# Fileset

[REPM2025_P1-38_Horikawa.pdf](https://mdr.nims.go.jp/filesets/7b8a99ad-6a76-414a-a5d5-d4ad28027e08/download)

## Creator

Takashi Horikawa, Masao Yamazaki, Masashi Matsuura, Satoshi Sugimoto

## Rights

[Creative Commons BY Attribution 4.0 International](https://creativecommons.org/licenses/by/4.0/)

## Other metadata

[Improvement of Hk and squareness in d-HDDR-treated Nd-Fe-B powders prepared using modified starting powder](https://mdr.nims.go.jp/datasets/fda61f9a-3d91-43a8-b42c-c209829bb87e)

## Fulltext

Improvement of Hk and squareness in d-HDDR-treatedNd-Fe-B powders prepared using modified starting powderT. Horikawa(a)(b), M. Yamazaki(a), M. Matsuura(b) and S. Sugimoto(b) (a) Aichi Steel corporation, (b) Tohoku UniversityH2 pressure (kPa) 30 100Br (T) 1.37 0.85HcJ (kA/m) 1199 1254(BH)max (kJ/m3) 344 124HDDR (Hydrogenation Disproportionation Desorption Recombination)1)1. T. Takeshita and R. Nakayama, Proc. 10th Int'l. Workshop on R. E. Magnets & Their Applications, Kyoto, (1989) 551.2. C. Mishima, et al., J. Magn. Soc. Jpn., 24 (2000) 407.REPM2025July 27th-31st, 2025at Tsukuba, JapanBackgroundResults and DiscussionAverage diameter (nm)Std. dev.(nm)Conv. 411 119Novel 357 105221208_443-as-1230530_509-1-3221202_449-3230526_500-2240304_550-2Summary・We developed a novel d-HDDR process using raw powders with particle size of 75-106 μm.・After GBD (4wt%), higher Hk (0.98 MA/m) and SQ (73%) were obtained.・ Two factors for these results are as follows:1. Less variations in DOA due to homogeneous lamellar/spherical and resultant high/low DOAfractions achieved by size-limited raw powders.2. Less variations in coercivity may be due to high homogeneity in GB structures achieved by lower Nd-rich component in raw powders.ProblemApproachIdeal d-HDDRFreq.Limited particle size ・ Homogeneous lamellar/spherical andhigh/low DOA volume fractions・ Removal of low DOA fine powders→ Less variation in DOA results in high Hk, SQHD DR GBDNd-Cu-Al diffusionLamellarSphericalHigh DOALowParticle sizeTo improve DOA 3,4)c-axis alignment: High AnisotropyFine grains: High coercivity→ Anisotropic bonded magnetsFine crystalgrains(~ 300 nm)c-axisalignment(Anisotropic)Mother alloy d-HDDR powder(~ 200 μm)[001]c-axisNd2Fe14BNd-rich grainboundaryd(dynamic)-HDDR 2)IsotropicAnisotropic0100400H2 pressure (kPa)20 40 60 80 1000(BH) max(kJ/m3)200300Nd2Fe14BgrainAnisotropy in HDDR powderNd2Fe14B + H2  →   Fe + NdH2 + Fe2B →   Nd2Fe14B + H2↑DRHDExperimentalOptimization of particle sizeMagnetic field, H / MA/m Magnetic polarization, J/ Am2/kg ・75-106 μm raw powder showed the best properties.・Good uniformity in particle size.・Low Nd content.Weight fraction / %Size range / μm3. T. Horikawa et al., Sci. Tech. Adv. Mater., 22 (2021) 729.4. T. Horikawa et al., The 170th Annual meeting of JIM, (2022) S7.2.[P1-38]Optimization of Nd content (mixing ratio of diffusing Nd-Cu-Al powder in GBD)Purpose・ To develop novel preparation process of raw powders with limitedparticle size for obtaining higher Hk and SQ by achieving homo-geneous lamellar/spherical and resultant high/low DOA fractions.・ To investigate the effect of such raw powders on magneticproperties and microstructures.－ 106-150 μm－ 75-106－ 53-75・GBD with 4wt% of Nd-Cu-Al showed well-balanced magnetic properties.