Investigation of Microstructural Features and Mechanical Characteristics of the Pressureless Sintered B4C/C(Graphite) Composites and the B4C-SiC-Si Composites Fabricated by the Silicon Infiltration Process

The B₄C/C(graphite) composites were fabricated by employing a pressureless sintering process. The pressureless sintered B₄C/C(graphite) composites exhibited extremely low mechanical characteristics. The liquid silicon infiltration technique was employed for enhancing the mechanical property of B₄C/C(graphite) composites. Since the porosity of the B₄C/C(graphite) composites was about 25-38%, the liquid silicon was able to infiltrate into the interior composites, thereby reacting with B₄C and graphite to generate silicon carbide. Thus, boron carbide, silicon carbide, and residual silicon were sintered together forming B₄C-SiC-Si composites. The pressureless sintered B₄C/C(graphite) composites were transformed into the B₄C-SiC-Si composites following the silicon infiltration process. This work comprises an investigation of the microstructure, phase composition, and mechanical characteristics of the pressureless sintered B₄C/C(graphite) composites and B₄C-SiC-Si composites. The XRD data demonstrated that the pressureless sintered bulks were composed of the B₄C phase and graphite phase. The pressureless sintered B₄C/C(graphite) composites exhibited a porous microstructure, an extremely low mechanical property, and low wear resistance. The XRD data of the B₄C-SiC-Si specimens showed that silicon infiltrated specimens comprised a B₄C phase, SiC phase, and residual Si. The B₄C-SiC-Si composites manifested a compact and homogenous microstructure. The mechanical property of the B₄C-SiC-Si composites was substantially enhanced in comparison to the pressureless sintered B₄C/C(graphite) composites. The density, relative density, fracture strength, fracture toughness, elastic modulus, and Vickers hardness of the B₄C-SiC-Si composites were notably enhanced as compared to the pressureless sintered B₄C/C(graphite) composites. The B₄C-SiC-Si composites also manifested outstanding resistance to wear as a consequence of silicon infiltration. The B₄C-SiC-Si composites demonstrated excellent wear resistance and superior mechanical characteristics.