Experimental Determination of Phase Equilibria in the La-Co-Zr System

The phase equilibria of the La-Co-Zr ternary system at 873 K and 1073 K were studied for the first time using equilibrated alloys employing scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and x-ray diffraction (XRD). The crystal structures of the formed phases in La-Co-Zr alloys annealed at 873 K and 1073 K were identified through Rietveld refinement of the XRD results. The SEM-EDS and XRD results reveal that no ternary intermetallic compounds were detected in the La-Co-Zr ternary system and the binary intermetallic compound La₅Co₁₉ was not observed in the La-Co binary system. The solid solubility of the third element in the binary La-Co and Co-Zr intermetallic compounds was measured by EDS composition measurements. It was found that the maximum solid solubility of Zr in LaCo₅ and LaCo₁₃ is 1.8 and 4.0 at.% at 1073 K and it is 2.3 and 4.7 at.% at 873 K, respectively, while the maximum solid solubility of La in Co₂₃Zr₆ and Co₂Zr is 1.3 and 1.6 at.% at 873 K and it is 3.8 and 6.1 at 1073 K. Furthermore, the solid solubility of Zr and La in the other La-Co and Co-Zr intermetallic compounds is negligible. Finally, the La-Co-Zr ternary isothermal sections at 873 K and 1073 K were established.