Corrosion of carbon-alloyed iron aluminides

The corrosion behaviour of two carbon-alloyed intermetallics of composition Fe-28.1Al-2.1C and Fe-27.5Al-3.7C has been studied and compared with th:lt of binary intermetallics. Potentiodynamic polarization studies indicated t hat the intermetallics exhibited active-passive behaviour in an acidic solu tion of pH = 1, whereas they exhibited stable passivity in a buffer solutio n of pH 8.4. Corrosion rates were also obtained by immersion testing. The v ariation of corrosion rate as a function of time was similar for both the i ntermetallics. The variation in corrosion rate as a funct:ion of time has b een explained based on the observed potentiodynamic polarization behaviour. Scanning electron microscopy of corroded surfaces indicated that the carbo n-alloyed intermetallics were susceptible to galvanic corrosion, due to the presence of carbides.