Researchers at Berkeley and Oak Ridge Labs Test a Multi-element High-Entropy Alloy with Surprising Results
A new concept in metallic alloy design – called “high‐entropy alloys” – has yielded a multiple-element material that not only tests out as one of the toughest on record, but, unlike most materials, the toughness as well as the strength and ductility of this alloy actually improves at cryogenic temperatures. This multi-element alloy was synthesized and tested through a collaboration of researchers at the U.S. Department of Energy (DOE)’s Lawrence Berkeley and Oak Ridge National Laboratories (Berkeley Lab and ORNL).
“We examined CrMnFeCoNi, a high‐entropy alloy that contains five major elements rather than one dominant one,” says Robert Ritchie, a materials scientist with Berkeley Lab’s Materials Sciences Division. “Our tests showed that despite containing multiple elements with different crystal structures, this alloy crystalizes as a single phase, face‐centered cubic solid with exceptional damage tolerance, tensile strength above one gigapascal, and fracture toughness values that are off the charts, exceeding that of virtually all other metallic alloys.”
Ritchie is the corresponding author along with ORNL’s Easo George of a paper in Science describing this research. The paper is titled “A fracture resistant high‐entropy alloy for cryogenic applications.” Co-authors are Bernd Gludovatz, Anton Hohenwarter, DhirajCatoor and Edwin Chang.
The tradition of mixing two metals together to create an alloy that possesses properties its constituent elements individually lack goes back thousands of years. In the 4th millennium BC, people began adding tin, a hard metal, to copper, a soft and relatively easy to work metal, to produce bronze, an alloy much stronger than copper. It was later discovered that adding carbon to iron yields the much stronger steel, and the addition of nickel and chromium to the mix yields steel that resists corrosion. Traditional alloys invariably feature a single dominant constituent with minor elements mixed in, and often rely on the presence of a second phase for mechanical performance.
“High‐entropy alloys represent a radical departure from tradition,” Ritchie says, “in that they do not derive their properties from a single dominant constituent or from a second phase. The idea behind this concept is that configurational entropy increases with the number of alloying elements, counteracting the propensity for compound formation and stabilizing these alloys into a single phase like a pure metal.”
Although high‐entropy alloys have been around for more than a decade, it has only been recently that the quality of these alloys has been sufficient for scientific study. George and his research group at ORNL combined high‐purity elemental starting materials with an arc-melting and drop-casting process to produce high quality samples of CrMnFeCoNi (chromium, manganese, iron, cobalt and nickel) in sheets roughly 10 millimeters thick. After characterizing these samples for tensile properties and microstructure, the ORNL team sent them to Ritchie and his research group for fracture and toughness characterization.
Ritchie, who holds the H. T. and Jessie Chua Distinguished Professor of Engineering chair at the University of California (UC) Berkeley, is an internationally recognized authority on the mechanical behavior of materials.
“As high entropy alloys are single phase, we reasoned that they would be ideal for cryogenic applications, such as storage tanks for liquefied natural gas, hydrogen and oxygen,” he says. “Our work is the first in-depth study that characterizes the fracture toughness properties of this class of alloys, and lo and behold, they are spectacular!”
Tensile strengths and fracture toughness values were measured for CrMnFeCoNi from room temperature down to 77 Kelvin, the temperature of liquid nitrogen. The values recorded were among the highest reported for any material. That these values increased along with ductility at cryogenic temperatures is a huge departure from the vast majority of metallic alloys, which lose ductility and become more brittle at lower temperatures. Ritchie and George believe that the key to CrMnFeCoN’s remarkable cryogenic strength, ductility and toughness is a phenomenon known as “nano-twinning,” in which during deformation, the atomic arrangements in adjacent crystalline regions form mirror images of one another.
“These nano-twins are created when the material undergoes plastic deformation at cryogenic temperatures,” Ritchie says. “This represents a mechanism of plasticity in addition to the planar-slip dislocation activity most metals undergo at ambient temperatures. The result of nano-twinning deformation is a continuous strain hardening, which acts to suppress the localized deformation that causes premature failure.”
Ritchie notes that the mechanical properties of CrMnFeCoNi and other high-entropy alloys have yet to be optimized.
“These high-entropy alloys may well be capable of even better properties,” he says.
This research was supported at both Berkeley Lab and ORNL by the DOE Office of Science.
For more about the research of Robert Ritchie go here
For more about the research of Easo George go here
# # #
Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.
DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov/.
Lynn Yarris | Eurek Alert!
Manchester scientists tie the tightest knot ever achieved
13.01.2017 | University of Manchester
CWRU directly measures how perovskite solar films efficiently convert light to power
12.01.2017 | Case Western Reserve University
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration
"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...
Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.
Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
16.01.2017 | Power and Electrical Engineering
16.01.2017 | Information Technology
16.01.2017 | Power and Electrical Engineering