Effects of Nd-rich phase on the improved properties and recoil loops for hot deformed Nd-Fe-B magnets

The magnetism of grain boundary (GB) phase plays a critical role in the coercivity of Nd–Fe–B magnets. In this work, the aggregation of the GB phase was formed in the hot-deformed magnet due to the low-density high-velocity compaction (HVC) precursor. The ferromagnetism of GB aggregation was confirmed by the analysis of 57Fe Mössbauer spectrometry, and its correlation to the magnetic performance was investigated by micromagnetic simulation. Results show that the soft magnetic GB aggregation is responsible for the low coercivity of the hot-deformed magnet. Moreover, an abnormal large openness of the recoil loop under the reversal magnetic field HR was presented in this work, and the underlying mechanism is interpreted by introducing demagnetization energy. To compensate for the problem of low density, low-melting-point Nd70Cu30 powders were added into the HVC magnet, which makes the GB aggregation paramagnetic and enhances the coercivity.

Section: Open Recoil Loopssupporting

confidence: 75%

Section: Open Recoil Loopsmentioning

confidence: 91%

Section: On the Magnetism Of Grain Boundary Phase And Its Contributio...mentioning

confidence: 99%

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On the magnetism of grain boundary phase and its contribution to the abnormal openness of recoil loops in hot-deformed magnets

Zhao¹,

Grenèche²

2019

“…However, there is still a huge gap between the coercivity and the anisotropy field of the Nd 2 Fe 14 B phase (µ o H A ~ 7 T). Many efforts have been made to further enhance their coercivity and thermal stability [2][3][4][5]. Heavy rare earth elements, such as Dy and Tb, can effectively improve the coercivity of the magnet due to the formation of (Dy/Tb) 2 Fe 14 B phase with higher magnetocrystalline anisotropy field [6,7].…”

Section: Introductionmentioning

confidence: 99%

Grain boundary diffusion of Dy films prepared by magnetron sputtering for sintered Nd–Fe–B magnets

Chen

Luo

Guan

et al. 2018

Self Cite

Dy films, deposited on the surface of sintered Nd-Fe-B magnets by magnetron sputtering, were employed for grain boundary diffusion source. High coercivity sintered Nd-Fe-B magnets were successfully prepared. Effects of sputtering power and grain boundary diffusion processes (GBDP) on the microstructure and magnetic properties were investigated in detail. The dense and uniform Dy films were beneficial to prepare high coercivity magnets by GBDP. The maximum coercivity value of 1189 kA m −1 could be shown, which was an amplification of 22.3%, compared with that of as-prepared Nd-Fe-B magnet. Furthermore, the improved remanence and maximum energy product were also achieved through tuning grain boundary diffusion processes. Our results demonstrated that the formation of (Nd, Dy) 2 Fe 14 B shell surrounding Nd 2 Fe 14 B grains and fine, uniform and continuous intergranular RE-rich phases jointly contribute to the improved coercivity.

“…The 'grain boundary diffusion process' (GBDP) is one feasible approach to enhance the coercivity and to minimize the remanence loss of the SMP RE 2 Fe 14 B magnets [17], which has been applied in industry for several years. The diffusion sources are usually RE-containing alloys or compounds [18][19][20][21][22][23][24][25][26][27]. When processed at temperatures in the vicinity of the melting point of the intergranular RE-rich phase, the extra RE atoms diffuse into the 2:14:1 phase grain, reducing the defect density close to the grain surface and forming continuous RE-rich grain boundary (GB) phase.…”

Section: Introductionmentioning

confidence: 99%

Magnetic performance change of multi-main-phase Nd–Ce–Fe–B magnets by diffusing (Nd, Pr)H_x

Zhang

Peng

et al. 2018

The grain boundary diffusion process (GBDP) is effective to enhance coercivity of the singlemain-phase (SMP) RE 2 Fe 14 B (rare earth (RE)) magnets through forming magnetic hardening shells surrounding the hard grain cores. Here, the GBDP was applied to the multi-main-phase (MMP) (Nd, Pr) 22.3 Ce 8.24 Fe bal M 1.0 B 1.0 (wt.%) magnets prepared by sintering the mixture of Ce-free and Ce-containing 2:14:1 powders, which have shown superior magnetic properties, especially coercivity, to the SMP ones at the same average composition. The remanence of the (Nd, Pr)H x diffused magnets increases gradually with the increase of diffusion temperature from 480 to 880 °C, the coercivity, however, slightly decreases. The highest (BH) max of 350.1 kJ m −3 is achieved when diffusing at 680 °C, which is 9.2% higher than 320.7 kJ m −3 for the as-prepared magnet. The remanence increment is due to the diffusion of Nd/Pr into the 2:14:1 phase grains, enlarging the intrinsic saturation magnetic polarization. The slight coercivity reduction is due to the gradual homogenization of RE distribution within the 2:14:1 grains of the undiffused parts, i.e. approaching the 'close to equilibrium (or SMP)' state, which offsets the positive contributions from the enrichment of Nd/Pr in the Ce-rich 2:14:1 phase and the formation of continuous RE-rich intergranular phase. These findings suggest that the GBDP effect on coercivity of the MMP Nd-Ce-Fe-B magnets is distinctly different from the SMP ones, and that the chemical heterogeneity should be carefully controlled to improve the magnetic properties of such high cost-performance permanent magnets.