Time Dependent Debonding of Aluminum/Alumina Interfaces under Cyclic and Static Loading

The structural integrity of oxide/metal interfaces is important in many applications. While most attention has focused on the debonding of oxide/metal interfaces by conducting strength and fracture toughness tests, very few investigations have looked at time dependant failure of interfaces under cyclic or static loading. Tests have been conducted on sandwich specimens consisting of 5 - 100 micron thick aluminum layers bonded between either polycrystalline or single crystal Al₂O₃ to determine cyclic fatigue-crack growth, as well as static loaded moisture-assisted crack-growth, properties of Al/Al₂O₃ interfaces. Under cyclic loading, crack growth was observed to occur predominantly by interfacial debonding, but was also observed to make excursions into the Al₂O₃. Static loading in a moist environment also caused interfacial cracks to deviate into the Al₂O₃ or alternatively to arrest. Due to the poor crack growth resistance of the Al₂O₃, cracks leaving the interface grew at faster rates than those at the interface. Trends in crack trajectories and crack growth rates are explained in terms of the degree of plastic constraint in the aluminum layer, the modulus mismatch, and the effects of environmental mechanisms.