They demonstrated a new material design in the form of a nanolayered composite consisting of alternating layers of metal (copper or nickel) and monolayer graphene that has ultra-high strengths of 1.5 and 4.0 GPa for copper–graphene with 70-nm repeat layer spacing and nickel–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. Ex situ and in situ transmission electron microscopy compression tests and molecular dynamics simulations confirm a build-up of dislocations at the graphene interface.
The copper-graphene composite that has 500 times the tensile strength of copper (1.5 gigapascals), and a nickel-grapehene composite that has 180 times the tensile strength of nickel (4 gigapascals). This is still some way off graphene’s tensile strength of 130 GPa — which is about 200 times stronger than steel (600 MPa) — but it’s still very, very strong. At 1.5 GPa, copper-graphene is about 50% stronger than titanium, or about three times as strong as structural aluminium alloys.
Schematic of metal–graphene multilayer system synthesis.
In separate research announced in May, 2013, Columbia Engineering researchers demonstrated that graphene, even if stitched together from many small crystalline grains, is almost as strong as graphene in its perfect crystalline form. This work resolves a contradiction between theoretical simulations, which predicted that grain boundaries can be strong, and earlier experiments, which indicated that they were much weaker than the perfect lattice. Scientists can grow sheets of graphene as large as a television screen by using chemical vapor deposition (CVD), in which single layers of graphene are grown on copper substrates in a high-temperature furnace. One of the first applications of graphene may be as a conducting layer in flexible displays. The graphene has a strength of 95 gigapascals. It has 90% of the strength of perfect molecular graphene and is stronger than molecular carbon nanotubes.
The copper-graphene multilayer material with an interplanar distance of 70nm exhibited 500 times greater (1.5GPa) strength than pure copper and nickel-graphene multilayer material with an interplanar distance of 100nm showed 180 times greater (4.0GPa) strength than pure nickel. It was found that there is a clear relationship between the interplanar distance and the strength of the multilayer material. A smaller interplanar distance made dislocation movement more difficult and therefore increased the strength of the material. Professor Han, who led the research effort, commented “the result is astounding as 0.00004% in weight of graphene increased the strength of the materials by hundreds of times” and that “improvements based on this success, especially enabling mass production with roll-to -roll process or metal sintering process, in the production of automobile and spacecraft lightweight, ultra-high strength parts may become possible. “In addition Professor Han mentioned that” the new material can be applied to coating material for nuclear reactor construction or other structural materials requiring high reliability.
The US Army Armaments Research, Development and Engineering Center developed a graphene-metal nanomaterial but failed to drastically improve the strength of the material. To maximize the increase in strength imparted by the addition of graphene, the KAIST research team created a layered structure of metal and graphene. Using CVD (Chemical Vapor Deposition) the team grew a single layer of graphene on a metal deposited substrate then deposited another metal layer and repeated the process to produce a metal-graphene multilayer composite material that, achieving a world first in doing so, utilized single layer of graphene. Micro-compression tests within Transmission Electronic Microscope and Molecular Dynamics simulation effectively showed the strength enhancing effect and the dislocation movement on an atomic level. The mechanical characteristics of the graphene layer within the metal-graphene composite material successfully blocked the dislocations and cracks from external damage from traveling inwards. Therefore the composite material displayed strength beyond conventional metal-metal multilayer materials.
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. Here we demonstrate a new material design in the form of a nanolayered composite consisting of alternating layers of metal (copper or nickel) and monolayer graphene that has ultra-high strengths of 1.5 and 4.0 GPa for copper–graphene with 70-nm repeat layer spacing and nickel–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. Ex situ and in situ transmission electron microscopy compression tests and molecular dynamics simulations confirm a build-up of dislocations at the graphene interface.
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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