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, Demetrio
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California Institute of Technology