The mechanical properties of co-continuous Si3N4/Al composites manufactured by squeeze casting

The co-continuous Si3N4/Al composites with different Al contents were fabricated through the squeeze casting of porous Si3N4 preforms with varied porosities obtained by combination of pressureless sintering and carbothermal reduction. The effects of volume fraction of Al phase and the heat treatment temperature on the mechanical properties were investigated. When the volume percentage of Al increased from 24.13% to 70.23%, the Vickers hardness of the composite decreased from 762.33 to 175.09 Hv, the flexural strength decreased from 795.06 to 331.53 MPa and the fracture toughness increased from 3.66 to 11.52 MPa m1/2. The rod-like β-Si3N4 grains contributed to the fracture toughness of composites by pull-out, crack deflection and crack bridging. With an increase in the heat treatment temperature, the degree of interfacial reaction increased, the fracture modes changed from ductile intergranular fracture to brittle intergranular fracture.