摘要:
文章采用分子动力学方法，以金属银为对象，模拟了面心立方金属的凝固和非晶化过程，借助于体系的内能变化、径向分布函数(RDF)、公共近邻分析(CNA)、原子可视化技术对凝固和晶化形核过程中的结构演变细节进行了描述。模拟结果表明，液态金属中就存在11% bcc结构的短程有序集团，随着液态金属不断过冷，bcc集团逐渐增加，在凝固前达到最高的31%，在非晶形成时，bcc集团大约有24%。当最近邻原子距离相同时，bcc结构单位原子所占体积大于fcc结构，有利于在液态金属和非晶中存在。这些bcc结构作为结晶时的非自发形核的核心，与周围的无序原子一起迅速转变为fcc结构和少量的hcp结构。在过冷液体和非晶系统中并没有发现fcc和hcp的结构，fcc结构为凝固和非晶晶化的很短周期中迅速转变而成。
The melting and solidification of Ag was simulated by molecular dynamics method. The structural transfor- mation of Ag during the metal solidification and amorphous crystallization was analyzed based on the variations of the internal energy, radial distribution function (RDF), common neighbor analysis (CNA), and atomic visualization technique. The simulation results showed that the embryonic crystals similar to body-centered cubic (bcc-like) structure (about 11%) already exist in the liquid metal, the content of bcc increases with cooling and it is up to 31% near the solidifying. About 24% bcc structure has in the amorphous structure. The volume per atom of bcc is larger than that of fcc, which is beneficial in the cooling liquid metal and amorphous structure. In the nucleation process, bcc-like embryonic crystals can be used as the nucleus with disorder atoms near the bcc to transform fcc crystal. There is no fcc and hcp structure in the cooling melt and amorphous structure. They are formed in the solidification directly.