Abstract:
A combined welding and soldering process for a structural part and a structural part are provided. The combined welding and soldering process can achieve joints which are stable at high temperatures between the components. All contacts between the components can be joined to one another optionally in accordance with their loading.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of European application No. 11186178.7 filed Oct. 21, 2011, which is incorporated by reference herein in its entirety. 
       FIELD OF INVENTION 
       [0002]    The application relates to a welding and/or soldering process for producing a structural part and to a structural part. 
       BACKGROUND OF INVENTION 
       [0003]    Soldering or welding processes for joining structural parts are prior art, soldered joints usually having a lower temperature resistance compared to the base material and also compared to welded joints on account of the relatively low melting temperature of the solder. However, soldered joints can also be produced at sites which are difficult to access. The welding process can only be carried out at sites which are easily accessed. 
       SUMMARY OF INVENTION 
       [0004]    It is an object of the application to produce a structural part from components which are joined to one another in an optimum manner. 
         [0005]    The object is achieved by a process and a structural part as claimed in the independent claims. The dependent claims list further measures which can be combined with one another, as desired, in order to achieve further features. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    In the drawings: 
           [0007]      FIGS. 1-4  show steps of the process according to the application, 
           [0008]      FIG. 5  shows a turbine blade or vane, 
           [0009]      FIG. 6  shows a gas turbine, 
           [0010]      FIG. 7  shows a list of superalloys. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0011]    The figures and the description represent merely embodiments of the application. 
         [0012]      FIG. 1  shows a structural part  1 ,  120 ,  130  which is to be produced and is to be joined together from at least two, such as from only two, components  4 ,  7 . 
         [0013]    The structural part  1 ,  120 ,  130  to be produced is a hollow structural part  1 ,  120 ,  130  having at least one hollow space  2 ′,  2 ″,  2 ′″ and has outer contact sites  11 ′,  11 ″, . . . accessible from the outside, but also on the inside inner contact sites  14 ′,  14 ″, . . . which are not accessible from the outside, at which components  4 ,  7  are moved into contact resting on one another. A solder  15 ′,  15 ″, . . . is applied to the inner contact sites  14 ′,  14 ″, . . . . 
         [0014]    In this case, a spacing  10 ′,  10 ″, . . . is to be provided in the region of the outer contact sites  11 ′,  11 ″, . . . between the components  4 ,  7  when the solder  15 ′,  15 ″, . . . is applied. 
         [0015]    The components  4 ,  7  are then pressed together (F) such that the spacing  10 ′,  10 ″, . . . as per  FIG. 1  is no longer present or is/becomes considerably smaller ( FIG. 2 ). While maintaining a force F, a welded joint or weld seam  16 ′,  16 ″ is produced at the outer contact sites ( FIG. 3 ) such that the components  4 ,  7  are already joined to one another. 
         [0016]    The welded joint  16 ′,  16 ″ can also be a continuous weld seam which, such as, runs around the entire structural part  1 ,  120 ,  130 . 
         [0017]    In the last step, as per  FIG. 4 , heat treatment is effected, such that only then a soldered joint  19 ′,  19 ″ is produced at the inner contact sites  14 ′,  14 ″, . . . by the already present solder  15 ′,  15 ″, . . . . The components are joined to one another at many inner and outer contact sites  11 ′,  11 ″,  14 ′,  14 ″, . . . . The solders are high-melting solders based on Ni, Ni—Co, Pd or Au or Au—Pd. 
         [0018]    The solder can be applied both in the form of solder paste and as a film or presintered solder sheet. Depending on the use of the structural part  1 ,  120 ,  130 , it has to be compatible with the base material of the components  4 ,  7 . 
         [0019]    The inner soldered joints  19 ′,  19 ″, . . . generally experience, in the case of turbine components  120 ,  130 , a lower temperature than the outer regions, where the welded joints  16 ′,  16 ″, . . . are located, and a sufficient strength of equal magnitude is provided universally. 
         [0020]    The materials for the components  4 ,  7  are nickel-based or cobalt-based superalloys as per  FIG. 7 . 
         [0021]      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 . 
         [0022]    The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
         [0023]    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 . As a guide vane  130 , the vane  130  may have a further platform (not shown) at its vane tip  415 . 
         [0024]    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 . 
         [0025]    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. 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 . 
