At extreme temperatures, friction can damage the metal parts used in jet engines, manufacturing equipment, and defense systems — but protective liquid lubricants quickly burn off or degrade above 700 degrees Celsius.
Researchers from Virginia Tech, Arizona State University, and Iowa State University have received a $2 million grant from the National Science Foundation (NSF) to solve that problem by manufacturing self-lubricating, wear-resistant metal alloys that won't break down even at ultra-high temperatures.
Wenjun (Rebecca) Cai is an associate professor in the department of Materials Science and Engineering , and Yao Fu is an associate professor in the Kevin T. Crofton Department of Aerospace and Ocean Engineering . Together, they’re leading the research at Virginia Tech as affiliates of Virginia Tech Made: The Center for Advanced Manufacturing and spoke about their work.
Cai: Above roughly 600 degrees Celsius, conventional liquid lubricants fail, and many traditional solid lubricants oxidize or lose their effectiveness. At the same time, components such as bearings, seals, turbine interfaces, and other moving contacts still experience friction and wear.
Our inspiration came from realizing that oxidation might provide the missing link. If we can make the alloy strong internally but cause its surface to form a stable, low-shear oxide during operation, we can potentially achieve structural strength and lubrication in the same material.
The idea of turning what is normally a degradation mechanism into a functional response is really the origin of this project.
Fu: Protective oxidation has a long history in materials science. What is exciting here is that we are deliberately designing the material and processing route so that oxidation becomes part of the desired functionality.
One challenge from the manufacturing and mechanics perspective is that a material’s high-temperature behavior is determined not only by its composition, but also by its microstructure and processing history. Additive manufacturing introduces unique microstructures, defect populations, dislocation networks and residual stresses, all of which can influence diffusion and oxidation. That complexity is a challenge, but it also gives us additional variables that we can potentially engineer to obtain the surface behavior we want.
Cai: Friction and wear are not just surface-science problems; they affect the efficiency, lifetime, and reliability of entire systems. A material that can generate and continuously regenerate its own lubricating oxide surface during operation could reduce dependence on conventional lubricants and coatings.
For aerospace propulsion, power-generation systems, and other extreme-temperature technologies, that could translate into lower frictional losses, reduced wear, longer component life, less maintenance, and greater reliability at higher operating temperatures. The broader vision is therefore not simply a better wear-resistant alloy, but materials that become functionally adaptive to the environment in which they operate.
Cai: Complex concentrated alloys give us an unusually large compositional design space. Instead of relying primarily on one base element with small additions of other elements, we can combine several principal elements and use their interactions to control strength, phase stability, diffusion, and oxidation.
For this project, that flexibility is especially powerful because we are trying to optimize two materials simultaneously: the metallic alloy underneath and the oxide that forms on its surface. Our central hypothesis is that configurational entropy can help stabilize a strong bulk alloy while also promoting stable, low-shear spinel oxides at the surface.
Fu: We are looking for compositions that maintain strength at high temperature while also providing the right chemistry and diffusion behavior to form desirable surface oxides. The ability to engineer both the bulk and surface response within the same alloy system is particularly attractive.
Cai: The traditional way of developing a new alloy can involve making one composition, testing it, changing the composition, making another, and repeating that process many times. With complex concentrated alloys, the number of possible combinations becomes enormous, so trial-and-error experimentation alone is neither practical nor efficient.
Our closed-loop framework connects theory, simulation, additive manufacturing, high-throughput experiments, characterization, tribology, and machine learning. We need to narrow the search space by predicting which compositions should form stable spinels, retain high-temperature strength, and follow desirable oxidation pathways. We then manufacture and test selected materials. Those experimental results are returned to the computational and machine-learning models, which update their predictions and identify the next most informative experiments.
Cai: One of the major goals [of the NSF funding] is not simply to discover one successful alloy. We want to create a reusable materials-discovery infrastructure. The project will generate open datasets, computational workflows, physics-guided machine-learning models, and inverse-design tools that connect composition and processing all the way to oxidation, mechanical properties, friction, and wear.
The longer-term value is that these tools should not be limited to self-lubricating alloys. The same framework — combining physical models, high-throughput experiments, uncertainty-aware AI, and closed-loop optimization — could be adapted to many other materials-discovery problems.
Fu: I think one of the most valuable outcomes will be the framework rather than any single alloy we discover. The same idea of connecting computational models, manufacturing, characterization, and experiments through a closed-loop framework can be applied to many other materials problems. For Virginia Tech Made in particular, this provides a pathway for using our additive-manufacturing capabilities not only for fabrication, but as part of an integrated materials-discovery platform.