Corrosion behavior of CoCrNi/mild steel medium entropy alloy thin films

CoCrNi is a prototypical medium entropy alloy (MEA) with superior mechanical properties along with outstanding oxidation and corrosion resistance. However, and despite extensive work on the metallurgical and mechanical properties of this alloy in the bulk form, there is limited work dedicated to the investigation of the corrosion behavior in thin-film form. In this work, equiatomic CoCrNi MEA thin films were fabricated by direct current (DC) magnetron sputtering. The polycrystalline thin films, 225–600 nm thickness range, were deposited on mild steel substrates and the corrosion characteristics were investigated in 3.5 wt% NaCl solution. The corrosion rates were determined for CoCrNi in both, bulk and thin-film form. The surface morphology and composition of the films were investigated after the corrosion experiments using scanning electron microscopy (SEM), confocal microscopy, and energy dispersive spectroscopy (EDS). The highest value of corrosion potential (Ecorr) was − 477.31 mV, while the lowest current density (Icorr) has a value of 0.0025 mA/cm2. At relatively small thicknesses, the CoCrNi films result in significant improvement in corrosion resistance, and the highest efficiency achieved relative to the mild steel was 94.79%. The deposited films could offer considerable enhancement to the performance of widely utilized mild steel.