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

非技术性腐蚀是最一般的术语，是由于表面的化学反应导致的材料分解，在日常生活中经常看到钢铁生锈。腐蚀无处不在，在汽车和水管中仅举几例，大多数金属会随着时间的推移而分解，在最极端的情况下会导致灾难性的故障。美国每年因腐蚀而产生的成本超过国民生产总值的3%。保护材料免受腐蚀对于新材料的设计至关重要。 材料腐蚀和降解的速度在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，涂层被放置在材料上，以保护其免受快速生锈。 例如，镍基高温合金被用于涡轮机叶片中用于能源生产和推进飞机，但是它们在极端高温环境中迅速降解。 通常向这些合金中添加少量元素，例如W、Mo、Cr，以显著降低腐蚀。 这项工作结合了最前沿的实验和计算工具，以在原子尺度上了解生锈是如何从最初的氧气撞击材料表面发展到镍基高温合金中保护性氧化物的发展，以及添加某些元素对控制和减少腐蚀的有益作用。 这些知识将有利于未来合金的设计，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一个基于视频的点播讲座组合。技术干燥和水腐蚀/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。这项工作将促进对以Cr、Mo和W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测合金和氧化物中的几何、电子和化学结构，实现了对合金表面转变为氧化物层的初始反应序列的机械理解。这项工作推进了对氧化的基本理解，并将注入计算方法的发展，以设计保护涂层和更好的合金。该提案旨在对二元和三元镍基合金的合金氧化的初始步骤进行详细的机械理解。Ni-Cr、Ni-Cr-Mo或Ni-Cr-W合金上氧化层的形成是用传统的表面科学和催化方法研究的，并提供了纳米尺度上所需的几何、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的电子光谱，从清洁合金开始，一直到封闭的氧化层，进行原位和操作观察，以获得广泛的合金成分和加工条件（T，p（O2））。大多数实验定位在NiO和氧化铬形成竞争的制度中。蒙特卡罗方法和密度泛函理论用于模拟原始合金中的元素分布，并结合偏析和扩散率的实验研究，以了解各种合金中的近表面Cr库存。表面相变，重建，和元素特定的成核途径有助于发展的氧化物异质性和显着修改的微量合金元素（W，Mo）。的Cabrera-莫特政权的异质性的传播进行测试与operando实验（环境压力的X射线光电子和吸收光谱）。本提案中开发的材料知识将提供对原子尺度机制的理解，这对于注入计算方法（包括机器学习方法）和实现未来预测能力至关重要。一个基于视频的组合按需表面科学讲座将开发整合教科书知识和相关文献。这些视频为UVa和詹姆斯麦迪逊大学（主要是本科院校）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的知识库。PI致力于外展和多样性，并将为拟议的研究项目招募UG学生。该奖项反映了NSF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-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.