Tensile and fatigue properties as influenced by environment of a FeAl alloy prepared by mechanical alloying

Abstract
In this study some mechanical properties of a FeAl-based alloy prepared by mechanical alloying, the FeAl 40 grade 3 alloy, and the impact of environmental attack on these properties are investigated. In particular one question was to determine whether the enhanced room-ductility observed in ambient air at room temperature is intrinsic to this alloy or due to a lesser sensitivity to environmental effect. In this aim series of tensile tests have been conducted in vacuum and under various gaseous atmospheres. The results show that this alloy does exhibit an enhanced ductility in inert environments, presumably due to grain boundary strengthening induced by oxide dispersion. However this ductility is severely altered in moist atmospheres and this loss of ductility is proven to be related to a kind of hydrogen embrittlement. Finally fatigue crack growth testing are carried under the same environmental conditions. It is deduced that the near-threshold fatigue crack growth enhancement observed in air is merely due to an adsorption-assisted mechanism, and not related to a crack tip embrittlement by hydrogen released by water vapour dissociation and dragged during cyclic deformation.