Evolution Of Surface Passive Film On Cu-bearing Stainless Steel And Its Effect On Antibacterial Property

Cu-bearing antibacterial stainless steel(SS)is a new type of structural and functional integration material,owning excellent properties of SS such as corrosion resistance,high toughness,conductivity and thermal conductivity.On this basis,it can inhibit the formation of bacterial biofilm and reduce the number of bacteria in the environment.It can avoid or effectively reduce both the bacterial infection in human body and the microbiologically influenced corrosion of SS.So it has a broad application prospects.However,the final application of Cu-bearing antibacterial SS still faces many problems and challenges.For the Cu-bearing antibacterial SS in different application environments,the improvement of antibacterial property requires a certain loss of corrosion resistance.Thus,the study in this thesis took the both electronic structure and composition of surface passive film,which are closely related to the corrosion resistance of SS,as the breakthrough point in order to better understand the mechanism of their effects on the antibacterial properties.The results can be used to optimize the composition design,heat treatment procedure and surface treatment process of Cu-bearing antibacterial SS.Firstly,a new antibacterial passivation treatment was developed to solve the inhibition effect of traditional passivation treatment on the antibacterial property of 316L-Cu SS.The results showed that 316L-Cu SS treated by antibacterial passivation behaved a long and effective antibacterial activity.Compared with 316L-Cu SS without passivation,the corrosion resistance of the passivated 316L-Cu SS was significantly improved.The increase of Cr2O3,Cr(OH)3 and CuO contents was the main reason for the improvement of pitting corrosion resistance.However Cu and CuO should be converted into Cu ions to play the antibacterial role,which resulted in a decrease of the uniform corrosion resistance of the surface passivation film.The new antibacterial passivation treatment showed excellent performance.In order to enlarge the application scope of medical 316L SS,and further clarify the effect of added Cu on the electronic structure and composition of the surface passive film.Thus the antibacterial property and corrosion resistance of medical 316L SS after antibacterial passivation treatment were studied.The results showed that that 316L SS treated by antibacterial passivation behaved stable and effective antibacterial activity.With extension of the passivation time,the antibacterial mechanism was changed from contact killing to ionic release killing.The pitting resistance of 316L SS after antibacterial passivation treatment was decreased compared with that of 316L SS after traditional nitric acid passivation.The excessive content of Cu led to the increase of NA and ND values in the surface passive film,which was reflected by the decrease of Rf value,accelerated the dissolution of passive film,and reduced the stability of passive film.A Cu-bearing 2205 duplex stainless steel(DSS)was developed to solve the problem of microbiologically influenced corrosion(MIC)of SS in the seawater treatment,oil platform,ship and other application environment.However,the antibacterial aging treatment could cause the formation of intermetallic phase in the matrix of SS,which resulted in an intensified corrosion of the material.Therefore,a solution treatment was conducted on the basis of adjusted composition and the analysis of thermodynamic calculation,which allowed formation of complete two-phases structure with ferrite(?-Fe)and austenite phase(?-Fe).Both the adjusted composition and the heat treatment of 2205-xCu DSS resluted in eliminating the contradiction between microbial corrosion resistance and corrosion resistance.The results showed that 2205-3Cu DSS after solution treatment at 1150 ? exhibited effective antibacterial property and obvious microbial corrosion resistance against Marinobacter salsuginis compared with 2205 DSS.The corrosion resistance of 2205-xCu DSS could affect the antibacterial property which was also directly related to the microbial corrosion resistance.The corrosion resistance of 2205-xCu DSS in the artificial seawater solution was analyzed to understand the reason for the improvement of microbial corrosion resistance.The nucleation mechanism,growth rate,electronic structure and composition for the surface passive film of 2205-3Cu DSS with excellent microbial corrosion resistance were studied and analyzed.The results showed that the nucleation mechanism was not changed by the addition of Cu,but the active sites of nucleation were decreased.With increase of the formation amount of pure Cu content on the surface,the growth rate of surface passive film was decreased.Therefore,the electronic structure of the surface passive film was affected by both nucleation mechanism and growth rate,and the sum of NA and ND values was increased accordingly.The change of characteristic parameters for the above passive film resulted in the decrease of uniform corrosion resistance of 2205-3Cu DSS,and accordingly the antibacterial property and microbial corrosion resistance were improved synchronously.The above research work solved the contradiction problem between antibacterial property and corrosion resistance for Cu-bearing SS applied in the medical field and marine engineering environment.The influence mechanism of Cu on the surface passive film characteristics,including the nucleation mechanism,growth rate,electronic structure and composition,and the effect of structure evolution of surface passive film on the antibacterial property and even the microbial corrosion resistance were proposed.The results of mechanism analysis laid a certain research foundation for further development and application of Cu-bearing antibacterial SS.