Subcritical crack growth at bimaterial interfaces: Part II. microstructural effects on fracture resistance of metal/ceramic interfaces

The flexural peel technique was used to study the fracture resistance of two model A1₂O₃/A1 interfaces. The bimaterial interface was formed by bonding high-purity A1₂O₃ with molten Al-5 pct Cu alloy under pressure. The specimens were then heat treated so that the Al-Cu alloy reached peakaged and extended-overaged conditions. The fracture resistance curve was established for two interfaces with either the peak-aged or overaged Al alloy. The fracture resistance of the interface with the peak-aged Al-Cu alloy was higher in terms of both the initiation and peak toughness. While the peak toughness of the interface scaled with the yield strength of the metal, the initiation toughness differed by a factor of 8. The difference in the initiation toughness is discussed in terms of the disparity in the interfacial microstructure.