Coercivity enhancement of hot-deformed NdFeB magnets by doping R80Ga20 (R = Pr, Dy, Tb) alloys

Significant coercivity (_iH_c) enhancement of hot deformed NdFeB magnets made from commercial MQU-F powders doped with 2 wt% R₈₀Ga₂₀ eutectic alloy powders is demonstrated, where R represents Pr, Dy and Tb. The experimental result shows that the coercivity of the hot deformed magnet is improved from 15.0 kOe to 17.2–18.7 kOe by doping R₈₀Ga₂₀ alloys, but (BH)_max is slightly decreased from 41.5 MGOe to 34.1–38.7 MGOe. The magnet doped with Tb₈₀Ga₂₀ exhibits higher _iH_c = 18.7 kOe with moderate (BH)_max = 38.7 MGOe among the doped magnets post-annealed at 600 °C. In addition, hot deformed NdFeB magnets doped with Tb₈₀Ga₂₀ alloy powders annealed at various temperatures were also explored. Increasing the annealing temperature from 600 °C to 700 °C, _iH_c is significantly enhanced to 24.0 kOe with attractive (BH)_max of 37.5 MGOe. Post-annealing treatment at higher temperature, i.e., 700 °C, could modify the microstructures and therefore improve the magnetic properties of the hot deformed magnets effectively. TMA analysis shows that the increase of T_C with annealing temperature reveals the increased amount of Tb entered into 2:14:1 phase. TEM with EDX analysis shows that the preference of Ga at grain boundary may reduce nucleation sites of reverse domain and strengthen pinning effect, contributing to coercivity enhancement. This study provides a useful method to enhance the coercivity of hot deformed NdFeB magnets larger than 20 kOe, which is also suitable for making thicker NdFeB MQ 3 magnets for high temperature applications.