Aluminum adds flex to metallic glass.

Aluminum adds flex to metallic glass

Until recently, expectations that lightweight, aluminum-rich glassy alloys could be substituted for denser materials in aerospace applications had been undermined by the brittle nature of these substances. But metallic glasses produced independently by U.S. and Japanese researchers now indicate that established processes can yield flexible, aluminum-rich glasses.

These alloys are more elastic because they contain a higher proportion of aluminum than do brittle glasses of similar compositions, says Joseph Poon of the University of Virginia in Charlottesville. As reported in the Sept. 23 SCIENCE, Poon, Yi He and Gary Shiflet produced metallic glasses with more than 90 percent aluminum. Previously such synthesized metallic glasses contained less than 80 percent aluminum.

The new alloys, in the form of ribbons, also include iron and cerium. Poon told SCIENCE NEWS that alloys--synthesized at Tohoku University in Sendai and described in the April JAPANESE JOURNAL OF APPLIED PHYSICS--contain about as much aluminum, but include nickel and yttrium instead of iron and cerium.

He says his team will now try to locate other groups of elements that produce flexible, aluminum-rich alloys and study their atomic structures using X-ray- and neutron-diffraction techniques to understand why certain combinations work and others do not. "There's no theory right now to explain this," he says.

"But," he adds, "the techniques for creating the alloys are well established." Poon says aerospace companies already are capable of synthesizing aluminum-rich glasses using melt spinning, the technique both teams used to produce their alloys. Other common rapid-solidification methods could produce the substances in various shapes and thicknesses, adds researcher He.

The materials also are well suited for constructing aircraft and space vehicles, Poon says, because they crystallize at relatively high temperatures. Glasses tend to weaken over time, "but a higher crystallization temperature means a slower rate of change."

With crystallization temperatures of about 300[deg.]C, some of these alloys could remain stable, and therefore durable, for periods longer than human lifetimes, Poon says. Materials that crystallize at about 100[deg.]C might last only a few years.

Poon's group also plans to investigate its evidence that pockets of iron atoms within the disordered alloys seem to arrange themselves at temperatures much lower than those at which the glasses exhibit order when they crystallize.