Superplastic Flow of Two-Phase Ceramics Containing Rigid Inclusions-ZirconiaiMullite

A continuum theory for non-Newtonian flow of a two-phase composite containing rigid inclusions is presented. I t pre-dicts flow suppression by a factor of (1- V)p, where V is the volume fraction of the rigid inclusion and q depends on the stress exponent and the inclusion shape. Stress concentra-tions in the rigid inclusion have also been evaluated. As the stress exponent increases, flow suppression is more pro-nounced even though stress concentration is less severe. To test this theory, superplastic flow of zirconia/mullite com-posites, in which zirconia is a soft, non-Newtonian super-plastic matrix and mullite is a rigid phase of various size, shape, and amount, is studied. The continuum theory is found to describe the two-phase superplastic flow reasonably well. [Key words: flow, composites, mullite, zirconia.] I