Abstract:
Even a layer system, provided with a protective coating and used in a hot gas atmosphere needs to be cooled. However, said cooling is often insufficient, as far as cooling pipes are arranged relatively far from the external surface of said layer system. In order to solve the problem, the inventive coolable layer system consists of intersecting cooling pipes.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is the US National Stage of International Application No. PCT/EP2004/002223, filed Mar. 4, 2004 and claims the benefit thereof. The International Application claims the benefits of European Patent application No. 03006962.9 EP filed Mar. 26, 2003, both of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to a coolable layer system in accordance with the preamble of the claims.  
       BACKGROUND OF THE INVENTION  
       [0003]     U.S. Pat. No. 5,080,557 has disclosed a layer system in which a porous structure through which a cooling medium flows is arranged beneath a wall. This layer structure is relatively thick and difficult to cool.  
         [0004]     U.S. Pat. No. 5,820,337, U.S. Pat. No. 5,640,767 and U.S. Pat. No. 5,392,515 show turbine blades or vanes which are formed from a substrate and in which cooling passages are arranged below an outer wall which includes the same material as the substrate. The cooling of the outermost coating on the outer wall is in many cases inadequate.  
         [0005]     EP 1 007 271 B1 shows an impingement-cooled gas turbine blade or vane which, however, does not have any cooling passages below the outer wall. The elevations serve to support the outer wall and do not form cooling passages.  
       SUMMARY OF THE INVENTION  
       [0006]     Therefore, it is an object of the invention to improve the cooling of a layer system.  
         [0007]     The object is achieved by a coolable layer system as claimed in the claims.  
         [0008]     The subclaims list further advantageous measures for improving the cooled layer system.  
         [0009]     The measures listed in the subclaims can be combined with one another in advantageous ways. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     Exemplary embodiments of the invention are explained below. In the drawings:  
         [0011]      FIG. 1  shows a first exemplary embodiment of the coolable layer system,  
         [0012]      FIG. 2  shows a further exemplary embodiment of a coolable layer system, and  
         [0013]      FIGS. 3, 4 ,  6  show further modifications of the coolable layer system, and  
         [0014]      FIG. 5  shows a specially designed cooling passage. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]      FIG. 1  shows a coolable layer system  1 .  
         [0016]     The layer system  1  has a substrate  4 . The substrate  4  is, for example, a ceramic or a metal, in particular a superalloy (nickel-base or cobalt-base) for gas turbine components (turbine blades or vanes, combustion chamber linings, etc.). At least one coating  7  has been applied to the substrate  4 . The coating  7  may be a metallic MCrAlY coating as used for gas turbine blades or vanes (M═Cr or Fe or Ni; Y=yttrium or rare earth).  
         [0017]     Moreover, it is also possible for a ceramic coating, for example a thermal barrier coating  9  ( FIG. 6 ), to be applied to the coating  7 .  
         [0018]     Starting from the surface  22  of the substrate  4 , in this case at least one cooling passage  10  is formed, for example within the coating  7 , i.e. the cooling passage  10  is formed by removal of material from the coating  7  or by application of the coating  7  in such a way that it leaves clear a corresponding cavity.  
         [0019]     Therefore, the majority of the peripheral surface of the cooling passage  10  is formed by the coating  7 . The surface  22  remains substantially unchanged.  
         [0020]     Cooling medium is supplied via a coolant feed  13  which is formed at least in the substrate  4  and leads into at least one cooling passage  10 .  
         [0021]     The cooling passages  10  are therefore arranged in the immediate vicinity of an outer surface, which can come into contact with a hot gas  8 . This allows better cooling of the coating  7 , which is exposed to higher temperatures than the substrate  4 .  
         [0022]      FIG. 2  shows a further exemplary embodiment of a coolable layer system  1 .  
         [0023]     In this case, the cooling passages  10  are formed not by passages within the coating  7  but rather, for example, by recesses  23  arranged in the substrate  4 .  
         [0024]     The coating  7  forms part of the inner surface of the cooling passage  10  and closes it off on the outer side.  
         [0025]     It is equally possible for the cooling passages  10  to be arranged both in the substrate  4  and in the coating  7 .  
         [0026]      FIG. 6  shows cooling passages  10  between two coatings  7 ,  9 .  
         [0027]     The cooling passage  10  may also be formed by a recess  23  (indicated by dashed lines) in the coating  7 .  
         [0028]     The cooling passages  10  shown in  FIGS. 1, 6  are produced, for example, in the following way.  
         [0029]     Webs comprising a filler material which in cross section correspond to the cooling passages  10  to be produced are laid on the surface  22  of the substrate  4  or on the surface of the coating  7 .  
         [0030]     The substrate  4  or the coating  7  is then coated with the coating  7  or the coating  9 , respectively (plasma  
         [0031]     spraying, physical vapor deposition (PVD), chemical vapor deposition (CVD), etc.).  
