NICKEL-CHROMIUM-ALUMINUM COMPOSITE BY ELECTRODEPOSITION

Abstract

An cicctrodcposited nickel-chromium-aluminum (NiCrAl) composite including nickel- chromium alloy and aluminum, and alloys or compounds formed by Al, Cr and Ni applied on turbine components comprises from 2 to 50 wt % chromium, from 0.1 to 6 wt % aluminum, and a remaining balance of nickel, wherein the NiCrAl composite is heat-treated to form an aluminum compound and to restore materials lost during repair processes of the turbine components.

Claims

1. A coated article, comprising: a turbine component; and a NiCrAl composite coated on a surface of the turbine component, wherein the NiCrAl composite is heat-treated to form a diffused NiCrAl alloy that includes an aluminum compound formed between nickel and aluminum and to restore materials lost during repair of the turbine component, and wherein the diffused NiCrAl composite includes from 2 to 50 wt % chromium, from 0.1 to 6 wt % aluminum, and a remaining balance of nickel.

2. The coated article of claim 1, wherein the NiCrAl composite comprises from 8 to 20 wt % chromium, from 0.1 to 6 wt % aluminum, and a remaining weight percentage of nickel.

3. The coated article of claim 1, wherein the coated article further includes a bond coat.

4. The coated article of claim 1, wherein the NiCrAl alloy is thicker than 10 m.

5. The coated article of claim 1, wherein the NiCrAl alloy is thicker than 125 m.

6. The coated article of claim 1, wherein the turbine component is a vane, a rotor blade, or a stator.

7-20. (canceled)

21. The coated article of claim 1, wherein the NiCrAl composite is formed by electrodeposition and heat treatment.

22. The coated article of claim 1, wherein the turbine component is a repaired turbine component.

23. The coated article of claim 1, wherein the turbine component is a vane, rotor blade or stator.

24. The coated article of claim 1, wherein the turbine component comprises a single crystal nickel-based superalloy.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0012] FIG. 1 illustrates an example of a plating bath filled with an electrolytic solution for electrodepositing either a NiCr alloy or aluminum on a turbine component according to an aspect of the present disclosure.

[0013] FIG. 2 is a cross-sectional view of a NiCr alloy electrodeposited on a metal substrate in a choline chloride-mixed metal chlorides solution.

[0014] FIG. 3 is a flow chart of a NiCrAl composite layer deposition process of the present disclosure.

[0015] FIG. 4A is a schematic cross-sectional view of a diffused NiCrAl composite alloy coated on a turbine component.

[0016] FIG. 4B is a micrograph of a diffused Al coated Ni superalloy.

[0017] The drawings depict various preferred embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein.

DETAILED DESCRIPTION

[0018] FIG. 1 illustrates an example of a plating bath filled with an electrolytic solution for electrodepositing a NiCr alloy or aluminum on a turbine component according to an aspect of the present disclosure. A turbine component 104 which is to be plated with a NiCr alloy and aluminum respectively is pre-treated prior to electrodeposition. A pre-treatment is typically performed to remove grease, oil, oxides and debris from the turbine component by mechanical abrasion, acid or alkaline etching, and/or electro-etching followed by surface activation, but is not specifically limited to the above processing steps and specified sequence.

[0019] Referring now to FIG. 1, there is provided a plating bath 102 containing an electrolytic solution that includes a room temperature ionic liquid including choline chloride, nickel chloride, chromium chloride, solvents, and surfactants like anionic, cationic, or Zwitterionic (amphoteric) surfactants. One of the surfactants includes one of more species of a sodium dodecyl sulfate, fluorosurfactants, cetyl trimethylammonium bromide (CTAB), or cetyl trimethyammonium chloride (CTAC). It is noted that the choline chloride based processing is low-cost and environmentally friendly. In one embodiment, a molar ratio of the choline chloride and chromium chloride ranges from 0.5 to 3.5, and polar aprotic and polar protic solvents are used to adjust the viscosity and conductivity of the plating bath 102 to attain a high quality NiCr alloy coating.

[0020] Specifically, protic solvents are preferred due to their ability to donate hydrogen bonds. The solvents further include formic acid, citric acid, Isopropanol (IPA), water, acetic acid, and ethylene glycol. In the embodiment, preferred solvent content is from 10 to 80 vol % relative to the mixture of choline chloride and metal chlorides including nickel and chromium chlorides.

[0021] Referring to FIG. 1, an external supply of current is provided to an anode 106 and a cathode which is a turbine component 104 to be plated with Ni and Cr. The current can be a direct current or an alternating current including a pulse or pulse reverse current (not shown). The amount of current supplied can be controlled during the electrodeposition to achieve a desired coating composition, density, and morphology.

[0022] When the current is supplied, the metal (Ni and/or Cr) at the anode is oxidized from the zero valence state to form cations with a positive charge. These cations, generally forming complexes with the anions in the solution, are reduced at the cathode to produce metallic deposit. The result is the reduction of Ni and Cr species from the electrolytic solution onto the turbine component to be restored. The turbine component 104 is a cathode during electrodeposition. The electrodeposition inevitably decomposes water in the bath 102, and thus the solution in the bath can be replenished to maintain consistent deposition quality.

