Abstract:
A method is provided for welding a substrate, in which an energy source and/or a material feed is or are moved in an oscillating motion over the surface of the substrate. The oscillating movement in a vertical and/or horizontal direction during welding results in smaller grains, which prevent the formation of fractures during welding.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to PCT Application No. PCT/EP2014/053389, having a filing date of Feb. 21, 2014, based off of DE Application No. 102014200834.4 having a filing date of Jan. 17, 2014, the entire contents of which are hereby incorporated by reference. 
     
    
     FIELD OF TECHNOLOGY 
       [0002]    The following relates to a welding method in which the welding beam is moved in oscillation. 
       BACKGROUND 
       [0003]    During the laser deposition welding of nickel-based superalloys having a high proportion of metallic phase γ′, hot cracks can already form during solidification of the melt. By reducing the beam diameter of the laser with a circular intensity distribution, smaller grains are achieved and solidification cracks can be avoided, but this reduces the rate of deposition of the material. 
       SUMMARY 
       [0004]    An aspect relates to a welding method which makes it possible to achieve small grains and high deposition rates. 
         [0005]    An oscillating motion in the horizontal direction should cause the solidification front to change constantly so as to produce an oscillating solidification form. As a result of a constantly changing solidification function, the grain growth is interrupted during the solidification of the melt and the microstructure solidifies in fine-grained form. The fine-grained quality of the microstructure causes the welding residual stresses which thus remain to be distributed over the grain boundaries so as to avoid cracks in the weld seam or in the weld metal. 
         [0006]    The welding method can be remelting or deposition welding. Both methods produce a melt and a solidification front. 
     
    
     
       BRIEF DESCRIPTION 
         [0007]    Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein: 
           [0008]      FIG. 1  shows an arrangement for welding; and 
           [0009]      FIGS. 2-4  show the sequence of the oscillating motion. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    The figures and the description represent only exemplary embodiments of the invention. 
         [0011]      FIG. 1  shows a device  1  for a welding method, in particular a laser welding method, on the basis of which embodiments of the invention will be explained in a non-limiting manner. 
         [0012]    The method is thus not limited to laser welding methods, but is also applicable for electron beam welding methods and other plasma welding methods with corresponding energy sources. 
         [0013]    Material  8  is deposited onto a substrate  3 , which, in the case of turbine blades or vanes, is a nickel-based or cobalt-based superalloy having a high γ′ proportion and therefore generally an alloy having poor weldability. 
         [0014]    A welding bead  6 , as part of the deposition weld, has already been generated. 
         [0015]    In the case of a remelt method, the welding bead is the remelted region. 
         [0016]    At those points where a laser, as an exemplary energy source  13 , directs the laser beams  15  ( FIG. 2 ) thereof onto the substrate  3 , there is a melt pool  7 . 
         [0017]    A powder nozzle, as the material feed  14 , preferably feeds powder  8 , with the powder  8  being melted, in this case by laser radiation  15 . The material  8  is fed in the form of powder, but may also be fed as a wire. This laser radiation  15  is in particular pulsed. 
         [0018]    The area to be welded is made up of a plurality of welding beads lying next to one another and if appropriate one above another and preferably has, in at least one direction, a length of greater than or equal to 4 mm. 
         [0019]      FIGS. 2, 3 and 4  show the for example triangular  44 ;  31 ,  34 ;  43 ,  49 ,  55  oscillating motion of the laser radiation  15 . 
         [0020]    The oscillating motion is preferably affected only in one plane. 
         [0021]    The triangular shape  44 ;  31 ,  34 ;  43 ,  49 ,  55  is preferably an acute-angled triangle, with a height (in the direction of movement  2 ) of the triangular shape  44  preferably being at least twice the magnitude of the base  24 . 
         [0022]    An oscillating motion preferably proceeds as follows: 
         [0000]    From a first starting point  21  ( FIG. 2 ), the laser radiation  15  moves counter to the direction of movement  2  at an angle with respect to the direction of movement  2  as far as a first deflection point  22 , where the laser radiation  15  is then moved perpendicularly with respect to the direction of movement  2  in a direction  24  as far as a second deflection point  23 . 
         [0023]    In order that the laser radiation  15  continues to move along as a whole in the direction of movement  2 , it then moves obliquely with respect to the direction of movement  2  in the direction of movement  2  in a first oblique direction  30  ( FIG. 3 ) to a second starting point  31 , which lies downstream of the first deflection point  22  in the direction of movement  2 . The second starting point  31  is level with the first deflection point  22 , displaced by a distance  4 . 
         [0024]    From there, the laser radiation  15  then moves forward again as far as a third deflection point  33 . The third deflection point  33  lies downstream of the first starting point  21  in the direction of movement  2 . A connecting line between points  21 ,  33  is parallel to the direction of movement  2 . From there, the laser radiation  15  oscillates again at an angle with respect to the direction of movement  2  counter to the direction of movement  2  as far as a fourth deflection point  34 . 
         [0025]    The fourth deflection point  34  is level with the second starting point  31  in a perpendicular direction with respect to the direction of movement  2  and level with the second deflection point  23  in the direction of movement  2 . 
         [0026]    In a second perpendicular direction of movement  36  which is perpendicular with respect to the direction of movement  2 , the laser radiation  15  moves back to the second starting point  31  of the triangular oscillating motion ( FIG. 3 ). 
         [0027]    The further triangular oscillating motion proceeding from  FIG. 3  can then be identified in  FIG. 4 , in which the laser radiation  15  oscillates in a second oblique direction  40  with respect to the direction of movement  2  in the direction of movement  2  to the seventh deflection point  55 . The seventh deflection point  55  is level with the point  34 . From there, the laser radiation  15  then moves in the direction of the third deflection point  33  to a fifth deflection point  43 , which lies downstream of the deflection point  33  as shown in  FIG. 3 . 
         [0028]    From the fifth deflection point  43 , the laser radiation  15  moves obliquely with respect to the direction of movement  2  counter to the direction of movement  2  in a third rearward motion  46  as far as a sixth deflection point  49 . From the sixth deflection point  49 , the laser radiation  15  oscillates perpendicularly with respect to the direction of movement  2  to the seventh deflection point  55 . 
         [0029]    Effectively, a triangular shape is always displaced in the direction of movement  2  for the course of the laser radiation  15 , such that the triangular shapes overlap. 
         [0030]    This represents only one procedure for the preferably triangular oscillation. 
         [0031]    On account of embodiments of the invention, this procedure achieves improved material properties. 
         [0032]    Although the present embodiments of has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. 
         [0033]    For the sake of clarity, it is to be understood that the use of ‘a’ or ‘an’ throughout this application does not exclude a plurality, and ‘comprising’ does not exclude other steps or elements.