Abstract:
On account of their type of coating, layer systems of the prior art often exhibit poor adhesion to the substrate. If the components are subject to high mechanical stresses, the layer can then become detached. The layer system according to the invention has separately produced anchoring means which allow stronger attachment to the substrate than the attachment of the outer layer to the substrate.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority of the European application No. 04023974.1 EP filed Oct. 7, 2004, which is incorporated by reference herein in its entirety.  
       FIELD OF THE INVENTION  
       [0002]     The invention relates to a layer system.  
       BACKGROUND OF THE INVENTION  
       [0003]     Nowadays, components which are intended for use at high temperatures are generally provided with protective layers. These may be metallic corrosion-resistant layers (MCrAlX layers) or ceramic thermal barrier coatings, as well as layer systems comprising both metallic corrosion-resistant layers and ceramic thermal barrier coatings. Plasma-enhanced powder spraying processes are used as the coating process for these coatings, on account of their relatively favorable economics. Layers of this type are attached to the substrate by mechanical interlock and subsequent diffusion heat treatment. In operation, the layer may become detached on occasion in highly stressed regions or at unfavorable areas of the component, i.e. areas which are subject to particularly high mechanical stresses. The layer flaking off in operation leads to damage to the base material, with the result that the component life is significantly reduced.  
         [0004]     U.S. Pat. No. 5,869,798 discloses a process in which elevations are produced on a surface by means of a welding process, the elevation consisting of a different material than the underlying substrate.  
         [0005]     EP 1 275 748 A2 discloses anchoring means which are arranged on a surface of a substrate or of an interlayer or project through a plurality of layers.  
         [0006]     DE 100 57 187 A1 discloses anchoring means which project into a metallic substrate in order to improve the bonding of a metallic material, such as ceramic, to the metallic substrate. The anchoring means do not extend as far as an outer surface.  
         [0007]     EP 0 713 957 A1 discloses a process in which a recess in a layer is filled with material.  
         [0008]     Further prior art is known from DE 30 38 416 A1 and from Journal of Materials Science 24 (1989), pages 115-123, entitled “Enhanced metal-ceramic adhesion by sequential sputter deposition and pulsed laser melting of copper films on sapphire substrates” by A. J. Pedraza, M. J. Godbole.  
       SUMMARY OF THE INVENTION  
       [0009]     Therefore, it is an object of the invention to provide a layer system which has improved attachment of a protective layer to a substrate and/or of layers to one another.  
         [0010]     The object is achieved by the layer system as claimed in the claims.  
         [0011]     The layer system according to the invention has separately produced anchoring means, which have a very good attachment to the substrate or to an interlayer arranged below on the substrate and are attached to the substrate or to the other layer in a different way than the layer.  
         [0012]     The subclaims list further advantageous measures. The measures listed in the subclaims can be advantageously combined with one another in any desired way. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     In the drawings:  
         [0014]      FIGS. 1, 2 ,  6 ,  7 ,  8  show layer systems,  
         [0015]      FIG. 3  shows a perspective plan view of a layer system,  
         [0016]      FIG. 4  shows process steps involved in the production of a layer system,  
         [0017]      FIG. 5  shows process steps involved in the production of a layer system,  
         [0018]      FIGS. 9, 20 ,  21 ,  22  show a layer system formed in accordance with the invention,  
         [0019]      FIGS. 10-12  show process steps involved in the production of a layer system,  
         [0020]      FIGS. 13, 14 ,  15  show process steps involved in the production of a layer system,  
         [0021]      FIGS. 16, 17  show process steps involved in the production of a layer system,  
         [0022]      FIG. 18  shows a gas turbine,  
         [0023]      FIG. 19  shows a combustion chamber, and  
         [0024]      FIG. 23  shows a turbine blade or vane. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]      FIG. 1  shows a layer system  1 ′ in accordance with the prior art. The layer system  1 ′ has a substrate  4 . At least an outer layer  9  is present on the substrate surface  5  of the substrate  4 . This outer layer  9  may be a metallic and/or ceramic outer layer  9 .  
         [0026]     In accordance with the prior art, the outer layer  9  is attached to the substrate  4  solely by mechanical interlock (surface roughness) on the underlying surface and a subsequent diffusion heat treatment.  
         [0027]     Working on the basis of  FIG. 1 ,  FIG. 2  shows a layer system  1  with continuous anchoring means  10  or inner anchoring means  13 .  
