Abstract:
A method for optimizing the coating of a component using a coupon by introducing the coupon into a depression of the component, in which the geometry of the component is not altered as compared to a component without a coupon, is provided. A component having a depression into which a coupon is fastened is also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2006/067659, filed Oct. 23, 2006 and claims the benefit thereof. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a method for optimizing the coating of a component, in which coupons are used, and to a component. 
       BACKGROUND OF INVENTION 
       [0003]    Components which are used in corrosive surroundings or hot surroundings often have layers which improve the corrosion protection or only allow use at higher temperatures. This applies, for example, to components of turbines in aircraft or turbines for the stationary generation of current. The turbine blades, but also combustion chamber elements, have a metallic protective layer for corrosion and/or oxidation protection and, in especially hot regions, a ceramic heat insulation layer. 
         [0004]    Depending on the component geometry, which changes as a result of the design, or another coating materials or coating methods, the coating parameters have to be checked and optimized. 
         [0005]    This may, of course, take place in that an entire component is coated and the adhesion of the layers to the substrate of the component and the adhesion of the layers to one another are investigated by the component being destroyed, that is to say being cut through completely, and by the cut surfaces being investigated by metallography. This, however, leads to the total loss of the component. 
         [0006]    It is also known to solder, adhere or weld coupons or wafers onto the surface of the component and to check the coating parameters. 
       SUMMARY OF INVENTION 
       [0007]    The object of the invention, therefore, is to improve the above-mentioned coating method. The object is achieved by means of a method according to the claims, in which a coupon is thus introduced into a depression of the component, and by means of a component according to the claims. 
         [0008]    The subclaims list further advantageous measures which may be combined with one another, as desired, in order to achieve further advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    In the drawing: 
           [0010]      FIG. 1  shows a procedure in the coating method according to the prior art, 
           [0011]      FIGS. 2 and 4  show an arrangement for the coating method of the present application, 
           [0012]      FIG. 3  shows diagrammatically the sequence of a coating method, 
           [0013]      FIG. 5  shows forms of the coupon, 
           [0014]      FIG. 6  shows a gas turbine, 
           [0015]      FIG. 7  shows a turbine blade in perspective, and 
           [0016]      FIG. 8  shows a combustion chamber in perspective. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0017]      FIG. 1  shows a component  1  or a turbine blade  120 ,  130  which has a surface  4  in the blade leaf region  406  ( FIG. 5 ), the blade leaf region  406  being coated. In this case, according to the prior art, a coupon  7  is soldered onto the blade tip  415 . These projects from the outer surface  4  of the component  1  contrary to the desired geometry of the component  1 . Since, according to the prior art, the coupon  7  projects from the surface  4  and this surface is relatively small in relation to the surface to be coated, the marginal effects at the edges of the coupon can influence the adhesion of the layer to the coupon  7 . Moreover, the spacing of the turbine surface  20  is also thereby reduced, so that the spacing in the coating of a component without coupons is not the same at the location where the coupon was. 
         [0018]      FIG. 2  shows an arrangement with a coupon  10  which overcomes the problems according to the prior art. 
         [0019]    A depression  19  is introduced into the component  1 ,  120 ,  130 ,  155 . This depression  19  has arranged in it a coupon  10 , so that the surface  5  of the latter is, in particular, at the same height as the surrounding surface  4  of the component  1 ,  120 ,  130 ,  155 . The coupon  10  may be clamped in mechanically or be fastened by means of weld spots  13 . The coupon  5  may likewise be soldered in. A high-temperature adhesive may also be used, which withstands the coating temperatures, but not necessarily the higher temperatures of use of the component. 
         [0020]    Preferably, the material of the coupon  10  consists of the same material as the substrate of the component  1 ,  120 ,  130 ,  155 . 
         [0021]    The figures illustrate the depression  19  as a blind hole, but the depression may also be a through hole, and therefore the term “depression  19 ” may apply both to blind holes and to through holes. 
         [0022]      FIG. 3  shows the sequence of the coating method diagrammatically from left to right. 
         [0023]    The arrangement according to  FIG. 2 , to which material  16  is applied, is shown on the left. Particularly in the case of turbine blades  120 ,  130 , the material is a metallic MCrAlX alloy and/or a ceramic heat insulation layer on top of this. 
