This Materials World Network award supports an international multidisciplinary research team from University of Pennsylvania, Johns Hopkins University, and University of Sydney (Australia) to elucidate the fundamental role of impurities on coupled grain boundary migration as manifest in the observation of stress-assisted room temperature grain growth in nanocrystalline metals. This study is motivated by recent findings that showed that deformation mechanisms in nanocrystalline metals are not only different to those in microcrystalline metals but are dynamic as well. Local grain boundary pinning by impurities is central to the understanding, and ultimately control, of stress-driven microstructural evolution, but until recently the atomic-level experimental characterization of local dopant concentration and spatial distribution has not been possible. Our global team will use state-of-the-art 3D atom probe tomography to investigate local structure and impurity segregation in nanocrystalline metal thin films that have been synthesized by reactive sputtering to introduce systematically varied amounts of dopants in the material. Special emphasis will be placed on characterizing the effect of intrinsic and extrinsic parameters (grain size, impurity content, boundary orientation, etc.) on both grain growth and the attendant, dynamic, mechanical behavior of nanocrystalline films.
Controlling impurity pinning of grain boundaries controlling stress-driven microstructural evolution offers a unique avenue for tailoring the mechanical properties of nanocrystalline materials. The combination of a microstructure's ability to augment its deformation mechanisms to accommodate stress via dynamic evolution and control of the threshold stress for grain boundary migration by local spatially controlled doping would facilitate atomic-level engineering and potentially introduce a new class of materials. Novel characterization and in situ testing tools and methods will be developed and utilized, pushing the frontier of experimental nanoscience. The proposed Materials World Network team will design and teach short courses about 3D atom probe tomography and in situ mechanical testing targeted at research and industrial scientists and engineers. The proposed integration of undergraduate students will engage young scientists and engineers in novel and international research activities, providing experiences and opportunities that will allow students to become better global citizens.
