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Dynamical and structural properties of Cu-Ti melts : A comparison of experiment and simulation

Jeudi 23 novembre 2023 14:00 - Duree : 1 heure
Lieu : ILL 4, Seminar Room Isabelle Grillo (no 163), 71 avenue des Martyrs - Grenoble

Orateur : Lucas KREUZER (German Aerospace Center - Cologne and FRM II, Munich - Germany)

Résumé :

Cu-Ti alloys feature a large, undercooled liquid region and a high glass-forming ability (GFA) and thus, provide the possibility to obtain two component bulk metallic glasses (BMGs). This unusual behaviour could be due to the special properties of the liquid Cu-Ti system : a positive excess volume and a negative enthalpy of mixing. However, the relevant atomic mechanisms responsible for such good GFA are still to be explored. Here we discuss the temperature-dependent dynamical and structural properties of Cu-Ti melts, within a compositional range of 24 to 69 at% Ti. Accurate experimental data about viscosity, density, and atomic structure, the Cu-Ti samples was obtained by using have been processed without any container using the electrostatic levitation technique.

Our experiments revealed a non-monotonous trend of the viscosity, with the highest values at intermediate Ti contents. Surprisingly, this dynamical trend is not reflected by the macroscopic packing fraction, meaning a high viscosity does not necessarily correlate with a dense packing. On the atomic scale, x-ray and neutron diffraction reveal a denser, local packing and a pronounced chemical short-range order. These short-range Cu-Ti interaction can explain the high viscosity at intermediate Ti contents.

In addition, ab-initio simulations have been performed on the binary CuTi system. While the overall structure can be reproduced almost perfectly, the simulations do not include the experimentally found chemical short-range order. As a consequence, the simulated dynamical properties deviate from the experimental results.

Contact : dubouloz@ill.fr

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