Abstract
The pronounced stress drop or yield-point phenomenon that is observed in partially ordered Fe-Al alloys which contain approximately 25 at.% Al has been evaluated by means of elevated temperature, constant strain-rate tests. The magnitude of the effect is found to depend on the particular combination of strain rate and test temperature employed. No stress drop is observed when complete Fe 3Al order is present. However, a stress drop is observed whenever FeAl or partial Fe 3Al order is present; this corresponds to a temperature region where the flow stress is unusually sensitive to the strain rate. Transmission electron microscopy revealed that the stress drop at yield is associated with an initially low dislocation density and rapid dislocation multiplication. Consequently, the yield phenomenon is believed to be of the type first discussed by Gilman and Johnston wherein a stress drop is caused by rapid dislocation multiplication in a structure in which the dislocation velocity is relatively insensitive to the stress.
Published Version
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