The dissociation of a screw superdislocation in the B2 structure

Cross-slip of a dissociated 〈111〉 screw superdislocation in the absence of an applied stress is studied within the frame of anisotropic elasticity in model B2 crystals. Lattice friction is ignored. The superdislocation can either be coplanar, and then confined to either of the {110} and {112} habit planes, or dihedral. The stability of these configurations is governed by the values of one elasticity parameter named N, by the ratio z between the antiphase boundary (APB) energies on these planes, and by the cross-slip angle α. The different situations of interest are studied. By contrast to what occurs in L12 alloys, it is shown that besides two alternative planar configurations, one may encounter dihedral stable or metastable configurations which add to the variety of possible locking configurations in B2 alloys. The relative stability of these possible locking modes is discussed in details with respect to N and z, for the different cases of cross-slip. On etudie le glissement d'une superdislocation vis dans un alliage de type B2, en l'absence de contrainte appliquee et de frottement de reseau. La dislocation dissociee peut adopter soit une forme plane soit une forme de diedre. La stabilite de ces configurations depend de l'anisotropie elastique par l'intermediaire d'un seul parametre denomme N, du rapport z des energies d'antiphase sur les plans de dissociation, et de l'angle α, entre les plans du diedre. Differentes situations sont etudiees, ainsi que leur stabilite relative. Contrairement au cas des alliages L12, on peut trouver des configurations stables sous le forme de diedres donc sessiles.