Abstract:
Short fibers in a solder or a welding material often do not have the desired strength. 
     The invention uses fiber mats ( 13 ) which have been introduced onto a surface ( 10 ) or into a recess ( 7 ) of a metallic component.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefits of European Patent application No. 05007095.2 filed Mar. 31, 2005 and is incorporated by reference herein in its entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a process for applying material to a component, to a fiber and to a fiber mat. 
     BACKGROUND OF THE INVENTION 
     Recesses which have to be filled in components are often filled with a solder, but the solder has lower mechanical strength characteristics than the base material of the component. 
     An improved solder is known from U.S. Pat. No. 5,666,643. However, the short fibers used therein do not produce the desired increase in mechanical strength. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the invention to overcome this problem. 
     The object is achieved by the process, by the fiber and by the fiber mat as claimed in the claims. 
     The dependent claims list further advantageous measures which can be combined with one another in any desired, advantageous way. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIGS. 1 to 4  show how a recess is filled in accordance with the invention, 
         FIGS. 5 to 12  show process steps in accordance with the invention, 
         FIG. 13  shows a turbine blade or vane, 
         FIG. 14  shows a combustion chamber, and 
         FIG. 15  shows a gas turbine. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Component and Fiber Mat 
       FIG. 1  shows a component  1 , comprising a substrate  4  with a surface  10  which has, for example, a recess  7  in the substrate  4 . 
     The component  1  may be a component of a turbine, in particular of a steam turbine or gas turbine  100  ( FIG. 15 ). The components are then, for example, turbine blades or vanes  120 ,  130  ( FIG. 13 ), heat shield elements  155  ( FIG. 14 ) or other housing parts  138  ( FIG. 15 ), which consist, for example, of nickel-base, cobalt-base and/or iron-base superalloys. 
     In particular in the case of the refurbishment of used components  1 , but also during the production of new components, recesses  7  in which, for example, a crack or defect was present have to be filled. 
     It is also possible for a coating or thickened portion to be applied over a large area, since the component  1 , for example in a defined region, does not have or no longer has the required thickness or wall thickness (in the case of a hollow component). 
     The recess  7  is filled with at least one fiber mat  13 . 
     Adapting the Fiber Mat to the Recess 
       FIGS. 1 to 4  show how the at least one fiber mat  13 ′,  13 ″,  13 ′″ is adapted to the recess  7 . 
     The single fiber mat  13  in  FIG. 1 , which shows a cross section through the substrate  4 , the recess  7  and the fiber mat  13 , reveals that the fiber mat  13  is adapted to the shape of the recess  7 . 
     In  FIG. 2 , the recess  7  is, for example, trapezoidal in cross section, and therefore the fiber mat  13  is preferably likewise trapezoidal in cross section. 
     Alternatively, it is also possible for a plurality of fiber mats  13 ′,  13 ″,  13 ′″ to be introduced into the recess  7  on top of one another ( FIG. 3 ) and/or next to one another (not illustrated), these mats having different dimensions, with their lateral extent being adapted to the recess  7  in such a way that the recess  7  is filled as completely as possible. 
       FIG. 4  shows a plan view of a recess  7  which has been filled with a single fiber mat  13  or a plurality of fiber mats  13 ′,  13 ″,  13 ′″. It can be seen from this that the lateral extent of the fiber mats  13 ,  13 ′,  13 ″ is also adapted to the recess  7 . 
     Introduction of Material Into a Fiber Mat 
       FIG. 5  shows how material  16  is introduced into the recess  7 . 
     First of all, the recess  7  is filled with a single fiber mat  13 . Then, in a further process step, a metallic material  16 , in particular a material such as or similar to the material of the substrate  4 , i.e. for example a superalloy, for example in paste or slurry form, is applied to the single fiber mat  13 . 
     As a result of a heat treatment, i.e. an increase in temperature (+T), the metallic material  16  melts and infiltrates the fiber mat  13 , thereby completely filling the fiber mat  13  in the recess  7  and forming a region  25  which has a high strength and good attachment to the component  1 . 
     The one metallic material  16  of one composition may also be introduced into the single fiber mat  13  in two or more steps ( FIG. 6 ). 
     This is required, for example, if the viscosity of the material  16  is too low and the material  16  is too prone to reaching regions of the surface  10  which are not to be provided with metallic material  16 . 
     Therefore, only some of the material  16  which is required to completely fill the recess  7  and the fiber mat  13  is applied to the single fiber mat  13  and made to infiltrate it by means of a heat treatment. After this step, the lower region of the fiber mat  13  has been filled with metallic material  16 . 
     In a second or further process step, further material  16  is applied to the fiber mat  13 , and a heat treatment is again used to introduce the material  16  into the remaining region of the fiber mat  13  which is to be filled, so that in a final process step the recess  7  and the fiber mat  13  have been completely filled with material ( FIG. 6 ). 
