Analysis of vacancies produced at non-equilibrium concentrations by interdiffusion

In this paper, we address the fundamental problem of chemical interdiffusion in binary alloys for the case where vacancies at non-equilibrium concentrations may be generated during the interdiffusion process. We take a very general phenomenological approach to interdiffusion but develop it in a new way. Both high vacancy and low vacancy concentrations are dealt with. For the commonly encountered small vacancy concentration case our strategy centres on directing the information about the driving force associated with the non-equilibrium vacancies (which is effectively not measurable) onto the velocity of inert marker(s) in the diffusion zone. Assuming access to independent knowledge of the two tracer diffusivities we derive expressions for the transport coefficient (for the case of non-equilibrium vacancies) using an analysis along Boltzmann Matano lines. Using the random alloy model we show that in principle it is possible to measure the relative concentration of non-equilibrium vacancies produced during interdiffusion.