         [0028]     The substrate  4  may be metallic or ceramic and in the case of gas turbine components is produced in particular from an iron-base, nickel-base or cobalt-based superalloy.  
         [0029]     For turbine blades or vanes  120 ,  130  ( FIG. 18 ), for example, a metallic corrosion-resistant layer  9  ( FIGS. 4, 5 ) of the MCrAlX type is applied to the substrate  4 , and then, for example, an outer layer, for example a ceramic thermal barrier coating  9  ( FIGS. 6, 7 ,  8 ), is additionally applied to the corrosion-resistant layer  9 , so that the corrosion-resistant layer then becomes an interlayer  7 .  
         [0030]     In the outer layer  9 , there is at least one continuous anchoring means  10  and/or at least one inner anchoring means  13 , a certain part  14  of which, for example, extends into the substrate  4 .  
         [0031]     The part  14 , i.e. the extent of the continuous anchoring means  10  or of the inner anchoring means  13  into the substrate  4 , constitutes the smaller part, based on the length or volume of the continuous anchoring means  10  or of the inner anchoring means  13 , so that the majority of the length or volume of the continuous anchoring means  10  or of the inner anchoring means  13  is located in the outer layer  9 .  
         [0032]     The material of the continuous anchoring means  10  or of the inner anchoring means  13  corresponds, for example, to the material of the outer layer  9  in which it is mostly arranged. If the continuous anchoring means  10  or the inner anchoring means  13  is arranged mostly in the outer layer  9 , the material of the continuous anchoring means  10  or of the inner anchoring means  13  corresponds, for example, to the material of the outer layer  9 . Therefore, if most of the continuous anchoring means  10  or of the inner anchoring means  13  is located in the interlayer  7  ( FIGS. 6, 7 ,  8 ), the material of the continuous anchoring means  10  or of the inner anchoring means  13  corresponds, for example, to the material of the interlayer  7 . The continuous anchoring means  10  or the inner anchoring means  13  in particular have a different type of attachment, in particular with an increased attachment force (more specifically: force per unit contact area) to the substrate  4  or to the interlayer  7  than the type of attachment of the interlayer  7  to the substrate  4  or of the outer layer  9  to the interlayer  7 .  
         [0033]     The continuous anchoring means  10  or the inner anchoring means  13 , by way of example, are attached to the substrate  4  by melt metallurgy using a suitably managed laser welding process. It is also conceivable for the outer layer  9  to be applied to defined locations by laser cladding (laser powder coating) and in this way to form continuous anchoring means  10  or inner anchoring means  13 . The continuous anchoring means  10  or inner anchoring means  13  can also be cast on or produced integrally during casting of the substrate  4 .  
         [0034]     The continuous anchoring means  10  or inner anchoring means  13  constitute bonding bridges for the outer layer  9  surrounding the continuous anchoring means  10  or inner anchoring means  13 . The continuous anchoring means  10  start from the substrate surface  5  of the substrate  4  and extend only as far as the outer surface  16  of the outer layer  9  (or if appropriate out of the substrate  4  if a part  14  is present).  
         [0035]     The inner anchoring means  13  are covered by the outer layer  9 , and consequently the inner anchoring means  13  do not extend as far as the outer surface  16  of the outer layer  9 , i.e. are arranged so as to end within the outer layer  9 . In this case, they  13  extend into the outer layer  9  over at least 10%, 20%, 30%, 40% or more of the thickness of the outer layer  9 .  
         [0036]     A corresponding statement also applies to the continuous anchoring means  10  or inner anchoring means  13  in the interlayer  7 .  
         [0037]     It is also possible for only continuous anchoring means  10  or only inner anchoring means  13  to be present in the outer layers  9 .  
         [0038]     The continuous anchoring means  10  or the inner anchoring means  13  are, for example, only present in locally limited form ( FIG. 3 ) on the substrate  4  or the interlayer  7 , namely where the mechanical stresses are highest. This is, for example, the region of the leading edge  409  ( FIG. 24 ) of a turbine blade or vane  120 ,  130 . The remaining blade or vane part  406  ( FIG. 24 ) would not then have any continuous anchoring means  10  or inner anchoring means  13 .  
         [0039]      FIG. 3  shows a plan view of an inner surface  8  of the interlayer  7  or of an outer surface  16  of the outer layer  9 . The inner anchoring means  13 , which do not extend as far as the inner surface  8  ( FIG. 6 ) of the interlayer  7 , are indicated by dashed lines.  
