Dislocation structures in polycrystalline Ni3Al alloy doped with palladium deformed at room temperature were investigated by transmission electron microscopy. The structure consists mainly of dislocations dissociated into a/2<011> super partials bounding an antiphase boundary. Dislocations dissociated into a/3<112> Shockley super-partials bounding a superlattice intrinsic stacking fault were often observed. The majority of the superlattice intrinsic stacking faults were truncated loops, i.e. the partials bounding the superlattice intrinsic stacking faults had a similar Burgers vector. These faulted loops were generated from antiphase boundary coupled dislocations, according to a mechanism for formation of superlattice intrinsic stacking faults proposed by Suzuki et al. and recently modified by Chiba et al.. The antiphase boundary energies for {111} and {100} slip planes were measured to be 144 and 102mJ/m2, respectively, and the superlattice intrinsic stacking fault energy was estimated to be 12mJ/m2 in this alloy. It was concluded that the dislocation structure in Ni74.5Pd2Al23.5 alloy deformed at room temperature was similar to that in binary Ni3Al and the difference in fault energies between these two alloys was small. Thus, it seems unlikely that the enhancement of ductility of Ni74.5Pd2Al23.5 results from only such a small decrease of the ordering energy of the alloy. Superlattice intrinsic stacking fault bounding dislocations also have no apparent influence on the ductilization of Ni74.5Pd2Al23.5 alloy.

Dislocation Dissociations and Fault Energies in Ni3Al Alloys Doped with Palladium. Sun, J., Lee, C.S., Lai, J.K.L., Wu, J.S.: Intermetallics, 1999, 7[12], 1329-35. See also: Transactions of Nonferrous Metals Society of China, 1999, 9[1], 93-4 and Materials Letters, 1997, 31[1-2], 1-4 and Intermetallics, 1999, 7[12], 1329-35