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Highlights • Nano- to submicron-sized process provides a way to optimize microstructure of HDDR powders. • The uniform Nd-rich phase distribution could effectively optimize the deformation ability. • The coercivity was increased from 1.18 T to 1.37 T for die-upset magnet with NSG HDDR powders. • The remanence was increased from 1.1 T to 1.25 T for die-upset magnet with NSG HDDR powders. Abstract Nano-crystalline and micron-crystalline Nd-Fe-B powders were employed to hydrogenation-disproportionation-desorption-recombination (HDDR) process to investigate the structural factors of deformation ability in HDDR powders. It was found that the deformation ability and magnetic properties of the final die-upset magnet were optimized significantly by nano-crystalline powders. Structure investigation shows that the variations in coercivity and deformation ability were attributed to the Nd-rich phase distribution in HDDR powders. Meanwhile, enhancement of remanence and squareness indicated the uniform distribution of Nd-rich phase and the narrow grain size distribution by using nano-sized crystalline powders were in favor of c-axis alignment of 2:14:1 phase. [ABSTRACT FROM AUTHOR]

Highlights • The improved magnetic properties of HDDR powders were obtained by optimizing the Nd-rich phase distribution of ingot powders. • The coercivity of HP magnets still could be improved with the addition of Pr-Cu eutectic alloys. • The effect of Pr-Cu addition on coercivity of Nd-Fe-B HDDR magnets was clarified. Abstract The effect on the Nd-rich phase distribution of the ingot for hydrogenation-disproportionation-desorption-recombination (HDDR) powders was studied. Coercivity of HDDR powders was elevated to 1.64 T by crushing the ingot into particles and annealing at 800 °C for 18 h. HDDR processed Nd-Fe-B powders blended with Pr-Cu powders and annealed at 580 °C for 3 h were hot-pressed to obtain fully dense magnets. The microstructure evolution in hot-pressed HDDR magnets proved the impact of Pr-Cu diffusion on coercivity that the coercivity of hot-pressed magnets was improved to 1.55 T significantly. Backscatter electron microscopy and transmission electron microscopy observations revealed that the variation in coercivity owing to the diffusion of Pr-Cu along the grain boundary with heat treatment. L-TEM images illustrated the thicker grain boundary layer can pin the motion of the domain wall more effectively, resulting in a higher coercivity in HP magnets. [ABSTRACT FROM AUTHOR]

• Excellent properties of hot-deformed magnets with high Ce content are obtained by Pr-Cu diffusion. • The effect of Pr-Cu diffusion on the coercivity enhancement of hot-deformed magnets is illustrated. • The temperature stability of coercivity of hot-deformed magnet after Pr-Cu diffusion is improved. The coercivity of hot-deformed (Ce,Nd,Pr)-Fe-B magnet was enhanced from 1.44 T to 1.71 T by the addition of 3 wt% Pr-Cu powders for grain boundary diffusion. Microstructure analysis has shown that the formation of thick grain boundary phase with non-ferromagnetism can well isolate the adjacent main phase grains and weaken the intergranular exchange coupling, which is beneficial to coercivity enhancement. Moreover, the size of platelet shaped grains inhibited by liquid phase inside the ribbon is also one of the reasons for the increase of coercivity. In addition, the temperature stability of coercivity was improved after the diffusion of Pr-Cu alloy. [ABSTRACT FROM AUTHOR]