Abstract:
Prior art protective layers can exercise their protecting function because they are depleted in a specific element which forms a protective oxide, or which is used as sacrificial material. When said material has been consumed, the protecting function can no longer be provided. The invention is characterized in that it consists in using powder particles comprising a reserve of the consumed material, which is delivered in delayed manner. Therefor, the material is enclosed in an envelope.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2006/050506, filed Jan. 30, 2006 and claims the benefit thereof. The International Application claims the benefits of European application No. 05007093.7 filed Mar. 31, 2005, 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 as claimed in the claims. 
       BACKGROUND OF THE INVENTION 
       [0003]    Components for high-temperature applications, for example turbine blades and combustion chamber walls of gas turbines, comprise 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. The aluminum in this case diffuses from the MCrAlX alloy onto the surface of the MCrAlX layer, so that the alloy becomes depleted in respect of the element aluminum. 
         [0004]    A preventively elevated proportion of aluminum in the MCrAlX alloy from the start, however, leads to inferior mechanical properties of an MCrAlX layer. 
         [0005]    Compressor blades, which are provided with protective layers against corrosion and erosion, are furthermore known. 
         [0006]    During production these comprise an inorganic binder with a metal, the metal being used as an electrolytic sacrificial element and therefore being electrically conductively connected to the substrate of the component. A suitable composition of such a protective layer is known from EP 0 142 418 B1. 
         [0007]    Here again, the problem is that the metal becomes consumed over time, so that the protective function is no longer fulfilled. 
         [0008]    Encapsulated abrasive ceramic powder particles, which consist of SiC (nonoxide ceramic), are known from U.S. Pat. No. 4,741,973. EP 0 933 448 B1 discloses oxide particles in a layer consisting of an aluminide. 
       SUMMARY OF INVENTION 
       [0009]    It is therefore an object of the invention to provide a matrix and a layer system, which have a longer protective effect. 
         [0010]    The object is achieved by a matrix and a layer system as claimed in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Further advantageous measures, which may arbitrarily be combined with one another in an advantageous way, are listed in the respective dependent claims. 
           [0012]      FIG. 1  shows a powder particle, 
           [0013]      FIGS. 2-6  show exemplary embodiments according to the invention, 
           [0014]      FIG. 7  shows a turbine blade, 
           [0015]      FIG. 8  shows a combustion chamber and 
           [0016]      FIG. 9  shows a gas turbine 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0017]      FIG. 1  shows a particle  1  in cross section for a matrix according to the invention. 
         [0018]    The particle  1  consists of a core  7  and a shell  4 . 
         [0019]    The core  7  comprises a first element (chemical element!) or a first compound. A compound consists of a plurality of chemical elements. 
         [0020]    The core  7  may consist of a metal, an organic compound (for example ceramic), a nonmetal oxide, a metal oxide i.e. an oxide, or a glass. 
         [0021]    The core  7  does not consist of silicon carbide (SiC) or nonoxide ceramic (for example Si 3 N 4 ). 
         [0022]    The core  7  may likewise consist of sintered powder particles or a powder grain. 
         [0023]    The core  7  is enclosed by a shell  4  which encapsulates the core  7  at least partially, in particular fully. 
         [0024]    The shell  4  may also be porously designed. 
         [0025]    The diameter of the core  7  may lie in the micro, submicro (&lt;1 μm) or nano range (≦500 nm). The greatest transverse length of a polyhedron (core  7 ) may also be understood as a diameter. 
         [0026]    The first element is in particular metallic and may for example be aluminum (Al). 
         [0027]    The first element may likewise be chromium (Cr), an aluminum-chromium alloy or an aluminide. The core  7  may likewise be a mixture of two metals (for example chromium and aluminum) that can sometimes form an alloy, but which are not alloyed. 
         [0028]    Alloys are also intended to be understood by the term metallic. 
         [0029]    Further examples of the first element iron (Fe), titanium (Ti), platinum (Pt), yttrium (Y), zinc (Zn), tin (Sn) and/or copper (Cu). 
         [0030]    The shell  4  comprises a second chemical element or a second compound, which is different to the first element of the first compound. 
         [0031]    The second compound, i.e. the material of the shell  4 , is in particular a ceramic (nonoxide or oxide ceramic) and is for example aluminum oxide and/or chromium oxide or another metal oxide such as iron oxide or titanium oxide or an oxide of the first metallic element or metallic compound. 
         [0032]    An organic material may likewise be used for the shell  4 , for example an Si—O—C compound. 
         [0033]    The Si—O—C compound is in particular produced from a polysiloxane resin. Polysiloxane resins are polymer-ceramic precursors of the structural formula XSiO 1.5 , where X may be =—CH 3 , —CH, —CH 2 , —C 6 H S , etc. The material is thermally crosslinked, inorganic constituents (Si—O—Si chains) and organic side chains predominantly of X being present beside one another. The precursors are subsequently ceramized via a heat treatment in an Ar, N 2 , air or vacuum atmosphere at temperatures of between 600° C. and 1200° C. The polymer network is thereby decomposed and restructured via thermal intermediate stages from amorphous to crystalline phases, an Si—O—C network being created starting from polysiloxane precursors. 
         [0034]    Precursors of the polysilane (Si—Si), polycarbosilane (Si—C), polysilazane (Si—N) or polybarosilazane (Si—B—C—N) type may likewise be used. 
         [0035]    The second element may likewise be metallic and for example consist of titanium (Ti) or constitute an alloy. 
         [0036]    Thus, for example, the following material combinations are possible for the particle  1  (organic=organic molecule): 
         [0000]    core  7  of SiOC—shell  4  of metal
 
