THERMODYNAMIC AND KINETIC-STUDY OF DIFFUSION PATHS IN THE SYSTEM CU-FE-NI

An understanding and modeling of diffusion paths in ternary systems re quires a combined thermodynamic and diffusion kinetic approach. The dr iving force for the intrinsic diffusion of each component is the gradi ent of the chemical potential (or activity) which can be calculated fr om the concentration profile if the thermodynamic properties of the sy stem are known. For studying the diffusion behavior in ternary metalli c systems, the Cu-Fe-Ni-system was chosen because of its experimental and thermodynamic simplicity. Concentration profiles and diffusion pat hs in single-phase areas and across an alpha/beta interface were studi ed experimentally at 1000 degrees C using the diffusion couple techniq ue. Coefficients for interdiffusion and tracer diffusion have been cal culated at the intersection points of two independent diffusion paths with a common composition. A concentration dependence for the tracer d iffusion coefficients for each component was calculated and found to b e consistent with the literature data in the binary Cu-Ni and Fe-Ni sy stems. The calculated vacancy flux in the couples was consistent with the experimentally observed marker shift.