Quasi-spherical jet-milled powders with uniform rare-earth-rich coverage for high-performance sintered NdFeB magnets

To simultaneously enhance remanence (B_r) and coercivity (H_cj) of NdFeB magnets, a powder-state regulation based on the characteristic columnar grain structure is developed. By matching the average powder particle size with the short-axis dimension of the columnar grains, the powder can be transformed from sharp-edged fragments into quasi-spherical particles with well-defined morphology during jet milling. The improved magnetic field alignment behavior originates from the synergistic optimization of particle size distribution and particle morphology. In addition, the quasi-spherical particles retain complete coverage of the rare-earth-rich (RE-rich) phase, which transforms into a uniform and continuous liquid phase during the heating stage of sintering. This effectively inhibits abnormal grain growth caused by direct contact between main-phase grains and weakens the intergranular magnetic exchange coupling. As a result, the B_r increases from 1.462 to 1.481 T, while the H_cj is markedly improved from 823.86 to 1073.8 kA/m. The results demonstrate that tailoring powder characteristics based on the columnar crystal structure enables the formation of quasi-spherical particles uniformly coated with RE-rich phase, thereby optimizing the microstructure of NdFeB magnets and enhancing the magnetic properties.