Abstract:
The susceptibility of cracking in the region of the edges ( 16 ) is prevented in a modified application process in the region of the edge, which surrounds a surface ( 13 ) which is to be welded, due to the use of a wider track of material or a different material for the external contour welding ( 2 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a 35 U.S.C. §§371 national phase conversion of PCT/EP2014/050584, filed Jan. 14, 2014, which claims priority of European Application No. 13151995.1, filed Jan. 21, 2013, the contents of which are incorporated by reference herein. The PCT International Application was published in the German language. 
       TECHNICAL FIELD 
       [0002]    The invention relates to deposition welding on a surface. 
       TECHNICAL BACKGROUND 
       [0003]    Deposition welding methods, in particular laser deposition welding methods, are known from the prior art and are used in particular also in the context of turbine blades in order to build up the blade tip with its contour over an entire surface or in the shape of walls of the blades. 
         [0004]    The rim region still represents a critical point, in both the context of the deposition welding and the tendency to cracks, since it is a transition from the material to the air. 
         [0005]    It is therefore an object of the present invention to solve the problem mentioned above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  shows a substrate in cross section, 
           [0007]      FIG. 2  shows a view of a welded face, 
           [0008]      FIG. 3  shows a turbine blade. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0009]    The figures and the description represent only exemplary embodiments of the invention. 
         [0010]      FIG. 1  shows a cross section through a substrate  7 , in which a deposition weld is already partially present. 
         [0011]    In particular, the region of the edge  19  of the substrate  7 , in this case preferably a blade tip, represents a critical region. 
         [0012]    For that reason, an outer contour weld  2  is first laid or applied. 
         [0013]    The outer contour weld  2  preferably is comprised of a different first welding material  16  than are the plurality of the inner welding tracks  10  which are comprised of a second welding material  11 . 
         [0014]    The outer contact weld is broader than the inner welding tracks  10 . Preferably, the breadth of the outer contact weld is at least 50% greater than the breadth of each of the inner welding tracks  10 . The outer contact weld preferably has only one welding track. 
         [0015]    Being of a different material means that at least one alloy fraction of a first welding material  16  differs by at least 20% from that of the second welding material  11 . 
         [0016]    Along the edge  19  of a face of a substrate to be welded, a material is used for the outer contact weld which is less prone to hot cracking. 
         [0017]    Inside this outer contour weld  2 , a deposition weld is then created in the face  13  therebetween, using a different welding material  11  which is closer to the mechanical properties of the substrate  7  than the material of the contour weld  2  and is more prone to cracking. 
         [0018]    Alternatively, the outer contour weld  2  can be generated using the same material as the material  11 , but the contour weld is substantially broader overall than the inner welding tracks  10 . 
         [0019]    Preferably, the outer contour weld  2  also projects over the corner or edge  19 . 
         [0020]      FIG. 2  shows a view of such a weld, in which the thick line represents the outer contour weld  2  which is laid all around the periphery of the face  13  to be welded, that is the weld  2  runs all along an edge  19  and here encloses a blade airfoil profile. In that context, multiple welding tracks  10 , made in any desired shape, are present in addition to the first material. 
         [0021]    Equally, different welding materials can be used for the outer contour weld  2  and the inner welding tracks  10 , and a broader outer contour weld  2 . 
         [0022]    The outer contour weld  2  represents a single welding track or welding bead. 
         [0023]      FIG. 3  shows a perspective view of a movable blade  120  or stationary blade  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  120 ,  130  has, in succession along the longitudinal axis  121 , a securing region  400 , an adjoining blade platform  403  and a blade airfoil  406  and a blade tip  415 . 
         [0026]    As a stationary blade  130 , the blade  130  may have a further platform (not shown) at its blade tip  415 . 
         [0027]    A blade root  183 , which is used to secure the movable blades  120 ,  130  to a shaft or a disk (not shown), is formed in the securing region  400 . 
         [0028]    The blade root  183  is designed, for example, in hammerhead form. Other configurations, such as a fir-tree or dovetail root, are possible. 
         [0029]    The blade  120 ,  130  has a leading edge  409  and a trailing edge  412  for a medium which flows past the blade airfoil  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  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. 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, a 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. 
         [0035]    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 structures. 
         [0036]    Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1. 
         [0037]    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. 
         [0038]    The density is preferably 95% of the theoretical density. 
         [0039]    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). 
         [0040]    The layer preferably has a composition Co-30Ni-28Cr-8Al-0.6Y-0.75i 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-12Al-0.6Y-3Re or Ni-12Co-21Cr-11Al-0.4Y-2Re or Ni-25Co-17Cr-10Al-0.4Y-1.5Re. 
         [0041]    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. it is unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, to be present on the MCrAlX. 
         [0042]    The thermal barrier coating covers the entire MCrAlX layer. Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0043]    Other coating processes are possible, e.g. 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. 
         [0044]    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. 
         [0045]    The blade  120 ,  130  may be hollow or solid in form. If the blade  120 ,  130  is to be cooled, it is hollow and may also have film-cooling holes  418  (indicated by dashed lines).