Creep of Temperature Stabilized Nanocrystalline Metals - a High Throughput Approach

该奖项支持将纳米晶金属蠕变映射为温度和应力的函数的基础研究，目前对此了解有限。高强度金属在许多结构应用中被用来减轻重量，包括飞机和汽车零部件。通常，金属是晶粒度在100微米左右的多晶材料。提高金属强度最有效的方法之一就是将晶粒度细化到纳米级。这种纳米晶金属在较高的温度下非常坚固，但在这种温度下通常会出现蠕变。热稳定的纳米晶金属是改善防护涂层和电接触的有力候选者，在核材料应用中引起极大的兴趣。该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方面的研究生和本科生。还将开展外联活动，开发YouTube视频，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。研制了微机械蠕变试验台，并将对其进行优化。第一个目标是合成纳米晶金属在大范围温度和应力范围内的第一张蠕变图。以前的工作表明，二次蠕变存在一个门槛应力，其大小与晶粒度成反比。目的二是研究这种阈值应力是否存在，并探讨其与颗粒大小的关系。目标三是部分通过使用透射电子显微镜来确定潜在的扩散和基于位错的机制。总而言之，该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.