Advanced Thermal Barrier Coatings for Turbine Components

72391S03-I Thermal barrier coatings (TBC) can provide improved engine performance, particularly with respect to specific fuel consumption. However, current thermal barrier coatings for turbine components do not have the required level of performance, due in part to catastrophic delamination from the substrate. This relatively poor reliability of TBCs has prevented their wide-scale use, and, when they have been used, large safety factors must be applied to account for coating loss. Previous work has shown that TBC failure almost always initiates in an area associated with the so-called thermally grown oxide (TGO), which consists of an oxide scale, usually alumina, that forms between the MCrAlX-type bond coat and the ZrO2-Y2O3 ceramic topcoat. As the TGO grows, strain incompatibility between the TGO and topcoat results in planar cracks that grow parallel to the original bond to topcoat interface and ultimately lead to delamination (spallation) of the topcoat. This project will improve TBC reliability by drastically modifying the nature of the TGO; namely, low aluminum bond coats, with the addition of palladium metal, will be used to reduce the thickness of the TGO at any given time. This will result in lower strain between the two coatings and increased TBC life. The protective effects of the palladium will offset the loss of oxidative protection caused by lowering the aluminum level. Phase I will develop the optimum chemistry for this coating and demonstrate its performance. Commercial Applications and Other Benefits as described by awardee: The new bond coat alloys should significantly increase coating reliability, thereby increasing the cost effectiveness of TBC despite the palladium cost. Applications include coating hot components for aircraft (commercial and military) turbines and utility turbines. Improved performance should result in greater fuel efficiency and reliability for these turbines.