A research team led by the University of Virginia (UVA) (Charlottesville, Virginia, USA) has developed new protective coatings that they believe will allow turbine engines to run at higher temperatures before components begin to fail.
“Hotter engines are more efficient,” says Elizabeth J. Opila, professor and chair of UVA’s materials science and engineering department and a lead researcher on the project.
Turbine engines are known for aircraft propulsion, but stationary turbines have many industrial uses, including power generation. They burn fuel to rotate turbine blades, converting mechanical energy to electricity.
“You get more work output per heat input at higher temperatures,” Opila explains. “The potential benefits drive interest in coatings that act as a barrier against the reactive gases produced by combustion at these high temperatures that can damage turbine blades.”
Efficiency translates to less fuel consumption and reduced emissions and operating costs—which helps account for why the U.S. Department of Energy’s ARPA-E ULTIMATE program funded the team’s work. They published their findings in the October 2024 print issue of Scripta Materialia.
Limitations of High-Temperature Materials
Two primary material systems are used in the hot section of modern turbine engines. According to the UVA researchers, these are:
- Coated nickel-based superalloys can tolerate up to about 2,200 °F (1,204.4 °C)—well short of the DOE’s goal of nearly 3,300 °F (1,815.6°C).
- Ceramic composites use several coating layers to protect against degradation from oxidation, a chemical reaction that occurs with exposure to air and moisture. However, these systems are limited by the melting temperature of one layer, silicon, which melts at 2,577 °F (1,413.9 °C).
In their work, the UVA-led team focused on another material option called refractory metal alloys. Refractory metals were studied extensively in the 1960s. While durable and heat-resistant, they were abandoned due to poor oxidation resistance.
To protect the alloy, the researchers experimented with rare earth oxides—chemical compounds that naturally possess strong protective properties—to come up with one do-it-all coating.
“By combining multiple rare earth oxides, tailoring properties to better protect the underlying substrate can be achieved with just a single layer,” says Kristyn Ardrey, a Ph.D. alumna of Opila’s lab and first author of the paper. “This allowed us to achieve better performance without complex multi-layer coatings.”
A Multidisciplinary Team Approach
Opila’s lab created and tested new combinations of rare earth elements, such as yttrium, erbium, and ytterbium. To predict the best combinations and improve performance, they worked with UVA associate professors Bi-Cheng Zhou and Prasanna Balachandran. Their labs specialize in computer simulations and machine learning, a form of artificial intelligence (AI).
The team applied the coatings to alloys using two standard manufacturing methods. One technique heats the material to a molten state before spraying on the surface. The other is applied as a liquid mixture that dries and hardens.
The researchers tested and compared how well each method performed under extreme heat and reactive conditions, such as exposure to high-temperature steam.
They also partnered with UVA Professor Patrick Hopkins’ ExSiTE Lab, which specializes in using lasers to measure heat resistance and material strength.
“This was a collaborative effort,” Opila says. “Using machine learning and computational methods allowed us to explore a huge range of possible material combinations, and Patrick’s lab was key to understanding the physical characteristics of the materials we developed.”
Future Work Scope
As one of the first research groups to experiment with multicomponent rare earth oxides, the team says it knows more testing and refinement are needed. Using computer simulations will help them continue improving the coatings and analyze the best ways to apply them.
But their results represent an important step forward in turbine engine technology—and that should be good for everyone.
“Reducing fuel consumption and emissions while improving engine performance is not only good for industries like energy and aviation,” Opila concludes. “It also means a cleaner environment and lower costs for everyday consumers.”
Further Publication Details
The team’s complete research article, titled “Opportunities for novel refractory alloy thermal/environmental barrier coatings using multicomponent rare earth oxides,” was first published online June 4, 2024.
Additional UVA contributors include Mackenzie J. Ridley, Kang Wang, William Riffe, Mukil Ayyasamy and Mahboobe Jassas, representing the departments of materials science and engineering; mechanical and aerospace engineering, and physics.
Kevin Reuwer, Giavanna Angelo, and Carolina Tallon of the materials science and engineering department at Virginia Tech University and Kevin Childrey and Jonathan Laurer of the Commonwealth Center for Advanced Manufacturing also were collaborators.
The U.S. Office of Naval Research provided additional funding.
Source: University of Virginia Engineering, engineering.virginia.edu.