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 degrees 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 B38.22C6, B51.02C1.82) 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.