Abstract:
The English-language Abstract from the international application is to be retained and is therefore not duplicated in the specification.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Phase application submitted under 35 U.S.C. §371 of Patent Cooperation Treaty application serial no. PCT/DE2008/001668, filed 10 Oct. 2008, and entitled WEAR PROTECTION COATING, which application claims priority to German patent application serial no. 10 2007 050 141.4, filed 19 Oct. 2007, and entitled VERSCHLEISSSCHUTZBESCHICHTUNG, the specifications of which are incorporated herein by reference in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention concerns a wear protection coating, in particular an erosion protection coating, preferably for gas turbine components, according to the general terms of the claims. 
       BACKGROUND 
       [0003]    Fluid-mechanically stressed components, such as, for example, gas turbine components, are subject to wear due to oxidation, corrosion, and erosion. A wear process is involved during erosion, which is caused by solid matter moved along with the flow of gas. In order to extend the service life of components that are stressed fluid mechanically, wear protection coatings are required which protect the components from wear, especially from erosion, corrosion, and oxidation. 
         [0004]    A multiple-layer, erosion-resistant coating for the surfaces of substrates is known from EP0674020B1. The erosion-resistant coat disclosed there provides a wear protection coating which consists of several multilayer systems applied repetitively to the substrate to be protected. Thus, in EP0674020B1, the multilayer systems applied repetitively are formed of two different layers each namely, on the one hand, a layer of a metallic material and on the other hand a layer of titanium diboride. 
         [0005]    EP0366289A1 discloses a further erosion-resistant as well as corrosion-resistant coating for a substrate. Also according to EP0366289A1, the wear protection coating is formed of several multilayer systems applied repetitively to the substrate to be coated, in which each multilayer system consists in turn of two different layers, namely a metallic layer, of titanium for instance, and a ceramic layer, for example of titanium nitride. 
         [0006]    A further erosion-resistant, wear protection coating is known from EP0562108B1. Thus, the wear protection coating disclosed there is formed in turn of several multilayer systems applied repetitively to a substrate to be coated. At the same time, FIG. 4 of EP0562108B1 discloses a wear protection coating formed of several multilayer systems applied repetitively, in which each multilayer system consists of four layers. 
         [0007]    The wear protection coatings are preferably vaporized onto the surface of a component to be coated and consequently to be protected, in which a wear protection coating can increase the roughness of an outer, flow-relevant surface of the component. The increase in roughness is aerodynamically unfavorable, since loss of flow can develop. Furthermore, an increase in roughness can lead to faster and more severe fouling, since the deposition of contamination on rough surfaces can occur more readily. Increased roughness also causes accelerated attack upon the surface of the component by erosion due to hard particles. Therefore, there exists a need to improve wear protection coatings. 
       SUMMARY 
       [0008]    Proceeding from this, the basis of the problem for the present invention is to create a new type of wear protection coating. 
         [0009]    This problem is solved by further improving the wear protection coating mentioned initially, by means of the features of the claims. According to the disclosure, an outer layer is formed as a smoothing layer, which compensates for unevennesses or roughnesses and/or defect sites of the wear protection coating. 
         [0010]    It is proposed, with the disclosure presented here, to apply an outer smoothing layer to the original wear protection coating, which compensates for unevennesses or roughnesses or even defect sites in the wear protection coating. A highly smoothed, superfinished surface is thereby provided, which causes a reduction in aerodynamic loss and counteracts fouling of the coated component. In addition, erosion resistance is improved. Additionally, an improvement in oxidation and corrosion resistance can be counted upon. 
         [0011]    Preferably, the smoothing layer is formed as a sol-gel layer, which exhibits a thickness on the order of magnitude of the unevennesses or roughnesses and/or defect sites to be compensated for. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Preferred improvements of the invention result from the subclaims and the following description. Embodiment examples of the invention are explained in detail using the FIGURE, without being limited thereto. 
           [0013]      FIG. 1  shows a highly schematic cross-section through a wear protection coating according to the invention in accordance with one embodiment example of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The invention presented here concerns a wear protection coating, especially an erosion protection coating, for a surface to be protected of a fluid-mechanically stressed component, especially a component of a gas turbine, such as, for example, a rotor blade or a guide vane of a gas turbine. 
         [0015]      FIG. 1  shows a highly schematic cross-section through a wear protection coating  10  according to the invention, which is applied to an outer surface  11  of a component  12 , especially a gas turbine vane, which is stressed fluid mechanically. 
         [0016]    An outer layer of the wear protection coating  10  according to the invention is formed as a smoothing layer  13 , in which the smoothing layer  13  compensates for unevennesses or roughnesses and/or defect sites of the original wear protection coating. 
         [0017]    At the same time, the smoothing layer  13  exhibits a thickness that is on the order of magnitude of the unevennesses or roughnesses and/or defect sites to be compensated for. The smoothing layer  13  preferably exhibits a thickness between 1 μm and 10 μm. Preferably, the thickness of the smoothing layer is between 5 μm and 10 μm. Alternatively, the thickness of the smoothing layer can be between 1 μm and 5 μm. 
         [0018]    As already stated, the smoothing layer  13  forms the outer stratum or layer of the wear protection coating according to the invention, whereby, in the embodiment example shown in  FIG. 1 , two multilayer systems  14 ,  15  are applied to the surface  11  to be coated of the component  12 , and in which each multilayer system  14 ,  15  includes a relatively soft, metallic layer  16  and a relatively hard, ceramic layer  17 . The outer smoothing layer  13  is applied to the outer, relatively hard, ceramic layer  17  of the outer multilayer system  15 . 
         [0019]    The smoothing layer  13  of the wear protection coating according to the invention is executed as a sol-gel layer. A fluid phase, a so-called sol, is applied for this purpose by dipping, spraying or daubing on the outer layer  17  of the outer multilayer system  15  and then drying and hardening by means of tempering. 
         [0020]    During the drying and the hardening, the fluid phase, namely the sol, is converted to a solid phase, into a so-called gel. The drying and hardening can be combined with heat treatment. 
         [0021]    The application of the smoothing layer  13 , formed as a sol-gel layer, to the outer hard layer  17  of the multilayer system  15  presents the advantage that the relatively hard layer  17  provides a protective effect for the relatively thin sol-gel layer and thus the smoothing layer  13 , which particularly supports the bonding of the smoothing layer  13  under mechanical load. 
         [0022]    Preferably, a sol-gel layer on a silicate base or carbon base or metal oxide base or polymer base is provided as the smoothing layer  13 . 
         [0023]    Accordingly, in the sense of the invention presented here, a wear protection coating can be provided as an outer layer, which compensates for unevennesses or roughnesses and/or defect sites of the original wear protection coating. The smoothing layer  13  is at the same time preferably formed as a sol-gel layer, with a thickness that is on the order of magnitude of the unevennesses or roughnesses and/or defect sites to be compensated for. Especially preferably, the smoothing layer  13  then finds application when the wear protection coating is formed of several multilayer systems, in which the smoothing layer is then applied to the outer layer of the outer multilayer system.