Partial recoating of a ceramic layer system and ceramic layer system

Abstract

The invention relates to a method for the local recoating of a ceramic layer system (1), in which a depression (16) is first created in a ceramic layer system (1) by means of a decoating process, wherein a ceramic coating is completely removed locally and a metallic coating is at least partially removed locally, wherein a metallic adhesion promoter layer (7) is then applied, wherein preferably a protection (19) is used around the depression (16), and after the complete application or repair of the metallic adhesion promoter layer (7'), a bevel is created within the depression (16) in its edge regions by material of the ceramic layer (10) around the depression (16) being gradually removed, and then, in the last step, new ceramic material (31) is applied into the modified depression (16').

Description

The invention relates to the partial recoating of a ceramic layer system and to a ceramic layer system.Ceramic layer systems comprising a metallic substrate with at least one ceramic layer as a protection against high temperatures and or corrosion are known and are used in the chemical industry, in furnaces and in turbines, in particular gas turbines.An exemplary ceramic layer is disclosed in EP 1 707 653 B1.Due to wear due to deployment, sometimes only local wear of a ceramic layer is present.The procedure according to the prior art consists in erecting the complete component and completely recoating it. In particular in layer systems which consist of a metallic lower layer and a ceramic upper layer, it is more complicated to remove these layers of metal and ceramic completely and apply them again completely.Metallic and ceramic layers are applied by spraying methods.U.S. Pat. No. 6,274,193 B1 discloses a repair in which the metallic coating is diffused in.It is therefore an object of the invention to solve the above problem.The object is achieved by a method according to claim 1 and a ceramic layer system according to claim 4.The dependent claims list further advantageous measures which can be combined with one another as desired in order to achieve further advantages.Figures 1, 6 show a ceramic vision system and method is shown schematically in Figures 2 to 5.A ceramic layer system 1 is schematically shown in FIG. 1.The ceramic layer system 1 has at least:a metallic substrate 4, which in turbine components is a nickel- or cobalt-based superalloy.For improved bonding due to the different coefficients of thermal expansion of metal and ceramic, a metallic adhesion promoter layer 7 is present, which, in use, forms an oxide layer (TGO), which serves for bonding a ceramic layer 10.The metallic adhesion promoter layer 7 is preferably based on a NiCoCrAlY alloy.The metallic adhesion promoter layer 7 preferably represents a coating, i.e. not a pure diffusion layer.The ceramic layer 10 can be formed in a single layer or two layers, i.e. comprise different materials in a two-layer system.Examples of these are an underlying ceramic layer of partially stabilized zirconium oxide PSZ such as 7YSZ and an overlying ceramic layer of fully stabilized zirconium oxide FSZ such as 20YSZ.Due to the wear, the layer thickness of the TBC has been locally reduced or no longer present (not shown).Therefore, the ceramic layer 10 is locally removed by means of a decoating method, in particular by means of a laser 13 (FIG. 2 ).The metallic adhesion promoter layer 7 is likewise preferably removed locally (FIG. 2 ).Water jet removal with / without abrasive material or other methods such as laser irradiation or laser beams guided in the water jet may also be used.Preferably, no material of the substrate 4 is removed.After the local removal of the ceramic layer 10 according to FIG. 1, the ceramic layer system 1' then has a depression 16.In the next step (FIG. 3 ), a metallic adhesion promoter layer is locally restored in the depression 16 by a coating system 22, so that a repaired adhesion promoter layer 7' is formed. The same material as in the original layer system 1 can be used, but it does not have to be used.Likewise, the metal adhesion promoter layer in the depression 16 can compensate for removed material of the substrate 4, if necessary.During the coating with the metal, the remaining surface of the ceramic layer system 1' is provided at least partially with a protection 19 (FIG. 3 ), but at least around the depression 16.However, it cannot be completely prevented that metal is cut off from the metallic coating material around the edge region of the depression 16.In any event, metallic material is present on the side surface 17 of the well 16 of the remaining ceramic layer 10', which material must be removed.Then, according to FIG. 4, the guard 19 is removed and, in the next step, the existing ceramic of the ceramic layer 10' of the ceramic layer system 1" is removed around the depression 16 in a wedge-shaped or step-shaped manner, so that no metallic material is present any longer on the existing ceramic coating 10''' of the ceramic layer system 1'''.In a final step, ceramic material 31 is applied in the modified trough 16' by a further or the same coating system 22, so that the ceramic layer system 11 thus produced is comparable to the original ceramic layer system 1 (FIG. 1 ).The region 34 of the ceramic coating filling the well 16' can be made with the same material of the materials or a different material is deliberately used to improve the use of the ceramic layer system 1 IV.Here, different material means that at least one constituent of the ceramic differs by at least 5%, in particular at least 10%, or a different stabilizer or an additional stabilizer for stabilized zirconium oxide is used.Preferably, a segmented coating is present for the ceramic layer 11, for example made of PSZ / FSZ, such as 8YSZ or 8YSZ / 20YSZ (FIG. 5 ).Preferably, for the ceramic layer part 34' in the well 16', a different microstructure is then applied, such as in particular highly porous material 34' instead of segmented microstructure (FIG. 6 ).This material 34' in the well 16' preferably has a porosity greater than 12%, in particular greater than 18%, and is in any case greater by 5%, absolutely 10% per unit area than the surrounding layer regions 10L, 10R (Fig. 6).Preferably, ceramic layer 10 is a segmented layer of yttria stabilized zirconia and layer portion 34' preferably comprises yttria and additional yttria stabilized zirconia.Likewise, the ceramic layer can have different thicknesses for the ceramic layer in an extension direction 12 of the ceramic layer system 11, so that different thicknesses are likewise used for the region 34' in which, for example, a continuous transition from the one layer thickness 10L to the thinner layer thickness 10R is produced or, as illustrated in FIG. 6, a gradation is preferably effected centrally between the two different layer thickness regions 10L, 10R.Thinner generally means that the layer thickness is at least 5%, in particular at least 10%, thicker or thinner.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedEP 1 707 653 B1

