Role of Defects and Stacking-Fault Energy in Deformation and Fracture of Nanotwinned Metals

非技术性总结：相干孪晶界是材料中的缺陷，在理论和实验上被广泛描述为完美的界面，在各种材料中发挥着重要作用。相干孪晶界在增强、保持延展性和保持高导电性方面的能力已得到充分证明。由于新开发的成像工具和计算模型，本研究中先进的计算和实验技术的集成将导致对含有这些缺陷的金属金属的塑性和断裂有一个根本的新认识。多学科研究团队将带来新的认识，并可能加速下一代结构材料的部署，这些材料具有耐受极端环境（如高辐射暴露和高温）的能力。该项目的教育和推广部分还将包括对本科生和研究生的研究培训和指导，组织国际研讨会，以及吸引和留住STEM大一和大二大学生的活动。技术总结：这项计算和实验相结合的研究旨在了解新观察到的弯曲孪晶边界缺陷在纳米孪晶金属变形和断裂中的基本作用，特别关注具有低和中等堆叠断层能量的面心立方金属。这个项目的目标有三个方面。首先，我们将研究Cu、Ag和Ag-Cu合金中新型纳米孪晶金属的新型扭结依赖塑性变形过程，方法包括原子模拟、透射电子显微镜内的新型纳米衍射映射技术、原位同步加速器x射线衍射拉伸测试和原子力显微镜纳米压痕实验。其次，我们将研究温度、层错能、缺陷密度和晶界结构对这些金属硬化和软化机制的影响。第三，采用准连续介质计算机模拟的多尺度方法来模拟孪晶边界缺陷和孪晶尺寸对断裂韧性的影响。该项目将受益于PI在纳米孪晶系统理论和计算材料研究方面的专业知识，并与劳伦斯利弗莫尔国家实验室和艾姆斯实验室的科学家合作，他们将对独立的纳米孪晶薄膜进行最先进的实验。

Non-technical Summary:Coherent twin boundaries are defects in materials, widely described as perfect interfaces theoretically and experimentally, playing a significant role in a variety of materials. The ability of coherent twin boundaries in strengthening, maintaining the ductility, and retaining high electrical conductivity is well documented. The integration of advanced computational and experimental techniques in this research will lead to a fundamentally new understanding of plasticity and fracture in metallic metals containing these defects because of newly-developed imaging tools and computational models. The multidisciplinary research team will allow new understanding and may accelerate the deployment of the next-generation structural materials with tolerance to extreme environments such as high radiation exposure and high temperature. The education and outreach components of this project will also include research training and mentoring of undergraduate and graduate students, organization of an international symposium, and activities for attraction and retention of freshman and sophomore college students in STEM.Technical Summary:This combined computational and experimental study aims to understand the fundamental role of newly-observed kink-like twin boundary defects in the deformation and fracture of nanotwinned metals, with a particular focus on face-centered cubic metals with low and intermediate stacking-fault energies. The objectives of this project are three-fold. First, we will study new kink-dependent plastic deformation processes in model nanotwinned metals in Cu, Ag and Ag-Cu alloys using atomistic simulations tightly coupled to a new nanodiffraction mapping technique inside a transmission electron microscope, in-situ synchrotron x-ray diffraction tensile tests, and atomic force microscopy nanoindentation experiments. Second, we will examine the impact of temperature, stacking-fault energy, defect density, and grain boundary structure on hardening and softening mechanisms in these metals. Third, a multiscale approach using quasi-continuum computer simulations will be deployed to model the effects of twin boundary defects and twin size on fracture toughness. This project will benefit from the expertise of the PI in theoretical and computational materials research in nanotwinned systems, and from collaboration with scientists at Lawrence Livermore National Laboratory and Ames Laboratory who will perform state-of-the-art experiments on freestanding nanotwinned films.