Microstructure–mechanical properties relations in SiC–TiB2 composite

Abstract

Densification and mechanical properties (fracture toughness, flexural strength and hardness) of SiC–TiB2 composite were studied. Pressureless sintering experiments were carried out on samples containing 0–50vol% of TiB2 created by in situ reaction between TiO2, B4C and carbon. Al2O3 and Y2O3 were used as sintering additives to create liquid phase and promote densification at sintering temperature of 1940°C. The sintered samples were subsequently heat treated at 1970°C. It was found that the presence of TiB2 serves as an effective obstacle to SiC grain growth as well as crack propagation thus increasing both strength and fracture toughness of sintered SiC–TiB2 composite. The subsequent heat treatment of sintered samples promoted the elongation of SiC matrix and further improved mechanical properties of the composite. The best mechanical properties were measured in heat-treated samples containing 12–24vol% TiB2. The maximum flexural strength of ∼600MPa was obtained in samples with 12vol% TiB2 whereas the maximum fracture toughness of 6.6MPam1/2 was obtained in samples with 24vol% TiB2. Typical microstructures of samples with the mentioned volume fractions of TiB2 consist of TiB2 particles (<5μm) uniformly dispersed in a matrix of elongated SiC plates.