Abstract
Coercivity enhancement effect of the anisotropic hot-deformed NdFeB magnets made from NdFeB MQU-F powders doped with 2 wt% low-melting R70Cu30 (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 R70Cu30 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 $\Delta _{i}\text{H}_{c}$ is 1.2 and 4.4 kOe for the magnets doped with Nd70Cu30 and Dy70Cu30 alloy powders, respectively. Most interestingly, Tb70Cu30-doped magnet followed with 700 °C post-annealing exhibits the highest coercivity i H c 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.
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