A model for strength anomaly in IVa-VIII B2 ordered intermetallics

Abstract

The strength anomaly in IVa-VIII B2 ordered intermetallics is characterized by compression tests. It is shown that CoTi, CoZr and CoHf display the positive temperature dependence of yield stress at intermediate temperatures, whereas FeTi does not display this characteristic. The activated slip systems of these intermetallic compounds are shown to be ⟨001⟩{110}. Also, TEM and HREM observations indicate that the ⟨001⟩ dislocation is not clearly dissociated into any superpartials but possesses an asymmetric, non-compact core structure. As the mechanism responsible for the strength anomaly, it is proposed that the core configuration of the (001) dislocation becomes sessile with help of temperature and applied stress. Finally, the observed strength anomaly operating at intermediate temperatures is discussed in correlation with the phase stability of B2 structure.