Electrodeposited nickel-chromium alloy

Abstract

A nickel-chromium (NiCr) alloy and a method for electrodepositing the NiCr alloy on a turbine engine component for dimensionally restoring the engine component are described. The engine component is restored by re-building wall thickness with the NiCr alloy including from 2 to 50 wt % chromium balanced with nickel. The turbine component coated with the NiCr alloy is heat-treated at a high temperature to homogenize composition of the alloy to mimic the base alloy and to restore materials lost during repair of the turbine component.

Claims

1. A method for electrodepositing a nickel-chromium (NiCr) alloy plated on a turbine component, the method comprising: pre-treating the turbine component; providing a plating bath containing a solvent, a surfactant, and an ionic liquid including choline chloride, nickel chloride, and chromium chloride, wherein a molar ratio of the choline chloride, combined chromium chloride, and nickel chloride ranges from 0.5 to 3.5, and the solvent comprises from 5 to 80 vol. % relative to a volume of a mixture of the choline chloride and metal chlorides including both nickel chloride and chromium chloride; electrodepositing the NiCr alloy onto a metallic substrate by providing an external supply of current to an anode and a cathode; and heat-treating the turbine component coated with NiCr alloy to re-build wall thickness and restore materials lost during repair of the turbine component.

2. The method according to claim 1, wherein the anode is an insoluble anode.

3. The method according to claim 1, wherein the anode is a NiCr alloy anode.

4. The method according to claim 1, wherein the anode includes is a Ni anode and a Cr anode.

5. The method according to claim 1, wherein the current is a direct current.

6. The method according to claim 1, wherein the current is an alternating current.

7. The method according to claim 1, wherein the solvent is a polar protic solvent.

8. The method according to claim 1, wherein the solvent is a polar aprotic solvent.

9. The method according to claim 1, wherein the solvent is chosen from one or more of formic acid, citric acid, isopropanol (IPA), water, acetic acid, glycine (amino-acetic acid), and ethylene glycol.

10. The method according to claim 1, wherein the surfactant is an anionic, a cationic, or an amphoteric surfactant.

11. The method according to claim 1, wherein the surfactant is sodium dodecyl sulfate; fluorosurfactants, cetyl trimethylammonium bromide (CTAB), or cetyl trimethylammonium chloride (CTAC).

12. The method according to claim 1, wherein the NiCr alloy compromises from 8 to 20 wt % chromium balanced by nickel.

13. The method according to claim 1, wherein the NiCr alloy is thicker than 2 mils (0.05 mm).

14. The method according to claim 1, wherein the NiCr alloy is thicker than 5 mils (0.125 mm).

15. The method according to claim 1, wherein the turbine component is a rotor blade, a stator, or a vane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a plating bath filled with an electrolytic solution for electrodepositing a NiCr alloy on turbine engine parts with a combined soluble and insoluble anode according to an aspect of the present disclosure.

(2) FIG. 2A illustrates a cross-sectional view of an article as coated with NiCr alloy formed by electrodeposition.

(3) FIG. 2B illustrates a cross-sectional view of an article of FIG. 2A after high temperature heat treatment to homogenize the composition.

(4) FIG. 3 is a flow chart of the process for electrodepositing a NiCr alloy for dimensional restoration of an engine component.

(5) 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

(6) Typically, electroplating is a process that uses electrical current to reduce dissolved metal ions, most likely metal ion complexes so that they form a coherent metal coating on an electrode that is, for example, a turbine engine component to be repaired. The process used in electroplating is called electrodeposition. The part to be plated with NiCr alloy is a cathode, and an anode is made of such metal as Ni, Cr, NiCr alloy, or any combination of these materials to be plated on the part, according to an embodiment. In another embodiment, an insoluble catalytic anode (e.g., iridium oxide, tantalum oxide, ruthenium oxide, or the like) can be used. Yet in another embodiment, an insoluble catalytic anode is used in conjunction with a soluble anode, and the soluble anode can be optionally used to adjust the bath composition as desired.

(7) FIG. 1 illustrates an electroplating bath filled with an electrolytic solution for electrodepositing a NiCr alloy suitable to be plated on a turbine engine part to be repaired according to an aspect of the present disclosure. The part to be plated is pre-treated prior to electrodeposition. The pre-treatment includes removing the existing coating, mechanically cleaning the surface, degreasing, acid or alkaline etching including electro-etching and final activation before the part is placed in the plating bath for deposit application. The electrodeposition inevitably decomposes water in the bath 102, and thus the solution in the bath needs to be replenished to maintain consistent deposition quality.

