| The excellent corrosion resistance of duplex stainless steel(DSS)is due to the passive film on the surface of DSS.However,because of the co-existed ferrite(a)and austenite(y),there is a difference between the passive film of DSS and the passive film of the single-phase.Therefore,in-depth study of structure and composition,growth process and stability of the passive film on DSS and a/y single-phase,can provide theoretical support for the development of new corrosion-resistant steel.In this work,the dynamic polarization,Mott-Schottky and other electrochemical and photoelectrochemical methods combined with electrochemical atomic force microscopy(EC-AFM),angular resolution X-ray photoelectron spectroscopy(AR-XPS)and Auger electron spectroscopy(AES)depth analysis were used to study the growth process,semiconductor characteristics,micro-electrochemical reaction and compositional differences of the passive film on DSS and a/y single phase.The results show that the electronic structure of 2205 DSS passive film is mainly controlled by the oxidation and dissolution of Fe.The semiconductor characteristics are mainly determined by the competitive dissolution process of Fe and Cr,and the corrosion resistance of passivation film is mainly determined by the element distribution in the passive film.The effects of hydrogen on the stability and microstructure of the passive films on DSS were investigated by using AC electrochemical impedance spectroscopy(EIS)and point defect model(PDM)analysis combined with various hydrogen characterization methods.The results show that hydrogen reduces the stability and improves the pitting sensitivity of the passive films on DSS.Droplet-like or needle-like bubbles with microcracks is formed on a phase,hydrogen induced martensite transformation occurs in the y phase,a'-martensitic transformation leads to shear cracking,and ?-martensite transformation results in parallel cracks.The critical hydrogen charging conditions and critical hydrogen concentrations used to distinguish the two effects were also clarified.The Devanthan-Stachurski double cell was combined with an autoclave to simulate the hydrogen diffusion process in deep sea environment Based on Fick's second law and considering the factor of reversible hydrogen traps,parameters such as hydrogen diffusion coefficient,capture rate and escape rate were calculated.The effects of hydrogen traps on hydrogen diffusion process under different hydrostatic pressures were studied by COMSOL finite element simulation.The results show that the hydrostatic pressure mainly affects the hydrogen trap,which leads to an increase in the hydrogen concentration in the traps and a decrease in the apparent hydrogen diffusion coefficient.It is known that the hydrogen embrittlement sensitivity of the duplex stainless steel increases under deep sea conditions. |
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