[SY-I8] New Approaches for Understanding Nanocrystalline Mechanics: Physical Microstructures, Grain Boundary Descriptors and Deformation Mechanisms
Invited
Engineering interest in nanocrystalline (NC) materials has been founded on the potential to improve mechanical properties such as increased strength/hardness, while scientific interest stems from the alternative fundamental mechanisms that are operative. Compared to their coarser-grained counterparts, the influence of interfaces (i.e., grain boundaries (GB)) becomes more significant in NC materials. Current simulation techniques for understanding NC mechanics rely on non-physical microstructures, first-order grain boundary descriptors that poorly capture the complexity of interfacial structure-property relationships, and a lack of quantitative approaches that can accurately capture the specific contribution of different deformation mechanisms. In this study, we propose utilizing higher-order GB descriptors to improve interfacial understanding, while determining polycrystalline behavior through networks connecting bulk and boundary behaviors. We perform atomistic modeling (e.g., Molecular Dynamics) studies of both favored CSL and general high-angle GBs for analyzing empirical and structural descriptors from atomic-scale behavior at the interfaces. These descriptors then aid in our GB network modeling to understand larger-scale polycrystalline behavior by unraveling the complexity surrounding the competition/cooperation between different deformation mechanisms. The importance of choosing physically-based atomistic microstructures and proper equilibration techniques in such simulations are also discussed. Finally, by utilizing continuum-based kinematic metrics, which can resolve the individual contribution of various deformation mechanisms such as GB and dislocation-mediated deformation to the total strain in the material, we help to further unravel the complex microstructural deformation behavior in NC metals.