Effect of SiC and TiC addition on microstructural and mechanical characteristics of microwave sintered ZrB2 based hybrid composites

The effects of SiC (20, 25, 30 vol %) and TiC (5, 10, 15 vol %) addition on microstructure, phase evolution, densification, and mechanical characteristics of microwave sintered ZrB2 based composites were investigated. The lattice parameters of secondary phases [(Zr, Ti)B2 and (Zr, Ti)C)] decreased with SiC and TiC addition. The analytically calculated residual stresses in the matrix and reinforcement phase were found to be tensile and compressive. The densification, microhardness, compression and flexural strength enhanced with SiC addition from 20 to 30 vol % in the ZrB2-5vol. % TiC composites. However, the fracture toughness decreased with SiC addition from 20 to 30 vol % due to larger SiC grain size and a higher degree of SiC interconnectivity in the composites. The mechanical characteristics further enhanced by the TiC addition from 5 to 15 vol % in the ZrB2 -25 SiC (vol. %) composites. The highest densification, microhardness, compression and flexural strength were observed for the ZrB2-25 SiC-10 TiC (vol. %) composite. Whereas the ZrB2-25 SiC-15 TiC (vol%) composite observed the highest fracture toughness due to higher compressive residual stress and prominent toughening mechanisms such as crack deflection, particles pull out and crack bridging.