Formation and evolution properties of clusters in a large liquid metal system during rapid cooling processes

Abstract

A molecular dynamics simulation study has been performed for a large liquid metal system consisting of 100,000 Al atoms to deeply investigate the transitions of microstructure configurations, especially the formation and evolution properties of the clusters during rapid cooling processes. To describe the structures of various short-range-order clusters in the liquid system and analyze the forming and evolving processes of various clusters, a new cluster-type index method has been proposed. It has been found that a bigger cluster configuration is formed by combined some middle clusters, and the middle clusters are also combined by several smaller clusters, and so on. It is certain that the bigger cluster configurations in this system are not taken on the multi-shells configurations accumulated with an atom as the center and the surrounding atoms arranged by some fixed pattern. Namely, the bigger clusters are not alike to those clusters obtained by gaseous deposition, ionic spray methods and so on, in which the crystals or quasi-crystals are formed by octahedral shell structures as verified in mass spectrum analysis. This is just the essential distinction between the cluster configurations of Al formed by two different ways. It also has been found that the clusters are in deed possessing a certain relative stability and continuity (namely hereditary effect). These results will give us an important enlightenment for understanding the forming mechanisms and microscopic processes of amorphous metals, and for learning the ways for how to control the cooling processes of liquid metals to enhance the macroscopic properties of metallic materials.