Abstract
Abstract Fatigue, a common damage and failure mechanism in bulk metals, is largely unexplored for thin films. In the present paper, we report on the fatigue behavior of Cu films with thicknesses in the range 0.4–3.1 μm on deformable substrates. Films thicker than 1 μm seem to behave like bulk Cu and follow a Manson-Coffin relationship with a fatigue exponent and ductility of about 0.5 and 20 %, respectively. For the sub-micron thick films, a clear size effect is observed: the damage morphology changes and the lifetime increases signaficantly. Based on a microscopical damage analysis, the following sequence for the fatigue damage evolution in the Cu films is suggested: (i) in large grains, extrusions at the film surface and voids at the interface to the substrate are formed, (ii) cracks are nucleated at these voads and grow towards the film surface, and (iii) cracks connect intergranularly to form a continuous pattern of cracks and extrusions in the film. It is argued that void nucleation is the result of ...
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