Molecular dynamics simulations were employed to study atomic motion within stationary and migrating asymmetric tilt grain boundaries. Several measures of the complexity of the atomic trajectories were used. These included the van Hove correlation function, the non-Gaussian parameter and dynamic entropy. There were 2 key types of dynamic event within the grain boundaries. These were string-like cooperative motions parallel to the tilt axis, which occurred over a characteristic time-scale of about 25ps, and atomic motion across the grain boundary plane which occurred at a characteristic time-scale of about 150ps. The characteristic times which were associated with each type of event decreased with increasing driving force for boundary migration. Evidence was presented as to how the driving force biased these types of event leading to boundary migration. It was concluded that, while string-like atomic motion was an intrinsic feature of grain-boundary dynamics and was important for grain-boundary migration, it was the second type of event that controlled grain-boundary migration rates.

Characterization of Atomic Motion Governing Grain Boundary Migration. H.Zhang, D.J.Srolovitz, J.F.Douglas, J.A.Warren: Physical Review B, 2006, 74[11], 115404 (10pp)