Determination and assessment of ternary interdiffusion coefficients from individual diffusion couples

Abstract

Two pairs of diffusion couples were assembled with α (fcc) Cu-Ni-Zn alloys characterized by similar thermodynamic activities for Cu and annealed at 775 °C. One pair of couples exhibited intersecting diffusion paths, and the other pair showed overlapping path segments. They were analyzed for interdiffusion fluxes, zero-flux-planes, and ternary interdiffusion coefficients directly from the concentration profiles. The analysis was based on converting profiles of concentrations to profiles of interdiffusion fluxes and evaluating moments of interdiffusion fluxes for the determination of interdiffusion coefficients over selected composition ranges. For the pair with intersecting diffusion paths, ternary interdiffusion coefficients were determined from the individual couples in the region of their common composition; these coefficients were in agreement with each other and with those determined by the Boltzmann-Matano analysis. For the pair of couples with overlapping diffusion path segments, interdiffusion coefficients calculated from each couple over the common path segment agreed with each other. In addition, the interdiffusion coefficients calculated over various composition regions were used to regenerate the concentration profiles of the individual couples. All calculations were carried out with the aid of a computer program called MultiDiFlux, which was developed by Dayananda and Ram-Mohan as a free educational and research tool for analysis of multicomponent diffusion.