Influence of Heat Treatment on the Corrosion Behavior of Electrodeposited CoCrFeMnNi High-Entropy Alloy Thin Films

In this paper, we investigate what effects heat treatment can have on potentiodynamically electrodeposited high-entropy thin film (HEA) CoCrFeMnNi alloys. We focused our study on the corrosion resistance in synthetic seawater, corroborated with the structure and microstructure of these thin films. Thin films of HEA alloys were deposited on a copper foil substrate, using an electrolyte based on the organic system dimethyl-sulfoxide (DMSO-(CH3)2SO)-acetonitrile (AN-CH3CN) (in a volume ratio of 4:1), which contains LiClO4 as electrolyte support and chloride salts of CoCl2, CrCl3 × 6H2O, FeCl2 × 4H2O, MnCl2 × 4H2O and NiCl2 × 6H2O. Using MatCalc PC software, based on the CALPHAD method, the structure and characteristics of the HEA system were investigated, and thermodynamic and kinetic criteria were calculated. The modeling process generated in the body-centered-cubic (BCC) or face-centered-cubic (FCC) structures a series of optimal compositions that are appropriate to be used in anticorrosive and tribological applications in a marine environment. Electrochemical measurements were carried out in an aerated artificial seawater solution at ambient temperature. In the experimental media, HEA thin films proved to have good corrosion resistance and were even better than the copper substrate. Corrosion resistance was improved after heat treatment, as shown by polarization and EIS tests. The structure and microstructure of HEA thin films before and after corrosion in artificial seawater were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The XRD data showed no significant changes in the structure of HEA heat-treated thin films after the corrosion in saline media. The data obtained by polarization and ESI are supported by results from SEM-EDS. This complex study reveals that, for HEA thin films, heat treatment leads to an increase in corrosion resistance. So, this finding suggests that thermal annealing is an appropriate method for improving the corrosion performance of HEA thin films.