EP2064371A1

EP2064371A1 - Method for electrochemically coating or stripping the coating from components

Info

Publication number: EP2064371A1
Application number: EP07820130A
Authority: EP
Inventors: Rene Jabado; Jens Dahl Jensen; Ursus KRÜGER; Daniel Körtvelyessy; Volkmar LÜTHEN; Ralph Reiche; Michael Rindler; Raymond Ullrich
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2006-09-18
Filing date: 2007-09-11
Publication date: 2009-06-03
Also published as: WO2008034739A1; DE102006044416A1; US20100072073A1

Abstract

The invention relates to a method for electrochemically coating or stripping the coating from components (1). In said method, the component (1) acts as an electrode and an electric field is established between the component (1) and a counter-electrode (3), said field allowing the deposition of a coating material that is dissolved in an electrolyte or the removal of a coating material (11) on the surface (2) of the component. During the deposition or removal process, the component (1) is covered with structures (5) consisting of an electrically insulating material.

Description

description

Process for the electrochemical coating or stripping of components

The present invention relates to a method for coating or stripping of components, for example for loading or stripping of turbine components with an MCrAlY coating.

The loading and stripping of components is now almost impossible to imagine vie ^¬ len fields of technology. For applying or removing a coating, injection processes and electrochemical processes are used. Of particular importance are coatings with a structured surface in addition to coatings with specific physical properties. As an example, here is a coating of components of turbomachines, which has a structure in the manner of a sharkskin. Such a structure has scales, which in turn are each provided with grooves. However, such coatings can be produced only with great effort due to the fine structures in their surface. The production is often carried out by spraying using suitable templates or masks. Injection processes, however, only allow the additive to produce structured surfaces, ie the production of a structure by additional application of material at certain points of the surface.

It is therefore an object of the present invention to provide an alternative method for producing a coating with a structured surface, which in particular also makes it possible to produce the structure in the coating surface by removing material. This object is achieved by a method for the electrochemical coating or stripping of components as defined in claim 1. The dependent claims contain advantageous embodiments of the method according to the invention.

In the method according to the invention for the electrochemical coating or stripping of components, the component serves as an electrode. Between the component and a counter electrode, an elec- innovative field is established, which leads to the deposition of a dissolved electrolyte in a coating material or Abtra ^¬ gene of a coating material located on the component surface. In the method according to the invention, the component is coated during the deposition or during the removal of structures made of an electrically insulating material.

The electrically insulating structures exert a shielding effect on the surface of the component, which leads to the fact that in the region of the structures, the electric field at the

Surface of the component is lower than that between the structural ^¬ structures. Depending on the polarity of the electric field, therefore, more material is deposited on surface areas which lie between the insulating structures than on surface areas which are covered by the structures. In reverse polarity of the electric field more coating material is removed in areas between the structures as in Be ^¬ rich, which are covered by the structures. Since the struc ^¬ ren can have very small dimensions, can be with them surface structures with very small dimensions on the coating surface of produce, for example, very fine grooves or very fine burrs. In particular, the method according to the invention, by removing coating material subsequently enables a surface structure in the Surface of a planar coating surface already applied to a component.

The structures of electrically insulating material may be threads, for example, which are connected in the form of a mesh ^{miteinan ¬} . The surface structure of the coating can be specified by the type of linking of the threads, ie by the structure of the network.

The deposition or removal in coating material can be carried out by using a continuously applied electric field or else by using a pulsed electric field, that is to say an electric field which is built up and broken down again in successive pulses.

