Interdeffusion in the Co-Ni system-III. Intrinsic diffusion coefficients

Abstract

The intrinsic diffusion coefficients¯D _Co and¯D _Ni in the Co—Ni system have been calculated with the use of the interdiffusion coefficient values, concentration gradient data (Part I) and from the observed inert markers displacements (Part II). The Darken euqations [1] were used in these calculations and for comparison's sake an attempt was made to apply the Van Loo treatment as well [2, 3].

The experimental difficulties related to the determination of the diffusants concentration in the Kirkendall interface are discussed. A simple method had been worked out which enabled us to determine this concentration from the Darken equations, from inert markers velocity and from the penetration curves data.

The activation enthalpiesΔ¯ H _Co andΔ¯ H _Ni have been calculated from the temperature dependence of the intrinsic diffusion coefficients;Δ¯ H _Co values are slightly higher thanΔ¯ H _Co values. The magnitude of the observed Kirkendall effect has been analyzed and compared with the results obtained in some other binary FCC and BCC systems.