Preparation of hot worked dual-main phase Nd-Ce-Fe-B magnets and properties modification by grain boundary diffusion

Hot pressed and hot deformed nanocrystalline Nd-Ce-Fe-B magnets were prepared by dual-alloy method using melt-spun Nd-Fe-B and Ce-Fe-B powders with various weight ratios. For both hot pressed and hot deformed magnets, increasing Ce-Fe-B addition reduces the magnetic properties, but 10 wt. % Ce-Fe-B leads to an abnormal increase of coercivity. As a result, the remanence Jr = 1.21 T, intrinsic coercivity Hcj = 1215 kA/ m, and maximum energy product (BH)max = 266 kJ/m3 are obtained for the magnets with 10 wt. % Ce-Fe-B. To modify their properties, the dual-main phase magnets are treated by grain boundary diffusion of Nd50Tb20Cu30 alloy. The coercivity of the deformed magnet with 10 wt. % Ce-Fe-B addition increased from 1215 kA/m to 1402 kA/m after diffusion, which is comparable to that of the as-diffused Nd-Fe-B magnets (1495 kA/m). For the magnet with 30 wt. % Ce-Fe-B addition, a 50% increase of coercivity, about 376 kA/m, was obtained by diffusion. The microstructure characterizations demonstrated that the modification of grain boundary phase by the elimination of RE5Fe17 phase and the formation more significant core-shell structure of the Nd-rich hard magnetic 2:14:1 phase by Tb diffusion are responsible for the improved coercivity.

Automated summary

Hot pressed and hot deformed nanocrystalline Nd-Ce-Fe-B magnets were prepared using dual-alloy method. Addition of Ce-Fe-B reduced the magnetic properties, but also led to an abnormal increase of coercivity at 10 wt.%. Grain boundary diffusion treatment improved the coercivity by modifying the grain boundary phase and forming a more significant core-shell structure.