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Plating as a maskant for nitride

We selectively gas nitride stainless steels and use electroless nickel plating as a maskant. We have had some problems with "leakage" of nitride through the nickel plating. Does anyone out there have experience with using platings as a maskant for gas nitriding?

What platings would you use as a maskant for gas nitride?

What thickness of plating?

Do you believe nitrogen atoms can diffuse through electroless nickel plating?

I have other questions on this subject so if there is someone out there who can help I would like to talk to you.

George Tompsett
1998

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George,

You did not specify the thickness of EN that you used. It has been a while, but I believe that EN is considered to have some pores up to about 1.5 thou thickness. The closer, the less gets thru it. Jim

James Watts
- Navarre, Florida
1997

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1997

George,

Its true that eless Ni is quite porous, the N may get through. If you can, after your electroless layer is down, pulse plate some Sulfamate Ni over it. That will close off the pores. You can pulse large grains for reduced grain boundary diffusion as well. I am assuming that this is allowed in your process sequence.

Regards,
Dave

Dave Kinghorn
Chemical Engineer
SUNNYvale, California

We have used tin as a stop off for nitriding, I think it was specified via a Rolls Royce aero engine spec.

Richard Guise
- Lowestoft, U.K.
1997

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We apply electroless nickel to a thickness of .001-.0015" thick.

George Tompsett
1997

Copper plating is the most common maskant for nitriding.

Thomas Scott
- Aerospace/Defense Coatings
1999

When nitriding aircraft crankshafts it is common practice to plate the flanged area where the prop mounts to mask it from nitriding. It is then dipped in heated oil to reflow the tin plating thus brightening it again as the surface is tarnished from the nitriding process.

Greg Gillespie
- San Antonio, Texas
2007