NSF Award
2406530
NON-TECHNICAL SUMMARY<br/><br/>This project aims to gain a fundamental understanding of the unique deformation behavior of metallic glasses (MGs). MGs possess excellent properties, such as extremely high strength, corrosion resistance, and unique magnetic characteristics, which can be harnessed for potential applications in various fields, including nanotechnology, electronics, and aerospace. Broader manufacturing and application of MGs require a better understanding of the atomic structure of MGs (i.e., how the atoms are arranged inside the material) and how this arrangement changes when force is applied, which defines the way MGs deform when in use, typically under various stress conditions. This project seeks to explore the details of MGs' atomic structure and gain critical insights into how to control this structure to obtain desired properties that can be utilized for many important applications in science and industry. By employing cutting-edge techniques such as time-resolved 4-dimensional scanning transmission electron microscopy (4D-STEM), machine learning-assisted data analysis, and computer simulations, the research team is mapping and monitoring the atomic structures within MGs and tracking how they change over time and under stress. A particular focus is given to understanding what types of atomic arrangements can lead to significant variations in the material's response to stress. The deformation process involves the softening of local volumes of material, a process that makes these volumes easier to deform as the deformation progresses. This research is investigating the detailed mechanism of this softening behavior and how it relates to the local atomic arrangements within the material. This work is providing crucial insights into why some MGs exhibit better ductility and resistance to failure than others, which will pave the way to harnessing this knowledge to design MGs with improved mechanical properties, making them more reliable for practical and industrial applications. The findings from this research are being integrated into undergraduate and graduate curricula, enhancing the educational experience for students. The project also includes outreach activities that are being conducted at local K-12 schools to inspire and educate young minds about materials science. Moreover, the project is offering internships to community college students from diverse backgrounds, providing them with hands-on research experience and encouraging their pursuit of STEM careers.<br/><br/>TECHNICAL SUMMARY<br/><br/>This project investigates structural heterogeneities and variations in shear transformation zone (STZ) properties to understand the softening behavior, autocatalysis, and strain localization in metallic glasses (MGs). The research integrates time-resolved 4-dimensional scanning transmission electron microscopy (4D-STEM), machine learning-assisted data analysis, atomistic simulations, and mesoscale STZ dynamics modeling. The core hypothesis is that the autocatalytic shear activities and resultant deformation localization in MGs are influenced by intrinsic structural heterogeneities and the softening behaviors of local atomic environments over time. To validate this hypothesis, the project is: 1) Performing 4D-STEM on MGs with slight compositional differences to identify dominant medium-range ordering (MRO) structures, their relaxation times, and evolution pathways. 2) Using machine learning to analyze the angular correlation functions from 4D-STEM data, determining the types, volume fractions, and spatial distributions of MROs. 3) Extending 4D-STEM to the time domain to track thermal relaxation of MRO symmetries and relate these changes to STZ activation energies. 4) Connecting experimental data to atomistic models to reveal atomic arrangements within MROs, using potential energy landscape analysis to determine how different MROs impose different barriers for STZ activation. 5) As well as integrating the activation energy information and other STZ properties into mesoscale simulations to investigate how heterogeneous distributions of local structures and STZ activation energies influence softening behavior and shear localization during deformation. This research is examining MGs that have undergone various thermomechanical treatments to understand how ageing and rejuvenation affect local structures and softening behaviors. The results are providing detailed insights into the complex interplay between atomic-scale structures and macroscopic mechanical properties in MGs, contributing to the development of MGs with improved ductility by mitigating autocatalysis and promoting dispersed shear band activities.<br/><br/>This project is jointly funded by the Division of Materials Research’s Metals and Metallic Nanostructures (MMN) and Ceramics (CER) Programs.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
