SUPERPLASTICITY IN CERAMIC MATERIALS .1. THE OBSERVATION OF A SUPERPLASTIC PARTITION IN CERAMICS

Recent developments in the understanding of the mechanical behaviour o f ceramics assessed for superplastic deformation indicate that stoichi ometric 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 M anchester and elsewhere, a ''superplastic partition'' is observed in c eramics which corresponds to a direct relationship with stoichiometric changes and a related ''metallic'' behaviour in ceramics. These chang es in stoichiometry and the associated ''metallic'' behaviour can prov ide mechanisms for resistance to cavity nucleation and propagation, re spectively. When this observation is linked with the Gifkins core-mant le concept and the findings of Molt, Cottrell and Gilman on insulator- metal transitions, this yields an improved appreciation of the superpl astic partition in ceramics.