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topic 0619

Electroless copper as a heat treat stop-off

A discussion started in 1996 but continuing through 2019


Q. Has anyone ever used electroless copper as an effective heat treatment stop-off maskant for either nitride or carburize?

Blair Smith
aerospace - Windsor Locks, Connecticut

affil. link
Electroless Copper and Nickel-Phosphorous Plating
from Abe Books



? Hi, Blair: An excellent question! But doesn't the copper have to be reasonably thick for it to work? Is there a thickness spec governing this? Out of curiosity, why would you prefer an electroless maskant?

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha


Q. Dear Ted:

Yes, typically the copper thickness must be .0007 to .001 inches thick. The more dense the copper the thinner the deposit thickness required. I am not aware of any specification that governs what thickness the copper plate must be in order to prevent heat treat leakage.

The reason for potentially using an electroless copper maskant is twofold. First, very often the areas which require masking (to prevent heat treatment) are internal diameters which are difficult to plate (even with internal conforming anodes). Second, many of our parts have very tight tolerances and an electroless deposit would allow us to use a masked surface as a reference datum from which we could machine away plate from other features which require heat treatment.


Blair Smith [returning]
aerospace - Windsor Locks, Connecticut


A. Blair,
Semantics: copper does not prevent the heat treatment of steel, it prevents decarburization of the surface of a carbon steel in the hardening process.
Considering the cost of electroless versus modern copper solutions, particularly non cyanide ones, the economics is the cost of masking. Several years ago, my experience with copper from a job shop was poor. We ended up using a salt bath for hardening. Eliminated a number of problems on a complex geometry part. Decarb went to nearly zero.

James Watts
- Navarre, Florida

October 10, 2019

Q. Hello.
We are Boronizing 4140 steel parts and the customer wants the cylindrical end masked on 3" of the shaft! We used a water soluble "copper" stop off paste. After boriding, the parts needed to be quenched and tempered. We were told the quench and temper could not be done in a vacuum so the heat treater used no vacuum. We've tried everything to remove the stop off but it was extremely hard and left a pattern in the metal? Do you have a better idea? Thanks.

Jim Dedmon
- Arlington Texas, USA

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