Thermal barrier coating material

#1. Field of the Invention

#This invention relates to thermal-insulating coatings for components exposed to high temperatures, such as the hostile thermal environment of a gas turbine engine. More particularly, this invention is directed to a thermal barrier coating (TBC) of yttria-stabilized zirconia (YSZ) and further alloyed with titania and/or niobia to decrease and stabilize the thermal conductivity of the TBC.

#2. Description of the Related Art

#FIG. 1 is a perspective view of a high pressure turbine blade.

#FIG. 2 schematically represents a cross-sectional view of the blade of FIG. 1 along line 2—2, and shows a thermal barrier coating system on the blade in accordance with a preferred embodiment of the invention.

#The present invention is generally applicable to components subjected to high temperatures, and particularly to components such as the high and low pressure turbine nozzles and blades, shrouds, combustor liners and augmentor hardware of gas turbine engines. An example of a high pressure turbine blade 10 is shown in FIG. 1. The blade 10 generally includes an airfoil 12 against which hot combustion gases are directed during operation of the gas turbine engine, and whose surface is therefore subjected to hot combustion gases as well as attack by oxidation, corrosion and erosion. The airfoil 12 is protected from its hostile operating environment by a thermal barrier coating (TBC) system schematically depicted in FIG. 2. The airfoil 12 is anchored to a turbine disk (not shown) with a dovetail 14 formed on a root section 16 of the blade 10. Cooling passages 18 are present in the airfoil 12 through which bleed air is forced to transfer heat from the blade 10. While the advantages of this invention are particularly desirable for high pressure turbine blades of the type shown in FIG. 1, the teachings of this invention are generally applicable to any component on which a thermal barrier coating may be used to protect the component from a high temperature environment.

#The TBC system 20 is represented in FIG. 2 as including a metallic bond coat 24 that overlies the surface of a substrate 22, the latter of which is typically a superalloy and the base material of the blade 10. As is typical with TBC systems for components of gas turbine engines, the bond coat 24 is preferably an aluminum-rich composition, such as an overlay coating of an MCrAIX alloy or a diffusion coating such as a diffusion aluminide or a diffusion platinum aluminide of a type known in the art. Aluminum-rich bond coats of this type develop an aluminum oxide (alumina) scale 28, which is grown by oxidation of the bond coat 24. The alumina scale 28 chemically bonds a TBC 26, formed of a thermal-insulating material, to the bond coat 24 and substrate 22. The TBC 26 of FIG. 2 is represented as having a strain-tolerant microstructure of columnar grains 30. As known in the art, such columnar microstructures can be achieved by depositing the TBC 26 using a physical vapor deposition technique, such as EBPVD. The invention is also believed to be applicable to noncolumnar TBC deposited by such methods as plasma spraying, including air plasma spraying (APS). A TBC of this type is in the form of molten splats, resulting in a microstructure characterized by irregular flattened grains and a degree of inhomogeneity and porosity.

#As with prior art TBC's, the TBC 26 of this invention is intended to be deposited to a thickness that is sufficient to provide the required thermal protection for the underlying substrate 22 and blade 10, generally on the order of about 75 to about 300 micrometers. According to the invention, the thermal-insulating material of the TBC 26 is based on binary yttria-stabilized zirconia (YSZ), but alloyed to contain niobia (Nb2O3) or titania (TiO2) as an oxide additive. Each of these oxides has been shown by this invention to have a significant effect on the thermal conductivity of YSZ, particular YSZ containing about three to about four weight percent yttria. Based on an investigation discussed below, these oxides in an amount of up to ten weight percent of a YSZ coating is believed to have the beneficial effect of lowering the thermal conductivity of the coating. Particularly suitable amounts for these oxide additives are about 0.2 to about 8 weight percent niobia, or about 0.1 to about 4 weight percent titania.