David John Wortman

Thermal barrier coatings for gas turbine use

Abstract The use of thermal barrier coatings on high-pressure turbine components can improve gas turbine efficiency through reduction of cooling airflow. However, the risk involved in reducing cooling airflow requires a highly reliable thermal barrier coating. This increased reliability will be achieved through several complementary approaches; material and process development, life prediction method development and engine service experience. The two processes available for deposition of thermal barrier coatings (plasma spray and physical vapor deposition) are compared, and the advantages and disadvantages of each discussed as they apply to gas turbine components. The results of bond coat material development which has increased the thermal cycle life of plasma spray thermal barrier coatings are presented. Improvements were achieved by two methods: (1) the use of creep-resistant bond coat compositions and (2) overaluminiding of the bond coat. Results of engine testing of thermal barrier coatings in an environment that produces hot corrosion are also presented.

Hot Corrosion Resistance of Thermal Barrier Coatings

The hot corrosion resistance of yttria stabilized zirconia (YSZ) thermal barrier coatings was evaluated using an atmospheric burner rig. The coatings were deposited by plasma spraying and electron beam physical vapor deposition (EB-PVD). The tests were performed for up to 2000 hours at 1700°F and 1300°F. The test parameters were designed to simulate the deposit chemistry and corrosion microstructures observed in marine gas turbine engines. The YSZ coating performed very well in the tests, with no spallation and little bond coat corrosion.Plasma sprayed YSZ coating was also evaluated by engine testing in a hot corrosive environment. Post test evaluation showed virtually no corrosion of the ceramic or the bond coat. Parts that were not ceramic coated had undergona severe corrosion. The results are discussed in terms of coating microstructures and the chemistry of the environment.Copyright

Bond Coat Development for Thermal Barrier Coatings

The use of thermal barrier coatings on high pressure turbine components can improve gas turbine efficiency through reduction of cooling airflow. However, to reduce cooling airflow, a highly reliable thermal barrier coating is required. This increased reliability will be achievable through several complimentary approaches: material and process development, life prediction method development and engine service experience. The results of bond coat material development which has increased the thermal cycle life of plasma spray thermal barrier coatings are presented. Improvements were achieved by two methods; 1) use of creep resistant bond coat compositions and 2) overaluminiding of the bond coat.Copyright