冷却速率对液态金属Cu凝固过程中微观结构演变影响的模拟研究

采用Quantum Sutton-Chen(Q-SC)多体势对液态金属Cu在四个不同冷却速率下的凝固过程进行了分子动力学模拟研究. 通过双体分布函数、键型指数、配位数、均方位移及可视化分析, 结果表明：冷却速率对液态金属Cu的微观结构演变有决定性影响. 当冷却速率为1.0×10¹⁴K/s时得到非晶态结构；当冷速分别为1.0×10¹³K/s，1.0×10¹²K/s和1.3×10¹¹K/s时，系统形成以1421键型为主体的面心立方(fcc)与六角密集(hcp)共存的混合晶体结构；且其结晶温度分别为373K，773K和873K，即冷速越慢，其结晶温度越高，结晶程度也越高；且冷速越慢，1421键型越多，混合晶体中面心立方(fcc)结构所占的比例越高. 同时发现，原子的平均配位数的变化与1551，1441，1661键型的变化密切相关, 反映出体系对称性结构的变化规律与配位数的变化有关. 在可视化分析中，进一步采用中心原子法展现出非晶态与晶体结构的2D截面，及在3D下混合晶体中两个基本原子团分别为面心立方(fcc)与六角密集(hcp)基本原子团的具体结构. 关键词： Q-SC多体势 液态金属Cu 凝固过程 分子动力学模拟

Simulation study of effect of cooling rate on evolution of microstructures during solidification of liquid metal Cu

A molecular dynamics simulation has been performed on the solidification process of liquid metal Cu by adopting the quantum Sutton-Chen many-body potentials at four different cooling rates. Through the pair distribution function，bond-type indices, coordination number, MSD, and visualized analysis, it is found that the cooling rate plays a critical role in the evolution of microstructures of liquid metal Cu. At the cooling rate of 1.0×0¹⁴K/s, the amorphous structures will be formed in the system; at the cooling rate of 1.0×10¹³K/s, 1.0×10¹²K/s and 1.3×10¹¹K/s, the mixed crystal structures of fcc and hcp formed mainly with 1421 bond-type will coexist in the system, and their corresponding crystallization temperatures are 373K, 773K, 873K, respectively. Namely, slower the cooling rate, higher the crystallization temperature, and higher the degree of crystallization; and slower the cooling rate, greater the number of 1421 bond-type, greater the proportion occupied by fcc in the mixed crystal. At the same time, it is found that the variation of the mean coordination number of atoms is closely related to that of 1551, 1441, 1661　bond-types, which reflects that the varying rule of the symmetric configurations in the system is related to the variation of the coordination number. In visualized analysis, the amorphous and crystal structures in 2D cross sections and the concrete structures of both the basic clusters of fcc and hcp in 3D were displayed by means of center-atom method.