Chromium Plating

Abstract

A method of chromium coating a substrate is described, which method comprises: a) depositing, preferably electrodepositing, a metallic layer onto the substrate comprising chromium from a plating bath that includes trivalent chromium and no, or substantially no, hexavalent chromium; b) physical vapor depositing a layer comprising chromium cn the layer deposited from step a). In one embodiment, in step a), the layer is chromium and is electrodeposited from a plating bath that includes trivalent chromium and no, or substantially no, hexavalent chromium. The metallic layer deposited in step a) is preferably a metal or an alloy of two or more metals and may be selected from the group consisting of chromium, copper, nickel, cobalt, zinc, lead iron, palladium and tin and alloys thereof, e.g. copper tin, copper zinc, tin lead, tin nickel, tin cobalt, tin zinc, iron nickel, cobalt nickel, zinc nickel, zinc iron, zinc iron nickel, zinc iron cobalt or palladium nickel. Copper and nickel are especially preferred. The coating formed by the method has a blue sheen that is usually associated with chromium electrodeposited from hexavalent chromium baths without having to use a hexavalent chromium bath, which is highly toxic.

1 . A method of chromium coating a substrate to provide a chromium deposit having a blue sheen, which method comprises:
 a) depositing a metallic layer on the substrate; and   b) physical vapor depositing a layer comprising chromium on the layer deposited from step a).   
   
   
       2 . A method as claimed in  claim 1  wherein step a) comprises electrodepositing a layer comprising chromium from a plating bath that includes trivalent chromium and no, or substantially no, hexavalent chromium. 
   
   
       3 . A method as claimed in  claim 1  wherein the metal deposited in step a) is a single metal or an alloy of two or more metals. 
   
   
       4 . A method as claimed in  claim 3 , wherein the metal deposited in step a) is selected from the group consisting of chromium, copper, nickel, cobalt, zinc, lead iron, palladium and tin and copper tin, copper zinc, tin lead, tin nickel, tin cobalt, tin zinc, iron nickel, cobalt nickel, zinc nickel, zinc iron, zinc iron nickel, zinc iron cobalt or palladium nickel. 
   
   
       5 . A method as claimed in  claim 3 , wherein the metal deposited in step a) is selected from chromium, copper and nickel. 
   
   
       6 . A method as claimed in  claim 1 , wherein the metal deposited in step a) is electrodeposited. 
   
   
       7 . A method as claimed in  claim 1 , wherein the metal deposited in step a) has a thickness of 0.05 to 1 μm. 
   
   
       8 . A method as claimed in  claim 7 , wherein the metal deposited in step a) has a thickness of 0.3 to 0.9 μm. 
   
   
       9 . A method as claimed in  claim 8 , wherein the metal deposited in step a) has a thickness of 0.5 to 0.8 μm. 
   
   
       10 . A method as claimed in  claim 1 , wherein the vapor deposited chromium layer (step b) has a thickness of 0.05 to 1.5 μm. 
   
   
       11 . A method as claimed in  claim 11 , wherein the vapor deposited chromium layer (step b)) has a thickness of 0.05 to 1 μm. 
   
   
       12 . A method as claimed in  claim 12 , wherein the layers vapor deposited chromium layer (step b)) has a thickness of 0.1 to 1 μm. 
   
   
       13 . A method as claimed in  claim 1 , wherein the layers formed in steps a) and b) consist substantially wholly of chromium and the layer formed in step a) is formed by electrodeposition. 
   
   
       14 . A method as claimed in  claim 1 , wherein step b) deposits the chromium layer directly on top of the layer formed in step a). 
   
   
       15 . A product having a chromium coating made by the method of  claim 1 .