Effects of Mn on the electrochemical corrosion and passivation behavior of CoFeNiMnCr high-entropy alloy system in H2SO4 solution

Abstract The present work investigates the influence of Mn on the electrochemical corrosion and passivation behaviors of CoFeNiMnCr high-entropy alloys in a 0.1 M H2SO4 solution. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) results showed that the addition of Mn caused a marked difference in the active dissolution regions and active-passive transition regions. It was deduced from EIS and the potential decay results that the alloyed Mn suppressed the passivation processes and increased the chemical dissolution rate of the passive films. By contrast, the alloyed Mn did not affect the protective properties of the passive films of the alloys. Surface analysis indicated that Mn addition had little influence on the composition and thickness of the passive films. Thus the passivation current densities and transpassive potentials of the CoFeNiMnCr high-entropy alloy remained almost unchanged with the addition of Mn.