Alloy development to minimize room temperature hydrogen embrittlement in iron aluminides

Abstract

Iron aluminides based on the stoichiometric compositions Fe 3Al and FeAl exhibit poor room temperature ductilities due to hydrogen embrittlement (HE). The presence of surface passive films reduces HE. Passivity-inducing elements Ti, Zr, V, Nb, Ta, Cr, Mo W, Si and Ni have been alloyed with Fe 3Al and these aluminides have been characterized for their thermomechanical and electrochemical behavior. All the alloying additions, except V, enhanced the passivity of the base intermetallic. The base Fe 3Al, Cr- and Ti-alloyed intermetallics could be rolled to 80% deformation at 1000 °C whereas the other alloyed intermetallics cracked during deformation processing. The Cr- and Ti-alloyed intermetallics exhibited significant room temperature ductilities. Microstructural studies of the alloyed intermetallics revealed that when the addition of passivity-inducing element results in the precipitation of brittle phases with Fe and Al, they crack during the processing operation. Cracks initiate from the precipitated brittle phases, propagate into the matrix and result in poor thermomechanical behavior. Therefore, the amount of passivity-inducing element addition should be kept below the solid solubility limit. This would enable the development of ductile iron aluminides. The addition of elements for irreversible hydrogen trapping and to prevent recrystallization is also discussed.