Materiali ceramici a base di allumina ottenuti con tecnologie di additive manufacturing indirette = Alumina-based ceramic materials obtained with indirect additive manufacturing technologies

The growing demand for high-performance components has driven interest in polymer–ceramic composites processed via Selective Laser Sintering (SLS). This thesis focuses on the formulation, processing, and characterization of PA12–alumina (Al₂O₃) composite powders for SLS, aiming to increase ceramic content while retaining acceptable printability. Various preparation routes were explored, including mechanical and chemical approaches. Mechanical mixing was performed using Turbula and high-shear blender mixers, while the Thermally Induced Phase Separation (TIPS) method was also tested as a chemical approach. However, the TIPS method proved to be significantly more complex and time-consuming compared to mechanical mixing. It required high-temperature operation, large volumes of solvent, and prolonged processing times, resulting in high energy and material consumption. These drawbacks made TIPS neither sustainable nor practical for composite powder preparation within the scope of this study. Consequently, mechanical blending was favored and pursued further. In contrast, the mechanical mixing techniques showed more promising results. Composite powders containing alumina from 30 to 80 wt.% were prepared and characterized to evaluate their morphology, homogeneity, and flowability. Scanning Electron Microscopy (SEM) was conducted on the powders to compare the effectiveness of the two mechanical mixing methods. The results demonstrated that both mechanical mixing methods, Turbula and high-shear blender, led to the formation of pseudo-composite structures. In these structures, the alumina phase formed a porous shell around the PA12 particles, and bonding during the SLS process occurred indirectly, as the melted polymer penetrated this shell to create bridges with neighboring particles. A detailed comparison of powder properties and printed part quality revealed the superiority of the blender over the Turbula mixer. SEM analysis showed that blender-mixed powders had a noticeably higher amount of alumina adhered to the surface of each PA12 particle, resulting in more homogeneous and stable coatings. This improved distribution was attributed to the higher frequency of collisions between alumina and polymer particles during blending, which enhanced Van der Waals interactions and adhesion. In contrast, Turbula mixing, with its lower mechanical energy, resulted in significant agglomeration, reduced flowability during powder spreading, and poor recoating behavior. The printed parts from Turbula-mixed powders exhibited numerous internal and surface defects, including voids and poor densification, whereas parts produced from blender-mixed powders had fewer defects and better surface quality. After establishing the blender as the more effective mixing technique, additional experiments focused on enhancing printability at high ceramic loadings. It was found that while fine alumina particles (~1 µm) compromised binder flow and limited successful fusion, using coarser alumina (~5 µm) improved the outcome. The larger particles created a more porous shell around the PA12, which better facilitated the penetration of the melted polymer and improved interparticle bonding. This adjustment enabled the successful printing of composite powders containing up to 80 wt.% alumina with acceptable quality. Overall, the study demonstrates the feasibility of incorporating high ceramic content into PA12 matrices for SLS applications, with insights into powder preparation, printing behavior.