Observation of passive films on Fe–20Cr–xNi (x = 0, 10, 20 wt.%) alloys using TEM and Cs-corrected STEM–EELS

•The cross-sectional TEM samples of the alloys were prepared by DB-FIB milling.•The thickness of the passive film on each alloy was estimated to be 2.5–2.7 nm thick.•Ni signal was not detected in the passive film of Fe–20Cr–10Ni alloy.•The passive film in pH 8.5 borate buffer solution exhibits an amorphous structure.

The structure and composition of passive film formed on Fe–20Cr–xNi (x = 0, 10, 20 wt.%) alloys in deaerated pH 8.5 borate buffer solution was examined by transmission electron microscope and Cs-corrected scanning transmission electron microscope-electron energy loss spectroscopy. Thickness of the passive film on each alloy was measured to be 2.5–2.7 nm and the passive film was enriched with Cr. The passive film formed on the alloys exhibited an amorphous structure, as confirmed by the lack of diffraction contrast and by the fast Fourier transform images taken within a region of the passive film on each alloy.