In the world of materials, strength (the amount of force a substance can withstand) and toughness (its capacity to resist fracturing) are not merely different attributes; they’re very difficult to achieve together. Now a collaboration of researchers from Caltech and the Department of Energy’s Lawrence Berkeley National Laboratory has created a form of glass that has both qualities. It’s stronger and tougher than steel or, indeed, any other known material. The material features palladium, a metal whose possible use in glasses was recognized 45 years ago.
“It’s probably the best damage-tolerant material we’ve seen,” says Robert Ritchie, a professor at the University of California, Berkeley, who tested the new material. He says no one has ever achieved such toughness from 100 percent glass and that the potential exists to mass-produce the glass.
Julia Greer, an assistant professor of Materials Science at Caltech, who was not involved with developing the material, says, “it has potential to overcome the limitations the metallic glasses always had.”
The work is outlined in a study published this week in the journal Nature Materials. Marios Demetriou, a professor at Caltech and lead author of the paper, says the work involved finding a particularly strong version of the simplest form of glass, called marginal glass, and then turning it into the even stronger form known as bulk glass.
“What we did here is find a very, very tough marginal glass made of palladium with small fractions of metalloids like phosphorus, silicon, and germanium, which yielded one-millimeter-thick samples. And we just said, let’s add very little of something that will make it bulk without making it brittle,” says Demetriou. By adding 3.5 percent silver to this marginal glass, Demetriou 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.