A very tough marginal glass made of palladium with small fractions of metalloids like phosphorus, silicon, and germanium, yielded one-millimeter-thick samples. By adding 3.5 percent silver to this marginal glass, Demetriou (Caltech) was able to increase the thickness to six millimeters while maintaining its toughness.
"The Achilles' heel of these metallic glasses is that when you pull them in tension or try to deform them somehow, they fail catastrophically," says Greer. This occurs through the formation of what's termed "shear bands," small defects which coalesce into vein-like patterns that rapidly evolve as cracks, causing the glass to break under extremely small strains. However, according to the researchers, the palladium glass generates so many of these bands that they form a blocking pattern that prevents cracks from propagating without impairing the material's overall properties.
The limitation is palladium's very high cost. Therefore, Ritchie says, although there are countless structural applications that could utilize this material's high strength and toughness—like automotive and aerospace components—many of them will prove impractical in the marketplace. Demetriou is more optimistic. He believes there's already demand for metallic glass and says a product like a dental implant made from the stuff could be available within the next five years. He says this would offer a "superior alternative" to traditional implants made of noble metals, which are softer and stiffer and thus more likely to wear or cause bone atrophy.
The first step is convincing a manufacturer that the material possesses "unique and unusual attributes," he says. Then a series of tests of its performance, longevity, and biological compatibility will be needed before ultimately determining whether the pricing would be competitive.
As for making large-scale structures like bridges, Demetriou says cost would probably prevent that. But he has hopes of developing something cheaper. "If we develop an iron or copper alloy with these properties," he says, "I'll tell you this: we will put steel out of business forever."
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