Experimental Investigation of the Isothermal Section at 800 °C of the Nd-Fe-Co Ternary System

The phase equilibrium of the ternary Nd-Fe-Co system at 800 °C was investigated by means of powder x-ray diffraction and scanning electron microscopy–energy dispersive x-ray spectroscopy. Seven binary compounds, i.e., Nd2Co17, NdCo5, Nd5Co19, Nd2Co7, NdCo3, NdCo2, Nd2Fe17 were identified to exist at this isothermal section. This isothermal section consists of ten single-phase, ten two-phase and six three-phase regions. All measured compositions and unit-cell refinements were performed at room temperature from quenched samples annealed at 800 °C for one week. The maximum solubility at 800 °C of Fe in NdCo2−x Fe x (MgCu2-type structure, Fd-3 m), NdCo3−x Fe x (PuNi3-type structure, R-3 m space group), Nd2Co7−x Fe x (Ce2Ni7-type structure, R-3 m), Nd5Co19−x Fe x (CeCo19-type structure, R-3 m space group), NdCo5−x Fe x (CaCu5-type structure, P6/mmm), Nd2Co17−x Fe x (Th2Zn17 type structure, R-3 m) and Nd2Fe17−x Co x (Th2Zn17 type structure, R-3 m) are about 31.6 at.% Fe, 47.9 at.% Fe, 13.3 at.% Fe, 8.6 at.% Fe, 10.37 at.%, 36.35 at.% Fe, and 58.23 at.% Fe respectively. The solid solubility range of Co in Nd2Fe17 form discontinuous series of 2 ranges is about 0-30.14 at.% Co, and 51.9-100 at.% Co and the solid solubility range of Fe in Nd2Co17 is about 0-48.1 at.% Fe, and 69.86-100 at.% Fe.