团簇连接对Cu10Ag90快速凝固中晶体结构的影响

Effect of cluster connection on crystal structure of Cu10Ag90 during rapid solidification

快速凝固得到的晶体通常都会形成多种孪晶结构,但其成因一直是一个谜.本文采用分子动力学模拟Cu10Ag90合金在0、20和40 GPa压强下的快速凝固过程,分别形成了五重孪晶、层片状孪晶和复杂晶体,通过最大标准团簇方法(LaSCA)分析了短程有序结构的演变和晶体团簇之间的连接形式.结果发现,结晶转变温度Tc随着压强的增大而升高,平均原子势能也随之增加.非晶共有近邻子团簇(CNS)会在温度降至Tc时转变为晶体CNS,同时晶体团簇数量急剧增加,结构有序度提升.此外,通过分析晶体团簇之间的连接方式发现,五重孪晶中心团簇截边十面体(tDh)只能与具有相同S422的HCP相连形成五重孪晶轴;FCC与HCP有相同的S421,但只能以彼此的顶层或者底层原子作为彼此的中心原子连接形成层片状结构;BCC与FCC、HCP虽然没有共同的CNS,但是可以通过D-S6结构及其变形体连接,其连接方式的多样性是形成复杂晶体的主要原因.这些结果为研究晶体结构不同排列方式提供了新的理解.

The crystals obtained by rapid solidification usually form multiple twin structures, butthe formation has been a mystery. The molecular dynamics simulations of the rapid solidification process of Cu10Ag90alloy at 0, 20 and 40 GPa pressures were used in this paper to form fivefold twins, lamellar twins and complex crystals, respectively. The evolution of the short-range ordered structure and the connection forms between crystal clusters were analyzed by the largest standard cluster analysis(LaSCA). It is found that the crystallization transition temperature Tcincreases with increasing pressure, and the average atomic potential energy also increases. Amorphous common neighbor sub-cluster(CNS) will transform into crystalline CNS when the temperature drops to Tc, while the number of crystalline clusters increases dramatically and the structural order is enhanced. In addition, by analyzing the connections between crystal clusters, it is found that the fivefold twin central cluster truncated-decahedron(tDh) can only be connected to HCP with the same S422 to form a fivefold twin axis;FCC and HCP have the same S421, but can only form a lamellar structure by connecting each other’s top or bottom atoms as each other’s central atoms;although BCC and FCC, HCP do not have a common CNS, but they can be connected by the D-S6 structure and its distorter, and the diversity of their connections is the main reason for the formation of complex crystals. These results provide a new understanding for the study of different arrangements of crystal structures.