Nital Etching Beryllium Copper

[mtharp]

I’m designing a part made from Beryllium Copper (AMS 4533) which will come to the machinist already in the precipitation hardened condition (AT temper). Because it will be hardened when it is machined (approx 180 ksi) would it be wise to perform an NDT to detect and machining abuse?

I know steels can be nital etched to reveal local heat affected zones. Is there a similar process for beryllium copper?

Also, is there a recommended post machine stress relieve heat treat cycle for this material?

 

[tbuelna]

mtharp,

Nital (temper etch inspection) is used to check for local de-tempering usually caused by excess heat generation in the part during grinding operations. The only time I've seen Nital etch required is when there is grinding of case hardened steel parts (ie. gear teeth or bearing journals). The Nital etching uses a nitric acid solution which would result in highly adverse reactions with the copper content of your BeCu alloy, so it's probably not suitable. I wouldn't expect that a nital etch is necessary in your case since BeCu has a high thermal conductivity, so it would be unlikely that normal machining operations would cause heat related problems.

You should finish machine your BeCu alloy in the PH and age hardened condition, since that will give the best finish. If you are removing lots of material from the stock size, you might want to rough machine, stress relieve and heat treat prior to final machining, since some BeCu alloys do tend to work harden.

BeCu heat treat and machining guidelines:

http://www.brushwellman.com/alloy/tech_lit/EG-Machining.pdf

http://www.brushwellman.com/alloy/tech_lit/EG-Heat Treatment.pdf

Good luck.
Terry

 

[mtharp]

tbuelna,

Thanks for the input. I've already looked through the brushwellman site as well as others and I couldn't find any literature on inspecting for heat affected zones on post machined BeCu. I am not going to worry about it.

Thanks again.