Abstract:
A modification process and modified article are disclosed. The modification process includes locating an area in an article, removing the area by machining to form a machined region, inserting a modification material into the machined region, securing the modification material to the article, machining the modification material flush with a geometry of the article, and applying a coating over at least a portion of the article. Another modification process includes locating an area under a suction side leading edge tip shroud fillet of an airfoil, removing the area by machining to form a hole, inserting a modification material having improved material properties as compared to an original base material into the hole, securing the modification material in place, machining the modification material and the airfoil to form a new fillet contour, and applying a coating over at least a portion of the airfoil. Also disclosed is the modified article.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to modification processes and modified articles. More specifically, the present invention is directed to modification processes for an increased stress area in a turbine component and modified turbine components. 
       BACKGROUND OF THE INVENTION 
       [0002]    Turbine components such as airfoils experience extreme stresses during operation. Some of those stresses include increased pressure and temperature which may be concentrated on specific areas of the turbine component. One specific area is under the suction side leading edge tip shroud fillet of an airfoil, where increased stress may lead to a creep rupture or cracking 
         [0003]    Stresses of this type can lead to early removal, discard and replacement of the expensive airfoil. This reduces the expected operational lifetime of the airfoil, increasing maintenance costs and operational costs of a system. 
         [0004]    One modification method includes weld build ups over an increased stress area, followed by machining The weld build ups reduce material properties and increase the risk of stressing additional areas at the weld interface with the blade and in the weld metal. Additionally, current modification processes do not sufficiently increase material properties of the increased stress areas of the airfoil to provide a usable modified article. 
         [0005]    A modification process to remove increased stress areas and increase material properties, as well as a modified article that do not suffer from one or more of the above drawbacks would be desirable in the art. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    In an exemplary embodiment, a modification process includes locating an area in an article, removing the area by machining to form a machined region, inserting a modification material into the machined region, securing the modification material to the article, machining the modification material flush with a geometry of the article, and applying a coating over at least a portion of the article. 
         [0007]    In another exemplary embodiment, a modification process includes locating an area under a suction side leading edge tip shroud fillet of an airfoil, removing the area by machining to form a hole in the airfoil, inserting a modification material into the hole, the modification material having improved material properties as compared to an original base material, securing the modification material in place, machining the modification material and the airfoil to form a new contour of the fillet, and applying a coating over at least a portion of the airfoil. 
         [0008]    In another exemplary embodiment, a modified article includes a turbine component, and a modification material secured within the turbine component at a location previous occupied by an original base material subject to increased stress. The modification material has improved material properties as compared to the original base material, the improved material properties increasing stress tolerance of the turbine component. 
         [0009]    Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a flow chart of a modification process according to an embodiment of the disclosure. 
           [0011]      FIG. 2  is a perspective side view of an increased stress area of a turbine blade according to an embodiment of the disclosure. 
           [0012]      FIG. 3  is a perspective side view of a machined region of a turbine blade according to an embodiment of the disclosure. 
           [0013]      FIG. 4  is a perspective view of a modification material in a machined region of a turbine blade according to an embodiment of the disclosure. 
           [0014]      FIG. 5  is a perspective view of a modified turbine blade according to an embodiment of the disclosure. 
       
    
    
       [0015]    Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Provided are an exemplary modification process and modified article. Embodiments of the present disclosure, in comparison to processes and articles not using one or more of the features disclosed herein, increase operational life of a turbine component, increase efficiency of turbine component repair, reduce scrappage of turbine components, decrease stress during modification, improve material properties of a modified article, increase stress resistance of turbine components, reduce or eliminate creep rupture stress, or a combination thereof 
         [0017]    Referring to  FIG. 1-FIG .  5 , in one embodiment, a modification process  100  removes an area  105  of an article  101 , and replaces the area  105  with a modification material  124  to increase an operational life of the article  101 . The article  101  is any suitable article such as, but not limited to, a turbine component. The modification process  100  includes removing a coating  108  (step  110 ) from the article  101 , locating (step  120 ) the area  105  in the article  101 , removing the area  105  (step  130 ) by machining while forming a machined region  115 , inserting (step  140 ) a modification material  124  into the machined region  115 , securing (step  150 ) the modification material  124  within the article  101 , machining (step  160 ) the modification material  124  to be flush with an existing geometry of the article  101 , inspecting (step  170 ) a modified portion, and re-applying (step  180 ) the coating  108  over the modified portion. In another embodiment, the modification process  100  includes drilling (step  190 ) internal cooling holes. 
