High damage-tolerance bio-inspired B4C/2024Al composites with adjustable mechanical performance by tuning ceramic thickness

Freeze casting is a promising approach for assembling lamellar metal-ceramic composites with an exceptional combination of strength and toughness. Although these mechanical properties can be optimized by regulating the microstructure of porous ceramic structures, the effect of lamellar thickness is rarely mentioned, especially for B4C/Al composites. Herein, by controlling the freezing temperature, we used freeze casting to create nacre-like B4C scaffolds with identical ceramic content yet different lamellar thicknesses and then infiltrated them with 2024Al alloy. The effects of lamellar thickness on the damage-tolerance behavior and toughening mechanisms are discussed. The refinement of lamellae decreases the probability of observing catastrophic flaws in ceramic layers, increasing strength from 534 +/- 14 to 578 +/- 15 MPa and increasing crack-initiation toughness (K-Ic) from 9.2 +/- 0.6 to 11.4 +/- 0.2 MPa m(1/2). These composites exhibit higher damage tolerance resulting from several toughening mechanisms, such as plastic deformation, crack deflection and blunting, and the uncracked-ligament bridging of ductile metal layers, which is reflected in the stable crack propagation during fracture and rising Rcurve behavior. Importantly, coarsening of the structure of composites allows the fracture behaviors transform from single to multiple crack propagation, thus absorbing much more fracture energy, with the valid crackgrowth toughness (K-Jc) enhancing markedly from 17.1 +/- 2.4 to 29.8 +/- 2.3 MPa m(1/2).

Automated summary

Freeze casting was used to create nacre-like B4C scaffolds with different lamellar thicknesses, which were infiltrated with 2024Al alloy. The effects of lamellar thickness on damage-tolerance behavior and toughening mechanisms were discussed, showing an increase in strength and toughness in composites with refined lamellae structure.