Materials World Network: Collaborative Research: Quantifying the Role of Impurities that Control Stress-Driven Grain Growth in Nanocrystalline Metals

该材料世界网络奖支持一个来自宾夕法尼亚大学、约翰霍普金斯大学和悉尼大学（澳大利亚）的国际多学科研究团队，阐明杂质在耦合晶界迁移中的基本作用，这在纳米晶金属的应力辅助室温晶粒生长的观察中得到了体现。最近的研究结果表明，纳米晶金属的变形机制不仅与微晶金属的变形机制不同，而且也是动态的。局部晶界被杂质钉住是理解和最终控制应力驱动的微观结构演变的核心，但直到最近，局部掺杂浓度和空间分布的原子水平实验表征还不可能。我们的全球团队将使用最先进的3D原子探针断层扫描技术来研究通过反应溅射合成的纳米晶金属薄膜的局部结构和杂质分离，从而在材料中系统地引入不同数量的掺杂剂。特别的重点将放在表征内在和外在参数（晶粒尺寸，杂质含量，边界取向等）对晶粒生长和纳米晶体薄膜的动态力学行为的影响。控制杂质对晶界的束缚，控制应力驱动的微观结构演变，为调整纳米晶材料的力学性能提供了一条独特的途径。微观结构通过动态演化来增强其变形机制以适应应力的能力，以及通过局部空间控制掺杂来控制晶界迁移的阈值应力，这两种能力的结合将促进原子水平工程的发展，并有可能引入一类新的材料。新的表征和原位测试工具和方法将被开发和利用，推动实验纳米科学的前沿。拟议中的材料世界网络团队将设计和教授针对研究和工业科学家和工程师的3D原子探针断层扫描和原位机械测试的短期课程。拟议的本科生整合将吸引年轻的科学家和工程师参与新颖的国际研究活动，提供经验和机会，使学生成为更好的全球公民。

This Materials World Network award supports an international multidisciplinary research team from University of Pennsylvania, Johns Hopkins University, and University of Sydney (Australia) to elucidate the fundamental role of impurities on coupled grain boundary migration as manifest in the observation of stress-assisted room temperature grain growth in nanocrystalline metals. This study is motivated by recent findings that showed that deformation mechanisms in nanocrystalline metals are not only different to those in microcrystalline metals but are dynamic as well. Local grain boundary pinning by impurities is central to the understanding, and ultimately control, of stress-driven microstructural evolution, but until recently the atomic-level experimental characterization of local dopant concentration and spatial distribution has not been possible. Our global team will use state-of-the-art 3D atom probe tomography to investigate local structure and impurity segregation in nanocrystalline metal thin films that have been synthesized by reactive sputtering to introduce systematically varied amounts of dopants in the material. Special emphasis will be placed on characterizing the effect of intrinsic and extrinsic parameters (grain size, impurity content, boundary orientation, etc.) on both grain growth and the attendant, dynamic, mechanical behavior of nanocrystalline films.Controlling impurity pinning of grain boundaries controlling stress-driven microstructural evolution offers a unique avenue for tailoring the mechanical properties of nanocrystalline materials. The combination of a microstructure's ability to augment its deformation mechanisms to accommodate stress via dynamic evolution and control of the threshold stress for grain boundary migration by local spatially controlled doping would facilitate atomic-level engineering and potentially introduce a new class of materials. Novel characterization and in situ testing tools and methods will be developed and utilized, pushing the frontier of experimental nanoscience. The proposed Materials World Network team will design and teach short courses about 3D atom probe tomography and in situ mechanical testing targeted at research and industrial scientists and engineers. The proposed integration of undergraduate students will engage young scientists and engineers in novel and international research activities, providing experiences and opportunities that will allow students to become better global citizens.