29 August 2013

Graphene used to make graphene-copper composite that’s 500 times stronger

Researchers at the Korean Advanced Institute of Science and Technology (KAIST) have created composite materials using graphene that are up to 500 times stronger than the raw, non-composite material. This is the first time that graphene has been successfully used to create strong composite materials - and due to the tiny amounts of graphene used (just 0.00004% by weight) this breakthrough could lead to much faster commercial adoption than pure graphene, which is still incredibly hard to produce in large quantities.

At this point, we shouldn’t be wholly surprised that graphene - which holds a huge number of superlative titles, including the strongest material known to man - can also be used to create strong composite materials. In this case, the KAIST researchers created a 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.

A diagram illustrating how to make graphene-copper and graphene-nickel composites

To create these composites, the KAIST researchers use a process called CVD (chemical vapor deposition) to grow monolayers (one-atom-thick layers) of graphene. These monolayers are then deposited onto a thin film of metal (copper or nickel). Another layer of metal is then evaporated (a method of deposition) on top of the graphene. This process is repeated, until you have a sandwich consisting of a few layers of metal and graphene. Different metal thicknesses were tested (between 70nm and 300nm), and it was found that thinner layers result in much stronger composites. Because graphene is so thin, the amount used is absolutely tiny: Just 0.00004% of the metals by weight.

How graphene prevents slip planes in copper/nickel graphene composites

The reason these composites are so strong is that the graphene stops the metal atoms from slipping and dislocating under stress. In a solid metal, if a slip plane forms (due to stress), the atoms will readily slip apart, causing a fracture. The layers of graphene stop the metal atoms from sliding - the metal atoms cannot physically pass through the super-strong graphene - so no fractures can form (pictured above). It’s essentially the metallic equivalent of steel-reinforced concrete. In case you were wondering, this is also one of the primary reasons why metals are nearly always used in alloy form - because there’s a mix of different metal atoms with different atom sizes, it’s much harder for slip planes to form.
Moving forward, the researchers will now need to find a way of mass-producing these graphene-based composites, preferably with a roll-to-roll or metal sintering process. These composites, due to their massive strength, could find myriad uses in the automotive and aerospace industries, or simply as a new tool for structural engineers and industrial design. Just the sheer fact that we now know that graphene can be used as a composite is massive news, too: If graphene can suddenly turn soft copper into a structural material, imagine what it might do for something like titanium or steel, or even commercial polymers like Kevlar.

Now read: Graphene transistors based on negative resistance could spell the end of silicon and semiconductors.

Research paper: doi:10.1038/ncomms3114 - “Strengthening effect of single-atomic-layer graphene in metal–graphene nanolayered composites”


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