In a development of the method according to the invention, a structured electrode is used as counterelectrode. The structuring can be realized, for example, in the form of burrs on the electrode surface. The structured electrode is used so that the structures protrude in the direction of the component which is to be coated or stripped. Due to the structure of the counter electrode, the field line density of the electric field on the component surface can be influenced. For example, in the range of ^degrees , the field line density in the area of the component surface is higher than between the ridges. In general, however, the structure of the counter electrode can not be made as fine as the threads of the aforementioned network. Applicable methods fertil a structured counter-electrode is therefore particularly advantageous if the coating surface ^¬ upper surface structures is to have with coarse-scale dimensions. For example, the already mentioned in the description ^¬ introduction structure in the manner of a shark skin was here overall in which a coarse-scale surface structure, namely the scales, is present, which is superimposed by a fine-scale surface structure, namely the grooves in the scales. The coarse-grained structure and the fine-scale structure can be produced simultaneously or sequentially. However, if only a coarse-scale structure, for example flakes without grooves, are to be produced in the coating on the component, the structured counterelectrode can also be used alone, ie without the structure of electrically insulating material.

For producing a coating surface in the manner of a shark skin in the form of structures of the counter electrode ^¬ de well as the distances between them can be selected so that a shed is formed in the structure located on the surface of the component coating. In other words, the patterning of the counterelectrode represents the inverse structure to the coarse-scale structure to be created in the coating surface. At the same time, the orientation of the electrically insulating threads as well as the distances between them may be selected with respect to each other such that during deposition or Removal of the coating material forming grooves in the individual scales of the scale structure. The resulting structure in the coating surface is a sharkskin-like structure. But it is also possible to produce the structure in the manner of a shark skin alone by means of electrically insulating threads, which form, for example, a network in which coarse-scale structures of fine-scale structures are superimposed. In particular, threads of different thicknesses can be used in such a net.

In the method according to the invention, it is possible in particular to use a counterelectrode which in its shape adjoins the mold the component is adapted. In this way, a constant distance between the central electrode surface and the component surface can be realized.

In the method according to the invention, in particular a so-called.

MCrAlX material as a coating material and a component ei ^¬ ner turbomachine, for example, a running or Leit ^¬ scoop of a gas turbine to find as to be wound or entschichtendes component use. An MCrAlX material is an alloy material in which M is a metal, in particular cobalt

(Co) or nickel (Ni), and X represents a rare earth element or hafnium (Hf) or silicon (Si) or yttrium (Y). Such materials are used as oxidation-inhibiting / corrosion-inhibiting coatings in turbomachines, such as gas turbines.

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

Fig. 1 shows a highly schematic of the arrangement of a Bau ^¬ part, a counter electrode and electrically isolie ^¬ render threads in carrying out the inventive method.

Fig. 2 shows the field line distribution between the component and the counter electrode during the coating.

Fig. 3 shows the field line distribution between the component and the counter electrode during stripping. Fig. 4 shows a network of electrically insulating threads, which can be used in the method according to the invention.

Fig. 5 shows the coating of a component using a patterned counter electrode.

Fig. 6 shows a rotor or vane of a Gasturbi ^¬ ne.

The arrangement of a component 1 to be coated or stripped, which serves as an electrode in the coating or Entschichtungsverfahren and a counter electrode 3 to the component 1 is shown in Fig. 1. The component 1 is coated with a network 5 of electrically non-conductive threads, which represents a structure of electrically insulating material. The electrode 1 and the counter electrode 3 are connected to opposite poles ei ^¬ ner voltage source 7, so that a potential ^¬ difference between the electrode 1 and the counter electrode 3 is formed, which leads to the formation of an electric field between the two.

Both the component 1 and the counter electrode 3 are during loading or Entschichtens in an electrolytically th, which is in Fig. 1 does not Darge ^¬ represents the sake of clarity. The plating bath comprising an electrolyte which is ge ^¬ dissolves in the aufzubringendes either a coating material or can resolve an up-to component 1 Be ^¬ coating material. By means of the space formed between the component 1 and the counter electrode 3 electric field may then be deposited for coating of the component 1 in the electrolyzer ^¬ th dissolved coating material 9 onto the surface of the component 1 (see Fig. 2). If by means of the method a stripping of parts of an already on Coating 11 located on the component 1 (see FIG. 3), coating material is removed from the coating 11 by means of the electrolyte. The applied electric field then ensures that the ions dissolved in the electrolyte are transported away from the surface of the component 1.