core  7  of SiOC—shell  4  of oxide (metal oxide or nonmetal oxide)
 
core  7  of SiOC—shell  4  of ceramic (organic or Si—O—C)
 
core  7  of SiOC—shell  4  of glass
 
core  7  of metal—shell  4  of metal
 
core  7  of metal—shell  4  of oxide (metal oxide or nonmetal oxide)
 
core  7  of metal—shell  4  of ceramic (organic or Si—O—C)
 
core  7  of metal—shell  4  of glass
 
core  7  of metal—shell  4  of polymer
 
core  7  of oxide—shell  4  of metal
 
core  7  of oxide—shell  4  of oxide (metal oxide or nonmetal oxide)
 
core  7  of oxide—shell  4  of ceramic (organic or Si—O—C)
 
core  7  of oxide—shell  4  of glass
 
core  7  of glass—shell  4  of metal
 
core  7  of glass—shell  4  of oxide (metal oxide or nonmetal oxide)
 
core  7  of glass—shell  4  of ceramic (organic or Si—O—C)
 
core  7  of glass—shell  4  of glass
 
         [0037]    The shell  4  may for example also have a gradient in the concentration of one of its constituents. For example, the core  7  of a powder particle  1  is formed from aluminum and the shell  4  partially from platinum, in which case the concentration of the material of the shell, preferably platinum, increases starting from the surface  25  of the core  7  as far as the outer surface  28  of the shell  4 . The concentration of the core material, i.e. for example aluminum, in the shell thus decreases from the inside outward and preferably has the same or a higher concentration on the surface  28  of the shell  4  compared with the aluminum of the matrix. 
         [0038]    Multilayered shells  4  may also be envisaged. 
         [0039]    The layer thickness of the shell  4  is for example up to ⅕, in particular up to 1/10 of the diameter of the core  7 , and is preferably 10 μm thick. 
         [0040]      FIG. 2  shows a matrix according to the invention of a layer  16 . The layer  16  is a part of a component  120 ,  130  ( FIGS. 7 ,  9 ), a combustion chamber element  155  ( FIG. 8 ) or a layer system  10 , which consists of a substrate  13  on which the layer  16  is arranged. 
         [0041]    The substrate  13  is for example a component for high temperatures, for example in steam or gas turbines  100  ( FIG. 9 ), consisting of a nickel-, cobalt- or iron-based superalloy. Such layer systems  10  may be employed for turbine blades  120 ,  130 , heat shield elements  155  or housing parts  138 . 
         [0042]    The layer  16  comprises a matrix of a matrix material, in which particles  1  are distributed homogeneously or locally differently (for example with a gradient). 
         [0043]    The particles  1  are preferably distributed homogeneously in the matrix. 
         [0044]    A plurality of layers  16 ,  19  may also be produced and used, the particles  1  being present in one or more sublayers or boundary layers. The particles  1  may be applied together by almost any coating method, i.e. by means of thermal plasma spraying (APS, VPS, LPPS), cold gas spraying, HVOF or an electrolytic coating method. 
         [0045]    The matrix of the layer  16  may be a metal, a ceramic, a glass or a ceramic/organic compound (for example Si—O—C). 
         [0046]    For example, the layer  16  is an alloy of the MCrAlX type and the particles  1  consist of a core  7  of aluminum. Aluminum-rich alloys are preferably used. The particles  1  may be distributed in the entire layer  16  or may be arranged locally concentrated near the outer surface  22  of the layer  16 . 
         [0047]    As already described above, the protective function of the MCrAlX alloy is obtained by the aluminum forming aluminum oxide, albeit while becoming depleted in the matrix material. 
         [0048]    Aluminum of the core  7  has for example a diffusion coefficient in the material of the shell  4  which is lower by at least 5%, in particular at least 10% at the working temperatures than aluminum in the matrix of the layer  16 , i.e. here in the MCrAlX alloy. 
         [0049]    At high temperatures, the aluminum diffuses slowly through the shell  4  into the matrix of the layer  16  and thus replenishes the aluminum which has been consumed in the matrix material by the oxidation, so that the original composition of the MCrAlX alloy changes scarcely or not at all over the operating time, until there is no longer any aluminum in the powder particles  1 . 
