Effect of sintering temperature on the mechanical properties and microstructures of pressureless-sintered B4C/SiC ceramic composite with carbon additive

Abstract

B4C/SiC (15 wt%) ceramic composite with 2 wt% carbon additive was fabricated via solid-phase pressureless sintering under an argon atmosphere for 60 min between 2100 °C and 2200 °C. The effects of the sintering temperature on the microstructure and mechanical properties of the B4C/SiC ceramic composites were studied in detail. The optimum values of the relative density, Vickers hardness, flexural strength, and fracture toughness of the B4C/SiC ceramic composite sintered at 2150 °C were 95.3%, 25.5 GPa, 296 MPa, and 2.81 MPa m1/2, respectively. The microstructural investigations revealed that when the sintering temperature increases from 2100 °C to 2150 °C, sintered necks begin to grow and the densification zone increases. With sintering temperatures above 2150 °C, the grains grow rapidly such that the pores are not eliminated, causing the formation of large closed pores and resulting in a decrease in the relative density and mechanical properties of the B4C/SiC ceramic composite. The plate-like and irregular SiC grains are uniformly dispersed in the B4C matrix to inhibit B4C grain growth. The interface between SiC and B4C is clean and narrow, and the clean boundary suggests strong binding, which contributes to the mechanical properties of the B4C/SiC ceramic composite. At 2150 °C, the C additive undergoes significant crystallisation, forming lamellar structures with high aspect ratios, thereby promoting the pores in the ceramic composite to be discharged to the outside through volume diffusion to obtain a denser sintered body. The interface between B4C and graphite is a semi-coherent interface that increases the flexural strength with a low defect concentration. The main toughening mechanisms of the B4C/SiC ceramic composite are crack deflection and crack branching around the SiC grains and crack bridging by SiC grains in the wake of the crack tip.