Reinforcement surface modification is often used to improve the mechanical properties of particle-reinforced metal matrix composites, however, the extent to which such modifications affect the interfacial properties is yet to be revealed. In this study, we fabricated SiC-Al composite bilayers where the SiC underwent different surface treatments before Al deposition. Four-point bending tests showed that the samples made from acid-pickled and thermally oxidized SiC possessed substantially higher interfacial toughness than their untreated counterpart, a presumption inferred from mechanical tests on bulk SiCp-Al composites but never justified quantitatively. These findings were rationalized by the different interfacial constituents and structure in these samples.

Bulk graphene (reduced graphene oxide)-reinforced Al matrix composites with a bioinspired nanolaminated microstructure were fabricated via a composite powder assembly approach. Compared with the unreinforced Al matrix, these composites were shown to possess significantly improved stiffness and tensile strength, and a similar or even slightly higher total elongation. These observations were interpreted by the facilitated load transfer between graphene and the Al matrix, and the extrinsic toughening effect as a result of the nanolaminated microstructure.

In particulate-reinforced metal matrix composites (MMCs), geometrically necessary dislocations (GNDs) form in the vicinity of reinforcement/matrix interfaces. In this study, the hardness distribution across the interface was studied using nanoindentation with high spatial resolution, for composites treated under different aging conditions. The size of the GND punched zone, as determined from the hardness measurement, was found to be in agreement with that estimated by transmission electron microscopy (TEM). Mechanical characterization of bulk composites revealed a reduction in failure strain with decreasing punched zone size, while the strength of the composites was found to depend more on the intrinsic strength of the matrix alloy. These observations were interpreted in terms of the load transfer capacity between the matrix and reinforcement through the interface.

Uniaxial compression tests were carried out on micro-pillars fabricated from nanolaminated graphene (reduced graphene oxide, RGO)-Al composites of different RGO concentrations and laminate orientations (the angle between laminate planes and the pillar axis). It was found that the strengthening capability of RGO can be enhanced by either orienting the RGO layers parallel with the loading direction or raising the RGO concentration. The stress–strain response of the micro-pillars was populated with discrete bursts, and the stress increments of the bursts scaled with the RGO concentration, regardless of the laminate orientation relative to the loading direction. These observations were interpreted by the variation in the load-bearing capacity of RGO in different laminate orientations, the dislocation annihilation at the RGO/Al interface, and a crack deflection mechanism provided by the robust RGO/Al interface that toughened the composites. This work underscores the importance of structural design and control in the stiffening, strengthening, and toughening of metal matrix composites, and the methodology developed may be applied to other composites with microstructural heterogeneity to probe their specific mechanical behaviors and structure-property correlations.