Every time a jet engine is started, it goes through a thermal cycle of extreme temperatures, reaching as high as 2,700 °F within the engine’s combustor. Over time, the expansion and contraction of engine parts caused by this cycle lead to cracking and degradation that shortens an engine’s lifespan and eventually necessitates costly replacement.
Among the many ways that NASA works to advance aviation are efforts to improve the life and performance of jet, or gas turbine, engines. Glenn Research Center scientist Dongming Zhu performed groundbreaking work developing thermal barrier coatings (TBCs) that outperform other TBC technologies, providing an unrivaled means of protecting these engines from the degrading effects of thermal stresses, prolonging their lifespans, and enhancing their reliability and fuel efficiency.
TBCs are ceramic coatings with low thermal conductivity, insulating the metal parts they are applied to and reducing thermal fatigue. The ceramic component is typically composed of zirconium oxide (zirconia) stabilized in a particular crystal structure through the addition of yttrium oxide (yttria). Through the addition of other oxides, Zhu created modified yttria-stabilized zirconia TBCs with both initial and post-exposure thermal conductivities that are even lower than existing coatings. Zhu’s breakthrough thermal and environmental barrier coating work was recognized by R&D Magazine in 2007 with an “R&D 100” award as one of the year’s 100 most technologically noteworthy inventions.
Now, through collaboration with a private industry coatings leader, Zhu’s NASA research is helping extend the service of military aircraft.
“NASA is the world leader in thermal barrier coatings,” says Andrew Sherman, founder and CEO of MesoCoat Inc., based in Euclid, Ohio. A subsidiary of Powdermet Inc., also based in Euclid and itself a NASA partner through the Small Business Innovation Research (SBIR) program, MesoCoat was founded in 2007 to develop and commercialize new coating techniques. Through a collaborative agreement with Glenn and under contract with the U.S. Air Force, MesoCoat is employing a specific composition of Zhu’s TBC technology to prolong the lifespan of engines in the Air Force’s aging, legacy aircraft. Since the commercial application is currently only for government use, no licensing agreement was required, though MesoCoat is engaged in discussions for commercial licensing terms.
“It’s very difficult to get new parts for these older engines,” says Sherman, “so the Air Force needs new technologies to extend the life of components” such as combustor cans and afterburner nozzles. The company’s NASA-derived technology is providing an ideal, cost-effective solution for this need.
Branded ZComP 844, MesoCoat’s nanocomposite TBC has cluster formations that inhibit radiation transfer in the TBC and improves the coating’s stability, Sherman explains, so that it has about half of the thermal conductivity of conventional thermal barriers.
“The NASA solution allows us to reduce the thermal conductivity, which reduces the engine part temperature as well as smoothes out thermal cycles, making them slower, much more uniform, and taking a lot of the thermal stresses off the part,” says Sherman. “By halving the thermal conductivity, we’re shaving around 30 to 50 degrees off the part temperature. As a result, you’re looking at a 50-percent increase in component life.” Reducing the thermal stresses on engine components also results in better performance and fuel efficiency.