Effects of directly added or reaction formed TiB2 on the microstructure and mechanical properties of pressureless-sintered B4C–TiB2 composites

Abstract The boron carbide matrix composites containing boron carbide (B 4 C), titanium diboride (TiB 2 ; 20 wt% and 30 wt%) and titanium carbide (TiC) were fabricated at 2130 °C using the pressureless sintering method. Different amounts of TiB 2 and TiC particles were added to B 4 C, and the TiB 2 content was chosen as the main variable to study the effect on the composites. The density, hardness, bending strength and fracture toughness measurements were performed to obtain the physical and mechanical properties of the samples. The obtained results indicate that by adding 30 wt% TiB 2 submicron particles at 2130 °C, the bending strength and fracture toughness of 277.6 MPa and 5.38 MPa·m 1/2 are obtained for the composite. The particle pullout and crack microbridging play an effective role in toughening the composite ceramics. The main toughening mechanisms of the B 4 C-TiB 2 composites are noted to be microcrack and crack deflection toughening owing to the residual stresses resulting from the mismatch of the thermal expansion coefficient between TiB 2 and B 4 C.