Abstract:
Protective layers, according to the prior art, achieve their protective function b depletion of a defined element that forms a protective oxide layer or that is exhausted as a sacrificial material. Once said material is exhausted, the protective function cannot be maintained. The invention is characterized by using particles ( 1 ) that contain a sustained-release depot of the exhaustible material. For this purpose, the material is present in a superstoichiometric form.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2007/051929, filed Mar. 1, 2007 and claims the benefit thereof. The International Application claims the benefits of European application No. 06006326.0 filed Mar. 27, 2006, both of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a matrix and to a layer system according to the claims. 
       BACKGROUND OF THE INVENTION 
       [0003]    Components for high temperature applications, for example turbine blades and combustion chamber walls of gas turbines, have protective layers against oxidation and corrosion. Such layers consist, for example, of an alloy of the MCrAlX type, a protective aluminum oxide layer being formed on this MCrAlX layer. In this case, the aluminum of the MCrAlX alloy diffuses onto the surface of the MCrAlX layer, so that the MCrAlX alloy undergoes a depletion of the element aluminum. 
         [0004]    However, a preventatively enhanced fraction of aluminum in the MCrAlX alloy from the outset, in order to counteract depletion, leads to poorer mechanical properties of the MCrAlX layer. 
         [0005]    Moreover, compressor blades are known which are provided with protective layers against corrosion and erosion. In production, these have an inorganic binder with a metal, the metal serving as a galvanic sacrificial element therefore being connected electrically conductively to the substrate of the component. A suitable composition of such a protective layer is known from EP 0 142 418 B1. 
         [0006]    Even here, there is the problem that the metal is in time consumed, so that the protective function is no longer performed. 
         [0007]    Encased powder particles which consist of Al are known from U.S. Pat. No. 6,635,362. 
         [0008]    EP 0 933 448 B1 discloses oxide particles in a layer consisting of an aluminide. 
         [0009]    WO 2002/066706 A2 shows a matrix with encased particles which consist of stoichiometric alloys. 
       SUMMARY OF INVENTION 
       [0010]    The object of the invention, therefore, is to indicate a matrix and a layer system which have a longer protective action. 
         [0011]    The object is achieved by means of a matrix according the claims and a layer system according to the claims. 
         [0012]    The respective subclaims list further advantageous measures which may advantageously be combined with one another, as desired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    In the drawings: 
           [0014]      FIGS. 1 ,  2  and  3  show layers or a substrate according to the invention, 
           [0015]      FIG. 4  shows a gas turbine, 
           [0016]      FIG. 5  shows a turbine blade in perspective, 
           [0017]      FIG. 6  shows a combustion chamber in perspective. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0018]    A compound consists of at least two or of a plurality of chemical elements and has a specific stoichiometry. An alloy (metallic compound) consists of at least two metallic elements. 
         [0019]    The particle  1  ( FIGS. 1 ,  2  and  3 ) consists of a compound which has at least one metal Me of a matrix of a layer  16  ( FIGS. 1 and 2 ) or of a substrate  13  ( FIG. 3 ) in a non-stoichiometric ratio. The at least one further chemical element Z, which with the metal Me forms the compound, may be a constituent of the matrix material or be a chemical element which is not contained in the matrix material. 
         [0020]    The compound, that is to say the material of the particle  1 , is, in particular, a compound of the metal Me with a non-metal, that is to say is a ceramic (non-oxide or oxide ceramic, an oxynitride, nitride, boride or carbide) and is preferably an oxide, preferably aluminum oxide and/or chromium oxide. The particle  1  also preferably has a nitride. The particle  1  preferably consists of a metal oxide and/or metal nitride. 
         [0021]    The particle  1  may also have a plurality of types of compounds: oxides, oxynitrides, nitrides, borides or carbides. 
         [0022]    Preferably, an above-stoichiometric compound Me a Z b−y  (y&gt;0), Me a+x Z b  (x&gt;0) or Me a+x Z b−y  (x&gt;0, y&gt;0) is used instead of Me a Z b , that is to say, for example (Z=nitrogen N) AlN 1−y  (y&gt;0), Al 1+x N (x&gt;0) or Al 1+x N 1−y  (x&gt;0, Y&gt;0) instead of AlN. 
