FLEXURAL STRENGTH OF LAPPED AND OXIDIZED SILICONIZED SILICON-CARBIDE

A siliconized silicon carbide composite has been microstructurally characterized, oxidized in air at 1350-degrees-C for times up to 1079 h, air-cooled, and tested in four-point bending in the lapped condition at various temperatures up to 1425-degrees-C, and in the pre-oxidized condition at room temperature and at 1300-degrees-C. The strength of the lapped specimens increased by 25% at temperatures up to 1350-degrees-C. Oxidation always decreased the strength of the material. After 315 h oxidation, the strength at room temperature and 1300-degrees-C was reduced by 50% and 40%, respectively. Preferential oxidation of the inter-grain regions formed pits up to 50-mu-m deep. Hot salt corrosion increased the amount of oxidation by nearly 800%, and formed pits about 100-mu-m deep. Microstructural details of the oxidation and fracture processes are presented, and the possible mechanisms of failure discussed.