Abstract:
The application of a peripheral weld before the removal of material produces an enlarged face for the subsequent build-up welding. A process for build-up welding on an outer face having an edge region of a component which is adjoined by a side face is provided. Material is removed to create the outer face but before the material is removed a peripheral weld is effected on the side

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to European Patent Office application No. 12191770.2 EP filed Nov. 8, 2012, the entire content of which is hereby incorporated herein by reference. 
       FIELD OF INVENTION 
       [0002]    The invention relates to the preparation of a face to be welded by weld pool backing at the edge region. 
       BACKGROUND OF INVENTION 
       [0003]    A successful, uniform build-up of a feathered edge and of the tip requires exact positioning (&lt;50 μm) during welding on the edge (frame contour). In laser welding, the track width is approximately 600 μm. If the edge is not positioned accurately, an undulatory build-up is obtained in the build-up direction, leading to the solidification of grains with a critical grain size (&gt;300 μm) and to cracking On account of the system technology, this small positioning accuracy cannot always be achieved. 
       SUMMARY OF INVENTION 
       [0004]    It is an object of the invention, therefore, to solve the aforementioned problem. 
         [0005]    This object is achieved by a process as claimed in the claims. 
         [0006]    The dependent claims list further advantageous measures which can be combined with one another, as desired, in order to achieve further advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIGS. 1-4  show steps of the process according to the invention, 
           [0008]      FIG. 5  shows a turbine blade or vane, 
           [0009]      FIG. 6  shows a list of superalloys. 
       
    
    