         [0050]    The effect achieved by this is that the lifetime of the protective layer  16  is extended considerably. 
         [0051]    The particles  1  may be present either only in the layer  16  (MCrAlX) or only in the substrate  13 . It is likewise possible for the particles to be arranged both in a layer  16  and in the substrate  13 . 
         [0052]    Irrespective of whether the particles  1  are also arranged in a layer  16  which is present on the substrate  13 , the following protective function is obtained when the particles  1  are present in the substrate  13 : During use of the layer system  10 , it may happen that the layer  16  (MCrAlX or MCrAlX+ceramic) is shed in a region  37 , so that a part of the surface  31  of the substrate  13  is unprotected ( FIG. 4 ). However, the particles  1  are arranged in the superficial region. Owing to further use of the layer system  10  at high temperatures T for a prolonged time t, the surface  31  of the substrate  13  corrodes in the region  37  so that the shells  4  of the particles  1  are abrasively or thermally disintegrated and the core  7  of the particle  1  is released. By reaction of the material of the core  7 , a protective function is obtained in the region  37  of the substrate  13 . In the case of superalloys which are used for gas turbine blades, the core  7  consists of aluminum or an alloy containing aluminum, so that a protective layer  40  of aluminum oxide, created by oxidation of the aluminum  7  of the core of the particles  1 , is formed in the region  37 . 
         [0053]    It may likewise be possible that the elevated temperatures which the particles  1  experience without a layer  16  in the region  37  increase the diffusion through the shell  4 , so that the aluminum can reach the surface in the region  37  even without breaking down the shell  4 , and can be oxidized there in order that a protective oxide layer  40  can be formed. 
         [0054]    These particles  1  may likewise be used to reinforce the superalloy, as is known from so-called ODS alloys. The size of the particles  1  preferably corresponds to the optimal size of the γ′ phase of a superalloy. 
         [0055]    The particles  1  are preferably already present in the melt and are co-cast. With respect to the arrangement and activity of ceramic particles in a superalloy, reference is made to the prior art relating to ODS alloys. The particles  1  then have the function: improving the mechanical properties and achieving an emergency backup property. 
         [0056]    The material of the shell  4  may likewise be selected so that the shell  4  is disintegrated by diffusion in the crystal structure of the matrix material of the layer  16  and optionally forms precipitates in the matrix material, and thus does not allow diffusion of the material of the core  7  directly into the matrix until after a certain time, since until this time the protective function for example of the MCrAlX layer is still provided. 
         [0057]    The second element or an element of the second compound of the shell  4  in this case has for example a higher diffusion coefficient in the matrix material than in the first element or in the first compound. 
         [0058]    The shell  4  may also be disintegrated abrasively and/or thermally and/or chemically, so that the core  7  is thereby released. 
         [0059]    A metal, for example aluminum, in the layer  16  of a compressor blade may also be enclosed by a shell  4  for example of aluminum oxide as described above, in which case the aluminum oxide contributes to increasing the erosion resistance when it is arranged at least in the vicinity of the surface. 
         [0060]    The layer  16  may likewise constitute a protective layer against corrosion and/or erosion of a compressor blade, in which case the effect of the particles  1  in a layer  16  with the chemical composition according to Patent EP 0 142 418 B1 is that enough sacrificial material is made available for the desired protective function to be obtained over a significantly longer period of time. 
         [0061]    The first element, in particular aluminum, is in this case enclosed by a shell  4  for example of a binder or polymer. 
         [0062]    There may in this case be a local concentration gradient of the particles  1  inside the layer  16  or also the substrate  13 . For example, the concentration of the particles  1  increases starting from the surface  31  of the substrate  13  as far as a surface  34  of the layer  16 . 
