Diffusion behavior and coercivity enhancement of Tb-containing NdFeB magnet by dip-coating TbH₃

There is a growing demand for high coercivity of NdFeB magnets with low heavy rare earth in the emerging applications. In this work, dip-coating 0.02 g and 0.09 g TbH3 on the Tb-containing NdFeB magnet enhance coercivity at room temperature, respectively. The highest coercivity achieve about 30 kOe at room temperature after diffusion, which can apply to traction motors of electric vehicles. The magnetic field intensity distribution of magnet was analyzed by finite element method. Microstructures show TbH3 coat contents and original composition of NdFeB magnet influences the formation of Tb-rich shell and grain boundary phase, and determine finally diffusion depth and Tb concentration. The Tb atoms diffuse into the interior of the magnet, forming a network Tb-rich shell existed around Nd2Fe14B grains, resulting in the coercivity enhancement.