EP3492622A1 - Verfahren zur formung einer porösen wärmebarrierenbeschichtung - Google Patents

Verfahren zur formung einer porösen wärmebarrierenbeschichtung Download PDF

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Publication number
EP3492622A1
EP3492622A1 EP18209695.8A EP18209695A EP3492622A1 EP 3492622 A1 EP3492622 A1 EP 3492622A1 EP 18209695 A EP18209695 A EP 18209695A EP 3492622 A1 EP3492622 A1 EP 3492622A1
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EP
European Patent Office
Prior art keywords
thermal barrier
barrier coating
feedstock material
substrate
controlling
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP18209695.8A
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English (en)
French (fr)
Inventor
Theodore R Grossman
Joshua L Margolies
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General Electric Co
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General Electric Co
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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
    • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
    • C23C4/12—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying
    • C23C4/134—Plasma spraying
    • 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
    • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
    • C23C4/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • 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
    • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
    • C23C4/04—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the coating material
    • C23C4/10—Oxides, borides, carbides, nitrides or silicides; Mixtures thereof
    • C23C4/11—Oxides
    • 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
    • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
    • C23C4/18—After-treatment

Definitions

  • the disclosure relates generally to methods for forming porous thermal barrier coatings. More particularly, the disclosure relates to controlling a porosity parameter of porous thermal barrier coatings.
  • Thermal barrier coatings are typically used in articles that operate at or are exposed to high temperatures. Aviation turbines and land-based turbines, for example, may include one or more components protected by the thermal barrier coatings.
  • materials used for thermal barrier coatings include rare earth-stabilized zirconia materials such as yttrium-stabilized zirconia (YSZ).
  • YSZ yttrium-stabilized zirconia
  • Rare earth stabilized zirconia materials have a thermal conductivity of about 2.2 W/m-K when evaluated as a dense sintered compact.
  • the YSZ is widely used as a thermal barrier coating material in gas turbines, in part, because of its high temperature capability, low thermal conductivity, and relative ease of deposition.
  • thermal barrier coatings may also be reduced by increasing the porosity of the coatings.
  • thermal barrier coatings may be formed using suitable deposition techniques, such as, for example, by air plasma spraying (APS) or by electron beam physical vapor deposition (EPVD).
  • APS air plasma spraying
  • EPVD electron beam physical vapor deposition
  • Thermal barrier coatings deposited by the APS process may typically have a microstructure characterized by irregular fattened grains surrounded by inhomogeneous porosity.
  • Thermal barrier coatings deposited by the EBPVD process may yield a columnar, strain-tolerant grain structure that may be able to expand and contract without causing stresses that lead to spallation.
  • the EBPVD process may be more capital intensive than the APS process. Therefore, there is a need for improved coating processes that enable control over the porosity of the thermal barrier coatings, thereby controlling the thermal conductivity of the thermal barrier coatings.
  • One embodiment of the disclosure is directed to a method of forming a porous thermal barrier coating by disposing a feedstock material on a substrate.
  • the feedstock material includes a gas-forming additive and a thermal barrier coating material.
  • the disposing step further includes controlling a porosity parameter of the porous thermal barrier coating by controlling the feedstock material feed rate, an amount of the gas-forming additive in the feedstock material, the temperature of the disposed feedstock material on the substrate, or combinations thereof.
  • Another embodiment of the disclosure is directed to a method of forming a porous thermal barrier coating by disposing a feedstock material using an air plasma spray process on a substrate.
  • the feedstock material includes a gas-forming additive and a thermal barrier coating material.
  • the disposing step further includes controlling a porosity parameter of the porous thermal barrier coating by controlling the temperature of the disposed feedstock material on the substrate using an auxiliary heat source.
  • Another embodiment of the disclosure is directed to a method of forming a porous thermal barrier coating including a graded porosity.
  • the method includes disposing a feedstock material on a substrate to form the porous thermal barrier coating, wherein the feedstock material includes a gas-forming additive and a thermal barrier coating material.
  • the disposing includes forming the graded porosity in the thermal barrier coating by controlling an amount of the gas-forming additive in the feedstock material, a temperature of the disposed feedstock material on the substrate using an auxiliary heat source, or a combination thereof.
