Title:
Method to restore an airfoil leading edge
Kind Code:
A1


Abstract:
The present invention provides methods and apparatus to restore a blade leading edge on a gas turbine engine component such as an airfoil of a turbine blisk. The method utilizes welding image technology and power control systems in order to provide effective welding with superalloy materials such as Inconel 713 and Inconel 625. The method includes machining away a damaged leading edge and providing a repaired region through successive depositions of superalloy powder filler through laser fusion welding. Deposition material is added until the repaired region exceeds the original dimensions of the airfoil. The airfoil is then machined and finished to return it to original airfoil dimensions.



Inventors:
Guo, Wen (Greenville, SC, US)
Renteria, Federico (Greenville, SC, US)
Application Number:
10/954497
Publication Date:
03/30/2006
Filing Date:
09/29/2004
Primary Class:
International Classes:
F04D29/38
View Patent Images:
Related US Applications:



Primary Examiner:
KOEHLER, CHRISTOPHER M
Attorney, Agent or Firm:
HONEYWELL INTERNATIONAL INC. (101 COLUMBIA ROAD, P O BOX 2245, MORRISTOWN, NJ, 07962-2245, US)
Claims:
What is claimed is:

1. A method for resurfacing a leading edge of an airfoil comprising the steps of: removing material from the leading edge of an airfoil; preparing at least the airfoil leading edge for welding; selecting a weld path using an image system; determining welding parameters in order to avoid cracking; and laser cladding filler material at least onto the airfoil leading edge, and along a selected weld path, using powder fusion welding of superalloy powder and the determined welding parameters.

2. The method according to claim 1 wherein the step of laser cladding filler material further comprises laser cladding filler material in a high stress region of the airfoil.

3. The method according to claim 1 wherein the substrate comprises Inconel 713.

4. The method according to claim 1 wherein the filler material comprises Inconel 625.

5. The method according to claim 1 wherein the laser cladding comprises laser cladding with a CO2 laser.

6. The method according to claim 1 wherein the laser cladding step further comprises laser cladding with an energy between about 50 and about 2500 watts.

7. The method according to claim 1 wherein the laser cladding step further comprises laser cladding wherein the laser directs a beam on the workpiece with an area of between about 0.02 and about 0.100 square inches.

8. The method according to claim 1 wherein the laser cladding step further comprises laser cladding wherein the laser traverses the workpiece surface at a rate of between about 3 and about 22 inches per minute.

9. The method according to claim 1 wherein the laser cladding step deposits filler material in a series of deposition steps.

10. The method according to claim 1 wherein the laser cladding step follows a single pass.

11. The method according to claim 1 wherein the laser cladding step follows a stitching pattern.

12. A method for resurfacing a damaged leading edge of a turbine blisk airfoil comprising the steps of: machining material away from the damaged leading edge to a selected height and depth whereby a machined area is formed; inspecting the machined area by fluorescent penetrating inspection; preparing at least the machined area for welding; determining a weld path with a laser image system on the machined area; performing a laser fusion welding of at least the machined area with a superalloy powder filler and a CO2 laser; and automatically controlling material deposition, energy, and laser travel velocities during the laser fusion welding to minimize heat cracking in the airfoil.

13. The method according to claim 12 wherein the step of performing a laser fusion welding further comprises performing a laser fusion welding across a high stress region of an airfoil.

14. The method according to claim 12 further comprising measuring the depth of the deposition and repeating a laser fusion welding until a desired thickness is achieved.

15. The method according to claim 12 wherein the superalloy powder filler comprises Inconel 625 superalloy powder.

16. The method according to claim 12 wherein the step of machining material further comprises machining material to a selected height and depth so as to remove damaged portions of the leading edge.

17. The method according to claim 12 wherein the step of inspecting the airfoil further comprises inspecting in order to confirm the absence of cracks that would disqualify the airfoil from repair.

18. The method according to claim 12 further comprising the step of machining a repaired airfoil to a desired contour.

19. The method according to claim 18 further comprising a rough machining.

20. The method according to claim 18 further comprising a final machining by hand blending.

21. The method according to claim 12 wherein the step of performing a laser fusion welding further comprises laser fusion welding with a co-axial powder feeder.

