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.
