Breaking through the strength-ductility trade-off in graphene reinforced Ti6Al4V composites

The graphene network (GN) reinforced Ti6Al4V composites with concurrently enhanced strength and ductility are fabricated based on powder metallurgy, in which the GN interlocks with the matrix intimately via the in-situ generation of interfacial TiC. The strengthening and toughening mechanisms of the composites are investigated through experiments and molecular dynamics (MD) simulations. Grain refinement, deformation compatibility, dislocation blocking, together with the restraint and bridging of cracks are provided by the embedded GN, improving both the strength and ductility of the composites. Interestingly, with a better ductility than Ti6Al4V, the composites possess a more brittle-like fracture surface. With the introduction of GN, the fracture mode of the composites is diverted from the transgranular fracture in Ti6Al4V to the mix of intergranular and quasi-cleavage fracture. The intergranular fracture is mainly ascribed to the brittle fracture of the TiC shell. And the propagation of cracks along cleavage plane in the matrix, working together with the impediment of cracks by GN, results in the quasi-cleavage fracture. Despite the brittle-like fracture surface, the restraint of crack propagation by dislocation-GN interactions, as well as the crack-bridging of GN, postpones the failure of the composites and thereby conduces to a good ductility.