Team’s HERO Coating Will Increase Materials’ Temperature Tolerance by 200 Degrees Celsius

Elizabeth J. Opila, professor of materials science and engineering and director of the Rolls-Royce University Technology Center on Advanced Material Systems at the University of Virginia, has earned a grant from the Advanced Research Projects Agency-Energy to increase turbine engine materials’ temperature tolerance by 200 degrees Celsius.

“This is an audacious goal for the materials science and engineering community,” Opila said. “In the turbine engine industry, a ten-degree improvement is cause for celebration.”

Opila earned a $600,000, phase-one award through the agency’s ULTIMATE program, which stands for ultrahigh temperature impervious materials advancing turbine efficiency. ARPA-E’s challenge is to develop ultrahigh temperature materials for gas turbine use in the aviation and power generation industries. To achieve this goal, ARPA-E has awarded funds to teams working on four mutually dependent research thrusts: alloy development; coatings for the alloys; systems engineering; and test and evaluation of the whole system.

Opila’s research aligns with the coatings research thrust, sharing her expertise in cutting-edge ceramics, alloys and coatings exposed to high temperatures and extreme environments such as hypersonic vehicle wing leading edges and combustion engines. Her research group, one of the largest in the nation dedicated to understanding material behaviors at high temperatures, exemplifies UVA Engineering’s research strength in materials processing, microstructure and mechanical property relationships.

Opila has assembled a team from the University of Virginia, Virginia Tech and the Commonwealth Center for Advanced Manufacturing to develop a coating that will enable a niobium alloy to perform at 1800 ºC (3272 ºF). Niobium is a high-strength material known to withstand extreme temperatures; a number of the ARPA-E awards for alloy development feature this element.

“ARPA-E has given us an opportunity to do good science and also really good engineering, to solve real-world problems by improving turbine efficiency,” Opila said. This translates into more energy savings, lower carbon emissions and economic benefits not only in the aviation and power generation industries.

The coating’s job is to protect the alloy from oxidation. This is a really tall order, Opila said, because alloys that perform well at these high temperatures are prone to rapid oxidation.

“Nature has given us the perfect material for a coating,” Opila said, referring to rare-earth oxides. Opila’s team will design the coating made with an equal or relatively large proportion of five or more rare-earth elements in the oxide, i.e., high-entropy rare-earth oxides, for which the team has named their project the HERO coating.

High-entropy rare-earth oxides exhibit two characteristics that are key to meeting the ARPA-E challenge. First, their primary function is to keep oxygen out. Second, a number of these rare-earth oxides can limit buildup of stress in the coating during use because their thermal expansion matches the underlying alloy. The substrate and coating heat up and cool off, or expand and contract, in the same direction and at the same rate.

Because rare-earth oxides are expensive, Opila’s team must consider both cost and material properties in their search for the ideal coating. A first step is to sift through the many rare-earth oxides, with all their properties and their costs. Prasanna Balachandran, assistant professor of materials science and engineering at UVA, will develop computational models to do the sifting. His data-driven approach combines artificial intelligence and quantum mechanics to propose the best composition of rare-earth oxides for the coating.

Bi-Cheng Zhou, assistant professor of materials science and engineering at UVA, will make sure coatings are chemically compatible with the niobium alloy they are designed to protect. Zhou will also draw on his expertise in computational thermodynamics and kinetics of materials to reduce oxygen transport, such that oxidation slows down over time as the oxide layer grows thicker and thicker. 

Patrick E. Hopkins, professor of mechanical and aerospace engineering with courtesy appointments in materials science and engineering and physics, will test coatings’ thermal properties. Opila will assess the coatings’ performance in the high-temperature, reactive environments for turbine engines, including the ability to withstand combustion gas and molten debris.

Two team members will lead efforts to make coatings for continued experimentation and performance testing. Carolina Tallon, assistant professor of materials science and engineering at Virginia Tech, will use a slurry process, mixing powders in a liquid to dip-coat the niobium substrate. Joshua Williams, a member of the surface engineering team at the Commonwealth Center for Advanced Manufacturing, will use a conventional air plasma spray technology to make the coatings.

Opila and Tallon previously collaborated on the development of ultrahigh-temperature ceramics funded by 4-VA, a consortium of eight universities in the Commonwealth of Virginia which awards small grants to enable and strengthen their collaboration. Opila previously worked with Williams as a recipient of a CCAM innovation award. “It’s very rewarding that these seed funding projects have paid off in a full-fledged proposal,” Opila said.