On the thermodynamic and kinetic properties of bulk glass forming metallic systems

摘要

Bulk metallic glasses (BMGs) are typically formed from the rapid quenching of multicomponent metallic melts. Good BMG-forming systems are associated with a large atomic size mismatch and deep eutectic formation between the constituent elements. As such, these densely packed BMG-forming liquids can be characterized through sluggish kinetics, which impedes the nucleation and growth of crystals, as well as a low driving force for crystallization that is present in the undercooled liquid. In this work, the equilibrium thermodynamic and kinetic properties of certain BMG-forming liquids are analyzed at temperatures near the melting point and in the deeply supercooled state near the glass transition. This includes determination of the viscosity and thermodynamic functions of the liquid. The non-equilibrium properties of the glassy state are also studied, looking at the phenomenology of structural relaxation as it relates to viscosity, enthalpy and free volume. A look at viscous flow in terms of configurational entropy and various models of the free volume is given. Finally, the molten viscous behavior of various BMG-forming alloys is investigated at temperatures above the melting point. The kinetics in the melt at high temperatures reveals a distinctively more fragile liquid state than at low temperatures near the glass transition. This behavior is revealed to be the result of a fragile-to-strong transition in the undercooled liquid, possibly due to polyamorphism.