US20050142394A1 - Thermal barrier coatings with lower porosity for improved impact and erosion resistance - Google Patents
Thermal barrier coatings with lower porosity for improved impact and erosion resistance Download PDFInfo
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- US20050142394A1 US20050142394A1 US10/748,518 US74851803A US2005142394A1 US 20050142394 A1 US20050142394 A1 US 20050142394A1 US 74851803 A US74851803 A US 74851803A US 2005142394 A1 US2005142394 A1 US 2005142394A1
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
- C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
- C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
- C23C28/321—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer with at least one metal alloy layer
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
- C23C14/08—Oxides
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
- C23C14/08—Oxides
- C23C14/083—Oxides of refractory metals or yttrium
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
- C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
- C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
- C23C28/321—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer with at least one metal alloy layer
- C23C28/3215—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer with at least one metal alloy layer at least one MCrAlX layer
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
- C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
- C23C28/34—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
- C23C28/345—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer
- C23C28/3455—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer with a refractory ceramic layer, e.g. refractory metal oxide, ZrO2, rare earth oxides or a thermal barrier system comprising at least one refractory oxide layer
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
- F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
- F01D5/12—Blades
- F01D5/28—Selecting particular materials; Particular measures relating thereto; Measures against erosion or corrosion
- F01D5/288—Protective coatings for blades
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
- F05D2230/00—Manufacture
- F05D2230/90—Coating; Surface treatment
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
- F05D2300/00—Materials; Properties thereof
- F05D2300/20—Oxide or non-oxide ceramics
- F05D2300/21—Oxide ceramics
- F05D2300/2118—Zirconium oxides
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
- F05D2300/00—Materials; Properties thereof
- F05D2300/60—Properties or characteristics given to material by treatment or manufacturing
- F05D2300/611—Coating
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
- Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
- Y10T428/12611—Oxide-containing component
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/249921—Web or sheet containing structurally defined element or component
- Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/26—Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/26—Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension
- Y10T428/263—Coating layer not in excess of 5 mils thick or equivalent
- Y10T428/264—Up to 3 mils
- Y10T428/265—1 mil or less
Definitions
- This invention relates to improving the impact and erosion resistance of thermal barrier coatings having reduced thermal conductivity. This invention further relates to articles having such coatings and methods for preparing such coatings for the article.
- thermal barrier coating 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.
- 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.
- thermal barrier coatings typically comprise the external portion or surface of these components are usually 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 (i.e., provide thermal insulation) and to limit (reduce) the operating temperature the underlying metal substrate of these parts and components is 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).
- the thermal barrier coating is usually prepared from a ceramic material, such as a chemically (metal oxide) stabilized zirconia.
- a ceramic material such as a chemically (metal oxide) stabilized zirconia.
- chemically phase-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 weight % yttria and about 93 weight % zirconia.
- the thickness of the thermal barrier coating depends upon the metal 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.
- thermal barrier coatings for turbine engine components
- such coatings are still susceptible to various types of damage, including objects ingested by the engine, erosion, oxidation, and attack from environmental contaminants.
- other properties of the thermal barrier coating can be adversely impacted.
- the composition and crystalline microstructure of a thermal barrier coating such as those prepared from yttria-stabilized zirconia, can be modified to impart to the coating an improved reduction in thermal conductivity, especially as the coating ages over time.
- such modifications can also unintentionally interfere with desired spallation resistance, as well as resistance to particle erosion, especially at the higher temperatures that most turbine components are subjected to.
- the thermal barrier coating can become more susceptible to damage due to the impact of, for example, objects ingested by the engine, as well as erosion.
- thermal barrier coatings having reduced thermal conductivity. It would be further desirable to be able to modify the chemical composition of yttria-stabilized zirconia-based thermal barrier coating systems to provide such reduced thermal conductivity, yet still retain at least acceptable impact and erosion resistance in such coatings.
- An embodiment of this invention relates to improving the impact and erosion resistance of a thermal barrier coating having reduced thermal conductivity that is used with an underlying metal substrate of articles that operate at, or are exposed, to high temperatures.
- This thermal barrier coating comprises a zirconia-containing ceramic composition having a c/a ratio of the zirconia lattice in the range of from about 1.0057 to about 1.0110 and stabilized in the tetragonal phase by a stabilizing amount of a stabilizing metal oxide, the thermal barrier coating having:
- This protected article comprises:
- Another embodiment of this invention relates to a method for preparing the thermal barrier coating on a metal substrate to provide a thermally protected article. This method comprises the steps of:
- the thermal barrier coatings of this invention provide several significant benefits when used with metal substrates of articles exposed to high temperatures, such as turbine components.
- the thermal barrier coatings of this invention provide a desirable balance of reduced thermal conductivity for the thermally protected article with improved impact and erosion resistance. This improvement in impact and erosion resistance for the thermal barrier coating can be achieved while allowing flexibility in using a variety of zirconia-containing ceramic compositions that can impart to the thermal barrier coating desirable reduced thermal conductivity properties.
- FIG. 1 represents a graphical plot of the calculated c/a ratios of the zirconia lattice as a function of yttria content.
- FIG. 2 represents graphical plots of the calculated stability level s of the zirconia lattice as a function of yttria, lanthana or ytterbia content.
- FIG. 3 represents graphical plots of the predicted normalized impact resistance values of thermal barrier coatings at various porosities as a function of yttria equivalent.
- FIG. 4 represents graphical plots of predicted normalized erosion resistance values of thermal barrier coatings at various porosities as a function of yttria equivalent.
- FIG. 5 is a side sectional view of an embodiment of the thermal barrier coating and coated article of this invention.
- zirconia-containing ceramic compositions refers to ceramic compositions where zirconia is the primary component that are useful as thermal barrier coatings that are capable of reducing heat flow to the underlying metal substrate of the article, i.e., forming a thermal barrier, and which have a melting point that is typically at least about 2600° F. (1426° C.), and more typically in the range of from about from about 3450° to about 4980° F. (from about 1900° to about 2750° C.).
- fraction of porosity refers to the volume fraction of porosity defined by unity (i.e., 1), minus the ratio of the actual density of the thermal barrier coating to its theoretical density.
- the term “comprising” means various compositions, compounds, components, layers, steps and the like can be conjointly employed in the present invention. Accordingly, the term “comprising” encompasses the more restrictive terms “consisting essentially of” and “consisting of.”
- Suitable zirconia-containing compositions useful herein include those which comprise at least about 91 mole % zirconia, and typically from about 91 to about 97 mole % zirconia, more typically from about 93.5 to about 95 mole % zirconia. These zirconia-containing compositions further comprise a stabilizing amount of stabilizing metal oxide.
