Effect of Pressure on Anelastic Relaxation in Silver-Zinc

Using a novel experimental apparatus, studies have been made of the effect of hydrostatic pressure up to 9000 kg/${\mathrm{cm}}^2$ on the rate of stress relaxation at constant small strain in an Ag-30 atomic percent Zn alloy, where the relaxation process is presumably diffusion limited. For temperatures between 110°C and 150°C the relaxation time is found to increase exponentially with pressure. The zero-pressure data are in good agreement with previous work by Nowick. At 9000 kg/${\mathrm{cm}}^2$ the relaxation time is about a factor of four greater than at 1 kg/${\mathrm{cm}}^2$, for all temperatures. The pressure dependence can be interpreted in terms of an "activation volume" of 5.36±0.07 ${\mathrm{cm}}^3$/mole, which is about half the atomic volume of the material. This may mean that the volume of formation of a vacancy is at most about half of the molar volume, which number is in accordance with a recent calculation by Tewordt.