Development of zirconia-based ceramics stabilized with different yttria contents shaped by extrusion 3D-printing

In this study, zirconia-based ceramics doped with different yttria contents (3, 4 or 5 mol.%) were processed by a material extrusion additive manufacturing technique, Direct Ink Writing (DIW). A gel-based approach, using polyethylene glycol (PEG), Laponite® nano-clay and Dibutyl Phthalate (DBP), was used for the development of ceramic inks with solid load ≈31 vol% and suitable rheological properties to be processed by DIW. Prismatic and cylindric samples were printed (crossed layers at 90°; print speed = 10 mm/s; nozzle Ø = 0.63 mm), dried, debinded and pre-sintered (up to 1100 °C for 2 h), being finally sintered at 1550 °C for 2 h. The sintered samples were evaluated by their microstructure, phase composition and relative density. The hardness and Young's modulus of the sintered samples, were evaluated locally, by dynamic nanoindentation varying the indentation loads: 250 mN → 1960 mN. The three sintered sample’ groups showed similar relative density (≈90 %), but different proportions of the three ZrO2 polytypes (monoclinic, tetragonal, and cubic) as crystalline phases in their composition. The microstructure of the sintered groups was characterized by bimodal grain size distributions, with larger grain sizes as yttria concentration increased and, consequently, higher presence of cubic phase and translucency. Vickers hardness of 1023 HV, 921.4 HV and 896.9 HV and fracture toughness of 5.45 MPa m1/2, 4.30 MPa m1/2 and 4.15 MPa m1/2 were obtained for 3Y-TZP, 4Y-PSZ and 5Y-PSZ, respectively, both influenced by relative density.