Turbine engines are used as the primary power source for various kinds of aircrafts. The engines are also auxiliary power sources that drive air compressors, hydraulic pumps, and industrial gas turbine (IGT) power generation. Further, the power from turbine engines is used for stationary power supplies such as backup electrical generators.
Most turbine engines generally follow the same basic power generation procedure. Compressed air is mixed with fuel and burned, and the expanding hot combustion gases are directed against stationary turbine vanes in the engine. The vanes turn the high velocity gas flow partially sideways to impinge on the turbine blades mounted on a rotatable turbine disk. The force of the impinging gas causes the turbine disk to spin at high speed. Jet propulsion engines use the power created by the rotating turbine disk to draw more air into the engine and the high velocity combustion gas is passed out of the gas turbine aft end to create forward thrust. Other engines use this power to operate one or more propellers, electrical generators, or other devices.
Many turbine engine and aeroengine components such as blades, guide vanes, combustor cans, and so forth are formed from a superalloy, and are often coated with a thermal barrier coating to extend the component life. Since a temperature gradient is produced across the thermal barrier coating during engine operation, the engine component functions at a reduced temperature with respect to the operating environment. In addition to providing a thermal barrier, if the coating material has a thermal expansion coefficient that differs from that of the underlying component material, the coating material typically is processed to have porosity that provides high in-plane compliance to accommodate a thermal expansion mismatch.
Both the protective properties and the in-plane compliance for the thermal barrier coating may be adversely affected if the engine component is exposed to some types of environmental contaminants. One class of contaminants that may potentially reduce a thermal barrier coating's protective and compliance characteristics includes dust, comprising oxides of calcium, magnesium, aluminum, silicon, and mixtures thereof, which are commonly referred to as CMAS. Another class of contaminants that can wick into porous thermal barrier coatings is molten sulfate salts, such as sodium sulfate, which is a constituent of sea salt. Molten CMAS and sulfate salts may penetrate the pores or channels in a thermal barrier coating. Upon cooling, the penetrated contaminates solidify and thereby reduce the coating's in-plane compliance. Cracking, fragmentation, and spalling in the thermal barrier coating may result from the reduced ability to tolerate compressive strain.
Hence, there is a need for a substrate coating that has thermal barrier properties, high in-plane compliance and is resistant to contamination and penetration from environmental contaminants such as CMAS that exist in a high temperature system. There is a further need for efficient methods for manufacturing a component that includes such a coating.