May 11th, 2012 by James Ayre
A research team at the University of Wisconsin-Madison and Iowa State University has discovered new atomic structures, on the nanometer-scale, in materials called metallic glasses.
Just published in the journal Physical Review Letters, the finding will eventually help fine-tune some of the properties of metallic glasses for manufacturing purposes.
Currently, metallic glasses are used in electrical transformer cores, but with the discovery, they can potentially be used to make very small, complex designs, down to the nano scale.
“Unlike conventional metallic alloys, metallic glasses can be molded like plastic-so they can be pushed or sucked or blown into very complicated shapes without any loss of material or machining,” says Paul Voyles, an associate professor of materials science at UW-Madison.
“Five or 10 years from now, there may be more commercial applications driven by those kinds of things than there are now,” he says.
It had been previously believed that all atoms in metallic glasses were arranged in pentagons in ‘five fold rotational symmetry’.
The researchers found that in certain glass, like a zirconium-copper-aluminum mix, there are also clusters of squares and hexagons, some forming chains located within the space of a few nanometers.
“One or two nanometers is a group of about 50 atoms-and it’s how those 50 atoms are arranged with respect to one another that’s the new and interesting part,” he says.
Measuring the atomic structure of glass at that scale had previously been difficult because of how compact it is, and at larger scales there is no order.
“But what happens in between, at this ‘magic’ length of one to three nanometers, is very hard to measure experimentally and is essentially unexplored in experiments and simulations,” says Voyles.
So the researchers used a state-of-the-art electron microscope. “And that, fundamentally, is what makes the experiments work and gives us access to this information that’s otherwise very difficult to obtain,” he says. “We can match our experimental probe in size right to the size of what we want to measure.”
They then combined that with state-of-the-art computational methods. “It’s the combination of those two things that gives us this new insight,” he says. “We can look at the results and abstract general principles about rotational symmetry and nanoscale clustering.”
“If we understand how the structure controls, for example, glass-forming ability or the ability to change shape on bending or pulling, and we understand how different elements participate in these different kinds of structures, that gives us a handle on controlling properties by adjusting the composition or adjusting the rate at which the material was cooled or heated to change the structure in some useful way,” he says.
The researchers next step will be to learn more about the properties of the more realistic models they developed.
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