Abstract: Heavy rare-earths (HREs)-based grain boundary diffusion (GBD), crucial for enhancing coercivity and thermal stability of Nd-Fe-B magnets, faces fundamental penetration depth limitation, precipitating a coercivity plateau and severely restricting development of renewable energy industries. Here, the stress-engineered strategy is proposed to seed gradient dislocations at grain boundaries/triple junction phases using a simply supported beam, constructing a high-throughput model that bridges dislocation density, GBD dynamics, and magnetic properties. Following GBD treatment with Tb₈₀Ga₁₀Al₁₀, the magnet achieves coercivity up to 2179 kA/m and thermal stability of -0.5083 %/°C. This enhancement stems from high-density dislocations reducing diffusion activation energy, maximizing Tb diffusion coefficient by 86.09 % and depth by 15 %, validated by electron probe microanalysis and X-ray diffraction. Consequently, Tb diffusion depth exhibits a positive correlation with dislocation density, forming a functionally graded grain structure with Nd-rich cores encapsulated by Tb-rich shells, observed directly via backscattered electrons & transmission electron microscope, and reconstructed via micromagnetic simulation. The microstructure-centric design philosophy enables deep GBD in Nd-Fe-B magnet, maximizing utilization efficiency of scarce HRE resources while simultaneously enhancing magnetic performance to meet carbon neutrality requirements.

Key words: Nd-Fe-B, Dislocations, Grain boundary diffusion, Coercivity, Micromagnetic simulation