Patent Description:
<CIT> describes is a method for the local initial application of a thermal barrier coating layer, or for the local repair of coating defects and/or deteriorations of components in the hot gas path of a gas turbine engine when those components are coated with a thermal barrier coating layer on a base metal of the component. The method includes at least the following steps: (I) in case of repair normally overall inspection of the whole component for the determination of location of defect/deterioration as well as of corresponding type of defect/deterioration of each place for a multitude of locations of the component; (II) if needed preparation of the surface in at least one location; (III) local application of a ceramic tissue together with a wet chemical thermal barrier coating layer deposition material for the formation of a patch of ceramic matrix composite; (IV) intermediate inspection of the patch and/or the surface (IV)b in case of repetitive and/or multi-step repair method subsequent layer application of a ceramic tissue together with a wet chemical thermal barrier coating layer deposition material for the formation of a patch of ceramic matrix composite at this location; (V) if needed surface finishing at the at least one location; (VI) final inspection of the at least one location provided that steps (IV)a, (V) and (VI) can be omitted with the provision that at least one of steps (IV)a or (VI) is carried out.

<CIT> describes a composite thermal barrier coating. The composite thermal barrier coating comprises an alloy layer, a bonding layer, a ZrO2-Y2O3 ceramic layer and an aluminium film layer. In the coating nano aluminium fibres are formed on the surface of the ZrO2-Y2O3 ceramic layer of the coating with the result that the surface porosity factor of the coating is minimised by the aluminium film layer filling any pores in the ZrO2-Y2O3 ceramic layer. The CMAS corrosion resistance of the coating is increased leading to a thermal barrier coating with a high corrosion resistance.

<NPL> describes techniques for the fabrication of yttria-stabilized zirconia nanofibers by electrospinning.

A repair process according to the present invention includes a repair process comprising: providing a core gaspath gas turbine engine article that has a substrate and a ceramic barrier coating disposed on the substrate, wherein the ceramic barrier coating has a damaged region; characterised in that the process comprises abrading the damaged region to provide a dimple in the ceramic barrier coating, wherein a remaining region of the ceramic barrier coating adj acent the dimple remains intact; and depositing a patch of networked ceramic nanofibers in the dimple, in which the ceramic nanofibers are elongated, randomly oriented filaments that have a maximum diameter of <NUM> nanometer to <NUM> nanometers and intertwined to form a tangled porous network and are comprised of or consist of zirconium oxide, the patch of networked ceramic nanofibers is deposited by a blow spinning process, and the blow spinning process comprises spraying a precursor solution through an inner nozzle while flowing a process gas from an outer concentric nozzle such that the precursor when sprayed elongates into ultra-thin filaments, followed by a thermal treatment to remove the binders and sinter the ceramic to convert the precursor solution to ceramic; the damaged region is a region which has a physical deformity or imperfection; in which the precursor solution comprises binders and zirconium, oxides and any dopants.

In an embodiment of the above embodiments, the ceramic barrier coating has a porous columnar microstructure and the networked ceramic nanofibers extend into pores of the porous columnar microstructure in the dimple.

In an embodiment of any of the above embodiments, the abrading includes spraying the damaged region with an abrasive media.

In an embodiment of any of the above embodiments, the abrasive media includes dry ice.

In an embodiment of any of the above embodiments, the damaged region is a spalled or worn region.

In an embodiment of any of the above embodiments, the depositing comprised of or consists of blow-spinning and sintering.

In an embodiment of any of the above embodiments, the sintering is comprised of or consists of heating using an energy beam.

An embodiment of any of the above embodiments in which the method includes polishing the patch to be flat with the remaining region of the ceramic barrier coating adjacent the patch.

In an embodiment of any of the above embodiments, the ceramic nanofibers are comprised of or consist of zirconium oxide.

In an embodiment of any of the above embodiments, the ceramic nanofibers are comprised of or consist of a material selected from the group consisting of yttria stabilized zirconia, gadolinia zirconate, and combinations thereof, and the ceramic barrier coating is comprised of or consists of a material selected from the group consisting of yttria stabilized zirconia, gadolinia zirconate, and combinations thereof.

