Effect of PrFe alloy grain boundary diffusion on coercivity and microstructure of sintered Nd-Fe-B magnets

A Ga-containing Nd-Fe-B magnet was diffused by Pr70Fe30 alloys. After diffusion, the coercivity of the diffused magnet increased from 15.77 kOe to a maximum of 22.20 kOe. Changing the diffusion source mass ratio resulted in a different grain boundary microstructure. The grain boundary structure improved in the surface region. The distribution of Ga was optimized to form continuous RE6Fe13Ga phases in the grain boundaries by diffusing Pr70Fe30 alloys. The improvement in coercivity is mainly attributed to the optimized grain boundary structure and the continuous RE6Fe13Ga phase. Furthermore, the structural changes and their causes at different stages of diffusion were analyzed.