FORMATION OF SIC-Y4AL2O9 COMPOSITES

Composites were prepared from a beta-SiC powder and a mixture of Y2O3 and Al2O3 powders in a molar ratio (Y2O3/Al2O3) of 2/1. The sintering temperature of composites increased from 1825 to 1950-degrees-C with an increase in beta-SiC content from 30 to 60 wt%. The oxide matrix was Y4Al2O9 for the SiC content of 30, 40 and 60 wt% or a mixture of Y4Al2O9, Y2O3, and Al2O3 for 45-55 wt%. Bending strength and fracture toughness were 480+/-50 MPa and 4.1+/-0.5 MPa.m1/2, respectively. Vickers hardness, Young's modulus and thermal conductivity varied proportionately to the ratio of beta-SiC to the oxide, but the coefficient of thermal expansion was constant.