Multilayered Coatings With Diamond-like Carbon

Abstract

Multilayered coatings include an adhesion base layer that can adhere to a metal substrate, and a top surface layer that has a surface roughness of less than or equal to about Ra 0.0254 .mu.m, wherein at least one of the layers comprises a diamond-like carbon.

Description

BACKGROUND OF THE INVENTION

[0001] The subject matter disclosed herein relates to multilayered coatings and, more specifically, to multilayered coatings with diamond-like carbon that can be applied to compressor blades of turbines.

[0002] In a gas turbine engine, the compressor section generally includes multiple stages that have a row of compressor blades (also referred to as "rotor blades" or "rotor airfoils") and stator blades (also referred to as "stator airfoils"). The compressor blades rotate about a rotor and, thusly, impart kinetic energy to the airflow through the compressor. Directly following the row of compressor blades is a row of stator blades, which remain stationary. Acting in concert, the compressor blades and stator blades turn the airflow and slow the air velocity, respectively, which can increase the static pressure of the airflow through the compressor section. Multiple stages of compressors blades and stator blades can be stacked in an axial flow compressor to achieve the required discharge to inlet air pressure ratio. Compressor and stator blades can thus be secured to rotor wheels and the stator case, respectively, by means of a dovetail or root or base attachment.

[0003] In operation, compressor blades may be subject to mechanical stresses and harsh operating conditions because of the rotational velocity of the compressor. These levels of stress combined with other operating conditions may affect the experienced levels of erosion or corrosion. For example, the ambient air pulled in through the compressor section can include constituents that may be corrosive and abrasive to the compressor blades and other such parts. Some components may further be subject to mixtures of hydrocarbon-based lubricating oils, carbonaceous soot, dirt, rust and the like.

[0004] Coatings may be applied to articles such as compressor blades to provide additional protection against these elements. However, some tough but smooth coatings such as diamond like carbons can experience high levels of internal compressive stresses as thickness increases.

[0005] Accordingly, alternative fluorinated coatings would be welcome in the art.

BRIEF DESCRIPTION OF THE INVENTION

[0006] In one embodiment, a multilayered coating is disclosed. The multilayered coating includes an adhesion base layer that can adhere to a metal substrate, and a top surface layer that has a surface roughness of less than or equal to about Ra 1 .mu.in., wherein at least one of the layers comprises a diamond-like carbon.

[0007] In another embodiment, a coated article is disclosed. The coated article includes a metal substrate comprising an outer surface and a multilayered coating covering at least a portion of the outer surface of the metal substrate. The coating includes an adhesion base layer that can adhere to a metal substrate, and a top surface layer that has a surface roughness of less than or equal to about Ra 0.0254 .mu.m, wherein at least one of the layers comprises a diamond-like carbon.

[0008] These and additional features provided by the embodiments discussed herein will be more fully understood in view of the following detailed description, in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The embodiments set forth in the drawings are illustrative and exemplary in nature and not intended to limit the inventions defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0010] FIG. 1 is a cross-sectional schematic illustration of a multilayered coating on a metal substrate according to one or more embodiments shown or described herein;

[0011] FIG. 2 is a cross-sectional schematic illustration of a multilayered coating on a metal substrate with intermediate layers according to one or more embodiments shown or described herein; and

[0012] FIG. 3 is a perspective view of a compressor blade with a multilayered coating according to one or more embodiments shown or described herein.

DETAILED DESCRIPTION OF THE INVENTION

[0013] One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the specific goals of developers, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0014] When introducing elements of various embodiments of the present invention, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0015] Referring to FIG. 1, a schematic representation of a cross section of a coated article 5 is illustrated comprising at least a metal substrate 20 and a multilayered coating 10.

[0016] The multilayered coating 10 is formulated with diamond-like carbon (also commonly referred to as "DLC") and additional elements such that it has sufficient adhesion to remain on the metal substrate 20, hydrophobicity and oleophobicity to help prevent corrosion, hardness to help protect against erosion and surface smoothness to not inhibit aerodynamic performance during operation. The multilayered coating 10 can generally comprise an adhesion base layer 12 that can adhere to a metal substrate 20 and a top surface layer 16 that has a surface roughness of less than or equal to about Ra 0.0254 .mu.m, wherein at least one of the layers comprises a diamond-like carbon. In some embodiments the multilayered coating 10 can further comprise one or more intermediate layers 14 between the adhesion base layer 12 and the top surface layer 16.

