Nanoscale Mechanisms in Alloy Oxidation: Binary and Ternary Ni-Based Alloys

非技术腐蚀在最一般的术语中是指材料由于表面的化学反应而分解，在日常生活中经常被视为钢铁上的铁锈。腐蚀无处不在，举几个例子，在汽车和水管中，随着时间的推移，大多数金属都会分解，在最极端的情况下，这可能会导致灾难性的故障。在美国，每年因腐蚀造成的损失占国民生产总值的3%以上。保护材料不受腐蚀是新材料设计的关键。材料腐蚀和降解的速度很大程度上取决于环境条件，如温度、湿度、盐度、有毒烟雾和辐射。通常情况下，会在材料上涂上涂层，以防止其迅速生锈。例如，镍基高温合金被用于生产能源和推进飞机的涡轮叶片，但它们在极端高温环境下会迅速降解。通常在这些合金中添加少量的元素，如W、Mo、Cr，以显著减少腐蚀。这项工作结合了前沿的实验和计算工具，以在原子尺度上了解从最初的氧撞击材料表面到镍基高温合金中保护性氧化物的形成，以及添加某些元素以控制和减少腐蚀的有益作用。这些知识将有助于未来合金的设计，特别是那些在极端环境中使用的合金。这项工作将有助于研究生和本科生的研究经验。此外，弗吉尼亚大学和詹姆斯·麦迪逊大学将合作开发基于视频的点播讲座组合。技术腐蚀和水腐蚀/氧化是材料损失和灾难性故障的主要原因。因此，耐腐蚀性被列为合金工程的设计标准。这项工作将加深对以铬、钼、钨为合金元素的镍基高温合金氧化机理的理解。通过在纳米尺度上探索合金和氧化物中的几何、电子和化学结构，可以从机理上理解合金表面转变为氧化层的初始反应顺序。这项工作促进了对氧化的基本理解，并将促进计算方法的发展，以设计保护涂层和更好的合金。这项建议旨在对二元和三元镍基合金氧化的初始步骤有一个详细的机理理解。用传统的表面科学和催化方法研究了镍铬、镍铬钼或镍铬钨合金表面氧化层的形成，并在纳米尺度上提供了所需的几何、电子和化学信息。这包括扫描隧道显微镜和同步加速器设施中的电子能谱仪，从清洁的合金开始，一直到封闭的氧化层，对各种合金成分和加工条件(T，p(O2))进行原位和操作观察。大多数实验都处于NiO和CrO形成竞争的区域。用蒙特卡罗方法和密度泛函理论模拟了原始合金中的元素分布，并结合偏析和扩散系数的实验研究来了解各种合金中近表面的铬含量。表面相变、重构和特定于元素的形核路径有助于氧化物异质性的发展，并被少量合金元素(W，Mo)显著改变。用OPANDO实验(常压、x射线、光电子和吸收光谱)测试了异质性向Cabrera-Mott区的传播。本提案中发展的材料知识将提供对原子尺度上的机制的理解，这对于注入计算方法，包括机器学习方法，以及实现未来的预测能力至关重要。将开发一个基于视频的点播表面科学讲座组合，将教科书知识和相关文献结合起来。这些视频为UVA和以本科为主的詹姆斯·麦迪逊大学(James Madison University)的本科生和研究生建立了表面科学、腐蚀、催化、薄膜生长和分析技术方面的知识库。PI致力于拓展和多样化，并将为拟议的研究项目招募UG学生。这一奖项反映了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-technicalCorrosion is in the most general terms the breakdown of a material due to chemical reactions at the surface, and is often seen in daily life as rust on steel and iron. Corrosion is everywhere, in cars and water pipes to name a few, and most metals will break down over time which can lead in the most extreme case to catastrophic failure. The annual cost incurred in the U.S. by corrosion is more than 3% of the gross national product. Protecting materials from corrosion is critical to the design of new materials. How fast a material corrodes and degrades depends strongly on the environmental conditions, such as temperature, and humidity, salinity, noxious fumes, and radiation. Often, coatings are placed on materials that protects it from rusting rapidly. For example, Ni-based superalloy are used in turbine blades for energy production and propelling airplanes, yet they degrade rapidly in the extreme high temperature environment. Small additions of elements are often added, such as W, Mo, Cr, to these alloys to dramatically reduce corrosion. This work combines forefront experimental and computational tools to gain understanding at the atomic scale on how rust develops from the initial oxygen striking the surface of a material to the development of a protective oxide in Ni-based superalloys, and the beneficial role of adding certain elements to control and reduce corrosion. Such knowledge will benefit the design of future alloys, especially those used in extreme environments. This work will contribute to graduate and undergraduate research experiences. Furthermore, a video-based portfolio of on-demand lectures will be developed through a collaboration between University of Virginia and James Madison University.TechnicalDry and aqueous corrosion/oxidation are leading causes of materials loss, and catastrophic failure. Corrosion resistance is therefore included as a design criterium in alloy engineering. The proposed work will advance understanding of oxidation mechanisms in Ni-based superalloys with Cr, Mo, and W as alloying elements. Mechanistic understanding of the initial reaction sequence where the alloy surface transforms into an oxide layer, is achieved by probing the geometric, electronic, and chemical structure in alloy and oxide at the nanometer scale. This work advances fundamental understanding of oxidation, and will infuse the development of computational methods to design protective coatings and better alloys. This proposal aims to develop a detailed mechanistic understanding of the initial steps in alloy oxidation of binary and ternary Ni-based alloys. The formation of oxide layers on Ni-Cr, and Ni-Cr-Mo or Ni-Cr-W alloys is studied with methods traditionally used in surface science and catalysis and afford the requisite geometric, electronic, and chemical information at the nanoscale. This includes scanning tunneling microscopy, and electron spectroscopies at synchrotron facilities with in-situ and operando observations starting with the clean alloy all the way to the closed oxide layer for a wide range of alloy composition and processing conditions (T, p(O2)). The majority of experiments are positioned in a regime where NiO and chromia formation compete. Monte Carlo methods, and density functional theory are used to model the element distribution in the pristine alloy and combined with experimental studies of segregation, and diffusivity to understand the near-surface Cr inventory in various alloys. Surface phase transformations, reconstructions, and element-specific nucleation pathways contribute to the development of oxide heterogeneity and are dramatically modified by minor alloying elements (W, Mo). The propagation of heterogeneity into the Cabrera-Mott regime is tested with operando experiments (ambient pressure x-ray photoelectron and absorption spectroscopies). The materials knowledge developed in this proposal will provide an understanding of mechanisms at the atomic scale, which are critical to infuse computational approaches, including machine learning approaches, and to achieve future predictive capabilities. A video-based portfolio of on-demand Surface Science lectures will be developed integrating textbook knowledge and pertinent literature. These videos build the knowledge base in surface science, corrosion, catalysis, thin film growth and analytical techniques for undergraduate and graduate students at UVa and James Madison University (Prof. Baber), a primarily undergraduate institution. The PI is committed to outreach and diversity, and will recruit UG students for the proposed research project.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.