Coercivity enhancement of thicker sintered NdFeB magnets by grain boundary diffusion with low-melting Tb75−xCexCu25 (x = 0–45) alloys

Abstract

Coercivity enhancement of thicker sintered NdFeB magnets with 5–10 mm in thickness by grain boundary diffusion (GBD) with low-melting Tb75−xCexCu25 alloy powders (x = 0–45) is demonstrated. For 5-mm-thick magnets, after GBD with Tb75−xCexCu25 alloys (x = 0–45), a significant iHc increment (ΔiHc) of 8.2–11.5 kOe with a slight decrease in Br is found. Although the magnet GBD treated with Tb75Cu25 exhibits the highest ΔiHc of 11.5 kOe, the coercivity enhancement per wt% Tb usage (ΔiHc/wt.% Tb) could be increased by about 2-folds with increasing x from 0 to 45. As for the 10-mm-thick magnets, large ΔiHc of 8.4 kOe and 7.4 kOe can also be attained by GBD with Tb75Cu25 and Tb55Ce20Cu25 powders, respectively. The optimized microstructure and the effective distribution of Tb and Ce at grain boundary after GBD with Tb75−xCexCu25 are the main factors for the coercivity enhancement. As a result, the magnetic properties, as well as the thermal stability of the sintered NdFeB magnets with 5–10 mm in thickness, are improved considerably. This work provides a cost-effective way to enhance the coercivity of the thicker sintered NdFeB magnets.