# Fileset

[REPM2025_P1-1_Fujimura.pdf](https://mdr.nims.go.jp/filesets/0bf39d82-9885-4eb0-9f13-40a94338498c/download)

## Creator

Kazumasa Fujimura, Takanori Kajiwara, Takashi Oikawa, Hiroshi Miyawaki

## Rights

[Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International](https://creativecommons.org/licenses/by-nc-nd/4.0/)

## Other metadata

[High performance HREE-free hot-deformed Nd-Fe-B magnets by Nd- Cu grain boundary diffusion](https://mdr.nims.go.jp/datasets/c5a7d176-1dfc-4a6d-ab1c-09437eb1fcaa)

## Fulltext

PowerPoint PresentationBase Magnet Nd-Cu GBD Treated (Coating Amounts of 4wt.%)RE Content inBase Magnet31.0 wt.% 29.4 wt.% 31.0 wt.% 29.4 wt.%Overall MicrostructurePowder InterfaceRegion(After Etching)Fine-grainedRegionIntroduction Experimental DetailsEffect of RE Content of Base Magnet on Magnetic Properties after GBD Achieved Magnetic PropertiesConclusion and OutlookNd-Fe-B magnets used in EVs require high coercivity to withstand high temperatures and high antimagnetic fields. One of the methods to improve the coercivity of hot-deformed Nd-Fe-B magnets without using heavy rare earth elements such as Dy and Tb is the grain boundary diffusion (GBD) process using light rare earth elements. In this study, we fabricated high-performance HREE-free Nd-Fe-B hot deformed magnet which is adequate for usage of EVs by diffusing Nd-Cu alloy into a hot-deformed magnet with low rare earth content. Fabrication of Nd-Fe-B hot-deformed magnetsKazumasa Fujimura 1), Takanori Kajiwara 1), Takashi Oikawa 1), and Hiroshi Miyawaki 2)1) Corporate Research & Development Center, Daido Steel Co., Ltd., Nakatsugawa, Gifu 509-9131, Japan2) Customer Solution Service Sect., Daido Steel Co., Ltd., Nagoya, Aichi, Japan t-kajiwara@ac.daido.co.jpInduction melting Melt spinning Cold pressHot press &Hot deformationConclusion OutlookCrushing✓ Although the decrease in Br due to GBD is relatively constant regardless of the initial HcJ of the base magnet, the increase in coercivity is more pronounced in magnets with lower initial HcJ. These findings indicate that base magnets with lower RE content and higher Br are advantageous for achieving better overall magnetic performance, making them well-suited for maximizing the benefits of the Nd-Cu GBD process.To further enhance coercivity and squareness, it is essential to increase the concentrations of Nd and Cu in the central region of the magnet and to minimize the coercivity gradient between the region near the coated surface and the center of the magnet.To achieve this, it is necessary to optimize the base magnet composition, the diffusion alloy composition, and the diffusion conditions.By using a base magnet with low RE composition, we successfully fabricated a magnet with HcJ of713 kA/m (150℃), Hk/HcJ ratio of 97% (150℃), and Br of 1.40 T (RT), without the use of HREEs.✓ A base magnet with low RE exhibits high magnetic alignment and a uniform microstructure, andits degree of orientation is maintained even after Nd-Cu grain boundary diffusion.✓ The enhancement in coercivity resulting from the Nd-Cu GBD becomes more pronounced as the coercivity of the base magnet decreases.High performance HREE-free hot-deformed Nd-Fe-B magnetsby Nd-Cu grain boundary diffusionA hot-deformed magnet with Br of 1.42 T at room temperature, HcJ of 541 kA/m at 150℃, andHk/HcJ of 98% at 150℃, containing 29.3 wt.% of RE elements, was used as the base magnet. After GBD with 4 wt.% of Nd-Cu alloy, the HcJ of the magnet was enhanced to 713 kA/m at 150℃ while maintaining Br of 1.40 T at room temperature without the use of HREEs. The Hk/HcJ maintained at 97% at 150℃, which is adequate for usage of EVs.80100120140160180200400 450 500 550 600 650 700Amount of Change in Coercivityby Applying Nd-Cu Diffusion,ΔHcJ 150℃ (kA/m)Coercivity of Magnet Before ApplyingNd-Cu Diffusion,  HcJ 150℃ (kA/m)-0.08-0.06-0.04-0.020.00400 450 500 550 600 650 700Amount of Change in Remanenceby Applying Nd-Cu Diffusion,ΔBr RT (T) Coercivity of Magnet Before ApplyingNd-Cu Diffusion,  HcJ 150℃ (kA/m)Mix oil and greasewith Nd-Cu powderPaste applicationHRE-GBD LRE-GBDMicrostructureMainly Applied Magnet Type Sintered magnet Hot-deformed magnetMechanism of Coercivity EnhancementFormation of Dy/Tb-rich shells on the surface of Nd2Fe14B grainsThe infiltrated eutectic alloy such as Nd-Cu widening the grain boundary phase, weakening the magnetic interaction between the Nd2Fe14B grainsKey Features・Excellent high-temperature stability・Heat treatment at 800-1000℃ ・HRE(Dy, Tb)-free・Low cost・Heat treatment at 500-700℃C1μm 200nm200nmNon-GBD LRE-GBDC C Nd-Cu grain boundary diffusion processEvaluation methodsNd-Cu alloy atomization Paste preparationApply Nd-Cu paste to both sides of the magnet’sｃ-planeDiffusion heat treatmentHeat treatment was carried out at 500-700℃ in vacuum.Magnetic property evaluation： DC fluxmeter, Pulsed high-field magnetometerMicrostructural analysis ： FE-SEMAnalysis of Nd and Cu concentration profile in the diffusion direction： EPMAHot-deformed magnet ✓ 4mm thick along theｃ-axisNd-Cu diffused hot-deformed magnet ｃ-axisｃ-axisｃ-axis+✓ HRE(Dy, Tb)-free✓ RE29-31 wt.