WO2008138384A1 - Material composition for use as a masking material for the protection of regions of a turbine component that are not to be coated and method for coating turbine components - Google Patents

Abstract

The invention relates to a method for coating turbine components, said turbine components comprising regions (2) to be coated and regions (9) not to be coated, with a corrosion- or oxidation-inhibiting coating material (15). The method comprises the following steps: masking the regions (9) not to be coated with a masking material (13) before applying the coating material (15), applying the coating material (15) to the turbine component by thermal spraying, and removing the masking material (13) after the application of the coating material (15). A material is used as the masking material that has viscous properties in a temperature range of 1000°C to 1500°C and that is solid and tough at temperatures below 1000°C. The masking material may particularly be produced from a composition that comprises polysiloxane, a solvent, and a filler comprising metal or carbon.

Description

 Material composition for use as

Masking material for protection of non-coating

Areas of a turbine component and method for

Coating of turbine components

The present invention relates to a material composition for use as a masking material for the protection of non-coating areas of a turbine component during the application of a corrosion-inhibiting and / or oxidation-inhibiting coating. In addition, the invention relates to a method for coating turbine components, which have areas to be coated and areas not to be coated, with a corrosion-inhibiting and / or oxidation-inhibiting coating material.

Turbine components, such as, for example, rotor blades or guide vanes of gas turbines or combustion chamber components, are exposed during operation of the turbine to a corrosive hot gas, namely the combustion exhaust gases. In order to protect the components against the corrosive and / or oxidative effect of this hot gas, they are provided with a coating system, which is usually a ceramic thermal barrier coating and an adhesive layer, also called "bond coat", between the ceramic thermal barrier coating and the actual component surface. While the ceramic thermal barrier coating is intended to reduce heat conduction to the underlying base material, the adhesion promoter layer also serves as a bonding layer for the ceramic thermal barrier coating to the base material of the component as a corrosion and / or oxidation inhibiting layer.

Although such a coating system increases the resistance of the turbine component to the attack of the corrosive and / or oxidative hot gas, the coating system is also subject to wear. The turbine component is therefore stripped and re-coated after a certain period of operation (so-called "refurbishment"). In order to further reduce the load caused by the corrosive and / or oxidative hot gas, the turbine components are usually also provided with cooling air holes, which allow the escape of cooling air from a cavity in fluid communication with a cooling air reservoir, so that above the Component surface forms a cooling air film. When coating the component, whether during the initial re-coating or as part of recoating, care must be taken that the cooling-air holes are not closed at the end of the coating process or reduced in their free diameter. Closed cooling air holes are referred to as the "coat over" effect, while cooling holes whose free diameter is reduced are referred to as "coat down" because coating material extends "down" on the inner walls of the cooling air holes the film cooling significantly impaired or completely impossible.

In the prior art, therefore, measures are taken, the

"Coat down" effect and the "coat over" effect during the spraying of the coating, which is usually done with a thermal spraying method, either completely avoid or at least reduce or subsequently effectively remove the disturbing coating material again. The reopening of closed or constricted cooling air bores takes place, for example, by means of a laser, by means of electroerosive methods or manually, and is therefore time consuming and expensive. Therefore, methods have been developed in which cooling air holes of turbine components are sealed prior to applying the coating by means of a masking material which is introduced into the cooling air holes. Subsequently, the material is allowed to harden and performs the coating process with the cooling air holes protected in this way. Thereafter, the masking material is removed again. In US 5,902,647 and EP 1 076 106 Bl, for example, methods are described in which the masking material is introduced into the holes in such a way that it projects beyond the outer surface of the turbine component.

WO 03/089679 A1 describes a method in which the masking material is introduced into the cooling air bores of a turbine blade in such a way that its surface terminates flush with the surface of the turbine component. By suitable choice of the masking material and filling materials in the masking material to ensure that the coating material does not adhere to the masking material. After the coating material has been introduced into the film cooling holes, it is set in light or ultrasound.

Excess masking material may interfere with the coating process and cause uneven results if masking is too prominent. However, unless it is selected so that the coating material does not adhere to the masking material, it is overcoated with the surface finish masking material. Therefore, not only the masking material itself but also the coating material on the masking material must be removed. This can sometimes be more costly and time consuming than reopening the holes if they are not protected by a masking material. Although the problem of "coat over" does not occur with the masking material described in WO 03/089679 A1, this masking material requires the supply of light or ultrasound to bind it, which can sometimes be difficult, especially if the light or the ultrasound must be supplied from the interior of the component.

