Grain boundary diffusion behaviors in hot-deformed Nd2Fe14B magnets by PrNd-Cu low eutectic alloys

Highlights: • The ultrahigh coercivities of the hot-deformed magnets are increased by grain boundary diffusion process from side and pole surfaces. • The excellent textures can be obtained by the side surface diffusion along the lateral intergranular phases. • Fe-rich crystalline phases are observed while Nd-rich amorphous phases are obtained. • It is hypothesized that higher coercivity may be obtained if the Fe-rich phases can be eliminated by appropriate optimization of diffusion process. High coercivity of hot-deformed Nd₂Fe₁₄B magnets was obtained by grain boundary diffusion. Comparable squareness and similar magnetic properties for samples diffusing from side and pole surfaces show little discrepancies if quantities of the infiltrated PrNd-Cu low eutectic alloys is enough to obtain sufficient diffusion. However, the microstructures and higher characteristic peak ratios show preferable orientation of grains near surfaces of the sample diffused from side surfaces than that from pole surfaces. Amorphous Nd-rich phases and crystal Fe-rich phases were both observed in the diffused magnets. The enhancement of coercivity is considered to be resulted from grain boundary optimization and magnetic isolation which is caused by the thickened nonmagnetic intergranular phases.