It was noted that variations in planar fault energies that were caused by changes in alloy composition could affect the thermally activated processes that governed plasticity in intermetallic alloys. Here, layered Korringa-Kohn-Rostoker coherent potential approximation calculations were performed for superlattice intrinsic stacking fault and antiphase boundary energies in binary and ternary alloys. The planar fault energies were calculated for alloys of the form, (Ti1-xAlx)1-yMy, where x was between 0.48 and 0.51, y was between 0 and 0.02, and M was Cr or Nb. In the case of Ti-rich alloys, ternary additions of up to 4at% were also considered. The (010) antiphase boundary energies were calculated for the binary alloy, while (111) superlattice intrinsic stacking fault and antiphase boundary energies were calculated for all of the binary and ternary alloys. The compositions, Ti50Al50 and (Ti50Al50)1-yCry, exhibited the maximum defect energies for this range of alloy compositions. The addition of Cr appeared to have little effect upon the defect energies of the Ti-rich alloys, but slightly reduced the (111) antiphase boundary in Al-rich alloys. The defect energies for Nb alloys were reduced relative to the binary alloys, with the fault energies increasing monotonically with increasing Al concentration. The variations in defect energies, with respect to both trend and magnitude, were used together with anisotropic elasticity theory so as to estimate the forces which were required in order to produce 2 possible <101]{111} super-dislocation glide barriers. The formation of <101]{111} super-dislocations, with portions on cross-slip octahedral planes, was favored over cross-slip onto the cube plane; for conservative estimates of the planar fault energy and applied stress. It was concluded that only moderate improvements could be made, in the high-temperature yield stress, due to the formation of <101]{111} super-dislocation barriers with changes in alloy composition.

C.Woodward, J.M.MacLaren: Philosophical Magazine A, 1996, 74[2], 337-57