Abstract:
A solder alloy including a base material, a solder, and an additive is provided. The solder alloy has the following formula:
       (1−x−y)*base material+x*solder+y*additive,   where  0.2≦ x≦ 0.8  and   0≦y&lt;0.8 and also (y&lt;1−x)&lt;(1−x).
 
The base material includes chromium, cobalt, aluminum, and tungsten. The solder includes chromium, cobalt, aluminum, tungsten, germanium and/or gallium and nickel. The additive may include boron, zirconium, hafnium, niobium, and carbon.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2010/054756, filed Apr. 12, 2010 and claims the benefit thereof. All of the applications are incorporated by reference herein in their entirety. 
       FIELD OF INVENTION 
       [0002]    The invention relates to a solder alloy and to a soldering process. 
       BACKGROUND OF INVENTION 
       [0003]    It is sometimes necessary to repair components after they have been produced, for example after casting or after they have been used and cracks have formed. 
         [0004]    There are various repair processes for this purpose, for example the welding process; in this process, however, it is additionally necessary to melt a substrate material of the component, and this may result in damage particularly to cast and directionally solidified components and in the evaporation of constituents of the substrate material. 
         [0005]    A soldering process is carried out at temperatures which are lower than the temperature for the welding process and therefore lower than the melting temperature of the substrate material. 
         [0006]    Nevertheless, the solder should have high strength in order that the crack filled with solder or the depression does not weaken the entire component at the high operating temperatures. 
       SUMMARY OF INVENTION 
       [0007]    It is therefore an object of the invention to provide a solder alloy which solves the problem mentioned above. 
         [0008]    The object is achieved by a solder consisting of a solder alloy as claimed in the claims, by a process as claimed in the claims and by a component as claimed in the claims 
         [0009]    The solder alloy consists of: 
         [0000]    (1−x−y)*base material+x*solder+y*additive,
 
where 0.2≦x≦0.8 and
 
0≦y&lt;0.8 and also (y&lt;1−x)&lt;(1−x).
 
wherein the base material comprises:
 
3 wt %-20 wt % chromium (Cr), in particular 9 wt %,
 
0.1 wt %-20 wt % cobalt (Co), in particular 9 wt %, 0.1 wt %-6 wt % aluminum (Al), in particular 5 wt %,
 
0.1 wt %-10 wt % tungsten (W), in particular 9 wt %, and optionally
 
0.1 wt %-6 wt % titanium (Ti), in particular&lt;1 wt %,
 
0.1 wt %-4 wt % molybdenum (Mo), in particular 1 wt %,
 
0.1 wt %-6 wt % tantalum (Ta), in particular 3 wt %, and nickel, and
 
wherein the solder comprises:
 
0.1 wt %-10 wt % chromium (Cr), in particular 4 wt %-8 wt %,
 
0.1 wt %-10 wt % cobalt (Co), in particular 4 wt %-8 wt %,
 
0.1 wt %-6 wt % aluminum (Al), in particular 1.5 wt %,
 
0.1 wt %-6 wt % tungsten (W), in particular 3 wt %, and germanium (Ge) and/or gallium (Ga),
 
in particular 18 wt % to 30 wt %, and nickel,
 
wherein the additive comprises:
 
0 wt %-0.015 wt % boron (B), in particular&lt;0.010 wt %,
 
0 wt %-0.1 wt % zirconium (Zr), in particular&lt;0.075 wt %,
 
0 wt %-1 wt % hafnium (Hf), in particular&lt;0.075 wt %,
 
0 wt %-1 wt % niobium (Nb), in particular&lt;0.8 wt %,
 
0 wt %-0.15 wt % carbon (C), in particular&lt;0.1 wt %.
 
