Synergistic enhancement of corrosion resistance in V-modified CoCrFeNiMn high entropy alloys: Mechanism of passivation film optimization and defect control

This study systematically investigates the effect of V content on the corrosion resistance and passivation behavior of (CoCrFeMnNi) 100-x V x (x = 2, 4, 6, 8) high-entropy alloys (HEAs) in 0.5 M H 2 SO 4 solution. Microstructural characterization revealed that all HEAs exhibit a primary FCC phase alongside a minor nano tetragonal phase. Electrochemical tests demonstrated that a significant enhancement in corrosion resistance with increasing V content. The improvement is attributed to the synergistic formation of a more protective and stable passivation film. XPS and ToF-SIMS analysis revealed that V promotes the enrichment of V 2 O 5 in the outer layer of the passivation film while simultaneously increasing the content of Cr 2 O 3 in the inner layer. This synergistic effect enhances the stability of film. Furthermore, the analysis results based on the PDM model and M − S test indicate that the improvement in corrosion resistance and passivation performance is consistent with the reduction in effective transport of cation vacancies in the passivation film, which inhibit defect aggregation and promote the formation of a thinner, denser, and more resistive passivation film. The formation of a double-layer structure passivation film can be influenced by a combination of factors, including selective dissolution, differences in element diffusion rates, and thermodynamic stability.