         [0040]     The continuous anchoring means  10  or the inner anchoring means  13  may have different geometries, such as circles, quilted-seam profiles (i.e. they are elongate and cross one another), wave shapes, parallel tracks and combinations thereof on the substrate surface  5 .  
         [0041]      FIG. 6  shows a further layer system  1 . The layer system  1  comprises a substrate  4 , an interlayer  7  and an outer layer  9 . The interlayer  7  is, for example, a metallic MCrAlX layer, and the outer layer  9  is, for example, a ceramic thermal barrier coating  9  on the interlayer  7 .  
         [0042]     Continuous anchoring means  10  or inner anchoring means  13  are present both in the interlayer  7  and in the outer layer  9 .  
         [0043]     The interlayer  7 , however, does not have to have continuous anchoring means  10  or inner anchoring means  13  ( FIG. 8 ). It is likewise possible for the anchoring means to be present only in the interlayer  7  ( FIG. 7 ).  
         [0044]     In this case, some or even all of the continuous anchoring means  10  or inner anchoring means  13  in the interlayer  7  and/or the outer layer  9  may have a part  14  which extends into the substrate  4  or the interlayer  7 .  
         [0045]     The continuous anchoring means  10  in the interlayer  7  or in the outer layer  9 , starting from the substrate surface  5  of the substrate  4  or from the inner surface  8  of the interlayer  7 , extend as far as the inner surface  8  of the interlayers  7  or as far as the outer surface  16  of the outer layer  9 , but not beyond, or they  13  are covered by the interlayer  7  or the outer layer  9 , so that the inner anchoring means  13  do not extend as far as the inner surface  8  of the interlayer  7  or the outer surface  16  of the outer layer  9 .  
         [0046]     The continuous anchoring means  10  or inner anchoring means  13  in the interlayer  7  improve the attachment of the interlayer  7  to the substrate  4 . The material of the continuous anchoring means  10  of the interlayer  7  may, for example, also be selected in such a way as to produce improved bonding of the outer layer  9  to the anchoring means  10  ( FIG. 7 ).  
         [0047]     The material composition of the continuous anchoring means  10  or inner anchoring means  13  in the interlayer  7  or the outer layer  9  is selected appropriately according to the particular demands.  
         [0048]     The material of the continuous anchoring means  10  or inner anchoring means  13 , for example, corresponds to the material of the interlayer  7  or of the outer layer  9  in which it is mostly arranged.  
         [0049]     Therefore, if the continuous anchoring means  10  or inner anchoring means  13  is located largely in the interlayer  7 , the material of the continuous anchoring means  10  or of the inner anchoring means  13  corresponds, for example, to the material of the interlayer  7 . If the continuous anchoring means  10  or the inner anchoring means  13  is arranged largely in the outer layer  9 , the material of the continuous anchoring means  10  or of the inner anchoring means  13  corresponds, for example, to the material of the outer layer  9 .  
         [0050]     The continuous anchoring means  10  or inner anchoring means  13  are present in particular in regions which are subject to high thermal and/or mechanical stresses.  
         [0051]     In the case of turbine blades or vanes, this means the leading edge  409 , the trailing edge  412  ( FIG. 24 ) or the transition between the main blade or vane part  406  and the platform  403  ( FIG. 24 ).  
         [0052]     The layer system  1  is, for example, a component of a gas turbine  100  ( FIG. 18 ) (or aircraft turbine) or of a steam turbine. Components of the turbines which are subject to high thermal stresses have a layer system of this type, for example turbine blades or vanes  120 ,  130 , heat shield elements  155  of a combustion chamber  110  and further casing parts which are located along the flow path of a hot steam or hot gas.  
         [0053]     The layer system  1  can be applied to a newly produced component and to components which are refurbished after use. In the latter case, the components first of all have degraded layers removed from them, any cracks repaired, and then the substrate  4  is recoated.  
