Abstract:
Methods and apparatus of fabricating gas turbine engine components are provided. The method includes positioning a non-consumable shield adjacent to an edge of the component such that a gap is defined between the shield and the component, wherein the shield and gap form a fluid flow restriction adjacent to the edge, and inducing an electrical current from an anode to the component through an electrolyte bath such that a coating is applied to the component.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to turbine engines, and more specifically to environmental coatings used with turbine engine components.  
         [0002]     At least some known gas turbine engines include a forward fan, a core engine, and a power turbine. The core engine includes at least one compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. The combustion gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work, such as powering an aircraft. A turbine section may include a stationary turbine nozzle positioned at the outlet of the combustor for channeling combustion gases into a turbine rotor disposed downstream thereof.  
         [0003]     The turbine nozzle may include a plurality of circumferentially spaced apart vanes. The vanes are impinged by the hot combustion gases exiting the combustor and are at least partially coated to facilitate protecting the vanes from the environment and to facilitate reducing wear. Specifically, in at least same engines, a platinum aluminide coating is be applied to turbine components, including the vanes to facilitate environmentally protecting the components. The application of platinum aluminide coatings is generally a three-step process that may include an electroplating process, a diffusion heat treatment, and an aluminiding process. During electroplating, platinum is plated over the surface of the component to be coated. Such that an electroplate coat of substantially uniform thickness is applied across the entire surface of the component. However, a magnetic field generated by current flow between the component to be coated and an anode used in coating may be non-uniformly distributed across the component, and more specifically such flux lines may be more dense adjacent sharp edges on the part, such as adjacent the trailing edge of the nozzle vane. As a result, a thicker coating of plating may be applied to such edges relative to the convex and concave surfaces of the airfoil portion of the vane. Over time, the uneven distribution of coatings may cause cracking: At least one known method of controlling the electroplate thickness adjacent the trailing edge requires that a disposable, metallic “robber” be positioned adjacent to the trailing edge to thieve current from the edge during the coating application. However, within such methods the effectiveness of the robber degrades over time and it may require frequent replacement.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0004]     In one embodiment, a method of fabricating a gas turbine engine component are provided. The method includes positioning a non-consumable shield adjacent to an edge of the component such that a gap is defined between the shield and the component, wherein the shield and gap form a fluid flow restriction adjacent to the edge, and inducing an electrical current from an anode to the component through an electrolyte bath such that a coating is applied to the component.  
         [0005]     In another embodiment, an electroplating apparatus is provided. The electroplating apparatus includes an electroplating bath that includes an electrolytic solution, a power source, an anode coupled to the power source, a component coupled to the power source and immersed within the electrolytic solution wherein the component includes a plating surface bordered by an edge, and a non-consumable shield positioned adjacent to the component edge such that a gap is defined between the edge and the shield and wherein the shield and the gap form a fluid flow restriction adjacent to the edge.  
         [0006]     In yet another embodiment, an electroplating apparatus is provided. The electroplating apparatus includes an electroplating bath including an electrolytic solution comprising platinum, a power source, an anode coupled to the power source, a component to be electroplated coupled to the power source and immersed within the electrolytic solution wherein the component includes a plating surface and an edge, and a non-consumable shield positioned adjacent to the edge such that a gap is defined between the edge and the shield and wherein the shield and the gap form a fluid flow restriction adjacent to the edge. The shield is configured to displace an electric field away from the edge to facilitate reducing an amount of electroplating deposited on the edge. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a longitudinal cross-sectional view of an exemplary high bypass ratio turbofan engine;  
         [0008]      FIG. 2  is a perspective view of an exemplary first stage, high pressure turbine nozzle segment that may be used with the gas turbine engine (shown in  FIG. 1 );  
         [0009]      FIG. 3  is a perspective view of an exemplary electroplating process for applying an electroplate coating to the vanes shown in  FIG. 2 .  
         [0010]      FIG. 4  is a cross-sectional view of high pressure turbine nozzle vane  118  that may be used in the electroplating process shown in  FIG. 3 ; and  
         [0011]      FIG. 5  is a graph of electroplate coating thickness readings taken at each of the plurality of test locations shown in  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]     As used herein, the term “component” may include any component configured to be coupled with a gas turbine engine that may be coated with a metallic film coating, for example a high pressure turbine nozzle vane. A high pressure turbine nozzle vane is intended as exemplary only, and thus is not intended to limit in any way the definition and/or meaning of the term “component”. Furthermore, although the invention is described herein in association with a gas turbine engine, and more specifically for use with a high pressure turbine nozzle vane for a gas turbine engine, it should be understood that the present invention is applicable to other gas turbine engine stationary components and rotatable components. Accordingly, practice of the present invention is not limited to high pressure turbine nozzle vanes for a gas turbine engine. In addition, although the invention is described herein in association with a electrolytic bath process, it should be understood that the present invention may be applicable to any electroplating process, for example, brush electroplating. Accordingly, practice of the present invention is not limited to an electroplating process using an electrolytic bath.  
