Abstract:
A substrate ( 4 ) is remelted prior to deposition welding, thereby substantially reducing stresses in the region of the interface between the deposition welded portion ( 13 ) and the substrate ( 4 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a 35 U.S.C. §§ 371 national phase conversion of PCT/EP2014/050295, filed Jan. 9, 2014, which claims priority of European Application No. 13151888.8, filed Jan. 18, 2013, the contents of which are incorporated by reference herein. The PCT International Application was published in the German language. 
         [0002]    The invention relates to a deposition welding method, in which an at least partial remelting is carried out beforehand in the region of that surface on which the material is deposited. 
     
    
     TECHNICAL BACKGROUND 
       [0003]    Remelting methods for closing cracks and deposition welding methods in order to compensate for a loss of material or to build up structure on a surface are known from the prior art. Also known is the use of a laser in the context of these methods. 
         [0004]    It is also known from the prior art to remelt column-solidified substrates or single-crystal substrates, wherein the latter occur in nickel-based superalloys of turbine blades. However, the edge region of the weld often experiences increased stresses between the substrate and the deposited region. 
         [0005]    The invention therefore has the object of solving the above-mentioned problem. 
         [0006]    Advantageous measures, which may be combined with one another in any desired manner in order to achieve further advantages, are disclosed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    In the figures: 
           [0008]      FIG. 1  shows a substrate, 
           [0009]      FIG. 2  shows a substrate with a remelted region, 
           [0010]      FIG. 3  shows a substrate according to  FIG. 2  with a deposition weld, 
           [0011]      FIGS. 4-7  show exemplary embodiments for the remelted region, 
           [0012]      FIG. 8  is a list of superalloys. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0013]    The figures and the description represent exemplary embodiments of the invention. 
         [0014]      FIG. 1  shows a known substrate  4  which is to be worked. The substrate  4  is preferably metallic and very preferably includes a cobalt-based or nickel-based superalloy, such as is in particular listed in  FIG. 8 . 
         [0015]    The substrate  4  can have a single-crystal, column-solidified or polycrystalline structure. 
         [0016]    A columnar structure has grain boundaries which are often encompassed by a deposition weld. 
         [0017]    A material  13  ( FIG. 3 ) is to be applied to a surface region  8  ( FIG. 2 ) of the surface  22  by means of deposition welding. 
         [0018]    In order to prepare this deposition weld, a remelt method is carried out beforehand in at least part of the surface region  8  which is to be welded. 
         [0019]    This remelt is effected by means of a high-energy beam, such as a welding beam  10  ( FIG. 2 ), in particular a laser beam  10 , which generates a remelt region  7  within and to a selected depth in the substrate  4 , and generates small grains. 
         [0020]    In this remelt process, no material is applied. This remelt process is preferably carried out in its entirety prior to the deposition welding. 
         [0021]    After the remelting has been carried out, a deposition weld  13  is applied over the remelted region  7 , as shown in  FIG. 3 . 
         [0022]    This can be effected in a great many ways, in particular by means of a laser deposition welding process. 
         [0023]    The remelt region  7  on which the deposition welding  13  is carried out can be remelted entirely and preferably in an exactly-fitting manner ( FIG. 7 ), and preferably somewhat beyond the region  7  ( FIG. 3 ). 
         [0024]    It is however also possible to carry out the remelting only at certain points within the surface region  8  in which the deposition weld  13  is to be generated. 
         [0025]    This is the case e.g. in column-solidified grains, for example in  FIG. 5 , in which a clear number of grain boundaries  19 ′,  19 ″ are present in the surface region  8  to be deposition welded, and wherein the remelt method is carried out preferably only along the grain boundaries  19 ′,  19 ″. Thus, a remelt region  7 ′,  7 ″ preferably encloses only grain boundaries  19 ′,  19 ″. 
         [0026]    One or more grain boundaries can be present in the surface region  8  to be deposition welded. 
         [0027]    As shown in  FIG. 6 , it is also possible to remelt only along the outer contour  22  of the surface region  8  of the remelt region  7 ,  7 ′, such that here a border of the surface region  8  of the deposition weld represents the remelt region  7 ,  7 ′. 
         [0028]    The procedures of  FIG. 5  and  FIG. 6  can also be combined . 
         [0029]    Polycrystalline or directionally solidified substrates  4  can be remelted in polycrystalline and, where relevant, in a directionally solidified fashion. 
         [0030]    Equally, the method can be used if a pool crater  16  or a depression  16  has to be filled. In that case, the bottom of the pool crater  16  is then remelted ( FIG. 4 ) 
         [0031]    forming a remelted region  7 ′. Equally, in the pool crater  16 , it is possible for only grain boundaries  19 ′,  19 ″ to be remelted as shown in  FIG. 5 . 
         [0032]    The surface region  8  preferably includes no cracks prior to remelting. 
         [0033]    Should cracks be present, they are preferably additionally closed separately beforehand, and in particular, preferably remelted and filled, before the method according to the invention is carried out. 
         [0034]    The surface region  8  which is remelted, including also with cracks which have or have not been closed, is larger than the surface of a remelted crack, i.e. at least 200% larger. 
         [0035]    The deposition welding  13  stands above the surface  22 , and in particular markedly so. It therefore does not serve to even out a pool crater with respect to the surface  22 . In  FIG. 2 , the surface  22  represents the bottom of the depression  16 . 
         [0036]    By virtue of the procedure as shown in  FIGS. 3 to 7 , stresses in the transition between the deposition weld  13  and the surface  22 , in particular in the transition region in the region of the edges, are markedly reduced.