Alloy is the strongest known material on Earth, and gets even stronger in cold weather

(ORDO NEWS) — An alloy of chromium, cobalt and nickel has just given us the highest fracture toughness ever measured for a material on Earth.

It has exceptionally high strength and ductility, resulting in what the team of scientists called “outstanding damage resistance.”

Moreover, paradoxically, these properties increase as the material gets colder, suggesting some interesting potential for applications in extreme cryogenic environments.

“When you’re designing structural materials, you want them to be strong, yet ductile and resistant to fracture,” says metallurgist Iso George, chair of the Advanced Alloy Theory and Engineering Department at Oak Ridge National Laboratory and the University of Tennessee.

“It’s usually a compromise between these properties. But this material combines both, and instead of becoming brittle at low temperatures, it becomes more durable.”

Strength, ductility and toughness are three properties that determine the durability of a material. Strength describes resistance to deformation.

Plasticity describes how plastic a material is. These two properties contribute to its overall strength: fracture resistance. Fracture strength is the resistance to further fracture of an already fractured material.

George and his colleague, senior author, mechanical engineer Robert Ritchie of the Berkeley National Laboratory and the University of California at Berkeley, have been working on a class of materials known as high-entropy alloys, or HEAs, for some time.

In most alloys, one element predominates with a small admixture of others. WES contain elements mixed in equal proportions.

One such alloy, CrMnFeCoNi (chromium, manganese, iron, cobalt and nickel), has been the subject of intense research after scientists noticed that its strength and ductility increase at liquid nitrogen temperatures without compromising toughness.

One of the derivatives of this alloy, CrCoNi (chromium, cobalt and nickel), has shown even more exceptional performance. characteristics. So George, Richie and their team cracked their fists and set to work to the limit.

Alloy is the strongest known material on Earth and gets even stronger in cold weather

Previous experiments with CrMnFeCoNi and CrCoNi have been carried out at liquid nitrogen temperatures up to 77 Kelvin (-196 °C , -321 °F) . The team took it even further, to liquid helium temperatures.

The results were incredible.

“The strength of this material at temperatures close to helium (20 kelvin, [-253°C, -424 °F] ) reaches 500 megapascals per square meter,” explains Ritchie.

“In the same units, the impact strength of a piece of silicon is one, the aluminum frame of a passenger plane is about 35, and the impact strength of some of the best steels is about 100. So 500 is a staggering number.”

To figure out how it works, the team used neutron diffraction, electron backscatter diffraction, and transmission electron microscopy to study CrCoNi down to the atomic level as it breaks down at room temperature and in extreme cold.

This included cracking the material. and measuring the stress required for crack growth, and then studying the crystal structure of the samples.

Atoms in metals are arranged in a repeating pattern in three-dimensional space. sional space. This pattern is known as the crystal lattice. The repeating components of the lattice are called elementary cells.

Sometimes boundaries are created between deformed and undeformed elementary cells. These boundaries are called dislocations, and when a force is applied to the metal, they move, allowing the metal to change shape. The more dislocations in a metal, the more malleable it is.

Irregularities in the metal can block the movement of dislocations; this is what makes the material durable. But if the dislocations are blocked, the material may crack instead of deforming, so high strength can often mean high brittleness. In CrCoNi, the researchers identified a specific sequence of three dislocation blocks.

Sliding occurs first, when the parallel parts of the crystal lattice slide off each other. This causes the elementary cells to no longer coincide perpendicular to the sliding direction.

The constant force results in nanotwinning, where the crystal lattices form a mirror arrangement on either side of the boundary. If we apply even more force, this energy will be used to change the shape of elementary cells from a cubic to a hexagonal crystal lattice.

“When you pull it, the first mechanism starts, and then the second begins, then the third, and then the fourth,” Richie says.

“Now a lot of people will say, well, we’ve seen nanotwinning in conventional materials, we’ve seen slip in conventional materials. This is true. This is nothing new, but the fact that they all happen in this magical sequence gives us these really amazing properties.”

The researchers also tested CrMnFeCoNi in liquid form. helium temperatures, but it is not as efficient as its simpler derivative.

The next step will be to explore the potential applications of such a material, as well as to search for other wind farms with similar properties.


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