Thermal Barrier Coatings Research could extend jet engine life

  • Published
  • By Erin Crawley
  • AFOSR Public Affairs (Quantech)
ARLINGTON, Va. --  A team of Princeton University scientists and engineers, funded by the Air Force Office of Scientific Research here, are paving the way for the development of new and improved thermal barrier coatings (TBC) that could increase the lifetime of jet engines. To make their predictions, the team developed and used state-of-the-art computer simulation models.

Professor Emily Carter, who presented the results at a recent program review, is the principal investigator on the project. Her research team is comprised of scientists and engineers from five different departments at Princeton, including: Mechanical and Aerospace Engineering, Applied and Computational Mathematics, Chemical Engineering, Electrical Engineering, and Chemistry.

In her presentation synopsis, Ms. Carter explained that aircraft engine components are protected by a multilayer, multi-component TBC, consisting of a NiAl-based alloy layer onto which is deposited yttria-stabilized zirconia. A layer of alumina grows between these two materials during zirconia deposition which thickens during engine use and limits the lifetime of the engine. According to Carter, most current TBCs fail after ~16,000 hours of thermal cycling.

"These coatings don't last forever, which means that essentially you have to take the engine out of service; you have to reapply the coating or replace parts," said Ms. Carter. "From a logistical point of view certainly it would be nice to extend the lifetime of these coatings."

The team then took steps toward solving the problem.

"In order to extend engine service life, it is critical to first understand mechanisms of failure, and then to use insights to design circumvention strategies," explained Ms. Carter.

Using AFOSR grant money to support her proposal, "High Temperature Evolution and Multiscale Modeling of the Roles of Impurities and Dopants on Thermal Barrier Coating Failure," Carter and team first conducted some fundamental calculations which revealed the weak links in the coating along with some characteristics of how the coating falls apart.

"We are looking at the atomic scale and trying to understand what are the chemical and physical properties [of the multi-layered coating] that can lead to the failure of this coating. We figured out what part of the coating fails and why," said Ms. Carter. After which, the team set out to re-engineer a new coating based on their findings. The team did this by essentially inserting different kinds of atoms at the weak link they had discovered in the coating, explained Ms. Carter.

As the research continued, Ms. Carter's team verified their findings.

"We showed on the computer that our hypothesis was verified. In other words, we showed that these re-designed coatings were much more stable," said Ms. Carter.

The next step is to find out how these coatings respond to high temperatures.

"It would also be really nice to make it so that these coatings are more robust at higher temperatures so that you could use them for faster airplanes with higher thrust and greater fuel efficiency," said Ms. Carter.

Over the years Ms. Carter has received a variety of AFOSR grants to support her research. Much of the groundwork for Ms. Carter's current project evolved from AFOSR funded research she conducted while at the University of California - Los Angeles (UCLA) between 1988 and 2004.

Ms. Carter said, "AFOSR has been instrumental in my work on past projects, and certainly on this project. Michael Berman [Program Manager at AFOSR] is the godsend program manager. He appreciates terrific science. He brings together people from within the Air Force and in universities in a way that I haven't really seen much of before. There are a few other people in other funding agencies that I've seen do this, but he's really exceptional."

By funding research programs such as the thermal barrier coating project, AFOSR continues to expand the horizon of scientific knowledge through its leadership and management of the Air Force's basic research program. As a vital component of the Air Force Research Laboratory, AFOSR supports Air Force's mission of control and maximum utilization of air and space. Many of the technological breakthroughs enjoyed by millions today, such as lasers, GPS, and the computer mouse trace their scientific roots to research first funded by AFOSR.