Alumina (Al₂O₃) ceramics are widely used in high-tech fields such as aerospace, energy, and electronics due to their excellent properties including high hardness, good wear resistance, high temperature stability, and chemical inertness. However, their intrinsic brittleness and high sensitivity to microdefects severely restricttheir practical application in advanced structural components. As a microcrack appears in conventional Al₂O₃ ceramics under an external load, a sudden catastrophic failure is likely to occur, greatly reducing the structural reliability and service life of the material. Therefore, developing a strategy that can effectively improve the toughness and damage tolerance of Al₂O₃ ceramics, while maintaining their inherent excellent properties becomes an urgent and important research topic in the field of structural ceramics. This work was to solve the intrinsic brittleness problem of Al₂O₃ ceramics via combining a structure design with a multi-scale interface regulation, which could be of great significance for promoting the design, development and practical application of high-performance Al₂O₃-based ceramics.

This study proposed an innovative strategy combining a structure design with a multi-scale interface regulation. Al₂O₃/h-BN/Al₂O₃ composite ceramic material with a fine three-dimensional structure and optimized interface properties was constructed through DLP-3D printing technology. The fracture toughness, damage tolerance and energy dissipation capacity of the composite ceramics were significantly improved via skillfully coordinating macro structural design (Gyroid structure) and micro interface modification (h-BN weak interface phase). The following procedure adopted was described. First, the Gyroid structure design was carried out for the Al₂O₃ phase to construct a continuous and stable three-dimensional structural skeleton based on the Digital Light Processing (DLP) 3D printing technology. DLP-3D printing technology was selected due to its advantages of high forming precision, fast printing speed, and ability to fabricate complex three-dimensional structures, which could accurately replicate the designed Gyroid structure and lay a foundation for the structural regulation of composite ceramics. Then, two-dimensional hexagonal boron nitride (h-BN) was introduced as a weak interface phase to regulate the interface properties between the Al₂O₃ structural skeleton and the Al₂O₃ filling phase, thereby constructing the Al₂O₃/h-BN/Al₂O₃ composite ceramic material. A series of composite ceramic samples with different h-BN interface phase contents were prepared to systematically investigate the influence of h-BN content on the material properties. Subsequently, various characterization techniques were used to characterize the phase composition, microstructure and forming quality of the composite ceramics. The mechanical properties such as fracture toughness (K_IC), fracture work, damage tolerance parameters, critical crack size and stress-strain behavior were comprehensively analyzed. Finally, the synergistic effect mechanism of the Gyroid structure and the two-dimensional h-BN weak interface phase on the toughening behavior, damage tolerance and energy dissipation of the composite ceramics was revealed through the analysis of fracture morphology and the summary of performance test results.

The Gyroid-Al₂O₃ ceramic skeleton prepared by DLP-3D printing technology has a good forming quality, and the actual volume fraction of the printed Al₂O₃ structure is 32.6%, which is close to the design value. This indicates that the DLP technology has a high precision in preparing the Gyroid structure, and there is still a certain regulation space to further optimize the printing precision of the structure. In addition, all composite ceramic samples also have a high relative density, which ensures the basic mechanical properties of the material. The composite ceramic with 15% h-BN interface phase (sample A15) shows the optimal comprehensive mechanical properties. Its fracture toughness (K_IC) reaches 5.42 MPa·m^1/2, which is 37% higher than that of pure Al₂O₃ ceramic, the fracture work is 264 J·m^-2, which is nearly 4 times higher than that of pure Al₂O₃, and the maximum fracture toughness (K_JC) can reach 15.40 MPa·m^1/2, which is 290% higher than that of pure Al₂O₃. Also, the critical crack size and damage tolerance parameter of the A15 sample are (201±20) μm and (0.77±0.01) m^1/2, respectively, which are 8.5 times and 2 times higher than those of pure Al₂O₃. Compared with conventional 3D printed ceramics and Al₂O₃ ceramics under conventional toughening strategies, the sample A15 still has significant advantages. The stress-strain behavior of the composite ceramics shows typical progressive failure characteristics and high energy absorption capacity, as well as a typical rising R-curve feature, indicating that the composite ceramics have a strong crack growth resistance and can effectively dissipate energy during the fracture process. The key innovation of this study is that the synergistic effect of the Gyroid structure and the two-dimensional h-BN weak interface phase effectively activates multiple toughening mechanisms such as crack deflection, crack branching, and interface delamination, which breaks through the inherent defect that conventional Al₂O₃ ceramics are extremely sensitive to microdefects, and significantly improves the energy dissipation capacity and structural reliability of the material. This material-structure integration design strategy provides an idea and theoretical guidance for the design and preparation of high-toughness and damage-tolerant composite ceramics.

This work constructed Al₂O₃/h-BN/Al₂O₃ composite ceramic materials with both high toughness and high damage tolerance. The composite ceramics showed progressive failure characteristics and high energy absorption capacity in the stress-strain behaviorand typical rising R-curve characteristics. The fracture toughness was increased by 37% and the fracture work was increased by nearly 4 times, compared with that of pure Al₂O₃. In addition, the critical crack size and damage tolerance parameters of the composite ceramics could also reach (201±20) μm and (0.77±0.01) m^1/2, which were enhanced by 8.5 and 2 times, respectively, compared with those of pure Al₂O₃. This could be due to the synergistic effect of the Gyroid structure and the two dimensional h-BN weak interface phase effectively activating multiple toughening mechanisms such as crack deflection, crack branching, and interface delamination, which could break through the inherent defect that conventional Al₂O₃ ceramics were extremely sensitive to microdefects, and significantly improve the energy dissipation capacity and structural reliability of the material. This material-structure integration design strategy could provide an idea and theoretical guidance for the design and preparation of high toughness and damage-tolerant composite ceramics.