COATING SYSTEM FOR IMPROVED LEADING EDGE EROSION PROTECTION

Abstract

A gas turbine engine includes airfoils. At least a portion of the airfoils are coated with a coating that provides for erosion and corrosion protection for the portion of the airfoils.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/779,722, filed 13 Mar. 2013, the disclosure of which is now incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to coatings, and more specifically to coating systems to reduce erosion and corrosion in gas turbine engines.

BACKGROUND

Gas turbine engines are used to power aircraft, watercraft, power generators, and the like. Gas turbine engines typically include a compressor, a combustor, and a turbine. The compressors and turbine of the turbine engine can include turbine disks or turbine shafts, as well as a number of blades mounted to the turbine disks/shafts that extend radially outwardly therefrom into the gas flow path. Also included in the turbine engine are rotating, as well as static, seal elements that channel the airflow used for cooling certain components such as turbine blades and vanes. The airflow channeled by these rotating, as well as static, seal elements carry corrodant deposits to the turbine blades. As the maximum operating temperature of the turbine engine increases, the turbine blades are subjected to higher temperatures. Debris entering the engine can present issues for the compressor and other components.

Alkaline sulfate, sulfites, chlorides, carbonates, oxides, and other corrodant salt deposits can be sources of erosion and corrosion. In addition, ingested dirt, fly ash, volcanic ash, concrete dust, sand, sea salt, etc. are a major source of erosion. This can lead to failure or premature removal and replacement of the compressor blades unless the damage is reduced or repaired. Conventional plasma vapor deposition (PVD) processes such as cathodic arc and E-beam PVD are widely used methods for depositing erosion resistant coatings on the airfoils of compressor blades and vanes. However, PVD processes such as cathodic arc and E-beam PVD typically introduce high residual stress on the leading edge of the compressor airfoils during the coating process. When high residual stress from the coating process is coupled with out-of-plane stress from the leading edge geometry and thermal expansion mismatch between coating and substrate, it can result in coating spallation in the as-coated condition providing insufficient leading edge erosion protection.

Coating methods and coating compositions for compressor blades and vanes that provide high angle solid particle erosion protection on the leading edge of compressor airfoils are desired. Coating methods and coating compositions that also provide lower angle solid particle erosion protection on the concave and convex sides of the airfoils are desired.

SUMMARY

The present application discloses one or more of the features recited in the appended claims and/or the following features which, alone or in any combination, may comprise patentable subject matter.

A coating system in accordance with the present disclosure may include the application of an erosion resistant coating to a portion of a gas turbine engine blade. In some embodiments, the coating may be applied to a preselected exterior surface of the airfoil blades. The coating may be applied to the leading edge surface of the airfoil to increase the erosion resistance of the leading edge. The coating may also be applied to the concave side surface, the convex side surface, or combinations thereof.

In some embodiments, the coating may be formed from tungsten-tungsten carbide, tungsten carbide cobalt, cobalt-chrome-tungsten carbide, chrome carbide-nickel, chrome carbide-nickel-chrome, or a diamond like carbon material. The process may also include a metallic bond coat layer positioned between the coating and the surface of the airfoil. The surface of the airfoil may also be nitrided or carburized before the application of the coating.

In some embodiments, the coating may be applied to the airfoil using high velocity oxygen fuel spray, high velocity air fuel spray, solution plasma spray, cold spray, chemical vapor deposition, electo spark deposition, plasma enhanced chemical vapor deposition, or air plasma spray method.

These and other features of the present disclosure will become more apparent from the following description of the illustrative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a turbine with portions broken away to show the vanes within the turbine;

FIG. 2 is a perspective view of a vane segment showing a series of airfoils;

FIG. 2A is a perspective view of a series of compressor blades with each compressor including an airfoil;

FIG. 3 is a sectional view taken along lines 3-3 of FIG. 2 showing an airfoil having the coating of the present disclosure formed on the leading edge of the airfoil;

FIG. 4 is a sectional view of an airfoil having the coating of the present disclosure formed on a surface of the leading edge of the airfoil;

FIG. 5 is a sectional view of an airfoil having the coating of the present disclosure formed on the leading edge and concave side of the airfoil;

FIG. 6 is a sectional view of an airfoil having the coating of the present disclosure formed on the leading edge and the concave and convex sides of the airfoil;

FIG. 7 is a sectional view of an airfoil having the coating of the present disclosure formed on the leading edge on an airfoil that has been nitrided or carburized and treated with a metallic bond coat layer.

FIG. 8 is a photograph of an airfoil sample showing erosion of the leading edge of the airfoil due to sand ingestion;

FIG. 9 is a photograph of another airfoil sample showing erosion to the leading edge of the airfoil; and

FIG. 10 includes photographs of test samples showing erosion of the leading edge of airfoil samples.

