Strength retention in SiC ceramics after long-term oxidation

The room-temperature flexural strengths of SiC ceramics change with increasing oxidation time at 12000C. When certain impurities (e.g. alumina, WC, and possibly others) are present, the strength continuously decreases approx. = 50% after 4500 h because of subsurface pit formation. Materials containing B and C or Si exhibit strength increases (greater than or equal to 40% after 4500 h). Surface oxide growth rates substantially decrease at times greater than or equal to 1850 h, which corresponds to an increase in cristobalite formation. 7 references, 3 figures