Influence of strain rate on yield stress and stress anomaly in an alloy based on Fe3Al

Iron aluminides show an anomalous peak in yield stress at an intermediate temperature, as superdislocations of 〈111〉 Burgers vector are replaced by dislocations of Burgers vector 〈100〉. Changes in yield stress and in dislocation configurations as a function of test temperature have been examined while deforming over a wide range of strain rates in order to determine the mechanisms responsible for the stress anomaly. The mechanical testing data provide some information about the process leading to the anomalous hardening but it is difficult to deduce the mechanisms operating from this. TEM studies show 〈111〉 superdislocations in climbed configurations preceding the transition in Burgers vector, and this at lower temperatures for slower testing speeds. The evidence obtained seems to support the model of the locking of dislocation segments by a local climb process as responsible for the anomalous stress behaviour.