New material combines the strength of steel and the moldability of plastic

Scientists at Yale University have done what materials scientists have been trying to do for decades – create a material that boasts the look, strength and durability of metal that can be molded into complex shapes as simply and cheaply as plastic. The scientists say the development could have the same impact on society as the development of synthetic plastics last century and they have already used the novel metals to create complex shapes, such as metallic bottles, watch cases, miniature resonators and biomedical implants, that are twice as strong as typical steel and can be molded in less than a minute.

Unlike the crystalline structure found in ordinary metals that makes them strong but also results in them requiring three separate steps for processing (shaping, joining and finishing), the metal alloys recently developed by the Yale team are amorphous metals known as bulk metallic glasses (BMGs), whose randomly arranged atoms and low critical cooling rate allows them to be blow-molded into complex shapes like plastics. This allows the researchers to combine the three traditional time- and energy-intensive metal processing steps into one blow molding process that takes less than a minute.

Although the different metals used to make the alloys, such as zirconium, nickel, titanium and copper, cost about the same as high-end steel, they can be processed as cheaply as plastic, according to Jan Schroers, a materials scientist at Yale that led the team.

The BMGs ability to soften and flow as easily as plastic at low temperatures and low pressures, without crystallizing like regular metal is what allows the material to be shaped with unprecedented ease, versatility and precision, Schroers said. To ensure the ideal temperature for blow molding was maintained, the team shaped the BMGs in a vacuum or in fluid.

"The trick is to avoid friction typically present in other forming techniques," Schroers said. "Blow molding completely eliminates friction, allowing us to create any number of complicated shapes, down to the nanoscale."

Schroers and his team have already fabricated a wide variety of shapes and devices using the new processing technique, including miniature resonators for microelectromechanical systems (MEMs) and gyroscopes, but they say that is just the beginning.

"This could enable a whole new paradigm for shaping metals," Schroers said. "The superior properties of BMGs relative to plastics and typical metals, combined with the ease, economy and precision of blow molding, have the potential to impact society just as much as the development of synthetic plastics and their associated processing methods have in the last century."

The new processing technique developed by the Yale researchers is described online in the current issue of Materials Today.