- This stabilizing metal oxide can be selected from the group consisting of yttria, calcia, ceria, scandia, magnesia, india, lanthana, gadolinia, neodymia, samaria, dysprosia, erbia, ytterbia, europia, praseodymia, and mixtures thereof.
- this metal oxide that is “stabilizing” will depend on a variety of factors, including the metal oxide used and the erosion and impact resistance.
- the stabilizing metal oxide comprises from about 3 about 9 mole %, more typically from about 5 to about 6.5 mole %, of the composition.
- the zirconia-containing ceramic compositions used herein typically comprise yttria, lanthana, or mixtures thereof as the stabilizing metal oxide, and more typically yttria.
- the zirconia-containing ceramic compositions used herein can also optionally comprise small amounts of hafnia, titania, tantala, niobia and mixtures thereof.
- the zirconia-containing ceramic compositions disclosed in the first of these copending applications comprise at least about 91 mole % zirconia and up to about 9 mole % of a stabilizer component comprising a first metal oxide selected from the group consisting of yttria, calcia, ceria, scandia, magnesia, india and mixtures thereof; a second metal oxide of a trivalent metal atom selected from the group consisting of lanthana, gadolinia, neodymia, samaria, dysprosia, and mixtures thereof; and a third metal oxide of a trivalent metal atom selected from the group consisting of erbia, ytterbia and mixtures thereof.
- a stabilizer component comprising a first metal oxide selected from the group consisting of yttria, calcia, ceria, scandia, magnesia, india and mixtures thereof; a second metal oxide of a trivalent metal atom selected from the group consisting of
- these ceramic compositions comprise from about 91 to about 97 mole % zirconia, more typically from about 92 to about 95 mole % zirconia and from about 3 to about 9 mole %, more typically from about from about 5 to about 8 mole %, of the composition of the stabilizing component;
- the first metal oxide typically yttria
- the second metal oxide typically lanthana or gadolinia
- the third metal oxide can comprise from about 0.5 to about 2 mole %, more typically from about 0.5 to about 1.5 mole %, of the ceramic composition, with the ratio of the second metal oxide to the third metal oxide typically being in the range of from about 0.5 to about 2, more typically from about 0.75 to about 1.
- the zirconia-containing ceramic compositions disclosed in the second of these copending applications comprise at least about 91 mole % zirconia and a stabilizing amount up to about 9 mole % of a stabilizer component comprising a first metal oxide having selected from the group consisting of yttria, calcia, ceria, scandia, magnesia, india and mixtures thereof and a second metal oxide of a trivalent metal atom selected from the group consisting of lanthana, gadolinia, neodymia, samaria, dysprosia, erbia, ytterbia, and mixtures thereof.
- a stabilizer component comprising a first metal oxide having selected from the group consisting of yttria, calcia, ceria, scandia, magnesia, india and mixtures thereof and a second metal oxide of a trivalent metal atom selected from the group consisting of lanthana, gadolinia, neodymia,
- these ceramic compositions comprise from about 91 to about 97 mole % zirconia, more typically from about 92 to about 95 mole % zirconia and from about 3 to about 9 mole %, more typically from about 5 to about 8 mole %, of the composition of the stabilizing component;
- the first metal oxide (typically yttria) can comprise from about 3 to about 6 mole %, more typically from about 4 to about 5 mole %, of the ceramic composition;
- the second metal oxide typically lanthana, gadolinia or ytterbia, and more typically lanthana
- the mole % ratio of second metal oxide (e.g., lanthana/gadolinia/ytterbia) to first metal oxide (e.g., yttria) is in the range of from about 0.1 to about 0.5, typically from about 0.
- Thermal barrier coatings of this invention comprise a zirconia-containing ceramic composition that is stabilized in a certain region of the tetragonal phase.
- the impact and erosion resistance properties of these thermal barrier coatings can be predicted on the basis of the effect of the zirconia lattice stability equivalent of the respective zirconia-containing ceramic compositions. Impact and erosion resistance performance have been found to be related to the zirconia lattice stability equivalent.
- This stability equivalent can be calculated based on the ratio of the zirconia lattice parameters c and a using equation (2) below:
- c a k 1 ⁇ ⁇ i ⁇ ( r i - r Zr ) ⁇ m i + k 2 ⁇ ⁇ i ⁇ ( V i - V Zr ) ⁇ m i ( 2 )
- c,a are the zirconia tetragonal lattice parameters
- r i is the ionic radius of the first metal oxide
- V i is the valence of the metal ion of the metal oxide added
- m i is the mole fraction of the metal oxide added
- k 1 and k 2 are constants.
- the lattice stability of these zirconia-containing ceramic compositions in the tetragonal phase can be calculated, including the effect of incremental additions of the stabilizing metal oxide, such as yttria.
- FIG. 1 represents a graphical plot of calculated c/a ratios for the zirconia lattice as a function of yttria content.
- the dotted line (base line) in FIG. 1 represents a zirconia-containing ceramic composition stabilized with the equivalent of about 4 mole % (7YSZ) that has a c/a ratio of about 1.0117.
- Similar lattice stability values can also be calculated for the incremental addition of other stabilizing metal oxides such as lanthana and ytterbia.
- s 1.0117 ⁇ c/a ratio
- the c/a ratio conversely increases. It has been further found that, as the c/a ratio increases, impact and erosion resistance improves, i.e., lowering the yttria level improves the impact and erosion resistance performance of the zirconia-containing ceramic composition.
- the zirconia-containing ceramic compositions of this invention that provide thermal barrier coatings with-reduced thermal conductivity have lower c/a ratios of about 1.0110 or less, and typically in the range of from about 1.0057 to about 1.0110, more typically in the range of from about 1.0069 to about 1.0096.
- the thermal barrier coatings resulting from these compositions will also tend to have poorer impact and erosion resistance performance, especially relative to coatings prepared from 7YSZ compositions. Accordingly, another mechanism is needed in order to achieve satisfactory erosion and impact resistance performance for thermal barrier coatings prepared from these zirconia-containing ceramic compositions having lower c/a ratios.
- the porosity level of the resultant thermal barrier coating also has a very significant effect on impact and erosion resistance performance.
- decreasing porosity has an exponential effect in improving impact performance, it has been further found to have only a more limited, linear effect in increasing thermal conductivity (i.e., increasing the K value) of thermal barrier coating. Accordingly, by controlling the porosity level of the thermal barrier coating formed from a zirconia-containing ceramic composition having lower c/a ratios within the range providing desired reduced thermal conductivity, an appropriate balance of reduced thermal conductivity and satisfactory erosion and impact resistance performance can be obtained.