(8) Referring now to FIG. 1, there is provided a plating bath 102 containing an electrolytic solution that consists of a room temperature ionic liquid, namely deep eutectic solvent, including choline chloride, nickel chloride, chromium chloride, solvents, and surfactants including anionic, cationic, or Zwitterionic (amphoteric) surfactants. An example of the surfactant is a sodium dodecyl surfate, fluorosurfactants, cetyl trimethylammonium bromide (CTAB), or cetyl trimethylammonium chloride (CTAC). It is noted that the choline chloride based metal 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.

(9) In one embodiment, 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. Specifically, protic solvents are preferred due to their hydrogen bond donating ability. The solvents include formic acid, citric acid, Isopropanol (IPA), water, acetic acid, glycine (aminoacetic acide) and ethylene glycol.

(10) In the embodiment, preferred solvent content is from 10 to 80 vol % relative to the mixture of choline chloride and metal chlorides including the nickel and chromium chlorides on a pre-mixing basis. Referring to FIG. 1, electroplating of the NiCr alloy begins by providing an external supply of current to an anode and a cathode that is the part to be repaired. An external supply of the current can be a direct current or an alternating current including a pulse or pulse reverse current (not shown). The regime and magnitude of the current can be controlled during the deposition to achieve desired coating composition, density, and morphology.

(11) The turbine part 104 to be plated is a cathode during electrodeposition. The anode 106 is, for example, 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 to suppress or eliminate other undesirable anodic reactions such as chlorine evolution, hexavalent chromium formation) is preferable, but the anode used is not specifically limited. A combination of soluble Ni anode and an insoluble catalytic anode can be used to control bath composition during the course of plating as well.

(12) FIG. 2A illustrates an article 200 as-coated by an electrodeposited NiCr alloy 206. Referring to FIG. 2A, a part 202 includes a turbine component that has at least one surface 204. A NiCr alloy deposit 206 on the surface 204 of the turbine part 202 adds wall thickness and the chromium lost during repair of the part. The coated NiCr alloy is compatible with the material forming the turbine part 202. The coating 206 may be applied directly to the surface 204 of the turbine part 202 which is formed from a wide range of metallic materials including, but not limited to, a single crystal nickel-based superalloy.

(13) The NiCr alloy coating 206 is subsequently heat-treated at high temperature (over 1000 C.) to allow inter-diffusion of elements, resulting in homogenized composition in the restored wall. FIG. 2B illustrates a cross-sectional view of an article of FIG. 2A after high temperature heat treatment with a schematic inter-diffusion zone 208. Referring to FIG. 2B, an interdiffusion zone 208 is formed along the interface region between the turbine part 202 and the NiCr alloy coating 206 as result of the high temperature heat-treatment.

(14) FIG. 3 is a flow chart of an electrodeposited NiCr coating process of the present disclosure. Forming a NiCr deposit of substantial thickness, for example, over 1 mil (0.025 mm), by electrodepositing a NiCr alloy on a turbine part begins at step 300 where the coating and damaged surface of the turbine part is first removed and cleaned down to the base alloy. Then, a mechanical and chemical cleaning of the part is carried out and the cleaned surface is then activated at step 301 prior to being placed into the plating bath for electrodeposition. At step 304, the NiCr alloy is electrodeposited on a metallic substrate of the turbine part by providing an external supply of current to an anode and the cathode. The electrodeposited NiCr alloy is then heat-treated at step 306 to restore materials lost during repair of the turbine component and homogenize the composition.

(15) In an embodiment, the electrodeposited NiCr alloy formed by the method disclosed above comprises from 2 to 50 wt % chromium balanced by nickel, and is capable of rebuilding a vane wall by more than 2 mils (0.05 mm) In another embodiment, the electrodeposited NiCr alloy formed by the method disclosed above comprises from 8 to 20 wt % chromium balanced by nickel, and is capable of rebuilding a turbine component wall by more than 5 mils (0.125 mm) The turbine component to be plated includes a vane, a rotor blade, or a stator.

(16) The NiCr alloy plated on the aero-engine parts including vanes minimizes the loss of key elements like chromium during repair services that are critical to high temperature oxidation resistance. Thus, the electrodeposited NiCr alloy that is plated on the turbine parts extends the repair cycles of the parts. The electrodeposited NiCr alloy is subject to the post heat treatment at high temperature (usually over 1000 C.) to homogenize the composition of the alloy and to restore materials lost during the repair of the turbine engine parts.

(17) The disclosed choline chloride based electrodeposition is a metal forming process that is cost-effective to restore dimensions of high temperature turbine parts with complex geometries and tighter tolerance, and is environmentally friendly.

(18) 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.