Enthalpy recovery and free volume relaxation in a Zr44Ti11Ni10Cu10Be25 bulk metallic glass

Research highlights: → The Zr44Ti11Ni10Cu10Be25 BMG is annealed at constant temperatures below Tg. → Enthalpy recovery and free volume change with annealing temperature are measured. → A linear relationship is found between enthalpy recovery and free volume change. → The formation energy for free volume in the glassy state is 622.7 ± 20 kJ/g-atom. - Abstract: We report on the free volume of the Zr44Ti11Ni10Cu10Be25 bulk metallic glass in terms of its enthalpy recovery and volumetric relaxation below the glass transition temperature, Tg. Glassy samples are isothermally annealed below Tg using differential scanning calorimetry and the resulting enthalpy recovery, ΔHr, is measured upon re-heating into the supercooled liquid region. Volumetric changes below Tg are measured isothermally using Thermo-Mechanical Analysis. The total changes in the relative free volume, Δνf/νm, between the initially glassy state and the equilibrium liquid are calculated from the volumetric relaxation. The measured values of ΔHr and Δνf/νm correlate well within the framework of free volume theory and a linear relationship is found between the two.