Complex architectures of Si-infiltrated Polymer-Derived Ceramics: computational design and hybrid additive manufacturing

The thesis introduces a novel hybrid additive manufacturing (AM) approach for the fabrication of complex cellular architectures made of Silicon-infiltrated polymer-derived ceramics with fine resolution and smaller details than those achievable with other ceramics AM approaches. The process involves the 3D printing of a porous polymeric preform through the selective laser melting of polyamide powders combined with preceramic polymer infiltration and pyrolysis. The optimized combination of the printing parameters allows fabricating discs with controlled relative density of 52%. Polycarbosilane was used to infiltrate the preform and to obtain the polymer-to-ceramic conversion into amorphous SiOC/SiC ceramics. Despite the high shrinking of ~25%, the parts maintained their pristine shape without distortion or macrocracks. Few cycles of infiltration ana pyrolysis were used to increase the relative density from 30% to 90%. The final densification was achieved with liquid silicon infiltration at high temperature producing the crystallization of the ceramic phase (derived directly from the precursor). Crystalline βSiC and Si composed the final nearly fully dense (98.3%) ceramic part with a volume fraction of 45% and 55%, respectively. The final Si-βSiC ceramics had a biaxial strength of 165 MPa. The process was expanded to the production of geometrically complex architectures thanks to the development of a computational design tool. It allows the generation of cellular structures with tunable topology and a quick parametrization of the geometrical quantities. The architectures of the rotated cube and the gyroid with 25 mm diameter, 44 mm height and 67% of geometric macroporosity were generated and used for the fabrication. The process was extended to the production of a wide range of polymer-derived ceramics using different preceramic polymers. Polycarbosilane, polycarbosiloxane, polysilazane and furan resin were used for the fabrication of SiC, SiOC, SiCN and C ceramics, respectively. The final densification was achieved with an optimized liquid silicon infiltration treatment on four different ceramics. The components had a final diameter of 19 mm and height of 33 mm and maintained their complex shape. The Si-βSiC ceramics, obtained with a reactive silicon infiltration, had a maximum true density of 3.173 g/cm3, with apparent density of 2.966 g/cm3 and a relative density of 0.935. The βSiC, RB-βSiC and Si composed the material with 38%, 58% and 4% of volume fractions, respectively. A maximum compressive strength of 25 MPa was achieved by these architectures, which is more than twice that found in literature. Also, a superior oxidation resistance at high temperature was assessed with respect to several SiSiC ceramics found in literature. Furthermore, Si-βSiC parts with much smaller features (e.g., gyroid surface thickness of 0.185 mm) than those achievable using binder jetting and denser struts (0.957) than those obtainable through the replica method were manufactured.