Magnetic Properties and Microstructure of TbF3 Diffused Nd2Fe14B Magnet with Surface Grinding AITranslate
Abstract AITranslate
Up to now，heavy rare earth was considered as the necessary element for the production of Nd2Fe14B-based sintered magnets with coercivity > 25 kOe，which have led to a sharp rise in the production cost of high coercivity Nd2Fe14B-based magnets. Heavy rare earth grain boundary diffusion was found to be an effective way to lower the consumption of heavy rare earth and simultaneously to minimize the magnetization decrease of high coercivity Nd2Fe14B-based magnets. As mentioned above，it can be easily found that the effects of the surface condition of the magnets on the diffusion process and magnetic properties were not have been studied. In general，the ground and polished magnet with a very flat surface was used for heavy rare earth grain boundary diffusion. However，in this paper，it was found that the surface condition had a great influence on the Tb grain boundary diffusion and the magnetic properties of Nd2Fe14B-based magnet. The flat surface was not the best choice for the coercivity enhancement of Nd2Fe14B-based magnet by heavy rare earth grain boundary diffusion. The magnetic properties of the samples were measured by a magnetic material tester （PERM-REM C-300）. The surface roughness of the magnet was measured by a step profiler （KLA P-6）. The microstructures were observed by scanning electron microscope （SEM，ZEISS SIGMA 500）. According to the demagnetization curve and magnetic properties of the magnet，the intrinsic coercivity （Hcj） of the magnet increased first and then decreased as the surface roughness decreased from 699 to 67.5 nm. The intrinsic coercivity of the magnet polished with 23 μm sandpaper （surface roughness： 199.8 nm） was 22.5 kOe，which was 50.1% higher than that of the original magnet （15.0 kOe），the increase rate of intrinsic coercivity of the magnet polished with 240 mesh sandpaper was 10.1%，and the increase rate of intrinsic coercivity of the magnet polished with 4.3 μm sandpaper was only 37.3%. It was proved that properly adjusting the surface roughness of the magnet could strengthen the promotion effect of diffusion process on the intrinsic coercivity of Nd-Fe-B magnet. All magnets had the typical structure core-shell structure of heavy rare earth diffusion sintered Nd-Fe-B magnets. In order to study intrinsic coercivity enhancement mechanism of diffused NdFeB magnets，according to BSE-SEM images near the surface and at different depths of magnets with different surface roughness，for magnets polished with 61 μm sandpaper，no core-shell structure was found at the depth of 150 μm from the surface，which meant that the diffusion depth of Tb diffusion was less than 150 μm. The thickness of Tb rich shell near the surface was significantly greater than that of 23 μm sandpaper polished magnet and 4.3 μm sandpaper polished magnet，indicating that most of the diffused Tb elements were concentrated near the magnet surface. Tb was rich near the surface and the diffusion depth was low，resulting in a low degree of intrinsic coercivity enhancement of the magnet. For magnets polished with 4.3 μm sandpaper，Tb diffusion depth was about 150 μm. At the same time，it was found that the shell phase rich in Tb were discontinuous compared with the magnet polished with 23 μm sandpaper. The magnet polished with 23 μm sandpaper had more and evenly distributed core-shell structure，which made Hcj increment after magnet diffusion the most. In order to further understand the influence mechanism of magnet surface conditions on Tb diffusion behavior，the surface of original magnets polished with different mesh sandpaper was characterized by SEM. The magnets polished wit 61，23 and 4.3 μm sandpaper were marked as Magnets A，C and E，respectively. In SEM images of Magnets A，C and E，the white area was rare-earth rich grain boundary phase. According to the statistics of Photoshop software，the area proportion of rare earth rich grain boundary phase of SEM images of the surface of Magnets A，C and E were calculated to be 1.14%，2.35% and 1.51%，respectively. The exposure of rare earth rich grain boundary phase on the surface of Magnet C was the largest and could be divided into two cases. The first was the exposure area of rare earth rich grain boundary phase in a relatively flat area，which could be considered to be similar to Magnet E，that was，the cross section of grain boundary phase. In the second case，most of the grain boundary phase in the hole was not stripped and covered by debris. On the contrary，it presented a three-dimensional shape，which increased the exposed area of surface grain boundary phase，The contact area between TbF3 and surface grain boundary phase was increased. It was found that after grinding with 23 μm sandpaper，the exposed grain boundary phase area of the magnet was the largest，and the grain boundary phase was the main channel for the diffusion of heavy rare earth elements，which was conducive to the diffusion of Tb element. Tb element could diffuse more into the interior of the magnet through the grain boundary phase，so as to maximize the increase of intrinsic coercivity.
