Electrocomposite coatings for hard chrome replacement

Abstract

The invention provides a method and system for electrolytically coating an article. The method includes providing an article to be coated and disposing the article in an electrolytic cell. The cell includes an anode, a cathode in operable communication with the article, and an electrolyte bath. During electrolysis, the electrolyte bath comprises cobalt ions, phosphorous acid, and tribological particles selected from the group consisting of refractory materials, solid lubricants and mixtures thereof dispersed therein. The method further includes applying steady direct electric current through the anode, the electrolyte bath and the cathode to coat the article with cobalt, phosphorous and the tribological particles. An improved composition of matter is also provided that may be used as a coating, or the composition may be electroformed on a mandrel to form an article made from the composition of matter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an electroplating system made in accordance with the present invention.

FIG. 2 is a photomicrograph showing the microstructure of a typical Co—P—SiC electrocomposite coating containing about 5-6 weight percent phosphorous made in accordance with the present invention.

FIG. 3 is a photomicrograph showing the microstructure of a typical Co—P—Cr₃C₂ electrocomposite coating containing about 5-6 weight percent phosphorous made in accordance with the present invention.

Claims

1. A method for electrolytically coating an article, comprising: a) providing an article to be coated;b) disposing the article in an electrolytic cell, the cell including an anode, a cathode in operable communication with the article, and an electrolyte bath, the electrolyte bath, during electrolysis, comprising cobalt ions, phosphorous acid, and tribological particles selected from the group consisting of refractory materials, solid lubricants and mixtures thereof dispersed therein; andc) applying steady direct electric current through the anode, the electrolyte bath and the cathode to coat the article with cobalt, phosphorous and the tribological particles.

2. The method of claim 1, wherein the electrolyte bath includes tribological particles of refractory material selected from the group consisting of ceramics, diamond and mixtures thereof.

3. The method of claim 2, wherein the electrolyte bath includes ceramic tribological particles selected from the group consisting of silicon carbide, chromium carbide, boron carbide, tungsten carbide, titanium carbide, silicon nitride, aluminum oxide, chromium oxide, and mixtures thereof.

4. The method of claim 1, wherein the electrolyte bath includes solid lubricant tribological particles selected from the group consisting of graphite, boron nitride, PTFE, molybdenum disulfide, tungsten disulfide, and mixtures thereof.

5. The method of claim 1, wherein the phosphorous acid is present in the electrolyte bath in a concentration from about 3 grams per liter to about 35 grams per liter.

6. The method of claim 1, wherein the phosphorous acid is present in the electrolyte bath in a concentration from about 3 grams per liter to about 25 grams per liter.

7. The method of claim 1, wherein the phosphorous acid is present in the electrolyte bath in a concentration from about 3 grams per liter to about 15 grams per liter.

8. The method of claim 1, wherein the article to be coated is the cathode.

9. The method of claim 1, wherein the anode includes a consumable cobalt portion adapted to release cobalt ions into the electrolyte bath as cobalt is deposited on an article to be coated.

10. The method of claim 9, wherein the anode comprises a cobalt plated electrode.

11. The method of claim 9, wherein the consumable cobalt portion includes pieces of cobalt disposed in a receptacle connected to the anode.

12. The method of claim 1, wherein the source of cobalt ions includes a soluble cobalt source selected from the group consisting of CoSO4, CoCl2, CoCO3, Co(SO3NH2)2 and mixtures thereof.

13. The method of claim 8, wherein the anode is formed at least in part from the consumable cobalt material.

14. The method of claim 1, wherein the tribological particles have an average dimension between about 0.1 micrometers and about 20 micrometers.

15. The method of claim 1, wherein the tribological particles have an average dimension between about 1.0 micrometers and about 5.0 micrometers.

16. The method of claim 11, wherein the anode is formed from a material selected from the group consisting of graphite, platinized copper, platinized titanium, platinized columbium and combinations thereof.

17. The method of claim 9, wherein the electrolyte bath further comprises a dissolution promoter for promoting the dissolution of the consumable material.

18. The method of claim 17, wherein the dissolution promoter includes a metal halide salt.

19. The method of claim 18, wherein the dissolution promoter is selected from the group consisting of sodium chloride, cobalt chloride, sodium bromide, cobalt chloride and combinations thereof.

20. The method of claim 1, wherein the electrolyte bath further comprises a buffering agent.

21. The method of claim 20, wherein the buffering agent comprises boric acid.

22. The method of claim 1, wherein the pH of the electrolyte bath is between about 0.5 and about 2.0.

23. The method of claim 22, wherein the pH of the electrolyte bath is between about 0.8 and about 1.2.

24. The method of claim 1, wherein the temperature of the electrolyte bath is between about 50° C. and about 90° C.

25. The method of claim 24, wherein the temperature of the electrolyte bath is between about 70° C. and about 80° C.

26. The method of claim 1, wherein the electric current has a current density between about 0.2 Amps/in2 to about 2.0 Amps/in2.

27. The method of claim 26, wherein the electric current has a current density between about 0.5 Amps/in2 to about 1.5 Amps/in2.

28. The method of claim 1, further comprising heat treating the article after it has been coated to cause the precipitation of cobalt-phosphides.

29. The method of claim 28, wherein the article is heat treated at a temperature between about 150° C. and about 500° C.

30. The method of claim 28, wherein the article is heat treated at a temperature between about 200° C. and about 400° C.

31. The method of claim 28, wherein the article is heat treated for about for a length of time between about 15 minutes and about 180 minutes.

32. The method of claim 1, wherein the concentration of cobalt in the electrolyte bath is between about 50 grams per liter and about 200 grams per liter.

33. The method of claim 32, wherein the cobalt concentration in the electrolyte bath is about 100 grams per liter.

34. The method of claim 32, wherein the tribological particles include silicon carbide particles in a concentration from about 10 grams per liter to about 200 grams per liter.

35. The method of claim 34, wherein the tribological particles include silicon carbide particles in a concentration from about 30 grams per liter to about 60 grams per liter.

36. The method of claim 1, wherein the tribological particles include chromium carbide particles in a concentration from about 10 grams per liter to about 200 grams per liter.

37. The method of claim 1, wherein the tribological particles include chromium carbide particles in a concentration from about 35 grams per liter to about 100 grams per liter.

38. The method of claim 1, wherein the cathode is made from a material suitable for electroforming a article thereon, wherein the article can be removed from the cathode after the article is formed.

39. An article having a coating formed according to the process of claim 1.

40. The article of claim 38, wherein the coating has a hardness of about 650-700 VHN.

41. An article having a coating formed according to the process of claim 28.

42. The article of claim 41, wherein the coating includes chromium carbide tribological particles and the coating has a hardness of about 1000 VHN.

43. The article of claim 41, wherein the coating includes silicon carbide tribological particles and the coating has a hardness of about 1150 VHN.

44. A system for electrolytically coating an article, comprising: a) an electrolytic cell including: i) an anode;ii) a cathode capable of being placed in operable communication with an article to be coated; andiii) an electrolyte bath in operable communication with the anode and the cathode, the electrolyte bath, during electrolysis, comprising cobalt ions, phosphorous acid, and tribological particles selected from the group consisting of refractory materials, solid lubricants and mixtures thereof dispersed therein; andb) a direct current power supply adapted to apply steady direct current across the anode, electrolyte bath and cathode to coat an article with cobalt, phosphorous and the tribological particles.

45. A composition of matter comprising cobalt, phosphorous and tribological particles selected from the group consisting of refractory materials, solid lubricants and mixtures thereof dispersed therein.