In-situ fabrication of Al2O3–SiC nanocomposites using B2O3 as sintering aid

Al2O3–SiC nanocomposites with 5 and 10 vol% SiC have been in-situ fabricated by sol-gel method followed by carbothermal reduction of alumina–silica gel using B2O3 as sintering aid. Green bodies were formed by cold isostatic pressing of calcined gel, which was prepared by an aqueous sol-containing aluminum chloride, TEOS, sucrose and boric acid. Pressureless sintering was carried out in Ar–12%H2 atmosphere at 1700 °C. Addition of B2O3 (1 or 3 wt%) was an effective densification aid in the Al2O3–5 vol% SiC composites, while the densification of Al2O3–10 vol% SiC composites was not affected by adding B2O3. The composite material containing 5 vol% SiC doped with 3 wt% B2O3 reached 98.7% of full density. Nano-sized β-SiC particles were formed in-situ by means of a reaction between mullite and carbon at 1600 °C. Scanning electron microscopy revealed that the spherical in-situ synthesized SiC nanoparticles were well distributed through the composite and located predominantly to the interior of alumina matrix grains.