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［1］Li J，Tang X，Sepehri-Amin H，Ohkubo T，Hioki K，Hattori A，Hono K. On the temperature-dependent coercivities of anisotropic Nd-Fe-B magnet ［J］. Acta Materialia，2020，199： 288.
［2］李岩峰，赖彬，朱明刚，冯海波，李卫，杜安. 烧结钕铁硼磁体边界相的调控技术机制 ［J］. 稀有金属，2015，39（11）： 988.
Y F Li，B Lai，M G Zhu，H B Feng，W Li，A Du. Mechanism on control technology of grain boundary phase in sintered Nd-Fe-B magnets ［J］. Chinese Journal of Rare Metals，2015，39（11）： 988.
［3］Zhang Z H，Jin J Y，Ma T Y，Liang L P，Yan M. Nd-Fe-B sintered magnets with low rare earth content fabricated via Dy71.5Fe28.5 grain boundary restructuring ［J］. Journal of Magnetism and Magnetic Materials，2020，498： 162.
［4］Woodcock T G，Zhang Y，Hrkac G，Ciuta G，Dempsey N M，Schrefl T，Gutfleisch O，Givord D. Understanding the microstructure and coercivity of high performance NdFeB-based magnet ［J］. Scripta Materialia，2012，67（6）： 536.
［5］Sagawa M，Fujimura S，Togawa N，Yamamoto H，Matsuura Y. New material for permanent magnets on a base of Nd and Fe （invited） ［J］. Journal of Applied Physics，1984，55（6）： 2083.
［6］刘国征，赵明静，赵瑞金，刘小鱼，鲁富强，李波. 钆对烧结钕铁硼磁体磁性能和相结构的影响 ［J］. 稀有金属，2010，34（1）： 121.
G Z Liu，M J Zhao，R J Zhao，X Y Liu，F Q Lu，B Li. Influence of substitution of Gd for Nd on microstructure and properties of sintered Nd-Fe-B magnets ［J］. Chinese Journal of Rare Metals，2010，34（1）： 121.
［7］Jin J Y，Yan M，Liu Y S，Peng B X，Bai G H. Attaining high magnetic performance in as-sintered multi-main-phase Nd-La-Ce-Fe-B magnets： toward skipping the post-sinter annealing treatment ［J］. Acta Materialia，2019，169： 248.
［8］Di J H，Ding G F，Tang X，Yang X，Gou S，Chen R J，Yan A. Highly efficient Tb-utilization in sintered Nd-Fe-B magnets by Al aided TbH2 grain boundary diffusion ［J］. Scripta Materialia，2018，155： 50.
［9］Nakamura H，Hirota K，Ohashi T，Minowa T. Coercivity distributions in Nd-Fe-B sintered magnets produced by the grain boundary diffusion processs ［J］. Journal of Physics D Applied Physics，2011，44（6）： 064003.
［10］崔熙贵，王兴华，崔承云，阴冠超，夏传达，方翠. 烧结钕铁硼的晶界扩散改性、 结构与性能研究进展 ［J］. 稀有金属，2018，42（3）： 315.
