Experimental study and thermodynamic re-assessment of the Ni–Zr system

The eutectic temperature between the NiZr and NiZr2 compounds was experimentally determined using Differential Scanning Calorimetry (DSC) to evaluate definitely the discrepancy among different sources. Based on the data of the literature reports and the present experiment results, the Ni–Zr binary system was re-assessed thermodynamically by means of CALPHAD (CALculation of PHAse Diagrams) technique. The substitutional solution model was used to describe the liquid phase and the three terminal solid solutions, fcc-A1 (Ni), bcc-A2 (βZr) and hcp-A3 (αZr), and their excess Gibbs energies were formulated with the Redlich–Kister polynomial. The sublattice-compound energy model was employed to describe the intermetallic compound (Ni5Zr) with a homogeneity range. The other compounds Ni7Zr2, Ni3Zr, Ni21Zr8, Ni10Zr7, Ni11Zr9, NiZr and NiZr2 were treated as stoichiometric phases. The parameters of all the Gibbs energy expressions were optimized. A set of self-consistent thermodynamic parameters has been obtained. The calculated phase diagram and thermodynamic properties agree well with the available experimental data.