Elastic constants, fault energies, and dislocation reactions in TiAl: A first-principles total-energy investigation

Abstract

First-principles total-energy calculations of the elastic constants and shear fault energies of TiAl are presented. We find a large elastic-shear anisotropy along the [011] direction, and high antiphase-boundary energies due to the strong cohesion between Ti and A1 layers as well as the formation of directional d bonds in the Ti layer. Shear faults of intrinsic type, extrinsic type and twin boundary type are predicted to be prevalent owing to their low energies. The anomalous temperature dependence of the flow stress is explained by the cross-slip-pinning and fault-dragging mechanisms. The intrinsic brittleness of TiAl is discussed in terms of these results.