Like non-metallic glasses, many bulk metallic glasses manifest a glass-transition temperature T g during heating prior to crystallisation. While the exact nature of the atomic structure of a metallic glass depends on its thermo-mechanical history (quench-rate, plastic deformation, ...), a unique and reproducible average atomic structure is attained if the glass transition temperature can be approached in a reversible manner. However, a metallic glass is always metastable and crystallises within a time t near or above its T g in such a way that any reciprocal or real-space information on the fully glassy state at T≥T g must be completed within acquisition times τ a≪t and this condition is in general difficult to attain with conventional X-ray diffraction devices. Here we report on experiments using high-energy, high-flux synchrotron light in the transmission for probing of the atomic structure of bulk metallic glasses. Examples are given of the determination of the isochoric glass transition T g and the quenched-in free-volume. Finally, we report on the evolution of the atomic structure in the supercooled liquid region (T>T g) and its role in the enhancement of glass formability.
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