In both cases, the threads of electrically non-conductive material, ie of a dielectric, ensure that the field line density between the threads is increased and correspondingly reduced in the area of the threads. In coating this results in that between the threads 5 more material aufgetra ^¬ gene is as below the threads (see FIG. 2). On stripping, on the other hand, this leads to more material being removed between the threads than below the threads (see FIG. 3).

In this way, a surface structure in a coating on the component 1 can be produced with the aid of the electrically insulating threads. In particular, this can be done both when applying the coating and when removing a coating. In particular, this offers the possibility to provide coated parts already subsequently by partiel ^¬ les removal of the coating with a surface structure.

A net 13, which is suitable as a structure of electrically insulating material, in particular for producing a surface structure in the manner of a shark skin, is shown in FIG. 4. The network includes first threads 15 which form a re ^¬ tively large-mesh net. Furthermore, second threads 17 are present, which have a relatively small distance from each other and extend diagonally to the first threads 15. The first threads 15 then lead to loading or stripping Formation of the coarse-scale scale structure, whereas the second threads 17 lead to the formation of grooves in the scales. The first and second threads 15 and 17 may in this case in particular also have different diameters. In the network 13, the first threads 15, which has the coarse-scale

Form network, a distance from each other, which is in the range of 10 to 100 microns. The second threads 17 for forming the fine-scale structure in the coating, however, have a distance from each other which is significantly less than 10 microns and is in particular in the range of 0.1 to 2 microns.

An alternative possibility for producing in particular the coarse-scale structures is shown in FIG. 5, which shows a component 1 and a counter-electrode 19. The counter electrode shown in Fig. 5, in contrast to the counter ^¬ electrode 3 of Figures 1 to 3, a structured E- lektrodenoberflache on. The structuring is realized by ridges 21, which protrude beyond the actual electrode surface. For coating or stripping of the component 1, the counter electrode 19 is oriented with respect to the component 1 such that the burrs 21 point in the direction of the component 1. When a voltage between the component 1 and the counter electrode 19, the field line density is in the range of the burr 21 relative to the other areas of the counter electrode ER höht 19, which also leads to an increase of the field line density at the Be ^¬ rich of the component 1, if the counter electrode 19 is not too far away from the component surface. On ^¬ due to the increased field line density is the rate at which coating material sawn up or is removed, in those regions of the component on which the ridges 21 against increased. FIG. 5 shows the deposition of coating material 9. However, it is also possible to remove material from a coating already on the component 1. For producing a structure in the manner of a shark skin, the burrs 21 may be arranged in the shape of a rhombus on the surface of the counter electrode 19. Adjacent ridges then have a distance of about 10 to 100 microns from each other. With the help of the ridges 21, scale-like structures can then be produced in a coating to be applied to the component 1 or already present. By means of an additionally arranged above the component 1 network, which has only the fine threads 17 of FIG. 4 and which is arranged with a appro ^¬ Neten orientation on the component surface 1, the grooves can be made in the shed. In this embodiment, therefore, the coating with egg ^¬ ner surface structure in the manner of a shark skin by means of a combination of a structured counter-electrode 19 and the use of electrically non-conductive threads 5 is prepared. If only the coarse-scale structure is to be produced, but can also be dispensed with the network. The production of the coarse-scale scale structure does not necessarily take place simultaneously with the production of the fine-scale groove structure. It is also possible to first create one of the two structures and then form the other structure in the pre-structured surface.

When using a structured counter-electrode 19 can be adjusted by the distance from the component surface 2 as diffuse the structure in the surface of the Be ^¬ coating should be. The further the counterelectrode is removed from the surface 2 of the component 1, the lower the increased field line density in the region of the ridges 21 on the surface 2 of the component 1 has an effect. In other Wor ^¬ th, the further the counter electrode is removed from the component 1, the more uniform the field line density is in the range of Component surface and the more diffuse the generated Ober ^¬ surface structure.

The described method can in particular be used for producing a coating with a structured surface on components of turbomachines. In particular, the method is suitable for applying an MCrAlX coating on guide vanes or guide vanes, as described below with reference to FIG. 6.

