OBSERVATIONS OF DISLOCATIONS RELEVANT TO THE ANOMALOUS YIELD STRESS IN L1(2)-ALLOYS

Latest research of the anomalous positive temperature dependence of the yield stress in L1(2) ordered intermetallic compounds has been dominated by explanations for the very small sensitivity of the flow stress to strain-rate changes. The Paidar-Pope-Vitek model, which is based on the assumption of local cross-slip pinning, has been successful in accounting for the orientation dependence and the tension/compression asymmetry of the yield stress, but it has been shown to be inconsistent with the experimentally observed small strain-rate sensitivity, owing chiefly to the weakness of the locks assumed. In the new model by Hirsch mobile jogs on the cube plane extend the cross-slipped segment and further cross-slip steps lead to the pinning of superkinks joining adjacent cross-slipped screws. In the new model, bypass of the locked configurations involves several specific dislocation configurations, some of which have been observed in using transmission electron microscopy, including superkinks, edge dipoles, switched partials, and anti-phase domain boundary tubes attached to edge dipoles.