     This stepwise approach to filling the single fiber mat  13  can also be utilized to produce a gradient in the composition of the metallic material  16 ′,  16 ″. A gradient of this type may be present, for example, in the case of an agent for reducing the melting point, which for example forms part of the material  16 ′,  16 ″ ( FIG. 7 ). 
     For example, in this way the lower region of the fiber mat  13  has a higher content of at least one agent for reducing the melting point, for example boron, silicon, titanium, hafnium and/or zirconium, in order to achieve good attachment to the substrate  4 . Toward the outside, the proportion of the agent for reducing the melting point is reduced, or even this agent is no longer present at all, in order to achieve a higher mechanical strength in the outer region. In this case, therefore, there is a gradient of the agent for reducing the melting point which runs in a direction  28  from the inside outward. 
     It is in this case preferable to use a single agent for reducing the melting point, preferably boron. It is also possible to produce a gradient of one or more other constituents of the metallic material, i.e. including an alloy. 
     Introduction of Material Into a Plurality of Fiber Mats 
     It is likewise possible for the recess  7  of the component  1  to be filled with a plurality of fiber mats  13 ′,  13 ″,  13 ′″ and to be infiltrated and filled with a single metallic material  16 , as has already been explained in  FIG. 5  or in  FIG. 6  ( FIG. 8 ). 
     Furthermore, if a plurality of fiber mats  13 ′,  13 ″,  13 ′″ are used, it is possible for the material to be introduced in steps ( FIG. 9 ). 
     In this case, first of all the first fiber mat  13 ′ is introduced into the recess  7 , and a first metallic material  16 ′ is applied and made to infiltrate into the fiber mat  13 ′. 
     Then, the second or further fiber mat  13 ″ is applied to the fiber mat  13 ′ which has been filled with metallic material  16 ′, and this second or further fiber mat  13 ″ is filled with a metallic material which is the same as that used in the first step  16 ′, or with a second material  16 ″, which differs from the first material  16 ′. It is in this case once again, as described above, possible to produce a concentration gradient in the composition. 
     Filling of the Recess Without Infiltration 
     It is also possible for the one metallic material  16  or a plurality of metallic materials  16 ′,  16 ″ to be present in the single fiber mat  13  from the outset, by virtue of it already having infiltrated into the fiber mat  13  by means of a slurry or melting. The fiber mat  13  which has been filled with metallic material  16  in this way is introduced into the recess  7 , and the heat treatment (+T) produces a good bond between the fiber mat  13  and the substrate  4  ( FIG. 10 ). 
     This procedure can also be carried out using a plurality of fiber mats  13 ′,  13 ″, the respective fiber mats  13 ′,  13 ″ already having a metallic material  16  or  16 ″, which may be identical or different ( FIG. 11 ). 
     In this case, the fiber mats  13 ′,  13 ″ which have been filled with metallic material are stacked in the recess  7 , and good bonding of the fiber mats to the substrate  4  is achieved by means of an increase in temperature. 
     The invention is not restricted to three fiber mats or three different materials. 
     The fiber mats consist of metallic and/or ceramic fibers. It is preferable to use ceramic fibers. In particular, it is also possible to use boron fibers. 
     It is particularly advantageous if a stop-off region  19  ( FIG. 12 ) is present in an outer region of the fiber mat  13 ,  13 ′,  13 ″,  13 ′″, which stop-off region  19  prevents the metallic material  16 ,  16 ′ from reaching the remaining surface  10  of the substrate  4 . This stop-off region  19  contains, for example, nickel and/or aluminum oxide, in particular as powder in paste form. 
     Fiber 
     The fiber used to form the fiber mat  13 ,  13 ′,  13 ″ is produced in particular 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. Drawn fibers are thermally crosslinked, with inorganic constituents (Si—O—Si chains) and organic side chains predominantly comprising X being present beside one another. Then, the fibers are ceramicized by means of a heat treatment in Ar, N 2 , air or vacuum atmosphere at temperatures between 600° C. and 1200° C. The polymeric network is in the process broken down and restructured, via intermediate thermal stages, from amorphous to crystalline phases, with a Si—O—C network being formed from polysiloxane precursors. 
     Fibers may also be produced from precursors of the polysilane type (Si—Si), polycarbosilane (Si—C), polysilazane (Si—N) or polyborosilazane (Si—B—C—N) type. 
     It is preferable for the polysiloxane also to contain a further element which can bond very securely to the silicon or carbon atoms of the polysiloxane. This is, for example, boron. This element can then be included in the metallic material  16 ,  16 ′,  16 ″,  16 ′″ which is used to infiltrate the fiber mat  13 ,  13 ′,  13 ″,  13 ′″ formed from these fibers. 
       FIG. 8  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 . 
     The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
     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 . 
     As a guide vane  130 , the vane  130  may have a further platform (not shown) at its vane tip  415 . 
     A blade or vane root  183 , which is used to secure the rotor blades  120 ,  130  to a shaft or a disk (not shown), is formed in the securing region  400 . 
     The blade or vane root  183  is designed, for example, in hammerhead form. Other configurations, such as a fir-tree or dovetail root, are possible. 
