Effect of post-sintering heat treatment on mechanical properties and microstructure of SiC–TiB2 composites

Dense SiC–TiB2 composites with 24 vol% TiB2 were fabricated by pressureless sintering at 1940 °C. Al2O3 and Y2O3 were used as sintering additives to create a liquid phase and promote densification. TiB2 was formed by an in situ reaction between TiO2, B4C and C. The sintered samples were subsequently heat-treated at temperatures ranging from 1850 °C to 2000 °C. The effect of temperature of post-sintering heat treatment on microstructure and mechanical properties of the SiC–TiB2 composite was presented. Heat treatment at 1970 °C considerably improved the strength and the fracture toughness of sintered samples while maintaining high density. The elongation of α-SiC grains during the heat treatment was found to be responsible for an increase in fracture toughness. The presence of liquid phase assisted the elongation of grains which, in turn, activated crack bridging and crack deflection toughening mechanisms. Maximum strength of 540 MPa was found to be the result of improved fracture toughness. Heat treatment at temperatures above 1970 °C led to a deterioration of mechanical properties.

Research highlights▶ Heat treatment improved fracture toughness and strength of SiC–TiB2 composite. ▶ The best mechanical properties were measured after the heat treatment at 1970  °C. ▶ Fracture toughness of the composite with 24 vol% TiB2 was 6.6 MPa m1/2.▶ Flexural strength was found to be 540 MPa. ▶ Improved mechanical properties were the result of elongation of SiC grains.