22. A resurfaced airfoil comprising: an airfoil integrally connected to a blisk, the airfoil including at least a leading edge, a trailing edge, a top edge, a substrate region, and a repaired region; wherein the repaired region: is welded by powder fusion repair to the substrate region, and extends from a welding surface to the airfoil leading edge and from the welding surface to the airfoil top edge.

23. The resurfaced airfoil according to claim 22 wherein the repaired region is formed by overlapping laser cladding depositions of powdered alloy.

24. The resurfaced airfoil according to claim 22 wherein the repaired region crosses a high stress region of the airfoil.

25. The resurfaced airfoil according to claim 22 wherein said repaired region further comprises a superalloy.

26. The resurfaced airfoil according to claim 25 wherein said repaired region further comprises Inconel 625.

27. The resurfaced airfoil according to claim 22 wherein said substrate region further comprises a superalloy.

28. The resurfaced airfoil according to claim 27 wherein said substrate region further comprises Inconel 713.

29. The resurfaced airfoil according to claim 22 wherein the substrate region further comprises a weld surface at which the repaired region is welded to the substrate region.

30. The resurfaced airfoil according to claim 29 wherein the weld surface is arcuate in shape.

31. The resurfaced airfoil according to claim 22 wherein the repaired region extends beyond the leading edge.

32. The resurfaced airfoil according to claim 22 wherein said repaired region and said substrate region further comprise a turbine blisk airfoil.

Description:

FIELD OF THE INVENTION

The present invention relates to laser welding. Additionally the invention relates to the apparatus and techniques used to repair the leading edge of airfoils that have suffered degradation or wear. More particularly, the invention relates to a method to restore, by laser welding techniques with powder filler, the leading edge on the blades of turbine blisks that have been eroded by foreign object damage.

BACKGROUND OF THE INVENTION

Turbine engines are used as the primary power source for many types of aircraft. The engines are also auxiliary power sources that drive air compressors, hydraulic pumps, and industrial gas turbine (IGT) power generation equipment. Further, the power from turbine engines is used for stationary power supplies such as backup electrical generators for hospitals and the like.

Most turbine engines generally follow the same basic power generation procedure. Compressed air generated by axial and/or radial compressors is mixed with fuel and burned, and the expanding hot combustion gases are directed against stationary turbine vanes in the engine. The vanes deflect the high velocity gas flow so as to impinge on the turbine blades mounted on a rotatable turbine disk. The force of the impinging gas causes the turbine disk to spin at high speed. Jet propulsion engines use the power created by the rotating turbine disk to draw more air into the engine, and the high velocity combustion gas is passed out of the gas turbine aft end to create forward thrust. Other engines use this power to turn one or more propellers, fans, electrical generators, or other devices.

In an attempt to increase the efficiencies and performance of contemporary gas turbine engines generally, engineers have progressively pushed the engine environment to more extreme operating conditions. The harsh operating conditions of high temperature and pressure that are now frequently specified place increased demands on engine component-manufacturing technologies and new materials. Indeed the gradual improvement in engine design has come about in part due to the increased strength and durability of new materials that can withstand the operating conditions present in the modern gas turbine engines. With these changes in engine materials, there has arisen a corresponding need to develop new repair methods appropriate for such materials.

One development in the design of gas turbine engine components has also been the introduction of integrally structured airfoil and rotor devices, blisks. A turbine blisk, for example, includes turbine airfoils that are integrally formed with the perimeter of a rotor disk by, for example, integral casting. This design provides the advantage of eliminating the connection between individual airfoils and the rotor at a dovetail. The blisk, by having a unitary construction, also provides a strong mechanical connection between the airfoil region and the rotor disk region thereby allowing for a more efficient positioning of the airfoils. This results in an improved performance of the blisk in terms of weight and component size.

The development of the blisk as a gas turbine engine component has presented challenges with respect to repair strategies. Individual airfoils are now permanently attached to the rotor disk, which means that damaged airfoils cannot easily be removed for repair, as has been done with individual turbine blades. Nonetheless, blisks do have a normal life cycle and must be repaired or replaced at the end. Blisks are impacted by foreign objects such as sand, dirt, and other such debris. Blade leading edge damage, for example, is a common failure experienced in blisks. The leading edge is subject to foreign object damage or erosion after a period of service time.

