Ho-Co and Ho-Co-Fe phase diagrams

Phase equilibria in the Ho-Co-Fe ternary and the boundary binary Ho-Co systems are investigated using dif-ferential thermal analysis, scanning electron microscopy, electron-probe microanalysis, and X-ray diffraction. Based on the experimental results, the binary Ho-Co phase diagram was revised resulting in confirmation of the general features of the previously published phase diagram, except for the mode of formation of the Ho3Co compound. The temperatures of most invariant reactions were adjusted. The ternary Ho-Co-Fe phase diagram was constructed over the whole concentration range. The liquidus and solidus projections, Scheil reaction scheme and isothermal sections at 1250, 1200 and 1000 degrees C are presented. The most prominent feature of this system is existence of three continuous solid solutions Ho2(Co,Fe)17, Ho(Co,Fe)3 and Ho(Co,Fe)2, which define the character of the solidus projection. Other binary compounds have significant solubility of third component. Among them Ho6Fe23 has a widest homogeneity range and dissolves up to 28.0 at.% Co at all studied temper-atures. All intermetallic phases are linear phases in terms of holmium. Five four-phase invariant reactions are found. One of them is of eutectic type and four ones are of U-type. Four invariant three-phase eutectic equilibria are present in the system.

Automated summary

The phase equilibria in the Ho-Co-Fe ternary and binary Ho-Co systems were investigated using various analysis methods. The phase diagram of the binary Ho-Co system was revised based on experimental results, while the ternary Ho-Co-Fe phase diagram was constructed. The system exhibits multiple solid solutions and invariant reactions.