Mechanical properties of ceramic–metal composites by pressure infiltration of metal into porous ceramics

High-volume-fraction Si3N4–Al-based composites have been fabricated by high-pressure casting method. The effects of chemical composition of infiltrated Al alloys, microstructures of Si3N4 preforms, and test temperature on the mechanical properties were investigated. The maximum four-point bending strength and fracture toughness of the composites reached 924 and 8.2 MPa(m), respectively. Increasing sintering temperature above 1650 °C for Si3N4 preforms resulted in an enhancement of fracture toughness at the expense of degradation in flexural strength. However, an increase in sintering time for Si3N4 preforms at moderately sintering temperature yielded an improvement in both flexural strength and fracture toughness of the corresponding composites. Both flexural strength and fracture toughness decreased with increasing temperature and CIP pressure due to inhomogeneous distribution of Al phase and some defects introduced into the preforms during the casting process. The Si3N4–6061 Al composite exhibited the lowest strength, which may be attributed to the presence of porosities and interfacial reactions.