Research and Application Progress on Production of Anisotropic NdFeB Magnetic Powder by HDDR Process

Hydrogenation-disproportionation-desorption-recombination (HDDR) process is an effective method to produce anisotropic NdFeB magnetic powders. The anisotropic bonded magnets prepared by HDDR process have excellent performance and light weight, which play an important role in improving the efficiency and reducing weight of micro-special motor. It has been industrialized and applied in automotive, drone and other fields. In order to improve the magnetic powder properties, the researchers are keeping investigating the HDDR process and the anisotropy mechanism. They optimize the grain boundary structure of the magnetic powders by using the grain boundary diffusion method to improve the coercivity and temperature stability of the magnetic powder, and apply the above achievements into the recycling of the waste sintered NdFeB to save rare earth resources. The magnetic property of the HDDR anisotropic magnetic powders is better than that of the isotropic magnetic powders, but the deformation plasticity comes after. The researchers attempt to take the HDDR magnetic powders as precursor material to fabricate hot deformation magnets to improve their performances. The effect of grain refinement of the HDDR process provides a new research approach for improving the coercivity of the sintered NdFeB magnets, however, until now, no ideal result has been obtained. In this paper, the development of HDDR process and its mechanism over the years are introduced, as well as its application in hot deformation magnets, sintered magnets and rare earth magnet recycling.