Patent Application
20130022471
The present subject matter relates generally to repairing tips or caps for turbine airfoils and, more particularly, to a ceramic-based tip or cap repair for a turbine airfoil.
In a gas turbine, air is pressurized by a compressor and then mixed with fuel and ignited within an annular array of combustors to generate hot gases of combustion. The hot gases flow from each combustor through a transition piece for flow along an annular hot gas path. Turbine stages are typically disposed along the hot gas path such that the hot gases flow through first-stage nozzles and airfoils and through the nozzles and airfoils of follow-on turbine stages. The turbine airfoils may be secured to a structural case or a plurality of rotor disks comprising the turbine rotor, with each rotor disk being mounted to the rotor shaft for rotation therewith.
A turbine airfoil generally includes an airfoil extending radially outwardly from a substantially planar platform and an attachment portion extending radially inwardly from the platform for securing the airfoil to one of the rotor disks. Certain airfoils can be composed of ceramic and ceramic matrix composite (CMC) materials for operation in a high temperature environment as exist in gas turbines. After the airfoil is put into service, however, the tip or cap of the rotating CMC airfoil can experience localized damage as the tip or cap comes into contact with a gas turbine shroud or due to foreign object damage. The damage to the CMC airfoil can lead to secondary damage if the CMC or ceramic fibers are exposed to the moisture or other contaminates in the gas turbine hot gas path steam.
As such, methods would be welcomed for repairing damage to a CMC airfoil, especially on the tip or cap to extend the working life of the airfoil.
Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
Methods are generally provided for repairing an article constructed from a CMC material. According to one exemplary method, a cavity located in the article can be filled with a ceramic paste (e.g., including a ceramic powder and a binder). The ceramic paste in the cavity can then be heated to remove the binder, thereby forming a porous ceramic material. A molten ceramic material can then be added to the porous ceramic material. In one particular embodiment, the cavity can be defined in an airfoil of the turbine airfoil (e.g., on a tip or cap of the airfoil).
For example, methods are generally provided for repairing a tip or cap of an airfoil constructed from a ceramic matrix composite material. According to one exemplary method, a cavity located on the tip or cap of the airfoil of the turbine airfoil can be filled with a ceramic paste (e.g., comprising a ceramic powder and a binder). The ceramic paste in the cavity can then be heated to remove the binder, thereby forming a porous ceramic material. A molten ceramic material (e.g., the molten ceramic material comprises silicon carbide) can then be added to the porous ceramic material.
Intermediates formed during the repair of a turbine airfoil are also generally provided. The intermediate can generally include an airfoil comprising a CMC material, a cavity defined in the airfoil, and a porous ceramic material filling the cavity.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
In general, methods are generally provided for repairing an article (e.g., a tip or cap of an airfoil in a gas turbine), along with the resulting repaired article (e.g., repaired airfoils). In particular, methods are generally provided for repairing articles (e.g., the tip or cap of an airfoil) constructed from ceramic matrix composite (CMC) material, along with the resulting repaired article (e.g., airfoils). Though discussed hereinafter with respect to an airfoil, the methods may be broadly applied to any article constructed from a CMC material.
CMC materials used to form the airfoil generally exhibit enhanced high temperature capabilities as compared to conventional metal-based airfoils. As such, the airfoil may reduce or eliminate the need for supplying a cooling medium (e.g., air and the like) to and/or through the tip or cap, thereby increasing the efficiency of the gas turbine. Additionally, because of the low densities of CMC materials, the weight of the tip or cap may be significantly less than conventional metal-based tips or caps, thereby reducing the loads generated by the tip or cap during operation of the gas turbine. In several embodiments of the present subject mater, it should be appreciated that the methods disclosed herein may be designed for retrofit applications and, thus, may be configured to be performed on pre-existing turbine airfoils.
Referring now to the drawings,
During operation of the gas turbine 10, the compressor section 12 pressurizes air entering the gas turbine 10 and supplies the pressurized air to the combustors of the combustor section 14. The pressurized air is mixed with fuel and burned within each combustor to produce hot gases of combustion. The hot gases of combustion flow in a hot gas path from the combustor section 14 to the turbine section 16, wherein energy is extracted from the hot gases by the turbine airfoils 24. The energy extracted by the turbine airfoils 24 is used to rotate the structural cases 22 which may, in turn, rotate the shaft 18. The mechanical rotational energy may then be used to power the compressor section 12 and generate electricity.
It should be understood, however, that the present disclosure is not limited to use in structural cases 22 in the turbine section 16 of a turbine system 10. Rather, the structural cases 22 and/or turbine airfoils 24 may be utilized in conjunction with any suitable section of the turbine system 10. For example, the structural cases 22 and/or turbine airfoils 24 may, in exemplary embodiments, be utilized in the compressor 12.