         [0023]    The compound for the particle  1  may likewise consist of an alloy which is a non-stoichiometric composition of the alloy. 
         [0024]    Thus, for example, an alloy Ni 1−y Al (y&gt;0) or NiAl 1+x (x&gt;0) is used instead of NiAl. 
         [0025]    Even below-stoichiometric compounds may be advantageous. 
         [0026]    Preferably, the particle  1  has only one metal element Me. 
         [0027]    Preferably, the particle  1  has two metal elements Me. The metal element Me in the compound, in the alloy or in the silicon chains is, in particular, aluminum (Al). 
         [0028]    The metal element may likewise be chromium (Cr). 
         [0029]    Furthermore, a chromium/aluminum alloy (Al—Cr) may be used, in order to produce a compound for the particle  1 . 
         [0030]    Likewise, an organic material R-Me-C—R, such as, for example, an Si-Me-O—C material (silicon chains) may be used for the particle  1  (Me=Al), C=carbon, R=carbon chain. 
         [0031]    The R-Me-C—R material is produced, in particular, from a polysiloxane resin. Polysiloxane resins are polymer-ceramic precursors of the structural formula R—SiO 1.5  with at least one metal element, in which case R may be ═—CH 3 , —CH, —CH 2 , —C 6 H s , etc. The material is cross-linked thermally, inorganic constituents (Si—O—Si chains) and organic side chains predominantly consisting of R being present next to one another. Subsequently, the precursors are ceramized via temperature treatment in Ar, N 2 , or an air or vacuum atmosphere at temperatures of between 600° C. and 1200° C. In this case, the polymer network is decomposed and is restructured via thermal intermediate stages from amorphous to crystalline phases, a Si—Al(=Me)-O—C network being obtained, starting from polysiloxane precursors. Likewise, precursors of the type polysilane (Si—Si), polycarbosilane (Si—C), polysilazane (Si—N) or polybarosilazane (Si—B—C—N) with metal elements Me may also be used. 
         [0032]    Here, the metal element Me does not have to be present in a non-stoichiometric ratio. It is sufficient for the compound to have the capability whereby the metal element Me can easily be released from the compound. 
         [0033]    The particle  1  may be a sintered powder particle or a powder grain. 
         [0034]    The diameter of the particle  1  may be in the micro, submicro (&lt;1 μm) or nanorange (≦500 nm). The diameter may also be understood as being the greatest transverse length of a polyhedron. 
         [0035]    The particles  1  preferably have no casing consisting of a different material. 
         [0036]      FIG. 1  shows a matrix according to the invention of a layer  16 . The layer  16  is part of a component  10  or layer system  10  consisting of a substrate  13  on which the layer  16  is arranged. 
         [0037]    The substrate  13  is, for example, a component for high temperatures, such as, for example, in steam or gas turbines  100  ( FIG. 5 ), consisting of a nickel-, cobalt- or iron-based superalloy. Such layer systems  10  are employed in turbine blades  120 ,  130  ( FIGS. 4 and 5 ), heat shield elements  155  ( FIG. 6 ) or housing parts  138  ( FIG. 4 ). 
         [0038]    The layer  16  has a matrix consisting of a matrix material in which the particles  1  are distributed homogeneously or locally in a different way (for example, with a gradient). The particle  1  thus constitutes a secondary phase in the matrix (layer, substrate). 
         [0039]    In this case, a local concentration gradient of the particles  1  within the layer  16  or the substrate  13  may be present. Thus, for example, starting from the surface  31  of the substrate  13 , the concentration of the particles  1  increases in the direction of a surface  34  of the layer  16 . 
         [0040]    In this case, a plurality of layers  16 ,  19  may also be produced and used, the particles  1  being present in one or more layers. 
         [0041]    The matrix of the layer  16  is preferably metal-based. For example, the layer  16  is an alloy of the type MCrAlX, and the particles  1  consist of an aluminum compound. The particles  1  may be distributed in the entire layer  16  or be arranged, concentrated locally, near the outer surface  22  of the layer  16  ( FIG. 2 ). 
         [0042]    The operation of the prolonged protective action is described by way of example by means of an MCrAlX layer. 
         [0043]    As already described further above, the protective function of the MCrAlX alloy arises in that the aluminum forms aluminum oxide, although this depletes the aluminum in the matrix material. 