  • Approximating language may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term such as "about” is not to be limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value.
  • range limitations may be combined and/or interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.
  • the terms “may” and “may be” indicate a possibility of an occurrence within a set of circumstances; a possession of a specified property, characteristic or function; and/or qualify another verb by expressing one or more of an ability, capability, or possibility associated with the qualified verb. Accordingly, usage of "may” and “may be” indicates that a modified term is apparently appropriate, capable, or suitable for an indicated capacity, function, or usage, while taking into account that in some circumstances, the modified term may sometimes not be appropriate, capable, or suitable.
  • the term “coating” refers to a material disposed on at least a portion of an underlying surface in a continuous or discontinuous manner. Further, the term “coating” does not necessarily mean a uniform thickness of the disposed material, and the disposed material may have a uniform or a variable thickness.
  • the term “coating” may refer to a single layer of the coating material or may refer to a plurality of layers of the coating material. The coating material may be the same or different in the plurality of layers.
  • disposed on refers to layers or coatings disposed directly in contact with each other or indirectly by having intervening layers there between, unless otherwise specifically indicated.
  • One embodiment of the disclosure is directed to a method of forming a porous thermal barrier coating.
  • the method includes disposing a feedstock material on a substrate to form the porous thermal barrier coating, wherein the feedstock material includes a gas-forming additive and a thermal barrier coating material.
  • the disposing step includes controlling a porosity parameter of the porous thermal barrier coating by controlling a feedstock material feed rate, an amount of the gas-forming additive in the feedstock material, a temperature of the disposed feedstock material on the substrate, or combinations thereof.
  • FIG. 1 illustrates a method 10 in accordance with some embodiments of the present disclosure.
  • the method 10 includes providing a substrate 110, at step 11, disposing a feedstock material 121 on the substrate 110 to form a disposed feedstock material 120, at step 12, and forming a porous thermal barrier coating 130 on the substrate 110, at step 13.
  • the substrate 110 may have any suitable geometry or profile, for example, a complex geometry, a non-planar profile, or a combination of both.
  • the term "complex geometry" refers to shapes not easily or consistently identifiable or reproducible, such as, not being square, circular, or rectangular.
  • the substrate 110 may be a part of a component exposed to a high temperature environment, for example, a turbine engine.
  • the turbine engine may be an aircraft engine.
  • the turbine engine may be any other type of engine used in industrial applications.
  • Non-limiting examples of such turbine engines include a land-based turbine engine employed in a power plant, a turbine engine used in a marine vessel, or a turbine engine used in an oil rig.
  • turbine engine components include turbine airfoils such as blades and vanes, turbine shrouds, turbine nozzles, buckets, combustor components such as liners and deflectors, heat shields, augmentor hardware of gas turbine engines, and other similar turbine components known to those skilled in the art.
  • the substrate 110 may include a ceramic matrix composite or a metallic superalloy.
  • suitable metallic superalloys include iron-based superalloys, cobalt based superalloys, nickel based superalloys, or combinations thereof.
  • the substrate 110 may be a pre-fabricated component of a turbine engine, or, may be manufactured before the disposing step.
  • the step 11, of providing the substrate may include one or more preparatory steps, for example, cleaning, polishing, disposing a bond coating, and the like.
  • the substrate 110 may be coated with a bond coating (not shown in Figures), at step 11.
  • the bond coating may be formed from a metallic oxidation-resistant material that protects the underlying substrate 110 and enables the porous thermal barrier coating 130 to more tenaciously adhere to substrate 110.
  • Suitable materials for the bond coating include MiCrAlY alloy powders, where M 1 represents a metal such as iron, nickel, platinum or cobalt.
  • Non-limiting examples of other suitable bond coat materials include metal aluminides such as nickel aluminide, platinum aluminide, or a combination thereof.
  • the feedstock material 121 is disposed on the substrate 110 to form a disposed feedstock material 120, at step 12.
  • the term "feedstock material” refers to a homogenous mixture of two or more materials forming a single phase, or, alternatively, to a heterogenous mixture of two or more materials forming more than one phase.
  • the feedstock material 121 may be in a solid form, in a liquid form, or in a semi-solid form. In certain embodiments, the feedstock material 121 is in the form of a powder.