         [0024]    It can be seen on the right side in  FIG. 3  that the coating  16  is present on the surface of the coupon  10  and there are no height differences with respect to a component  1 ,  120 ,  130 ,  155  in which there is no depression having a coupon. This is also accomplished in that the gap between the coupon  10  of the depression  19  and the surrounding substrate  6  is very small, so that impinging material cannot even enter this gap or the gap is closed very quickly with little material. The coupon  10  can be employed in various coating methods. These are low-temperature spraying methods, such as cold-gas spraying or HVOF, thermal spraying methods, such as all plasma spraying methods (VPS, APS, LPPS, etc) and also PVD or CVD methods or an EB-PVD method. 
         [0025]    After coating, the coupons  10  can easily be removed together with the coating, since they were only clamped in mechanically or fastened by means of 1, 2 or 3 coating spots  13 ,  13 ′. This coupon  10  can be investigated destructively by metallography. The component  1 ,  120 ,  130 ,  155  may preferably have a plurality of coupons  10 . 
         [0026]    The component  1 ,  120 ,  130 ,  155 , which, after coating, likewise has a coating in the same way as the coupon  10 , can be used again in that the coating  16  is removed, a new coupon is soldered into the depression  19  and further test series are carried out with the same component. Likewise, in the case of a new test series at another location, a new depression  19  can be formed and the depression previously used can be soldered shut. 
         [0027]    It is likewise possible, in a first step for the optimization of coating parameters of a component  1 ,  120 ,  130 ,  155 , to use a corresponding component without a depression, in which a piece of the component having coatings  16  is then cut out at the relevant locations, such as, for example, the leading edge, trailing edge, curved regions, as shown in  FIG. 5 , the location thus cut out corresponding to the depression  19  which can then be correspondingly coated together with a coupon in a further optimization step. In particular, this type of introduction of coupons is relevant in regions of a component which are particularly sharply curved, such as, for example, a leading edge  409  or trailing edge  412  or a turbine blade  120 ,  130  at the blade tip  415 . 
         [0028]    A coupon  10  may also be introduced into a depression  19  and, where appropriate, be reworked together with the component  1 ,  120 ,  130 ,  155 , so that its surface  5  is at the same height as the surrounding surface  4  of the component  1 ,  120 ,  130 ,  155 . Preferably, the outer geometry of the component  1 ,  120 ,  130 ,  155  with a coupon  10  has the same geometry as the component without a coupon  10  or depression  19 . 
         [0029]    In  FIG. 4 , the coupon  10  is leant against one side  21  of the depression  19  and is held in the depression  19  on the other side  20  of the depression  19  by means of a connection point  13  by a solder, weld spot or adhesive. 
         [0030]      FIG. 5  shows various locations where a coupon is present. 
         [0031]    This may be in the region of the leading edge  409 , even the inner geometry of the coupon conforming to the geometry within the blade. 
         [0032]    The coupon  10 , which is introduced in the region of the leading edge  409 , is of U-shaped design and preferably extends from the delivery side via the leading edge onto the suction side. It would likewise be possible to attach the coupon either only on the suction side or only on the delivery side. 
         [0033]    In the region of the blade tip  415 , too, a U-profile may be introduced, which extends, in particular, from the suction side as far as the delivery side. A further location where a turbine blade has a curved region is the region of the blade leaf  406  to the blade platform  403 . A curved coupon  10  may also be present at this transition  420 . 
         [0034]      FIG. 6  shows a gas turbine  100  by way of example in a part longitudinal section. 
         [0035]    The gas turbine  100  has inside it a rotor  103  rotary-mounted about an axis of rotation  102  and having a shaft  101 , said rotor also being designated as a turbine rotor. 
         [0036]    An intake casing  104 , a compressor  105 , a, for example, toroidal combustion chamber  110 , in particular annular combustion chamber, with a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust gas casing  109  succeed one another along the rotor  103 . The annular combustion chamber  110  communicates with a, for example, annular hot gas duct  111 . There, for example, four turbine stages  112  connected one behind the other form the turbine  108 . Each turbine stage  112  is formed, for example, from two blade rings. A guide vane row  115  is followed, as seen in the direction of flow of a working medium  113 , in the hot gas duct  111  by a row  125  formed from moving blades  120 . 
         [0037]    The guide vanes  130  are in this case fastened to an inner casing  138  of a stator  143 , whereas the moving blades  120  of a row  125  are attached to the rotor  103 , for example, by means of a turbine disk  133 . A generator or a working machine (not illustrated) is coupled to the rotor  103 . 
