Presentation Information
[P1-26]A Novel Methods to Fabricate Fine-grained Nd-Fe-B Sintered Magnets: Reduction-diffusion & Pressless Process
*Sumin Kim1, So-Yeon Kim1, Jae-Ho Byun1, Tea-Hoon Kim1, Jeong-Goo Lee1 (1. Korea Institute of Materials Science (Korea))
Keywords:
Nd-Fe-B,grain refinement,reduction-diffusion,pressless process,permanent magnets
Nd-Fe-B permanent magnets are crucial components in power systems, motors, and generators, offering high efficiency and high output performance. As a result, their importance is rapidly increasing in advanced industries such as electric vehicles (EVs), wind power generation, robotics, aerospace, and defense. To ensure stable operation and reliability in various environmental conditions, high coercivity is essential. However, achieving high coercivity in Nd-Fe-B sintered permanent magnets without relying on heavy rare-earth elements such as Dy or Tb necessitates grain refinement. As the grain size decreases, the coercivity mechanism shifts toward coherent rotation, effectively enhancing the magnet’s coercivity. This effect remains theoretically valid down to the critical single domain diameter of approximately 300 nm.
Despite these advantages, fabricating Nd-Fe-B sintered magnets with refined grains presents two major challenges. The first is the production of ultrafine Nd-Fe-B powders. To obtain Nd-Fe-B powders in the submicron range near the critical single domain diameter, He gas-based jet milling is required. However, this process is significantly more expensive than conventional N2 gas-based jet milling, raising concerns about economic feasibility. Therefore, developing a cost-effective process for producing ultrafine Nd-Fe-B powders at the submicron scale is crucial.The second challenge lies in the poor alignment of ultrafine powders and the rapid grain growth during sintering. To overcome these issues, a low-pressure alignment process with a lubricant is introduced to enhance powder alignment, while the incorporation of grain growth inhibitors is essential to suppress grain coarsening during sintering.
Herein, we present the fabrication of submicron-sized, single-crystalline 2:14:1 powders using the Reduction-Diffusion (RD) process and demonstrate the synthesis of high performance sintered magnets utilizing RD powders through the Pressless Process (PLP).
Despite these advantages, fabricating Nd-Fe-B sintered magnets with refined grains presents two major challenges. The first is the production of ultrafine Nd-Fe-B powders. To obtain Nd-Fe-B powders in the submicron range near the critical single domain diameter, He gas-based jet milling is required. However, this process is significantly more expensive than conventional N2 gas-based jet milling, raising concerns about economic feasibility. Therefore, developing a cost-effective process for producing ultrafine Nd-Fe-B powders at the submicron scale is crucial.The second challenge lies in the poor alignment of ultrafine powders and the rapid grain growth during sintering. To overcome these issues, a low-pressure alignment process with a lubricant is introduced to enhance powder alignment, while the incorporation of grain growth inhibitors is essential to suppress grain coarsening during sintering.
Herein, we present the fabrication of submicron-sized, single-crystalline 2:14:1 powders using the Reduction-Diffusion (RD) process and demonstrate the synthesis of high performance sintered magnets utilizing RD powders through the Pressless Process (PLP).