It is therefore an object of the present invention to provide an advantageous material composition for use as a masking material for protecting areas of a turbine component that are not to be coated during the application of a masking material corrosion-inhibiting and / or oxidation-inhibiting coating to provide. It is a further object of the present invention to provide an advantageous method for coating turbine components.

These objects are achieved by a material composition according to claim 1 and a method for coating turbine components according to claim 8. The dependent claims contain advantageous embodiments of the invention.

The material composition according to the invention comprises polysiloxane ([R ₂ SiO] _n , wherein R stands for an organic group such as methyl, ethyl, phenyl, etc.), a solvent and a filler comprising metal and / or carbon. The polysiloxane may in particular be a methylsiloxane, ie a polysiloxane of the form [CH ₃ SiO _1-5 I _n . Suitable solvents are, in particular, organic solvents, for example terpenol-based solvents. The filler may in particular be selected from the group consisting of carbon powder, metal powder, strontium carbonate (SrCO ₃ ), calcium carbonate (CaCO ₃ ), sodium carbonate (Na ₂ CO ₃ ), lithium carbonate (Li ₂ CO ₃ ) and magnesium carbonate ( Magnesite, MgCO ₃ ) and mixtures thereof.

The material composition according to the invention is particularly suitable for use as a masking material for protection of non-coating areas of a turbine component, such as the walls of cooling air holes, during the application of a corrosion-inhibiting and / or oxidation-inhibiting coating. The reason for this is that a masking material can be realized with the material composition according to the invention, which has viscous properties in a temperature range of 1000 ⁰ C to 1500 ° C, while it is solid and tough at temperatures below 1000 ⁰ C. This is a catching and encapsulation of the hot, usually fused and sometimes even molten coating particles that actually hit on the component surface in thermal spraying and adhere there, by the Masking material possible. When hot coating particles strike the masking material, they penetrate the masking material to a certain depth, then cool and are finally frozen by the masking material.

In a material composition of the invention which is particularly suitable as a masking material, the volume fraction of the filler in the total volume of polysiloxane and filler is at least 70%, in particular at least 90%.

The method according to the invention for coating turbine components which have areas to be coated and areas which are not to be coated, with a corrosion-inhibiting and / or oxidation-inhibiting coating material comprises the steps:

Masking the regions not to be coated with a masking material, which may in particular comprise the material composition according to the invention, before applying the coating material;

Application of the coating material to the turbine component by thermal spraying, some atmospheric plasma spraying (APS) or high-velocity oxy- gen fuel (HVOF); and

Removal of the masking material after application of the coating material.

In the method according to the invention is used as a masking material, a material which has viscous properties in a temperature range of 1000 ⁰ C to 1500 ⁰ C, while it is solid and tough at temperatures below 1000 ⁰ C. Such a material can be particularly with the inventive

Realize material composition. In the process according to the invention, the hot, mostly molten and sometimes even molten coating particles in the areas not to be coated, for example the walls of cooling air bores, are collected and encapsulated by the masking material which is viscous during the coating. When they strike the masking material they penetrate due to its viscosity at the prevailing temperatures during spraying to a certain depth in the masking material and then cool. They are finally frozen by the masking material. After coating, the surfaces of the encapsulated spray particles are then ideally largely covered with masking material. In addition, before the particles cool, as they pass through the masking material, there are no large sintered areas, neither between the spray particles, nor between the spray particles and the component surface that is not to be coated. Therefore, the "frozen" coating material can easily be removed along with the masking material after the component has cooled.

The masking material used in the process according to the invention is, in particular, a material which, in addition, embrittles to room temperature during cooling of the component. While an increase in the volume of the masking material takes place during the spraying of the coating material due to the picked-up metal particles, which can lead to a slight beading on the component surface, but mainly takes place in the direction of the component interior, the masking material shrinks to room temperature during the cooling. When the room temperature is reached, therefore, the areas of the component which are not to be coated are provided with embrittled masking material doped with metal particles, which can be removed by gentle mechanical blasting, for example with dry ice or a high-pressure water jet. The masking material which embrittles on cooling to room temperature can also be realized with the material composition according to the invention. In an advantageous development of the method according to the invention, the masking material is applied as a curable paste on or in the areas not to be coated or introduced and then cured before the coating material is applied. In the invention

Material composition, the amount of the solvent can be set so that the material composition is present as a spreadable paste. As spreadable paste, the masking material is particularly easy on or in the non-coated areas of the turbine component or bring.

