Cu-enhanced microbiological corrosion resistance of CoNiV medium-entropy alloy

Microbiologically influenced corrosion (MIC) critically compromises the integrity of metal structures. This study investigates the effect of copper on the MIC behavior of CoNiV-Cu_x medium-entropy alloys (MEAs) in Desulfovibrio vulgaris environments. In sterile medium, increasing Cu reduced the combined film and charge transfer resistance, whereas in inoculated medium, the trend reversed. After 360 h, CoNiV-Cu₁₀ MEA formed a protective oxide layer (δ_eff = 0.912 nm), three times thicker than CoNiV MEA. The corrosion current and passivation current were significantly lower in Cu-rich alloys under MIC. The apparently adverse effect of Cu in sterile conditions was associated with modifications in passive film defect chemistry and charge-transfer processes, whereas under MIC conditions, Cu addition enhanced passive film stability, suppressed microbial adhesion, and improved MIC resistance. These findings provide insight for designing Cu-alloyed MEAs with superior performance in MIC environments.