液态金属Al凝固过程中的团簇结构与幻数特性

采用分子动力学方法,对含有100000个Al原子的液态金属系统在凝固过程中团簇结构的形成特性进行了模拟研究,并采用原子团类型指数法(CTIM)来描述各种类型的团簇结构组态.研究结果显示:在液态金属Al的凝固过程中,只有与1551键型相关的二十面体原子团(12 0 12 0)及其组合形成的各种团簇结构,对微结构的演变起着关键的、决定性的作用;由不同数目、不同类型基本原子团组成的各种层次的团簇结构,都在一定的原子数区段内呈现出峰值,即幻数点;系统的幻数序列为:13(13), 19(21), 25～28(27), 31～33(29～30) ,37、39,…(括号内为液态时对应的幻数值),与Harris等人的实验结果甚为相符.本模拟研究所用的团簇结构按层次区段来研究幻数序列的方法,可为实验结果提供更为合理的模型解释.

Cluster Structions and Magic Number Characteristics during solidification Process of Lipuid Metal Al

A simulation study on the formation characteristics of cluster structures during rapid cooling process in a liquid metal system consisting of 100 000 Al atoms has been performed by molecular dynamics method. A cluster-type index method (CTIM) has been used to describe the structural configurations of various clusters. The results demonstrate that, during the solidification process of liquid metal Al, only the icosahedral clusters (12 0 12 0) related to the 1551 bond-types and various cluster structures formed by their combination play the key and critical role for the microstructure evolution; the cluster structures of various levels formed by different numbers and different types of basic clusters would present the peak values in a certain section of atomic number, namely the magic numbers; the magic number order in the system is 13(13); 19(21); 25～28(27); 31～33(29～30); 37,39;…(the numbers in the brackets are the corresponding values in liquid state) as shown in detail in Table 1 and Fig.4, this is quite in agreement with the experimental results obtained by Harris et al. The method used here to research the magic numbers from the cluster structures according to the level order and sections will give these experimental results a rather scientific and reasonable model explanation.