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  Thermal barrier coating protected by alumina and method for preparing sameUSPTO Application #: 20060165893Title: Thermal barrier coating protected by alumina and method for preparing same Abstract: A thermal barrier coating for an underlying metal substrate of articles that operate at, or are exposed to, high temperatures, as well as being exposed to environmental contaminant compositions. This coating comprises an optional inner layer nearest to the underlying metal substrate comprising a non-alumina ceramic thermal barrier coating material in an amount up to 100%, and an outer layer having an exposed surface and comprising at least about 50% of a non-alumina ceramic thermal barrier coating material and alumina in an amount up to about 50% and sufficient to protect the thermal barrier coating at least partially against environmental contaminants that become deposited on the exposed surface. This coating can be used to provide a thermally protected article having a metal substrate and optionally a bond coat layer adjacent to and overlaying the metal substrate. The thermal barrier coating can be prepared by optionally forming the inner layer of the non-alumina ceramic thermal barrier coating material, and then codepositing the alumina and non-alumina ceramic thermal barrier coating material to form the outer layer. (end of abstract)
Agent: Jagtiani + Guttag - Fairfax, VA, US Inventors: Bangalore Aswatha Nagaraj, Brett Allen Boutwell, Robert George Baur USPTO Applicaton #: 20060165893 - Class: 427248100 (USPTO) Related Patent Categories: Coating Processes, Coating By Vapor, Gas, Or Smoke The Patent Description & Claims data below is from USPTO Patent Application 20060165893. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE PARAGRAPH [0001] This application is a continuation of U.S. application Ser. No. 10/990,542; filed Nov. 18, 2004, which is a divisional of U.S. application Ser. No. 10/317,732, filed Dec. 12, 2002, now U.S. Pat. No. 6,893,750, issued May 17, 2005. The entire disclosure and contents of the above patent and applications is hereby incorporated by reference. BACKGROUND OF THE INVENTION [0003] The present invention relates to thermal barrier coatings containing alumina for protection and mitigation against environmental contaminants, in particular oxides of calcium, magnesium, aluminum, silicon, and mixtures thereof that can become deposited onto such coatings. The present invention further relates to articles with such coatings and a method for preparing such coatings for the article. [0004] Thermal barrier coatings are an important element in current and future gas turbine engine designs, as well as other articles that are expected to operate at or be exposed to high temperatures, and thus cause the thermal barrier coating to be subjected to high surface temperatures. Examples of turbine engine parts and components for which such thermal barrier coatings are desirable include turbine blades and vanes, turbine shrouds, buckets, nozzles, combustion liners and deflectors, and the like. These thermal barrier coatings are deposited onto a metal substrate (or more typically onto a bond coat layer on the metal substrate for better adherence) from which the part or component is formed to reduce heat flow and to limit the operating temperature these parts and components are subjected to. This metal substrate typically comprises a metal alloy such as a nickel, cobalt, and/or iron based alloy (e.g., a high temperature superalloy). [0005] The thermal barrier coating usually comprises a ceramic material, such as a chemically (metal oxide) stabilized zirconia. Examples of such chemically stabilized zirconias include yttria-stabilized zirconia, scandia-stabilized zirconia, calcia-stabilized zirconia, and magnesia-stabilized zirconia. The thermal barrier coating of choice is typically a yttria-stabilized zirconia ceramic coating. A representative yttria-stabilized zirconia thermal barrier coating usually comprises about 7% yttria and about 93% zirconia. The thickness of the thermal barrier coating depends upon the metal substrate part or component it is deposited on, but is usually in the range of from about 3 to about 70 mils (from about 76 to about 1778 microns) thick for high temperature gas turbine engine parts. [0006] Under normal conditions of operation, thermal barrier coated metal substrate turbine engine parts and components can be susceptible to various types of damage, including erosion, oxidation, and attack from environmental contaminants. At the higher temperatures of engine operation, these environmental contaminants can adhere to the heated or hot thermal barrier coating surface and thus cause damage to the thermal barrier coating. For example, these environmental contaminants can form compositions that are liquid or molten at the higher temperatures that gas turbine engines operate at. These molten contaminant compositions can dissolve the thermal barrier coating, or can infiltrate its porous structure, i.e., can infiltrate the pores, channels or other cavities in the coating. Upon cooling, the infiltrated contaminants solidify and reduce the coating strain tolerance, thus initiating and propagating cracks that cause delamination, spalling and loss of the thermal barrier coating material either in whole or in part. [0007] These pores, channel or other cavities that are infiltrated by such molten environmental contaminants can be created by environmental damage, or even the normal wear and tear that results