Stronger than steel

Add to molten metal a pinch of this element, a dash of that— perhaps a smidgen of yttrium, a rare earth element—and with enough tweaking over time, cooking it at temperatures of more than 1,000 degrees and cooling it at varying rates, you may get a stronger steel. Possibly a lot stronger.

An endless series of experiments has been the recipe of success for three U.Va. men of steel: physicist Joe Poon, materials scientist Gary Shiflet and materials physicist Vijayabarathi Ponnambalam.

As a result of nearly two decades of research, the U.Va. team has discovered a nonmagnetic “amorphous” material that is three times stronger than conventional steel and has superior anticorrosion properties.

A future variation of this material—they call it DARVA-Glass 101— could be used for making ship hulls, lighter automobiles, tall buildings, corrosion-resistant coatings, surgical instruments, electronic devices and recreational equipment such as tennis rackets, golf clubs and bicycles. The scientists say commercial use of the wear-resistant material could be available within three to five years.

“Amorphous steels can potentially revolutionize the steel industry,” Poon said.

The material, made up of steel alloys that possess a randomized arrangement of atoms—thus “amorphous” steel—was discovered by modifying an earlier version of amorphous steel first reported by the team two years ago to the Materials Research Society.

That discovery made waves in the world of materials research—even The Wall Street Journal covered it—but Poon, Shiflet and Ponnambalam knew the material could be even better. They went back to the lab and last spring reported on the more advanced DARVA-Glass 101 in the Journal of Materials Research. The world at large took notice, and a wide variety of popular newspapers and magazines covered the discovery. This steel is the talk of the town among materials scientists.

The defense department is particularly interested. The U.Va. project is sponsored by the Defense Advanced Research Projects Agency (DARPA), the military’s research arm that funds investigations into materials and technologies that seem futuristic but have very real potential for applicability in the relatively near future.

“They have very high standards for success and progress,” Poon said, “and they are mission-oriented.”

“We’ve managed to keep our project funded by continually making improvements to the steel and by making it bigger,” Shiflet added. “There is little doubt that our material will be of military and industrial value.”

The material is of interest to the Navy for making nonmagnetic ship hulls, especially for submarines, which are detectable by the magnetic field of their hulls. The amorphous steel that the U.Va. team is refining is nonmagnetic, potentially making a ship invisible to magnetism detectors and mines that are detonated by magnetic fields. The new material also may be useful for producing lighter but harder armor-piercing projectiles. The publicly traded company Liquidmetal Technologies owns an exclusive license to the amorphous steel invented by the U.Va. scientists.

According to Poon and Shiflet, researchers have been making amorphous steel in very small quantities for years but have had great difficulty scaling up the material to sizes large enough for practical use. But the U.Va. team has succeeded in producing large-size amorphous steel samples that could be further scaled up in industrial labs for mass production. They achieved this by adding a small dose of yttrium to create their newest version of the composite.

When the scientists began work on this project less than three years ago, their earliest version was a magnetic metal of less than one-tenth of an inch thick. Their most recent amorphous steel is nonmagnetic and one-half inch thick.

The team is continually “trying to fool nature,” as Shiflet put it, always seeking to come up with something better and stronger. During the last two years the U.Va. scientists have produced more than 100 variations of their material on the journey toward the creation of DARVA-Glass 101.

The “glass” in the material’s name refers to the frozen liquid structure of the material, somewhat like glass, which is a liquid made solid by rapid cooling. But DARVA-Glass 101 is an aluminum-based metal composite “frozen” to a solid state by rapid cooling. The material is quite versatile; it can be machined as well as manipulated like a plastic.

“It can be squeezed, compressed, flattened and shaped,” Poon said.

But it’s not perfect.

“The problem with making a high- tech material is that while nature gives you something, it also takes something away,” Shiflet said. “We have been able to achieve great strength and nonmagnetic properties for the material, but it is still somewhat brittle.”

 So it’s back to the lab for more refinement, more innovation.

“Discovery is going on all the time,” Poon said. “We need to toughen the material more. We can always make it better.”

The testing process can be as simple as dropping a sample onto a concrete floor from a height of about six feet—Poon calls it a poor man’s way of testing whether the material is brittle. The newest version of the amorphous steel can withstand about 20 drops, which Poon said is moderately brittle. They also have instruments for more precise testing of their materials.

The research team continually revises its strategies based on each new knowledge gained and what they think may happen if they try something else, perhaps something outrageous. They also use computer models to make rational guesses about how a metal may respond to different temperatures or to the introduction of new elements.

“The models help validate theory,” Shiflet said. “They provide guidelines and help us identify trends so we can make intelligent decisions.” But ultimately the science still comes down to long hours and years of experimentation in the lab, learning how to manipulate real materials according to the laws of nature.

“It’s labor intensive,” Poon said.

Editor's Note: Joe Poon and Gary Shiflet were named to the 2004 Scientific American 50 -- the magazine's annual list recognizing leadership in science and technology from the past year.