         [0063]    During the compression of air in the compressor, water may be formed which under certain circumstances, in conjunction with other elements contained in the air, forms an electrolyte that can lead to corrosion and erosion on the compressor blades. In order to prevent the corrosion and/or erosion, compressor blades are therefore generally provided with coatings. In particular coatings  16 , which comprise a for example phosphate-bound base matrix with metal particles such as aluminum particles dispersely distributed therein, may be envisaged in this case. The protective effect of such a coating consists in the metal particles embedded in the base coating, together with the (nobler) metal of the compressor blade and the electrolyte, forming an electrolytic cell in which the metal particles form so-called sacrificial anodes. The oxidation or the corrosion then takes place in the sacrificial anodes, i.e. in the metal particles and not in the metal of the compressor blade. 
         [0064]    The phosphate-bound base matrix of the coating has glass-ceramic properties, is thermally stable, likewise corrosion-resistant and protects against mechanical effects such as abrasion and erosion. 
         [0065]    Besides the metal particles, the coating may contain further particles As fillers. Colorant particles may be mentioned by way of example at this point. 
         [0066]    Besides phosphate-bound coatings, other types of coatings  16  may be envisaged. 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 coating  16  based on phosphate/borate and EP 0 933 446 B1 describes a coating based on phosphate/permanganate. 
         [0067]      FIG. 3  shows another exemplary application of the layer  16  according to the invention. 
         [0068]    The layer system  10  consists of a substrate  13 , a layer  16  according to the invention with a further layer  19  on the matrix of the layer  16 . 
         [0069]    This is for example a layer system  10  for high-temperature applications, the substrate  13  again constituting a superalloy as described above and the layer  16  comprising a matrix of the MCrAlX type. The layer  19  then constitutes a ceramic thermal insulation layer, the protective aluminum oxide layer (TGO) being formed between the layer  16  and the layer  19  (not shown). The particles  1  are, for example, concentrated near the interface between the layers  16  and  19 . 
         [0070]    A component may also be envisaged which is made of a material that comprises the particles  1 , i.e. they are present not in a coating but in a solid material. 
         [0071]      FIG. 5  shows another particle  1  according to the invention. 
         [0072]    The particle  1  again consists of the core  7 , an inner shell  4 ′ around the core  7  and a further shell  4 ″ around the inner shell  4 ′. 
         [0073]    The particle  1  may also comprise multilayered shells  4 . The core  7  preferably comprises a metal, the shell  4 ′ a ceramic and the outer shell  4 ″ a metal. 
         [0074]    It is likewise advantageous for the core  7  to consist of a metal, for the inner shell  4 ′ to consist of a metal which in particular is different to the material of the core  7 , and for an outer shell  4 ″ to consist of a ceramic. 
         [0075]    The core  7  may likewise be a cavity, the inner shell  4 ′ of metal and the outer shell  4 ″ of ceramic. 
         [0076]    Another particle  1  for a matrix  1  according to the invention is depicted in  FIG. 6 . 
         [0077]    The particles  1  comprise a three-layered shell. 
         [0078]    Exemplary embodiments for the sequence of the material in the shell materials  4 ′,  4 ″,  4 ′″ are presented in the following table. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 material 
                 material 
                 material 
                 material 
                 material 
                 material 
                 material 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 4′ 
                 metal 
                 metal 
                 metal 
                 metal 
                 ceramic 
                 ceramic 
                 ceramic 
               
