Fig. 1. Experimental procedure and time stream for the different measurements.

Fig. 2. Microstructure characteristics for the ultra-thin 316L foil: (a) EBSD diffraction band contrast map, (b) inverse pole figure in direction Z (IPF Z) map, (c) grain size distribution, and (d) XRD pattern in comparison with the wrought 316L.

Fig. 3. Cross-section EBSD images (scale bar: 10 μm): (a) IPF Z map, (b) phase contrast map (red for austenite), (c) KAM map; and (d) SEM/EDX images showing oxide inclusions in the ultra-thin 316L foil.

Fig. 4. (a) Polarisation curves for the ultra-thin 316L foil, (b) comparison of corrosion potential and breakdown potential, and (c) corrosion current density with typical wrought 316L [42], [43], [44], [45], [46], [47].

Fig. 5. XPS spectra of O 1s for the passive film formed on (a) ultra-thin 316L foil and (b) wrought 316L after one-week exposure in 3.5 wt.% NaCl at pH 7, measured at various incident angles of the X-ray.

Fig. 6. Percentages of the O in oxides, hydroxides, and adsorbed H2O in the passive film formed on ultra-thin 316L foil and wrought 316L after one-week exposure in 3.5 wt.% NaCl at pH 7, measured at (a) 0° and (b) 60° incident angles, respectively.

Fig. 7. XPS spectra (a) Fe 2p3/2, (b) Cr 2p3/2, (c) Ni 2p3/2, and (d) Mo 3d5/2 of the natural passive film formed on the wrought 316L and the ultra-thin 316L foil after one-week exposure in 3.5 wt.% NaCl at pH 7, measured at a 0° incident angle. Percentages of the (e) oxidic components (ox?+?hyox) and (f) metallic layer for Fe, Cr, Ni, and Mo on the wrought 316L and the ultra-thin 316L foil.

Fig. 8. XPS spectra (a) Fe 2p3/2 and (b) Cr 2p3/2 of the passive film formed on the wrought 316L and the ultra-thin 316L foil after one-week exposure in 3.5 wt.% NaCl at pH 7, measured at a 60° incident angle. Percentages of the oxidic components (ox+hyox) for Fe and Cr on (c) the wrought 316L and (d) the ultra-thin 316L foil.

Fig. 9. (a) Angle dependence of the oxide content and the Cr and Fe components in the passive film, and (b) estimated thickness of the passive film on the wrought 316L and the ultra-thin 316L foil formed after one-week exposure in 3.5 wt.% NaCl at pH 7.

Fig. 10. (a) Bode plots for the ultra-thin 316L foil measured at OCP after 24 h of exposure in 3.5 wt.% NaCl at different pH values, (b) the evolution of Rp and Ceff from 1 to 24 h, and (c) the thicknesses of passive film calculated from the capacitance at various pH conditions.

Fig. 11. (a) Bode plots for the ultra-thin 316L foil measured after 24 h of polarisation at different potentials in 3.5 wt.% NaCl at pH 7, and (b) the evolution of Rct and Ceff from 1 to 24 h.

Fig. 12. (a) Mott-Schottky plots and (b) donor/acceptor density of the passive films formed on the ultra-thin 316L foil in 3.5 wt.% NaCl at different formation potentials and pH values, measured with the frequency of 100 Hz.

Fig. 13. ToF-SIMS depth profiles for the ultra-thin 316L foil: (a, b) as-received; and polarised at (c, d) 0.2 V and (e, f) 0.6 V at pH 7; and (g, h) polarised at 0.2 V at pH 2.

Fig. 14. Schematic diagram showing the evolution of the passive film on the surface of the ultra-thin 316L foil in chloride solution.