In an embodiment of any of the above embodiments, the ceramic barrier coating has a thickness t1 taken at the remaining portion adjacent the damaged region, and the patch has a thickness t2 that is less than the thickness t1.

In an embodiment of the above aspect the core gaspath gas turbine engine article is an airfoil.

In an embodiment of any of the above embodiment, the abrading includes spraying the damaged region with an abrasive media.

In an embodiment of the above embodiment, the abrasive media is comprised of or consists of dry ice.

In an embodiment of any of the above embodiments, the depositing is comprised of or consists of blow-spinning and sintering.

An embodiment of any of the above embodiments in which the process includes polishing the patch to be flat with the remaining region of the ceramic barrier coating adjacent the patch.

The present invention comprises a core gaspath as turbine engine article comprising: a substrate; a ceramic barrier coating disposed on the substrate, the ceramic barrier coating including a dimple; and a patch of networked ceramic nanofibers disposed in the dimple, in which the networked ceramic nanofibers comprise elongated, randomly oriented filaments that have a maximum diameter of <NUM> nanometer to <NUM> nanometers and intertwined to form a tangled porous network and are comprised of or consist of zirconium oxide filaments intertwined to form a tangled network of filaments that contact each other, and the patch of networked ceramic nanofibers was formed by a blow spinning process, and the blow spinning process comprised spraying a precursor solution through an inner nozzle while flowing a process gas from an outer concentric nozzle such that the precursor when sprayed elongates into ultra-thin filaments, followed by a thermal treatment to remove the binders and sinter the ceramic to convert the precursor solution to ceramic.

In an embodiment of any of the above embodiments, the ceramic nanofibers are comprised of or consists of a material selected from the group consisting of yttria stabilized zirconia, gadolinia zirconate, and combinations thereof, and the ceramic barrier coating is comprised of or consists of a material selected from the group consisting of yttria stabilized zirconia, gadolinia zirconate, and combinations thereof.

Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including but not limited to three-spool architectures.

The inner shaft <NUM> is connected to the fan <NUM> through a speed change mechanism, which in the exemplary gas turbine engine <NUM> is illustrated as a geared architecture <NUM> to drive a fan <NUM> at a lower speed than the low speed spool <NUM>.

The engine <NUM> in one embodiment of the present invention is a high-bypass geared aircraft engine. The low pressure turbine <NUM> pressure ratio is pressure measured prior to the inlet of low pressure turbine <NUM> as related to the pressure at the outlet of the low pressure turbine <NUM> prior to an exhaust nozzle. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including but not limited to direct drive turbofans.

"Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R) / (<NUM> °R)]^<NUM> (where °R = K x <NUM>/<NUM>).

<FIG> illustrates a turbine engine article <NUM> according to an embodiment of the present invention. The article <NUM> is a rotatable turbine blade of the engine <NUM> (see also <FIG>). It is to be understood that, although the embodiments herein may be described with reference to the turbine blade, this invention is also applicable to static turbine vanes, other types of airfoils, seals, combustors, or other gas turbine engine components.

The turbine blade generally includes a platform <NUM>, an airfoil section <NUM> that extends from the platform <NUM>, and a root <NUM>. The article <NUM> is subjected during use to extreme temperatures in the engine <NUM>. The article <NUM> includes a coating system to protect against the high temperatures and environmental effects that might otherwise damage the article <NUM>. The coating system may include a ceramic barrier coating. Such ceramic barrier coatings can be subject to damage during use, such as damage from spalling, erosion, or wear. From time to time and inasmuch as feasible, such articles are repaired in order to extend use.

<FIG> depict an example repair process for a representative portion of the article <NUM>. For a turbine blade, the portion may be on the platform <NUM>, airfoil section <NUM>, or root <NUM>. As will also be appreciated, the article <NUM> may have numerous portions which are repaired in a similar manner as described below.

The article <NUM> is formed of a substrate <NUM> and a coating system <NUM>. Most typically, the substrate <NUM> will be formed of a superalloy, such as a nickel- or cobalt-based alloy. Alternatively, the substrate <NUM> may be formed of a ceramic or ceramic composite material.

