Patent Description:
Examples of known barrier coatings are as follows:
<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.

<CIT> describes a surface treatment product having a granular ceramic coating layer deposited thereon. The granular ceramic coating layer deposits a ceramic coating layer on an oxidation treatment or anodized coating layer in a granular form. To achieve this, the present invention comprises: a base material; a porous first coating layer on which a pore or a grain boundary is formed by performing either a spray coating treatment, the oxidation treatment, or the anodic oxidation treatment on a surface of the base material; and a second coating layer on which a ceramic coating layer is formed by spray-coating a ceramic suspension on a surface of the first coating layer to cover the pore or the grain boundary of the first coating layer. <CIT> describes a ceramic thermal barrier coating (TBC) having first and second layers, the second layer having a lower thermal conductivity than the first layer for a given density. The second layer is formed of a material with anisotropic crystal lattice structure. Voids in the first layer make the first layer less dense than the second layer. Grooves are formed in the TBC for thermal strain relief. The grooves may align with fluid streamlines over the TBC. A dense top layer may provide environmental and erosion resistance.

<CIT> describes an apparatus and method for producing non-woven nanofibers from polymers. The method for producing non-woven micro nanofibers from polymers comprises the use of electrospinning and melt blowing elements. The apparatus comprises a source of compressed gas, a pressure gauge, a hypodermic syringe with a pump for controlling the injection rate of the polymeric solutions, a pulverizing apparatus and a collector preferably with controlled rotation speed. The technology described is capable of producing micro and nanofibers having diameters similar to those produced by electrospinning, also on an industrial scale.

The present invention comprises a gas turbine engine component according to claim <NUM> which includes a substrate, and a ceramic barrier coating or layer disposed on the substrate. The ceramic barrier coating has a porous columnar microstructure with the pores being defined by the gaps between the columnar microstructure, and a layer of networked ceramic nanofibers is disposed on the ceramic barrier layer. The nanofibers seal the pores of the porous columnar microstructure in which the networked ceramic nanofibers comprise filaments intertwined to form a tangled network of filaments with pores between the filaments.

In an embodiment of the above embodiment, 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.

In an embodiment of any of the above embodiments, the ceramic barrier coating is comprised of or consists of zirconium oxide.

In an embodiment of any of the above embodiments, 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 substrate is a metal alloy.

In an embodiment of any of the above embodiments, the layer has a thickness of <NUM> micrometer to <NUM> micrometers or of <NUM> micrometer to <NUM> micrometers.

In an embodiment of any of the above embodiments, the ceramic barrier coating has a thickness t1 and the layer has a thickness t2, and t2 is less than t1 by a factor of at least <NUM>.

In an embodiment of any of the above embodiments, the ceramic nanofibers of the layer extend into the pores of the porous columnar microstructure.

An embodiment of any of the above embodiments includes an additional ceramic barrier coating disposed on the layer of the networked ceramic nanofibers.

In an embodiment of any of the above embodiments, the additional ceramic barrier coating is comprised of or consists of zirconia stabilized with an element selected from the group consisting of cesium, titanium, and combinations thereof.

In an embodiment of any of the above embodiments, the material of the ceramic nanofibers and the ceramic barrier coating are independently selected from the group consisting of yttria stabilized zirconia, gadolinia zirconate, and combinations thereof, and the layer has a thickness of <NUM> micrometer to <NUM> micrometers.

The gas turbine component of the present invention comprises an airfoil which includes an airfoil section, a porous ceramic barrier coating disposed on the airfoil section, and a layer of networked ceramic nanofibers disposed on the porous ceramic barrier coating. The nanofibers seal the pores of the porous barrier coating, in which the networked ceramic nanofibers comprise filaments intertwined to form a tangled network of filaments with pores between the filaments.

In an embodiment of the above embodiment, the porous barrier coating has a porous columnar microstructure.

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, 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.

In an embodiment of any of the above the airfoil includes an additional ceramic barrier coating disposed on the layer of the networked ceramic nanofibers.

