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，在高温和腐蚀性大气等极端环境下，它控制着一系列广泛的现象，如扩散率、导电性和抗失效能力。缺乏强有力的GB结构-性质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GBs的性质，有必要首先了解原子在这些缺陷上的排列方式。根据五个晶体自由度的不同，GBs的原子能级结构可能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排列)。为了研究这种不同的原子结构阵列，PI和他的团队将开发一种新的几何框架，将GBs的原子结构量化为三维多面体单元。其目标是将GBs的复杂性降低到最小的基本结构单元集。这样的分类将有助于有效地计算结构-性质关系。该职业奖还支持将外展与研究相结合。为此，PI和他的团队将与当地一所大学早期高中合作，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。该协会还将通过在该协会的实验室进行暑期研究实习，培训下一代中学教师进行科学过程。PI还将开发用于教学的开源计算机模块，并传播在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工艺-结构-性能关系方面发挥着核心作用。晶界(GB)性质(能量和莫比石)及其各向异性深刻地影响着显微组织特征的演化机制。结构材料中钢骨的力学性能控制着疲劳、应力腐蚀开裂、蠕变、动载和冲击破坏等一系列的失效现象。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GB结构随GB结晶学的变化，将识别一类新的基本晶界结构，它将为在完整的五维晶体参数空间中预测一般界面的结构和能量提供基础。为了计算这组最小的界面，PI和他的团队将开发一个高效和自动化的GB结构模拟器。我们将模拟结构简单的单原子、面心立方金属系统(Al、Ni和Cu)中不同结晶学性质的GBS。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)，并将确定一组受欢迎的GB。降阶模型的热力学性质将以零开尔文的国标能量作为模型热力学性质进行评估。将通过分析最受欢迎的一组GB的软振动模式来分析动力学特性，如GB的移动性。这一职业奖还支持推广与研究的结合。为此，PI和他的团队将与当地一所大学早期高中合作，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。该协会还将通过在该协会的实验室进行暑期研究实习，培训下一代中学教师进行科学过程。国际和平研究所还将开发开放源码计算机模块，用于教授与界面结晶学理论有关的概念，并传播在研究方案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.