Effect of heat treatment temperature on structure and mechanical properties of Si₃N_4p/Al composites

Si₃N_4p/Al composites prepared by squeeze casting were heat treated at 800-950°C. The phases, flexural strength, hardness, KIC and fracture morphology of the composites were tested and examined by XRD and SEM. The results indicate that 850°C is a critical temperature for heat treatment at which there occurs notable interface reaction between β-Si₃N₄ and aluminum, and hardness and strength of the composites significantly increases after heat treatment at temperature higher than 850°C, but its KIC decreases. Experiments of 45%vol Si₃N_4p/Al composites heat treated at 950°C show that the flexural strength, hardness, and KIC are 498MPa, 373HBS5/750, and 7MPa·m^1/2, respectively, indicating a good combination of strength and toughness. Transgranular cleavage of Si₃N₄ particles and ductile tearing of Al alloy matrix prevails, and debonding of Si₃N₄ particle/Al alloy interface is also observed in the composites.