Regensburg 2010 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 18: Topical Session Glass Dynamics V

MM 18.3: Vortrag

Dienstag, 23. März 2010, 11:00–11:15, H16

Enthalpy and free volume relaxation in a Zr-Ti-Ni-Cu-Be bulk metallic glass alloy — •Zach Evenson and Ralf Busch — Chair of Metallic Materials, Saarland University, PO Box 151150, 66041 Saarbruecken, Germany

We report on the enthalpy and free volume relaxation kinetics of the Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ (Vitreloy 1b) bulk metallic glass as measured with dilatometric and calorimetric methods. Using Differential Scanning Calorimetry (DSC) samples are relaxed into the metastable equilibrium liquid at temperatures below the calorimetric glass transition (T_g); the resulting enthalpy recovery (Δ H^recov.) is then measured upon re-heating into the supercooled liquid region. It is found that the sample volume also relaxes into a metastable equilibrium liquid state, observed on a long time scale. These volumetric changes are measured isothermally using Thermal Mechanical Analysis (TMA). The total changes in the free volume (Δ v_f/v_m) from the initially glassy state and the equilibrium liquid are calculated during annealing at the same temperatures as in DSC. The equilibrium free volume change is found to relax with a stretched exponential behavior and is best fitted with a Kohlrausch-Williams-Watts (KWW) function with beta-values approaching unity close to the glass transition. The measured values of Δ H^recov. and Δ v_f/v_m correlate well within the framework of free volume theory and a linear relationship is found between the two.