6 shows a perspective view of a rotor blade 120 or guide vane show ^¬ 130 of a turbomachine, which extends along a longitudinal axis of the 121st

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 at its blade tip 415 another platform (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, in all regions 400, 403, 406 of the blade 120, 130, for example, ^massive metallic materials, in particular 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 known; 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, for example, by directed solidification from the melt. These are casting methods in which the liquid metallic alloy solidifies to a monocrystalline structure, ie to a monocrystalline workpiece, or directionally. Here, dendritic crystals are aligned along the heat flow and form either a columnar crystal grain structure (columnar, ie grains that run the entire length of the workpiece and here, the general usage, referred to as directionally solidified who ^¬ den) or a monocrystalline structure, ie the whole work ^¬ piece consists of a single crystal. In these processes, it is necessary to avoid the transition to globulitic (polycrystalline) solidification, since non-directional growth necessarily produces 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 meant single crystals that no grain boundaries or have at most Kleinwinkelkorngrenzen, as well as Stängel- crystal structures that have probably extending in the longitudinal direction 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 documents are concerning. the solidification method of the ^¬ Of fenbarung.

Likewise, the blades 120, 130 may have coatings against corrosion or oxidation, e.g. B. (MCrAlX; M is at least one element of the group consisting of iron (Fe), cobalt (Co), Ni ^¬ ckel (Ni), X is an active element and stands for yttrium (Y) and / or silicon and / or at least one element the rare earth, 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 should be part of this disclosure with regard to the chemical composition of the alloy. 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).

On the MCrAlX may still be present a thermal barrier coating, which is preferably the outermost layer, and consists for example of ZrO2, Y2O3-ZrO2, ie it is not, partially ^¬ or fully stabilized by yttria and / or calcium oxide and / or magnesium oxide. The heat-insulating layer covers the entire MCrAlX layer. Suitable coating processes, such as electron beam evaporation (EB-PVD), produce stalk-shaped grains in the thermal barrier coating. Other coating methods are conceivable, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The heat- insulating layer may have porous, micro- or macro-cracked Kör ^¬ ner 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 need to be deprotected after use (e.g., 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 also has, if necessary, film cooling holes 418 ^(indicated by dashed lines) on.

The invention described in the embodiments allows the production of coatings having a structured surface process by means of electrochemical deposition or etching ^¬. Therefore, it allows not only the additive Her ^¬ provide a structured surface but also the structuring of an existing Beschichtungsoberfla ^¬ che by partial removal of the coating.

Claims

claims

1. A method for electrochemical coating or stripping of components (1), in which the component (1) serves as an electrode and in which between the component (1) and a counter electrode (3, 19) an electric field is built up, which From ^{deposition of} a coating material dissolved in an electrolyte or for removal of a coating material (11) located on the component surface (2), the component (1) emanates from structures (5) during the deposition or during the ablation an electrically insulating material, characterized in that the structures comprise threads (5) which are arranged around the component (1) in the form of a net.

2. The method according to claim 1, characterized in that the electric field up in successive pulses and is degraded again.

3. The method according to any one of the preceding claims, characterized in that as a counter electrode (19) a structured electrode is used such that the structures (21) of the structured electrode (19) in the direction of the component (1) before ^¬ stand.

4. The method according to claim 3, characterized in that as structures in the counter electrode (19) burrs (21) are used in the electrode surface.

5. The method according to claim 3 or 4, characterized in that the shape of the structures (21) of the counter electrode (19) ^¬ as the distances between them are chosen so that when depositing or removal of the coating material, a scale structure in which on the Forming the surface (2) of the component (1) located coating material and that the orientation of the electrically insulating threads (5) and the distances between them are selected with respect to each other so that during deposition or removal of the coating material grooves in the individual scales of the scale structure train.

6. The method according to any one of the preceding claims, characterized in that as a counter electrode (3, 19) in its shape to the shape of the component (1) adapted electrode is used.

7. The method according to any one of the preceding claims, characterized in that find a coating material MCrAlX material and as a component of a turbine component use.