Atomic force microscopy and X-ray photoelectron spectroscopy study on the passive film for Type 316L stainless steel

The surface of Type 316L (UNS S31603) stainless steel (SS) passtve film formed in nitric acid (HNO3) solution was studied by x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results of immersion testing and electrochemical behavior of the samples in the corrosive media showed that the sensitivity of pitttng corrosion about the passive films: on Type 316L SS formed in passive solution was Largely Lower than that of the passive film formed in air, and the corrosion resistance was improved greatly. XPS analysis indicated that a stable mixture compound layer was formed. Ferric oxide hydroxyl (FeOOH) or ferric hydroxide (Fe[OH](3)) and chromic oxide hydroxyl (CrOOH) or chromic hydroxide (Cr[OH](3)) were in the outer Layer of the passive film, which could promote the repassivity of the passive film and enhance the corrosion resistance of samples. There existed oxides of Cr, Fe, and Ni in the different depths of the passive film that formed an effective barrier layer so that the SS could keep from attack the corrosive media effectively. The presence of Mo6+ and Mo4+ was found in the outer layer of the passive film. The surface morphologies of Type 316L SS samples before and after passivation treatment were observed with AFM. Results showed that the HNO3 passivation treatment could change the surface roughness of the samples, It was discussed that the smoothness of the surface on the passive films, played an important role in the Local corrosion of Type 316L SS.