Researchers have proven that a metal alloy of chromium, cobalt and nickel is officially the strongest material on Earth – more than 100 times stronger than the miracle material graphene. (will open in a new tab).
In a new study published Dec. 1 in the journal Science (will open in a new tab), the researchers subjected the ultra-strong alloy to extremely low temperatures to test how resistant the material was to fracture. Scientists have long known that this alloy is a hard cookie, but to the team’s surprise, the alloy only became stronger and more resistant to cracking when the temperature dropped sharply.
This superior fracture toughness is in stark contrast to most materials, which the study authors say become more brittle at sub-zero temperatures.
“People talk about the strength of graphene, and it is measured as just 4 megapascals per meter,” study co-author Robert Ritchie said. (will open in a new tab), a professor of engineering at the University of California at Berkeley and a senior scientist at the Lawrence Berkeley National Laboratory, told Live Science. “The impact strength of aluminum alloys used in aircraft is 35 megapascals per meter. The strength of this material is between 450 and 500 megapascals per meter… these are staggering numbers.”
Potential applications for such a durable material range from space infrastructure to shatter-resistant containers for clean energy use here on Earth. However, Ritchie noted that two of the three elements of the alloy (nickel and cobalt) are prohibitively expensive, limiting the use of the alloy in the lab for the foreseeable future.
strange alloy
Chromium (will open in a new tab)cobalt (will open in a new tab)and nickel (will open in a new tab) the alloy is an example of a high entropy alloy (HEA). Unlike most alloys, which consist of one element with fewer additional elements added, HEAs consist of an equal mixture of each of the constituent elements.
According to the authors of the study, this HEA is extremely malleable, or ductile, meaning it can flex under pressure to resist fracture. Several features of the alloy’s molecular structure make it unusually malleable. One key mechanism, for example, causes the atoms within an alloy to shift under pressure, allowing them to move relative to each other. This, along with various other mechanisms, allows the material to continue to deform as pressure increases without breaking or breaking.
“Each of these mechanisms kick in at a later stage when you increase the load on the material, and this is the perfect recipe for high strength,” Ritchie added. “Remarkably, these mechanisms become more efficient at lower temperatures.”
The researchers first tested the strength of the alloy by exposing it to liquid nitrogen at about minus 321 degrees Fahrenheit (minus 196 degrees Celsius). As the strength of the alloy only improved, the team wondered how much more they could push the boundaries of the material.
Dong Liu (will open in a new tab), a physicist at the University of Bristol in England, and his colleagues developed an experiment to expose an alloy to liquid helium, which can be cooled to supercold temperatures of minus 424 F (minus 253 C). The team then watched neutrons scatter away from the material in a process called neutron diffraction to look into the structure of the alloy and see how cracks form as pressure increases.
The experiment showed that when it came to toughness, the alloy knocked the graphene out of the water.
“Graphene has a very high strength but is not resistant to damage,” Liu said in an interview with Live Science. “It’s very fragile and shatters like a mug you throw on the floor and it shatters into pieces.”
Liu added that another disadvantage of graphene is that its high strength is only maintained at an exceptionally small scale, the nanometer level. Meanwhile, samples of the chromium-cobalt-nickel alloy tested by Liu and her team were the size of a pack of cigarettes, meaning that HEA retained its strength at the scale of everyday objects.
Materials of the future
Although more testing is needed before this material can be put into practice, Liu is optimistic that the alloy can be used in many projects, both in space and on Earth. For example, HEA can be used in hydrogen. (will open in a new tab)storage containers that could make sustainable hydrogen vehicles more feasible.
“If you drive a car with a hydrogen vessel made of something very fragile, you are essentially carrying a bomb with you,” Liu said. “But not from this material.”
Ritchie, meanwhile, is cautious about suggesting a potential use for the alloy, as moving material from the lab to the “real world” requires a lot of knowledge and time, while the cost of nickel and cobalt remains prohibitive. However, he is interested in developing recipes for new alloys that could be just as strong using other elements.
“There are 50 usable elements in the periodic table,” Ritchie said. “A combination of three, five or seven of them means that there are millions of new alloys.”
Originally published on LiveScience.com (will open in a new tab).