  • the feedstock material 121 includes a gas-forming additive and a thermal barrier coating material.
  • the feedstock material 121 includes a homogeneous mixture of the gas-forming additive and the thermal barrier coating material.
  • the gas-forming additive is pre-dissolved into the thermal barrier coating material to form the feedstock material 121.
  • a porosity parameter of the porous thermal barrier coating 130 may be controlled. For example, by controlling one or more of the amount, the size, or the distribution of the gas-forming additive in the feedstock material 121.
  • gas-forming additive refers to a material which, at an elevated temperature, is capable of oxidizing into a non-reactive and insoluble (with the thermal barrier coating material) gas that is entrapped by the thermal barrier coating material, thereby forming pores.
  • suitable gas-forming additives include, but are not limited to, graphite, carbides, oxycarbides, nitrides, or combination thereof.
  • the gas forming additive includes elemental carbon.
  • the gas forming additive forms a gas, for example, carbon monoxide, carbon dioxide, nitrous oxide, or any suitable gas depending on the composition of the gas-forming additive employed.
  • the insoluble gas is entrapped in the thermal barrier coating during the disposing or the post-disposing steps, thereby forming pores.
  • a substantial amount of the gas formed is entrapped in the thermal barrier coating material.
  • substantially amount of the gas refers to at least 90 volume % of the gas formed. This is in contrast to fugitive materials employed to form porous coatings, wherein the coating materials are subjected to elevated temperatures such that the fugitive materials decompose or oxidize, and the resulting gases are expelled from the coatings, thereby resulting in pores.
  • thermal barrier coating refers to a coating that includes a material capable of reducing heat flow to the underlying substrate of the article, that is, form a thermal barrier.
  • the composition of the porous thermal barrier coating in terms of the type and amount of the thermal barrier coating materials may depend upon one or more factors, including the composition of the adjacent bond coat layer (if present), the coefficient of thermal expansion (CTE) characteristics desired for the thermal barrier coating, and the thermal barrier properties desired for the thermal barrier coating.
  • thermal barrier coating materials include zirconias, pyrochlores, or combinations thereof.
  • the thermal barrier material includes chemically stabilized zirconias (for example, metal 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, lanthana-stabilized zirconias, gadolinia-stabilized zirconias, as well as mixtures of such stabilized zirconias.
  • chemically stabilized zirconias for example, metal oxides blended with zirconia
  • the thermal barrier coating material includes yttria-stabilized zirconias.
  • Suitable yttria-stabilized zirconias may include from about 1 wt % to about 20 wt % yttria (based on the combined weight of yttria and zirconia), and more typically from about 3 wt % to about 10 wt % yttria.
  • An example yttria-stabilized zirconia thermal barrier coating includes about 7 wt % yttria and about 93 wt % zirconia.
  • These chemically stabilized zirconias may 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.
  • a second metal e.g., a lanthanide or actinide oxide
  • porous thermal barrier coating refers to a coating including a plurality of pores.
  • porosity parameter of the porous thermal barrier coating refers to one or more of pore size, pore size distribution, number of pores, or pore microstructure of the plurality of pores, in the porous thermal barrier coating 130.
  • the pore size provides an indication of the median or average size of the pores in the porous thermal barrier coating 130.
  • the pore size distribution provides a quantitative description of the range of pore sizes present across the length, breadth and thickness of the porous thermal barrier coating 130.
  • Pore volume is the percentage of volume occupied by the plurality of pores in the total volume occupied by the porous thermal barrier coating 130, and is also referred to as the "total porosity" of the porous thermal barrier coating 130.
  • the total porosity of the plurality of pores in the porous thermal barrier coating 130 may be controlled.
  • One or more of the pore size, the pore shape, the number of pores, the pore size distribution, or the pore microstructure in the porous thermal barrier coating 130 may be controlled using the methods described in the present disclosure.
  • an average pore size of the plurality of pores in the porous thermal barrier coating 130 is in a range from about 0.1 microns to about 25 microns. In some embodiments, an average pore size of the plurality of pores in the porous thermal barrier coating 130 is in a range from about 0.25 microns to about 5 microns.
