Abstract:
In previously known electrodeposition methods, alloys can be deposited only badly on a substrate from the components thereof. The inventive method allows an alloy layer to be deposited on a substrate by pulsing the current/voltage used for electrode position.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is the US National Stage of International Application No. PCT/DE2003/004155, filed Dec. 16, 2003 and claims the benefit thereof. The International Application claims the benefits of German Patent application No. 10259362.0 DE filed Dec. 18, 2002, both of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to a method for the deposition of an alloy on a substrate.  
       BACKGROUND OF THE INVENTION  
       [0003]     There are various known methods for applying layers to a substrate. These include, for example, plasma spraying, electrodeposition or vapor deposition processes, inter alia.  
         [0004]     An article by G. Devaray im Bulletin of Electrochemistry 8 (8), 1992, pp. 390-392 entitled “Electrodeposited composites—a review on new technologies for aerospace and other fields” gives an overview of methods for the electrochemical deposition of layers.  
         [0005]     DE 101 13 767 A1 discloses an electroplating method.  
         [0006]     DE 39 43 669 C2 discloses a method and an apparatus for electrolytic surface treatment, in which the parts of the compound used for coating are intimately mixed by vibratory movement and/or rotary movement, so that a uniform electrolytic layer is deposited.  
         [0007]     Other electrolytic coating methods are known from GB 2 167 446 A, EP 443 877 A1 and from the article by J. Zahavi et al. in Plating and Surface Finishing, January 1982, pp. 76 ff “Properties of electrodeposited composite coatings”, in which undissolved particles are used in the electrolyte in order for these particles also to be deposited in the layer.  
         [0008]     Electrochemical Society Proceedings Vol. 95-18, pp. 543 ff von Sarhadi et al. entitled “Development of a low current density electroplating bath . . . ” describes the use of baths which contain cobalt, nickel or iron compounds.  
         [0009]     U.S. Pat. No. 6,375,823 B1 describes an electrolytic coating method in which an ultrasound probe is used.  
         [0010]     DE 195 45 231 A1 describes a method for the electrolytic deposition of metal layers which uses a pulsed current or pulsed voltage method. However, this is only employed to reduce ageing phenomena in deposition baths.  
         [0011]     US 2001/00 54 559 A1 discloses an electrolytic coating method which uses pulsed currents to prevent the undesired evolution of hydrogen during electrolytic coating of metals.  
         [0012]     DE 196 53 681 C2 discloses a method for the electrolytic deposition of a pure copper layer which uses a pulsed current or pulsed voltage method.  
         [0013]     DE 100 61 186 C1 describes a method for electrolytic deposition which uses periodic current pulses.  
         [0014]     In the article entitled “Electrodeposited composite coatings for protection from high temperature corrosion” in Trans IMF 1987, 65, 21ff, V. Sova describes an electrolytic deposition method, in which particles which are not dissolved in the electrolyte are used for the layer which is to be applied. The article also describes the use of pulsed currents.  
         [0015]     Layers applied using the known methods have poor adhesion to the substrate under the conditions of some intended uses. Moreover, it is only possible to deposit materials with a constant composition.  
       SUMMARY OF THE INVENTION  
       [0016]     Therefore, it is an object of the invention to overcome the above problems.  
         [0017]     The object is achieved by a method for the deposition of an alloy on a substrate in accordance with the claims.  
         [0018]     The use of pulsed currents or the generation of graduated layers improves the bonding of layers to the substrate and/or the deposition rate.  
         [0019]     Further advantageous configurations of the method are listed in the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     An exemplary embodiment of the invention is explained in more detail in the figures, in which:  
         [0021]      FIG. 1  shows an apparatus for carrying out the method according to the invention, and  
         [0022]      FIG. 2  shows a sequence of a current/voltage pulse which is used for a method according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]      FIG. 1  shows an apparatus  1  for carrying out the method according to the invention.  
         [0024]     An electrolyte  7 , an electrode  10  and a substrate  13  that is to be coated are arranged in a vessel  4 . The substrate  13  which is to be coated is, for example, a combustion chamber lining, a housing part or a turbine blade or vane, made from a nickel-, cobalt- or iron-base superalloy, of a gas or steam turbine, which, however, may also already have a layer on the substrate (MCrAlY).  
         [0025]     The substrate  13  and the electrode  10  are electrically conductively connected to a current/voltage source  16  via electrical supply conductors  19 . The current/voltage source  16  generates pulsed electric currents/voltages ( FIG. 2 ).  
