Pr–Tb synergistic strengthening on coercivity of Nd-Ce-Fe-B magnets grain boundary diffused with Pr-Tb-Al-Ga alloys

Abstract

Sintered Nd-Ce-Fe-B magnets were grain boundary diffused (GBDed) with PrxTb80–xAl10Ga10 (at%) (x = 0, 20, 40, 60, 80) alloys. The effect of Pr/Tb content in diffusion source on magnetic properties, microstructure and elements distribution of GBDed magnets was investigated. When Pr is used to substitute for 75% Tb in diffusion source, Tb consumption per unit coercivity improvement of GBDed magnet reduces by 77%, compared with the Tb80Al10Ga10 diffused magnet. Tb element diffuses into magnets and then forms Tb-rich shell with high magneto-crystalline anisotropy field surrounding main phase grains, resulting in substantial coercivity improvement. Pr with low melting point diffuses deeply along liquid grain boundary phase during GBD process. It can eliminate some sharp defects of main phase grains and make grain boundaries smooth, which provides diffusion channels for further diffusion of Tb element. Therefore, there are more diffusion channels for Tb and less Tb enriched at surface region, making Tb diffuse more deeply and improving Tb utilization efficiency. This method significantly improves the coercivity, and realizes the green, efficient and high-quality utilization of heavy rare earth (HRE) elements.