Four-dimensional (4D) printing, as an advanced additive manufacturing technology, enables the fabricated structures to undergo programmable shape or performance changes over time in response to external stimuli. This technology has a significant application potential in aerospace, communication, and biomedical engineering. However, achieving ceramic structures with high precision, complex shapes, and excellent shape memory functionality remains a major challenge. The main difficulty lies in the inability to formulate ceramic slurry suitable for high-resolution printing and precisely controlling the shape memory behavior of the printing precursors and the sintering process. To address these challenges, this study was to use a photopolymerization 4D printing technique to prepare alumina ceramic precursors with shape memory effects. An effective printing of ceramic specimens was ensured via formulating high-solid-content ceramic slurry and optimizing their rheological properties. The shape memory performance was characterized, and the debinding and sintering strategy was adopted based on the results of thermal analysis to obtain dense and crack-free ceramic parts. Also, the shape recovery was achieved through Joule heating, having an application potential of the ceramic precursors in aerospace intelligent hinges. This study could provide a feasible technical approach for designing and manufacturing shape memory ceramic structures through 4D printing and offer practical methods for developing advanced intelligent ceramic components.

For the preparation of the ceramic slurry, polyurethane acrylate, acrylic isoprene ester, and ethyl (2,4,6-trimethylbenzoyl) phenylphosphoric acid ester were mixed in a weight ratio of 51∶45∶4 to prepare the shape memory polymer (SMP) resin. Afterwards, the SMP resin was mixed with alumina powder in a weight ratio of 55∶45, and was stirred by a mechanical mixer under heating and ultrasonic vibration for 30 min to obtain a uniform ceramic slurry. The rheological properties of the slurry were tested using a rotational rheometer. The 3D printing was completed by a vat photopolymerization (VPP) printer, with the process parameters including a layer thickness of 50 μm, a laser power of 100 mW, and a scanning interval of 0.03 mm. To characterize the shape memory performance, the rectangular samples (1.5 mm×5.0 mm×30.0 mm) were heated at 80 ℃ to deform, and then cooled to 25 ℃ to fix the temporary shape. The shape fixation rate (R_f) and shape recovery rate (R_r) were calculated based on the shape fixation angle and shape recovery angle, and 10 cycles of tests were conducted. The glass transition temperature (T_g) of the printed precursor was determined by a dynamic thermal mechanical analyzer (DMA). The chemical structure evolution before and after curing was analyzed by Fourier transform infrared spectroscopy (FTIR). The potential applications in fields such as aerospace intelligent hinges were initially demonstrated under the influence of Joule heating. The temperature rise rate was tested by thermogravimetric differential scanning calorimetry (TG-DSC) in a nitrogen environment at a rate of 10 ℃ per minute, starting from 30 ℃ to 800 ℃, to guide the debinding and sintering processes.

The prepared ceramic slurry exhibits a distinct shear-thinning behavior, with decreasing viscosity significantly as the shear rate increases, making it suitable for use in UV photopolymerization-based printers. The dynamic thermomechanical analysis reveals a glass transition temperature (T_g) of approximately 76.24 ℃ for the ceramic precursor. The printed precursor demonstrates excellent shape memory properties, achieving R_f and R_r rates of approximately 97% and 98%, respectively, for 10 test cycles, confirming stable and reliable shape memory performance. The Fourier transform infrared spectra confirm that the ceramic slurry successfully undergoes a photopolymerization and forms a cross-linked network. Furthermore, complex structures such as box and flower models are successfully printed, and they show the excellent shape recovery under thermal stimulation, highlighting a flexibility of this process for fabricating intricate shapes. The study utilizes the Joule heating as an external stimulus to drive shape recovery, demonstrating a potential of ceramic precursor as an intelligent hinge for aerospace applications. The thermogravimetric-differential scanning calorimetry indicates key temperature stages for organic component decomposition. In addition, a debinding and sintering strategy is implemented, effectively preventing cracking and deformation, and yielding dense, crack-free alumina ceramic parts.

This study fabricated an alumina ceramic precursor with a shape memory effect by the photopolymerization 4D printing technology, and systematically investigated its printing process, shape memory performance, and sintering behavior. The study demonstrated that the configured ceramic slurry had excellent shear thinning properties and rheological performance, making it suitable for high-precision stereolithography printing. The precursor printed was found to exhibit a significant shape memory function, with a shape fixation rate of approximately 97% and a shape recovery rate of approximately 98%. It could be controlled to undergo shape reconstruction and recovery through thermal stimulation. The shape recovery of the precursor structure was achieved through the Joule heating, demonstrating its potential application in fields such as aerospace intelligent hinges. Moreover, the thermal analysis results indicated that the optimized degreasing and sintering process could yield structurally complete and dense ceramic parts. This research could provide a feasible technical approach for 4D printing of ceramic materials and the design of shape memory structures, having a significant theoretical and application value.