液态Mg_7Zn_3合金快速凝固过程中微观结构演变机理的模拟研究

Simulation study of evolution mechanisms of microstructures during rapid solidification of liquid Mg_7 Zn_3 alloy

采用分子动力学方法对液态Mg7Zn3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、Honeycutt-Andersen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1×1012K·s-1的凝固过程中,Zn-Zn原子之间的相互成键的概率明显增加,形成以1551,1541,1431键型为主的非晶态结构.其特征键型1551随温度变化的拐点与系统的玻璃转变温度Tg相对应,可成为一种确定Tg的新方法.由1551键型构成的二十面体基本原子团(120120)对非晶态结构的形成起决定性作用,并在大团簇结构通过中、小团簇之间相互竞争(拉锯式的得而复失、失而复得)、兼并而形成的过程中,演变成为大团簇结构的主体.

A simulation study has been performed for the rapid solidification process of liquid Mg7Zn3 alloy by using molecular dynamics method.The pair distribution function g（r） curves,the bond-type index method of Honeycutt-Andersen （HA）,the cluster-type index method and the genetic tracking method have been used to analyze the formation and evolution properties of cluster structures during the solidification process.The results show that the bonding probability between ZnZn atoms is increased obviously during the solidification process at cooling rate of 1 × 1012K·s-1.The amorphous structures are formed mainly with the 1551,1541 and 1431 bond-types,and the turning point of the relation curve of the characteristic 1551 bond-type with temperature is corresponding to the glass transition temperature Tg,thus it maybe become a new method to determine Tg.The basic cluster （12 0 12 0） consisting of 1551 bond-type plays a key role in forming amorphous structure,and becomes the main body of the large clusters which are formed by the combination of some middle and small clusters with distinctly different sizes,through mutual competition by unceasing annex and evolution in a seesaw manner （in turn of obtaining and losing）.