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Nanocrystalline multi-main-phase (MMP) Nd-Ce-Fe-B magnet can effectively suppress the magnetic dilution effect of Ce. However, its low coercivity and poor thermal stability have not been adequately overcome. In this work, a novel low-melting-point Gd 60 Y 10 Cu 15 Al 15 alloy was introduced into MMP Nd-Ce-Fe-B magnet through intergranular addition for simultaneously enhancing its coercivity and thermal stability. The results show that the intrinsic coercivity H cj is obviously improved, and its maximum increment is ∼12.3 % at 4 wt% Gd 60 Y 10 Cu 15 Al 15 alloy. Especially, the increase in H cj is more significant, and an abnormally increase in the maximum energy product (BH) max occurs at high temperature of 150 °C. Meanwhile, the reversible temperature coefficients of H cj (β) and B r (α) are improved simultaneously. These findings imply the enhanced thermal stability for the MMP magnet with Gd 60 Y 10 Cu 15 Al 15 addition. The microstructural characterizations, compositional analyses and micromagnetic simulations reveal that the competitive effects of the formed non-ferromagnetic grain boundary (GB) phase and Y or Gd diffusion into the main phase lead mainly to a synergistic improvement in the coercivity and thermal stability of the magnet. This work is expected to provide a promising cost-effective approach for developing the high-performance thermally-stable Nd-Ce-Fe-B magnet and explore more possibilities for effective utilization of Y or Gd rare-earth resources. • The Research Highlights in this paper are as follows: • A novel low-melting-point Y-Gd based alloy was developed and used to modify the nanocrystalline MMP Nd-Ce-Fe-B magnet. • H cj and thermal stability of nanocrystalline MMP magnet are synergistically enhanced. • Microstructure evolutions and composition distributions are revealed. • The enhanced mechanisms for H cj and thermal stability are systematically analyzed. [ABSTRACT FROM AUTHOR]

• Thermally-stable high-performance nanocrystalline MMP Nd-Ce-Fe-B magnet is fabricated by grain boundary engineering. • H cj and thermal stability are obviously improved with simultaneously enhanced (BH) max. • Microstructure evolution is revealed, and the Dy diffusion model is proposed. • The underlying mechanisms for enhanced magnetic properties and thermal stability are systematically analyzed. Low coercivity and poor thermal stability are still the main challenges for practical application of low-cost Nd-Ce-Fe-B magnet. To solve these challenging problems, a strategy to simultaneously improve the coercivity and thermal stability of Nd-Ce-Fe-B magnet through combining the nanocrystalline multi-main-phase (MMP) structure and grain boundary engineering is demonstrated. In this study, nanocrystalline MMP Nd-Ce-Fe-B magnet was grain boundary engineered by co-adding DyF 3 and Cu powders. The results show that the intrinsic coercivity H cj is significantly improved, and meanwhile optimum maximum energy product (BH) max is achieved at 2 wt% DyF 3 -Cu. Moreover, the superior reversible temperature coefficients of H cj (β) and B r (α) are both achieved, implying the improved thermal stability for the DyF 3 -Cu added magnet. Microstructural and compositional characterizations indicate that the modified RE-rich phase, the inhibited abnormal grain growth near the flake boundary, and the diffused Dy towards main phase grains are the main reasons for simultaneously enhanced magnetic properties and thermal stability. Thus, combining the nanocrystalline MMP structure and grain boundary engineering will be a promising approach for preparing thermally-stable high-performance Nd-Ce-Fe-B magnet. [ABSTRACT FROM AUTHOR]

Nanostructured multi-main-phase (MMP) Nd-Ce-Fe-B magnet produced by melt-spinning powders has great potential for achieving high performance. However, the inferior intrinsic properties of the Ce 2 Fe 14 B phase lead to the low coercivity and thermal stability of this magnet. In this study, low-melting-point Pr 68 Cu 32 powders were introduced into nanostructured MMP magnet through intergranular addition to further improve its coercivity and thermal stability. When only 2 wt% Pr 68 Cu 32 was added, the intrinsic coercivity H cj and thermal stability were significantly improved with a slight reduction in the remanence B r and the maximum energy product (BH) max. The microstructure evolution of MMP magnet with adding Pr 68 Cu 32 was revealed by microstructural and compositional characterization and thermodynamic calculation, and a schematic model was proposed. Furthermore, mechanisms underlying changes in magnetic properties were systematically analyzed by combining micromagnetic simulation. ● Grain boundary modification is adopted for fabricating high-performance nanostructured MMP Nd-Ce-Fe-B magnet. ● H cj and thermal stability are significantly improved with a slight reduction in B r and (BH) max. ● Microstructure and microchemistry evolution are investigated and a corresponding model is proposed. ● Mechanisms underlying changes in magnetic properties are systematically analyzed. [ABSTRACT FROM AUTHOR]

Abstract: To improve the corrosion resistance and magnetic properties, Al85Cu15 (at.%) compound powders were added to (Pr, Nd)14.8Fe78.7B6.5 sintered magnets as grain boundary modifiers. The corrosion resistance was found to be remarkably improved by small additions of Al85Cu15 powders. When 1.2wt% Al85Cu15 was added, the corrosion rate of magnets in humid environments was reduced by two orders of magnitude. This is partly due to the stability enhancement of the (Pr, Nd)-rich intergranular phase by Cu and Al. In addition, the occurrence of the Cu-rich phase ((Pr, Nd)22Fe56Cu10Al2O10), whose open-circuit potential is higher than the (Pr, Nd)-rich intergranular phase, may be another reason for the improvement of the corrosion resistance. Furthermore, the magnetic properties of (Pr, Nd)14.8Fe78.7B6.5 were also improved by adding 0.3–1.2wt% Al85Cu15. Optimum addition amount was 0.6wt%. The improvement of the magnetic properties may be related to the microstructural modification and the increase of magnet density. [Copyright &y& Elsevier]