Atomic Mobility in a Cu-Al Alloy after Quenching and Neutron Irradiation

Abstract

A study of atomic mobility in a Cu-Al (17 atomic percent Al) solid solution is carried out by anelastic relaxation methods. Measurements are made under equilibrium conditions, after quenching, and after neutron irradiation. The results differ significantly in two ways from the quenching experiments of Kauffman and Koehler on pure gold. First, the ratio $\frac{J}{Q}$ (where $J$ is the activation energy for migration of the appropriate lattice defect, and $Q$ the activation energy for equilibrium atomic diffusion) is 0.6 in the present experiments and only 0.36 for the quenched gold. This difference in ratio corresponds to a difference of about two orders of magnitude in the vacancy concentration at the melting point. Second, in contrast to the behavior of the pure metal, the irradiated Cu-Al alloy shows no evidence for the annealing of point defects in the range of temperature in which quenching effects anneal out. It is therefore difficult to reconcile the present results with those on pure gold if one assumes that the same lattice defect is responsible for both. A survey of other quenching experiments and of measurements on the annealing of cold worked metals provides additional evidence for a defect for which $\frac{J}{Q}=0.5-0.6\mathrm{}$ in various metals. A tentative interpretation of existing data may be given in terms of the assumption that the low-mobility (high $\frac{J}{Q}$ defect is the single vacancy while the high-mobility defect is the divacancy.