Dynamic internal friction during the superplastic deformation of eutectic alloy samples with an average grain size of 6μ was measured using strain rates of 10-6 to 10-4/s. An expression was derived for the dynamic internal friction, and was used to deduce the activation volume at various strain rates. It was found that the activation volume remained almost constant with strain, for given test conditions, except at the beginning of deformation. The activation volume decreased with increasing strain rate or applied stress. The magnitude of the activation volume was of the order of 10-27m3. This implied that the elementary process of superplastic deformation was perhaps associated with the motion of grain-boundary steps or jogged dislocations along grain boundaries. The present results indicated that the dynamic internal friction technique was a useful tool for detecting microscopic processes of superplastic deformation.

Dynamic Internal-Friction Study of Superplastic Deformation in a Pb-Sn Alloy P.Zhang, Q.P.Kong, H.Zhou: Philosophical Magazine A, 1998, 77[2], 437-46