Electrodeposited CoFeNi Medium-Entropy Alloy Coating on a Copper Substrate from Chlorides Solution with Enhanced Corrosion Resistance

Medium-entropy alloys (MEAs) exhibit properties comparable or even superior to high-entropy alloys (HEAs). Due to their very good resistance in thermomechanical conditions and corrosive environments and unique electrical and magnetic properties, medium-entropy alloys are good candidates for coating applications. One of the most economically effective methods of producing metallic coatings is electrodeposition. In this work, the structure of an electrodeposited CoFeNi medium-entropy alloy coating on a copper substrate from a metal chlorides solution (FeCl2 ∙ 4H2O + CoCl2 ∙ 6H2O + NiCl2 ∙ 6H2O) with the addition of boric acid (H3BO3) was investigated. The coating was characterized by a nanocrystalline structure identified by transmission electron microscopy examination and X-ray diffraction methods. Based on XRD and TEM, the face-centered cubic (FCC) phase of the CoFeNi MEA coating was identified. The high corrosion resistance of the MEA coating in a 3.5% NaCl environment at 25 °C was confirmed by electrochemical tests.