Combination of Laser Shock Peening with Cavitation, Shot and Ultrasonic Impact Hardening for Stainless Steels Surface Characteristics Improving

Abstract

This paper’s aims are to compare the effects of advanced mechanical surface treatments on the surface characteristics of AISI 304 austenitic stainless steel. The laser shock peening (LSP), combined with the water jet cavitation peening (WjCP), water jet shot peening (WjSP), and multi-pin ultrasonic impact peening (UIP), is applied to improve the surface quality and increase the hardness, hardening depth, and the compressive residual stress values in the near-surface layers. The laser shock processing is implemented using a sub-merged laser peening system with a wavelength of 1064 nm. The outcomes of the LSP treatment combined with other peening techniques in different se-quences (applied prior or post it) are studied. The experimental results show as compared to the combined LSP + WjCP and LSP + WjSP techniques, the combined LSP + UIP technique results in a lower surface roughness (Ra ∼ 0.15 µm) and higher surface macrohardness (∼ 39.0 HRC5) supported by nanoscale grain structure with grain size of 15–100 nm, which is observed by XRD and TEM analysis. The surface macrohardness is respectively increased by about 48%, 68%, and 80% after the combined WjCP + LSP, WjSP + LSP, and UIP + LSP techniques in comparison with the original sample (22.1 HRC5). All combined peening techniques lead to an increase in the residual stresses values as compared to the single LSP process, providing the hardening depth of about 1 mm.