National Lab, University Develop Tougher, Stronger Glass

Robert Ritchie (Roy Kaltschmidt, Berkeley Lab)

A group of engineering and materials scientists have developed a new type of damage-tolerant metallic glass, demonstrating a strength and toughness that they say goes beyond that of any known material. The team had members from California Institute of Technology in Pasadena and the U.S. Department of Energy’s Lawrence Berkeley National Laboratory in Berkeley, California.

The new metallic glass is a microalloy featuring palladium, a metal with a high “bulk-to-shear” stiffness ratio that counteracts the intrinsic brittleness of glassy materials. Materials scientist Robert Ritchie (pictured right), who led the Berkeley Lab’s contribution to the research says, “The result is that glass undergoes extensive plasticity in response to stress, allowing it to bend rather than crack.”

Glassy materials have a non-crystalline, amorphous structure that make them strong but almost always brittle. Metals, on the other hand, have a crystalline structure with built-in obstacles that keep cracks from spreading, like they do in glass. Metallic glasses can be a particular problem, since shear bands can form and extend throughout the material leading to catastrophic failures at the smallest strains.

Earlier research created a metallic glass with added crystalline capabilities that kept open cracks from spreading. The Berkeley-Cal Tech team built on this earlier discovery to produce a pure glass material whose unique chemistry promotes more plasticity through the formation of multiple shear bands before the bands turn into cracks.

Ritchie says adding the palladium made a big difference, in that it gives the glass a new and unusual plasticity that combats cracking. “This promotes a fracture toughness comparable to those of the toughest materials known,” says Ritchie. “The rare combination of toughness and strength, or damage tolerance, extends beyond the benchmark ranges established by the toughest and strongest materials known.”

The team’s findings are published in the 9 January 2011 online issue of the journal Nature Materials (paid subscription required).

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