Diffusion composition path patterns in ternary systems

Abstract

A new viewpoint on the analysis of diffusion behavior in ternary systems is presented, in which the matrix of diffusion coefficients is replaced by the “relative penetration tendencies” of the three species. An approximate but physical approach is combined with a linear approximation description of concentration-penetration curves for individual species in diffusion couples. The approximation makes the calculation of the diffusion path and Kirkendall shift for a given ternary couple very simple and straightforward: this in turn facilitates the calculation of a complete pattern of composition paths and Kirkendall shifts on the Gibbs triangle for any given model of relative penetration tendencies of the components. The availability of such patterns makes it easy to recognize and model the relative penetration tendencies in systems for which the composition path pattern has been experimentally determined.

The approach is then successfully applied to generating relatively simple penetration tendency models which reproduce experimental composition path and Kirkendall shift patterns in Cu-Ni-Zn, Fe-Ni-Co, and Cu-Ag-Au.