A new concept in metallic alloy design — called "high‐entropy alloys" — has yielded a multiple-element material that tests out as one of the toughest on record. Unlike most materials, the strength and ductility of the alloy actually improves at cryogenic temperatures.

“We examined CrMnFeCoNi, a high‐entropy alloy that contains five major elements rather than one dominant one,” says Robert Ritchie, a materials scientist with Berkeley Lab’s Materials Sciences Division. “Our tests showed that despite containing multiple elements with different crystal structures, this alloy crystallizes as a single phase, face‐centered cubic solid with exceptional damage tolerance, tensile strength above one gigapascal, and fracture toughness values that are off the charts, exceeding that of virtually all other metallic alloys.”

Tensile strengths and fracture toughness values were measured for CrMnFeCoNi from room temperature down to 77 Kelvin, the temperature of liquid nitrogen. The values recorded were among the highest reported for any material. That these values increased along with ductility at cryogenic temperatures is a huge departure from the vast majority of metallic alloys, which lose ductility and become more brittle at lower temperatures.

The single-phase, high-entropy alloys would be ideal for cryogenic applications, such as storage tanks for liquefied natural gas, hydrogen, and oxygen.

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