Grain rolling as a mechanism of superplastic deformation

Abstract

Various deformation processes taking part in superplastic behaviour of fine-grain metallic as well as ceramic materials are critically reviewed. An essential feature of stable large plastic deformations seems to be grain boundary sliding accompanied by stress concentrations at the triple junctions. Grain rolling induced by the shear deformation of grain layers is discussed in detail as the deformation mode which meets the experimental observations of equiaxed grain shape and of strain rate sensitivity close to 0.5. In the limit case of small stresses, the model based on grain rolling turns into diffusional creep.