- the porosity level of the thermal barrier coatings of this invention is defined herein by the fraction of porosity of the coating.
- the thermal barrier coatings useful in this invention that provide an appropriate balance of reduced thermal conductivity with satisfactory impact and erosion resistance have a fraction of porosity of from about 0.15 to about 0.25, more typically from about 0.18 to about 0.20.
- thermal conductivity data is obtained by the laser flash method. See ASTM standard E1461-01.
- Impact and erosion resistance data is obtained by testing thermal barrier coatings by the method described in Bruce, “Development of 1232C (2250 F) Erosion and Impact Tests for Thermal Barrier Coatings,” Tribology Trans., (1998), 41(4); 399 - 410 , which is incorporated by reference.
- This data obtained by the Bruce method is then normalized by coating thickness to provide an impact and erosion index that represents the impact and erosion resistance of the coating at a thickness of 1 mil. Generally, the higher the index is, the better will be the impact and erosion resistance of the coating.
- equations (3), (4) and (5) can be solved simultaneously to optimize zirconia-containing ceramic compositions that can be processed into thermal barrier coatings that have the desired balance of reduced thermal conductivity with satisfactory impact and erosion resistance performance.
- FIGS. 3 and 4 graphically represent plots of predicted normalized impact and erosion resistance values (in g/mil), respectively, of thermal barrier coatings at various porosities (i.e., defined by the fraction of porosity) as a function of yttria equivalent (in mole %), the yttria equivalent also corresponding to particular c/a ratios.
- FIG. 3 shows impact resistance to be an exponential function of c/a ratio and porosity
- FIG. 4 shows erosion resistance to be a linear function of c/a ratio and porosity.
- the thermal barrier coatings of this invention are defined in terms of the c/a ratio of the zirconia-containing ceramic composition, the fraction of porosity p, and an impact and erosion resistance property defined by at least one of the above formulas (a) or (b), and more typically defined by both of formulas (a) and (b).
- I is typically at least about 70 g/mil, more typically at least about 90 g/mil, while E is typically at least about 80 g/mil, more typically at least about 100 g/mil.
- compositions having the previously specified c/a ratios that can be formulated into thermal barrier coatings having the previously specified fraction of porosity, to satisfy the indicated impact and erosion resistance properties I and E are as follow: TABLE 3 Metal Oxide (Mole %) Composition 1 Composition 2 Zirconia 94.0 95.0 Total Stabilizer 6.0 5.0 Yttria 4.8 3.6 Lanthana 1.2 1.4 Porosity 0.18-0.20 0.23-0.25
- Thermal barrier coatings of this invention are useful with a wide variety of turbine engine (e.g., gas turbine engine) parts and components that are formed from metal substrates comprising a variety of metals and metal alloys, including superalloys, and are operated at, or exposed to, high temperatures, especially higher temperatures that occur during normal engine operation.
- turbine engine parts and components can include turbine airfoils such as blades and vanes, turbine shrouds, turbine nozzles, combustor components such as liners and deflectors, augmentor hardware of gas turbine engines and the like.
- the thermal barrier coatings of this invention can also cover a portion or all of the metal substrate.
- the thermal barrier coatings of this invention are typically used to protect, cover or overlay portions of the metal substrate of the airfoil rather than the entire component, e.g., the thermal barrier coatings could cover the leading edge, possibly part of the trailing edge, but not the attachment area. While the following discussion of the thermal barrier coatings of this invention will be with reference to metal substrates of turbine engine parts and components, it should also be understood that the thermal barrier coatings of this invention are useful with metal substrates of other articles that operate at, or are exposed to, high temperatures.
- FIG. 5 shows a side sectional view of an embodiment of the thermally barrier coating used with the metal substrate of an article indicated generally as 10 .
- article 10 has a metal substrate indicated generally as 14 .
- Substrate 14 can comprise any of a variety of metals, or more typically metal alloys, that are typically protected by thermal barrier coatings, including those based on nickel, cobalt and/or iron alloys.
- substrate 14 can comprise a high temperature, heat-resistant alloy, e.g., a superalloy.
- Such high temperature alloys are disclosed in various references, such as U.S. Pat. No.
- High temperature alloys are also generally described in Kirk-Othmer's Encyclopedia of Chemical Technology, 3rd Ed., Vol. 12, pp. 417-479 (1980), and Vol. 15, pp. 787-800 (1981).
- Illustrative high temperature nickel-based alloys are designated by the trade names Inconel®, Nimonic®, René® (e.g., René® 80-, René® (95 alloys), and Udimet®.
- the type of substrate 14 can vary widely, but it is representatively in the form of a turbine part or component, such as an airfoil (e.g., blade) or turbine shroud.
- article 10 can also include a bond coat layer indicated generally as 18 that is adjacent to and overlies substrate 14 .
- Bond coat layer 18 is typically formed from a metallic oxidation-resistant material that protects the underlying substrate 14 and enables the thermal barrier coating indicated generally as 22 to more tenaciously adhere to substrate 14 .
- Suitable materials for bond coat layer 18 include MCrAlY alloy powders, where M represents a metal such as iron, nickel, platinum or cobalt, or NiAl(Zr) compositions, as well as various noble metal diffusion aluminides such as nickel aluminide and platinum aluminide, as well as simple aluminides (i.e., those formed without noble metals).
- This bond coat layer 18 can be applied, deposited or otherwise formed on substrate 10 by any of a variety of conventional techniques, such as physical vapor deposition (PVD), including electron beam physical vapor deposition (EB-PVD), plasma spray, including air plasma spray (APS) and vacuum plasma spray (VPS), or other thermal spray deposition methods such as high velocity oxy-fuel (HVOF) spray, detonation, or wire spray, chemical vapor deposition (CVD), pack cementation and vapor phase aluminiding in the case of metal diffusion aluminides (see, for example, U.S. Pat. No. 4,148,275 (Benden et al), issued Apr. 10, 1979; U.S. Pat. No. 5,928,725 (Howard et al), issued Jul.
- PVD physical vapor deposition
- EB-PVD electron beam physical vapor deposition
- APS air plasma spray
- VPS vacuum plasma spray
- CVD chemical vapor deposition
- pack cementation and vapor phase aluminiding in the
- the deposited bond coat layer 18 has a thickness in the range of from about 1 to about 20 mils (from about 25 to about 500 microns).
