Process for deposition of crack-free and corrosion-resistant hard chromium and chromium alloy layers

Abstract

An electrolytic plating composition and related plating process where the composition comprises chromium ions, a mineral acid, halogen oxoanion, alkylsulfonic acid, and a source of sulfoacetic acid for electrolytically coating a surface of a substrate with a chromium layer or a chromium alloy layer.

1 . A process for electrolytically coating a surface of a substrate with a chromium-based layer, the process comprising: 
 contacting the surface of the substrate with an electrolytic plating composition comprising a source of chromium ions, a mineral acid, a source of halogen oxoanion, an alkylsulfonic acid, and a source of sulfoacetic acid selected from the group consisting of sulfoacetic acid, a sulfoacetate salt, a sulfoacetate ester, a sulfoacetate anhydride, and a reactant which generates sulfoacetic acid; and    supplying an external source of electrons to electrolytically deposit the chromium-based layer onto the surface of the substrate.    
   
   
       2 . The process of  claim 1  wherein the halogen oxoanion is an alkali metal salt or alkaline earth metal salt of the halogen oxoanion, and the composition has an initial concentration of halogen oxoanion between about 0.001 M and about 0.1 M.  
   
   
       3 . The process of  claim 2  wherein the salt of the halogen oxoanion is selected from the group consisting of an iodate salt, a periodate salt, a chlorate salt, a chlorite salt, a perchlorate salt, a hypochlorite salt, a bromate salt, and combinations thereof, and the composition has an initial concentration of halogen oxoanion between about 0.001 M and about 0.1 M.  
   
   
       4 . The process of  claim 1  wherein: 
 the source of chromium ions is selected from the group consisting of chromium(VI) oxide; chromate (CrO 4   2− ) salts of sodium, potassium, and ammonium; dichromate (Cr 2 O 7   2− ) salts of sodium, potassium, and ammonium; and combinations thereof; and the composition has an initial concentration of chromium ions between about 0.5 M and about 5 M;    the source of halogen oxoanion is a salt selected from the group consisting of an iodate salt, a periodate salt, a chlorate salt, a chlorite salt, a perchlorate salt, a hypochlorite salt, a bromate salt, and combinations thereof, and the composition has an initial concentration of halogen oxoanion between about 0.001 M and about 0.1 M;    the source of alkylsulfonic acid is selected from the group consisting of methanesulfonic acid, methanedisulfonic acid, ethylsulfonic acid, propylsulfonic acid, salts thereof, and combinations thereof, and the composition has an initial concentration of the alkylsulfonic acid of between about 0.01 and 0.1 M;    the composition has an initial concentration of sulfoacetic acid in the range of about 0.03 and about 0.3 M; and    the composition has a pH of less than 1.    
   
   
       5 . The process of  claim 1  wherein: 
 the source of chromium ions is selected from the group consisting of chromium(VI) oxide; chromate (CrO 4   2− ) salts of sodium, potassium, and ammonium; dichromate (Cr 2 O 7   2− ) salts of sodium, potassium, and ammonium; and combinations thereof; and the composition has an initial concentration of chromium ions between about 2 M and about 3 M;    the source of halogen oxoanion is a salt selected from the group consisting of an iodate salt, a periodate salt, a chlorate salt, a chlorite salt, a perchlorate salt, a hypochlorite salt, a bromate salt, and combinations thereof, and the composition has an initial concentration of halogen oxoanion between about 0.007 M and about 0.03 M;    the source of alkylsulfonic acid is selected from the group consisting of methanesulfonic acid, methanedisulfonic acid, ethylsulfonic acid, propylsulfonic acid, salts thereof, and combinations thereof, and the composition has an initial concentration of the alkylsulfonic acid of between about 0.02 and 0.04 M;    the composition has an initial concentration of sulfoacetic acid in the range of about 0.06 and about 0.12 M; and    the composition has a pH of less than 1.    
   
   
       6 . The process of  claim 1  wherein the external source of electrons provides a current density between about 20 A/dm 2  and about 150 A/dm 2 .  
   
   
       7 . The process of  claim 1  wherein the electrolytic plating composition has a temperature between about 20° C. and about 90° C.  
   
   
       8 . The process of  claim 1  wherein the chromium-based layer has a hardness of more than 800 HV 0.1.  
   
   
       9 . The process of  claim 1  wherein the chromium-based layer has a corrosion resistance of greater than 200 hours when tested according to DIN 50021 SS.  
   
   
       10 . An electrolytic plating composition for electrolytically coating a surface of a substrate with a chromium layer or a chromium alloy layer, the composition comprising: 
 a source of chromium ions;    a mineral acid;    a source of halogen oxoanion;    a source of alkylsulfonic acid; and    a source of sulfoacetic acid selected from the group consisting of sulfoacetic acid, a sulfoacetate salt, a sulfoacetate ester, a sulfoacetate anhydride, and a reactant which generates sulfoacetic acid.    
   
   
       11 . The electrolytic plating composition of  claim 10  wherein the source of chromium ions is selected from the group consisting of chromium(VI) oxide; chromate (CrO 4   2− ) salts of sodium, potassium, and ammonium; dichromate (Cr 2 O 7   2− ) salts of sodium, potassium, and ammonium; and combinations thereof.  
   
   
       12 . The electrolytic plating composition of  claim 10  wherein the source of chromium ions has an initial concentration of chromium ions between about 1M and about 4M.  
   
   
       13 . The electrolytic plating composition of  claim 10  wherein the source of chromium ions is added to yield an initial concentration of chromium ions between about 2 M and about 3 M.  
   
   
       14 . The electrolytic plating composition of  claim 10  wherein the composition has an initial pH less than about 1.  
   
   
       15 . The electrolytic plating composition of  claim 10  wherein the source of halogen oxoanion is an alkali metal salt or alkaline earth metal salt of the halogen oxoanion.  
   
   
       16 . The electrolytic plating composition of  claim 15  wherein the salt is selected from the group consisting of an iodate salt, a periodate salt, a chlorate salt, a chlorite salt, a perchlorate salt, a hypochlorite salt, a bromate salt, and combinations thereof.  
   
   
       17 . The electrolytic plating composition of  claim 16  having an initial concentration of halogen oxoanion between about 0.001 M and about 0.1 M.  
   
   
       18 . The electrolytic plating composition of  claim 16  having an initial concentration of halogen oxoanion between about 0.005 M and about 0.08 M.  
   
   
       19 . The electrolytic plating composition of  claim 16  having an initial concentration of halogen oxoanion between about 0.007 M and about 0.03 M.  
   
   
       20 . The electrolytic plating composition of  claim 10  wherein the source of alkylsulfonic acid is selected from the group consisting of methanesulfonic acid, methanedisulfonic acid, ethylsulfonic acid, propylsulfonic acid, salts thereof, and combinations thereof.  
   
   
       21 . The electrolytic plating composition of  claim 20  wherein the source of alkylsulfonic acid is added in an initial concentration between about 0.015 M and about 0.06 M.  
   
   
       22 . The electrolytic plating composition of  claim 10  having an initial concentration of sulfoacetic acid between about 0.03 M and about 0.3 M.