Understanding the role of monolayer graphene during long range shock strengthening of metal-graphene heterostructure

Abstract

Graphene has been extensively used in graphene reinforced metal composite, with strengthening effects due to its ability to block dislocation from propagation during the traditional low strain rate deformation process. Laser shock peening has been applied in graphene/metal composites with graphene concentration of 2–10% with a relatively close distance between the graphene layers. This work discovered a strong long-range coupling effects of graphene as a super-strong nanomaterial and shock-wave transmitter during laser shock processing under room temperature LSP and cryogenic temperature (cLSP), under extremely low graphene concentration (1.42 × 10−6% vol.). Compared with simple compressed graphene-copper heterostructure, the yield strength of LSP and cLSP processed samples increases by 40%, and 76% respectively. We found that under laser shock peening (LSP) process, the shock wave can pass through long-distance to generate dislocation transportation from one layer to another graphene with the shock wave interaction between graphene layers separated very far away. Graphene plays an important role not only as a transmitter of shock waves, but also as a strong wall to bounce back shock waves to generate high dislocation density around graphene layers. We have designed experiments to compare the deformation behavior of the laminates under three deformation conditions: compression, LSP, and cLSP, respectively. It was found that the compressed sample has very few parallel dislocation arrays beneath the graphene interface, indicating that graphene blocks the dislocation movement and has very limited strengthening effects. The LSP processed samples contain much high dislocation density, while even higher density dislocation and strength are found in cLSP due to faster shock transportation in graphene/metal layers under cryogenic conditions. Finite element modeling was used to investigate the shock wave interaction with the graphene and metal layer under various conditions, which is consistent with experiments. Molecular dynamics simulation is used to simulate the microstructure of the laminates under various conditions and validated by experiments. This work provides a starting point to understand the long-range strengthening effects of 2D nanomaterials of extremely low concentrations and provide new design strategies for manufacturing graphene-metal nanocomposite and their strengthening approaches.