EP3090075A1 - Hot corrosion-protected articles and manufacture methods - Google Patents

Abstract

A coated article (22) comprises a substrate (100) and a coating system (102) atop the substrate. The coating system has a nickel-based first layer (104) and a chromium-based second layer (108) atop the first layer.

Description

HOT CORROSION-PROTECTED ARTICLES AND MANUFACTURE METHODS

CROSS REFERENCE TO RELATED APPLICATION

[0001] Benefit is claimed of US Patent Application No.

61/920,546, filed December 24, 2013, and entitled "Hot

Corrosion-Protected Articles and Manufacture Methods", the disclosure of which is incorporated by reference herein in its entirety as if set forth at length. BACKGROUND

[0002] The disclosure relates to gas turbines. More

particularly, the disclosure relates to protective coatings for hot section components. [0003] An exemplary gas turbine is discussed in the context of a gas turbine engine used for aircraft propulsion. Such an engine has a core gaspath passing sequentially through one or more compressor sections for compressing ingested air, a combustor section for combusting the compressed air and an introduced fuel to generate high pressure/temperature

combustion gases, and one or more turbine sections for

extracting work from the combustion gases to drive the

compressor sections. With an exemplary turbofan engine, the turbine sections also drive a fan which, in turn drives air along a flowpath bypassing the core flowpath. Exemplary turbine sections are axial turbines wherein flow passes through one or more stages of rotating blades interspersed with stationary vanes or counter-rotating blades. The blades of a given stage may be unitarily formed with or mounted to the periphery of a disk. The disks of each section may be mounted to co-rotate with each other and any compressor section driven thereby. Exemplary compressor sections are also axial, although centrifugal compressors and turbines are also known . [0004] Engine components (e.g., combustor panels, vanes, blades, disks, air seals, and the like) exposed to the

combustion gases and heat are particularly subject to

corrosion and erosion. Additionally, due to temperature increase with sequential stages of compression, the higher pressure portions of the compressor sections may be subject to significant operational heating. [0005] A variety of substrate materials and protective coatings have been developed for these components. Exemplary substrate materials include a number of cast or

powdermetallurgical (PM) forged nickel-based superalloys and/or cobalt-based superalloys. The centrifugal loading to which disks are exposed makes disks a particular area of concern for substrate materials.

[0006] US Patent 6,521,175 of Mourer, et al . , issued February 18, 2003, and entitled "Superalloy optimized for

high-temperature performance in high-pressure turbine disks" discloses an advanced nickel-base superalloy for powder metallurgical (PM) manufacture of turbine disks. More recent alloys have been proposed in US Patent 8,147,749, of Reynolds, issued April 3, 2012, and entitled "Superalloy compositions, articles, and methods of manufacture" and US Patent

Application Publications 2013/0209265A1 and 2013/0209266A1, both of Reynolds, et al . , published August 15, 2013 and entitled "Superalloy Compositions, Articles, and Methods of Manufacture" .

[0007] Thermal barrier coating (TBC) systems have been developed for hot section components. Typical susch systems have one or more insulative ceramic layers (e.g.,

zirconia-based such as yttria-stabilzed zirconia (YSZ) and/or gadolinia-stabilized zirconia (GSZ) ) . Such coatings may be used in combination with metallic bondcoats.

[0008] On disks and certain areas of certain other components, it may be impractical or unnecessary to apply a ceramic TBC . For example, at disk rims and portions inboard thereof

temperatures may be sufficiently lower than directly in the gaspath (e.g., to which airfoils are exposed) that the

insulative benefit of ceramic TBC may be traded for improved hot corrosion protection of a metallic coating system.