  • the plurality of pores in the porous thermal barrier coating 130 may be characterized any suitable shape. In certain embodiments, the shape of the pores in the porous thermal barrier coating may be substantially spherical. In some embodiments, spheroidal porosity in the porous thermal barrier coating 130 may provide a strain tolerant microstructure, thereby allowing the thermal barrier coating to operate under the gas turbine operating conditions for much longer periods.
  • the feedstock material 121 is disposed on the substrate 110 using a suitable apparatus 115.
  • the feedstock material 121 may be disposed on a bond coating (if present) or on the substrate 110 directly by any of a variety of techniques, including vapor disposition, such as physical vapor deposition (PVD), electron beam physical vapor deposition (EBPVD); plasma spray, such as air plasma spray (APS), suspension plasma spray (SPS), and vacuum plasma spray (VPS); other thermal spray deposition methods such as high velocity oxy-fuel (HVOF) spray, detonation, or wire spray; chemical vapor deposition (CVD), sol-gel method, or combinations of two or more of the afore-mentioned techniques.
  • PVD physical vapor deposition
  • EBPVD electron beam physical vapor deposition
  • plasma spray such as air plasma spray (APS), suspension plasma spray (SPS), and vacuum plasma spray (VPS)
  • HVOF high velocity oxy-fuel
  • CVD chemical vapor deposition
  • sol-gel method sol-gel
  • the particular technique used for disposing, depositing or otherwise forming the porous thermal barrier coating 130 may depend on one or more of the composition of the porous thermal barrier coating 130, the thickness, and the physical structure desired for the porous thermal barrier coating 130.
  • the feedstock material 121 is disposed using plasma spray techniques, in particular, APS technique.
  • the gas-forming additive and the thermal barrier coating material is co-deposited as a feedstock material 121 on the substrate 110 or the bond coating (if present).
  • co-depositing may be achieved by blending, mixing or otherwise combining the gas-forming additive and the thermal barrier coating material together (for example, as powders) to provide a mixture that is then deposited onto substrate/bond coating.
  • the blending or mixing of the gas-forming additive and the thermal barrier coating material may be effected prior to providing the feedstock material to the deposition apparatus 115 (for example, an APS gun), or may be effected in the deposition apparatus 115 itself, therein forming the feedstock material.
  • the gas-forming additive is mixed and dissolved in the thermal barrier coating material prior to providing the feedstock material 121 to the deposition apparatus 115.
  • disposed feedstock material refers to an as-deposited feedstock material, i.e., feedstock material that has not been subjected to additional steps (e.g., heating), or, alternately to a feedstock material that has been subjected to additional steps (e.g., heating via an auxiliary heat source) after the disposing step.
  • disposed feedstock material as used herein is differentiated from a "porous thermal barrier coating” such that in the "disposed feedstock material” the thermal barrier coating material is in a partially or completely molten state, and the pores may still not be entrapped within the coating.
  • the disposing step 12 further includes controlling the feedstock material 121 feed rate, an amount of the gas-forming additive in the feedstock material 121, or the temperature of the disposed feedstock material 120 on the substrate 110 to form a porous thermal barrier coating 130.
  • the porosity parameter (and therefore, a total porosity) of the porous thermal barrier coating 130 is controlled. Without being bound by any theory, it is believed that, in the absence of this controlling step, an uncontrolled, non-spheroidal, or randomly distributed porosity in the porous thermal barrier coating 130 may result.
  • the porosity parameter of the porous thermal barrier coating 130 is controlled by controlling one or both a feedstock material 121 feed rate and an amount of the gas-forming additive in the feedstock material 121.
  • feed rate refers to rate of deposition of the feedstock material 121 on the substrate 110, using a suitable deposition apparatus 115.
  • the term "feed rate” refers to the spray rate of the feedstock material 121.
  • the porosity parameter of porous thermal barrier coating 130 is controlled by controlling an amount of the gas-forming additive in the feedstock material 121 in a range from about 0.1 wt % to about 10 wt %.
  • the porosity parameter of porous thermal barrier coating 130 is controlled by controlling an amount of the gas-forming additive in the feedstock material 121 in a range from about 0.5 wt % to about 5 wt %.
