Chemical Composition, Chemical States, and Resistance to Localized Corrosion of Passive Films on an Fe‐17%Cr Alloy

The resistance to pitting of an Fe‐17%Cr alloy in neutral chloride solution was studied, as a function of chloride concentration and of polarization time (aging), using combined electrochemical measurements and XPS analyses. Potentiodynamic experiments (at 1 V/h) show that pitting occurs at chloride concentrations above . Potentiostatic polarizations of the alloy in the passive region were performed in a chloride solution (pH 6), at +390 mV/SHE (in the passive region), for different times (5 min, 1 h, and 27 h). Prolonged polarization induces better protective properties of this film (lower residual current) and better resistance to pitting (higher pitting potential). XPS analyses of the passive films show that these properties are related to transformations of the passive layer with time. The increased pitting resistance observed is attributed to chromium enrichment in the passive layer and a thickening of the inner oxide layer of the passive film. Chloride ions are not incorporated in the oxide layer, but are present in the outer layer of hydroxide.