Correlating structural heterogeneity to deformation in metallic glasses

该奖项支持金属玻璃（mg）结构-性能关系的综合实验和计算研究。玻璃在自然界中无处不在，其中许多具有优越的性能（比晶体好得多），可以用于重要的应用。例如，金属玻璃（mg）是具有玻璃状（无序）原子结构的多组分金属合金，其优异的性能，包括高强度和弹性能，在新型结构应用中显示出巨大的前景。然而，这种应用目前受到mgg延展性差的限制。为了了解mggs的变形行为，需要了解它们的原子结构以及不同长度尺度上的结构异质性如何影响它们的塑性变形方式。使用先进的电子显微镜和中尺度计算机模拟的独特组合，pi将研究从MG加工中继承的局部原子有序如何影响其重要的力学性能，并通过调整合金成分和热处理，在纳米尺度上通过工程结构异质性来寻求改善MG延展性的机会。该奖项的教育部分将使用电子显微镜技术，向K12学生和教师（包括残疾学生）介绍MGs的科学和工程，并激励他们选择科学和工程作为他们的大学专业，并在这些领域从事他们的职业。该奖项支持对纳米级结构非均质性与金属玻璃（mg）变形行为之间关系的综合实验和计算研究。特别是，pi将使用纳米衍射结合两种先进的分析方法（波动显微镜和角相关函数），以前所未有的定量水平揭示mg中范围（纳米级）原子顺序（mro）的细节，包括它们的类型、大小、体积分数和分布。这些结构细节将被表征为mg的成分和热历史的函数，并与它们的变形行为相关。然后，pi将把实验确定的MRO信息结合到基于非均匀随机剪切转变区（STZ）模型的中尺度计算机模拟中，以建立对MRO如何影响剪切带和整体变形的新认识。首先，根据纳米衍射揭示的详细的MRO结构，在模拟中假设一套变形规则，然后将模拟结果（包括整体延性和剪切带状模式）与实验观测结果进行匹配，研究MRO与stz之间可能的联系。这种完全集成的实验和计算研究将为纳米级结构非均质性如何影响STZ激活和整体变形提供重要见解。通过该奖项，pi将超越传统表征方法的限制，探索mg纳米级结构的非均质性，并揭示成分、热历史、MRO和机械性能之间的重要联系。结合实验确定的结构非均质性的模拟将提供新的见解，以了解纳米尺度的mg结构非均质性如何影响其整体变形行为，超出了先前模拟的空间和时间限制。该奖项还将深入了解纳米级结构非均质性与先前提出的塑性载流子和结构缺陷（如STZ、自由体积分布和最近提出的几何上不受欢迎的基序）之间的关系。新的结构-性能关系的建立将为通过调整纳米级结构非均质性来设计具有增强机械性能（特别是延展性）的mg提供新的可能性。

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.