Marine Microbiologically Influenced Corrosion Resistance Of 2205 Duplex Stainless Steel By Supersonic Fine Particle Bombardment

Duplex stainless steel（DSS）is widely used in the marine engineering field due to its excellent corrosion resistance,but it still faces the threat of severe marine microbiologically influenced corrosion（MIC）in complex marine environments.Many studies have shown that high-energy bombardment technology can impart a dense and stable passivation film on the surface of the material,leading to higher surface residual compressive stress,which is beneficial to improve the corrosion resistance and offer the potential for inhibiting bacterial adhesion.Supersonic fine particle bombardment（SFPB）is a kind of high-energy bombardment technology which can deal with complex shapes and large-area structures as well as high bombardment efficiency.However,there are few studies on the corrosion resistance of SFPB treated stainless steel,especially MIC is rarely reported.In this study,2205 duplex stainless steel（2205 DSS）,a commonly used material for marine engineering,was modified by SFPB.The effects of SFPB treatment on the surface morphology,structure,hydrophobic properties and antibacterial properties of2205 DSS were comprehensively investigated.Based on the corrosion performance of2205 DSS in sterile and Pseudomonas aeruginosa（P.aeruginosa）inoculated medium,the effect of SFPB on the MIC of 2205 DSS was evaluated using electrochemical test technique.The results revealed that SFPB lightly increased the surface roughness of 2205DSS,but did not produce local defects such as microcracks.At the same time,the SFPB reduced the surface electron work function,increased the surface hardness,and improved the hydrophobic properties.Transmission electron microscopy image showed that there were a large number of dislocation entanglements in the near surface region,which was the main reason for the increase of residual compressive stress on the surface.The results of spread plate method and live/dead staining showed that SFPB significantly improved the antibacterial performance of 2205 DSS mainly due to the reduction of surface electron work function and the increase of residual compressive stress.The effects of P.aeruginosa on the microbiologically influenced corrosion behavior of 2205 DSS were studied by electrochemical testing techniques.The results showed that open circuit potential E_OCP,polarization resistance（R_p）,and charge transfer resistance(R_ct)measured in the sterile medium were larger than that in the P.aeruginosa inoculated medium during the whole soaking period of 7 d,indicating that P.aeruginosa accelerated the corrosion of 2205 DSS.The potentiodynamic polarization curve shows that the passive current density（i_p）of the 2205 DSS increases with the immersion time in both sterile and P.aeruginosa inoculated medium,but i_p in the bacterial solution was higher than that in the sterile medium at 1 d,3 d,and 7 d,which further proved that P.aeruginosa accelerated the corrosion process of 2205 DSS.Scanning electron microscopy（SEM）images showed that the amount of bacteria adhering to the surface gradually increased with the immersion time.After soaking for3 days,the bacteria on the sample aggregated to form small clusters.And the bacteria aggregated to form a bacterial biofilm after 7 days.The bacterial biofilm accelerates the pitting according to the size and depth of the corrosion pits,resulting in severe localized corrosion.X-ray photoelectron spectroscopy（XPS）results revealed that CrO₃formed on the 2205 DSS surface in P.aeruginosa inoculated medium,resulting in MIC pitting corrosion.The corrosion behavior of 2205 DSS in sterile and P.aeruginosa inoculated medium before and after SFPB was studied by electrochemical test.The short-term（24h）and long-term（14 d）electrochemical tests showed that the linear polarization resistance R_p and charge transfer resistance R_ct of SFPB 2205 DSS were higher than2205 DSS,indicating that SFPB improved the corrosion resistance of 2205 DSS.The polarization curve showed that the SFPB 2205 DSS had a smaller passive current density i_p and a higher pitting potential E_pit,further indicating that the SFPB improved the uniform corrosion resistance and pitting resistance of the 2205 DSS.The number of bacteria adhering to the SFPB 2205 DSS sample after polarization was significantly less than that 2205 DSS,implying that SFPB effectively reduced the MIC pitting due to bacterial adhesion.At the same time,large amount of dislocation entanglement in the near surface region of SFPB 2205 DSS lead to the enhancement of the surface residual compressive stress,which increased the activity of the passivation film and its repassivation ability,thus exhibiting better corrosion resistance.In summary,SFPB can effectively improve the marine MIC resistance of 2205DSS.Our work provides a new idea for MIC protection of marine engineering steel.