US researchers develop crack-resistant metallic glass

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.

‘Because of the high bulk-to-shear modulus ratio of the palladium-containing material, the energy needed to form shear bands (or narrow zones of intense shearing strain) is much lower than the energy required to turn these shear bands into cracks,’ said Robert Ritchie, a materials scientist who led the Berkeley contribution to the research.

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 inherently strong but invariably brittle. While the crystalline structure of metals provides microstructural obstacles such as inclusions and grain boundaries that inhibit cracks from propagating, there is nothing in the amorphous structure of a glass to stop crack propagation. The problem is especially acute in metallic glasses, where single shear bands can form and extend throughout the material leading to catastrophic failures.