Optimization Adhesion in Cold Spraying onto Hard Substrates: A Case Study for Brass Coatings

In state-of-the-art manufacturing of sliding bearings, brass components are soldered to respective parts, which is costly and energy intensive. Most bearings contained lead, which has to be omitted due to associated health risks. Cold spraying can be employed as additive manufacturing technique and allows to deposit the requested bearings in desired lead-free layout where needed. Aside from the coating strength and tribological behavior to be met as bearing material, 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 from grit impact conditions, surface topography on particle deformation and bonding in cold spraying. Through systematic tuning of blasting conditions, coating adhesion can be increased by approximately a factor of two, thus meeting the requirements for new lead-free bearings. For reference, nickel bond coats were investigated as alternative method to optimize the adhesion of cold-sprayed brass coatings. The results showed that the respective adhesion strength can exceed the optimized maximum adhesion strength by ideal surface roughness.