METHOD FOR CREATING A TEXTURED BOND COAT SURFACE
A method for creating a textured surface (52) of bond coat material (18) for improving the performance of a thermal barrier coating system (12). A plurality of columns (62) of bond coat material are formed by spraying (52) the material through a corresponding plurality of openings (32) in a mask (30) applied to a surface (40) to be textured. The openings may be formed in only a region (34) of the mask in response to an image of the surface to be textured. The mask and excess material (54) applied over the mask are then removed to reveal the textured surface.
This invention relates generally to the field of materials technology, and more particularly to a method for creating a textured surface in a bond coat of a thermal barrier coating system.
BACKGROUND OF THE INVENTIONCeramic thermal barrier coating systems are used on gas turbine engine hot gas path components to protect the underlying metal alloy substrate from combustion gas temperatures that exceed the safe operating temperature of the alloy. A typical thermal barrier coating system may include a bond coat, such as an MCrAIY material, deposited onto the substrate alloy and a ceramic topcoat, such as yttria stabilized zirconia, deposited onto the bond coat. It is known that strong adhesion between the layers of such systems is critical for proper functioning and long life of the coating system, and that a degree of surface roughness in the interface between the layers provides a beneficial mechanical interlock in that regard.
Bond coat material is often deposited by a spray process, such as High Velocity Oxy-Fuel (HVOF) or Air Plasma Spray (APS). It is known to control spray parameters when depositing a bond coat layer in order to achieve a degree of surface roughness in the deposited coating. However, the degree of roughness and the shape of the surface features in the deposited coating that are created by controlling the spray parameters are limited.
It is also known to texture the surface of a bond coat layer prior to the deposition of a ceramic insulating layer by using a material removal process, such as laser ablation, micromachining or photolithography, such as described in U.S. Pat. No. 5,723,078. As the firing temperatures of advance gas turbine engines continue to increase, further improvements in thermal barrier coating systems and methods of applying such coatings are desired.
The invention is explained in the following description in view of the drawings that show:
The present invention envisions depositing a layer of bond coat material over and through a mask containing a plurality of openings formed there through such that the bond coat material is deposited onto the underlying surface in a pattern corresponding to the plurality of openings. In this manner, a predetermined surface pattern can be achieved with a high degree of precision and with vertical dimensions that exceed those achievable by simply varying the spray parameters when depositing the coating.
For component repair applications, a damaged region of a thermal barrier coating system is removed, such as by grinding, and that region must be recoated. In one embodiment, the region to be recoated is imaged, such as with a digital camera or other scanning device, and the image is used to determine a corresponding region 34 of the mask 30 into which are formed the openings 32. Regions 36 of the mask 30 surrounding or remote from the region 34 of the openings 32 remain effectively solid. The mask 30 of
After the damaged region of thermal barrier coating 12 is removed from the component 10 of
Attachment of the mask 30 to the surface 40 may be accomplished by any known technique and will depend upon the material of construction of the mask 30. For example, a polymer or ceramic mask 30 may be attached with an adhesive, and a metallic or ceramic mask may be attached by brazing. The selection of attachment method is made with consideration of the fact that the mask must be removed from the component surface 40 at a later stage of the process. For example, if a polymer mask 30 is attached with an adhesive, it may be advantageous to select an adhesive that will volatize at a temperature near the volatization temperature of the polymer so that both can be removed in a single heating step.
