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采用分子动力学方法对不同冷速下液态金属镁(Mg)快速凝固过程中的微观结构演变进行了模拟研究.并采用能量-温度(E-T)曲线、双体分布函数、Honeycutt-Andersen键型指数法、原子团簇类型指数法(CTIM-3)以及三维可视化等方法系统地考察了凝固过程中微观结构演变与相转变过程.结果发现:在以冷速为1×10~(11)K/s的凝固过程中,亚稳态bcc相优先形成,随后大量解体,其变化规律符合Ostwald规则,系统最终形成以hcp结构为主体与fcc结构共存,中间还夹杂部分bcc结构的致密晶体结构.在1×10~(12)K/s冷速下,结晶过程呈现迟缓现象,形成bcc结构的初始温度降低,系统形成以hcp居多、与bcc和fcc三相共存的结构,且因相互竞争、相互制约而导致不易形成粗大的晶粒结构.而在1×10~(13)K/s冷速下,系统则形成以1551,1541,1431键型为主的多种非晶态基本原子团组成的非晶态结构.此外,在冷速1×10~(12)与1×10~(13)K/s之间的确存在一个形成非晶态结构的临界冷速.
The molecular dynamics simulations were used to simulate the microstructure evolution during rapid solidification of liquid magnesium (Mg) at different cooling rates. The energy-temperature (ET) curve, the bilayer distribution function, the Honeycutt-Andersen bond index (CTIM-3) method and three-dimensional visualization method were used to systematically investigate the microstructure evolution and phase transformation during the solidification process. The results show that when the cooling rate is 1 × 10 ~ (11) K / s In the solidification process, the metastable bcc phase is preferentially formed and then disintegrated in a large amount, and its variation is in accordance with the Ostwald rule. The system eventually forms a dense crystal structure with the hcp structure as the main component and the fcc structure as the main component, Under the cooling rate of 10 ~ (12) K / s, the crystallization slowed down and the initial temperature of the bcc structure decreased. The system formed mostly hcp and coexisted with bcc and fcc. Due to competition and mutual restraint Resulting in not easy to form coarse grain structure.At 1 × 10 ~ (13) K / s cooling rate, the system is formed by the 1551,1541,1431 key type based on a variety of amorphous basic atomic group In addition, the cooling rate of 1 × 10 ~ (12) and 1 × 10 ~ (13) K / s There is indeed a formation of amorphous structure critical cooling rate.