CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/486,205 filed Jun. 17, 2009 , now U.S. Pat. No. 7,832,620 and claims priority of European application No. 08011375.6 filed Jun. 23, 2008. All of the applications are incorporated by reference herein in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a soldering process with a plurality of temperature plateaus. 
     BACKGROUND OF THE INVENTION 
     Soldering is a known process for the connection of workpieces or for repair. 
     Components are also often provided with soldering inserts, the solder material, the substrate of the component and the soldering insert having different materials. 
     In soldering, care must be taken to ensure that no voids which reduce mechanical activity occur in the soldered joint. 
     SUMMARY OF THE INVENTION 
     The object of the invention, therefore, is to indicate a method in which no voids occur during soldering. 
     The object is achieved by a method according to the independent claim. The dependant claims list further advantageous measures which may be combined with one another, as desired, in order to achieve further advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawing: 
         FIG. 1  shows a component with a soldering insert, 
         FIG. 2  shows a soldering insert, 
         FIGS. 3 and 4  show the thermal soldering method, 
         FIG. 5  shows a gas turbine, 
         FIG. 6  shows a turbine blade in perspective, 
         FIG. 7  shows a combustion chamber in perspective, and 
         FIG. 8  shows a list of superalloys used. 
     
    
    
     The figures and the description illustrate only exemplary embodiments of the invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a component  1 ,  120 ,  130 ,  155  with a substrate  4 . 
     The substrate  4  preferably has the material RENE80 or Alloy 247 LC CC. Further superalloys advantageously to be used are listed in  FIG. 7 . 
     The substrate  4  has a depression or a hole  13  which is to be closed. This takes place by soldering by means of a solder material  9 , or the hole  13  is closed by means of a soldering insert  7  or  7 ′ ( FIG. 2 ) and a solder material  9 . This may take place in that solder material  9  is applied to the soldering insert  7  over a large area, as is the case of the soldering insert  7 ′, preferably a contraction  10  is present as a solder repository for solder material  9 . 
     The soldering insert  7 ,  7 ′ preferably consists of the material IN625 or Hastelloy X. 
     The solder material  9  used is preferably the solder alloy NI105 which has a soldering temperature of 1190° C., or the solder alloy AMDRY788 which has a soldering temperature of 1230° C. 
     According to the invention, preferably, the method is carried out with a plurality of temperature plateaus  16 ′,  16 ″, . . . Preferably, three ( FIG. 4 ) or four ( FIG. 3 ) temperature plateaus  16 ′,  16 ″, . . . are used, in order to improve the tie-up of the solder material  9  to the substrate  4  by diffusion. 
       FIG. 3  illustrates a temperature profile in which various temperature plateaus  16 ′,  16 ″ are used. In this case, in a first step, the component  1 ,  120 ,  130 ,  155  is heated to a temperature T′ and is held there preferably for two hours. The temperature T′ of the first temperature plateau  16 ′ is preferably the highest temperature T max  in the entire soldering method, hence T′&gt;T″, T′″, T″″, . . . , with the result that the solder material  9  is melted down completely at the start. 
     The temperature T′=T max  is preferably higher than the customarily used soldering temperature of this solder material  9  (1190° C. in the case of NI105), so that 1200° C. is used for NI105. However, the customary soldering temperature may also be used, as with AMDRY788 (1230° C.). 
     After the first temperature plateau  16 ′, a lowering of the temperature T to preferably below the temperature T″ of the following temperature plateau  16 ″, preferably to 650° C., most preferably to room temperature, takes place. In the case of Rene80 and Alloy 247, the temperature preferably amounts to 540° C. 
     This is followed by a reheating to a second temperature plateau  16 ″ with the temperature T″. This preferably also applies to the transitions between the further temperature plateaus  16 ″,  16 ′″, . . . In this case, a holding time preferably of two to four hours, in particular for four hours, is used. 
     The temperature T″ of the second temperature plateau  16 ″ is lowered preferably by at least 90° C., in particular by 100° C., in relation to the temperature T′ of the first temperature plateau  16 ′. 