The coating system <NUM> includes a ceramic barrier coating <NUM> disposed on the substrate <NUM>. An optional bond coat <NUM> that has a thermally grown oxide region 74a is disposed between the ceramic barrier coating <NUM> and the substrate <NUM>. The bond coat <NUM> may be MCrAlY, where M is nickel, iron or cobalt, Cr is chromium, Al is aluminum, and Y is yttrium. A portion of the bond coat <NUM> may oxidize to form the thermally grown oxide region 74a, which facilitates bonding of the ceramic barrier coating <NUM>.

In an embodiment of the present invention, the ceramic barrier coating <NUM> is formed primarily of zirconium oxide. For instance, the zirconium oxide may be a stabilized or partially stabilized zirconia, such as yttrium stabilized zirconia or gadolinia stabilized zirconia, or a zirconate that is doped with a rare earth stabilizer, such as yttria or gadolinia. The ceramic barrier coating <NUM> may, for example, be deposited by plasma spray or physical vapor deposition, which generally result in a porous structure.

In the illustrated embodiments, the ceramic barrier coating <NUM> has a columnar microstructure, represented schematically by microstructural columns 72a. Such a columnar microstructure is a result of fabrication by electron beam physical vapor deposition. The columns 72a are substantially perpendicular to the bond coat <NUM> and substrate <NUM>. There are pores 72b defined by the gaps between the columns 72a. Such a columnar microstructure facilitates coating durability.

The repair process begins with the providing of the article <NUM> for repair, where the ceramic barrier coating <NUM> has a damaged region 72c. The "providing" may include identifying that the article <NUM> is in need of repair. In this regard, known inspection techniques may be used to detect and assess damage. More typically however, the article for repair will have already been identified and the "providing" may refer to the selection of the article to begin the repair process.

The damaged region 72c is be a region of the ceramic barrier coating <NUM> which has a physical deformity or imperfection, especially to a point or degree that is unacceptable for the given article <NUM>. Most typically, the damaged region 72c will be the result of physical phenomena that are incurred during use of the article <NUM> in its intended operating environment. As an example, the phenomena may be related to thermal-mechanical stresses that cause spallation, impact events that cause erosion, rubbing events that cause wear, or combinations of these. In these regards, the physical deformity may be a spalled, eroded, and/or worn portion of the ceramic barrier coating <NUM>. Alternatively, damage may be incurred prior to use or outside of use, such as during handling and transport of the article <NUM>. In the illustrated example, the physical deformity is a depression <NUM> in the ceramic barrier coating <NUM>. In another alternative, the physical deformity may be an imperfection, such as a crack or void, that results from original fabrication of the ceramic barrier coating <NUM>. For instance, a fabrication imperfection that renders the article <NUM> unacceptable for its intended use may be repaired using the repair process of the present invention to render the article acceptable for its intended use.

The next step in the repair process includes abrading the damaged region 72c. The depression <NUM> may contain debris or other undesirable substances which could be detrimental to the ceramic barrier coating <NUM> or hinder the remainder of the repair process. In this respect, the abrading facilitates removal of much or all of the debris, as well as possibly small portions of the ceramic barrier coating <NUM> in the vicinity of the damaged region 72c. The abrading thereby produces a fresh, clean surface in the ceramic barrier coating <NUM>.

As an example, the abrading may include spraying an abrasive media <NUM> from a spray nozzle <NUM> onto the damaged region 72c. For instance, the abrasive media <NUM> may be carried in a pressurized process gas. The abrasive media <NUM> strikes the damaged region 72c and thereby removes the debris and possibly a portion of the ceramic barrier coating <NUM>. The pressure of the process gas may be controlled in order to control removal of the debris and ceramic barrier coating <NUM>. In one embodiment, the abrasive media <NUM> includes particles of dry ice, which is solid carbon dioxide. The dry ice facilitates clean removal because it is substantially nonreactive at normal pressure and temperature (NTP) with the ceramic barrier coating <NUM> and thus does not leave residue or stains. Additionally, the dry ice rapidly evaporates and thus does not leave a mess.

