Abstract
Si3N4/SiC composite ceramics containing 20mass% dispersed SiC particles were fabricated by hot-pressing at 1800°C under 35MPa for 2h. SiC powders with average particle sizes of 0.03, 0.27, 0.60 and 1.20μm were used, and the influence of the SiC particle size on the microstructure and mechanical properties (3-point bending strength and fracture toughness values) was investigated. As a result, grain growth and α-β transformation in Si3N4 matrix were prevented by the dispersed SiC particles. The Si3N4 matrix grain size decreased with decreasing SiC particle size, and in Si3N4/SiC (0.03μm) and Si3N4/SiC (0.27μm), α-phase remained. The fracture toughness decreased with decreasing Si3N4 matrix grain size. Accordingly, the fracture toughness was not improved by the dispersed SiC particles. In Si3N4/SiC (0.03μm), the bending strength showed a maximum value of 1161MPa at room temperature and 950MPa at 1400°C. It is considered that the remarkable improvement in the strength of Si3N4/SiC (0.03μm) is attributed to fine grains of Si3N4 matrix. On the other hand, other composites showed almost the same strengths as monolithic Si3N4.
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