Probing the structure of a liquid metal during vitrification

Using aerodynamic levitation, vitrification of a ternary Zr-Cu-Al alloy was observed in-situ by high energy synchrotron radiation X-ray diffraction in the temperature range from above the liquidus Tliq to well below the glass transition temperature Tg. The evolution of the atomic structure was studied using pair distribution functions (PDF) and molecular dynamic (MD) simulations. Vitrification was rendered possible due to the enhanced stability of the undercooled Zr-Cu melt after Al addition. Results indicate three regimes in the liquid alloy's structural pathway to vitrification. Short (SRO) and medium range order (MRO) develop significantly during cooling the liquid phase to the glassy state. The rate of structural rearrangements is enhanced in the super-cooled liquid between Tliq-140 K and Tg. The populations of atomic clusters with icosahedral local symmetry become predominant as Tg is approached and facilitate vitrification and suppression of crystal nucleation and growth. The scenario of a possible fragile to strong transition in the super-cooled liquid is discussed.