Effects of TiB₂ Particles on the Microstructure Evolution and Mechanical Properties of B₄C/TiB₂ Ceramic Composite

B₄C/TiB₂ ceramic composites reinforced with three size scales (average particle size: 7 μm, 500 nm, and 50 nm) of TiB₂ were prepared by using a pressureless sintering furnace at 2100 °C under Ar atmosphere for 60 min. The results demonstrated that during the sintering process, TiB₂ located on the boundaries between different B₄C grains could inhibit the grain growth which improved the mass transport mechanism and sintering driving force. A semi-coherent interface between B₄C and SiC was found, which is supposed to help to reduce the interface energy and obtain good mechanical properties of the B₄C/TiB₂ ceramic composite. On sample cooling from sintering temperature to room temperature, the residual tensile stress fields formed at the TiB₂ interfaces owning to the thermo-elastico properties mismatched, which might have contributed to increase the ability of the sample to resist crack propagation. The results showed that the relative density, Vickers hardness, and fracture toughness of the composite with 20 wt.% submicron and 10 wt.% nano-TiB₂ were significantly improved, which were 98.6%, 30.2 GPa, and 5.47 MPa·m^1/2, respectively.