during the operation of the engine. However, this porous structure of pores, channels or other cavities in the thermal barrier coating surface more typically is the result of the processes by which the thermal barrier coating is deposited onto the underlying bond coat layer-metal substrate. For example, thermal barrier coatings that are deposited by (air) plasma spray techniques tend to create a sponge-like porous structure of open pores in at least the surface of the coating. By contrast, thermal barrier coatings that are deposited by physical (e.g., chemical) vapor deposition techniques tend to create a porous structure comprising a series of columnar grooves, crevices or channels in at least the surface of the coating. This porous structure can be important in the ability of these thermal barrier coating to tolerate strains occurring during thermal cycling and to reduce stresses due to the differences between the coefficient of thermal expansion (CTE) of the coating and the CTE of the underlying bond coat layer/substrate. [0008] For turbine engine parts and components having outer thermal barrier coatings with such porous surface structures, environmental contaminant compositions of particular concern are those containing oxides of calcium, magnesium, aluminum, silicon, and mixtures thereof. See, for example, U.S. Pat. No. 5,660,885 (Hasz et al), issued Aug. 26, 1997 which describes these particular types of oxide environmental contaminant compositions. These oxides combine to form contaminant compositions comprising mixed calcium-magnesium-aluminum-silicon-oxide systems (Ca--Mg--Al--SiO), hereafter referred to as "CMAS." During normal engine operations, CMAS can become deposited on the thermal barrier coating surface, and can become liquid or molten at the higher temperatures of normal engine operation. Damage to the thermal barrier coating typically occurs when the molten CMAS infiltrates the porous surface structure of the thermal barrier coating. After infiltration and upon cooling, the molten CMAS solidifies within the porous structure. This solidified CMAS causes stresses to build within the thermal barrier coating, leading to partial or complete delamination and spalling of the coating material, and thus partial or complete loss of the thermal protection provided to the underlying metal substrate of the part or component. [0009] Accordingly, it would be desirable to protect these thermal barrier coatings having a porous surface structure against the adverse effects of such environmental contaminants when used with a metal substrate for a turbine engine part or component, or other article, operated at or exposed to high temperatures. In particular, it would be desirable to be able to protect such thermal barrier coatings from the adverse effects of deposited CMAS. BRIEF DESCRIPTION OF THE INVENTION [0010] The present invention relates to a thermal barrier coating for an underlying metal substrate of articles that operate at, or are exposed, to high temperatures, as well as being exposed to environmental contaminant compositions, in particular CMAS. This thermal barrier coating comprises: [0011] a. an outer layer overlaying the metal substrate and having an exposed surface, and comprising: [0012] (1) at least about 50% of a non-alumina ceramic thermal barrier coating material; and [0013] (2) alumina in an amount of up to about 50% and sufficient to protect the thermal barrier coating at least partially against environmental contaminants that become deposited on the exposed surface; [0014] b. optionally an inner layer adjacent to and underlying the outer layer and overlaying the metal substrate, and comprising a non-alumina ceramic thermal barrier coating material in an amount up to 100%; and [0015] The present invention also relates to a thermally protected article. This protected article comprises: [0016] a. a metal substrate; [0017] b. optionally a bond coat layer adjacent to and overlaying the metal substrate; and [0018] c. a thermal barrier coating as previously describe adjacent to and overlaying the bond coat layer (or overlaying the metal substrate if the bond coat layer is absent). [0019] The present invention further relates to a method for preparing the thermal barrier coating. This method comprises the steps of: [0020] 1. optionally forming over the underlying metal substrate (or bond coat layer) an inner layer comprising a non-alumina ceramic thermal barrier coating material in an amount up to 100%; and [0021] 2. codepositing on the inner layer, or the underlying metal substrate or bond coat layer in the absence of the inner layer, a non-alumina ceramic thermal barrier coating material and alumina so as to form the outer layer having an exposed surface, the outer layer comprising at least about 50% non-alumina ceramic thermal barrier coating material and up to about 50% alumina and in an amount sufficient to protect the thermal barrier coating at least partially against environmental contaminants that become deposited on the exposed surface. [0022] The thermal barrier coating of the present invention are provided with at least partial and up to complete protection and mitigation against the adverse effects of environmental contaminant compositions that can become deposited on the surface of such coatings during normal turbine engine operation. In particular, the thermal barrier coating of the present invention are provided with at least partial and up to complete protection or mitigation against the adverse effects of CMAS deposits on such coating surfaces. The