Thermal and thermomechanical effects on defect evolution in an Al-Li superplastic alloy

A commercial Al-Li alloy, in which the superplastic microstructure is devel oped by "strain-assisted continuous recrystallization" in early stages of h ow, was studied using positron annihilation lifetime spectroscopy. Results revealed that exposing the material to a temperature of 525 degrees C (opti mal temperature of superplastic deformation for this alloy) led to agglomer ation of single vacancies into vacancy clusters of size of approximately fo ur vacancies. Evidence for superplastic strain-induced cavitation was not f ound at 450 degrees C up to an elongation of 432% and at 525 degrees C up t o 341%, the initial strain rate of deformation in both cases being 1.0 x 10 (-3) s(-1). These results have practical significance.