Stress-dependent solute energetics in W-Re alloys from first-principles calculations

We present a systematic study of Re solute transport energetics in W using density functional theory calculations. The study focuses on substitutional solute diffusion in the presence of dislocation strain fields as a first step toward capturing the essential physics of solid solution hardening/softening in W-Re alloys. We calculate the heat of solution, the vacancy formation energy and the solute migration energy as functions of both hydrostatic and shear strains. Our results show that the vacancy formation energy scales with hydrostatic deformation, whereas it decreases with increasing shear strain. The migration energy decreases with hydrostatic deformation, whereas it displays path-length-dependent behavior under shear deformation. In addition, we compute the binding energies of an Re solute atom to the cores of 1/2 < 111 > screw and edge dislocations, and find the binding energy to be highest in the tensile lobe of the edge core. Finally, we obtain the dilatational stress due to a solute atom as a function of distance. Our calculations are then used to parameterize the jump rate of Re atoms in W as a function of the underlying stress state. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.