# Fileset

[REPM2025_O11-4_Wolz.pdf](https://mdr.nims.go.jp/filesets/1b21261c-3f27-482d-8c1b-8b6fa1b7d343/download)

## Creator

Aymeric Wolz, Jean-Paul Garandet, Camille Flament, Olivier Tosoni

## Rights

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

## Other metadata

[In-Depth investigation of the sub-micronic equiaxed grain microstructure of a NdFeB permanent magnet fabricated by Laser Powder Bed Fusion](https://mdr.nims.go.jp/datasets/b5e0fea7-c584-44ee-9210-ba0dc196b90f)

## Fulltext

Présentation PowerPointDisposition : Titre CEA-LitenIn-depth investigation of the sub-micronic equiaxed grain microstructure of a NdFeB permanent magnet fabricated by Laser Powder Bed FusionAymeric WOLZ, Olivier Tosoni, Camille Flament, Jean-Paul GarandetCEA LITEN – Laboratory of Materials and Magnetic Components (LMCM)Univ. Grenoble Alpes, CEA, LITEN, Grenoble, 38000, FranceDisposition : VideThe Laser Powder Bed Fusion TechniqueP : laser powerVscan : Scan speede : powder bed thickness h : hatch distancehVscanPPrevious layere1/16powderDisposition : VideState-of-the-art[1] Pelevin I, Lyange M, Fedorenko L, Chernyshikhin S, Tereshina I. The Laser Powder Bed Fusion of Nd2Fe14B Permanent Magnets: The State of the Art. Condensed Matter. 2025; 10(2):22. https://doi.org/10.3390/condmat10020022No possibility for grain alignment→ Br < 0.8 TCommercial Powder (RE content under 2:14:1 stoichiometry )Tailored Powder (RE content over 2:14:1 stoichiometry )Nd-rich grain boundary phases Low coercivity Higher coercivityCommercial powder:8%at RE2.5%at Ti 2.5%at ZrTailored powder:14.4%at RE2%at Cu[1]RE2Fe14B stoichiometry : 11.7%at. RE2/16Fe-rich grain boundaryphases  Disposition : VideObjectives and Approach02APPROACH• Fabrication of a tailored powder• Fabrication of NdFeB samples by L-PBF• Magnetic characterization and selection of an optimal sample• Microstructure investigation down to the nanoscale• Elaboration of a solidification model to explain the formation of the microstructure01OBJECTIVES• Fabricate samples by L-PBF with a specific high RE content powder composition but free ofHRE• Describe the microstructure of a L-PBF sample and propose a formation mechanismPowder Samples Properties Microstructure3/16Disposition : VideStrip CastingHydrogenDecrepitationJet MillingAnnealingLaser Powder BedFusionAnnealingSample elaborationSEM BSE powder micrography40 μm angular powderRaw MaterialsPowderSamplesPowder composition (%mass.)RE32.8Co1B1Al0.15Cu0.1Ga0.25FeBal.4/16Disposition : VideMagnetic properties• Annealing realized at 600°C for 10 min. + 470°C for 1h• Maximum as-built properties : Br = 0.67 T and HcJ = 1170 kA.m-1• Maximum annealed properties : Br = 0.69 T and HcJ = 1440 kA.m-1 (1.8 T)Best parameter setP=120 WV=1250 mm.s-1h=70 μme=30 μm5/16Energy per built volume [J.mm-3]EBV =𝑃𝑉×𝑒×ℎDisposition : VideMicrostructure investigation500 nm6/16• Most of the microstructure is composed of smallmagnetic grains• Non continuous grain boundary phase (GBP)• Annealing does reorganise the GBP plus recombine α-Fe clusters with Nd-rich to obtain additional Nd2Fe14B grainsS-TEM HAADFONd FeCuDisposition : VideMicrostructure investigation7/16• Most of the microstructure is composed of smallmagnetic grains• Non continuous grain boundary phase (GBP)• Annealing does reorganise the GBP plus recombine α-Fe clusters with Nd-rich to obtain additional Nd2Fe14B grainsS-TEM HAADFONd FeCuA BDisposition : VideMorphology of magnetic grains500 nm1 μmEquiaxed grainsColumnar grainsSEM ImagingS-TEM Imaging10 μm8/16Disposition : VideNucleation and growth process of the Nd2Fe14B phase▪ For the formation of equiaxed grains by a heterogeneous nucleation process, 3 components are needed :❑ Seeding/Nucleating particles already in solid state in the melt❑ Sufficient undercooling to initiate the nucleation❑ Enough time to allow the equiaxed grains to grow and to block the columnar front[2] M. Opprecht, J.-P. Garandet, G. Roux, C. Flament, An understanding of duplex microstructures encountered during high strength aluminium alloy laser beam meltingprocessing, Acta Materialia, Volume 215, 2021, 117024, ISSN 1359-6454, https://doi.org/10.1016/j.actamat.2021.117024.