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Many researches have shown that nanotwinned structure and graphene reinforcing phase can improve the mechanical properties of aluminum (Al) metal, but the synergistic effect of the two on nanoindentation mechanical response of Al matrix composites is rarely reported. In this research, based on molecular dynamics simulations, the nanoindentation mechanical properties and microscopic deformation mechanisms of graphene/nanotwinned Al matrix composites are studied. The effect of the inclination angle and spacing of the twin boundaries (TBs), the insertion position of the graphene sheet, the graphene coating and the layer number of the graphene sheet on the nanoindentation mechanical properties of the Al matrix composites is analyzed. The nanoindentation mechanical properties of nanotwinned Al strongly depend on the inclination angle of TBs, and the dislocation slip modes mainly includes three types: hard mode I (dislocation pile-up penetration mode), soft mode I (partial dislocation parallel twin boundary slip mode) and hard mode II (dislocation limited slip mode). Moreover, as the twin boundary spacing increases, the dislocation slip mode starts to weaken until the nanoindentation mechanical properties are insensitive to the twin inclination orientation. The insertion of the graphene sheet weakens the indentation mechanical properties of the nanotwinned Al matrix composite, which is attributed to the interaction of the graphene with the dislocations and the subsequent absorption of part of them. The weakening effect depends on the distance between the graphene/Al interface and the plastic zone. What's more, graphene coating can improve the indentation mechanical properties of composites. In addition to the load bearing effect of graphene in the elastic stage, this strengthening effect is also attributed to the combined action of graphene and TBs in the plastic stage, which makes the dense dislocation network widely distributed around the indentation of graphene coating and induces the interfacial strain hardening. [ABSTRACT FROM AUTHOR]

Many studies have shown that both the nanotwinned structure and the graphene reinforcing phase can improve the mechanical properties of aluminum, but the synergistic effect of the two on the strengthening and toughening mechanisms of aluminum matrix composites has rarely been reported. In this work, the mechanical properties and microscopic deformation mechanisms of graphene/nanotwinned aluminum matrix composites under uniaxial tensile load are studied by molecular dynamics simulations. The effects of the distribution patterns of graphene and twin boundaries (TBs), their angles and the number of graphene layers on the mechanical behaviors of graphene/nanotwinned aluminum matrix composites are analyzed. It is found that the synergistic effect of TBs and graphene results in secondary reinforcement of aluminum matrix composites in the plastic stage, resulting in enhanced strength and toughness. Moreover, the elastic modulus, strength and toughness of graphene/nanotwinned aluminum matrix composites increase linearly with the number of graphene layers. By analyzing the microscopic deformation and dislocation evolution of aluminum matrix composites, the mechanisms of dislocation derivation and propagation induced by graphene and TBs are explored. In addition, it is found that there is a competition between graphene and TBs for the dislocation evolution, and the graphene can weaken the dislocation blocking effect of TBs. Finally, it is proved that the angle between graphene and TBs will weaken the mechanical properties of the composites. The effect of the TB angle on the mechanical properties of graphene/nanotwinned aluminum matrix composites is discussed in three cases, depending on the stress-strain curve and the microstructure deformation mechanism. • The effect of graphene and TBs on mechanical properties of Al-matrix is studied. • The influence of distribution patterns and layer number of graphene is analyzed. • The effect of the inclination angle of TBs and graphene is considered. • The mechanisms of dislocation derivation and propagation is explored. [ABSTRACT FROM AUTHOR]