Investigation of printing and post-processing parameters for enhancing the high-strength of zirconia ceramics via direct ink writing

Direct ink writing (DIW) of alumina-toughened zirconia (ATZ) and 3 mol% yttria-stabilized zirconia (3Y-TZP) enables fabrication of complex parts, not achievable by conventional methods, providing the printing parameters are optimized. This study investigates the influence of the nozzle diameter, printing strategy, humidity, line spacing and layer thickness on the quality of the printed material. The drying protocols were optimized and the printing parameters were correlated to the sintering shrinkage and density, mechanical performance and defect formation. Optimal results were obtained when printing at 95 % non-condensing relative humidity with a 75 % line spacing and layer thickness relative to the 200 µm nozzle, using a 90° raster angle and contour design. Drying was done at 30°C with a gradually reducing humidity from 95 % to 40 % over 7 days. Sintered ATZ and 3Y-TZP had densities of 98.4 ± 0.6 and 99.1 ± 1.8 % and characteristic strengths of 859 (m = 10.7) and 841 MPa (m = 4.4).