The curing of the masking material, particularly when a material composition according to the invention reduction is used as a masking material can be brought about by a heat treatment at a temperature below 600 ^0C. In this case, the polysiloxanes are crosslinked so that a matrix of inorganic constituents, for example Si-O-Si chains, and organic side chains, predominantly of -CH ₃ , are present next to one another, into which the carbonaceous and / or metal-powder-containing filler is embedded. The crosslinking can ensure reliable retention of the introduced or applied masking material in or on the regions of the turbine component which are not to be coated.

In a further embodiment of the invention, the masking material used is in particular a ceramizable material which is ceramified before the coating material is applied. In particular, the material composition according to the invention is suitable as a ceramizable material. The ceramization can be brought about by a pyrolysis treatment at a temperature within a temperature range between 600 and 1200 ⁰ C ⁰ C. In this case, the pyrolysis can be carried out, for example, in an argon atmosphere, in air or in vacuo. In particular, it is also possible to carry out the pyrolysis during the preheating of the turbine component before the application of the coating material, so that no additional process step is obtained. For example. During the ceramization of the material composition according to the invention, the polymeric network of the cured masking material is decomposed and restructured via thermal intermediates of amorphous to crystalline phases. When the pyrolysis is carried out in an argon atmosphere or under vacuum, a silicon oxy carbide glass (SiOC glass) is formed, when it is carried out in air, a quartz glass (SiO ₂ glass), also called cristobalite, is formed. While quartz glasses have a softening temperature of 1050 ⁰ C, have silicon oxycarbide glasses a softening temperature of about 1350 ⁰ C. The incorporation of carbon into the SiO ₂ matrix of quartz glass, it is possible to raise the softening temperature and a glass for the Hochtem - To provide temperature range. By selectively adding carbonaceous and / or metal powder-containing fillers such as, for example, strontium carbonate, calcium carbonate, sodium carbonate, lithium carbonate and magnesium carbonate, it is possible to lower the silicon oxide carbide glass in its softening temperature. Depending on the choice of the filler, which may be present in particular as a combination of two or more of said fillers, and the volume fraction of the filler in the total volume of polysiloxane and filler in the material composition according to the invention, it is therefore possible a defined softening temperature window in the range in particular between 1050 ⁰ C and 1350 ⁰ C open, in which the glass has a sufficiently high viscosity for collecting and encapsulating the hot coating material particles. In particular, with the material composition according to the invention, a viscosity can be brought about which is high enough to hold the material approximately in cooling air bores of the turbine blade without flowing out, but low enough to absorb the kinetic energy of the impinging coating particles and to encapsulate them.

The inventive method for coating turbine components can in particular as a method for applying MCrAlX material may be formed as a coating material. M is at least one element of the group consisting of iron (Fe), cobalt (Co) and nickel (Ni), X for yttrium (Y) and / or silicon (Si) and / or at least one element of the rare earths or Hafnium (Hf).

Further features, properties and advantages of the present invention will become apparent from the following description of embodiments with reference to the accompanying figures.

FIG. 1 shows a cross-section through a cooling-air bore which was protected during the application of an MCrAlX coating with a masking material made of a material composition according to the invention.

Figures 2 to 7 show various stages of the coating process of the invention.

FIG. 8 shows by way of example a gas turbine in a longitudinal partial section.

FIG. 9 shows a perspective view of a moving blade or guide vane of a turbomachine that extends along a longitudinal axis.

FIG. 10 shows a combustion chamber of a gas turbine.

FIG. 8 shows by way of example a gas turbine 100 in a longitudinal partial section.

