Abnormal grain growth inhibition of extrusion-based 3D-Printed 3Y-TZP ceramics sintered by flash sintering

This study investigated the combination of Direct Ink Writing (DIW) and Flash Sintering of zirconia stabilized with 3 mol. % Y2O3 (3Y-TZP). The samples were printed in two stacking configurations, and flash sintering was performed without current ramp control (FS) and using current ramp (CRFS) for comparison purposes. In both conditions, an electric field of 80 V cm-1 and a current density of 150 mA mm-2 were applied. The physical, microstructural, and mechanical properties of the printed samples were evaluated. The stacking configuration influenced both the grain size gradients and mechanical properties. Furthermore, controlling the current density ramp resulted in a slight homogenization of the grains' size across different regions of the sample (core, edge, and flat surfaces). The presence of zirconia polymorphs, such as ZrO2-t and ZrO2-c, as well as a distorted form of the tetragonal phase (ZrO2-t'), was observed in the samples. These phases were affected by both the printing strategy and the current ramp control during the flash sintering step. In addition, the samples demonstrated typical values of Vickers hardness for 3Y-TZP (ranging from 10.5 to 11.8 GPa) and fracture toughness (ranging from 3.6 to 4.7 MPa m1/2), with a minor current density ramp control influence. Therefore, both FS and CRFS techniques represent viable pathways for producing dense 3D printed ceramic materials.