Simultaneous enhancement of coercivity and electric resistivity of Nd-Fe-B magnets by Pr-Tb-Al-Cu synergistic grain boundary diffusion toward high-temperature motor rotors

To high-power permanent magnetic motors, it is critical for Nd-Fe-B magnets to maintain the desirable coercivity at high-temperature operating conditions. To address this, two approaches have been proven effective: (1) enhancing the room temperature coercivity; (2) reducing the eddy current loss. However, these two items are difficult to be simultaneously achieved. Here, the grain boundary diffusion (GBD) of the Pr-Tb-Al-Cu-based source is applied to enhance the coercivity and electric resistivity at room temperature from 1101 kA m-1 and 2.13 × 10–6 Ω m to 1917 kA m-1 and 2.60 × 10–6 Ω m, and those at 120 °C from 384 kA m-1 and 4.31 × 10–6 Ω m to 783 kA m-1 and 4.86 × 10–6 Ω m, respectively. Such optimization is ascribed to the improved formation depth of Tb-rich 2:14:1 shells with large magnetocrystalline anisotropy and the increased intergranular Pr-based oxides with high electric resistivity, induced by the coordination effects of Tb and Pr, as proven by the atomic-scale observations and the first principles calculations. It thus results in the simultaneously improved output power and energy efficiency of the motor because of the combination of magnetic thermal stability enhancement and eddy current loss reduction, as theoretically confirmed by electromagnetic simulation.