Chinese researchers announced in March that they had created glass that can be bent into right angles without shattering. But this isn’t glass as we know it: The new glass is opaque, twice as strong as window glass, and made of metal.
As solids, metals have an orderly atomic structure; in liquid metals, the arrangement becomes random, as in glass. To create metallic glass, scientists supercool liquid metals, effectively “freezing” the random array in place. These bulk metallic glasses, or BMG, are two to three times stronger than the crystalline form of the metals.
Superstrong BMG has already been used in the manufacture of high-tech golf clubs and tennis rackets; in 2001, the collector on NASA’s Genesis spacecraft, which caught particles from the solar wind, was made of BMG.
But since the 1980s, when scientists began making BMG, the materials have exhibited a fatal flaw. Paradoxically, the stronger they are, the more vulnerable they are to cracks, says Wei Hua Wang, a physicist who helped develop the new glass at the Chinese Academy of Sciences. A tiny fracture in the original type of BMG spreads quickly and becomes catastrophic.
To create a glass that is both strong and flexible, Wang and his colleagues altered an existing BMG recipe, combining zirconium, copper, nickel, and aluminum. Realizing that small changes in the metal mixture would lead to large variations in brittleness, they sought a combination that would keep cracks from spreading. “The plasticity of the glass is very sensitive to the composition,” Wang explains.
After two years, the scientists produced bendable BMG. It contains hard areas of high density surrounded by soft regions of low density. The result: When a crack begins in one place, it dissipates quickly in the surrounding regions, leaving the whole flexible.
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