Effects of carbon and silicon on microstructure and mechanical properties of pressureless sintered B4C/TiB2 composites

Abstract

B4C/TiB2 ceramic composites were fabricated by reinforcing carbon and silicon (10 wt.% total mass) with the help of pressureless sintering at 2150 °C. The influence of C and Si additives on the phase composition, microstructures and mechanical properties of B4C/TiB2 ceramic composites were investigated through the characterizations of XRD, SEM, BSEM and EDS. Compared to B4C/TiB2 ceramic composites without C-Si additives, coarsely plate-like SiC grains were formed in composites at a C: Si mass ratio ∼0:10. By increasing the C:Si mass ratio, the size of the plate-like SiC grains decreases, while the amount of plate-like SiC grains increases. When the C:Si mass ratio was 7:3, multilamellar graphite appeared on the B4C grain boundary. Moreover a large number of lamellar graphite grains appeared at a mass ratio of C:Si ∼10:0. Graphite reacted with B2O3 on the B4C grain boundary, and the sintered body shrank quickly. Due to the presence of lamellar graphite, the relative density of the sintered body significantly increased from 89.2% to 98.9%. The mechanical properties such as flexural strength ∼336 MPa (∼26.79% increment) and fracture toughness ∼ 5.11 MPam1/2 (∼21.19% increment) were significantly improved compared with the B4C/TiB2 ceramic composite.