Grain-Boundary-Engineering of Recycled Nd–Fe–B Magnets From Single-Phase RE2Fe14B Powder via Rare-Earth–Cu Alloys

For the purpose of creating more resource-ecient Nd–Fe–B magnets, RE2Fe14B single grains were recycled, and the Nd-rich
secondary phase was replaced with binary and ternary rare-earth–Cu alloy additions. The e ect on the microstructure evolution
and the magnetic properties of such recycled magnets consolidated by spark plasma sintering (SPS) was investigated. RE2Fe14B
single-phase powder was recovered from end-of-life (EoL) magnets via hydrogen processing of magnetic scrap (HPMS), followed by
removal of secondary phases through selective acid leaching. SPS densification behavior, phase stability, and magnetic performance
showed a strong dependence on the composition of the added alloys (Nd70Cu30, Nd33Cu67, and Nd50Tb20Cu30) at a fixed addition
level of 10 wt.%. The Nd70Cu30 eutectic alloy enabled e ective grain-boundary wetting, yielding a coercivity of 450 kA/m and a
remanence of 0.94 T. On the contrary, the addition of the rare-earth-lean Nd33Cu67 alloy led to incomplete densification, matrix
phase decomposition, and low coercivity (115 kA/m), which were attributed to insucient liquid-phase formation and localized
overheating due to the Joule e ect. The best magnetic performance was achieved in the sample prepared with the Nd50Tb20Cu30
alloy, reaching a coercivity of 1500 kA/m and a remanence of 0.93 T. Microstructural analysis revealed the formation of a core–shell
grain structure, indicating e ective liquid-phase redistribution and Tb enrichment in the shell regions during SPS consolidation.
This work highlights the e ects of rare-earth–Cu alloy composition on liquid-phase formation and magnetic hardening at grain
surfaces, enabling single-grain grain-boundary engineering in recycled magnets consolidated from single-phase Nd2Fe14B.