The equilibrium core structure of an isolated (a/2)110]{111} screw dislocation was calculated by using a first-principles pseudopotential plane-wave method within the local-density approximation of density functional theory. The local dislocation strain field was here self-consistently coupled to the long-range elastic field by using a flexible boundary-condition method. This first-principles adaptation of the Green’s function boundary condition method made it possible to simulate the dislocation within a very small periodic cell, without impairing the accuracy of the final core configuration. Super-cells with 210, 288 or 420 atoms were used to evaluate the local screw and edge displacements of a straight (a/2)<110]{111} screw dislocation in γ-TiAl. The predicted dislocation core was non-planar, with significant portions of the dislocation core spread onto conjugate {111} glide planes. The non-planar nature of the dislocation core suggested that the dislocation was sessile and would readily glide on either of two {111} slip planes. The dislocation core also produced small but significant edge components that were expected to interact strongly with non-glide (Escaig) stresses to produce a significant non-Schmid behavior. Initial estimates of the lattice frictional stress for a pure (111) shear stress were of the order of 1% of the shear modulus.

Ab initio Simulation of (a/2)110] Screw Dislocations in γ-TiAl. C.Woodward, S.I.Rao: Philosophical Magazine, 2004, 84[3], 401-13