Atomistic study of ordinary screw dislocations in single-phase and lamellar γ-TiAl

Abstract

Computer simulation of the core structure and glide of ordinary screw dislocations in single-phase L1₀ TiAl and in two lamellae forming a twin γ/γ-interface has been performed using recently constructed Bond-Order Potentials (BOPs). BOPs represent a semi-empirical, numerically efficient scheme that works within the orthogonal tight-binding approximation and is able to capture the directionality of bonding. We have studied dislocation glide in perfect L1₀ TiAl and along a twin interface, transmission of an ordinary screw dislocation between lamellae, and the core structure, mobility and detachment of an interfacial screw dislocation from a twin boundary under applied shear stresses in directions parallel and perpendicular to a (111) plane. Our results show that the glide of ordinary straight screw dislocations under applied stresses in L1₀ TiAl is characterized by zigzag movement on two conjugated {111} planes. The non-planar core of the screw dislocation is distorted asymmetrically when the elastic centre of the dislocation is close to a twin γ/γ-interface and the dislocation moves on one of the (111) planes, depending on the magnitude of the corresponding Schmid factor. Ordinary dislocations become ordinary interfacial dislocations when they reach the interface. With increasing applied stress they can glide into the adjacent lamella, leaving no remnant interfacial dislocation.

Acknowledgements

This research was supported by the EPSRC grant no. EP/C015649/1. The authors wish to thank Prof. V. Vitek of University of Pennsylvania for helpful discussions during the course of this work.