         [0010]    Further advantageous developments of the solder alloy are: 
         [0000]    it uses only one element selected from the group consisting of titanium, molybdenum and tantalum for the base material,
 
it uses at least two elements selected from the group consisting of titanium, molybdenum and tantalum for the base material,
 
in particular only two elements from this group,
 
it comprises titanium, molybdenum and tantalum for the base material,
 
it has a nickel-based base material,
 
in particular it comprises nickel as remainder for the base material, it has a nickel-based solder,
 
in particular the solder comprises nickel as remainder,
 
it is nickel-based,
 
in particular it comprises nickel as remainder,
 
it contains no deliberate addition of boron (B),
 
in particular B&lt;20 ppm,
 
it contains no silicon (Si),
 
it comprises no zirconium (Zr),
 
it comprises no hafnium (Hf),
 
it comprises no niobium (Nb),
 
it comprises no carbon (C),
 
it contains no titanium (Ti),
 
it contains no molybdenum (Mo),
 
it contains no tantalum (Ta),
 
it has the greatest proportion by weight for nickel (Ni),
 
it comprises gallium (Ga) and no germanium (Ge),
 
it comprises germanium (Ge) and no gallium (Ga),
 
it comprises gallium (Ga) and germanium (Ge),
 
it comprises at least 0.006 wt % zirconium (Zr),
 
advantageous values for zirconium (Zr), boron (B), carbon (C), molybdenum (Mo), gallium (Ga), germanium (Ge),
 
hafnium (Hf), niobium (Nb), tungsten (W), tantalum (Ta), chromium (Cr), cobalt (Co), aluminum (Al) and titanium (Ti) are listed in the dependent claims,
 
good soldering results were obtained where
 
0.3&lt;x&lt;0.5
 
and/or
 
where y=0
 
or where 0.2≦Y,
 
in particular 0.3≦Y≦0.5,
 
it contains no manganese,
 
it consists of nickel, germanium, chromium, aluminum, cobalt, tungsten and titanium,
 
it consists of nickel, germanium, chromium, aluminum, cobalt, tungsten, tantalum and titanium,
 
it consists of nickel, germanium, chromium, aluminum, cobalt, tungsten, titanium, carbon and molybdenum,
 
it consists of nickel, germanium, cobalt, chromium, titanium, tungsten, molybdenum, tantalum and aluminum,
 
it consists of nickel, germanium, chromium, aluminum, cobalt, carbon, molybdenum, tungsten, tantalum and titanium,
 
it consists of nickel, carbon, germanium, chromium, cobalt, aluminum, molybdenum, tungsten, tantalum, niobium, titanium and zirconium,
 
the process includes that the solder alloy is directionally solidified in polycrystalline form (CC), in particular in polycrystalline components,
 
a further advantageous development of the process consists in the fact that the solder ( 10 ) is directionally solidified.
 
         [0011]    The component contains a solder consisting of the solder alloy mentioned above. 
         [0012]    The component can be advantageously developed respectively as follows, it being possible for these features to be combined with one another in any desired way in an advantageous manner: 
         [0000]    the substrate of the component is directionally solidified,
 
the substrate of the component is not directionally solidified,
 
the chromium content of the solder alloy corresponds to the chromium content of the substrate of the component,
 
the cobalt content corresponds to the cobalt content of the substrate of the component,
 
the aluminum content of the solder alloy is reduced compared to the aluminum content of the substrate of the component,
 
in particular is reduced by 10%,
 
the titanium content of the solder alloy is lower than the titanium content of the substrate of the component, if the germanium contents are between 18 wt % and 30 wt %,
 
in particular is lower by at least 10%, the solder alloy comprises no molybdenum.
 
         [0013]    The dependent claims list further advantageous measures which can advantageously be combined with one another in any desired way. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    In the drawings: 
           [0015]      FIG. 1  shows a cross-sectional view of a component after treatment with the solder according to the invention, 
           [0016]      FIG. 2  shows a perspective view of a turbine blade or vane, 
           [0017]      FIG. 3  shows a perspective view of a combustion chamber, 
           [0018]      FIG. 4  shows a gas turbine, and 
           [0019]      FIG. 5  shows a list of superalloys. 
       