[0017] The adhesion base layer 12 of the multilayered coating 10 comprises a first layer of the multilayered coating 10 that adheres to the underlying metal substrate 20 once applied. The metal substrate 20 can comprise any type of metal and/or alloys such as, for example, iron based alloys (e.g., stainless steels), nickel based alloys, cobalt based alloys and the like.

[0018] In some embodiments, the adhesion base layer 12 may comprise DLC. DLC refers to the commercially available films of amorphous hydrocarbons that can be formed, for example, through vapor phase deposition and can provide high hardness and wear resistance with a smooth surface. In such embodiments, the DLC may be, for example, less than or equal to about 10 .mu.m thick, or from about 2 .mu.m to about 10 .mu.m thick, or even from about 5 .mu.m to about 10 .mu.m thick.

[0019] In other embodiments, the adhesion base layer 12 may comprise silicon. In such embodiments, the silicon may be, for example, less than about 0.5 .mu.m thick, or from about 0.3 .mu.m to about 0.4 .mu.m thick, or about 0.4 .mu.m thick.

[0020] The top surface layer 16 of the multilayered coating 10 comprises the outermost layer of the multilayered coating 10 and has a relatively smooth surface roughness. For example, the top surface layer 16 can have a surface roughness of less than or equal to about Ra 0.0254 .mu.m (Ra 1 .mu.in), or from about Ra 0.00254 .mu.m (Ra 0.1 .mu.in) to about Ra 0.0254 .mu.m (Ra 1 .mu.in), or from about Ra 0.00508 .mu.m (Ra 0.2 .mu.in) to about Ra 0.01016 .mu.m (Ra 0.4 .mu.in), or generally less than or equal to about Ra 0.0127 .mu.m (Ra 0.5 .mu.in). As used herein, "Ra" refers to the surface roughness parameter determined through the arithmetic average of absolute values as should be appreciated by those skilled in the art.

[0021] In other embodiments, the top surface layer 16 may comprise DLC. Such embodiments can increase the corrosion resistance and fouling resistance while still providing a smooth surface finish to the overall multilayered coating 10. For example, the top surface layer 16 may comprise DLC when the adhesion base layer 12 comprises silicon as discussed above, and/or when the multilayered coating 10 comprises one or more intermediate layers as will become appreciated herein. In such embodiments, the DLC may be, for example, from about 10 .mu.m to about 15 .mu.m thick, or be from about 11 .mu.m to about 13 .mu.m thick, or be about 10.5 .mu.m thick.

[0022] In other embodiments, the top surface layer 16 may comprise silicon carbide. Such embodiments can increase the erosion resistance of the overall multilayered coating 10. For example, the top surface layer 16 may comprise silicon carbide when the adhesion base layer 12 comprises DLC as discussed above. In such embodiments, the silicon carbide may be, for example, less than or equal to about 10 .mu.m thick, from about 2 .mu.m to about 10 .mu.m thick, or even from about 5 .mu.m to about 10 .mu.m thick.

[0023] Referring now to FIG. 2, in some embodiments, the multilayered coating 10 can comprise one or more intermediate layers 14 between the adhesion base layer 12 and the top surface layer 16. The one or more intermediate layers 14 can comprise one or more layers of the same type of material, or a plurality of layers of multiple types of material.

[0024] For example, in some embodiments, at least one of the one or more intermediate layers 14 may comprise silicon, germanium, titanium, chromium, nitrogen, fluorine, sulfur or combinations thereof

[0025] The use of silicon as an intermediate layer 14 can increase the adhesion between the overall multilayered coating 10. In such embodiments, the one or more intermediate layers 14 comprising silicon can be less than about 0.5 .mu.m thick, or from about 0.3 .mu.m thick to about 0.4 .mu.m thick, or be about 0.4 .mu.m thick. Intermediate layers 14 can be surrounded by layers of different compositions, the same composition or combinations thereof. For example, in some embodiments, the one or more intermediate layers 14 can comprise from 1 layer to about 5 layers of silicon, and may be disposed on top of the base adhesion layer 12, which itself can also comprise silicon.

