COATING FOR THERMALLY AND ABRASIVELY LOADED TURBINE BLADES

Abstract

A method for coating a substrate surrounding a gas turbine blade, including the following steps: in a first step, a MCrAlY matrix is applied by means of a PVD method; in a further step, an oxide layer is applied by means of a PVD method.

Claims

1. Method for coating a substrate surrounding a gas turbine blade, comprising the steps: in a first step, application of a MCrAlY matrix by means of a PVD method in a further step, application of a layer by means of a PVD method, wherein the layer comprises at least one oxide and/or boride and/or carbide and/or nitride.

2. Method according to claim 1, characterized in that the PVD method of the first and/or of the further step is a cathodic spark evaporation method.

3. Method according to claim 1, characterized in that the material source for the PVD method of the further step is an AlCr target and the coating method is a reactive method in the course of which oxygen is used.

4. Method according to claim 1, characterized in that the coating is executed as a layer system which comprises two layers or that the coating is executed as a layer system which comprises a multi-layer alternating coating system.

5. Layer system for a gas turbine blade tip comprising at least a first layer with MCrAlY matrix and at least a second layer, wherein the second layer comprises at least one oxide and/or boride and/or carbide and/or nitride.

6. Layer system according to claim 5, characterized in that the layer system is a multi-layer coating system in which the first and second layer alternate.

7. Gas turbine blade with a coating system according to claim 5.

Description

[0017] FIG. 1 shows schematically a layer system according to the invention made up of an MCrAlY layer and an overlying oxide layer.

[0018] FIG. 2 shows schematically a multilayer coating system according to the invention.

[0019] FIG. 3 shows the schematic representation of a turbine.

[0020] FIG. 4 shows a SEM of the cross-section of a multilayer coating system according to the invention after it had been exposed to a temperature of 1200 C. for 10 hours.

[0021] FIG. 5 shows the X-ray diffractogram of an abrasive phase of an aluminum oxide-chromium oxide.

[0022] The turbine shown in FIG. 3 has at least one turbine blade 5 on a rotating disc 3 with a blade base 7 and a blade tip 9. FIG. 3 also shows a run-in layer 11 on a turbine liner 1 opposite the blade tip 9 and separated from it by a gap G.

[0023] On a blade tip made of a superalloy (may for example be single crystal) a coating of the composition MCrAlYaluminum chromium oxide, or a multilayer coating of alternating layers of MCrAlYaluminum chromium oxide is deposited.

[0024] The MCrAlY is deposited from a MCrAlY material source (=target) by plasma-enhanced cathodic spark evaporation. The MCrAlY layer can have thicknesses of 0.1-100 micrometers according to the required oxidation resistance.

[0025] The oxide layer is now deposited on the MCrAlY adhesion and anti-oxidation layer. The aluminum chromium oxide layers are deposited from metallic AlCr Targets by means of reactive cathodic spark evaporation in an oxygen atmosphere. The oxide layer can have a thickness of 0.5 to 50 microns.

[0026] In order to suppress harmful diffusion processes and thus increase the service life, the oxide layer can also be deposited as a multi-layer coating in which the MCrAlY layer alternates with an aluminum-chromium oxide layer at regular or other intervals of 0.1-20 micrometers.

[0027] In this concept, the oxide coating provides a diffusion barrier, which simultaneously also serves as an abrasive phase that is not sensitive to oxidation. The MCrAlY layer adhering directly to the substrate also provides excellent adhesion to the blade tip and the sum of all MCrAlY layers in the entire blade tip coating prevent inwardly oriented diffusion processes and efficiently protect the substrate from oxidation.

[0028] In very general terms, it can be said that the hardness of the overall layer system according to the invention can be adjusted by the ratio of abrasive phase to MCrAlY in order to enable optimal removal of the run-in layer. For example, layers with oxide phases in the range of 7 to 25 GPa can be adjusted. However, if harder abrasive phases such as nitrides, borides or carbides are used, the hardness can be increased up to 45 GPa. For example, the layer in FIG. 4 has a hardness of approx. 13 GPa.

[0029] If aluminum oxide-chromium oxide is used as the abrasive phase, it forms in the cathodic spark evaporation a mixed crystal in the corundum structure with a strong preferred orientation, as can be seen in FIG. 5. In the corundum structure, the mixed oxide is in its thermally stable high-temperature modification and can therefore reach the high application temperatures without phase transformation. The volume changes associated with the phase transformation, which can lead to the failure of the layer, can thus be prevented.