X G Cui，X H Wang，C Y Cui，G C Yin，C D Xia，C Fang. Research progress in grain boundary diffusion modification，microstructures and properties of sintered Nd-Fe-B magnets ［J］. Chinese Journal of Rare Metals，2018，42（3）： 315.
［11］张金伟，张曼，赵奔奔，刘杰胜，彭浩，谭晓明. Nb添加量对金属陶瓷显微组织和磁学性能的影响 ［J］. 有色金属工程，2024，14（2）： 9.
J W Zhang，M Zhang，B B Zhao，J S Liu，H Peng，X M Tan. Effect of Nb additions on the microstructure and magnetic properties of the cermet ［J］. Nonferrous Metals Engineering，2024，14（2）： 9.
［12］辛宇，刘相局，王春丽，刘娜珍，蒋全通，段继周. 共价有机骨架材料修饰碳糊电极电化学检测铜离子 ［J］. 分析试验室，2023，42（9）： 1199.
Y Xin，X J Liu，C L Wang，N Z Liu，Q T Jiang，J Z Duan. Electrochemical detection of copper ions with covalent organic frame material modified carbon paste electrode ［J］. Chinese Journal of Analysis Laboratory，2023，42（9）： 1199.
［13］Xu F，Wang J，Dong X P，Zhang L T，Wu J S. Grain boundary microstructure in DyF3-diffusion processed Nd-Fe-B sintered magnets ［J］. Journal of Alloys & Compounds，2011，509（30）： 7909.
［14］卢立伟，康伟，黎小辉，罗骏，马旻，陈伟.时效处理对Mg-Zn-Gd-Er稀土镁合金的组织和力学性能的影响［J］.稀有金属，2022，46（9）： 1153.
L W Lu，W Kang，X H Li，J Luo，M Ma，W Chen. Microstructure and mechanical properties of Mg-Zn-Gd-Er rare earth magnesium alloy via aging treatment ［J］. Chinese Journal of Rare Metals，2022，46（9）： 1153.
［15］Wang X，Zhu M G，Xia F，Zhang M L，Liu F，Guo Y J，Zhang L L，Zhang G R，Li W. Effects of grain boundary ternary alloy doping on corrosion resistance of （Ce，Pr，Nd）-Fe-B permanent magnets ［J］. Journal of Rare Earths，2021，39（8）： 979.
［16］刘湘涟. 添加Dy2O3的钕铁硼磁体的烧结行为与性能 ［J］. 稀有金属，2012，36（6）： 6.
X L Liu. Sintering behavior and properties of Nd-Fe-B magnets with Dy2O3 addition ［J］. Chinese Journal of Rare Metals，2012，36（6）： 6.
［17］Jing Z，Guo Z H，He Y N，Zhang M L，Wang X，Zhu M G，Li W. Coercivity enhancement of nanocrystalline hot-deformed Nd-Fe-B magnets by low-melting eutectic MM-Cu （MM=La，Ce，Pr，Nd） alloys addition ［J］. Journal of Rare Earths，2020，38（6）： 594.
［18］Li D，Suzuki S，Kawasaki T，Machida K I. Grain interface modification and magnetic properties of Nd-Fe-B sintered magnets ［J］. Japanese Journal of Applied Physics，2008，47（10）： 7876.
［19］赵玲，胡立威，王斗，刘学. 激光熔化沉积Cu-Fe合金的液相分离组织及力学性能研究 ［J］. 铜业工程，2023，（2）： 44.
L Zhao，L W Hu，D Wang，X Liu. Microstructure and mechanical properties of Cu-Fe alloy prepared by laser melting deposition ［J］. Copper Engineering，2023，（2）： 44.
［20］Cao X J，Chen L，Guo S，Li X B，Yi P P，Yan A R，Yan G L. Coercivity enhancement of sintered Nd-Fe-B magnets by efficiently diffusing DyF3 based on electrophoretic deposition ［J］. Journal of Alloys and Compounds，2015，631： 315.
