New class of metal materials is its strong suit


A snapshot of atomistic simulation models that contain twin boundary defects. Those defects play an important role in determining strengthening or softening of nanocrystalline-nanotwinned metals. (Download Image)

In a perfect world, engineers would like metals to be strong and electrically conducive without any defects.

But no metal is perfect. It loses strength due to synthetic defects, causing a softening of the material.

Lawrence Livermore National Laboratory (LLNL) scientists and collaborators have created a new class of metal material that keeps its strength and electroconductivity by overcoming the defects. The material could be used in electrical wiring as well as electronics.

The research breaks the existing trade-off between strength and electrical conductivity and demonstrates the potential for creating interface-dominated material with unprecedented mechanical and physical properties.

“We asked how can we make a material with defects but overcome the softening while retaining the electroconductivity,” said LLNL material scientist Morris Wang, corresponding author of the research appearing in the journal Nature Materials.

After determining which metals could work together through computer simulations, the team chose silver. Silver is naturally electroconductive but as the grain size gets smaller and smaller, to the size that would fit in an electronic device, it begins to break down. These defects cause a softening of the material.

Researchers added a micro-alloy of copper to the silver. “At the nanoscale, these two metals don’t like to mix, such that the copper goes to the location of the defects and locks down the motion of those defects, so the material is no longer softening but actually is getting stronger,” Wang said.

At the same time, the material did not lose any electrical conductivity. Wang said silver is just one example of how to overcome the defects-caused softening, but the same strategy could be applied to other metals as well.

“For real world applications, if you use the right combination of metals, you sacrifice very little,” Wang said. “You’re able to achieve a new kind of material that has high strength and still maintains its electrical properties.”

Other Livermore researchers include Jianchao Ye and Dognxia Qu. Other institutions include the University of Vermont, Ames Laboratory, Los Alamos National Laboratory and the University of California Los Angeles.

The work was funded by LLNL’s Laboratory Directed Research and Development program.

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