Effect of oxidation on the room-temperature flexural strength of reaction-bonded silicon carbides

Abstract

The oxidation behavior of reaction-bonded silicon carbide (RBSC) and the effect of oxidation on the room-temperature flexural strength of RBSC were investigated. Four different types of RBSC, each having various SiC particle-size distributions and free silicon contents, were exposed to air at 1300 degrees C for up to 200 h, Parabolic weight gains, with respect to oxidation time, were observed in all the specimens, The strength of the RBSC increased after oxidation for up to 50 h, because of the blunting of cracks by the silica layer that was formed on the surface. However, with further oxidation, the beneficial role of the oxide layer was negated by the cracks that were newly generated on the surface because of the thermal mismatch between the substrate and the silica layer. The amount of free silicon had a negligible effect on the strength retention of the specimens after the oxidation processes.