A coupled phase diagram and first-principles design strategy for high-efficiency multiphase rare-earth alloy diffusion sources in sintered Nd-Fe-B magnets
来源：ScienceDirect
This study presents a high-performance rare-earth alloy diffusion source design for sintered Nd-Fe-B magnets, intends to overcome the limitations associated with empirical and “trial-and-error” development approaches. Phase diagram simulations were employed to construct a multiphase, low-melting-point diffusion source alloy system, while first-principles calculations were utilized to systematically evaluate the solubility of different elements in the Nd2Fe14B main phase and explore their regulatory effects on microstructural evolution. Building upon these computational and thermodynamic analyses, three advanced diffusion sources − TbAlBi, TbBiZn, and TbAlGa − were successfully developed. Among them, the TAB alloy demonstrates the most remarkable performance, achieving a coercivity enhancement of 854.66 kA/m with only 0.35 wt% Tb. Its superior performance arises from three key factors: (i) the enhanced effective diffusion of Tb, enabling effective migration into the grain interior and the formation of a uniform, narrow Tb-rich shell; (ii) the synergistic interaction between Al and Bi, which refines the grain boundary-main phase interface and enhances microstructural continuity; and (iii) the complex multiphase transformations that provide additional diffusion driving forces. The combined contribution of these mechanisms renders TbAlBi significantly more effective than TbAlGa and TbBiZn in enhancing coercivity. This work thus provides new theoretical insights and mechanistic foundations for the compositional design of rare-earth diffusion sources and the performance optimization of sintered Nd-Fe-B magnets.