Influence of Oxygen Content on Grain Boundary Control of Sintered NdFeB Magnet

A large number of research works were involved in the Grain boundary diffusion (GBD) process. The influences of parameters, such as the types of coating compound, coating method and annealing technology on the GBD process, were investigated. However, there are few reports focusing on the influence of oxygen content in magnets on the effect of GBD process. In this work, influence of different oxygen contents in initial magnets on the effect of GBD process was studied by using Tb4O7 and TbHx as coating compounds, respectively. The coercivity (Hcj) increment of Tb4O7/TbHx GBD treated magnets is similar when Tb increment value is lower than 7 mg•cm-2. If Tb increment value is 11 mg•cm-2, the Hcj increment of TbHx GBD treated magnet is obviously higher than that of Tb4O7 GBD treated magnet. From EPMA mappings, it can be obviously seen that the O and Tb of magnet diffused by Tb4O7 are more centralized than that of magnet diffused by TbHx. If Tb increment value is 11 mg•cm-2, the Hcj increment of TbHx GBD treated magnet (3060×10-6) is obviously higher than that of Tb4O7 GBD treated magnet. © 2019, Editorial Office of Journal of the Chinese Society of Rare Earths. All right reserved.