Electrochemical stability of laser shock peened 17-4 PH stainless steel

In this study influence of laser shock peening without protective coating (LSPwC) on electrochemical stability of 17-4 PH martensitic stainless steel was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. For this purpose room-temperature ISPwC was performed with laser pulses of 10 ns duration at two pulse densities (2500 and 6250 pulses cm(-2)). LSPwC increased the surface roughness to a maximum of 1.1 mu m, influenced by material-ablation during peening and the peened surfaces showed slight enhancement in oxidation. Corrosion behavior in 3.5% NaCl solution was found to be insignificantly influenced by peening induced surface roughness. On the peened surfaces due to melted/re-solidified layer no deleterious inclusions were found and thereby the charge transfer resistance was improved. Peening did not suppress the secondary delta-ferrite phase in the martensite matrix, which acted as strong pit initiators. Pitting corrosion occurred preferentially at the regions where delta-ferrite phase present both at unpeened and peened conditions. Morphology of the pits formed on peened conditions is discussed.