Superplasticity in ceramic materials .1. The observation of a ''superplastic partition'' in ceramics

Recent developments in the understanding of the mechanical behaviour of ceramics assessed for superplastic deformation indicate that stoichiometric changes at interfaces and an associated ''metallic'' behaviour can account for the superplastic behaviour in the absence of a grain boundary glassy phase. Based on the experimental work carried out in Manchester and elsewhere, a ''superplastic partition'' is observed in ceramics which corresponds to a direct relationship with stoichiometric changes and a related ''metallic'' behaviour in ceramics. These changes in stoichiometry and the associated ''metallic'' behaviour can provide mechanisms for resistance to cavity nucleation and propagation, respectively. When this observation is linked with the Gifkins core-mantle concept and the findings of Molt, Cottrell and Gilman on insulator-metal transitions, this yields an improved appreciation of the superplastic partition in ceramics.