<FIG> depicts the article <NUM> after the abrading. The abrading has removed debris and a portion of the ceramic barrier coating <NUM> such that a dimple <NUM> remains in the ceramic barrier coating <NUM>. A remaining region of the ceramic barrier coating, a representative portion of which is shown at <NUM>, adjacent the dimple <NUM>, remains intact after the abrading step. For instance, "intact" may refer to this region as being unchanged in physical character before and after the abrading. In this example, the dimple <NUM> is only modestly larger than the damaged region 72c and does not extend entirely through the thickness of the ceramic barrier coating <NUM>.

The next step in the repair process, depicted in <FIG>, is the deposition of a patch <NUM> into the dimple <NUM>. The patch <NUM> is composed of networked ceramic nanofibers <NUM>. <FIG> illustrates a magnified view of the networked ceramic nanofibers <NUM>. The nanofibers <NUM> are elongated, randomly oriented filaments that have a maximum diameter of <NUM> nanometer to <NUM> nanometers. More typically, the diameter will be <NUM> nanometer to <NUM> nanometers, <NUM> nanometer to <NUM> nanometers, or <NUM> nanometer to <NUM> nanometers. The filaments are non-linear and curve or turn such that the filaments are intertwined to form a tangled porous network. As used herein, "networked" refers to the intertwining of the fibers or filaments. Where the filaments contact each other, they may be bonded together as a result of the process used to form the patch <NUM>.

The nanofibers <NUM> are formed of of a ceramic that comprises or consists of zirconium oxide. For instance, the zirconium oxide may be a stabilized or partially stabilized zirconia, such as yttrium stabilized zirconia or gadolinia stabilized zirconia, or a zirconate that is doped with a rare earth stabilizer, such as yttria or gadolinia.

The patch <NUM> of networked ceramic nanofibers <NUM> fills the dimple <NUM> and seals the pores 72b of the ceramic barrier coating <NUM>. The nanofibers <NUM> may also mechanically interlock with the surface roughness in the dimple <NUM> that results from the abrading, thereby providing good bonding between the patch <NUM> and the ceramic barrier coating <NUM>. In that regard, the pressure of the process gas may also be controlled to produce a desirable level of roughness for mechanical interaction with the nanofibers <NUM>.

The pores 72b in the ceramic barrier coating <NUM> may be prone to infiltration of debris and other material during use of the article <NUM> that could damage the ceramic barrier coating <NUM>, bond coat <NUM>, or underlying substrate <NUM>. In particular, since the pores 72b are also substantially perpendicular to the bond coat <NUM> and substrate <NUM>, they can provide a direct path of infiltration for CMAS (calcium-magnesium-aluminosilicate) and foreign material. In this regard, the networked ceramic nanofibers <NUM> seal the pores 72b in the dimple <NUM>. As an example, the networked ceramic nanofibers <NUM> may infiltrate partially into the pores 72b during deposition, thereby enhancing sealing.

Although the patch <NUM> of networked ceramic nanofibers <NUM> is itself porous, the networked ceramic nanofibers <NUM> provide a sponge-like structure of smaller pores that provides superior thermal insulation. Therefore, the patch <NUM> of networked ceramic nanofibers <NUM>, even if formed of the same composition as the ceramic barrier coating <NUM>, provides thermal sealing of the ceramic barrier coating <NUM>. As an example based on zirconia, the patch <NUM> of networked ceramic nanofibers <NUM> may have a thermal conductivity of approximately <NUM> Watts per meter-Kelvin.

Additionally, the filaments of the networked ceramic nanofibers <NUM> are also flexible and strain tolerant. The flexibility of the filaments may further facilitate entrapment of foreign particles, debris, or materials, as well as act as a "bumper" to absorb impact of particles and debris. The patch <NUM> of networked ceramic nanofibers <NUM> thereby provides thermal and physical sealing/protection.

It is noted that networked ceramic nanofibers are not known for being produced on barrier coatings as a patch. Rather, networked ceramic nanofibers have been produced in a screen-like cage structure. As a result, use of a patch of networked ceramic nanofibers has not been suggested in combination with a ceramic barrier coating, nor have the thermal and physical sealing benefits of a patch of ceramic nanofibers been realized for protection with a ceramic barrier coating.

