应变效应对金属Cu表面熔化影响的分子动力学模拟

Molecular dynamics simulation of strain effects on surface melting for metal Cu

采用Mishin镶嵌原子势,通过分子动力学方法模拟了金属Cu的(110)表面在不同应变下的熔化行为,分析了表面熔化过程中系统结构组态和能量的变化以及固液界面迁移情况.金属Cu的(110)表面在低于热力学熔点的温度下发生预熔化,准液体层的厚度随温度升高而增加.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为1380K,与实验结果1358K吻合良好.应变效应(包括拉伸和压缩)导致热力学熔点降低,并促进表面预熔化进程.在相同温度条件下,准液体层的厚度随应变绝对值的增加而增大.应变效应导致的固相自由能增加是金属Cu(110)表面热稳定性下降的主要因素,且表面应力和应变方向的异同也会影响表面预熔化的进程.

Molecular dynamics simulations of surface melting process at different strain values were performed for metal Cu（ 110）. The variation of the structure and energy in the system and the movement of the interface position between solid and liquid during surface melting were observed. The interaction between atoms in the system adopts the embedded atom potential proposed by Mishin. Cu（110） surface premelts below thermal melting point and the thickness of quasi-liquid film grows with temperature increasing. Beyond the thermal melting point, the velocity of the interface between solid and liquid is linearly proportional to temperature, the melting point is extrapolated to be 1380K which accords with the experimental data of 1358K. Strain lowers the melting point and accelerates the premelting process. The thickness of quasi-liquid grows with increasing strain at the same temperature. The increase of solid free energy induced by strain is the main factor that decreases surface thermal stability, the direction of strain relative to the surface stress also effects the premelting process.