液态金属Ga急冷凝固中微观结构转变的模拟研究

Simulation study of microstructure transition of liquid metals Ga during rapid cooling solidifications

采用分子动力学方法对液态金属Ga的快速凝固过程进行计算机模拟跟踪研究,运用HA键型指数法和原子团类型指数法分析了金属原子Ga的成键类型和形成的基本原子团结构。发现:与通常的液态金属(如Al)相反,随着温度的降低,二十面体及与二十面体相关的1551,1541键型数目明显下降;与立方体(fcc,bcc),六角密集结构相关的1421,1422键型数目明显增加;而与菱面体相关的1321,1311键型的数目却显著增加,逐渐占据优势。最后形成一种新型的以菱面体结构为主、夹杂着立方体(fcc,bcc)、六角密集(hcp)等团簇结构所组成的非晶态结构。这正是非晶态金属Ga的g(r)曲线分裂的第二峰的顺序为前低后高,而与非晶态金属Al的g(r)曲线(其分裂的第二峰的顺序为前高后低)明显不同的微观结构上的物理根源。

A computer simulation tracking study for the rapid solidification processes of liquid metal Ga system has been performed by using molecular dynamics method. Adopting the Honeycutt-Andersen （HA） bond-type index method and the cluster-type index method, the bond-types and the basic cluster configurations formed by metal Ga atoms are analyzed. It has been found that, contrary to conventional metals （such as Al）, with decreasing temperature, the number of icosahedron and the relative numbers of 1551,1541 bond types related to the icosahedron decreased obviously; the total number of 1421, 1422 bond types, related to the cubic （fcc,bcc） and hcp structures increased obviously; and the total number of 1311, 1301 bond types, related to the rhombohedral structure, increased remarkably, and gradually played a dominant role. Finally, an amorphous structure was formed mainly with rhombohedral structures and mixed up with clusters of cubic （f. c. c, b.c. c）and h. c. p structures. This is just the physical origin in microstructure for the obvious difference between the g（r） curves of amorphous metal Ga having a splitting second peak with a lower front sub-peak and a higher behind one, with those of amorphous metal Al having a splitting second peak with a higher front sub-peak and a lower behind one.