The effect of pressure-assisted grain boundary diffusion on magnetic properties and microstructure of Nd-Fe-B magnet using TbF3 prepared by screen printing

The screen printing technology (SPT) was utilized to prepare TbF3 coatings on Nd-Fe-B magnets. The effect of pressure-assisted grain boundary diffusion on magnetic properties and microstructure of Nd-Fe-B magnet has been intensively investigated. The results indicated that the intrinsic coercivity increment (Delta Hci) enhanced with increasing diffusion temperature and time. Meanwhile, the pressure could promote grain boundary diffusion process and shorten diffusion time obviously. Microstructural and compositional analyses indicated that the appropriate temperature and time were essential to develop the core-shell structure within a certain depth, which played a key role in the coercivity enhancement of magnet. Meanwhile, the thickness and continuity of Tbrich shells decrease with diffusion depth. Furthermore, the pressure can strengthen the adhesion of TbF3 coatings to base magnet, promoting the diffusion of Tb element into deeper regions and the formation of Tb-rich shells. The diffusion behavior and role of F element in magnet were also explored. The results confirmed that the diffusion depth of F was close to that of Tb element. However, the F element did not diffuse into 2:14:1 phase but formed NdOF phase distributing at grain boundaries.