THE ROLE OF DEFORMATION LOCALIZATION IN SUPERPLASTIC FLOW

The model Zn-22%Al alloy is used to show superplastic deformation takes place when localized deformation bands separating the material volume into large grain conglomerates are formed and developed. The formation of these bands is due to the cooperative grain boundary sliding which can be stimulated by intragranular sliding. The number and shape of the bands, as well as their contribution to the total elongation (the technique of surface markers was used) depend on strain rate. The movement of grain in the specimen volume takes place by the mutual displacement and rotation of grain conglomerates. The data presented can serve as a basis for the development of general physical theory of superplasticity based on macroscopic and mezoscopic deformation.