Anelastic Measurements of Atomic Mobility in Substitutional Solid Solutions

Abstract

A recently developed method for obtaining atomic mobility in solid solutions from the rate of anelastic relaxation makes possible the measurement of mobilities at temperatures far below those at which conventional diffusion experiments can be carried out. It is shown that the anelastic effects obtained in substitutional solid solutions are due to a phenomenon of stress-induced ordering and that the relaxation rate is determined primarily by the rate of movement of the slower atomic species. This method is applied to a series of silver-zinc solid solutions (silver rich) and the relaxation time measured as a function of temperature and concentration. The results show a slight deviation from an Arrhenius law, but a mean heat of activation may be obtained for each alloy concentration. Values for the heat of activation as a function of zinc concentration range from 36.1 kcal/mole at 15.8 atom percent zinc to 32.5 kcal/mole at 30.2 atom percent zinc. The entropy of activation, in each case, is positive and in reasonable agreement with Zener's "strain theory." A correlation of the magnitude of the anelastic effects for various specimens of the same composition with the rigidity modulus of these specimens, shows that the contribution to the torsional anelasticity from grains with $〈111〉$ direction close to the specimen axis is much larger than from grains aligned in the $〈100〉$ direction.