Comparison on the Coercivity Enhancement of Hot-Deformed Nd2Fe14B-Type Magnets by Doping R70Cu30 (R = Nd, Dy, and Tb) Alloy Powders

Coercivity enhancement effect of the anisotropic hot-deformed NdFeB magnets made from NdFeB MQU-F powders doped with 2 wt% low-melting R
₇₀
Cu
₃₀
(R = Nd, Dy, and Tb) powders was explored. Post-annealing treatment at 600 °C and 700 °C was employed to modify the microstructures and therefore improve the magnetic properties of the hot-deformed magnets. Doping R
₇₀
Cu
₃₀
alloy powders into the hot-deformed NdFeB magnets is effective in enhancing the coercivity from 15.1 kOe to 16.3-23.6 kOe, depending on the rare-earth elements adopted. The coercivity increment Δ
_i
H
_c
is 1.2 and 4.4 kOe for the magnets doped with Nd
₇₀
Cu
₃₀
and Dy
₇₀
Cu
₃₀
alloy powders, respectively. Most interestingly, Tb
₇₀
Cu
₃₀
-doped magnet followed with 700 °C post-annealing exhibits the highest coercivity iHc of 23.6 kOe and the highest coercivity increment of 8.5 kOe. TEM analysis shows that annealing treatment not only modifies the grain boundary of the platelet 2:14:1 phase but also promotes more Tb atoms entering into 2:14:1 crystal. As a result, the coercivity of the magnets is effectively enhanced.