Synergistic Strengthening and Toughening of 3D-Printed Bioinspired Alumina Composites with a Multi-Scale Bouligand...

Inspired by the Bouligand helicoidal architecture of the dactyl club of the peacock mantis shrimp, this study employed direct ink writing (DIW) 3D printing to construct a three-level synergistic toughening system composed of nano-SiO₂, microscale flake alumina, and a macroscale helicoidal structure. The effects of nano-SiO₂ content, Bouligand helix angle, and flake alumina content on the flexural strength and fracture toughness of the composite ceramics were systematically investigated. The results showed that the optimal nano-SiO₂ addition was 7 wt%, yielding a fracture toughness of 1.03 MPa·m^1/2, which was 13% higher than that of pure alumina. The introduced intergranular glassy phase transformed the rigid grain-boundary bonding into a moderately strong gradient interface, resulting in higher fracture toughness for all SiO₂-containing samples than for pure alumina. The Bouligand structure further increased the fracture toughness to a maximum of 1.45 MPa·m^1/2 at a helix angle of 10°, representing a 39% improvement over the 0° sample. When microscale flake alumina was incorporated into the optimal matrix containing 7 wt% SiO₂, the best overall mechanical performance was achieved at a flake alumina content of 5 wt%, where the flakes directly dissipated fracture energy through pull-out, fracture, and bridging mechanisms. The synergistic effect of the three structural levels was most pronounced at a helix angle of 20°, at which the sample containing 5 wt% flake alumina achieved a fracture toughness of 2.07 MPa·m^1/2 with almost no loss in flexural strength, corresponding to a 113% improvement over the sample without flake alumina. These results demonstrate that three-level synergy can be achieved through nanoscale interfacial optimization, microscale energy dissipation by reinforcing phases, and macroscale crack deflection induced by the helicoidal structure, thereby providing important theoretical and experimental support for the multiscale design of high-performance bioinspired ceramic materials.