Abstract:
The present application provides a method of repairing a turbine blade. The method may include the steps of removing an existing squealer tip from the turbine blade in whole or in part, positioning the turbine blade in an additive manufacturing system, and building up an extension of a replacement squealer tip on the turbine blade in whole or in part.

Description:
TECHNICAL FIELD 
       [0001]    The present application and the resultant patent relate generally to gas turbine engines and more particularly relate to systems and methods for three-dimensional turbine airfoil squealer tip repair with improved internal cooling geometry for an extended component lifetime. 
       BACKGROUND OF THE INVENTION 
       [0002]    Cast turbine blades often include a structure known as a “squealer tip”. A squealer tip is a relatively small extension of the blade. The squealer tip may have a cross-sectional shape conforming to that of the blade and may be integral with or mounted on the radially outer end of the blade. After a period of time in service, the squealer tip may be eroded, oxidized, and/or corroded by impingement of the hot combustion gases. Because the turbine blade may be expensive to produce, repair or refurbishment of the damaged blade may be preferred if possible. The repair of a turbine blade squealer tip may be performed by grinding away the damaged material and then welding or otherwise attaching replacement material. Cooling the squealer tip also may extend the overall useful component lifetime. Providing cooling, however, has been difficult due to manufacturing constraints. 
         [0003]    There is thus a desire for improved systems and methods for turbine blade squealer tip repair and refurbishment. Moreover, such improved systems and methods also may provide internal squealer tip cooling passages so as to extend the overall component lifetime. 
       SUMMARY OF THE INVENTION 
       [0004]    The present application and the resulting patent provide a method of repairing a turbine blade. The method may include the steps of removing an existing squealer tip from the turbine blade in whole or in part, positioning the turbine blade in an additive manufacturing system, and building up an extension of a replacement squealer tip on the turbine blade in whole or in part. Building up an extension of a replacement squealer tip may include creating a cooling passage or a number of cooling passages through the extension. 
         [0005]    The present application and the resultant patent further provide a turbine blade for use in a gas turbine engine. The turbine blade may include an airfoil and a squealer tip built up on the airfoil. The squealer tip may include a cooling passage therein. The squealer tip may be made from a superalloy suitable for an additive manufacturing process. 
         [0006]    The present application and the resultant patent further provide a method of repairing a turbine blade. The method may include the steps of removing an existing squealer tip from the turbine blade in whole or in part, positioning the turbine blade in an additive manufacturing system, building up a superalloy extension of a replacement squealer tip on the turbine blade in whole or in part, and creating a cooling passage through the superalloy extension. 
         [0007]    These and other features and improvements of the present application and the resultant patent will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic diagram of a gas turbine engine showing a compressor, a combustor, a turbine, and a load. 
           [0009]      FIG. 2  is a perspective view of a turbine blade with cracks within a squealer tip. 
           [0010]      FIG. 3  is a perspective view of the turbine blade of  FIG. 2  with the squealer tip removed. 
           [0011]      FIG. 4  is a perspective view of a repaired turbine blade with an improved squealer tip as may be described herein. 
           [0012]      FIG. 5  is a partial sectional view of the squealer tip of  FIG. 4  with a cooling passage. 
           [0013]      FIG. 6  is a flow chart showing exemplary steps in repairing a squealer tip as may be described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring now to the drawings, in which like numerals refer to like elements throughout the several views,  FIG. 1  shows a schematic view of gas turbine engine  10  as may be used herein. The gas turbine engine  10  may include a compressor  15 . The compressor  15  compresses an incoming flow of air  20 . The compressor  15  delivers the compressed flow of air  20  to a combustor  25 . The combustor  25  mixes the compressed flow of air  20  with a pressurized flow of fuel  30  and ignites the mixture to create a flow of combustion gases  35 . Although only a single combustor  25  is shown, the gas turbine engine  10  may include any number of combustors  25 . The flow of combustion gases  35  is in turn delivered to a turbine  40 . The flow of combustion gases  35  drives the turbine  40  so as to produce mechanical work. The mechanical work produced in the turbine  40  drives the compressor  15  via a shaft  45  and an external load  50  such as an electrical generator and the like. 
         [0015]    The gas turbine engine  10  may use natural gas, various types of syngas, liquid fuels, and/or other types of fuels and blends thereof. The gas turbine engine  10  may be any one of a number of different gas turbine engines offered by General Electric Company of Schenectady, New York, including, but not limited to, those such as a 7 or a 9 series heavy duty gas turbine engine and the like. The gas turbine engine  10  may have different configurations and may use other types of components. Other types of gas turbine engines also may be used herein. Multiple gas turbine engines, other types of turbines, and other types of power generation equipment also may be used herein together. 
