20.500.12556/RUL-182842 Single-grain grain-boundary engineering with Nd-Cu for sustainable recycling and reprocessing of Nd-Fe-B magnets The sustainable recycling and reprocessing of Nd-Fe-B magnets are essential for reducing critical-material dependency in next-generation permanent-magnet manufacturing. This study introduces a single-grain, grain-boundary-engineering strategy that revitalizes RE$_2$Fe$_{14}$B grains recovered and extracted via chemical leaching from end-of-life (EoL) wind-turbine magnets. The study showed that the selective leaching disrupted the matrix grains, producing Nd-, Dy-, and Fe-based oxides that shaped the subsequent microstructural evolution. A detailed transmission-electron-microscopy (TEM) study was employed to track the chemical and structural evolution of the modified grain boundaries and to correlate these changes with microstructural and magnetic performance. Nd$_{70}$Cu$_{30}$ additions proved decisive in dissolving RE$_2$Fe$_{14}$B-based surface oxides into the liquid phase and reprecipitating them at the triple pockets as oxygen-rich secondary phases, enabling surface reconstruction and liquid-phase sintering. The magnetic properties of bulk Nd-Fe-B magnet samples improved markedly with Nd-Cu additions (0–30 wt%): the remanence increased to ≈ 1.05 T, saturating above 5 wt% Nd-Cu due to enhanced grain alignment. The coercivity rose continuously from 50 to 825 kA/m with increasing Nd-Cu, governed primarily by grain-boundary characteristics rather than grain size. The maximum energy product also increased from 10 to 195 kJ/m$^3$ under the same additions. Simulations showed that the effect of in-plane anisotropy due to the presence of RE-oxides at the surface of the Nd$_2$Fe$_{14}$B grains reduces the coercivity. On the other hand, the better grain alignment markedly enhances the coercivity. The low-Fe-concentration grain boundaries, considered to be paramagnetic, act as an effective magnetic decoupling phase. Conversely, excessive non-magnetic secondary phases in the triple pockets generate local demagnetizing fields that lower the coercivity. Thus, optimizing the oxygen pathways with Nd-Cu additions enables the sustainable recycling and reprocessing of Nd-Fe-B magnets by replacing the Nd-rich phases with resource-efficient Nd$_{70}$Cu$_{30}$. The study demonstrates the potential of microstructural single-grain, grain-boundary re-engineering to enhance the properties of recycled magnets. Nd-Fe-B magnets recycling Nd-Cu eutectic spark plasma sintering single-grain grain-boundary engineering fizika kemija materiali Nd-Fe-B magneti recikliranje Nd-Cu evtektik iskrovno plazemsko sintranje inženirstvo mej zrn na ravni posameznega zrna true false true Angleški jezik Slovenski jezik Članek v reviji 2026-05-25 14:15:00 2026-05-25 14:15:12 2026-05-26 04:35:53 0000-00-00 00:00:00 2026 0 0 15 str. Vol. 1050, art. 185605 Jan. 2026 0000-00-00 Zaloznikova Objavljeno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 620.1/.2 1873-4669 10.1016/j.jallcom.2025.185605 262745091 1-s2.0-S0925838825071695-main.pdf 1-s2.0-S0925838825071695-main.pdf 1 E45771BC4FB53DB4272F4319A3FE67D2 a47a3872cc0b3f266edfbb050ce8d6540cfe8f6c829205ca81ce3750e6f717c3 0de43d82-5834-11f1-b0ab-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=234432 https://www.sciencedirect.com/science/article/pii/S0925838825071695 0 0c2a9408-5833-11f1-b0ab-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=234431 Naravoslovnotehniška fakulteta 0 0 0