Dissociated structure of superlattice dislocations in Ni 3Ga with the L1 2 structure

Abstract

Multiplied dislocations in Ni 3Ga single crystals with the Ll 2 structure have been studied by the weak-beam technique of transmission electron microscopy. Non-screw dislocations multiplied on {111} plane at low temperature are shown to be dissociated into two unit dislocations with b = a 2 〈llO〉 bounding the antiphase boundary on the {111} plane whose energy is estimated to be 110 ± 30mJ/m 2; whereas straight screw dislocations are found to have undergone a sessile transition by the Kear-Wilsdorf mechanism. Dislocations multiplied on {100} plane at high temperatures are widely dissociated, bounding the antiphase boundary on the {100} plane whose energy is 17 ± 5 mJ m 2. The energy criterion for the dissociation schemes of a superlattice dislocation on {111} plane in the LI 2 structure has been calculated based on the ísotropic elasticity theory of dislocations. The formation process of superlattice intrinsic stacking faults during deformation is also discussed.