EFFECT OF HYDROGEN WATER ATMOSPHERES ON CORROSION AND FLEXURAL STRENGTH OF SINTERED ALPHA-SILICON CARBIDE

Sintered α‐SiC was exposed for 10 h to H2 containing various partial pressures of H2O (PH2O from 5×10−6 to 2×10−2 atm; 1 atm≅105 Pa) at 1300° and 1400°C. Weight loss, surface morphology, and room‐temperature flexural strength were strongly dependent on PH2O. The strength of the SiC was not significantly affected by exposure to dry H2 at a PH2O of 5×10−6 atm; and following exposure at PH2O >5×10−3 atm, the strength was even higher than that of the as‐received material. The increase in strength is thought to be the result of crack blunting associated with SiO2 formation at crack tips. However, after exposure in an intermediate range of water vapor pressures (1×10−5<PH2O <1×10−3 atm), significant decreases in strength were observed. At a PH2O of about 1×10−4 atm, the flexural strength decreased approximately 30% and 50% after exposure at 1300° and 1400°C, respectively. The decrease in strength is attributed to surface defects caused by corrosion in the form of grain‐boundary attack and the formation of pits. The rates of weight loss and microstructural changes on the exposed surfaces correlated well with the observed strength changes. Copyright © 1990, Wiley Blackwell. All rights reserved