液态Ca50Zn50合金快速凝固过程中微观结构的演变特性

采用分子动力学方法对液态Ca50Zn50合金的快速凝固过程进行了模拟研究.并采用双体分布函数、HA键型指数法、原子团类型指数法(CTIM)和可视化等方法对凝固过程中微观结构的演变特性进行了分析.结果表明：由于Ca，Zn原子的半径差异较大，导致总双体分布函数的第1峰明显分裂成为3个次峰，随着温度下降，半径较小的Zn原子互为近邻的几率明显增加.系统中1551键型所构成的二十面体基本原子团(12 0 12 0)的数量占绝对优势，对非晶态结构的形成起主导作用.系统中基本原子团的中心原子主要是原子半径较小的Zn原子.具有短程序的基本原子团之间大多以共顶点(VS)，共棱线(ES)，共面(FS)和相互交叉(IS)的方式相结合，在凝固形成非晶态的过程中，基本原子团大多以相互交叉(IS)的方式相结合，最后形成各种不同尺寸的、原子结合比较紧密、结构比较稳定的较大团簇.

Evolution Properties of Microstructures during Solidification Process of Liquid Ca50Zn50 Alloy

A simulation study has been carried out for the solidification process of liquid Ca50Zn50 alloy by using molecular dynamics method. The pair distribution function g(r) curves, bond-type index method, cluster-type index method (CTIM) and three-dimensional visualizing analysis method have been used to analyze the evolution properties of microstructures during the solidification process. The results show that, owing to the difference of atomic radius for Ca and Zn, the first peak of the total pair distribution function gtot(r) curve is split into three secondary peaks. With the decrease of temperature, the propability of Zn atoms being close to each other is increased obviously. In the system, the icosahedron basic cluster (12 0 12 0) consisting of 1551 bon-types plays a key role in forming amorphous structure. And the center atoms of basic clusters in the system are mainly the Zn atoms with smaller size. Most basic clusters with short-range order would be linked to each other in the manners of vertex-sharing(VS), edge-sha ring (ES) , face-sharing (FS) and intercross-sharing (IS) atoms. During the solidification process of forming amorphous state, most basic clusters would be linked with the manner of intercross-sharing (IS) atoms to form various larger clusters with different sizes, more tightness of connecting and more stability of structure.