Mechanical properties and microstructure evolution of pressureless-sintered B₄C–SiC ceramic composite with CeO₂ additive

Boron carbide ceramic composites (B₄C)-silicon carbide (SiC) with the cerium oxide (CeO₂) additive, which was varied from 0 wt% to 9 wt%, were prepared by pressureless sintering at 2150 °C for 60 min. The effect of CeO₂ additive content on the microstructure and mechanical properties of the B₄C–SiC ceramic composites was investigated in detail. In-situ synthesised cerium hexaboride (CeB₆) was identified in the B₄C–SiC ceramic composites. B-rich transition zones (such as B_38.22C₆, B_51.02C_1.82) were formed between the B₄C and CeB₆ grains, which introduced local lattice distortion to increase the sintering driving force. The thermal conductivity coefficient of CeB₆ was higher than that of B₄C, which benefited the delivery of heat quantity and helped achieve a highly dense and uniform sintered body. When the CeO₂ additive was excessively increased (more than 5 wt%), the CeB₆ grains had a large grain size and exhibited an increase in the amount of generated carbon monoxide (CO) gas, which led to an increase in the porosity of the B₄C–SiC ceramic composites and decrease in the mechanical properties. The optimum values of the relative density, Vickers hardness, flexural strength, and fracture toughness of the B₄C–SiC ceramic composite with 5 wt% CeO₂ additive were 96.42%, 32.21 GPa, 380 MPa, and 4.32 MPa m^1/2, respectively.