Correlating structural heterogeneity to deformation in metallic glasses

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Non-Technical SummaryThis award supports an integrated experimental and computational study of structure-property relationship of metallic glasses (MGs). Glasses are ubiquitous in nature, and many of them have superior properties (much better than crystals) that can be utilized for important applications. For example, metallic glasses (MGs) are multi-component metallic alloys with glassy (disordered) atomic structure, and their excellent properties, including high strength and elastic energy, have shown great promises for novel structural applications. However, such applications are currently limited by the poor ductility of MGs. To understand the deformation behavior of MGs, it is required to understand their atomic structure and how structural heterogeneities at different length scales influence the way they plastically deform. Using a unique combination of advanced electron microscopy and mesoscale computer simulation, the PIs will investigate how the local atomic ordering that is inherited from processing of the MGs affects their important mechanical properties, and seek opportunities to improve MG ductility by engineering structural heterogeneities at the nanoscale through adjusting alloy composition and heat treatment. The PIs will use electron microscopy techniques for the educational component of this award to introduce science and engineering of MGs to K12 students and teachers, including students with disabilities, and to motivate them to choose science and engineering as their college major and to pursue their careers in these fields.Technical SummaryThis award supports an integrated experimental and computational study of the correlation between nanoscale structural heterogeneities and deformation behavior of metallic glasses (MGs). In particular, the PIs will use nanodiffraction combined with two advanced analysis methods (fluctuation microscopy and angular correlation function) to reveal the details of medium range (nanoscale) atomic orders (MROs) in MGs, including their type, size, volume fraction, and distribution, at an unprecedented quantitative level. These structural details will be characterized as function of composition and thermal history of the MGs and correlated to their deformation behavior. The PIs will then incorporate the experimentally determined MRO information into mesoscale computer simulations based on a heterogeneously randomized shear transformation zone (STZ) model to establish new understanding on how the MROs affect shear banding and overall deformation. The possible connection between MRO and STZs will be investigated by first assuming a set of deformation rules in the simulations according to the detailed MRO structures revealed by the nanodiffraction, and then matching the simulation results (including overall ductility and shear banding patterns) to the experimental observations. Such a fully integrated experimental and computational study will provide important insights into how the nanoscale structural heterogeneity affects STZ activation and the overall deformation. Through this award the PIs will probe nanoscale structural heterogeneities in MGs beyond the limits of the conventional characterization methods, and reveal important connections among composition, thermal history, MRO, and mechanical properties. Simulations incorporating the experimentally determined structural heterogeneity will offer new insights into how structural heterogeneities at the nanoscale in MGs affect their overall deformation behavior beyond the spatial and temporal limits of previous simulations. This award will also provide insights into how the nanoscale structural heterogeneity is related to the previously suggested plasticity carriers and structural defects in MGs, such as STZ, free volume distribution, and the recently suggested geometrically unfavored motifs. The new structure-property relationship established will provide new possibilities in designing MGs with enhanced mechanical properties (in particular, ductility) by tuning the nanoscale structural heterogeneities.