In an embodiment of any of the above, the additional ceramic barrier coating includes zirconia stabilized with an element selected from the group consisting of cesium, titanium, and combinations thereof, and the layer has a thickness of <NUM> micrometer to <NUM> micrometers.

The present invention also comprises a method of fabricating a gas turbine component which includes providing a substrate and a ceramic barrier coating disposed on the substrate. The ceramic barrier coating has a porous columnar microstructure with the pores being defined by the gaps between the columnar microstructure. A layer of networked ceramic nanofibers is deposited by solution blow-spinning on the ceramic barrier coating in which the networked ceramic nanofibers comprise filaments intertwined to form a tangled network of filaments with pores between the filaments.

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 an article <NUM> according to 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 examples herein may be described with reference to the turbine blade, the present invention is also applicable to static turbine vanes, 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>. As described below, the article <NUM> includes a coating system to protect against the high temperatures and environmental effects that might otherwise damage the article <NUM>.

<FIG> illustrates a sectioned view through a representative portion of the airfoil section <NUM>, although the example could also apply to the platform <NUM>, root <NUM>, or other thermally-exposed portion if the article <NUM> is not a blade. The view is a section through an outer wall, in which the gaspath side is represented at GS. The wall is formed of a substrate <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.

There is a conformal coating system <NUM> disposed on the gaspath side of the substrate <NUM>. In this example, the coating system <NUM> includes a porous barrier coating <NUM> disposed on the substrate <NUM>. As an example, the porous 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 porous barrier coating <NUM> may, for example, be deposited by plasma spray or physical vapor deposition, which generally result in a porous structure. Optionally, a bond layer may be utilized between the barrier coating <NUM> and the substrate <NUM>, to promote bonding and resist spallation.

A layer <NUM> of networked ceramic nanofibers <NUM> is disposed on the porous barrier coating <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 layer <NUM>.

The nanofibers <NUM> are formed of a ceramic, such as an oxide. In one example, the ceramic is 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 layer <NUM> of networked ceramic nanofibers <NUM> seals the pores of the porous barrier coating <NUM>. For instance, although the layer <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 layer <NUM> of networked ceramic nanofibers <NUM>, even if formed of the same composition as the porous barrier coating <NUM>, provides thermal sealing of the porous barrier coating <NUM>. As an example based on zirconia, the layer <NUM> of networked ceramic nanofibers <NUM> may have a thermal conductivity of approximately <NUM> Watts per meter-Kelvin.

Additionally, the pores of the layer <NUM> of networked ceramic nanofibers <NUM> are much smaller than the pores of the porous barrier coating. Therefore, the layer <NUM> of networked ceramic nanofibers <NUM> serves to block debris or foreign material (e.g., calcium-magnesium-aluminosilicate or "CMAS") that might otherwise infiltrate into the pores of the porous barrier coating <NUM> and cause damage, thereby sealing the porous barrier coating <NUM>. 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 the impact of particles and debris. The layer <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. Rather, networked ceramic nanofibers have been produced in a screen-like cage structure. As a result, use of a layer of networked ceramic nanofibers barrier coating has not been suggested in combination with a thermal barrier coating, nor have the thermal and physical sealing benefits of a layer of ceramic nanofibers been realized for protection of a substrate and thermal barrier coating.

<FIG> illustrates a further example in which the coating system <NUM> includes an additional barrier coating <NUM> disposed on the layer <NUM> of networked ceramic nanofibers <NUM>. The barrier coating <NUM> may be selected to provide additional protection to the article <NUM>, such as additional resistance to CMAS. In one example, the barrier coating <NUM> is formed of zirconate stabilized with an element selected from the group consisting of cesium, titanium, and combinations thereof.

