Marianna Rinaldi

In this work, polyether‐ether‐ketone (PEEK) – magnetite nanocomposites, having filler content of 50, 60, and 70 wt%, have been developed and 3D‐printed via Fused Filament Fabrication to manufacture high‐performance space‐compliant soft magnetic parts. The nanocomposites present high thermal stability and high transition temperatures typical of the high‐performance PEEK matrix. Mechanical properties show increased stiffness up to 12.6 GPa of elastic modulus, but reduced tensile strength and ductility due to the high content of ceramic nanofiller. The 3D‐printed magnets present soft magnetic features, matching the properties of bare magnetite particles but with a lower, although still high, saturation magnetization (up to 52 Am²/kg), which scales with the particle percentage in the non‐magnetic polymer matrix. This confirms the effectiveness of both the extrusion and 3D printing processes in upholding the structural integrity of the magnetic filler. The electrical insulating nature, which prevents eddy current losses, ease of manufacturing complex shapes, and recyclability make these materials promising for 3D‐printed magnetic components in space applications, supporting sustainable future space exploration.Highlights: Magnetite/high performance polymer 3D‐printable nanocomposites were developed. Magnets with interesting soft magnetic properties were 3D‐printed. The polyether‐ether‐ketone matrix grants suitability for space applications.

Electric motors are ubiquitous on spacecraft and their smooth operation relies on the presence of naturally magnetic materials. The employment of conventional metal‐based magnets causes some inconveniences such as high values of specific gravity and the limited reproducibility of complicated geometries. The introduction of novel polymer‐based magnetic materials processed via additive manufacturing represents a brilliant answer to these needs. This paper describes the first‐time development of a polyether ether ketone‐magnetite (Fe₃O₄) soft magnetic composite. The material was prepared by adding 50 wt% magnetic microparticles to the polymeric matrix. The composite material was extruded in form of filaments and 3D printed via fused filament fabrication. The thermomechanical characterization demonstrated the stability of the material at both processing ad use temperatures, while the magnetic analysis reported a typical soft magnetic behavior with 25.7 A m² kg⁻¹ magnetization at saturation. The measured properties were employed as inputs for the finite element analysis of an axial flux brushless direct current electric motor, as a proof of concept. The simulation of the electromechanical behavior of the motor showed promising performance for the composite material, reaching the maximum deliverable torque of about 0.8 Nm (compliant to small power aerospace applications such as micro‐actuators and mini control moment gyroscopes) with weight savings up to 50%.

Thermally conductive but electrically insulating polymer matrix composites are of great interest in many engineering applications such as thermal management applications (i.e., heat sinks in microelectronic packaging, cooling of mechatronic components and mechanisms). Among possible functional fillers, hexagonal boron nitride seems to be one of the most promising choice due to its high thermal conductivity, and in this work, it was used as filler of polyamide 6 matrix. The resulting composites were first prepared in the form of pellets, extruded into filaments, and successively 3D printed, with the aim to study and compare the thermal performances of the 3D printed samples to the ones manufactured using traditional compression molding technique. The thermal conductivity of 25% wt and 45% wt loaded compression molded samples were 1 and 2.5 W/mK, respectively, while the neat polymer showed a thermal conductivity of 0.29 W/mK. 3D printed samples showed the same trend, namely increasing thermal conductivity with filler amount, despite a great influence of the 3D printing processing parameters (i.e., melt rheology and printing temperature), which lower the resulting thermal conductivity. 3D printed 25% and 45% by weight loaded samples showed a through plane thermal conductivity of 0.67 and 0.92 W/mK, respectively, and in‐plane thermal conductivity of 0.96 and 1.52 W/mK due to the presence of porosity and filler alignment along the printing direction.

Fused filament fabrication is an additive layer manufacturing technique. It was extensively used at the beginning for the manufacturing of prototypes, and it has been adopted during the last few years for the manufacturing of fully functional components. Polyetheretherketone (PEEK) has been thoroughly investigated as a composite matrix because of its outstanding mechanical properties and thermal and chemical stability. This study is focused on PEEK nanocomposites with different amounts of carbon nanotubes (CNTs) (i.e. 3, 5, 10 wt%) produced in the form of a filament and successively 3D printed. The influence of the CNT presence on printability was studied and correlated to the nanocomposite feedstock thermal and microstructural properties, defining a substrate temperature processability window. Interestingly the addition of CNTs significantly limits the processability window due to the influence on the crystallization process and viscosity. Moreover, the thermal and mechanical properties of 3D printed bulk samples were investigated in view of the PEEK/CNT nanocomposite feedstock properties. © 2021 Society of Chemical Industry

Recent improvements in additive layer manufacturing (ALM) have provided new designs of geometrically complex structures with lighter materials and low processing costs. The use of additive manufacturing in spacecraft production is opening up many new possibilities in both design and fabrication, allowing for the reduction of the weight of the structure subsystems. In this aim, polymeric ALM structures can become a choice, in terms of lightweight and demisability, as far as good thermomechanical properties. Moreover, provided that fused-deposition modeling (FDM) is used, nanosats and other structures could be easily produced in space. However, the choice of the material is a crucial step of the process, as the final performance of the printed parts is strongly dependent on three pillars: design, material, and printing process. As a high-performance technopolymer, polyether ether ketone (PEEK) has been adopted to fabricate parts via ALM; however, the space compatibility of 3D-printed parts remains not demonstrated. This work aimed to realize a nanosat polymeric structure via FDM, including all the phases of the development process: thermomechanical design, raw material selection, printing process tuning, and manufacturing of a proof of concept of a technological model. The design phase includes the application of topology optimization to maximize mass saving and take full advantage of the ALM capability. 3D-printed parts were characterized via thermomechanical tests, outgassing tests of 3D-printed parts are reported confirming the outstanding performance of polyether ether ketone and its potential as a material for structural space application.

Permanent Rare Earth magnets are becoming more and more important in efficient motors and generators with high energy density. Among them NdFeB magnets are the most employed, with NdFeB having higher remanence, high coercivity and energy product. Nevertheless,their poor corrosion resistance makes them susceptible to degradation of the magnetic properties. One possible solution is the development of innovative polymeric composite magnetic materials. The preparation of NdFeB powders filled polymeric matrix (PEEK), with a double goal of protecting the magnetic alloy is proposed, thus preventing it from corrosion, and to realize a new material that can be shaped in the form of filaments. This material was used as feedstock in the 3D printing process to produce high performance magnets with customized and optimized design. The PEEK-NdFeB filaments were produced with three percentages of filler amount(i.e. 25, 50 and 75 wt%). PEEK neat filaments were produced as reference. The influence of the filler on the main thermomechanical properties of the resulting composites, as well as its effect onthe 3D printing process were evaluated by means of different investigation techniques (DSC, DMTA, XRD, tensile testing). The magnetic properties exhibited by Fused Filament Fabrication (FFF) printed parts confirmed the feasibility of employing such a combination of an innovative manufacturing technique and high-performance PEEK-NdFeB compounds.The characterization carried out on both neat and composite filaments evidenced that the presence of the filler slightly decreased the thermal stability, increased the elastic modulus while decreasing ductility and maximum tensile strength. By means of DSC analysis, it was confirmed that the crystallinity is influenced by the presence of the filler. Magnetic measurement performed on the 3D printed parts demonstrate that interesting magnetic properties were achieved, confirming the feasibility of the magnetic 3D printed composite with PEEK.