Activation of self-passivating metals using reagent coatings for low temperature nitrocarburization

Abstract

A method for treating a workpiece made of self-passivating metal and having a Beilby layer including applying a coating to a surface of the workpiece, the coating including a reagent, treating the coating to thermally alter the reagent, wherein the thermal altering of the reagent activates and/or hardens the surface.

We claim: 
     
         1 . A coating composition for treating a workpiece made of self-passivating metal and having a Beilby layer comprising:
 a reagent vehicle; and   a reagent comprising a guanidine [HNC(NH 2 ) 2 ] moiety and associated with HCl to activate the Beilby layer for low temperature interstitial surface hardening,   
     
     
         2 . The coating composition of  claim 1 , wherein the reagent includes at least one of an oxygen-free nitrogen halide salt and a non-polymeric N/C/H compound. 
     
     
         3 . The coating composition of  claim 1 , wherein the reagent vehicle includes at least one of a powder, a water-based liquid, an oil, and a solvent. 
     
     
         4 . The coating composition of  claim 3 , wherein the oil is a paraffinic oil. 
     
     
         5 . The coating composition of  claim 4 , wherein the paraffinic oil is hydrocarbon or emulsion based. 
     
     
         6 . The coating composition of  claim 4 , wherein the paraffinic oil does not chemically interfere with an activation or hardening process. 
     
     
         7 . A workpiece having a Beilby layer treated according to a method comprising:
 applying a coating to at least a portion of a surface of the workpiece, the coating including a reagent; and   treating the coating to thermally alter the reagent, wherein the thermal altering of the reagent activates the surface for hardening.   
     
     
         8 . The workpiece of  claim 7 , wherein the applying a coating includes providing the reagent as part of a paraffinic oil. 
     
     
         9 . The workpiece of  claim 8 , wherein the paraffinic oil is hydrocarbon or emulsion based. 
     
     
         10 . The workpiece of  claim 8 , wherein the paraffinic oil is evaporated in a furnace to leave the reagent and modify the portion. 
     
     
         11 . The workpiece of  claim 10 , wherein the evaporating includes applying a vacuum. 
     
     
         12 . The workpiece of  claim 10 , wherein the evaporating is performed at a temperature below an activation or hardening temperature of the reagent. 
     
     
         13 . The workpiece of  claim 8 , wherein the paraffinic oil does not chemically interfere with an activation or hardening process. 
     
     
         14 . The workpiece of  claim 7 , wherein the method comprises hardening the surface. 
     
     
         15 . The workpiece of  claim 14 , wherein the hardening includes at least one of nitriding, carburizing, nitrocarburizing, and carbonitriding. 
     
     
         16 . The workpiece of  claim 15 , wherein the thermal altering the reagent supplies at least one of nitrogen and carbon for hardening. 
     
     
         17 . The workpiece of  claim 7 , wherein the reagent includes at least one of an oxygen-free nitrogen halide salt and a non-polymeric N/C/H compound. 
     
     
         18 . The workpiece of  claim 7 , wherein the reagent vehicle includes at least one of a powder, a water-based liquid, an oil, and a solvent.