Patent Application
20150354394
The present technology generally relates to high temperature abradable coatings and to methods of manufacturing high temperature abradable coatings, in particular to turbine shrouds with high temperature abradable coatings.
Materials which abrade relatively readily may be used to form seals between a rotating component (rotor) and a fixed component (stator). Typically, the rotor wears away a portion of a stator having the abradable material, so as to form a seal characterized by a relatively small gap between the rotor and stator. An application of abradable seals is in turbines (e.g., gas turbines), in which a rotor including a plurality of blades mounted on a shaft is surrounded by a stationary shroud. In the high pressure turbine (HPT) section, these shrouds define a hot gas flowpath in the turbine. Minimizing the clearance between the blade tips and the inner wall of the shroud reduces leakage of the hot gas around the blade tips leading to improved turbine efficiency.
To reduce blade tip wear, it is known to use patterned abradable architectures on the shroud flowpath surface. By reducing the solidity of the shroud surface in contact with the passing blade, the relative blade tip wear is reduced. While a patterned shroud surface may reduce blade wear, it can decrease turbine efficiency due to leakage losses over the passing blade tips. As a result, substantially smooth, continuous-flowpath surface abradable structures are desired to reduce leakage, while patterned abradable surfaces are desired to minimize blade tip wear. One approach to resolve this apparent contradiction of shroud flowpath surfaces has been to use highly porous abradable materials with a substantially smooth, continuous flowpath surface. However, such materials are found to be highly friable, suffering low durability under erosive and other harsh-environment conditions.
As a result, a need exists for methods of making abradable shrouds and resulting abradable shrouds that include an architecture and microstructure that balances the contradictory requirements of high flowpath solidity, low blade tip wear, and good durability in service.
According to one example of the present technology, a method of manufacturing a turbine shroud comprises forming a porous friable coating over a barrier coating system provided on a substrate of the turbine shroud to form a substantially smooth continuous flowpath surface.
According to another example of the present technology, a shroud for a turbine, comprises a substrate having an outer surface configured to be disposed adjacent tips of rotating turbine blades and at least partially defining an outer annulus of a turbine flowpath; a barrier coating system overlying at least a portion of the outer surface of the substrate; and a porous friable coating overlying at least a portion of the barrier coating system, the porous friable coating defining a substantially smooth continuous flowpath surface.
These and other objects, features and advantages of this disclosure will become apparent from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings.
Approximating language as used herein throughout the specification and claims 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 or terms, such as “about,” is not limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value.
As discussed above, conventional turbine shrouds include either a patterned surface or a substantially smooth surface configured to abrade when/if a turbine blade contacts the shroud. A substantially smooth abradable surface of a shroud maintains flowpath solidity but can result in severe blade tip wear. Patterned abradable shroud surfaces result in significantly reduced blade tip wear as compared to unpatterned or substantially smooth-flowpath shrouds, but allow leakage across the blade tip that leads to decreased turbine efficiency. The present technology provides shroud coatings, coated shrouds and methods of coating shrouds that include a hybrid architecture that balances the apparently contradictory requirements of high flowpath solidity, low blade tip wear, and high durability.
Referring to
Referring to
The shroud 10 may include a coating system 20 disposed over the substrate 12. The coating system 20 may comprise one or more component or material and may be positioned between the substrate 12 and the abradable coating 14. The coating system 20 may include a bondcoat, a barrier coating, or a bondocat and a barrier coating. For example, the substrate 12 may be metal, and the coating system 20 of the shroud 10 may include a thermal barrier coating (TBC) applied thereon. The TBC-based coating system 20 may contain one or more TBC layers. The one or more TBC layers may be zirconia-based. The one or more TBC layers of the coating system 20 may include yttria-stabilized zirconia (YSZ), such as zirconia containing 7-8 weight percent yttria. The one or more TBC layers of the coating system 20 may include fully stabilized zirconia (FSZ).
The substrate 12 may be a ceramic, and the coating system 20 may include an environmental barrier coating (EBC) applied thereon. The EBC-based coating system 20 may contain one or more EBC layers. The one or more EBC layers of the coating system 20 may be silicate-based. The one or more EBC layers of the coating system 20 may include one or more rare earth silicates, such as RE2Si2O7 and/or RE2SiO5, where RE comprises one or more of Y, Er, Yb, and Lu.
The coating system 20 may include a bondcoat overlying the substrate 12. The coating system 20 may include an EBC or TBC coating applied over the bond coat. The bond coat may provide oxidation resistance to the substrate 12 and/or to assist in maintaining adherence of the EBC/TBC coating. The shroud 10 may include a TBC-coated metallic substrate 12, and the coating system 20 may include a bond coat between the substrate 12 and the TBC coating including a NiAl, (Pt,Ni)Al, or (Ni,Co)CrAlY type of composition. The shroud 10 may include an EBC-coated ceramic substrate 12, and the coating system 20 may include a Si-based bond coat between the substrate 12 and the EBC coating.
