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  • A metallic-glass rod before heating and molding (left); a molded metallic-glass part (middle); the final part trimmed of excess material (right).
    Credit: Marios D. Demetriou
  • A piece of metallic glass is heated and squished in just 10 milliseconds.
    Credit: Georg Kaltenboeck
  • A piece of metallic glass being heated and squished in milliseconds, as seen in these infrared snapshots.
    Credit: Joseph P. Schramm
05/12/2011 10:00:00

Strong, Tough, and Now Cheap: Caltech Researchers Have New Way to Process Metallic Glass


"We've redefined how you process metals," says William Johnson, the Ruben F. and Donna Mettler Professor of Engineering and Applied Science. "This is a paradigm shift in metallurgy." Johnson leads a team of researchers who are publishing their findings in the May 13 issue of the journal Science.


Metallic glasses, which were first discovered at Caltech in 1960 and later produced in bulk form by Johnson's group in the early 1990s, are not transparent like window glass. Rather, they are metals with the disordered atomic structure of glass. While common glasses are generally strong, hard, and resistant to permanent deformation, they tend to easily crack or shatter. Metals tend to be tough materials that resist cracking and brittle fracture—but they have limited strength. Metallic glasses, Johnson says, have an exceptional combination of both the strength associated with glass and the toughness of metals.

Credit: Georg Kaltenboeck




If the solid metallic glass is heated to about 500–600 degrees C, it reaches the same fluidity that liquid plastic needs to have when it's processed. But it takes time for heat to spread through a metallic glass, and by the time the material reaches the proper temperature throughout, it has already crystallized.

So the researchers tried a new strategy: to heat and process the metallic glass extremely quickly. Johnson's team discovered that, if they were fast enough, they could heat the metallic glass to a liquid state that's fluid enough to be injected into a mold and allowed to freeze—all before it could crystallize.


Credit: Joseph P. Schramm

The current pulse heats the entire rod—which was 4 millimeters in diameter and 2 centimeters long—at a rate of a million degrees per second. "We uniformly heat the glass at least a thousand times faster than anyone has before," Johnson says. Taking only about half a millisecond to reach the right temperature, the now-softened glass could be injected into a mold and cooled—all in milliseconds. To demonstrate the new method, the researchers heated a metallic-glass rod to about 550 degrees C and then shaped it into a toroid in less than 40 milliseconds. Despite being formed in open air, the molded toroid is free of flow defects and oxidation.


The other authors on the Science paper, "Beating crystallization in glass-forming metals by millisecond heating and processing," are Caltech's Georg Kaltenboeck, Marios D. Demetriou, Joseph P. Schramm, Xiao Liu, Konrad Samwer (a visiting associate from the University of Gottingen, Germany), C. Paul Kim, and Douglas C. Hofmann. This research benefited from support by the II-VI Foundation.

Written by Marcus Woo