Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Caltech-led team creates damage-tolerant metallic glass

13.01.2011
Amorphous palladium-based alloy demonstrates unprecedented level of combined toughness and strength; could be of use in biomedical implants

Glass is inherently strong, but when it cracks or otherwise fails, it proves brittle, shattering almost immediately. Steel and other metal alloys tend to be tough—they resist shattering—but are also relatively weak; they permanently deform and fail easily.

The ideal material, says Marios Demetriou, a senior research fellow at the California Institute of Technology (Caltech), has the advantage of being both strong and tough—a combination called damage tolerance, which is more difficult to come by than the layperson might think. "Strength and toughness are actually very different, almost mutually exclusive," he explains. "Generally, materials that are tough are also weak; those that are strong, are brittle."

And yet, Demetriou—along with William Johnson, Caltech's Ruben F. and Donna Mettler Professor of Engineering and Applied Science, and their colleagues—report in a recent issue of the journal Nature Materials that they have developed just such a material. Their new alloy—a combination of the noble metal palladium, a small fraction of silver, and a mixture of other metalloids—has shown itself in tests to have a combination of strength and toughness at a level that has not previously been seen in any other material.

"Our study demonstrates for the first time that this class of materials, the metallic glasses, has the capacity to become the toughest and strongest ever known," Demetriou says. Indeed, the researchers write in their paper, these materials allow for "pushing the envelope of damage tolerance accessible to a structural metal."

What gives metallic glasses their unusual qualities is the fact that they are made of metals—with the inherent toughness that comes with that class of material—but have the internal structure of glass, and thus its strength and hardness. (Despite its name, it is this internal structure that is the only glasslike thing about metallic glass: the material is not transparent, Demetriou notes, and is both optically and electronically like metal.)

The problem with trying to increase strength in ordinary metals is that their atoms are organized in a crystal lattice, Demetriou explains. "And whenever you try to make something as perfect as a crystal, inevitably you will create defects," he says. Those defects, under stress, become mobile, and other atoms move easily around them, producing permanent deformations. While this rearrangement around defects results in an ability to block or cap off an advancing crack, producing toughness, it also limits the strength of the material.

On the other hand, glass has an amorphous structure, its atoms scattered about without a specific discernible pattern. In metallic glasses—also called amorphous metals because of their structure—this results in an absence of the extended defects found in crystalline metals. The actual defects in glasses are generally much smaller in size and only become active when exposed to much higher stresses, resulting in higher strengths. However, this also means that the strategy used in ordinary metals to stop a crack from growing ever longer—the easy and rapid rearrangement of the atoms around defects into a sort of cap at the leading edge of a crack—is not available.

"When defects in the amorphous structure become active under stress, they coalesce into slim bands, called shear bands, that rapidly extend and propagate through the material," says Demetriou. "And when these shear bands evolve into cracks, the material shatters."

It was this tendency to shatter that was thought to be one of the limiting factors of metallic glasses, which were first developed in the 1960s at Caltech. The assumption was that, despite their many benefits, they could never match or exceed the toughness of the toughest steels.

But what the Caltech scientists found, much to their surprise, was that creating more of a problem could actually solve the problem. In the new palladium alloy, so many shear bands form when the material is put under stress that it "actually leads to higher toughness, because the bands interact and form networks that block crack propagation," Demetriou explains. In other words, the number of shear bands that form, intersect, and multiply at the tip of an evolved crack is so high that the crack is blocked and cannot travel very far. In essence, then, the shear bands act as a shield, preventing shattering. Thus, the palladium glass acts very much like the toughest of steels, using an analogous blocking mechanism of arresting cracks.

"And," Demetriou adds, "this high toughness does not come at the expense of strength. This material has both strength and toughness, which is why it falls so far outside what's previously been possible. That's why this material is so special."

The palladium alloy described in the paper could soon be of use in biomedical implants, says Demetriou. "One example is dental implants," Demetriou says. "Many noble-metal alloys, including palladium, are currently used in dentistry due to their chemical inertness and resistance to oxidation, tarnish, and corrosion. Owing to its superior damage tolerance, the present palladium glass can be thought of as a superior alternative to conventional palladium dental alloys. Plus, the absence of any elements considered toxic or allergenic—nickel, copper, aluminum—from the composition of this alloy will likely promote good biological compatibility."

The class of such tough metallic glasses potentially could be used in other structural applications like automotive and aerospace components, the team says. But this particular alloy is unlikely to be part of any large-scale manufacturing process. "It's prohibitively expensive," says Demetriou. "The cost is much too high for any large-scale, widespread use."

Still, he notes, the fact that it was created at all, with these particular properties, tells scientists that this level of toughness and strength is well within reach. Now it's just a matter of figuring out specifically what gives this alloy its unique damage tolerance, and how that can be replicated with an alloy containing less-expensive, less-precious metals.

In addition to Demetriou and Johnson, the other authors on the Nature Materials paper, "A Damage-Tolerant Glass," are Caltech graduate student Glenn Garrett, visitor in applied physics and materials science Joseph Schramm, and lecturer in applied physics and materials science Douglas Hofmann; Robert Ritchie from the Lawrence Berkeley National Laboratory (LBNL) and UC Berkeley; and Maximilien Launey, formerly of LBNL and now at the Cordis Corporation. Their work was supported by the National Science Foundation and the U.S. Department of Energy.

Deborah Williams-Hedges | EurekAlert!
Further information:
http://www.caltech.edu

More articles from Materials Sciences:

nachricht Triboelectric nanogenerators boost mass spectrometry performance
28.02.2017 | Georgia Institute of Technology

nachricht Nano 'sandwich' offers unique properties
28.02.2017 | Rice University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Safe glide at total engine failure with ELA-inside

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded after a glide flight with an Airbus A320 in ditching on the Hudson River. All 155 people on board were saved.

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded...

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

New technology offers fast peptide synthesis

28.02.2017 | Life Sciences

WSU research advances energy savings for oil, gas industries

28.02.2017 | Power and Electrical Engineering

Who can find the fish that makes the best sound?

28.02.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>