Phenomenological coefficients for matter transport by the dumbbell mechanism in a concentrated f.c.c. alloy

Abstract

The phenomenological coefficients for matter transport are calculated for a model of transport by dilute dumbbell defects in a concentrated f.c.c. alloy of two components; the defects and substitutional atoms mix randomly and different binding energies for dumbbells of different atom compositions are allowed. The kinetic theory calculations use the same theoretical framework as in earlier studies of the Manning random alloy model for vacancy migration; terms of highest order in fluctuations in the occupancy variables for the substitutional atoms are neglected. The final expressions contain Brillouin zone integrals which are functions of the alloy composition and defect jump frequencies; these integrals must be calculated numerically for each thermodynamic state of interest. Moderate agreement with earlier Monte Carlo simulations is found when the ratio of largest to smallest jump frequency is 10 to 1. The difficulties in formulating a more accurate and self-consistent theory based on the kinetic equations, comparable with the Manning theory for vacancy transport, are indicated.