[0023] The anode 106 includes a NiCr alloy anode, a Ni and/or Cr anode, or any combination of these materials that can be chosen to satisfy different requirements. An insoluble catalytic anode (catalyzing oxygen evolution electrode) is preferred, but the type of anode used is not specifically limited to the above anode. A second layer of aluminum is deposited from a different plating bath, where the anode is pure aluminum. Aluminum electrodeposition is conducted in a water free environment and has been known to approach 100% efficiency because both hydrogen evolution and oxygen evolution are avoided.

[0024] In one embodiment, the NiCr alloy includes from 2 to 50 wt % chromium and a remaining weight percentage of nickel. In a preferred embodiment, the NiCr alloy comprises from 8 to 20 wt % chromium, and a remaining weight percentage of nickel. The electrodeposited NiCr alloy is thicker than at least 10 m. In a preferred embodiment, the electrodeposited NiCr alloy is thicker than 125 m. The top aluminum layer can vary in thickness, ranging from 2 m to more than 125 m.

[0025] FIG. 2 is a cross-sectional view of the NiCr alloy 202 formed on a metal substrate 200 in a choline chloride-mixed metal chlorides solution. Referring to FIG. 2, a NiCr coating thicker than about 70 um is formed on the substrate 200. The NiCr coating 202 and aluminum deposit may be applied directly to a surface of a turbine component which is formed from a wide range of metallic materials including, but not limited to, a single crystal nickel-based superalloy, and the copper substrate 200 represents a turbine component. The NiCr aluminum composite 202 coated on a turbine component is subject to a post heat-treatment to homogenize the composition and add wall thickness back to the turbine component and replenish chromium and aluminum lost during the repair of the component.

[0026] FIG. 3 is a process flow chart of applying a NiCr aluminum composite layer described in the present disclosure. Typically, a turbine component to be coated with a NiCrAl composite layer is pre-treated prior to the electrodeposition to remove foreign materials like debris, oxides and grease/oil from its surface. A method for electrodepositing a nickel-chromium-aluminum (NiCrAl) alloy on a turbine component begins at step 300 where a first plating bath filled with a solution is provided. The solution includes a solvent, a surfactant, and an ionic liquid including choline chloride, nickel chloride, and chromium chloride, wherein a molar ratio of the choline chloride and chromium chloride ranges from 0.5 to 3.5, and the solvent comprises from 5 to 80 vol. % relative to a mixture of the choline chloride and metal chlorides including the nickel and chromium chlorides, as disclosed above with reference to FIG. 1.

[0027] At step 302, electrodepositing a NiCr alloy on the turbine component is performed. An external supply of current is provided to a cathode and an anode in the first plating bath. The turbine component is the cathode, and a metal source is the anode. The component coated with NiCr alloy is then rinsed and dried and prior to aluminum deposition. Additional surface preparation required for aluminum deposition is also performed. At step 304, a second plating bath filled with an ionic liquid including Lewis acidic 1-ethyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium chloride and an aluminum salt is provided for aluminum deposition on the NiCr alloy coated component. At step 306, electrodepositing aluminum (Al) onto the NiCr alloy is performed in the second plating bath to form a NiCrAl composite on the turbine component. Once the NiCrAl composite is formed on the turbine component, at step 308, a post heat-treatment of the NiCrAl alloy at 1100 C. or at a higher temperature is applied to the coated article to homogenize the composition, to form alloys and intermetallic compounds, and to restore key materials lost during previous repair processes or service of the turbine component, as shown in FIGS. 4A and 4B.

[0028] FIG. 4A is a cross-sectional view of a diffused NiCrAl alloy coated on a turbine component. The coated article 400 comprises a turbine component 402 which is typically made of Ni-based superalloy, a NiCr alloy 404, a NiCrAl zone 406, an Al coating 408, and a bond coat 410 which is typically re-applied after the dimensional restoration of the turbine component.

[0029] The coated article 400 is subject to a post heat-treatment at a high temperature as described above to form a diffused NiCrAl alloy 404/406/408. Referring to FIG. 4, aluminum (Al) diffuses from Al coating 408 to NiCr alloy 404 to form a NiCrAl zone 406, chromium (Cr) diffuses from the NiCr alloy 404 to the Al coating 408, and Ni and/or Cr from the NiCr alloy 404 diffuses into bond coat 410 and turbine component 402, respectively, to homogenize the composition, to form an aluminum compound between nickel and aluminum, and to restore materials lost during previous repair processes of the turbine component. FIG. 4B is a micrograph of an Al deposit 420 on a Ni superalloy 422 before heat-treatment, and a diffused Al coated Ni superalloy 424 after heat-treatment at a high temperature.

[0030] In one embodiment, the NiCrAl composite includes from 2 to 50 wt % chromium, from 0.1 to 6 wt % aluminum, and a remaining weight percentage of nickel. In the embodiment, the electrodeposited NiCrAl alloy is thicker than 10 m. In a preferred embodiment, the NiCrAl alloy includes from 8 to 20 wt % chromium, from 0.1 to 6 wt % aluminum, and a remaining balance of nickel. In the preferred embodiment, the electrodeposited NiCrAl composite is thicker than 125 m. The coated article includes turbine vanes, rotor blades, or stators.

[0031] It is to be understood that the disclosure of the present invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible to modification of form, size, arrangement of parts, and details of operation. The disclosure of the present invention rather is intended to encompass all such modifications which are within its spirit and scope of the invention as defined by the following claims.