       [0010]    The figures and the description represent merely exemplary embodiments of the invention. 
       DETAILED DESCRIPTION OF INVENTION 
       [0011]      FIG. 1  shows a tip  4  of a component  1 ,  120 ,  130  ( FIG. 5 ) with an outer wall  10  and a base  7  therebetween. 
         [0012]    The base  7  has a certain thickness D, if the component  1 ,  120 ,  130  is hollow. 
         [0013]    The outer wall  10  has to be repaired since it has been corroded and/or eroded and/or abraded during use. 
         [0014]    According to the prior art, the wall  10  is simply removed and build-up welding takes place. 
         [0015]    According to the invention, before the wall  10  is cut off or material  31  is removed (indicated by dashed lines here), a weld  13  is applied to a side face  14  of the component  1 . The weld  13  begins at most, in particular at least, level with the base  7  and extends from the height of the base  7  over a certain depth h, which, in this exemplary embodiment, with a thickness D of the base  7 , must not be greater than the thickness D. 
         [0016]    In the next step, material, in particular the wall  10 , is removed in a region  31 , this preferably taking place by milling, in order to produce an outer face  28  to which the material  19  is to be applied. 
         [0017]    The material can also be removed by a laser and in the same machining apparatus. 
         [0018]    As a result of this material removal, the outer wall  10  and/or a part of the base  7  is removed, and therefore in this case the base  7  still has a thickness d≦D here. 
         [0019]    The result is the outer face  28 , which is extended, at its edge region  22  or at edges  22 , by the weld  13  which has been partially cut away, in that the weld  13 ′ has a virtually planar face  16  beyond the edge  22 . 
         [0020]    The tip  4  is then built up again by known build-up processes, in particular by laser build-up welding. Owing to the face  16 , which constitutes an overhang, welds can be made in the edge region  22  beyond the edge region  22  without welding material sinking down into the edge region  22 . Thus, there is then at least one welding bead  33  on the outer face  28  of the component  1 ,  120 ,  130  and the part of the weld  13 ′, without said welding bead  33  sinking down. Then, the base  7  is strengthened again and at least the outer wall  10  is built up again. 
         [0021]    It is necessary for the weld  13  to be present only where material is removed and applied in the edge region  22 . It can therefore also be peripheral. 
         [0022]    The component  1  is preferably a turbine blade or vane  120 ,  130  comprising, as the material, a nickel-based or cobalt-based superalloy, in particular as per  FIG. 6 . 
         [0023]      FIG. 5  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 . 
         [0024]    The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
         [0025]    The blade or vane  120 ,  130  has, in succession along the longitudinal axis  121 , a securing region  400 , an adjoining blade or vane platform  403  and a main blade or vane part  406  and a blade or vane tip  415 . 
         [0026]    As a guide vane  130 , the vane  130  may have a further platform (not shown) at its vane tip  415 . 
         [0027]    A blade or vane root  183 , which is used to secure the rotor blades  120 ,  130  to a shaft or a disk (not shown), is formed in the securing region  400 . 
         [0028]    The blade or vane root  183  is designed, for example, in hammerhead form. Other configurations, such as a fir-tree or dovetail root, are possible. 
         [0029]    The blade or vane  120 ,  130  has a leading edge  409  and a trailing edge  412  for a medium which flows past the main blade or vane part  406 . 
         [0030]    In the case of conventional blades or vanes  120 ,  130 , by way of example solid metallic materials, in particular superalloys, are used in all regions  400 ,  403 ,  406  of the blade or vane  120 ,  130 . 
         [0031]    Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949. 
         [0032]    The blade or vane  120 ,  130  may in this case be produced by a casting process, by means of directional solidification, by a forging process, by a milling process or combinations thereof. 
         [0033]    Workpieces with a single-crystal structure or structures are used as components for machines which, in operation, are exposed to high mechanical, thermal and/or chemical stresses. 
         [0034]    Single-crystal workpieces of this type are produced, for example, by directional solidification from the melt. This involves casting processes in which the liquid metallic alloy solidifies to form the single-crystal structure, i.e. the single-crystal workpiece, or solidifies directionally. 
         [0035]    In this case, dendritic crystals are oriented along the direction of heat flow and form either a columnar crystalline grain structure (i.e. grains which run over the entire length of the workpiece and are referred to here, in accordance with the language customarily used, as directionally solidified) or a single-crystal structure, i.e. the entire workpiece consists of one single crystal. In these processes, the transition to globular (polycrystalline) solidification needs to be avoided, since non-directional growth inevitably forms transverse and longitudinal grain boundaries, which negate the favorable properties of the directionally solidified or single-crystal component. 
         [0036]    Where the text refers in general terms to directionally solidified microstructures, this is to be understood as meaning both single crystals, which do not have any grain boundaries or at most have small-angle grain boundaries, and columnar crystal structures, which do have grain boundaries running in the longitudinal direction but do not have any transverse grain boundaries. This second form of crystalline structures is also described as directionally solidified microstructures (directionally solidified structures). 
         [0037]    Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1. 
         [0038]    The blades or vanes  120 ,  130  may likewise have coatings protecting against corrosion or oxidation, e.g. (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon and/or at least one rare earth element, or hafnium (Hf)). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. 
         [0039]    The density is preferably 95% of the theoretical density. 
         [0040]    A protective aluminum oxide layer (TGO=thermally grown oxide layer) is formed on the MCrAlX layer (as an intermediate layer or as the outermost layer). 
         [0041]    The layer preferably has a composition Co-30Ni-28Cr-8Al-0.6Y-0.7Si or Co-28Ni-24Cr-10Al-0.6Y. In addition to these cobalt-based protective coatings, it is also preferable to use nickel-based protective layers, such as Ni-10Cr-12A1-0.6Y-3Re or Ni-12Co-21Cr-11Al-0.4Y-2Re or Ni-25 Co-17Cr-10Al-0.4Y-1.5Re. 
         [0042]    It is also possible for a thermal barrier coating, which is preferably the outermost layer and consists for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, to be present on the MCrAlX. 
         [0043]    The thermal barrier coating covers the entire MCrAlX layer. 
         [0044]    Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0045]    Other coating processes are possible, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may include grains that are porous or have micro-cracks or macro-cracks, in order to improve the resistance to thermal shocks. The thermal barrier coating is therefore preferably more porous than the MCrAlX layer. 
         [0046]    Refurbishment means that after they have been used, protective layers may have to be removed from components  120 ,  130  (e.g. by sand-blasting). Then, the corrosion and/or oxidation layers and products are removed. If appropriate, cracks in the component  120 ,  130  are also repaired. This is followed by recoating of the component  120 ,  130 , after which the component  120 ,  130  can be reused. 
         [0047]    The blade or vane  120 ,  130  may be hollow or solid in form. If the blade or vane  120 ,  130  is to be cooled, it is hollow and may also have film-cooling holes  418  (indicated by dashed lines).