Scientists create world’s strongest material

By Mark Waghorn via SWNS

The world's strongest material has been created by scientists.

It's around 500 times harder than diamond - the most resistant naturally occurring element on Earth.

The metal alloy contains a cocktail of chromium, cobalt and nickel (CrCoNi).

It opens the door to indestructible cars and planes and buildings that can withstand earthquakes.

CrCoNi is highly malleable - and also resists permanent deformation. Remarkably its qualities improve as it gets colder - unlike alternatives.

Project co-leader Professor Robert Ritchie said: "The toughness of this material near liquid helium temperatures (-424 Fahrenheit) is as high as 500 megapascals square root meters.

"In the same units, the toughness of a piece of silicon is one, the aluminum airframe in passenger airplanes is about 35 and the toughness of some of the best steels is around 100.

"So, 500, it's a staggering number."

CrCoNi belongs to a class known as HEAs (high entropy alloys) - made of an equal mix of each constituent element.

The atomic recipes bestow an extraordinarily high combination of strength and bendiness when stressed.

Co-leader Professor Easo George said: "When you design structural materials, you want them to be strong but also ductile and resistant to fracture.

"Typically, it's a compromise between these properties. But this material is both, and instead of becoming brittle at low temperatures, it gets tougher."

HEAs have been a hot area of research since they were first developed about 20 years ago.

But the technology required to push the materials to their limits in extreme tests was not available until recently.

The team at California University in Berkeley created CrCoNi almost a decade ago but
it took ten years to find facilities that could test it in such cold temperatures.

Many solid substances, including metals, exist in a crystalline form characterized by a repeating 3D atomic pattern, called a unit cell.

It makes up a larger structure called a lattice - where weaknesses occur. This is what causes a metal spoon to bend, for instance, when force is applied.

Scanning techniques showed CrCoNi's toughness is due to a trio of obstacles that come into effect in a particular order when force is applied to the material.

The sequence ensures the metal keeps flowing - but also keeps meeting new resistance from obstacles far past the point that most materials snap from the strain.

Ritchie said: "So as you are pulling it, the first mechanism starts and then the second one starts, and then the third one starts, and then the fourth.

"Now, a lot of people will say, well, we've seen nanotwinning in regular materials, we've seen slip in regular materials. That's true.

"There's nothing new about that, but it's the fact they all occur in this magical sequence that gives us these really tremendous properties."

The study in the journal Science may force the materials experts to reconsider long-held notions about how physical characteristics give rise to performance.

Ritchie said: "It’s amusing because metallurgists say that the structure of a material defines its properties, but the structure is the simplest you can imagine – it’s just grains."

George foresees uses in situations where environmental extremes could destroy standard metallic alloys, such as in in the frigid temperatures of deep space.

His team are also investigating how alloys made of more abundant and less expensive elements could be coaxed into having similar properties.

There is a global shortage of cobalt and nickel due to their demand in the battery industry.

Ritchie said real-world use is still a little way off as many safety trials will be required.

He said: "When you are flying on an airplane, would you like to know that what saves you from falling 40,000 feet is an airframe alloy that was only developed a few months ago?

"Or would you want the materials to be mature and well understood? That's why structural materials can take many years, even decades, to get into real use."