     In  FIG. 3 , this step is also repeated a second time. 
     The temperature T′″ of the third temperature plateau  16 ′″ is likewise lowered, but not as markedly between T′ and T″, to be precise preferably by 15° C. 
     After the second temperature plateau  16 ″, a lowering preferably to below the temperature T′″ of the third, that is to say following temperature plateau  16 ′″ takes place. This is followed by a reheating to the temperature T′″. 
     As the last step, heat treatment, preferably at a temperature T″″ lowered anew, is carried out for a markedly longer holding time of twelve or twenty hours. 
     The holding temperature of the last temperature plateau  16 ″″ is lowered preferably by 190° C. in relation to the penultimate temperature T′″. 
     This method is suitable preferably for Rene80 with the solders NI105 and C0101. 
       FIG. 4  illustrates a three-step soldering method with three temperature plateaus  16 ′,  16 ″,  16 ′″. 
     In this case, in a first step, the component  1 ,  120 ,  130 ,  155  is heated to a temperature T′ and is held there for preferably two hours. The temperature T′ of the first temperature plateau  16 ′ is preferably the highest temperature T max  in the entire soldering method, hence T′&gt;T″, T′″, with the result that the solder material  9  is melted completely at the start. 
     This maximum temperature T max  is preferably higher than the customarily used soldering temperature of this solder material  9  (1190° C. in the case of NI105), so that 1200° C. is used for NI105. 
     After the first temperature plateau  16 ′, a lowering of the temperature T preferably to below the temperature T″ of the following temperature plateau  16 ″ takes place. 
     This is followed by a reheating to a second temperature plateau  16 ″ with the temperature T″. This preferably also applies to the transitions between the further temperature plateaus  16 ″,  16 ′″. In this case, a holding time preferably of two to four hours, in particular for four hours, is used. 
     The following preferably applies in each case: 
     T′−T″=30° C. to 150° C., in particular 120° C. to 150° C.; 
     T″−T′″=30° C. to 210° C., in particular 180° C. to 210° C. 
     The holding times for the first two temperature plateaus  16 ′,  16 ″ are preferably identical, preferably 2 h. 
     Preferably, the holding time of the third temperature plateau  16 ′″ is at least twice as long, preferably ten times as long. Since the temperature of the third temperature plateau  16 ′″ is lower, the diffusion rates are reduced and the holding times are prolonged. 
     Preferably, a ramp  19 , that is to say a lower heating rate, is used to run up to the highest temperature T′, in order to avoid overheating. 
     Preferably, the substrate material used is also Alloy 247 LL CC ( FIG. 4 ). In this case, preferably, the solder alloy AMDRY788 is used. 
       FIG. 5  shows a gas turbine  100  by way of example in a longitudinal part section. 
     The gas turbine  100  has inside it a rotor  103  rotary-mounted about an axis of rotation  102  and having a shaft  101 , which rotor is also designated as a turbine rotor. 
     An intake casing  104 , compressor  105 , a, for example, toroidal combustion chamber  110 , in particular annular combustion chamber, with a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust gas casing  109  follow one another along the rotor  103 . 
     The annular combustion chamber  110  communicates with a, for example, annular hot-gas duct  111 . There, for example, four turbine stages  112  connected in series form the turbine  108 . 
     Each turbine stage  112  is formed, for example, from two blade rings. As seen in the direction of flow of a working medium  113 , a row  125  formed from moving blades  120  follows a guide vane row  115  in the hot-gas duct  111 . 
     The guide vanes  130  are in this case fastened to an inner casing  138  of a stator  143 , whereas the moving blades  120  of a row  125  are attached to the rotor  103 , for example, by means of a turbine disk  133 . 
     A generator or a working machine (not illustrated) is coupled to the rotor  103 . 
