Grain boundary sliding model for superplastic deformation

Abstract

Comparison of the data for superplastic Pb–Sn eutectic with the existing theories on diffusion accommoda ted grain boundary sliding shows mixed agreement. In the superplastic region the observed deformation rates are about 102–103 times faster than Coble creep. In the present study, this discrepancy is resolved by a physically realistic three-dimensional grain rearrangement model for superplastic deformation. This model assumes that the ‘macroaccommodation’ during superplastic flow results in grain rearrangement due to grain boundary sliding and ‘microaccommodation’ at triple points is diffusional. The proposed model carries all the structural features of superplastic deformation and the constitutive equation predicts faster strain rates than the existing theories on diffusion accommodated grain boundary sliding. The model gives an activation energy equal to that for grain boundary diffusion. The model predicts the observed grain size dependence of the strain rate and also a threshold stress for superplastic flow.