     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 . 
     In the case of conventional blades or vanes  120 ,  130 , by way of example solid metallic materials, in particular superalloys, are used in all regions  400 ,  403 ,  406  of the blade or vane  120 ,  130 . 
     Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949; these documents form part of the disclosure with regard to the chemical composition of the alloy. The blade or vane  120 ,  130  may in this case be produced by a casting process, also by means of directional solidification, by a forging process, by a milling process or combinations thereof. 
     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. 
     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. 
     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. 
     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). 
     Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1; these documents form part of the disclosure. 
     The blades or vanes  120 ,  130  may likewise have coatings protecting against corrosion or oxidation (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and represents 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, which are intended to form part of the present disclosure with regard to the chemical composition of the alloy. 
     It is also possible for a thermal barrier coating, consisting for example of ZrO 2 , Y 2 O 4 —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. 
     Columnar grains are produced in the thermal barrier coating by means of suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
     Refurbishment means that after they have been used, protective layers may have to be removed from components  120 ,  130  (e.g. by sandblasting). Then, the corrosion and/or oxidation layers and products are removed. If appropriate, cracks in the component  120 ,  130  are also repaired by means of the process according to the invention. This is followed by recoating of the component  120 ,  130 , after which the component  120 ,  130  can be reused. 
     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). 
       FIG. 9  shows a combustion chamber  110  of a gas turbine  100 . The combustion chamber  110  is configured, for example, as what is known as an annular combustion chamber, in which a multiplicity of burners  107  which produce flames  156  and are arranged circumferentially around the 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 . 
     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 . 
     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 a material that is able to withstand high temperatures (solid ceramic blocks). 
     These protective layers may be similar to the turbine blades or vanes, i.e. for example in the case of 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 represents 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, which are intended to form part of the present disclosure with regard to the chemical composition of the alloy. 
     It is also possible for a, for example, ceramic thermal barrier coating, consisting for example of ZrO 2 , Y 2 O 4 —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 coating. 
     Columnar grains are produced in the thermal barrier coating by means of suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
     Refurbishment means that after they have been used, protective layers may have to be removed from heat shield elements  155  (e.g. by sandblasting). Then, the corrosion and/or oxidization 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. 
     Moreover, on account of the high temperatures in the interior of the combustion chamber  110 , a cooling system can be provided for the heat shield elements  155  and/or for their holding elements. The heat shield elements  155  are in this case, for example, hollow and may also have film-cooling holes (not shown) opening out into the combustion chamber space  154 . 
       FIG. 10  shows, by way of example, a partial longitudinal section through a gas turbine  100 . 
     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 a turbine rotor. 
     An intake housing  104 , a compressor  105 , a, for example, toroidal combustion chamber  110 , in particular an annular combustion chamber  106 , with a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust-gas housing  109  follow one another along the rotor  103 . 
     The annular combustion chamber  106  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 . 
     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 . 
     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 . 
     A generator (not shown) is coupled to the rotor  103 . 
     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. 
     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. 
     To be able to withstand the temperatures which prevail there, they have to be cooled by means of a coolant. 
     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). 
     By way of example, iron-base, nickel-base or cobalt-base 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 . 
     Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949; these documents form part of the disclosure with regard to the chemical composition of the alloys. 
     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 represents yttrium (Y) and/or silicon 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, which are intended to form part of the present disclosure with regard to the chemical composition. 
     It is also possible for a thermal barrier coating, consisting for example of ZrO 2 , Y 2 O 4 —ZrO 2 , i.e. unstabilized, partially stabilized or completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, to be present on the MCrAlX. 
     Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
     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 . 
     LIST OF DESIGNATIONS 
     
         
           1  Component 
           4  Substrate 
           7  Recess 
           10  Surface 
           13 ,  13 ′,  13 ″,  13 ′″ Fiber mat 
           16 ,  16 ′,  16 ″,  16 ′″ Material, paste 
           19  Stop-off region 
           25  Region 
           28  Direction 
           100  Gas turbine 
           101  Shaft 
           102  Axis of rotation 
           103  Rotor 
           104  Intake housing 
           105  Compressor 
           107  Burner 
           108  Turbine 
           109  Exhaust-gas housing 
           110  Combustion chamber 
           111  Hot-gas passage 
           112  Turbine stages 
           113  Working medium 
           115  Row of guide vanes 
           120  Rotor blade 
           121  Longitudinal axis 
           125  Row of rotor blades 
           130  Guide vane 
           133  Turbine disk 
           135  Air 
           138  Inner housing 
           140  Securing ring 
           143  Stator 
           153  Combustion chamber wall 
           154  Combustion chamber space 
           156  Flames 
           155  Heat shield element 
           183  Blade or vane root 
           400  Securing region 
           403  Blade or vane platform 
           406  Main blade or vane part 
           409  Leading edge 
           412  Trailing edge 
           415  Blade or vane tip 
           418  Film-cooling holes 
         M Working medium 
         +T Increase in temperature