[0009] As gas turbine operating temperatures new engine designs continue to increase relative to their predecessors, high pressure compressor disks and high pressure turbine disks are entering into a temperature regime where deposit-induced hot corrosion (even in the absence of direct exposure to combustion gas) presents a substantial durability risk. While these components (or at least some relevant portions thereof) are not exposed to combustion gas (e.g., are not directly along the core gaspath and may be partially isolated therefrom by seals and the like) , deposits can develop as a result of ingestion of particulate matter from the atmosphere. In addition, substantial concentrations of SO₂ gas, which is known to exacerbate hot corrosion attack, can be present in the atmosphere in certain regions of the world. Hot corrosion is most severe in geographic regions which have elevated levels of airborne particulate matter and gaseous pollution, man-made or otherwise. [0010] There are also substantial problems when aircraft operate in coastal regions, because ingested sea salt can also result in severe hot corrosion attack. The polycrystalline Ni-base superalloys of typical turbine and compressor disks do not have sufficient hot corrosion resistance. Thus there is an increasing need for disks (and certain legacy components) to have hot corrosion-resistant coatings in order to meet life requirements. In addition to providing hot corrosion

resistance, these coatings are advantageously designed such that debits to low cycle fatigue are minimal. This can be accomplished by developing coatings that are either ductile or only loosely adherent to the superalloy substrate.

[0011] US Patent 4,346,137, of Hecht, issued August 24, 1982, and entitled "High temperature fatigue oxidation resistant coating on superalloy substrate" discloses an MCrAlY TBC bondcoat which may be used as underplatform blade coating without . [0012] US Patent Application Publication 2010/0009092 Al, of Tryon et al . , published January 14, 2010 and entitled

"Economic Oxidation and Fatigue Resistant Metallic Coating" discloses another MCrAlY TBC bondcoat. [0013] US Patent 8,124,246, of Tolpygo, issued February 28, 2012, and entitled "Coated Components and Methods of

Fabricating Coated Components and Coated Turbine Disks" discloses use of sequential diffusion coating of chromium and noble metal on such a superalloy disk.

SUMMARY

[0014] One aspect of the disclosure involves a coated article comprising a substrate and a coating system atop the

substrate. The coating system has a nickel-based first layer and a chromium-based second layer atop the first layer.

[0015] A further embodiment may additionally and/or

alternatively include the substrate being a nickel-based superalloy . [0016] A further embodiment may additionally and/or alternatively include the first layer being essentially pure nickel and the second layer is essentially pure chromium.

[0017] A further embodiment may additionally and/or

alternatively include the substrate being a powder

metallurgical substrate. [0018] A further embodiment may additionally and/or

alternatively include the coated article being a turbine engine disk.

[0019] A further embodiment may additionally and/or

alternatively include the first layer having a characteristic thickness ΤΊ of 13 micrometers to 51 micrometers and the second layer having a characteristic thickness 2 of 13 micrometers to 51 micrometers. [0020] A further embodiment may additionally and/or

alternatively include the coating system consisting of said first layer and said second layer.

[0021] A further embodiment may additionally and/or

alternatively include the coating system lacking a ceramic layer .

[0022] A further embodiment may additionally and/or

alternatively include a method for manufacturing the coated article. The method comprises: plating the first layer; and plating the second layer. [0023] A further embodiment may additionally and/or alternatively include the first layer plating being

electroplating. [0024] A further embodiment may additionally and/or

alternatively include the second layer plating being

electroplating.

[0025] A further embodiment may additionally and/or

alternatively include forming the substrate by forging of a powder metallurgical material.

[0026] A further embodiment may additionally and/or

alternatively include a method for using the coated article. The method comprises: installing the article in a gas turbine engine; and running the gas turbine engine to heat the

article .

[0027] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 is an exploded partial view of a gas turbine engine turbine disk assembly.

[0029] FIG. 2 is a schematic sectional view of a surface region of the disk showing a substrate and coating.

[0030] FIG. 3 is a photomicrograph of a section of the

substrate and coating.