The gas turbine 100 has inside a rotatably mounted about a rotation axis 102 rotor 103 with a shaft 101, which is also referred to as a turbine runner. Along the rotor 103 follow one another an intake housing 104, a compressor 105, for example a toroidal combustion chamber 110, in particular annular combustion chamber, with a plurality Coaxially arranged burners 107, a turbine 108 and the exhaust housing 109th

The annular combustion chamber 110 communicates with an annular annular hot gas channel 111, for example. There, for example, four turbine stages 112 connected in series form the turbine 108.

Each turbine stage 112 is formed, for example, from two blade rings. As seen in the direction of flow of a working medium 113, in the hot gas channel 111 of a row of guide vanes 115, a series 125 formed of rotor blades 120 follows.

The guide vanes 130 are fastened to an inner housing 138 of a stator 143, whereas the moving blades 120 of a row 125 are attached to the rotor 103 by means of a turbine disk 133, for example.

Coupled to the rotor 103 is a generator or work machine (not shown).

During operation of the gas turbine 100, air 105 is sucked in and compressed by the compressor 105 through the intake housing 104. The compressed air provided at the turbine-side end of the compressor 105 is supplied to the burners 107 where it is mixed with a fuel. The mixture is then burned to form the working medium 113 in the combustion chamber 110. From there, the working medium flows

113 along the hot gas channel 111 past the guide vanes 130 and the blades 120. On the blades 120, the working medium 113 expands in a pulse-transmitting manner, so that the blades 120 drive the rotor 103 and this drives the machine coupled to it.

The components exposed to the hot working medium 113 are subject to thermal loads during operation of the gas turbine 100. The guide vanes 130 and rotor blades 120 of the first turbine stage 112, viewed in the flow direction of the working medium 113, are subjected to the greatest thermal stress in addition to the heat shield elements lining the annular combustion chamber 110. To withstand the prevailing temperatures, they can be cooled by means of a coolant. Likewise, substrates of the components can have a directional structure, ie they are monocrystalline (SX structure) or have only longitudinal grains (DS structure).

As the material for the components, in particular for the turbine blade 120, 130 and components of the combustion chamber 110, for example, iron-, nickel- or cobalt-based superalloys are used. 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.

Likewise, blades 120, 130 may be anti-corrosion coatings (MCrAlX; M is at least one member of the group

Iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and / or silicon, scandium (Sc) and / or at least one element of rare earth or hafnium). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 Bl, EP 0 412 397 B1 or EP 1 306 454 A1.

On the MCrAlX may still be present a thermal barrier coating, and consists for example of ZrO ₂ , Y ₂ O ₃ -ZrO ₂ , ie it is not, partially or completely stabilized by yttrium oxide and / or calcium oxide and / or magnesium oxide.

By suitable coating methods, e.g. Electron beam evaporation (EB-PVD) produces stalk-shaped grains in the thermal barrier coating.

The vane 130 has a guide vane foot (not shown here) facing the inner housing 138 of the turbine 108 and a vane head opposite the vane foot. The vane head faces the rotor 103 and fixed to a mounting ring 140 of the stator 143. FIG. 9 shows a perspective view of a moving blade 120 or guide blade 130 of a turbomachine that extends along a longitudinal axis 121.

The turbomachine may be a gas turbine of an aircraft or a power plant for power generation, a steam turbine or a compressor.

The blade 120, 130 has, along the longitudinal axis 121, a fastening area 400, an adjacent blade platform 403 and an airfoil 406 and a blade tip 415.

As a guide blade 130, the blade 130 may have another platform at its blade tip 415 (not shown).

In the mounting region 400, a blade root 183 is formed, which serves for attachment of the blades 120, 130 to a shaft or a disc (not shown). The blade root 183 is designed, for example, as a hammer head. Other designs as Christmas tree or Schwalbenschwanzfuß are possible.

The blade 120, 130 has a leading edge 409 and a trailing edge 412 for a medium flowing past the airfoil 406.

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.

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 writings are with respect. the chemical composition of the alloy part of the disclosure. The blade 120, 130 can be made by a casting process, also by directional solidification, by a forging process, by a milling process or combinations thereof. Workpieces with a monocrystalline structure or structures are used as components for machines which are exposed to high mechanical, thermal and / or chemical stresses during operation.

The production of such monocrystalline workpieces takes place e.g. by directed solidification from the melt. These are casting processes in which the liquid metallic alloy is transformed into a monocrystalline structure, i. to the single-crystal workpiece, or directionally solidified.