  • the amount of gas-forming additive in the feedstock material 121 may be varied over the duration of the disposing step such that the disposed feedstock material 120 includes a graded content of the gas-forming additive, thereby forming a graded porosity in the resultant porous thermal barrier coating 130.
  • the term "amount of gas-forming additive” refers to an average amount of gas-forming additive in the feedstock material 121 over the entire duration of the disposing step.
  • the porosity parameter of porous thermal barrier coating 130 is controlled by controlling the feedstock material 121 feed rate in a range from about 2.5 gm/min to about 100 gm/min. In some embodiments, the porosity parameter of porous thermal barrier coating 130 is controlled by controlling the feedstock material 121 feed rate in a range from about 20 gm/min to about 50 gm/min. The feed rate may be controlled by using a valve or any other suitable method. This is in contrast to methods used to form porous thermal barrier coatings, wherein the feed rate or the amount of the gas-forming additive in the feedstock material are not controlled, which may result in uncontrolled and random porosity.
  • the porosity parameter of porous thermal barrier coating 130 is controlled by controlling the temperature of the disposed feedstock material 120 on the substrate 110.
  • the temperature of the disposed feedstock material 120 on the substrate 110 may be controlled by controlling one or more of the temperature of the feedstock material 121 before depositing (e.g., by pre-heating the feedstock material), temperature of deposition (e.g., the spray temperature if using APS for deposition or by using an auxiliary heat source during deposition); or the temperature of the substrate 110 on which the feedstock material is being deposited.
  • the temperature of the disposed feedstock material 120 on the substrate 110 is controlled by a combination of pre-heating the substrate and by maintaining the disposed feedstock material temperature.
  • the disposed feedstock material 120 on the substrate 110 is heated to a temperature greater than a temperature that the substrate 110 can withstand.
  • the term "temperature that the substrate can withstand” refers to a temperature beyond which the substrate may start to deform, melt, or change form.
  • the disposed feedstock material may be heated to a temperature similar to a turbine engine operating temperature. Depositing and heating the feedstock material to a temperature similar to the engine operating temperature may result in reduced coating stresses of the interface, while at that temperature, therefore, potentially improving the lifetime of the thermal barrier coating in the engine.
  • the disposed feedstock material 120 on the substrate 110 is heated to a temperature in a range from about 1000 °C to about 1500 °C. In certain embodiments, the disposed feedstock material 120 on the substrate 110 is heated to a temperature in a range from about 1150 °C to about 1300 °C.
  • the disposed feedstock material 120 may be heated using an auxiliary heat source.
  • auxiliary heat source refers to a heat source employed in addition to the primary apparatus used for disposing the feedstock material 121.
  • the APS apparatus may include a primary heat source that is distinct and separate from the auxiliary heat source.
  • Suitable auxiliary heat sources include, but are not limited to, infrared (IR) sources, plasma sources, inductors, or combinations thereof.
  • the auxiliary heat source is a plasma source that is different from the plasma source used for the APS process.
  • the auxiliary heat source includes an induction coil.
  • Another embodiment of the disclosure is directed to a method of forming a porous thermal barrier coating using an auxiliary heat source.
  • the method includes disposing a feedstock material using an air plasma spray process on a substrate to form the porous thermal barrier coating, wherein the feedstock material includes a gas-forming additive and a thermal barrier coating material, and wherein the disposing step includes controlling a porosity parameter of the porous thermal barrier coating by controlling a temperature of the disposed feedstock material on the substrate using the auxiliary heat source.
  • FIG. 2 illustrates a method 20 in accordance with an embodiment of the present disclosure.
  • the method 20 includes providing a substrate 110, at step 14; disposing a feedstock material using an APS apparatus 115 on the substrate 110 to form a disposed feedstock material 120, at step 15; and forming a porous thermal barrier coating 130 on the substrate 110, at step 16.
  • the method further includes, controlling a temperature of the disposed feedstock material, at step 15, using an auxiliary heat source 125.
  • suitable auxiliary heat sources are described herein earlier.
  • Fig. 2 illustrates a single auxiliary heat source 125, one or more heat sources 125 may be employed depending on the size and shape of the substrate.
  • one or more of the configuration of the auxiliary heat source 125, the placement of the auxiliary heat source 125, and the proximity of the auxiliary heat source 125 to the substrate 110 may be varied depending on the degree of heating required.
