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 degrees 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 tau 1 (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.