Iron-tungsten coating formulations and processes

Abstract

An electrolyte solution for iron-tungsten plating is prepared by dissolving in an aqueous medium a divalent iron salt (e.g., iron (II) sulfate) and an alkali metal citrate (e.g., sodium citrate, potassium citrate, or other alkali metal citrate) to form a first solution, dissolving in the first solution a tungstate salt (e.g., sodium tungstate, potassium tungstate, or other potassium tungstate) to form a second solution, and dissolving in the second solution a citric acid to form the electrolyte solution. An iron-tungsten coating is formed on a substrate using the electrolyte solution by passing a current between a cathode and an anode through the electrolyte solution to deposit iron and tungsten on the substrate.

What is claimed is: 
     
         1 . A method of forming an iron-tungsten alloy coating layer comprising:
 preparing an electrolyte solution consisting of an aqueous medium; a divalent iron salt; an alkali metal citrate; a tungstate salt comprising an alkali metal tungstate; a citric acid; and sodium hydroxide, potassium hydroxide, sulfuric acid, or a combination thereof by:
 dissolving in the aqueous medium, the divalent iron salt in an amount ranging from about 0.05 to about 0.5 mol per liter of the electrolyte solution and the alkali metal citrate in an amount ranging from about 0.05 to about 2 mol per liter of the electrolyte solution to form a first solution; 
 dissolving in the first solution the tungstate salt in an amount ranging from about 0.1 to about 1.5 mol per liter of the electrolyte solution to form a second solution; and 
 dissolving in the second solution the citric acid in an amount ranging from about 0.01 to about 1 mol per liter of the electrolyte solution to form the electrolyte solution; and 
   passing a current between a cathode and an anode through the electrolyte solution to form the iron-tungsten alloy coating layer when the pH of the electrolyte solution is maintained at about 3 to about 12.   
     
     
         2 . The method of  claim 1 , wherein the divalent iron salt comprises iron (II) sulfate, iron (II) halide, iron (II) nitrate, iron (II) acetate, or iron (II) perchlorate. 
     
     
         3 . The method of  claim 1 , wherein the alkali metal citrate comprises sodium citrate or potassium citrate. 
     
     
         4 . The method of  claim 1 , wherein the tungstate salt comprises sodium tungstate or potassium tungstate. 
     
     
         5 . The method of  claim 1 , wherein the citric acid comprises anhydrous citric acid or citric acid monohydrate. 
     
     
         6 . The iron-tungsten alloy coating layer made by the method of  claim 1 . 
     
     
         7 . The method of  claim 1 , wherein the pH is maintained at about 7 to about 12 to form an iron-tungsten alloy coating layer having a tungsten content ranging from about 18 to about 28 At %. 
     
     
         8 . The iron-tungsten alloy coating layer made by the method of  claim 7 . 
     
     
         9 . The method of  claim 1 , wherein the pH is maintained at about 3 to about 7 to form an iron-tungsten alloy coating layer having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At %. 
     
     
         10 . The iron-tungsten alloy coating layer made by the method of  claim 9 . 
     
     
         11 . The method of  claim 1 , wherein the step of passing the current forms a plurality of iron-tungsten alloy coating layers comprising at least one iron-tungsten alloy coating layer having a tungsten content ranging from about 18 to about 28 At % and at least one iron-tungsten alloy coating layer having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At %. 
     
     
         12 . The plurality of iron-tungsten alloy coating layers made by the method of  claim 11 . 
     
     
         13 . The plurality of iron-tungsten alloy coating layers of  claim 12 , wherein a thickness of the at least one iron-tungsten alloy coating layer having a tungsten content ranging from about 18 to about 28 At % is equal to a thickness of the at least one iron-tungsten alloy coating layer having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At %. 
     
     
         14 . The plurality of iron-tungsten alloy coating layers of  claim 12 , wherein a thickness of the at least one iron-tungsten alloy coating layer having a tungsten content ranging from about 18 to about 28 At % is different from a thickness of the at least one iron-tungsten alloy coating layer having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At %. 
     
     
         15 . A method of forming an iron-tungsten alloy coating layer comprising:
 preparing an electrolyte solution consisting of an aqueous medium; a divalent iron salt comprising iron (II) sulfate, iron (II) halide, iron (II) nitrate, iron (II) acetate, or iron (II) perchlorate; an alkali metal citrate comprising sodium citrate or potassium citrate; a tungstate salt comprising an alkali metal tungstate; a citric acid; and sodium hydroxide, potassium hydroxide, sulfuric acid, or a combination thereof by:
 dissolving in the aqueous medium, the divalent iron salt in an amount ranging from about 0.05 to about 0.5 mol per liter of the electrolyte solution and the alkali metal citrate in an amount ranging from about 0.05 to about 2 mol per liter of the electrolyte solution to form a first solution; 
 dissolving in the first solution the tungstate salt in an amount ranging from about 0.1 to about 1.5 mol per liter of the electrolyte solution to form a second solution; and 
 dissolving in the second solution the citric acid in an amount ranging from about 0.01 to about 1 mol per liter of the electrolyte solution to form the electrolyte solution; and 
   passing a current between a cathode and an anode through the electrolyte solution to form the iron-tungsten alloy coating layer when the pH of the electrolyte solution is maintained at about 3 to about 12.   
     
     
         16 . The iron-tungsten alloy coating layer made by the method of  claim 15 . 
     
     
         17 . The method of  claim 15 , wherein the pH is maintained at about 7 to about 12 to form an iron-tungsten alloy coating layer having a tungsten content ranging from about 18 to about 28 At %. 
     
     
         18 . The iron-tungsten alloy coating layer made by the method of  claim 17 . 
     
     
         19 . The method of  claim 15 , wherein the pH is maintained at about 3 to about 7 to form an iron-tungsten alloy coating layer having a tungsten content ranging from about 5 to about 18 At % or about 28 to about 40 At %. 
     
     
         20 . An iron-tungsten coating on a substrate:
 comprising an alloy of iron and tungsten having a tungsten content ranging from about 18 to about 28 At %,   having a hardness of about 700 HV to 900 HV, and   having a surface morphology as shown in  FIG.  13 A ,  FIG.  13 B ,  FIG.  16 A , or  FIG.  18   .