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Despite that metallic glasses are among the most studied metallic materials, still very little is known on the evolution of their unique structural, dynamical and elastic properties under compression, owing to the difficulty to perform in-situ high pressure experiments. Coupling the brightest x-rays available in synchrotrons with cutting edge high pressure technologies, we provide direct evidence of the microscopic structural and dynamical mechanisms occurring under in-situ high pressure compression and decompression in the GPa range, from the onset of the perturbation up to a severely-deformed state. We show that while pressure promotes density increasing through quasi-elastic structural deformations, the atomic mobility exhibits a hysteresis and is enhanced up to a factor 15 even at temperatures well below the glass transition. This surprising behaviour results from a competition between fast avalanche-like atomic rearrangements and slow relaxation processes triggered by an anomalous super-diffusive collective particle displacement. These results provide new insights on the effect of deformation in non-ergodic materials and support the occurrence of string-like diffusion of liquid-like atoms in metallic glasses. They explain also the macroscopic impressive rejuvenation and strain hardening reported recently under ex-situ densifications., This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No 948780)., Peer Reviewed, Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura::9.5 - Augmentar la investigació científica i millorar la capacitat tecnològica dels sectors industrials de tots els països, en particular els països en desenvolupament, entre d’altres maneres fomentant la innovació i augmentant substancialment, d’aquí al 2030, el nombre de persones que treballen en el camp de la investigació i el desenvolupa­ment per cada milió d’habitants, així com la despesa en investigació i desenvolupament dels sectors públic i privat, Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura, Postprint (author's final draft)

The particle motion associated to the a-relaxation in supercooled liquids is still challenging scientists due to its difficulty to be probed experimentally. By combining synchrotron tech- niques, we report the existence of microscopic structure-dynamics relationships in Pt42.5 Cu27 Ni 9.5P 21 and Pd 42.5Cu 27 Ni9.5 P21 liquids which allows us to disentangle structural and kinetic contributions to the a-process. While the two alloys show similar kinetic fragilities, their structural fragilities differ and correlate with the temperature dependence of the stretching parameter describing the decay of the density fluctuations. This implies that the evolution of dynamical heterogeneities in supercooled alloys is determined by the rigidity of the melt structure. We find also that the atomic motion not only reflects the topological order but also the chemical short-range order, which can lead to a surprising slowdown of the a- process at the mesoscopic length scale. These results will contribute to the comprehension of the glass transition, which is still missing., We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III beamline P02.1 and we would like to thank Alexander Schoekel and Michael Wharmby for assistance. Further we want to thank our colleagues B. Adam, L. Ruschel, S.S. Riegler, H. Jiang, V. Lemkova, H. Voigt and J. Schmauch for collaboration and fruitful discussions concerning the topic. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and inno- vation programme (Grant Agreement No 948780). The research activity has been sup- ported by the project CALIPSOplus under the Grant 307 Agreement 730872 from the EU Framework Program for Research 308 and Innovation HORIZON 2020. The authors declare that they have no competing interests. All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials., Peer Reviewed, Postprint (published version)

The isothermal crystallization times and critical cooling rates of the liquid phase are determined for the two bulk metallic glass forming alloys Au49Ag5.5Pd2.3Cu26.9Si16.3 and Au51.6Ag5.8Pd2.4Cu20.2Ga6.7Si13.3 by using fast differential scanning calorimetry, covering the whole timescale of the crystallization event of the metallic melt. In the case of Au49Ag5.5Pd2.3Cu26.9Si16.3, a typical crystallization nose was observed, whereas for the Au51.6Ag5.8Pd2.4Cu20.2Ga6.7Si13.3, a more complex crystallization behavior with two distinct crystallization noses was found. Even for the complex crystallization behavior of the Au51.6Ag5.8Pd2.4Cu20.2Ga6.7Si13.3 alloy it is shown that the minimal isothermal nose time does allow for a quantification of the macroscopic critical thickness. It is discussed in contrast to the critical cooling rate, which is found to allow less exact calculations of the critical thickness and thus does not correlate well with the critical cooling rate from macroscopic experiments. Additionally the crystallization data of Au49Ag5.5Pd2.3Cu26.9Si16.3 was modeled using classical nucleation theory with the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation, enabling a determination of the interfacial energy.