冷却速率对液态Ni凝固过程中微观结构演变影响的模拟研究

用分子动力学方法和EAM模型势对液态金属Ni原子系统在不同冷却速率下凝固过程中微观结构的演变进行了模拟研究.结果表明, 冷却速率对微结构演变有决定性影响, 当冷速为1.0×10¹⁴和 4.0×10¹³ K•s^-1时, 系统将形成以1551、1541和1431三种键型为主的非晶态结构. 当冷速为2.0×10¹³和 1.0×10¹² K•s^-1时, 系统将形成不同的晶态结构；前者形成以1421、1422二种键型为主的 fcc 与hcp结构共存的晶态结构；后者形成以1421键型为主的fcc 结构占绝对优势的晶态结构, 其结晶起始温度Tc分别为1073 K和1173 K.同时发现, 原子的平均配位数（最近邻数）对温度和冷速的变化相当敏感, 且其突变点正好与结晶转变温度Tc相对应, 这将为液态金属结晶转变过程的研究提供一条新途径.

A Simulation Study for Effects of Cooling Rate on Evolution of Microstructures during Solidification Process of Liquid Metal Ni

A simulation study has been performed for the evolutions of microstructures in a liquid metal Ni system during solidification process under different cooling rates by means of molecular dynamics method and EAM model potential. It shows that the cooling rate plays a critical role to the evolution of microstructures. As the cooling rate being 1.0×10¹⁴ K•s^-1 and 4.0×10¹³ K•s^-1, the amorphous structures would be formed in the system with 1551, 1541 and 1431 bond-types as the main body in the system. As the cooling rate being 2.0×10¹³ K•s^-1 and 1.0×10^{12 K•s-1, both kinds of crystal structures would be formed, respectively；the first one possesses the coexist of the fcc and hcp structures with 1421 and 1422 bond-types as the main body；the second one possesses only the fcc structure with 1421 bond-type as the main body；and their crystallization transition temperatures Tc, would be 1073 and 1173 K, respectively. At the same time, it is found that the mean coordination number of atoms (i.e. the nearest neighbor number) in the system is rather sensitive to the variation of temperature and cooling rate, and their sudden transition points, as shown in Fig. 5, just corresponding to the crystallization transition temperatures Tc, this will give us a new way for researching the crystallization transition processes of liquid metals.}