［21］Sun Y C，Zhu M G，Liu W，Han R，Li W. Effect of magnetic layer thickness on magnetic properties of Ce-Fe-B thin films ［J］. Journal of Rare Earths，2018，36（6）： 619.
［22］Sepehri-Amin H，Ohkubo T，Hono K. The mechanism of coercivity enhancement by the grain boundary diffusion process of Nd-Fe-B sintered magnets ［J］. Acta Materialia，2013；61（6）： 1982.
［23］Sawatzki S，Kübel C，Ener S，Gut O. Grain boundary diffusion in nanocrystalline Nd-Fe-B permanent magnets with low-melting eutectics ［J］. Acta Materialia，2016，115： 354.
［24］Li X B，Liu S，Cao X J，Zhou B B，Chen L，Yan A，Yan G L. Coercivity and thermal stability improvement in sintered Nd-Fe-B permanent magnets by intergranular addition of Dy-Mn alloy ［J］. Journal of Magnetism & Magnetic Materials，2016，407： 247.
［25］Cao X J，Chen L，Guo S，Fan F C，Chen R J，Yan A. Effect of rare earth content on TbF3 diffusion in sintered Nd-Fe-B magnets by electrophoretic deposition ［J］. Scripta Materialia，2017，131： 24.
［26］Zhou G F，Fu S Y，Sun X K，Chuang Y C. Influence of annealing on the magnetic properties and microstructure of NdFeB based magnets ［J］. Physica Status Solidi （A），2010，121（1）： 257.
Basic Information:
DOI：10.13373/j.cnki.cjrm.XY22030031
Chinese Library Classification Number:TM273
Citation Information:
Up to now，heavy rare earth was considered as the necessary element for the production of Nd2Fe14B-based sintered magnets with coercivity > 25 kOe，which have led to a sharp rise in the production cost of high coercivity Nd2Fe14B-based magnets. Heavy rare earth grain boundary diffusion was found to be an effective way to lower the consumption of heavy rare earth and simultaneously to minimize the magnetization decrease of high coercivity Nd2Fe14B-based magnets. As mentioned above，it can be easily found that the effects of the surface condition of the magnets on the diffusion process and magnetic properties were not have been studied. In general，the ground and polished magnet with a very flat surface was used for heavy rare earth grain boundary diffusion. However，in this paper，it was found that the surface condition had a great influence on the Tb grain boundary diffusion and the magnetic properties of Nd2Fe14B-based magnet. The flat surface was not the best choice for the coercivity enhancement of Nd2Fe14B-based magnet by heavy rare earth grain boundary diffusion. The magnetic properties of the samples were measured by a magnetic material tester （PERM-REM C-300）. The surface roughness of the magnet was measured by a step profiler （KLA P-6）. The microstructures were observed by scanning electron microscope （SEM，ZEISS SIGMA 500）. According to the demagnetization curve and magnetic properties of the magnet，the intrinsic coercivity （Hcj） of the magnet increased first and then decreased as the surface roughness decreased from 699 to 67.5 nm. The intrinsic coercivity of the magnet polished with 23 μm sandpaper （surface roughness： 199.8 nm） was 22.5 kOe，which was 50.1% higher than that of the original magnet （15.0 kOe），the increase rate of intrinsic coercivity of the magnet polished with 240 mesh sandpaper was 10.1%，and the increase rate of intrinsic coercivity of the magnet polished with 4.3 μm sandpaper was only 37.3%. It was proved that properly adjusting the surface roughness of the magnet could strengthen the promotion effect of diffusion process on the intrinsic coercivity of Nd-Fe-B magnet. All magnets had the typical structure core-shell structure of heavy rare earth diffusion sintered Nd-Fe-B magnets. In order to study intrinsic coercivity enhancement mechanism of diffused NdFeB magnets，according to BSE-SEM images near the surface and at different depths of magnets with different surface roughness，for magnets polished with 61 μm sandpaper，no core-shell