[0026] The use of silicon and germanium can reduce internal stresses within the overall multilayered coating 10. In some embodiments, such as when an intermediate layer 14 of silicon and germanium is disposed on top of a single layer of silicon (e.g., when the adhesion base layer 12 comprises silicon), the one or more intermediate layers 14 comprising silicon and germanium can be less than about 0.5 .mu.m thick or be from about 0.2 .mu.m to about 0.3 .mu.m thick. In such embodiments, the multilayered coating 10 may comprise from 1 to about 3 intermediated layers 14 of silicon and germanium. In some embodiments, such as when an intermediate layer 14 of silicon and germanium is disposed on top of a plurality of layers of silicon, the one or more intermediate layers 14 comprising silicon and germanium can be from about 8 .mu.m to about 10 .mu.m thick. In such embodiments, the multilayered coating 10 may comprise from 1 to about 5 intermediate layers 14 of silicon and germanium.

[0027] In some embodiments, at least one of the one or more intermediate layers 14 may comprise DLC or doped DLC or other suitable variations of DLC. Doped DLC can comprise DLC doped with one or more additional elements such as, for example, silicon and/or germanium. In some embodiments, the DLC can be doped with fluorine to increase hydrophobicity. In some embodiments, the DLC can be doped with polydimethylsiloxane (PDMS) to increase oleophobicity.

[0028] For example, in some embodiments, at least one of the one or more intermediate layers 14 may comprise DLC doped with silicon and germanium. In such embodiments, the one or more intermediate layers 14 comprising DLC doped with silicon and germanium can be from about 8 .mu.m to about 10 .mu.m thick. The one or more intermediate layers 14 can comprise a single layer of DLC doped with silicon and germanium or a plurality of layers of DLC doped with silicon and germanium being disposed adjacent to one another, disposed with different intermediate layers 14 there between, or combinations thereof.

[0029] In some embodiments, at least one of the one or more intermediate layers 14 may comprise DLC doped with just silicon. In such embodiments, the one or more intermediate layers 14 comprising DLC doped with silicon can be from about 1 .mu.m to about 10 .mu.m thick, or be from about 5 .mu.m to about 7 .mu.m thick. The one or more intermediate layers 14 can comprise a single layer of DLC doped with silicon and germanium or a plurality of layers of DLC doped with silicon and germanium being disposed adjacent to one another, disposed with different intermediate layers 14 there between, or combinations thereof.

[0030] The adhesion base layer 12, the top surface layer 16 and the optional one or more intermediate layers 14 of the multilayered coating 10 can thereby be utilized in a variety of different combinations incorporating different elements and materials to tailor its properties (e.g., hardness, surface roughness, erosion/corrosion resistance, hydrophobicity, oleophobicity, etc.) for a specific application.

[0031] In one particular embodiment, the multilayered coating 10 can comprise an adhesion base layer 12 of DLC and a top surface layer 16 of silicon carbide. In such an embodiment, each layer can be from about 5 .mu.m to about 10 .mu.m thick. In another embodiment, the multilayered coating 10 can comprise a plurality of alternating layers of DLC and silicon carbide such that the adhesion base layer 12 is DLC, the intermediate layers 14 comprise both layers of silicon carbide and layers of DLC, and the top surface layer 16 comprises silicon carbide.

[0032] In another particular embodiment, the multilayered coating 10 can comprise an adhesion base layer 12 of silicon with a thickness of about 0.3 .mu.m to about 0.4 .mu.m. A first intermediate layer 14 can comprise silicon and germanium for a thickness of from about 0.2 .mu.m to about 0.3 .mu.m. A second intermediate layer 14 can comprise DLC doped with silicon and germanium for a thickness of from about 8 .mu.m to about 10 .mu.m. A third intermediate layer 14 can comprise the same or similar DLC doped with silicon and germanium for a thickness of from about 8 .mu.m to about 10 .mu.m, or have a thickness of from about 8 .mu.m to about 9 .mu.m. A fourth intermediate layer 14 can comprise DLC doped with silicon for a thickness of from about 5 .mu.m to about 7 .mu.m, or have a thickness of from about 5 .mu.m to about 7 .mu.m. Finally, the multilayered coating 10 can comprise top surface layer of DLC with a thickness of from about 10 .mu.m to about 12 .mu.m.