In this process, dendritic crystals are aligned along the heat flow and form either a columnar grain structure (columnar, i.e. grains which run the full length of the workpiece and here, in common language use, are referred to as directionally solidified) or a monocrystalline structure, i. the whole workpiece consists of a single crystal. In these processes, one must avoid the transition to globulitic (polycrystalline) solidification, since undirected growth necessarily forms transverse and longitudinal grain boundaries which negate the good properties of the directionally solidified or monocrystalline component. Is generally speaking of directionally solidified structures speech, so are both single crystals meant that have no grain boundaries or at most small angle grain boundaries, as well

Stem-crystal structures, which probably have longitudinally extending grain boundaries, but no transverse grain boundaries. These second-mentioned crystalline structures are also known as directionally solidified structures.

Such methods are known from US Pat. No. 6,024,792 and EP 0 892 090 A1; These writings are with respect. the solidification process part of the disclosure.

Similarly, the blades 120, 130 coatings against

Have corrosion or oxidation, z. (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 element of the rare earths, or hafnium (Hf)). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 Bl, EP 0 412 397 B1 or EP 1 306 454 A1.

The density is preferably 95% of the theoretical density.

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).

Preferably, the layer composition comprises Co-30Ni-28Cr-8Al-0,6Y-0,7Si or Co-28Ni-24Cr-10Al-0, 6Y. Besides these cobalt-based protective coatings, nickel-based protective layers such as Ni-10Cr-12Al-0.6Y-3Re or Ni-12Co-21Cr-IIAl-O, 4Y-2Re or Ni-25Co-17Cr-10Al-0.4Y-1 are also preferably used , 5Re.

On the MCrAlX may still be present a thermal barrier coating, which is preferably the outermost layer, and consists for example of ZrO ₂ , Y ₂ O ₃ -ZrO ₂ , ie it is not, partially or completely stabilized by yttria and / or calcium oxide and / or magnesium oxide. The thermal barrier coating covers the entire MCrAlX layer.

By suitable coating methods, e.g. Electron beam evaporation (EB-PVD) produces stalk-shaped grains in the thermal barrier coating.

Other coating methods are conceivable, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may have porous, micro- or macro-cracked grains for better thermal shock resistance. The thermal barrier coating is therefore preferably more porous than the MCrAlX layer. Refurbishment means that components 120, 130 may have to be freed of protective layers after use (eg by sandblasting). This is followed by removal of the corrosion and / or oxidation layers or products. If necessary, will also

Cracks in component 120, 130 repaired. This is followed by a re-coating of the component 120, 130 and a renewed use of the component 120, 130.

The blade 120, 130 may be hollow or solid. If the blade 120, 130 is to be cooled, it is hollow and may still film cooling holes 418 (indicated by dashed lines) on.

FIG. 10 shows a combustion chamber 110 of a gas turbine. The combustion chamber 110 is designed, for example, as a so-called annular combustion chamber, in which a multiplicity of burners 107 arranged in the circumferential direction about an axis of rotation 102 open into a common combustion chamber space 154 which generates 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 around.

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 ⁰ C to 1600 ° C. In order to lend a comparatively long service life to 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 of heat shield elements 155.

Each heat shield element 155 made of an alloy is equipped on the working fluid side with a particularly heat-resistant protective layer (MCrAlX layer and / or ceramic coating) or is made of high-temperature-resistant material (solid ceramic stones). These protective layers may be similar to the turbine blades, so for example MCrAlX means: M is at least one element of the group iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and / or silicon and / or at least one element of the rare earths, or hafnium (Hf). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 Bl, EP 0 412 397 B1 or EP 1 306 454 A1.

On the MCrAlX, for example, a ceramic thermal barrier coating may be present and consists for example of ZrO ₂ , Y ₂ O ₃ -ZrO ₂ , ie it is not, partially or completely stabilized by yttria and / or calcium oxide and / or magnesium oxide. Suitable coating processes, such as electron beam evaporation (EB-PVD), produce stalk-shaped grains in the thermal barrier coating.

Other coating methods are conceivable, e.g. Atmospheric plasma spraying (APS), LPPS, VPS or CVD. The heat-insulating layer may have porous, micro- or macro-cracked grains for better thermal shock resistance.