DETAILED DESCRIPTION OF THE DRAWINGS

For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to a number of illustrative embodiments illustrated in the drawings and specific language will be used to describe the same.

The present disclosure is directed to a coating system that provides an enhanced airfoil 14 including leading edge erosion protection for a turbine 11, as shown in FIGS. 1-2A. More particularly, the present disclosure is directed to one or more coatings that provide enhanced high angle solid particle erosion protection on compressor airfoils 14, as shown, for example, in FIGS. 3-7. The coating is primarily applied to the leading edge 12 of the airfoils 14, as shown in FIGS. 3, 4, and 7. The coating(s) may also provide low angle solid particle erosion protection on the concave 16 and convex 18 sides of the airfoils 14, as shown in FIGS. 5 and 6.

The coating 31, for example, formed on the leading edge 12 of the airfoils 14 is selected from group consisting of tungsten-tungsten carbide, tungsten carbide cobalt, cobalt-chrome-tungsten carbide, chrome carbide-nickel, chrome carbide-nickel-chrome, and diamond like carbon. The coating 31 on the leading edge 12 is preferably applied by use of a high velocity oxygen fuel (HVOF) spray, a high velocity air fuel (HVAF) spray, a solution plasma spray, a cold spray, chemical vapor deposition (CVD), electro spark deposition, plasma enhanced chemical vapor deposition (PE-CVD), or air plasma spray method. By applying the coating 31 primarily to the leading edge 12, weight increase of the airfoils 14 is minimized. The coating 31 also provides increased corrosion resistance.

In one illustrative embodiment, airfoil 14 may have first coating 31 applied to leading edge 12 while a second coating 32 is applied to both concave surface 16 and convex surface 18 as shown in FIG. 3. In another illustrative embodiment, airfoil 14 may have first coating 31 applied to leading edge 12 while second coating 132 is applied over first coating and on both concave and convex surfaces 16 and 18 as shown in FIG. 4. In still yet another illustrative example, airfoil 14 may have a coating 231 applied to both leading edge 12 and concave surface 16 while omitting any coating on convex surface 18 as shown in FIG. 5. In another illustrative embodiment, airfoil 14 may have a coating 331 applied to leading edge 12, concave surface 16, and convex surface 18 as shown in FIG. 6. In still yet another illustrative example, airfoil 14 may have a first coating 431 applied to leading edge 12, concave surface 16, and convex surface 18 and a second coating 432 applied over first coating 431 at leading edge 12.

In still yet another example, airfoil 14 may have a first coating applied to leading edge 12, a second coating applied to concave surface 16, and a third coating applied to convex surface 18. The first, second, and third coatings may be all the same, all different, or any suitable combination thereof.

In addition, the first coating may be applied to leading edge 12, concave surface 16, and convex surface 18. One or more coatings may be applied over the first coating on one or more of the leading edge 12, concave surface 16, and convex surface 18. In some examples, the first coating may be the same or different than the one or more coatings.

The coatings 31, 32, 132, 231, 331, 431, 432 discussed previously are selected from the group consisting of TiAlN, AlTiN, TiAlN/TiN multilayer, TiAlN/Cr multilayer, tungsten-tungsten carbide, tungsten carbide cobalt, cobalt-chrome-tungsten carbide, chrome carbide-nickel, chrome carbide-nickel-chrome, and diamond like carbon. The coatings 31, 32, 132, 231, 331, 431, 432 may be applied by applied by PVD, HVOF, HVAF, solution plasma spray, cold spray, CVD, electro spark deposition, or PE-CVD.

Conventional PVD processes such as cathodic arc and E-beam PVD are widely used methods for depositing erosion resistant coatings. However, PVD processes such as cathodic arc and E-beam PVD typically introduce high residual stress on the leading edge of the compressor airfoils during the coating process. When high residual stress from the coating process is coupled with out-of-plane stress from the leading edge geometry and thermal expansion mismatch between coating and substrate, it can result in coating spallation in the as-coated condition and insufficient leading edge erosion protection during engine operation. Coatings applied by HVOF, HVAF, solution plasma spray, cold spray, CVD, electro spark deposition, and PE-CVD can introduce lower residual stresses on the leading edge 12 of the compressor airfoil 14 when the right coating materials are used, which leads to better high angle solid particle erosion protection on the leading edge 12.