[0033] While specific embodiments of multilayered coatings 10 have been presented herein, it should be appreciated that these are non-limiting examples and other multilayered coatings 10 incorporating additional and/or alternative materials or have additional and/or alternative layering configurations may also be realized.

[0034] The overall multilayered coating 10 can thereby comprise a range of total thicknesses and a variety of total layers. For example the overall multilayered coating 10 can have a total thickness up to about 40 .mu.m, up to about 30 .mu.m, or from about 20 .mu.m to about 30 .mu.m as a result of relatively low internal stresses compared to a coating comprising a single DLC layer. Moreover, the multilayered coating 10 can have up to or over at least about 20 individual layers counting the adhesion base layer 12, the top surface layer 16, and a plurality of intermediate layers 14 there between. In some embodiments, the multilayered coating 10 can comprise any other number of plurality of layers. For example, in some embodiments, the multilayered coating 10 can comprise at least 10 layers, or at least 15 layers, or at least 20 layers, or even at least 25 layers. The number of layers in the multilayered coating may be selected based at least in part on the level of corrosion and erosion protection required. Each of the layers may be disposed in any suitable manner as should be appreciated to those skilled in the art. For example, the layers of the multilayered coating 10 can be deposited using various commercially available deposition techniques and within a temperature range of from about 120.degree. C. to about 200.degree. C.

[0035] As a result of the multiple layers incorporating the materials described herein, the multilayered coating 10 can be tailored to possess a variety of properties for protecting the underlying metal substrate 20 and providing a relatively smooth surface. For example, the multilayered coating 10 can have a hardness of from about 10 GPa to about 30 GPa to resist erosion from foreign objects.

[0036] The multilayered coating 10 can also be hydrophobic and oleophobic to help prevent the resident buildup of fluids such as water and oil. "Hydrophobic" refers to the physical property of a material that is water repellent. "Oleophobic" refers to the physical property of a material that is oil repellent. Specifically, surfaces with low surface energy for a foulant (e.g. water and/or oil) should have a high contact angle and should provide reduced adhesion with the foulant relative to a surface which is wet by the foulant or with which the foulant has low contact angle. As used herein, the term "contact angle" is the angle formed by a static liquid droplet on the surface of a solid material. The higher the contact angle, the less the interaction of the liquid with the surface. Thus, it is more difficult for the foulant to wet or adhere to the surface if the contact angle of the oil or other foulant with the surface is high. For example, the multilayered coating 10 can have a contact angle of at least about 80.degree., at least about 92.degree., or at least about 100.degree.. This can provide increased corrosion resistance to external foulants such as hydrogen sulfide, hydrofluoric acid and hydrochloric acid.

[0037] As discussed above, the metal substrate 20 of the coated article 5 can comprise any metal substrate 20 such as one utilized in a gas turbine. Metal substrates 20 can include, but not be limited to, iron based alloys (e.g., stainless steels), nickel based alloys, cobalt based alloys and the like. For example, referring now to FIG. 3, in some embodiments, the metal substrate can comprise a compressor blade 50. The compressor blade 50 can include an airfoil 52, which, when spun about the rotor, imparts kinetic energy to air flowing through the compressor, and a base or root 53. The airfoil 52 generally includes a suction-side 56 (i.e., convex-side) and a pressure-side 57 (i.e., concave-side).

[0038] The root 53 can include a platform 54, which is the outward radial face of the root 53 from which the airfoil 52 extends. The platform 54 may be integrally joined to the root 53 of the compressor blade 50. The platform 54 defines the radial inner boundary of the airflow across the airfoil 52. As one of ordinary skill in the art will appreciate, the root 53 further generally includes a dovetail 55 that connects via a complimentary groove in the rotor wheel (not illustrated) to secure the compressor blade 50 in the appropriate position within the compressor.

