Local atomic structures in grain boundaries of bulk nanocrystalline aluminium: A molecular dynamics simulation study

Abstract

The microstructures of grain boundaries (GBs) in bulk nanocrystalline aluminium have been investigated by a large-scale molecular dynamics method. Bulk nanocrystalline aluminium is obtained directly by liquid quenching at an appropriate cooling rate, which has narrow grain-size distribution and high-angle GBs. It is found that up to 89.75% GB atoms (named as GB1 atoms) are located at the nearest-neighbour coordination shell around nanograins; others (named as GB2 atoms) are mainly at triple junctions. Local atomic structures in the GBs are quantified in terms of a recently developed method, in which the neighbours of an atom are identified with a parameter-free topological criterion rather than a fixed cut-off distance rc. The results demonstrate that though there are a large number of different cluster types in both the GB1 and the GB2 regions, only a few ones with FCC-like order appear with high frequency in the GB1 region and play a crucial role in the microstructural feature of the GB1. The GB1 region displays short-to-long range order. The GB2 region presents ICO- and BCC-like short-range orders whose degrees are in between the liquid and amorphous, but the medium-range order at the cluster-scale is very weak.