Corrosion behavior and passivation property of CoCrFeNi HEA in a simulated seawater environment containing CO₃^2-/HCO₃^-

This work systematically studied the corrosion behavior and passivation property of CoCrFeNi high-entropy alloys (HEAs) in a simulated seawater environment. The results reveal that the addition of CO32-/HCO3- results in the secondary passivation of the HEA in NaCl solution, and secondary passivation film possesses higher dissolution rate in comparison with primary passive film. H+ ions ionized by HCO3- facilitate the charge transfer process, thin the thickness of passive film, and increase the disordered degree of the film. Moreover, the presence of HCO3- promotes the nucleation and growth of metastable pits, and enhances the pitting sensitivity. Furthermore, an increase in CO32- concentration accelerates the dissolution of passive film, weakens the compactness and protective performance of the film, and increases the probability that metastable pitting evolves into stable pitting, as well aggravates the corrosion of the HEA. In addition, the corrosion resistance of the HEA is diminished due to the formation of microgalvanic corrosion cells between matrix and inclusion. The selective dissolution of elements occurred in the HEA.