         [0044]    At high temperatures, the aluminum diffuses slowly out of the particles  1  to the matrix of the layer  16  and thus fills the matrix material up again with the aluminum consumed as a result of oxidation, so that the original composition of the MCrAlX alloy scarcely changes or does not change at all, until aluminum is no longer contained in the particle  1 . 
         [0045]    What is achieved thereby is that the useful life of the protective layer  16  is prolonged considerably. 
         [0046]    The particles  1  are released diffusively in the matrix in two different ways. Either they are penetrated by the atoms of the matrix material, these being the atoms of the gamma phase in the case of nickel-based materials, or the non-metallic ceramic-forming bond partner diffuses into the particle inward and the metallic element dissolves in the matrix. 
         [0047]    In the case of nickel-based materials, the metallic element, preferably aluminum, dissolves in the gamma phase. In the latter instance, a stoichiometric core of the corresponding ceramic composition would remain and, due to particle hardening, would have a permanently consolidating action for the γ′-phase. 
         [0048]    These particles  1  may likewise be used for reinforcing a superalloy. The size of the particles  1  preferably corresponds to the optimal size of the γ′-phase of a superalloy. 
         [0049]    The non-melted particles  1  are then preferably already present in the melt and are cast together with the latter. As regards the type of arrangement and type of operation of a secondary phase in a superalloy, reference is made to the prior art. The particles  1  then have the following functions: improving the mechanical properties and achieving an emergency running property. 
         [0050]    The stoichiometry may also be selected such that the above-stoichiometric fraction dissolves slowly due to diffusion in the crystal structure of the matrix material of the layer  16  and, where appropriate, forms precipitations in the matrix material and therefore allows a diffusion of the material of the particle  1  directly into the matrix only after a certain time, since, up to this time point, the protective function of, for example, the MCrAlX layer is still afforded. 
         [0051]    Irrespective of whether the particles  1  are also arranged in a layer  16  present on the substrate  13 , in the presence of the particles  1  in the substrate  13  a further protective function is obtained: 
         [0052]    While the layer system  10  is being used, it may happen that the layer  16  (MCrAlX or MCrAlX+outer ceramic layer) flakes off in a region  37 , so that part of a surface  31  of the substrate  13  is unprotected ( FIG. 3 ). However, in the near-surface region, the particles  1  are preferably arranged in a high concentration ( FIG. 2 ). 
         [0053]    Due to the further use of the layer system  10  at high temperatures T for a longer time t, the surface  31  of the substrate  13  corrodes in the region  37 , with the result that that of the particles  1  is released. A reaction of the material of the particle  1  results in the protective function in the region  37  of the substrate  13 . In the case of superalloys which are used for the gas turbine blades, the particle  1  has aluminum, and therefore a protective layer  40  is formed from aluminum oxide which has occurred due to the oxidation of the aluminum of the particle  1 . 
         [0054]    The particles  1  may be present either only in the layer  16  (MCrAlX) or only in the substrate  13 . It is likewise possible that the particles are arranged both in a layer  16  and in the substrate  13 . 
         [0055]    Likewise, the layer  16  may constitute a protective layer against the corrosion and/or erosion of a compressor blade, the particles  1  in a layer  16 , preferably having the chemical composition according to the patent EP 0 142 418 B1, resulting in sufficient sacrificial material being made available for a markedly longer period of time, so that the desired protective function is obtained. 
         [0056]    In this case, an aluminum-containing compound is used for the particle. 
         [0057]    During the compression of air in the compressor, water may occur which, under certain circumstances, in conjunction with other elements contained in the air, forms an electrolyte which may lead to corrosion and erosion on the compressor blades. 
         [0058]    In order to prevent the corrosion and/or erosion, compressor blades are therefore provided, as a rule, with coatings. In this case, in particular, coatings  16  are considered which comprise a, for example, phosphate-bound basic matrix with metal particles, such as, for example, aluminum particles, distributed dispersively therein. In the protective action of a coating of this type, the metal particles embedded in the basic coating form, together with the (nobler) metal of the compressor blade and the electrolyte, a galvanic cell in which the metal particles form what are known as sacrificial anodes. The oxidation or corrosion then takes place in the sacrificial anodes, that is to say in the metal particles, not in the metal of the compressor blade. 