alumina present in the outer exposed layer of the thermal barrier coating usually combines with these CMAS deposits and thus typically raises the melting point of such deposits sufficiently so that the deposits do not become molten, or alternatively increases the viscosity of such molten deposits so that they do not flow readily, at higher temperatures normally encountered during turbine engine operation. As a result, these CMAS deposits are unable to infiltrate the normally porous surface structure of the thermal barrier coating, and thus cannot cause undesired partial (or complete) delamination and spalling of the coating. [0023] In addition, the thermal barrier coatings of the present invention are provided with protection or mitigation, in whole or in part, against the infiltration of corrosive (e.g., alkali) environmental contaminant deposits. The thermal barrier coatings of the present invention are also useful with worn or damaged coated (or uncoated) metal substrates of turbine engine parts and components so as to provide for these refurbished parts and components protection and mitigation against the adverse effects of such environmental contaminate compositions. In addition to turbine engine parts and components, the thermal barrier coatings of the present invention provide useful protection for metal substrates of other articles that operate at, or are exposed, to high temperatures, as well as to such environmental contaminate compositions. BRIEF DESCRIPTION OF THE DRAWINGS [0024] FIG. 1 is a side sectional view of an embodiment of the thermal barrier coating and coated article of the present invention. [0025] FIG. 2 is a side sectional view of another embodiment of the thermal barrier coating and coated article of the present invention. [0026] FIG. 3 is a side sectional view of yet another embodiment of the thermal barrier coating and coated article of the present invention. DETAILED DESCRIPTION OF THE INVENTION [0027] As used herein, the term "CMAS" refers environmental contaminant compositions that contain oxides of calcium, magnesium, aluminum, silicon, and mixtures thereof. These oxides typically combine to form compositions comprising calcium-magnesium-aluminum-silicon-oxide systems (Ca--Mg--Al--SiO). [0028] As used herein, the terms "alumina" and "aluminum oxide" refer interchangeably to those compounds and compositions comprising Al.sub.2O.sub.3, including unhydrated and hydrated forms. [0029] As used herein, the term "non-alumina thermal barrier coating material" refers to those coating materials (other than alumina) that are capable of reducing heat flow to the underlying metal substrate of the article, i.e., forming a thermal barrier. These materials usually have a melting point of at least about 2000.degree. F. (1093.degree. C.), typically at least about 2200.degree. F. (1204.degree. C.), and more typically in the range of from about 2200.degree. to about 3500.degree. F. (from about 1204.degree. to about 1927.degree. C.). Suitable non-alumina ceramic thermal barrier coating materials include various zirconias, in particular chemically stabilized zirconias (i.e., various metal oxides such as yttrium oxides blended with zirconia), such as yttria-stabilized zirconias, ceria-stabilized zirconias, calcia-stabilized zirconias, scandia-stabilized zirconias, magnesia-stabilized zirconias, india-stabilized zirconias, ytterbia-stabilized zirconias as well as mixtures of such stabilized zirconias. See, for example, Kirk-Othmer's Encyclopedia of Chemical Technology, 3rd Ed., Vol. 24, pp. 882-883 (1984) for a description of suitable zirconias. Suitable yttria-stabilized zirconias can comprise from about 1 to about 20% yttria (based on the combined weight of yttria and zirconia), and more typically from about 3 to about 10% yttria. These chemically stabilized zirconias can further include one or more of a second metal (e.g., a lanthanide or actinide) oxide such as dysprosia, erbia, europia, gadolinia, neodymia, praseodymia, urania, and hafnia to further reduce thermal conductivity of the thermal barrier coating. See U.S. Pat. No. 6,025,078 (Rickersby et al), issued Feb. 15, 2000 and U.S. Pat. No. 6,333,118 (Alperine et al), issued Dec. 21, 2001, both of which are incorporated by reference. Suitable non-alumina ceramic thermal barrier coating materials also include pyrochlores of general formula A.sub.2B.sub.2O.sub.7 where A is a metal having a valence of 3+ or 2+ (e.g., gadolinium, aluminum, cerium, lanthanum or yttrium) and B is a metal having a valence of 4+ or 5+ (e.g., hafnium, titanium, cerium or zirconium) where the sum of the A and B valences is 7. Representative materials of this type include gadolinium-zirconate, lanthanum titanate, lanthanum zirconate, yttrium zirconate, lanthanum hafnate, cerium zirconate, aluminum cerate, cerium hafnate, aluminum hafnate and lanthanum cerate. See U.S. Pat. No. 6,117,560 (Maloney), issued Sep. 12, 2000; U.S. Pat. No. 6,177,200 (Maloney), issued Jan. 23, 2001; U.S. Pat. No. 6,284,323 (Maloney), issued Sep. 4, 2001; U.S. Pat. No. 6,319,614 (Beele), issued Nov. 20, 2001; and U.S. Pat. No. 6,387,526 (Beele), issued May 14, 2002, all of which are incorporated by reference. Continue reading... Full patent description for Thermal barrier coating protected by alumina and method for preparing same Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Thermal barrier coating protected by alumina and method for preparing same patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. 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