液态Ca7Mg3合金快速凝固过程中团簇结构的形成特性

采用分子动力学方法对液态Ca7Mg3合金凝固过程中团簇结构的形成特性进行了模拟研究. 采用双体分布函数、Honeycutt-Andersen(HA)键型指数法、原子团类型指数法(CTIM)以及遗传跟踪等方法对凝固过程中团簇结构的形成演变特性进行了分析. 结果表明: 在以冷速为1×1012 K·s-1 的快速凝固条件下, 系统形成以1551、1541、1431键型为主的非晶态结构; 二十面体基本原子团(12 0 12 0)在快速凝固过程中对非晶态结构的形成起决定性作用; 在合金凝固过程中, 团簇的稳定性不仅与构成团簇的基本原子团类型有关, 还与中心原子类型以及中心原子之间的连接方式有关. 由于(12 0 12 0)基本原子团能量较低并且在低温具有较好的遗传特性, 基本原子团之间很容易连接在一起组成更大的团簇. 所形成的团簇结构显著不同于那些由气相沉积、离子溅射等方法所获得的团簇结构.

Formation Properties of Cluster Structures during the Rapid Solidification of Liquid Ca7Mg3 Alloy

A molecular dynamics simulation was performed to examine the formation properties of clusters during the solidification of liquid Ca7Mg3 alloy. Pair distribution functions, Honeycutt-Andersen (HA) bond-type index method, cluster-type index method, and genetic tracking were used to analyze the formation and evolution of cluster structures during rapid solidification processes. Results show that amorphous structures are mainly formed with the 1551, 1541, and 1431 bond-types at a cooling rate of 1×1012 K·s-1. The basic cluster (12 0 12 0) plays a key role in the formation of amorphous structures during rapid solidification processes. The stability of a cluster is related to the type of basic clusters and also the type of central atoms as well as the bonding modes between all central atoms. Bonding among the basic clusters (12 0 12 0) allows the formation of larger clusters because of the lower energy and the better genetic characteristic of the basic cluster (12 0 12 0). These bigger clusters are obviously different from those obtained by gaseous deposition and ionic spray methods.