Effects of Heat Treatment in a Wet Hydrogen Atmosphere on the Reliability of Sintered α‐Silicon Carbide

Sintered α‐SiC was exposed, for times up to 2 h, to a flowing wet H₂ atmosphere (P_H2O= 1 × 10^‐4 MPa) at temperatures of 1300°, 1400°, and 1500°C. The effect of such conditions on the reliability of the ceramic was estimated by comparing the Weibull modulus of the groups of specimens, tested in four‐point flexure, before and after exposure. The Weibull modulus of as‐polished specimens was 6.7, indicating a wide variation in room‐temperature flexural strength. The Weibull modulus was increased to 14.2 by the heat treatment for 2 h in wet H₂ at 1400°C. The average strength was also improved from 347 to 446 MPa by such exposure. Heat treatment at 1300° and 1500°C also improved the reliability of the material, as indicated by increases in the Weibull modulus, but to less a degree than did exposure at 1400°C. The increases in reliability and average strength were attributed to the blunting of surface flaws by the formation of a thin SiO₂ layer on the sample surface.