Patent Publication Number: US-10328526-B2

Title: Laser powder deposition weld rework for gas turbine engine non-fusion weldable nickel castings

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to PCT Patent Application No. PCT/US14/62194 filed Oct. 24, 2014, which claims priority to U.S. Provisional Application Ser. No. 61/897,616 filed Oct. 30, 2013, which are hereby incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     The present disclosure relates to a weld rework method and, more particularly, to a weld rework of a gas turbine engine component. 
     A gas turbine engine utilizes various relatively large, complex components cast from high temperature Nickel alloy. An example of such a component is the Mid Turbine Frame (MTF). The MTF includes a plurality of hollow vanes arranged in a ring-vane-ring structure in which the rings define inner and outer boundaries of a core combustion gas path while the vanes are disposed across the gas path. Tie rods often extend through the hollow vanes to interconnect an engine mount ring and a bearing compartment. 
     Casting components such as the MTF hollow vanes commonly result in flaws that are rework welded as part of the normal manufacture process. Various methods of rework with a filler alloy equivalent to that of the parent component non-fusion weldable base alloy, although effective, are relatively slow and expensive. In one rework example, a half-inch (13 mm) sized defect requires upward of ten hours to rework. Alternate methods of rework welding utilize an alternate filler alloy which is more weldable to facilitate a relatively quicker weld rework, but such an approach may face the cracking issue at the substrate alloy. The filler alloy may not be fully compatible with the material properties of the substrate alloy such as oxidation resistance or not be compatible with coatings and may shorten component service life. 
     SUMMARY 
     A method of reworking a component, according to one disclosed non-limiting embodiment of the present disclosure, includes at least partially filling a cavity in a non-fusion weldable base alloy with a multiple of layers of a multiple of laser powder deposition spots formed of a filler alloy. Each of the multiple of laser powder deposition spots at least partially overlaps at least one of another of the multiple of laser powder deposition spots. The filler alloy is different than the non-fusion weldable base alloy. 
     In a further embodiment of the present disclosure, the method includes forming a wall that surrounds the cavity at an incline angle. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the method includes forming the incline angle at about 30 to 75 degrees. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the method includes forming the cavity with a generally rectilinear periphery. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the method includes at least partially overlaying at least one of the multiple of laser powder deposition spots onto the wall. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the method includes forming the cavity with a generally rectilinear periphery. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the method includes laser powder deposition forming each of the multiple of laser powder deposition spots to a diameter of about 1.16 mm (0.045 inches). 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the method includes at least partially overlapping each of the multiple of laser powder deposition spots by about 0.7 mm (0.028 inches). 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the non-fusion weldable base alloy is a high gamma prime nickel based alloy. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the non-fusion weldable base alloy is a polycrystalline cast nickel base superalloy. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the filler alloy is PWA 795 and the non-fusion weldable base alloy is MAR-M 247. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the method includes applying a non-fusion weldable base alloy cap at least partially within the cavity and over the filler alloy. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the method includes electro-spark depositing the non-fusion weldable base alloy cap. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the method includes applying a coating over the non-fusion weldable base alloy. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the non-fusion weldable base alloy cap is about 0.010 inches (0.25 mm) thick. 
     A cast component for a gas turbine engine, according to another disclosed non-limiting embodiment of the present disclosure, includes a non-fusion weldable base alloy with a cavity filled with a multiple of layers of a multiple of laser powder deposition spots formed of a filler alloy. Each of the multiple of laser powder deposition spots at least partially overlaps at least another of the multiple of laser powder deposition spots. The filler alloy is different than the non-fusion weldable base alloy. A non-fusion weldable base alloy cap is at least partially within the cavity and over the filler alloy. 
     A further embodiment of any of the foregoing embodiments of the present disclosure, the filler alloy is PWA 795 and the non-fusion weldable base alloy is MAR-M 247. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, each of the multiple of laser powder deposition spots are of a diameter of about 1.16 mm (0.045 inches) and overlap at least one other of the multiple of laser powder deposition spots by about 0.7 mm (0.028 inches). 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the non-fusion weldable base alloy cap is about 0.010 inches (0.25 mm) thick. 
     In a further embodiment of any of the foregoing embodiments of the present disclosure, the component is a portion of a mid-turbine frame. 