         [0013]      FIG. 1  is a longitudinal cross-sectional view of an exemplary high bypass ratio turbofan engine  10 . Engine  10  includes, in serial axial flow communication about a longitudinal centerline axis  12 , a fan  14 , a booster  16 , a high pressure compressor  18 , a combustor  20 , a high pressure turbine  22 , and a low pressure turbine  24 . High pressure turbine  22  is drivingly connected to high pressure compressor  18  with a first rotor shaft  26 , and low pressure turbine  24  is drivingly connected to booster  16  and fan  14  with a second rotor shaft  28 .  
         [0014]     During operation of engine  10 , ambient air passes through fan  14 , booster  16 , and compressor  18 , the pressurized air stream enters combustor  20  where it is mixed with fuel and burned to provide a high energy stream of hot combustion gases. The high-energy gas stream passes through high-pressure turbine  22  to drive first rotor shaft  26 . The gas stream passes through low-pressure turbine  24  to drive second rotor shaft  28 , fan  14 , and booster  16 . Spent combustion gases exit out of engine  10  through an exhaust duct (not shown).  
         [0015]     It should be noted that although the present description is given in terms of a turbofan aircraft engine, embodiments of the present invention may be applicable to any gas turbine engine power plant such as that used for marine and industrial applications. The description of the engine shown in  FIG. 1  is only illustrative of the type of engine to which some embodiments of the present invention is applicable.  
         [0016]      FIG. 2  is a perspective view of an exemplary first stage, high pressure turbine nozzle segment  114  that may be used with the gas turbine engine  10  (shown in  FIG. 1 ). High pressure turbine nozzle segment  114  may be positioned axially between combustor  20  and high pressure turbine  22  such that a row of first stage turbine rotor blades (not shown) is positioned downstream from high pressure turbine nozzle segment  114 . A plurality of high pressure turbine nozzles  114  may be circumferentially spaced about axis  12  to form a high pressure turbine nozzle (not shown). High pressure turbine nozzle segment  114  includes at least one nozzle vane  118  coupled at opposite radial ends to a respective radially inner band  120  and a respective radially outer band  122 . High pressure turbine nozzle segment  114  are typically formed in arcuate segments having two or more vanes  118  per segment  114 . Vanes  118  may be cooled during operation against a flow of hot combustion gases  116  using a flow of cooling air  124  that may be channeled from, for example, a discharge of compressor  18  to individual vanes  118  through outer band  122 .  
         [0017]     Each vane  118  includes a generally concave pressure sidewall  126 , and a circumferentially opposite generally convex, suction sidewall  128 . Sidewalls  126  and  128  may extend longitudinally in span along a radial axis of the nozzle between bands  120  and  122  wherein a root  130  couples to inner band  120  and a tip  132  couples to outer band  122 . Sidewalks  126  and  128  extend chorale or axially between a leading edge  134  and an opposite trailing edge  136 .  
         [0018]      FIG. 3  is a perspective view of an exemplary electroplating process  200  for applying an electroplate coating to vanes  118  (shown in  FIG. 2 ). In the exemplary embodiment, vane  118  may energized to a predetermined negative voltage with respect to a grid  202  such that when an electrolyte solution containing metal ions, for example, platinum covers a surface of vane  118 , for example, sidewall  126 , the metal ions in the electrolyte solution may be preferentially attracted to and bonded to sidewall  126  to form an electroplate coating  204 . In the exemplary embodiment, a non-conducting, non-consumable shield  206  is positioned adjacent trailing edge  136  such that a longitudinal axis  208  of shield  206  is substantially parallel to trailing edge  136  and separated by a gap  210  having a predetermined distance  212 . In the exemplary embodiment, distance  212  is approximately thirty mils. In an alternative embodiment, distance  212  is a distance greater than or less then thirty mils. In the exemplary embodiment, shield  206  is fabricated from a non-conducting material, for example, plastic and has an outside diameter  218 , for example, three-quarters inches, that is substantially greater than the thickness  220  of vane  118  at trailing edge  136 . The relatively larger diameter of shield  206  with respect to the thickness of trailing edge  136  substantially blunts the geometry of trailing edge  136  and facilitates blocking at least a portion of the electrical current through trailing edge  136 . Additionally, the close clearance of distance  212  to trailing edge  136  facilitates reducing a flow of electrolyte solution proximate trailing edge  136 . Shield  206  may be formed to follow the contour of an irregularly shaped or curved edge while maintaining gap distance  212 . Additionally, shield  206  may include an irregular cross-section, for example, shield  206  may be a hollow or solid and may include a groove or slot configured to be aligned with edge  136  for optimizing the flow restrictive gap distance  212  and/or the electrical characteristics of the electric field proximate gap distance  212 .  