    
    
       [0020]    The figures and the description represent merely exemplary embodiments of the invention. 
       DETAILED DESCRIPTION OF INVENTION 
       [0021]      FIG. 1  shows a component  1  which is treated with a solder  10  consisting of a solder alloy according to the invention. 
         [0022]    The component  1  comprises a substrate  4  which, particularly in the case of components for high temperature applications, in particular in the case of turbine blades or vanes  120 ,  130  ( FIG. 2 ) or combustion chamber elements  155  ( FIG. 3 ) for steam or gas turbines  100  ( FIG. 4 ), consists of a nickel-based or cobalt-based superalloy ( FIG. 5 ). 
         [0023]    The solder  10  can preferably be used for all the alloys according to  FIG. 5 . These may preferably be the known materials PWA 1483, PWA 1484, Rene 80 or Rene N5. 
         [0024]    The solder  10  is also used in blades or vanes for aircraft. 
         [0025]    A crack  7  or a depression  7  which is to be filled by soldering is present in the substrate  4 . The cracks  7  or depressions  7  preferably have a width of about 200 μm and may have a depth of up to 5 mm. 
         [0026]    In this case, the solder material  10  consisting of a solder alloy is applied into or close to the depression  7 , and the solder material  10  is melted by heat treatment (+T) below a melting temperature of the substrate  4  and completely fills the depression  7 . 
         [0027]    The solder alloy consists of 
         [0000]    (1−x−y)*base material+x*solder+y*additive,
 
where 0.2≦x≦0.8 and
 
0≦y≦0.8 and also (y&lt;1−x)&lt;(1−x),
 
wherein the base material comprises:
 
3 wt %-20 wt % chromium (Cr), in particular 9 wt %,
 
0.1 wt %-20 wt % cobalt (Co), in particular 9 wt %,
 
0.1 wt %-6 wt % aluminum (Al), in particular 5 wt %,
 
0.1 wt %-10 wt % tungsten (W), in particular 9 wt %, and optionally
 
0.1 wt %-6 wt % titanium (Ti), in particular&lt;1 wt %,
 
0.1 wt %-4 wt % molybdenum (Mo), in particular 1 wt %,
 
0.1 wt %-6 wt % tantalum (Ta), in particular 3 wt %, and nickel, and
 
wherein the solder comprises:
 
0.1 wt %-10 wt % chromium (Cr), in particular 4 wt %-8 wt %,
 
0.1 wt %-10 wt % cobalt (Co), in particular 4 wt %-8 wt %,
 
0.1 wt %-6 wt % aluminum (Al), in particular 1.5 wt %,
 
0.1 wt %-6 wt % tungsten (W), in particular 3 wt %, and germanium (Ge) and/or gallium (Ga),
 
in particular 18 wt % to 30 wt %, and nickel,
 
wherein the additive comprises:
 
0 wt %-0.015 wt % boron (B), in particular≦0.010 wt %,
 
0 wt %-0.1 wt % zirconium (Zr), in particular≦0.075 wt %,
 
0 wt %-1 wt % hafnium (Hf), in particular≦0.075 wt %, 0 wt %-1 wt % niobium (Nb), in particular≦0.8 wt %,
 
0 wt %-0.15 wt % carbon (C), in particular≦0.1 wt %.
 
This is therefore a physical mixture of two (base material and solder) or three (+additive) powders.
 
         [0028]    The addition of germanium (Ge) preferably dispenses with the addition of boron (B). 
         [0029]    The addition of germanium (Ge) preferably dispenses with the addition of silicon (Si). 
         [0030]    The addition or the presence of silicon and/or carbon is preferably avoided since they form brittle phases in the solder. 
         [0031]    The addition or the presence of iron and/or manganese is likewise preferably avoided since these elements form low-melting phases or non-oxidizing phases. 
         [0032]    As a melting point reducer, it is possible to use 
         [0000]    gallium (Ga) and no germanium (Ge) or
 
germanium (Ge) and no gallium (Ga) or
 
gallium (Ga) and germanium (Ge).
 
