简单金属固液界面固化过程生长机制的分子动力学研究

Molecular Dynamics Study on Growth Mechanism of Pure Metals Solid-Liquid Interface During Solidification

采用分子动力学方法,研究两种简单金属Ni、 Al固液界面的动力学过程.结果表明:两种金属表现出相同的特征,即界面温度存在某个特征值(T~*),生长速度在这个特征温度附近达到最大值.高于这个温度时,随着过冷温度(熔点温度与界面温度差)的增加生长速度单调增加,低于这个温度时, Ni的生长速度几乎不变,而Al的生长速度随过冷温度的增加而快速减小到零.在此基础上,基于高温BGJ碰撞约束模型和低温W-F扩散模型分析界面的生长机制,发现在小过冷温区和深过冷温区存在碰撞机制和扩散机制的渐变过程,不同温区二者所起的主导作用不同,生长机制的转变是T~*存在的原因.

Solidification of solid-liquid interface of simple metals(Ni and Al) is investigated with molecular dynamics simulation. Two metals show a common feature that growth rate approach to a maximum at a critical temperature(T~*). Above T~*, growth behaviors are similar as reflected by monotonically increased growth rate with increasing undercooling temperature. However, below T~*, grow rate is nearly constant for Ni, while it rapidly decreases to zero for Al with increasing undercooling temperature. High-temperature Broughton-Gilmer-Jackson(BGJ) model and low-temperature Wilson-Frenkel(W-F) model are used to describe growth mechanism. At small undercooling and deep undercooling temperature zone, solid-liquid interface is formed by gradual change between collision and diffusion mechanism, and the dominated one varies in different temperature ranges.