Molecular-dynamics method for the simulation of grain-boundary migration

A molecular-dynamics method for the simulation of the intrinsic migration behavior of individual, Bat grain boundaries introduced recently* is discussed. A constant driving force for grain-boundary migration is generated by imposing an anisotropic elastic strain on a bicrystal such that the elastic-energy densities in its two halves are different. For the model case of a large-planar-unit-cell, high angle (001) twist boundary in Cu we show that an elastic strain of similar to 1% - 4% is sufficient to drive the continuous, viscous movement of the boundary at temperatures well below the melting point. The driving forces thus generated (at the high end of the experimentally accessible range) enable a quantitative evaluation of the migration process during the time frame of 10(-9)s typically accessible by molecular-dynamics simulation. For this model high-angle grain boundary we demonstrate that (a) the drift velocity is, indeed, proportional to the applied driving force thus enabling us to determine the boundary mobility, (b) the activation energy for grain-boundary migration is distinctly lower than that for grain-boundary self-diffusion or even self-diffusion in the melt and (c) in agreement with earlier simulations the migration mechanism involves the collective reshuffling during local disordering ("melting") of small groups of atoms on one grain and subsequent resolidification onto the other grain.