%Comparison between heavy rare-earth and light rare-earth grain boundary diffusion processes14.20.6 1.1 1.60.130.6c-axisComparison of Br (RT) and HcJ (150℃) between Nd-Cu GBD-treated and non-treated hot-deformed magnetsDemagnetization curves of a base magnet with low rare-earth content before and after Nd-Cu grain boundary diffusionBr(T)HcJ(kA/m)HcJ 150℃ (kA/m)Hk/HcJ 150℃(%)(A) High-coercivity,high-squareness sample1.37 1780 729 97(B) Low-coercivity,low-squareness sample1.39 1706 688 93Changes in Nd and Cu concentrations with distance from the coating surface in high- and low-squareness Nd-Cu GBD treated hot-deformed magnetsSchematics of specimen extraction for overall magnetic property evaluation and local coercivity measurementLocal coercivity with distance from the coating surface in high- and low-squareness Nd-Cu GBD treated hot-deformed magnetsOverall magnetic properties of samples subjected to Nd and Cu concentration profiling and partial coercivity measurements1500155016001650170017501800185019000.0 0.5 1.0 1.5 2.0RT-HcJ (kA/m)Distance (mm)Overall HcJ of (A)Overall HcJ of (B)The sample exhibiting high coercivity and squareness shows a small difference in Nd and Cu concentrations between the coated surface and the center, while a small difference in local coercivity between the surface and the center. To further improve coercivity and squareness, it is essential to increase the Nd concentration at the center and to reduce the coercivity gradient.MagnetNd-Cu pasteNd-Cu pasteExpand in theｃ-axis directionCoercivity Gradient of SamplesBr (RT) and HcJ (150℃) of Nd-Cu GBD treated Nd-Fe-B hot-deformed magnets with different RE contents in the base magnetJs (RT) and Br/Js (RT) of Nd-Fe-B hot-deformed magnets as a function of Nd-Cu alloy coating amountFE-SEM images of Nd-Fe-B base magnets with Initial RE contents of 31.0 wt.% and 29.4 wt.%, before and after Nd-Cu GBD treatmentAmount of change in Br (RT) and HcJ (150℃) after 4 wt.% of Nd-Cu grain boundary diffusionHeavy-rare-earth-free hot-deformed magnets with various RE contents were fabricated followed by Nd-Cu GBD. Magnets with lower RE content in the base magnet exhibited a more favorable balance between remanence (Br) and coercivity (HcJ) after GBD. This is attributed to the following two reasons: ✓ Lower rare-earth content in the base magnet reduces the formation of agglomerated Nd-rich phases and suppresses the grain growth, thereby improving the magnetic orientation factor. This feature is maintained even after Nd-Cu GBD.C C10μm10μm1μm1μm200nm 200nmC C10μm10μm1μm1μm200nm200nmC C C CC C C C1.321.341.361.381.401.421.441.46400 450 500 550 600 650 700 750 800RT-Br (T)150℃-HcJ (kA/m)4 wt.%〇：Base Magnet●：Nd-Cu GBD Treated (2 & 4 wt.% coating)2 wt.%RE31.0 wt.%RE30.1 wt.%RE29.7 wt.%RE29.4 wt.%4 wt.%2 wt.%4 wt.%2 wt.% 4 wt.%2 wt.%1.441.461.481.501.521.541.560 1 2 3 4Saturation Magnetization, Js (T)Nd-Cu Alloy Coating Amount (wt.%)RE29.4 wt.%RE29.7 wt.%RE30.1 wt.%RE31.0 wt.%0.900.910.920.930.940.950.960.970 1 2 3 4Magnetic Orientation Factor, Br/JsNd-Cu Alloy Coating Amount (wt.%)RE29.4 wt.%RE29.7 wt.%RE30.1 wt.%RE31.0 wt.%Low RE contentLow RE content1.251.301.351.401.451.50500 600 700 800 900RT-Br (T) 150℃-HcJ (kA/m)Tb-GBD processedsintered magnetΔBr is constantΔHcJ increasesHot-deformed magnetwith Nd-Cu GBDHot-deformed magnetwithout GBD Coarse grains Coarse grainsNd-rich phase agglomeratesNd-rich phase agglomeratesFew Nd-rich phasesOverall magnetic property evaluation Local coercivity measurement●■(A) High HcJ, High Hk/HcJ(B) Low HcJ, Low Hk/HcJSurface Center-0.20.00.20.40.60.81.01.21.41.60.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0Increace in Cu concentrationby Nd-Cu GBD (wt.%)Distance (mm)(A) High HcJ, High Hk/HcJ(B) Low HcJ, Low Hk/HcJSurface Center Surface-10123450.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0Increace in Nd concentrationby Nd-Cu GBD (wt.%)Distance (mm)Surface Center Surface(A) High HcJ, High Hk/HcJ(B) Low HcJ, Low Hk/HcJ0.00.20.40.60.81.01.21.41.6-2000 -1800 -1600 -1400 -1200 -1000 -800 -600 -400 -200 0Magnetization, J (T)Magnetic field, H (kA/m)Base magnetNd-Cu GBD Base magnetNd-Cu GBD@150℃@RTNote: Demagnetization curves at room temperature were measured using a pulsed high-field magnetometer, with Br corrected using DC fluxmeter values. Demagnetization curves at 150℃ were also measured using a DC fluxmeter. スライド 1