On the yield stress anomaly in stoichiometric FeAl

A vacancy-hardening model has recently been proposed to explain the yield stress anomaly in FeAl (George and Baker, Philos. Mag. (1997) in press) in which the yield stress rise with increasing temperature at intermediate temperatures is associated with frictional drag of vacancies on dislocations, whereas its fall at high temperatures is ascribed to dislocation creep. One implication of the model is that the yield anomaly should be observable even in stoichiometric FeAl (where it has not yet been seen) by rapid straining. Here, we report on compression tests on both polycrystals and single crystals of stoichiometric FeAl as a function of temperature and strain rate, and show that this prediction was borne out, i.e. at a strain rate of 1.6 s−1 a yield peak was observed, whereas at a strain rate of 1×10−4 s−1 a slow decrease in yield stress was observed with increasing temperature.