Low cost, environmentally favorable, chromium plate replacement coating for improved wear performance

Abstract

A coating which improves the wear performance of a part is described. The coating is applied over an article such as a part or a workpiece using an electroplating process. The coating broadly includes a cobalt material matrix with a hardness of at least 550 HV and a plurality of carbide particles distributed throughout the cobalt material matrix. The cobalt material matrix may be a cobalt-phosphorous alloy. The particles interspersed throughout the matrix may be chrome carbide or silicon carbide particles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of an actuator;

FIG. 2 is a SEM photomicrograph at 500× magnification of a cobalt-phosphorous coating without any particles;

FIG. 3 is a SEM photomicrograph at 500× magnification of a cobalt-phosphorous coating containing silicon carbide particles;

FIG. 4 is a SEM photomicrograph at 500× magnification of a cobalt-phosphorous coating containing chrome carbide particles;

FIG. 5 is a cross sectional photomicrograph of the chrome carbide containing coating which was tested as described hereinafter; and

FIG. 6 is a cross sectional photomicrograph of the silicon carbide containing coating which was tested as described hereinafter.

Claims

1. A coating for improving the wear performance of an article, said coating comprising: a cobalt material matrix with a hardness in the range of 550 to 1000 HV; anda plurality of carbide particles throughout the cobalt material matrix.

2. The coating of claim 1, wherein said cobalt material matrix comprises a cobalt phosphorous alloy.

3. The coating of claim 2, wherein said phosphorous in the final coating is present in an amount of from 4.0 to 6.0 wt %.

4. The coating of claim 1, wherein said carbide particles is selected from the group consisting of chrome carbide and silicon carbide particles.

5. The coating of claim 1, wherein said carbide particles are present in an amount in the range of from 15 to 30 vol %.

6. The coating of claim 1, wherein each said carbide particle has an average particle size in the range of from about 2.0 to 10 microns.

7. The coating of claim 1, wherein said coating has a hardness in the range of from 550 to 650 HV.

8. The coating of claim 1, wherein said coating has a hardness in the range of from 650 to 1000 HV.

9. An article having a coating comprising a cobalt material matrix with a hardness in the range of 550 to 1000 HV and a plurality of carbide particles throughout the cobalt material matrix.

10. The article of claim 9, wherein said article comprises an actuator bore.

11. The article of claim 9, wherein said article comprises a propeller dome.

12. The article of claim 9, wherein said article comprises a propeller yoke.

13. The article of claim 9, wherein said article comprises a propeller anti-torque arm.

14. The article of claim 9, wherein said article comprises a fuel control bore.

15. The article of claim 9, wherein said article comprises a gun barrel.

16. The article of claim 9, wherein said cobalt material matrix comprises a cobalt phosphorous alloy.

17. The article of claim 16, wherein said phosphorous in the final coating is present in an amount of from 4.0 to 6.0 wt %.

18. The article of claim 9, wherein said carbide particles is selected from the group consisting of chrome carbide and silicon carbide particles.

19. The article of claim 9, wherein said carbide particles are present in an amount in the range of from 15 to 30 vol %.

20. The article of claim 9, wherein each said carbide particle has an average particle size in the range of from about 2.0 to 10 microns.

21. The article of claim 9, wherein said coating has a hardness in the range of from 550 to 650 HV.

22. The article of claim 9, wherein said coating has a hardness in the range of from 650 to 1000 HV.

23. A process for forming a coating on an article, said process comprising the steps of: providing an article to be coated;providing an electroplating bath solution having a chemistry of from about 180 to 210 g/l cobalt chloride, from about 0.05 to 2.0 g/l cobalt carbonate, from 45 to 55 g/l ortho-phosphoric acid, and from about 5.0 to 15 g/l of phosphorous acid;said electroplating bath solution providing step further comprising placing a volume of carbide particles in said bath solution sufficient to result in from about 15 to 30 vol % of carbide particles in a final coating; andplacing said article in contact with said bath solution and applying a current to deposit said coating onto said article.

24. The process of claim 23, further comprising maintaining said bath at a temperature in the range of from about 65 to 85 degrees Centigrade.

25. The process of claim 23, further comprising maintaining said bath at a pH of from about 0.7 to 1.7.

26. The process of claim 23, wherein said current applying step comprises applying a current density in the range of from about 45 to 350 amps/sq. ft.

27. The process of claim 23, wherein said current applying step comprises immersing an anode in said bath, which anode is formed from a consumable cobalt material or an inert material.

28. The process of claim 23, further comprising removing said part from said electroplating bath and heat treating said article with said electroplated coating at a temperature in the range of from about 200 to 400 degrees Centigrade for a time period in the range of from about 1.0 to 2.0 hours.

29. The process according to claim 23, further comprising agitating said carbide particles within said electroplating bath solution to provide an even distribution of said carbide particles across the coating.