The Golden Gate bridge is made out of a relatively low strength steel, so it won’t break when an earthquake rattles the Bay Area.
When you have a structure, you tend not to use the higher strength one. As you increase strength, you decrease the toughness.
A tough material is less likely to fracture. The stronger a material is, the more likely the structure will break.
That is the problem. You can’t win because you want the material to be both things!
But researchers at the University of California at Berkeley and California Institute of Technology have created a metallic glass that can get around that problem. The new metallic glass is stronger and tougher than steel (and any other material known to man).
Robert Ritchie, a Berkeley materials scientist, said “trying to get high strength and high toughness is very difficult. One of the holy grails is to get both high strength and high toughness [in materials]. We call that damage tolerance.”
To make this metallic glass, the researchers used five elements to confuse the material. That way, the material couldn’t flex into automatic memory and form its normal, crystal structure.
This is unusual, considering all metals have crystalline structures. Window panes are amorphous and aren’t crystalline in structure.
Like glass, the fabricated material was not crystalline.
“We learned to make metals in this amorphous state,” Ritchie said. “There are stronger materials and there may be tougher materials, we know of no other material with the combination [we've made]. Strength and toughness are mutually exclusive, and we’ve achieved it in a material that you wouldn’t expect - in glass. Glass is usually brittle,” Ritchie said.
The group from Cal Tech made the material from five or more elements. They melted it and it cooled quickly. The material wasn’t able to crystallize, so it formed an amorphous material. The Cal Tech team cut the material into little rods and sent them to Ritchie’s team at Berkeley to basically destroy the metallic glass.
The experiments didn’t involve throwing the metallic glass against the floor though. Instead, Ritchie ran the metallic glass through mechanical testing machines. The machines could barely make the material crack.
In the future, the new material could be used in nuclear pressure vessels because it has the same toughness as the material used today. A better material could help nuclear reactors avoid a catastrophic failure.
Let’s remember that the new material was born out of academic curiosity. People have been fascinated with ways of finding materials that have both strength and toughness. Ritchie seems to have actually made a material that lives up to the dream.
It will be interesting to see how this material will be used in the future.
Photo: Max Launey