Dresden 2017 – wissenschaftliches Programm
MM 69: Topical session: Dynamics, relaxation and deformation in deeply supercooled metallic liquids and glasses VII - thermodynamics and structure
MM 69.6: Vortrag
Donnerstag, 23. März 2017, 18:45–19:00, IFW A
Thermodynamic and kinetic properties as well as low temperature relaxations of Mg-based bulk metallic glasses — •Maximilian Frey, Ralf Busch, and Isabella Gallino — Chair of Metallic Materials, Saarland University
A broad set of thermodynamic and kinetic properties of four Mg-based metallic glass forming systems was established using calorimetric studies, thermophysical analysis, as well as thermomechanical analysis. Beside considerations about the fragilities of these alloys, especially the appearance of a secondary relaxation event occuring at temperatures distinctly below the glass transition was analysed via modulated DSC scans and isochronal DMA measurements. The definition of the Johari-Goldstein-type secondary relaxation as a general feature of metallic glasses has become increasingly popular in recent literature. However, the present relaxation signals exhibit characteristics, which are atypical for this kind of secondary event, like e.g. relatively high activation energies of about 135 kJ/g-atom. In combination and consistency with other works also investigating a Mg-based alloy via DMA and XPCS, a model is presented that explains the secondary relaxation event through a broad structural relaxation time spectrum. In this light, the corresponding measurement signals are interpreted as the premature thawing of defect regions, which exhibit increased free volume and are embedded in the surrounding more densely packed glassy backbone.