The yield stress and slip plane in Fe
3Al
0.8Si
0.2 having the critical ordering temperature of the B2-DO
3 transformation
Tc=1028 K were investigated at temperatures between 77 and 1100 K with respect to their dependence on temperature and orientation. A peak in the yield stress takes place at 880 K except in the crystal whose maximum resolved shear stress plane coincides with the twinning {112} plane. In the crystals which exhibit the peak in strength, the operative slip plane changes from {110} on which the antiphase boundary energy is lowest (below the peak temperature) to the maximum resolved shear stress plane (above the peak). The peak in strength is attributed to the Stoloff and Davies’ model based on the transition from superdislocations to imperfect dislocations below
Tc. In the crystal exhibiting no peak, the yield stress is remarkably higher than that in the crystals exhibiting a peak, at temperatures between 350 and 880 K, where the operative slip plane is the twinning {112}. The yielding is related to the generation of imperfect dislocations.
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