3% yttria-stabilized tetragonal phase zirconia ceramics (3Y-TZP) show a significant potential in aerospace application due to their low thermal conductivity, excellent high-temperature stability, and mechanical strength. However, it is difficult for conventional forming methods of porous ceramics to meet the requirements for complex structural designs. Digital Light Processing (DLP) is an important additive manufacturing method to fabricate components with complex geometries and high-precision, which can balance micron-scale resolution and efficient production. The macro-microporous structure of multiscale porous ceramics can take full advantage of multilevel porosity advantages, balancing thermal insulation and mechanical properties. Therefore, in this paper, DLP technology was combined with the pore-forming agent method to achieve the controllable molding of zirconia ceramics with multilevel pores. The printability of high solid-loading porous ceramic slurry was optimized, and the effect of sintering temperature on the microstructural evolution and mechanical properties of ceramics was investigated.

The ceramic slurry was prepared through batched addition of ball-milled and dried 3Y-TZP powder into a photosensitive resin premix, followed by thorough homogenizationin a model DSG2300Z homogenizer at 1200 r/min. 3Y-TZP slurries with 40% solid loading were prepared with different dispersants. Their rheological behavior was analyzed by a model MCR302 rheometer to identify the optimal dispersant type and content. Subsequently, the slurries with different solid loadings were prepared, and the appropriate solid loading was selected. Based on the optimized parameters, liquid organic pore-forming agent (i.e., polyethylene glycol (PEG) 400) was added at different volume fractions of 5%, 10%, and 15% to replace of the equivalent resin volume fractions. The optimal slurry composition was determined by rheological property.

The green body was prepared using a DLP printer with 405 nm UV light to cure the resin. The argon debinding and air decarbonization-sintering combined processes were then determined by thermogravimetry-differential scanning calorimetry (TG–DSC) on the green body. The ceramic components were subsequently held at different sintering temperatures (i.e., 1400, 1450, 1500 ℃) for 2 h, respectively. The microstructures of 3Y-TZP powder, green body, and sintered ceramics were determined by field-emission scanning electron microscopy (MAIA3 LMH, Tescan Co., Czech Republic). The chemical composition of the ceramic powders and dispersant was characterized using Fourier infrared spectrometry (IRPrestige-21, Shimadzu Co., Japan). The phase composition was analyzed by X-ray diffraction (d8 advance, Bruker Co., Germany). Three-point bending tests were conducted on ceramic specimens (50 mm×5 mm×4 mm) to evaluate the mechanical strength. The span was 20 mm and the load loading rate was 0.5 mm·min^–1. The microstructural porosity was measured by Archimedes water displacement method.

In this study, the slurry formulation for porous zirconia ceramics is optimized. Compared with dispersants KH560 and Solsperse41000, a dispersant KOS110 effectively reduces slurry viscosity. The infrared spectroscopy analysis reveals that KOS110 undergoes esterification reactions with zirconia particles through hydroxyl groups(-OH), thereby enhancing the dispersion of ceramic particles. The slurry viscosity initially decreases and then increases as the content of KOS110 increases, and reaches the lowest value at 3% addition. The yield stress and K value of the slurry are lowest when 3% KOS110 is added, proving that the rheological behavior of the slurry is optimal at this time. Increasing solid loading reduces interparticle distances in the dispersed slurry. When solid content exceeds 50%, the viscosity increases dramatically. Therefore, 50% solid loading can ensure a printability and a high solid content.

The introduction of PEG into 3Y-TZP slurry can form lubricating layers between ceramic particles through free molecular movement, improving the dispersion of the slurry. The optimal rheological performance is achieved at 10% PEG addition. The optimized high-solid 3Y-TZP slurry demonstrates a superior formability, which can be used to print 3Y-TZP hierarchical porous ceramic green body. When the sintering temperature increases from 1400 ℃ to 1500 ℃, the ceramic particles gradually transition from loose to tightly packed arrangement, accompanied by porosity reduction. After sintering at 1500 ℃, the ceramic samples have both appropriate porosity and strength. The flexural strength reaches 717 MPa and the porosity is 4.03%. The XRD patterns show that the ceramic crystal phase is a stable tetragonal phase after sintering at this temperature.

3Y-TZP ceramics with a multidimensional pore structure were prepared by DLP technology combined with the pore-forming agent method. The effects of dispersant type and content on the rheological behavior of ceramic slurries with 40% solid content were investigated. The results indicated that 3% mass fraction of KOS110 could effectively improve the rheology of the slurry due to the chemical bonding and steric hindrance. The solid content and PEG content were synergistically optimized. The results showed that an effective lubrication layer could be formed between ceramic particles when 10% PEG was added to replace the photosensitive resin at 50% solid content. The viscosity of the slurry at this time met the requirements for DLP printing. After DLP printing and high temperature sintering at 1500℃, the 3Y-TZP ceramic was structurally stable and had both high appropriate porosity and mechanical strength.