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-bonded silicon carbide (RBSC) made from alpha-SiC grains of 0.2 and 23.65 mum with a free Si content of 16.5 and 26% and 16.5 and 24%, respectively, were measured from room temperature to 1370-degrees-C (1350-degrees-C in the case of K(IC)). The modulus of rupture (MOR) increased to 1300-degrees-C, followed by a sharp decrease to 1370-degrees-C. The K(IC) 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 free Si contents were made by varying the pressure and composition during fabrication, and were tested for room temperature MOR and K(IC), which decreased linearly with volume per cent of free Si.