     When the gas turbine  100  is in operation, air  135  is sucked in by the compressor  105  through the intake casing  104  and is compressed. The compressed air provided at the turbine-side end of the compressor  105  is routed to the burners  107  and is mixed there with a fuel. The mixture is then burnt in the combustion chamber  110  so as to form the working medium  113 . The working medium  113  flows from there along the hot-gas duct  111  past the guide vanes  130  and the moving blades  120 . At the moving blades  120 , the working medium  113  expands so as to transmit a pulse, with the result that the moving blades  120  drive the rotor  103  and the latter drives the working machine coupled to it. 
     The components exposed to the hot working medium  113  are subject to thermal loads while the gas turbine  100  is in operation. The guide vanes  130  and moving blades  120  of the first turbine stage  112 , as seen in the direction of flow of the working medium  113 , are subjected to the most thermal load, in addition to the heat shield elements lining the annular combustion chamber  110 . 
     In order to withstand the temperatures prevailing there, these can be cooled by means of a coolant. 
     Substrates of the components may likewise have a directional structure, that is to say they are monocrystalline (SX structure) or have only longitudinally directed grains (DS structure). 
     For example, iron-, nickel- or cobalt-based superalloys are used as material for the components, in particular for the turbine blade  120 ,  130  and components of the combustion chamber  110 . 
     Such superalloys are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949; these publications are part of the disclosure in respect of the chemical composition of the alloys. 
     The guide vane  130  has a guide vane foot (not illustrated here) facing the inner casing  138  of the turbine  108  and a guide vane head lying opposite the guide vane foot. The guide vane head faces the rotor  103  and is secured to a fastening ring  140  of the stator  143 . 
       FIG. 6  shows a perspective view of a moving 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 station for electricity generation, a steam turbine or a compressor. 
     The blade  120 ,  130  has successively along the longitudinal axis  121  a fastening region  400 , a blade platform  403  contiguous to the latter and also a blade leaf  406  and a blade tip  415 . 
     As a guide vane  130 , the blade  130  may have a further platform (not illustrated) at its blade tip  415 . 
     In the fastening region  400 , a blade foot  183  is formed, which serves (not illustrated) for fastening the moving blades  120 ,  130  to a shaft or a disk. 
     The blade foot  183  is configured, for example, as a hammer head. Other configurations as a pinetree or dovetails are possible. 
     The blade  120 ,  130  has a leading edge  409  and a trailing edge  412  for a medium which flows past the blade leaf  406 . 
     In conventional blades  120 ,  130 , for example, solid metallic materials, in particular superalloys, are used in all the 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 publications are part of the disclosure in respect of the chemical composition of the alloy. 
     The blade  120 ,  130  may in this case be manufactured by a casting method, also by means of directional solidification, by a forging method, by a milling method or by combinations of these. 
     Workpieces with a monocrystalline structure or structures are used as components for machines which are exposed to high mechanical, thermal and/or chemical loads during operation. 
     The manufacture of monocrystalline workpieces of this type takes place, for example, by directional solidification from the melt. This involves casting methods in which the liquid metallic alloy solidifies into the monocrystalline structure, that is to say into the monocrystalline workpiece, or directionally. 
     In this case, dendritic crystals are oriented along the heat flow and form either a columnar-crystalline grain structure (columnar, that is to say grains which run over the entire length of the workpiece and here, according to general linguistic practice, are designated as being directionally solidified) or a monocrystalline structure, that is to say the entire workpiece consists of a single crystal. In these methods, the transition to globulitic (polycrystalline) solidification must be avoided, since undirected growth necessarily results in the formation of transverse and longitudinal grain boundaries which nullify the good properties of the directionally solidified or monocrystalline component. 
     When directionally solidified structures are referred to in general terms, this means both monocrystals which have no grain boundaries or at most low-angle grain boundaries and columnar-crystal structures which have grain boundaries running in the longitudinal direction, but no transverse grain boundaries. Where these second-mentioned crystalline structures are concerned, directionally solidified structures are also referred to. 
     Such methods are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1; these publications are part of the disclosure in respect of the solidification method. 
     The blades  120 ,  130  may likewise have coatings against corrosion or oxidation, for example (MCrAlX; M is at least one element of the group iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon and/or at least one rare earth element or hafnium (Hf)). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1 which are to be part of this disclosure in respect of the chemical composition of the alloy. 
