[P1] RE-Fe-B Magnets

[P1-7] Microstructural Optimization and Coercivity Enhancement in Nd-Ce-Fe-B Magnets through Grain boundary diffusion of Pr-La Mixed Alloy

*Ye Ryeong Jang¹ (1. Yonsei University (Korea))

Keywords:

Rare earth magnet,Nd-Ce-Fe-B,Grain boundary diffusion process,Light rare earth,Chemically induced liquid film migration

We report on the magnetic and microstructural characteristics observed in Nd-Ce-Fe-B sintered magnets following grain boundary diffusion process (GBDP) with Pr-La-Cu-Ga alloys. The microstructural feature of the shell and grain boundary phase (GBP) in GBD treated with Pr-La-Cu-Ga and Pr-Cu-Ga were characterized via the electron probe microanalysis and high-angle annular dark-field scanning transmission electron microscopy analysis. The GBDP with Pr-containing alloys forms a high-anisotropy Pr-rich shell, enhancing coercivity; however, this shell formation casess chemically induced liquid film migration (CILFM), resulting in undesirable grain growth in the magnets, which restricts the improvement of coercivity. The introduction of La in the boundary diffusion source increased coercivity from 13.7 kOe (11.3kOe before heat treatment) to 20 kOe without the use of heavy rare earth (HRE) elements. The formation of Pr-enriched thin RE-rich shell is more advantageous for enhancing coercivity. The RE concentration in the high-anisotropy RE-rich shell can be more effectively controlled by suppressing CILFM. It was confirmed that CILFM effectively suppressed using La due to its low solubility in the 2:14:1 phase. Our study shows that utilization of La can be a costeffective solution to prevent undesirable grain growth by CILFM and increase the coervity.