Direct ink writing of chopped carbon fibers reinforced polymer-derived SiC composites with low shrinkage and high strength

The chopped carbon fiber reinforced SiC (C_f/SiC) composite has been regarded as one of the excellent high-temperature structural materials for applications in aerospace and military fields. This paper presented a novel printing strategy using direct ink writing (DIW) of chopped fibers reinforced polymer-derived ceramics (PDCs) with polymer infiltration and pyrolysis (PIP) process for the fabrication of C_f/SiC composites with high strength and low shrinkage. Five types of PDCs printing inks with different C_f contents were prepared, their rheological properties and alignment of carbon fiber in the printing filament were studied. The 3D scaffold structures and bending test samples of C_f/SiC composites were fabricated with different C_f contents. The results found that the C_f/SiC composite with 30 wt% C_f content has high bending strength (～ 7.09 MPa) and negligible linear shrinkage (～ 0.48%). After the PIP process, the defects on the C_f/SiC composite structures were sufficiently filled, and the bending strength of C_f/SiC composite can reach up to about 100 MPa, which was about 30 times greater than that of the pure SiC matrix without C_f. This work demonstrated that the printed C_f/SiC composites by using this method is beneficial to the development of the precision and complex high-temperature structural members.     

Engineering of silicone-based mixtures for the digital light processing of Åkermanite scaffolds

Silicones mixed with oxide fillers are interesting precursors for several bioactive glass-ceramics. A key point is represented by the coupling of synthesis and shaping, since highly porous bodies, in form of foams or scaffolds, are first manufactured with silicones in the polymeric state, at low temperature, and later subjected to ceramic transformation. After successful application of direct ink writing, the present study illustrates the tuning of silicone-based mixtures in order to form åkermanite (Ca₂MgSi₂O₇) reticulated scaffolds by digital light processing. This implied the selection of commercial silicones, producing stable and homogeneous blends with a photocurable resin and enabling the manufacturing of defect-free printed scaffolds, before and after firing, without fillers. The blends were further refined with the introduction of fillers, followed by firing at 1100 °C, in air. Optimized samples (from H44 resin) and reactive fillers (including up to 4.5 wt.% borax additive), led to crack-free and phase-pure scaffolds with microporous struts.     

Suitability of Biosilicate® glass-ceramic powder for additive manufacturing of highly porous scaffolds

The Biosilicate® glass-ceramic is one of the most promising alternatives to the 45S5 Bioglass® in terms of bioactivity, osteoconductivity, osteoinductivity, non-cytotoxicity, and antibacterial properties, with significant advantages in the manufacturing of specific components of complex shapes for bone tissue application. Unlike in 45S5 glass, the crystallization does not lead to a degradation of bioactivity. In the present paper, we explored the suitability of Biosilicate® for the manufacturing of highly porous scaffolds (porosity of 50–80 vol%) by using modern additive manufacturing technologies, such as direct ink writing (DIW) and digital light processing (DLP). Both techniques could be easily applied to fine powders of Biosilicate® mixed with fugitive binders. Significant densification of the struts, despite the limited powder packing, could be achieved using liquid-assisted sintering, in turn, triggered by the phosphate-enriched residual glass phase, already at 1000 °C. The strength-to-density ratio could be variously tuned (from 1.5 to 9.5 MPa cm³/g), especially with DLP-derived samples, by adjusting both the firing temperature and the scaffold topology.     

Direct writing of textured ceramics using anisotropic nozzles

Direct writing is a unique means to align anisotropic particles for the fabrication of textured ceramics by templated grain growth (TGG). We show that alignment of tabular barium titanate (BT) template particles (20–40 μm width and 0.5–2 μm thickness) in a PIN-PMN-PT matrix powder (d₅₀ = 280 nm) is significantly improved during direct writing using anisotropic nozzles at high printing rates. The particle orientation distribution in as-printed filaments, and the texture orientation distribution in sintered ceramic filaments are shown to directly correlate with COMSOL Multiphysics-predicted torque distributions for direct writing with aspect ratio 2, 3 and 5 oval nozzles. Electromechanical strain properties of the textured piezoelectric ceramics significantly improved relative to random ceramics when printed with anisotropic nozzles. Simulations of aspect ratio 20 nozzles and nozzles with interior baffles demonstrate significantly increased torque and near elimination of constant shear stress cores (i.e. plug flow).