Capillarity-driven shrinkage of grains with tilt and mixed boundaries studied by molecular dynamics
Capillarity-driven shrinkage of grains with tilt and mixed boundaries studied by molecular dynamics
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DOI：
10.1016/j.actamat.2016.08.060
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发表时间：
2016-11
期刊：
影响因子：
9.4
通讯作者：
L. Barrales-Mora;D. Molodov
中科院分区：
文献类型：
--
作者：
L. Barrales-Mora;D. Molodov
采用分子动力学方法模拟了毛细力作用下铝中孤立圆柱形晶粒的收缩行为，系统研究了晶界特征对晶粒收缩行为的影响。研究了具有纯倾斜和各种混合倾斜-扭转14.25°边界的晶粒<100>。模拟结果证实了具有纯倾斜晶界的收缩晶粒同时向更高的取向差旋转。然而，研究结果也表明，即使是轻微的变化，从纯倾斜的晶界字符的混合倾斜扭曲是足以避免晶粒旋转。观察到的收缩晶粒的动力学是强烈依赖于晶界的字符。混合边界的流动性估计是远远高于纯倾斜边界。此外，计算晶粒的收缩动力学被发现随晶粒尺寸的减小而变化。收缩后期表现为颗粒面积变化率的停滞或降低。小晶粒的这种行为归因于缺乏消除晶界中位错（边界结构单元）的机制。据推测，这种收缩停滞的纳米尺寸的晶粒（≤6 nm）可以有助于纳米晶材料的热稳定性。
Molecular dynamics simulations of isolated cylindrical grains in aluminum shrinking under capillary forces were carried out to systematically study the effect of grain boundary character on grain shrinkage behavior. Grains with pure tilt and various mixed tilt-twist 14.25°<100> boundaries were examined. The simulation results confirmed that the shrinking grains with pure tilt boundary simultaneously rotated towards higher misorientations. However, the results also showed that even a minor change of the grain boundary character from pure tilt to mixed tilt-twist is enough to avoid grain rotation. The observed kinetics of the shrinking grains was strongly dependent on the character of grain boundaries. The mobility of the mixed boundaries was estimated to be much higher than that of the pure tilt boundary. Also, the shrinkage kinetics of computed grains was found to vary with a decreasing grain size. The advanced stage of shrinkage was characterized by the stagnation or decrease of the rate of grain area change. This behavior of small grains was attributed to a lack of mechanisms for the elimination of the dislocations (boundary structural units) in the grain boundary. It is hypothesized that such shrinkage stagnation of nanosized grains (≤6 nm) can contribute to the thermal stability of nanocrystalline materials.