Lawrence Berkeley National Laboratory, in collaboration with Oak Ridge National Laboratory, published findings on the new material earlier this month and found that contrary to the behavior of most materials on Earth, this particular alloy is actually I explained that it becomes tougher and more ductile under low temperature conditions.
“When you design a structural material, you want it to be not only strong but also ductile and resistant to fracture,” said one of the project’s co-leaders and director of advanced alloy theory and development at ORNL and the University of Tennessee. President Easo George said. .
This alloy is composed of chromium, cobalt, and nickel (CrCoNi) and is a member of a subset of alloys known as high entropy alloys.
“The toughness of this material near the temperature of liquid helium (20 Kelvin, -424 Fahrenheit) is as high as 500 megapascal square root meters,” said another project leader, Berkeley Lab’s Materials Science Division. said Robert Ritchie, senior faculty scientist at . Richie went on to explain what these numbers mean for beginners. According to scientists, under the same conditions, silicon is 1, aluminum used in airplanes is about 35, and the toughness of the highest steel is 100 megapascal square root meter, the unit used to measure materials. can only manage. resistance to destruction.
“So 500 is a staggering number,” Richie said.
George and Ritchie began their work almost a decade ago, but limited resources limited the two researchers to testing the alloy at liquid nitrogen temperatures. They are”[find] facilities that allow stress testing of samples in such cold environments, and [recruit] Team members equipped with the necessary analytical tools and experience to analyze what is happening within materials at the atomic level,” according to a government press release announcing their findings, and further on the properties of the new materials. Discussed.
Using neutron diffraction, electron backscatter diffraction, and transmission electron microscopy, Ritchie, George, and colleagues at the Berkeley Lab, the University of Bristol, the Rutherford Appleton Laboratory, and the University of New South Wales have previously generated We investigated the lattice structure of the CrCoNi sample. Destroyed at room temperature and 20 K. Cracks are then measured. )
Images and atomic maps generated from these techniques reveal that the toughness of alloys is due to a trio of dislocation disturbances that affect in a specific order when a force is applied to the material. . First, the movement of dislocations causes regions of the crystal to slide away from other regions lying in parallel planes. This motion displaces the layers of unit cells so that their patterns no longer match the direction perpendicular to the gliding motion, creating a kind of disturbance. When more force is applied to the metal, a phenomenon called nanotwinning occurs. In this phenomenon, regions of the lattice form mirror symmetry across the boundary. Finally, as forces continue to act on the metal, the energy injected into the system changes the arrangement of the unit cell itself, causing the CrCoNi atoms to switch from a face-centered cubic crystal to another arrangement known as hexagonal close-packing.
This series of atomic interactions ensures that the metal continues to flow, but also continues to encounter new resistance from obstacles, well past the point where most materials snap from strain. When you pull it, the first mechanism starts, then the second mechanism starts, then the third mechanism starts, then the fourth mechanism starts,” Ritchie explains. “Now a lot of people will say, well, we’ve seen nano-twinning in regular materials, we’ve seen slip in regular materials. That’s true. Nothing new about it, but these The fact that everything happens in this magical sequence gives us these truly wonderful properties.”
According to Lawrence Berkeley National Laboratory, the material is expensive but could have practical uses in deep space exploration.
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