Dislocation dissociations and fault energies in Ni 3Al alloys doped with palladium

Abstract

Dislocation structures in polycrystalline Ni 3A1 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<0 1 1> super partials bounding an anti-phase boundary (APB). Dislocations dissociated into a/3<112> super Shockley partials bounding a superlattice intrinsic stacking fault (SISF) were often observed. 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-coupled dislocations, according to a mechanism for formation of SISFs proposed by Suzuki et al. (Suzuki K, Ichihara M, Takeuchi S. Acta Metall 1978;26:183) and recently modified by Chiba et al. (Chiba A, Hanada S. Philos Mag 1994;69:751). The APB energies for {111} and {100} slip planes are measured to be 144±20 and 102±11 mJ/m 2, respectively, and the SISF energy has been estimated to be 12 mJ/m 2 in this alloy. It is concluded that the dislocation structure in Ni 74.5Pd 2Al 23.5 alloy deformed at room temperature is similar to that in binary Ni 3Al and the difference in fault energies between these two alloys is small. Thus, it seems unlikely that the enhancement of ductility of Ni 74.5Pd 2Al 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 74.5Pd 2Al 23.5 alloy.