Stripping HVOF Nickel Bound

[SSC]

Hey all,

I am currently knee deep (turn of phrase) in learning to strip HVOF sprayed WcCoCr from various parts and substrates using an Electrolytic Rochelle Method. It's going quite well.

Just today I was asked if it would be possible to strip another Carbide spray however Nickel bound instead.

I'm positive the above mentioned method will not work, as it attacks the Cobalt contained in the afore mentioned powder.

So any suggestions as far as a chemical bath I could use?

[Gordon]

Hi SSC

See here
http://www.gordonengland.co.uk/sef/Threa...-V-coating

[SSC]

Thanks so much for the reply Gordon,

In waiting for a response I decided to see what effect a Rochelle salts bath would actually have. I assumed none, however I was incorrect. The Rochelle salts / Soda Ash electrolytic method worked wonders. It actually stripped the coating faster than it did with the WcCrCo. Not sure the science on how it worked but it did.

[Gordon]

Hi SSC

Thanks for feedback, good to know. What substrates are you using?

[SSC]

In this particular case 4140.

The stripping did eat away some of the substrate, but very minimal from what I could see.

[MichiganMan]

Not sure the science on how it worked but it did.

I'm no expert on this particular topic, but I believe the reason it works is that the same type of redox reaction that occurs with the cobalt takes place with the nickel binder in the other coating. I think what is going on chemically (in simplified reactions) is Co(s)->Co2+(aq) and in the case of the Nickel it would be Ni(s)->Ni2+(aq). This method should work well to remove most of the common coatings that can be applied (as far as the chemical mechanism is concerned). I would expect that the biggest issues that could pop up are what the extent of damage to the substrate piece will be, and is there a potential for a replacement reaction from the salts and metals to produce a solid bound to the substrate that would not be easily removed. You may occasionally encounter a coating that is more resistant to the oxidation reaction, but I'd expect that to be a pretty infrequent occurrance. You may also need to be careful in subsequent surface preparation if the reaction can produce hygroscopic bi-products, because any trapped under a coating applied later would draw moisture down the the surface and cause corrosion/premature failure.

[FWisniewski]

I was wondering if using Rochelle salts would have any effect on Chrom plating?