Dysprosium Diffusion Behavior and Microstructure Modification in Sintered Nd-Fe-B Magnets via Dual-Alloy Method

Dysprosium diffusion and microstructure alteration behaviors in sintered Nd-Fe-B magnets via dual-alloy method have been investigated. The sintered magnets were prepared by blending Dy-free and Dy-rich powders with varying proportions. Results indicate that Dy element has already diffused from Dy-rich powders into the 2:14:1 phase of Dy-free powders and tended to homogenize in the bulk magnet, attributed to the coalescence of grains and dysprosium element concentration gradient. In addition, Dy and Pr/Nd elements counterdiffusion process redistributes the grain boundaries homogeneously. The fracture surfaces of magnets prepared via dual-alloy method almost appear intergranular fracture. It demonstrates that both of (Nd/Pr, Dy)₂Fe₁₄B phase formation and microstructure alteration have favored to coercivity enhancement and thermal stability improvement of the magnets.