The option of throwing out worn engine components such as turbine blisks and replacing them with new ones is not an attractive alternative. Blisks are very expensive due to costly material and manufacturing processes. Consequently there is a strong financial need to find an acceptable and efficient repair method for turbine blisks.

Turbine blisks used in modern gas turbine engines are frequently castings from a class of materials known as superalloys. The superalloys include nickel-based, cobalt-based and iron-based superalloys. Inconel 713 is a typical superalloy used in blisk construction. In the cast form, turbine blisks made from advanced superalloys include many desirable properties such as high elevated-temperature strength and good environment resistance. Advantageously, the strength displayed by this material remains present even under stressful conditions, such as high temperature and high pressure, experienced during engine operation.

Disadvantageously, the superalloys generally are very difficult to weld successfully. Traditional repair methods have proven less than satisfactory for superalloy materials. For example, with regard to turbine blades, as opposed to turbine blisks, known welding techniques often include heating a turbine blade to high temperatures, ranging from 1800° F. to 2000° F. before the welding process. However, at such an elevated temperature the turbine blade may experience heat cracking and fracturing, rendering the blade unusable for further engine service. Other welding techniques similarly suffer from a lack of thermal control and provide too much localized heat during welding to render an effective repair with superalloy blisk airfoils. Superalloys are susceptible to microcracking during localized heating. Moreover, the complex geometry of the airfoil, and particularly, the shape of the leading edge, makes it difficult to deposit filler or cladding material thereon. Finally, the turbine blisk airfoil has a region that experiences high stress. It has proven difficult to provide filler or cladding material across a high stress region with sufficient strength and adherence such that the airfoil can be returned to service. Thus previous repair strategies used on blisks have avoided the high stress region.

Hence, there is a need for a turbine airfoil restoration method that addresses one or more of the above-noted drawbacks and needs. Namely, a repair method is needed that can fully restore geometry, dimension and desired properties of degraded turbine blisk airfoils and/or a method that allows control of welding parameters so that blisk repairs may be affected without heat cracking and damage to the airfoil and/or a method that allows for repairs across the high stress zone of a turbine blisk. Finally, it would be desired to provide a method to restore a blisk airfoil that, by virtue of the foregoing, is therefore less costly as compared to the alternative of replacing worn parts with new ones. The present invention addresses one or more of these needs.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and methods for use in restoring turbine blisk airfoils through laser welding techniques. In one embodiment, the invention provides a powder-fed CO2 laser welder that is capable of welding superalloy filler material to the superalloy substrate of the blisk. The damaged leading edge of the turbine blisk is cut back, and filler material is welded into the leading edge area. The surface contour of the blisk is then restored to a desired geometry.

In one embodiment, and by way of example only, there is provided a method for resurfacing the leading edge of an airfoil comprising the steps of: removing material from the leading edge of an airfoil; preparing the airfoil for welding; selecting a weld path using an image system; determining welding parameters in order to avoid cracking; and laser cladding filler material onto the airfoil. The laser cladding of filler material may take place in a high stress region of the airfoil.

In a further embodiment, still by way of example only, there is provided a method for resurfacing the damaged leading edge of a turbine blisk airfoil comprising the steps of: machining material away from a damaged leading edge to a selected height and depth; inspecting the machined area by fluorescent penetrating inspection; preparing the leading edge for welding; determining a weld path with a laser image system; and performing a laser fusion welding with a superalloy powder filler and a CO2 laser. The laser fusion may use a coaxial powder feeder nozzle. The laser fusion welding may take place across a high stress region of an airfoil. The method may include measuring the depth of the deposition and repeating a laser fusion welding until a desired thickness is achieved. The superalloy powder filler may comprise Inconel 625 superalloy powder, and the substrate may be composed of Inconel 713. The machining step may include machining material to a selected height and depth so as to remove damaged portions of the leading edge. Inspecting the airfoil may further comprise inspecting in order to confirm the absence of cracks that would disqualify the airfoil from repair. The method may also include machining a repaired airfoil to a desired contour.

