Multiscale Fundamental Investigation of Micromechanisms of Cyclic Deformation and Fatigue in an Ultrafine Grained Aluminum Alloy

超细晶粒铝合金循环变形和疲劳微观机制的多尺度基础研究

• 批准号: 1435810
• 负责人: Rajiv Mishra
• 金额: $ 33.99万
• 依托单位: University of North Texas
• 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 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1435810&HistoricalAwards=false
• 关键词: Multiscale; Fundamental; Investigation; Micromechanisms; Cyclic

Advanced materials improve the quality of life and significantly impact the sustainability of society. The friction stir processing technique can produce ultrafine-grained aluminum alloys with both higher strength and higher high cycle fatigue life when compared to conventional alloys. However, how the improved mechanical properties emerge from the unique microstructure is not well understood. The microstructure in these new materials consists of grains smaller than one micrometer and a high fraction of stable high-angle grain boundaries. These microstructural features strongly influence the dislocation-based deformation mechanisms. This award supports fundamental research on advanced computational modeling of cyclic deformation mechanisms as well as experimental investigations and characterization to establish microstructure-property relationship for an ultrafine-grained aluminum alloy system. The research will generate knowledge in advancing computational materials engineering for the selected alloy system but will be broadly applicable to similar engineering materials. Results from this research will contribute to the national goal of accelerating the insertion of new materials in the engineering practice. This work will support graduate student research and also help incorporate new understanding of deformation mechanisms into undergraduate courses such as mechanical behavior of materials and advanced materials by microstructural design.This award supports an integrated computational and experimental approach to systematically study the correlation between cyclic deformation and heterogeneous microstructures of dispersion containing ultrafine-grained alloys. Well-proven concepts of persistent slip bands and extrusion/intrusion in microcrystalline alloys do not apply directly to ultrafine-grained materials because their smaller grain sizes and more high-angle grain boundaries change dislocation micromechanisms of multiplication, recovery and substructure formation. A multi-grain modeling strategy with three-dimensional discrete dislocation dynamics will be used to predict mesoscale dislocation processes and the initiation of slip localization at early stages of cyclic deformation. Specifically, this strategy will use information generated by atomistic simulations to create dislocation-grain boundary models for the discrete dislocation dynamics method. Incorporating dislocation-grain boundary and dislocation-precipitate models, the dislocation dynamics simulations will provide insights into dislocation-based damage accumulation processes in heterogeneous alloy systems. Experimental activities involve performing interrupted mini-fatigue tests and microstructure characterizations using orientation imaging microscopy and transmission electron microscopy to obtain cyclical stress/strain curves, grain size distributions and dislocation arrangements at various stages of high cycle fatigue. These efforts will provide insights into damage accumulation and evolution, help verify computational prediction with early stage data, and build a database of the entire fatigue behavior of the ultrafine-grained alloys.

先进材料提高了生活质量，并对社会的可持续发展产生重大影响。与传统合金相比，摩擦搅拌加工技术可以生产具有更高强度和更高循环疲劳寿命的超细晶粒铝合金。然而，如何从独特的微观结构中改善机械性能还没有得到很好的理解。 这些新材料的微观结构由小于1微米的晶粒和高比例的稳定大角度晶界组成。 这些微观结构特征强烈地影响基于位错的变形机制。该奖项支持循环变形机制的先进计算建模的基础研究以及实验研究和表征，以建立超细晶铝合金系统的微观结构-性能关系。该研究将为所选合金系统的先进计算材料工程提供知识，但将广泛适用于类似的工程材料。这项研究的结果将有助于加快在工程实践中插入新材料的国家目标。 该研究成果将支持研究生的研究，并有助于将对变形机制的新认识融入到材料的力学行为和先进材料的微观结构设计等本科课程中。该奖项支持一种综合的计算和实验方法，系统地研究循环变形与含弥散超细晶合金的非均匀微观结构之间的相关性。微晶合金中持久滑移带和挤压/侵入的成熟概念并不直接适用于超细晶材料，因为它们的较小晶粒尺寸和更高角度的晶界改变了位错增殖、恢复和子结构形成的微观机制。一个多晶粒建模策略与三维离散位错动力学将被用来预测中尺度位错过程和开始在循环变形的早期阶段的滑移局部化。具体而言，该策略将使用原子模拟产生的信息来创建离散位错动力学方法的位错晶界模型。通过对位错-晶界模型和位错-沉淀模型的分析，位错动力学模拟将为研究非均质合金系统中基于位错的损伤累积过程提供新的思路。实验活动涉及使用取向成像显微镜和透射电子显微镜进行中断的微型疲劳试验和微观结构表征，以获得循环应力/应变曲线，晶粒尺寸分布和位错排列在高周疲劳的各个阶段。这些努力将提供对损伤累积和演变的见解，帮助验证早期数据的计算预测，并建立超细晶粒合金的整个疲劳行为的数据库。