Fragility, thermodynamic properties, and thermal stability of Pd-rich glass forming liquids

The thermal stability characteristics of three different Pd-rich bulk glass forming alloys, i.e. Pd40Ni40P20, Pd77.5Cu6Si16.5, and Pd43Cu27Ni10P20, have been investigated by continuous cooling experiments and by heating experiments following rapid melt quenching. Fragility parameters for these alloys are obtained from equilibrium viscosity data and, more directly if available, from the temperature-dependence of the average relaxation times obtained by modulation calorimetry. In addition, specific heat capacity data have been determined in dependence of temperature for the crystal, the undercooled liquid state and for the glass, respectively. Thus, a complete set of experimental data is available that allows a detailed comparison between the fragility characteristics and the thermal stabilities of the different alloy systems. As one result of this comparison, it is indicated that fragility and thermal stability are not correlated for these alloys, indicating further that vitrification is governed by nucleation control, i.e. by the avoidance of any nucleation.