Experimental investigation and thermodynamic modeling of Cu–Nb–Si system

The phase equilibria of the Cu—Nb—Si system were investigated via a combination of key equilibrated alloys, thermodynamic modeling and first-principles calculations. Sixteen ternary alloys were prepared to determine the isothermal sections at 600 and 700 °C, by means of X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM−EDS). The three- and two-phase regions were determined. The existence of ternary compound τ1 (Cu4Nb5Si4) was confirmed. The solubilities of Cu in the NbSi2 and Nb5Si3 phases were measured. Based on the experimental equilibria data from the literature and the present work, a thermodynamic description of the Cu—Nb—Si system was carried out by using the calculation of phase diagrams (CALPHAD) method supported by first-principles calculations. The substitutional 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—Si system were conclusively obtained. Most of the reliable experimental data were reproduced by the present thermodynamic modeling.