MMaterialsgateNEWS 2017/05/30

Related MaterialsgateCARDS

High pressure key to lighter, stronger metal alloys, Stanford scientists find

Shocking complex metal mixtures with high pressure could lead to desirable properties such as higher heat resistance and allow power plants and engines to run hotter and more efficiently.

High pressure could be the key to making advanced metal mixtures that are lighter, stronger and more heat-resistant than conventional alloys, a new study by Stanford researchers suggests.

Humans have been blending metals together to create alloys with unique properties for thousands of years. But traditional alloys typically consist of one or two dominant metals with a pinch of other metals or elements thrown in. Classic examples include adding tin to copper to make bronze, or carbon to iron to create steel.

In contrast, “high-entropy” alloys consist of multiple metals mixed in approximately equal amounts. The result is stronger and lighter alloys that are more resistant to heat, corrosion and radiation, and that might even possess unique mechanical, magnetic or electrical properties.

Despite significant interest from material scientists, high-entropy alloys have yet to make the leap from the lab to actual products. One major reason is that scientists haven’t yet figured out how to precisely control the arrangement, or packing structure, of the constituent atoms. How an alloy’s atoms are arranged can significantly influence its properties, helping determine, for example, whether it is stiff or ductile, strong or brittle.

“Some of the most useful alloys are made up of metal atoms arranged in a combination of packing structures,” said study first author Cameron Tracy, a postdoctoral researcher at Stanford’s School of Earth, Energy & Environmental Sciences and the Center for International Security and Cooperation (CISAC).

A new structure

To date, scientists have only been able to re- create two types of packing structures with most high-entropy alloys, called body-centered cubic and face-centered cubic. A third, common packing structure has largely eluded scientists’ efforts — until now.

In the new study, published online in the journal Nature Communications, Tracy and his colleagues report that they have successfully created a high-entropy alloy, made of common and readily available metals, with a so-called hexagonal close-packed (HCP) structure.

“A small number of high-entropy alloys with the HCP structure have been made in the last few years, but they contain a lot of exotic elements such as alkali metals and rare earth metals,” Tracy said. “What we managed to do is to make an HCP high-entropy alloy from common metals that are typically used in engineering applications.”

The trick, it appears, is high pressure. Tracy and his colleagues used an instrument called a diamond-anvil cell to subject tiny samples of a high-entropy alloy to pressures as high as 55 gigapascals – roughly the pressure one would encounter in the Earth’s mantle. “The only time you would ever naturally see that pressure on the Earth’s surface is during a really big meteorite impact,” Tracy said.

High pressure appears to trigger a transformation in the high-entropy alloy the team used, which consisted of manganese, cobalt, iron, nickel and chromium. “Imagine the atoms as a layer of ping pong balls on a table, and then adding more layers on top. That can form a face-centered cubic packing structure. But if you shift some of the layers slightly relative to the first one, you would get a hexagonal close-packed structure,” Tracy said.

Scientists have speculated that the reason high-entropy alloys don’t undergo this shift naturally is because interacting magnetic forces between the metal atoms prevent it from happening. But high pressure seems to disrupt the magnetic interactions.

“When you pressurize a material, you push all of the atoms closer together. Oftentimes, when you compress something, it becomes less magnetic,” Tracy said. “That’s what appears to be happening here: compressing the high-entropy alloy makes it non-magnetic or close to non-magnetic, and an HCP phase is suddenly possible.”

Stable configuration

Interestingly, the alloy retains an HCP structure even after the pressure is removed. “Most of the time, when you take the pressure away, the atoms snap back to their previous configuration. But that’s not happening here, and that’s really surprising,” said study coauthor Wendy Mao, an associate professor of geological sciences at Stanford’s School of Earth, Energy & Environmental Sciences.

The team also discovered that by slowly cranking up the pressure, they could increase the amount of hexagonal close-pack structure in their alloy. “This suggests it’s possible to tailor the material to give us exactly the mechanical properties that we want for a particular application,” Tracy said.

For example, combustion engines and power plants run more efficiently at high temperatures but conventional alloys tend to not perform well in extreme conditions because their atoms start moving around and become more disordered.