         [0019]      FIG. 4  is a cross-sectional view of high pressure turbine nozzle vane  118  that may be used in electroplating process  200  (shown in  FIG. 3 ). Vane  118  includes concave pressure sidewall  126  and convex suction sidewall  128  that each extend axially between leading edge  134  and trailing edge  136 . A plurality of thickness test locations are located at predetermined locations about a perimeter of vane  118  and are labeled  401 - 410 .  
         [0020]      FIG. 5  is a graph  500  of electroplate coating thickness readings taken at each of the plurality of test locations  401 - 410  (shown in  FIG. 4 ). Graph  500  includes an x-axis  502  whose units correlate with each respective test location,  401 - 410  (shown in  FIG. 4 ). For example, electroplate coating thickness reading  401  is taken proximate leading edge  134 , electroplate coating thickness reading  406  is taken proximate trailing edge  136 , and electroplate coating thickness readings  404  and  409  are taken proximate convex side  128  and proximate concave side  126  respectively. A y-axis  504  may be graduated in units of mils indicative of a thickness of a plating coating corresponding to the respective location,  401 - 410 .  
         [0021]     In the exemplary embodiment, a trace  506  joins points on graph  500  corresponding to an exemplary electroplate process for coating nozzle vane  118  with a metallic film coating. Trace  506  illustrates readings taken using the electroplate process wherein shield  206  is not utilized to form a flow restrictive gap distance  212  adjacent edge  136 . Trace  506  illustrates a metallic film coating thickness at location  406  that is approximately 100% greater than the metallic film coating thickness at locations  401 - 405  and  407 - 410 .  
         [0022]     A trace  508  illustrates readings taken at locations  401 - 410  after using the electroplate process wherein shield  206  is utilized to form a flow restrictive gap distance  212  adjacent edge  136  and to displace an electric field adjacent edge  136 . Shield  206  facilitates plating a uniform metallic film coating thickness at locations  401 - 410 . Trace  506  illustrates a metallic film coating thickness at location  406  that is approximately only  25 % greater than the metallic film coating thickness at locations  401 - 405  and  407 - 410 . Using shield  206  results in a more uniform metallic film coating thickness around the perimeter of vane  118 .  
         [0023]     A thickness ration may be defined as a ratio of a maximum thickness from locations around the perimeter of the airfoil (t max ) to a minimum thickness (t min ),  
         Thickness  Ratio     =         t   MAX       t   MIN       .         
 
         [0024]     Trace  508  exhibits a thickness ratio of approximately 1.94, using the above formula, while trace  506  exhibits a thickness ratio of approximately 3.03, which represents a 40% improvement in uniformity of the metallic film coating thickness about the perimeter of vane  118 .  
         [0025]     The above-described methods and apparatus are cost-effective and highly reliable for providing a substantially uniform metallic film coating thickness on gas turbine engine components, such as a high pressure turbine first stage nozzle. Specifically, the shield positioned adjacent the edge of the nozzle vane to be coated, defines an electrolyte flow restrictive gap and displaces a portion of the electric field adjacent the edge. Restricting the electrolyte flow adjacent the edge permits the electrolyte to be depleted in the gap and reduces the metallic ion concentration available for plating the edge. Displacing a portion of the electric field adjacent the edge facilitates reducing the electroplating motive force and thus, the rate of plating on the edge. The methods and apparatus facilitate fabrication of machines, and in particular gas turbine engines, in a cost-effective and reliable manner.  
         [0026]     Exemplary embodiments of electroplating methods and apparatus components are described above in detail. The components are not limited to the specific embodiments described herein, but rather, components of each apparatus may be utilized independently and separately from other components described herein. Each electroplating method and apparatus component can also be used in combination with other electroplating methods and apparatus components.  
         [0027]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.