To achieve a further reduction in weight of titanium alloys and to satisfy the increasing demand of energy-saving for aerospace and automotive applications, a graphene oxide nanosheet-reinforced Ti6Al4V (GO/TC4) composite was successfully fabricated using spark plasma sintering (SPS). Contrary to the Widmanstätten microstructure of a monolithic TC4 sample, the microstructure of the composites displayed a typical basket-weave structure in virtue of the introduced residual tensile stress generated from the mismatch of coefficients of thermal expansion (CTE) between GO and TC4 during the phase transformation. Meanwhile, the in situ-formed TiC nanolayer and diffusion layer were identified at the GO–TC4 interface, which is expected to endow a stronger interfacial bonding. As compared with the TC4 sample, the TC4 composite with the addition of 0.27 wt.% GO exhibited a 0.2% yield strength of 921.8 MPa, an ultimate tensile strength of 1040.1 MPa, and an elongation of 5.3%, displaying a better balance of strength and ductility than that of the composite with a higher GO addition (0.54 wt.%). The synergetic strengthening mechanisms such as Orowan strengthening, enhanced dislocation density strengthening, and load transfer were confirmed. Among them, load transfer contributed greatly to the strength of the composites due to improved interfacial bonding between the GO fillers and TC4 matrix.

Multi-layer graphenes (MLGs) reinforced Cu matrix composites were fabricated using spark plasma sintering in this research. Microstructure observation indicated that MLGs homogeneously disperse in the matrix to result in grain refinement. Instrumented spherical micro-indentation tests were conducted to evaluate micro-mechanical properties of the composites, and the elastic modulus and indentation yield strength of the 1.5 wt.% MLG/Cu composite increase up to ~ 36% and ~ 41% than those of the unreinforced Cu, respectively. Grain refinement, the enhanced dislocation density (EDD) due to the thermal expansion mismatch between Cu matrix and MLGs and Orowan are thought to be the main strengthening mechanisms in this research.