・Higher DOA (78.3%), Hk (0.98 MA/m) and SQ (73%) due to limited particle size.Hk and squareness (SQ, Hk/HcJ) were low,which may be due to variations in DOA and coercivity among powder particles.Anisotropy induction model 3,4)High DOA* (inside)Low DOA(surface, crack)Nd2Fe14B500 nmFine lamellar Coarse lamellarFeNdH2Coarseningwith HDSphericalFe2BH2Raw powderFeNdH2DRHD30 kPaSurfaceInsideCrystallographic alignmentin Fe and NdH2No alignmentin Fe and NdH2*Degree of anisotropyNd-rich component in raw powder diffuses into powder particles during d-HDDR, and result in the formation of inhomogeneous distribution of GBtriple junctions and prevents smooth GBD.After d-HDDR1 μmAdditional factor for low HkVariation in coercivityDRHDH2 decrepitation at 23°CHigh DOACrack free,single crystalContinuous GB LamellarFracture at GBJr = 1.37 TDOA = 75%Crack,polycrystalline(multiple c-axes)Spherical Low DOADiscontinuousgrain boundaries (GB)Transgranularfracture Jr = 1.29 TDOA = 69%We developed high temperature hydrogen decrepitation processto obtain larger volume fraction of lamellar and high DOA regions.However, low DOA regions at surface were still inevitably formed.Annealingat 700°CProcessingat 500°CMagnetic field, H / MA/m Magnetic polarization, J/ Am2/kg DOA 77.1%DOA 78.3%－ Conventional (GBD 4wt%)－ Novel (GBD 4wt%)Size distribution of raw powders■ Conv.（< 212 μm）Nd 28.5 wt%■ Novel（75-106 μm）Nd 27.3 wt%Fe Nd250 μm Fe Nd250 μmNovelConventional1 μm 1 μmGB distribution (after GBD 4wt%)Conventional: Nd-rich component in raw powder induces inhomogeneous distribution of GB triple junctions, which may prevent smooth diffusion during GBD. Novel: Low amount of Nd-rich component results in the formation of obstacle-free GBs after d-HDDR, achieving more smooth diffusion and resultant homogeneous GB distribution during GBD.(quantitative evaluation in progress)Particle size dependence of demagnetization curvesMagnetic field, H / MA/m Magnetic polarization, J/ Am2/kg － < 212 μm－ 150-212－ 106-150－ 75-106－ 53-75－ 25-53ConventionalFreq.Particle sizeBroadHD DR< 212 μmRaw powderLamellarSpherical dominant(fine powders)High DOAVery low(fine powders)Volume fraction of spherical and low DOA onpowder surface varies with powder size.This induces the variations in the total DOAamong powder particles.low DOA in fine powdersNd-richBroad particle sizedistribution of raw powderSpherical LowAdditional processes to limit the particle size.Fine particles as well as Nd-rich component are removed through these processes.Novel processConventional d-HDDR processAnnealing700°C, 1hH2 decrep.500°C, 1hCrushing, sieving< 212 μmSieving150-212 μmH2 decrep.180°C, 4hSieving tolimited sizeCrushingd-HDDRHD: 30 kPa, 820°C, 3hDR: 1 kPa, 820°C, 0.5hvac., 820°C, 1.5hGBDNd-Cu-Al 2–6 wt%vac., 800°C, 1hFracture at GBMixing with Nd-Cu-Alfine powderNd content / wt%6wt%4wt%6wt%Nd content / wt%No GBD2wt%4wt%2wt%4wt%4wt%4wt%1 μmNovel1 μmConventionalCrystal grain size (after GBD 4wt%)・Sharp grain size distribution indicates the formation of more homogeneous microstructures.・Homogeneous GB distribution → Less variations in coercivityMagnetic field, H / MA/m Magnetic polarization, J/ Am2/kg － d-HDDR with HTH2 decrepitation－ Typical d-HDDRTo decrease spherical and low DOA volume fraction, reduction of surface and crack regions are effective.○△ Conventional○● Novel スライド 1