Élaboration et caractérisation de céramiques 3D en couplant la chimie des précurseurs avec l'impression 3D

Advanced 3D ceramics with complex architectures are currently in increasing demand for various applications under severe conditions. They present important properties such as chemical stability, oxidation and corrosion resistance and important mechanical properties making them reliable components in aerospace, electronics and biomedical field. In particular, Si-based ceramics are characterized by excellent thermochemical properties and creep resistance. Additive manufacturing (AM) is the technology of choice to design near net-shape objects with a perfect control of the geometry and porosity at different scales. However, traditional ceramic powders are difficult to print due to their hardness and brittleness. Preceramic polymers are suitable to 3D printing as they can be easily editable by chemical modification at molecular state and adapted to different AM technologies. In this work, we combined 3D printing with the Polymer-Derived Ceramics (PDCs) route to fabricate complex geometrical Si-based ceramic objects. Two AM technologies were studied: Fused Deposition Modeling (FDM) based on fusion of a thermoplastic filament and UV-LCD based on resin photopolymerization under UV radiation. Characterization of preceramic polymers and the derived 3D ceramic objects were systematically presented. The influence of the preceramic polymers composition and structure on the 3D printing ability was highlighted. This will facilitate the polymer selection and the rational design for fabricating tailor-made 3D printed PDC components. First, we designed 3D silicon carbonitride (SiCN) and silicon carbide (SiC) ceramics through indirect 3D printing by coupling FDM with a replica approach. Polylactic acid (PLA) honeycomb patterns were first printed by FDM and dip-coated with polyvinylsilazane (PVZ) or allylhydrydopolycarbosilane (AHPCS), respective precursors of SiCN and SiC. Prior to dip-coating, preceramic polymers were chemically crosslinked with dicumyl peroxide. Subsequent pyrolysis under controlled atmosphere allows thermal crosslinking of polymers at 130°C, decomposition of PLA at 320°C and conversion of preceramic polymers into the corresponding 3D ceramics at 1000°C. Volume shrinkage was observed due to decomposition of PLA and polymer-to-ceramic conversion. A tentative to fabricate SiBC (derived from boron-modified AHPCS) was also performed where we studied the effect of boron on the behavior of Si-C systems. Second, we prepared Si-based photocurable preceramic polymers, precursors of SiOC, SiC and SiCN, according to two approaches: i) mixing the polymer with a commercial photo-resin and ii) synthesis of a UV-sensitive polymer by functionalizing the preceramic backbone with photosensitive units. We then applied UV-LCD direct printing on such polymers. Several parameters influencing the printing resolution and quality were considered during UV-LCD: UV exposure time, thickness of each layer and number of layers. In the first approach, two types of SiOC ceramic precursors were used: methyl silsesquioxane (Silres MK) which will be dissolved in suitable solvents and liquid polymethylhydrosiloxane (PMHS). These polymers were mixed in a controlled ratio with a commercial photo-resin. A better mechanical behavior of the pellet-shaped ceramic is observed with Silres MK due to its higher ceramic yield. In the second approach, UV-curable Silres MK preceramic polymer is prepared either by a simple mixture with photosensitive agents (Trimethylolpropane triacrylate (TMPTA) and/or 1,6 hexanediol diacrylate (HDDA) or by grafting triacrylate functions of 3-(trimethoxysilyl) propyl methacrylate (TMSPM) on the Si-OH of Silres MK. 3D SiOC ceramics obtained after pyrolysis show a conservation of the pellet shape almost without cracks. Our approach was also translated to the fabrication of SiC and SiCN non-oxide ceramics proving the versatility of this technique for synthesizing photosensitive preceramic oxide and non-oxide polymers.