Fundamental Influences of Grain Size on Oxidation Behavior of Nanocrystalline Alumina-Forming Alloys

晶粒尺寸对纳米晶氧化铝合金氧化行为的基本影响

• 批准号: 1411280
• 负责人: Mark Weaver
• 金额: $ 35.61万
• 依托单位: University of Alabama Tuscaloosa
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1411280&HistoricalAwards=false
• 关键词: Fundamental; Influences; Grain; Size; Oxidation

Non-Technical Summary:This research program will elucidate and quantify how grain refinement to nanometer length scales can influence the oxidation resistance and thermal stability of oxidation resistant coatings and alloys. This will be accomplished using model alloys capable of forming aluminum oxide scales, and will utilize a combination of experimental and thermodynamic modeling techniques to define the mechanistic influences of grain refinement on oxidation behavior. The proposal is timely in that significant resources are being expended to increase operating temperatures and fuel efficiencies in power generating systems. This will require that the structural materials being used form more stable and protective oxide scales. This fundamental research program will provide fundamental information that will allow to stabilize and exploit nanocrystalline microstructures to improve the oxidation resistance of structural materials. The relevance of the project to advanced coating technologies is important and provides a strong practical motivation for the work. The fundamental knowledge generated will be broadly applicable to other alloy systems subjected to high temperature oxidation. The results will be disseminated through publications and presentations and the students in the project will benefit from exposure to a variety of state of the art scientific techniques. Technical Summary:The research objective of this proposal is to elucidate and quantify how grain refinement to nanometer length scales can influence the oxidation resistance and thermal stability of oxidation resistant coating alloys. This fundamental work, which will be conducted using model alumina-forming alloys, will provide some of the necessary information to facilitate the use of nanocrystalline materials in high temperature oxidation environments. It is well documented that grain refinement promotes selective oxidation which can lead to the formation of a protective oxide scale. Furthermore, it has been shown that this effect can be greatly enhanced by nanocrystallization resulting in a rapid initial and transient stage (i.e., stage I) of oxidation. In nanocrystalline materials, it is hypothesized and generally accepted that the accelerated growth of protective chromia or alumina scales results from the existence of numerous grain boundaries which provide rapid diffusion pathways for oxide forming elements and abundant sites for the nucleation and growth of a continuous oxide scale. Though this hypothesis seems intuitive, it has been noted that no systematic studies have been conducted to experimentally establish or verify the intrinsic mechanisms underlying this behavior.The intellectual challenge to be addressed in this research is to provide quantitative understanding of the relationships between microstructure (i.e., grain size and grain orientation) and diffusivity and to apply this understanding to explain the selective oxidation and interdiffusion processes that occur in multicomponent coating systems containing grain refined microstructures. This research relies on: (1) processing methods capable of delivering materials with precisely controlled compositions and microstructures; (2) the application of appropriately selected analytical techniques coupled with thermodynamic modeling to quantitatively determine and validate the mechanisms underlying the improved oxidation resistances reported in grain refined coatings.The relevance of the project to advanced coating technologies is important and provides a strong practical motivation to the work in addition to offering good career options for the students involved.

非技术摘要：该研究计划将阐明和量化纳米长度尺度的晶粒细化如何影响抗氧化涂层和合金的抗氧化性和热稳定性。 这将使用能够形成氧化铝鳞片的模型合金来实现，并将利用实验和热力学建模技术的组合来定义晶粒细化对氧化行为的机械影响。 该提案是及时的，因为正在花费大量资源来提高发电系统的运行温度和燃料效率。 这将要求所使用的结构材料形成更稳定和具有保护性的氧化皮。 该基础研究计划将提供稳定和利用纳米晶体微观结构以提高结构材料的抗氧化性的基本信息。 该项目与先进涂层技术的相关性很重要，并为这项工作提供了强大的实际动力。 所产生的基础知识将广泛适用于遭受高温氧化的其他合金系统。 研究结果将通过出版物和演示文稿传播，参与该项目的学生将受益于各种最先进的科学技术。技术摘要：本提案的研究目的是阐明和量化纳米长度尺度的晶粒细化如何影响抗氧化涂层合金的抗氧化性和热稳定性。 这项基础工作将使用模型氧化铝形成合金进行，将为促进纳米晶材料在高温氧化环境中的使用提供一些必要的信息。 有充分证据表明，晶粒细化会促进选择性氧化，从而导致保护性氧化皮的形成。 此外，已经表明，通过纳米结晶化可以大大增强这种效果，从而导致氧化的快速初始和瞬态阶段（即第一阶段）。 在纳米晶体材料中，人们假设并普遍认为，保护性氧化铬或氧化铝氧化皮的加速生长是由于存在大量晶界，这些晶界为氧化物形成元素提供了快速扩散路径，并为连续氧化皮的成核和生长提供了丰富的位点。 尽管这一假设似乎很直观，但值得注意的是，尚未进行系统研究来通过实验建立或验证这种行为背后的内在机制。本研究要解决的智力挑战是提供对微观结构（即微观结构）之间关系的定量理解。 、晶粒尺寸和晶粒取向）和扩散率，并应用这种理解来解释在含有晶粒细化微观结构的多组分涂层系统中发生的选择性氧化和相互扩散过程。 这项研究依赖于：（1）能够提供成分和微观结构精确控制的材料的加工方法； (2) 应用适当选择的分析技术与热力学模型相结合，定量确定和验证晶粒细化涂层中报告的抗氧化性改善的机制。该项目与先进涂层技术的相关性很重要，并为以下方面提供了强大的实际动力：这项工作除了为相关学生提供良好的职业选择外。