     The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiments. The drawings that accompany the detailed description can be briefly described as follows: 
         FIG. 1  is a schematic cross-section of an example gas turbine engine architecture; 
         FIG. 2  is an exploded view of a Mid-Turbine Frame module; 
         FIG. 3  is a perspective view of a Mid-Turbine Frame vane singlet as an example workpiece that has a casting defect; 
         FIG. 4  is an expanded cross-sectional view of a casting defect in a cast component; 
         FIG. 5  is a flowchart illustrating a method to rework a cast component according to one disclosed non-limiting embodiment; 
         FIG. 6  is an expanded cross-sectional view of one step to rework a casting defect in the cast component; 
         FIG. 7  is a top down view of a cavity formed to remove the casting defect; 
         FIG. 8  is an expanded cross-sectional view of one step to rework a casting defect in the cast component according to another disclosed non-limiting embodiment; 
         FIG. 9  is an expanded cross-sectional view illustrating one step of a filler alloy being formed in the cavity to rework a casting defect in the cast component; 
         FIG. 10  is a top down view of a cavity illustrating one layer of a multiple of laser powder deposition spots of a filler alloy being formed in the cavity; 
         FIG. 11  is an expanded cross-sectional view of a filler alloy application step to rework a casting defect in the cast component; 
         FIG. 12  is an expanded cross-sectional view of a non-fusion weldable base alloy cap one step to rework a casting defect in the cast component; 
         FIG. 13  is an expanded cross-sectional view of a blending step to rework a casting defect in the cast component; and 
         FIG. 14  is an expanded cross-sectional view of a coating step to rework a casting defect in the cast component. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbo fan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . The fan section  22  drives air along a bypass flowpath and into the compressor section  24 . The compressor section  24  drives air along a core flowpath for compression and communication into the combustor section  26 , which then expands and directs the air through the turbine section  28 . Although depicted as a turbofan in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines such as a turbojets, turboshafts, three-spool (plus fan) turbofans with an intermediate spool as well as industrial gas turbines. 
     The engine  20  generally includes a low spool  30  and a high spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine case assembly  36  via several bearing structures  38 . The low spool  30  generally includes an inner shaft  40  that interconnects a fan  42 , a low pressure compressor (“LPC”)  44  and a low pressure turbine (“LPT”)  46 . The inner shaft  40  may drive the fan  42  directly or through a geared architecture  48  (see  FIG. 1 ) to drive the fan  42  at a lower speed than the low spool  30 . An exemplary reduction transmission is an epicyclic transmission, namely a planetary or star gear system. 
     The high spool  32  includes an outer shaft  50  that interconnects a high pressure compressor (“HPC”)  52  and a high pressure turbine (“HPT”)  54 . A combustor  56  is arranged between the HPC  52  and the HPT  54 . The inner shaft  40  and the outer shaft  50  are concentric and rotate about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
     Core airflow is compressed by the LPC  44  then the HPC  52 , mixed with the fuel and burned in the combustor  56 , then expanded over the HPT  54  and the LPT  46 . The LPT  46  and HPT  54  rotationally drive the respective low spool  30  and high spool  32  in response to the expansion. The main engine shafts  40 ,  50  are supported at a plurality of points by the bearing structures  38  within the engine case assembly  36 . 
     The engine case assembly  36  generally includes a plurality of modules, including a fan case module  60 , an intermediate case module  62 , a Low Pressure Compressor (LPC) module  64 , a High Pressure Compressor (HPC) module  66 , a diffuser module  68 , a High Pressure Turbine (HPT) module  70 , a mid-turbine frame (MTF) module  72 , a Low Pressure Turbine (LPT) module  74 , and a Turbine Exhaust Case (TEC) module  76 . It should be understood that additional or alternative modules might be utilized to form the engine case assembly  36 . 
     With reference to  FIG. 2 , the MTF module  72  generally includes an outer turbine case  80 , a mid-turbine frame (MTF)  82  which defines a plurality of hollow vanes  84 , a plurality of tie rods  86 , a multiple of tie rod nuts  88 , an inner case  90 , a HPT seal  92 , a heat shield  94 , a LPT seal  96 , a multiple of centering pins  98  and a borescope plug assembly  100 . The MTF module  72  supports a compartment  38  through which the inner and the outer shafts  40  and  50  are rotationally supported. It should be appreciated that various other components may additionally or alternatively be provided within the MTF  82 , for example only, the LPT seal  96  may alternatively be referred to as an intermediate seal in other engine architectures. 