               
                 4″ 
                 metal 
                 ceramic 
                 ceramic 
                 metal 
                 metal 
                 metal 
                 ceramic 
               
               
                 4″′ 
                 ceramic 
                 metal 
                 ceramic 
                 metal 
                 metal 
                 ceramic 
                 metal 
               
               
                   
               
             
          
         
       
     
         [0079]    The metal of the shell  4 ′ may be different to the metal of the shell  4 ″ or  4 ′″. 
         [0080]    Here again, the core  7  may be a cavity. 
         [0081]    The metals of the shells  4 ′,  4 ″ (FIG.  5 ) and  4 ′″ ( FIG. 6 ) may also be different to the metal of the core  7 . 
         [0082]    The layer thicknesses of the shells  4 ′,  4 ″,  4 ′″ may be individually adapted, and above all different. 
         [0083]      FIG. 7  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 . 
         [0084]    The turbomachine may be a gas turbine of an aircraft or of a power plant for electricity generation, a steam turbine or a compressor. 
         [0085]    The blade  120 ,  130  comprises, successively along the longitudinal axis  121 , a fastening region  400 , a blade platform  403  adjacent thereto and a blade surface  406  and a blade tip  415 . 
         [0086]    As a guide vane  130 , the vane  130  may have a further platform (not shown) at its vane tip  415 . 
         [0087]    A blade root  183  which is used to fasten the rotor blades  120 ,  130  on a shaft or a disk (not shown) is formed in the fastening region  400 . 
         [0088]    The blade root  183  is configured, for example, as a hammerhead. Other configurations as a fir tree or dovetail root are possible. 
         [0089]    The blade  120 ,  130  comprises a leading edge  409  and a trailing edge  412  for a medium which flows past the blade surface  406 . 
         [0090]    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 . 
         [0091]    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 documents are part of the disclosure in respect of the chemical composition of the alloy. 
         [0092]    The blades  120 ,  130  may in this case be manufactured by a casting method, also by means of directional solidification, by a forging method, by a machining method or combinations thereof. 
         [0093]    Workpieces with a monocrystalline structure or structures are used as components for machines which are exposed to heavy mechanical, thermal and/or chemical loads during operation. 
         [0094]    Such monocrystalline workpieces are manufactured, for example, by directional solidification from the melt. These are casting methods in which the liquid metal alloy is solidified to form a monocrystalline structure, i.e. to form the monocrystalline workpieces, or directionally. 
         [0095]    Dendritic crystals are in this case aligned along the heat flux and form either a rod crystalline grain structure (columnar, i.e. grains which extend over the entire length of the workpiece and in this case, according to general terminology usage, are referred to as directionally solidified) or a monocrystalline structure, i.e. the entire workpiece consists of a single crystal. It is necessary to avoid the transition to globulitic (polycrystalline) solidification in this method, since nondirectional growth will necessarily form transverse and longitudinal grain boundaries which negate the good properties of the directionally solidified or monocrystalline component. 
         [0096]    When directionally solidified structures are referred to in general, this is intended to mean both single crystals which have no grain boundaries or at most small-angle grain boundaries, and also rod crystal structures which, although they do have grain boundaries extending in the longitudinal direction, do not have any transverse grain boundaries. These latter crystalline structures are also referred to as directionally solidified structures. Such methods are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1; these documents are part of the disclosure in respect of the solidification method. 
         [0097]    The blades  120 ,  130  may likewise comprise coatings against corrosion or oxidation, for example (MCrAlX; M is at least one element from the group iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or and/or silicon at least one rare-earth element, for example hafnium (Hf)). Such alloys are known, for example, from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1, which are intended to be part of this disclosure in respect of the chemical composition of the alloy. 
