Abstract:
A system and method for repairing turbine components. The system includes means for obtaining a rapidly solidified material having a means of forming a rapidly solidified repair material and a means for melting the rapidly solidified repair material at a repair site located in a region of the turbine component. The means for obtaining the rapidly solidified material include melt spinning, planar flow, and melt extraction systems. Means for melting the rapidly solidified repair material include a welding torch, an electron beam, a laser beam, a welding torch, a TIG welder, and a plasma torch. A method for using the repair system includes the steps of providing a molten repair material, contacting the molten repair material with a rotating drum, thereby rapidly solidifying the repair material, melting the rapidly solidified repair material and portion of the turbine component at a repair site, and resolidifying the molten repair material and turbine component portion, thereby repairing a defect located at the repair site.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of application Ser. No. 09/138,729, filed on Aug. 24, 1998 and now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the repair of turbine components. In particular, the present invention relates to a system for repairing turbine components. More particularly, the present invention relates to a method of using a system for repairing turbine components. 
     BACKGROUND OF THE INVENTION 
     Turbines components, such as blades, nozzles, vanes, airfoils, tips and the like (hereinafter “turbine components”) are frequently formed from superalloys, for example, nickel-based superalloys, that have a directionally solidified single-crystal structure. The turbine components can be manufactured with defects, including cracks, surface defects, imperfections and holes. These defects must be repaired for reliable, proper, and dependable performance of the turbines. Turbine components also develop defects during service throughout their lifetime. These service-related defects may occur by wear, oxidation, and erosion. Such defects include cracks, surface defects, imperfections, and holes. These turbine component defects must be repaired for proper, dependable, and reliable operation of the turbine. 
     A previous defect repair method provided a repair material that filled the defect. The repair material was preferably the same material as a turbine component. The repair material was melted, and re-solidified to the turbine component at the defect site. The process was intended to provide an integral repaired structure, with a turbine defect site proximate the defect melting and re-solidifying with the repair material. Thus, repair material and the turbine component material formed a solid, one-piece repaired member. 
     Nickel-based superalloy repair materials are often used in a repair process for turbine components. The nickel base superalloy turbine component material will re-solidify with the nickel-based superalloy repair material to provide the turbine component with a structure similar to, and compatible with, its original metallurgical microstructure. 
     Repair material can take many different forms dependent on the defect. A wire repair material is often used for turbine blade tip repairs because turbine blade defects are commonly cracks and a melt feed from wire can be shaped to conform with a turbine blade tip shape. The wire repair material, also referred to as a weld wire, may be formed from a nickel-based superalloy composition for repairing a turbine component formed from a nickel-based superalloy. A nickel-based superalloy composition weld wire can be manufactured by powder metallurgy processes in conjunction with mechanically working to a wire form. 
     Powder metallurgy processes for producing nickel-based superalloy compositions often produce high volume fractions of strengthening precipitates, such as gamma prime (γ′) material. The γ′ material, which is produced in amounts up to about 70% by volume, makes weld wire brittle with low workability, and difficult to form into small diameter wires, and difficult to handle. The γ′ containing material is not ductile (will not exhibit plastic deformation) and will not bend. A brittle repair material is not well suited for further thermo-mechanical processing. A powder metallurgy-produced material also contains undesirable inclusions and contaminant intrinsic to powder metallurgy processes. Further, powder metallurgy produced wires are difficult to manufacture because conversion of raw material to wire uses conventional thermo-mechanical processes, which are expensive, time consuming, and generally not practical for materials with high γ′ volume fractions, for example up to about 70%. 
     Known powder metallurgy processes involve numerous steps and operations, including powder generation, consolidation, thermo-mechanical processing, and final grinding. The numerous steps present many opportunities for process error, such as foreign matter added during the process to contaminate the repair material. Foreign matter often leads to inclusions and contamination of the powder, which is undesirable. If a site is repaired using contaminated material, a resultant repaired site may not be acceptable, because it is not metallurgically sound. The repaired site will not be homogeneous due to the inclusions and contaminants, and an inherently weak spot may result where failure of the turbine component may occur, which, of course, is undesirable. The non-bending of brittle wire repair material also makes the wire material undesirable for a wire feed in tungsten inert gas (TIG) weld repair, where a wire is fed at a nozzle of a weld gun to melt the repair material. 
     A brittle repair material, such as a wire, is difficult to bend and conform to a crack-like defect without breakage. Breakage of the wire leads to discontinuities in the repair material at the repair site prior to melting. If the repair site is not full of repair material, prior to melting, due to discontinuities, the defect will not be completely filled and incomplete repaired sites may result. These incomplete repaired sites lead to voids in the repaired turbine component structure, which are undesirable. 