[0003] U.S. Pat. No. 6,274,193 B1

[0007]

Claims

Method for locally recoating a ceramic layer system (1), in which a depression (16) is first produced in a ceramic layer system (1) by means of a decoating method, wherein locally at least one ceramic coating is removed completely and optionally a metallic coating is locally at least partially, wherein then optionally a metallic adhesion promoter layer (7) is locally applied, wherein preferably a protection (19) is used at least on the surface of the ceramic layer (1') around the depression (16), and after the complete application or repair of the metallic adhesion promoter layer (7'), a bevelling of the ceramic layer (1'') is produced within the depression (16) in its edge regions by material of the ceramic layer (10'') being removed stepwise around the depression (16), and then, in the last step, new ceramic material (31) is applied into the modified depression (16').Method according to claim 1, wherein a microstructure of the layer (11) is produced for the new region (34, 34') which is different from the microstructure of the ceramic layer (10) of the ceramic layer system (1), preferably the ceramic layer (10) represents a segmented layer and the new region (34, 34') has a significantly higher porosity and / or is not segmented.Method according to claim 1 or 2, wherein for the material of the layer (11) for the region (34) a material is used which is different from the material of the ceramic layer (10) of the ceramic layer system (1), preferably the ceramic layer (10) represents a segmented layer of yttria-stabilized zirconia and a ceramic layer part (34, 34') in the trough (16') comprises yttria and yttria-stabilized zirconia.Ceramic layer system (11, 111), in particular produced according to a method according to one or more of Claims 1, 2 or 3, in which the ceramic layer system (11) has three different regions (10L, 34, 34', 10R), wherein a central region (34, 34') between two regions (10L, 10R) has a significantly higher porosity and / or a significantly different material than the surrounding regions (10L, 10R).The ceramic layer system of claim 4, wherein the region (34') has a stepped or decreasing coating thickness.Ceramic layer system according to Claim 4 or 5, in which the regions (10L, 10R) surrounding the region (34, 34') have a segmented microstructure.

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