Search

EP-3572554-B1 - METHOD FOR COATING A METALLIC SURFACE

EP3572554B1EP 3572554 B1EP3572554 B1EP 3572554B1EP-3572554-B1

Inventors

  • Pillhöfer, Horst
  • MORANT, MAX
  • Lautenbacher, Philipp
  • Hilser, Ludwig

Dates

Publication Date
20260513
Application Date
20190405

Claims (11)

  1. Method for providing a metallic surface of a component of a turbomachine with a coating in order to produce a diffusion layer, in which method one or more layers of one or more metal-containing slips are applied onto the surface, the slip(s) containing at least particulate metal and binder, and at least one metal-containing slip comprising aluminum and/or an aluminum alloy, and, after all the slip layers have been applied, the coated substrate being heated to a temperature that allows the aluminum in the layer(s) to diffuse into the coated surface of the substrate, characterized in that at least one of the slips contains at least one coloring and/or chromophoric substance that has no influence on the properties of the finished coating and/or can be decomposed by thermal treatment, and the local thickness of the applied slip layer is determined on the basis of the local color intensity of the layer, the determination of the local color intensity of the applied slip layer including a comparison with calibrated color charts and the like and/or a measurement using photosensors, and the color charts having been created in a fundamental experiment using known layer thicknesses.
  2. Method according to any of the preceding claims, characterized in that the metallic surface comprises or consists of an alloy based on nickel, cobalt and/or iron.
  3. Method according to any of the preceding claims, characterized in that the at least one coloring and/or chromophoric substance comprises at least one metal-containing pigment.
  4. Method according to any of the preceding claims, characterized in that the at least one coloring and/or chromophoric substance comprises at least one organic dye.
  5. Method according to claim 4, characterized in that the at least one organic dye can be thermally decomposed with loss of its color.
  6. Method according to any of the preceding claims, characterized in that the at least one coloring and/or chromophoric substance comprises at least one substance that results in a coloration of the slip when irradiated with UV and/or IR rays.
  7. Method according to any of the preceding claims, characterized in that two or more slip layers are applied, the already-applied layer being dried, if necessary, before applying a layer onto an already-applied layer.
  8. Method according to claim 7, characterized in that the first layer is formed using a slip containing the at least one coloring and/or chromophoric substance, and a second layer made from a slip containing no coloring and/or chromophoric substance is applied onto the first layer.
  9. Method according to claim 8, characterized in that one or more further slip layers are applied onto the second layer, slips which have the coloring and/or chromophoric substance and slips without the coloring and/or chromophoric substance being alternated between.
  10. Method according to any of the preceding claims, characterized in that the slip(s) are applied by manual spraying.
  11. Method according to any of the preceding claims, characterized in that the coated area of the metallic substrate is at least 4 cm 2 in size.

Description

BACKGROUND OF THE INVENTION AREA OF INVENTION The present invention relates to a method for coating a metallic surface, for example a surface of a component of a turbomachine, with a metal-containing slurry, and in particular a method that enables the visual assessment of the uniformity of the thickness of the applied slurry layer. STATE OF THE ART In the field of gas turbines, such as stationary gas turbines or aircraft engines, turbine blades made of, for example, nickel- or cobalt-based superalloys are typically coated with diffusion-resistant layers to protect them against oxidation and corrosion at the high temperatures encountered during operation. For this purpose, a slurry containing aluminum and/or chromium is applied to the blade or a portion thereof, usually in several layers. The coated blade is then heated to high temperatures (e.g., 600°C to 1200°C) to cause the metals in the slurry to diffuse into the blade surface, thereby improving its resistance to oxidation and corrosion. The slurry is usually applied to the blade by manual spraying, as robot-assisted spraying is too expensive and time-consuming, and malfunctions in the slurry supply and the spray nozzle are difficult or impossible to detect. However, when manually applying the slip in one or more layers, it is difficult or impossible to achieve a uniform thickness of the slip layer. This is because a typical slip, consisting of metal powder, binder, and solvent, is usually gray before and after drying, the same color as the surface of the metallic substrate onto which it is applied. This makes it practically impossible to visually assess whether and to what extent the applied slip layer has a uniform thickness. For this reason, the coating of metal substrates with metal-containing slip has so far been limited to relatively small component areas, such as the underplatform area of a turbine blade, since larger areas to be coated (e.g., the entire blade) are not feasible. (entire guide vane) the resulting diffusion layers exhibit large, unacceptable variations in layer thickness. US 2005/0031877 reveals details on the production of a diffusion layer on a metallic surface and US 2007/0044704 discloses the use of color pigments in coating compositions for assessing the uniformity of the coating application. REVELATION OF THE INVENTION TASK OF INVENTION It is therefore an object of the present invention to provide a method for coating a metallic surface with a metal-containing slurry, which makes it possible to assess, without great effort, visually and/or with simple technical aids, whether and to what extent the applied slurry layer has a uniform thickness. TECHNICAL SOLUTION This problem is solved by a method with the features of an independent method claim. Advantageous embodiments are the subject of dependent claims. In the inventive method for providing a metallic surface of a component of a turbomachine with a uniformly thick coating to produce a diffusion layer, one or more layers (preferably at least two layers) of one or more metal-containing slurries are applied to the surface to be coated, wherein, before applying a layer to an already applied layer, the already applied layer is preferably dried. The slurry(ies) contains at least particulate metal and a binder, wherein at least one metal-containing slurry comprises aluminum and/or an aluminum alloy, and wherein, after all slurry layers have been applied, the coated substrate is heated to a temperature that allows the aluminum in the layer(s) to diffuse into the coated surface of the substrate. At least one of the slurries used, or the (sole) slurry used, contains at least one coloring and/or coloring substance that has no influence on the properties of the finished coating and/or can be decomposed by thermal treatment. The local thickness of the applied slurry layer can be determined based on the local color intensity of the layer. Determining the local color intensity of the applied slurry layer involves a comparison with calibrated color charts and the like, and/or a measurement with photosensors. The color charts were created in a fundamental experiment with known layer thicknesses. By comparing color intensities at different locations on the layer, the uniformity of the layer thickness can also be assessed. Additionally, the layer thickness can be adjusted to achieve the most uniform layer thickness possible across the entire surface to be coated. In other words, in the inventive method, the thickness of the slurry layer at a specific location on the coated surface is determined and/or assessed based on the color intensity at that location, with a smaller layer thickness resulting in lower color intensity than a larger layer thickness. A substantially uniform color intensity across the entire surface to be coated thus indicates a substantially uniform layer thickness. In the case of uneven color intensity, more slurry can be applied (e.g., sprayed) to areas with lower color in