     Therefore, it is desirable to provide a powder metallurgically-produced repair material and a single-step process for forming repair material. The repair material should provide a low volume fraction of γ′ precipitates, thus making it less brittle and more ductile; and contain fewer contaminants and inclusions than materials formed by conventional powder metallurgy processes. The single-step process should produce a repair material that is amenable to further thermo-mechanical processing, such as, but not limited to swaging, wire drawing, and finishing operations. A turbine component, which is repaired with this material will be metallurgically sound due to the lack inclusions and contaminants in the repair material. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system for providing a repair material and repairing a turbine component. The present invention also provides methods of using the system to repair turbine components as well. 
     Accordingly, one aspect of the present invention is to provide a turbine component repair system. The turbine control system comprises: a means for forming a rapidly solidified turbine repair material; and a means for melting the rapidly solidified repair material at the repair site, wherein the repair material bonds to the turbine component upon resolidification, thus repairing the turbine component. 
     A second aspect of the present invention is to provide a method of repairing a turbine component comprising the steps of: providing a rapidly solidified turbine repair material; disposing the rapidly solidified turbine repair material on a region of the turbine component that includes a defect to be repaired; melting the rapidly solidified repair material and a portion of the turbine component proximate to the defect; and resolidifying the rapidly solidified repair material and the portion of the turbine component, wherein the rapidly solidified repair material bonds to the portion of the turbine component, thereby removing the defect and repairing the component. 
     A third aspect of the invention is to provide a method for providing a rapidly solidified turbine repair material comprising the steps of molten providing a repair material and contacting the molten repair material with a peripheral surface of a rotating drum, wherein the molten repair material is cooled, thereby forming the rapidly solidified turbine repair material. 
     Finally, a fourth aspect of the present invention is to provide a method of repairing a turbine component comprising the steps of: providing a molten repair material; contacting the molten repair material with a peripheral surface of a rotating drum, wherein the molten repair material is cooled, thereby forming the rapidly solidified turbine repair material; obtaining the rapidly solidified repair material; disposing the rapidly solidified repair material on a region of the turbine component, wherein the region includes a defect to be repaired; melting the rapidly solidified repair material and a portion of the turbine component proximate to the defect; and resolidifying the rapidly solidified repair material and the portion of the turbine component, wherein the rapidly solidified repair material bonds to the portion of the turbine component, thereby removing the defect and repairing the turbine component. 
    
    
     These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a part-schematic part-sectional representation of a RS powder producing system; 
     FIG. 2 is a view along line  11 — 11  in FIG. 1; 
     FIG. 3 is a part-schematic part-sectional representation of another RS powder producing system; 
     FIG. 4 is a view along line IV—IV in FIG. 2; and 
     FIG. 5 is a schematic representation of a further RS powder producing system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides processes for manufacturing repair material, such as weld wire. The invention describes the process with respect to a weld wire repair material, however this is merely exemplary of repair material types within the scope of the invention. Other forms, shapes and configurations of repair material are within the scope of the invention. 
     Processes to form a repair material, such as one of a sheet, fiber, and powder, comprise substantially one-step processes that produce a rapidly solidified (RS) material. By rapidly solidifying a material, the material is solidified at a very rapid rate, for example at rates higher than about 10 4 ° C./sec, however quench rates are not solely determinative of rapidly solidified materials. A RS material may be discerned from its microstructure. A RS material generally possesses relatively few, if any, inclusions and contaminants, which is desirable in a repair material, and has a very fine grain structure or is amorphous. RS material contains few inclusions and contaminants, such as foreign matter that contaminates a process, because a number of processing steps is minimal and the solidification rate is rapid. The reduced process steps and rapid solidification rate minimize chances of contaminants entering the process and resultant material. 
     RS material is produced by a rapid solidification that suppresses formation of γ′ precipitates for example in a volume percent in a range between about 20% and about 30% and reduces γ′ precipitates sizes compared to materials produced by prior processes that have a lower solidification rate. An inclusion density (volume fraction) of γ′ for RS material is less than about 10%. The rapid solidification rates occur at quench rates greater than or equal to 10 4 ° C./s. The resultant RS repair material comprises a fine scale microstructure, where the repair material composition will be ductile, essentially contaminant-free, and desirable for turbine component repair. Any precipitate forming elements in the material, such as, but not limited to, titanium (Ti) and aluminum (Al), remain in solid solution during rapid solidification processes. 