         [0098]    The density is preferably 95% of the theoretical density. 
         [0099]    On the MCrAlX layer (as an interlayer or as the outermost layer), a protective aluminum oxide layer is formed (TGO=thermally grown oxide layer). The MCrAlX layer or the substrate comprises a matrix according to the invention. 
         [0100]    On the MCrAlX, there may also be a thermal insulation layer which is preferably at the outermost layer and consists for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. it is non-stabilized or partially or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
         [0101]    The thermal insulation layer covers the entire MCrAlX layer. 
         [0102]    Rod-shaped grains are generated in the thermal insulation layer by suitable coating methods, for example electron beam deposition (EB-PVD). 
         [0103]    Other coating methods are conceivable, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal insulation layer may comprise grains which are porous or affected by micro- or macrocracks for better thermal shock resistance. The thermal insulation layer is thus preferably more porous than the MCrAlX layer. 
         [0104]    Refurbishment means that components  120 ,  130  may need to have protective layers removed from them after their use (for example by sandblasting). Corrosion and/or oxidation layers or products are then removed. Optionally, cracks in the component  120 ,  130  will also be repaired. The component  120 ,  130  is then recoated and the component  120 ,  130  is used again. 
         [0105]    The blade  120 ,  130  may be designed to be a hollow or solid. If the blade  120 ,  130  is intended to be cooled, it will be hollow and optionally also comprise film cooling holes  418  (represented by dashes). 
         [0106]      FIG. 8  shows a combustion chamber  110  of a gas turbine  100 . The combustion chamber  110  is designed for example as a so-called ring combustion chamber, in which a multiplicity of burners  107  arranged in the circumferential direction around a rotation axis  102 , which produce flames  156 , open into a common combustion chamber space  154 . To this end, the combustion chamber  110  in its entirety is designed as an annular structure which is positioned around the rotation axis  102 . 
         [0107]    In order to achieve a comparatively high efficiency, the combustion chamber  110  is designed for a relatively high temperature of the working medium M, i.e. about 1000° C. to 1600° C. In order to permit a comparatively long operating time even under these operating parameters which are unfavorable for the materials, the combustion chamber wall  153  is provided with an inner lining formed by heat shield elements  155  on its side fining the working medium M. 
         [0108]    Each heat shield element  155  made of an alloy is equipped with a particularly heat-resistant protective layer on the working medium side (MCrAlX layer and/or ceramic coating), or is made of refractory material (solid ceramic blocks). 
         [0109]    These protective layers may be similar to the turbine blades, i.e. for example MCrAlX: M is at least one element from the group iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or at least one rare-earth element, for example hafnium (Hf). Such alloys are known, for example, from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1, which are intended to be part of this disclosure in respect of the chemical composition of the alloy. 
         [0110]    The MCrAlX layer or the substrate of the heat shield element  155  comprises of the matrix according to the invention. 
         [0111]    On the MCrAlX, there may also be an e.g. ceramic thermal insulation layer which consists for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. it is non-stabilized or partially or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
         [0112]    Rod-shaped grains are generated in the thermal insulation layer by suitable coating methods, for example electron beam deposition (EB-PVD). 
         [0113]    Other coating methods are conceivable, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal insulation layer may comprise grains which are porous or affected by micro- or macrocracks for better thermal shock resistance. 
         [0114]    Refurbishment means that heat shield elements  155  may need to have protective layers removed from them after their use (for example by sandblasting). Corrosion and/or oxidation layers or products are then removed. Optionally, cracks in the heat shield element  155  will also be repaired. The heat shield elements  155  are then recoated and the heat shield elements  155  are used again. 
