Patent Publication Number: US-9885240-B2

Title: Repair article of a gas turbine engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 12/107,849, filed Apr. 23, 2008, now U.S. Pat. No. 8,539,659. 
    
    
     BACKGROUND OF THE INVENTION 
     This disclosure relates to a repair method and a repaired article. More particularly, the disclosure relates to a repair method for providing a repaired article having properties that are substantially equal to or better than properties of the original article. 
     In many instances, there is a desire to repair an article rather than replace the article with a new article. For instance, airfoils used as blades or vanes in a gas turbine engine are relatively expensive. Due to the expense, repairing the airfoils may be more cost efficient than replacing the airfoils with new airfoils. 
     The erosion, wear, or corrosion may gradually change the original design geometry of the airfoil and degrade the aerodynamic efficiency of the airfoil. To repair the airfoil, the eroded, worn, or corroded section may be removed and replaced with a repair section to restore the aerodynamic efficiency. The repair section may be welded onto the airfoil and then machined to attain the original design geometry. Although effective, one potential drawback is that the heat from welding may negatively influence the mechanical properties of the repair section and airfoil. For instance, heat-affected regions of the repair section and airfoil may include undesirable microstructural phases that contribute to lower than desired mechanical properties. 
     Therefore, there is a continuing need for new repair processes that provide repaired articles having properties that are substantially equal to or better than the original properties of the article. 
     SUMMARY OF THE INVENTION 
     The disclosed repair method and repaired article are for providing the repaired article with physical properties that are substantially equal to or better than the physical properties of the original article. 
     In one example, a method of repairing the article includes at least partially removing an undesirable section of the article, attaching a repair section to the article at a location from which the undesirable section has been removed, and mechanically working the repair section to thereby achieve a reduction in a cross-sectional area of the repair section. 
     In another aspect, a method of repairing the article includes at least partially removing an undesirable section of the article, welding a repair section to the article at a location from which the undesirable section has been removed, and mechanically cold working the repair section to thereby achieve a 10%-50% reduction in a cross-sectional area of the repair section. 
     The disclosed examples may be used to repair an article. For example, a repaired article may include a body extending between a first side and a second side, where the body includes a repair section having an associated thickness between the first side and the second side. The repair section includes regions of plastic deformation distributed entirely through the thickness. For example, the plastic deformation contributes to restoring fatigue strength. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
         FIG. 1  illustrates an example article for repair. 
         FIG. 2  illustrates an example method for repairing the article. 
         FIG. 3  illustrates an example implementation of a removal step of a repair method. 
         FIG. 4  illustrates an example implementation of an attaching step and a mechanical working step of a repair method. 
         FIG. 5  illustrates an example of the article after being repaired. 
         FIG. 6  illustrates an example mechanical working step that includes roll planishing. 
         FIG. 7  illustrates an example mechanical working step that includes hammer planishing. 
         FIG. 8  schematically illustrates an image of a repair section having regions of plastic deformation. 
         FIG. 9  illustrates an example microstructure that is substantially free of a delta phase. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates selected portions of an example article  10  that is to be repaired. In this example, the article  10  is illustrated as a rotatable airfoil blade that may be used within a gas turbine engine. However, it is to be understood that the article  10  may alternatively be a relatively static airfoil vane. For example, airfoil blades and vanes are commonly used in a compressor and turbine sections of the engine. Alternatively, the article  10  may be any other type of article and is not limited to the disclosed examples. 
     The article  10  may be fabricated from any suitable type of metallic alloy, such as a nickel-based alloy. The nickel-based alloy may include about 50-55 wt % nickel, about 17-21 wt % chromium, about 0.65-1.15 wt % titanium, about 0.2-0.8 wt % aluminum, about 4.75-5.5 wt % columbium, about 0-1 wt % cobalt, about 2.8-3.3 wt % molybdenum, and a balance of iron. In some examples, the nickel-based alloy includes only the above elements. In other examples, the nickel-based alloy may include impurities that do not affect the properties of the alloy or impurities that are unmeasured or undetectable in the alloy. 
