Pr80Al20 surface-coated DyF3 modified sintered Nd-Fe-B magnets for large coercivity increment via grain boundary diffusion

• Published in: Journal of alloys and compounds Vol. 899; p. 163270
• Main Authors: Li, Feifei, Li, Jiajie, Ur Rehman, Sajjad, Zhang, Lili, Hu, Yikuan, Yang, Munan, Yu, Xiaoqiang, Zhong, Shuwei, Liang, Tongxiang
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 05.04.2022; Elsevier BV
• Subjects: Coercivity; Core-shell structure; Diffusion coating; Grain boundaries; Grain boundary diffusion; Magnetic anisotropy; Magnets; Microstructure; Neodymium; Praseodymium; Sintered Nd-Fe-B magnet; Sintering (powder metallurgy); Surface coating; Core-shell structure; Grain boundary diffusion; Sintered Nd-Fe-B magnet; Surface coating; Coercivity
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.163270

•A novel composite Pr80Al20 particle surface-coated with DyF3 was designed as diffusion source.•Huge coercivity increments of 11.63 kOe and 10.52 kOe reported in this paper exceed the maximum values in literature for GBD with Dy-containing sources in sintered Nd-Fe-B magnets.•The optimized Pr-Al-rich GB phases effectively improve the diffusion efficiency and depth of Dy.•The combined strengthening effect of magnetic isolation by the continuous Pr-Al-rich GB phases and magnetic hardening by Dy-Pr-rich shells significantly improve the coercivity of the magnets. [Display omitted] A large coercivity increment of 11.63 kOe is obtained by grain boundary diffusion with composite powders of Pr80Al20 surface-coated DyF3. The coercivity increases from the original 12.76 kOe to 24.39 kOe and 23.28 kOe in PA-0.7 and PA-0.9 diffused magnets (Pr80Al20:DyF3 = 7:3, 9:1 in wt%), which shows an increase of 91.15% and 82.45%, respectively. The temperature coefficient of coercivity of diffused magnets is improved due to the high magnetic anisotropy field (HA) of (Nd, Pr, Dy)2Fe14B and the optimized microstructure. Excellent diffusion efficiency and Dy diffusion depth are obtained owing to the betterment of Pr-Al-rich grain boundary (GB) phases. Microstructural features show that the combined strengthening effect of magnetic isolation by the continuous Pr-Al-rich GB phases and magnetic hardening by Dy-Pr-rich shells significantly improve the coercivity of the PA-0.7 and PA-0.9 diffused magnets. Especially, no accumulation of Dy element occurs in the PA-0.9 diffused magnet. The composite diffusion sources provide a new method to improve diffusion efficiency of Dy.