| Microstructure and fracture behavior of pressurelessly-sintered SiAlON-SiC composite containing different SiC contents was investigated using high-resolution electron microscopy(HREM) and micro-indentation fracture(MIF) technique. The SiAlON-6%SiC composite showed the highest Vickers hardness and fracture toughness. The composite contained nanometer-size SiC particles dispersed homogeneously both in SiAlON grains and at grain boundaries. The grain boundary were formed with a 1-2㎚ thick amorphous layer regardness of the SiC content. The interface between SiAlON and SiC embedded in the grain, however, were formed without any amorphous layer. The typical fracture mode of the monolithic SiAlON was intergranular. That is, cracks propagate along The SiAlON grain boundaries with amorphous layers. In SiAlON-6wt%SiC, mixed mode of intergranular and transgranular fracture was observed, which seems to be caused by the nanometer-size SiC distributed in the SiAlON grains. In SiAlON-12wt%SiC, cracks propagated more straight through the SiAlON grains with submicron-size SiC particles, and the typical fracture mode was transgranular. |
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