     The example article  10  includes an airfoil  12  having a leading edge  14 , a trailing edge  16 , a first side  18 , and a second side  20 . For example, the first side  18  and the second side  20  may correspond to a pressure side and a suction side when used within a gas turbine engine. The airfoil  12  also extends between a tip  22  and a base platform  24  that is used to mount the article  10  within an engine. As can be appreciated, the design of the illustrated blade may vary, and the illustrated design is not intended to be a limitation on this disclosure. 
     The article  10  has been subjected to a period of use within a gas turbine engine, for example. As a result, the article  10  has developed an undesirable section  34 . For example, the undesirable section  34  may be an eroded section, worn section, corroded section, or other type of section exhibiting blemishes from use of the article  10 . In examples where the article  10  is not an engine component, there may be other causes of the undesirable section  34  that are related to the particular use of the article  10 . 
     The undesirable section  34  in this example is located at the leading edge  14  of the article  10 . However, in other examples, the undesirable section  34  may be located at the trailing edge  16 , tip  22 , base platform  24 , or other portions of the article  10 . 
       FIG. 2  illustrates an example method  40  for repairing the undesirable section  34  of the article  10 . For instance, it may be desirable to repair the undesirable section  34  to restore an aerodynamic efficiency of the article  10 . As can be appreciated, there may also be other reasons for the desirability of repairing the article  10 . 
     The example method  40  generally includes a removal step  42 , an attaching step  44 , and a mechanical working step  46 . The disclosed method  40  may be used alone or in combination with additional steps to repair the article  10 , such as precipitation heat treating, planishing, or other mechanical working steps. In the removal step  42 , the undesirable section  34  is at least partially removed from the article  10 . For instance, the undesirable section  34  may be machined to either completely or partially remove the undesirable section  34 . The attaching step  44  includes attaching a repair section to the article  10 . Finally, the mechanical working step  46  includes mechanically working the repair section to reduce a cross-sectional area of the repair section. 
       FIGS. 3-5  illustrate an example application of the method  40  to repair the article  10 . For instance,  FIG. 3  illustrates the article  10  after the undesirable section  34  has been removed. The undesirable section  34  may be removed using any suitable technique, such as cutting, grinding, blasting, and chemical etching. Upon removal, there is a void  48  in the location from which the undesirable section  34  was removed. 
     Referring to  FIG. 4 , a repair section  50  is then attached to the article  10  in the location of the void  48 . The repair section  50  may nominally have the same composition as the alloy of the article  10 . In one example, the repair section includes about 50-55 wt % nickel, about 17-21 wt % chromium, about 0.65-1.15 wt % titanium, about 0.2-0.8 wt % aluminum, about 4.75-5.5 wt % columbium, about 0-1 wt % cobalt, about 2.8-3.3 wt % molybdenum, and a balance of iron. 
     The repair section  50  may be attached to the article  10  using any suitable technique. For example, the repair section  50  may be attached using a welding technique. In this regard, the repair section  50  may also be considered as a welded repair section. In some examples, the welding technique is gas tungsten arc welding, laser powder weld deposition, plasma arc welding, micro-metal inert gas welding, or other type of welding technique. Additionally, the repair section  50  may be formed in any suitable manner. For example, the repair section  50  may be pre-fabricated and then attached to the article  10 , or the repair section  50  may be formed by depositing a powder, wire, or other welding material on the article  10 . 
     As can be appreciated, the repair section  50  in this example is larger in size than the original geometry of the article  10 . The original geometry is represented by dashed line  52 . For instance, the repair section  50  initially includes an associated cross-sectional area  54  extending between the first side  18  and the second side  20 . The cross-sectional area  54  is larger than cross-sectional area  56  of the original geometry of the article  10 . In some examples, the repair section  50  may be machined down to the cross-sectional area  54  after attaching the repair section  50 , in preparation for the mechanical working step  46 . 
     The article  10  may then be placed into a die  60  to conduct the mechanical working step  46 . In this example, the mechanical working step includes forging the article  10  at a relatively cold temperature (e.g., room temperature); however, it is to be understood that the mechanical working step  46  may include other types of mechanical working operations, such as planishing or other metalworking operations. 