- the thickness is more typically in the range of from about 1 about 3 mils (from about 25 to about 76 microns).
- the thickness is more typically in the range of from about 3 to about 15 mils (from about 76 to about 381 microns).
- the thermal barrier coating (TBC) 22 is adjacent to and overlies bond coat layer 18 .
- the thickness of TBC 22 is typically in the range of from about 1 to about 100 mils (from about 25 to about 2540 microns) and will depend upon a variety of factors, including the design parameters for article 10 that are involved. For example, for turbine shrouds, TBC 22 is typically thicker and is usually in the range of from about 30 to about 70 mils (from about 762 to about 1778 microns), more typically from about 40 to about 60 mils (from about 1016 to about 1524 microns).
- TBC 22 is typically thinner and is usually in the range of from about 1 to about 30 mils (from about 25 to about 762 microns), more typically from about 3 to about 20 mils (from about 76 to about 508 microns).
- the composition and thickness of the bond coat layer 18 , and TBC 22 are typically adjusted to provide appropriate CTEs to minimize thermal stresses between the various layers and the substrate 14 so that the various layers are less prone to separate from substrate 14 or each other.
- the CTEs of the respective layers typically increase in the direction of TBC 22 to bond coat layer 18 , i.e., TBC 22 has the lowest CTE, while bond coat layer 18 has the highest CTE.
- TBC 22 can be applied, deposited or otherwise formed on bond coat layer 18 by physical vapor deposition (PVD), and in particular electron beam physical vapor deposition (EB-PVD) techniques.
- PVD physical vapor deposition
- EB-PVD electron beam physical vapor deposition
- the particular technique used for applying, depositing or otherwise forming TBC 22 will typically depend on the composition of TBC 22 , its thickness and especially the physical structure desired for TBC 22 . PVD techniques tend to be useful in forming TBCs having a strain-tolerant columnar structure.
- TBC 22 is typically formed from zirconia-containing ceramic compositions of this invention by EB-PVD techniques to provide a strain-tolerant columnar structure.
- TBCs 22 can also be utilized to form TBCs 22 from the zirconia-containing ceramic composition. See, for example, U.S. Pat. No. 5,645,893 (Rickerby et al), issued Jul. 8, 1997 (especially col. 3, lines 36-63) and U.S. Pat. No. 5,716,720 (Murphy), issued Feb. 10, 1998) (especially col. 5, lines 24-61) and U.S. Pat. No. 6,447,854 (Rigney et al), issued Sep. 10, 2002, which are all incorporated by reference.
- Suitable EB-PVD techniques for use herein typically involve a coating chamber with a gas (or gas mixture) that preferably includes oxygen and an inert gas, though an oxygen-free coating atmosphere can also be employed.
- the zirconia-containing ceramic composition is then evaporated with electron beams focused on, for example, ingots of the ceramic composition so as to produce a vapor of metal ions, oxygen ions and one or more metal oxides.
- the metal and oxygen ions and metal oxides recombine to form TBC 22 on the surface of metal substrate 14 , or more typically on bond coat layer 18 .
- the porosity of TBC 22 can be controlled within the desired range previously described by adjusting the conditions under which the PVD/EB-PVD technique is carried out during deposition of the zirconia-containing ceramic composition on the bond coat layer 18 , in particular the pressure and/or temperature conditions (e.g., by reducing the pressure).
Abstract
Description
- This invention was made with Government support under Contract No. N00019-96-C-0176 awarded by the JSF Program Office. The Government has certain rights to the invention.
- This invention relates to improving the impact and erosion resistance of thermal barrier coatings having reduced thermal conductivity. This invention further relates to articles having such coatings and methods for preparing such coatings for the article.
- Components operating in the gas path environment of gas turbine engines are typically subjected to significant temperature extremes and degradation by oxidizing and corrosive environments. Environmental coatings and especially thermal barrier coating 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 typically comprise the external portion or surface of these components are usually 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 (i.e., provide thermal insulation) and to limit (reduce) the operating temperature the underlying metal substrate of these parts and components is 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).
- The thermal barrier coating is usually prepared from a ceramic material, such as a chemically (metal oxide) stabilized zirconia. Examples of such chemically phase-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 weight % yttria and about 93 weight % zirconia. The thickness of the thermal barrier coating depends upon the metal 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.
- Although significant advances have been made in improving the durability of thermal barrier coatings for turbine engine components, such coatings are still susceptible to various types of damage, including objects ingested by the engine, erosion, oxidation, and attack from environmental contaminants. In addition, in trying to achieve reduced thermal conductivity, other properties of the thermal barrier coating can be adversely impacted. For example, the composition and crystalline microstructure of a thermal barrier coating, such as those prepared from yttria-stabilized zirconia, can be modified to impart to the coating an improved reduction in thermal conductivity, especially as the coating ages over time. However, such modifications can also unintentionally interfere with desired spallation resistance, as well as resistance to particle erosion, especially at the higher temperatures that most turbine components are subjected to. As a result, the thermal barrier coating can become more susceptible to damage due to the impact of, for example, objects ingested by the engine, as well as erosion.
- Accordingly, it would be desirable to be able to improve the impact and erosion resistance of thermal barrier coatings having reduced thermal conductivity. It would be further desirable to be able to modify the chemical composition of yttria-stabilized zirconia-based thermal barrier coating systems to provide such reduced thermal conductivity, yet still retain at least acceptable impact and erosion resistance in such coatings.
- An embodiment of this invention relates to improving the impact and erosion resistance of a thermal barrier coating having reduced thermal conductivity that is used with an underlying metal substrate of articles that operate at, or are exposed, to high temperatures. This thermal barrier coating comprises a zirconia-containing ceramic composition having a c/a ratio of the zirconia lattice in the range of from about 1.0057 to about 1.0110 and stabilized in the tetragonal phase by a stabilizing amount of a stabilizing metal oxide, the thermal barrier coating having:
-
- 1. a fraction of porosity of from about 0.15 to about 0.25; and
- 2. an impact and erosion resistance property defined by at least one of the following formulas:
I=exp. [5.85−(144×s)−(3.68×p)]; (a)
E=[187−(261×p)−(9989×s)]; (b)
wherein s=1.0117−c/a ratio; p is the fraction of porosity; I is at least about 70 g/mil; and E is at least about 80 g/mil.
- Another embodiment of this invention relates to a thermally protected article. This protected article comprises:
-
- A. a metal substrate;
- B. optionally a bond coat layer adjacent to and overlaying the metal substrate; and
- C. a thermal barrier coating (as previously described) adjacent to and overlaying the bond coat layer (or overlaying the metal substrate if the bond coat layer is absent).