         [0059]    The phosphate-bound basic matrix of the coating has glass-ceramic properties, is thermally stable and likewise corrosion-resistant and protects against mechanical actions, for example abrasion and erosion. 
         [0060]    In addition to the metal particles, the coating may contain further particles as fillers. Colorant particles may be mentioned at this juncture as an example. 
         [0061]    In addition to phosphate-bound coatings, further types of coatings  16  may be considered. EP 0 142 418 B1, EP 0 905 279 A1 and EP 0 995 816 A1 describe coatings based on chromate/phosphate. EP 1 096 040 A2 describes a phosphate/borate-based coating  16  and EP 0 933 446 B1 describes a phosphate/permanganate-based coating. 
         [0062]    These layers, too, may have a matrix according to the invention. 
         [0063]    The particles  1  can be applied together by means of virtually any coating method, that is to say by means of thermal plasma spraying (APS, VPS, LPPS), cold gas spraying, HVOF or an electrolytic coating method.  FIG. 2  shows a further example of the use of the layer  16  according to the invention. 
         [0064]    The layer system  10  consists of a substrate  13 , and of a layer  16  according to the invention with a further layer  19  on the matrix of the layer  16 . 
         [0065]    This is, for example, a layer system  10  for high temperature applications, the substrate  13  again being a superalloy, as described above, and the layer  16  having a matrix of the type MCrAlX. The layer  19  is then a ceramic heat insulation layer, the protective aluminum oxide layer (TGO) being formed between the layer  16  and the layer  19 . The particles  1  according to the invention are, for example, concentrated near the interface between the layers  16  and  19 . 
         [0066]    A component may likewise be envisaged, consisting of a material which has the particles  1 , that is to say they are not present in a coating, but, instead, in a solid material. 
         [0067]      FIG. 4  shows by way of example a gas turbine  100  in a longitudinal part section. 
         [0068]    The gas turbine  100  has inside it a rotor  103  rotatably mounted about an axis of rotation  102  and having a shaft  101 , said rotor also being designated as a turbine rotor. 
         [0069]    Arranged successively along the rotor  103  are an intake housing  104 , a compressor  105 , a, for example, toroidal combustion chamber  110 , in particular annular combustion chamber, having a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust gas housing  109 . 
         [0070]    The annular combustion chamber  110  communicates with a, for example, annular hot gas duct  111 . There, for example, four turbine stages  112  connected in series form the turbine  108 . 
         [0071]    Each turbine stage  112  is formed, for example, from two blade rings. As seen in the flow direction of a working medium  113 , a row  125  formed from moving blades  120  follows a guide vane row  115  in the hot gas duct  111 . 
         [0072]    The guide vanes  130  are in this case fastened to an inner housing  138  of a stator  143 , whereas the moving blades  120  of a row  125  are mounted on the rotor  103 , for example, by means of a turbine disk  133 . 
         [0073]    A generator or a working machine (not illustrated) is coupled to the rotor  103 . 
         [0074]    When the gas turbine  100  is in operation, air  135  is sucked in through the intake housing  104  by the compressor  105  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, at the same time forming the working medium  113 , in the combustion chamber  110 . 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, with the result that the moving blades  120  drive the rotor  103  and the latter drive the working machine coupled to it. 
         [0075]    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 flow direction of the working medium  113 , are subjected to the highest thermal load in addition to the heat shield elements lining the annular combustion chamber  110 . 
         [0076]    In order to withstand the temperatures prevailing there, these can be cooled by means of a coolant. 
         [0077]    Substrates of the components may likewise have a directional structure, that is to say they are monocrystalline (SX structure) or have only longitudinally directed grains (DS structure). 
         [0078]    The material used for the components, in particular for the turbine blade  120 ,  130  and components of the combustion chamber  110 , is, for example, iron-, nickel- or cobalt-based superalloys. 
         [0079]    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 regard to the chemical composition of the alloys. 
         [0080]    The guide vane  130  has a guide vane root (not illustrated here) facing the inner housing  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 . 
         [0081]      FIG. 5  shows a perspective view of a moving blade  120  or guide vane  130  of a turbomachine which extends along a longitudinal axis  121 . 
