Dong Hyun Lee1,2,Seong Chan Kim1,3,Juyoung Baek1,Donghwan Kim4,Sang Hyub Lee4,Hyesun Yoo2,Dalhyun Do3,Dong Hwan Kim1,JongWook Roh2,Jeongmin Kim1
Daegu Gyeongbuk Institute of Science and Technology1,Kyungpook National University2,Keimyung University3,Star Group Ind. Co., Ltd.4
Dong Hyun Lee1,2,Seong Chan Kim1,3,Juyoung Baek1,Donghwan Kim4,Sang Hyub Lee4,Hyesun Yoo2,Dalhyun Do3,Dong Hwan Kim1,JongWook Roh2,Jeongmin Kim1
Daegu Gyeongbuk Institute of Science and Technology1,Kyungpook National University2,Keimyung University3,Star Group Ind. Co., Ltd.4
A strong coercivity enhancement of the commercial NdFeB magnets with the magnetic properties of <sub>i</sub>H<sub>c</sub> = 22.76–22.48 kOe and (BH)<sub>max</sub> = 48.61–48.58 MGOe is demonstrated by the grain boundary diffusion (GBD) process with low-melting point Tb<sub>80</sub>Al<sub>(x-20)</sub>Cu<sub>x</sub><sub> </sub>(x = 0–20) alloys. The maximum coercivity enhancement was obtained from the diffused magnet with Tb<sub>80</sub>Al<sub>15</sub>Cu<sub>5</sub>, in which the value increased from 12.25 to 22.76 kOe by GBD process. Microstructural investigation with the electron probe micro analysis reveals that the enhancement of coercivity in the GBD magnets is mainly due to magnetic isolation by continuous Nd-rich grain boundary phases and Tb-rich shells. Tb diffusion through grain boundaries at a lower temperature than 900 °C, and consequently developed continuous and thin Tb-rich shell structures. Especially, the partial replacement of Tb by Al and Cu in diffusion sources resulted in higher coercivity with consuming fewer Tb elements (0.8 wt%) in the samples with Tb<sub>80</sub>Al<sub>(x-20)</sub>Cu<sub>x</sub><sub> </sub>which are much lower than that in the samples with Tb metal (1.0 wt%). The results show that Cu and Al addition in diffusion source can effectively improve Tb diffusion efficiency by modifying intergranular Nd-rich phase. This work may shed light on the reduction of heavy rare earth in NdFeB sintered magnets.