Effect of substrate surface roughness on properties of cold-sprayed copper coatings on SS316L steel

The development of thick pure copper coatings on SS316 substrates with desired properties for Tokamaks is still a challenging task. The solution to this task can help to fulfill the demanding requirements of in-vessel materials for plasma passivation. In the present work, the effect of substrate surface roughness on several properties of cold-sprayed copper coatings was investigated. Effect of post-heat-treatment on the properties of the developed coatings was also studied. The developed coatings were characterized using various techniques viz.; scanning electron microscopy/energy dispersive spectroscopy, X-ray diffraction, optical microscopy, microhardness, nanoindentation, electrical and thermal conductivity measurements, and density and porosity analyses. The novelty of the article includes in-situ micro-tensile testing of the developed coatings to understand their fracture mechanism, which showed multi-crack failure. Moreover, the cracks were found to be originating from the multi-splat boundary junctions, followed by growth along the splat boundaries. Additionally, gamma-rays and heavy-nuclei irradiation along with thermal cyclic exposure studies were also performed to elucidate the actual environmental performance of the coatings. The coatings developed on the mirror-finished surface were found to have better mechanical and physical properties as compared to the coatings developed on the rough substrate surface; prior as-well-as post-heat-treatment.