MOLECULAR DYNAMICS SIMULATION OF GRAIN BOUNDARY MIGRATION IN

MOLECULAR DYNAMICS SIMULATION OF GRAIN BOUNDARY MIGRATION IN THREE DIMENSION Hao Zhang and D. J. Srolovitz, Princeton Materials Institute, Princeton University Moneesh Upmanyu, Oak Ridge National Laboratory Lasar Shvindlerman, Gunther Gottstein, RWTH, Aachen Germany Srivilliputhur. Srinivasan, Los Alamos National Laboratory materials phenomena: recrystallization, grain growth, …. • Anisotropy in grain boundaries • misorientation (3), inclination (2) • 2 x anisotropy in energy • 10 – 100 x anisotropy in mobility • Impurity effects • Segregation • Drag • 100 – 105 x mobility • Local velocity • Absolute reaction rate theory (Turnbull, 1951) Atomic Model Grain Boundary Enthalpy Z • FCC Aluminum <111> Tilt Grain Boundary • Periodic along X, Y and Z • Constant Temperature • EAM – Al z • Grain boundary migration is central to many Modeling Approach Grain Boundary Migration Introduction • Steady-state velocity h v(y) • Grain growth (capillarity-induced w migration) γgb. H : Grain Boundary Enthalpy M*: Reduced Mobility Driving Force dependence of Migration Steady State Migration Reduced Mobility vs. Misorientation Simulation • During grain boundary migration, Σ 13 Experiment Σ 13 Σ 7 half-loop shape grain has self-similar behavior • and are constant, except for initial and final transient • Grain boundary velocity is constant during migration • Final transient is associated with finite simulation cell size For sufficiently low driving forces (large w): • Reduced mobility is independent of driving force • Grain Boundary Enthalpy is independent of loop width Temperature Dependence of Mobility • Reduced Mobility exhibits maximum at Σ 7 for each temperature • Reduced Mobility exhibits local extrema at Σ 7 and Σ 13 for each temperature • At each misorientation, raising the temperature • Experimental reduced mobility is much increases the reduced mobility Activation Energy vs. Misorientation Simulation Σ 13 Σ 7 Compensation Effect Experiment Σ 7 smaller than simulation results Grain Boundary Enthalpy vs. Misorientation Σ 13 Σ 7 • The variation of pre-exponential factor and activation energy for • Simulation results show that activation energies of Σ 7 and Σ 13 are local minima • Reduced Mobility is well described by Arrhenius relation • Low Σ boundaries exhibit low activation energies • Experiments also show a minimum at Σ 7 • Activation energies for boundary migration are much smaller in simulation than in experiment (impurity drag? ) grain boundary migration are strongly correlated • There is a linear relation between the logarithm of the pre- exponential factor and the activation energy near high symmetry misorintations • Grain boundary enthalpy exhibits local minima near high symmetric orientations