Adhesion strength of Cu splats on Cu and Steel substrates

Keywords: Cold spray; Copper splats; Splat adhesion testing, Surface roughness Abstract Significant work has been done to study bonding at metallic interfaces in cold sprayed materials. Most work has been carried out on a bulk level to assess bond strength of coatings. Few studies have focused on the bond strength at the particle level. This study employed a micromechanical splat adhesion test to measure the adhesion strength of copper splats to Cu and steel substrates with varying roughness. Using cold spray, commercially pure Cu particles were deposited onto mild steel and pure copper substrates. Spherical-shaped copper powders of particle size (38-53µm) were used. The substrates have different surface roughness ranging from ~20 nm for polished to ~300 nm for as received. Microstructural analysis was performed to reveal the deformation characteristics of the powder particles and to examine the failed interfaces after the scratch test. Adhesion strength of copper splats on mild steel substrate exhibited a slight variation as a function of the substrate roughness. However, Cu splats on Cu substrates showed more variation in adhesion strength with changes in substrate roughness. The results are discussed with respect to the bonding mechanisms, splat and substrate microstructure and their properties.