Open Access Conference Proceedings

The effect of low-temperature treatment on the structure and hysteretic properties of sintered Nd-Fe-B magnets, which were prepared using strip-casting alloy (wt.%) Nd - 24%, Pr – 6.5%, Dy – 0.5%, B – 1%, Al – 0.2%, Fe – balance and 2 wt.% DyH2 addition, was studied. Hysteretic properties of the magnets subjected to the optimum heat treatment (1-h holding at 500 ˚C followed by quenching in gaseous nitrogen) are Br = 1.29 T, jHc = 1309 kAm-1, Hk = 1220 kAm-1, (BH)max = 322 kJm-3. The subsequent combined heat treatment in vacuum or inert atmosphere, which includes the stepped or progressive heating from 250 to 500 ˚C (the total heating time is to 20 h), does not change hysteretic properties of magnets upon heating within this temperature range, whereas magnets of the same composition, but prepared by traditional technology, demonstrate the abrupt decrease of hysteretic properties (jHc and Hk) upon heating in a temperature range of 350 to 400 ˚C. The degradation of magnetic properties (decrease in jHc and Hk to 1105 and 960 kAm-1, respectively) of magnets prepared from hydride-containing powder mixtures is observed only after the repeated annealing at 550 ˚C. The hysteretic properties of the magnets can be restored completely by heat treatment 1050 ˚C (1 h) + 500 ˚C (2 h). X-ray diffraction analysis and scanning electron microscopy were used to demonstrate the evolution of microstructure and phase composition of magnets in the course of annealings.

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