Phase equilibria in the Gd-Ni binary and Mg-Ni-Gd ternary systems

Phase equilibria of the Gd-Ni binary and Mg-Ni-Gd ternary systems were critically investigated using equilibrated alloys and differential scanning calorimeter measurements. The phase diagram of the Gd-Ni binary system was updated from scanning electron microscopy with energy-dispersive X-ray spectrometry, X-ray diffraction, and differential scanning calorimeter results obtained on binary samples over the entire composition range. Major changes made in the present work include the absence of the Gd3Ni2 and GdNi4 compounds and the congruent melting point of the GdNi compound. An isothermal section of the Mg-Ni-Gd ternary system at 673 K was constructed from the investigations on 22 ternary alloys. In total, six ternary compounds were identified in this work, three of which were observed to crystallize in the Cu4MgSn (tau 1), Mo2FeB2 (tau 2), and Ru4Al3B2-type (tau 3) structures, respectively. As in most of the Mg-rare-earth metal transition metal ternary systems, a long-period-stacking ordered phase was identified to have an 18R structure and a melting temperature of 806 K. Noticeable solid solubility of Ni in the Mg5Gd and Mg3Gd binary compounds was observed.