Glassy Metals May Be the Structural Material of the Future
(Civil Engineering)
Jessica Binns
A strong metal need not be a heavy metal, and research pioneered by William Johnson, a professor of materials science at the California Institute of Technology, has proved just that. His lab in Pasadena has developed a substance called glassy metal-or amorphous metal-that is less than half the weight of conventional alloys and more than twice as strong. Amorphous metals are also remarkably malleable and behave in much the same way as plastic.
One basic property sets these new materials apart from the average metal alloys: amorphous metals are rapidly cooled and their atoms frozen in place before there is a chance for crystallization to occur. Because glassy metals do not contain crystals, they are not subject to the denting, corrosion, and tearing problems that result when the crystals that are typical of conventional metals are pushed out of alignment.
Currently, the major drawback of glassy metals is their price. Because they are created with such expensive metals as zirconium, titanium, beryllium, nickel and copper, 1 lb (0.45 kg) of the product costs between $10 and $20, as opposed to steel, which typically costs $0.25 per pound, or aluminum, which costs about $1 per pound. The cost currently “precludes using amorphous metal in larger-scale applications,” says Johnson. However, research is being done to determine if the material’s properties can be obtained with such less-expensive metals as iron. Johnson says research at the University of Virginia has developed iron-based amorphous metal alloys that can be cast in thicknesses up to 1 cm. His company, Liquidmetal Technologies of Lake Forest, California, has licensed patents on the iron-based material filed by the university.
Glassy metals cast in sheets hold promise for creating vehicles and aircraft that are environmentally more benign. “The fuel economy of a car is intimately tied up with its weight,” says Johnson. If a car is lighter, it will ultimately be cleaner in terms of emissions because it will need less gasoline to run. Similarly, airplanes using amorphous metal in their structural elements may require significantly less fuel. “A pound out of the weight of the jet over the lifetime of the aircraft is worth a couple hundred thousand dollars in fuel,” says Johnson.
One of the material’s most exciting properties is its ability to be formed into foam. Says Johnson, “This material is particularly amenable to foaming because it’s thick and very plastic.” Although foam formed with amorphous metal is predominantly composed of air, it is significantly stronger than polystyrene, he says. When flanked by thin glassy metal panels, the capabilities of amorphous foam are intriguing: the combination would be rustproof and fireproof, would act as an insulator, would reduce sound, would be impervious to insets, and would be not only strong but also extremely light, Johnson says. “If you make thick foam panels, you can leverage the stiffness and strength of the panel by making it thicker without making it heavier,” he explains. “You take the same material and foam it (to obtain) a larger dimension.”
Johnson sees a world of possibilities for commercial applications of glassy metals but cautions, “We’re not going to see bridges of amorphous metal anytime in the near future.” Still, it is not inconceivable that in 30 years glassy metals will be competitive with conventional alloys and suitable for large-scale applications. For now, the best applications for this emerging material will involve structures for which performance and strength-t-weight ratios confer the greatest value. For this reason, Johnson’s thoughts turned to the National Aeronautics and Space Administration (NASA). “The reason you might look (at outer space) first is because that’s the most weight-sensitive structural application you can think of,” he says, adding that he has proposed that NASA create a solar collector from his glassy metal concoction.
Transporting the light metal to space and creating a foam from it there to form a structure would be cheaper than hauling a heavy metal into orbit, he adds. His proposal is still in the early stages, but Johnson is optimistic about it. “If you want the strongest frame for the least weight,” he says, “these glassy metal foam materials would be one of the best out there.”
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