Oxidation resistance of SiC ceramics sintered in the solid state or in the presence of a liquid phase

Abstract

The present paper reports on the oxidation resistance of liquid phase sintered SiC. The results are compared to the behavior shown by solid state sintered samples after oxidation under exactly the same conditions. The microstructural characteristics of the oxide scales formed on both kinds of SiC- ceramics are also reported. The specimens used for oxidation treatments were obtained in fully dense form through pressureless sintering or hipping at a temperature of 1,850 C in the case of liquid phase sintered SiC (LPSSC) and at 1,950 C for solid state sintered SiC (SSC). As expected SSC is more resistant to oxidation than LPSSC, mainly due to the crystallinity of the oxide product formed on the surface of the specimens and the absence of an intergranular phase in the as-sintered materials. LPSSC, containing YAG as intergranular phase, is more resistant to oxidation at low temperatures than the samples with additions of Y{sub 2}O{sub 3} and SiO{sub 2}. At higher temperatures however this tendency is reversed due to the massive formation of Y{sub 2}Si{sub 2}O{sub 7} that covers all the surface of the sample providing a better oxidation resistance than the glassy phases formed on the Y{sub 2}O{sub 3} and Al{sub 2}O{sub 3}more » containing samples.« less