Probing the atomic structure and physical properties of super-cooled liquid alloys during vitrification

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The scope of this work is to uncover how the structure of liquid metals changes in their pathway to vitirification. A metallic glass is formed when a melted alloy is cooled rapidly enough so that crystallization is avoided upon solidification. However, the way the atomic structure of the liquid converts to the glassy structure is generally unknown, mainly because the acquisition of structural information in the supercooled liquid regime is hindered by crystallization. In this work we were able to overcome this limitation and achieve in-situ vitrification of various metallic alloys in a high energy synchrotron beam using a state of the art aerodynamic levitation technique. This important achievement allowed the acquisition of structural data in the whole range from the liquid through the super-cooled liquid and the glassy state offering a unique possibility to study the structural evolution during vitrification. The results indicate the existence of three non-crystalline regimes in the liquid’s pathway to vitrification. The structural evolution below the melting temperature deviates from that of the liquid, pointing to a crossover in the evolution of the liquid’s structure. The local order in the short and medium range (SRO and MRO) increases rapidly as the supercooled liquid approaches the glass transition temperature Tg, below which the structure “freezes”. The structural rearrangements in the supercooled liquid are found to be correlated with a rapid increase in viscosity of metallic liquid upon cooling.