Effect of cerium addition on the corrosion behaviour of carbon-alloyed iron aluminides

The effect of Ce addition on the microstructure and corrosion behavior of carbon-alloyed iron aluminides Fe–20.0Al–2.0C, Fe–18.5Al–3.6C and Fe–19.2Al–3.3C–0.07Ce (in at.%) has been studied. The potentiodynamic polarization behaviour of the alloys was evaluated in freely aerated 0.25 mol/l H2SO4. A 0.05% C steel was used for comparison purposes. All the alloys exhibited active–passive behaviour in the acidic solution. The addition of Ce destroyed passivity as indicated by lower breakdown potentials in polarization studies. This has been related to the finer distribution of the carbides in the microstructure. Corrosion rates were evaluated by immersion testing. The iron aluminide with Ce addition exhibited a lower corrosion rate compared to the aluminides without Ce addition. This has been attributed to modifications in surface film with Ce addition. Scanning electron microscopy of corroded surfaces indicated that the carbon-alloyed intermetallics were susceptible to localized galvanic corrosion due to the presence of carbides in the microstructure.