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

The oxidation behavior of reaction-bonded silicon carbide (RBSC) and the ef fect of oxidation on the room-temperature flexural strength of RBSC were in vestigated. Four different types of RBSC, each having various SiC particle- size distributions and free silicon contents, were exposed to air at 1300 d egrees 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 increas ed 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 oxidati on, the beneficial role of the oxide layer was negated by the cracks that w ere newly generated on the surface because of the thermal mismatch between the substrate and the silica layer. The amount of free silicon had a neglig ible effect on the strength retention of the specimens after the oxidation processes.