- Another embodiment of this invention relates to a method for preparing the thermal barrier coating on a metal substrate to provide a thermally protected article. This method comprises the steps of:
-
- A. optionally forming a bond coat layer on the metal substrate;
- B. depositing on the bond coat layer (or on the metal substrate in the absence of the bond coat layer) the zirconia-containing ceramic composition previously described to form the thermal barrier coating having the previously described porosity and impact/erosion resistance properties.
- The thermal barrier coatings of this invention provide several significant benefits when used with metal substrates of articles exposed to high temperatures, such as turbine components. The thermal barrier coatings of this invention provide a desirable balance of reduced thermal conductivity for the thermally protected article with improved impact and erosion resistance. This improvement in impact and erosion resistance for the thermal barrier coating can be achieved while allowing flexibility in using a variety of zirconia-containing ceramic compositions that can impart to the thermal barrier coating desirable reduced thermal conductivity properties.
-
FIG. 1 represents a graphical plot of the calculated c/a ratios of the zirconia lattice as a function of yttria content. -
FIG. 2 represents graphical plots of the calculated stability level s of the zirconia lattice as a function of yttria, lanthana or ytterbia content. -
FIG. 3 represents graphical plots of the predicted normalized impact resistance values of thermal barrier coatings at various porosities as a function of yttria equivalent. -
FIG. 4 represents graphical plots of predicted normalized erosion resistance values of thermal barrier coatings at various porosities as a function of yttria equivalent. -
FIG. 5 is a side sectional view of an embodiment of the thermal barrier coating and coated article of this invention. - As used herein, the term “zirconia-containing ceramic compositions” refers to ceramic compositions where zirconia is the primary component that are useful as thermal barrier coatings that are capable of reducing heat flow to the underlying metal substrate of the article, i.e., forming a thermal barrier, and which have a melting point that is typically at least about 2600° F. (1426° C.), and more typically in the range of from about from about 3450° to about 4980° F. (from about 1900° to about 2750° C.).
- As used herein, the term “fraction of porosity” refers to the volume fraction of porosity defined by unity (i.e., 1), minus the ratio of the actual density of the thermal barrier coating to its theoretical density.
- As used herein, the term “comprising” means various compositions, compounds, components, layers, steps and the like can be conjointly employed in the present invention. Accordingly, the term “comprising” encompasses the more restrictive terms “consisting essentially of” and “consisting of.”
- All amounts, parts, ratios and percentages used herein are by mole unless otherwise specified.
- Zirconia-containing ceramic compositions useful in this invention impart improved thermal conductivity properties to the resulting thermal barrier coatings, and in particular lower thermal conductivity. Thermal conductivity K is defined by the following equation (1):
K=α×(1−p)×C p ×D t (1)
where α is the thermal diffusivity, p is the fraction of porosity, Cp is the specific heat (in J*K/g), and Dt is the theoretical density. As be seen from equation (1) above, the thermal conductivity depends on thermal diffusivity and porosity. - Suitable zirconia-containing compositions useful herein include those which comprise at least about 91 mole % zirconia, and typically from about 91 to about 97 mole % zirconia, more typically from about 93.5 to about 95 mole % zirconia. These zirconia-containing compositions further comprise a stabilizing amount of stabilizing metal oxide. This stabilizing metal oxide can be selected from the group consisting of yttria, calcia, ceria, scandia, magnesia, india, lanthana, gadolinia, neodymia, samaria, dysprosia, erbia, ytterbia, europia, praseodymia, and mixtures thereof. The particular amount of this metal oxide that is “stabilizing” will depend on a variety of factors, including the metal oxide used and the erosion and impact resistance. Typically, the stabilizing metal oxide comprises from about 3 about 9 mole %, more typically from about 5 to about 6.5 mole %, of the composition. The zirconia-containing ceramic compositions used herein typically comprise yttria, lanthana, or mixtures thereof as the stabilizing metal oxide, and more typically yttria. The zirconia-containing ceramic compositions used herein can also optionally comprise small amounts of hafnia, titania, tantala, niobia and mixtures thereof.
- Particularly suitable zirconia-containing ceramic compositions for use herein are disclosed in copending U.S. nonprovisional applications entitled “CERAMIC COMPOSITIONS USEFUL FOR THERMAL BARRIER COATINGS HAVING REDUCED THERMAL CONDUCTIVITY” (Spitsberg et al), Ser. No., ______, filed ______, 2003, Attorney Docket No. 129967 and “CERAMIC COMPOSITIONS USEFUL IN THERMAL BARRIER COATINGS HAVING REDUCED THERMAL CONDUCTIVITY” (Spitsberg et al), Ser. No., ______ filed ______, 2003, Attorney Docket No. 129968, both of which are incorporated by reference. The zirconia-containing ceramic compositions disclosed in the first of these copending applications comprise at least about 91 mole % zirconia and up to about 9 mole % of a stabilizer component comprising a first metal oxide selected from the group consisting of yttria, calcia, ceria, scandia, magnesia, india and mixtures thereof; a second metal oxide of a trivalent metal atom selected from the group consisting of lanthana, gadolinia, neodymia, samaria, dysprosia, and mixtures thereof; and a third metal oxide of a trivalent metal atom selected from the group consisting of erbia, ytterbia and mixtures thereof. Typically, these ceramic compositions comprise from about 91 to about 97 mole % zirconia, more typically from about 92 to about 95 mole % zirconia and from about 3 to about 9 mole %, more typically from about from about 5 to about 8 mole %, of the composition of the stabilizing component; the first metal oxide (typically yttria) can comprise from about 3 to about 6 mole %, more typically from about 3 to about 5 mole %, of the ceramic composition; the second metal oxide (typically lanthana or gadolinia) can comprise from about 0.25 to about 2 mole %, more typically from about 0.5 to about 1.5 mole %, of the ceramic composition; and the third metal oxide (typically ytterbia) can comprise from about 0.5 to about 2 mole %, more typically from about 0.5 to about 1.5 mole %, of the ceramic composition, with the ratio of the second metal oxide to the third metal oxide typically being in the range of from about 0.5 to about 2, more typically from about 0.75 to about 1.33.
