Microstructural effects on cavitation, flow localization and fracture in superplastic metals

Cavitation is a major concern in parts fabricated by the superplastic forming process, partly because of the damage produced within the parts and also because of the possibility of flow localization and fracture during forming operation. Several micromechanical aspects of cavitation are critically examined here. When plasticity effects are minimal at low deformation rates diffusional cavity growth kinetics are appropriate, however within the dislocation plasticity regime as well as in the superplasticity regime, constrained diffusional and plasticity-induced growth have been proposed. Due to extensive grain boundary sliding and grain rotation effects in the superplastic regime, the behavior is considerably more complicated. Major impact of these phenomena on the degree of cavitation through their effects on cavity initiation and growth has been discussed. Dynamics of cavitation and its effect on strain localization leading to fracture have been examined. Strain localization and fracture are critically affected by microstructural evolution effects such as dynamic grain growth.