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 h igh 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 sensiti vity exponent. This discrepancy is proposed to be associated with cavi tation behavior. In the composite, cavities preferentially initiate at the ends of particulate reinforcements and parallel to the applied st ress. These cavities subsequently grow, coalesce, and eventually led t o premature failure. Experimental results indicate that cavity growth is plasticity-controlled and can be described by a model proposed by S towell.