金属Cu低指数表面熔化行为的分子动力学模

采用Mishin镶嵌原子势, 通过分子动力学方法模拟了金属Cu的低指数表面在不同温度的表面熔化行为, 分析了熔化过程中系统结构组态的变化以及固-液界面迁移情况. 金属Cu的(100)和(110)表面在低于熔点发生预熔化, 而(111)表面存在明显的过热现象. 准液体层的厚度随温度升高而增加, 热稳定性与表面的密排顺序一致, 按(111)、(100)、(110)顺序增大. 当温度高于热力学熔点时, 固液界面的移动速度与温度成正比, 外推得到热力学熔点约为1360～1380 K, 与实验结果1358 K吻合良好. 动力学系数定义为界面移动速度与过热程度的比值, 表现为明显的各向异性: k100=39 cm?s?1?K?1, k110=29 cm?s?1?K?1, k111=20 cm?s?1?K?1. k100与k110之间的比例符合collision-limited理论, (111)密排面有与其它低指数表面不同的熔化方式.

Molecular Dynamics Simulations of Low Index Surfaces Melting Behaviors for Metal Cu

Molecular dynamics simulations of low index direction surfaces in melting processes at different temperatures were performed for metal Cu. The variation of the structure in the system and the movement of the interface position between solid and liquid during surface melting process were observed. The interaction between atoms in the system was calculated by adopting the embedded atom potential proposed by Mishin. The order in the stability follows the same order as in the packing density: (110), (100) and (111). The solid-liquid interface remains unchanged during the surface melting process around temperature 1360～1380 K which coincides well with the experiment datum 1358 K. The kinetic coefficient is defined as the ratio of the interface velocity to undercooling. The values of kinetic coefficient for low interface (100), (110), (111) are anisotropic: k100=39 cm?s?1?K?1, k110=29 cm?s?1?K?1, k111=20 cm?s?1?K?1. The relationship between the kinetic coeficients in directions (100) and (110) agrees well with the collision-limited theory, however the kinetic coefficient of direction (111) is 4 times less than the theoretical limit.