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

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 (H-A) of (Nd, Pr, Dy)(2)Fe14B 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. (C) 2021 Elsevier B.V. All rights reserved.