Mar Aging 300 Pitting and corrosion from copper stripping

[mfgenggear]

I need some help.

Received a batch of parts from our Heat Treat supplier.
Parts where selective copper plated, & 2-stage nitride,
copper stripped in ammonium hydroxide solution , then post baked .
brief outline some steps omitted.

#1) Parts are badly pitted, see attached pic.
what is the cause of the pitting?

#2) I researched this and it seems the stripper can attack
the parent material. if the conditions are so.

can someone please explain to me in detail what causes this.
And how can it be prevented?

Thanks in Advance

 

[unclesyd]

I have Cu plated or had Cu plated literally thousands of parts from carbon steel to tool steel and have never seen anything like this. I've seen all manner of things go wrong with nitriding, again nothing like this. I haven't done any Mar 300.
It looks like it took the whole nitrided layer.
This looks like corrosion that you would get if the part was left in an acid bath for an extended period of time.

How was the part precleaned prior to the Cu plating?

Which Cu plating process was used?

After the Ammonium Hydroxide was an acid dip used?

Do the pits have sharp edges or are they relatively smooth?

Until this problem is resolved you might want to look at the different nitriding stop offs on the market. Here is good one from Duffy.

http://www.duffycompany.com/Condursal_N523.htm

 

[EdStainless]

I agree with Syd, it looks like they screwed up the stripping big time. Though this might relate to the surface prep before plating.
Find another stop off.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[mfgenggear]

The parts should have been solvent cleaned then aluminum oxide blasted prior to Nitride.
Then selective copper plated.

After nitride the parts where phosphoric acid etched to
remove the white layer from Nitride.

Then where verified for white layer removal with a copper sulfate solution. if white layer is still present
no copper will adhere to the nitrided surface.

Then stripped, neutralized & cleaned

The vendor was proposing that it was bad copper plating.
Therefore there was phosphoric acid leakage in between or through the copper.

I believe the parts sat in the Ammonium Hydroxide because the bore has severe pitting localized in at 12 o’clock approximately 25-30 % of that quadrant & "the outside dia you saw from my pic" is at 6 o'clock, at the same direction but opposite of the inside bore
I believe the inside bore is where it was located during
stripping thus the worst localized pitting

is this scenario plausible, the worst pitting occurs because that's where it’s been located from.

 

[unclesyd]

I'm searching the windmills of my mind.

I believe that the H3PO4 might be the culprit. For your type damage the acid would have to have been hot.

Did they add Hydrogen Peroxide to the Ammonium Hydroxide solution to speed up the the Cu stripping process?

 

[mfgenggear]

unclesyd

I will have to investigate the actual solution if my supplier will give it up

I want to apologies for asking for comments on some my post.

That said let me say I not looking for a solution from this board, what I needed was some guide as the approach to resolve the cause & what the corrective action should be.

Some suggested different stop off median. I was kind of
Interested if any one has had this problem and how they resolved it. OK i was hoping some one could say exactly why it happened or lead me the right direction.