Refurbishment means that heat shield elements 155 may be replaced by after use

Protective layers must be freed (for example by sandblasting). This is followed by removal of the corrosion and / or oxidation layers or products. If necessary, cracks in the heat shield element 155 are also repaired. This is followed by a recoating of the heat shield elements 155 and a renewed use of the heat shield elements 155.

Due to the high temperatures inside the combustion chamber 110 may also be provided for the heat shield elements 155 and for their holding elements, a cooling system. The heat shield elements 155 are then hollow and have, for example possibly still in the Brennkammerräum 154 opening cooling holes (not shown).

Hereinafter, the material composition of the present invention will be described by way of concrete examples.

The material composition comprises polysiloxane, a solvent, and a metal and / or carbon filler. The polysiloxane may be an organic, for example. Terpeniol based solvent in particular, methyl siloxane, ie CH ₃ SIOI, ₅ and the solvent. In particular, carbon powder, metal powder, strontium carbonate, calcium carbonate, sodium carbonate, lithium carbonate and magnesium carbonate, individually or in combination, are suitable as fillers. The filler serves to define a defined softening temperature window in the temperature range between 1000 ⁰ C and 1500 ⁰ C, in particular in the temperature range from 1050 ⁰ C to 1350 ⁰ C. In this case, the filler serves primarily to lower the softening temperature of a silicon oxychloride glass which is produced by pyrolysis of the material composition in an argon atmosphere or under reduced pressure. Without filler, this glass has a softening temperature of about 135O ⁰ C to 1400 ⁰ C. If a softening temperature in the lower range of the temperature range of 1000 ⁰ C to 1500 ⁰ C is to be achieved, for example. 1050 ⁰ C, then this can except by Adding the filler also achieve that the material composition is subjected to a pyrolysis in air, whereby instead of the Siliziumoxikarbid- glass, a quartz glass is formed. The proportion of filler in this case can be extremely low. In general, however, a pyrolysis in an argon atmosphere or vacuum atmosphere and the addition of a filler in non-vanishing amount to be preferred. Overall, therefore, the softening temperature window can be defined very precisely by selecting the pyrolysis atmosphere and, in particular, by choosing the filler. Four concrete examples of the material composition according to the invention are described below.

First concrete example

In a first concrete example of the material composition, this includes methylsiloxane and strontium carbide. The volume fraction of strontium carbide in the total volume of methylsiloxane and strontium carbide is 80%. To this mixture is added a terpinyol-based solvent in such a metered amount as to form a spreadable paste. The material composition can be cured by a heat treatment with a temperature of not more than 600 ⁰ C, whereby a green body with a polymer matrix or a polymer network is formed. The polymer network comprises Si-O-Si chains as basic inorganic constituents and organic side chains consisting predominantly of -CH ₃ . The strontium carbonate is embedded in the network. The green body can then be ceramified by a pyrolysis. In the present example, the pyrolysis takes place in vacuo or alternatively in an argon atmosphere. The polymer network of the green body is decomposed and restructured via thermal intermediates of amorphous to crystalline phases. The organic components are expelled during this process. The result of the pyrolysis is a Siliziumoxikarbid glass, which has a softening temperature due to the addition of strontium carbonate, which is above 1050 ⁰ C and below 135O ⁰ C.

Second concrete example

The second concrete example includes the same components as the first concrete example, but in different volume proportions. The components themselves will therefore not be discussed again. In the second concrete example, the volume fraction of strontium carbonate is compared to the first Example further increased, namely to 95%. The result of making such material composition silicon oxycarbide glass has due to the higher Strontiumkarbonatanteils a Erweichungstemperaturfenster which is shifted compared to the first concrete example to lower temperatures, but is still in the temperature range between 1050 ⁰ C and 135 ° C ^0.