         [0054]      FIG. 7  shows a further exemplary embodiment of a layer system  1 . In this layer system  1 , the continuous anchoring means  10  or inner anchoring means  13  are present only in the interlayer  7 . The outer layer  9  is present on the interlayer  7 . A contact surface of the continuous anchoring means  10  against the inner surface  8  improves the bonding of the outer layer  9  compared to a comparable contact surface with the interlayer  7 . This is achieved, for example, by virtue of the fact that the contact surfaces of the continuous anchoring means  10  form nuclei, for example of aluminum oxide, at the inner surface  8  for epitaxial growth, for example, of an outer layer  9  on the interlayer  7 . Even without interlayer  7  ( FIGS. 4, 5 , right-hand side), an improved layer system  1  is achieved by virtue of the fact that the continuous anchoring means  10  or the inner anchoring means  13  lead to improved attachment of the outer layer  9  to the substrate  4 .  
         [0055]     In this context, it is not necessary for some or not imperative for all of the continuous anchoring means  10  or inner anchoring means  13  to have a part  14  extending into the substrate  4 .  
         [0056]      FIG. 8  shows a further exemplary embodiment of a layer system  1 . The continuous anchoring means  10  or inner anchoring means  13  are only present in the outer layer  9  in this exemplary embodiment.  
         [0057]     In this case, some but not necessarily all of the continuous anchoring means  10  or inner anchoring means  13  extend into the substrate  4  or into the interlayer  7 .  
         [0058]     By way of example,  FIG. 4  shows process steps involved in a process for producing a layer system  1 . In a first step, the at least one outer layer  9  is applied to the substrate  4  in a known way.  
         [0059]     The outer layer  9  is treated, for example, with a laser  17  or an electron beam gun  17 , which emits a corresponding laser or electron beam  19 . As a result of this type of treatment, the material of the outer layer  9  is locally converted, for example partially melted, down to the substrate surface  5  of the substrate  4  or even beyond it by way of a part  14  into the substrate  4 , so as to produce melt-metallurgical attachment of material from the outer layer  9  into the substrate  4 . This process produces continuous anchoring means  10  which extend from the substrate surface  5  to the outer surface  16  of the outer layer  9 .  
         [0060]     The statements which have been made in connection with the outer layer  9  (without interlayer  7 ) apply similarly to an interlayer  7  to which an outer layer  9  is also applied.  
         [0061]      FIG. 5  shows a further production process. In a first step, first of all the continuous anchoring means  10  or inner anchoring means  13  are applied to the substrate  4 , i.e. produced separately. This can be done in various ways, such as for example by means of a suitably guided laser welding process or laser cladding. The continuous anchoring means  10  or inner anchoring means  13  in particular have a very strong attachment, in particular by melt metallurgy, to the substrate  4 .  
         [0062]     However, the continuous anchoring means  10  or inner anchoring means  13  may also already have been produced during production of the substrate  4 , for example by a casting process.  
         [0063]     In a subsequent process, the outer layer  9  is applied, with the continuous anchoring means  10  or inner anchoring means  13  being surrounded by the material of the outer layer  9  and forming bonding bridges for the layer  9 .  
         [0064]     The material of the continuous anchoring means  10  or inner anchoring means  13  may be the same as the material of the outer layer  9  or the same as the material of the substrate  4  or may alternatively also have a different material composition.  
         [0065]     The statements which have been made in connection with the outer layer  9  (without interlayer  7 ) apply in a similar way to an interlayer  7  to which an outer layer  9  is also applied.  
         [0066]      FIG. 9   a  shows a component  1  according to the invention (cross section through a continuous anchoring means  10 ). The continuous anchoring means  10  has a larger cross-sectional area  11  at the outer surface  16  than at the substrate surface  5  below ( FIG. 9   b , plan view of  FIG. 9   a ).  
         [0067]     The shape of the continuous anchoring means  10  in cross section is in this case, for example, in the form of a bell. The cross-sectional contour may also take other shapes, such as for example a parabolic profile, in which case the parabola is open at the top  16  ( FIG. 9   b ).  
         [0068]     The cross section of the continuous anchoring means  10  is in this case, by way of example, round in form ( FIG. 9   b ). Other cross sections are possible (oval). The cross-sectional area of the continuous anchoring means  10  at the substrate surface  5  is indicated by dashed lines.  
         [0069]     In this case, the continuous anchoring means  10  may likewise extend into the substrate  4  (not shown).  
         [0070]     The material of the continuous anchoring means  10  may, in the outer layer  9 , for example, correspond to the material of the substrate  4  (metallic) or may be ceramic.  
         [0071]     In particular, the material of the outer layer  9  consists of an alloy of the MCrAlX type, in which case the anchoring means  10  include a material of an alloy of the MCrAlX type, which corresponds to that of the outer layer  9  or has been modified.  
