In recent years, the application of various additions (hydrides, oxides, intermetallic compounds, etc.) in powder mixtures for manufacturing Nd-Fe-B magnets shows promise as the method that allows one to increase the hysteretic characteristics of the magnets at the expense of realized grain-boundary diffusion and grain-boundary structuring processes. The processes allow one to introduce both the heavy rare-earth metals and copper that was shown also to favour the increase in the hysteretic parameter of Nd-Fe-B-based compositions. In the present work, we consider the alloys Tb3(Co1-x,Cux) with x = ~0.4 as additions to Nd-Fe-B-based powder mixtures. The alloys were prepared by arc melting in an argon atmosphere and subjected to homogenizing annealing at 600 °C for 90 h. The phase composition and phase equilibria in the system were studied by X-ray diffraction analysis, differential thermal analysis (DTA), optical and scanning electron microscopy, electron microprobe analysis, and low-temperature thermal magnetic analysis. The composition was shown to be three-phase, Tb3(Co,Cu), Tb12(Co,Cu)7, and Tb(Co,Cu) that is the primarily solidified phase in the system. The copper solubility in the Tb3Co and Tb12Co7 compounds and cobalt solubility in the TbCu compound were determined. A portion of the isothermal section of the Tb-Co-Cu system with at 600 °C was constructed. The possibility of the hydrogenation of the Tb3(Co1-x,Cux) composition with x = ~0.4 with the formation of TbHx, Co, Cu was demonstrated.Keywords: Grain boundary diffusion, Nd-Fe-B magnets, Tb-Co-Cu system, phase equilibria
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