The patch <NUM> of networked ceramic nanofibers <NUM> may be deposited directly into the dimple <NUM>. The patch <NUM> of networked ceramic nanofibers <NUM> is deposited by a blow-spinning process. Blow-spinning involves spraying a precursor solution through an inner nozzle while flowing a process gas from an outer concentric nozzle such that the precursor when sprayed elongates into ultra-thin filaments. The filaments deposit in the dimple <NUM> and, after further processing, are converted into the ceramic nanofibers. The precursor solution includes binders and salts of the constituents that will form the ceramic, such as zirconium, oxygen, and any dopants. An example binder includes polyvinylpyrrolidone, and example salts may include aqueous oxynitrate, nitrate, nitrite, or chloride salts of zirconium and the selected dopants, zirconyl chloride, or metal organics such as zirconium isobutoxide or isopropoxide in a solvent. The amounts of the constituents may be controlled in order to control the final composition of the ceramic nanofibers. After spinning, the filaments are then thermally treated to remove binders, etc. and sinter the ceramic. The thermal treatment may include heating the filaments to temperatures from <NUM> to <NUM>, in one embodiment of the present invention. It is during the thermal treatment that the filaments may diffuse and thereby bond together where they are in contact. The thermal treatment may also cause diffusion at points of contact between the nanofibers <NUM> and the ceramic barrier coating <NUM>, thereby providing additional bonding.

In an alternative embodiment" the thermal treatment may be conducted using an energy beam, such as a laser. In particular, the energy beam can be aimed to impinge on the patch <NUM>, with minimal or no impingement on the remaining regions <NUM> of the ceramic barrier coating <NUM> adjacent the patch <NUM>. The effects of the heating can thus be confined to the patch <NUM>, while avoiding the expenditure of time and energy to heat the entire article <NUM>.

After deposition, the patch <NUM> may project from the ceramic barrier coating <NUM>, which generally has a continuous, smooth outer surface. If desired, as depicted in <FIG>, the patch <NUM> can be polished such that it is flush with the remaining region <NUM> of the ceramic barrier coating <NUM> adjacent the patch <NUM>, as represented at <NUM>.

At the remaining region <NUM>, the ceramic barrier coating <NUM> may define a thickness t1. The patch <NUM> may also define a maximum thickness t2, wherein the thickness t2 is less than the thickness t1. The thickness t2 being less than the thickness t1 is a representation that the patch <NUM> is not as thick as the ceramic barrier coating <NUM>. That is, the patch <NUM> most typically will be a relatively small piece of material that mends a relatively small region of the coating <NUM>. In particular, the ceramic barrier coating <NUM> thus has a locally thin portion at the dimple <NUM>. This locally thin portion, but for the patch <NUM>, may otherwise be prone to CMAS or foreign substance infiltration.

Claim 1:
A repair process comprising:
providing a core gaspath gas turbine engine article (<NUM>) that has a substrate (<NUM>) and a ceramic barrier coating (<NUM>) disposed on the substrate (<NUM>), wherein the ceramic barrier coating (<NUM>) has a damaged region (72c); characterised in that the process comprises
abrading the damaged region (72c) to provide a dimple (<NUM>) in the ceramic barrier coating (<NUM>),
wherein a remaining region (<NUM>) of the ceramic barrier coating (<NUM>) adjacent the dimple (<NUM>) remains intact; and
depositing a patch (<NUM>) of networked ceramic nanofibers (<NUM>) in the dimple (<NUM>), in which the ceramic nanofibers (<NUM>) are elongated, randomly oriented filaments that have a maximum diameter of <NUM> nanometer to <NUM> nanometers and intertwined to form a tangled porous network and are comprised of or consist of zirconium oxide,
the patch (<NUM>) of networked ceramic nanofibers (<NUM>) is deposited by a blow spinning process,
the blow spinning process comprises spraying a precursor solution through an inner nozzle while flowing a process gas from an outer concentric nozzle such that the precursor when sprayed elongates into ultra-thin filaments, followed by a thermal treatment to remove the binders and sinter the ceramic to convert the precursor solution to ceramic;
the damaged region (72c) is a region which has a physical deformity or imperfection; in which
the precursor solution comprises binders and zirconium, oxides and any dopants.