Thermophysikalische Eigenschaften nicht-Zr-basierter metallischer Massivgläser
Zusammenfassung der Projektergebnisse
The investigations of this project examined several non-Zr-based multicomponent bulk metallic glasses (BMGs) employing an ensemble of experimental techniques including differential scanning calorimetry (DSC/MDSC/FSC), dynamic mechanical analysis (DMA), dilatometry (TMA), x-ray photon correlation spectroscopy (XPCS), and in-situ high-intensity synchrotron X-ray scattering (XRD). The main outcomes are: 1) a comprehensive description of the thermodynamic, kinetic, and structural aspects for several non-Zr based BMGs; 2) new insights into the glass forming nature of BMG-forming systems; 3) experimental advances made in understanding the nature of the relaxation phenomenon in BMGs and its implications to the macroscopic and microscopic properties changes of the relaxing glass. This work shows that BMG-forming liquids can be categorized in terms of one of the following major thermodynamic and kinetic factors that can stabilize the supercooled liquid state, alternatively: interfacial energy, driving force for crystallization, or fragility. All of the examined BMGs-forming melts show an intermediate kinetic fragility between SiO2 and macromolecular materials and small thermodynamic driving force for crystallization leading to sluggish crystallization kinetics, leaving time for good glass forming ability and bulk casting thicknesses. We can relate the kinetics to the thermodynamics of the supercooled liquid via the Adam-Gibbs equation. Liquid-liquid transitions emerge to be a common phenomenon in BMGs. This is observed as a dynamic crossover from fragile kinetic behavior at high temperature to strong kinetic behavior at low temperature in the supercooled liquid and in the vicinity of the glass transition. Physical aging of BMGs is mostly observed to be non-exponential in nature, characteristic of stretched dynamic responses of physical properties. A hierarchical mechanism of the relaxation pathway was experimentally observed by means of DSC, FSC, MDSC and XPCS. The scenario of a strong length-scale dependence of the microscopic dynamics in the glassy state has emerged, which relativizes previous macroscopic measurements where aging close to Tg occurs on timescales similar to the intrinsic relaxation time. Studies based on the XPCS technique show that the structural relaxation processes that underlie aging in BMGs-forming systems are intermittent and highly heterogeneous. Long-time annealing can result in trapping the glass configuration in a deep local energy minimum, and even in leading to structural crossovers from a fragile to a strong liquid.
Projektbezogene Publikationen (Auswahl)
- Thermo-physical characterization of the Fe67Mo6Ni3.5Cr3.5 P12C5.5B2.5 Bulk Metallic Glass Forming Alloy, Acta Materialia 118 (2016) 129-139
B. Bochtler, O. Gross, I. Gallino, R. Busch
(Siehe online unter https://doi.org/10.1016/j.actamat.2016.07.031) - On the high glass-forming ability of Pt-Cu-Ni/Co-P-based liquids, Acta Materialia 141 (2017) 109–119
O. Gross, S.S. Riegler, M. Stolpe, B. Bochtler, A. Kuball, S. Hechler, R. Busch, I. Gallino
(Siehe online unter https://doi.org/10.1016/j.actamat.2017.09.013) - The kinetic fragility of Pt-P- and Ni-P-based bulk glass forming liquids and its thermodynamic and structural signature, Acta Materialia 132 (2017) 118-127
O. Gross, B. Bochtler, M. Stolpe, S. Hechler, W. Hembree, R. Busch, and I. Gallino
(Siehe online unter https://doi.org/10.1016/j.actamat.2017.04.030) - Hierarchical aging pathways and reversible fragile-to-strong transition upon annealing of a metallic glass former, Acta Materialia 144 (2018) 400-410
I. Gallino, D. Cangialosi, Z. Evenson, L. Schmitt, S. Hechler, M. Stolpe, and B. Ruta
(Siehe online unter https://doi.org/10.1016/j.actamat.2017.10.060)
