Strengthening in Metal/Graphene Composites: Capturing the Transition from Interface to Precipitate Hardening.

A promising materials engineering method for improving the strength of crystalline materials is to add obstacles to dislocation motion that induce interface hardening (IH) or precipitate hardening (PH). In this study, molecular dynamics simulations are performed for Ni/graphene composites, revealing for the first time that graphene can strengthen the Ni matrix not only strictly via IH or PH but also through a continuous transition between the two. When graphene behaves like an interface, dislocation pileups form, whereas when it behaves as a precipitate, complex Orowan looping occurs by dislocation cross-slip. IH transitions to PH when the integrity of the graphene-dislocation configuration (GDC) deteriorates, leading to a reduced strengthening effect. Furthermore, the deformation of graphene is found to be an effective signature to indicate the real-time strengthening. This observation relates the graphene strengthening effect on metals to a combination of parameters, such as the GDC integrity, graphene deformation, and dislocation evolution, opening an avenue to tune the mechanical properties by controlling the dislocation movements and manipulating the dislocation-obstacle interaction mechanisms.