The dislocation structure in L1₂ ordered alloy Ni₃Ge

Abstract

The dislocation structure in polycrystalline Ni₃Ge deformed at room temperature has been studied transmission electron microscopy. The structure consists mainly of screw 〈110〉 dislocations and superlattice intrinsic stacking fault (SISF)-coupled partial dislocations. A few dislocations are present as antiphase boundary (APB)-coupled partials. Two kinds of SISF partial dislocation are observed: SISF pairs with dissimilar Burgers vectors and SISF pairs with antiparallel Burgers vectors. The energies of the APBs on {111} and {001} planes have been estimated to be 169 and 148 mJ m⁻² respectively, and the SISF energy has been measured to be between 15 and 30 mJ m⁻². Dissimilar SISF partials appeared to be formed the dissociation of a segment of a segment of a perfect dislocation, confirming a mechanism for SISF formation first suggested by Pak, Saburi and Nenno in 1976. Anomalous yield stress behaviour in the low-temperature region (below room temperature) is attributed mainly to mechanism(s) based on SISF dissociation.