Method for repairing a coating of a hot-gas component

Abstract

The invention relates to a method for repairing a hot-gas component (01) which has a metal main body (02) with an adhesion promoter layer (03) and a protective coating (04). The starting point for the method is the presence of damage (07) within a repair region (06). First, the coating (03, 04) is removed in the repair region (06), wherein a peripheral edge (08) forms the end of the remaining protective coating (04) with respect to the repair region (06). Then, a new adhesion promoter layer (13) is applied in the repair region (06), including in sections at the peripheral edge (08). The new adhesion promoter layer (13) is then removed again from the peripheral edge (08) before, in the final step, a new protective coating (14) is applied in the repair region (14).

Description

Description TITLE Method for repairing a coating on a hot gas component TECHNICAL AREA

[0001] The invention relates to a method for repairing a coating on a hot gas component, wherein the coating in the damaged area is first removed and subsequently rebuilt. BACKGROUND

[0002] In gas turbines, hot gas components are subject to high thermal stresses. Especially when dealing with metallic components, these are often coated with a so-called TBC coating (TBC = thermal barrier coating). To ensure the adhesion of the TBC coating to the metallic substrate, an adhesion promoter layer, known as a bond coat, is generally applied between the TBC coating and the metallic substrate.

[0003] Due to the thermal and dynamic stresses on the hot gas components, cracks and other damage, particularly to the coating, occur over their service life. Depending on the extent of the damage, this necessitates either replacement of the hot gas component or repair. In favorable cases, the coating is then rebuilt.

[0004] This usually involves first removing the existing coating in the damaged area. The coating is then rebuilt, typically by first applying the adhesion promoter layer and then the TBC coating, just as in the original manufacturing process.

[0005] The transition between the old and new coatings repeatedly proves problematic. These are often points where new cracks develop during the ongoing use of the repaired component. SUMMARY OF THE INVENTION

[0006] The object of the present invention is to improve the quality of the component after a repair of the coating, so that a longer service life can be achieved.

[0007] The problem is solved by a method according to the invention as described in claim 1. Advantageous embodiments are the subject of the dependent claims.

[0008] The method is used to repair a hot gas component in which a metallic base body has an adhesion promoter layer and a protective coating, and damage is present in the coating within a repair area.

[0009] First, the coating in the repair area is removed, leaving a border to define the edge of the remaining protective coating. Next, a new adhesion promoter layer is applied to the repair area, starting with a section at the border. This new adhesion promoter layer is then removed from the border before, finally, a new protective coating is applied to the repair area. DESCRIPTION OF THE INVENTION

[0010] The generic method is used to repair a hot gas component. The specific type of hot gas component is initially irrelevant. The method is particularly preferred for gas turbine components. This could include, for example, a combustion chamber, a This could be a transition part following the combustion chamber, a housing part in contact with hot gas, or a turbine blade.

[0011] The hot gas component of this type has a metallic base body with a coating. The coating comprises at least an adhesion promoter layer and a protective coating. The specific type of coating is initially irrelevant.

[0012] The protective coating is intended to reduce the thermal and, where applicable, chemical or mechanical stress on the metallic substrate. Conversely, an adhesion promoter layer is present to enable the protective coating to adhere to the substrate.

[0013] The protective coating is advantageously a so-called TBC coating (thermal barrier coating). A TBC coating is a high-temperature-resistant ceramic coating used to protect components from extreme temperatures. It exhibits greater temperature resistance and preferably low thermal conductivity. Therefore, the TBC coating can significantly reduce the stresses on the base body of the hot gas component resulting from its use.

[0014] The adhesion promoter layer is advantageously a so-called MCrAlY coating. MCrAlY is a group of alloys consisting primarily of nickel (Ni) or cobalt (Co) as the main component, along with chromium (Cr), aluminum (Al), and yttrium (Y) as alloying elements. MCrAlY coatings advantageously serve as adhesion promoters between the metallic substrate and a ceramic thermal barrier layer, such as the TBC coating. They compensate for the thermal expansion between the substrate and the ceramic layer. MCrAlY coatings offer good oxidation and corrosion resistance at temperatures up to approximately 1000°C. The aluminum oxide layer on the surface protects against further oxidation. The adhesion promoter layer has an adhesion layer thickness, and the protective coating has a protective layer thickness. Depending on the function of each layer, the protective layer thickness is usually significantly greater than the adhesion layer thickness.

[0016] The generic procedure is applied when the protective coating and / or the adhesion promoter layer exhibits damage that is repairable, but further use of the hot gas component without repair is not practical. The damage may include, for example, cracks or flaking.

[0017] Typically, several individual damages within a specific area are grouped together, so that the defined repair area is repaired in a single procedure. However, the procedure can also be used for a single damage, meaning the repair area would only encompass that one damage. At a minimum, a repair area is defined for the single damage, and usually for multiple damages.

[0018] First, it is necessary to remove the coating in the repair area, i.e., both the protective coating and the adhesion promoter layer.

[0019] Removing the coating in the repair area creates an edge as the end of the existing protective coating adjacent to the repair area. In this regard, it is irrelevant whether further layers located between the bonding agent layer and the base body are present, or whether the base body is partially removed.

[0021] Before the actual reconstruction of the coating, it may be necessary to repair damage to the base body, either by welding or other material application.

[0022] To restore the coating, the first step, as is typical, is to apply a new adhesion promoter layer to the repaired area. Care is usually taken to ensure that the new adhesion promoter layer does not directly border the existing protective coating.

[0023] The protective coating is then applied to the repair area, as is standard practice.