“High-entropy alloys, however, already possess a high degree of disorder due to their highly intermingled natures,” Tracy said. “As a result, they have mechanical properties that are great at low temperatures and stay great at high temperatures.”

In the future, materials scientists may be able to fine-tune the properties of high-entropy alloys even further by mixing different metals and elements together. “There’s a huge part of the periodic table and so many permutations to be explored,” Mao said.

Source: Stanford's School of Earth, Energy & Environmental Sciences – 25.05.2017.

Investigated and edited by:

Dr.-Ing. Christoph Konetschny, Inhaber und Gründer von Materialsgate
Büro für Material- und Technologieberatung
The investigation and editing of this document was performed with best care and attention.
For the accuracy, validity, availability and applicability of the given information, we take no liability.
Please discuss the suitability concerning your specific application with the experts of the named company or organization.

You want additional material or technology investigations concerning this subject?

Materialsgate is leading in material consulting and material investigation.
Feel free to use our established consulting services

MMore on this topic

The project received support from the Regional Science Foundation and the Russian Foundation for Basic Research in the competition for oriented interdisciplinary research in 2016.

The results of the research were published in the journals "Physics of the Solid State", "Vacuum" and "Journal of Superconductivity and Novel Magnetism". The authors of the project say that with the help of this technology special nanopowders are produced, which are used as modifying additives in the production of aluminum alloys. This method will significantly improve the operational properties of the foundry products, and reduce the energy costs for its final processing. Igor Karpov, head of the laboratories of the UNESCO Science and Education Center "New Materials and Technologies" of SibFU, says that aluminum and iron obtained using the technology... more read more

In order to develop new materials, material engineers need to be able to predict how fast impurity atoms diffuse, or spread, in a crystal over a range of temperatures.

Using new computational techniques, researchers at the University of Illinois at Urbana-Champaign have constructed the first exact model for diffusion in magnesium alloys. While magnesium is the lightest structural metal, this new model could mean big things for material engineers, as it can also be used to predict how atoms diffuse in many other materials. Einstein first described the fundamental mechanism of diffusion, but it has only been modeled exactly for a few crystals. "Computer analysis of the magnesium crystal revealed hidden broken symmetries that impact how different atoms would move in magnesium," explained Dallas Trinkle, an associate professor of materials science... more read more

Credit: Rob Felt, Georgia Tech

A simple technique for producing oxide nanowires directly from bulk materials could dramatically lower the cost of producing the one-dimensional (1D) nanostructures.

That could open the door for a broad range of uses in lightweight structural composites, advanced sensors, electronic devices - and thermally-stable and strong battery membranes able to withstand temperatures of more than 1,000 degrees Celsius. The technique uses a solvent reaction with a bimetallic alloy - in which one of the metals is reactive - to form bundles of nanowires (nanofibers) upon reactive metal dissolution. The process is conducted at ambient temperature and pressure without the use of catalysts, toxic chemicals or costly processes such as chemical vapor deposition. The produced nanowires can be used to improve the electrical, thermal and mechanical properties of functional... more read more

Researchers at the Department of Energy’s Oak Ridge National Laboratory and partners Lawrence Livermore National Laboratory and Wisconsin-based Eck Industries have developed aluminum alloys that are both easier to work with and more heat tolerant than existing products.

What may be more important, however, is that the alloys—which contain cerium—have the potential to jump-start the United States’ production of rare earth elements. ORNL scientists Zach Sims, Michael McGuire and Orlando Rios, along with colleagues from Eck, LLNL and Ames Laboratory in Iowa, discuss the technical and economic possibilities for aluminum–cerium alloys in an article in JOM, a publication of the Minerals, Metals & Materials Society. The team is working as part of the Critical Materials Institute, an Energy Innovation Hub created by the U.S. Department of Energy (DOE) and managed out of DOE's Advanced Manufacturing Office. Based at Ames, the institute works to... more read more

MaterialsgateNEWSLETTER

Partner of the Week

Search in MaterialsgateNEWS

Books and products

MaterialsgateFAIR:
LET YOURSELF BE INSPIRED