CAREER: Mapping the Genome of Metallic Grain Boundaries - Structure, Thermodynamics and Kinetics

非技术摘要：晶界（GB）是工程材料中的二维缺陷，它控制着各种现象，如扩散率，导电性和在高温和腐蚀性气氛等极端环境下的抗破坏性。缺乏强有力的GB结构-性能关系被认为是理解多晶材料行为的最大障碍之一。为了分析GB的性质，有必要首先了解原子在这些缺陷处的排列方式。GB的原子级结构可以从高度有序的堆积到完全无序的排列（如在金属玻璃中观察到的），这取决于五个晶体学自由度。为了研究这种多样化的原子结构，PI和他的团队将开发一种新的几何框架来量化作为三维多面体单元的GB的原子结构。我们的目标是减少的复杂性的GB的基本结构单元的最小集合。这样的分类将有助于结构-性质关系的有效计算。该职业奖还支持外展与研究的整合。为此，PI和他的团队将与当地一所早期大学高中合作，为高中生开发演示和计算机模拟练习，以探索材料科学和工程的概念。PI还将通过在PI实验室的暑期研究实习来培训下一代中学教师的科学过程。PI还将开发用于教学的开源计算机模块，并传播研究计划期间开发的模拟工具。技术摘要：界面在理解多晶材料的加工-结构-性能关系方面发挥着核心作用。微观结构特征的演变机制受到晶界（GB）性质（能量和迁移率）及其各向异性的深刻影响。结构材料中晶界的力学性能决定了材料的疲劳、应力腐蚀开裂、蠕变、动态和冲击载荷下的失效等一系列失效现象。即使是新型抗损伤结构材料的设计也需要对界面的结构特征和性能进行量化。为了更好地理解原子结构并量化作为GB晶体学函数的GB结构的变化，一类新的基本晶界结构，这将为预测完整的五维晶体学参数空间中的一般界面的结构和能量提供基础集，将被识别。为了计算这个最小的接口集，PI和他的团队将开发一个高效的自动化GB结构模拟器。将模拟结构简单的单原子、面心立方金属系统（Al、Ni和Cu）中不同晶体学特征的GB。将分析GB中原子的Voronoi网络和Delaunay镶嵌，以计算三维多面体结构单元模型（SUM），并确定一组有利的GB。将以零开尔文GB能量作为模型热力学性质，评估GB热力学性质的降阶模型。动力学特性，如GB迁移率，将通过分析所青睐的GB的软振动模式进行分析。该CAREER奖还支持将外联与研究相结合。为此，PI和他的团队与当地的早期大学高中合作，将为高中生开发演示和计算机模拟练习，以探索缺陷的概念及其在材料科学和工程中的作用。PI还将通过在PI实验室的暑期研究实习来培训下一代中学教师的科学过程。PI还将开发开源计算机模块，用于教授与界面晶体学理论有关的概念，并用于传播研究计划期间开发的模拟工具。

Non-Technical Abstract:Grain boundaries (GBs) are two-dimensional defects in engineering materials that govern a wide array of phenomena such as diffusivity, conductivity and resistance to failure under extreme environments like high temperatures and corrosive atmospheres. The lack of robust GB structure-property relationships is considered to be one of the biggest obstacles to understanding the behavior of polycrystalline materials. To analyze the properties of GBs, it is necessary to first understand the way in which atoms are arranged at these defects. The atomic level structure of GBs may range from a highly ordered packing to a completely disordered arrangement (such as those observed in metallic glasses) depending on five crystallographic degrees of freedom. To investigate such a diverse array of atomistic structures, the PI and his team will develop a novel geometrical framework to quantify the atomistic structure of GBs as three-dimensional polyhedral units. The objective is to reduce the complexity of GBs to a minimal set of fundamental structural units. Such a classification will facilitate an efficient computation of structure-property relationships. This CAREER award also supports the integration of outreach with research. To this end, the PI and his team, in collaboration with a local Early College High School, will develop demonstrations and computer simulation exercises for high-school students to explore concepts in materials science and engineering. The PI will also train the next generation of secondary school teachers in the scientific process through summer research internships in the PI's lab. The PI will also develop open-source computer modules for teaching and disseminate the simulation tools developed during the research program.Technical Summary:Interfaces play a central role in understanding the processing-structure-property relationships in polycrystalline materials. The mechanisms for the evolution of microstructural features are profoundly influenced by the grain boundary (GB) properties (energies, and mobilites) and their anisotropies. A wide array of failure phenomena such as fatigue, stress corrosion cracking, creep, failure under dynamic and shock loading etc. are controlled by the mechanical properties of GBs in structural materials. Even the design of novel damage resistant structural materials requires the quantification of the structural features and the properties of interfaces.To better understand the atomistic structure and quantify the variation in GB structure as a function of GB crystallography, a new class of fundamental grain boundary structures, which will provide the basis set for the prediction of the structure and energy of a general interface in the complete five-dimensional crystallographic parameter space, will be identified. In order to compute this minimal set of interfaces, the PI and his team will develop an efficient and automated GB structure simulator. GBs of varying crystallographic character in the structurally simple mono-atomic, face-centered cubic metallic systems (Al, Ni and Cu) will be simulated. The Voronoi network and the Delaunay tessellation of the atoms in the GB will be analyzed to compute a three-dimensional polyhedral Structural Unit Model (SUM) and a favored set of GBs will be identified. Reduced order models for thermodynamic properties of GBs will be evaluated with the zero-Kelvin GB energy as a model thermodynamic property. The kinetic properties, such as GB mobility, will be analyzed through the analysis of the soft vibrational modes of the favored set of GBs.This CAREER award also supports the integration of outreach with research. To this end, the PI and his team, in collaboration with a local Early College High School, will develop demonstrations and computer simulation exercises for high-school students to explore the concepts of defects and their role in materials science and engineering. The PI will also train the next generation of secondary school teachers in the scientific process through summer research internships in the PI's lab. The PI will also develop open-source computer modules for teaching concepts pertaining to the crystallographic theory of interfaces and for the dissemination of simulation tools developed during the research program.