[0024] However, according to the invention, the new adhesion promoter layer is applied right up to the edge, so that no gap or reduction in the adhesive layer thickness occurs between the old and new adhesion promoter layers. This, however, means that in certain sections the new adhesion promoter layer abuts the existing protective coating directly along the edge.

[0025] Therefore, in an intermediate step, material is removed again. The plan is to remove the new adhesion promoter layer above the intended adhesive layer thickness continuously along the edge. This ensures that the new adhesion promoter layer does not abut the existing protective coating.

[0026] Finally, a new protective coating is applied to the repaired area, so that the original properties of the hot gas component are essentially restored (at least as far as the repaired area is concerned).

[0027] This advantageous process, involving the initial application of the new adhesion promoter layer to a larger area and the subsequent removal of the new adhesion promoter layer from the edge, restores the original properties of the coating in the repaired area without any loss of performance. This minimizes the risk of future damage arising from the interface between the old and new adhesion promoter layers.

[0028] The removal of the damaged coating in the repair area can be carried out in various ways. There are well-known and proven methods for this. At a minimum, it is advantageous if the edge, forming the perimeter of the repair area, is vertical or slightly inclined. For this purpose, an angular range is defined between a surface perpendicular to the surface of the base body or the hot gas component and a surface inclined at an angle of 30° to the surface. This means that the edge is advantageously located within an angular range of 60° to 90° relative to the surface. It is particularly advantageous, on the one hand with regard to the removal of the damaged coating and on the other hand with regard to the subsequent application of the new adhesion promoter layer, if the edge is located within an angle range between 75° and 85°.

[0030] When removing the new adhesion promoter layer at the edge, it is possible to leave the edge unchanged. However, this makes the complete removal of the new adhesion promoter layer from the edge more difficult, and the fact that the edge remains intact throughout the two process steps leads to a poorer bond between the new protective coating and the existing protective coating at the edge.

[0031] Therefore, it remains advantageous if, when removing the new adhesion promoter layer from the edge, the edge itself and, to some extent, the existing protective coating are also removed, thus creating a new edge. This improves the bond between the existing and new protective coatings along the new edge. It is advantageous if the new edge deviates from a perpendicular surface (relative to the surface) at a larger angle. Therefore, it is advantageous if the new edge is located at an angle between 15° and 75° relative to the surface or relative to a perpendicular surface. In particular The removal of the new adhesion promoter layer and the adjacent protective coating is advantageous, so that the new edge is located at an angle between 30° and 60°. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIGS. 1 to 5 schematically outline the sequence for repairing a hot gas component 01 within a repair area 06. DESCRIPTION OF THE EXECUTION FORM EN

[0033] Figure 1 shows a sectional sketch of a hot gas component 01a, which initially comprises a base body 02 with a coating. In this example, the coating includes an adhesion promoter layer 03 and a protective coating 04.

[0034] The starting point for the procedure is the presence of damage 07 at least in the coating 03, 04. Some cracks in the adhesion promoter layer 03 and the protective coating 04 are sketched here as examples.

[0035] For a contiguous area with damage 07, a repair area 06 is defined. In a first step, the coating, i.e., the adhesion promoter layer 03 and the protective coating 04, is removed in the repair area 06 – see Figure 2. This results in the existing protective coating 04 being limited along a continuous edge 08.

[0036] In this example, an edge edge 08 is sketched, which is oriented approximately at an angle of 10° relative to the vertical, i.e., approximately at an angle of 80° to the surface of the hot gas component 01 or the base body 02.

[0037] Figure 3 illustrates the result of the next step, which involves applying a new adhesion promoter layer 13 to the base body 02 in the repair area 06. It is essential that the new adhesion promoter layer is completely is applied all around up to the edge 08 and thus comes into direct contact with the existing protective coating 04.

[0038] In an additional intermediate step, the area of ​​the new adhesion promoter layer 13 that protrudes above the adhesive layer thickness is removed - see Figure 4. At the same time, the previous edge 08 along with an adjacent area of ​​the previous protective coating 04 is removed, so that a new edge 18 is formed.

[0039] In this example, the new edge 18 of the existing protective coating is designed to extend along an angle of approximately 45°.

[0040] Figure 5 shows a sketch of the restored hot gas component 01 b, in which 01a the repair area 06 is also provided with a new protective coating 14.

Claims

Claims What is claimed:

1. Method for repairing a hot gas component (01 a), wherein the hot gas component (01 a) comprises a metallic base body (02) and an adhesion promoter layer (03) and a protective coating (04), wherein the protective coating (04) and / or the adhesion promoter layer (03) has damage (07) in a repair area (06); comprising the steps - Removal of the protective coating (04) and the adhesion promoter layer (03) in the repair area (06), wherein an edge edge (08) forms the end of the remaining protective coating (04) to the repair area (06); - Application of a new adhesion promoter layer (13) in the repair area (06), whereby an application is carried out section by section on the edge (08); - Removal of the new adhesion promoter layer (13) from the edge (08); - Application of a new protective coating (14) in the repair area (06).

2. Method according to claim 1, wherein the hot gas component (01 a) is a combustion chamber of a gas turbine.

3. Method according to claim 1 or 2, wherein the adhesion promoter layer (03) is an MCrAIY coating; and / or wherein the protective coating (04) is a TBC coating.

4. Method according to any one of claims 1 to 3, wherein the edge (08) is formed within an angle between 60° and 90°, in particular between 75° and / or 85°.

5. Method according to one of claims 1 to 4, wherein, in the removal of the new adhesion promoter layer (13), the protective coating (04) at the edge edge (08) is removed at the same time and a new edge edge (14) is formed.

6. Method according to claim 5, wherein the new edge (14) is formed within an angle between 15° and 75°, in particular between 30° and / or 60°.

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