The role of interfacial microstructure in the fracture of particulate reinforced metal matrix composites was examined in a cast Al2O3/AlCu composite, heat-treated to different aging conditions. It was found that the composite has a high plane strain fracture toughness in the peak-aged condition and the toughness decreases with decreasing yield strength following high temperature overaging of the composite. Interfacial studies have shown that the high fracture toughness is related to the beneficial role of a soft interfacial layer, which permits the ductility of the matrix to be fully realized during fracture. When such a compliant interfacial layer is removed, e.g. by extended overaging, a significant drop in fracture toughness was observed. Based on experimental observations and micromechanical modelling, it was shown that the variation of fracture toughness with aging condition is consistent with the transition of fracture mechanism from near-interface failure to interfacial failure.
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