Strength Retention in SiC Ceramics after Long‐Term Oxidation

The room‐temperature flexural strengths of Sic ceramics change with increasing oxidation time at 1200°C. When certain impurities (e.g. alumina, WC, and possibly others) are present, the strength continuously decreases ∼50% after 4500 h because of subsurface pit formation. Materials containing B and C or Si exhibit strength increases (≥240% after 4500 h). Surface oxide growth rates substantially decrease at times ≥1850 h, which corresponds to an increase in cristobalite formution.