Thermodynamic Analysis of the Phase Equilibria in the Nb-Ni-Zr System

Abstract

A thermodynamic study of phase equilibria in the Nb-Ni-Zr system has been carried out experimentally and using the CALPHAD method. To enable the thermodynamic description of the constituent binary systems, the results from a previous evaluation were adopted for the Nb-Ni, Ni-Zr and Nb-Zr systems. However, some modifications of the thermodynamic parameters of the Ni-Zr system were made based on recent experimental data on the binary and ternary phase equilibria. The phase boundaries involving the liquid phase in the Nb-Ni-Zr ternary system at the constant 60 mol%Ni and 20 mol%Zr were determined experimentally using differential scanning calorimetry (DSC). The thermodynamic parameters of the Nb-Ni-Zr ternary system were evaluated by combining the experimental results from DSC with reported phase boundaries of the isothermal sections at 773 and 1073 K. The calculated results reproduced the DSC results as well as the experimental isothermal sections. Furthermore, the amorphous-forming ability of Nb-Ni-Zr ternary alloys was evaluated by incorporating the thermodynamic properties from the phase diagram calculations into the Davies-Uhlmann kinetic formulations. The calculated critical cooling rates in the observed metallic glass forming compositional range were found to be lower than those in the observed amorphous forming range by one or more orders of magnitude.