[Editors] MIT: Solving the mysteries of metallic glass

[Elizabeth Thomson]

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Solving the mysteries of metallic glass
--New understanding could lead to significant new materials
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For Immediate Release
MONDAY, DEC. 22, 2008

Contact: Elizabeth A. Thomson, MIT News Office
E: thomson at mit.edu, T: 617-258-5402

Photo Available

CAMBRIDGE, Mass. — Researchers at MIT and the National University of  
Singapore have made significant progress in understanding a class of  
materials that has resisted analysis for decades. Their findings could  
lead to the rapid discovery of a variety of useful new kinds of glass  
made of metallic alloys with potentially significant mechanical,  
chemical and magnetic applications.

The first examples of metallic alloys that could be made into glass  
were discovered back in the late 1950s and led to a flurry of research  
activity, but, despite intense study, so far nobody had solved the  
riddle of why some specific alloys could form glasses and others could  
not, or how to identify the promising candidates, said Carl. V.  
Thompson, the Stavros Salapatas Professor of Materials Science &  
Engineering and director of the Materials Processing Center at MIT. A  
report on the new work, which describes a way to systematically find  
the promising mixes from among dozens of candidates, was published  
last week in Science.

Glasses are solids whose structure is essentially that of a liquid,  
with atoms arranged randomly instead of in the ordered patterns of a  
crystal. Generally, they are produced by quickly cooling a material  
from a molten state, a process called quenching.

“It is very difficult to make glasses from metals compared to any  
other class of materials, such as semiconductors, ceramics and  
polymers,” Thompson said. Decades of effort by scientists around the  
world have focused on “understanding and on exploiting the remarkable  
properties of these materials, and on understanding why some alloy  
compositions can be made into glasses and others cannot,” he said.

They still haven’t solved that “why,” Thompson said. But this new work  
does “provide a very specific and quantitative new insight into the  
characteristics of liquid alloys that can most readily be quenched  
into the glassy state,” he said, and thus provides a much more rapid  
way of discovering new alloys that have the right properties.

The research was the result of a collaboration between Thompson and  
MIT post-doc Johannes A. Kalb with Professor Yi Li and graduate  
student Qiang Guo at the National University of Singapore, working  
together across thousands of miles of separation through the Singapore- 
MIT Alliance. Essentially, the work consisted of producing an array of  
different alloys with slightly varying proportions of two metals, each  
deposited on a separate microscopic finger of metal. Then, they  
analyzed the changes in density of each different mixture when the  
glass crystallized, and found that there were a few specific  
proportions that had significantly higher density than the others —  
and those particular alloys were the ones that could readily form  
glasses. Of three of these special proportions they found, two were  
already known glass-forming alloys, but the third was a new discovery.

The new work could even lead to a solution to the longstanding puzzle  
of why only certain alloys make glasses, he said. “I expect these new  
results, and the technique we developed to obtain them, will play a  
key, and hopefully decisive, role in solving the mystery of metallic  
glass formation.”

Such materials could have a variety of applications because of their  
unusual physical and magnetic properties, Thompson said. They are  
“soft” magnetically, meaning that it’s very easy to change the  
magnetic orientation of the material. This is a highly desirable  
characteristic for the cores of transformers, for example, which must  
switch their magnetic orientation dozens of times per second.  
Transformers made from metallic glasses could potentially greatly  
reduce the amount of electricity wasted as excess heat in conventional  
transformers, reducing the need for new generating plants.

In addition, these glasses are unusually hard mechanically and have a  
high degree of springiness (known technically as a high “elastic  
modulus”). This springiness could make them a useful material for some  
sports equipment such as golf clubs or tennis rackets, Thompson said.  
Although metallic glasses are relatively expensive, he said, for some  
people interested in the best-performing sports equipment, or in  
virtually unbreakable housings for cellphones, for example, “no  
expense is too high.”

The new research is a major accomplishment for the Singapore-MIT  
Alliance, Thompson said, and would not have been possible without the  
high-quality communications and collaboration tools it provides.  
Despite their physical separation, “Prof. Li and I have been working  
together now for almost ten years,” he said. “We routinely meet via  
video conferencing and have both been deeply involved in the co- 
supervision of the remarkable PhD student, Qiang Guo, who carried out  
this research.”

Thompson said he sees such collaborations as a significant example of  
a growing trend. “I think this and other accomplishments within the  
SMA program demonstrate that the future of research lies in technology- 
mediated collaborations among people with common interests and  
complementary capabilities, regardless of where the different parts of  
the team are located,” he said.

The research was supported by the SMA program, and Kalb was partially  
supported through a fellowship from the German Alexander Von Humboldt  
Foundation.

--END--


Written by David Chandler, MIT News Office
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