A comparative examination of superplastic flow and fracture in metals and ceramics

Although metals and ceramics can exhibit superplastic elongations to failure of >500%, there are significant differences in their mechanical behavior and fracture characteristics. The transition from superplastic to non-superplastic behavior at low stresses is sensitive to impurity content. However, with an increase in purity, while the transition is retarded to lower stresses in metals, the transition occurs at higher stress in ceramics. The cavitation behavior also appears to be different. While metallic alloys typically exhibit rounded small cavities suggesting quasi-equilibrium diffusion growth, ceramics display crack-like cavity profiles indicating surface diffusion controlled cavity growth.