An examination of the influence of strain rate on the stress anomaly in Fe3Al

The anomalous stress peak found at intermediate temperatures has been examined in Fe–25Al and Fe–28Al alloys by hardness testing over a wide range of temperatures, using a wide range of strain rates, and studying dislocation structures in samples both slowly cooled as well as rapidly quenched after deformation. The anomalous stress rise has been found to show little strain-rate dependence, while the stress peak temperature and the high-temperature range of falling stress has been shown to be highly strain-rate dependent. There is no clear change of dislocation structure as the yield stress increases, and the stress fall is sometimes associated with 〈111〉 superdislocations and other times with 〈100〉 dislocations, depending on the strain rate considered. Such 〈100〉 dislocations appear to be created as mobile 〈111〉 superdislocations of different Burgers vector react together, which happens more readily at higher temperatures and lower strain rates, and this probably affects work hardening behaviour and flow stress levels after yield, but not the yielding process itself. The absence of any clear evidence of a dislocation pinning process operating during deformation makes it difficult to determine the mechanisms responsible for the stress rise and then fall.