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X-ray diffraction analysis and simulation of X-ray diffraction patterns are used to study the phase composition of sintered (Nd, Pr, Dy)-Fe-B magnets prepared from powder mixtures with 2 % DyH2 addition. After optimum heat treatment, which includes 1-h holding at 500 C followed by quenching in gaseous nitrogen, the magnets exhibit high magnetic properties: Br = 1.29 T, jHc = 1309 kA/m, Hk = 1220 kA/m, (BH)max = 322 kJ/m3. The phase composition of the magnets comprises the principal hard magnetic phase based on the Nd2Fe14B compound, (Nd,Pr,Dy)-rich phase and (Nd,Pr,Dy)-O oxides. The magnets are subjected to progressive low-temperature heatings in a temperature range of 250-500 C, annealing at 550C, medium-temperature annealing at 900C, and high-temperature annealing at 1070C to study the stability of hysteretic magnetic characteristics. The heat treatments are shown to lead to changes in the lattice parameters of the Nd2Fe14B-based phase and appearance of additional reflections, which can be related to the formation and dissolution of the impurity Nd1.1Fe4B4 phase. Thermal magnetic analysis is used to study the possibility of existence of the phase. The data obtained demonstrate the higher thermal stability of hysteretic properties of magnets prepared from hydride-containing powder mixtures. These data are of importance for deciding the optimum heat treatment of Nd-Fe-B-based magnets and the prediction of their service stability.
Keywords: Permanent magnets, strip casting, thermomagnetic analysis, X-ray diffraction analysis© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.