         [0018]    The article  101  may be any suitable article such as, but not limited to a turbine component, an airfoil, (such as a turbine airfoil identified as a General Electric Company 7FA or a S2B), a bucket  102 , a shroud  103 , a nozzle, a hot gas path component, or a combination thereof The area  105  may be any portion of the article  101  that is subject to various increased stresses including, but not limited to, stress-rupture, increased temperature, alternating stresses, fatigue, and/or pressure. In one embodiment, the area  105  includes a section of distressed material such as, a pit, a crack, erosion, or a combination thereof. In another embodiment, the distressed material may be formed from any one of a number of sources, the modification process  100  being directed to the removal of the distressed material (step  130 ) after location (step  120 ) of the area  105  through any suitable means of inspection. Suitable means of inspection include, but are not limited to visual inspection, magnetic particle inspection (for ferrous alloys), eddy current, acoustic emission, pulsed laser, infrared, ultrasonic, radiographic, fluorescent penetrant inspection (FPI), or a combination thereof. 
         [0019]    In one embodiment, the coating  108  is removed (step  110 ) from the base material  109  of the article  101  prior to locating (step  120 ) the area  105 . However, depending upon the inspection technique utilized, the area  105  may be located prior to removal of the coating  108 , so that the sequence of these steps may be interchangeable. The coating  108  is removed (step  110 ) by any suitable method capable of exposing the base material  109 . Suitable methods of removing (step  110 ) the coating  108  include, but are not limited to, water jet processes, chemical stripping, mechanical stripping, or a combination thereof. In one embodiment, the area  105  is located (step  120 ) without removing the coating  108  (step  110 ), after which removing the area  105  (step  130 ) by machining also removes the coating  108 , eliminating the need for a separate step. 
         [0020]    Removing the area  105  (step  130 ) by machining forms the machined region  115  having any suitable geometry, the size of the machined region  115  being dependent on the size of the area  105 . A suitable geometry of the machined region  115  includes, but is not limited to, extending partially through the article  101 , extending fully through the article  101 , a hole, a cylinder, a cone, an oval, a portion of a sphere, a channel, a recess, or a combination thereof. In one embodiment, removing the area  105  (step  130 ) includes conventional machining or non-conventional machining, such as, but not limited to, thermal energy machining, chemical energy machining, laser machining, electrical energy machining (i.e. electrical discharge machining (EDM)), or a combination thereof. When removing the area  105  (step  130 ), the machining method preferably also removes any distressed material surrounding the area  105 . In one embodiment, a plurality of the areas  105  are removed (step  130 ) by machining, forming a plurality of the machined regions  115 . 
         [0021]    Upon removing the area  105  (step  130 ) by machining, the modification material  124  is inserted (step  140 ) into the machined region  115  by any suitable method such as, but not limited to, laser deposition, layer by layer deposition, physical placement of the modification material  124  within the machined region  115 , or a combination thereof. The modification material  124  may have any suitable composition including, but not limited to, the same composition as a base material  109  of the article  101 , a composition substantially similar to the base material  109 , a composition having superior material properties as compared to the base material  109 , or a combination thereof. Superior material properties, as used herein, refers to an increased material strength, an increased ability to withstand stress, an increased ability to withstand strain, a decreased occurrence of distressed material formation, or a combination thereof. It is necessary to identify the material comprising the base material  109  in order to select the proper replacement material for the modification material  124 . 
         [0022]    For example, in one embodiment, the modification material  124  is a single crystal grain structure composition, characterized by a nominal weight percentage of about 7.5% cobalt, about 7.5% chromium, about 6.5% tantalum, about 6.2% aluminum, about 5.0% tungsten, about 3.0% rhenium, about 1.5% molybdenum, about 0.15% hafnium, about 0.05% carbon, about 0.004% boron, between about 0.002% and about 0.03% yttrium, and a balance of nickel. 
         [0023]    In another example, the modification material  124  is an equiaxed grain structure composition, characterized by a nominal weight percentage of between about 8.0% and about 8.7% Cr, between about 9% and about 10% Co, between about 5.25% and about 5.75% Al, up to about 0.9% Ti (for example, between about 0.6% and about 0.9%), between about 9.3% and about 9.7% W, up to about 0.6% Mo (for example, between about 0.4% and about 0.6%), between about 2.8% and about 3.3% Ta, between about 1.3% and about 1.7% Hf, up to about 0.1% C (for example, between about 0.07% and about 0.1%), up to about 0.02% Zr (for example, between about 0.005% and about 0.02%), up to about 0.02% B (for example, between about 0.01% and about 0.02%), up to about 0.2% Fe, up to about 0.12% Si, up to about 0.1% Mn, up to about 0.1% Cu, up to about 0.01% P, up to about 0.004% S, up to about 0.1% Nb, and a balance of nickel. 
