Quantitative Determination of Dislocation Core Structure and Mobility Using Atomic Resolution Microscopy and Multiscale Modeling: Application to High Entropy Alloys

非技术描述：位错是晶体中的线性移动缺陷，它控制着金属的强度和延展性。尽管在原子尺度上对位错的结构和运动进行建模方面取得了巨大的进步，但验证这些模型预测的能力明显滞后。例如，还没有同时应用多种显微方法来表征位错。这项研究将开发创新的分析技术，有助于塑造缺陷分析的未来，并可移植到其他金属材料、陶瓷和半导体。在历史上，一直采用自上而下的方法，使用宏观测量来推断缺陷及其流动性上的力。这项研究使自下而上的方法能够确定这些基本量，通过利用先进的原子尺度建模和多尺度探测器利用电子显微镜的革命性进步。这些进展被应用于高熵合金--一种新型材料，具有吸引人的和不同寻常的特性，包括在较低温度下提高强度和断裂韧性。这项研究推进了实验和计算方法，以在根本缺陷水平上理解这些显着特性的起源。这个项目将交叉显微镜和计算内容的新教育方法结合在一起。它还为本科生提供参与跨学科高级顶峰项目的机会。这项研究通过参与俄亥俄州教育部的数学和科学项目，影响了大学前的教育。它还为高中科学教师提供专业发展，通过一年一度的“教师材料夏令营”和针对8-12年级的在线教学材料存储库。技术描述：位错结构和行为的原子论和第一性原理计算已成为金属和合金力学行为的“自下而上”建模的重要组成部分，它们也是材料基因组计划中计算材料设计的关键组成部分。然而，存在一个固有的问题：原子尺度的计算往往缺乏适当长度尺度的验证。这个项目的目的是改变自下而上的建模，开发一种协调的方法，用于对位错核心结构和迁移率的定量、实验信息的测量。这是通过将原子分辨率扫描电子显微镜的最新进展与原子尺度计算和多尺度建模相结合而实现的。用计算技术对实验数据进行分析，量化误差并提取位错和其他缺陷上的局部变形、局部应变能和热力学作用力。利用原位加热和纳米钻孔在试件中制造非平衡位错组态，进行了热力学研究。这为静态和动态研究基本位错行为开辟了令人兴奋的新可能性。这种创新的方法被应用到一个强烈的、当前感兴趣的材料系统中，对该材料系统来说，位错能级结构和行为很重要，但目前尚不清楚--即“高熵”合金。一种五组分面心立方固溶体合金已经获得了令人振奋的初步结果，并在最初的研究中得到了推广。在项目期间，随着新的合金行为的发现，这些应用得到了扩展。所提出的动态测量的实验和计算程序最初是使用小角度的Al双晶结构来开发的，该结构提供了具有明确的位错结构的简单的“模型”系统。这项变革性的研究建立了稳健的协议，以指导静态和动态位错分析的新兴方面。例如，所提出的显微镜方法被共同应用于表征相同类型的缺陷结构。这项研究与提出的创新分析技术相结合，有助于塑造缺陷分析的未来，并可移植到其他金属材料、陶瓷和半导体。

Non-Technical Description: Dislocations are linear, mobile defects in crystals that control the strength and ductility of metals. Despite tremendous advances to model the structure and movement of dislocations at the atomic scale, the ability to validate these model predictions is significantly lagging. For instance, multiple microscopy methods have not been applied in concert to characterize dislocations. This research will develop innovative analysis techniques that help shape the future of defect analysis and are transportable to other metallic materials, ceramics, and semiconductors. Historically, top-down approaches have been employed whereby macroscopic measurements are used to deduce forces on defects and their mobility. This research enables a bottoms-up approach to determine these fundamental quantities, by leveraging revolutionary advances in electron microscopy with advanced atomic-scale modeling and multi-scale probes. These advances are applied to the high entropy alloys -a new class of materials with attractive and unusual properties, including increased strength and fracture toughness at lower temperatures. This research advances experimental and computational approaches to understand the origin of these remarkable properties at a fundamental defect level. This project synergizes new educational approaches that cross-cut microscopy and computational content. It also provides opportunities for undergraduate students to participate in interdisciplinary senior capstone projects. This research impacts pre-college education, through participation in the Ohio Department of Education Math and Science Program. It also offers professional development for high school science teachers, through an annual 'Materials Camp for Teachers' and an on-line repository of instructional materials targeted for grades 8-12.Technical Description: Atomistic and first principles calculations of dislocation structure and behavior have become an essential part of 'bottoms-up' modeling of the mechanical behavior of metals and alloys, and they are a key component of computational materials design in the Materials Genome Initiative. However, an inherent problem exists: atomic-scale calculations often lack validation at an appropriate length scale. The aim of this project is to transform bottoms-up modeling, by developing a coordinated approach for quantitative, experimentally-informed measurements of dislocation core structures and mobility. This is achieved by coupling recent advances in atomic resolution scanning electron microscopy with atomic-scale computations and multi-scale modeling. The experimental data are analyzed with computational techniques that quantify errors and extract local deformation, local strain energy, and thermodynamic forces on dislocations and other defects. Thermo-mechanical studies are conducted using in-situ heating and nano-drilling of holes in specimens to create non-equilibrium dislocation configurations. This opens up exciting, new possibilities for both static and dynamic study of fundamental dislocation behavior. This innovative approach is applied to a material system of keen, current interest, for which dislocation-level structure and behavior is important but presently unknown - namely the 'high entropy' alloys. Exciting preliminary results for a five-component fcc solid solution alloy have been obtained and are extended during initial studies. The applications are expanded during the program and as new alloy behavior is discovered. Experimental and computational procedures for the proposed dynamic measurements are developed initially using low-angle Al bicrystal structures that offer a simple 'model' system with well-defined dislocation structures. This transformative research establishes robust protocols to guide the emerging aspects for both static and dynamic dislocation analysis. For instance, the proposed microscopy methods are applied in concert to characterize the same type of defect structures. This research, when combined with the proposed innovative analysis techniques, helps to shape the future of defect analysis and is transportable to other metallic materials, ceramics, and semiconductors.