Nanostructured Surface Modification of AISI 304 Stainless Steel by Laser Shock Peening Followed by Ultrasonic Impact Peening

Laser shock peening (LSP) combined with ultrasonic impact peening (UIP) was proposed both to improve surface roughness and enhance the subsurface grain refinement and residual stress values. In this study, the effects of the submerged LSP, multi-pin UIP, and LSP followed by UIP treatments on the surface characteristics of AISI 304 austenitic stainless steel were studied. The peened specimens were compared in terms of surface roughness/hardness, near-surface grain size, and residual stress. The nano-sized grains were formed on the surfaces in the combined LSP+UIP treated specimen were smaller than those of the LSP and UIP treated specimens. Compared to the untreated specimen (~22 HRC5), the surface hardness was increased by about 30%, 73%, and 78% after the LSP, UIP, and combined LSP+UIP treatments, respectively. The lowest surface roughness and highest compressive residual stress values were observed after combined LSP+UIP peening technique.