Abstract
The high cycle fatigue (HCF) behavior of several Fe 3Al-type alloys was determined in the temperature range 25–600°C. Two types of order were created by heat treatment: D0 3-type by slow cooling, and B 2-type (off-stoichiometric) by water quenching. D0 3-type order was effective in prolonging high cycle fatigue lives in Fe-28.7%Al, but not in Fe-23.7%Al at 25°C. This difference was attributed to the presence of superlattice dislocations in the former. The fatigue resistance of D0 3 material was not as severely degraded at elevated temperatures as was that of B2 material. A substantial creep contribution to fatigue behavior was noted in tests on B2 material at 560 and 600°C. Fracture surfaces consisted primarily of transgranular cleavage facets in all alloys and conditions of order, but crack initiation was intergranular in unnotched Fe 3Al tested in HCF. Fatigue striations were observed only at 500°C. The results are discussed in terms of dislocation configurations and two-phase microstructures observed by transmission electron microscopy in certain alloys and test conditions.
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