     Each of the tie rods  86  are mounted to the inner case  90  and extend through a respective vanes  84  to be fastened to the outer turbine case  80  with the multiple of tie rod nuts  88 . That is, each tie rod  86  is typically sheathed by a vane  84  through which the tie rod  86  passes. The other vanes  84  may alternatively or additionally provide other service paths. The multiple of centering pins  98  are circumferentially distributed between the vanes  84  to engage bosses  102  on the MTF  82  to locate the MTF  82  with respect to the inner case  90  and the outer turbine case  80 . It should be understood that various attachment arrangements may alternatively or additionally be utilized. 
     With reference to  FIG. 3 , the MTF  82  in one disclosed non-limiting embodiment is manufactured of a multiple of cast singlets  110  (one shown). The multiple of singlets  110  are brazed together to define a ring-vane-ring configuration in which an inner platform  112  is spaced from an outer platform  114  by the multiple of vanes  84 . Alternatively, the MTF  82  may be cast as a unitary component. The MTF  82  in this example is manufactured of a high gamma prime nickel based alloy such as MAR-M 247 polycrystalline cast nickel base superalloy. It should be appreciated that the MAR-M 247 polycrystalline cast nickel base superalloy is utilized in this example as the non-fusion weldable base alloy with the MTF  82  as the workpiece, however, other non-fusion weldable base alloys and other cast workpieces will also benefit herefrom. 
     In some components, even under normal acceptable manufacture, the casting process may result in the formation of casting defects (illustrated schematically by area D; also shown in  FIG. 4 ). Each casting defect is typically less than about 1 inch (25 mm) in size. It should be appreciated that various casting defect sizes and locations will benefit herefrom. Furthermore, various cast nickel based alloys may be reworked, repaired or remanufactured in accordance to the disclosed method. 
     With reference to  FIG. 5 , one disclosed non-limiting embodiment of a rework method  200  initially includes removal of the casting defect D (see  FIG. 4 ) such as through machining, grinding or other operation (step  202 ; see  FIGS. 6 and 7 ). Removal of the casting defect D forms a cavity C. Removal of the casting defect D may be performed to form a wall W around the periphery of the cavity C at a specific incline angle α. In one example, the incline angle may be about 30 to 75 degrees. It should be appreciated that the cavity C may define a circular, rectilinear (see  FIG. 8 ) or other periphery. 
     In another disclosed non-limiting embodiment, removal of a casting defect may result in a through hole CH (see  FIG. 8 ). Again, an incline angle of the wall W that surrounds the cavity C may define an incline angle within about 30 to 75 degrees. A backing P such as a metal plate closes the through hole CH (see  FIG. 8 ). The thickness of the backing can be as thin as about 0.003 inches (0.08 mm) and temporarily mechanically attached to the workpiece such as by a clamp. The backing P is removed after the rework. 
     Next, a laser powder deposition system  300  (illustrated schematically in  FIG. 9 ) is utilized to deposit a filler alloy F of an alloy powder as discrete laser powder deposition spots S in the cavity C (see  FIG. 10 ). Laser powder deposition processes are methods with which metal powder is injected into the focused beam of a high-power laser under controlled atmospheric conditions. The focused laser beam melts the surface of the target material and generates a small molten pool of base material. Powder delivered into this same spot S is absorbed into the melt pool, thus generating a spot S that may, for example, range from about 0.005 to 0.040 inch (0.127 mm-1 mm) thick and 0.040 to 0.160 inch (1 mm-4.1 mm) wide. In one disclosed non-limiting embodiment the laser powder deposition system  300  is mounted to an automated end effector adapted to direct the focused laser beam and metal powder injection in a known orientation relative to the surface of the workpiece. It should be appreciated that the automated end effector, the workpiece, or both can be tilted or otherwise adjusted during the process to obtain a desired angle, however, even if the angle is changed during the process, an angle greater than about 15 degree may still be required for the laser energy to be effectively absorbed. 
