Influence of Sintering Orientation on Microstructures of 3D-Printed Zirconia

Objectives: This study aimed to evaluate the influence of sintering orientation on the microstructures of 3D-printed zirconia.
Methods: 3D printer utilizing zirconia slurry was used to fabricate green bodies, followed by sintering to produce the final zirconia specimens. Three groups were compared based on sintering orientation: Group A (parallel to the 3D-printing orientation), Group B (perpendicular, with the Y-axis as the sintering height), and Group C (perpendicular, with the X-axis as the sintering height). Shrinkage ratio, bulk density, scanning electron microscopy with energy-dispersive spectrometry, X-ray diffraction, and micro-computed tomography tests were conducted.
Results: There were no significant differences in shrinkage ratio, density, or phase composition among groups. Grain size distribution was consistent across groups, with over 50% of grains measuring between 0.3 and 0.6 µm. Reduced zirconium content was observed in interlayer bonding regions prior to sintering, a phenomenon that resolved post-sintering in all groups. However, Group B and Group C exhibited less compact grain boundaries and increased microdefects compared to Group A. Cracks, exclusive to Group C, primarily initiated and propagated in interlayer regions. SEM analysis of fracture surfaces revealed intergranular failure, indicating bonding and subsequent fracturing of grains.
Conclusions: Sintering orientation affected the microstructures of 3D-printed zirconia. Perpendicular orientations were associated with looser grain boundaries, increased microdefects, and the presence of cracks.