The dynamic internal friction which occurred during the constant-load creep of a 38wt%Pb eutectic alloy was studied under superplastic conditions at steady-state creep rates of 10-6 to 10-4/s. The activation volume which was deduced from the data on dynamic internal friction was of the same order of magnitude (10-27m3) as that for superplastic deformation during constant-rate tensile tests. The activation volumes for superplastic deformation during both creep and tensile tests were found to decrease linearly with increasing stress. These results suggested that grain-boundary sliding during superplastic deformation was associated with the motion of grain-boundary ledges. The stress dependence of the activation volume was thought to be caused by the stress-dependence of the microstructure of the grain boundaries. A higher stress led to smaller ledges and micro-facets, and hence to a smaller activation volume.

Activation Volume for the Creep of a Superplastic Pb-Sn Alloy Evaluated by Dynamic Internal Friction. P.Zhang, Q.P.Kong: Philosophical Magazine A, 1999, 79[1], 1-8