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Surface treatment for Cr-Fe alloy

2007

I am a researcher and I am trying to plate either Co or Ni on to 23% Cr-77% Fe alloy. Right now I am using a plating solution containing 12 g/l cobalt chloride, 105 g/l sodium
citrate, ammonium hydroxide and 0.3 g/l dextrin. Prior to plating, I polish the surface to a mirror finish followed by etching in 10% HF solution, cleaning with soap solution and rinsing with Tap/DI water. For plating I use a current density of 1-5 mA/cm2 and I do not get any Co deposit at all. Can any one suggest me a better way to do this?

Thanks.

Prabhu Ganesan
Researcher - South Carolina

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2007

An acidic, 'Wood's Nickel' solution is commonly used to provide a 'strike plating' of nickel. An initial anodic treatment (or even no current) activates the surface after which the current is reversed to plate nickel. Rinse in DI water and immerse into the subsequent plating solution before the rinsewater can dry (and the surface becomes passive). Search this site for more info.

ASTM B254, 'Standard Practice for Preparation of and Electroplating on Stainless Steel,' can be purchased as a download if in a hurry and lacking plating books.

I don't understand your pretreatment. If cleaning is needed, it should precede etching. Soap leaves a film; use an alkaline detergent. DI water rinsing may help if you have hard tapwater.

Most electrolytic nickel plating is performed in acidic solutions such as Watts or nickel sulfamate baths. Do you have access to ASM Handbook Vol. 5 Surface Engineering or other metal finishing books?

I'm not familiar with the alkaline cobalt or nickel plating recipes; this resembles an alkaline electroless solution lacking the sodium hypophosphite. Anyone else?

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.