Hydrogen embrittlement of brass

A. You should check the ductility of your nickel solution. A good bright nickel solution should have a ductility of 0.1-0.3 depending on the age of the solution and the type of brighteners. What type of nickel solution are you using? Additive free nickel solutions like sulfamate should have a ductility of 0.5. Ductility is inversely proportional to brightness.

A. Mr. Hughes: I agree with George's opinion. Your problem sounds more like a problem in your plate causing a physical phenomena called "notch fracture", meaning that the plate is cracking first, then the crack is forming a weak leading edge which is propagating to the inner substrate. I don't have any information that brass could be embrittled by H+. In this respect I would also like to hear from others.

A. Hi Kjell,

We electroless nickel plate (.0002"-4" thick) 360 brass sleeves all the time and one of our adhesion tests require us to crush with pliers approx. 50 sleeves per lot plated. When unplated parts are subjected to this test the brass sleeve flattens with minor cracks, however after plating the samples always brake into four pieces. At this point I would assume that the sleeves are subject to some hydrogen embrittlement. The sleeve is .350" O.D. x .275" long with a wall thickness of .050" so I don't think the plating thickness is a factor.

I hope I have been of some help and perhaps others with more experience can add more insight into this phenomena.

A. My guess is the preplate processing that is causing the problem.

A. Hi Paul,

Conventional opinion is that hydrogen embrittlement of such material doesn't happen. Your experience is a strong challenge to that, and certainly warrants following up. As the most basic preliminary question, do you expose the sleeves to heat at any time before or after plating? If so, what happens if you expose unplated sleeves to the same heat cycle then crush them?

A. Hi James & Bill,
Sorry for the delay but I wanted to run some casual tests to further confirm my assumption about HE in 360 brass.

1) James you are right about the preplate cycle, it does induce approx. 20-25% embrittlement. The plating bath contributes the rest. (Numbers are subjective as I am using pliers.)
2) Bill, the highest temp. the parts are exposed to is 190 °F in the plating bath. Cleaner, about 160-170 °F. We ran a test, enclosing a sample lot in a heat sealed polypro bag, clamped to the barrel to expose the parts to the thermal cycle with no exposure to chemicals. No effect was noticed on the parts.
3)Baked the parts removed from barrel after precleaning and prior to plating at 375 °F 3.25 hrs. Parts returned to preprocess ductility. (Our normal bake is 250 °F) I have not had time to relief bake plated parts but will do so today.

If either of you would like some samples of each test (Bare, Precleaned-unplated, precleaned & baked, plated, plated and baked) please feel free to contact me.

I was always led to believe HE was associated with high carbon until I ran into this phenomenon. I hope someone with better instrumentation can pick up the ball from here. I will help in any manner I can, to the best of my ability.

Kjell, I hope this information is of some help.

A. Paul,

Parts did not return to normal after baking @ 375 °F 3-1/2 hrs. After extensive research it was determined that the breaking was due to the E/N plating, and not HE.

Hi. I'm no metallurgist, but as a layman I've heard that, exactly opposite to the way steel hardens if quenched but stays soft if very slowly cooled, copper & brass harden if slowly cooled but stay annealed if quenched. Hopefully a metallurgist can flesh out my understanding or correct my misunderstanding :-)

Regards,

A. Good day John.

From what I am reading, it is clearly an adhesion issue. What is the composition of the brass? Does it contain lead,and if so, an acid dip with fluoboric will deal with the lead, as it is insoluble. Is the brass electrocleaned anodically or cathodically? A loaded cleaner operated cathodically can deposit impurities to the surface of the brass. An electrocleaner operated anodically can produce oxides on the surface which can cause adhesion issues.
I use an acid dip @ 10% sulfuric with bifluoride to remove any "smut/oxides" produced either anodically/cathodically electrocleaned.
Regarding the nickel plating, excess brighteners can cause adhesion issues, as high TOC values. Has there been a analysis done on Total Organic Carbon? Has there been any hull cell testing to determine LCD coverage? What are the sulphate and chloride concentrations? I think baking parts will show adhesion issues.
I bake SS parts (head light bulb shields) @ 650 °F for 2 hrs that are plated semi bright nickel, bright nickel, chrome (micro cracked) to determine adhesion failures,and rarely discover any.
Hope this helps.

Regards,