SUPERPLASTICITY IN CERAMIC AND METAL-MATRIX COMPOSITES AND THE ROLE OF GRAIN-SIZE, SEGREGATION, INTERFACES, AND 2ND PHASE MORPHOLOGY

Structural ceramics and ceramic composites have been shown to exhibit superplasticity in recent times and this discovery has attracted treme ndous interest. Although the number of ceramics that have been found t o exhibit superplasticity is now quite large, there are considerable g aps in the understanding of the detailed requirements for superplastic ity in ceramics. Additionally, superplastic behavior at very high stra in rates (1 s-1) in metallic-based materials is an area of increasing research. In this case, the phenomenon has been observed quite extensi vely in aluminum alloy-based metal matrix composites and mechanically alloyed aluminum- and nickel-based materials. Again, the details of th e structural requirements of this phenomenon are not yet understood. I n the present paper, experimental results on superplasticity in cerami c-based materials and on high strain rate behavior in metallic-based m aterials are presented. The roles of grain size, grain boundary and in terface chemistry, and second phase morphology and compatibility with the matrix material will be emphasized.