Abstract
The surface of the tested specimens of high nickel-chromium non-magnetic alloy (type 304 austenitic stainless steel) was modified by advanced mechanical surface treatments. The aim of the study is to compare the effects of ultrasonic impact treatment, submerged laser shock peening, water jet cavitation peening, and water jet shot peening, on the surface morphology, microstructure, and corrosion properties of SS 304 alloy. The surface roughness and near-surface microhardness, hardening depth, and residual macrostresses were estimated and compared. The potentiodynamic polarization tests for corrosion measurement of the unpenned and ultrasonic impact treatment ultrasonic impact treatment, submerged laser shock peening, water jet cavitation peening, and water jet shot peening-processed specimens in 3.5% NaCl solution were performed. The results showed that the studied surface peening methods contribute to a significant reduction in grain size which leads to considerable hardening. At the same time, the change in corrosion behavior is dissimilar after the ultrasonic impact treatment, submerged laser shock peening, water jet cavitation peening, and water jet shot peening processing due to the formation of different phase composition and microrelief on the surface. The effects of the phase composition, grain size, and surface roughness on the corrosion behavior of mechanically treated surfaces of the SS 304 alloy were investigated. The water jet shot peening and multi-pin ultrasonic impact treatment processes provide the highest passivation ability of the studied samples owing to single nanoscale austenite formed in the top surface layer. The multi-pin ultrasonic impact treatment and water jet shot peening treatments are the most effective methods for improving the corrosion performance of the studied Fe-based alloy due to the formation of nanoscale grain structure and new surface texture with reduced roughness (Ra ≤ 2 µm).