Ni熔体凝固过程中临界晶核和亚临界晶核的分子动力学模拟

本文用分子动力学模拟研究了Ni熔体以不同冷速凝固后微观结构的演变规律, 并通过理论计算确定出了Ni熔体凝固后获得理想非晶的临界条件. 模拟结果发现冷速小于10¹¹ K/s时, Ni 熔体凝固后形成晶态组织; 冷速在10¹¹ K/s到10^14.5 K/s之间时, Ni熔体凝固后形成由晶态结构与非晶态结构组成的混合组织. 冷速小于10¹⁰ K/s, Ni 熔体凝固后形成的晶态组织具有fcc结构; 冷速在10¹⁰ K/s到10^14.5 K/s之间时, Ni熔体凝固后组织中的晶态由fcc和hcp结构层状镶嵌排列构成. 通过分析模拟结果和计算结果, 确定出了Ni熔体凝固后形成理想非晶的临界冷速为10^14.5 K/s. 并发现Ni熔体中临界晶核(冷速等于10^14.5 K/s)和亚临界晶核(冷速大于10^14.5 K/s) 均由fcc和hcp组成层状偏聚结构, 这表明Ni熔体中生长的晶体、临界晶核和晶胚的结构是相同的. 关键词： 分子动力学模拟 晶体团簇 临界冷速 结构

Molecular dynamics simulation of the critical and subcritical nuclei during solidification of nickel melt

The microstructures of nickel solidified at different cooling rates are studied by using molecular dynamics simulation and the critical condition for nickel melt to form ideal metallic glass is calculated. The simulation results show that the crystal structure is obtained after the nickel melt has been solidified at a cooling rate that is lower than 10¹¹ K/s; while a mixture is composed of crystal structure and amorphous structure when the cooling rate is in a region from 10¹¹ K/s to 10^14.5 K/s. The solidified crystal of nickel is of fcc structure when the cooling rate is lower than 10¹⁰ K/s, while it changes into crystal structure composed of fcc and hcp when the cooling rate is between 10¹⁰ K/s and 10^14.5 K/s. By analyzing the calculation and simulation results, it is determined that the critical cooling rate for nickel melt to form ideal metallic glass is 10^14.5 K/s. Moreover, it is found that the structures of the subcritical nuclei (the cooling rate is higher than 10^14.5 K/s), critical nuclei (the cooling rate is 10^14.5 K/s), and the growing crystal (the cooling rate is lower than 10^14.5 K/s) are the lamellar structures composed of fcc and hcp atoms, which indicates that the subcritical nuclei, critical nuclei and the growing crystal have the same structures.