Phase Equilibria in the La-Co-Ti Ternary System at 873 K and 1073 K

Abstract

The phase equilibria of the La-Co-Ti ternary system were investigated through the equilibrated alloy method using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD). The phase formation in La-Co-Ti alloys annealed at 873 K and 1073 K was determined by using the EDS composition measurements and the XRD Rietveld refinements. Five La-Co binary intermetallic compounds (LaCo₁₃, LaCo₅, β-La₂Co₇, La₂Co₃, La₂Co_1.7) and five Co-Ti binary intermetallic compounds (Co₃Ti, Co₂Ti(h), Co₂Ti(c), CoTi and CoTi₂) were observed, while the intermetallic compound La₅Co₁₉ was not found. Two ternary intermetallic compounds La₂Co_17-xTi_x (0.5 ≤ x ≤ 1.3) with a Th₂Zn₁₇-type structure and LaCo_12-xTi_x (1.5 ≤ x ≤ 1.7) with a ThMn₁₂-type structure were detected at 873 K, while the ternary intermetallic compound La₂Co_17-xTi_x (0.5 ≤ x ≤ 1.3) is only existent at 1073 K. Furthermore, the measured phase compositions show that the solubility of the third element in the La-Co and Co-Ti binary intermetallic compounds is negligible (less than 1 at.%). Two isothermal sections of the La-Co-Ti ternary system at 873 K and 1073 K were constructed finally.