         [0026]     The electrolyte  7  contains the individual constituents of an alloy which are to be deposited on the substrate  13 . For example, the electrolyte  7  contains a first constituent  28  and a second constituent  31  of an alloy.  
         [0027]     The constituents  28 ,  31  are deposited on the substrate  13  by suitable selection of the process parameters ( FIG. 2 ). Gradients can also be produced in the chemical composition of the layer to be produced by suitable selection of the process parameters.  
         [0028]     By way of example, an alloy MCrAlY, in which M stands for at least one element selected from the group consisting of iron, cobalt or nickel, is deposited on the substrate  13 . The alloying elements Cr, Al, Y and any further elements are introduced either by the addition of suitable soluble salts to the electrolyte or by suspending fine-grain, insoluble powders in the electroplating bath, with these powders being deposited as solid particles. By way of example, at least two constituents are dissolved, for example in the form of salts, in the electrolyte  7 .  
         [0029]     The layer can be homogenized or densified by a subsequent thermal process, or defined phases can be established in the layer.  
         [0030]     An ultrasound probe  22 , which may be arranged in the electrolyte  7  and is controlled by an ultrasound transmitter  25 , improves the hydrodynamics and the mixing of the constituents  28 ,  31  in the region of the substrate  13 , so as to accelerate the deposition process.  
         [0031]     The oscillation frequency is, for example, above 1 kHz.  
         [0032]     The current/voltage level, the pulse duration and the interpulse period are defined for at least one and in particular for every constituent  28 ,  31  of the alloy.  
         [0033]      FIG. 2  shows an example of a series of repeating current pulses ( 40 ).  
         [0034]     A sequence  34  comprises at least two blocks  37 . In  FIG. 2 , there are four blocks  37 . However, there may also be three, five or more blocks  37 .  
         [0035]     Each block  37  comprises at least one current pulse  40 . In  FIG. 2 , each block comprises three, four or six current pulses  40 . However, it is also possible to use two, five or more than six current pulses  40  per block  37 . A current pulse  40  is characterized by its duration t on , the intensity I max  and its shape (square-wave, delta-wave, etc.). The pauses between the individual current pulses  40  (t off ) and the pauses between the blocks  37  are also important process parameters.  
         [0036]     The sequences may likewise change over the course of time.  
         [0037]     The sequence  34  consists, for example, of a first block  37  with three current pulses  40 , between each of which there is a pause. This is followed by a second block  37 , which has a higher or lower current intensity, since it is adapted to a different constituent  28 ,  31 , and comprises six current pulses  40 . After a further pause, there then follow four current pulses  40  in the opposite direction, i.e. with an altered polarity, in order to correct the alloy composition, the hydrogen desorption or to effect activation.  
         [0038]     Each block  37  may therefore include a different number of current pulses  40 , pulse durations t on  or interpulse periods t off .  
         [0039]     The sequence  34  is concluded by a further block  37  of four current pulses.  
         [0040]     The sequence can be repeated a number of times.  
         [0041]     The individual pulse times t on  are preferably of the order of magnitude of approximately 1 to 100 milliseconds. The duration of the block  37  is of the order of magnitude of up to 10 seconds, which means that up to 5000 pulses are emitted in a block  37 .  
         [0042]     It is optionally possible for a low potential (base current) to be applied both during the pulse sequences and during the interpulse period. This avoids interruption to the electrodeposition, which can cause inhomogeneities.  
         [0043]     The parameters of a block  37  are adapted to a constituent  28 ,  31  of the alloy, in order to achieve the optimum deposition of this constituent  28 ,  31 . These parameters can be determined in individual tests. An optimized block  37  leads to an optimized deposition of the constituent optimized for this block  37 , i.e. the duration and nature of the deposition are improved. The other constituents are likewise also deposited.  
         [0044]     This optimization can be carried out for at least one further constituent, for example all the constituents  31  of the alloy. The result is that the composition of the constituents  28 ,  31  is optimized.  
         [0045]     The level of the constituents  28 ,  31  in the layer to be applied can be defined, for example, by the duration of the individual blocks  37 .  
         [0046]     Gradients can likewise be produced in the layer. This is done by correspondingly lengthening or shortening the duration of the block  37 , the current/voltage intensity or the number of pulses  40  per block which is optimally adapted to a constituent  28 ,  31  (i.e. the sequence  34  is altered).  
         [0047]     A sequence  34  can also be altered if, for example, the deposition rate of a constituent  28 ,  31  alters over the course of time on account of the layer which has already been deposited.  
         [0048]     It is also possible for further non-alloying constituents, such as for example secondary phases, to be contained in the electrolyte  7  and deposited.