The toughest material on Earth

Scientists have measured the highest toughness ever recorded of any material while investigating a metallic alloy made of chromium, cobalt and nickel. The metal is extremely ductile, which in materials science means highly malleable, and impressively strong, meaning that the metal resists permanent deformation. The strength and ductility of the metal also improve as it becomes colder. This runs counter to most other materials in existence.

The team was led by researchers from Lawrence Berkeley National Laboratory and Oak Ridge National Laboratory.

Microscopy-generated images show the path of a fracture and accompanying crystal structure deformation in the CrCoNi alloy at nanometer scale during stress testing at 20 K (-424 F). The fracture is propagating from left to right. Image courtesy of R. Ritchie/Lawrence Berkeley National Laboratory

“When you design structural materials, you want them to be strong but also ductile and resistant to fracture,” said project co-lead Easo George, the governor’s chair for advanced alloy theory and development at ORNL and University of Tennessee. “Typically, it’s a compromise between these properties. But this material is both, and instead of becoming brittle at low temperatures, it gets tougher.”

“The toughness of this material near liquid helium temperatures (20 kelvin, -424 Fahrenheit) is as high as 500 megapascals square root meters,” said research co-leader Robert Ritchie, senior faculty scientist at Berkeley Lab’s materials sciences division and Chua professor of engineering at University of California, Berkeley. “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.”