Solid-state phase equilibria in the Co-Pt-Tb ternary system at 1173Â K

The solid-state phase equilibria in the Co-Pt-Tb ternary system at 1173 K (Tb ≤ 70%) were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS) techniques. The 1173 K isothermal section consists of 14 single-phase regions, 25 two-phase regions and 12 three-phase regions. At 1173 K, we have observed that the maximum solubility of Tb in α-(Co, Pt) is below 1.5 at.%Tb, with the maximum solid solubility of Pt in the compounds Co17Tb2, Co7Tb2, Co3Tb and Co2Tb being below 1 at.%Pt, 2 at.%Pt, 3.5 at.%Pt and 2 at.%Pt, respectively. Furthermore, the maximum solid solubility of Co in the compounds Pt5Tb, Pt3Tb, Pt4Tb3, PtTb, Pt4Tb5, Pt3Tb5, PtTb2 and PtTb3 is below 1 at.%Co, whereas in Pt2Tb it reaches 17 at.%Co. With the introduction of Co, the Pt4Tb3 phase gradually decomposes into the two neighboring compounds PtTb and Pt2Tb, while with the Co content exceeded 9 at.%Co, the Pt4Tb3 phase disappears. No new ternary compounds or Co5Tb were observed in our study.