  • the heating of the disposed feedstock material 120 is effected by one or more of pre-heating the substrate 110, simultaneously disposing and heating the feedstock material 121, or heating the disposed feedstock material 120 after the disposing step 12,15.
  • the heating of the disposed feedstock material 120 is effected by pre-heating the substrate 110 prior to the disposing step 12,15.
  • the substrate 110 may be pre-heated to a first temperature using the auxiliary heat source 125 and the feedstock material 121 may be deposited on the pre-heated substrate.
  • the first temperature may be sufficient to melt the thermal barrier coating material or maintain an already molten thermal barrier coating material in the molten state, but lower than the temperature that the substrate 110 can withstand.
  • the feedstock material may be further heated to a second temperature using the auxiliary heat source 125.
  • the second temperature may be sufficient to result in oxidation of the gas-forming additive thereby forming a gas in the molten thermal barrier coating material, but greater than the temperature that the substrate can withstand.
  • the auxiliary heat source may heat the disposed feedstock material 120 to a temperature greater than the melting point of these superalloys, such that the gases are formed.
  • the method may further include cooling the disposed feedstock material 120 to form the porous thermal barrier coating 130, at step 13,16.
  • the gas-forming additive containing feedstock material 121 is deposited at a temperature such that the gas-forming additive oxidizes and forms a gas. This gas may form while the feedstock material is still molten causing the gas bubbles to form pores.
  • the rate of cooling of the disposed feedstock material 120 is such that these pores are entrapped within the disposed feedstock material 120.
  • the porosity of these entrapped pores may be controlled using the methods described herein.
  • the auxiliary heat source 125 may be further controlled such that the heating from the auxiliary heat source 125 may be effected to generate a graded porosity in the porous thermal barrier coating 130.
  • Another embodiment of the disclosure is directed to a method of forming a porous thermal barrier coating including a graded porosity.
  • the method includes disposing a feedstock material on a substrate to form the porous thermal barrier coating, wherein the feedstock material includes a gas-forming additive and a thermal barrier coating material.
  • the disposing includes forming the graded porosity in the thermal barrier coating by controlling an amount of the gas-forming additive in the feedstock material, a temperature of the disposed feedstock material on the substrate using an auxiliary heat source, or a combination thereof.
  • graded porosity refers to a variation in the volume percentage of the porous thermal barrier coating 130 occupied by the plurality of the pores, across a thickness of the porous thermal barrier coating 130.
  • the volume percentage occupied by the plurality of the pores may be referred to as the "porosity" in that specific region.
  • graded porosity encompasses a discrete variation in porosity, a continuous variation in porosity, or a combination thereof.
  • the method may include forming a graded porosity in the porous thermal barrier coatings 130 such that the porosity continuously increases or decreases across a thickness of the porous thermal barrier coating 130 from a region disposed proximate to the substrate 110 (or the bond coating if present) to a surface of the porous thermal barrier coating 130.
  • the feedstock material 121 may be disposed on the substrate 110 (or the bond coating if present) in the form of discrete layers such that there is a step change (increase or decrease) of the porosity across the different layers of the resulting porous thermal barrier coating 130.
  • the method includes forming a porous thermal barrier coating 130 such that regions proximate to the substrate 110 (or the bond coating if present) and the surface of the porous thermal barrier coating 130 may be substantially free of porosity.
  • the intermediate region may have a graded porosity that may be discrete or continuous. Further the porosity in the intermediate region may increase or decrease depending on the desired properties of the porous thermal barrier coating. Without being bound by any theory, it is believed that a graded porosity across a thickness of the porous thermal barrier coating 130 may provide desired performance characteristics, depending on the end-use application. For example, by minimizing the porosity in a layer/region proximate to the surface of the porous thermal barrier coating, erosion or impact resistance of the coating may be enhanced. In some other applications, a porous surface of the thermal barrier coating may be desired, for example, to improve sacrificial properties of the coating.
  • the porosity of the porous thermal barrier coating 130 in different regions/layers of the thermal barrier coating 130 may be varied by varying one or both of a number of pores in the different regions/layers and an average size of the plurality of pores in the different regions/layers.
