Cerium Conversion Coating for Corrosion Protection of Medium-Entropy Alloy

Abstract

It was found that Fe50Mn30Co10Cr10 medium entropy alloy (MEA) had superior mechanical properties higher than those of CoCrFeMnNi high entropy alloys (HEA). However, poor corrosion due to the higher manganese content is one of the main challenges restricting the further application of Fe50Mn30Co10Cr10 MEA. In order to improve the corrosion resistance of MEA, a new cerium chemical conversion coating based on a mixed solution of Ce(NO3)3．6H2O and H2O2 has been first proposed in this study. The electrochemical behavior of bare and coated samples was evaluated by using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). In addition, Field Emission Scanning Electron Microscope (FE-SEM), Transmission Electron Microscope (TEM), Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS) were utilized to characterize the microstructure and composition of the coatings. The preliminary results showed that, from the potentiodynamic curves, the corrosion potential increases and the corrosion current density decreases by one order of magnitude for Ce-coated sample. Also, the cerium conversion process improves the pitting potential of the Fe50Mn30Co10Cr10 MEA. The AES result revealed that the thickness of cerium conversion film formed on the surface of Fe50Mn30Co10Cr10 MEA is around 25 nm.