     The die  60  includes a pair of die halves  62  that define a cavity  64  that is contoured to the shape of the original article  10 . The cavity  64  may enclose the entire article  10  (airfoil  12  and base platform  24 ), only the airfoil  12 , only the repair section  50 , or the repair section with some overlap of the airfoil  12  (e.g., to facilitate fixturing). The die halves  62  compress and plastically deform the repair section  50  to reduce the cross-sectional area  54  down to no less than the cross-sectional area  56  of the original geometry of the article  10 . The die halves  62  are then opened, and the article  10  is removed. Any flash material from the repair section  50  may then be trimmed, leaving the article  10  and repair section  50  having a geometry that is substantially equal to the original geometry as illustrated in  FIG. 5 . 
     As an alternative to forging, or in addition to forging, the mechanical working step  46  may include planishing. As illustrated in  FIG. 6 , the planishing may be roll planishing where the repair section  50  is rolled between rollers R to reduce the cross-sectional area  54  down to no less than the cross-sectional area  56  of the original geometry of the article  10 . As illustrated in  FIG. 7 , the planishing may be hammer planishing where the repair section  50  is hammered between a reciprocating hammer  57   a  and a planish stake  57   b  to reduce the cross-sectional area  54  down to no less than the cross-sectional area  56  of the original geometry of the article  10 . The planishing may be conducted manually or using an automated or semi-automated planishing machine. 
     Mechanically working the repair section  50  causes plastic deformation entirely through the cross-sectional area  56  of the repair section  50 . For instance, the mechanical working causes dislocations within the microstructure of the alloy used to form the article  10 . The dislocations contribute to improving the physical properties of the repair section  50 , such as increasing ultimate tensile strength, fatigue strength, and hardness. For example, the properties of the repair section  50  are substantially equal to or better than the properties of the original article  10  because of the dislocations. 
     The degree of mechanical working that is used may also be varied, depending upon the desired properties of the repair section  50 . For instance, a greater degree of mechanical working may be used to achieve a relatively greater degree of fatigue strength, or a relatively lower amount of mechanical working may be used to achieve a desired lower fatigue strength. In some examples, the mechanical working reduces the cross-sectional area  54  to the cross-sectional area  56  by 10%-50%. In a further example, the reduction is about 30%. 
     The plastic deformation of the repair section  50  is distributed entirely through the cross-sectional area  56  of the repair section  50 . For instance, the distribution and degree of plastic deformation may be determined using scanning electron microscope electron back-scatter imaging. Such a technique is generally known in the art and need not be detailed in this disclosure. 
       FIG. 8  illustrates an example schematic image  68  using scanning electron microscope electron back-scatter diffraction patterns (Orientation Imaging Microscopy). In this example, the image  68  is a cross-section of the repair section  50  extending between the first side  18  and the second side  20  of the article  10 . Plastic deformation is represented by regions  70  (shown as specks). As can be appreciated from the image  68 , the regions  70  are distributed entirely through the cross-section between the sides  18  and  20 . Plastic deformation distributed entirely through the thickness provides the entire repair section  50  with improved physical properties. 
     Referring to  FIG. 9 , the method  40  may also be used to achieve a desirable microstructure  80 . For example, the microstructure  80  includes regions of Laves phase  82  distributed within a matrix  84  of the alloy composition. In this example, the microstructure  80  is substantially free from, and in some examples entirely free of, orthorhombic delta phase regions of Ni 3 Cb, which is a needle-shaped phase that is known to degrade physical properties (e.g., fatigue strength). For instance, the disclosed method  40  may be used to avoid a solution heat treating step that typically results in the formation of the delta phase. In some repair processes, an article having a repair section may be heat treated at 1750° F. or higher to homogenously solutionize elements within the alloy, and then be aged at approximately 1150-1350° F. (621-732° C.) to precipitation strengthen the alloy. The heat treating typically contributes to the formation of the delta phase. However, using the disclosed method  40 , the solution heat treating step can be eliminated because the plastic deformation and dislocations from the mechanical working contribute to improving fatigue strength and thereby lessen the need for heat treating. Therefore, at least the heat treating step may be eliminated, although it still may be desirable to utilize the aging process to achieve a degree of precipitation strengthening. 
     The method  40  may also be used in combination with additional steps to further restore the original geometry and/or performance of the article  10 . For instance, various mechanical finishing steps may be used to restore the article  10 . The article  10  may be peened, coated, vibratory finished, or otherwise processed. 
     Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.