     The density preferably lies around 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). 
     The layer composition preferably has Co-30Ni-28Cr-8Al-0.6Y-0.7Si or Co-28Ni-24Cr-10Al-0.6Y. In addition to these cobalt-based protective coatings, preferably nickel-based protective layers are also used, 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. 
     On the MCrAlX, a heat insulation layer may also be present, which is preferably the outermost layer and consists, for example, of ZrO 2 , Y 2 O 3 —ZrO 2 , that is to say it is not or is partially or completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
     The heat insulation layer covers the entire MCrAlX layer. 
     By means of suitable coating methods, such as, for example, electron beam vapor deposition (EB-PVD), columnar grains are generated in the heat insulation layer. 
     Other coating methods may be envisaged, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The heat insulation layer may have porous microcrack- or macrocrack-compatible grains for better thermal shock resistance. The heat insulation layer is therefore preferably more porous than the MCrAlX layer. 
     The blade  120 ,  130  may be of hollow or solid design. If the blade  120 ,  130  is to be cooled, it is hollow and, if appropriate, also has film cooling holes  418  (indicated by dashes). 
       FIG. 7  shows a combustion chamber  110  of the gas turbine  100 . The combustion chamber  110  is configured, for example, as what is known as an annular combustion chamber, in which a multiplicity of burners  107  arranged around an axis of rotation  102  in the circumferential direction issue into a common combustion chamber space  154  and generate flames  156 . For this purpose, the combustion chamber  110  is configured as a whole as an annular structure which is positioned around the axis of rotation  102 . 
     To achieve a comparatively high efficiency, the combustion chamber  110  is designed for a comparatively high temperature of the working medium M of about 1000° C. to 1600° C. In order to make it possible to have a comparatively long operating time even in the case of these operating parameters which are unfavorable for the materials, the combustion chamber wall  153  is provided on its side facing the working medium M with an inner lining formed from heat shield elements  155 . 
     Moreover, on account of the high temperatures inside the combustion chamber  110 , a cooling system may be provided for the heat shield elements  155  or for their holding elements. The heat shield elements  155  are then, for example, hollow and, if appropriate, also have cooling holes (not illustrated) issuing into the combustion chamber space  154 . 
     Each heat shield element  155  consisting of an alloy is equipped on the working medium side with a particularly heat-resistant protective layer (MCrAlX layer and/or ceramic coating) or is manufactured from materials resistant to high temperature (solid ceramic bricks). 
     These protective layers may be similar to those of the turbine blades, that is to say, 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 rare earth element or hafnium (Hf). Such alloys are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1 which are to be part of this disclosure in respect of the chemical composition of the alloy. 
     On the MCrAlX, a, for example, ceramic heat insulation layer may also be present and consists, for example, of ZrO 2 , Y 2 O 3 —ZrO 2 , that is to say it is not or is partially or completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. 
     By means of suitable coating methods, such as, for example, electron beam vapor deposition (EB-PVD), columnar grains are generated in the heat insulation layer. 
     Other coating methods may be envisaged, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The heat insulation layer may have porous microcrack- or macrocrack-compatible grains for better thermal shock resistance. 
     Refurbishment means that turbine blades  120 ,  130  and heat shield elements  155 , after use, must, where appropriate, be freed of protective layers (for example, by sandblasting). A removal of the corrosion and/or oxidation layers or products then takes place. If appropriate, cracks in the turbine blade  120 ,  130  or in the heat shield element  155  are also repaired. This is followed by a recoating of the turbine blades  120 ,  130  and heat shield elements  155  and by a renewed use of the turbine blades  120 ,  130  or of the heat shield elements  155 .
A method in which no voids occur during the soldering processes is provided. A component with a soldering material is heated using a first temperature plateau for a first time duration such that the solder material is completely melted. Each subsequent heating is at a temperature plateau with a temperature that is lower than a temperature of the previous plateau.