An Intermediate TCE Nanocomposite Coating for Thermal Barrier Coatings
- PDF / 893,705 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 54 Downloads / 239 Views
Q4.7.1
An Intermediate TCE Nanocomposite Coating for Thermal Barrier Coatings Otto J. Gregory1, Markus A. Downey1, Steve Wnuk2 and Vince Wnuk2 1
Chemical Engineering Department University of Rhode Island Kingston, RI 02881 2
HPI Inc. 100 Park Street Ayer, MA 01432 Abstract A NiCoCrAlY /Al2O3 nanocomposite coating was developed for Inconel 718 substrates to improve thermal barrier coatings (TBC’s) based on thermally sprayed NiCoCrAlY and alumina. This intermediate TCE coating was deposited by rf sputtering techniques and was instrumental in increasing the fatigue life of both TBC’s and thermal spray instrumentation. Combinatorial chemistry techniques were employed to screen a large number of NiCoCrAlY / Al2O3 compositions to yield an optimal composite coating such that the TCE of the metallic bond coat was matched to the ceramic top coat. The resulting combinatorial libraries were thermally fatigued and the composition of the library with the longest fatigue life was determined by X-ray energy dispersive analysis (EDS). A sputtering target of the optimal composition was fabricated by thermal-spraying a mixture of NiCoCrAlY and alumina to simulate the results from the combinatorial chemistry experiments and form a nanocomposite with the desired properties. The sputtered intermediate TCE coating improved the fatigue life of the TBC’s by 160% when compared to as-sprayed TBC’s formed on Inconel 718 substrates. When a thermally grown oxide was formed on the surface of NiCoCrAlY bond coated substrates prior to deposition of the intermediate TCE coating, a 200% increase in fatigue life was realized. Techniques for extending the fatigue life of other thermal barrier coating systems using this approach will be discussed. Introduction Ceramic thermal barrier coatings (TBC’s) are commonly used in aircraft engines and power generation turbines to reduce metal interface temperatures and thus, reduce the oxidation of the nickel and cobalt based superalloys exposed to the hot gases. The integrity and durability of these TBC’s is critical for the safe and economical operation of gas turbine engines [1]. With advanced engine designs relying more and more on state-of-the-art coating technologies and new high-temperature materials, the operating temperatures of turbine engines are being pushed to higher levels, which tends to shorten the fatigue life of TBC’s. A typical TBC system employs a metallic bond coat that is used to impart oxidation resistance to the underlying nickel or cobalt based superalloy substrate and a ceramic top coat for thermal protection and/or electrical isolation [2]. The bond coat is typically a NiCoCrAlY alloy designed to form a protective aluminum oxide layer for oxidation resistance and the ceramic coating based on either zirconia or alumina, depending on the nature of the application. These materials are typically applied to the surface of turbine components using thermal spray techniques. Similar in construction and design to standard TBC’s used for thermal protection are the dielectric coatings used for
Data Loading...