         [0033]    The base material comprises only one, two or three elements selected from the group consisting of titanium, molybdenum and tantalum. 
         [0034]    The base material is in particular nickel-based. 
         [0035]    The solder is in particular nickel-based. 
         [0036]    The alloy preferably contains no zirconium (Zr), no hafnium (Hf), no manganese (Mn), no niobium (Nb) and/or no carbon (C). 
         [0037]    Advantageous proportions for zirconium (Zr), boron (B) and carbon are listed in the dependent claims 
         [0038]    Good soldering results were obtained where 0.3≦x≦0.5 and/or y=0 or 
       0.2≦Y, 
       [0039]    in particular 0.3≦Y≦0.5. 
         [0040]    Preferred values for molybdenum (Mo), gallium (Ga), germanium (Ge), hafnium (Hf), niobium (Nb), tungsten (W), tantalum (Ta), chromium (Cr), cobalt (Co), aluminum (Al) and titanium (Ti) are listed in the dependent claims. 
         [0041]    The solder alloy preferably consists of nickel, germanium, chromium, aluminum, cobalt, tungsten and titanium. 
         [0042]    The solder alloy likewise preferably consists of nickel, germanium, chromium, aluminum, cobalt, tungsten, tantalum and titanium. 
         [0043]    The solder alloy likewise preferably consists of nickel, germanium, cobalt, chromium, aluminum, tungsten, titanium, carbon and molybdenum. 
         [0044]    The solder alloy likewise preferably consists of nickel, germanium, cobalt, chromium, titanium, tungsten, molybdenum, tantalum and aluminum. 
         [0045]    The solder alloy likewise preferably consists of nickel, germanium, chromium, aluminum, cobalt, carbon, molybdenum, tungsten, tantalum and titanium. 
         [0046]    The solder alloy likewise preferably consists of nickel, carbon, germanium, chromium, cobalt, aluminum, molybdenum, tungsten, tantalum, niobium, titanium and zirconium. 
         [0047]    The addition of rhenium can also preferably be dispensed with. The solder material  10  may be joined to the substrate  4  of the component  1 ,  120 ,  130 ,  155  in an isothermal process or a temperature gradient process. A gradient process is preferably suitable when the substrate  4  has a directional structure, for example an SX or DS structure, such that the solder material  10  then also has a directional structure. However, a directionally solidified structure in the solder may also be provided in an isothermal process. 
         [0048]    Equally, the component  1  does not need to have a directionally solidified structure (but rather a CC structure). 
         [0049]    The solders in CC substrates of components may likewise be soldered and solidified in a CC structure, the solders then being solidified in polycrystalline form (CC). 
         [0050]    The following solders are of particular interest especially for the polycrystalline solidification of the solders: 
         [0051]    During the melting (isothermal process or gradient process), use is preferably made of an inert gas, in particular argon, which reduces the vaporization of chromium from the substrate  4  at the high temperatures, or a reducing gas (argon/hydrogen) is used. 
         [0052]    The solder material  10  may also be applied to a large area of a surface of a component  1 ,  120 ,  130 ,  155  in order to thicken the substrate  4 , in particular in the case of hollow components. The solder material  10  is preferably used to fill cracks  7  or depressions  7 . 
         [0053]      FIG. 2  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 . 
         [0054]    The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
         [0055]    The blade or vane  120 ,  130  has, 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  and a blade or vane tip  415 . 
         [0056]    As a guide vane  130 , the vane  130  may have a further platform (not shown) at its vane tip  415 . 
         [0057]    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 . 
         [0058]    The blade or vane root  183  is designed, for example, in hammerhead form. Other configurations, such as a fir-tree or dovetail root, are possible. 
         [0059]    The blade or vane  120 ,  130  has a leading edge  409  and a trailing edge  412  for a medium which flows past the main blade or vane part  406 . 
         [0060]    In the case of conventional blades or vanes  120 ,  130 , by way of example solid metallic materials, in particular superalloys, in particular the superalloys according to  FIG. 5 , are used in all regions  400 ,  403 ,  406  of the blade or vane  120 ,  130 . 
         [0061]    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. 
         [0062]    The blade or vane  120 ,  130  may in this case be produced by a casting process, by means of directional solidification, by a forging process, by a milling process or combinations thereof. 