As shown in
The thickness of the abradable coating 14 as measured from the outer-most surface of the coating system 20 to the flowpath surface 30 may be within the range of about 0.1 mm and about 2 mm, and more preferably within the range of about 0.2 mm and about 1.5 mm. The abradable coating 14 may be initially manufactured thicker than as described above, and machined or otherwise treated to achieve the thicknesses described above. For example, after forming or manufacturing the abradable coating 14 with the first and second regions 16, 18, the abradable coating 14 may be machined, polished, or otherwise treated by removing material from the abradable coating 14 so as to provide a desired clearance between the blade tips 122 and the flowpath surface 30. The treating of the abradable coating 14 from the as-manufactured condition to create the desired flowpath surface 30 may reduce the thickness of the abradable coating 14. The flowpath surface 30 may be substantially smooth. The flowpath surface 30 may include some curvature in the circumferential and/or axial directions. As another example, the substrate 12 may include curvature, and the curvature of the flowpath surface 30 may substantially conform to that of the substrate 12.
With reference to
The second regions 18 may be less dense than the first regions 16. For example, the second regions 18 may include about 20% to about 65% porosity, while the first regions 16 may include less than about 20% porosity. The second regions 18 may include about 25% to about 50% porosity, while the first regions 16 may include less than about 15% porosity. Both the first and second regions 16, 18 of the abradable coating 14 may be capable of withstanding temperatures of at least about 1150° C., for example at least about 1300° C.
A method of manufacturing the second regions 18 of the abradable coating 14 may include use of one or more fugitive filler material to define the volume fraction, size, shape, orientation, and spatial distribution of the porosity. The filler material may include fugitive materials and/or pore inducers, such as but not limited to polystyrene, polyethylene, polyester, nylon, latex, walnut shells, inorganic salts, graphite, and combinations thereof. The filler material of the second regions 18 may act to decrease the in-use density of the second material. At least a portion of the filler material of the second regions 18 may be evaporated, pyrolized, dissolved, leached, or otherwise removed from the second regions 18 during the manufacturing process (such as subsequent heat treatments or chemical treatments or mechanical treatments) or during use of the shroud 10. The method of manufacturing the second regions 18 of the abradable coating 14 may include use of one or more sintering aids, such as to form lightly sintered powder agglomerates.
The first and second regions 16, 18 of the abradable coating 14 may include substantially the same composition or material. For example, the first and second regions 16, 18 of the abradable coating 14 may both substantially include stabilized zirconia (such as with metallic substrates) or rare earth silicates (such as with ceramic substrates). Both the first and second regions 16, 18 of the abradable coating 14 may substantially include stabilized zirconia, and the substrate 12 of the shroud 10 may be nickel-based and/or cobalt-based. Both the first and second regions 16, 18 of the abradable coating 14 may substantially include rare earth silicates, and the substrate 12 of the shroud 10 may be SiC-based and/or Mo—Si—B-based. The composition or material of the first and second regions 16, 18 may substantially differ. At least one of the first and second regions 16, 18 may substantially include, or be formed of, one or more materials of the underlying coating system 20 (e.g., an EBC/TBC and/or bond coat containing coating system 20).
As shown in
The first regions 16 of the abradable coating 14 of the shroud 10 may include or be defined by ridges extending from the coating system 20 to the flowpath surface 30. For example, as shown in
At least one of the first and second regions 16, 18 of the abradable coating 14 of the shroud 10 may extend linearly, non-linearly (e.g., may include one or more curves, bends, or angles), may or may not intersect with each other, may form a regular or irregular pattern, or consist of combinations thereof or any other arrangement, pattern or orientation such that—during incursions—the turbine blades pass through the first and second regions 16, 18 of the abradable coating 14 and the first regions 16 corral the second regions 18.
Referring to
The center-to-center distance between adjacent ridges of the first regions 16 may be within the range of about 1 mm and 6 mm, for example within the range of about 2 mm and 5 mm. The solidity of first regions 16, defined as the fraction of the total surface area of the flowpath surface 30 comprised of first regions 16, may be within the range from about 2% to about 50%, and more preferably may be within the range from about 5% to about 20%.
Referring to
The method 200 may include forming or obtaining 204 a coating system on a surface of the shroud substrate 12. Forming or obtaining 204 the coating system on the surface of the shroud substrate may include forming or obtaining a TBC coating on at least one surface of the shroud substrate or forming or obtaining 204 an EBC coating on at least one surface of the shroud substrate.
