Normally, with metals, there is a trade-off between strength and electrical conductivity, but new materials may change that. A team of researchers managed to use defects to make silver much stronger than usual, while still maintaining its electrical conductivity. Not only that, but it pushes decades-old theoretical limits.
Defects are an inevitable part of metals, and over time they often cause problems such as brittleness or softening. Combining different metals into alloys can help overcome some of these problems, but often at the expense of electrical conductivity. Finding the best of both worlds is the goal of researchers.
The solution sounds simple enough: They mixed a tiny amount of copper with silver. The end result is 42 per cent stronger than the previous strongest silver, while still conducting electricity. But what's most impressive about the new alloy is that it exceeds the so-called "Hall-Page limit."
The Hall-Petch relationship, which has been a hallmark of materials science for more than 70 years, suggests that as metal grains get smaller, the material itself becomes stronger, but with a limit. When the grains become too small (a few nanometers wide), their boundaries become unstable and the material softens again.
The researchers managed to push this limit by creating a metal called a "nanocrystalline nano-twin". Since copper atoms are slightly smaller than silver atoms, they tend to fall into defects at grain boundaries. This prevents the movement of defects that cause the material to soften. At the same time, the copper atoms do not obstruct electrons from passing through the silver atoms, thus maintaining their electrical conductivity.
The team says the method could be applied to many other metals besides silver. The technology could eventually be used to make more efficient solar panels, lighter aircraft or safer nuclear power plants.
