Determining Pathways for Improved Oxidation Resistance in Compositionally Complex Alloys

金属合金广泛用作许多高温应用中的结构材料，例如发电厂、飞机发动机和火箭发动机。 传统的合金通常由一种或两种主要合金元素制成，并添加其他低浓度合金元素以改善合金性能。 近年来，高熵合金，又称复杂高熵合金，由于其新颖的结构和性能而受到人们的广泛关注。 与传统合金不同，高熵合金由五种或五种以上的主要合金元素以几乎相等的浓度组成。 与传统合金相比，这些浓缩合金具有出色的物理性能，包括高温强度，耐腐蚀性和耐辐射性，尽管迄今为止对其原因知之甚少。 本项目研究高熵合金高温氧化的基本机理，并建立化学和微观结构在控制氧化行为中的作用。 通过这个项目，一群不同的学生和科学家，包括妇女和历史上黑人学院和大学的学生，将接受培训，使用计算和实验工具测试，表征，建模和预测高熵合金的氧化行为。 该项目将推进我们的目标，开发具有改进的抗氧化性的材料，这将有助于提高燃料效率和更持久的发电厂，改进喷气和火箭发动机，以及更安全的核电厂。技术概述高熵合金（HEAs）和相关的复杂浓缩合金（CCA）正在获得越来越多的关注，从世界各地的研究人员寻找替代传统/遗留材料。氧化限制了许多先进材料在高温环境中的应用，而对高熵合金氧化行为的研究很少。 这些研究大多集中在制造（例如，铸态、烧结态等）合金而不解决微观结构参数的影响（即，晶粒/相尺寸、形态或分布）。本研究将使用耦合的实验和计算方法来建立氧化如何发生在AlCoCrFeNi HEAs/CCA，并将提供一个框架，可用于设计和制造HEAs/CCA表现出增强的抗氧化性。本研究将使用基于CALPHAD的热力学模型来预测相平衡和氧化产物，并将使用TC-PRISMA补充DICTRA来模拟由于氧化相沉淀。 模拟的微观结构和相将使用互相关分析电子显微镜和原子探针断层扫描技术进行验证，以量化溶质偏析行为和相分布和晶界特征对氧化的影响。 这项研究将有助于高质量的热力学和动力学数据库的开发，改进和验证，也将提供必要的技术见解，以促进抗氧化HEAs的开发，用于高温结构应用。 该项目的研究生预算将采用冶金和陶瓷工程，薄膜科学和材料加工，微观结构表征和材料选择的原则。 他们将从该项目中受益，参与先进的制造、化学和微观结构表征研究，并使用最先进的分析和计算工具对反应材料进行建模。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-TECHNICAL SUMMARYMetal alloys are widely used as structural materials in many high temperature applications such as power plants, aircraft engines, and rocket motors. Conventional alloys are typically made of one or two primary alloying elements with addition of other low-concentration alloying elements to improve alloy properties. Recently, high entropy alloys, also known as complex concentrated alloys, have received significant interest due to their novel structures and properties. Unlike conventional alloys, high entropy alloys consist of five or more principal alloying elements in nearly equal concentrations. These concentrated alloys exhibit outstanding physical properties compared to conventional alloys including high-temperature strength, corrosion resistance, and radiation tolerance, though the reasons why are poorly understood to date. This project investigates the fundamental mechanisms of high temperature oxidation in high entropy alloys and establishes the roles of chemistry and microstructure in controlling oxidation behavior. Through this project a diverse group of students and scientists, including women and students from Historically Black Colleges and Universities, will be trained to test, characterize, model and predict the oxidation behavior of high entropy alloys using computational and experimental tools. This project will advance our goals towards developing materials with improved oxidation resistance which will contribute towards more fuel efficient and longer lasting power plants, improved jet and rocket engines, and safer nuclear power plants.TECHNICAL SUMMARYHigh entropy alloys (HEAs) and the related complex concentrated alloys (CCAs) are garnering increased attention from the researchers worldwide searching for alternatives to conventional/legacy materials. Oxidation limits the application of many advanced materials in high temperature environments and there have been very few investigations of the oxidation behavior of high entropy alloys. Most of those studies centered on as-fabricated (e.g., as-cast, as-sintered, etc.) alloys without addressing the influences of microstructural parameters (i.e., grain/phase size, morphology, or distribution). This research will use a coupled experimental and computational approach to establish how oxidation occurs in AlCoCrFeNi HEAs/CCAs and will provide a framework that can be used to design and fabricate HEAs/CCAs exhibiting enhanced oxidation resistance. This research will use CALPHAD based thermodynamic modeling to predict phase equilibria and oxidation products and will use TC-PRISMA complemented with DICTRA to simulate phase precipitation due to oxidation. The simulated microstructures and phases will be validated using cross-correlative analytical electron microscopy and Atom Probe Tomography techniques to quantify solute segregation behavior and the influences of phase distribution and grain boundary character on oxidation. This research will contribute towards the development, improvement and validation of high-quality thermodynamic and kinetic databases and will also provide necessary technical insights to facilitate the development of oxidation resistant HEAs for use in high temperature structural applications. The graduate student budgeted for the project will employ the principles of metallurgical and ceramic engineering, thin film science and materials processing, microstructural characterization, and materials selection. They will benefit from this project by being involved in advanced research on the fabrication, chemical and microstructural characterization, and modeling of reacting materials using state-of-the-art analytical and computational tools.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.