Abstract:
Disclosed are a method and a device for filling material separations on the surface. In methods known in prior art, which are used for filling material separations, the substrate is often influenced in a negative manner by high processing temperatures and dissimilar additives. The inventive method overcomes said disadvantage, taking place at low temperatures and allowing the material separation to be completely filled without using dissimilar substances.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is the US National Stage of International Application No. PCT/DE2003/003954, filed Dec. 1, 2003 and claims the benefit thereof. 
     The International Application claims the benefits of German Patent application No. 10259361.2 DE filed Dec. 18, 2002, both of the applications are incorporated by reference herein in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a method and an apparatus for filling material separations in accordance with the preamble of the claims. 
     BACKGROUND OF THE INVENTION 
     Material separations at an inner and/or outer surface of a component—for example comprising a substrate or a layer—such as for example cracks, drilled holes or manufacturing-related, operationally induced notches, often have to be closed up again by welding or soldering processes. These methods use high temperatures in the vicinity of the material separation which is to be filled, leading to thermal stresses in the substrate/layer of a component, which can lead to cracks. The material which is used in the welding or soldering processes to fill the material separation often has a considerably reduced mechanical strength compared to the material of the substrate, with the result that the ability of the component to be repaired is limited. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the invention to provide a method and an apparatus for filling material separations in which the abovementioned drawbacks are overcome. 
     The object is achieved by a method and an apparatus in accordance with the claims. 
     Further advantageous refinements of the method and apparatus according to the invention are listed in the subclaims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments are shown in the figures, in which: 
         FIG. 1  shows an apparatus which is used to carry out the method according to the invention, 
         FIG. 2  shows a crack which is filled in steps, and 
         FIG. 3  shows a time profile for a current between substrate and electrode, 
         FIG. 4  shows a further time profile for a current between substrate and electrode, and 
         FIG. 5  shows a widened material separation. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an apparatus  40  according to the invention which is used to carry out the method according to the invention. Material is introduced into a material separation  4  in a substrate  1  or a layer  1  extending from a surface  2  in an electrolytic process at low temperatures, for example lower than 100° C. 
     The substrate  1  with its material separation  4  is electrically connected to an electrode  7 , which together are arranged in an electrolyte  10  which is present in a vessel  46 . There is an electric voltage source  25  between the electrode  7  and the substrate  1 , so that an electric current can flow. 
     The electrolyte  10  contains the material which is introduced into the material separation  4 . The solution of the electrolyte  10  may include constituents of the composition of the substrate  1  in the form of particles and/or ions. 
     The process of the method according to the invention can take place at room temperature or low temperatures, which means that prior to use of the method according to the invention the substrate  1  can have a suitable mask (waxes, polymers) applied to it in a simple way at the locations at which coating is not desired, and can thus be protected against being coated. 
     The use of a flow of current which varies over the course of time makes it possible to effect targeted deposition of the constituents, for example an alloy, from the electrolyte  10  into the material separation  4  of the component  1 . 
     Required materials properties can be set, for example, by a subsequent heat treatment, as is necessary, for example, for nickel-base and cobalt-base superalloys for turbine blades and vanes in order to obtain the desired γ-γ′ precipitations or to achieve a phase change or phase adjustment. 
     The deposition of material of the same or a similar type to the material of the substrate  1 , in the form of particles and/or ions, results in a significantly improved strength than with soldering or welding processes, since in the latter cases, constituents which are foreign to the substrate penetrate into the material separation  4  as a result of the soldering or welding additions. This is not the case when using electrolytic deposition. 
     In this case, material of the substrate  1  or layer  1  or material which has similar properties can be used. 
     The deposition process in the material separation  4  can optionally be improved by additional ultrasound excitation by means of at least one ultrasound probe  19 , which is operated by an ultrasound source  22 , in the electrolyte  10 . The ultrasound excitation inter alia effects continuous mixing of the electrolyte  10 , so that there are no inhomogeneities in the electrolyte  10  and its constituents. Furthermore, porous parts of a layer formed by the filling material are cavitationally removed by the effect of the ultrasound waves. 
     A further improvement of the method can preferably be achieved by the use of pulsed currents. 
     Furthermore, the method can be improved by an eddy-current probe  16  being arranged in the region of the material separation  4 , for example being placed on top of it, producing a corresponding interaction volume  28  in the substrate  1  around the material separation  4 , i.e. the interaction volume  28  is mechanically excited, i.e. generates oscillations in the substrate  1 . 
     The eddy-current probe  16  surrounds, for example, the opening  43  of the material separation  4  at the surface  2  toward the electrolyte  10 , but does not cover this opening. The eddy-current probe  16  is operated by a controllable eddy-current generator  13 . The depth of penetration δ, i.e. the depth to which the interaction volume  28  extends into the substrate  1  from the surface  2 , is given by the following formula: 
     