The next step is to apply a bond coat material 50, such as with a known thermal spray process 52, as illustrated in
The bond coat material 50 that adheres to the top of the mask 30 is considered excess material 54, and it is removed to again expose the mask 30, as illustrated in
The mask 30 is then removed from the component 10 to reveal a textured surface 56 including the desired pattern 60 of bond coat material formed on the surface 40, as illustrated in
Surface features having a height (direction perpendicular to the coating surface) of up to 25 microns may be achieved by controlling thermal spray parameters. The present invention enables the production of surface features with heights of greater than 25 microns and up to about 400 microns, or in the range of 200-400 microns. And while the embodiment illustrated herein incorporates round openings 32 and a circular cross-section in the columns 62 at equidistant spacings, surface features having various other cross-sectional shapes may be formed, and particularly shapes that inhibit the growth of cracks parallel to bond surface. Moreover, the pattern 60 of surface features 62 may vary from one region of the component 10 to another, either within the same mask 30 or by using different masks in different regions. In one embodiment, at least one of a cross-sectional shape of the openings or a spacing between openings is varied across the mask 30.
The process described herein may be applied to other layered coating systems. For example, hard wear surfaces and abradable coatings are used in various regions of components of gas turbine engines subjected to mechanical wear. The size, shape, number and/or pattern of surface features that may be achieved using the processes described herein may be useful in achieving particular mechanical properties within a coating system. For example, an abradable ceramic material 70 may be deposited over the structure of
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
Claims
1. A method comprising:
- removing a portion of an existing thermal barrier coating from a gas turbine engine component to reveal a region of a surface to be coated;
- forming a mask comprising a plurality of openings formed therethrough corresponding to a desired pattern of surface features to be created in a replacement bond coat layer;
- applying the mask to the region of the surface to be coated;
- depositing bond coat material over the mask and onto a base layer of the bond coat material disposed on the surface through the openings in the mask; and
- removing the mask and excess bond coat material deposited over the mask to reveal the replacement bond coat layer having the desired pattern of surface features disposed on the base layer of the bond coat material.
2. The method of claim 1, further comprising:
- removing all layers of the portion of the existing thermal barrier coating to reveal a region of a superalloy material surface of the component; and
- applying the base layer of the bond coat material onto the superalloy material surface prior to applying the mask.
3. The method of claim 1, further comprising:
- forming the mask of a polymer material;
- removing the excess bond coat material using a mechanical process; and
- removing the mask using a heating step.
4. The method of claim 1, further comprising:
- obtaining an image of the region of the surface to be coated;
- using the image to form the mask to comprise openings only in a region of the mask corresponding to the region of the surface to be coated.
5. The method of claim 1, further comprising varying at least one of a cross-sectional shape of the openings or a spacing between openings across the mask.
6. A method comprising:
- forming a mask comprising a plurality of holes corresponding to a desired pattern of surface features of a bond coat of a thermal barrier coating system;
- applying the mask to a surface to be coated;
- directing a spray of bond coat material over the mask and onto the surface through the holes in the mask;
- removing bond coat material deposited onto the mask; and
- removing the mask to reveal the desired pattern of surface features in the bond coat material deposited onto the surface.
7. The method of claim 6, further comprising forming the plurality of holes in the mask in response to an image of the surface to be coated.
8. The method of claim 6, further comprising varying a size, shape or spacing of the holes across the mask.
9. A method comprising:
- forming a mask comprising a plurality of openings;
- applying the mask to a surface of a gas turbine engine component;
- directing a spray of an alloy material through the openings of the mask and onto the surface;
- removing the mask and any excess alloy material deposited onto the mask to reveal a pattern of the alloy material on the surface; and
- applying a ceramic material over the patterned alloy material.
10. The method of claim 9, further comprising applying a ceramic insulating material over the patterned alloy material.
11. The method of claim 9, further comprising applying an abradable ceramic material over the patterned alloy material.
12. The method of claim 9, further comprising forming the plurality of holes in the mask in response to an image of the surface to be coated.
13. The method of claim 9, wherein the gas turbine engine component comprises a base layer of bond coat material that defines the surface onto which the spray of alloy material is directed.
Type: Application
Filed: Jun 27, 2013
Publication Date: Jan 1, 2015
Inventors: Gary B. Merrill (Orlando, FL), Ahmed Kamel (Orlando, FL)
Application Number: 13/928,413
International Classification: F01D 5/00 (20060101); F01D 25/14 (20060101);