冷速对液态合金Ca_(50)Zn_(50)快速凝固过程中微观结构演变的影响  

Effects of cooling rates on microstructural evolution during solidification process of liquid Ca_(50)Zn_(50) alloy

作　　者：郑乃超[1,2] 刘海蓉[2] 刘让苏[1] 梁永超[1] 莫云飞[1] 周群益[1] 田泽安[1] 

机构地区：[1]湖南大学物理与微电子科学学院,长沙410082 [2]湖南大学材料科学与工程学院,长沙410082

出　　处：《物理学报》2012年第24期410-419,共10页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:50831003;50571037;51102090)资助的课题~~

摘　　要：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.A simulation study is performed on the effects of six different cooling rates on microstructural evolution during solidification process of liquid CasoZnso alloy with larger atomic size difference by using the molecular dynamics method. The pair distribution function, Honeycutt-Andersen （HA） bond-type index method, cluster-type index method （CTIM-2） and three-dimensional visualization method are adopted to deeply analyze the microstructural evolution. The results show that there is a critical cooling rate （in a range of 1 ×10^12 and 5 ×10^11 K/s） for forming amorphous or crystal structure. When the cooling rate, such as 1 ×10^14 K/s, 1 ×10^13 K/s, 1 ×10^12 K/s and 5 ×10^11 K/s, is above the critical cooling rate, the amorphous structures are formed mainly to be the 1551, 1541 and 1431 bond-types or the icosahedron basic clustr （12 0 12 0 0 0）; while the cooling rate is under the critical cooling rate, such as at 1 ×10^12 K/s, the partial crystal structures are formed mainly to be the 1441 and 1661 bond-types or the bcc clusters （14 6 0 8 0 0） （containing part of hcp （12 0 0 0 6 6） and fcc （12 0 0 0 12 0） basic crystal clusters） in the system. In the cooling rate range of forming amorphous structure, the first peak of the pair distribution function g（r） is split obviously into three secondary peaks corresponding to the nearest neighbor as Zn-Zn, Ca-Zn and Ca-Ca, respectively, and with the decrease of cooling rate, the secondary peak formed by the like atoms is inereased and the secondary peak formed by unlike atoms is reduced. With the decrease of cooling rate, the Zn atoms can be easily segregated to form the larger clusters; the lower the cooling rate, the bigger the number of basic icosahedrons formed in the system, and the amorphous system is more stable. In the cooling rate range of forming crystal structure, a great number of Zn atoms are segregated to form the bulk bcc crystal structures and part of Ca atoms are segregated to form some hcp and fcc crystal clusters.

关 键 词：液态Ca-Zn合金 冷却速率 微结构演变 分子动力学模拟 

分 类 号：TG139.8[一般工业技术—材料科学与工程]