Hot corrosion-protected articles and manufacture methods

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.

Claims

1. A coated article comprising: a nickel-based superalloy substrate; and a coating system atop the substrate and comprising: a nickel-based first layer, by weight at least 80% nickel; and a chromium-based metallic second layer, by weight at least 80% chromium, directly atop the first layer and having an exposed surface and being thicker than the first layer.

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

3. The coated article of claim 1 wherein: the coating system lacks a ceramic layer.

4. A method for manufacturing the coated article of claim 1, the method comprising: plating the first layer; and plating the second layer.

5. The method of claim 4 wherein: the first layer plating is electroplating.

6. The method of claim 4 wherein: the second layer plating is electroplating.

7. The method of claim 4 further comprising: forming the substrate by forging of a powder metallurgical material.

8. The method of claim 4 wherein: the coating system consists of said first layer and said second layer.

9. 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.

10. A method for manufacturing a coated article, the article comprising: a nickel-base superalloy substrate; and a coating system atop the substrate and comprising: a nickel-based first layer; and a chromium-based second layer atop the first layer, the method comprising: plating nickel as by weight at least 80% nickel; plating chromium as by weight at least 80% chromium directly to the plated nickel; and with a surface of the chromium exposed, heating.

11. The method of claim 10 further comprising: forming the substrate by forging of a powder metallurgical material.

12. The method of claim 10 wherein: the first layer plating is electroplating.

13. The method of claim 10 wherein: the second layer plating is electroplating.

14. The method of claim 10 wherein: the first layer has a characteristic thickness of 13 micrometers to 51 micrometers; and the second layer is thicker than the first layer and is directly atop the first layer.

15. A coated article comprising: a nickel-based superalloy substrate; and a coating system atop the substrate and comprising: a nickel-based first layer, by weight at least 80% nickel; and a chromium-based metallic second layer, by weight at least 80% chromium, directly atop the first layer, the first layer having a thickness of 15% to 33% of a thickness of the second layer.

16. A method for using the coated article of claim 15, the method comprising: installing the article in a gas turbine engine; and with the second layer having an exposed surface, running the gas turbine engine to heat the article.

17. A coated article comprising: a nickel-based superalloy substrate; and a coating system atop the substrate and comprising: a nickel-based first layer of at least 80% nickel by weight and having a characteristic thickness T1 of 6 micrometers to 50 micrometers; and a chromium-based metallic second layer of at least 80% chromium by weight atop the first layer and having an exposed surface and being thicker than the first layer.

18. The coated article of claim 17 being a turbine engine disk.

19. A method for manufacturing a coated article, the article comprising: a nickel-base superalloy substrate; and a coating system atop the substrate and comprising: a nickel-based first layer having a characteristic thickness T1 of 6 micrometers to 50 micrometers; and a chromium-based second layer atop the first layer, the second layer having an exposed surface and being thicker than the first layer, the method comprising: plating nickel as by weight at least 80% nickel; plating chromium as by weight at least 80% chromium; and with a surface of the chromium exposed, heating.

20. The method of claim 19 wherein: the coated article is a turbine engine disk.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an exploded partial view of a gas turbine engine turbine disk assembly.

(2) FIG. 2 is a schematic sectional view of a surface region of the disk showing a substrate and coating.

(3) FIG. 3 is a photomicrograph of a section of the substrate and coating.

(4) FIG. 4 is a photomicrograph of a section of a substrate and a prior art MCrAlY overlay coating.

(5) Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

(6) 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).

(7) 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.

(8) 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 T.sub.1 and T.sub.2. An exemplary surface 112 of the second layer is exposed and, thus, it does not bear any further coating layer (namely, a ceramic TBC).

(9) Exemplary T.sub.1 is 6.0 micrometers to 50 micrometers, more narrowly 6.0 micrometers to 25 micrometers or 6.0 micrometers to 15.0 micrometers. Exemplary T.sub.2 is 6.0 micrometers to 50 micrometers, more narrowly 6.0 micrometers to 25 micrometers or 10.0 micrometers to 20.0 micrometers.

(10) 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.

(11) 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 T.sub.1.

(12) 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 T.sub.2. 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.

(13) 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 Cr.sub.2O.sub.3 scale during exposure which may add to robustness and protection.

(14) 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.

(15) 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.

(16) 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.

(17) 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.