       
         
           
             δ 
             = 
             
               503 
               
                 
                   f 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   σ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     μ 
                     r 
                   
                 
               
             
           
         
       
     
     in which f is the frequency of the eddy-current, σ is the conductivity of the substrate  1  and μ r  is the permeability constant of the substrate/layer  1 . 
     Therefore, the depth of penetration δ and the interaction volume  28  can be set by means of the frequency f. 
       FIG. 2  shows how a first material separation  4  in a substrate  1  can be filled in an improved way. 
     First of all, a region M 1  in the region of the end  34  of the crack is surrounded, by suitable selection of the frequency f 1 , so that the interaction volume  28  surrounds the region M 1  while M 1  is being filled. 
     In a second step, a second region M 2  is filled with material, with the frequency f 2  being selected in such a way that the interaction volume  28  only extends as far as the region M 1  which has previously been filled or if appropriate only partially surrounds it. 
     Further regions M 3 , M 4 , . . . as far as a surface  2  are filled with material by continuously increasing the frequency (f 3 , f 4 , . . . ). 
     Of course, it is also possible for the frequency f to be continuously matched to the remaining depth of the material separation. 
     Taking account of the altered conductivity in the interaction volume  28 , automatic control of the process is possible, since the filling material in the material separation  4  changes the conductivity of the substrate  1  in the interaction volume  28 , which is measured and used for control purposes. 
       FIG. 3  shows a time profile of the current of the voltage source  25 . This may be formed from currents which are pulsed or varied over the course of time and can be repeated periodically. 
     The current is primarily composed of cathode components (substrate  1 ) and anode components (electrode  7 ). The pulse duration t on , during which a current I is flowing, the interpulse period t off  between the pulses  40  and a maximum intensity of the current I max  can be varied. It is also possible to alter the shape  37  of the current signal. All the parameters (I max , t off , t on , . . . ) may be a function of time and can be repeated periodically in order to optimize the method. 
     An alloy (for example NiAl) is deposited by the individual constituents alternately being deposited to an increased extent. By way of example, for each individual alloying constituent Ni, Al there are different optimum parameters (I max , t off , t on , . . . ), which means that, for example, a first current pulse  40  is optimum for the element nickel (ion in the electrolyte  10 ) and the second, subsequent current pulses  40  are optimum for aluminum. Even during the current pulse which is matched to one element, the other element is still being deposited, albeit to a lesser extent. 
     The pulses are constantly repeated, so that the constituents of the alloy are optimally mixed. 
     The proportion by weight of one alloying constituent in the material separation can be set by means of the pulse duration. 
       FIG. 4  shows an example of a series of current pulses  40  which are repeated. 
     A sequence  34  comprises at least two blocks  77 . Each block  77  comprises at least one current pulse  40 . 
     A current pulse  40  is characterized by its duration t on , the intensity I max off  and its shape  37  (square-wave, delta-wave, . . . ) . 
     The interpulse periods between the individual current pulses  40  (t off ) and the interpulse periods between the blocks  77  are equally important process parameters. 
     The sequence  34  comprises, for example, a first block  77  of three current pulses  40 , between each of which there is an interpulse period. This is followed by a second block  77 , which has a higher current intensity and comprises six current pulses  40 . This is followed, after a further interpulse period, by four current pulses  40  in the reverse direction, i.e. with a changed polarity. 
     The sequence  34  is concluded by a further block  77  of four current pulses. 
     The sequence can be repeated a number of times. The individual pulse times ton are preferably of the order of magnitude of approximately 1 to 10 milliseconds. The total duration of the block  77  is of the order of magnitude of up to 10 seconds, which means that up to 500 pulses are emitted in one block  77 . 
     It is optionally possible to apply a low potential (base current) both during the pulse sequences and during the interpulse periods. 
     This prevents the electrodeposition from being interrupted, which can cause inhomogeneities. 
     The parameters of a block  77  are matched to one constituent of an alloy which is to be deposited, for example in order to optimize the deposition of this constituent. These parameters can be determined in individual tests. By way of example, the level of the constituents of the alloy in the layer to be applied can be defined by the duration of the individual blocks  77  in order, for example, to produce gradients in the layer. This is done by correspondingly lengthening or shortening the duration of the block  77  which is optimally matched to one constituent of the alloy. 
       FIG. 5  shows a widened material separation  4 . 
     To improve the deposition, the material separation  4  is widened before being filled. This can be done by drilling, EDM or other methods in order, for example, to increase the diameter. 
     The dashed line shows the material separation  4  prior to the widening.