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采用分子动力学方法对六种不同冷速对原子尺寸相差较大的液态合金Ca50Zn50凝固过程中微观结构演变的影响进行了模拟研究,并采用双体分布函数﹑Honeycutt-Andersen(HA)键型指数法、原子团类型指数法(CTIM-2)﹑可视化等方法进行了深入分析,结果表明:系统存在一个临界冷速,介于和5×1011K/s与1×1011K/s之间,在临界冷速以上(如1×1014K/s,1×1013K/s,1×1012K/s和5×1011K/s)时,系统形成以1551,1541,1431键型或二十面体基本原子团(12012000)等为主体的非晶态结构;在临界冷速以下时,系统形成以1441和1661键型或bcc基本原子团(1460800)为主体(含有少量的hcp(1200066)和fcc(12000120)基本原子团)的部分晶态结构.在非晶形成的冷速范围内,其总双体分布函数的第一峰明显分裂成与近邻分别为Zn-Zn,Ca-Zn,Ca-Ca相对应的三个次峰;且随着冷速的下降,同类原子近邻的次峰峰值升高、异类原子近邻的次峰峰值下降;Zn原子容易偏聚,随着冷速降低,二十面体的数量增多,非晶态结构也越稳定.在晶态形成的冷速范围内,Zn原子已大量偏聚形成大块bcc晶态结构,Ca原子也部分形成hcp和fcc晶态结构.
The effects of six different cooling rates on the microstructure evolution of liquid-phase alloy Ca50Zn50 with different cooling rates were simulated by molecular dynamics method. The catagory distribution function, Honeycutt-Andersen (HA) bond index (CTIM-2) and visualization methods. The results show that there is a critical cooling rate between 5 × 10 11 K / s and 1 × 10 11 K / s in the critical cold (Eg, 1 × 1014K / s, 1 × 1013K / s, 1 × 1012K / s, and 5 × 1011K / s), the system formed 1551,1541,1431 bond or icosahedral basic elementary groups As the main part of the amorphous structure; below the critical cooling rate, the system formed by the 1441 and 1661 key or bcc elementary radicals (1460800) as the main body (containing a small amount of hcp (1200066) and fcc (12000120) atomic radical part In the cooling rate range of amorphous formation, the first peak of the total body distribution function is obviously split into three sub-peaks corresponding to the nearest neighbor Zn-Zn, Ca-Zn and Ca-Ca, respectively. And with the decrease of cooling rate, the sub-peak of similar atom near neighbor increases, the sub-peak of near atom of heterogeneous atom decreases Zn atom tends to segregate with increasing cooling rate, the number of icosahedrons increases and the amorphous structure becomes more stable. In the cooling rate range of crystal formation, a large number of Zn atoms have been segregated to bulk bcc crystallites Structure, Ca atoms also partially form hcp and fcc crystalline structures.