[0031] FIG. 4 is a photomicrograph of a section of a substrate and a prior art MCrAlY overlay coating. [0032] Like reference numbers a designations in the various drawings indicate like elements

DETAILED DESCRIPTION

[0033] FIG. 1 shows a gas turbine engine disk assembly 20 including a disk 22 and a plurality of blades 24. The disk is generally annular, extending from an inboard bore or hub 26 at a central aperture to an outboard rim 28. A relatively thin web 30 is radially between the bore 26 and rim 28. The

periphery of the rim 28 has a circumferential array of

engagement features 32 (e.g., dovetail slots) for engaging complementary features 34 of the blades 24. In other

embodiments, the disk and blades may be a unitary structure (e.g., so-called "integrally bladed" rotors or disks).

[0034] The disk 22 may be formed by a powder metallurgical forging process (e.g., as is disclosed in U.S. Pat. No.

6,521,175) . In an exemplary process, the elemental components of the alloy are mixed (e.g., as individual components of refined purity or alloys thereof) . The mixture is melted sufficiently to eliminate component segregation. The melted mixture is atomized to form droplets of molten metal. The atomized droplets are cooled to solidify into powder

particles. The powder may be screened to restrict the ranges of powder particle sizes allowed. The powder is put into a container. The container of powder is consolidated in a multi-step process involving compression and heating. The resulting consolidated powder then has essentially the full density of the alloy without the chemical segregation typical of larger castings. A blank of the consolidated powder may be forged at appropriate temperatures and deformation constraints to provide a forging with the basic disk profile. The forging is then heat treated in a multi-step process involving high temperature heating followed by a rapid cooling process or quench. The quench for the heat treatment may also form strengthening precipitates (e.g., gamma prime and eta phases) of a desired distribution of sizes and desired volume percentages. Subsequent heat treatments are used to modify these distributions to produce the requisite mechanical properties of the manufactured forging. The increased grain size is associated with good high-temperature creep-resistance and decreased rate of crack growth during the service of the manufactured forging. The heat treated forging is then subject to machining of the final profile and the slots.

[0035] FIG. 2 schematically shows a section of the disk (e.g., along a rim portion such as an outer diameter (OD) surface or a front surface or a rear surface) . The disk has a forged PM substrate 100 as discussed above. A coating system 102 lies atop the substrate and has an overall thickness T. The

exemplary coating system comprises a lower or inner/inboard first layer 104 (e.g., atop a surface 106 of the substrate) and an upper or outer/outboard second layer 108 (e.g., atop a surface 110 of the first layer) . The respective first and second layers have thicknesses ΤΊ and T₂. An exemplary surface 112 of the second layer is exposed and, thus, it does not bear any further coating layer (namely, a ceramic TBC) .

[0036] Exemplary Ti is 6.0 micrometers to 50 micrometers, more narrowly 6.0 micrometers to 25 micrometers or 6.0 micrometers to 15.0 micrometers) . Exemplary T₂ is 6.0 micrometers to 50 micrometers, more narrowly 6.0 micrometers to 25 micrometers or 10.0 micrometers to 20.0 micrometers) .

[0037] In operation, the second layer provides corrosion resistance. The second layer material is chromium-based (e.g., with chromium as a largest by-weight content, more

particularly at least 50% chromium by weight, more

particularly at least 80% and may consist essentially of chromium (e.g., offering equivalent performance to pure chromium and likely at least 95% chromium) . With a second layer material that is relatively brittle, the first layer provides a relatively ductile interface with the substrate to prevent cracks in the second layer from propagating into the substrate. The first layer material is nickel-based (e.g., nickel as a largest by-weight component, more particularly at least 50% nickel by weight, more particularly at least 80% and may consist essentially of nickel (e.g., offering equivalent performance to pure nickel and likely at least 95% nickel) . As applied, one or both layers may be pure or relatively pure chromium and nickel, respectively but may be subject to some diffusion with each other or the substrate.

[0038] An exemplary process for depositing the first layer is plating (e.g., electroless or electroplating). This may be applied directly to the machined substrate to build to the thickness ΤΊ.

