A MODEL FOR STRENGTH ANOMALY IN IVA-VIII B2 ORDERED INTERMETALLICS

The strength anomaly in IVa-VIII B2 ordered intermetallics is characte rized by compression tests. It is shown that CoTi, CoZr and CoHf displ ay 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 b e (001){110}. Also, TEM and HREM observations indicate that the (001) dislocation is not clearly dissociated into any superpartials but poss esses an asymmetric, non-compact core structure. As the mechanism resp onsible for the strength anomaly, it is proposed that the core configu ration of the (001) dislocation becomes sessile with help of temperatu re and applied stress. Finally, the observed strength anomaly operatin g at intermediate temperatures is discussed in correlation with the ph ase stability of B2 structure.