         [0038]    While the gas turbine  100  is in operation, air  135  is sucked in by the compressor  105  through the intake casing  104  and is compressed. The compressed air provided at the turbine-side end of the compressor  105  is routed to the burners  107  and is mixed there with a fuel. The mixture is then burnt in the combustion chamber  110  so as to form the working medium  113 . The working medium  113  flows from there along the hot gas duct  111  past the guide vanes  130  and the moving blades  120 . At the moving blades  120 , the working medium  113  expands so as to transmit a pulse, so that the moving blades  120  drive the rotor  103  and the latter drives the working machine coupled to it. 
         [0039]    The components exposed to the hot working medium  113  are subject to thermal loads while the gas turbine  100  is in operation. The guide vanes  130  and moving blades  120  of the first turbine stage  112 , as seen in the direction of flow of the working medium  113 , are subjected to the most thermal load, in addition to the heat shield elements lining the annular combustion chamber  110 . In order to withstand the temperatures prevailing there, these may be cooled by means of a coolant. Substrates of the components may also have a directional structure, that is to say they are monocrystalline (SX structure) or have only longitudinally directed grains (DS structure). Materials which may be used for the components, in particular for the turbine blade  120 ,  130  and components of the combustion chamber  110 , are, for example, iron-, nickel- or cobalt-based superalloys. 
         [0040]    Such superalloys 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; these publications are part of the disclosure with respect to the chemical composition of the alloys. 
         [0041]    The blades  120 ,  130  may also have coatings against corrosion (MCrAlX; M is at least one element of the group 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). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1 which are to be part of this disclosure with respect to the chemical composition. On the MCrAlX, a heat insulation layer may also be present and consists, for example, of ZrO 2 , Y 2 O 3 —ZrO 2 , that is to say it is not or is partially or completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. By means of suitable coating methods, such as, for example, electron beam vapor deposition (EB-PVD), columnar grains are generated in the heat insulation layer. 
         [0042]    The guide vane  130  has a guide vane root (not illustrated here) facing the inner casing  138  of the turbine  108  and a guide vane head lying opposite the guide vane root. The guide vane head faces the rotor  103  and is secured to a fastening ring  140  of the stator  143 . 
         [0043]      FIG. 7  shows a perspective view of a moving blade  120  or guide vane  130  of a turbo machine, which extends along a longitudinal axis  121 . 
         [0044]    The turbo machine may be a gas turbine of an aircraft or of a power station for electricity generation, a steam turbine or a compressor. 
         [0045]    The blade  120 ,  130  has successively along the longitudinal axis  121  a fastening region  400 , a blade platform  403  contiguous to the latter and also a blade leaf  406  and a blade tip  415 . As a guide vane  130 , the blade  130  may have a further platform (not illustrated) at its blade tip  415 . 
         [0046]    In the fastening region  400 , a blade root  183  is formed, which serves (not illustrated) for fastening the moving blades  120 ,  130  to a shaft or a disk. The blade root  183  has, for example, a hammer head configuration. Other configurations as a pine tree or dovetail root are possible. For a medium which flows past the blade leaf  406 , the blade  120 ,  130  has a leading edge  409  and a trailing edge  412 . 
         [0047]    In conventional blades  120 ,  130 , for example, solid metallic materials, in particular superalloys, are used in all regions  400 ,  403 ,  406  of the blade  120 ,  130 . 
         [0048]    Such superalloys 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; these publications are part of the disclosure with respect to the chemical composition of the alloy. The blade  120 ,  130  may in this case be manufactured by a casting method, also by means of directional solidification, by a forging method, by a milling method or by combinations of these. 
         [0049]    Workpieces with a monocrystalline structure or structures are used as components for machines which are exposed to high mechanical, thermal and/or chemical loads during operation. The manufacture of monocrystalline workpieces of this type takes place, for example, by directional solidification from the melt. This involves casting methods in which the liquid metallic alloy solidifies into the monocrystalline structure, that is to say into the monocrystalline workpiece, or directionally. In this case, dendritic crystals are oriented along the heat flow and form either a columnar-crystalline grain structure (columnar, that is to say grains which run over the entire length of the workpiece and here, according to general linguistic practice, are designated as being directionally solidified) or a monocrystalline structure, that is to say the entire workpiece consists of a single crystal. These methods must avoid the transition to globulitic (polycrystalline) solidification, since transverse and longitudinal grain boundaries are necessarily formed as a result of undirected growth and nullify the good properties of the directionally solidified or monocrystalline component. When directionally solidified structures are referred to in general terms, these mean both monocrystals which have no grain boundaries or at most low-angle grain boundaries and columnar crystal structures which, although having grain boundaries running in the longitudinal direction, have no transverse grain boundaries. With regard to the second-mentioned crystalline structures, directionally solidified structures are also referred to. Such methods are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1; these publications are part of the disclosure in respect of the solidification method. 
