Experimental investigation of mechanical behavior at the microstructure of copper-graphene thin films

Abstract

Graphene reinforcements in the metal matrix cause improvement in mechanical properties. The interaction of graphene depends on the microstructure and deformation of the metal matrix. At the nano and micro scale, metal graphene composites are mainly evaluated by indirect techniques like nanoindentation, which only induces specific deformation and failure mechanisms. In this work, nanolayered copper–graphene composites are fabricated to study the impact of graphene particles’ reinforcements on the mechanical behavior during uniaxial tensile loading. The stress required for film cracking increases in the ten-layer copper films (channel cracks) by 50% and the four-layer copper films (microcracks) by 121% with graphene reinforcement. Electron microscopy reveals that the graphene particles’ presence at the interfaces causes deflections in the crack paths leading to improved mechanical performance. The graphene particles also affect the grain boundary sliding (cause of microcracks) in the four-layer samples, increasing the crack onset strain from 1.3% to 2.4%. Comparing the energy release rate ratio of deflection and penetration to the fracture toughness ratio of the copper–graphene interface and graphene particle shows that crack deflection is expected. Molecular dynamics simulations also show that the deflection of cracks is due to graphene stopping the growth of plastic zones, which leads to delaminations at the interface.