Advancing recycling of end-of-life NdFeB permanent magnets for additive manufacturing

Recycling end-of-life rare-earth-based permanent magnets, which are key components across many strategic sectors, offers a promising solution to address the geopolitical, economic, and environmental issues of the rare-earth industry. Among the proposed strategies, the magnet-to-magnet approach, where end-of-life magnets are transformed into fine powders to manufacture new magnets, has attracted considerable attention as it allows for complete material recovery and waste minimization through environmentally friendly processes. While the best performance can be obtained by using the powders to produce sintered magnets, additive manufacturing, especially the fused filament fabrication 3D printing technology using magnetic polymer composites as inks, has emerged as a promising and sustainable method for manufacturing bonded permanent magnets with complex geometries while minimizing waste production. This PhD research aims to advance sustainable methods for producing NdFeB magnets by recycling EoL products. The primary focus was on exploring magnet-to-magnet recycling techniques to create powders with micrometer-scale dimensions and magnetic properties similar to those of the original magnets, thus enabling their use in producing novel permanent magnets, particularly through 3D printing. The process involved pulverizing the magnets through hydrogen decrepitation, followed by high-energy ball milling to generate fine powders. These powders were then used to create dense pellets, demonstrating the feasibility of manufacturing new permanent magnets from recycled materials. Additionally, preliminary studies with commercial NdFeB powders were conducted to evaluate the potential for producing NdFeB-based polymer composites and 3D printing filaments. Furthermore, advanced modeling and simulations were used to study the alignment of recycled NdFeB powders within polymer matrices under an applied magnetic field, offering valuable insights for the production of high-performance anisotropic permanent magnets via magnetic-field-assisted 3D printing. The research findings confirm that sustainable methods for producing NdFeB magnets from recycled end-of-life products are indeed feasible. Key processes, such as hydrogen decrepitation and high-energy ball milling, were optimized to generate micrometer-sized powders with magnetic properties comparable to those of original magnets. While recycled magnets may not fully replicate the performance of their original counterparts, they can effectively bridge the gap between ferrites and high-performance NdFeB, making them suitable for lower-performance applications. The study also demonstrated that dense pellets with uniform magnetic characteristics can be produced, underscoring the potential for using recycled powders to manufacture new magnets. Additionally, preliminary investigations with commercial NdFeB powders indicated that magnetic polymer composites with controlled thermal and magnetic properties can be developed for 3D printing applications. Furthermore, the research showed that recycled powders can be aligned within polymer matrices using an external magnetic field, with alignment efficiency influenced by factors such as field strength, particle shape, and initial orientation, as well as interparticle interaction, thereby enhancing their applicability in 3D printing. These findings contribute significantly to the development of high-performance permanent magnets from recycled materials, promoting sustainability in magnet production.