Coercivity enhancement with reduced Tb usage for NdFeB sintered magnets by grain boundary diffusion with multicomponent Tb-Ce-Al-Cu-Zn alloy powders

In this work, coercivity enhancement and thermal stability improvement for NdFeB sintered magnets by grain boundary diffusion (GBD) with Tb75Cu25-xZnx (x = 0–25) alloy powders are investigated. The coercivity (iHc) is enhanced from 10.6 kOe to 19.5–22.5 kOe by GBD with Tb75Cu25-xZnx (x = 0–25). Proper Zn addition into diffusion source can further improve the coercivity and its thermal stability for NdFeB sintered magnets. Besides, the costs of the diffusion sources have been significantly reduced by multicomponent Tb75-y-zAlyCez (Cu, Zn)25 alloy powders, and nearly without sacrificing the magnetic properties. Coercivity is significantly increased to 20.3–22.1 kOe by GBD with Tb75-yAlyCu20Zn5 (y = 0–30) alloy powders, and large coercivity increment (ΔiHc) of 11.0–11.5 kOe is found for y = 0–30. To further reduce the Tb usage, Tb45-zCezAl30Cu20Zn5 (z = 0–25) alloy powders are adopted as diffusion sources. Although the ΔiHc is gradually decreased as Ce content increases, the large coercivity of 18.4–21.6 kOe can be attained for z = 0–25. The formation of (Nd, Tb)2Fe14B shells can inhibit the nucleation of reverse domain. While Ce, Al, Cu and Zn prefer to distribute at grain boundary and triple junction, which can strengthen the decoupling effect between adjacent grains. Both effects contribute to the large coercivity enhancement. The optimized magnetic properties of iHc = 20.5 kOe, ΔiHc = 9.9 kOe and (BH)max = 49.1 MGOe can be achieved for the magnet GBD with Tb30Ce15Al30Cu20Zn5 alloy powders.