The airfoil 30 may generally extend radially outwardly from the platform 32 and may include an airfoil base 34 disposed at the platform 32 and an airfoil tip or cap 36 disposed opposite the airfoil base 34. Thus, the airfoil tip or cap 36 may generally define the radially outermost portion of the turbine airfoil 24. The airfoil 30 may also include a pressure side wall 38 and a suction side wall 40 (
Additionally, the turbine airfoil 24 may also include an airfoil cooling circuit 46 extending radially outwardly from the attachment portion 28 for flowing a cooling medium, such as air, water, steam or any other suitable fluid, throughout the airfoil 30. The airfoil cooling circuit 46 may generally have any suitable configuration known in the art. Thus, in several embodiments, the cooling circuit 46 may include a plurality of cooling channels or passages 48 (one of which is shown in the cross-sectional view of
It should be appreciated that the various components of the turbine airfoil 24 (e.g., the airfoil 30, platform 32 and attachment portion 28) may generally be formed from a ceramic matrix composite (CMC) material. In general, the CMC material used to form the turbine airfoil 24 may comprise any suitable CMC material known in the art and, thus, may generally include a ceramic matrix having a suitable reinforcing material incorporated therein to enhance the material's properties (e.g., the material strength and/or the thermo-physical properties). In several embodiments, the CMC material used may be configured as a continuous fiber reinforced CMC material. For example, suitable continuous fiber reinforced CMC materials may include, but are not limited to, CMC materials reinforced with continuous carbon fibers, oxide fibers, silicon carbide monofilament fibers or other CMC materials including continuous fiber lay-ups and/or woven fiber performs. In other embodiments, the CMC material used may be configured as a discontinuous reinforced CMC material. For instance, suitable discontinuous reinforced CMC materials may include, but are not limited to, particulate, platelet, whisker, discontinuous fiber, in situ and nano-composite reinforced CMC materials or mixtures thereof. Moreover, it should be appreciated that the disclosed turbine airfoil 24 may be formed from the CMC material using any suitable manufacturing process known in the art. For example, suitable manufacturing processes may include, but are not limited to, injection molding, slip casting, tape casting, infiltration methods (e.g., chemical vapor infiltration, melt infiltration and/or the like) and various other suitable methods and/or processes.
In normal use, defects can be formed in the turbine airfoil 24, and particularly along the airfoil 30.
The ceramic paste 50 generally includes a ceramic powder, a binder, and optionally ceramic fibers. The ceramic powder can include silicon carbide (SiC), silicon dioxide (SiO2), Alumina oxide (Al2O3), carbon, or mixtures thereof. The binder can include suitable composition configured to hold the ceramic powder (and optional ceramic fibers, if present) together as a paste, and can include but is not limited to, an epoxy binder, a polymeric binder, an adhesive (e.g., glue),silicon dioxide (SiO2), Alumina oxide (Al2O3), carbon, boron, or mixtures thereof.
In one particular embodiment, the ceramic paste 50 includes SiC and an epoxy binder. In this embodiment, SiC fibers may or may not be included in the ceramic paste 50 if desired. The SiC fibers, when included, can be coated to prevent absorption by the CMC matrix exposed on the cavity 26. For example, the SiC fibers can be coated with boron (B) or carbon (C) particles, any other suitable particle, or mixtures thereof.
After application into the cavity 26, the ceramic paste 50 can then be heated to remove the binder from the cavity 26, leaving a porous ceramic material 52 in the cavity 26. For example, the ceramic paste 50 in the cavity 26 can be heated to 100° C. or greater, such as about 110° C. to about 200° C. Heating can be achieved either locally (e.g., heating only the porous ceramic material 52 and the immediate area around the cavity 26) or entirely (e.g., heating the entire airfoil 30 and/or turbine airfoil 24). At these elevated temperatures, the binder in the ceramic paste 50 will begin to decompose, sublimate, and/or evaporate from the ceramic paste 50 to leave only a porous ceramic material 52 in the cavity 26, as shown in
The porous ceramic material 52 and cavity 26 can then be further heated to temperatures for receiving a molten ceramic material to fill pores in the porous ceramic material 52, thereby forming a ceramic patch to fill the cavity 26. For example, the porous ceramic material 52 and cavity 26 can be heated (either locally or with the entire airfoil 30 and/or turbine airfoil 24) to temperatures of greater than about 1000° C., such as about 1100° C. to about 1500° C.
The molten ceramic material 54 can generally include ceramic material, such as silicon carbide (SiC), silicon dioxide (SiO2), Alumina oxide (Al2O3), carbon or mixtures thereof. In one embodiment, the molten ceramic material 54 can be substantially pure SiC (e.g., being substantially free from other compounds). As used herein, the term “substantially free” means no more than an insignificant trace amount present and encompasses completely free (e.g., 0 molar % up to 0.0001 molar %).
After infusion of the molten ceramic material 54, the cavity 26 (and the rest of the turbine airfoil 24) can be cooled, allowing the porous ceramic material 52 and molten ceramic material 54 to cure and set into a ceramic patch 56 filling the cavity 26 (
As described in greater detail above, one particular embodiment of the method of repairing a turbine airfoil constructed from a CMC material can be summarized as follows: filling a cavity on a CMC turbine airfoil with a ceramic paste, heating the ceramic paste to remove the binder forming a porous structure in the cavity, further heating the porous structure, adding molten material to fill pores in the porous structure, and cooling the molten material and the porous structure to form a ceramic patch in the cavity. Other steps can be included (e.g., shaping the porous structure, shaping the ceramic patch, etc.) in this method as desired.
This written description uses examples to disclose the invention, 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 incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
