Ab-Initio Simulation of a/2<110> Screw Dislocations Gamma-TiAl
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NORTHWESTERN UNIV EVANSTON IL DEPT OF MATERIALS SCIENCE AND ENGINEERING
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The equilibrium core structure of an isolated a2110111 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 a2110111 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.
- Properties of Metals and Alloys
- Quantum Theory and Relativity
- Solid State Physics