The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Removal of thermal spray coatings (WC-Co) from Steel plate

I have a sample made of steel and have 2 layers of coating on it, the first one that is coated on steel is Zinc plate and on top of the zinc is the thermal spray coating materials of WC-Co.
I would like to know the best method to remove WC-Co from Zinc plate and the process must not induce any chemical reaction or damage to WC-Co , so that I can have a stand alone coating ( WC-Co ) after the procedure ?

Roaidi
Aircraft Engines - Shah Alam , Malaysia
2006

Most chemicals that attack or dissolve iron, also attack cobalt though at a lower rate. As I see it, your only chance would be to try to take advantage of the intrinsic porous nature of the sprayed coat and try to dissolve the intermediate zinc layer by use of a strong alkaline such as sodium or potassium hydroxide (no effect on steel or cobalt) coming in from the porous side. By the way, it surprises me to know you really got a good adhesion of the sprayed carbide over a zinc plated metal. Most manufacturers disregard it as a good surface to coat on. What method did you use, plasma, HVOF, a conventional oxygas gun? Have you tried inserting a sharp knife in between?

Guillermo Marrufo
Monterrey, NL, Mexico
2006

---

It has been stated at this site a few hundred times, that you may not come up with new methods that have not been approved by the engine OEM or you must have an internationally recognized engineering facility to test and prove your new method.
Zinc can be stripped by nearly any acid while the Cobalt matrix is relatively unaffected by most dilute acids other than nitric acid.

James Watts
- Navarre, Florida
2006