EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

3D printing of lightweight mullite honeycomb structures could be successfully demonstrated by the FDM (Fused Deposition Modeling) technique. To achieve 3:2 mullite from preceramic polymers, continuous ceramic filaments containing an alumi-na powder, a polysiloxane polymer and EVA (Ethylene vinyl acetate) as a thermo-plastic component with a diameter of 1.75 mm were made. A temperature above 1550°C was needed to fully convert the alumina and the SiO2 residue of the pol-ysiloxane powder into pure mullite. To obtain a dense microstructure, a sintering aid (0, 0.5 and 1 wt.% MgO) was used to investigate the densification process. Sintering of the sample with 1 wt.% MgO for 5h at 1600°C, a dense mullite structure could be achieved. Viscosity of all three thermoplastic feedstocks and their sintering behavior (SEM, XRD) was investigated to understand the effect of MgO content and sintering dwell time. Rectangular probes were printed in vertical and horizontal direction for four-point flexural test. Based on the results, printing direction and sintering additive strongly affected the mechanical strength. Interestingly, using MgO, no significant change in mechanical behavior influenced by the printing direction could be ob-served.