Forming or obtaining 204 a coating system on an outer surface of the shroud substrate may include applying the coating system to at least a portion of an outer surface of the substrate by spraying, rolling, printing or otherwise mechanically and/or physically applying the coating system over at least a portion of a surface of the substrate. Forming or obtaining 204 a coating system on an outer surface of the shroud substrate may include treating as-applied coating system material to cure, dry, diffuse, sinter or otherwise sufficiently bond or couple the coating system to the substrate.
The method 200 may include forming 206 a relatively dense abradable scaffold on at least a portion of the shroud substrate, such as over the coating system 20 described above, including forming 206 the relatively dense abradable scaffolds or first regions 16.
In some embodiments forming 206 a relatively dense abradable scaffold on at least a portion of the shroud substrate includes forming a relatively dense, strong patterned structure that provides mechanical integrity to the abradable coating while having sufficiently low solidity so as to support blade tip incursion with minimal blade wear. Forming 206 a relatively dense abradable scaffold on at least a portion of the shroud substrate may be performed before forming 208 relatively porous friable filler regions that readily abrade in response to blade incursion within the scaffold to form a flowpath surface.
Forming 206 a relatively dense abradable scaffold on at least a portion of the shroud substrate may include at least one additive manufacturing method or technique, such as thermally spraying the relatively dense abradable material of the scaffold (e.g., the materials of the first region 16 discussed above) through a patterned mask to form the scaffold pattern or structure of the ridges of first regions 16. Forming 206 a relatively dense abradable scaffold on at least a portion of the shroud substrate may include direct-write thermal spraying the relatively dense abradable material in the form of a scaffold. The direct-write thermal spraying may include utilizing a small-footprint gun and dynamic aperture to form the scaffold. Forming 206 a relatively dense abradable scaffold on at least a portion of the shroud substrate may include dispensing a slurry paste in the form of a green scaffold pattern on the coating system, followed by heat treating the slurry paste so as to sinter it and form the relatively dense scaffold.
Forming 206 a relatively dense abradable scaffold on at least a portion of the shroud substrate may include applying a continuous blanket layer of relatively dense abradable material, followed by removal of portions of the blanket layer to selectively define the scaffold or pattern of the relatively dense abradable material. Removal of portions of the blanket layer to selectively define the scaffold or pattern may include machining portions of the blanket layer to selectively define the scaffold or pattern may be performed utilizing a mill, water jet, laser, abrasive grit blaster, or combinations thereof to remove portions of the blanket layer of relatively dense abradable material.
Forming 206 a relatively dense abradable scaffold on at least a portion of the shroud substrate may include screen printing, slurry spraying or patterned tape-casting ceramic powder with binder and, potentially, one or more sintering aid, so as to form a green scaffold or pattern which, upon sintering, forms a relatively dense abradable material (e.g., the materials of the first regions 16 discussed above).
Forming 208 relatively porous friable filler regions between the dense abradable scaffold may include back-filling, depositing or otherwise applying relatively porous friable filler regions (e.g., the materials of the second regions 18 discussed above) in-between the relatively dense abradable scaffold.
Forming or obtaining 208 relatively porous friable filler regions in-between the dense abradable scaffold may include applying relatively porous friable filler material by thermal spray (with or without a mask) in-between the relatively dense abradable scaffold or pattern. The relatively porous friable filler material may be ceramic powder having the composition of the first regions 16 discussed above. The ceramic powder may include at least one additive, such as a fugitive filler material, pore inducer, and/or sintering aid (as discussed above), such that the at least one additive is co-deposited, such as via thermal spray, with the ceramic powder.
Forming 208 relatively porous friable filler regions in-between the dense abradable scaffold may include applying relatively porous friable filler material as a slurry. The slurry formulation may be a ceramic slurry formulation and include at least one additive, such as a fugitive filler material, pore inducer, and/or sintering aid such that the at least one additive is co-deposited with the ceramic slurry formulation. Forming 208 relatively porous friable filler regions in-between the dense abradable scaffold may include applying a relatively porous friable filler by tape-casting or screen printing. The particle size distribution of the particles of the slurry is selected to provide a highly porous microstructure having coarse particles partially sintered at contact points. Forming 208 relatively porous friable filler regions in-between the dense abradable scaffold may include sintering the filler material. Forming 208 relatively porous friable filler regions in-between the dense abradable scaffold may include applying relatively porous friable filler material as a slurry formulation with pre-agglomerated or pre-aggregated particles.
