Creep of Temperature Stabilized Nanocrystalline Metals - a High Throughput Approach

该奖项支持绘制纳米晶金属蠕变图的基础研究，目前人们对纳米晶金属蠕变作为温度和应力的函数的理解有限。高强度金属在许多结构应用中用于减轻重量，包括飞机和汽车部件。通常，金属是多晶材料，晶粒尺寸约为100微米。提高金属强度的最有效方法之一是将晶粒尺寸减小到纳米级。这种纳米晶金属在高温下非常坚固，但在这些温度下通常会发生蠕变。热稳定纳米晶金属是改进保护涂层、电触点和核材料应用的重要候选材料。本项目将有利于培养机械性能评价、纳米加工、电沉积和电子显微镜等方面的研究生和本科生。还将开展拓展活动，将漫画人物的虚构超能力与现实生活中的材料增强联系起来，制作YouTube视频。开发了微机械蠕变试验平台，并将对其进行优化。目的一是合成纳米晶金属在广泛温度和应力范围内的第一张蠕变图。先前的研究表明，次级蠕变存在一个阈值应力，该阈值应力与晶粒尺寸成反比。目的二是研究阈值应力是否存在，并探讨其与晶粒尺寸的关系。目的三是确定潜在的扩散和位错为基础的机制，部分通过使用透射电子显微镜。总之，本项目致力于显著提高对纳米晶金属蠕变的基本理解。

This award supports fundamental research to map nanocrystalline metal creep, for which there is limited understanding, as a function of temperature and stress. High strength metals are used to reduce weight in many structural applications including aircraft and automobile components. Typically, metals are polycrystalline materials with grain size on the order of one hundred micrometers. One of the most effective methods to increase metal strength is to reduce the grain size to the nanometer scale. Such nanocrystalline metals are extremely strong at higher temperatures but typically suffer from creep at these temperatures. Thermally stabilized nanocrystalline metals are strong candidates for improved protective coatings, electrical contacts and are of great interest in nuclear material applications. This project will be beneficial for the training of graduate and undergraduate students in mechanical property evaluation, nanofabrication, electrodeposition and electron microscopy. Outreach activities will also be performed to develop YouTube videos relating fictional super powers of comic book characters to real-life materials enhancements. A micromachined creep test platform has been developed and will be optimized. Objective one is to synthesize the first creep maps of nanocrystalline metals over a wide range of temperature and stresses. Previous work suggests that there is a threshold stress for secondary creep that scales inversely with grain size. Objective two is to investigate if this threshold stress exists and to explore its dependence on grain size. Objective three is to determine the underlying diffusion and dislocation-based mechanisms, in part through the use of transmission electron microscopy. In summary, this project endeavors to significantly improve the fundamental understanding of creep in nanocrystalline metals.