SUPERPLASTICITY IN ADVANCED MATERIALS

The ability to achieve a high tensile ductility in a polycrystalline m aterial is of interest both from a scientific point of view and also b ecause of potential applications in the materials forming industry. Th e superplasticity of conventional metallic alloys is now well-document ed and understood reasonably well. However, the field of superplastici ty has expanded recently beyond the traditional metallic alloys to inc lude evidence of superplastic-like behavior in a very wide range of ne w and advanced materials. To date, superplasticity has been reported i n mechanically alloyed metals, metal matrix composites, ceramics, cera mic matrix composites and intermetallic compounds. This review present s an overview of these new developments using the established behavior of conventional metallic alloys as a standard for comparison with the mechanical properties of these new materials. As will be demonstrated , the new materials often exhibit significant differences in their flo w characteristics in comparison with the traditional superplastic meta llic alloys. The successful utilization of superplastic materials in f orming applications requires an understanding of the failure processes occurring in the materials in terms of both the localization of exter nal flow and the accumulation of internal damage through the nucleatio n and growth of cavities. These problems are also addressed in this re view.