Ceramic particles have been introduced into metal matrices to improve the strength and stiffness of metals, albeit at the cost of the ductility unfortunately. Simultaneously increasing the strength and ductility of metal matrix composites (MMCs) is still a challenge. Accumulative orthogonal extrusion process (AOEP), which disperses nanoparticles and refines grain structures of particles reinforced MMCs via severe plastic deformation, is proposed in this paper. The high strength (687 MPa) and superior ductility (14.8%) are simultaneously achieved in the resultant TiB₂ particles reinforced Al–Zn–Mg–Cu matrix composites, and the underlying mechanisms are discussed in terms of particles’ influences. GRAPHICAL ABSTRACT IMPACT STATEMENT An easily realized SPD technology is proposed to effectively optimize the structures of nanoparticles reinforced composites in industrial scale. High strength and good ductility are simultaneously achieved in the resultant composites.

The fracture behaviour of artificial metamaterials often leads to catastrophic failures with limited resistance to crack propagation. In contrast, natural materials such as bones and ceramics possess microstructures that give rise to spatially controllable crack path and toughened material resistance to crack advances. This study presents an approach that is inspired by nature’s strengthening mechanisms to develop a systematic design method enabling damage-programmable metamaterials with engineerable microfibers in the cells that can spatially program the micro-scale crack behaviour. Machine learning is applied to provide an effective design engine that accelerate the generation of damage-programmable cells that offer advanced toughening functionality such as crack bowing, crack deflection, and shielding seen in natural materials; and are optimised for a given programming of crack path. This paper shows that such toughening features effectively enable crack-resisting mechanisms on the basis of the crack tip interactions, crack shielding, crack bridging and synergistic combinations of these mechanisms, increasing up to 1,235% absorbed fracture energy in comparison to conventional metamaterials. The proposed approach can have broad implications in the design of damage-tolerant materials, and lightweight engineering systems where significant fracture resistances or highly programmable damages for high performances are sought after.

In-situ pre-decorated different content of TiB₂ particle reinforced 2024 Al matrix composites (xTiB₂/2024Al composite, x = 0, 1, 2, 4, 6, 8 wt.%) were printed by laser powder bed fusion (LPBF). A quantitative equation was established to quantify heterogeneous nucleating potency by TiB₂ nanoparticles on the grain size of the LPBFed samples. Optimized mechanical properties were obtained in the as-printed 4TiB₂/2024Al alloy which proved the feasibility of replacing the wrought part with the LPBFed one. This manuscript provides a method to determine the optimized content of TiB₂ nanoparticles to change the noncastable material to the printable one. GRAPHICAL ABSTRACT IMPACT STATEMENT This manuscript provides a method to determine the optimized TiB₂ content to change the noncastable material to the printable one, and can potentially guide the introduction of many other nanoparticles.