         [0024]    Following insertion (step  140 ) of the modification material  124  into the machined region  115 , the modification material  124  is secured (step  150 ) within the article  101 . The securing (step  150 ) of the modification material  124  includes, but is not limited to, brazing, welding, friction welding, laser welding, or a combination thereof. In one embodiment, brazing includes positioning any suitable filler material in the machined region  115  between the modification material  124  and the article  101  and heating the article  101  and the modification material  124  to a temperature above the melting temperature of the filler material, but below the melting point of the base material  109 . In another embodiment, the filler material has a composition, by weight, of about 14% Cr, about 9% Co, about 4% Al, about 2.5% B, and a balance of nickel. In one embodiment, the filler material has a composition, by weight, between about 13% and about 15% Cr, between about 9% and about 11% Co, between about 3.2% and about 3.8% Al, between about 2.2% and about 2.8% Ta, between about 2.5% and about 3.0% B, up to about 0.10 Y (with or without being present), incidental impurities, and a balance Ni. In another embodiment, the brazing is performed in a vacuum and includes heating at between about 2125° F. and about 2175° F. for between about 15 minutes and about 30 minutes, then diffusing at between about 1975° F. and about 2025° F. for between about 2 hours and about 4 hours. These materials are exemplary. It will be understood that the selection of the filler material will be dependent upon the base material  109 , which in turn will dictate brazing parameters for the substrate material/base material combination. 
         [0025]    In one embodiment, the modification material  124  is a plug  125  having a geometry corresponding to the machined region  115 . For example, in another embodiment, the plug  125  has a conical geometry corresponding to conical geometry of the machined region  115 . The machined region  115  having the conical geometry provides superior mechanical retention of the plug  125  having the corresponding geometry. In one embodiment, the plug  125  is friction welded within the machined region  115 . The friction welding includes rotating the plug  125  with respect to the article  101  to generate a heat that secures the plug  125  (step  150 ) within the article  101 . During friction welding, the machined region  115  having a conical geometry reduces a heat input as compared to the cylindrical geometry. 
         [0026]    After the securing (step  150 ) of the modification material  124 , the machining of the modification material  124  (step  160 ) forms a surface flush with an existing geometry of the article  101  or re-contours the modification material  124  and a portion of the article  101 . For the article  101 , this restores aerodynamics to the modified component. The article  101  is then inspected (step  170 ) and the coating  108  is then re-applied (step  180 ) over the base material  109 . 
         [0027]    The coating  108  is re-applied (step  180 ) using any suitable coating method including, but not limited to, vapor deposition, slurry deposition, or any thermal spray process including high velocity oxygen fuel spraying (HVOF), high velocity air fuel spraying (HVAF), vacuum plasma spray (VPS), air plasma spray (APS), ion plasma deposition (IPD), electron-beam physical vapor deposition (EBPVD), cold spray, or a combination thereof. The coating  108  is any suitable material, such as but not limited to MCrAlX, NiAl, PtAl, PtNiAl, or a combination thereof. MCrAlX is an alloy having M selected from one or a combination of iron, nickel, cobalt, and combinations thereof; and Cr is chromium, Al is aluminum, and X is an element selected from the group of solid solution strengtheners and gamma prime formers consisting of Y, Tc, Ta, Re, Mo, and W and grain boundary strengtheners consisting of B, C, Hf, Zr, and combinations thereof. 
         [0028]    In one embodiment, removing the areas  105  (step  130 ) by machining exposes the internal cooling holes extending within the article  101 . In another embodiment, the inserting (step  140 ) and the securing (step  150 ) of the modification material  124  within the machined region  115  may cover and/or close off the internal cooling holes. In a further embodiment, the internal cooling holes are restored by drilling (step  190 ) through the modification material  124  permitting cooling air to flow through the internal cooling holes that were covered and/or closed off by the securing of the plug  125  (step  150 ), and restoring a cooling airflow to the modified portion of the article  101 . The drilling (step  190 ) includes, but is not limited to, a shaped-tube electrochemical machining (STEM), an electron discharge machining (EDM), or a combination thereof. The drilling (step  190 ) is done either before or after the coating  108  is re-applied. In one embodiment, the article  101  does not include the internal cooling holes and the drilling (step  190 ) is not performed. 
         [0029]    In one embodiment, the area  105  is an increased stress area of the article  101 . The increased stress area is exposed to stresses such as, but not limited to, increased temperatures, increased pressures, damaging airborne particles, or a combination thereof. For example, in one embodiment, the area  105  is located in a fillet  106  between the bucket  102  and the shroud  103  on a suction side  108  of the airfoil. The fillet  106  attaches the shroud  103  to the bucket  102 , and includes weld material or heat affected zone (HAZ) material which may experience further increased damage as compared to the airfoil since this material may have different properties. In another embodiment, when the area  105  is located in the fillet  106 , the machining of the modification material  124  (step  160 ) includes a machining of the fillet  106 , which re-contours the fillet  106  and forms a flush surface between the fillet  106  and the modification material  124 . In a further embodiment, the re-contouring of the fillet  106  may increase the radius of the fillet  106 . The increased radius of the fillet  106  may improve a stress resistance of the article  101 . Stress resistance, as used herein, refers to an increased ability to withstand stress without forming increased stress areas. 
         [0030]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.