Coating processes – Applying superposed diverse coating or coating a coated base – Metallic compound-containing coating
Reexamination Certificate
1999-02-26
2001-07-17
Turner, Archene (Department: 1775)
Coating processes
Applying superposed diverse coating or coating a coated base
Metallic compound-containing coating
C427S402000, C427S419200, C427S419300, C427S419700, C427S419800
Reexamination Certificate
active
06261643
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a composite that protects thermal barrier coatings deposited on gas turbine and other heat engine parts from the deleterious effects of environmental contaminants. Particularly, the invention relates to a composite thermal barrier coated part having multiple surface protective coatings on the ceramic thermal barrier coating.
BACKGROUND OF THE INVENTION
Thermal barrier coatings (TBCs) are deposited onto gas turbine and other heat engine parts to reduce heat flow and to limit the operating temperature of metal parts. These coatings generally are a ceramic material, such as chemically stabilized zirconia. Yttria-stabilized zirconia, scandia-stabilized zirconia, calcia-stabilized zirconia, and magnesia-stabilized zirconia are contemplated as thermal barrier coatings. The thermal barrier coating of choice is a yttria-stabilized zirconia ceramic coating. A typical thermal barrier coating comprises about 8 weight percent yttria-92 weight percent zirconia. The thickness of a thermal barrier coating depends on the application, but generally ranges between about 5-60 mils thick for high temperature engine parts.
Metal parts provided with thermal barrier coatings can be made from nickel, cobalt, and iron based superalloys. Thermal barrier coatings are especially suited for parts and hardware used in turbines. Examples of turbine parts would be turbine blades, buckets, nozzles, combustion chamber liners, and the like.
Thermal barrier coatings are a key element in current and future gas turbine engine designs expected to operate at high temperatures which produce high thermal barrier coating surface temperatures. The ideal system for a high temperature engine part consists of a strain-tolerant thermal barrier ceramic layer deposited onto a bond coat which exhibits good corrosion resistance and closely matched thermal expansion coefficients.
Under service conditions, thermal barrier coated engine parts can be susceptible to various modes of damage, including erosion, oxidation, and attack from environmental contaminants. At temperatures of engine operation adherence of these environmental contaminants on the hot thermal barrier coated surface can cause damage to the thermal barrier coating. Environmental contaminants form compositions, which are liquid at the surface temperatures of thermal barrier coatings. Chemical and mechanical interactions occur between the environmental contaminant compositions and the thermal barrier coatings. Molten contaminant compositions can dissolve the thermal barrier coating or can infiltrate its pores and openings, initiating and propagating cracks causing delamination and loss of thermal barrier coating material.
Some environmental contaminant compositions that deposit on thermal barrier coated surfaces contain oxides of calcium, magnesium, aluminum, silicon, and mixtures thereof. These oxides combine to form contaminant compositions comprising calcium-magnesium-aluminum-silicon-oxide systems (Ca—Mg—Al—Si—O), herein referred to as CMAS. Damage to thermal barrier coatings occurs when the molten CMAS infiltrates the thermal barrier coating. After infiltration and upon cooling, the molten CMAS, or other molten contaminant composition, solidifies. The stress build up in the thermal barrier coating is sufficient to cause spallation of the coating material and loss of the thermal protection that it provides to the underlying part.
There is a need to reduce or prevent the damage to thermal barrier coatings caused by the reaction or infiltration of molten contaminant compositions at the operating temperature of the engine. This can be accomplished by providing the TBC ceramic coat with multiple protective coatings that reduce damage to the thermal barrier coating from molten contaminants.
SUMMARY OF THE INVENTION
The present invention satisfies this need by providing a protected thermal barrier coating composite comprising at least two continuous protective coatings covering an outer surface of a thermal barrier coating. The invention also includes a protected thermal barrier coated engine part comprising an engine structural component with a bond coat, a thermal barrier coating on the bond coat and at least two protective layers on the thermal barrier coating. The protective coatings reduce or prevent attack of the thermal barrier coating from environmental contaminants and their corresponding contaminant compositions. Contemplated protective coatings include impermeable barrier coatings, sacrificial oxide coatings, and non-wetting coatings.
The invention includes a method for making a thermal barrier coating-protecting-composite which comprises depositing an impermeable barrier or sacrificial oxide first coating on the thermal barrier coating, and then depositing at least one other coating that is non-wetting, sacrificial or impermeable on the first coating.
Herein, the terms “impermeable barrier coating”, “sacrificial oxide coating”, and “non-wetting coating” are defined as follows.
An impermeable coating is defined as a protective layer which inhibits liquid contaminant compositions from infiltrating into or reacting with the thermal barrier coating at the operating temperature of the thermal barrier coating. The impermeable barrier is a dense, non-cracked, non-porous layer comprising oxides, non-oxides, or metallic coatings in conjunction with thermal barrier coatings.
A sacrificial oxide coating is defined as a layer which when in contact with the environmental contaminant composition raises the melting temperature or viscosity of the contaminant composition as it forms on the hot surfaces of the composite. As a result, the contaminant composition does not flow or form a reactive liquid. The sacrificial oxide coating undergoes chemical or physical changes when in contact with the contaminant composition at operating temperatures by dissolving in the contaminant composition or reacting with it to form a by-product material which is not liquid or at least more viscous than the original contaminant composition.
A non-wetting coating is defined as an outer layer which minimizes contact between underlying layers and the molten contaminant composition by providing a surface that is non-wetting to environmental contaminant compositions. As a result, the contaminant composition's ability to penetrate the thermal barrier coating via capillary action is decreased and the integrity of the composite at high temperature performance is enhanced.
Environmental contaminants are materials that exist in the environment and are ingested into engines from air and fuel sources, and impurities and oxidation products of engine components, such as iron oxide.
The term “operating temperature” means the surface temperature of the thermal barrier coating during its operation in a given application, such as a gas turbine engine. Such temperatures are above room temperature, and generally are above 500° C. High temperature operation of thermal barrier coated parts is usually above 1000° C.
DESCRIPTION OF THE INVENTION
It has been discovered that a composite comprising a thermal barrier coated part with at least two protective coatings on the ceramic thermal barrier coating exhibit decreased damage from environmental contaminants that form molten contaminant compositions at the operating temperatures of the engine system. The protective coatings are impermeable coatings, sacrificial oxide coatings, and non-wetting coatings.
Examples of composites of this invention include a thermal barrier coating and a bond coat on a part made of an alloy selected from the group consisting of nickel based alloys, cobalt based alloys, iron based alloys, and mixtures thereof, with the following protective layers: an impermeable barrier first coating and a sacrificial oxide second coating; an impermeable barrier first coating with a non-wetting second coating; an impermeable barrier first coating with another type of an impermeable barrier as a second coating; an impermeable barrier first coating with a sacrificial oxide second coating and a non-w
Borom Marcus Preston
Hasz Wayne Charles
Johnson Curtis Alan
General Electric Company
Johnson Noreen C.
Stoner Douglas E.
Turner Archene
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