Environment-sensitive fracture of iron aluminides under monotonic tensile loading

In the present study, the environmental sensitivity under tensile loading o f a high-performance Fe-40Al alloy prepared by mechanical alloying is inves tigated. Testing performed under various environmental conditions reveals a significant loss of ductility in the presence of a moist atmosphere withou t concomitant change in the stress-strain relationship and fracture mode. F urthermore, this embrittlement is essentially controlled by water vapor. In addition, it is shown that increasing the strain rate improves the final e longation in air up to the intrinsic ductility determined in an inert atmos phere. This embrittlement is attributed to the hydrogen released by the dis sociation of water vapor molecules and subsequently swept into the material by mobile dislocations. Tests were designed and carried out specifically t o assess the respective roles of exposure duration and straining in this pr ocess. Finally, a model is proposed to account for this phenomenon and the mechanisms are discussed.