An alloy of chromium, cobalt, and nickel has just given us the highest fracture toughness ever measured in a material on Earth. It has exceptionally high strength and ductility, leading to what a team of scientists has called “outstanding damage tolerance”.
Moreover – and counterintuitively – these properties increase as the material gets colder, suggesting some interesting potential for applications in extreme cryogenic environments. 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.
Strength, ductility, and toughness are three properties that determine how durable a material is. Strength describes resistance to deformation and ductility describes how malleable a material is. These two properties contribute to its overall toughness: the resistance to fracture. Fracture toughness is the resistance to further fracture in an already-fractured material. Most alloys are dominated by one element, with small proportions of others mixed in. HEAs contain elements mixed in equal proportions.
One such alloy, CrMnFeCoNi (chromium, manganese, iron, cobalt, and nickel), has been the subject of intense study after it was noticed that its strength and ductility increase at liquid nitrogen temperature without compromising toughness.
One derivative of this alloy, CrCoNi (chromium, cobalt, and nickel), displayed even more exceptional properties. The previous experiments on CrMnFeCoNi and CrCoNi had been conducted at liquid nitrogen temperatures, up to 77 Kelvin (-196°C, -321°F). It was pushed it even further, to liquid helium temperatures.
The results were beyond striking.

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