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Phase-field Crystal Study Of Grain-boundary Premelting

机译：晶界预熔的相场晶体研究

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We study the phenomenon of grain-boundary premelting for temperatures below the melting point in the phase-field crystal model of a pure material with hexagonal ordering in two dimensions. We investigate the structures of symmetric tilt boundaries as a function of misorientation θ for two different inclinations and compute in the grand canonical ensemble the "disjoining potential" V(w) that describes the fundamental interaction between crystal-melt interfaces as a function of the premelted layer width w, which is defined here in terms of the excess mass of the grain boundary via a Gibbs construction. The results reveal qualitatively different behaviors for high-angle grain boundaries that are uniformly wetted, with w diverging logarithmically as the melting point is approached from below, and low-angle boundaries that are punctuated by liquid pools surrounding dislocations, separated by solid bridges. The latter persist over a superheated range of temperature. This qualitative difference between high- and low-angle boundaries is reflected in the w dependence of the disjoining potential that is purely repulsive [V'(w) < 0 for all w] for misorientations larger than a critical angle θ_c, but switches from repulsive at small w to attractive at large w for θ < θ_c. In the latter case, V(w) has a minimum that corresponds to a premelted boundary of finite width at the melting point. Furthermore, we find that the standard wetting condition γ_(gb)(θ_c)=2γ_(sl) gives a much too low estimate of θ_c when a low-temperature value of the grain-boundary energy γ_(gb) is used. In contrast, a reasonable lower-bound estimate can be obtained if y_(gb) is extrapolated to the melting point, taking into account both the elastic softening of the material at high homologous temperature and local melting around dislocations.
机译：在二维六边形有序的纯材料的相场晶体模型中，我们研究了温度低于熔点时的晶界预熔融现象。我们研究了对称倾斜边界的结构作为两个不同倾角的失向θ的函数的关系，并在大典范合奏中计算了“解离势” V（w），该值描述了晶体熔体界面之间的基本相互作用与预熔融的关系层宽度w，在此根据通过吉布斯构造的晶界的多余质量来定义。结果表明，均匀润湿的高角度晶界在质上有不同的行为，随着熔点从下方接近，w呈对数分叉；低角度晶界被位错周围的液池所打断，并由实心桥隔开。后者在过热温度范围内持续存在。高角度和低角度边界之间的质量差异反映在分离势的w依赖性上，该分离势是纯排斥性的（对于所有w而言，V'（w）<0），对于大于临界角θ_c的取向错误，但从排斥性切换当θ<θ_c较小时，从小到大。在后一种情况下，V（w）的最小值对应于在熔点处具有有限宽度的预熔融边界。此外，我们发现当使用晶界能γ_（gb）的低温值时，标准润湿条件γ_（gb）（θ_c）=2γ_（sl）给出的θ_c估计值太低。相反，如果将y_（gb）外推到熔点，则可以得到合理的下界估计值，同时考虑到材料在高同源温度下的弹性软化和位错周围的局部熔化。

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