Sviluppo di magneti compositi innovativi per la stampa ALM di componenti aerospaziali = Development of innovative polymeric composite magnets for the ALM printing of aerospace components

The use of permanent magnets is crucial for several space applications as motors, sensors, actuators, etc. One of the most used magnetic alloy for space application is Neodymium Iron Boron (NdFeB), as it is characterized by superiormagnetic properties (high remanence, high coercivity and energy product), nevertheless it is known to offer very poor corrosion resistance. Even though the sintering process grants the best achievable magnetic performance, the low corrosion resistance of sintered NdFeB magnet limites the use of these components as they easily degrade even in controlled environments, as clean rooms. In this regard, several issues linked to the corrosion of NdFeB magnets during Long Term Storage were experienced by the European Space Agency (ESA) in the frame of different missions. Failure investigations were conducted at the European Space Agency facility in the Netherlands (ESTEC) to understand the origin of this issue that was identified in the corrosion susceptibility of the bulk material. A qualification of a large variety of protecting coatings was performed in close collaboration with industrial partners of the European space industry. Despite protective coatings were found in general, to be a valid solutions, still in some cases they were proven not solve completely the problem. The use of polymeric composite magnetic materials, made of a polymeric matrix binding together and preserving the magnetic alloy powder, might be another possible solution. This could lead to to the realization of lighter, corrosion resistance materials althought with lower magnetic properties than sintered magnets. Moreover, considering the recent development of many advanced manufacturing technologies, as additive layer manufacturing (ALM), another possible advantage of introducing polymeric magnetic composites is their 3D printability, paving the way to completely new designs of magnetic components. This PhD was devoted to the study, synthesis, characterization and 3D printing of innovative polyetheretherketone (PEEK) and NdFeB permanent magnets. The matrix was chosen being PEEK a space compliant material, offering superior physical-chemical, thermal and mechanical properties. Two different PEEK blends were prepared and used starting from commercially available PEEK powders. The NdFeB alloy in form of powder (either melt spun or gas atomized) was selected as magnetic filler. Then composite masterbatches were realized by planetary mixing and extrusion to prepare filaments containing different amounts of filler (i.e. 25%, 50%, 75%, 80% wt) suitable for Fused Deposition Modeling (FDM). All filaments were successively FDM printed and fully characterized from thermal, mechanical and magnetic perspective. These composite materials exhibit superior corrosion resistance, lower densities and good 3D printability with respect to the sintered ones confirming that the development of a new corrosion resistant magnetic material has been successfully achieved in the frame of this work. This thesis contains the description and a critical discussion of the experimentation carried out during the PhD, as well as concluding remarks about possible advantages and drawbacks in the use of the newly introduced ALM printed polymeric composites magnets.