用分子动力学模拟研究晶界预熔和晶粒合并的结构分离势
Structural disjoining potential for grain boundary premelting and grain coalescence from molecular-dynamics simulations
摘要：
我们描述了一个分子动力学框架的直接计算的短程结构力的晶界预熔化和晶粒聚结凝固。该方法应用于（i）一个西格玛9 <115>120度扭曲和（ii）一个西格玛9 <110>{411}对称倾斜边界在一个经典的嵌入原子模型的元素镍的比较研究。虽然这两个边界的特点是高度无序的结构附近的熔点，在这些边界中的无序区域的宽度的温度依赖性的性质是定性不同的。前者的边界显示的行为与一个gramically发散的预熔层厚度从下面的熔化温度接近一致，而后者显示的行为具有有限的晶界宽度在熔点。它表明，这两种类型的行为可以定量描述内的尖锐的界面热力学形式主义，涉及宽度依赖的界面自由能，被称为分离的潜力。边界（i）的分离势计算显示出对宽度的单调指数依赖性，而边界（ii）的分离势具有弱吸引极小值。这项工作的结果进行了讨论，最近的模拟和理论研究的热力学力的晶界预熔。
英文摘要：
We describe a molecular dynamics framework for the direct calculation of the short-ranged structural forces underlying grain-boundary premelting and grain-coalescence in solidification. The method is applied in a comparative study of (i) a Sigma 9 <115> 120 degress twist and (ii) a Sigma 9 <110> {411} symmetric tilt boundary in a classical embedded-atom model of elemental Ni. Although both boundaries feature highly disordered structures near the melting point, the nature of the temperature dependence of the width of the disordered regions in these boundaries is qualitatively different. The former boundary displays behavior consistent with a logarithmically diverging premelted layer thickness as the melting temperature is approached from below, while the latter displays behavior featuring a finite grain-boundary width at the melting point. It is demonstrated that both types of behavior can be quantitatively described within a sharp-interface thermodynamic formalism involving a width-dependent interfacial free energy, referred to as the disjoining potential. The disjoining potential for boundary (i) is calculated to display a monotonic exponential dependence on width, while that of boundary (ii) features a weak attractive minimum. The results of this work are discussed in relation to recent simulation and theoretical studies of the thermodynamic forces underlying grain-boundary premelting.
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