         [0016]      FIG. 2  is a perspective view of an example of a turbine blade  55 . In this example, the turbine blade  55  may be a stage one bucket although any type of blade may be used herein. Generally described, the turbine blade  55  includes an airfoil  60 . The airfoil  60  may extend from a leading edge  62  to a trailing edge  64  with a concave pressure side outer wall  66  and a convex suction side outer wall  68 . The turbine blade  55  also may include a downwardly extending shank  70  and an attachment in the form of a dovetail  75 . A platform  80  may extend transversely between the airfoil  60  and the shank  70  and the dovetail  75 . The radial end of the airfoil  60  may include a squealer tip  85 . The squealer tip  85  may be an extension of the outer sidewalls  66 ,  68 . The squealer tip  85  may define a recessed tip cap  90  therein. The turbine blade  55  and the squealer tip  85  described herein are for the purposes of example only. Many other designs and configurations may be known. 
         [0017]    As described above, the squealer tip  85  may be subjected to high temperatures and may rub against a seal structure such as a stationary shroud. As a result, cracks  95  may develop in the squealer tip  85  due to thermally induced stress and material loss due to oxidation and the like. In order to repair the turbine blade  55 , the squealer tip  85  may be machined down as is shown in  FIG. 3  so as to remove the cracks  85  or other types of worn out, damaged, or otherwise defective locations. The squealer tip material may be machined in a conventional fashion. 
         [0018]      FIGS. 4 and 5  show an improved turbine blade  100  as may be described herein. The turbine blade  100  may be the turbine blade  55  described above with the squealer tip  85  machined down and with an improved squealer tip  110  built thereon. The improved squealer tip  110  may include a squealer tip extension  120  built thereon so as to extend radially upward from the outer sidewalls  66 ,  68 . The squealer tip extension  120  may be built-up in any suitable size, shape, or configuration. 
         [0019]    The improved squealer tip  110  may have one or more cooling passages built into the squealer tip extension  120  or otherwise. The cooling passages  130  may have any suitable size, shape, or configuration. The cooling passages  130  may be in communication with a source of a cooling medium such as air extending through the airfoil  60  from the compressor  15  or elsewhere. The inside of the cooling passages  130  may have rough surfaces, such as dimples or other types of surface features so as to increase the overall heat transfer effect. An aluminide coating and the like also may be used within the cooling passages  130  to increase the oxygen resistance at elevated temperatures. Other components and other configurations may be used herein. 
         [0020]    Instead of conventionally welding or otherwise attaching a squealer tip extension to the airfoil  60 , in this example, the squealer tip extension  120  may be built up on the airfoil  60  in an additive manufacturing process, i.e., three dimensional printing. Specifically, the squealer tip extension  120  may be printed or built up via a direct metal laser sintering (DMLS) process and the like in any suitable size, shape, or configuration. DMLS is an additive manufacturing process that uses a laser to sinter a metallic powder material and binds the material together to create a solid structure. Selective laser sintering and other types of sintering and/or melting techniques or other types of additive manufacturing processes and the like also may be used herein to create the squealer tip  110  or other component. Moreover, the use of a DMLS process or other type of three-dimensional printing allows the creation of the cooling passages  130  or other type of complex internal geometry. The DMLS or other type of three-dimensional printing process allows the cooling passages  130  to be created therein with any desired geometry so as to provide improved cooling thereto. An electron beam (EB) welding process and the like also may be used herein. 
         [0021]    Because three dimensional printing is a welding process, materials with adequate weldability may be used. For example, the powdered material adjacent to the original airfoil  60  may be a superalloy powder in the easy to weld range (Al≦−0.5 Ti+3 according to the Chart of Strain Age Cracking Susceptibility of Superalloy) for “buttering” or the initial build-up. Suitable materials may include Haynes 230, Haynes 282, and similar materials. A hard to weld superalloy powder (Al≧−0.5 Ti+3) then may be used to build up the squealer tip extension  120 . Suitable materials may include Haynes 214, GTD111, Rene 108, and similar materials. The superalloy materials in general may have high oxidation resistance. Other types of materials also may be used herein. 
         [0022]      FIG. 6  shows a flowchart of exemplary steps in carrying out the methods described herein in whole or in part. At step  140 , the existing squealer tip  85  may be machined down on the airfoil  60  as is shown in  FIG. 3 . At step  150 , a build plate in a DMLS machine or other device may be modified to accept the airfoil  60  of the turbine blade  55 . At step  160 , the DMLS machine may print or buildup the squealer tip extension  120  of the improved squealer tip  110  directly on the airfoil  60 . This printing or buildup step also may include the creation of the cooling passages  130  or other types of internal geometries therein. The improved turbine blade  100  may now be ready for use or other types of processing. The method steps described herein are not exclusive. Other or different method steps may be used in any desired order to create the squealer tip  110  or other component herein. 
         [0023]    The systems and methods described herein thus provide for the fast and efficient repair of turbine blades and squealer tips with the use of advanced superalloy materials with improved oxidation resistance. Moreover, the improved turbine blade  100  may include the cooling passage  130  within the squealer tip  110  for improved cooling and an enhanced overall component lifetime. Such cooling passages  130  generally were not possible given existing manufacturing constraints. Moreover, the systems and methods described herein may be used to upgrade existing turbine blades with such cooling features. 
         [0024]    It should be apparent that the foregoing relates only to certain embodiments of the present application and the resultant patent. Numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.