Working with graduate student Atakan Peker, Johnson zeroed in on an alloy with five elements: zirconium, titanium, nickel, copper, and beryllium. Every day, starting in January 1992, Peker patiently mixed these metals in varying amounts. Ten months later, he scored. “Atakan walked in and said, ‘I melted the alloy, and when it cooled back down, I think it was amorphous,’” recalls Johnson.
No cryogenics, no fancy cooling strategies. The stuff cooled to room temperature and solidified as a glass, complete with a characteristic mirror finish. “That was the turning point,” says Johnson, his eyes distant at the happy memory. “The crystallization was orders and orders of magnitude slower than anything we had seen. We discovered later that this stuff was such a good glass former, we could probably make it two inches thick!”
Over the next six months, Johnson and Peker made “several hundred” glassy alloys with varying amounts of those elements, leading to a particularly promising version they dubbed Vitreloy. It proved to be just as amazing as Johnson had predicted. The strongest titanium alloys in common use in the world, when formed into a one-inch-diameter bar, can hoist 175,000 pounds. A same-size bar of Vitreloy can lift 300,000 pounds.
Still, it had a major weakness. Pure Vitreloy had a nasty tendency to shatter like glass. “With a golf driver, a crack would form after a few hits, and eventually you would have club shards flying in all directions,” says Johnson, throwing his hands wide to indicate an exploding clubface. Materials scientists call this catastrophic shear failure. Conventional metals don’t do it because the crystal dislocations bunch up around a crack tip, making the surrounding area stronger. “What this material needed was the ability to fail gracefully, like normal metals do,” says Johnson.
In 2000 Johnson and his team came up with Liquidmetal2, which marries the strength and elasticity of glassy metal to the graceful failure of ordinary metal. It is 80 percent glass and 20 percent crystal. The crystals act like horsehair in old-fashioned plaster, cross-reinforcing the crack-prone amorphous metal. “Now I have matched the toughness and impact resistance of the best alloys out there, with two to three times the strength,” says Johnson. “Now I really have something.”
A bright jumble of shiny parts and gadgets spills across Johnson’s desk: cell phone cases, camera bodies, golf clubheads, folding knives, and nasty-looking three-inch-long cannon shells. All were created by Liquidmetal Technologies. Founded in 1987 and headquartered in Lake Forest, California, with a manufacturing plant in Pyongtaek, South Korea, it is the world’s first commercial manufacturer of bulk metallic glass products and has about a dozen pilot projects under way for the U.S. military and for private companies. “Things are busy,” says Johnson.
Though the material is expensive, Liquidmetal is doing a booming business spraying it over cheaper metals, instantly rendering boilers, oil-well drill heads, and other industrial parts more durable and slippery. “The economizer tubes on our coal-fired boilers were corroding and popping every six months,” says John Berg, maintenance director for Cogentrix Energy, headquartered in Charlotte, North Carolina. But after spray-coating the tube interiors with Liquidmetal in 1992, “it’s still there, and we’ve had virtually no leaks at all.”
Meanwhile, Liquidmetal golf clubs have been on the market since 1998, with about 40,000 drivers sold so far. The clubs exploit the amorphous alloy’s amazing springiness, or what materials scientists call a high elastic-strain limit. Under severe stress, most materials permanently deform. Whacking a golf ball with a typical titanium driver head creates a tiny, permanent dimple in the clubface, which steals energy from the ball. But a metallic glass clubface flexes like a trampoline and then springs all the way back, returning all the potential energy to the ball and adding as much as 30 yards to a pro’s drive. Liquidmetal tennis racket frames, introduced last year and used by Andre Agassi and other pros, have a similar virtue. “The response you get from the racket is pure . . . there is no energy lost during contact with the ball,” contends Bill Mountford, director of tennis at the United States Tennis Association’s national center in Flushing Meadows, New York.
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Images Courtesy of Professor Michael Widom, Physics Department, Carnegie Mellon University