         [0063]    Workpieces with a single-crystal structure or structures are used as components for machines which, in operation, are exposed to high mechanical, thermal and/or chemical stresses. 
         [0064]    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 solidifies directionally. 
         [0065]    In this case, dendritic crystals are oriented along the direction of heat flow and form either a columnar crystalline grain structure (i.e. grains which run over the entire length of the workpiece and are referred to here, in accordance with the language customarily used, as directionally solidified) or a single-crystal structure, i.e. the entire workpiece consists of one single crystal. In these processes, a transition to globular (polycrystalline) solidification needs to be avoided, since non-directional growth inevitably forms transverse and longitudinal grain boundaries, which negate the favorable properties of the directionally solidified or single-crystal component. 
         [0066]    Where the text refers in general terms to directionally solidified microstructures, this is to be understood as meaning both single crystals, which do not have any grain boundaries or at most have small-angle grain boundaries, and columnar crystal structures, which do have grain boundaries running in the longitudinal direction but do not have any transverse grain boundaries. This second form of crystalline structures is also described as directionally solidified microstructures (directionally solidified structures). 
         [0067]    Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1. 
         [0068]    The blades or vanes  120 ,  130  may likewise have coatings protecting against corrosion or oxidation e.g. (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 rare earth element, or hafnium (Hf)). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. 
         [0069]    The density is preferably 95% of the theoretical density. 
         [0070]    A protective aluminum oxide layer (TGO=thermally grown oxide layer) is formed on the MCrAlX layer (as an intermediate layer or as the outermost layer). 
         [0071]    The layer preferably has a composition Co-30Ni-28Cr-8A1-0.6Y-0.75i or Co-28Ni-24Cr-10Al-0.6Y. In addition to these cobalt-based protective coatings, it is also preferable to use nickel-based protective layers, such as Ni-10Cr-12Al-0.6Y-3Re or Ni-12Co-21Cr-11Al-0.4Y-2Re or Ni-25Co-17Cr-10Al-0.4Y-1.5Re. 
         [0072]    It is also possible for a thermal barrier coating, which is preferably the outermost layer and consists for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, to be present on the MCrAlX. 
         [0073]    The thermal barrier coating covers the entire MCrAlX layer. 
         [0074]    Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0075]    Other coating processes are possible, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may include grains that are porous or have micro-cracks or macro-cracks, in order to improve the resistance to thermal shocks. The thermal barrier coating is therefore preferably more porous than the MCrAlX layer. 
         [0076]    Refurbishment means that after they have been used, protective layers may have to be removed from components  120 ,  130  (e.g. by sand-blasting). Then, the corrosion and/or oxidation layers and products are removed. If appropriate, cracks in the component  120 ,  130  are also repaired. This is followed by recoating of the component  120 ,  130 , after which the component  120 ,  130  can be reused. 
         [0077]    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). 
         [0078]      FIG. 3  shows a combustion chamber  110  of a gas turbine. The combustion chamber  110  is configured, for example, as what is known as an annular combustion chamber, in which a multiplicity of burners  107 , which generate flames  156 , arranged circumferentially around an axis of rotation  102  open out into a common combustion chamber space  154 . For this purpose, the combustion chamber  110  overall is of annular configuration positioned around the axis of rotation  102 . 
         [0079]    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 service life even with 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 . 
         [0080]    On the working medium side, each heat shield element  155  made from an alloy is equipped with a particularly heat-resistant protective layer (MCrAlX layer and/or ceramic coating) or is made from material that is able to withstand high temperatures (solid ceramic bricks). 
         [0081]    These protective layers may be similar to the turbine blades or vanes, i.e. for example 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 rare earth element or hafnium (Hf). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. 
         [0082]    It is also possible for a, for example, ceramic thermal barrier coating to be present on the MCrAlX, consisting for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
