Effect of marine Pseudoalteromonas sp. on the microstructure and corrosion behaviour of 2205 Duplex stainless steel

摘要

A new generation of Fe-based alloys, such as duplex stainless steels (DSS), has been applied in marine environment because of their high corrosion resistance. This property is attributed to the high alloy contents of chromium, nickel and molybdenum. When exposed to oxygen; these elements allow the formation of a passive film on the surface of alloys, protecting it from aggressive chemical species, such as chlorides in marine environments. However, these alloys suffer from localized corrosion like microbiologically influenced corrosion (MIC). Antony et al. studied the behaviour of 2205 duplex stainless steel in the presence of sulphate-reducing bacteria (SRB) and found that SRB can modify passive film and depolarize cathodic reactions. Also, it is reported the formation of a biofilm on the surface has an important influence on the initiation of localized corrosion; while there is no report about the effect of aerobic bacteria on the corrosion mechanism of these alloys. In this work, the effects of marine isolated bacterium Pseudoalteromonas sp. on the microstructure and corrosion behaviour of 2205 duplex stainless steel was investigated using electrochemical and surface analysis methods. This bacterium is an aerobic, Gram-negative which isolated from East Sea (China). Electrochemical studies showed that E_(OCP) shifted to a negative direction in the presence of bacteria, indicating the activation of the metal surface because of chloride ions and metabolic by-products. The corrosion current density increased and charge transfer resistance decreased in the presence of Pseudoalteromonas sp. by exposure time which confirmed the corrosivity of this bacterium on 2205 DSS. Anodic current density also greatly increased in the presence of the bacteria after 30 days and induced a localized attack on the metal surface. EDS results showed a high concentration of chloride ions in the biofilm structure and a decrease in Cr content beneath the biofilm layer and near cracks. Indeed, the adhesion of bacteria and the formation of the porous biofilm on the metal surface resulted in chloride ion accumulation on the metal surface and induced the localized corrosion. In addition, the process of bacterial attachment on the metal surfaces at different exposure times was studied by FESEM technique.