CAREER: Connecting Grain Boundary's Metastability Evolution to Mechanical Behavior of Nanocrystalline Alloys During Non-Equilibrium Processing

非技术概述：工程金属广泛用于先进的能源、交通和国防应用。有趣的是，纳米晶体金属是由微小的纳米大小的晶体紧密排列在一起制成的，具有优越的强度和更高的耐久性。在每个晶体中，金属原子以高度有序的方式排列。然而，由于晶体彼此之间可以有不同的空间取向，邻近晶体之间边界附近的原子不再排列良好，被视为缺陷。这些缺陷对提高机械强度起着决定性的作用。因此，为了了解这些缺陷是如何提高机械强度的，PI和他的团队将使用阿贡国家实验室提供的同步加速器x射线源，并结合PI开发的先进原子建模技术，以确定在各种应力、温度和机械变形速率下变形过程中这些原子在这些缺陷附近的运动。这些见解将用于推进纳米晶体金属的时间依赖性和环境敏感性机械性能的预测理论。这项研究的结果也将利用虚拟现实（VR）辅助教学创新的课堂教学。此外，该项目旨在通过外展到各种平台来指导下一代STEM劳动力，激励资源不足的K-12学生和具有不同背景的潜在未来工程师，并吸引公众并提高他们对材料科学的认识，从而产生更广泛的影响。技术概述：了解复杂环境下亚稳晶界的行为对于开发先进能源、交通和国防应用所需的经济高效的纳米晶合金至关重要。本项目的主要目标是建立描述极端条件下晶界结构和亚稳态演化的基本基础，并利用这一基础来解释和预测非平衡加工下晶界介导的变形和由此产生的纳米晶合金的力学性能。该项目将结合先进的原子采样技术、势能景观理论和机器学习工具：(i)通过诱导特定位置的扰动，在无序原子堆积环境中获得基本结构重排和相关活化能谱的集合；（ii）通过使用随机样本共识机器学习算法进行非仿射位移场分析，实现易发生塑性变形的核原子的自动检测；（iii）建立自洽动力学理论，构建晶界各亚稳态在势能格局中的连通性，并预测随时间变化的亚稳态演化；（iv）利用势能景观辅助的新型原子建模协议，发现亚稳晶界与钉位错在多个时间尺度上的相互作用机制。该项目还将进行设计的假设驱动实验，包括x射线衍射、亚烧蚀飞秒激光脉冲和纳米压痕，以验证模型和理论预测。本研究将直接将晶界内的原子水平过程（如短程原子重排和非仿射原子位移）与纳米晶合金的宏观行为联系起来，这可能有助于开发纳米晶合金的新设计/加工空间，确定优化路线，以在复杂环境下获得具有增强性能和耐用性的新状态。该研究计划将与教育创新和推广活动相结合，包括：(i)在开发的关于结构材料的晶界和其他缺陷的新课程中利用虚拟现实和其他先进技术；（ii）通过参加密歇根大学和国家实验室的暑期学校，指导STEM领域的下一代劳动力；（iii）透过不同平台外展资源不足的小至十二年级学生和不同背景的潜在未来工程师，并分享PI的研究和职业道路，为他们提供资讯和启发，并推广高等教育；（iv）探索有吸引力的场所，如博物馆，以吸引公众，提高他们对材料科学的认识。该奖项由材料研究部的金属和金属纳米结构以及凝聚态物质和材料理论项目共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Summary:Engineering metals are used broadly for advanced energy, transportation, and defense applications. Intriguingly, nano-crystalline metals, which are made of tiny nanometer-sized crystallites packed tightly together, exhibits superior strength and improved durability. Within each crystallite, the metal atoms are arranged in a highly orderly manner. However, as the crystallites can have various spatial orientations with respect to each other, the atoms near the boundaries between neighboring crystallites are no longer well aligned and are viewed as defects. These defects play a decisive role in the enhanced mechanical strength. Thus, to understand how these defects improve the mechanical strength, the PI and his team will use synchrotron X-ray sources available at the Argonne National Laboratory complemented with advanced atomistic modeling techniques developed by the PI in order to determine the motion of these atoms near these defects during deformation under various stresses, temperatures, and rates of mechanical deformation. Such insights will be used to advance predictive theory of the nano-crystallite metals’ time-dependent and environment-sensitive mechanical performances. The outcome of this research will also be leveraged into classroom instruction using a virtual reality (VR)-assisted teaching innovation. In addition, this project aims for broader impacts by outreaching to a variety of platforms to mentor the next generation workforce in STEM, inspire under-resourced K-12 students and potential future engineers with diverse backgrounds, and engage the public and increase their awareness of material science.Technical Summary:Understanding the behavior of metastable grain boundaries at complex environments is crucial to develop cost-effective and high-performance nanocrystalline alloys demanded in advanced energy, transportation, and defense applications. The primary objective of this project is to establish a fundamental basis to describe the structural and metastability evolution of grain boundaries at extreme conditions, and to use this basis to explain and predict the grain boundary-mediated deformation and the resultant mechanical properties of nanocrystalline alloys taking place under non-equilibrium processing. The project will combine advanced atomistic sampling techniques, potential energy landscape theory, and machine learning tool to: (i) obtain the ensemble of elementary structural rearrangements and associated activation energy spectra in disordered atomic packing environments by inducing location-specific perturbations; (ii) enable an automated detection of kernel atoms prone to plastic deformation through the non-affine displacement field analysis using a random sample consensus machine learning algorithm; (iii) establish a self-consistent kinetic theory to construct the connectivity between grain boundaries’ various metastable states in the potential energy landscape and to predict the evolution of time-dependent metastability; and, (iv) discover the interaction mechanisms between metastable grain boundaries and pinning dislocations across multiple timescales using potential energy landscape-assisted novel atomistic modeling protocol. This project will also carry out designed hypothesis-driven experiments, including X-ray diffraction, sub-ablation femtosecond laser pulses, and nano-indentation, to validate the modeling and theoretical predictions. The proposed research will directly link the atomic level processes (e.g., short-range atomic rearrangements and non-affine atomic displacement) inside the grain boundaries with the macroscopic behavior of nanocrystalline alloys, which may facilitate exploiting new design/processing space of nanocrystalline alloys, identifying optimized routes to access novel states with enhanced performance and durability under complex environments.The research program will be integrated with educational innovations and outreach activities, including: (i) utilizing virtual reality and other advanced techniques in the developed new course on the subject of grain boundaries and other defects in structural materials; (ii) mentoring the next generation workforce in STEM fields by participating in Summer Schools both at the University of Michigan and at National Laboratories; (iii) outreaching to under-resourced K-12 students and potential future engineers with diverse background through various platforms, and sharing the PI’s research and career path to inform and inspire them and to promote higher education; and, (iv) exploring the attractive venues such as museums to engage the public and increase their awareness of materials science.This award is cofunded through the Metals and Metallic Nanostructures and Condensed Matter and Materials Theory programs in the Division of Materials Research.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.