Atomic dynamics of grain boundaries in bulk nanocrystalline aluminium : a molecular dynamics simulation study

Dynamics of grain boundary (GB) atoms in the bulk nanocrystalline aluminium is investigated by means of a large-scale molecular dynamics simulation. It is found that the GB atoms in the nanocrystalline aluminium display the glassy dynamics. Their dynamic features are, on one hand, similar to those in the glass systems and bicrystal GBs, in terms of the time-correlation functions of mean-square displacement (MSD) and non-Gaussian parameter (NGP). But on the other hand, these GB atoms also demonstrate some different dynamic behaviors due to the more complicated microstructure. In particular, the immobile GB atoms are localized into their equilibrium positions due to the strong cage effect, and they are mainly at the surfaces of grains, especially the large grains, while the mobile GB atoms are active and can easily hop away from the cage around them. These mobile GB atoms gather together at the surfaces of small grains and the triple junction regions of GBs, and they form some abnormally big clusters. The size distribution of these clusters significantly deviates from the power law.