Dy-distribution in the grains of high-energy (Nd,Dy)-Fe-B magnets

Sintered (Nd,Dy)-Fe-B-magnets were manufactured by adding low melting RE₃Co or RE₃Co₂ alloys (RE=Nd or/and Dy) to basic alloys with compositions close to the Nd₂Fe₁₄B stoichiometry. The remanent polarizations and the coercivities of sintered and annealed magnets with about 2 wt.% Dy range from 1.39 to 1.42 T and from 6.6 to 13.5 kOe, respectively. For example the magnet manufactured with an addition of 5 wt.% Dy_1.5 Nd_1.5Co₂ achieves a remanence of 1.42 T and a coercivity of 9.0 kOe. The energy density of this magnet amounts to 46.8 MGOe (375 kJ/m³). The microstructure of the magnets consists of large RE₂Fe₁₄B-grains with dimensions up to 50 μm. WDX analysis revealed that the Dy-distribution in these grains is inhomogeneous: there is no Dy in the central region, while a Dy-concentration of 5 wt.% was detected in the border region of the φ-grains. Adjustment of the composition and of the processing route results in magnets with a remanent polarization of 1.4 T and a coercivity of 15 kOe