MOISTURE AND HYDROGEN-INDUCED EMBRITTLEMENT OF IRON ALUMINIDES

It is now apparent that Fe3Al and FeAl alloys with less than 40 at.% Al are intrinsically ductile. Brittleness is manifested only in environments providing ready access to hydrogen. Microstructure, alloy content and surface condition may alter somewhat the susceptibility to embrittlement by moisture or by hydrogen, but are key considerations in alloy design for toughness or ductility when aluminum content is within the Fe2Al-FeAl range. The susceptibility of iron aluminides to moisture and to hydrogen is a major factor hampering their development as structural alloys. Other properties which need to be improved include tensile strength and creep and impact resistance, but approaches to achieve improved strength properties must consider the susceptibility to the external environment. Development of alloys with less than 16% Al appears to be attractive for situations where reduced strength and oxidation resistance can be tolerated because of the insensitivity of these alloys to embrittlement. However, it must be realized that these alloys are not intermetallics.