The method of manufacture of super-hard metals without damage to their electrical conductivity

All metals have structural defects that ultimately affect their strength – the more defects in the metal, the more soft or brittle. To solve this problem, scientists create new metal alloys. This approach allows us to obtain more stable metal connections, but at the same time leads to the loss of increased their electrical conductivity. And this, in turn, limits the possibilities of use of new alloys in various tasks. Recent discovery of American scientists offers a solution to this issue. About the discovery reported in the article published by the journal Nature Materials.

The authors of the discovery were researchers from the University of Vermont who developed the mechanism of production of new alloys, allowing to make the metal much stronger, but at the same time to maintain their conductivity.

How to create a strong and electrically conductive metal

The solution was surprisingly quite simple. For example, scientists at the nanoscale mixed trace (in other words, very small) amount of copper with silver and as a result were able to obtain the durable silver alloy — it is 42 percent stronger than any silver alloy available today. But this is not the most important thing. The main thing is that by becoming stronger, while silver has not lost its properties of electrical conductivity. Recall that the silver itself has the highest conductivity among metals.

Model of the atomic structure of the grains (particles) of silver with splashes of copper (marked in green) filling the defects in the metal

Thanks to a new production method, scientists were able to overcome the so-called theoretical limit of Hall-Petch, which was maintained for the last 70 years. It is called the law of Hall-Petch. Under this limit, the smaller the grains (particles) of metal, the stronger becomes the structure of matter. However, there is some restriction. When the grain of the metal become too small – the size of a few nanometers – the boundaries of these grains becomes unstable, starts to move and deform, which leads to the fact that the metal again “softened”.

Scientists have been able to overcome this limit by creating what they call “nanocrystalline anotherbeanname metal”. As the copper atoms the size is somewhat less of silver atoms, they are able to penetrate into the structure defects at the grain boundaries of silver. This prevents defects in its structure from motion, making the metal stronger. At the same time, particles of copper do not create problems for the movement of electrons through the silver, allowing the metal to retain its electrical conductivity.

This new class of materials and we are only beginning to understand how they work, says Frederic Sansoz.