[0039] The substrate 10 (e.g., the compressor blade 50) can comprise the multilayered coating 10 covering at least a portion of the outer surface 25 (e.g., the suction-side 56 and/or the pressure-side 57) to form the coated article 5. The multilayered coating 10 of the coated article 5 can thus comprise an adhesion base layer that can adhere to a metal substrate, a top surface layer that has a surface roughness of less than or equal to about Ra 0.0254 .mu.m, wherein at least one of the layers comprises a diamond-like carbon as discussed above.

[0040] In some embodiments where the metal substrate 20 comprises the compressor blade 50, the compressor blade 50 may comprise a late stage compressor blade 50. As used herein, "late stage" refers to the last or one of the last few stages of the compressor section for the turbine. In such embodiments, the coating described herein can thereby provide a relatively thick coating for strong erosion and corrosion protection for the compressor blade 50 while still providing a smooth surface without significantly impacting its aerodynamics in operation.

[0041] It should now be appreciated that multilayered coatings may be provided to protect underlying substrates from a variety of external forces and environmental conditions. The multilayered coatings embodying the compositions presented herein can protect against corrosion and erosion from external objects while still providing a smooth surface. Moreover, the multilayered coatings can be provided in a relatively thick amount while still including one or more layers of DLC.

[0042] While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

1. A multilayered coating comprising: an adhesion base layer that can adhere to a metal substrate; and a top surface layer that has a surface roughness of less than or equal to about Ra 0.0254 .mu.m; wherein at least one of the layers comprises a diamond-like carbon.

2. The multilayered coating of claim 1 further comprising one or more intermediate layers between the adhesion base layer and the top surface layer.

3. The multilayered coating of claim 2, wherein at least one of the one or more intermediate layers is selected from the group consisting of silicon and germanium.

4. The multilayered coating of claim 3, wherein the at least one of the one or more intermediate layers comprising silicon or germanium is from about 0.1 .mu.m to about 0.5 .mu.m thick.

5. The multilayered coating of claim 2, wherein at least one of the one or more intermediate layers is doped diamond-like carbon.

6. The multilayered coating of claim 5, wherein the at least one of the one or more intermediate layers comprising doped diamond-like carbon is from about 5 .mu.m to about 10 .mu.m thick.

7. The multilayered coating of claim 2, wherein the adhesion base layer comprises silicon.

8. The multilayered coating of claim 2, wherein the top surface layer comprises diamond-like carbon.

9. The multilayered coating of claim 2, wherein the multilayered coating comprises at least 10 layers.

10. The multilayered coating of claim 1, wherein the adhesion base layer is selected from the group consisting of silicon and diamond-like carbon.

11. The multilayered coating of claim 1, wherein the top surface layer is selected from the group consisting of silicon carbide and diamond-like carbon.

12. The multilayered coating of claim 1, wherein the at least one of the layers that comprises a diamond-like carbon is from about 5 .mu.m to about 10 .mu.m thick.

13. The multilayered coating of claim 1, wherein the multilayered coating is at least about 20 .mu.m thick.

14. The multilayered coating of claim 1, wherein the multilayered coating has a hardness of at least about 10 GPa.

15. A coated article comprising: a metal substrate comprising an outer surface; and a multilayered coating covering at least a portion of the outer surface of the metal substrate, wherein the coating comprises: an adhesion base layer that can adhere to a metal substrate; a top surface layer that has a surface roughness of less than or equal to about Ra 0.0254 .mu.m; and wherein at least one of the layers comprises a diamond-like carbon.

16. The coated article of claim 15, wherein the metal substrate comprises a compressor blade for a turbine.

17. The coated article of claim 16, wherein the compressor blade is a late stage compressor blade.

18. The coated article of claim 15 further comprising one or more intermediate layers between the adhesion base layer and the top surface layer.

19. The coated article of claim 18, wherein at least one of the one or more intermediate layers is selected from the group consisting of silicon, germanium, titanium, chromium, nitrogen, fluorine, sulfur and doped diamond-like carbon.

20. The coated article of claim 15, wherein the at least one of the layers that comprises a diamond-like carbon is from about 5 .mu.m to about 10 .mu.m thick.