Reducing Tb Consumption and Enhancing the Magnetic Thermal Stability of Sintered Nd-Fe-B Magnets Through Grain Boundary Diffusion Using Dehydrogenated Tb-Al Alloy

We report the effect of Al addition on the magnetic properties and thermal stability of Tb-diffused Nd-Fe-B magnets (12 mm × 12 mm × 5 mm). The Tb-Al-H-diffused magnet showed significant improvement in magnetic thermal stability over the TbH-diffused magnet. With the help of the low-melting-point Tb 78 Al 22 , the diffusion temperature was lowered, and the consumption of expensive Tb was reduced. More important, the microstructure analysis clearly showed a complete reduction in the accumulation of Tb near the surface, a sufficient diffusion depth of Tb, and a continuous grain boundary phase of the Tb-shell inside the magnet. Further, we found that the improved thermal stability of the Tb-Al-H diffused magnet was attributable to the well-formed and decoupled core-shell structures deep inside the magnet. Furthermore, results reveal that the most important properties for motor application of the magnet, ( BH ) max and flux loss (180 °C), are improved by sufficiently reducing the Tb content with the aid of Al.