Pitting Susceptibility of Chromium Modified Passive Films of a B2-FeAl Intermetallic Alloy

The effect of chromium on the pitting corrosion resistance of an iron aluminide B2-FeAl alloy (40 at/o Al) has been evaluated in chloride borate solutions. Chromium was permanently incorporated into the passive film of FeAl by repetitive oxidation-reduction cycles from alkaline chromate solution. Although the Cr-modified passive FeAl surface was found to have a pitting behaviour comparable to that of stainless Fe-Cr steels containing Cr in the range 12-24 at/o, the XPS analysis showed that Cr enrichment within the passive film of FeAl was not as high suggesting that the protective properties of the film would be due to a synergistic effect between Cr and Al. The use of the Kirchheim model allowed to predict the ternary alloy composition in equilibrium with the Cr-modified modified passive film one.