Forming 208 relatively porous friable filler regions in-between the dense abradable scaffold may include producing high aspect ratio tabular particles via, for example, hydrothermal synthesis, combustion synthesis, tape casting, fine extrusion, and/or combinations thereof. Forming 208 relatively porous friable filler regions in-between the relatively dense abradable scaffold may include aligning the high aspect ratio tabular particles via, for example, electrophoretic deposition, slip casting, tape casting, extrusion, and/or combinations thereof
The method 200 may include treating 210 the abradable coating, such as the relatively dense abradable scaffold and relatively porous friable filler regions. Treating 210 the abradable coating may include treating the flowpath surface of the abradable coating formed by the relatively dense abradable scaffold and relatively porous friable filler regions to form a substantially smooth flowpath surface, such as by leveling and/or smoothing of the as-manufactured flowpath surface. Treating 210 the abradable coating may include grinding, sanding, etching or otherwise removing high areas of the flowpath surface formed by the relatively dense abradable scaffold and/or relatively porous friable filler regions. Treating 210 the flowpath surface may include an assembly grind to remove prominent portions (e.g., tips) of the relatively dense abradable scaffold (e.g., ridges) or relatively porous friable filler (e.g., valleys) to bring the flowpath surface of the abradable coating to a substantially common height so as to achieve a substantially smooth, continuous flowpath surface. Treating 210 the abradable coating may include heat treating the abradable coating which may include sintering the relatively dense abradable scaffold and/or the relatively porous friable filler regions. Heat treating 210 the abradable coating may include heating the relatively dense abradable scaffold and/or the relatively porous friable filler region to burn out, evaporate or otherwise remove fugitive materials and/or pore inducers therein via the application of heat.
Referring to
As shown in
The method 400 may include forming 322 a relatively dense abradable scaffold (e.g., the first regions 16 described above) in-between the relatively porous friable pattern so as to form a substantially smooth flowpath surface 30. Forming 322 a relatively dense abradable scaffold in-between the relatively porous friable pattern on the shroud substrate may include applying the relatively dense abradable scaffold on the substrate via a method or technique as described above with respect to the forming 208 relatively porous friable filler regions in-between the dense abradable scaffold of the method 200 of
Referring to
As shown in
The method 400 may include selectively densifying 426 portions of the substantially continuous blanket layer of relatively porous friable material to form a relatively dense abradable scaffold within the layer (e.g., the first regions 16 discussed above). Selectively densifying 426 portions of the substantially continuous blanket layer of relatively porous friable material may include screen-printing or otherwise introducing sintering aids into/onto the substantially continuous blanket layer of relatively porous friable material in a scaffold pattern. The substantially continuous blanket layer of relatively porous friable material, with the scaffold pattern of screen-printed sintering aids, may be subsequently sintered to form a relatively dense abradable scaffold in the relatively porous friable layer to form the abradable coating. Selectively densifying 426 portions of the substantially continuous blanket layer of relatively porous friable material may include selectively sintering (e.g., such as using laser beam or electron-beam localized heat sources) portions of the layer in a scaffold pattern in the relatively porous friable layer so as to form the relatively dense abradable scaffold of the abradable coating.
Referring to
The method 500 may include thermally spraying 528 an abradable material through a patterned mask to substantially concurrently or simultaneously form a relatively dense abradable scaffold and a relatively porous friable filler. Thermally spraying 528 through the patterned mask to form a relatively dense abradable scaffold and relatively porous friable filler regions in-between the scaffold may include simultaneously forming both structures. For example, abradable materials may be thermally sprayed 528 through a patterned mask configured to produce the dense ridges or first regions 16 described above and spaced such that the second regions 18 discussed above are formed from overspray that is retained between the ridges or first regions 16. For example, the mask opening width, spacing between mask openings, gap between mask and surface being coated, thickness of the mask material, cross sectional shape of the openings, and combinations thereof may be configured to substantially contemporaneously form the relatively dense abradable scaffold and relatively porous friable filler regions in-between or within the scaffold. The mask could be configured with movable elements that adjust opening widths and/or standoff distance of the mask as the abradable coating thickness increases to more completely fill the relatively dense abradable scaffold with the relatively porous friable filler regions. An additional slurry coating of relatively porous friable filler material may subsequently be utilized to more completely fill the relatively dense abradable scaffold with the relatively porous friable filler regions.
The method 500 may include treating 510 the flowpath surface. Treating 510 the flowpath surface may include removing prominent portions of the abradable coating to a substantially uniform thickness, so as to obtain a substantially smooth flowpath surface.
Referring to
The coating system as disclosed herein may be, for example, as described in U.S. 2011/0052925, U.S. 2014/0037969, or U.S. application Ser. No. 14/204,367, the entire contents of each being incorporated herein by reference.
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described examples (and/or aspects thereof) may be used in combination with each other. It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular example. Thus, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or increases one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
This written description uses examples to describe the claimed inventions, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any of the methods. The patentable scope of each invention is defined by the claim.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14300520 | Jun 2014 | US |
| Child | 14587744 | US | |
| Parent | 14300666 | Jun 2014 | US |
| Child | 14300520 | US |
