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 creep properties was investigated. Creep tests were performed by 4-point bending for 100h at 1250-1350°C under 250-450MPa in air. Grain growth in the Si3N4 matrix was prevented by the dispersed SiC particles. The Si3N4 matrix grain size decreased with decreasing SiC particle size. Steady state creep strain rate ε increased with decreasing Si3N4 matrix grain size. Accordingly, the creep properties were not improved by the dispersed SiC particles. Stress exponents, n were 1.5-2.7. It was assumed that the creep deformation was controlled by grain boundary sliding accompanied by cavitation. Moreover, weight gains of Si3N4/SiC composite ceramics were larger than that of monolithic Si3N4 after creep tests. However, the bending strength of Si3N4/SiC slightly increased.
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