     The repair material manufacturing processes within the scope of the invention comprise, but are not limited to, melt-spinning, melt extraction and planar flow casting. Planar flow casting is a derivative of a melt-spinning process. These processes provide a fast, less expensive, and less intensive step-wise manufacture of material, such as nickel-based superalloy powders, when compared to conventional powder metallurgy processes. These manufacturing processes provide a ductile repair material that is essentially homogeneous with relatively few inclusions and contaminants. 
     A homogeneous repair material, when used to repair a turbine component formed of a similar material, results in a substantially homogeneous repaired site that includes few, if any, inclusions and contaminants. If the turbine component is formed from a directionally solidified single-crystal microstructure, a micro-crystalline repair material composition is a desirable. The repair material will re-solidify with the melted turbine component material to form a compatible grain structure with the initial turbine component material. Alternatively, the repair material is instantly formed with a compatible microstructure as the turbine component. 
     To repair a turbine component crack defect, a weld wire is disposed in the defect, for example, by deforming the weld wire to conform with the defect. The weld wire repair material and a surrounding turbine component site (defect site) are melted by an appropriate source of energy, such as an electron beam. The melted repair material and turbine component defect site re-solidify together. The re-solidified repaired turbine component site possesses a microstructure, for example a directionally solidified single-crystal microstructure, that is the same as a remainder of the turbine component. Thus, the repaired site is integral with similar microstructure metallurgically sound and unlikely to fail at the repaired site. 
     Systems and processes to produce RS materials, as embodied by the invention, will now be discussed with respect to forming a nickel-based, superalloy RS material weld wire. The processes can be used to produce other repair materials, and a nickel-based, superalloy RS powder and weld wire is merely exemplary of the invention. 
     Melt-spinning (also known as free-jet melt-spinning) rapidly solidifies molten metal to form RS material, where the RS material (often referred to as “fiber”) size is dependent on an intended use. For example, a RS material produced by melt-spinning is produced in lengths having a range from a few microns to a continuous length. A thickness and width of a RS repair material produced by melt-spinning are in a range between about 50 μm to about 100 μm. 
     FIG. 1 is a schematic representation of a melt spinning (MS) system  1 . A melting chamber (also known as a crucible)  10  comprises an interior portion  11 , an inlet  12  and an outlet  14 . A heater device  16  is provided in thermal communication with the chamber  10 . The heater device  16  comprises any appropriate heating device construction. Although FIG. 1 illustrates the heater structure  16  disposed on an exterior  13  of the chamber  10  as a separate element, the heater structure  16  may be formed integrally with the chamber  10 . Alternatively, the heater device  16  is disposed in the interior portion  11  of the chamber  10  (not illustrated). 
     The inlet  12  of the chamber  10  permits inert gas to enter the chamber  10 . The inert gas provides pressure to extrude molten repair material  22  from the chamber  10 . The inlet  12  communicates with a top wall  18  of the chamber  10 , where the top wall  18  comprises a separate element from the chamber  10 . Alternatively, the top wall  18  may be formed integrally with the chamber  10 . The top wall  18  is attached to the chamber by any manner, for example integral therewith, to insure a chamber  10  that maintains pressure within the interior portion  11 . As illustrated in FIG. 1, the top wall  18 , in one exemplary embodiment of the invention, is attached the chamber  10  with screw threads  20 . 
     The outlet  14  of the chamber  10  comprises a nozzle plate  17  with a substantially circular outlet nozzle  15  with a diameter in a range between about 0.5 mm and about 2.0 mm, as illustrated in FIG.  2 . The nozzle plate  17 , although illustrated in FIG. 2 as substantially circular may comprise any shape corresponding to the shape of the chamber  10 . The outlet  14  is disposed at a lower portion of the chamber  10 , so molten repair material  22  is extruded out of the chamber  10  by the inert gas as a molten stream  23 . Alternatively, the molten repair material  22  free-falls from the chamber  10  under the force of gravity. 
     The molten material stream  23  exits from the nozzle and strikes a rotating drum  24 . The rotating drum  24  is positioned below the outlet  14  for example, separated by a distance “d” in a range between about 1.0 and about 5.0 mm. The drum  24  comprises at least one groove  26  on its periphery  21  (the distance around a circumference of the drum&#39;s cross-section). The groove  26  comprises a shape and size to produce RS material  28  in a desired shape, such as, but not limited to, elongated lengths greater than one (1) periphery, definite lengths less than one periphery, and varying thicknesses and widths. For example, if an elongated length of RS material is desired, the groove  26  is continuous around the periphery  21  of the wheel  24  with an appropriate width and depth. A continuous length of RS repair material  28  is formed by pulling off an undivided, elongated (with a length equal to or greater than one (1) periphery), continuous length of repair material from a continuous groove  26  and collecting it. Alternatively, if RS repair material  29  of a set length is desired, at least one protrusion  31  is located in the groove  26 . The protrusions  31  divide the groove  26  into sub-grooves  32 . Each sub-groove  32  defines a set length in the groove  26  between protrusions  31 , and defines a length of the RS repair material  29  equal to the set length. 
