assisted by intrinsic and extrinsic antistructural atoms of either atomic species. The Ising alloy model is used to illustrate the formalism, but the formalism can be adapted to other models. Expressions are developed for the tracer diffusion coefficients, the phenomenological coefficients, the intrinsic diffusion coefficients, the interdiffusion coefficient and the various correlation factor components. Results for the tracer and collective correlation factors and the vacancy wind factor (in interdiffusion) are in excellent agreement with results from Monte Carlo computer simulations based around single vacancy jumps. (author)