Influences of the pre-oxidation time on the microstructure and flexural strength of monolithic B₄C ceramic and TiB₂-SiC/B₄C composite ceramic

B₄C is a structural ceramic, which is very sensitive to cracks and flaws. The present study aims to improve its mechanical performance using pre-oxidation process. The monolithic B₄C ceramic and TiB₂-SiC/B₄C (B₄C-TSC) composite ceramic were fabricated using spark plasma sintering technique, and they were pre-oxidized at 800 °C in the air. The effect of pre-oxidation time on microstructure and flexural strength was systematically investigated. The results indicated that 30 min was the optimum pre-oxidation time for both B₄C ceramic and B₄C-TSC ceramic. At this pre-oxidation time, the maximum flexural strength of 601.5 and 785.2 MPa were obtained for B₄C ceramic and B₄C-TSC ceramic, respectively. The improved flexural strength was primarily ascribed to the formation of glassy oxide layer during the pre-oxidation process and, in turn, the crack healing effect on the surface of the ceramics. Further increasing pre-oxidation time reduced flexural strength due to the pore formation induced by a large amount of CO gas and an intensive evaporation of B₂O₃ glass phase.