     The cavity C is filled with a multiple of layers of a multiple of laser powder deposition spots S applied with the laser powder deposition system  300  generally at room temperature. In one example, each laser powder spot S overlays the adjacent laser powder deposition spots S by about 50%. That is, the multiple of laser powder deposition spots S in each layer form a matrix of overlapping laser powder deposition spots S. The outer most laser powder deposition spots S are located at least partially on the wall W. That is, the incline angle of the wall W permits each layer to at least partially overlap the wall W as well as permit the laser from the laser powder deposition system  300  direct access into the cavity C. It should be appreciated that the incline angle may be at least partially adjusted by adjusting the angle of incidence of the laser beam to the workpiece. In one disclosed non-limiting embodiment the laser powder deposition system  300  is mounted to an automated end effector adapted to direct the focused laser beam and metal powder injection in a known orientation relative to the surface of the workpiece. It should be appreciated that the automated end effector, the workpiece, or both can be tilted or otherwise adjusted during the process to obtain a desired angle, however, even if the angle is changed during the process, an angle greater than about 15 degree may still be required for the laser energy to be effectively absorbed. 
     Additional layers of laser powder deposition spots S are progressively applied to at least partially fill the cavity C (see  FIG. 11 ). That is, although each spot S is generally equivalent, a greater number of laser powder deposition spots are typically applied in each layer so as to fill the cavity C. When each subsequent layer of the laser powder deposition spots S is applied, the laser to layer distance may also be adjusted to ensure that the laser to layer distance is maintained generally constant so that the laser power and powder quantity per spot S is generally maintained constant. The metal powder may be an alloy with a matched composition or under-matched composition to include, but not be limited to, Hastelloy X, PWA 795, MERL 72, Alloy 625 and others. 
     In one specific disclosed non-limiting embodiment, a cavity C in a MTF  82  workpiece manufactured of a non-fusion weldable base alloy B of MAR-M 247 polycrystalline cast nickel base superalloy is filled with a filler alloy F of PWA 795. That is, the non-fusion weldable base alloy of the workpiece is of one material while the filler alloy F is of a different material. 
     If an application requires the use of a matching alloy at the surface to meet a required material property, a layer of non-fusion weldable base alloy BC may optionally be applied at least partially within the cavity C and over the filler alloy F (step 206 ; see  FIG. 12 ). That is, the non-fusion weldable base alloy B of the workpiece is utilized to cover or cap the cavity C that is primarily filled with the filler alloy F. In this example, the cap of non-fusion weldable base alloy BC is MAR-M 247 that is electro-spark deposited to completely fill the cavity C. In this example, the cap of non-fusion weldable base alloy BC may be about 0.010 inches (0.25 mm) thick. It should be appreciated that the cap of non-fusion weldable base alloy BC is not always necessary. 
     Electro-spark deposition may also be referred to as “spark hardening”, “electrospark toughening” or “electrospark alloying. It should be appreciated that other techniques may be utilized as, since only a relatively thin cap of non-fusion weldable base alloy BC is applied, a relatively slow technique is still readily utilized. That is, a technique that may otherwise be too slow and expensive to fill the entire cavity C, is readily utilized to form the thin cap of non-fusion weldable base alloy B. 
     Once the cavity C is filled or at least partially filled with a multiple of layers of the multiple of laser powder deposition spots S and the optional cap of non-fusion weldable base alloy BC is applied, the filler alloy F may be post weld treated (step  208 ). Examples of post weld treatment include, but are not limited to, heat treatment, hot isostatic pressing, and/or others. 
     Next, the multiple of laser powder deposition spots S and/or cap of non-fusion weldable base alloy BC may be blended into the workpiece to form a desired profile (step  210 ; see  FIG. 13 ). That is, the cap of non-fusion weldable base alloy BC results in contiguous surface of the common non-fusion weldable base alloy B over the cavity C. 
     Finally, as the cap of non-fusion weldable base alloy BC provides the contiguous surface, the workpiece may be readily coated with a coating T (see  FIG. 14 ). That is, the cap of non-fusion weldable base alloy BC is fully compatible with an oxidation, thermal barrier or other coating T tailored to the non-fusion weldable base alloy BC such that full benefit thereof is received. 
     The method may reduce the typical repair time down from several hours to, for example, several minutes. This reduces the overall expense to cast components of high gamma prime nickel based alloy such as MAR-M 247 polycrystalline cast nickel base superalloy as well as the repair and remanufacture of other nickel alloy castings. 
     The use of the terms “a” and “an” and “the” and similar references in the context of description (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or specifically contradicted by context. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. It should be appreciated that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting. 
     Although the different non-limiting embodiments have specific illustrated components, the embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments. 
     It should be appreciated that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be appreciated that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. 
     Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure. 
     The foregoing description is exemplary rather than defined by the features within. Various non-limiting embodiments are disclosed herein; however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be appreciated that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.