The hardness of this new material belonging to metals far exceeds that of steel, say the scientists.
Scientists have measured the highest hardness ever recorded, of any material. While researching a metal alloy made of chromium, cobalt and nickel (CrCoNi) they created the hardest material on Earth to date.
Metal is not only extremely ductile, which, in materials science, means very malleable, and impressively strong (meaning it resists permanent deformation), but it its strength and ductility improve as it cools. This goes against most other existing materials.
The team, led by researchers from the Lawrence Berkeley National Laboratory (Berkeley Lab) and the Oak Ridge National Laboratory (ORNL), in the United States, published a study describing their unprecedented findings in Science.
“When you design structural materials, you want them to be strong, but also ductile and resistant to fracture,” project co-director Easo George, an expert in Advanced Alloy Theory and Development at ORNL and the University of Tennessee, said in a statement.
“Usually it’s a compromise between these properties. But this material is both, and instead of becoming brittle at low temperatures, it becomes stronger,” he added.
What would be the hardest material on Earth?
CrCoNi is a subset of a class of metals called high entropy alloys (HEAs). All alloys in use today contain a high proportion of one element with lower amounts of additional elements added, but HEAs are made from an equal mixture of each constituent element.
These balanced atomic recipes seem to give some of these materials an extraordinarily high combination of strength and ductility when stressed. On the whole, these characteristics constitute what is called “toughness”.
HEAs have been a hot area of research since they were first developed some 20 years ago, but the technology needed to push materials to their limits in extreme tests wasn’t available until recently.
“The hardness of this material near liquid helium temperatures (20 Kelvin) is as high as 500 square root megapascals,” said research co-leader Robert Ritchie, a senior faculty scientist in the Science Division of Berkeley Lab Materials.
“In the same units, the hardness of a piece of silicon is one, the aluminum frame of airliners is about 35, and the hardness of some of the best steels is around 100. So, 500, that’s a staggering number,” he concluded.