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!
Nanobionics Supercharge Photosynthesis
22.05.2015 | Department of Energy, Office of Science
Mesoporous Particles for the Development of Drug Delivery System Safe to Human Bodies
22.05.2015 | National Institute for Materials Science
Physicists have developed an innovative method that could enable the efficient use of nanocomponents in electronic circuits. To achieve this, they have developed a layout in which a nanocomponent is connected to two electrical conductors, which uncouple the electrical signal in a highly efficient manner. The scientists at the Department of Physics and the Swiss Nanoscience Institute at the University of Basel have published their results in the scientific journal “Nature Communications” together with their colleagues from ETH Zurich.
Electronic components are becoming smaller and smaller. Components measuring just a few nanometers – the size of around ten atoms – are already being produced...
Development and implementation of an advanced automobile parking navigation platform for parking services
To fulfill the requirements of the industry, PolyU researchers developed the Advanced Automobile Parking Navigation Platform, which includes smart devices,...
The world's first electrical car and passenger ferry powered by batteries has entered service in Norway. The ferry only uses 150 kWh per route, which...
On Tuesday, 19 May 2015 the research icebreaker Polarstern will leave its home port in Bremerhaven, setting a course for the Arctic. Led by Dr Ilka Peeken from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) a team of 53 researchers from 11 countries will investigate the effects of climate change in the Arctic, from the surface ice floes down to the seafloor.
RV Polarstern will enter the sea-ice zone north of Spitsbergen. Covering two shallow regions on their way to deeper waters, the scientists on board will focus...
Nanoengineers at the University of California, San Diego developed a gel filled with toxin-absorbing nanosponges that could lead to an effective treatment for skin and wound infections caused by MRSA (methicillin-resistant Staphylococcus aureus), an antibiotic-resistant bacteria. This "nanosponge-hydrogel" minimized the growth of skin lesions on mice infected with MRSA - without the use of antibiotics. The researchers recently published their findings online in Advanced Materials.
To make the nanosponge-hydrogel, the team mixed nanosponges, which are nanoparticles that absorb dangerous toxins produced by MRSA, E. coli and other...
20.05.2015 | Event News
18.05.2015 | Event News
12.05.2015 | Event News
22.05.2015 | Materials Sciences
22.05.2015 | Information Technology
22.05.2015 | Materials Sciences