         [0115]    Owing to the high temperatures inside the combustion chamber  110 , a cooling system is also provided for the heat shield elements  155  or their holding elements. The heat shield elements  155  are then for example hollow and optionally also comprise cooling holes (not shown) opening into the combustion chamber space  154 . 
         [0116]      FIG. 9  shows by way of example a gas turbine  100  in a longitudinal partial section. 
         [0117]    The gas turbine  100  internally comprises a rotor  103 , or turbine rotor, mounted so that it can rotate about a rotation axis  102  and having a shaft  101 . 
         [0118]    Successively along the rotor  103 , there are an intake manifold  104 , a compressor  105 , an e.g. toroidal combustion chamber  110 , in particular a ring combustion chamber, having a plurality of burners  107  arranged coaxially, a turbine  108  and the exhaust manifold  109 . 
         [0119]    The ring combustion chamber  106  communicates with an e.g. annular hot gas channel  111 . There, for example, four successively connected turbine stages  112  form the turbine  108 . 
         [0120]    Each turbine stage  112  is formed for example by two blade rings. As seen in the flow direction of a working medium  113 , a row  125  formed by rotor blades  120  follows in the hot gas channel  111  of a guide vane row  115 . 
         [0121]    The guide vanes  130  are fastened on the stator  143  while the rotor blades  120  of a row  125  are fitted on the rotor  103 , for example by means of a turbine disk  133 . 
         [0122]    Coupled to the rotor  103 , there is a generator or a work engine (not shown). 
         [0123]    During operation of the gas turbine  100 , air  135  is taken in by the compressor  105  through the intake manifold  104  and compressed. The compressed air provided at the turbine-side end of the compressor  105  is delivered to the burners  107  and mixed there with a fuel. The mixture is then burnt to form the working medium  113  in the combustion chamber  110 . From there, the working medium  113  flows along the hot gas channel  111  past the guide vanes  130  and the rotor blades  120 . At the rotor blades  120 , the working medium  113  expands by imparting momentum, so that the rotor blades  120  drive the rotor  103  and the work engine coupled to it. 
         [0124]    During operation of the gas turbine  100 , the components exposed to the hot working medium  113  experience thermal loads. Apart from the heat shield elements lining the ring combustion chamber  110 , the guide vanes  130  and rotor blades  120  of the first turbine stage  112 , as seen in the flow direction of the working medium  113 , are thermally loaded most greatly. 
         [0125]    In order to withstand the temperatures prevailing there, they may be cooled by means of a coolant. 
         [0126]    The substrates may likewise comprise a directional structure, i.e. they are monocrystalline (SX structure) or comprise only longitudinally directed grains (DS). 
         [0127]    Iron-, nickel- or cobalt-based superalloys, for example, are used as material for the components, in particular for the turbine blades and vanes  120 ,  130  and components of the combustion chamber  110 . 
         [0128]    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 documents are part of the disclosure in respect of the chemical composition of the alloy. 
         [0129]    The blades and vanes  120 ,  130  may likewise comprise coatings against corrosion (MCrAlX; M is at least one element in the group iron (Fe), cobalt (Co), nickel (Ni), X stands for yttrium (Y) and/or silicon, scandium (Sc) and/or at least one rare-earth element or hafnium). Such alloys are known, for example, from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1, which are intended to be part of this disclosure in respect of the chemical composition of the alloy. 
         [0130]    On the MCrAlX, there may also be a thermal insulation layer which consists for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. it is non-stabilized or partially or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
         [0131]    Rod-shaped grains are generated in the thermal insulation layer by suitable coating methods, for example electron beam deposition (EB-PVD). 
         [0132]    The guide vanes  130  comprise a guide vane root (not shown 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 fixed on a fastening ring  140  of the stator  143 .