High Strength and Fatigue Resistant Metal-Graphene Nanolayered Composite

Graphene, when alternated with metal thin films in the form of metal-graphene nanolayered composite, can effectively hinder dislocation propagation to result in ultra high strength and fatigue resistant composite material. Metal-graphene nanolayered composite is, therefore, expected to have enhanced reliability when used as electrodes for flexible, stretchable devices, which are typically subjected to extreme mechanical strain.

Article | Special Issue

Graphene is a single atomic layer material with excellent mechanical properties and has the potential to enhance the strength of composites. Its two-dimensional geometry, high intrinsic strength and modulus can effectively constrain dislocation motion, resulting in the significant strengthening of metals. A new material design in the form of a nanolayered composite consisting of alternating layers of metal and monolayer graphene is reported to have ultra-high strengths of 1.5 and 4.0 GPa for Cu-graphene with 70 nm repeat layer spacing and Ni-graphene with 100 nm repeat layer spacing, respectively. The ultra-high strengths of these metal-graphene nanolayered structures indicate the effectiveness of graphene in blocking dislocation propagation across the metal-graphene interface.

The same graphene interface, which has a strong sp₂ bonding, can simultaneously serve as an effective interface for deflecting the fatigue cracks that are generated under cyclic bendings. Cu-graphene nanolayered composites with repeat layer spacing of 100 nm were tested for bending fatigue at 1.6% and 3.1% strain up to 1,000,000 cycles, which showed for the first time a 5−6 fold enhancement in fatigue resistance compared to the conventional Cu thin film. Fatigue cracks that are generated within the Cu layer are stopped by the graphene interface, which is evidenced by cross-sectional scanning electron microscopy and transmission electron microscopy images. Molecular dynamics simulations for uniaxial tension of Cu-graphene nanolayered composite indicated limited accumulation of dislocations at the film/substrate interface, which makes the fatigue crack formation and propagation through thickness of the film difficult in this materials system.

High-strength and fatigue-resistant properties of metal-graphene nanolayered composite make this material a promising candidate for electrodes in flexible, stretchable devices, which typically are subjected to extreme mechanical strains. However, there is a need to develop a scalable method of fabrication; our earlier studies used vacuum-based deposition of metal layers and wet transfer of graphene layers, both of which are time-consuming processes. In order to largely enhance the scalability for production, the vacuum-based deposition of metal and wet transfer of graphene have been replaced with electrodeposition of metal and roll-based dry transfer of graphene to greatly enhance the scalability of the nanolayered composite fabrication. Fabricated Cu-graphene nanolayered composites with layer spacing of 200 nm, 300 nm, and 400 nm were tested under compression, and the strengths are calculated to be 1.38 GPa, 1.15 GPa, and 1.06 GPa, respectively. The strengths are similar to those from wet transferred graphene and sputter deposited metal, but the new fabrication method for this metal-graphene nanolayered composite has greatly enhanced scalability, thereby opening up the potential of this new material for future industrial applications.