In still a further embodiment, and still by way of example only, there is provided a resurfaced airfoil comprising: an airfoil with a leading edge, a trailing edge, and a top edge integrally connected to a blisk; a substrate region of the airfoil; a repaired region of the airfoil laser welded by powder fusion repair to the substrate region wherein the repaired region extends from a welding surface to a leading edge of the airfoil and from a welding surface to a top edge of the airfoil. The repaired region may be formed by overlapping laser cladding depositions of powdered alloy, and the repaired region may cross a high stress region of the airfoil. Material of the repaired region may comprise a superalloy such as Inconel 625. Material of the substrate region may comprise a superalloy such as Inconel 713. The substrate region may further comprise a weld surface, which may be arcuate shaped, at which the repaired region is welded to the substrate region.

Other independent features and advantages of the method to restore an airfoil leading edge will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a turbine blisk airfoil that may be restored according to an embodiment of the present invention.

FIG. 2 is a perspective view of a laser welding system that may be used to perform airfoil restoration according to an embodiment of the present invention.

FIG. 3 is a perspective view of a turbine blisk airfoil with damaged area machined away according to an embodiment of the present invention.

FIG. 4 is a flow chart that illustrates steps in an exemplary embodiment of the method to restore an airfoil leading edge.

FIG. 5 is a photomicrograph showing a substrate region and a repaired region of a restored airfoil according to an embodiment of the present invention.

FIG. 6 is a photomicrograph showing a substrate region and a repaired region of a restored airfoil according to an embodiment of the present invention.

FIG. 7 is a photomicrograph showing a substrate region and a repaired region of a restored airfoil according to an embodiment of the present invention.

FIG. 8 is a photomicrograph showing a substrate region and a repaired region of a restored airfoil according to an embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. Reference will now be made in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

A typical airfoil 10 of a turbine blisk is illustrated in FIG. 1. Such a blade may have a different geometric and dimension design, depending on the engine model and its application. For a typical aero-engine, a turbine blisk airfoil is typically a few inches in length. Airfoil 10 is characterized by a complex geometry that changes in three dimensions. A gas turbine airfoil may be welded to, or cast in unitary form, with hub 11 shown in partial view. In an engine assembly multiple such turbine airfoils are positioned in adjacent circumferential position along the hub or rotor disk. Multiple blisks or other rotor assemblies may be sequentially positioned in the engine. Airfoil 10 is a cuplike structure that includes a concave face 13 and a convex face (not shown) on the reverse side of the airfoil. Airfoil 10 extends radially outwardly from the hub. A top edge 12 defines the radial end of the airfoil.

In operation, gases impinge on concave face 13 of airfoil 10 thereby providing the driving force for the turbine engine. Pressure develops on concave face 13 while suction develops on the convex face. This force acting on the airfoil thereby spins hub 11. Turbine airfoil 10 also includes leading edge 17 and trailing edge 18 which represent the edges of the airfoil that firstly and lastly encounter an air stream passing around it. Leading edge 17 is subject to wear and degradation. Partly this arises from debris and contaminants carried in the airstream. This debris impacts leading edge at high velocity thus leading to nicks, wear, and erosion, all of which impair the engine performance.

Referring now to FIG. 2 there is shown a schematic diagram of a general apparatus for laser generation and control that may be used in airfoil restoration according to an embodiment of this invention. Laser generating means 20 generates a laser used in the welding system. A laser is directed through a laser conveyance which may include passing the laser through beam guide 21, through mirror 22, and through focus lens 23. In some embodiments, beam guide 21, mirror 22, and focus lens 23 may not be present, or may have different configurations. The laser then impinges on a surface of a work piece 24. Components such as beam guide 21, mirror 22, and focus lens 23 are items known in the art of laser powder fusion welding. Beam guide 21 may include fiber optic materials such as fiber optic laser transmission lines.

A means for providing a filler or cladding material is also included for use with the laser. Preferably this filler material may be provided in powder feeder 25. In such an embodiment the powder is fed onto the workpiece 24 through powder feed nozzle 26. A coaxial or off-axis arrangement may be used with powder feed nozzle 26 with respect to the main laser. Alternatively, filler material may be provided through other means such as a wire feed.

