In-Situ TEM and SEM Studies of Fundamental Deformation and Failure Processes of Nano-Grained FCC Metals Using MEMS Stages

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This grant is on a study of the mechanical properties of nano-grained Cu, Al and Ni using MEMS stages with emphasis on in-situ testing to characterize the underlying deformation mechanisms that involve dislocation-dominated versus grain-boundary controlled as small grain sizes are approached. Another objective is to investigate the failure modes in nano-grained materials since dramatic changes are expected as the crack tip dimension becomes comparable to the grain or particle size. Understanding these processes at this length scale are important if reliable devices and new structural materials are to be constructed intelligently from these nanoscale building blocks. A major goal of the project is to use a novel microelectromechanical-based tensile test device that was designed and fabricated at the University of Illinois to measure the mechanical properties and to simultaneously observe the operative deformation and fracture process of two- and three-dimensional nanograin structures. The same device will be used in both the scanning and transmission electron microscopes, and thus it will be possible for the first time to directly correlate macroscopic mechanical properties with deformation and fracture processes in ultra-fine grained materials as a function of grain size. The aim is to investigate these aspects in FCC metals such as Cu, Al and Ni. In addition to the experimental studies, molecular dynamics simulations will be made to predict deformation mechanisms as grain size is reduced to nanometer size. The model predictions will be correlated with the experimental results.The outcome of the proposed program will provide the foundation for developing new physical-based models for predicting the mechanical response of structures and devices containing nanosized grains and particles. The grant involves graduate student participation along with outreach program that has been in place at the University of Illinois.