Third concrete example

In the third concrete example, the coating composition comprises methylsiloxane and calcium carbonate. The calcium carbonate has a volume fraction of the total volume of siloxane and calcium carbonate of 80%. To this mixture is added a terpinyol-based organic solvent in an amount which turns the mixture into a spreadable paste. Subsequently, the paste is subjected to a heat treatment of not higher than 600 ^° C. to cure it. This results in a green body with a matrix or a polymer network, which comprises Si-O-Si chains as inorganic base constituents and organic side chains, which predominantly consist of - CH ₃ . The calcium carbonate is embedded in the polymer network of the green body. The green body is then subjected to pyrolysis in vacuo. Alternatively, pyrolysis in an argon atmosphere is also possible. During pyrolysis, the polymer network of the green body is decomposed and restructured via thermal intermediates of amorphous to crystalline phases. The organic constituents are expelled during this process. The result of the pyrolysis is a silicon oxy carbide glass, the softening temperature of which is reduced by the addition of the calcium carbonate to a softening temperature window of below 1350 ^° C. But it is above 1050 ⁰ C. Fourth concrete example

The material composition according to the fourth concrete example has the same constituents as the material composition according to the third concrete example. The material components will therefore not be discussed again. Compared to the third example, the volume fraction of calcium carbonate in the total volume of siloxane and calcium carbonate is increased to 95%. By increasing the calcium carbonate content, the temperature window of the resulting silicon oxy carbide glass is further reduced from the silicon oxy carbide glass resulting from the material composition of the third concrete example. But it is still above 1050 ⁰ C.

The silicon oxycarbide glasses produced from the material composition according to Examples 1 to 3 all have a softening temperature window which makes it possible to use the material as masking material for a MCrAlX coating process by means of plasma spraying or by means of other thermal spraying methods. The softening temperature window is chosen so that the viscosity of the silicon oxy carbide glass at the surface temperature of the component prevailing during the coating enables the hot, mostly molten and partially molten MCrAlX particles to be collected and encapsulated. In other words, on the one hand, the viscosity is high enough for the glass to hold in the cooling air holes of the turbine blade without flowing out, but on the other hand low enough to absorb the kinetic energy of the MCrAlX particles and to encapsulate them before releasing them Reach the wall of the cooling air hole.

Figure 1 illustrates the transverse section of a cooling air bore in a turbine blade filled with the paste according to the fourth example. The blade was then subjected to a heat treatment at 500 ⁰ C to 600 ⁰ C unterzo- to cure the paste. Thereafter, a pyrolysis at about 1000 ⁰ C to 1200 ⁰ C was carried out in argon atmosphere to ceramise the cured paste. The figure shows the finish after coating the component surface with a MCrAlX coating. There are the base material 1 of the turbine blade, for example, a nickel or cobalt base superalloy, the MCrAlX coating 3 and a cooling air holes 5, which is filled with the Siliziumoxicarbid glass according to the fourth example. In the figure in the figure dark colored Siliziumoxikarbid glass, which is already cooled in the figure again, clearly encapsulated MCrAlX particles and particle groups 7 (in the figure as light inclusions in the dark Siliziumoxikarbid glass to see) can be seen. The walls 9 of the cooling air holes 5 are free of MCrAlX material. It can also be seen that no "coat-over layer" has formed over the silicon oxycarbide glass.

The silica-carbide glass shrank to room temperature during cooling of the turbine blade and is highly brittle. The shrinkage can be seen in Figure 1 at the projecting into the interior of the cooling air holes distribution of the encapsulated MCrAlX particles 7. Due to the strong embrittlement, the glass together with the encapsulated MCrAlX particles 7 can now be removed from the cooling air bore by means of dry ice blasting. As an alternative to dry ice blasting, blasting with a high-pressure water jet can also take place.

The coating method according to the invention will be described in more detail below with reference to FIGS. 2 to 7. The

Figures show schematically the turbine blade shown in Figure 1 during different stages of the coating process. Figure 2 shows the uncoated turbine blade. There are the base material 1, the blade surface 2 and a limited by walls 9 cooling air hole 5 can be seen. Into the cooling air bore 5, a paste having a material composition according to one of Examples 1 to 4 is brushed flush with the surface 2. Thereafter, the turbine blade is subjected to a heat treatment at a temperature in the range between 300 ° C and 600 ⁰ C, wherein the paste pasted to a green body 11, as described with reference to Examples 1 to 4, hardens. The turbine blade with the arranged in the cooling air hole green body 11 is shown in Figure 3.