     The stream  23  of molten repair material  22  contacts the drum  24 . The molten material  22  cools in the grooves  26  by contact with the drum  24 . The drum  24  may be supplied with a cooling medium (not illustrated) in its interior  27  to facilitate solidification of RS material  28  in the grooves  26 . 
     The drum  24  rotates at a sufficient speed so most of the RS repair material  29  is thrown off the drum  24  by centrifugal forces imparted to the RS repair material  29 . Any RS repair material  29  in the grooves  26  will be removed by an optional brush  30 . The brush  30  rotates in a direction opposite to the drum  24  to remove the RS repair material  29  from the drum  24 . For example, as illustrated, the drum  24  rotates in a first direction (counter-clockwise) and the brush  30  rotates in a second direction (clockwise) opposite the first direction. The opposite rotations ensure that any RS repair material  29  remaining will be removed. 
     The RS powder  28  is collected in a receptacle  32 . The receptacle  32  takes any appropriate form, so long as it collects the RS repair material  29 . If RS repair material  28  is formed of a continuous length, the RS material  28  is wound on an appropriate collector receptacle, such as but not limited to a spool (not illustrated). 
     A planar flow casting system  100  is illustrated in FIG.  3 . Planar flow casting is a rapid solidification process that is related to melt spinning. In the planar flow casting system  100 , the chamber is essentially similar to the chamber  10  used in a melt spinning system. Accordingly, a further discussion of the chamber&#39;s features is omitted. 
     The planar flow casting system  100  differs from a melt spinning system  1  in that the outlet from the chamber is modified. Alternatively, a planar flow casting system  100  differs from a melt spinning system  1  in that the rotating drum comprises altered structure to form the RS repair material. Further, as another alternative, a planar flow casting system  100  differs from a melt spinning system  1  in that the outlet from the chamber comprises a modified structure and the drum is altered. The following description of the planar flow casting system  100  discusses a modified outlet and an altered drum, however the scope of the invention includes either feature used independently. 
     In FIG. 3, the chamber  10  comprises an outlet  40 . The outlet  40  is disposed proximate a rotating drum  44 . The outlet  40  is closer, for example in a range between about 2.5×10 −5  m to about 10 −4  to the rotating drum  44  than the positioning of the outlet  14  and the drum  24  in the melt spinning system  1  of FIG.  1 . The distance from the outlet  40  to the drum  44  ensures that jetting of the repair material stream  42  does not occur in the planar flow casting system  100 . 
     The outlet  40  comprises a rectangular nozzle  41  (FIG.  4 ). Thus, the repair material stream  42  is fed out of the outlet  40  as a substantially rectangular stream. For example, the nozzle has a cross-section with a thickness formed in a range between about 5 mm and about 20 mm, with a width formed in a range between about 0.5 m to about 1.0 mm. 
     The rotating drum  44  comprises notches  48  on its periphery. The notches  48  form the RS material when the stream  42  strikes the drum  44 . The ultimate desired shape of the repair material is dependent on a size and shape of the notches  48 . For example, the notches  48  may be elongated, such as extending about the entire periphery  49  of the wheel  44 , with a single notch  48  defining a length of the RS repair material  46 . Alternatively, a plurality of notches  48  is provided with variable or equidistant spacing between the notches  48  defining lengths of RS repair material  46 . The illustrated notch configuration is merely exemplary and is not meant to limit the invention in any way. 
     The repair material stream  42  contacts the drum  44 , and is received in the notches  48 . As the molten repair material cools in the notches  48 , RS repair material  46  is formed. The rotating drum  44  rotates at a speed sufficient to throw RS repair material  46  off the drum  44 . A brush  30 , as provided in the melt spinning system  1 , may also be provided to remove RS repair material  46  remaining on the drum  44 . Also, the drum  44  may be cooled as in the melt spinning system  1 . 
     In both the melt spinning and planar flow casting systems,  1  and  100  respectively, a periphery configuration (surface structure of the drum) of the drum, such as the groove  26  and notches  48 , form the RS material. The solidification rates of both systems are rapid enough to produce RS material comprising few, if any, inclusions and foreign matter, with fine micro-crystalline microstructure. For example, a volume fraction of inclusions is less than about 1% and the inclusion size is less than about 25 microns (2.5×10 −5  m). The volume fraction of γ′ is less than about 10% and the γ′ size is less than about 1 micron (10 −6  m). 
