Material extrusion based additive manufacturing of large zirconia structures using filaments with ethylene vinyl acetate based binder composition

This study demonstrates the feasibility of fabricating large complex zirconia structures using a material extrusion-(MEX) based additive manufacturing process, called fused deposition modeling (FDM) or fused filament fabrication (FFF). For this purpose, a feedstock based on ethylene-vinyl acetate and stearic acid containing 45 vol.-% zirconia powder was extruded into filaments and used for printing on a consumer-grade FDM/FFF printer. To detect structural failures after each processing step, disks made out of 4 printed layers were selected. After printing, debinding and sintering a fractography analysis of the disks was evaluated using an optical and scanning electron microscope to identify the defects. To avoid defect formation during printing, a new approach, dynamic infill technique, was employed and resulted in void-free printed disks with a smooth top surface. This approach was essential to study the origin of failures in the post-processing steps. Model free-kinetic analysis was used to investigate the activation energy of the binder decomposition and to design a thermal debinding program with a constant 0.1%/min mass loss rate of the thermoplastic binder. Based on the kinetic studies it could be demonstrated that sufficient thermal binder burnout could be achieved by integration of solvent extraction and wicking debinding steps. Using ring-on-ring test it could be observed, that an edge-initiated failure resulted in low average strength (91 MPa) of the sintered disks. Finally, printed and defect-free sintered 120 mm high vase could be successfully achieved using the model free-kinetic designed debinding program.