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.

1 . A coating for improving the fatigue performance of an article, said coating comprising:
 a) a cobalt material matrix;   b) said cobalt material matrix consisting of a cobalt phosphorous alloy, wherein the phosphorous in the final coating is present in an amount between about 7 weight percent and about 12 weight percent.   
     
     
         2 . The coating of  claim 1 , wherein the cobalt material matrix is substantially free of tribological particles, and wherein the phosphorous in the final coating is present in an amount between about 10 weight percent and about 12 weight percent. 
     
     
         3 . The coating of  claim 1 , wherein the coating further includes a plurality of tribological particles throughout the cobalt material matrix, the tribological particles having an average particle size in the range of from about 2 to 10 microns, and wherein the phosphorous in the final coating is present in an amount between about 7 weight percent and about 8 weight percent. 
     
     
         4 . The coating of  claim 1 , wherein the coating has an as-plated hardness of about 650-700 VHN and has a fatigue life that is greater than an otherwise identical but uncoated article. 
     
     
         5 . The coating of  claim 1 , wherein the article has a fatigue life that is at least twice as great as an otherwise identical but uncoated article. 
     
     
         6 . The coating of  claim 1 , wherein the article has a fatigue life that is at least three times as great as an otherwise identical but uncoated article. 
     
     
         7 . The coating of  claim 3 , wherein the tribological particles include ceramic material 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. 
     
     
         8 . The coating of  claim 3 , wherein the tribological particles include solid lubricant material selected from the group consisting of graphite, boron nitride, PTFE, molybdenum disulfide, tungsten disulfide, and mixtures thereof. 
     
     
         9 . A method for electrolytically coating an article to enhance its fatigue performance, comprising:
 a) providing an article to be coated;   b) disposing the article in an electrolytic cell, the cell including a soluble anode, a cathode in operable communication with the article, and an electrolyte bath, the electrolyte bath, during electrolysis, comprising cobalt ions from the soluble anode, phosphorus obtained by separately introducing phosphorous acid into the bath, wherein the pH of the electrolyte bath is between about 1.2 and about 2.2; and   c) applying steady direct electric current through the anode, the electrolyte bath and the cathode at a current density of about 0.3 Amps/in 2  and about 0.8 Amps/in 2  to coat the article with a coating that is essentially free of nickel and contains cobalt and phosphorous, wherein the weight percent of phosphorus in the resulting coating is between about 7% and about 12%.   
     
     
         10 . The method of  claim 9 , wherein the weight percent of phosphorus in the resulting coating is between about 7% and about 8%, and further wherein the coating is substantially free of tribological particles. 
     
     
         11 . The method of  claim 9 , wherein the electrolyte bath further includes tribological particles selected from the group consisting of refractory materials, solid lubricants and mixtures thereof dispersed therein, wherein the resulting coating includes the tribological particles after coating the article, and further wherein the weight percent of phosphorus in the resulting coating is between about 10% and about 12%. 
     
     
         12 . The method of  claim 9 , wherein the temperature of the electrolyte bath is between about 70° C. and about 75° C. 
     
     
         13 . The method of  claim 9 , wherein the phosphorous acid is introduced in a granular form. 
     
     
         14 . The method of  claim 9 , wherein the resulting coated article has an as-plated hardness of about 650-700 VHN and has a fatigue life that is greater than an otherwise identical but uncoated article. 
     
     
         15 . The method of  claim 9 , wherein the resulting coated article has a fatigue life that is at least twice as great as an otherwise identical but uncoated article. 
     
     
         16 . The method of  claim 9 , wherein the resulting coated article has a fatigue life that is at least three times as great as an otherwise identical but uncoated article.