Other components of the laser welding system include a vision CCD camera 27 and video monitor 28. The image taken by the camera 27 can also be fedback to the controller screen 30 for positioning and welding programming. Controller 30 is similarly connected to operable pieces of the welding system and thereby controls features such as welding power, energy power (on/off and pulse/continuous) laser beam size, weld path, welding velocity, and filler delivery. The workpiece 24 is held on a work table 29. An inert gas shield (not shown) is fed through guides (not shown) onto the workpiece 24. The inert gas shield is directed onto a portion of the surface of the workpiece 24 during laser welding.

Controller 30 preferably includes a computer numerically controlled (CNC) positioning and digital imaging system. CNC controller 30 coordinates components of the system and allows for automated, programmed welding. The controller 30 also guides movement of the laser and powder feed across the face of the workpiece 24. The controller 30 thus allows for a fully automated laser welding operation. Moreover, the imaging and vision aspects of the controller allow it to select weldpaths (and welding parameters) so as to minimize or effectively eliminate stress and heat-related damage to the workpiece. In a preferred embodiment, movement of the workpiece in the XY plane is achieved through movement of the worktable. Movement in the up and down, or Z-direction is achieved by control of the laser arm; i.e., pulling it up or lowering it. Alternative methods of control are possible, such as controlled movement of the workpiece in all three directions, X, Y, and Z as well as rotation and tilt.

It will be appreciated that the geometric configuration of airfoils on a blisk can lead to space limitations with respect to welding machinery. The components of the welding system that come into close contact with the blade leading edge must be sufficiently compact so that physical maneuvering is possible. Thus, in a preferred embodiment, a CO2 laser with a concentric powder nozzle is selected as the close contact laser system. This permits the application of sufficient material and energy in the direction of a blade leading edge to affect repairs.

A damaged airfoil such as illustrated in FIG. 1 can be restored to a desired shape using, for example, an apparatus as illustrated in FIG. 2. In a first step of the repair process, damaged material on an engine component is machined. For example damaged leading edges of a blisk are machined so as to remove the damaged portion. The remaining airfoil material should not suffer from any degree of damage that would prevent a restored airfoil from returning to service. In a preferred embodiment, the leading edges 17 (or other damaged area such as a tip or top edge) are machined back to predetermined limits. The limits may refer to a degree of machining in a lateral direction starting from the leading edge 17 and a depth direction starting the top edge 12 of the blade. The predetermined limits provide a margin of safety whereby any damaged material is removed. When an automated machining operation is to be used, it is preferred that all airfoils be machined to the same limits. The limits of machining may be determined by an inspection step of the airfoils. Known methods of machining or grinding may be used for the material removal. It is preferably done by automated means using a multi-axis numerically controlled milling machine. In one embodiment, digital information regarding the blade's blueprint or actual geometry is used to program the desired machining operation.

Referring now to FIG. 3 there is shown an airfoil after a machining. The portion of the airfoil that has been cut away leaves a generally arcuate shaped area on the substrate region 31 of the blade, which is the remaining mass of the airfoil. The cut away portion also reveals a weld surface 32 on substrate region. Weld surface 32 extends from leading edge 17 to top edge 12.

The machined airfoil may optionally receive an inspection, such as a fluorescent penetration inspection. This inspection can determine whether the substrate region 31 has any imperfections that would disqualify the blade from service even after repair. Additionally, the inspection can confirm that all damaged material has been removed. Once material has been removed, the area of the airfoil that is now exposed may also be prepared for welding. This may include standard treatments such as grit blasting and solution treatment.

In a further step filler material is deposited by laser welding techniques on welding surface 32. Preferably, filler material is deposited through the use of powder fusion welding. In this system, filler material in powder form is discharged so that it is melted by the laser beam and welds on the desired surface of the workpiece. Weld paths are chosen to avoid stress-concentration areas. During welding a single weld bead is preferred. However, if the bead is not of sufficient dimension to cover the entire machined surface, then a stitch pattern may be used to provide a desired weld build-up as well as area coverage. Processing parameters are also chosen to control thermal input during the welding operation. It is preferred to minimize the amount of heat discharged through the laser to the minimum amount necessary to affect laser welding. Further, the area of the laser beam spot and laser velocity are similarly determined in order to regulate the heat experienced by the substrate and the stress caused by the laser welding process. Thus, the welding operation avoids microcracking in the weld area and the heat affected zone.

