On the thermodynamics, kinetics, and sub-Tg relaxations of Mg-based bulk metallic glasses

The four Mg-based bulk metallic glass forming alloys Mg59.5Cu22.9Ag6.6Gd11, Mg61Cu28Gd11, Mg54Cu28Ag7Y11, and Mg65Cu25Y10 are investigated to gain insight into their thermodynamic and kinetic properties. Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) in three point beam bending mode are used. The gathered data sets are used to evaluate the origin of the high glass forming ability of these systems, which is found in low thermodynamic driving forces for crystallization and sluggish kinetics. Furthermore, sub-Tg effects are observed via dynamic mechanical analysis (DMA) and modulated differential scanning calorimetry (MDSC) of as-cast samples. These are interpreted as related to the α-relaxation time spectrum instead of being caused by a Johari-Goldstein-type relaxation mechanism.