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.

非技术总结：本研究项目将阐明和量化晶粒细化到纳米长度尺度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完成，并将利用实验和热力学建模技术的结合来定义晶粒细化对氧化行为的机理影响。这项建议是及时的，因为大量的资源正在用于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保护性的氧化层。这个基础研究项目将为稳定和利用纳米晶微结构来提高结构材料的抗氧化性提供基础信息。该项目与先进涂层技术的相关性是重要的，并为这项工作提供了强大的实际动力。所产生的基本知识将广泛适用于其他经受高温氧化的合金体系。研究结果将通过出版物和演讲传播，参与该项目的学生将受益于接触各种最新的科学技术。技术概述：本课题的研究目的是阐明和量化晶粒细化到纳米尺度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铝成形合金进行，将提供一些必要的信息，以促进纳米晶材料在高温氧化环境中的使用。有充分的证据表明，晶粒细化促进选择性氧化，从而导致保护性氧化垢的形成。此外，研究表明，纳米晶化可以极大地增强这种效应，从而导致快速的初始和瞬态氧化阶段（即阶段I）。在纳米晶材料中，人们假设并普遍接受的观点是，大量的晶界的存在，为氧化形成元素提供了快速扩散的途径，并为连续氧化鳞的成核和生长提供了丰富的场所，从而加速了保护性铬或氧化铝鳞片的生长。虽然这一假设似乎是直观的，但人们注意到，还没有进行系统的研究来实验建立或验证这种行为背后的内在机制。本研究中需要解决的智力挑战是提供微观结构（即晶粒尺寸和晶粒取向）与扩散率之间关系的定量理解，并应用这一理解来解释在包含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。本研究依赖于：(1)能够提供具有精确控制成分和微观结构的材料的加工方法；(2)应用适当选择的分析技术与热力学建模相结合，定量确定和验证晶粒细化涂层中抗氧化性能改善的机制。该项目与先进涂层技术的相关性非常重要，除了为参与的学生提供良好的职业选择外，还为工作提供了强大的实践动力。