X-ray photoelectron spectroscopy and electrochemical investigation of the passive behavior of high-entropy FeCoCrNiMox alloys in sulfuric acid

The passive and electrochemical behaviors of FeCoCrNiMox high-entropy alloys in sulfuric acid were investigated by X-ray photoelectron spectroscopy and electrochemical methods. The passive film is a bilayer structure composed of an outer layer with a mixed Cr/Fe oxides and hydroxides, and an inner layer that contains a strong enrichment of Cr(III) species with higher Cr(ox)/Cr(hyd) ratio. The Cr/Mo ratio in the alloy determines the passive ability and the compositions of the passive film. Further, the protective capacity of the films depends on the compositions. Mo markedly impacts the polarization behavior of the FeCoCrNiMox alloys in sulfuric acid and the alloys with Mo have high corrosion resistance to chloride ion in a sulfuric acid environment. The correlation between passivation characteristics and electrochemical behavior has been clarified in the study.