Preparation of anisotropic (Ce, Nd, Pr)-Fe-B powder with HDDR method from wasted sintered magnets

With the wide application of Ce-contained rare earth (RE) permanent magnets, recycling of wasted Ce-contained magnets has drawn more and more attention. Hydrogenation-disproportionation-desorption-recombination (HDDR) method was used to prepare anisotropic magnetic powder from wasted (Ce, Pr, Nd)-Fe-B sintered magnet (N45 magnet). The influence of hydrogen pressure in disproportionation (P-dis) and desorption (P-des) and the dispmportionation time (t(dis)) on the magnetic properties and microstructures of HDDR powders was studied. The P-dis, P-des and t(dis) were optimized to be 50 kPa, 5 kPa and 5 h, respectively. The optimized anisotropic HDDR (Ce, Pr, Nd)-Fe-B powder possessed the coercivity of 10.15 kOe, remanence of 11.14kG and the degree of alignment of 0.77. This coercivity has reached 83 % of that of the recycled N45 magnet. Microstructure examination with scanning electron microscope revealed that the optimized HDDR powder is consisted of flake-shaped particles with hierarchical structure. The distribution of rE-rich phase has been significantly influenced by P-dis, P(des )and t(dis). The optimized HDDR particles exhibited the best homogeneous distribution of rE-rich phase. The result of transparent electron microscopy (TEM) and energy dispersive spectrometry demonstrated the nature of (Ce, Pr, Nd)-rich phase and (Ce, Pr, Nd)(2)Fe14B for the rE-rich phase and RE2Fe14B grain phase, respectively. Examination with high-resolution TEM revealed that the optimized t(dis) resulted in the largest thickness of (Ce, Pr, Nd)-rich phase at grain boundaries and the consequent maximum coercivity of HDDR particles. The orientation of the optimized HDDR particles was analyzed with X-ray diffractometer and electron back-scatter diffractometer. The result revealed well textured HDDR particles and the subordinate nanograins with preferred (001) orientation, suggesting the inherited texture of these HDDR particles from the initial (Ce, Pr, Nd)(2)Fe14B grains in N45 sintered magnet. This HDDR method was proved to be a prospective strategy in recycling of Ce-contained sintered magnets.

Automated summary

This study successfully recycled anisotropic magnetic powder from wasted magnets using the HDDR method, and optimized the preparation parameters to obtain powder with good magnetic properties and microstructure. The results show that this method has potential in recycling Ce-contained sintered magnets.