When scientists at Lawrence Berkeley National Laboratory set out to design and test two promising new metal alloys against the most punishing temperatures imaginable, they reached out to UCI's metal processing team, as large, high-quality samples needed to be processed and manufactured.

Diran Apelian, distinguished professor of materials science and engineering, collaborated on the material design, and produced and processed bulk samples of two novel high-entropy alloys (HEAs) from elemental feedstocks, enabling the testing that led to a major breakthrough. The paper, led by UC Berkeley scientists and published in Nature, found these new alloys defy the temperature limitations, paving the way for a wide range of applications.

"The Nb-based refractory HEAs have so many applications in aerospace, energy production and defense," Apelian said. "The properties we have been able to observe in these novel materials have opened a whole new vista and a new chapter in metallurgy."

Materials scientists have long sought a metal capable of withstanding the extreme heat of jet engines, turbines and rockets while remaining resilient in extreme cold. Most metals become brittle at low temperatures - a phenomenon called the ductile-to-brittle transition - making them impractical for many extreme applications. The two new alloys maintain exceptional toughness from 20 Kelvin (-423 degrees Fahrenheit) to 1,300 degrees Celsius (2,372 degrees Fahrenheit).

HEAs are a relatively new class of metals made from near-equal mixtures of multiple elements, rather than the one- or two-element formulas of traditional alloys. The two alloys — Nb45Ta25Ti15Hf15 and Nb70Ti30 — achieved toughness levels of 100 MPa√m at cryogenic temperatures and above 250 MPa√m at room temperature, far surpassing the toughest existing body-centered cubic (BCC) materials, such as steel, under the same extreme conditions. 

Apelian, who has collaborated with Berkeley researchers Robert Ritchie and David Cook for several years, produced the alloys from elemental feedstocks using electric arc melting and plasma melting, followed by solid-state processing including rolling. That specialized expertise in bulk metals processing made UCI an essential partner in the collaboration. The finished samples were subjected to an extensive battery of stress and fracture tests, from cryogenic experiments at Berkeley Lab to neutron diffraction studies at the ISIS Neutron and Muon Source in the United Kingdom.

Jet engines, hypersonic aircraft, spacecraft and next-generation power systems all depend on materials that can perform reliably under extreme conditions. The study shows that high-temperature BCC HEAs can overcome the brittleness once thought to be an unavoidable feature of the material class.

The research was funded by the U.S. Department of Energy.

  • Paul McQuiston