[0039] An exemplary process for depositing the second layer is plating. Exemplary plating is electroplating. This may be applied directly to the first layer (e.g., after any washing) to build to the thickness T₂. Exemplary electroplating is disclosed in US Patent Application Publication 2013/0220819 entitled "Electrodeposition of Chromium from Trivalent

Chromium Using Modulated Electric Fields", the disclosure of which is incorporated by reference in its entirety herein as if set forth at length. Such use of a trivalent chromium bath avoids toxicity concerns of hexavalent chromium.

[0040] FIG. 3 is a micrograph of an exemplary such two layer coating system 102. The lower layer 104 is directly atop the substrate and is thinner than the upper layer 104 (e.g. about 15% to 33% of the upper layer thickness) . For comparison, FIG. 4 shows a baseline MCrAlY. Several things appear. First, it is seen that cracks 120 in the upper layer 108 normal to the surface (outer surfaces 106, 110, and 112 of the substrate and respective layers) have not propagated into the lower layer 104. The lower layer ductility, is believed to help avoid such crack propagation. In operation, these cracks 120 may

effectively seal up with a protective Cr₂0₃ scale during exposure which may add to robustness and protection.

[0041] Second, a dark boundary 122 is seen between the two layers. This is a very thin gap that appears to have been created during the sectioning/mounting process for generating the micrograph. Also, it is seen that, compared to the MCrAlY, there is a lower degree of apparent interdiffusion with the substrate. Finally, it is seen that, compared to the MCrAlY, there is a lower degree of apparent surface roughness of the exposed coating surface.

[0042] The use of "first", "second", and the like in the following claims is for differentiation within the claim only and does not necessarily indicate relative or absolute

importance or temporal order. Similarly, the identification in a claim of one element as "first" (or the like) does not preclude such "first" element from identifying an element that is referred to as "second" (or the like) in another claim or in the description.

[0043] Where a measure is given in English units followed by a parenthetical containing SI or other units, the

parenthetical ' s units are a conversion and should not imply a degree of precision not found in the English units.

[0044] One or more embodiments have been described.

Nevertheless, it will be understood that various modifications may be made. For example, when applied to an existing baseline configuration, details of such baseline may influence details of particular implementations. Accordingly, other embodiments are within the scope of the following claims.

Claims

CLAIMS What is claimed is:

1. A coated article (22) comprising:

a substrate (100); and

a coating system (102) atop the substrate and comprising: a nickel-based first layer (104); and

a chromium-based second layer (108) atop the first layer .

2. The coated article of claim 1 wherein:

the substrate is a nickel-based superalloy.

3. The coated article of claim 1 wherein:

the first layer is essentially pure nickel; and

the second layer is essentially pure chromium.

4. The coated article of claim 1 wherein:

the substrate is a powder metallurgical substrate.

5. The coated article of claim 1 being a turbine engine disk .

6. The coated article of claim 1 wherein:

the first layer has a characteristic thickness ΤΊ of 13 micrometers to 51 micrometers; and

the second layer has a characteristic thickness T₂ of 13 micrometers to 51 micrometers.

7. The coated article of claim 1 wherein:

the coating system consists of said first layer and said second layer.

8. The coated article of claim 1 wherein:

the coating system lacks a ceramic layer.

9. A method for manufacturing the coated article of claim 1, the method comprising:

plating the first layer; and

plating the second layer.

10. The method of claim 9 wherein:

the first layer plating is electroplating.

11. The method of claim 9 wherein:

the second layer plating is electroplating.

12. The method of claim 9 further comprising:

forming the substrate by forging of a powder metallurgical material .

13. The method of claim 9 wherein:

the first layer has a characteristic thickness of 13

micrometers to 51 micrometers; and

the second layer has a characteristic thickness of 13

micrometers to 51 micrometers.

14. The method of claim 9 wherein:

the coating system consists of said first layer and said second layer.

15. A method for using the coated article of claim 1, the method comprising:

installing the article in a gas turbine engine; and

running the gas turbine engine to heat the article.