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：位错是晶体中线性的、可移动的缺陷，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取得了巨大的进步，但验证这些模型预测的能力却明显滞后。例如，多种显微镜方法尚未应用于一致表征位错。这项研究将开发创新的分析技术，帮助塑造缺陷分析的未来，并可用于其他金属材料，陶瓷和半导体。从历史上看，自上而下的方法已经被采用，通过宏观测量来推断缺陷上的力和它们的迁移率。这项研究通过利用电子显微镜的革命性进步和先进的原子尺度建模和多尺度探针，实现了一种自下而上的方法来确定这些基本量。这些进展被应用于高熵合金——一种具有吸引人的和不寻常的性能的新材料，包括在低温下增加的强度和断裂韧性。这项研究推进了实验和计算方法，以了解这些显著特性在基本缺陷水平的起源。这个项目协同新的教育方法，横切显微镜和计算内容。它还为本科生提供了参与跨学科高级顶点项目的机会。这项研究通过参与俄亥俄州教育数学和科学计划，影响了大学前教育。它还通过一年一度的“教师材料营”和针对8-12年级教学材料的在线资源库，为高中科学教师提供专业发展。技术描述：位错结构和行为的原子和第一性原理计算已经成为金属和合金力学行为“自下而上”建模的重要组成部分，它们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：原子尺度的计算通常缺乏在适当长度尺度上的验证。该项目的目的是通过开发一种协调的方法来定量地、实验地测量位错核心结构和迁移率，从而改变自下而上的建模。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来实现的。实验数据分析与计算技术，量化误差和提取局部变形，局部应变能，和热力学力对位错和其他缺陷。热力学研究是通过原位加热和纳米钻孔在样品中产生非平衡位错构型来进行的。这为基本位错行为的静态和动态研究开辟了令人兴奋的新可能性。这种创新的方法被应用于一个敏锐的，当前感兴趣的材料系统，其中位错水平的结构和行为是重要的，但目前未知-即“高熵”合金。获得了一种五组分fcc固溶体合金的令人振奋的初步结果，并在初步研究中得到了扩展。在程序中，随着新的合金性能的发现，应用范围不断扩大。提出的动态测量的实验和计算程序最初是使用低角度Al双晶结构开发的，该结构提供了一个具有良好定义的位错结构的简单“模型”系统。这一变革性的研究建立了强大的协议，以指导静态和动态错位分析的新兴方面。例如，所提出的显微镜方法被一致地应用于表征相同类型的缺陷结构。这项研究，当与提出的创新分析技术相结合时，有助于塑造缺陷分析的未来，并可用于其他金属材料，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.