Experimental investigation of phase equilibria in the Zr-Nb-Cr system at 1573Â K and 1373Â K

Phase equilibria in the Zr-Nb-Cr system at 1573 K and 1373 K were characterized by X-ray diffraction (XRD) and electron probe microanalysis (EPMA) coupled with wavelength-dispersive spectroscopy (WDS). Three single-phase regions and two two-phase regions were identified in the isothermal sections of 1573 K and 1373 K. The single-phase regions are BCC (Cr), C15 and BCC (Zr, Nb), and the two-phase regions are BCC (Cr) + C15 and BCC (Zr, Nb) + C15. With the temperature decreasing from 1573 K to 1373 K, the BCC (Zr, Nb) phase region narrows slightly, while the C15 phase region shrinks noticeably in the Nb-rich direction. The problems concerning sample equilibration and weight loss in the experiments were discussed, and the C15 single-phase region was explored based on the site occupancy modelled by the compound energy formalism (CEF) coupled with first-principles calculations.