         [0032]     Then, the webs comprising the filing material are removed. The material for the webs consists, for example, of graphite, which can be pyrolyzed or leached out after the coating with the coating  7 ,  9 .  
         [0033]     Other materials are also possible for the filling material.  
         [0034]     To produce the cooling passages  10  shown in  FIG. 2 , corresponding recesses  23  are introduced into the surface  22  of the substrate. The recesses  23  are filled, for example, with a filling material which prevents material of the coating  7  from penetrating into the cooling passages  10  during the coating of the substrate  4 .  
         [0035]     After the coating  7  has been applied or an outer wall has been applied, the filling material is removed again, so that the cooling passages  10  are formed.  
         [0036]      FIG. 3  shows the arrangement of cooling passages  10  in accordance with  FIGS. 1, 2  and  6  on a surface of a component  1  (layer system).  
         [0037]     The layer system  1  is, for example, a turbine blade or vane which extends along a radial direction  16 . At least one cooling passage  10  extends in an axial direction  19 , perpendicular (at 90°) to the radial direction  16 .  
         [0038]     The cooling passages  10  may also run at an angle other than 90° to the radial axis  16  ( FIG. 4 ), for example approximately parallel to the radial direction  16  (0°).  
         [0039]     It is also possible for all the cooling passages  10  to extend in one direction. Groups of cooling passages may also run parallel to one another.  
         [0040]      FIG. 4  shows a further possible arrangement of cooling passages  10  in accordance with  FIGS. 1, 2  and  6  on a surface  22  or a coating  7  of a component  1 .  
         [0041]     At least two cooling passages  10  cross one another and are in communication with one another, i.e. a cooling medium can flow out of the cooling passage  10  into another cooling passage  10 . Consequently, there is no need for complex, meandering cooling passages, since the crossed pattern of the cooling passages  10  covers at least part and in particular all of the surface of the component  1  which is to be cooled, i.e. the crossed pattern and the crossings of the cooling passages extend at least partially or completely over or beneath the surface that is to be cooled.  
         [0042]     In  FIG. 4 , by way of example, there are eight crossings of cooling passages  10 .  
         [0043]     The surface to be cooled may be a subregion or all of the surface of a main blade or vane part of a turbine blade or vane (component  1 ).  
         [0044]     If a cooling passage  10  has become blocked at one location, the cooling medium can nevertheless continue to flow via the other cooling passages.  
         [0045]     The cooling medium K flows via an inlet for example into the cooling passages  10 ′ and  10 ″. From the cooling passage  10 ″, the cooling medium passes directly into the cooling passage  10 ′″ and  10 ″″, etc.  
         [0046]     The cooling passages  10  are in this case arranged, for example, in groups that are crosswise with respect to one another, with the cooling passages  10  within a group running parallel to one another.  
         [0047]     Other arrangements of cooling passages  10  which cross one another are conceivable.  
         [0048]     It is also possible for cooling passages  10  which cross one another and meandering cooling passages  10  to cover a surface that is to be cooled by virtue of meandering cooling passages being connected to cooling passages which cross one another.  
         [0049]      FIG. 5  shows a specially designed cooling passage  10 , for example based on  FIG. 1 .  
         [0050]     Since the cooling passage  10  at least partially adjoins the coating  7  (not shown) or an outer wall, the cooling passage  10  of the layer system  1  that is to be produced, without coatings or an outer wall, has an opening  24  at the surface  22 .  
         [0051]     The angle α between the surface  22  and the inner surface of the cooling passage  10  at the opening  24  is not 90°. This means that the cooling passage  10  has undercuts  26  with respect to the surface  22 .  
         [0052]     As a result, in the event of a high thermal gradient between outer, hot coating  7 ,  9  or the wall and cooling passage  10 , thermal stresses between the coatings  7 ,  9  or the wall and the substrate  4  are reduced.  
         [0053]     A cooling passage  10  with undercuts  26  of this type may also be arranged in the coating  7  ( FIG. 6 ).  
         [0054]     A cooling passage  10  with undercuts  26  in the substrate  4  is produced, for example, using a milling cutter or grinding head  25  which is of spherical, hemispherical or conical form at one end.  
         [0055]     First of all, the milling cutter  25  or some other form of cylindrical drill produces a hole in the substrate  4  by virtue of being moved in a drilling direction  29  which is virtually perpendicular to the surface  22  of the substrate  4 . Then, the milling cutter  25  is moved to and fro in a direction  32  perpendicular to the drilling direction  29 , as indicated by the arrow, thereby producing the undercuts  26  in the substrate  4 .  
         [0056]     The various positions of the milling cutter  25  during the movement to and fro are indicated by dashed lines.