Portland, Ore. - In the world of materials, plastics have promised to be the wave of the future since their invention, but don't count metals out yet. By doping some ferrous base alloys with large rare-earth or yttrium atoms, researchers have been able to prevent crystallization, enabling "amorphous" (noncrystalline) steel that is three times stronger than regular steel, one-third the weight and nonmagnetic to boot. The research was sponsored by the Defense Advanced Research Projects Agency's (Darpa's) Structural Amorphous Metals Program.
In their liquid state, metals are amorphous because their atoms are not ordered in a crystalline structure. When a metal slowly cools into the solid state, all the atoms line up in a repetitive pattern, enabling magnetism to get a grip.
In contrast, amorphous materials have atoms that are oriented randomly, making them nonmagnetic. That is the structure of the metal called Darva-Glass 101. Darva-Glass 101 is predated by Darva-Glass 1, invented in 2002 at the University of Virginia, which contains iron, chromium, manganese, molybdenum, carbon and boron.
"To make Darva-Glass 101 we added a small amount of rare-earth element or yttrium to Darva-Glass 1. The large size of the added atom exerts enough atomic-level stress to destabilize crystallization and form instead an amorphous structure," said physics professor Joseph Poon. Poon and his University of Virginia colleagues Gary Shiflet, professor of materials science and engineering, and materials physicist Vijayabarathi Ponnambalam developed the new material.
Separately, a government research group at Tennessee's Oak Ridge National Laboratory, led by Chain Liu, a materials scientist, reported adding a large-atom yttrium to Darva-1 to achieve a similar amorphous steel that also shows promise.
Both groups also report that the amorphous structure makes it more difficult for surface oxidation (rust) to corrode the metal. With all its superior features, however, the material is brittle, and it could be as many as five years before that problem is solved and commercial use can be made of the metal. The University of Virginia scientists have given an exclusive license for Darva-Glass 1 to Liquidmetal Technologies Inc. (www.liquidmetal.com; Lake Forest, Calif.).
Possible applications for Darva-Glass 101 include its use in automobiles and as lighter, more corrosion-free ship hulls. The material may also find applications as a corrosion-resistant coating, for delicate yet strong surgical instruments and for lighter recreational equipment such as tennis racquets, golf clubs and bicycles.
The novel microstructures of amorphous metals are not confined by the limitations imposed by a crystalline lattice. Shiflet said amorphous metals can be treated like normal steel in machines or they can be manipulated like a plastic-squeezed, compressed, flattened and shaped. Its easy formability makes it a prime material for submarines, because its lack of a magnetic response foils the sensors that often trigger mines to explode.
Because the material is stronger, it could also be machined into very thin layers that could lighten armor that is nevertheless still immune even to armor-piercing bullets. And for electronic devices, the metal could be used not only for lighter cases but also for internal structural supports that allow devices to be thinner overall.