Most aluminum alloys are only good up to 200 degrees Celsius, which means they couldn’t be used in high-temperature conditions, like in engines.

Now, professors at the McCormick School of Engineering and Applied Science at Northwestern University (David N. Seidman, Walter P. Murphy, David C. Dunand, James N. and Margie M. Krebs) have created a new kind of aluminum alloy by engineering it at the nano level to give it high-strength and corrosion resistance to high temperatures [Monachon et al., Small (2010) 6, 1728].

The scientists combined aluminum with lithium (which has a lower density than aluminum and makes the material more lightweight) and scandium—that helps strengthen aluminum. They also added ytterbium, which also acts as a strengthener but is much cheaper than scandium.

The researchers have devised a process of timed heating that naturally arranges the atoms into nano-particles with a new kind of structure—a core surrounded by two shells. The core is ytterbium-rich, while the first shell is rich in scandium and the second shell contains mostly lithium. This core/shell-shell structure has been achieved by chemists in liquid solutions but this is the first time it has been achieved by processing solely in the solid-state.

The core/shell-shell nano-particles make the material much stronger because they act as strong obstacles for line defects that can glide through the material, and their layered structure helps make the material much more resistant to high temperatures.

“We have shown that this process works in the solid state,” Dunand said. “It shows we can make nano-particles that are complex and tuned to the properties we need. It could be applicable to a large number of alloys.”

The researchers also found that some nano-particles had a structure they weren’t expecting—a single particle with two cores and two outer shells, like a double-yolked egg. This is the first time this type of structure has been observed.

“That was the whipped cream on the cake,” Seidman said. The professors said further research is needed on what such a structure could do for materials.

“It’s the best when something unexpected happens,” Dunand said. “The next step is to figure out whether this particle is superior to the single-core particles.”

Jonathan Agbenyega