Effect of HIP Treatment on the Fracture Strength of Reaction-Sintered SiC

Abstract

Three reaction-sintered silicon carbides (RS-SiC) with different free Si contents and different porosities were heat-treated at 1780°C for 2h in Ar under a pressure of 200MPa by hot isostatic pressing (HIP) and 0.1MPa by usual heat-treatment. The capsule-free HIP-treated specimen lost 4% free Si by evaporation and exhibited a strength of 130MPa, about 72% lower than that of the as-received specimen. Nevertheless, the capsule HIP-treated specimen was free from pores, and exhibited a strength of 346MPa, about 25% lower than that of the as-received specimen. The HIP-treatment of the Si-free specimen in a capsule did not change the strength. However, the strength of the Ar-heated (0.1MPa) specimen without free Si was 270MPa, 32% higher than that before Ar-heating, showing an increase of the bonding area between grains due to mass transport by surface diffusion and/or evaportion-condensation. For the HIP-treated specimen, the decrease in the strength of the specimen with free Si may be attributed to the decrease in the bonding area resulting from penetration of liquid Si into SiC grain boundaries at elevated temperature; the unchanged strength of porous specimens without free Si may be due to the constant bonding area between grains because of no mass transport by surface diffusion and/or evaporation-condensation.