If coating spray methods such as HVOF, HVAF, solution plasma spray, and cold spray are used, a powder size less than 50 μm is used normally to obtain a smooth surface finish. The powder size is preferably smaller than 20 μm to obtain the desired finish on the airfoil 14. For both the leading edge coatings 12 and the convex 18 and the concave 16 side coatings, Ni, Ti, Cr, or other metallic bond coat layers 24 can be used between the coatings and the airfoil 14. The surface of the airfoil 14 can be nitrided and carburized 431 before the application of the coating 432 to improve corrosion and erosion resistance, as shown, for example, in FIG. 7.

In one example, the thickness of the coating 31, 231, 331, 432 on the leading edge 12 is from about 10 μm to about 100 μm. In another example, the thickness of the coating 31, 231, 331, 432 on the leading edge 12 is from about 35 μm to about 75 μm. The thickness of the coating 32, 132, 231, 331 on the concave 16 and convex side 18, for example, is from about 5 μm to about 50 μm. In another example, the thickness of the coating 32, 132, 231, 331 on the concave 16 and convex 18 sides is from about 15 μm to about 35 μm. The thickness of the metallic bond coat layer 431, for example, is from about 2.5 μm to about 10 μm. The nitrided or carburized depth on the airfoil 14, for example, is from about 10 μm to about 50 μm.

FIG. 8 is a photograph of an airfoil sample showing erosion of the leading edge of the airfoil due to sand ingestion. In this photograph, the leading edge 12 of the airfoil 14 was coated with TiN applied by cathodic arc physical vapor deposition (PVD). As can be seen the Leading Edge Preferential Erosion (LEPER) is present and is detrimental to gas turbine performance. Another airfoil sample showing erosion to the leading edge of the airfoil is shown in FIG. 9. The leading edge 12 of the airfoil 14 was treated with TiAlN applied by cathodic arc physical vapor deposition (PVD). As can be seen, Leading Edge Preferential Erosion (LEPER) is present in the edge of the airfoil.

A series of photographs of erosion test result samples are shown in FIG. 10 from testing performed by the University of Cincinnati. In these tests, the leading edges of the airfoil samples were subjected to a particulate applied in a series of stages. In the first stage, 0.995 Kg of 95% Arizona Road Dust (ARD) A4 (silica based sand with 80 μm nominal diameter) with 5% Mil E-5007C crushed quartz (75˜100 μm) was used. The photographs taken at stage one indicate the amount of erosion that has occurred to the leading edge of the test samples. The samples were subjected to multiple stages of erosion testing including a ninth stage where 1.1 Kg of ARD A4 was used. The photographs taken at stage nine indicate the amount of erosion that occurred to the leading edge of the test samples. As can be seen, the tungsten carbide tungsten (WC/W) sample applied with the chemical vapor deposition (CVD) method shows a clean edge with no erosion. The coating microstructure is tungsten carbide (WC) particles dispersed in tungsten (W).

While the disclosure has been illustrated and described in detail in the foregoing drawings and description, the same is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments thereof have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected.

Claims

1. A method for coating a portion of a gas turbine engine blade, the method comprising the steps of

providing a gas turbine blade, the blade further comprising an airfoil section having an exterior surface and

applying a coating layer to a preselected exterior surface selected from the group consisting of the leading edge surface, the concave side surface, the convex side, and combinations thereof, the coating layer selected from the group consisting of tungsten-tungsten carbide, tungsten carbide cobalt, cobalt-chrome-tungsten carbide, chrome carbide-nickel, chrome carbide-nickel-chrome, and diamond like carbon,

wherein the coating layer at the leading edge surface has a thickness from about 10 μm to about 100 μm.

2. The method of claim 1, wherein the coating layer at the leading edge surface has a thickness from about 35 μm to about 75 μm.

3. The method of claim 2, wherein the coating layer at the concave and convex surfaces is from about 5 μm to about 50 μm.

4. The method of claim 1, further including the step of applying a metallic bond coat layer to the exterior surface of the airfoil before the coating layer.

5. The method of claim 4, wherein the metallic bond coat layer has a thickness from about 2.5 μm to about 10 μm.

6. The method of claim 5, wherein the metallic bond coat layer is selected from the group consisting of Ni, Ti, and Cr.

7. The method of claim 1, further including the step of nitriding the surface of the airfoil.

8. The method of claim 7, wherein the nitrided depth is from about 10 μm to about 50 μm.

9. The method of claim 1, further including the step of carburizing the surface of the airfoil.

10. The method of claim 9, wherein the carburized depth is from about 10 μm to about 50 μm.

11. The method of claim 1, wherein the coating is applied using coating spray methods from the group consisting of HVOF, HVAF, solution plasma spray, electo spark deposition, and cold spray.

12. The method of claim 11, wherein the coating powder size is less than 50 μm.

13. The method of claim 12, wherein the powder size is less than 20 μm.