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系统;它们的微观结构由在内部界面处连接的晶粒组成，称为晶界（GB）。由于其纳米晶粒尺寸，纳米晶（NC）金属表现出独特的性能组合，而这些性能在粗晶粒对应物中并不常见。然而，NC金属在加工过程中或在使用条件下容易发生快速晶粒粗化，这反过来限制了它们在许多工程应用中的使用，例如结构，能源和电子。最近的实验结果表明，GB溶质偏析的设计策略，以操纵界面性能和开发热稳定的NC金属。通过协调的实验和计算研究，该项目的主要研究目标是获得基本的见解GB的几何形状中的溶质偏析的作用和由此产生的影响NC合金的热稳定性。该项目的实验部分将在桑迪亚国家实验室（CINT-SNL）的综合纳米技术中心进行。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之间未来合作和伙伴关系的催化剂。此外，该项目提供了一个肥沃的途径，以培养未来一代的工程师和科学家的跨学科技能，必要的职业生涯在知识密集型产业在南卡罗来纳州，这是一个新兴的先进制造业枢纽。虽然最近取得了很大的进步，对使用GB溶质偏析设计热稳定的NC金属，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中的各向同性假设-溶质原子均等且均匀地偏析到所有GB。这是一个过于简单的假设，因为GB属性受边界几何形状的影响很大。本计画借由阐明晶界几何形状对溶质偏析行为的影响，增进目前对界面偏析的了解。该项目的实验重点将在桑迪亚国家实验室（CINT-SNL）的综合纳米技术中心进行，这将使PI能够利用一套尖端的高分辨率显微镜设施。PI将在CINT-SNL使用包括像差校正扫描透射电子显微镜、能量色散X射线光谱和X射线衍射在内的工具进行原位高温实验、样品的详细断层扫描重建、化学绘图以及NC系统中纹理和GB特征的取向成像显微镜，目的是表征和量化各种GB类型的GB溶质浓度。PI将进行分析，采用界面吸附的分析模型，实验数据，以获得偏析能量，作为输入参数，最近开发的介观模型的GB偏析和NC合金的微观结构演变。使用实验知情的模型，我们将进行系统的计算研究，以阐明各向异性GB溶质偏析对晶粒生长和NC合金的热稳定性的影响。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.