Dissolution and repair of passive film on Cu-bearing 304L stainless steels immersed in H2SO4 solution

The antibacterial Cu-bearing 304L stainless steel is a new kind of structural and functional integrated metal material. In this work, evolution behavior of passive film of different heat treated Cu-bearing 304L stainless steel immersed in 0.5?M H₂SO₄ solution was investigated by using electrochemical measurements, atomic force microscopy (AFM) observation and X-ray photoelectron spectroscopy (XPS) analysis. The results show that the solution and aging treated samples have the similar polarization behaviors. The passive film impedance experiences an initial decrease within 7?days followed by a subsequent increase, while the defect density of passive film presents the opposite trend. Meanwhile, the evolution of surface morphology and the estimated thickness of the passive film confirm that it experiences initial dissolution and follow-up repair. Furthermore, the Cr³⁺ content in passive film undergoes sequential reduction to increase, however the variation tendency of Cu²⁺ content is just opposite, indicating that the content variation of Cr and Cu in passive film reflects the competitive process of film dissolution and repair. In addition, compared with solution treated samples, aged samples have a bigger i_corr value and the rougher passive film. This indicates that the passive film of solution treated steel is more compact and stable.