Physical Aging Studies in Bulk Metallic Glasses

Physical properties of glasses, such as density, viscosity, electrical resistivity or enthalpy, evolve slowly but continuously with time at temperatures below the glass transition temperature. This is the physical aging process, which is an universal property of any class of glass. It is governed by thermodynamics as the glass attempts to re-establish thermodynamic equilibrium and it is steered by sluggish kinetics. Like any other non-equilibrium system, the glass evolves into states with lower free energy and leads to structural changes at the microscopic level.