Thermal analysis, fragility and viscosity of Au-based metallic glasses

Metallic glasses based on Au of composition Au49Cu26.9Ag5.5Pd2.3Si16.3 and (Au49Cu26.9Ag5.5Pd2.3Si16.3)99X1 where X = Ti and In, have been produced and characterized in ribbon form. They show a glass transition and a rather wide undercooled liquid region before crystallisation.The fragility index (m) of the alloys was investigated with two methods involving differential scanning calorimetry (DSC) measurements. In one method the glass transition temperature was determined at different scanning rates in the range 0.3–100 °C/min and its trend fitted to give m. In the other m was obtained from the temperature span of the glass transition range at the scanning rate of 20 °C/min. Implications for viscosity in the undercooled liquid are derived and thoroughly discussed ending with a VFT (Vogel–Fulcher–Tammann) expression for it.