The turbine blade with the green body 11 is then subjected to pyrolysis with a pyrolysis between 900 ⁰ C and 1200 ⁰ C. After pyrolysis, the cooling air bore 5 is filled with a silicon oxycarbide glass body 13. This represents the actual masking material that protects the cooling air hole 5 during the spraying of a MCrAlX coating. The spraying of the MCrAlX coating 15, which takes place by means of a thermal spraying process, is shown in FIG. While the splashed MCrAlX particles 17 deposit on the surface 2 of the turbine blade to the MCrAlX coating 15, they penetrate in the area of the cooling air hole 5 in the during the

Spraying process prevailing surface temperatures viscous Siliziumoxikarbid glass 13 a. As they enter, they release their kinetic energy to the glass 13 and are encapsulated by it. The encapsulated MCrAlX particles are shown in FIG. 5 as large dark regions 19 in the glass 13. Virtually no MCrAlX material is deposited on the glass 13 itself, since all MCrAlX particles penetrate it.

After the injection process is finished, the turbine blade cools down. In the process, the silicon oxy carbide glass 13 shrinks and embrittles, so that a depression 6 is formed in the surface in the region of the cooling air bore 5. The turbine blade after cooling is shown in Figure 6. FIG. 6 corresponds to the cut of FIG. 1.

After cooling, the brittle glass 13 is removed by means of a dry ice jet or high-pressure water jet together with the encapsulated MCrAlX particles 19 embedded therein. The result is a turbine blade provided with an MCrAlX coating 15 having cooling air holes 5 in which there is no coat down effect (Figure 7).

Claims

claims 1. Material composition, in particular for use as a masking material for Protection of non-coating areas of a turbine component during the application of a corrosion-inhibiting and / or oxidation-inhibiting coating, comprising: polysiloxane, a solvent and a filler comprising metal and / or carbon. The composition of matter of claim 1, wherein the polysiloxane is a polysiloxane of the form [CH ₃ SiOi, ₅ ] _n . A material composition according to claim 1 or 2, wherein the solvent is an organic solvent 4. A material composition according to claim 3, wherein the solvent is a terpenol-based solvent. 5. A material composition according to any one of claims 1 to 4, wherein the filler is selected from the group consisting of carbon powder, metal powder, strontium carbonate, calcium carbonate, sodium carbonate, lithium carbonate and magnesium carbonate and mixtures thereof. 6. Material composition according to one of claims 1 to 5, in which the volume fraction of the filler in the total volume of polysiloxane and filler is at least 70%. Material composition according to claim 6, in which the volume fraction of the filler in the total volume of polysiloxane and filler is at least 90%. 8. A method for coating turbine components which have regions (2) to be coated and regions (9) which are not to be coated, with a corrosion-inhibiting and / or oxidation-inhibiting coating material (15) comprising the steps: Masking the regions (9) to be coated with a masking material (13) before applying the coating material (15), applying the coating material (15) to the turbine component by thermal spraying and Removing the masking material (13) after application of the coating material (15), characterized in that as masking material (13) a material is used which has viscous properties in a temperature range of 1000 ⁰ C to 1500 ⁰ C, while it is solid and tough at temperatures below 1000 ⁰ C. 9. The method according to claim 8, characterized in that as masking material (13) a material is used which also embrittles on cooling of the component to room temperature. 10. The method according to claim 9, characterized in that the masking material (13) is removed after cooling the component to room temperature by means of a blasting process. 11. The method according to any one of claims 8 to 10, characterized in that the masking material (13) is applied as a curable paste on or in the uncoated areas (9) and is then cured before the coating material (15) is applied. 12. The method according to claim 11, characterized in that the curing is brought about by a heat treatment at a temperature below 600 ⁰ C. 13. The method according to any one of claims 8 to 12, characterized in that as the masking material (13) a ceramizable material is used, which is ceramized before the coating material (15) is applied. 14. The method according to claim 13, characterized in that the ceramification is brought about by a pyrolysis treatment at a temperature from the temperature range between 600 ⁰ C and 1200 ⁰ C. 15. The method according to claim 14, characterized in that the turbine component is preheated prior to the application of the coating material (15) and the ceramization is brought about during the preheating. 16. The method according to any one of claims 14 or 15, characterized in that the pyrolysis is carried out in an argon atmosphere, in air or in vacuo. 17. The method according to any one of claims 8 to 16, characterized in that as masking material (13) a masking material having a material composition according to one of claims 1 to 7 is used. 18. The method according to any one of claims 8 to 17, characterized in that as coating material (15) a MCrAlX material is used.