Method for repairing a rubbing surface of a turbomachine variable-pitch blade

1. A method for repairing a worn surface of a variable-pitch blade for a turbomachine, said surface being a rubbing surface and exhibiting a deficit of material as a result of wear thereof, the method comprising:

filling said deficit of material by depositing a metallic product using electrolysis, said metallic product being deposited on said surface of the blade by buffer electrolysis performed by providing a single buffer electrode made of graphite which is impregnated with an electrolytic solution and which is moved along inside said deficit, then

forming at least one thin layer of a hard material with a low coefficient of friction on the deposited metallic product and on the surrounding part of said surface, wherein said thin layer of said hard material is an outer layer that forms a new rubbing surface of said variable-pitch blade, and

wherein said thin layer of said hard material has a hardness higher than that of the deposited metallic product.

2. A method according to claim 1 , wherein the metallic product is deposited on said surface of the blade by bath electrolysis.

3. A method according to claim 1 , wherein the metallic product is deposited on said surface of the blade by bath electrolysis in miniature, the electrolytic solution covering only or almost only that region of the surface that exhibits a deficit of material.

4. A method according to claim 1 , wherein the deposited metallic product contains nickel.

5. A method according to claim 4 , wherein said hard material comprises cobalt.

6. A method according to claim 4 , wherein said hard material comprises tungsten.

7. A method according to claim 4 , wherein said step of forming at least one thin layer comprises forming a plurality of layers on said deposited metallic product, wherein an outermost layer is said outer layer and comprises chromium.

8. A method according to claim 7 , wherein at least at least one of the plurality layers formed on said deposited metallic product, other than said outer layer, comprises at least one of cobalt and tungsten.

9. A method according to claim 1 , wherein nickel sulphamate is used by way of electrolytic solution.

10. A method according to claim 1 , wherein the deposited metallic product is grounded before said thin layer of hard material is formed thereon.

11. A method according to claim 1 , wherein the thin layer of hard material is formed by buffer electrolysis or by thermal spraying, for example of the plasma or HVOF type, or by PVD.

12. A method according to claim 1 , wherein the thin layer of hard material is based on nickel, cobalt, tungsten or chromium, or on a combination of these elements including nickel-cobalt, nickel-tungsten or cobalt-tungsten.

13. A method according to claim 1 , wherein the thin layer has a thickness of between 40 and 50 μm.

14. A method according to claim 1 , wherein said method is free of any step of machining said blade before said filling step.

15. A method according to claim 1 , wherein said filling of said deficit of material with said metallic product is performed directly on said surface of said variable-pitch blade.

16. A method according to claim 1 , wherein said filling of said deficit of material with said metallic product is performed by contacting only a portion of a mounting plate of said blade where said deficit is located with an electrolytic solution.

17. A method according to claim 16 , wherein said filling of said deficit of material with said metallic product is performed by dipping said mounting plate in a bath of said electrolytic solution.

18. A method according to claim 17 , wherein said filling of said deficit of material with said metallic product is performed while keeping a shank portion of said blade out of said electrolytic solution.

19. A method according to claim 18 , wherein said filling of said deficit of material with said metallic product is performed while keeping an airfoil portion of said blade in said electrolytic solution and protecting said airfoil portion from contacting said electrolytic solution.

20. A method according to claim 18 , wherein said protecting is performed by applying sticky tape to said airfoil portion before dipping said airfoil portion in said electrolytic solution.

21. A method according to claim 1 , wherein said electrolytic solution is nickel sulphamate.

22. A method according to claim 1 , wherein said hardness of said hard material is higher than that of a part of the turbomachine, wherein said part rubbed said worn rubbing surface thereby forming said deficit of material and wherein said part is to rub against said new rubbing surface after said worn rubbing surface is repaired.

23. A method according to claim 1 , wherein the blade comprises austenitic steel.