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Metallic glass iPhone gets closer

A metallic-glass rod before heating and molding (left); a molded metallic-glass part (middle); the final product with its excess material trimmed off (right).
A metallic-glass rod before heating and molding (left); a molded metallic-glass part (middle); the final product with its excess material trimmed off (right).Marios D. Demetriou

A new breakthrough in the manufacturing of so called metallic glass, a material that is stronger than steel and titanium, could lead to a new generation of super-tough cell-phone cases and airplane parts, according to a new study.

Metallic glass is not transparent like windows. Rather they are metals that have non-crystalline structure.

While glass is generally strong, hard, and resistant to deformation, it tends to easily crack or shatter. Metals resist cracking and brittle fracture, but have limited strength. Metallic glass combines the strength of glass with the toughness of metals.

Metallic glass has been around since 1960 and produced in bulk form since the 1990s, but the manufacturing process has been prohibitively expensive for mass producing things such as cell phone cases.

Now, researchers at the California Institute of Technology have developed a new technique that allows them to make metallic glass parts using the same inexpensive process used to produce plastic parts.

"We've redefined how you process metals," William Johnson, a professor of engineering and applied science who led the research, said in a news release.

Making metallic glass

Current metallic glass parts are produced by heating a metal above 1,000 degrees Celsius, which is above the melting point of the crystalline phase. Then, the molten metal is cast into a steel mold where it is cooled before it crystallizes.

The problem is that steel molds are typically designed to withstand temperatures of around 600 degrees Celsius. As a result, molds often break and need to be replaced, which makes the process expensive.

The new process involves heating and processing the metallic glass quickly to between about 500 and 600 degrees Celsius, where it has the same fluidity as liquid plastic — fluid enough to be injected into a mold and allowed to freeze all before it crystallizes. 

The trick is heating the metallic glass quickly. They do this with a process called ohmic heating, which passes a brief jolt of power — about a megawatt — to heat a small rod of metallic glass in about a millisecond.

The current pulse heats the entire rod, about 4 millimeters in diameter and 2 millimeters 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 said. 

Since it takes only about half a millisecond to reach the moldable liquid state, the material can be injected into a mold and cooled all before crystals form.

From donuts to iPhone cases?

To prove the point, the researchers heated the rod to 550 degrees Celsius and molded it into a toroid, a donut-shaped object, in less than 40 milliseconds. The new shape is still metallic glass. 

"We end up with inexpensive, high-performance, precision net-shape parts made in the same way plastic parts are made – but made of a metal that's 20 times stronger and stiffer than plastic," Johnson said. 

The process, which is detailed in the May 13 issue of Science, has been patented and is being developed for commercialization. A metallic-glass case for the iPhone? It really could be right around the corner.

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John Roach is a contributing writer for Connect with the Cosmic Log community by hitting the "like" button on the Cosmic Log Facebook page or following's science editor, Alan Boyle, on Twitter (@b0yle).