Comparison on the coercivity enhancement of the sintered NdFeB magnets by grain boundary diffusion with Tb70Cu30 powders prepared by different milling methods

Coercivity enhancement of the sintered NdFeB magnets by grain boundary diffusion (GBD) with Tb70Cu30 powders prepared by different milling methods has been compared. The commercial NdFeB sintered magnets with the magnetic properties of Br=14.0 kG, iHc= 17.5 kOe and (BH)max= 48.4 MGOe are chosen as original magnets. The coercivity increment of the NdFeB magnets is 7.6 kOe and 9.4 kOe after GBD with Tb70Cu30 alloy powders made by high energy ball milling (HEBM) and low-energy ball milling (LEBM), respectively. Higher coercivity increment can be obtained for the magnet GBD treated with Tb70Cu30 powders prepared by LEBM, mainly related to their platelet shape. The platelet shape powders may provide the wider contact area between GBD source and the surface of the magnets. The above effect is helpful in improving diffusion efficiency and enhancing coercivity accordingly. As a result, magnetic properties of Br=13.6 kG, iHc= 25.1 kOe and (BH)max= 46.1 MGOe are achieved.