Chloride-Induced Localized Corrosion of Fe3Al-Type Iron Aluminides: Beneficial Effects of Cr And Mo Additions

Abstract

ABSTRACTIn this study, an acid-chloride electrolyte at pH = 4 (H2SO4) and containing 200 ppm Cl- was used to define the effects of Cr concentration (0–6 at.%) and Mo additions (0–2 at.%) on the aqueous corrosion behavior of iron aluminides containing 28 at.% Al. For the Fe-28Al composition, cyclic-anodic-polarization testing indicated passivation, but with a relatively low breakdown potential for pitting corrosion, and a protection potential lower than the open-circuit corrosion potential. Cr additions alone proved beneficial by continuously increasing the pitting potential. However, even at the highest Cr level, 6%, the protection potential was still lower than the corrosion potential, indicating that pitting could initiate after an incubation period. Mo additions were found to raise the protection potential, such that at 1 and 2% Mo levels (4 % Cr), it was higher than the corrosion potential, indicating significantly improved resistance to the initiation of localized corrosion. Immersion testing showed that the latter compositions remained passivated with no localized corrosion for a period of four months, at which point the tests were terminated. The overall results indicated that for satisfactory resistance to chlorideinduced localized corrosion, both higher Cr levels (4–6 at.%) and Mo additions (1–2 at.%) are desirable.