Investigation on Microbiologically Influenced Corrosion Behavior of CrCoNi Medium-Entropy Alloy by Pseudomonas Aeruginosa

The CrCoNi medium-entropy alloy (MEA) has excellent strength and toughness, and can be used as the basis for the development of promising engineering alloys in the future. However, microbiologically influenced corrosion (MIC) of CrCoNi MEA has rarely been reported. Especially, pseudomonas aeruginosa (P. aeruginosa) is the typical bacteria associated with MIC, which is widely distributed in the ocean and soil. It can form biofilm on the surface of steel and accelerate the corrosion of carbon steels and stainless steels (SSs). In this study, the electrochemical experiments such as open current potential (OCP), linear polarization resistance (LPR), electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP) were used to investigate the MIC behavior of CrCoNi MEA caused by P. aeruginosa, in comparison with 316L SS. Surface analysis techniques such as FESEM and CLSM were used to observe the P. aeruginosa biofilm and pitting morphology on the coupon surface. The results show that P. aeruginosa could form an uneven biofilm on the surface of CrCoNi MEA coupons. The P. aeruginosa accelerated the corrosion rate of CrCoNi MEA, which was demonstrated by a negative shift of open circuit potential, a decrease of polarization resistance and charge transfer resistance, and an increase of corrosion current density in P. aeruginosa medium. The P. aeruginosa biofilm could destroy the passive film of the CrCoNi MEA coupons, which led to the maximum pit depth of the coupons exposed in P. aeruginosa medium (4.8 mu m) for 14 d much deeper than that in sterile medium (2.3 mu m). Compared with 316L SS, CrCoNi had higher open circuit potential, lower corrosion current density and corrosion rate, and higher repairability of passive film. Meanwhile, the maximum pit depth on the CrCoNi MEA coupons in P aeruginosa medium was shallower than that of 316L SS (5.8 mu m)