On the fragility of Nb-Ni-based and Zr-based bulk metallic glasses

The heating rate dependencies of the glass transition temperature of the Ni65Nb35, Ni60Nb35Sn5, Ni59.35Nb34.45Sn6.2, Ni-60(Nb40Ta60)(34)Sn-6, and Ni57Fe3Nb35Sn5 metallic glass-forming alloys were investigated with a differential scanning calorimeter (DSC). The relaxation time for each DSC experiment was plotted versus inverse temperature, and a Vogel-Fulcher-Tamman (VFT)-type relation was fitted to the data. The fragilities of the alloys were characterized with the fragility parameter, D*, and the VFT temperature, T-0, which are the fit parameters from the VFT relation. It was found that for the binary alloy D*=6.2, for the ternary alloys D*=11.0, and that for the quaternary alloys D* was between 16.4 and 19.0. These D* increase monotonically as the number of components in the alloy is increased. It was also found that the fragilities of Zr-based alloys show a similar trend. (C) American Institute of Physics.