Microstructures and mechanical properties of spark plasma sintered Al-SiC composites containing high volume fraction of SiC

Al-SiC ceramic-matrix composites containing high volume fraction of SiC were synthesized by spark plasma sintering (SPS) technique with sintering temperatures ranging from 1500°C to 1800°C, a pressure of 50MPa, and a heating rate of 150°C/min, using Al and SiC powders. Microstructures and mechanical properties of the composites sintered at different temperatures were investigated. Results reveal that the Al-SiC composites synthesized by SPS process consist of Al, SiC, Si, and Al₄C₃ phases. The volume fraction of Al₄C₃ and Si phases in the composites were reduced remarkably with increasing the sintering temperature up to 1700°C. As a result, the composite sintered at 1800°C provides the optimal combination of dense microstructures and excellent properties, including the relative density of 99.6%, micro-hardness of 25.5GPa, bending strength of 451MPa, and fracture toughness of 6.05MPam^1/2. Compared with the monolithic SiC ceramics, both the bending strength and the fracture toughness of the composites are improved due to the dense microstructures, fine SiC grains, and infiltration of the molten Al into the interfaces of the SiC grains.