Strength-toughness synergy in CrCoNi-Al hierarchical lamellar composites rendered by constituent grain size matching

• Hierarchical lamellar CrCoNi reinforced Al matrix composites were developed. • Grain size ratio R = 9.2 achieved the optimal strength-energy dissipation synergy. • High strength stemmed from HDI strengthening, load-sharing and grain refinement. • High energy dissipation originated from formation of dense microcracks and crack deflection. Traditional metal matrix composites (MMCs) often suffer from prominent strength-toughness trade-off arising from inherent property and structural discrepancies between the reinforcement and matrix phases. This work presents a special grain size matching strategy to optimize mechanical compatibility and interfacial structure of MMCs. Using a metal–metal CrCoNi medium entropy alloy reinforced aluminum (Al) matrix hierarchical lamellar composite (CrCoNi-Al) as a model system, which is fabricated by a two-step high-energy ball milling process followed by a controlled consolidation, we validate this strategy and successfully identify an optimal design window, where the CrCoNi-Al composite with grain size ratio of ∼ 9.2 (Al: CrCoNi) possessed the ultimate tensile strength of 425 ± 3 MPa and the total energy dissipation density (toughness) of 19.1 ± 1.3 MJ/m 3 , respectively, 86 % and 41 % higher than those in the untailored composite with grain size ratio of ∼ 19.7. The high strength, induced by the grain size matching strategy , primarily originated from heterogeneous deformation induced (HDI) strengthening, effective load-sharing by the CrCoNi lamellae, as well as grain refinement within the Al matrix. On the other hand, the high toughness was mainly attributed to the formation of high-density microcracks and crack deflection occurring inside multiple CrCoNi lamellae. The insights gained here indicate that the grain size matching strategy may provide a novel and viable route for developing next-generation structural materials with enhanced resilience for demanding applications.