         [0026]    In the case of conventional blades or vanes  120 ,  130 , by way of example solid metallic materials, such as superalloys, are used in all regions  400 ,  403 ,  406  of the blade or vane  120 ,  130 . 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. The blade or vane  120 ,  130  may in this case be produced by a casting process, by directional solidification, by a forging process, by a milling process or combinations thereof. 
         [0027]    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. 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. 
         [0028]    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. 
         [0029]    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). Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1. 
         [0030]    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. The density is 95% of the theoretical density. 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). 
         [0031]    The layer has a composition Co-30Ni-28Cr-8Al-0.6Y-0.75Si or Co-28Ni-24Cr-10Al-0.6Y. In addition to these cobalt-based protective coatings, it is also 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. 
         [0032]    It is also possible for a thermal barrier coating, which is the outermost layer, to be present on the MCrAlX, consisting 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. 
         [0033]    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). 
         [0034]    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 more porous than the MCrAlX layer. 
         [0035]    Refurbishment means that after they have been used, protective layers may have to be removed from structural parts  120 ,  130  (e.g. by sand blasting). Then, the corrosion and/or oxidation layers and products are removed. If appropriate, cracks in the structural part  120 ,  130  are also repaired. This is followed by recoating of the structural part  120 ,  130 , after which the structural part  120 ,  130  can be reused. 
         [0036]    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). 
         [0037]      FIG. 6  shows, by way of example, a partial longitudinal section through a gas turbine  100 . 
         [0038]    In the interior, the gas turbine  100  has a rotor  103  with a shaft  101  which is mounted such that it can rotate about an axis of rotation  102  and is also referred to as the turbine rotor. 
         [0039]    An intake housing  104 , a compressor  105 , a, for example, toroidal combustion chamber  110 , such as an annular combustion chamber, with a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust-gas housing  109  follow one another along the rotor  103 . 
         [0040]    The annular combustion chamber  110  is in communication with a, for example, annular hot-gas passage  111 , where, by way of example, four successive turbine stages  112  form the turbine  108 . 
         [0041]    Each turbine stage  112  is formed, for example, from two blade or vane rings. As seen in the direction of flow of a working medium  113 , in the hot-gas passage  111  a row of guide vanes  115  is followed by a row  125  formed from rotor blades  120 . 
         [0042]    The guide vanes  130  are secured to an inner housing  138  of a stator  143 , whereas the rotor blades  120  of a row  125  are fitted to the rotor  103  for example by a turbine disk  133 . A generator (not shown) is coupled to the rotor  103 . 
         [0043]    While the gas turbine  100  is operating, the compressor  105  sucks in air  135  through the intake housing  104  and compresses it. The compressed air provided at the turbine-side end of the compressor  105  is passed to the burners  107 , where it is mixed with a fuel. The mix is then burnt in the combustion chamber  110 , forming the working medium  113 . From there, the working medium  113  flows along the hot-gas passage  111  past the guide vanes  130  and the rotor blades  120 . The working medium  113  is expanded at the rotor blades  120 , transferring its momentum, so that the rotor blades  120  drive the rotor  103  and the latter in turn drives the generator coupled to it. 
         [0044]    While the gas turbine  100  is operating, the structural parts which are exposed to the hot working medium  113  are subject to thermal stresses. The guide vanes  130  and rotor blades  120  of the first turbine stage  112 , as seen in the direction of flow of the working medium  113 , together with the heat shield elements which line the annular combustion chamber  110 , are subject to the highest thermal stresses. To be able to withstand the temperatures which prevail there, they may be cooled by a coolant. 
         [0045]    Substrates of the structural parts may likewise have a directional structure, i.e. they are in single-crystal form (SX structure) or have only longitudinally oriented grains (DS structure). 
         [0046]    By way of example, iron-based, nickel-based or cobalt-based superalloys are used as material for the structural parts, such as for the turbine blade or vane  120 ,  130  and structural parts of the combustion chamber  110 . 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. 
         [0047]    The blades or vanes  120 ,  130  may likewise have coatings protecting against corrosion (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, scandium (Sc) and/or at least one rare earth element, or hafnium). 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. 
         [0048]    It is also possible for a thermal barrier coating to be present on the MCrAlX, consisting 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. Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0049]    The guide vane  130  has a guide vane root (not shown here), which faces the inner housing  138  of the turbine  108 , and a guide vane head which is at the opposite end from the guide vane root. The guide vane head faces the rotor  103  and is fixed to a securing ring  140  of the stator  143 .