Interdiffusion between metals of widely different self-diffusion rates

Interdiffusion between metals of widely different diffusional characteristic is interesting in view of the fact that several anomalous features appear during interdiffusion owing to the large difference between the fluxes of the diffusing species. In some binary systems, it has been observed that the interdiffusion coefficients determined by multi-phase couples are smaller than those determined through the single-phase couples. This observation implies that the Boltzmann-Matano analysis is unapplicable to such cases. In the present article, this phenomenon is reviewed in the Au-Fe and Au-Ni systems, which have large differences in the diffusivities between the components. Recent experimental results on diffusion enhanced by vacancies induced under elevated hydrogen pressure are helpful to resolve the problems.