Magnetic Properties of Ce85Al15 Doped NdFeB Sintered Magnet by Grain Boundary Diffusion of Tb70Cu30 Powders

Magnetic properties' modification and coercivity enhancement of NdFeB sintered magnets prepared by the dual-alloy (DA) sintering together with grain boundary diffusion (GBD) treatment are demonstrated. For the original NdFeB magnet, (BH)(max) of 51.4 MGOe and H-i(c) of 14.9 kOe are obtained. For the magnet made with the same composition as the former but doped with Ce85Al15 (CeAl) powders, magnetic isolation due to the distribution of Ce and Al at GB increases the coercivity effectively, yet few Ce entering into grain interior decreases B-r, (BH)(max), and Curie temperature slightly. In addition, the coercivity of the above magnets can be further enhanced to 22.7-25.1 kOe by GBD with different amounts of Tb70Cu30 (TbCu) powders. The clear core-shell structure, which consists of (Nd, Tb)(2)Fe14B phase with higher magnetocrystalline anisotropy field (H-A) as the shell and Nd2Fe14B phase as the core, is observed. CeAl helps to form a continuous and smooth GB. The diffusion source of TbCu could infiltrate into the magnet along such smooth GB and form a homogeneous core-shell structure. As a result, coercivity is remarkably enhanced from 14.9 kOe for DA sintered magnet with 2 wt% CeAl to 25.1 kOe for the magnet GBD with TbCu. Most importantly, various levels of NdFeB magnets, such as 52M, 35-50SH, and 45UH, could be easily attained by modifying the amounts of CeAl for DA sintered magnets and/or GBD with TbCu powders.

Automated summary

This study demonstrates the modification of magnetic properties and enhancement of coercivity of NdFeB sintered magnets using dual-alloy (DA) sintering and grain boundary diffusion (GBD) treatment. Addition of CeAl powders increases the coercivity, while incorporating TbCu powders through GBD further enhances the coercivity and achieves different levels of NdFeB magnets.