MODEL FOR INTERFACE REACTION CONTROL IN SUPERPLASTIC DEFORMATION OF NONSTOICHIOMETRIC CERAMICS

Experiments on superplastic deformation of ceramics that are non-stoichiometric, or which may have interfaces of non-stoichiometric character, exhibit two properties that differ from those of stoichiometric ceramics: (a) they have high superplastic ductilities, indicating unusual resistance to interface cavitation; (b) their stress-strain-rate response has the appearance of a threshold stress. A model that is based upon the idea that interfaces in non-stoichiometric ceramics may harbor a space charge layer is presented as an explanation for the threshold stress. The fundamental origin of the space charge lies in the electronic structure of the interfaces in non-stoichiometric ceramics (which is poorly understood). If correct, these ideas highlight the importance of electrical effects in understanding the mechanisms that determine the mechanical properties of interfaces in structural ceramics.