Abstract：Abstract: As a promising heavy rare earth thermal diffusion technology, the coating method has the advantages of low cost and simple operation. It has become the mainstream technology for increasing coercivity of sintered NdFeB magnets. In order to obtain a good thermal diffusion effect, a large amount of DyF3 powder should be coated on surface of the magnets, which causes unnecessary waste. In this paper, the influence of different DyF3 coating amount on the performance of the sintered NdFeB magnets and Dy element dis-tribution process are studied. A homemade special DyF3 coating is employed for thermal diffusion treatment. The novel coating is mainly composed of main filler (DyF3) and organic components (solvent, thickened resin, dispersant, wetting dispersing agent, etc.). Due to the characteristics of fast drying, good fluidity and strong adhesion, a stable DyF3 coating layer with controllable coating amount can be easily obtained on the magnet surface. The results show that Dy concentration is the driving force of the thermal diffusion, so the coating amount has an important influence on the enhancement of coercivity. When the coating amount is lower, the thermal diffusion of Dy element is not sufficient, resulting in the limited enhancement of coercivity. With the increase of coating amount, Dy element is fully diffused and evenly distributed in the grain boundary, which makes the magnet has the best comprehensive magnetic properties. When continue to increase the amount of coating, Dy element begins to enter the main phase grains, causing the deterioration of the magnetic properties. Consequently, the amount of heavy rare earth coating should be within the appropriate range, too much or too little will not be conducive to the effect of thermal diffusion. In this work, the optimal coating amount of DyF3 is 0.81 wt.%. After thermal diffusion, the magnet achieves the best comprehensive performance, and the coercivity increases from 14.60 kOe to 19.78 kOe.
[1]郭在在, 刘国玺, 牟晓明, 燕东明, 傅宇东, 高 鹏.永磁薄膜的研究进展[J].稀有金属, 2010, 34(S1):109-114[2]Guo Z Z, Liu G X, Mu X M, Yan D M, Fu Y D, Gao P.Research progress in NdFeB permanent magnetic thin film[J].Chinese Journal of Rare Metals, 2010, 34(S1):109-114[3]Lewis L, Laura H, Jiménez V.Perspectives on permanent magnetic materials for energy conversion and power generation[J].Metall Mater Trans A, 2013, 44(S1):220-220[4] Li D, Li Y, Pan D.Prospect and status of iron-based rare-earth-free permanent magnetic materials [J]. J Magn Magn Mater, 2019, 469:535.[J].J Magn Magn Mater, 2019, 469(S1):535-544[5] Vishina A, Vekilova O Y, Bj?rkman T, Bergman A, Herper H C, Eriksson O.High-throughput and data-mining approach to predict new rare-earth free per-manent magnets [J]. Phys Rev B, 2020, 101:1.[J].Phys Rev B, 2020, 101(1):1-9[6]Minowa T.Rare earth magnets: conservation of energy and the environment[J].Resour Geol, 2010, 58(4):414-414[7]Nakamura H, Hirota K, Shimao M.Magnetic properties of extremely small NdFeB sintered[J].IEEE Trans Magn, 2005, 41(10):3844-3844[8]Hono K, Sepehri-Amin H.Strategy for high coercivity NdFeB magnets[J].Scr. Mater., 2012, 67(6):530-535[9] Zhang Y F, Han J Z, Liu S Q, Wan M F, Tian H D.Coercivity enhancement by grain refinement for Anisotropic Nd2Fe14B type magnetic powders [J]. Scr. Mater, 2015, 110:57.[J].Scr. Mater, 2015, 110(1):57-60[10]Yue M, Liu W Q, Zhan D T.Tb nanoparticles doped NdFeB sintered permanent magnet with enhanced coercivity[J].Appl. Phys. Lett, 2009, 94(9):2083-2085[11]Liu W Q, Sun H, Yi X F, Liu X C, Zhang D T, Yue M, Zhang J X.Coercivity enhancement in NdFeB sintered permanent magnet by Dy nanoparticles doping[J].J. Alloys. Compd, 2010, 501(1):67-69[12]Kiash A, Mottram R S, Harris I R.Densification of a Nd13Fe78NbCoB7 type sintered magnet by (Nd,Dy)-hydride additions using a powder blending tech-nique[J].J. Alloys. Compd, 1999, 287(1):206-214[13]Ni J, Ma T, Yan M.Changes of microstructure and magnetic properties of NdFeB sintered magnets by doping Al-Cu[J].J. Magn. Magn. Mater, 2011, 323(21):2549-2553[14] Li J J, Huang X G, Zeng L L, Ouyang B, Yu X Q, Yang M N.Tuning magnetic properties, thermal stability and microstructure of NdFeB magnets with diffusing PrZn films [J]. J. Mater. Sci. Technol, 2020, 41:81.[J].J. Mater. Sci. Technol, 2020, 41(8):81-87[15] Li W D, Yang L J, Zhang Q, Xu C, Zhu Q H, Song Z L.Effect of the grain boundary Tb/Dy diffused microstructure on the magnetic properties of sin-tered NdFeB magnets [J]. J. Magn. Magn. Mater, 2020, 502:166491.[J].J. Magn. Magn. Mater, 2020, 502(1):166491-166491[16] Li W, Zhang Q, Zhu Q, Xiao S, Xu C, Yang L J.Formation of anti-shell/core structure of heavy rare earth elements (Tb, Dy) in sintered NdFeB magnet after grain boundary diffusion process [J]. Scr. Mater, 2019, 163: 40.[J].Scr. Mater, 2019, 163(1):40-43[17]Sepehri-Amin H, Liu J, Ohkubo T, Hioki K, Hattori A, Hono K, Enhancement of coercivity of hot-deformed NdFeB anisotropic magnet by low-temperature grain boundary diffusion of Nd60Dy20Cu20 eutectic alloy [J.Scr[J].Mater, 2013, 69(9):647-650[18] Chen F G, Zhang T Q, Wang J, Zhang L T, Zhou G F, Coercivity enhancement of a Nd-Fe-B sintered magnet by diffusion of Nd70Cu30 alloy under pres-sure [J].Scr. Mater, 2015, 107:38.[J].Scr. Mater, 2015, 107(1):38-41[19] Wu D, Yue D, Liu W Q, Chen J W, Yi X F, Magnetic domain switching in NdFeB sintered magnets with superior magnetic properties [J].Mater. Res. Lett, 2018, 4:255.[J].Mater. Res. Lett, 2018, 4(6):255-260[20] Liu W Q, Chang C, Yue M, Yang J S, Coercivity, microstructure, and thermal stability of sintered NdFeB magnets by grain boundary diffusion with TbH3 nanoparticles [J].Rare Metals, 2017, (09):1.[J].Rare Metals, 2017, 09(1):1-5[21] Chen F G, Zhang T Q, Wang J, Zhang L T, Zhou G F, Coercivity enhancement of a NdFeB sintered magnet by diffusion of Nd70Cu30 alloy under pressure [J].Scr. Mater, 2015, 107:38.[J].Scr. Mater, 2015, 107(1):38-41[22]于濂清, 黄翠翠, 袁永锋.含量对高磁能积烧结磁性能和耐蚀性影响[J].粉末冶金工业, 2008, 18(6):19-22[23]Yu L Q, Huang C C, Yuan Y F, Effect of Nd, Dy content on magnetic propertises and corrosion resistance of NdFeB [J].Powder metallurgy industry, 2008, 18(6):19.[J].Powder metallurgy industry, 2008, 18(6):19-22
2021, Vol. 28 