structure was found at the depth of 150 μm from the surface，which meant that the diffusion depth of Tb diffusion was less than 150 μm. The thickness of Tb rich shell near the surface was significantly greater than that of 23 μm sandpaper polished magnet and 4.3 μm sandpaper polished magnet，indicating that most of the diffused Tb elements were concentrated near the magnet surface. Tb was rich near the surface and the diffusion depth was low，resulting in a low degree of intrinsic coercivity enhancement of the magnet. For magnets polished with 4.3 μm sandpaper，Tb diffusion depth was about 150 μm. At the same time，it was found that the shell phase rich in Tb were discontinuous compared with the magnet polished with 23 μm sandpaper. The magnet polished with 23 μm sandpaper had more and evenly distributed core-shell structure，which made Hcj increment after magnet diffusion the most. In order to further understand the influence mechanism of magnet surface conditions on Tb diffusion behavior，the surface of original magnets polished with different mesh sandpaper was characterized by SEM. The magnets polished wit 61，23 and 4.3 μm sandpaper were marked as Magnets A，C and E，respectively. In SEM images of Magnets A，C and E，the white area was rare-earth rich grain boundary phase. According to the statistics of Photoshop software，the area proportion of rare earth rich grain boundary phase of SEM images of the surface of Magnets A，C and E were calculated to be 1.14%，2.35% and 1.51%，respectively. The exposure of rare earth rich grain boundary phase on the surface of Magnet C was the largest and could be divided into two cases. The first was the exposure area of rare earth rich grain boundary phase in a relatively flat area，which could be considered to be similar to Magnet E，that was，the cross section of grain boundary phase. In the second case，most of the grain boundary phase in the hole was not stripped and covered by debris. On the contrary，it presented a three-dimensional shape，which increased the exposed area of surface grain boundary phase，The contact area between TbF3 and surface grain boundary phase was increased. It was found that after grinding with 23 μm sandpaper，the exposed grain boundary phase area of the magnet was the largest，and the grain boundary phase was the main channel for the diffusion of heavy rare earth elements，which was conducive to the diffusion of Tb element. Tb element could diffuse more into the interior of the magnet through the grain boundary phase，so as to maximize the increase of intrinsic coercivity.
quote
| GB/T 7714-2015 | [1] Nengjun Yu, Jianghui Sun, Minxiang Pan, et al. Magnetic Properties and Microstructure of TbF3 Diffused Nd2Fe14B Magnet with Surface Grinding[J]. Chinese Journal of Rare Metals, 2025, 49(2): 299-304. DOI:10.13373/j.cnki.cjrm.XY22030031. |
| MLA | [1] Nengjun Yu, et al., "Magnetic Properties and Microstructure of TbF3 Diffused Nd2Fe14B Magnet with Surface Grinding." Chinese Journal of Rare Metals, vol. 49, no. 2, 2025, pp. 299-304, https://doi.org/10.13373/j.cnki.cjrm.XY22030031. |
| APA | [1] Nengjun Yu, Jianghui Sun, Minxiang Pan, Liang Chen, Qiong Wu, & Hongliang Ge. (2025). Magnetic Properties and Microstructure of TbF3 Diffused Nd2Fe14B Magnet with Surface Grinding. Chinese Journal of Rare Metals, 49(2), 299-304. https://doi.org/10.13373/j.cnki.cjrm.XY22030031 |
| IEEE | [1] Nengjun Yu, Jianghui Sun, Minxiang Pan, Liang Chen, Qiong Wu, and Hongliang Ge, "Magnetic Properties and Microstructure of TbF3 Diffused Nd2Fe14B Magnet with Surface Grinding," Chinese Journal of Rare Metals, vol. 49, no. 2, pp. 299-304, 2025, doi: 10.13373/j.cnki.cjrm.XY22030031. keywords: {NdFeB-based sintered magnets;TbF diffusion;magnetic properties;surface grinding} |