Experimental Investigation of Isothermal Sections and Thermodynamic Modeling on the Cu-Nb-Ni System

Abstract

Ternary alloys samples with 22, 25 and 23 different compositions were prepared for determining isothermal sections at 1123, 1223 and 1373 K, respectively. The microstructures, phase constituents and phase compositions of the annealed Cu-Nb-Ni alloys were analyzed by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD) methods. Two three-phase regions, \(\text{fcc} + {\text{NbNi}_{{3}}}+{\text{Nb}_7}{\text{Ni}_6}\), fcc + bcc(Nb) + Nb₇Ni₆, and three two-phase regions, \(\text{fcc} + {\text{NbNi}_{{3}}},{\text{Nb}_7}{\text{Ni}_{{6}}}+{\text{NbNi}_{{3}}}\), fcc + Nb₇Ni₆, are determined for isothermal sections at 1123 and 1223 K. Two three-phase regions, \(\text{liquid} + {\text{NbNi}_{{3}}}+{\text{Nb}_7}{\text{Ni}_6}\), liquid + bcc(Nb) + Nb₇Ni₆, and three two-phase regions, \(\text{fcc} + {\text{NbNi}_{{3}}},{\text{Nb}_7}{\text{Ni}_{{6}}}+{\text{NbNi}_{{3}}}\), liquid + Nb₇Ni₆, are determined for isothermal sections at 1373 K. The solubilities of Cu in NbNi₃ and Nb₇Ni₆ were determined to be ~ 9.6 at.% and ~ 11.4 at.% at 1123 K, ~ 10.8 at.% and ~ 12.4 at.% at 1223 K and ~ 11.2 at.% and ~ 12.8 at.% at 1373 K, respectively. No ternary compounds were found. Based on the experimental phase equilibria data from the literature and the present work, a thermodynamic description of the Cu-Nb-Ni system was carried out by CALPHAD method. The substitutional solution model and sublattice model were employed to describe the solution phases and intermediate phases, respectively. A set of self-consistent thermodynamic parameters of the Cu-Nb-Ni system was conclusively obtained. Most of the reliable experimental data were reproduced by the present thermodynamic modeling.