Structure and Dynamics of Metallic Glass Alloys

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NON-TECHNICAL SUMMARY:Glasses are ubiquitous materials, including window glass and most plastics. Glasses made up of metallic elements have exceptionally high strength, good compatibility as implants into the human body, and are potentially useful for catalysis and as moving parts in microscale machines. However, atoms in glasses are disordered - jumbled up like the grains in a pile of sand - instead of sitting in a regular ordered array like the atoms in conventional metal alloys like steel. This disorder makes it challenging to understand how the atoms are arranged and how they move with respect to one another. This project investigates the atomic arrangements and atomic motions of metallic glass alloys using a nanometer-diameter beam of high energy electrons in an advanced scanning transmission electron microscope. How the electrons scatter off the sample atoms in the solid state at room temperature reveals how the atoms are arranged. How the electron scattering changes with time when the sample is melted inside the microscope reveals how the atoms move. Understanding atomic arrangements and movements helps materials scientists understand why metallic glasses have such exceptional properties and helps them design new metallic glass materials for new applications. This project also builds capacity for advanced electron microscopy research on metals by creating and distributing software that supports new experiments, and it supports engagement of undergraduate students and the general public with the excitement of seeing atoms - the fundamental building blocks of matter - live in the electron microscope.TECHNICAL SUMMARY:This project supports research into the structure and atomic dynamics of metallic glasses using coherent electron nanodiffraction in the form of fluctuation electron microscopy and electron correlation microscopy. Studies of static structure using fluctuation microscopy and hybrid reverse Monte Carlo modeling are building toward a general structural model of nanometer-scale order in metallic glass alloys. Studies of dynamics in the supercooled liquid state using electron correlation microscopy are testing models of the glass-forming liquid fragility based on spatially heterogeneous dynamics and may provide fundamental insight into the glass transition in metallic alloys. Additional techniques to extract structural information from subtle angular correlations in electron nanodiffraction from glasses are being developed. The project also supports research capacity building by dissemination of software for data acquisition and analysis for fluctuation microscopy and electron correlation microscopy, and outreach activities bringing the excitement of state-of-the-art electron microscopy to the general public.