- The zirconia-containing ceramic compositions disclosed in the second of these copending applications comprise at least about 91 mole % zirconia and a stabilizing amount up to about 9 mole % of a stabilizer component comprising a first metal oxide having selected from the group consisting of yttria, calcia, ceria, scandia, magnesia, india and mixtures thereof and a second metal oxide of a trivalent metal atom selected from the group consisting of lanthana, gadolinia, neodymia, samaria, dysprosia, erbia, ytterbia, and mixtures thereof. Typically, these ceramic compositions comprise from about 91 to about 97 mole % zirconia, more typically from about 92 to about 95 mole % zirconia and from about 3 to about 9 mole %, more typically from about 5 to about 8 mole %, of the composition of the stabilizing component; the first metal oxide (typically yttria) can comprise from about 3 to about 6 mole %, more typically from about 4 to about 5 mole %, of the ceramic composition; the second metal oxide (typically lanthana, gadolinia or ytterbia, and more typically lanthana) can comprise from about 0.5 to about 4 mole %, more typically from about 0.8 to about 2 mole %, of the ceramic composition, and wherein the mole % ratio of second metal oxide (e.g., lanthana/gadolinia/ytterbia) to first metal oxide (e.g., yttria) is in the range of from about 0.1 to about 0.5, typically from about 0.15 to about 0.35, more typically from about 0.2 to about 0.3.
- Thermal barrier coatings of this invention comprise a zirconia-containing ceramic composition that is stabilized in a certain region of the tetragonal phase. The impact and erosion resistance properties of these thermal barrier coatings can be predicted on the basis of the effect of the zirconia lattice stability equivalent of the respective zirconia-containing ceramic compositions. Impact and erosion resistance performance have been found to be related to the zirconia lattice stability equivalent. This stability equivalent can be calculated based on the ratio of the zirconia lattice parameters c and a using equation (2) below:
wherein c,a are the zirconia tetragonal lattice parameters, ri is the ionic radius of the first metal oxide, Vi is the valence of the metal ion of the metal oxide added, mi is the mole fraction of the metal oxide added and k1 and k2 are constants. See Kim, “Effect of Ta2O5, Nb2O5, and HfO2 Alloying on the Transformability of Y2O3-Stabilized Tetragonal ZrO2,” J. Am. Ceram. Soc., (1990) 73 (1) pp. 115-120. - Using equation (2) above, the lattice stability of these zirconia-containing ceramic compositions in the tetragonal phase can be calculated, including the effect of incremental additions of the stabilizing metal oxide, such as yttria. This is illustrated by
FIG. 1 which represents a graphical plot of calculated c/a ratios for the zirconia lattice as a function of yttria content. The dotted line (base line) inFIG. 1 represents a zirconia-containing ceramic composition stabilized with the equivalent of about 4 mole % (7YSZ) that has a c/a ratio of about 1.0117. Similar lattice stability values can also be calculated for the incremental addition of other stabilizing metal oxides such as lanthana and ytterbia. This is illustrated byFIG. 2 which represents graphical plots of the calculated stability level s (s=1.0117−c/a ratio) of the zirconia lattice as a function of yttria (base line), lanthana or ytterbia content. As can be seen inFIG. 2 , lanthana addition has the greatest effect on lattice stability. - Referring again to
FIG. 1 , as the level of yttria decreases in the zirconia-containing ceramic composition, the c/a ratio conversely increases. It has been further found that, as the c/a ratio increases, impact and erosion resistance improves, i.e., lowering the yttria level improves the impact and erosion resistance performance of the zirconia-containing ceramic composition. - While increasing the c/a ratio of the zirconia-containing ceramic composition generally improves the impact and erosion resistance performance of the resulting thermal barrier coating, these higher c/a ratios also have a significant and undesirable effect in increasing thermal conductivity (i.e., the K value is higher) of such coatings. Indeed, the zirconia-containing ceramic compositions of this invention that provide thermal barrier coatings with-reduced thermal conductivity have lower c/a ratios of about 1.0110 or less, and typically in the range of from about 1.0057 to about 1.0110, more typically in the range of from about 1.0069 to about 1.0096. Because the zirconia-containing ceramic compositions of this invention have lower c/a ratios, the thermal barrier coatings resulting from these compositions will also tend to have poorer impact and erosion resistance performance, especially relative to coatings prepared from 7YSZ compositions. Accordingly, another mechanism is needed in order to achieve satisfactory erosion and impact resistance performance for thermal barrier coatings prepared from these zirconia-containing ceramic compositions having lower c/a ratios.
- While the c/a ratio of the zirconia-containing composition has a very strong, exponential effect on impact resistance performance, and a less strong, linear impact on erosion resistance performance, it has been found that the porosity level of the resultant thermal barrier coating also has a very significant effect on impact and erosion resistance performance. Moreover, while decreasing porosity has an exponential effect in improving impact performance, it has been further found to have only a more limited, linear effect in increasing thermal conductivity (i.e., increasing the K value) of thermal barrier coating. Accordingly, by controlling the porosity level of the thermal barrier coating formed from a zirconia-containing ceramic composition having lower c/a ratios within the range providing desired reduced thermal conductivity, an appropriate balance of reduced thermal conductivity and satisfactory erosion and impact resistance performance can be obtained. The porosity level of the thermal barrier coatings of this invention is defined herein by the fraction of porosity of the coating. The thermal barrier coatings useful in this invention that provide an appropriate balance of reduced thermal conductivity with satisfactory impact and erosion resistance have a fraction of porosity of from about 0.15 to about 0.25, more typically from about 0.18 to about 0.20.
- In order to be able to select zirconia-containing ceramic compositions having a balance of satisfactory impact and erosion resistance performance by controlling the porosity within the c/a ratio range having reduced thermal conductivity, experimental data is obtained on thermal conductivity, impact resistance and erosion resistance properties of a variety coatings and compositions. Thermal conductivity data is obtained by the laser flash method. See ASTM standard E1461-01. Impact and erosion resistance data (in g/mil) is obtained by testing thermal barrier coatings by the method described in Bruce, “Development of 1232C (2250 F) Erosion and Impact Tests for Thermal Barrier Coatings,” Tribology Trans., (1998), 41(4); 399-410, which is incorporated by reference. This data obtained by the Bruce method is then normalized by coating thickness to provide an impact and erosion index that represents the impact and erosion resistance of the coating at a thickness of 1 mil. Generally, the higher the index is, the better will be the impact and erosion resistance of the coating.