<FIG> illustrates an additional example coating system <NUM> on the substrate <NUM>. In this disclosure, like reference numerals designate like elements where appropriate and reference numerals with the addition of one-hundred or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding elements which do not include the addition of one hundred or multiples thereof. In this example, the coating system <NUM> includes a bond layer <NUM> and a ceramic barrier coating <NUM> disposed on the substrate <NUM>. The bond layer <NUM> may be MCrAlY, where M is nickel, iron or cobalt, Cr is chromium, Al is aluminum, and Y is yttrium. A portion 82a of the bond layer <NUM> may oxidize to form a thermally grown oxide scale, which facilitates bonding of the ceramic barrier coating <NUM>.

Like the coating <NUM>, the ceramic barrier coating <NUM> may include zirconium oxide. The zirconium oxide may be a stabilized or partially stabilized zirconia, such as yttriam 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>, however, has a columnar microstructure, represented schematically by microstructural columns 174a. Such a columnar microstructure is a result of fabrication by electron beam physical vapor deposition. The columns 174a are substantially perpendicular to the bond layer <NUM> and substrate <NUM>. There are pores 174b defined by the gaps between the columns 174a. Such a columnar microstructure facilitates coating durability. The pores 174b, however, may be prone to infiltration of debris and other material that could damage the coating <NUM> or underlying substrate <NUM>. In particular, since the pores are also substantially perpendicular to the bond layer <NUM> and substrate <NUM>, they can provide a direct path of infiltration for CMAS and foreign material. In this regard, the layer <NUM> of networked ceramic nanofibers <NUM> seals the pores 174b. As an example, the networked ceramic nanofibers <NUM> may infiltrate partially into the pores 174b during fabrication, thereby further enhancing sealing.

Due to the thermal insulation and sealing provided by the layer <NUM> of networked ceramic nanofibers <NUM>, the barrier coating <NUM>/<NUM> can be made thinner than it would be without the layer <NUM> of networked ceramic nanofibers <NUM>, yet achieve similar overall performance. Use of a thinner barrier coating <NUM>/<NUM> may also benefit rigidity and adhesion, while also lowering weight and reducing fabrication time.

In any of the above examples, the layer <NUM> of networked ceramic nanofibers <NUM> may have a thickness of <NUM> micrometer to <NUM> micrometers. Most typically, however, the thickness will be from <NUM> micrometer to <NUM> micrometers. The thickness is less than the thickness of the barrier coating <NUM>/<NUM>. For instance, the barrier coating <NUM>/<NUM> may have a thickness t1 and the layer <NUM> of networked ceramic nanofibers <NUM> may have a thickness t2, where t2 is less than t1 by a factor of at least <NUM>. Most typically, the barrier coating <NUM>/<NUM> will have a thickness of approximately <NUM> micrometers to <NUM> micrometers, or approximately <NUM> micrometers. The thickness of the layer <NUM> of networked ceramic nanofibers <NUM> may be adjusted to control the thermal and physical sealing described above.

The layer <NUM> of networked ceramic nanofibers <NUM> may be fabricated directly on to the barrier coating <NUM>/<NUM>. For example, the process may include first providing the substrate <NUM> and barrier coating <NUM>/<NUM>. For instance, the substrate <NUM> may be formed in a prior process and the barrier coating <NUM>/<NUM> deposited thereon prior to the application of the layer <NUM>. The layer <NUM> of networked ceramic nanofibers <NUM> may then be 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 on the carrier coating <NUM>/<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 consolidate the ceramic. It is during the thermal treatment that the filaments may diffuse and thereby bond together where they are in contact.

Claim 1:
A gas turbine engine component (<NUM>) comprising:
a substrate (<NUM>);
a ceramic barrier coating (<NUM>) disposed on the substrate, the ceramic barrier (<NUM>) coating having a porous columnar microstructure with the pores being defined by the gaps between the columnar microstructure; and
a layer (<NUM>) of networked ceramic nanofibers (<NUM>) disposed on the ceramic barrier coating (<NUM>) and sealing the pores (174b) of the porous columnar microstructure, in which the networked ceramic nanofibers comprise filaments intertwined to form a tangled network of filaments with pores between the filaments.