Adhesion control by shot peening assisted cold spray

Cold spraying of Al6061 shows great potential for multiple applications in the aerospace industry, in particular enabling new cost- and resource-efficient repair schemes. In addition to excellent cohesive properties, such repair-oriented cold spray deposits must ensure sufficiently high adhesion to the part or substrate. Despite dealing with the same materials in repair, low adhesion could be a problem by comparatively low surface deformability. Nitrogen as a process gas for cold spraying of high-strength Al6061 necessitates high process temperatures to reach sufficiently high particle velocities for forming bulk-like deposits. At associated high impact temperature, the particles behave rather soft during high-speed deformation. Thus, the material jets needed for bonding are not necessarily in contact with the substrate surface, which limits interfacial bonding between deposit and substrate and adhesion. For improving adhesion strength, this study investigates the use of shot peening to modify the initial bonding layer between deposit and substrate by facilitating surface deformation. For a variety of conditions, respective interface microstructures, as well as consequences for adhesion, are described. The analyses of high adhesive strengths also involve evaluating alternative, adhesive-free testing methods. In summary, the contribution should allow for suggesting new concepts in adhesion improvement and testing.