Surface strengthening of steel by high-velocity cold spray shot peening

Cold spray, conventionally a powder consolidation process to deposit materials, shares many attributes with the shot peening process that is used to strengthen metal surfaces. In the latter process, no material deposition occurs, but all particles (shots) bounce off upon impact, resulting in plastic deformation and residual compressive stress in the substrate material surface. It is possible to take advantage of the high particle impingement velocity (up to 2000 m/s) achieved by the cold spray equipment and use the process as a supersonic shot peening process to strengthen metal surfaces. In this work, cold spray shot peening was used to treat IF steel. Different impact materials (i.e., metal, ceramics) and numbers of impact passes were evaluated and the microstructure and hardness evolution in IF steel were analyzed. Based on the experimental results, the potential of cold spray shot peening to achieve surface nanocrystallization and properties enhancement in metallic materials is discussed.