Abstract
Si3N4/SiC composite ceramics which contained 20wt% dispersed SiC particles (0.03-1.20μm) and 8wt% Y2O3 as the sintering additive were fabricated by hot-pressing at 2073K under 35MPa for 2h.The influence ofpowder preparation on the microstructure and mechanical properties was investigated. The sintering materials which were prepared by mixing with distilled water and burning in air (W series) contained larger amounts of oxygen than those which were prepared by mixing with ethanol and without burning (E series). In comparing W and E of equal SiC particle size, in the Si3N4 matrix grain diameter of W was larger than that of E. Accordingly, the fracture toughness and the bending strength at room temperature of W increased and decreased, respectively. Furthermore, the observed grain boundary phases of E were Y20N4Si12O48 and Y2Si3N4O3, but W was Y20N4Si12O48 Only. It is estimated that Y20N4Si12O48 is lower softening temperature than Y2Si3N4O3. Therefore, compared to E, the strength of W which contained larger amounts of Y20N4Si12O48 decreased at high temperatures. In 2W and 2E which contained 0.03μm SiC particles, the bending strength showed a maximum value of 882MPa and 950MPa at 1673K, respectively. It is considered that the remarkable improvement in the strength of 2W and 2E are attributed to the fine grains of the Si3N4 matrix.
