Short-loop recycling of NdFeB trades a reduced ecological burden for a higher sensitivity towards contamination, as the powder is usually further processed as-is. In this investigation, the known effects of common contaminants (O, C, Ni, Cu, and Zn) introduced due to product design choices, namely from coating material and adhesive residue or a lack of corrosion protection, are reviewed. This study focuses on the impact of such contaminants on the magnetic properties and microstructure of recycled magnets via HPMS and re-sintering. Because of the lack of information regarding the practical effects of metallic coating residues, the impact of Ni contamination on the properties of re-sintered NdFeB magnets is assessed. HPMS processed scrap powder is blended with Ni powder and recycled by sintering. It is found that Ni partially substitutes Fe in the φ-phase, as expected from the literature review, leading to detrimental effects on the coercivity and remanence. The formation of an α-(Fe, Ni) phase is observed. The acceptable limit of Ni contamination without detrimental effects is found to be around 0.25 wt.%; however, due to the substitution in the φ-phase, the contamination is irreversible via short-loop recycling and would accumulate over multiple lifecycles.

The recycling of NdFeB magnets is essential to reduce reliance on critical rare earth elements and mitigate the environmental burden of virgin magnet production. Hydrogen Processing of Magnetic Scrap (HPMS) offers an efficient method to extract magnet powders from end-of-life (EOL) products, yet oxidation and microstructural degradation during powder preparation limit the magnetic performance of recycled magnets. In this work, rapid Radiation-Assisted Sintering (RAS) was systematically evaluated for the first time as a consolidation route for HPMS-derived powders. Magnets prepared via RAS exhibited performance comparable to those obtained by conventional sintering. When oxygen uptake during milling was prevented, the addition of 1 wt.% NdH₃ to the already oxygen-burdened recycled powder improved the intrinsic coercivity and squareness of the demagnetization curve. The best-performing samples achieved B_r = 1.18 T, (BH)_max = 263 kJ/m³, and H_ci = 742 kA/m at 100 °C, surpassing the properties of the original EOL magnets. Furthermore, the study revealed that, when the HPMS powder fragments preferentially break along grain boundaries, the resulting near-equilibrium powder particles exhibit limited growth, thereby restraining grain coarsening. These findings highlight the strong potential of RAS for more energy-efficient magnet-to-magnet recycling and provide new insight into optimizing HPMS powder processing to achieve enhanced magnetic performance.

Demagnetization is an essential step for the demounting and safe handling of end-of-life NdFeB. Thermal demagnetization in air is a straightforward option to demount adhesive-fixed or segmented magnets. However, this process is suspected to increase the uptake of contaminants like O, C and Zn from coatings and adhesives, potentially degrading the recyclate quality. This study tests the effects of thermal demagnetization in air at 400 °C for 15 to 240 min on variously coated samples with different initial oxidation levels. Furthermore, the possible reversal of the contaminant uptake is explored. Samples with low previous oxidation levels showed significant uptake in oxygen with a minimal diffusion depth, while the uptake depended on the used coating. The best protectiveness was achieved with NiCuNi with an increase in oxygen of only around 30%. Epoxy (up to ~130% O uptake) and Zn coatings (up to ~80% O uptake) disintegrated during the treatment and offered less protection but still made a difference compared to uncoated samples (up to ~220% O uptake). Samples with high initial oxidation levels show no clear tendency towards further oxygen uptake and the carbon uptake is generally low, likely due to contemporary epoxy coatings featuring a passivation underneath as a barrier layer. Zn infiltration, which carried organic debris, was observed. Short demagnetization times proved to be favorable for limiting the depth of the diffusing contaminants. Mechanical coating removal after thermal demagnetization in air can mitigate the contaminant uptake, producing clean, recyclable end-of-life material.

Highly filled magnetic filaments require binder systems that balance powder loading, melt flow, filament strength, and strand stability during material extrusion (MEX). Here, a polyolefin-based binder composed of a thermoplastic elastomer and grafted polyolefin (TPE + gPO) was used to prepare SmFeN- and SrFe12O19-based magnetic filaments. The feedstocks were compounded, extruded into 2.85 mm filaments using a single-screw extrusion line with automatic spooling, and printed by MEX into ring-shaped specimens. Thermogravimetric analysis confirmed high powder contents, with residual masses of approximately 89 wt.% for SmFeN and 85 wt.% for SrFe12O19. The filaments showed good dimensional control, with a diameter of 2.85 ± 0.07 mm and ovality <= 0.017 mm. Small-amplitude oscillatory rheology at 200-240 °C showed pronounced shear-thinning behavior and an elastic-dominant response (G’ > G’’) over 0.01-100 Hz, supporting flow through the nozzle and shape retention after deposition. Mechanical testing confirmed sufficient handling performance, with maximum flexural stress of 36.1 ± 0.1 MPa for SrFe12O19 and flexural modulus up to 5.5 ± 0.2 GPa for SmFeN. The results demonstrate that the TPE + gPO binder provides a suitable processing window for highly filled magnetic filaments for MEX-printed bonded magnets.

Highly filled magnetic filaments require binder systems that balance powder loading, melt flow, filament strength, and strand stability during material extrusion (MEX). Here, a polyolefin-based binder composed of a thermoplastic elastomer and grafted polyolefin (TPE + gPO) was used to prepare Sm₂Fe₁₇N₃- and SrFe₁₂O₁₉-based magnetic filaments. The feedstocks were compounded, extruded into 2.85 mm filaments using a single-screw extrusion line with automatic spooling, and printed by MEX into ring-shaped specimens. Thermogravimetric analysis confirmed high powder contents, with residual masses of approximately 89 wt.% for Sm₂Fe₁₇N₃ and 85 wt.% for SrFe₁₂O₁₉. The filaments showed good dimensional control, with a diameter of 2.85 ± 0.07 mm and ovality ≤ 0.017 mm. Small-amplitude oscillatory rheology at 200–240 °C showed pronounced shear-thinning behavior and an elastic-dominant response (G′ > G″) over 0.01–100 Hz, supporting flow through the nozzle and shape retention after deposition. Mechanical testing confirmed sufficient handling performance, with a maximum flexural stress of 36.1 ± 0.1 MPa for SrFe₁₂O₁₉ and a flexural modulus up to 5.5 ± 0.2 GPa for Sm₂Fe₁₇N₃. The results demonstrate that the TPE + gPO binder provides a suitable processing window for highly filled magnetic filaments for MEX-printed bonded magnets.