A COMPARATIVE-STUDY OF SUPERPLASTICITY AND CAVITATION IN MECHANICALLY-ALLOYED IN9021 AND A SICP/IN9021 COMPOSITE

The superplastic properties and cavitation behavior of a mechanically-alloyed 15 vol.% SiCp/IN9021 composite and IN9021 alloy have been both investigated. Both materials exhibited superplasticity at extremely high strain rates (5-300 s(-1)) at 823 K. It was found that the optimum superplastic strain rate for the largest elongation does not coincide with the strain rate for the maximum value of the strain rate sensitivity exponent. This discrepancy is proposed to be associated with cavitation behavior. In the composite, cavities preferentially initiate at the ends of particulate reinforcements and parallel to the applied stress. These cavities subsequently grow, coalesce, and eventually led to premature failure. Experimental results indicate that cavity growth is plasticity-controlled and can be described by a model proposed by Stowell.