Isothermal section of the Ho–Co–Fe system at 773 K

The 773 K isothermal section of the phase diagram of the Ho–Co–Fe ternary system was investigated by using X-ray diffraction technique, metallographic analysis and scanning electron microscopy with energy dispersive analysis. The isothermal section of the ternary system consists of 6 three-phase regions, 16 two-phase regions and 11 single-phase regions. Three pairs of corresponding compounds of Ho–Co and Ho–Fe systems, i.e., Ho2Co17 and Ho2Fe17, HoCo3 and HoFe3, HoCo2 and HoFe2, form a continuous series of solid solution. At 773 K the compound Ho6Fe23−xCox was found to have a wide homogeneity range from 0 to 29 at.% Co. The maximum solid solubilities of Fe in Co, Ho2Co7, Ho12Co7 and Ho3Co were determined to be about 10, 9, 2 and 5 at.% Fe, respectively. The maximum solid solubility of Co in Fe is found to be 78 at.% Co.

Research highlights▶ The phase relationship of the Ho–Co–Fe ternary system at 773 K is investigated for the first time. ▶ The isothermal section of the system at 773 K is determined and the isothermal section consists of 6 three-phase regions, 16 two-phase regions and 11 single-phase regions. ▶ The solid solubilities of Co in Fe and Ho6Fe23 and Fe in Co, Ho2Co7, Ho12Co7 and Ho3Co at 773 K are determined by experimental method.