- The (normalized) data obtained for thermal conductivity, impact resistance, and erosion resistance are used to develop appropriate transfer functions. These transfer functions are represented as follows:
K=f(c/a, p) (3)
I=f(c/a, p) (4)
E=f(c/a, p) (5)
wherein K is thermal conductivity, I is the normalized impact resistance (i.e., impact index), E is the normalized erosion resistance (i.e., erosion index), c/a is defined as before, and p is the fraction of porosity. Using a standard Excel “solver” procedure, equations (3), (4) and (5) can be solved simultaneously to optimize zirconia-containing ceramic compositions that can be processed into thermal barrier coatings that have the desired balance of reduced thermal conductivity with satisfactory impact and erosion resistance performance. From statistical analysis of a large population of experimental data (about 50 data points), the transfer function (4) for impact resistance (I) and the transfer function (5) for erosion resistance (E) were found to be represented by formulas (a) and (b) below:
I=exp. [5.85−(144×s)−(3.68×p)] (a)
E=[187−(261×p)−(9989×s)] (b)
wherein s=1.0117−c/a ratio; and p is the fraction of porosity. The regression fit is about 85% for formulas (a) and (b) above. - Using formulas (a) and (b) above,
FIGS. 3 and 4 graphically represent plots of predicted normalized impact and erosion resistance values (in g/mil), respectively, of thermal barrier coatings at various porosities (i.e., defined by the fraction of porosity) as a function of yttria equivalent (in mole %), the yttria equivalent also corresponding to particular c/a ratios.FIG. 3 shows impact resistance to be an exponential function of c/a ratio and porosity, whileFIG. 4 shows erosion resistance to be a linear function of c/a ratio and porosity. These normalized impact and erosion resistance values are also presented in the following Tables 1 and 2:TABLE 1 Predicted Normalized Impact Resistance (g/mil) Yttria Equivalent Porosity c/a Ratio (Mole %) 0.1 0.15 0.18 0.2 0.25 0.27 0.3 0.33 1.0167 1.6 494 411 368 342 284 264 237 212 1.0148 2.5 370 308 276 256 213 198 177 159 1.0138 3 321 267 239 222 185 171 154 137 1.0117 4 240 200 179 166 138 129 115 103 1.0110 4.1 218 182 163 151 126 117 105 94 1.0096 5 180 150 134 125 104 96 86 77 1.0077 6 135 112 101 94 78 72 65 58 1.0069 6.4 122 102 91 85 70 65 59 52 1.0057 7 101 84 75 70 58 54 49 43 -
TABLE 2 Predicted Normalized Erosion Resistance (g/mil) Yttria Equivalent Porosity c/a Ratio (Mole %) 0.1 0.15 0.18 0.2 0.25 0.27 0.3 0.33 1.0167 1.6 211 198 190 185 172 166 159 151 1.0148 2.5 191 178 170 165 152 146 139 131 1.0138 3 181 168 160 155 142 137 129 121 1.0117 4 161 148 140 135 122 117 109 101 1.0110 4.1 154 141 133 128 115 110 102 94 1.0096 5 141 128 120 115 102 97 89 81 1.0077 6 121 108 100 95 82 77 69 61 1.0069 6.4 114 101 93 88 75 70 62 54 1.0057 7 101 88 80 75 62 57 49 41 - The thermal barrier coatings of this invention are defined in terms of the c/a ratio of the zirconia-containing ceramic composition, the fraction of porosity p, and an impact and erosion resistance property defined by at least one of the above formulas (a) or (b), and more typically defined by both of formulas (a) and (b). For thermal barrier coatings of this invention having the previously specified c/a ratios (for the zirconia-containing ceramic composition) and fraction of porosity, I is typically at least about 70 g/mil, more typically at least about 90 g/mil, while E is typically at least about 80 g/mil, more typically at least about 100 g/mil. Some illustrative zirconia-containing compositions having the previously specified c/a ratios that can be formulated into thermal barrier coatings having the previously specified fraction of porosity, to satisfy the indicated impact and erosion resistance properties I and E are as follow:
TABLE 3 Metal Oxide (Mole %) Composition 1Composition 2Zirconia 94.0 95.0 Total Stabilizer 6.0 5.0 Yttria 4.8 3.6 Lanthana 1.2 1.4 Porosity 0.18-0.20 0.23-0.25 - Thermal barrier coatings of this invention are useful with a wide variety of turbine engine (e.g., gas turbine engine) parts and components that are formed from metal substrates comprising a variety of metals and metal alloys, including superalloys, and are operated at, or exposed to, high temperatures, especially higher temperatures that occur during normal engine operation. These turbine engine parts and components can include turbine airfoils such as blades and vanes, turbine shrouds, turbine nozzles, combustor components such as liners and deflectors, augmentor hardware of gas turbine engines and the like. The thermal barrier coatings of this invention can also cover a portion or all of the metal substrate. For example, with regard to airfoils such as blades, the thermal barrier coatings of this invention are typically used to protect, cover or overlay portions of the metal substrate of the airfoil rather than the entire component, e.g., the thermal barrier coatings could cover the leading edge, possibly part of the trailing edge, but not the attachment area. While the following discussion of the thermal barrier coatings of this invention will be with reference to metal substrates of turbine engine parts and components, it should also be understood that the thermal barrier coatings of this invention are useful with metal substrates of other articles that operate at, or are exposed to, high temperatures.