         [0083]    Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0084]    Other coating processes are possible, e.g. atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may include grains that are porous or have micro-cracks or macro-cracks, in order to improve the resistance to thermal shocks. 
         [0085]    Refurbishment means that after they have been used, protective layers may have to be removed from heat shield elements  155  (e.g. by sand-blasting). Then, the corrosion and/or oxidation layers and products are removed. If appropriate, cracks in the heat shield element  155  are also repaired. This is followed by recoating of the heat shield elements  155 , after which the heat shield elements  155  can be reused. 
         [0086]    Moreover, a cooling system may be provided for the heat shield elements  155  and/or their holding elements, on account of the high temperatures in the interior of the combustion chamber  110 . The heat shield elements  155  are then, for example, hollow and may also have cooling holes (not shown) opening out into the combustion chamber space  154 . 
         [0087]      FIG. 4  shows, by way of example, a partial longitudinal section through a gas turbine  100 . 
         [0088]    In the interior, the gas turbine  100  has a rotor  103  with a shaft  101  which is mounted such that it can rotate about an axis of rotation  102  and is also referred to as the turbine rotor. 
         [0089]    An intake housing  104 , a compressor  105 , a, for example, toroidal combustion chamber  110 , in particular an annular combustion chamber, with a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust-gas housing  109  follow one another along the rotor  103 . 
         [0090]    The annular combustion chamber  110  is in communication with a, for example, annular hot-gas passage  111 , where, by way of example, four successive turbine stages  112  form the turbine  108 . 
         [0091]    Each turbine stage  112  is formed, for example, from two blade or vane rings. As seen in the direction of flow of a working medium  113 , in the hot-gas passage  111  a row of guide vanes  115  is followed by a row  125  formed from rotor blades  120 . 
         [0092]    The guide vanes  130  are secured to an inner housing  138  of a stator  143 , whereas the rotor blades  120  of a row  125  are fitted to the rotor  103  for example by means of a turbine disk  133 . 
         [0093]    A generator (not shown) is coupled to the rotor  103 . 
         [0094]    While the gas turbine  100  is operating, the compressor  105  sucks in air  135  through the intake housing  104  and compresses it. The compressed air provided at the turbine-side end of the compressor  105  is passed to the burners  107 , where it is mixed with a fuel. The mix is then burnt in the combustion chamber  110 , forming the working medium  113 . From there, the working medium  113  flows along the hot-gas passage  111  past the guide vanes  130  and the rotor blades  120 . The working medium  113  is expanded at the rotor blades  120 , transferring its momentum, so that the rotor blades  120  drive the rotor  103  and the latter in turn drives the generator coupled to it. 
         [0095]    While the gas turbine  100  is operating, the components which are 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 elements which line the annular combustion chamber  110 , are subject to the highest thermal stresses. 
         [0096]    To be able to withstand the temperatures which prevail there, they may be cooled by means of a coolant. 
         [0097]    Substrates of the components may likewise have a directional structure, i.e. they are in single-crystal form (SX structure) or have only longitudinally oriented grains (DS structure). 
         [0098]    By way of example, iron-based, nickel-based or cobalt-based superalloys are used as material for the components, in particular for the turbine blade or vane  120 ,  130  and components of the combustion chamber  110 . 
         [0099]    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. 
         [0100]    The blades or vanes  120 ,  130  may also have coatings which protect against corrosion (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, scandium (Sc) and/or at least one rare earth element or hafnium). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. 
         [0101]    A thermal barrier coating, consisting for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, may also be present on the MCrAlX. 
         [0102]    Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0103]    The guide vane  130  has a guide vane root (not shown here), which faces the inner housing  138  of the turbine  108 , and a guide vane head which is 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 .