Real-time evolution and characterization of passive films on individual ferrite and austenite phases of duplex stainless steel

The passive film growth process, the composition of passive films, and the electrochemical behavior of ferrite and austenite individual phases on the unbroken surface of 2205 duplex stainless steel (DSS) were investigated by scanning electron microscopy, energy dispersive spectrometry, Kelvin probe force microscopy, magnetic force microscopy, in situ electrochemical atomic force microscopy, and Auger electron spectroscopy depth analysis. The electrochemical characteristics of the α/γ individual phases on the unbroken 2205 DSS surface were similar. The distribution of elements resulted in an element gradient at α/γ phase boundaries with a 2–6-μm width. Three stages of passive film formation were defined: nucleation, rapid growth, and stable growth. An even distribution of alloying elements with a difference in the concentration of Fe and Cr in the barrier layer was observed in the two-layer passive film of α/γ individual phases on the intact 2205 DSS surface. The preferential dissolution occurring on DSS was also discussed.