Experimental investigation of the phase equilibria in the Tb-Co and Tb-Co-Fe systems and magnetic properties of phases

Phase equilibria in the Tb-Co and Tb-Co-Fe systems were investigated experimentally for the first time by a combination of scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and differential thermal analysis (DTA). Based on the experimental data from the present work, the Tb-Co system was constructed. Magnetic properties of Tb2Co17 and Tb2Co7 were measured with vibrating-sample magnetometer (VSM). The liquidus and solidus projections, the melting diagram, the isothermal sections at 1200 and 1000 °C, the vertical sections on isoconcentrates 20, 30 and 40 at% Tb and the Scheil reaction scheme for the Tb-Co-Fe system over the whole concentration range were constructed. No ternary intermetallic phase exists in the system, but the three continuous solid solutions Tb2(Co,Fe)17, Tb(Co,Fe)3 and Tb(Co,Fe)2 were found and the TbCo5 and Tb2Co7 phases have extended homogeneity ranges in the ternary system, where large amounts of Co can be substituted by Fe in both cases. The ternary Tb-Co-Fe system contains five four-phase invariant reactions encompassing one of E- and four of U-type reactions. The system also contains two three-phase invariant reactions.