         [0072]      FIG. 20  shows a further exemplary embodiment of a component  1  according to the invention. The layer system  1  comprises a substrate  4 , an interlayer  7  and an outer layer  9 . The substrate  4  is, for example, a superalloy, and the interlayer  7  consists of an alloy of the MCrAlX type, to which an outer ceramic thermal barrier coating  9  has then been applied. Likewise, as illustrated in  FIG. 9   a , in this case the continuous anchoring means  10  are formed only in the interlayer  7 .  
         [0073]     In  FIG. 21 , the continuous anchoring means  10  is arranged only in the outer layer  9 . In  FIG. 22 , the continuous anchoring means  10  are arranged both in the interlayer  7  and in the outer layer  9 .  
         [0074]     Furthermore, inner anchoring means  13  may also be present in the exemplary embodiments shown in  FIGS. 9, 20  to  22 .  
         [0075]     Should the outermost layer  9  flake off or have local damage in the region of the continuous anchoring means  10 , the continuous anchoring means  10  ensures that the interlayer  7  remains on the substrate  4  and the substrate  4  is still protected.  
         [0076]     The material of the continuous anchoring means  10  may also be selected in such a way that it serves as a growth nucleus, in particular for epitaxial growth, when coating the interlayer  7  with the material of the outer layer  9 , for example a ceramic material. In particular, the material of the interlayer  7  consists of an alloy of the MCrAlX type, in which case the anchoring means  10  likewise consist of an alloy of the MCrAlX type, which may if appropriate have been modified with respect to the composition of the interlayer  7 .  
         [0077]     In particular, the material class of the continuous anchoring means  10  or of the inner anchoring means  13  corresponds to the material class of the interlayer  7  or of the outer layer  9  in which it is arranged: metal or ceramic.  
         [0078]     FIGS.  10  to  12  show a process for producing the layer system  1 .  
         [0079]     The outer layer  9  and the continuous anchoring means  10  or inner anchoring means  13  are produced, for example, in layers, i.e. the outer layer  9  is produced, and thereafter or simultaneously the continuous anchoring means  10  or the inner anchoring means  13  are produced. On no account are the anchoring means at least mostly or completely produced first of all ( FIG. 5 ), followed by the layer, or vice-versa ( FIG. 4 ).  
         [0080]     Therefore, starting from the substrate  4 , which does not yet have any outer layer  9 , material for the outer layer  9  is applied in layers, and the continuous anchoring means  10  or inner anchoring means  13  are likewise produced in layers. Depending on whether continuous anchoring means  10  or inner anchoring means  13  are produced, laser heating, for example, is applied at the locations where a continuous anchoring means  10  or inner anchoring means  13  is to be formed, melting the material, i.e. temporarily and locally increasing the temperature.  
         [0081]     If an inner anchoring means  13  is to be produced ( FIG. 11 ), which is not intended to extend as far as the outer surface  16  of the layer  9 , beyond a certain height the outer layer  9  is no longer melted locally ( FIG. 12 ).  
         [0082]     The statements made in connection with the outer layer  9  (without interlayer  7 ) apply in a corresponding way for an interlayer  7 , to which an outer layer  9  is also applied.  
         [0083]     FIGS.  13  to  15  show a further production process.  
         [0084]     In this case, an outer layer  9  is already present on the substrate  4 . This is the case in particular if the component  1  is a component which is to be repaired, i.e. has already been used and in particular has local damage in the form of a recess  34 .  
         [0085]     This recess  34  has, for example, been weakened or was exposed to high demands in use, and in a first step is treated for example by means of a laser  17  (or electron beam gun) and its laser beams  19  ( FIG. 13 ), so that continuous anchoring means  10  or inner anchoring means  13  are formed ( FIG. 14 ).  
         [0086]     In a further process step, the recess  34  is filled with layer material  25  from a material feed  22  (for example powder feed), for example by laser build-up welding, in which case either only layer material  25  forms the filling, without the inner anchoring means  13  shown in  FIG. 14  being formed any further, so as to produce an inner anchoring means  13  which does not extend as far as the outer surface  16 , or alternatively, for example, the laser  17  for the laser build-up welding is also used, for example, to allow the continuous anchoring means  10  shown in  FIG. 14  to grow as far as the outer surface  16 .  
