Microstructures and mechanical characterizations of high-performance nacre-inspired Al/Al2O3 composites

Herein, we adopted a simple way to fabricate nacre-inspired “brick-and-mortar”-structured composites with freeze-cast alumina and pure Al. The ceramic layer thickness (2.5–16.6 μm) and alumina volume fraction (8–48%, resulting from the volume shrinkage of the scaffolds after sintering) were controlled by varying the slurry concentration (5, 10, 15 and 20 vol%). The Al/8 vol% Al2O3 composite, with a relatively thick metal layer (24.8 ± 5.7 μm) and low density (2.78 g/cm3), exhibited a bending strength of 319 ± 13 MPa and fracture toughness of 138 ± 7 MPa m1/2. Compared to the Al/8 vol% Al2O3 composite, the Al/20–48 vol% Al2O3 composites had higher bending strengths (332–368 MPa) but lower fracture toughness values (87–41 MPa m1/2). The relationships between the cracking modes and structural features in the composites were discussed to account for the strengthening and toughening mechanisms. This work provides new ideas and solutions concerning the design and fabrication of nacre-mimetic metal-ceramic composites.