A multidisciplinary team led by the Department of Energy's Pacific Northwest National Laboratory and North Carolina State University combined atomic-scale experiments with theory to predict how high-entropy alloys behave under high-temperature oxidation. Their research, published in Nature Communications, aims to create rapid design and testing cycles for oxidation-resistant complex metal alloys.

"We are working toward developing an atomic-scale model for material degradation of these complex alloys, which then can be applied to design next-generation alloys with superior resistance to extreme environments for a wide variety of applications such as the aerospace and nuclear power industries," said Arun Devaraj, co-principal investigator of the study and a PNNL materials scientist specializing in understanding metal degradation in extreme environments. "The goal here is to find ways to rapidly identify medium- to high-entropy alloys with the desired properties and oxidation resistance for your chosen application."

The team studied a high-entropy alloy with equal amounts of cobalt, chromium, iron, nickel, and manganese, known as the Cantor alloy. They used advanced atomic-scale methods to understand the arrangement of each element in the alloy and its oxide. Chromium and manganese quickly formed stable oxides on the surface, while iron and cobalt diffused through these oxides to form additional layers. Adding aluminum created a barrier that reduced overall oxidation and increased resistance to high-temperature degradation.

"This work sheds light on the mechanisms of oxidation in complex alloys at the atomic scale," said Bharat Gwalani, co-corresponding author of the study. Gwalani, formerly at PNNL and now an assistant professor at North Carolina State University, added, "By understanding the fundamental mechanisms involved, this work gives us a deeper understanding of oxidation across all complex alloys."

"Right now there are no universally applicable governing models to extrapolate how a given complex, multi-principal element alloy will oxidize and degrade over time in a high-temperature oxidation environment," said Devaraj. "This is a substantial step in that direction."

The team developed the Preferential Interactivity Parameter model for predicting oxidation behavior in complex alloys. They aim to expand research to develop alloys with exceptional high-temperature properties quickly through rapid sampling and analysis. The next steps include automated experimentation and integrating additive manufacturing methods with artificial intelligence to evaluate new alloys.

"That kind of discovery loop for materials discovery will be very relevant for further expanding our knowledge of these novel alloys," said Devaraj, who also has a joint faculty appointment at the Colorado School of Mines.

In addition to Gwalani and Devaraj, contributors included PNNL scientists Sten Lambeets, Matthew Olszta, Anil Krishna Battu, and Thevuthasan Suntharampillai; Martin Thuo, Aram Amassian, Andrew Martin, Aniruddha Malakar, and Boyu Guo of NCSU; Elizabeth Kautz, an assistant professor at North Carolina State with a joint appointment at PNNL; Feipeng Yang and Jinghua Guo of Lawrence Berkeley National Laboratory; and Ruipeng Li of Brookhaven National Laboratory.

The team used in situ atom probe tomography at PNNL, electron microscopy, and synchrotron-based grazing incidence wide-angle X-ray scattering at the National Synchrotron Light Source II, and X-ray absorption measurements at the Advanced Light Source. This research was supported by the DOE Office of Science, Basic Energy Sciences, Materials Sciences, and Engineering Division as part of the Early Career Research Program.

Research Report:Mechanistic understanding of speciated oxide growth in high entropy alloys

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