Browsing by Author "Antonowicz, Jerzy"

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    Devitrification of thin film Cu-Zr metallic glass via ultrashort pulsed laser annealing
    (Elsevier, 2021-08-03) Antonowicz, Jerzy; Zalden, P.; Sokolowski-Tinten, K.; Georgarakis, Konstantinos; Minikayev, R.; Pietnoczka, A.; Bertram, F.; Chaika, M.; Chojnacki, M.; Dłużewski, P.; Fronc, K.; Greer, A. Lindsay; Jastrzębski, C.; Klinger, D.; Lemke, Ch.; Magnussen, O. M.; Murphy, B.; Perumal, K.; Sobierajski, R.
    In this work we report on an ultrashort pulsed laser annealing-driven devitrification of thin film Cu67Zr33 metallic glass characterized by micro-beam X-ray diffraction and electron microscopy techniques. The essential feature of ultrashort pulsed laser annealing is ultrafast heating (1014 K/s) by femtosecond optical excitation followed by extremely rapid cooling (1010–12 K/s) due to heat dissipation into the film substrate. During repetitive optical excitation, we take X-ray diffraction snapshots of the intermediate, frozen-in stages of the glass-crystal transformation to study its kinetics. A quantitative analysis of the diffraction patterns supported by electron microscopy result shows that the glass-crystal transformation proceeds by a rapid formation of an energetically favourable layer of crystalline ZrO2 on the free surface of the glassy film accompanied by nucleation and growth of fcc-Cu in the residual amorphous matrix. We demonstrate that at low effective annealing temperatures the devitrification kinetics of both products is correlated, while at high temperatures they decouple and ZrO2 forms an order of magnitude faster than Cu
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    In-situ monitoring the structural pathway of a Ti-based alloy from metallic liquid to metallic glass
    (Elsevier, 2025-04-25) Georgarakis, Konstantinos; Stiehler, Martin E.; Hennet, Louis; Guo, Yaofeng; Antonowicz, Jerzy; Louzguine-Luzgin, Dmitri V.; Jolly, Mark R.; Andrieux, Jérôme; Vaughan, Gavin B. M.; Greer, A. Lindsay
    A metallic glass is formed when a molten metallic alloy is cooled rapidly enough that crystallisation is avoided. However, the way the atomic structure of the liquid converts to that of the glass is generally unknown. The main challenge is the sufficiently fast experimental acquisition of structural data in the undercooled liquid regime necessitated by the high cooling rates needed to avoid crystallisation. In the present study, using aerodynamic levitation, the Ni-free Ti-based alloy Ti40Zr10Cu34Pd14Sn2 was vitrified in-situ in a high-energy synchrotron X-ray beam while diffraction data were acquired during cooling from above the liquidus temperature Tliq to well below the glass-transition temperature Tg. The structure in the undercooled liquid regime shows an accelerated evolution. Both the local order in the short (SRO) and medium range (MRO) increases rapidly as the undercooled liquid approaches Tg, below which the amorphous structure “freezes”. Nevertheless, distinct differences between the evolution of SRO and MRO were observed. The structural rearrangements in the undercooled liquid are found to be correlated with a rapid increase in viscosity of the metallic liquid upon cooling. The new findings shed light on the evolution of the atomic structure of metallic liquids during vitrification and the structural origins of the sluggish kinetics that suppress nucleation and growth of crystalline phases.
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    Structural pathways for ultrafast melting of optically excited thin polycrystalline Palladium films
    (Elsevier, 2024-06-14) Antonowicz, Jerzy; Olczak, Adam; Sokolowski-Tinten, Klaus; Zalden, Peter; Milov, Igor; Dzięgielewski, Przemysław; Bressler, Christian; Chapman, Henry N.; Chojnacki, Michał; Dłużewski, Piotr; Rodriguez-Fernandez, Angel; Fronc, Krzysztof; Gawełda, Wojciech; Georgarakis, Konstantinos
    Due to its extremely short timescale, the non-equilibrium melting of metals is exceptionally difficult to probe experimentally. The knowledge of melting mechanisms is thus based mainly on the results of theoretical predictions. This work reports on the investigation of ultrafast melting of thin polycrystalline Pd films studied by optical laser pump – X-ray free-electron laser probe experiments and molecular-dynamics simulations. By acquiring X-ray diffraction snapshots with sub-picosecond resolution, we capture the sample's atomic structure during its transition from the crystalline to the liquid state. Bridging the timescales of experiments and simulations allows us to formulate a realistic microscopic picture of the crystal-liquid transition. According to the experimental data, the melting process gradually accelerates with the increasing density of deposited energy. The molecular dynamics simulations reveal that the transition mechanism progressively varies from heterogeneous, initiated inside the material at structurally disordered grain boundaries, to homogenous, proceeding catastrophically in the crystal volume on a picosecond timescale comparable to that of electron-phonon coupling. We demonstrate that the existing models of strongly non-equilibrium melting, developed for systems with relatively weak electron-phonon coupling, remain valid even for ultrafast heating rates achieved in femtosecond laser-excited Pd. Furthermore, we highlight the role of pre-existing and transiently generated crystal defects in the transition to the liquid state.