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Chrome on Titanium
2

Chrome on Titanium

Chrome on Titanium

(OP)
Any ideas on how to to keep the chrome on Titanium?

RE: Chrome on Titanium

2
Not many details – is chromium plating flaking off titanium parts?  How was the plating done, and what is the application?

Plating comes off titanium due to poor adhesion to the surface oxide film which forms ~instantaneously in the presence of oxygen (air and water), i.e., the Ti passivates.  This prevents the strong adhesion of metal atom to metal atom bonding obtained when plating onto more noble metals such as copper and iron.  Even with proper activation, titanium repassivates rapidly upon rinsing and transferring through air to the plating tank.  For some procedures for plating on Ti, see
ASTM B481-68(2003)e1 Standard Practice for Preparation of Titanium and Titanium Alloys for Electroplating
http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/...
 and finishing.com Letters #13456 and #24365:
http://www.finishing.com/134/56.html
http://www.finishing.com/243/65.html

My preference is to acid activate, rinse very rapidly (never let the parts dry) and then put on a nickel ‘strike’ coat from a Wood’s nickel solution.  The Wood’s Ni solution contains ~10 vol. % hydrochloric acid, so it can re-activate the Ti surface prior to turning on the electroplating current.  Other metals can then be plated onto the Ni strike coat.

To improve adhesion, do an adhesion bake after first plating additional Ni (from either a Watts Ni or sulfamate Ni solution) and the Cr.  The procedure is given in ASTM B481, Para. 4.2.4:  Heat in inert gas for 1-4 hours at 540-800oC.  This causes interdiffusion bonding between the Ti and Ni.

Hope this helps.  More details are welcome.  I suggest that any other plating questions be posted in the Materials Engineers Paint/coatings engineering Forum Forum332.
Ken

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