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We constructed a nacre-inspired laminate-reticular hierarchical architecture in Cu/(TiC−Cr 3 C 2) composites by tuning the wettability between loose freeze-cast ceramic lamellae and Cu melt. This unique architecture takes full advantage of superb intrinsic strength of the ceramic particles and toughness of the metal, stimulating multiple extrinsic toughening mechanisms such as synergistic deformation of the metal and ceramic layers, ductile-ligament bridging and multi-cracking mode. As a consequence, the resultant composites containing ~30 vol% ceramics exhibited exceptional damage-tolerant properties with a fracture toughness of 62.6 ± 1.0 MPa⋅m1/2 and a bending strength of 639 ± 27 MPa. Image, graphical abstract [ABSTRACT FROM AUTHOR]

[Display omitted] • A simple method is proposed to construct a nacre-inspired "brick–mortar" structure. • The feature of freeze-cast scaffolds depends notably on ceramic particle size. • In-situ reaction increases the hard-phase content in composites up to 86 vol%. • The presence of "mortars" promotes multiple cracking and improves toughness. The construction of a hierarchically ordered "brick-and-mortar" structure with a high content of "brick" phase is a key challenge in the preparation of nacre-mimetic composites. Herein, inspired by the transverse cracks in the ceramic lamellae after freeze-drying caused by the secondary nucleation of ice crystals during directional freezing of water-based ceramic slurry, we propose a new idea to use these structural defects and an in-situ reaction to construct composites with a nacre-like "brick-and-mortar" structure and high hard-phase content. This uses ice-templating to first prepare lamellar TiO 2 scaffolds with transverse cracks that separated the ceramic lamellae into "brick" whose size was controlled by adjusting the initial ceramic particle size (50, 300, and 700 nm). After the reactive infiltration, these cracks were filled with molten Al, leading to the formation of a "brick-and-mortar" structure with a high hard-phase content (86 vol%). The increasing ceramic particle size reduced the hard-phase content but significantly increased the aspect ratio (height/width) of the ceramic "brick" and the fracture toughness. The excellent damage tolerance was attributed to multiple toughening mechanisms, i.e. , multiple cracking, crack deflection, and uncracked-ligament bridging of the metal layers. The existence of "mortar" increased the probability of the formation of multiple cracking. [ABSTRACT FROM AUTHOR]

We prepared Al/TiC composites with different ceramic volume fractions (15, 25 and 35 vol%) using ice-templating and pressure infiltration. The thickness of the lamellar layer and the porosity in the ceramic layer of the TiC scaffolds were controlled by varying the slurry concentration. The Al/15 vol%TiC composite had a thick metal layer and a low-density ceramic layer, which effectively dissipated the stress at the crack tip and fractured in a multiple-crack-propagation mode, giving bending strength of 355±3 MPa and fracture toughness of 81±2 MPa m 1/2 . However, the Al/25 vol%TiC and Al/35 vol%TiC composites had much higher bending strength (417−500 MPa) but lower fracture toughness (46−33 MPa m 1/2 ) as compared to the Al/15 vol%TiC composite, and they fractured in a single-crack-propagation mode. In addition, an increase in the brittle TiAl 3 phase with increasing ceramic volume at the fracture surface greatly deteriorated the toughness of the Al/TiC composites. Finally, the relationship between cracking mode and structure features in the laminated composites was discussed to account for the toughening mechanism. [ABSTRACT FROM AUTHOR]