Abstract
A commercial reaction-sintered silicon carbide (RS-SiC) was heat-treated at 1600°C in vacuum to remove the free Si, and the resulting SiC bulk with about 19% porosity was further heat-treated at 1600°-2000°C for 0.2-20h in vacuum of 0.65Pa. Although the second heat-treatment did not significantly change the porosity, grain growth and oxygen content in the porous RS-SiC, the heat-treatment at 1780°C for 2h increased the bending strength of the porous RS-SiC from 205MPa to 322MPa and caused the transition from intergranular to transgraular fracture. The strengthening effect may be attributed to the increased bonding area between grains due to evaporation-condensation and surface diffusion, and to relaxation of stress concentration due to the change in pore shape. However, the strength decreased by heat-treatment at 1780°C for 10h or 2000°C because of the decrease in the bonding area and the volume of SiC matrix due to the decomposition of the SiC in vacuum.