  • a graded porosity across a thickness of the porous thermal barrier coating is formed by controlling an amount of the gas-forming additive in the feedstock material, a temperature of the disposed feedstock material on the substrate using an auxiliary heat source, or a combination thereof
  • a graded porosity across a thickness of the porous thermal barrier coating 130 may be formed, for example, by controlling an amount of the gas-forming additive in the feedstock material 121.
  • the amount of gas-forming additive in the feedstock material 121 By varying the amount of the gas-forming additive in the feedstock material 121, the amount of gas-forming additive in the disposed feedstock material 120 over a duration of the disposing step 12, 15 may be varied. Therefore, resulting in a graded content of the gas-forming additive in disposed feedstock material 120.
  • This graded content of the gas-forming additive in the disposed feedstock material 120, upon oxidation may result in a graded porosity.
  • the amount of gas-forming additive in the feedstock material 121 may be varied by providing a plurality of feeds to the deposition apparatus 115 with varying gas-forming additive content, and controlling the feed into the deposition apparatus 115.
  • a graded porosity across a thickness of the porous thermal barrier coating 130 may be formed, for example, by controlling the temperature of the disposed feedstock material 120.
  • the auxiliary heat source 125 may be turned on or off, during the duration of the disposing step 15 depending on the desired gradation in porosity. For example, for layers/regions where minimal porosity is desired, the auxiliary heat source 125 may be turned off, thereby minimizing the formation of gases in those layers/regions.
  • the method 30 includes providing a substrate 110, at step 31; disposing a thermal barrier coating material 112 on the substrate 110, at step 32; disposing a feedstock material 121 on the thermal barrier coating material 112 to form a plurality of layers of disposed feedstock material (120',120"), at step 33; disposing the thermal barrier coating material 112 on an outermost layer 120" of the disposed feedstock material 120", at step 34, and forming a porous thermal barrier coating 130 on the substrate 110, at step 35.
  • the method further includes, controlling a temperature of the disposed feedstock material 120', 120", at step 33, using an auxiliary heat source 125.
  • auxiliary heat source 125 may also be used in steps 32 and 34 to dispose the thermal barrier coating material 112 on the substrate 110. It should be noted that although Fig. 3 illustrates two layers of disposed feedstock material (120', 120"), multiple layers of disposed feedstock material may be present on the thermal barrier coating material 112 depending on the total porosity requirement.
  • the amount of gas-forming additive in the disposed feedstock material 120' may be different than the amount in the disposed feedstock material 120".
  • the amount of gas-forming additive in the disposed feedstock material 120 may be varied by varying an amount of the gas-forming additive in the feedstock material 121. This variation in the amount of gas-forming additive in different layers may lead to variation in the total porosity of each layer thereby producing the porous thermal barrier coating 130 with a graded porosity.
  • the porous thermal barrier coating 130 includes a plurality of layers (112, 120', 120") such that the porosity of each layer is different.
  • the temperature of the disposed feedstock material 120' may be different from a temperature of the disposed feedstock material 120".
  • the temperature of the disposed feedstock material 120 may be varied by controlling the auxiliary heat source 125. This variation of the temperature in the different layers may lead to variation in the total porosity of each layer, thereby producing the porous thermal barrier coating 130 with a graded porosity.
  • the porous thermal barrier coating 130 includes a plurality of layers (112, 120', 120") such that the porosity of each layer is different.
  • Figures 4 and 5 illustrate a sectional view of a schematic of a porous thermal barrier coating 130 including a plurality of pores 132, formed using the methods in accordance with some embodiments of the disclosure.
  • controlling the porosity parameter of the porous thermal barrier coating 130 includes controlling an average pore size of a plurality of pores 132 in the porous thermal barrier coating 130 in a range from about 0.1 microns to about 25 microns.
  • controlling the porosity parameter of the porous thermal barrier coating 130 includes controlling an average pore size of a plurality of pores 132 in the porous thermal barrier coating 130 in a range from about 0.25 microns to about 5 microns.
  • controlling the porosity parameter of the porous thermal barrier coating 130 includes controlling an average pore volume of a plurality of pores 132 in the porous thermal barrier coating 130 in a range from about 1 volume % to about 10 volume %. In some embodiments, controlling the porosity parameter of the porous thermal barrier coating 130 includes controlling an average pore volume of a plurality of pores 132 in the porous thermal barrier coating 130 in a range from about 5 volume % to about 10 volume %.