- The various embodiments of the thermal barrier coatings of this invention are further illustrated by reference to the drawings as described hereafter. Referring to the drawings,
FIG. 5 shows a side sectional view of an embodiment of the thermally barrier coating used with the metal substrate of an article indicated generally as 10. As shown inFIG. 5 ,article 10 has a metal substrate indicated generally as 14.Substrate 14 can comprise any of a variety of metals, or more typically metal alloys, that are typically protected by thermal barrier coatings, including those based on nickel, cobalt and/or iron alloys. For example,substrate 14 can comprise a high temperature, heat-resistant alloy, e.g., a superalloy. Such high temperature alloys are disclosed in various references, such as U.S. Pat. No. 5,399,313 (Ross et al), issued Mar. 21, 1995 and U.S. Pat. No. 4,116,723 (Gell et al), issued Sep. 26, 1978, both of which are incorporated by reference. High temperature alloys are also generally described in Kirk-Othmer's Encyclopedia of Chemical Technology, 3rd Ed., Vol. 12, pp. 417-479 (1980), and Vol. 15, pp. 787-800 (1981). Illustrative high temperature nickel-based alloys are designated by the trade names Inconel®, Nimonic®, René® (e.g., René® 80-, René® (95 alloys), and Udimet®. As described above, the type ofsubstrate 14 can vary widely, but it is representatively in the form of a turbine part or component, such as an airfoil (e.g., blade) or turbine shroud. - As shown in
FIG. 5 ,article 10 can also include a bond coat layer indicated generally as 18 that is adjacent to and overliessubstrate 14.Bond coat layer 18 is typically formed from a metallic oxidation-resistant material that protects theunderlying substrate 14 and enables the thermal barrier coating indicated generally as 22 to more tenaciously adhere tosubstrate 14. Suitable materials forbond coat layer 18 include MCrAlY alloy powders, where M represents a metal such as iron, nickel, platinum or cobalt, or NiAl(Zr) compositions, as well as various noble metal diffusion aluminides such as nickel aluminide and platinum aluminide, as well as simple aluminides (i.e., those formed without noble metals). Thisbond coat layer 18 can be applied, deposited or otherwise formed onsubstrate 10 by any of a variety of conventional techniques, such as physical vapor deposition (PVD), including electron beam physical vapor deposition (EB-PVD), plasma spray, including air plasma spray (APS) and vacuum plasma spray (VPS), or other thermal spray deposition methods such as high velocity oxy-fuel (HVOF) spray, detonation, or wire spray, chemical vapor deposition (CVD), pack cementation and vapor phase aluminiding in the case of metal diffusion aluminides (see, for example, U.S. Pat. No. 4,148,275 (Benden et al), issued Apr. 10, 1979; U.S. Pat. No. 5,928,725 (Howard et al), issued Jul. 27, 1999; and See U.S. Pat. No. 6,039,810 (Mantkowski et al), issued Mar. 21, 2000, all of which are incorporated by reference and which disclose various apparatus and methods for applying diffusion aluminide coatings, or combinations of such techniques, such as, for example, a combination of plasma spray and diffusion aluminide techniques. Typically, plasma spray or diffusion techniques are employed to depositbond coat layer 18. Usually, the depositedbond coat layer 18 has a thickness in the range of from about 1 to about 20 mils (from about 25 to about 500 microns). For bond coat layers 18 deposited by PVD techniques such as EB-PVD or diffusion aluminide processes, the thickness is more typically in the range of from about 1 about 3 mils (from about 25 to about 76 microns). For bond coat layers deposited by plasma spray techniques such as APS, the thickness is more typically in the range of from about 3 to about 15 mils (from about 76 to about 381 microns). - As shown in
FIG. 5 , the thermal barrier coating (TBC) 22 is adjacent to and overliesbond coat layer 18. The thickness ofTBC 22 is typically in the range of from about 1 to about 100 mils (from about 25 to about 2540 microns) and will depend upon a variety of factors, including the design parameters forarticle 10 that are involved. For example, for turbine shrouds,TBC 22 is typically thicker and is usually in the range of from about 30 to about 70 mils (from about 762 to about 1778 microns), more typically from about 40 to about 60 mils (from about 1016 to about 1524 microns). By contrast, in the case of turbine blades,TBC 22 is typically thinner and is usually in the range of from about 1 to about 30 mils (from about 25 to about 762 microns), more typically from about 3 to about 20 mils (from about 76 to about 508 microns). - The composition and thickness of the
bond coat layer 18, andTBC 22 are typically adjusted to provide appropriate CTEs to minimize thermal stresses between the various layers and thesubstrate 14 so that the various layers are less prone to separate fromsubstrate 14 or each other. In general, the CTEs of the respective layers typically increase in the direction ofTBC 22 tobond coat layer 18, i.e.,TBC 22 has the lowest CTE, whilebond coat layer 18 has the highest CTE. - Referring to the
FIG. 5 ,TBC 22 can be applied, deposited or otherwise formed onbond coat layer 18 by physical vapor deposition (PVD), and in particular electron beam physical vapor deposition (EB-PVD) techniques. The particular technique used for applying, depositing or otherwise formingTBC 22 will typically depend on the composition ofTBC 22, its thickness and especially the physical structure desired forTBC 22. PVD techniques tend to be useful in forming TBCs having a strain-tolerant columnar structure.TBC 22 is typically formed from zirconia-containing ceramic compositions of this invention by EB-PVD techniques to provide a strain-tolerant columnar structure. - Various types of PVD and especially EB-PVD techniques well known to those skilled in the art can also be utilized to form TBCs 22 from the zirconia-containing ceramic composition. See, for example, U.S. Pat. No. 5,645,893 (Rickerby et al), issued Jul. 8, 1997 (especially col. 3, lines 36-63) and U.S. Pat. No. 5,716,720 (Murphy), issued Feb. 10, 1998) (especially col. 5, lines 24-61) and U.S. Pat. No. 6,447,854 (Rigney et al), issued Sep. 10, 2002, which are all incorporated by reference. Suitable EB-PVD techniques for use herein typically involve a coating chamber with a gas (or gas mixture) that preferably includes oxygen and an inert gas, though an oxygen-free coating atmosphere can also be employed. The zirconia-containing ceramic composition is then evaporated with electron beams focused on, for example, ingots of the ceramic composition so as to produce a vapor of metal ions, oxygen ions and one or more metal oxides. The metal and oxygen ions and metal oxides recombine to form
TBC 22 on the surface ofmetal substrate 14, or more typically onbond coat layer 18. The porosity ofTBC 22 can be controlled within the desired range previously described by adjusting the conditions under which the PVD/EB-PVD technique is carried out during deposition of the zirconia-containing ceramic composition on thebond coat layer 18, in particular the pressure and/or temperature conditions (e.g., by reducing the pressure). - While specific embodiments of the method of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the present invention as defined in the appended claims.
Claims (30)
I=exp. [5.85−(144×s)−(3.68×p)]; (a)
E=[187−(261×p)−(9989×s)]; (b)
I=exp. [5.85−(144×s)−(3.68×p)]; (a)
E=[187−(261×p)−(9989×s)]; (b)
I=exp. [5.85−(144×s)−(3.68×p)]; (a)
E=[187−(261×p)−(9989×s)]; (b)
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US10/748,518 US6916561B1 (en) | 2003-12-30 | 2003-12-30 | Thermal barrier coatings with lower porosity for improved impact and erosion resistance |
SG200406177A SG112919A1 (en) | 2003-12-30 | 2004-10-26 | Thermal barrier coating with lower porosity for improved impact and erosion resistance |
EP20040256625 EP1550744A1 (en) | 2003-12-30 | 2004-10-27 | Thermal barrier coatings with lower porosity for improved impact and erosion resistance |
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US7364802B2 (en) * | 2003-12-30 | 2008-04-29 | General Electric Company | Ceramic compositions useful in thermal barrier coatings having reduced thermal conductivity |
US20110143043A1 (en) * | 2009-12-15 | 2011-06-16 | United Technologies Corporation | Plasma application of thermal barrier coatings with reduced thermal conductivity on combustor hardware |
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