2, Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut, United States
We have used electron correlation microscopy (ECM) to image the nanometer scale heterogeneities in the relaxation dynamics of the supercooled liquid of a metallic glass forming alloy . The length and time scales of the heterogeneous dynamics are central to the glass transition and influence nucleation and growth of crystals from the liquid. Electron correlation microscopy (ECM) experiments use time-resolved tilted dark field transmission electron microscopy with sub-nanometer resolution for direct measurement of those length and time scales. ECM data on Pt-based metallic glass nanowires above the glass transition temperature (Tg) reveal a relaxation time scale that varies from a few seconds to hundreds of seconds and a length scale that varies from 0.8 to 1.4 nm. They also demonstrate the existence of a ~1 nm thick near-surface layer with an order of magnitude shorter relaxation time than inside the bulk which may influence crystallization of the wires. Additional measurements of the surface layer relaxation time below the bulk Tg, and its connection to enhanced surface diffusion in metallic glasses and surface crystallization will be discussed.
 P. Zhang, J. J. Maldonis, Z. Liu, J. Schroers, P. M. Voyles, Nat. Commun. 9, 1129 (2018)