Pitting Corrosion Resistance of 316L Stainless Steel in Physiological and Marine Chloride Environment

Abstract

This experiment compares the pitting corrosion resistance of 316L stainless steel in two chloride environments, 3.5 wt.% NaCl, simulated seawater, and phosphate-buffered saline (PBS), which is a physiological medium, in potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Findings point to the conclusion that the PBS + NaCl solution is more violent with the passive film of the 316 L stainless steel. An experiment with potentiodynamic polarization indicated that this electrolyte had a lower pitting potential than sal-ammoniac and indicated that the electrolyte was more subject to the initiation of pits. EIS analysis confirms these results with the lowering of the charge transfer resistance and changed capacitive behavior, which was evidence of the formation of a thinner, less stable, and more defective passive film. Quantitative analysis of the electrochemical behavior was done through equivalent circuit models with a constant phase element (CPE). In general, the integrated electrochemical measures indicate that, despite the overall good corrosion performance of 316L stainless steel, the passive film is more prone to localized corrosion in compound chloride-rich environments, including physiological fluids. Such intuitions are essential in the choice of materials and determining the risk of corrosion in the engineering of marine structures and biomedical implants.