Investigation of the electrochemical behaviour of Fe-28Mn-6Si-5Cr shape memory alloy in alkaline media

The electrochemical characterization of a Fe-28Mn-6Si-5Cr shape memory steel (SMS) has been conducted and the results compared with those obtained for a low carbon steel. Oxide films were generated in a highly alkaline medium and subsequently evaluated for stability under aggressive conditions, i.e. high chloride content and decreasing alkalinity. The films were artificially thickened using cyclic voltammetry (CV), providing a novel interpretation of the redox process involved, based on the composition of the steels. The film characterization was performed by X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). It was observed that the SMS film thickness was approximately twice that of carbon steel, perhaps due to its high Mn content. Conversely, the Mott-Schottky study suggested both films exhibited n-type semiconductor characteristics, with the film generated on the carbon steel being more defective. This could be a contributing factor to its increased sensitivity to pH decrease in the presence of chlorides. The morphology of the corroded surface was examined by scanning electron microscopy (SEM), which revealed the presence of abundant pits on SMS surface initiated around the MnS inclusions.