         [0050]    The blades  120 ,  130  may likewise have coatings against corrosion or oxidation, for example (MCrAlX; M is at least one element of the group 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)). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1 which are to be part of this disclosure in respect of the chemical composition of the alloy. The density preferably lies at 95% of the theoretical density. A protective aluminum oxide layer (TGO=thermal grown oxide layer) forms on the MCrAlX layer (as an intermediate layer or as the outermost layer). 
         [0051]    On the MCrAlX, a heat insulation layer may also be present, which is preferably the outermost layer and consists, for example, of ZrO 2 , Y 2 O 3 —ZrO 2 , that is to say it is not or is partially or completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. The heat insulation layer covers the entire MCrAlX layer. 
         [0052]    By means of suitable coating methods, such as, for example, electron beam vapor deposition (EB-PVD), columnar grains are generated in the heat insulation layer. 
         [0053]    Other coating methods may be envisaged, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The heat insulation layer may have porous microcrack or macrocrack compatible grains for better thermal shock resistance. The heat insulation layer is therefore preferably more porous than the MCrAlX layer. 
         [0054]    Refurbishment means that components  120 ,  130 , have to, after use, where appropriate, be freed of protective layers (for example, by sandblasting). A removal of the corrosion and/or oxidation layers or products then takes place. If appropriate, cracks in the component  120 ,  130  are also repaired. This is followed by a recoating of the component  120 ,  130  and a renewed use of the component  120 ,  130 . 
         [0055]    The blade  120 ,  130  may be of hollow or solid design. If the blade  120 ,  130  is to be cooled, it is hollow and, if appropriate, also has film cooling holes  418  (indicated by dashes). 
         [0056]      FIG. 8  shows a combustion chamber  110  of a gas turbine. The combustion chamber  110  is configured, for example, as what is known as an annular combustion chamber, in which a multiplicity of burners  107  arranged around an axis of rotation  102  in the circumferential direction issue into a common combustion chamber space  154  and generate flames  156 . For this purpose, the combustion chamber  110  is configured as a whole as an annular structure which is positioned around the axis of rotation  102 . 
         [0057]    To achieve a comparatively high efficiency, the combustion chamber  110  is designed for a comparatively high temperature of the working medium M of about 1000° C. to 1600° C. In order to allow a comparatively long operating time even in the case of these operating parameters which are unfavorable for the materials, the combustion chamber wall  153  is provided on its side facing the working medium M with an inner lining formed from heat shield elements  155 . Each heat shield element  155  consisting of an alloy is equipped on the working medium side with a particularly heat-resistant protective layer (MCrAlX layer and/or ceramic coating) or is manufactured from material resistant to high temperature (solid ceramic bricks). These protective layers may be similar to those of the turbine blades, that is to say, for example, MCrAlX means: M is at least one element of the group 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). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1 which are to be part of this disclosure in respect of the chemical composition of the alloy. 
         [0058]    On the MCrAlX, a, for example, ceramic heat insulation layer may also be present and consists, for example, of ZrO 2 , Y 2 O 3 —ZrO 2 , that is to say it is not or is partly or completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
         [0059]    By means of suitable coating methods, such as, for example, electron beam vapor deposition (EB-PVD), columnar grains are generated in the heat insulation layer. 
         [0060]    Other coating methods may be envisaged, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The heat insulation layer may have porous microcrack or macrocrack compatible grains for better thermal shock resistance. 
         [0061]    Refurbishment means that heat shield elements  155 , after use, must, where appropriate, be freed of protective layers (for example, by sand blasting). A removal of the corrosion and/or oxidation layers or products then takes place. If appropriate, cracks in the heat shield element  155  are also repaired. This is followed by a recoating of the heat shield elements  155  and a renewed use of the heat shield elements  155 . Moreover, on account of the high temperatures inside the combustion chamber  110 , a cooling system may be provided for the heat shield elements  155  or for their holding elements. The heat shield elements  155  are then, for example, hollow and, if appropriate, also have cooling holes (not illustrated) issuing into the combustion chamber space  154 .