An Intermediate TCE Nanocomposite Coating for Thermal Barrier Coatings

摘要

A NiCoCrAlY /Al_2O_3 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 / Al_2O_3 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.