Thermal and viscoelastic properties of a strong bulk metallic glass former

The fragility index of a Zr_42.1Ti_12.9Cu_11.5Ni_10.2Be_23.3 bulk metallic glass former is investigated in differential scanning calorimetry and dynamic viscoelastic experiments. The kinetic nature of the glass transition provides a means of analysing the dynamical changes in the supercooled liquid state from the heating rate dependence of the calorimetric glass transition and primary crystallization temperatures. The difference in the fragility index between these two temperatures is positively correlated to the degree of structural change throughout the supercooled liquid region. This provides a straightforward method of comparing the structural robustness of metallic glasses to temperature changes in the supercooled liquid state. Such an analysis reveals that the Zr alloy is a relatively strong liquid. Comparisons to the kinetic behaviour of Pd₄₈Ni₃₂P₂₀ and Pt₆₀Ni₁₅P₂₅ indicate that a significant increase in the glass forming ability of metallic alloys is accompanied by only a moderate decrease in the fragility parameter. In the case of the viscoelastic response of the Zr alloy in the vicinity of the calorimetric glass transition, the master functions obtained by time-temperature superposition could be modelled reasonably well using generalized Maxwell equations which allow for dynamic heterogeneity.