Decohesion behavior in copper–sapphire interface under mode I cyclic loading

Decohesion behavior of a CuAl2O3 (sapphire) interface has been studied under a mode I cyclic loading condition. Double cleavage drilled compressive (DCDC) specimens with a Cu layer thickness of 60 and 100 μm were used. The interface decohesion front was smooth without growth and coalescence of voids; this behavior was different from that observed under quasi-static monotonic loading of the same material. XPS analysis revealed that the decohesion occurred between the Cu–sapphire interface. The relationship between interface decohesion strain energy release rate range, ΔG∞, and the fatigue-interface crack propagation rate, da/dN  , was independent of the thickness of the Cu layer with the same threshold value of ΔG∞th≈3.4 J/m2. This Cu layer thickness independent interface decohesion behavior was explained by a small frontal plastic decohesion zone under cyclic loading.