Formation mechanism of low valence oxide dominant defects in CoCrFeNiMn HEAs passive film: The regulatory effect of increasing V content

In this study, (CoCrFeNiMn) 100-x V x (x = 2, 4, 6, 8) high entropy alloys (HEAs) were prepared in a vacuum furnace. The effects of increasing V content on the corrosion behavior and passivation film of the HEAs in 3.5 wt% NaCl solution was investigated. Electrochemical test results indicate that the corrosion resistance of the HEAs improves with increasing V content, manifested as an expanded passivation range and a reduced defect density in the passivation film. Further analysis reveals that a higher V content promotes the formation of V₂O₅, which enhances the enrichment of protective Cr₂O₃ through external barrier effects and interfacial chemical environment regulation, while simultaneously reducing the proportion of loose Fe/Mn oxides. This optimizes the composition and structure of the passivation film. Moreover, point defect model (PDM) analysis shows that the introduction of V further suppresses point defect migration and elemental transport within the passivation film. The resulting synergistic effect improves the density and stability of the passivation film, ultimately enhancing the corrosion resistance of the HEAs in NaCl solution.