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

Abstract

B 4 C 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 B 4 C ceramic and TiB 2 -SiC/B 4 C (B 4 C-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 B 4 C ceramic and B 4 C-TSC ceramic. At this pre-oxidation time, the maximum flexural strength of 601.5 and 785.2 MPa were obtained for B 4 C ceramic and B 4 C-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 B 2 O 3 glass phase. • The monolithic B 4 C and TiB 2 -SiC/B 4 C ceramic were fabricated by spark plasma sintering followed by pre-oxidation at 800 °C. • The in-situ formed oxide glass (B 2 O 3 ) can effectively heal the cracks and flaws on the surfaces of the ceramics. • The flexural strength is 43% and 72% increase compared to the corresponding untreated ceramics at 800 °C for 30 min. • The optimum pre-oxidized time is about 30 min as the two kinds of ceramics are processed at 800 °C.