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 °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. © 2020