Metal Deposition Process Using Electroplasma

Abstract

A process for treating a surface of an electrically conductive workpiece is provided, comprising placing a movable workpiece within a reaction chamber, wherein the reaction chamber includes an anode, and wherein the workpiece is a cathode; creating a gap between the anode and the cathode, wherein the anode includes a plurality of orifices; applying an aqueous electrolyte into the reaction chamber through the orifices in the anode and onto the workpiece, and applying the aqueous electrolyte from below the workpiece, to establish an electrically conductive medium around the workpiece, applying a DC voltage to the electrically conductive medium in excess of 30 VDC, such that a foam is formed within the reaction chamber, wherein the foam comprises a gas/vapor phase and a liquid phase which fills the entire reaction chamber; adjusting the voltage to establish an electro-plasma discharge between the anode and workpiece, sufficient to cause positive ions in the electrically conductive medium to become concentrated near the surface of the workpiece and cause micro-zonal melting of the surface in the area of discreet plasma bubbles; and moving the workpiece through the reaction chamber and away from the electrically conductive medium to allow re-freezing of the molten surface of the workpiece. The process applies to both cleaning and coating of the workpiece, wherein coating is achieved via sacrificial anodes.

We claim: 
     
         1 . A process for treating a surface of an electrically conductive workpiece, comprising:
 (a) placing a movable workpiece within a reaction chamber, wherein the reaction chamber includes an anode, and wherein the workpiece is a cathode;   (b) creating a gap between the anode and the cathode, wherein the anode includes a plurality of orifices;   (c) applying an aqueous electrolyte into the reaction chamber through the orifices in the anode and onto the workpiece, and applying the aqueous electrolyte from below the workpiece, to establish an electrically conductive medium around the workpiece,   (d) applying a DC voltage to the electrically conductive medium in excess of 30 VDC, such that a foam is formed within the reaction chamber, wherein the foam comprises a gas/vapor phase and a liquid phase which fills the entire reaction chamber;   (e) adjusting the voltage to establish an electro-plasma discharge between the anode and workpiece, sufficient to cause positive ions in the electrically conductive medium to become concentrated near the surface of the workpiece and cause micro-zonal melting of the surface in the area of discreet plasma bubbles; and   (f) moving the workpiece through the reaction chamber and away from the electrically conductive medium to allow re-freezing of the molten surface of the workpiece.   
     
     
         2 . The process of  claim 1 , wherein the workpiece is exposed to the electro-plasma for a duration sufficient to clean the workpiece from oxide scales, lubricants, coatings, dirt and organic substances. 
     
     
         3 . The process of  claim 1 , wherein the workpiece is exposed to the electro-plasma for a duration sufficient to modify a surface profile of the workpiece to form a morphology which reduces wetting, serves as a carrier for drawing lubricants, and is passivated against corrosion. 
     
     
         4 . The process of  claim 1 , wherein the positive ions include one or more metals to form one or more coatings of the metals on the workpiece. 
     
     
         5 . The process of  claim 4 , wherein the coating includes a conductive metal coating comprised of independent layers of different metals on the workpiece. 
     
     
         6 . The process of  claim 4 , wherein the coating includes two or more conductive metals forming an alloy on the workpiece. 
     
     
         7 . The process of  claim 1 , wherein the positive ions are derived from one or more sacrificial anodes. 
     
     
         8 . The process of  claim 1 , wherein the aqueous electrolyte is heated to a select temperature to increase the effectiveness of the process. 
     
     
         9 . The process of  claim 8 , wherein the heated aqueous electrolyte is introduced into the reaction chamber and becomes a foam as electrical current is applied between the anode and the workpiece, sufficient to cause ebullition at the surface of the workpiece. 
     
     
         10 . The process of  claim 1 , wherein the effectiveness of the electrically conductive medium is increased by the addition of foaming agents and surfactants. 
     
     
         11 . The process of  claim 2 , wherein the cleaned surface of the workpiece exhibits a surface morphology comprising craters and spheroids sufficient to carry lubricant for drawing of the workpiece. 
     
     
         12 . The process of  claim 3 , wherein an iron oxide (FeO) layer on the surface is reconstituted into alpha (amorphous) iron, and wherein surface grain size is substantially reduced to nano-sized grains that are tightly packed against one another sufficient to reduce corrosive penetration. 
     
     
         13 . The process of  claim 4 , wherein deposition of the metals is achieved without an initiation or growth of an intermetallic layer between the workpiece and the coating metals. 
     
     
         14 . The process of  claim 4 , wherein deposition of the metals is achieved without creation of a phase diffusion boundary layer on the coating metal. 
     
     
         15 . The process of  claim 4 , wherein deposition of the metals is achieved without causing hydrogen embrittlement to the coating metals. 
     
     
         16 . The process of  claim 1 , wherein the workpiece defines a core, and wherein the temperature of the core of the workpiece is maintained at or below a predetermined temperature sufficient to control the dissociation of oxygen and hydrogen, and to suppress the formation of oxygen bubbles at the surface of the workpiece. 
     
     
         17 . The process of  claim 16 , wherein the predetermined temperature is about 950 C. 
     
     
         18 . The process of  claim 4 , wherein downward pressure is maintained within the electro-plasma against the workpiece sufficient to cause deposition of the coating metals to form in a plane parallel to the surface of the workpiece. 
     
     
         19 . The process of  claim 1 , wherein the workpiece is subjected to the electro-plasma across a plurality of isolated reaction chambers. 
     
     
         20 . The process of  claim 1 , wherein the reaction chamber includes exhaust ports above the workpiece adapted to permit expanding gas to vent from the reaction chamber.