INFLUENCE OF GRAIN-SIZE, FREE SILICON CONTENT AND TEMPERATURE ON THE STRENGTH AND TOUGHNESS OF REACTION-BONDED SILICON-CARBIDE

The flexural strength and fracture toughness (K(IC)) of reaction-bonde d silicon carbide (RBSC) made from alpha-SiC grains of 0.2 and 23.65 m um with a free Si content of 16.5 and 26% and 16.5 and 24%, respective ly, were measured from room temperature to 1370-degrees-C (1350-degree s-C in the case of K(IC)). The modulus of rupture (MOR) increased to 1 300-degrees-C, followed by a sharp decrease to 1370-degrees-C. The K(I C) increased with temperature, from room temperature to 1350-degrees-C . The RBSC made from 0.2-mum alpha-SiC grains was superior in MOR and K(IC) to that made from 23.65-mum alpha-SiC. The RBSCs with varying fr ee Si contents were made by varying the pressure and composition durin g fabrication, and were tested for room temperature MOR and K(IC), whi ch decreased linearly with volume per cent of free Si.