In a preferred embodiment, the power of the laser projected onto the welding area 32 is between about 50 to about 2500 watts and more preferably between about 50 to about 1500 watts. The powder feed rate of powder filler material is between about 1.5 to about 20 grams per minute and more preferably about 1.5 to about 10 grams per minute. Traveling speed for the motion of the substrate work table 29 relative to the laser beam is about 3 to about 22 inches per minute and more preferably about 5 to about 14 inches per minute. The size of the laser beam spot projected onto the welding area 32 is about 0.02 to about 0.1 inches in diameter and more preferably about 0.04 to about 0.06 inches. The laser-welded bead width that results through the laser welding is thus about 0.02 to about 0.100 inches and more preferably about 0.04 to about 0.06 inches in width.

Multiple passes may be used to build up a required dimension of material where one pass overlaps a previous pass and successive passes are laid atop a previous pass. Similarly, the method allows for cladding of an area greater than that covered in a single pass by laying successive passes alongside previous passes thus covering a desired area. If needed, repetitions of the laser welding passes can be done in order to achieve a required level of buildup and/or coverage over a required area; this is accomplished by depositing successive layers of filler material on top of one another. Upon conclusion of a first pass, or other passes, the controller can check the thickness of the weld deposit. If needed, additional weld deposits can then be conducted.

Laser welding depositions continue until sufficient material has been deposited. Sufficient material is deposited when the deposited material now occupies the volume of material that had been machined away from the airfoil. Thus, deposited material preferably extends to a point beyond leading edge 17 and top edge 12 of the airfoil in its original condition. The result is a mass of newly deposited material that occupies a repaired region. The material of the repaired region is fusion welded with the material of the substrate region. Further the weld is characterized by a lack of any degree of cracks, voids, or discontinuities that would disqualify the turbine blisk from service.

The powder or filler used in the laser welding process is compatible with the alloy comprising the workpiece. The dimension of filler powder is measured by its mesh size. Preferred powder size ranges from +100 mesh to −325 mesh. In one preferred embodiment, Inconel 625 powder is used as a filler material to restore an airfoil whose substrate is made of Inconel 713. Some superalloy filler materials that are also suitable for the practice of this invention and that are commercially available in powder and wire form include: HS188, Stellite 694, Hastelloy X, Inconel 625, INCO 738, INCO 939, MarM247, Rene 80, and C 101. Some matrix or base superalloys, which are suitable for the practice of this invention and may be laser welded include: Inconel 713, INCO738, C101, MarM-247, Rene80, GTD111, Rene125, Rene142, SC 180, Rene N5 and N6, CMSX-2, CMSX-4 and CMSX-10, and PWA 1480 and 1484.

INCONEL is a trade name owned by Inco Alloys International, Inc. The name INCONEL refers to a number of nickel-based superalloys. Several of the Inconel superalloys are used in aerojet applications. The same or similar superalloys may be manufactured by sources which may use a different name. Inconel 625 and 713, which are preferred alloys for use in the present invention, have the following general compositions:

INCONEL 625INCONEL 713
Wt %Wt. %
ElementCompositionElementComposition
Carbon 0.1 maxCarbon 0.20 max.
Manganese 0.5 maxManganese 1.0 max.
Sulphur0.015 maxSulphur0.015 max.
Silicon 0.5 max.Silicon 1.0 max.
Chromium  20-23Chromium11.00-14.00
Molybdenum  8-10Molybdenum 3.5-4.5
Titanium 0.4 maxTitanium 0.25-1.25
Aluminum 0.4 maxAluminum 5.5-6.5
Iron   5 max.Iron 5.0 max.
Cobalt   1 max.Co + Ta 1.0-3.0
Niobium3.15-4.15Nickelremainder
Phosphorous 0.15 max
Nickelremainder

After completion of the laser powder fusion step, the airfoil may be machined and finished so as to return the airfoil to a desired shape or geometry. A rough machining might be necessary to remove abundant weld metal prior to a final machining. A final machining may then be performed by hand blending or a CNC milling operation. A preferred geometry is the blueprint geometry of the original airfoil, although, as is understood in the art, approximations to this shape are acceptable. In a preferred embodiment, material in the repaired region is initially overdeposited with respect to the starting boundaries of the airfoil, the leading edge and the top edge. However, it is also preferred not to unnecessarily overdeposit material as this leads to wastage of material and further processing to restore the airfoil to a desired shape.

