Electrochemical properties of Fe₂O₃-Cr ₂O₃ thin films and pitting behavior of Fe-Cr alloys in neutral NaCl solutions

Fe₂O₃-Cr₂O₃ thin films with various chromium cationic fractions, X_Cr, were prepared by ion-beam sputter deposition. The thinning rate of the films in 0-1M Cl -containing solutions with pH 0.2 - 8.0 was measured in-situ by using an automatic ellipsometer. The pitting behavior of vacuum induction melted Fe-Cr alloys with 10-30% Cr was also measured in IM Cl -containing solutions with pH 0.2 - 5.9. The composition of passive films on the alloys was analyzed by AES. Pit initiation sites were observed by SEM and analyzed by EPMA. The results showed pitting on the Fe-20Cr alloy in IM NaCl starts at Cr₂O₃ inclusions partly covered by sulfide. It is presumed that the X_Cr value of repassivation film formed inside a pit determines the repassivation of the pit through the suppression or no suppression of the reductive dissolution of the film.