Abnormal grain growth in ultrafine grained metals under high cycle loading

高循环载荷下超细晶粒金属的异常晶粒生长

• 批准号: 2224372
• 负责人: Olivier Pierron
• 金额: $ 53.62万
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-11-01 至 2025-10-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2224372&HistoricalAwards=false
• 关键词: Abnormal; grain; growth; ultrafine; grained

NON-TECHNICAL SUMMARYMost technologically important metals are polycrystalline, and are made of many small clusters called grains. The size of these grains is a key parameter, as grain size has a strong influence on a material’s strength. The same metal is much stronger if its grains are smaller. For this reason, ultrafine grained metals, with grain sizes less than one micrometer, are a very important class of structural materials due to their particularly high strength, with critical applications in the aerospace and nuclear industry, among others. Another significant advantage of small grained metals is that they tend to have better fatigue properties and are less likely to form detrimental cracks under cyclic loading. It is therefore crucial to keep small grain sizes throughout the lifetime of an ultrafine grained structural metal; otherwise its mechanical properties can degrade catastrophically. In this project, the PIs are developing new understanding of the mechanics of grain growth, so that grain size can be properly controlled. The PIs focus specifically on abnormal grain growth, where a small fraction of grains grow drastically large and fast compared to other grains and as a result consume other grains. While this phenomenon is well understood at high temperatures and high strains, little is known about abnormal grain growth in the rarely explored range of high cycle loading (applying a large number of cycles with low strain at room temperature). The outreach activities in this project include a summer enrichment program in material science and engineering, targeting high school students from underrepresented groups in the STEM fields, and involving high school teachers, graduate and undergraduate students to develop the curriculum and implement the program. TECHNICAL SUMMARYThe overarching goal of this proposal is to achieve a fundamental understanding of the origins of abnormal grain growth in ultrafine grained metals under high-cycle loading at room temperature. The central hypothesis of this proposal is that the elastic anisotropy effect dominates the driving force for grain growth in the high-cycle loading regime at room temperature, resulting in abnormal grain growth behavior. The PIs test this hypothesis through high-throughput characterization of cyclic-load-induced grain growth in ultrafine grained metals inside a scanning electron microscope equipped with electron back scattered diffraction. Fabrication and testing of six different metallic films with varying degrees of elastic anisotropy, with face-centered cubic or body-centered cubic structures are the focus of the work. These experiments can characterize the evolution of grain size distribution and orientation as a function of applied cycles, for various strain amplitudes (up to 1%). The PIs use micromechanics and phase field modeling to determine the thermodynamic driving forces in terms of strain energy densities and the grain boundary mobilities for abnormal grain growth. The integrated experiments and modeling are being used to identify the predominant factors and loading ranges controlling abnormal grain growth, including its kinetics, in face-centered cubic and body-centered cubic metals at room temperature.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.

非技术总结最重要的金属是多晶，由许多称为晶粒的小簇制成。这些谷物的大小是一个关键参数，因为晶粒尺寸对材料的强度有很大影响。如果其谷物较小，则相同的金属要强得多。因此，由于其特殊的高强度，在航空航天和核工业中的关键应用等，其谷物尺寸少于一个千分尺的谷物尺寸少于一个千分尺等是非常重要的结构材料。小粒金属的另一个重要优点是，它们倾向于具有更好的疲劳性能，并且在环状载荷下形成有害裂纹的可能性较小。因此，至关重要的是，在超细颗粒结构金属的整个生命周期中保持小晶粒尺寸。否则，其机械性能会造成灾难性的降解。在这个项目中，PI正在对谷物生长的机制发展新的了解，以便可以正确控制晶粒尺寸。 PI专门集中在异常的谷物生长上，与其他谷物相比，一小部分谷物的生长大大又快，因此其他谷物的消耗。尽管这种现象在高温和高应变中得到了充分的了解，但对于很少探索的高周期载荷范围（在室温下施加了大量低应变的循环），谷物的生长异常知之甚少。该项目的外展活动包括材料科学和工程领域的夏季丰富计划，针对来自STEM领域中代表性不足小组的高中生，以及涉及高中教师，毕业生和本科生以开发课程并实施该计划。技术总结该提案的总体目标是对在室温下高周期载荷下超细颗粒金属中异常谷物生长的起源进行基本了解。该提议的中心假设是，弹性各向异性效应在室温下高周期载荷方案中晶粒生长的驱动力占主导地位，从而导致异常的晶粒生长行为。 PIS通过高通量表征在扫描电子显微镜内部的超细颗粒金属中的环状颗粒生长进行高通量表征，该假设通过具有电子背部散射衍射。具有不同程度的弹性各向异性（具有面部中心的立方或以身体为中心的立方结构）的六种不同金属膜的制造和测试是工作的重点。这些实验可以表征晶粒尺寸分布和方向的演变，这是各种应变放大器（最多1％）的应用周期的函数。 PI使用微力学和相位场建模来确定热力学驱动力，以应变能密度和晶界迁移率异常。综合实验和建模用于在室温下以面部中心和身体为中心的立方金属来确定控制异常谷物生长的主要因素和负载范围。这一奖项反映了NSF的立法任务，并通过使用基金会的智力效果评估了NSF的立法任务，并被认为是通过评估诚实的。