Deciphering the potentiodynamic polarization curves of iron aluminides Fe3Al and Fe3Al+Cr

The potentiodynamic polarization curves of Fe3Al and Fe3Al + Cr intermetallics obtained in aerated pH 4 H2SO4 acidic solution have been theoretically analyzed. The role of chromium in minimizing the hydrogen embrittlement (HE) of the intermetallic Fe, Al (resulting in its poor ductility) has been addressed based on the analysis. In the case of the chromium-alloyed iron aluminide, calculations indicate that hydrogen liberation does not occur on the surface due to the shift of the corrosion mixed potential to a value nobler than the electrode potential for the hydrogen evolution reaction. This shift occurs due to the induction of passivity on alloying with Cr resulting in the formation of a passive film. The minimization of HE of iron aluminides on alloying with Cr can thus be understood.