SUPERPLASTIC BEHAVIOR AND CAVITATION IN HIGH-STRAIN-RATE SUPERPLASTICSI3N4P AL-MG-SI COMPOSITES/

High-strain-rate superplastic behavior has been investigated for Si3N4 p/Al-Mg-Si (6061) composites with a V-f = 20 and 30 pct, respectively, where V-f is the volume fraction of reinforcements. A maximum elongat ion was attained at a temperature close to the onset temperature for m elting for both composites, The maximum elongation for the 30 vol pct composite was larger than that for the 20 vol pct composite. Developme nt of cavities transverse to the tensile direction is responsible for the lower maximum elongation of the 20 vol pct composite. However, dev elopment of the transverse cavities was limited to the optimum superpl astic temperature for the 30 vol pct composite. The differential scann ing calorimetry (DSC) investigation showed that a sharp endothermic pe ak appeared for the 30 vol pct composite, indicating that sufficient p artial melting occurs. It is, therefore, likely that the stress concen trations are sufficiently relaxed by a liquid phase and that the devel opment of transverse cavities is limited for the 30 vol pct composite.