The phase equilibrium of the Ni⁻Al⁻La ternary system in a nickel-rich region was observed at 800 °C and 1000 °C using scanning electron microscopy backscattered electron imaging, energy dispersive X-ray spectrometry and X-ray diffractometry. The solubility of Al in the Ni₅La phase was remeasured at 800 °C and 1000 °C. Herein, we report a new ternary phase, termed Ni₂AlLa, confirmed at 800 °C. Its X-ray diffraction (XRD) pattern was indexed and space group determined using Total Pattern Solution (TOPAS), and the suitable lattice parameters were fitted using the Pawley method and selected-area electron diffraction. Ni₂AlLa crystallizes in the trigonal system with a space group R3 (no. 146), a = 4.1985 Å and c = 13.6626 Å. A self-consistent set of thermodynamic parameters for the Al⁻La and Ni⁻La binary systems and the Ni⁻Al⁻La ternary system includes a Ni₂AlLa ternary phase, which was optimized using the CALPHAD method. The calculated thermodynamic and phase-equilibria data for the binary and ternary systems are consistent with the literature and measured data.
Keywords: CALPHAD; Ni-Al-La; lanthanides; superalloys; thermodynamic optimization.