Overcoming strength-ductility trade-off in bimodal metal matrix composite with 3D graphene-strengthened hetero-interface

Strength-ductility synergy has long been a challenge in the development of advanced metallic materials. In this study, we fabricated a novel bimodal-structured nickel matrix composite, which features in-situ synthesized three-dimensional graphene networks (3DGN) strengthening the hetero-interfaces between coarse-grained and fine-grained zones (CGZ and FGZ). Compared to the bimodal matrix, this 3DGN-reinforced composite exhibits remarkable enhancements of 30 % in yield strength, 40 % in ultimate tensile strength, and 40 % in uniform elongation, respectively, representing the highest comprehensive performance among nickel matrix composites and pure nickel obtained through cold rolling, severe plastic deformation, and dynamic plastic deformation as reported in the previous literature. The superior strength-ductility combination originates from the incorporation of 3DGN, which enables multiple strengthening and toughening mechanisms. Specially, the strength and strain hardening capability have been enhanced through improved dislocation storage capacity, a stronger hetero-deformation induced (HDI) hardening effect, and the activation of numerous stacking fault ribbons. Moreover, high-density dispersed microcracks in the FGZ relieve strain/stress concentrations while being constrained within the CGZ, further enhancing tensile ductility. This study provides new insights into addressing the inherent strength-ductility paradox in metal matrix composites. [Display omitted] •A novel bimodal-structured nickel matrix composite with 3D graphene networks was fabricated.•3D graphene networks strengthen hetero-interfaces, enhancing strength-ductility synergy.•3DGN-reinforced composite shows 30 % increase in yield strength, 40 % in tensile strength, and 40 % in uniform elongation.•Enhanced strain hardening through improved dislocation storage, HDI hardening, and stacking fault activation.•Dispersed microcracks in fine-grained zones relieve stress without compromising ductility.