计算晶界“相图”
Computing Grain Boundary 'Phase' Diagrams
摘要：
晶界（GB）可以被视为二维（2-D）界面相（也称为“络合物”），可以经历界面类相变。由于体相图和相图计算（CALPHAD）方法是现代材料科学的基础，我们建议将它们扩展到GB具有同样重要的影响。这篇透视文章回顾了一系列的研究来计算GB对应体相图。首先，一个现象学的界面热力学模型被开发来构建GB λ图，以预测高温GB无序和相关的趋势，在烧结和其他性能的金属和陶瓷材料。同时，利用Ising型晶格统计热力学模型来构建GB吸附图，其预测一级GB吸附（a.k.a.隔离）过渡和临界现象。这两个简化的热力学模型强调GB结构（无序）和化学（吸附）方面，分别。随后，混合蒙特卡罗和分子动力学原子模拟被用来计算更严格和准确的GB“相”图。计算的热力学和结构性能的GB图进一步扩展到包括机械性能。此外，机器学习与原子模拟相结合，以预测GB属性作为高熵合金中给定GB的5-D空间中的四个独立组成变量和温度的函数，或者作为7-D空间中二元合金的5个GB宏观（晶体学）自由度（DOF）加上温度和组成的函数。其他相关的研究进行了审查。展望了未来的研究方向，包括高熵晶界和电（或电化学）诱导晶界相变两个新兴领域。
英文摘要：
Grain boundaries (GBs) can be treated as two-dimensional (2-D) interfacial phases (also called 'complexions') that can undergo interfacial phase-like transitions. As bulk phase diagrams and calculation of phase diagram (CALPHAD) methods are a foundation for modern materials science, we propose to extend them to GBs to have equally significant impacts. This perspective article reviews a series of studies to compute the GB counterparts to bulk phase diagrams. First, a phenomenological interfacial thermodynamic model was developed to construct GB lambda diagrams to forecast high-temperature GB disordering and related trends in sintering and other properties for both metallic and ceramic materials. In parallel, an Ising-type lattice statistical thermodynamic model was utilized to construct GB adsorption diagrams, which predicted first-order GB adsorption (a.k.a. segregation) transitions and critical phenomena. These two simplified thermodynamic models emphasize on the GB structural (disordering) and chemical (adsorption) aspects, respectively. Subsequently, hybrid Monte Carlo and molecular dynamics atomistic simulations were used to compute more rigorous and accurate GB 'phase' diagrams. Computed GB diagrams of thermodynamic and structural properties were further extended to include mechanical properties. Moreover, machine learning was combined with atomistic simulations to predict GB properties as functions of four independent compositional variables and temperature in a 5-D space for a given GB in high-entropy alloys or as functions of five GB macroscopic (crystallographic) degrees of freedom (DOFs) plus temperature and composition for a binary alloy in a 7-D space. Relevant other studies are examined. Future perspective and outlook, including two emerging fields of high-entropy grain boundaries (HEGBs) and electrically (or electrochemically) induced GB transitions, are discussed.
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