         [0087]     The continuous anchoring means  10  or inner anchoring means  13  may but does not have to have a part  14  (indicated by dashed lines) extending into the substrate  4 , or may be of the form shown in  FIG. 9 .  
         [0088]     The layer material  25  may be material of the outer layer  9  or of the substrate  4 , but may also have a different composition. Also, it is possible for an outer layer  9  to be locally absent in the recess  34  and for material of, for example, the outer layer  9  to be applied, producing continuous anchoring means  10  or inner anchoring means  13 .  
         [0089]     The statements made in connection with the outer layer  9  (without interlayer  7 ) apply in a corresponding way to an interlayer  7  to which an outer layer  9  is also applied.  
         [0090]      FIGS. 16, 17  show a further exemplary embodiment of a process for producing a layer system  1 .  
         [0091]     By way of example, a plasma torch  31  ( FIG. 16 ) is used to produce the outer layer  9 .  
         [0092]     By means of a laser  17  and its laser beams  19 , a continuous anchoring means  10  or inner anchoring means  13  is produced, for example simultaneously, for example by melting, as a result of the material being treated by means of the laser  17 , i.e. for example partially melted, at least from time to time at the locations intended for the continuous anchoring means  10  or inner anchoring means  13 .  
         [0093]     It is also possible to use two lasers  17 ,  17 ′ ( FIG. 17 ), in which case one laser  17 ′ is used for the build-up process, for example laser build-up welding with the aid of a material feed  22 , which delivers the layer material  25 , and a laser  17  which, as in  FIG. 16 , produces the continuous anchoring means  10  or inner anchoring means  13 .  
         [0094]     The statements made in connection with the outer layer  9  (without interlayer  7 ) correspondingly also apply to an interlayer  7  to which an outer layer  9  is subsequently applied.  
         [0095]     In  FIGS. 13, 14 ,  15 ,  16  and  17 , the interlayer  7  or the outer layer  9  and the continuous anchoring means  10  or inner anchoring means  13  can be produced in layers.  
         [0096]     It is also possible for electron beam guns to be used instead of the lasers  17 ,  17 ′ or plasma torches  31 . The use of lasers, plasma torches is not restricted to the embodiments on continuous anchoring means  10  or inner anchoring means  13  which have a part  14  extending into the substrate  4  or into the interlayer  7  or to a specific cross-sectional shape as shown in  FIG. 9 .  
         [0097]      FIG. 18  shows a gas turbine  100  in longitudinal part section. In the interior, the gas turbine  100  has a rotor  103  which is mounted so as to rotate about an axis of rotation  102  and is also referred to as the turbine rotor. An intake casing  104 , a compressor  105 , a, for example, torroidal combustion chamber  110 , in particular an annular combustion chamber  106 , with a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust-gas casing  109  follow one another along the rotor  103 . The annular combustion chamber  106  is in communication with a, for example, annular hot-gas duct  111 . There, by way of example, four turbine stages  112  connected in series form the turbine  108 . Each turbine stage  112  is formed from two blade or vane rings. As seen in the direction of flow of a working medium  113 , a row  125  of rotor blades  120  follows a row  115  of guide vanes in the hot-gas duct  111 .  
         [0098]     The guide vanes  130  are in this case secured to the stator  143 , whereas the rotor blades  120  of a row  125  are arranged on the rotor  103  by means of a turbine disk  133 . A generator (not shown) is coupled to the rotor  103 .  
         [0099]     While the gas turbine  100  is operating, the compressor  105  sucks in air  135  through the intake casing  104  and compresses it. The compressed air which is provided at the turbine-side end of the compressor  105  is passed to the burners  107 , where it is mixed with a fuel. The mixture is then burnt, forming the working medium  113  in the combustion chamber  110 . From there, the working medium  113  flows along the hot-gas duct  111  past the guide vanes  130  and the rotor blades  120 . The working medium  113  expands at the rotor blades  120  in such a manner as to transfer its momentum, so that the rotor blades  120  drive the rotor  103  and the latter drives the generator coupled to it.  
         [0100]     When the gas turbine  100  is operating, the components 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 bricks which line the annular combustion chamber  106 , are subject to the highest thermal stresses. To be able to withstand the temperatures prevailing there, these components are cooled by means of a cooling medium. It is likewise possible for the blades or vanes  120 ,  130  to have coatings protecting against corrosion (MCrAlX; M=Fe, Co, Ni, X=Y, rare earths) and heat (thermal barrier coating, for example ZrO 2 , Y 2 O 4 —ZrO 2 ).  
