Determining Pathways for Improved Oxidation Resistance in Compositionally Complex Alloys

NON-TECHNICAL SUMMARY

Metal alloys are widely used as structural materials in many high temperature applications such as power plants, aircraft engines, and rocket motors. Conventional alloys are typically made of one or two primary alloying elements with addition of other low-concentration alloying elements to improve alloy properties. Recently, high entropy alloys, also known as complex concentrated alloys, have received significant interest due to their novel structures and properties.

Unlike conventional alloys, high entropy alloys consist of five or more principal alloying elements in nearly equal concentrations. These concentrated alloys exhibit outstanding physical properties compared to conventional alloys including high-temperature strength, corrosion resistance, and radiation tolerance, though the reasons why are poorly understood to date.

This project investigates the fundamental mechanisms of high temperature oxidation in high entropy alloys and establishes the roles of chemistry and microstructure in controlling oxidation behavior. Through this project a diverse group of students and scientists, including women and students from Historically Black Colleges and Universities, will be trained to test, characterize, model and predict the oxidation behavior of high entropy alloys using computational and experimental tools.

This project will advance our goals towards developing materials with improved oxidation resistance which will contribute towards more fuel efficient and longer lasting power plants, improved jet and rocket engines, and safer nuclear power plants. TECHNICAL SUMMARY

High entropy alloys (HEAs) and the related complex concentrated alloys (CCAs) are garnering increased attention from the researchers worldwide searching for alternatives to conventional/legacy materials. Oxidation limits the application of many advanced materials in high temperature environments and there have been very few investigations of the oxidation behavior of high entropy alloys.

Most of those studies centered on as-fabricated (e.g., as-cast, as-sintered, etc.) alloys without addressing the influences of microstructural parameters (i.e., grain/phase size, morphology, or distribution). This research will use a coupled experimental and computational approach to establish how oxidation occurs in AlCoCrFeNi HEAs/CCAs and will provide a framework that can be used to design and fabricate HEAs/CCAs exhibiting enhanced oxidation resistance.

This research will use CALPHAD based thermodynamic modeling to predict phase equilibria and oxidation products and will use TC-PRISMA complemented with DICTRA to simulate phase precipitation due to oxidation. The simulated microstructures and phases will be validated using cross-correlative analytical electron microscopy and Atom Probe Tomography techniques to quantify solute segregation behavior and the influences of phase distribution and grain boundary character on oxidation.

This research will contribute towards the development, improvement and validation of high-quality thermodynamic and kinetic databases and will also provide necessary technical insights to facilitate the development of oxidation resistant HEAs for use in high temperature structural applications. The graduate student budgeted for the project will employ the principles of metallurgical and ceramic engineering, thin film science and materials processing, microstructural characterization, and materials selection.

They will benefit from this project by being involved in advanced research on the fabrication, chemical and microstructural characterization, and modeling of reacting materials using state-of-the-art analytical and computational tools.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.