The ternary Gd-Li-Mg system: Phase diagram study and computational evaluation

The binary Gd-Li and the ternary Gd-Li-Mg systems mere studied experimental ly by thermal analysis and phase equilibration and also by thermodynamic ca lculations using the CALPHAD method. Ternary phase equilibria at 250 degree sC were studied with 55 different alloys that were annealed for 400 h and a nalyzed by x-ray diffractometry, A thermodynamic assessment of the binary G d-Li system was also performed and the calculated phase diagram is presente d. In the Gd-Li-Mg system, ternary solubilities of Li in GdMg (up to 5 at.% Li), GdMg2 (up to approximately 3 at.% Li), and GdMg3 (up to 5 at.% Li) we re found at 250 degreesC. No ternary compound was observed. Lattice paramet ers for different compositions are given for these phases. Thermal analysis using a ternary hey sample of composition near the invariant reaction L' = L + (beta Gd) + GdMg provided the data that were needed to determine a the rmodynamic parameter for the ternary liquid. Thermodynamic data sets for th e ternary solid solution phases were also developed, Based on the present d ata sets and those of the binary Gd-Mg and Li-Mg systems from the literatur e, the phase equilibria in the entire ternary system were calculated. Isoth ermal and vertical sections of the phase diagram and the projection of the liquidus surface are shown. These calculated phase diagrams are well suppor ted by the experimental data.