Temperature dependences of interface reactions and Tb diffusion behavior of Pr-Tb-Cu-Al alloys/Nd-Fe-B magnet

Interface reactions and structure of Pr52.5Tb17.5Cu30, Pr60Tb20Al20 and Pr60Tb10Cu15Al15 (at%) alloys with Nd-Fe-B magnets processed at various temperatures were systematically investigated. The alloys first melted and diffused through grain boundaries, and a higher temperature was required to form Tb-rich shells. Compared to Pr52.5Tb17.5Cu30 and Pr60Tb20Al20, Pr60Tb10Cu15Al15 with Al/Cu co-doping promoted Tb diffusion through grain boundaries especially at a lower temperature than 800 degrees C, and consequently developed continuous and thin Tb-rich grain boundaries. We presented two-step diffusion process with Pr60Tb10Cu15Al15, including low-temperature diffusion to accelerate Tb diffusion through grain boundaries and subsequent high-temperature diffusion to mainly promote Tb grain diffusion. Consequently, due to more homogeneous Tb distribution and resulting thinner Tb-rich grain boundaries, coercivity increment of 11 kOe was achieved by introducing only 0.33 wt% Tb, obviously lower than 0.48 wt% in conventional one-step diffusion magnet. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The interface reactions and structure of Pr52.5Tb17.5Cu30, Pr60Tb20Al20, and Pr60Tb10Cu15Al15 alloys with Nd-Fe-B magnets processed at different temperatures were investigated. The Pr60Tb10Cu15Al15 alloy with Al/Cu co-doping showed enhanced Tb diffusion through grain boundaries, leading to thinner Tb-rich grain boundaries and higher coercivity increment. The two-step diffusion process of Pr60Tb10Cu15Al15 resulted in more homogeneous Tb distribution and thinner Tb-rich grain boundaries, achieving 11 kOe coercivity increment with only 0.33 wt% Tb.