Synthesis of α-SiC/α-SiAlON composites by spark plasma sintering: Phase formation and microstructures development

Abstract

α-SiC/α-SiAlON composites with 80 wt% α-SiC (6H phase) were fabricated by spark plasma sintering at 1800–2000 °C in a 0.6 atm nitrogen atmosphere. The effects of the temperatures on the phase development, microstructures and mechanical properties were investigated. The results showed the Si 3N 4, AlN, Al 2O 3, and Y 2O 3 particles were isolated by the 6H-SiC to prevent α-SiAlON formation at 1800 °C. The Si 3N 4 decomposed at 1900 °C and above, thus added Si in the phase compositions. The α-SiC grains grew anisotropic in the sintering liquids at 1800 °C and 1900 °C, forming the self-reinforcing microstructures, and accordingly increased the flexural strength and fracture toughness. In cooling down immediately after the temperature reached 2000 °C, a transitory hold at 1700 °C transformed the 6H-SiC into the 3C polytype in 30 s. The electric current was suspected of activating this polytype transformation.