Densification of in-situ toughened SiC-YAG composites

Densification, beta --> alpha phase transformation, elongated SiC grain growth and microstructure, and mechanical properties, especially toughness, of in-situ toughened SiC-YAG composites were investigated in detail. By using packing powders with same compositions as packed samples, the evaporation of Al2O3 was inhibited and full densification (>99% of theoretical density) of in-situ toughened SiC-YAG was achieved. The beta --> alpha phase transformation occurrs st 1950 degrees C, however, remained beta-SiC can be still found by XRD after post-heated at 2100 degrees C for 4h. The content of liquid phase and alpha-SiC seeds has no effect on the phase transformation rate. Following phase transformation and grain growth during post-heating, further densification of in-situ SiC-YAG continues' and the network microstructure consisting of elongated;SiC grains can be obtained. Finally, the SEPB fracture toughness achieved is near 7.0 MPa.m(1/2).