Thermal shock behavior of pressureless liquid phase sintered SiC ceramics

The thermal shock behavior of pressureless liquid phase sintered (PLPS) SiC ceramics with Al2O3 and Y2O3 as sintering additives was investigated by using water quenching method with the temperature difference from 200 degrees C to 1400 degrees C. It was found the residual flexural strength of PLPS SiC dropped quickly to about 100 MPa when the temperature difference reached 600 degrees C due to the cracks induced by thermal stress. The residual flexural strength of the PLPS SiC increased when the temperature difference reached 1300 degrees C and 1400 degrees C due to the formation of SiO2 oxide layers, which acted as thermal barriers to reduce the thermal stress on the surface of the SiC ceramics. However, comparing the microstructure of specimens quenched at Delta T=1300 degrees C and 1400 degrees C, the slight decrease of residual flexural strength at Delta T= 1400 degrees C was due to the formation of large amount of through pores in the oxide layer, which was speculated to be the strength-limiting flaw above 1300 degrees C. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.