Comparison on the coercivity enhancement of sintered NdFeB magnets by grain boundary diffusion with low-melting (Tb, R)75Cu25 alloys (R= None, Y, La, and Ce)

A significant coercivity enhancement of the commercial NdFeB magnets with the magnetic properties of (BH)max = 48.4 MGOe and iHc = 17.5 kOe through grain boundary diffusion (GBD) with low-melting Tb55R20Cu25 alloys is demonstrated. Adopting Tb55R20Cu25 alloys as GBD sources is effective in increasing coercivity to 29.0 kOe for R = None, 23.8 kOe for R = Y, 25.6 kOe for R = La, 28.0 kOe for R = Ce, respectively. Yet, (BH)max is slightly reduced to 46.2-48.2 MGOe. The preferential appearance of Cu at grain boundary and triple junction of the grains, and the core-shell structure occurred due to Tb at grain surface remarkably enhance the coercivity. Interestingly, higher coercivity enhancement per wt% Tb usage (ΔiHc/wt%Tb) of 7.2 kOe/wt% for the magnet with Tb55Ce25Cu25 than 5.9 kOe/wt% for that with Tb75Cu25 has been found due to the magnetic isolation effect caused by the preferential appearance of Ce at grain boundary, though a slight lower coercivity enhancement was found for the samples with R = Y and La. Lower melting point (637 °C) for Tb55Ce20Cu25 than Tb75Cu25 (743 °C) leads to larger diffusion depth of Tb into the magnet and therefore contributes to higher efficiency of coercivity enhancement for the magnet with R=Ce.A significant coercivity enhancement of the commercial NdFeB magnets with the magnetic properties of (BH)max = 48.4 MGOe and iHc = 17.5 kOe through grain boundary diffusion (GBD) with low-melting Tb55R20Cu25 alloys is demonstrated. Adopting Tb55R20Cu25 alloys as GBD sources is effective in increasing coercivity to 29.0 kOe for R = None, 23.8 kOe for R = Y, 25.6 kOe for R = La, 28.0 kOe for R = Ce, respectively. Yet, (BH)max is slightly reduced to 46.2-48.2 MGOe. The preferential appearance of Cu at grain boundary and triple junction of the grains, and the core-shell structure occurred due to Tb at grain surface remarkably enhance the coercivity. Interestingly, higher coercivity enhancement per wt% Tb usage (ΔiHc/wt%Tb) of 7.2 kOe/wt% for the magnet with Tb55Ce25Cu25 than 5.9 kOe/wt% for that with Tb75Cu25 has been found due to the magnetic isolation effect caused by the preferential appearance of Ce at grain boundary, though a slight lower coercivity enhancement was found for the samples with R = Y and La...

[1]  Huangzhong Yu,et al.  Grain boundary diffusion treatment of sintered NdFeB magnets by low cost La-Al-Cu alloys with various Al/Cu ratios , 2019, Journal of Magnetism and Magnetic Materials.

[2]  Z. W. Liu,et al.  Microstructure and improved properties of sintered Nd-Fe-B magnets by grain boundary diffusion of non-rare earth , 2019, Journal of Magnetism and Magnetic Materials.

[3]  Shuai Guo,et al.  Highly efficient Tb-utilization in sintered Nd-Fe-B magnets by Al aided TbH2 grain boundary diffusion , 2018, Scripta Materialia.

[4]  H. Sepehri-Amin,et al.  Coercivity enhancement of Nd-Fe-B hot-deformed magnets by the eutectic grain boundary diffusion process using Nd-Ga-Cu and Nd-Fe-Ga-Cu alloys , 2018 .

[5]  Zhenlun Song,et al.  The dual trend of diffusion of heavy rare earth elements during the grain boundary diffusion process for sintered Nd-Fe-B magnets , 2018 .

[6]  Jiheng Li,et al.  Microstructure modification and coercivity enhancement of Nd-Ce-Fe-B sintered magnets by grain boundary diffusing Nd-Dy-Al alloy , 2017 .

[7]  M. W. Lee,et al.  Microstructure and Magnetic Properties of NdFeB Sintered Magnets Diffusion-Treated with Cu/Al Mixed Dyco Alloy-Powder , 2017 .

[8]  K. Peng,et al.  Influence of annealing temperature on the Dy diffusion process in NdFeB magnets , 2017 .

[9]  Lanting Zhang,et al.  Anisotropic behavior of grain boundary diffusion in hot-deformed Nd-Fe-B magnet , 2017 .

[10]  Yoshinori Fujikawa,et al.  Effects of Grain Boundary Phase on Coercivity of Dysprosium-Free Rare Earth Magnet , 2016 .

[11]  S. Kobe,et al.  High-coercivity Nd-Fe-B magnets obtained with the electrophoretic deposition of submicron TbF3 followed by the grain-boundary diffusion process , 2016 .

[12]  D. Miller,et al.  Dysprosium-free melt-spun permanent magnets , 2014, Journal of physics. Condensed matter : an Institute of Physics journal.

[13]  Boping Hu,et al.  Study of sintered Nd-Fe-B magnet with high performance of Hcj (kOe) + (BH)max (MGOe) > 75 , 2013 .

[14]  H. Sepehri-Amin,et al.  Strategy for high-coercivity Nd–Fe–B magnets , 2012 .

[15]  J. Coey.  Permanent magnets: Plugging the gap , 2012 .

[16]  Christina H. Chen,et al.  Magnetic Materials and Devices for the 21st Century: Stronger, Lighter, and More Energy Efficient , 2011, Advanced materials.

[17]  S. Sugimoto,et al.  Current status and recent topics of rare-earth permanent magnets , 2011 .

[18]  H. Nakamura,et al.  Coercivity Enhancement by Grain Boundary Diffusion Process to Nd-Fe-B Sintered Magnets , 2006, INTERMAG 2006 - IEEE International Magnetics Conference.

[19]  Satoshi Hirosawa,et al.  Magnetization and magnetic anisotropy of R2Fe14B measured on single crystals , 1986 .