Referring now to FIG. 4 there is shown a flowchart that illustrates steps in a preferred embodiment of the method to restore an airfoil leading edge. In step 41 an airfoil is machined to remove damaged material. In step 42 the machined airfoil optionally receives an inspection to confirm the removal of the damaged portion of the airfoil. In step 43, filler material is deposited onto the airfoil. And in step 44 the airfoil is machined to a desired shape.

The following example is illustrative of the principles of the invention. A set of turbine rotor blades were selected for leading edge restoration. The selected blades had been in service in a third stage turbine rotor assembly of the GTCP331-250, a Garret Auxiliary Power Unit (APU). The blades had been subjected to FOD (foreign object damage) through routine usage. The base metal of the turbine blades was Inconel 713. The weld filler material was Inconel 625.

In a first step the blades were cleaned by soaking them in an alkaline solution and subjecting the blades to a vapor blasting.

The blade leading edge was machined. The machining was to a depth and height so as to removes nicks, wear, and erosion damage on the blade leading edge. The machining extended to a maximum of 0.500″ in length down the leading edge from the existing tip height and to a maximum of 0.080″ in depth back from the leading edge. The length and depth of machining was chosen such that all regions of wear, damage, and erosion were removed.

The blades received a visual and Fluorescent Penetrating Inspection (FPI) to determine reparability. Cracks or other imperfections that would disqualify the blade from service were noted. This step confirmed that all surface defects were removed after machining.

The surface areas to be welded received a welding preparation. This included grit blasting the surface areas with 220 grit aluminum oxide at 40 psi.

The blades then received a laser cladding on the machined leading edge. The laser welding used an Inconel 625 alloy powder as the filler material. A Huffman 205 CO2 laser system was used to perform the laser cladding operation.

The leading edge of the blades then received both a rough machining and a finish blend machining to remove excessive weld material. The finish blending also restored the blade contour to an original, or approximately original, profile.

The blades were also subjected to a heat treatment with stress relief cycle.

Next the welded area received a chemical etch. An etchant such as ferric chloride solution may be used. The etching allows for an accurate FPI reading. The blades then received an FPI inspection at the welded leading edge. The FPI inspection was in accordance with ASTM-E1417, Type I, Method D, and Sensitivity level 4. No cracks were identified.

At this point in the procedure, the blades are restored. They may be returned to service. However, as a further examination, the restored blades were cut up and subjected to a metallurgical analysis in order to evaluate the quality of the repair.

The blades were sectioned according to a plan that would allow for evaluation of the weld along multiple axes. Cut up plan A followed a transverse cross-section at different heights, A1 and A2. Cut up plan B followed the edge of the weld, a vertical cut along the blade. Cut up plan C followed a cord length of the airfoil. The mounts that resulted from the sectioning were polished with 0.05 micron silica and etched with Kalling's reagent. The mounts were polished three times, except for the Section C mounts, which did not have adequate metal for three polishes. The results of the metallurgical inspection are shown in the following table. Photomicrographs of the mounts are shown in FIGS. 5 through 8.

MaterialMetallurgical
Cut-Up PlanPolishesRemovalResults
C10.019″OK
20.012″OK
C10.022″OK
(See FIG. 5)
20.010″OK
A10.015″OK
20.021″OK
(See FIG. 6)
30.034″OK
A10.017″OK
(See FIG. 7)
20.009″OK
30.024″OK
A10.014″OK
20.012″OK
30.036″OK
B10.021″OK
20.018″OK
(See FIG. 8)
30.030″OK

As shown in FIGS. 5 through 8, the metallurgical evaluation of the cut-up mounts revealed microstructures with acceptable fusion and penetration of the Inconel 625 weld material 51 with the base metal 53. No defects such as cracks, major porosity, or lack of fusion were found in the weld, the interface, and the base metal. The heat-affected zone was examined carefully, and no micro-cracks were observed.

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 to 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.