  • controlling the porosity parameter of the porous thermal barrier coating 130 includes controlling the pore microstructure of the plurality of pores 132 in the porous thermal barrier coating 130.
  • the porous thermal barrier coating 130 includes a plurality of pores 132 such that at least some pores of the plurality of pores are intragranular.
  • the term "intragranular" as used herein means that the pores are present inside the grains.
  • the porous thermal barrier coating 130 includes a plurality of pores 132 such that at least some pores of the plurality of pores are intergranular (present between the grains), or, present at the grain boundaries. In certain embodiments, greater than 50 % of the plurality of pores are intragranular. In certain embodiments, greater than 80 % of the plurality of pores are intragranular.
  • FIG. 4 illustrates a schematic of a microstructure of the porous thermal barrier coating 130 formed, in accordance with some embodiments of the present disclosure.
  • the microstructure of the porous thermal barrier coating 130 as illustrated in Fig. 4 is characterized by grains 134 having a plurality of grain boundaries 136.
  • the microstructure further includes plurality of pores 132 present inside the grains 134 (intragranular pores).
  • FIG. 5 illustrates another schematic of a microstructure of the porous thermal barrier coating 130 formed, in accordance with some embodiments of the present disclosure.
  • the microstructure of the porous thermal barrier coating 130 as illustrated in Fig. 5 is characterized by grains 134 having a plurality of grain boundaries 136.
  • the microstructure further includes plurality of pores 132 present inside the grains 134 (intragranular pores) and plurality of pores 138 at or between the grain boundaries 136 (intergranular pores).
  • FIG. 6 illustrates a scanning electron microscopy (SEM) photomicrograph of a porous thermal barrier coating 130 formed by coating a mixture of YSZ and elemental carbon, using the APS process.
  • the microstructure of the porous thermal barrier coating 130 as illustrated in Fig. 6 is characterized by grains 134 having a plurality of grain boundaries 136.
  • the microstructure further includes plurality of susbtantially spherical pores 132 present inside the grains 134 (intragranular pores). The pores 132 are generated by entrapped carbon-containing gas.
  • gas-forming additive e.g., elemental carbon
  • gases e.g., carbon monoxide, carbon dioxide, and the like
  • gases because of being insoluble in the thermal barrier coating material, may be trapped within the thermal barrier coating material.
  • the pressure exerted by the entrapped gas on the surrounding thermal barrier material may inhibit pore coarsening and redistribution in the microstructure, such that the thermal barrier coating retains fine porosity and the microstructure of the thermal barrier coating may be thermally stabilized.
  • the controlled porosity may further result in lower thermal conductivity of the porous thermal barrier coating.
  • the porous thermal barrier coatings may provide enhanced thermal protection, because for the same coating thickness, the temperature gradient across the coating is higher.
  • the turbine engine components can be designed for thinner thermal barrier coatings and, where applicable, lower cooling air flow rates. This may lead to reduction in processing and material costs, and promote component life and engine efficiency.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Plasma & Fusion (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Coating By Spraying Or Casting (AREA)
  • Turbine Rotor Nozzle Sealing (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
  • Laminated Bodies (AREA)
EP18209695.8A 2017-12-04 2018-12-03 Verfahren zur formung einer porösen wärmebarrierenbeschichtung Withdrawn EP3492622A1 (de)

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US15/830,062 US20190169730A1 (en) 2017-12-04 2017-12-04 Methods of forming a porous thermal barrier coating

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CN112339264B (zh) * 2019-08-07 2021-12-14 中国科学院福建物质结构研究所 一种基于熔融沉积成型的保温隔热制件及其制备方法
EP4073019A4 (de) * 2019-12-12 2024-04-24 Nelumbo Inc. Keramische verbundstoffe
CN115073882B (zh) * 2021-03-15 2023-07-21 中国科学院福建物质结构研究所 一种原位固化的环氧树脂制件及其制备方法

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JP2019099921A (ja) 2019-06-24
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US20190169730A1 (en) 2019-06-06
CA3024842C (en) 2021-05-18

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