Abstract:
A process for setting the average flow rate within a hollow component is provided. The process includes setting a relatively small wall thickness in a first region with a relatively large flow cross section using a first diffusion coating process and setting a relatively large wall thickness by a second different diffusion process in a second region with a relatively small flow cross section. The use of different diffusion coatings in a component allows the flow of coolant through a component to be set in a controlled manner.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2011/052684, filed Feb. 23, 2011 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 10001849.8 EP filed Feb. 23, 2010. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a process for setting the coolant consumption within actively cooled components and to a component. 
       BACKGROUND OF INVENTION 
       [0003]    Components which are used at high temperatures, e.g. turbine blades or vanes in gas turbines, have active cooling, during which a coolant is introduced into the interior and runs through the turbine blade or vane through coolant ducts, and if appropriate emerges from film-cooling holes. 
         [0004]    In this case, it is important that the turbine blade or vane is not cooled excessively, since this greatly increases the coolant consumption, which in turn would reduce the efficiency of the turbine because the cooling air is mostly taken from the compressor. 
         [0005]    It is therefore important to set the coolant consumption by optimally setting the flow rate. 
       SUMMARY OF INVENTION 
       [0006]    The object is achieved by a process as claimed in the claims and by a component as claimed in the claims. 
         [0007]    The dependent claims list further advantageous measures which can be combined with one another, as desired, in order to obtain further advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIGS. 1 ,  2  and  3  show schematic illustrations of the invention, 
           [0009]      FIG. 4  shows a turbine blade or vane, 
           [0010]      FIG. 5  shows a gas turbine, 
           [0011]      FIG. 6  shows a list of superalloys. 
       
    
    
       [0012]    The figures and the description show merely exemplary embodiments of the invention. 
       DETAILED DESCRIPTION OF INVENTION 
       [0013]      FIG. 1  schematically shows at least part of an inner duct  10  of the component  1 . 
         [0014]    The duct  10  is in particular a cooling duct  10  and can be divided into various regions, here preferably into two regions  4  and  7 , which have a greater cross section at the start at the inlet  9  than at the outlet  11 . 
         [0015]    Accordingly, there are regions  4 ,  7  with different flow cross sections. 
         [0016]    The regions  4 ,  7  do not have to lie at the inlet  9  or at the outlet  11 . 
         [0017]    In the case of a turbine blade or vane, the inlet  9  is located in the region of the root  400  ( FIG. 4 ), and the outlet  11  is located in the region of the trailing edge  412  ( FIG. 4 ). 
         [0018]    The component  1 ,  120 ,  130  can have a plurality of cooling ducts. 
         [0019]    The invention proposes providing the various regions  4 ,  7  with diffusion coatings, which lead to the thickening and thus to a constriction of the passage through the cooling duct  10  at various regions  4 ,  7 . 
         [0020]    Therefore, a diffusion coating  19 , which leads to the wall thickening ( FIG. 2 ), is produced by a first diffusion coating process by means of a material  13  only in the first region  4 . 
         [0021]    In a second step, material  16  is applied only in the second region  7 , in order to likewise produce a diffusion coating in the region  7 , which leads to a second diffusion coating  22 , which, however, leads to a greater thickening than in the region  4  in particular owing to a different coating process. 
         [0022]    The material  16  can correspond to the material  13  of the first coating process, or can be different. 
         [0023]    The diffusion coatings  19  and  22  preferably form a continuous diffusion coating  25 . 
         [0024]    For the regions  4 ,  7 , this is preferably an aluminization process, where NiAl is used for the region  4  for the diffusion coating process and/or Ni 2 Al 3  is used for the region  7  for diffusion coating. 
         [0025]    The two coating processes can also be employed at the same time, as shown in  FIG. 3 . 
         [0026]    It is preferable for the entire inner region of the turbine blade or vane  120 ,  130  to be coated. 
         [0027]      FIG. 5  shows, by way of example, a partial longitudinal section through a gas turbine  100 . 
         [0028]    In the interior, the gas turbine  100  has a rotor  103  with a shaft which is mounted such that it can rotate about an axis of rotation  102  and is also referred to as the turbine rotor. 
         [0029]    An intake housing  104 , a compressor  105 , a, for example, toroidal combustion chamber  110 , in particular 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 . 
         [0030]    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 . 
         [0031]    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 . 
         [0032]    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 means of a turbine disk  133 . 
         [0033]    A generator (not shown) is coupled to the rotor  103 . 
         [0034]    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. 
         [0035]    While the gas turbine  100  is operating, the components 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. 
         [0036]    To be able to withstand the temperatures which prevail there, they may be cooled by means of a coolant. 
         [0037]    Substrates of the components may likewise have a directional structure, i.e. they are in single-crystal form (SX structure) or have only longitudinally oriented grains (DS structure). 
         [0038]    By way of example, iron-based, nickel-based or cobalt-based superalloys are used as material for the components, in particular for the turbine blade or vane  120 ,  130  and components of the combustion chamber  110 . 
         [0039]    Superalloys of this type are known, for example, from EP 1 204 776 B 1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949. 
         [0040]    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 . 
         [0041]      FIG. 4  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 . 
         [0042]    The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
         [0043]    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 . 
         [0044]    As a guide vane  130 , the vane  130  may have a further platform (not shown) at its vane tip  415 . 
         [0045]    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 . 
         [0046]    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. 
         [0047]    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 . 
         [0048]    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 . 
         [0049]    Superalloys of this type are known, for example, from EP 1 204 776 B 1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949. 
         [0050]    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. 
         [0051]    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. 
         [0052]    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. 
         [0053]    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. 
         [0054]    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). 
         [0055]    Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1. 
         [0056]    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. 
         [0057]    The density is preferably 95% of the theoretical density. 
         [0058]    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). 
         [0059]    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-12Al -0.6Y-3Re or Ni-12Co-21Cr-11Al -0.4Y-2Re or Ni-25Co-17Cr-10Al -0.4Y-1.5Re. 
         [0060]    It is also possible for a thermal barrier coating, which is preferably 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. 
         [0061]    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). 
         [0062]    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. 
         [0063]    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).