Effect of micro-shot peening on microstructure and fluoride-induced corrosion performance of AISI 904L superaustenitic stainless steel

Micro-shot peening (MSP), as an efficient surface engineering technique, is employed to create a severely deformed surface consisting of nanograins on AISI 904L alloy. The fluoride-induced corrosion performance of the micro-shot peened (MSPed) AISI 904L and its solution-annealed counterpart is comparatively investigated using electrochemical techniques, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses. Based on the DC and AC electrochemical measurements, MSPed AISI 904L exhibits a corrosion film with higher resistance and lower passivity current density at the expense of a higher initial corrosion rate. Both samples suffer corrosion in HF solution; however, the solution-annealed one shows deeper and larger localized attacks. The dense distribution of crystallographic defects on the MSPed sample significantly increases the diffusion of alloying elements to the corrosion front. The XPS results reveal that: (i) a corrosion film with a higher contribution of alloying elements (namely, Cr and Mo) is developed on the MSPed one, and more importantly, (ii) its corrosion film contains more oxide compounds and fewer fluorides and hydroxides. A physical model is suggested, and the protection mechanism induced by MSP is discussed.