Masking method for producing a combination of blade tip hardfacing and erosion-protection coating

Abstract

A method for manufacturing a blade (1) for a turbomachine, the blade having a hardfacing on its tip (4) and an erosion-protection coating (13) at least on its airfoil (3) is provided. Initially, a blade tip hardfacing is applied to the blade tip and, subsequently, a mask (10) is positioned in the region of the blade tip hardfacing, the mask covering the blade tip hardfacing, and, subsequently, the erosion-protection coating is deposited. The mask is removed after the erosion-protection coating is completed. A blade for a turbomachine, the blade having a hardfacing on its tip (4) and an erosion-protection coating (13) at least on its airfoil (3) is also provided. The erosion-protection coating at least partially covers the blade tip hardfacing, and the thickness of the erosion-protection coating decreases continuously in and/or toward the region of the blade tip hardfacing.

Claims

1. A blade for a turbomachine, the blade comprising: a tip; an airfoil having a leading edge and a trailing edge; a hardfacing on the tip and an erosion-protection coating at least on the airfoil, the hardfacing having hardfacing sides extending from the leading edge and the trailing edge and a hardfacing outer surface extending between the hardfacing sides; the erosion-protection coating at least partially covering the tip hardfacing on the hardfacing outer surface, a thickness of the erosion-protection coating decreasing continuously in or toward a region of the tip hardfacing wherein a maximum or average thickness of the erosion-protection coating on the hardfacing outer surface is less than half of the average thickness of a remaining erosion-protection coating.

2. The blade as recited in claim 1 wherein the maximum or average thickness of the erosion-protection coating on the hardfacing outer surface is less than one-third of the average thickness of the remaining erosion-protection coating.

3. The blade as recited in claim 2 wherein the maximum or average thickness of the erosion-protection coating on the hardfacing outer surface is less than 10% of the average thickness of the remaining erosion-protection coating.

4. The blade as recited in claim 1 wherein the tip hardfacing is surrounded by or embedded in the erosion-protection coating.

5. The blade as recited in claim 4 wherein boron nitride particles in the blade tip hardfacing extend through the erosion protection coating on the hardfacing outer surface.

6. A method for manufacturing a blade for a turbomachine, the blade having a tip and an airfoil, the blade having hardfacing on the tip and an erosion-protection coating at least on the airfoil, the method comprising; applying initially a blade tip hardfacing to the blade tip, the hardfacing having hardfacing sides and a hardfacing outer surface extending between the hardfacing sides; and positioning subsequently a mask in the region of the blade tip hardfacing, the mask covering the blade tip hardfacing outer surface; depositing subsequently the erosion-protection coating; and removing the mask after the erosion-protection coating is deposited, the erosion protection coating the airfoil and at least partially coating the hardfacing outer surface wherein the erosion protection coating covers the hardfacing outer surface with a thickness less than the erosion protection coating on the hardfacing sides.

7. The method as recited in claim 6 wherein boron nitride particles in the hardfacing project out of the erosion protection coating.

8. The method as recited in claim 6 wherein the erosion protection coating on the hardfacing outer surface is removed during use.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings show purely schematically in

(2) FIG. 1: a perspective view of a blade, such as may be used in turbomachines, with a mask for the deposition of an erosion-protection coating;

(3) FIG. 2: a top view showing the airfoil of the blade of FIG. 1 without the blade root, but with the mask positioned thereabove, and in

(4) FIG. 3: a portion of a turbine blade after various steps of the inventive method as illustrated in subfigures a) through e).

DETAILED DESCRIPTION

(5) Other advantages, characteristics and features of the present invention will become apparent from the following detailed description of exemplary embodiments. However, the present invention is not limited to such exemplary embodiments.

(6) FIG. 1 shows, in a purely schematic perspective view, a blade as may be used in a turbomachine, such as, for example, a stationary gas turbine or an aircraft engine. Blade 1 has a blade root 2 which may be inserted into a disk which rotates with a shaft of the turbomachine. Blade 1 further has an airfoil 3 which is disposed in the flow duct of the turbomachine and which either compresses the fluid flowing through the turbomachine or is driven by the passing fluid. Located at the radially outer end of blade 1 is the blade tip 4, which, in order to prevent flow losses, lies as closely adjacent as possible to a surrounding flow duct casing or even cuts into the same. To this end, blade tip 4 is provided with a blade tip hardfacing (see FIG. 3) which also has a cutting function, allowing blade tip 4 to cut into a surrounding flow duct casing, respectively into sealing material attached thereto. The blade tip hardfacing may be formed by, for example, a coating containing a nickel matrix 6 with cubic boron nitride particles 7 embedded therein.

