Terminator-like: Molding metal as if plastic

It's hard to beat the versatility of plastic on a production line. Melt and inject it into molds, let it cool and harden, and out comes an endless variety of parts at high speeds.

Metals can't always compete - except, perhaps, in the movie "Terminator 2," where an evil android can promptly transform molten metal into whatever shape is needed to challenge Arnold Schwarzenegger.

But now, off screen in a laboratory at the California Institute of Technology, researchers have found an ingenious way to coax metal alloys to solidify into a range of shapes as though they were plastics being molded - and thus create stronger products. And, as such, molded metal might someday be useful as structural components or as casings to protect laptops and smart phones, for example.

In the May 13 issue of Science, William L. Johnson, a professor of engineering and applied science at Caltech in Pasadena, along with colleagues, published a new, ultrafast method for heating and injecting a metallic alloy into a mold to create shapes.

"We use the method to create precision parts," he said. "The alloy can be squeezed into just about any shape you want, and it will be far stronger and stiffer than plastic."

Johnson and a co-author, Marios D. Demetriou, a senior research fellow at Caltech, have formed a company, Glassimetal Technology, and are setting up an engineering and prototype center in Pasadena to demonstrate the process, Johnson said.

The name "Glassimetal" refers to the alloys called metallic glasses or glassy metals that the company uses in its new manufacturing process. These metallic glasses were invented at Caltech just over 50 years ago, said A. Lindsay Greer, a professor of materials science at the University of Cambridge in England.

"Metallic glasses are materials with striking properties," he said. "They are quite hard, but also rather formable like plastics - an attractive combination."

Greer says the alloys have the disorderly atomic structure of glass, rather than the orderly one of conventional metals. This microstructure means that the alloys can do what glass does - congeal into a solid without crystallizing first, a property that gives both glass and these glassy alloys great inherent strength.

One company using glassy metals for its products is Metglas Inc., a unit of Hitachi Metals America, in Conway, S.C. Metglas supplies ribbon made of metallic glass used inside distribution transformers for electrical utilities, and within anti-theft devices placed on goods to set off an alarm at store exits, said Ryusuke Hasegawa, vice president for research.

Johnson's new method should make it possible to use the alloys to create a huge variety of shapes, Hasegawa said. "There will be many applications," he said. "With this process, you can make structural parts that are strong and hard."

Greer of Cambridge said metallic glasses like the zirconium-based one used by Johnson might raise the cost of manufacturing. "Because the alloys are expensive," Greer said, "these materials will probably be used mainly in niche applications where the benefits of the properties give you sufficiently better performance to justify the expense." But the manufacturing method Johnson has created could be economical enough to chip away at some of this extra expense, he said.

This manufacturing process overcomes a drawback of metallic glasses: They crystallize quickly when heated, losing the microstructure that makes them so strong. But Johnson's method is so quick that it circumvents the problem. The entire process of shaping and cooling takes two-hundredths of a second, so fast that the material turns viscous and can be molded without crystallization.

The rapid heating is done by passing an electric current through the alloy. "Nature has been kind here," Greer said of the process. "If you tried passing an electric current through most other materials besides metallic glasses, it probably wouldn't work."