Microstructure and mechanical properties of liquid-phase-sintered SiC with AlN and Y2O3 additions

Pressureless liquid-phase sintering of β-SiC with AlN and Y2O3 was investigated to improve its strength property at high temperatures. For the sintered SiC with 1 wt% Y2O3, the grain size decreased with an increase in the AlN addition up to 10 wt% and the aspect ratio of the grains increased up to 5 wt% AlN. The densified SiC with 10 wt% AlN and 1 wt% Y2O3 additions sintered at 2100 °C for 5 h had flexural strengths of 870 MPa at RT and 755 MPa at 1400 °C. This strength behavior is explained in terms of the microstructure being composed of fine plate-like grains interlocking with very few pores and with a high refractoriness of the grain boundary phase. The fracture toughness of the SiC decreased with increasing AlN addition.