New Technique Churns Out Metallic Glass Like Plastic
CREDIT: Marios D. Demetriou
A new technique can squeeze cylinders of metallic glass, a material often stronger than the toughest steel, into any shape as easily as working with plastic. By switching to this process, companies like Apple or HTC could produce lighter, stronger products at much cheaper prices.
High-precision stainless steel parts like iPhone cases are typically milled from hunks of solid metal. The process is laborious, time-consuming and expensive. The new part-forming method, however, can heat, shape and cool blanks of ultra-strong metallic glass in a matter of microseconds.
"This is about meeting the economics of plastic, which is incredibly cheap, with the durability of stainless steel," said materials scientist William Johnson of Caltech. He is also the former vice chairman of technology at Liquidmetal Technologies, a company from which Apple has recently and exclusively licensed metallic-glass technologies.
When metal parts aren't cut from solid blanks, they're cast out of metallic dust or melted and poured into molds. But in the process, crystals form and weaken the overall structure to impacts, bending, corrosion and other conditions.
Cool a molten material quickly enough, however, and its atoms can't organize into crystals. The resulting phase is an amorphous state known as glass. Although some metallic glasses are brittle like shatter-prone window panes, Johnson and his colleagues recently showed metallic glass rich with palladium exceeds the known limits of strength and durability of pretty much anything.
"How tough is it? Tougher than toughest steel and, in terms of brittleness or cracking, better than or as good as steel," Johnson told InnovationNewsDaily.
In the new study, published May 13 in the journal Science, Johnson and seven colleagues describe a way to mold such metallic glass like plastic a feat that's incredibly difficult, since most metallic glass will crystallize if not evenly heated, formed and cooled in less than a second.
"With plastic, it takes a long time to crystallize . You pretty much have all day to heat and form the parts you want," Johnson said. "Metallic glasses are the definition of unforgiving."
To mold-inject metallic glass, the researchers wedged a 1-inch-tall cylinder of the stuff into a circular mold. In 30 microseconds less time than it takes to blink an eye the contraption melted the metallic glass, formed it into the mold and cooled the shape back into glass.
However, the process has two main drawbacks. First, metallic glass of the type licensed by Apple contains toxic chemicals. And the alternative type of metallic glass that works in this process costs too much to produce savings for the consumer.
"The best metallic glass material doesn't exist yet," Johnson said. "That would be a glassy iron chromium. In other words, glassy stainless steel."
When a safe and relatively inexpensive material arrives, Johnson and his team's process will be waiting to generate a great number of ultra-strong parts in a matter of microseconds.
"Someone will eventually cook up a really good recipe," Johnson said.
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