Adhesion of Cold Sprayed Brass Coatings for Lead-Free Bearings

Abstract

Abstract In state-of-the-art manufacturing of sliding bearings, brass components are soldered to respective parts, which is costly and energy-intensive. Furthermore, up to now most bearings still contain lead, which by EU regulations for new part has to be omitted due to associated health risks. Cold spraying can be employed as additive manufacturing technique and opens the perspective to deposit the requested bearings in desired leadfree layout where needed. Aside cohesion and tribological behaviour, sufficient adhesion of the coating is essential for applications. The present study aims to systematically elucidate the influence of surface roughness on adhesion. The surface roughness was adjusted by varying the grit blasting material, grit size, blast pressure, blast distance and substrate material with the aim to study influences by impact conditions, surface topography on particle deformation and bonding in cold spraying. The results show that the adhesion strength reaches a maximum for a certain roughness. The ideal surface roughness to ensure good adhesion of cold-sprayed coatings apparently depends on specific impact conditions related to the powder material strength but also on the substrate material strength and particle size distribution. By systematic tuning of blasting conditions, coating adhesion can be increased by about a factor of two, thus meeting the requirements for new lead-free bearings.