PROCESSING, MECHANICAL-PROPERTIES, AND OXIDATION BEHAVIOR OF SILICON OXYNITRIDE CERAMICS

Silicon oxynitride ceramics were prepared by hot-pressing an equimolar Si3N4 + SiO2 mixture with 3 mol% CeO2. The Ce2O3/SiO2 ratio of intergranular phase (liquid phase) increased as the formation of Si2N2O proceeded. The intergranular liquid remained as a glass on cooling until the Ce2O3/SiO2 ratio exceeded a certain value, at which point the liquid crystallized. There were great differences in thermal and mechanical properties and oxidation behavior between the specimen containing intergranular glassy phase and the one containing intergranular crystalline phase (Ce5(SiO4)3N-Ce4.67(SiO4)3O). The specimen containing the intergranular glassy phase showed excellent high-temperature strength and oxidation resistance.