Superplasticity in ceramic and metal matrix composites and the role of grain size, segregation, interfaces, and second phase morphology

Structural ceramics and ceramic composites have been shown to exhibit superplasticity in recent times and this discovery has attracted tremendous interest. Although the number of ceramics that have been found to exhibit superplasticity is now quite large, there are considerable gaps in the understanding of the detailed requirements for superplasticity in ceramics. Additionally, superplastic behavior at very high strain rates (1 s^-1) in metallic-based materials is an area of increasing research. In this case, the phenomenon has been observed quite extensively in aluminum alloy-based metal matrix composites and mechanically alloyed aluminum- and nickel-based materials. Again, the details of the structural requirements of this phenomenon are not yet understood. In the present paper, experimental results on superplasticity in ceramic-based materials and on high strain rate behavior in metallic-based materials are presented. The roles of grain size, grain boundary and interface chemistry, and second phase morphology and compatibility with the matrix material will be emphasized. © 1993.