Direct ink writing of 3Y-TZP ceramics using PEG-Laponite® as additive

This study investigated a new colloidal ink, containing Laponite® nanoclay as additive, to develop ZrO₂-based ceramic prototypes by Direct Ink Writing (DIW). The ink developed contained 31 vol% 3Y-TZP as solid load and 69% v/v of gel containing 7.5% (w/w) Laponite®, polyethylene glycol (PEG), and dibutyl phthalate. The rheologyical behavior of this ceramic ink was analyzed and its extrudability was optimized. The samples were DIW 3D-printed at a speed of 10 mm/s with nozzle diameter of 0.41 mm. After drying for 24 h, the zirconia samples underwent debinding and were pre-sintered at 1100 °C under a heating rate of 1 °C/min. After pre-sintering, the samples were sintered at 1550 °C for 2 h. Subsequently, the sintered samples were characterized by Scanning Electron Microscopy and X-ray diffractometry. Fracture toughness was measured by Vickers indentation, whereas nano-hardness and Young's modulus were assessed by dynamic Vickers nanoindentation (250–1960 mN loads). A relative density of 89.3 ± 0.5% was found. The following crystalline phases were observed: monoclinic-ZrO₂ (34%), tetragonal-ZrO₂ (31%), and cubic-ZrO₂ (35%). This behavior is probably due to the segregation of Y⁺³ between the zirconia grains, favored by the presence of Laponite® nanoclay during the sintering process. The microstructure of the prototypes showed two distinct populations of ZrO₂ grains with average particle sizes of 1 μm (monoclinic and tetragonal phases) and >5 μm (cubic phase). Vickers hardness (HV_1000gF) was 952 ± 40 HV and fracture toughness was 4.6 ± 1.1 MPa m^1/2. A Young's modulus of ∼200 GPa and hardness values of 1837.9 and 1943.3 HV were found for loads of 250 and 1960 mN, respectively.