Bonding between aluminium and copper in cold spraying: Story of asymmetry

Abstract

The bonding mechanism in cold spraying is still a matter of some debate, which requires further investigation. In the present work, aluminium powder was cold sprayed onto a copper substrate and copper powder was cold sprayed onto an aluminium substrate using the same process gas and spray parameters. Separate experiments were performed to produce thick (∼400 μm) coatings and isolated particle impacts. Deposits were characterised using scanning electron microscopy and image analysis. The coating–substrate interfacial bonding was assessed via a method in which, following a short heat treatment at 400°C, intermetallics grow at the interface where metal to metal contact has been established. In addition, the bond strength values of deposits were determined using a standard pull-off test. It was found that the copper particles deposited onto an aluminium substrate resulted in significant substrate deformation, whereas aluminium particles caused minimal deformation of the copper substrate. Furthermore, the former displayed a higher degree of metallurgical bonding at the coating/substrate interface in comparison with the latter. These results suggest that the removal of oxide films from the surfaces was greater when copper was the material being sprayed rather than aluminium. The impact behaviour of the two materials and the removal of oxide due to deformation at high strain rate are discussed with the aid of the Johnson–Cook plasticity model.