[2]9/16LiquidzoneColumnarfrontDisposition : VideIntragrain Nd oxide inclusions200 nmHV: 200 kVO200 nmHV: 200 kVNdONd• Nd oxide inclusions as the only intragranular phase• Size of ≃ 90 nm for this case (Typically 30 to 100 nm)• Nd2O3 hexagonal structure 10/16Disposition : Vide-80 -60 -40 -20 001x107 Gth (K.m-1)  Vs (m.s-1)Depth (μm)0.00.10.20.3• The growth of the equiaxed grains dependson the local cooling conditions. The followingrelationship can be established in LPBF [2]:𝑅𝑚𝑎𝑥 = 𝑓 𝑉𝑠, 𝐺𝑡ℎ =𝑉𝑠2 × 𝐺𝑡ℎ × 𝐾With K a kinetic constant (cm.K-1.s-1), Vs, Gth• Vs (solidification velocity) and Gth (thermalgradient) can be estimated thanks to FiniteElements thermal model developed usingComsol Multiphysics software [3].• Thermal cooling conditions have beenextracted vertically at the center of a meltpoolKinetic aspect of the growth processDetermination of cooling conditions by FiniteElements simulation[2] M. Opprecht, J.-P. Garandet, G. Roux, C. Flament, An understanding of duplex microstructures encountered during high strength aluminium alloy laser beam meltingprocessing, Acta Materialia, Volume 215, 2021, 117024, ISSN 1359-6454, https://doi.org/10.1016/j.actamat.2021.117024.[3] A. Wolz, R. Caniou, O. Tosoni, C. Rado, et J.-P. Garandet, « On the Effectof Cooling Parameters on Solidification Structure in NdFeB Alloys », Advanced Engineering Materials, vol. n/a, no n/a, p. 2400978, doi: 10.1002/adem.202400978.11/16Disposition : Vide-80 -60 -40 -20 00.0010.010.1110Maximal grain radius (μm)Depth (μm) Kinetic constant K=2• We’ve been able to represent themaximum equiaxed grain size possibledepending on the vertical location insideof the melt poolEvaluation of the grain growthBottom of the meltpoolUpper part of the melt pool 12/16Disposition : Vide-80 -60 -40 -20 00.0010.010.1110Maximal grain radius (μm)Depth (μm) Kinetic constant K=2r = 0,3 μmColumnarEquiaxedEvaluation of the grain growthBottom of the meltpoolUpper part of the melt pool• We’ve been able to represent themaximum equiaxed grain size possibledepending on the vertical location insideof the melt pool• We placed the critical value to reach toblock the columnar front (r=300 nm)which is the size of the effectiveequiaxed grains observed in the samples• This confirm that in the edges of the meltpool the microstructure is columnar, anda transition to an equiaxed structureoccurs after a few microns.13/16Disposition : VideConclusion01MAGNETIC PROPERTIES• High coercivity samples compared to the L-PBF state of the art, up to 1440 kA.m-1.• Nearly isotropic samples and remanence still limited (<0,7 T)• Annealing heat treatments at 600°C+470°C strongly improve the coercivity14/16Disposition : Vide01MAGNETIC PROPERTIES• High coercivity samples compared to the L-PBF state of the art, up to 1440 kA.m-1.• Nearly isotropic samples and remanence still limited (<0,7 T)• Annealing heat treatments at 600°C+470°C strongly improve the coercivity02MICROSTRUCTURAL ANALYSIS [4]• A mainly sub-micronic equiaxed Nd2Fe14B grains microstructure was obtained.• The grain boundaries are mainly composed of Nd-rich phase• Isolated punctual phases like Nd oxides, α-Fe, Nd1+ƐFe4B4Conclusion[4] A. Wolz, O. Tosoni, C. Flament, J.-P. Garandet, High–coercivity HRE–free NdFeB magnets by laser powder bed fusion, Journal of Magnetism and Magnetic Materials, Volume 630, 2025, 173363, ISSN 0304-8853, https://doi.org/10.1016/j.jmmm.2025.173363. 15/16Disposition : Vide03FORMATION OF THE MICROSTRUCTURE• Systematic Nd-oxide inclusions (30 to 100 nm) appear as likely candidates to play the role ofnucleating agent.• A simple kinetic model can explain the presence of both equiaxed and columnar grain inside of thesamples.Conclusion01MAGNETIC PROPERTIES• High coercivity samples compared to the L-PBF state of the art, up to 1440 kA.m-1.• Nearly isotropic samples and remanence still limited (<0,7 T)• Annealing heat treatments at 600°C+470°C strongly improve the coercivity02MICROSTRUCTURAL ANALYSIS• A mainly sub-micronic equiaxed Nd2Fe14B grains microstructure was obtained.• The grain boundaries are mainly composed of Nd-rich phase• Isolated punctual phases like Nd oxides, α-Fe, Nd1+ƐFe4B416/16Disposition : FIN CEA GrisMany thanks for yourattentionFeel free to ask questions !Aymeric WOLZCEA Grenoble, Litenaymeric.wolz@cea.fr