Development of a nacre-like metal-ceramic composite with a brick-and-mortar structure and high ceramic content

The notion of replicating the "brick-and-mortar" microstructure and fracture resistance of nacre in synthetic materials has recently generated significant interest but has yielded few real technological advances. In the present study, we demonstrated the fabrication of a nacre-inspired composite using the structural defects (i.e., the transverse cracks in the ceramic lamellae) caused by secondary ice crystal nucleation during bidirectional freeze-casting, followed by pressure infiltration and hot pressing. We synthesized an Al/Al2O3 composite with a fine brick-and-mortar structure (with a metal mortar thickness of 10 mu m) and 75 vol% Al2O3 that exhibited similar component and structural characteristics to nacre. This composite exhibited both enhanced strength and toughness with no obvious trade-off observed. Toughening was induced by marked crack deflection, coupled with significant crack bridging and brick pull-out, as observed in nacre. This strategy is simple and flexible and can easily be extended to other material systems, opening an avenue for the development of other lightweight, high-strength, and tough biomimetic materials.