Phase Equilibria of the Mg-Gd-Ce System at 500 °C

The phase equilibria of the Mg-Gd-Ce system at 500 °C were investigated by means of the electron probe microanalysis (EPMA) and x-ray diffraction (XRD) on equilibrated alloys. The existence of the so-called normal tetragonal CeMg12(I) and long-range ordered CeMg12(II) was confirmed in the present work. The following five three-phase equilibria were well determined: (1) (Mg) + CeMg12(I) + Ce5Mg41, (2) (Mg) + Ce5Mg41 + GdMg5, (3) Ce5Mg41 + GdMg5 + (Ce,Gd)Mg3, (4) (Ce,Gd)Mg3 + GdMg2 + (Ce,Gd)Mg and (5) (Ce,Gd)Mg + (δCe) + (βCe). The solubility of Ce in GdMg5 and in GdMg2 was measured to be 7.8 and 8.7 at.% Ce, respectively. The solubility of Gd in CeMg12(I), in Ce5Mg41 and in (δCe) were measured to be 1.0, 4.6 and 2.4 at.% Gd, respectively. Two continuous series of solid solutions form between GdMg3 and CeMg3, and between GdMg and CeMg. The overall isothermal section at 500 °C was constructed based on the present data with a few extrapolations.