THE DISLOCATION-STRUCTURE IN L1(2) ORDERED ALLOY NI3GE

The dislocation structure in polycrystalline Ni3Ge deformed at room te mperature has been studied by transmission electron microscopy. The st ructure consists mainly of screw <110> dislocations and superlattice i ntrinsic stacking fault (SISF)-coupled partial dislocations. A few dis locations are present as antiphase boundary (APB)-coupled partials. Tw o kinds of SISF partial dislocation are observed: SISF pairs with diss imilar Burgers vectors and SISF pairs with antiparallel Burgers vector s. The energies of the APBs on {111} and {001} planes have been estima ted to be 169 and 148 mJ m-2 respectively, and the SISF energy has bee n measured to be between 15 and 30 mJ m-2. Dissimilar SISF partials ap peared to be formed by 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 beh aviour in the low-temperature region (below room temperature) is attri buted mainly to mechanism(s) based on SISF dissociation.