Metal Makeover: Recasting Metals as Glass-For War and More
Weiss, Peter Ulrich, Science News
Some of the brass directing U.S. Navy research funding appears to have gone off the deep end: The Navy has been sinking serious money into the possibility of building future warships out of glass. Since the late 19th century, shipbuilders have opted for metals, mainly various grades of steel. Yet recently, military agencies have spent tens of millions of dollars on the concept of boats with glass hulls. As fractured as the idea may seem, it just might make maritime history.
There's no plan to abandon the tried-and-true building of iron-sided ships. In fact, the new glass-bottomed boats being considered actually would be made of a kind of steel. That's because under certain conditions, a metal's orderly crystalline structure can be transformed into a hodge-podge of atoms that typifies glasses. In other words, the material becomes an amorphous or glassy metal, which can have remarkable strength or other desirable properties.
Earlier this year, two independent teams of materials scientists reported the first steels that are not only glassy but that also can be formed into relatively large pieces, a prerequisite for shipbuilding. Measurements indicate that those substances are up to three times as strong as conventional steels. What's more, the glassy steels--even though they are iron alloys--exhibit little tendency to corrode, even in seawater, and are nonmagnetic at room temperature.
The upshot of these developments could be ships with thinner, yet stronger, hulls than conventional craft have. Less likely to rust than ordinary vessels, such ships also would require less maintenance, according to military sponsors of the research. Furthermore, because they would be nonmagnetic, the vessels could better evade detection and enemy mines.
Despite the promise of these new glassy steels, they're not factory-ready yet, most notably because they're too brittle. Ships made of the stuff would crack at sea, if they ever got there in the first place.
If efforts to overcome this flaw succeed, ships may prove to be only one small part of the future of such steels. Because the materials outperform ordinary steels in many ways, their potential uses span the range of structures, vehicles, equipment, tools, and weapons now made from conventional steel. What's more, as the flagship for a whole new class of materials, glassy steel also may spur interest in other glassy metals, which are also known as metallic glasses.
"We could potentially move into the age of amorphous metals, says Leo Christodoulou of the Defense Advanced Research Projects Agency (DARPA) in Arlington, Va.
PEDAL TO THE METAL Since 1959, when Pol Duwez of the California Institute of Technology in Pasadena made the first metallic glass from gold and silicon, materials researchers have created thousands of glassy alloys from metals such as aluminum, nickel, titanium, copper, and iron.
Because those alloys combine traits of both glasses and metals, they often exhibit remarkable properties. For one, they're typically two to three times stronger and harder than conventional crystalline metals are. Indeed, just last year a Japanese team reported making a cobalt-based glassy metal that seems to be the strongest metal ever made. That work by Akihisa Inoue of Tohoku University in Sendai and his colleagues appeared in the October 2003 Nature Materials.
Glassy alloys also appear to be tops among metals at recovering a shape after being deformed. "They make the world's best springs," says Gary J. Shiflet of the University of Virginia in Charlottesville. They also absorb energy from an explosion better than conventional metals do.
As a raw material, glassy metals offer another advantage over conventional metals: They behave as plastics do. Manufacturers can heat them to a viscous, taffy like state and inject them into molds to make objects of a specific size and shape, all in one step. Traditional ways of making parts out of ordinary metals often yield objects only approximately the size needed in a final product. …