DISLOCATION DISSOCIATIONS AND FAULT ENERGIES IN Ni₃Al ALLOYS DOPED WITH PALLADIUM

Dislocation structures in polycrystalline Ni₃A1 alloy doped with palladium deformed at room temperature have been investigated by transmission electron microscopy. The structure consists mainly of dislocations dissociated into a/2⟨011⟩ super partials bounding an anti-phase boundary (APB). Dislocations dissociated into u/3⟨112⟩ super Shockley partials bounding a superlattice intrinsic stacking fault (SISF) are also common debris. The majority of the SISFs are truncated loops, i. e. the partials bounding the SISF are of similar Burgers vector. These faulted loops are generated from APB-coupIed dislocations, according to a mechanism for formation of SISFs proposed by Suzuki et al, and recently modified by Chiba et al. The APB energies for {111} and {010} slip planes are measured to be 144±20mJ/m² and 102 ±11 mj/m² respectively, and the SISF energy has been estimated to be 12mJ/m² in this alloy. It is concluded that the dislocation structure in Ni_74.5Pd₂A1_23.5 alloy deformed at room temperature is similar to that in binary Ni₃A1, and the difference in fault energies between these two alloys is small. Thus, it seems unlikely that the enhancement of ductility of Ni_74.5Pd₂A1_23.5 results from only such a small decrease of the ordering energy of the alloy. SISF bounding dislocations also have no apparent influence on the ductilization of Ni_74.5Pd₂A1_23.5 alloy.