The corrosion behavior of a high nitrogen face-centered-cubic (f.c.c.) phase (γ N ) formed on plasma-based low-energy nitrogen ion implanted AISI 304L austenitic stainless steel in a borate buffer solution with a pH value of 8.4 was investigated by using anodic polarization, electrochemical impedance spectroscopy, Mott-Schottky analysis and Auger electron spectroscopy/x-ray photoelectron spectroscopy. Compared with original austenitic stainless steel, the γ N phase layer on austenitic stainless steel possessed a significant improvement in corrosion resistance in the borate buffer solution with an apparent decrease of passivation current density and an increase of corrosion potential. A larger electrochemical impedance with a maximal phase angle of the 83 • over low frequency range was obtained for the γ N phase layer. The donor and acceptor densities of the γ N phase layer and the corresponding flat band potential decreased, relative to that of original austenitic stainless steel. The protective passive film on the γ N phase layer was observed as n-type and p-type semiconductors in the potential range above and below the flat band potential, respectively. It was composed of hydroxide/oxides of iron and chromium in the outer region and oxides of chromium and iron in the inner region both accompanied by chromium and iron nitrides, unlike original stainless steel which had pure iron and chromium on outermost surface. The calculated passive film thickness of 2.82 ± 0.67 nm on the γ N phase layer by the power law distribution was compared with the measured thickness of 6.5 nm by AES/XPS. The improvement mechanism of nitrogen atoms in the γ N phase layer on corrosion properties in the borate buffer solution was proposed by means of an applied point defect model.In order to improve combined properties in wear and corrosion resistance of Fe-Cr-Ni austenitic stainless steel, a series of nitrogenmodified processes has been successfully used to form the modified layer composed of a single high nitrogen face-centered-cubic (f.c.c.) phase (γ N ) with a peak nitrogen concentration up to 35 at.% on the austenitic stainless steel. 1 It was verified that the γ N phase layer on austenitic stainless steel has superior pitting corrosion resistance and equivalent general corrosion resistance in comparison with that of original austenitic stainless steel in NaCl, 2-14 and Na 2 SO 4 15 and H 2 SO 4 2,6,10,16,17 aqueous solutions. However, a few reports have described the corrosion resistance of the γ N phase layer on austenitic stainless steel in borate solution, 18,19 although different nitrogenmodified austenitic stainless steel has been made in an effort to increase hardness and wear resistance of austenitic stainless steel for use in nuclear power systems. 20 Moreover, corrosion fatigue cracking in borate solution is one of the typical failure types for Fe-Cr-Ni austenitic stainless steel applied in nuclear power equipment, which is always initiated by destruction and dissolution of the passive film on austenitic stainless steel. 2...

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