Step aside Gorilla glass – this is King Kong glass. Scientists have developed a new type of damage-tolerant metallic glass which they say demonstrates a strength and toughness beyond that of any known material.
It’s a microalloy based on palladium, a metal with a high ‘bulk-to-shear’ stiffness ratio that counteracts the intrinsic brittleness of glassy materials. And the team reckons it can improve it even further.
“The rare combination of toughness and strength, or damage tolerance, extends beyond the benchmark ranges established by the toughest and strongest materials known,” says Robert Ritchie of Berkeley Lab.
“These results mark the first use of a new strategy for metallic glass fabrication and we believe we can use it to make glass that will be even stronger and more tough.”
Glassy materials have a non-crystalline, amorphous structure that give them fantastic strength – but invariably make them brittle. While the crystalline structure of metals can provide tiny obstacles that inhibit cracks from propagating, there’s nothing in the amorphous structure of a glass to do the same. The problem’s especially acute in metallic glasses.
The team, from Berkely and CalTech, had already created a metallic glass, dubbed DH3,in which the propagation of cracks was blocked by the introduction of a second, crystalline phase of the metal.
They’ve now produced a pure glass material with a unique chemical composition that allows it to form multiple shear bands before the bands turn into cracks.
Initial samples were microalloys of palladium with phosphorous, silicon and germanium that yielded glass rods approximately one millimeter in diameter. Adding silver to the mix enabled the team to increase this to six millimeters. The size is limited by the need to cool the liquid metals rapidly for the final amorphous structure.
“Our game now is to try and extend this approach of inducing extensive plasticity prior to fracture to other metallic glasses through changes in composition,” says Ritchie.
“The rule of thumb is that to make a metallic glass we need to have at least five elements, so that when we quench the material, it doesn’t know what crystal structure to form and defaults to amorphous.”