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： 位错是晶体中控制金属强度和延展性的线性、移动的缺陷。 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进展，但验证这些模型预测的能力却显着滞后。 例如，多种显微镜方法尚未被一致地应用于表征位错。 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，并可移植到其他金属材料，陶瓷和半导体。 历史上，已经采用自上而下的方法，其中宏观测量用于推断缺陷上的力及其移动性。这项研究使自下而上的方法来确定这些基本量，通过利用先进的原子尺度建模和多尺度探针的电子显微镜的革命性进展。 这些进展应用于高熵合金-一类具有吸引人的和不寻常的特性的新材料，包括在较低温度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，以了解这些显着属性的起源在一个基本的缺陷水平。该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部的数学和科学项目，影响了大学预科教育。它还为高中科学教师提供专业发展，通过每年的“教师材料营”和针对8- 12年级的教学材料在线存储库。技术描述： 位错结构和行为的原子和第一原理计算已经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，并且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：原子尺度的计算往往缺乏适当的长度尺度的验证。 该项目的目的是通过开发一种协调的方法，对位错核心结构和流动性进行定量的、实验性的测量，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。实验数据进行了分析与计算技术，量化误差和提取局部变形，局部应变能，和热力学力的位错和其他缺陷。 热机械研究进行原位加热和纳米钻孔的标本中创建非平衡位错配置。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到一个材料系统的敏锐，当前的利益，其中位错水平的结构和行为是重要的，但目前未知的-即“高熵”合金。 令人兴奋的五元面心立方固溶体合金的初步结果已经获得，并在初步研究中扩展。随着新合金行为的发现，应用在程序中得到了扩展。实验和计算程序提出的动态测量开发最初使用低角度铝双晶体结构，提供了一个简单的“模型”系统与定义良好的位错结构。 这项变革性的研究建立了强大的协议，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一致地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.