Bio-inspired gradient-heterogeneous Al/Al2O3 composites: Strength–toughness synergistic design and fracture mechanisms

Inspired by natural hierarchical structures, this study presents a novel biomimetic Al/Al 2 O 3 composite featuring a gradient-heterogeneous architecture that effectively addresses the long-standing strength–toughness trade-off in metal–ceramic systems. A high-resolution vat photopolymerization 3D printing process was used to fabricate complex ceramic scaffolds with a multi-scale design, incorporating a turtle shell-inspired gradient in porosity and wall thickness, along with layered, tubular, and hexagonal cellular units derived respectively from nacre, ram horns, and beehives. Through pressure infiltration of molten aluminum, a fully interpenetrating composite with strong interfacial bonding was achieved. The resulting material exhibits a spatially tailored gradient in mechanical properties, achieving a surface strength of 634 MPa and a core energy absorption capacity of 14.36 MJ/cm 3 . In situ mechanical testing and finite element analysis reveal that multi-scale synergistic toughening mechanisms—including architecture-guided crack deflection, distributed plastic deformation, and stress redistribution—collectively contribute to the enhanced performance. This work demonstrates the potential of additive manufacturing-enabled structural programming to engineer composites with spatially optimized mechanical properties, offering a new paradigm for the design of advanced structural materials.