Activation volume for the creep of a superplastic Pb-Sn alloy evaluated by dynamic internal friction

Abstract

Abstract The dynamic internal friction (DIF) during constant-load creep of a Pb-62 wt% Sn eutectic alloy has been studied in the superplastic condition with steady-state creep rate in the range 10−6-10−4S−1. The activation volume V a evaluated from the data on DIF is of the same order of magnitude (10−27 m3) as that for superplastic deformation in constant-rate tensile tests on the same alloy. The activation volumes for superplastic deformation in both creep and tensile tests are found to decrease linearly with increase in stress. These results suggest that the grain boundary sliding in superplastic deformation of the Pb-Sn alloy is associated with the motion of grain-boundary ledges. The stress dependence of V a is possibly caused by the stress dependence of the microstructure of grain boundaries. A higher stress leads to a smaller size of ledges and microfacets, and hence a smaller V a.