Continuous fiber-like 316L-Al2O3 composites by one step co-extrusion 3D printing: an experimental and computational study

Continuous fiber-like 316L-Al2O3 composites filaments and scaffolds were produced by co-extrusion Direct Ink Writing (DIW) in a customized setup. The rheological properties of the inks were optimized to ensure a continuous core and a shell capable of retaining its shape without slumping and bridging upon printing. The core area over the total area of the composite filaments was controlled by adjusting the printing pressure, allowing to tune their ratio from ~6 % to ~30 %, while maintaining a constant strut diameter of ~1.5 mm. Sintering temperatures were selected as a compromise between achieving densification of the Al2O3 shell and preventing embrittlement of the 316L core. The 316L ductile behavior was preserved by the Al2O3 shell matrix upon sintering at 1350 ◦C. The potential of the technology was also explored by 3D printing multi-layered 3D scaffolds, which confirmed that the developed inks can withstand direction changes and span distance up to 1.5 mm. The mechanical response of the composites was evaluated through four-point bending tests on filaments, and the results were used as input parameters for finite element simulations aimed at better interpreting the experimental output. The two main factors influencing the mechanical behavior were the core-shell adhesion and the ratio of core diameter to the total filament diameter. 3D scaffolds were tested under compression load, and the results confirmed the effect of core size on their mechanical response. This work highlights the potential of co-extrusion DIW to produce a new class of composite materials possessing continuous reinforcement following the orientation of the printing path posing them at the edge between interpenetrating and continuous fibers composites.