Cavitation and fracture in high strain rate superplastic Al alloy/Si 3 N 4(p) composites

Abstract

Constant stress tensile tests have been carried out and cavitation resulting from tensile superplastic flow has been examined using metallographic and densitometric techniques in high strain rate superplastic Al–Mg–Si/Si₃N_4(p) and Al–Cu–Mg/Si₃N_4(p) composites (where ‘p’ denotes particulate). The elongations to failure depended strongly on the applied stress, and the elongations decreased rapidly at high stresses within the range having the same stress exponent of 2. Cavities developed parallel to the tensile direction at low stresses, but perpendicular to the tensile direction at high stresses. The development of cavities perpendicular to the tensile direction is probably responsible for low elongations in the high stress range. The rates of increase of the cavity volume for the composites were much lower than that for a superplastic 7475 alloy. This can probably be attributed to the presence of a discontinuous liquid phase for the composites.

MST/3354