         [0101]     The guide vane  130  has a guide vane root (not shown here) facing the inner casing  138  of the turbine  108  and a guide vane head 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 .  
         [0102]      FIG. 19  shows a combustion chamber  110  of a gas turbine  100 . The combustion chamber  110  is configured, for example, as what is known as an annular combustion chamber, in which a multiplicity of burners  107 , which are arranged around the turbine shaft  103  in the circumferential direction, open out into a common combustion chamber space. For this purpose, the combustion chamber  110  as a whole is configured as an annular structure which is positioned around the turbine shaft  103 .  
         [0103]     To achieve a relatively high efficiency, the combustion chamber  110  is designed for a relatively high temperature of the working medium M of approximately 1000° C. to 1600° C. To allow a relatively long operating time even under these operating parameters, which are unfavorable for the materials, the combustion chamber wall  153  is provided, on its side which faces the working medium M, with an inner lining formed from heat shield elements  155 . On the working medium size, each heat shield element  155  is equipped with a particularly heat-resistant protective layer or is made from material that is able to withstand high temperatures. Moreover, on account of the high temperatures in the interior of the combustion chamber  110 , a cooling system is provided for the heat shield elements  155  and/or for their holding elements.  
         [0104]      FIG. 24  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 .  
         [0105]     The turbomachine may be a gas turbine of an aircraft or a power plant for power generation, a steam turbine or a compressor.  
         [0106]     The blade or vane  120 ,  130  includes, 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 . When used as guide vane  130 , the vane  130  may have a further platform at its vane tip  415  (not shown).  
         [0107]     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 . The blade or vane root  183  is configured, for example, in hammerhead form. Other configurations, as a fir tree root or dovetail root are possible. The blade or vane  120 ,  130  has a leading edge  409  and a trailing edge  412  with a respect to a medium which flows past the main blade or vane part  406 .  
         [0108]     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 . 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; these documents form part of the present disclosure with regard to the chemical composition of the alloy. The blade or vane  120 ,  130  may in this case be produced by a casting process, also by means of directional solidification, by a forging process, by a milling process or by combinations thereof.  
         [0109]     Workpieces with a single-crystal structure or structures are used as components for machines which are exposed to high mechanical, thermal and/or chemical stresses in operation. 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 directionally. Dendritic crystals are formed along the direction of heat flow and form either a columnar grain structure (i.e. grains which run over the entire length of the workpiece and are referred to here, in accordance with the usual terminology, as directionally solidified) or a single-crystal structure, i.e. the entire workpiece comprises a single crystal. In these processes, transition to the globular (polycrystalline) solidification needs to be avoided, since non-directional growth inevitably leads to the formation of transverse and longitudinal grain boundaries which negate the good properties of the directionally solidified or single-crystal component. Wherever the text refers in general terms to directionally solidified microstructures, this is also to be understood as encompassing single crystals which do not have any grain boundaries or at most have small-angle grain boundaries, as well as columnar crystal structures, which do have grain boundaries running in the longitudinal direction but do not have any transverse grain boundaries. This second type of crystalline structures is also referred to as directionally solidified microstructures (directional solidified structures). Processes of this type are known from U.S. Pat. No. 6,024,794 and EP 0 892 090 A1; these documents form part of the disclosure.  
         [0110]     It is also possible for the blades or vanes  120 ,  130  to have coatings protecting against corrosion or oxidation (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 of the rare earth elements, or hafnium (Hf)). Alloys of this type are known from EP0486489 B1, EP0786017 B1, EP 0 412 397 B1 or EP 1 306 454 A1, which are intended to form part of the present disclosure with regard to the chemical composition of the alloy.  
         [0111]     It is also possible for a thermal barrier coating consisting, for example, of ZrO 2 , Y 2 O 4 —ZrO 2 —i.e. this coating is not stabilized, is partially stabilized or is completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide—to be present on the MCrAlX. Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD).  
         [0112]     Refurbishment means that components  120 ,  130 , after they have been used, if appropriate have protective layers removed (e.g. by sand blasting). Then, the corrosion and/or oxidation layers and products are removed. Any cracks in the component  120 ,  130  are also repaired. Then, the component  120 ,  130  is recoated and the component  120 ,  130  is reused.  
         [0113]     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).