Phase Equilibria in the La-Co-Ti Ternary System at 873 K and 1073 K
摘要
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, La2Co1.7) 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 La2Co17-xTix (0.5 ≤ x ≤ 1.3) with a Th2Zn17-type structure and LaCo12-xTix (1.5 ≤ x ≤ 1.7) with a ThMn12-type structure were detected at 873 K, while the ternary intermetallic compound La2Co17-xTix (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.