Atomic-Scale Simulation of Grain Boundary Kinetics during Recrystallization
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Atomic-Scale Simulation of Grain Boundary Kinetics during Recrystallization Z. Trautt1,2,3 and M. Upmanyu1,3,4 1 Group
for Simulation and Theory of Atomic-scale Material Phenomena (stAMP)
2 Department
of Physics, Colorado School of Mines, Golden, CO 80401
3 Engineering 4 Materials
Division, Colorado School of Mines, Golden, CO 80401
Science Program, Colorado School of Mines, Golden, CO 80401.
Abstract We present two-dimensional molecular dynamics (MD) simulations of symmetric tilt grain boundary kinetics, driven by stored energy of deformation. The latter is introduced by prescribing a well-defined gradient in dislocation density across a flat grain boundary. Bicrystals simulations reveal that the boundary motion, albeit jerky, increases linearly with simulation time. We also employ a control simulation to extract the driving force for motion, which then yields a unique boundary mobility. Preliminary comparisons with curvature driven boundary migration for misorientations 30◦ and 22.78◦ suggest that misorientation dependence of boundary migration is significantly less anisotropic, in turn implying that the mechanism of motion itself is different.
Introduction Motion of crystalline interfaces, in particular grain boundaries, is central to fundamental annealing phenomena. During secondary recrystallization, motion of grain boundaries between recrystallized nuclei and deformed grains is driven by both boundary curvature and stored energy of deformation due to a dislocation density gradient across the grain boundary, or p-SIBM (plastic strain induced boundary motion). Subsequent coarsening of boundary microstructure is determined by the anisotropy in grain boundary mobilities and energies. While there exist several experimental and atomic-scale simulation studies on grain boundary motion due to boundary curvature [1, 2, 3, 4, 5] and elastic strain e-SIBM) [6], there is considerable vacuum in atomic-scale understanding of grain boundary-dislocation interactions that result in p-SIBM (see [7, 5] for details).
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Clearly, controlling recrystallization kinetics entails quantifying grain boundary properties rex that relate p-SIBM rate vgb to the driving force F. For a flat boundary between grains with differing dislocation densities, F = −∆g s , where g s is the volume density of stored energy of deformation due to dislocation line lengths. Then, rex = −Mgb G⊥ ∇ρd , vgb
(1)
where Mgb is the grain boundary mobility, G⊥ is the total energy per dislocation and ∇ρd is the gradient in dislocation density across the grain boundary. This relation follows from a linear gradient approximation for the atomic flux at the boundary [8, 9].1 This study focusses on kinetics and underlying mechanisms of p-SIBM during secondary recrystallization. The goal of this paper is to i) simulate p-SIBM by imposing a (asymmetrically) prescribed dislocation density gradient across individual grain boundaries and ii) to extract grain boundary mobilities. In followup studies, the anisotropy due to boundary misorientation θgb and
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