RII Track-4: Experimentally-informed Mesoscale Modeling of Anisotropic Grain Boundary Solute Segregation in Nanocrystalline Alloys

几乎所有的结构材料都是多晶体系；它们的微观结构是由在内部界面连接的结晶颗粒组成的，称为晶界（GBs）。由于纳米级的晶粒尺寸，纳米晶（NC）金属表现出独特的性能组合，而这些特性在粗晶金属中是不常见的。然而，在加工过程中或在使用条件下，数控金属易受快速晶粒粗化的影响，这反过来限制了它们在许多工程应用中的使用，如结构，能源和电子。最近的实验结果表明，GB溶质偏析是一种设计策略，可以操纵界面性能并开发热稳定的数控金属。通过协调的实验和计算研究，本项目的主要研究目标是获得GB几何在溶质偏析中的作用及其对NC合金热稳定性的影响的基本见解。该项目的实验部分将在桑迪亚国家实验室（CINT-SNL）的集成纳米技术中心进行。该项目将使PI处于纳米材料、冶金和界面物理创新研究的最前沿，并将成为克莱姆森大学和CINT-SNL未来合作和伙伴关系的催化剂。此外，该项目为培养下一代工程师和科学家提供了一个肥沃的途径，这些工程师和科学家具备在南卡罗来纳州这个新兴的先进制造业中心的知识密集型产业中工作所必需的跨学科技能。虽然最近在使用GB溶质偏析来设计热稳定的数控金属方面取得了很大的进展，但我们目前的理解仍然缺乏，因为大多数现有的努力依赖于偏析的各向同性假设-溶质原子均匀地偏析到所有GB。这是一个过于简单的假设，因为GB属性受到边界几何形状的极大影响。本项目通过阐明GB几何形状对溶质偏析行为的影响，推进了目前对界面偏析的理解。该项目的实验重点将在桑迪亚国家实验室（CINT-SNL）的集成纳米技术中心进行，该中心将允许PI利用一套尖端的高分辨率显微镜设备。PI将使用工具，包括像差校正扫描透射电子显微镜，能量色散x射线光谱学和CINT-SNL的x射线衍射，进行原位高温实验，样品的详细层析重建，化学测绘，以及NC系统中纹理和GB特征的定向成像显微镜，目的是表征和量化各种GB类型的GB溶质浓度。PI将使用界面吸附分析模型对实验数据进行分析，以获得偏析能，作为最近开发的NC合金中GB偏析和微观结构演变的中尺度模型的输入参数。利用实验模型，我们将进行系统的计算研究，以阐明各向异性GB溶质偏析对NC合金晶粒生长和热稳定性的影响。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。

Nearly all structural materials are polycrystalline systems; their microstructures are comprised of crystalline grains that are joined at internal interfaces, termed grain boundaries (GBs). Owing to their nanometric grain size, nanocrystalline (NC) metals exhibit unique combinations of properties that are not commonly observed in their coarse-grained counterparts. However, NC metals are susceptible to rapid grain coarsening during processing or under service conditions, which in turn limits their use in many engineering applications, such as structural, energy, and electronics. Recent experimental findings suggest GB solute segregation as a design strategy to manipulate interface properties and develop thermally stable NC metals. Through coordinated experimental and computational studies, the main research objective of this project is to gain fundamental insights into the role of GB geometry in solute segregation and the resultant impact on the thermal stability of NC alloys. The experimental portion of this project will be conducted at the Center for Integrated Nanotechnologies at Sandia National Laboratories (CINT-SNL). This project will uniquely position the PI to be at the forefront of innovative research on nanomaterials, metallurgy and interface physics, and it will serve as a catalyst for future collaborations and partnerships between Clemson University and CINT-SNL. Further, this project provides a fertile avenue to train future generation of engineers and scientists with the interdisciplinary skill set necessary for careers in knowledge-intensive industries in South Carolina, which is an emerging advanced manufacturing hub.While great strides have been recently made towards the use of GB solute segregation to design thermally stable NC metals, our current understanding is still lacking as most existing efforts rely on the isotropy assumption in segregation - solute atoms segregate equally and uniformly to all GBs. This is an overly simplistic assumption as GB properties are greatly influenced by the boundary’s geometry. This project advances the current understanding of interface segregation by elucidating the impact of GB geometry on solute segregation behavior. The experimental thrust of this project will be performed at the Center for Integrated Nanotechnologies at Sandia National Laboratories (CINT-SNL), which will allow the PI to take advantage of a suite of cutting-edge high-resolution microscopy facilities. The PI will use tools, including aberration-corrected scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction at CINT-SNL to conduct in situ high-temperature experiments, detailed tomographic reconstructions of samples, chemical mapping, and orientation imaging microscopy of texture and GB character in NC systems with the goal of characterizing and quantifying GB solute concentration for a wide range of GB types. The PI will perform analysis, employing analytical models of interface adsorption, of the experimental data to obtain segregation energies that serve as input parameters to a recently developed mesoscale model of GB segregation and microstructural evolution in NC alloys. Using the experimentally informed model, we will perform systematic computational studies to elucidate the impact of anisotropic GB solute segregation on grain growth and thermal stability of NC alloys.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.