Ab-Initio Simulation of a/2<110> Screw Dislocations Gamma-TiAl
Abstract
The equilibrium core structure of an isolated a/2<110?111! screw dislocations is calculated using a first-principles pseudopotential-planewave method within the Local Density Approximation of Density Functional Theory. In this work the local dislocation strain field is self-consistently coupled to the long-range elastic field using a flexible boundary condition method. This ab-inition adaptation of the Greens Function Boundary Condition method makes it possible to stimulate the dislocation in a very small periodic cell without compromising the fidelity of the final core configuration. Supercells of 210, 288, and 420 atoms are used to evaluate the local screw and edge displacement of a straight a/2<110?111! screw dislocations in y-TiAl. The predicted dislocation core is non-planar with significant portions of the dislocation core spread on conjugate ?111! glide planes. By applying a pure (111) shear stress the lattice friction stress is estimated to be approximately 0.006 micro in reasonable agreement with experimental observations. The non-planar character of the dislocation core suggests that the dislocation is sessile, and would readily glide on either of two ?111! slip planes. The dislocation core also produces small but significant edge components that are expected to interact strongly with non-glide (e.g., Escaig) stresses producing significant non-Schmid behavior.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 2004
- Accession Number
- ADA429899
Entities
People
- C. E. Woodward
- S.I. Rao
Organizations
- Northwestern University