(7) Airfoil 3 also has a coating for protecting blade 1, this coating being an erosion-protection coating intended to protect the material of blade 1 from erosive wear. Such an erosion-protection coating may be composed of a multi-layer coating which may be formed by a plurality of alternately deposited hard and soft layers, in particular ceramic layers and metal layers.

(8) FIG. 1 further shows that, for applying an erosion-protection coating that is to be deposited mainly on the airfoil as well as on leading edge 8 and trailing edge 9 of the blade, the region of blade tip 4 is masked by a mask 10 which is held by two posts 11,12 located in the region of leading edge 8 and trailing edge 9.

(9) As shown in the schematic view of FIG. 1, mask 10 is positioned at a distance from blade tip 4. This distance may be selected to be very small.

(10) Mask 10 is shaped to correspond to the shape of blade tip 4 and, accordingly, also has a curved shape, as shown in the embodiment of FIG. 1.

(11) FIG. 2 shows the blade of FIG. 1 in a top view in which only the airfoil is shown by a dashed line and which illustrates the arrangement of mask 10 from above. It is clear that mask 10 corresponds to the shape of blade tip 4, and in particular of the top surface thereof, in terms of its dimensions and its shape in a plane transverse to the radial direction of the blade 1. As can clearly be seen in FIG. 2, mask 10 has the same banana-shaped configuration as the top surface of blade tip 4. In the view of FIG. 2, mask 10 is configured with a small overhang, making it slightly larger than the top surface of blade tip 4. However, instead of being oversized, mask 10 may also be dimensioned slightly smaller than the top surface of blade tip 4, depending on the desired amount of coverage of blade tip hardfacing 5 with erosion-protection coating 13,14. For this purpose, it is also possible to vary the distance at which mask 10 is positioned from blade tip 4. In the extreme case, mask 10 may also rest directly on blade tip 4.

(12) FIG. 3 illustrates in subfigures a) through e) the various stages during the manufacture of a blade having a blade tip hardfacing on blade tip 4 and an erosion-protection coating on airfoil 3. Subfigure a) of FIG. 3 shows a portion of a blade 1 including airfoil 3 and blade tip 4.

(13) As shown in FIG. 3b), a blade tip hardfacing 5 is applied to blade tip 4, the hardfacing being composed of a nickel matrix 6 and cubic boron nitride particles 7 embedded therein. The application of blade tip hardfacing 5 is accomplished, for example, by electrodeposition of nickel matrix 6 in which the cubic boron nitride particles are embedded. However, the blade tip hardfacing may also be accomplished in any other suitable manner.

(14) After blade tip hardfacing 5 is completed, mask 10 is positioned so that erosion-protection coating 13,14 can be applied (see FIG. 3c)).

(15) Erosion-protection coating 13,14 can be deposited by physical vapor deposition (PVD) and, more specifically, by depositing the respective sub-layers of the multi-layer erosion-protection coating using various techniques of thermal evaporation or sputter deposition. In the process, blade 1 is coated over its entire surface both on airfoil 3 and on blade tip 4 on top of blade tip hardfacing 5. However, mask 10 reduces the deposition of the erosion-protection coating in the region of blade tip 4, so that the erosion-protection coating 14 obtained is thinner compared to the thicker erosion-protection coating 13 in the region of airfoil 3 (see FIG. 3d)). In particular, the thickness of erosion-protection coating 14 in the region of blade tip 4 is so small that the particles of hard material in the form of boron nitride particles 7 which are embedded in the tip hardfacing project out of erosion-protection coating 14. In any case, the thin erosion-protection coating 14 in the region of blade tip 4, respectively blade tip hardfacing 5, is so thin that it does not impair the cutting effect of the particles of hard material, respectively BN particles 7.

(16) Following the deposition of erosion-protection coating 13,14, mask 10 and its supporting posts 11,12 are removed, leaving a blade 1 which has a thicker erosion-protection coating 13 in the region of the airfoil and a thinner erosion-protection coating 14 in the region of the blade tip, respectively blade tip hardfacing 5. In this connection, the relative terms thicker and thinner each refer to the respective other portion of erosion-protection coating 13,14.

(17) Blade tip hardfacing 5 is embedded in and surrounded by the adjoining erosion-protection coating 13 without the erosion-protection coating excessively covering the abrasive surface of blade tip hardfacing 5 that is in contact with a sealing material located opposite thereto.

(18) Although the present invention has been described in detail with reference to the above exemplary embodiments, it is not limited to such exemplary embodiments. Rather, various modifications may be made by omitting individual features or by combining features in different ways, without departing from the protective scope of the appended claims.

LIST OF REFERENCE NUMERALS

(19) 1 blade 2 blade root 3 airfoil 4 blade tip 5 blade tip hardfacing 6 Ni matrix 7 BN particle 8 leading edge 9 trailing edge 10 mask 11,13 post 13 erosion-protection coating on the airfoil 14 erosion-protection coating in the region of the blade tip