The Difference between Activation Energies for the Layer Growth and Interdiffusion in an Intermediate Phase Formed in a Poly-Phase Diffusion Couple

Abstract

The purpose of this study was to account for the origin of the difference between activation energies for the layer growth and interdiffusion in an intermediate phase which was formed in a poly-phase diffusion couple. It was shown that this difference between the two activation energies seems to originate from the temperature dependence of the homogeneity range of the phase. Accordingly, the activation energy of the layer growth (Q_K²) is equal to a sum of the energy of the interdiffusion (Q_D) and that attributable to the temperature dependence of the homogeneity range of the phase (Q_g).
As a practical example, the energy difference for the β phase in an Al–Cu system was indicated quantitatively. For the β phase, Q_K² is 43.6 kcal/mol, Q_D is 27.8 kcal/mol, and Q_g is 18.3 kcal/mol. The sum of Q_D and Q_g is 46.1 kcal/mol, which coincides with Q_K² within the experimental accuracy.
It is also concluded that the activation energy for a layer growth does not coincide with that for an interdiffusion in the phase where the change in the concentration with temperature at that phase boundary is found.