Understanding Grain Boundary Multiplicity and Its Role in Deformation Mechanisms of Nanocrystalline Metals

非技术性的SUMMARYA颗粒是原子周期性排列的微晶。不同取向的颗粒之间的界面，即晶界，强烈影响(如果不是决定的话)材料的许多机械和物理性能，如强度、延性(材料在断裂前弯曲的能力)和抗辐射损伤。越来越多的科学数据表明，金属中的晶界可以有许多不同类型的原子排列(也称为多重性)，它们之间的转变会导致重大的性质变化。如果我们更好地了解晶界的多样性及其结构-性能关系，科学家和工程师就可以设计出合成策略来定制晶界，以提高纳米结构金属的机械性能。在这个项目中，加州大学欧文分校的曹鹏辉博士和辛火林博士将使用最前沿的计算建模和电子显微镜工具在原子水平上研究晶界多重性，并揭示其在确定纳米晶金属如何变形方面的关键作用。对晶界多重性的基本了解有助于设计具有理想机械性能的工程金属，用于结构应用，如航空航天和核能系统。基于项目的教育计划旨在吸引来自不同背景的高中生参与，从而激励和使未被充分代表的少数族裔追求STEM职业生涯。技术总结该项目的重点是揭示晶界的3D原子结构，并从根本上了解晶界结构的多样性如何影响纳米结构金属的塑性变形机制。科学地假设，纳米晶金属的塑性变形机制可以通过调整晶界多重数来调节。为了验证这一中心假设，我们提出了结合原子模拟、反应路径模拟、理论建模、电子断层扫描和原位透射电子显微镜实验的研究任务。这项计算和实验相结合的研究旨在解决四个主要问题：(1)如何确定晶界的三维原子结构，揭示晶界缺陷、结构单元和多重性；(2)晶界缺陷和多重性如何影响晶界的迁移性和迁移机制；(3)是否有可能通过调整晶界状态和结构多重性来控制塑性变形，从而提高纳米金属的塑性和延性？(4)缺陷晶界或相变晶界可以实现哪些新的变形机制？从这项研究中获得的物理见解将推动对纳米结构金属结构-性能关系的开发，通过控制边界的结构、多样性和晶体分布，为有效地调整力学行为奠定基础。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYA grain is a crystallite where the atoms are periodically arranged. The interface between differently oriented grains, i.e., grain boundaries, strongly influences, if not determine, many mechanical and physical properties of materials, such as strength, ductility (material’s ability to bend before breaking), and resistance to radiation damage. Increasing scientific data suggests that grain boundaries in metals can have many different kinds of atomic arrangements (also known as multiplicity), and the transition between them leads to significant property changes. If we have a better understanding of grain boundary multiplicity and its structure-property relationship, scientists and engineers can devise synthesis strategies to tailor grain boundaries towards enhanced mechanical performance of nanostructured metals. In this project, Dr. Penghui Cao and Dr. Huolin Xin at UC Irvine will use forefront computational modeling and electron microscopy tools to study grain boundary multiplicity at the atomic level and reveal its critical role in determining how nanocrystalline metals deform. A fundamental understanding of grain boundary multiplicity could facilitate the design of engineering metals with desirable mechanical properties for structural applications, such as aerospace and nuclear energy systems. The project-based education plan aims to attract the participation of high school students from diverse backgrounds and thereby motivate and enable underrepresented minorities to pursue STEM careers.TECHNICAL SUMMARYThis project centers on revealing the 3D atomic structure of grain boundaries and fundamentally understanding how grain boundary structure multiplicity influences plastic deformation mechanisms of nanostructured metals. Scientifically, we hypothesize that the plastic deformation mechanisms in nanocrystalline metals can be tuned by tailoring grain boundary multiplicity. To test this central hypothesis, we propose research tasks combining atomistic simulation, reaction pathway simulations, theoretical modeling, electron tomography, and in-situ transmission electron microscopy experiments. This integrated computational and experimental study aims to address four major questions: (1) How to determine the 3D atomic structure of grain boundaries, revealing boundary defects, structure units, and multiplicity? (2) How do grain boundary defects and multiplicity influence mobility and migration mechanisms of grain boundaries? (3) Is it possible to control plastic deformation by tailoring grain boundary state and structure multiplicity, which results in enhanced plasticity and ductility in nanocrystalline metals? (4) What are the new deformation mechanisms which can be enabled by defective grain boundary or transformed boundary? The physical insights gained from this research will advance the exploitation of structure-property relationships in nanostructured metals, laying the groundwork for effective tailoring of mechanical behaviors through controlling structure, multiplicity, crystallographic distribution of boundaries.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.