Diffusion in phases with several components and sublattices

Diffusion in multicomponent alloys is discussed in order to extend earlier treatments to phases with sublattices. Both a phenomenological approach and some physical models are applied. Care is taken so that the driving forces and the fluxes are chosen in a way obeying the requirements of irreversible thermodynamics. The Onsager reciprocal relation will thus be obeyed. Two kinds of models have been considered, exchange between two atoms and exchange between an atom and a vacancy.For phases with several sublattices a number of difficulties arise and only a few cases of great practical importance are considered. The connection between practical diffusion coefficients and phenomenological coefficients is given. The use of different concentration variables in Fick's second law is discussed.