Presentation Information
[P1-15]Effect of Coating Methods on the Magnetic Properties of Grain Boundary Diffusion Processed Nd-Fe-B Sintered Magnets
*Jaehyuk Kim1,2, Ye Ryeong Jang1, Dong Hyun Lee4, Seong Chan Kim2, Ju Young Beak2, Donghwan Kim5, Sang Hyub Lee5, Sumin Kim6, Jong Wook Roh4, Dalhyun Do3, Dong Hwan Kim2, Jeongmin Kim2, Wooyoung Lee1 (1. Yonsei Univ. (Korea), 2. DGIST (Korea), 3. Keimyung Univ. (Korea), 4. Kyungpook National Univ. (Korea), 5. Star Group (Korea), 6. KIMS (Korea))
Keywords:
Nd-Fe-B,Grain Boundary Diffusion Process,Coating method,Magnetic properties
The grain boundary diffusion (GBD) process has emerged as an effective method for enhancing the coercivity of sintered Nd–Fe–B magnets while minimizing the consumption of heavy rare-earth elements (HREs) such as Tb and Dy. Conventional bulk doping leads to a homogeneous distribution of HREs throughout the magnet, resulting in unnecessary material waste and a reduction in remanence (Br). In contrast, the GBD process selectively diffuses HREs along grain boundaries, therby improving coercivity more efficiently. However, the effectiveness of this process is significantly influenced by the coating method and diffusion pathway. In this study, the effect of different TbHx coating methods on the magnetic properties of GBD processed Nd–Fe–B magnets was analyzed. Commercial sintered Nd–Fe–B magnets were coated using dip coating and spray coating, followed by the diffusion process. The coercivity (Hc) increased from 12.8 kOe to 24.4 kOe with dip coating and further to 26.8 kOe with spray coating. Meanwhile, a slight decrease in remanence (Br) was observed, from 14.5 kG to 14.0 kG for dip-coated magnets and 14.3 kG for spray-coated magnets.The results indicate that spray coating enables a more uniform diffusion process, leading to superior coercivity enhancement compared to dip coating. In dip-coated samples, diffusion from side wall regions was inefficient, and the diffusion direction was perpendicular to the magnet’s alignment. This caused HREs to penetrate the grain interior rather than diffusing along the grain boundaries. In contrast, spray coating facilitated a more uniform and controlled diffusion pathway along the grain boundaries, therby maximizing coercivity improvement. This study highlights the critical role of optimizing the HRE coating method in the GBD process to achieve high coercivity while minimizing rare earth consumption. The findings demonstrate that spray coating provides higher diffusion efficiency than dip coating, offering a cost effective and sustainable approach for producing high performance Nd–Fe–B magnets.
