Fatigue Damage Behavior and Its Controlling Factor in Copper Films Bonded to Base Metal –Noting Displacement Field in Films and Resin Bonding Layer–

Abstract

As model specimens of surface film-bonded materials, pure copper films with the thickness of 100, 50, 30μm were bonded to the surface of steel base plate by epoxy resin bonding or by diffusion bonding. As a result of fracture surface observation for the fatigue crack initiation at the notch root, there was a tendency for the fracture surface morphology to show fracture with intergranular cracking for the epoxy-bonded copper film but shear type with transgranular cracking for the diffusion-bonded film, respectively. Moreover, many fatigue cracks with very few slips were caused only on the surface film at the multiple sites sufficiently away from the notch root on the epoxy-bonded films. In contrast, on the diffusion-bonded film, a fatigue crack with many slips was caused only at the notch root and propagated through the thickness including the base plate. Furthermore, some thin extrusion-like bulging could be observed partially along the fatigue crack on the epoxy-bonded film, while many pairs of “intrusion” and “extrusion” were observed predominantly at the slip band near the fatigue crack on the diffusion-bonded film as well as on the bulk metal specimens. The difference in fatigue damage behavior between the epoxy-bonded and diffusion-bonded films was discussed in terms of elastic displacement field propagated by wave into the films from the base plate subjected to cyclic deformation.