     Melt extraction is another process within the scope of the invention to produce RS repair material. FIG. 5 is a schematic representation of a melt extraction system  200 , as embodied by the invention. In FIG. 5, a chamber  51  holds molten metal  52 . The chamber  51  is insulated to maintain the metal in a molten form. Alternatively, the chamber  51  comprises heater device (not illustrated) to maintain the metal in its molten condition. 
     A drum  54  is rotatably mounted on an axis  53  so that a portion  55  of the drum  54  is in contact with the molten metal  52 . At least a periphery  56  of the drum  53  contacts the molten metal  52  surface. Alternatively, the portion  55  is in contact with the molten metal, where the periphery  56  of the drum  53  is below the molten metal  52  surface a distance “d”. The contact between the drum  54  and molten metal  52  varies dependent on the nature of RS material desired, however some contact occurs between the drum  54  and the molten material  52 . 
     The molten metal  52  and drum  54  are maintained in contact with one another, for example by feeding more material into the chamber  51 , either as a molten material or as a solid material where it can melt in the chamber  51 . Alternatively, the drum  54  adjusts to the level of the molten material  52  to maintain contact at portion  55 . The drum  54  comprises a coolant-filled interior  59 , such as a water-filled interior. Thus, molten metal  52  rapidly solidifies into RS material  60  on the drum  54 . The drum  54  rotates about axis  55 , so formed RS material  60  flies off the drum  54 . 
     The periphery  56  of the drum  54  comprises notches  58 . The notches  58  are sized and shaped to capture molten metal  52  as the drum  54  contacts the molten metal  52 . The size and shape of the notches  58  control the size of the RS material  60 . The notches  58  can be sized to produce RS material  60  with varying lengths, thicknesses, and widths. The notches  58  do not need to be all of the same size. Notches  58  of differing sizes can be provided on one drum  54 , to produce RS materials of differing sizes, without requiring separate drums. 
     RS materials  28 ,  29 ,  46 , and  60 , which are formed by the above one-step rapid solidification processes, are usable in their as-produced form as RS repair material. The as-produced form is often wire. If a turbine component defect size is larger than the as-produced powder or a larger repair material is desired, two or more RS materials  28 ,  29 ,  46 , and  60  are combinable to form an enlarged RS repair material. The RS materials  28 ,  29 ,  46 , and  60  can be combined together by any appropriate method, either physically or metallurigally. For example, two or more RS materials  28 ,  29 ,  46 , and  60  are physically connected, such as by one of braiding, weaving, and crimping together to form a repair material, which is larger than a single powder fiber. RS repair materials can be further connected to each other to form a large spool of weld wire. Alternatively, the RS material  28 ,  29 ,  46 ,  60  can be consolidated into a repair material by known metallurgy processes. These processes include, but are not limited to, hot-isostatic pressing (HIP), powder rolling, sintering, sintering and re-rolling, and roll briquetting. The final shape of the RS repair material depends on the ultimate use of the repair material and a defect type, size and shape. 
     Of the above described rapid solidification processes, fiber melt extraction provides varying dimensions of RS material depending on notch dimensions. Thus, the RS material produced by this process is desirable, since the repair material can be used without significant after-powder manufacturing processing steps. 
     Turbine components and turbine component tips are repaired using repair material produced as described herein. Typically turbine components comprise a nickel-based superalloy, for example a material selected from one of directionally solidified nickel-based superalloy and a nickel-based superalloy single-crystal. The nickel-based superalloy repair materials comprise the same material as the turbine component. Alternatively, the nickel-based superalloy repair material comprises a different material as the turbine component. 
     The RS repair material may also be used to repair a turbine blade tip. To repair a turbine blade tip, the RS repair material is positioned at the tip, for example by wrapping the RS repair material around the turbine tip thus covering the turbine tip. If the RS repair material is provided in set length of weld wire pieces, these weld wire pieces are individually positioned at the tip. Alternatively, the RS repair material may be provided as a continuous weld wire, where the continuous weld wire is disposed over the portions of the turbine blade tip. Once positioned at the tip, the weld wire is melted, by an appropriate energy source, and re-solidified with the turbine blade tip. 
     Alternatively, the wire repair material is used with a TIG weld repair process. This process is often used to replace ground away portions of a turbine component. The wire is melted and disposed on the turbine essentially in the same step. 
     While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within the scope of the invention.