Anomalous mass transport in the vicinity of the interface of two metallic media

Diffusion of nickel in copper was studied experimentally in a temperature range of 250–375°C in the “coating (nickel)-metal (copper)” system using a radioactive isotope ⁶³Ni. Anomalously high values of the diffusion coefficients and an anomalously low value of the activation energy were found. To explain the effect, a new way of describing the diffusion phenomena in the vicinity of the interface of two metallic media is suggested, which takes into account the presence of high gradients of chemical potentials near the boundary. Based on the principles of nonlinear thermodynamics of irreversible processes, a system of differential equations of diffusion in the vicinity of the interface was obtained. Analysis of the kinetics of the diffusion zone formation revealed that chemical-potential gradients significantly accelerate the diffusion process in the vicinity of the interface. A comparison of the calculated kinetics of the formation of a diffusion zone with that obtained upon the experimental investigation of diffusion shows their qualitative agreement.