         [0082]    The turbomachine may be a gas turbine of an aircraft or of a power station for electricity generation, a steam turbine or a compressor. 
         [0083]    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 . 
         [0084]    As a guide vane  130 , the blade  130  may have (not illustrated) a further platform at its blade tip  415 . 
         [0085]    In the fastening region  400 , a blade root  183  is formed, which serves for fastening the moving blades  120 ,  130  to a shaft or a disk (not illustrated). 
         [0086]    The blade root  183  is configured, for example, as a hammer head. Other configurations as a pinetree or dovetail root are possible. 
         [0087]    The blade  120 ,  130  has a leading edge  409  and a trailing edge  412  for a medium which flows past the blade leaf  406 . 
         [0088]    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 . 
         [0089]    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. 
         [0090]    The blade  120 ,  130  may in this case be manufactured by means of a casting method, also by means of directional solidification, by a forging method, by a milling method or by combinations of these. 
         [0091]    Workpieces having a monocrystalline structure or structures are used as components for machines which are exposed during operation to high mechanical, thermal and/or chemical loads. 
         [0092]    The manufacture of monocrystalline workpieces of this type is carried out, for example, by directional solidification from the melt. Casting methods are adopted here, in which the liquid metallic alloy solidifies to the monocrystalline structure, that is to say to the monocrystalline workpiece, or directionally. 
         [0093]    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 are designated here, according to general linguistic practice, as being directionally solidified) or a monocrystalline structure, that is to say the entire workpiece consists of a single crystal. In these methods, the transition to globulitic (polycrystalline) solidification must be avoided, since, due to undirected growth, transverse and longitudinal grain boundaries are necessarily formed which nullify the good properties of the directionally solidified or monocrystalline component. 
         [0094]    When directionally solidified structures are referred to in general, this means both monocrystals which have no grain boundaries or, at most, low-angle grain boundaries, and columnar-crystal structures which have grain boundaries running in the longitudinal direction, but no transverse grain boundaries. The second-mentioned crystalline structures are also referred to as directionally solidified structures. 
         [0095]    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 with respect to the solidification method. 
         [0096]    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 0486 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 of the alloy. 
         [0097]    The density preferably lies at 95% of the theoretical density. 
         [0098]    A protective aluminum oxide layer (TGO=thermal grown oxide layer) is formed on the MCrAlX layer (as an intermediate layer or as the outermost layer). 
         [0099]    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. 
         [0100]    The heat insulation layer covers the entire MCrAlX layer. Columnar grains are generated in the heat insulation layer by means of suitable coating methods, such as, for example, electron beam evaporation (EB-PVD). Other coating methods may also be envisaged, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. 
         [0101]    The heat insulation layer may have porous microcrack- or macrocrack-susceptible grains for better thermal shock resistance. The heat insulation layer is therefore preferably more porous than the MCrAlX layer. 
         [0102]    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). 
         [0103]      FIG. 6  shows a combustion chamber  110  of the 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  arranged around an axis of rotation  102  in the circumferential direction issue into a common combustion chamber space  154  and generate the flames  156 . For this purpose, the combustion chamber  110  is configured in its entirety as an annular structure which is positioned around the axis of rotation  102 . 
         [0104]    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 make a comparatively long operating time possible 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 . 
         [0105]    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 . 
         [0106]    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 a material resistant to high temperature (solid ceramic bricks). 
         [0107]    These protective layers may be similar to those of the turbine blades, that is to say, 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 a 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 with respect to the chemical composition of the alloy. 
         [0108]    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 partially or completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
         [0109]    Columnar grains are generated in the heat insulation layer by means of suitable coating methods, such as, for example, electron beam evaporation (EB-PVD). 
         [0110]    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-susceptible grains for better thermal shock resistance. 
         [0111]    Refurbishment means that turbine blades  120 ,  130  or heat shield elements  155 , after being used, must, where appropriate, be freed of protective layers (for example by sandblasting). A removal of the corrosion and/or oxidation layers or products is then carried out. If appropriate, cracks in the turbine blade  120 ,  130  or in the heat shield element  155  are also repaired. This is followed by a recoating of the turbine blades  120 ,  130  and heat shield elements  155  and a renewed use of the turbine blades  120 ,  130  or of the heat shield elements  155 .