Fracture toughness of intermetallic compound particulate reinforced aluminum alloy die castings

The fracture toughness,K_max which dose not satisfy the requirement for the plane-strain, of aluminum alloy die castings reinforced with NiAI and Ni3Al, intermetallic compound, and SiC particles has been studied by 3 point bending tests in the temperature range from 20°C to 300°C. The K_max s were almost comparable in the materials investigated; the highest in unreinforced alloy, and then SiC-, Ni3Al- and NiAl-particulate reinforced one in the order. These appear to be attributed to the microscopic characteristics observed in the fracture surfaces and longitudinal cross-sections: (1) debond at matrix/particle interface and fracture of particles, (2) size and aspect ratio of particles, and (3) precipitates in the matrix. The_max decreased with an increase in particulate volume fraction because of decrease in the amount of plastic deformation in the matrix and damages associated with particles. The K_maxs in the reinforced alloys at 20°C were comparable to those at 200°C. The temperature dependencies of K_max appeared to be associated with those of 0.2% proof stress.