Navigation Links
Caltech-led team creates damage-tolerant metallic glass
Date:1/12/2011

PASADENA, Calif.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 toughthey resist shatteringbut 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 tougha 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, Demetrioualong with William Johnson, Caltech's Ruben F. and Donna Mettler Professor of Engineering and Applied Science, and their colleaguesreport in a recent issue of the journal Nature Materials that they have developed just such a material. Their new alloya combination of the noble metal palladium, a small fraction of silver, and a mixture of other metalloidshas 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 metalswith the inherent toughness that comes with that class of materialbut 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 glassesalso called amorphous metals because of their structurethis 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 longerthe easy and rapid rearrangement of the atoms around defects into a sort of cap at the leading edge of a crackis 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 allergenicnickel, copper, aluminumfrom 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.


'/>"/>

Contact: Deborah Williams-Hedges
debwms@caltech.edu
626-395-3227
California Institute of Technology
Source:Eurekalert  

Related biology news :

1. Caltech-led researchers find negative cues from appearance alone matter for real elections
2. Caltech-led team provides proof in humans of RNA interference using targeted nanoparticles
3. East-African human ancestors lived in hot environments, says Caltech-led team
4. NIH awards $11.5 million for new Caltech-led membrane-protein center
5. Early-stage gene transcription creates access to DNA
6. MIT creates tiny backpacks for cells
7. Florida professor creates endowment for insect scientists
8. Crustacean shell with polyester creates mixed-fiber material for nerve repair
9. NYSCF Fellow lead author on study that creates blood vessel cells from stem cells
10. $15 million stimulus award creates national consortium for revealing scientific resources
11. Antarctica glacier retreat creates new carbon dioxide store
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Caltech-led team creates damage-tolerant metallic glass
(Date:6/23/2017)... N.Y. and ITHACA, N.Y. ... ) and Cornell University, a leader in dairy research, ... with bioinformatics designed to help reduce the chances that ... With the onset of this dairy project, Cornell University ... Consortium for Sequencing the Food Supply Chain, a food ...
(Date:5/6/2017)... May 5, 2017 RAM Group ... a new breakthrough in biometric authentication based on ... mechanical properties to perform biometric authentication. These new sensors ... material created by Ram Group and its partners. This ... transportation, supply chains and security. Ram Group is ...
(Date:4/13/2017)... , April 13, 2017 UBM,s Advanced ... will feature emerging and evolving technology through ... Innovation Summits will run alongside the expo portion of ... sessions, panels and demonstrations focused on trending topics within ... advanced design and manufacturing event will take place June ...
Breaking Biology News(10 mins):
(Date:9/20/2017)... Station, TX (PRWEB) , ... ... ... Services, LLC (IPS), a leading global provider of engineering, architecture, project controls, ... provider of prefabricated cleanrooms, today announced the unveiling of the iCON™ brand ...
(Date:9/20/2017)... ... September 20, 2017 , ... Foresight Institute, ... and other transformative technologies, announced the winners for the 2017 Foresight Institute Feynman ... Theory in nanotechnology/molecular manufacturing. , Established in 1993 and named in honor of ...
(Date:9/19/2017)... (PRWEB) , ... September 19, 2017 , ... ... Philadelphia’s largest group of funded early-stage tech companies. “Grit” author Angela Duckworth and ... Also joining the ic@3401 community is Cooley, an international law firm with decades ...
(Date:9/19/2017)... ValGenesis Inc., the global leader in Enterprise ... the strategic partnership with VTI Life Sciences (VTI). This ... using the latest technology available in the ValGenesis VLMS ... efficient and cost-effective validation services using ValGenesis VLMS. VTI ... VLMS system. The ...
Breaking Biology Technology: