“We’ve discovered a new mechanism at work at the nanoscale that allows us to make metals that are much stronger than anything ever made before—while not losing any electrical conductivity,” says Frederic Sansoz, a materials scientist and mechanical engineering professor at the University of Vermont who co-led the new discovery.
This fundamental breakthrough promises a new category of materials that can overcome a traditional trade-off in industrial and commercial materials between strength and ability to carry electrical current.
By mixing a trace amount of copper into the silver, the team showed it can transform two types of inherent nanoscale defects into a powerful internal structure. “That’s because impurities are directly attracted to these defects,” explains Sansoz. In other words, the team used a copper impurity—a form of doping or “microalloy” as the scientists style it—to control the behavior of defects in silver. Like a kind of atomic-scale jiu-jitsu, the scientists flipped the defects to their advantage, using them to both strengthen the metal and maintain its electrical conductivity.
To make their discovery, the team—including experts from UVM, Lawrence Livermore National Lab, the Ames Laboratory, Los Alamos National Laboratory and UCLA—started with a foundational idea of materials engineering: as the size of a crystal—or grain—of material gets smaller, it gets stronger. Scientists call this the Hall-Petch relation. This general design principle has allowed scientists and engineers to build stronger alloys and advanced ceramics for over 70 years. It works very well.
“We’ve broken the world record, and the Hall-Petch limit too, not just once but several times in the course of this study, with very controlled experiments,” says Sansoz.
Sansoz is confident that the team’s approach to making super-strong and still-conductive silver can be applied to many other metals. “This is a new class of materials and we’re just beginning to understand how they work,” he says. And he anticipates that the basic science revealed in the new study can lead to advances in technologies—from more efficient solar cells to lighter airplanes to safer nuclear power plants. “When you can make material stronger, you can use less of it, and it lasts longer,” he says, “and being electrically conductive is crucial to many applications.”