On the Passive Behavior of the Cantor Alloy in Acidic Environment

High-entropy alloys (HEA) consisting of five or more elements in equimolar or near-equimolar ratios, represent an emerging class of materials showing an exceptional combination of properties such as high strength and ductility, improved fatigue resistance, fracture toughness, and thermal stability. They show considerable potential for use as corrosion resistant alloys to support our infrastructure especially for use in extreme environments. The possibility of high corrosion resistance with single phase HEAs has been demonstrated but the absence of single primary element in the HEA makes the prediction of its corrosion resistance extremely difficult. EIS was originally developed as a tool for corrosion research and is well suited for the identification of complex mechanism involving adsorption intermediates, and 2D and 3D formation of thin films in the nanometer range. Additionally, EIS can be used for a comprehensive description of the passive film properties. This project focus on the well-defined Cantor alloy to studies its passivation in sulfuric acid solution with various chloride ions contents. EIS and linear wseep voltammetry have been used in order to describe the passive film formation as well as the passive film stability (Fig. 1). A specific attention has been paid in order to finely describe the passive film properties as a function of the applied potential and the chloride contents. In parallel, the resistance of the passive film was studied using the pumped-micropipette delivery/substrate collection (Pumped-MD/SC) mode of scanning electrochemical microscopy (SECM), which allows to generate a single pitting on the alloy and to study its initiation, propagation and repassivation as a function of the potential and the chloride ion concentration. This approach allows in particular to get rid of the stochastic aspect of the localized corrosion and to perform quantitative analysis of the exchanged charge during the single-pit propagation. Figure 1: Current potential curve and EIS diagrams measured at different potential for describing the passive film formation on Cantor alloy in chloride containing sulfuric acid solution. Figure 1