Simulation study on the formation and evolution properties of nano-clusters in rapid solidification structures of sodium

摘要

A tracing simulation study has been performed on the rapid solidification process of a liquid metal system consisting of 50 000 Na atoms using the molecular dynamics method. The formation and evolution of nano-clusters in rapid solidification have been investigated by using the cluster-type index method. It is found that the defective icosahedrons, instead of icosahedrons, in liquid and supercooled liquid play a dominant role in the formation of amorphous structures of Na. The formation and evolution of nano-clusters in the rapid solidification process have generally undergone a complicated evolution process: the small cluster is formed dispersedly and aggregates continuously in the liquid, through a middle-cluster including more than one hundred atoms by absorbing some surrounding atoms in the supercooled liquid, and finally the nano-clusters are formed by combining several middle-clusters. The nano-clusters are formed more easily in liquid metal Na than in liquid metal Al, and the configurations of nano-clusters are also obviously different from those obtained by gaseous deposition, ionic spray methods and so on.