Etching Alloy 625 1

[tensilecvn]

Hi All,

I am having issues trying to etch an Alloy 625 sample in the laboratory (sample from a 1.25" Dia bar). The structure reveals quite a lot of what i believe is banding of carbides. I am not sure if this is detrimental or beneficial, as we have good tensile results and a pass on a G28 corrosion test.
The issue is when we etch the micro, we cannnot resolve the grain boudaries clearly. The certificate from the supplying mill contains photos with the grain boundaries clearly visible (along with the banding we are seeing), but does not detail the etchant used.

Our laboratory informas me they have tried several times to re-polish and etch, and we have also removed other samples from the parent material but the same issue occurs.

Any advice or suggestions would be greatly appreciated

Thanks

 

[metengr]

Either contact the supply mill requesting the etchant information or contact Special Metals. The technical support at Special Metals is excellent and will help you.

Or

thread330-333389

Or

http://www.tms.org/superalloys/10.7449/1994/Superalloys_1994_489_498.pdf

 

[EdStainless]

This is why many of us own books (you know, paper) on metallographic etching. You can't remember them all.

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P.E. Metallurgy, Plymouth Tube

 

[tensilecvn]

Thanks guys.

We have tried the normal etchants we use to no avail.

I have found a couple more exotic etchants which we will try. Failing that, we will contact the mill for the inforamtion and try to replicate in-house

 

[EdStainless]

Have you tried an aggressive oxalic acid electro-etch?

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P.E. Metallurgy, Plymouth Tube

 

[tensilecvn]

Thanks Edstainless

That did the trick

 

[SMF1964]

I've had good luck with 10% Oxalic Acid, but something odd tends to deposit on the polished surface, a crystalline deposit of some sort. Using a plastic "miniature turkey baster" to keep the solution flowing on the surface keeps it from building up and messing up the etch.

Mixed Acids etch (my old lab tech used to call it "#89") - Acetic, HCl and Nitric with a drop or two of glycerine and allow to "mellow for 5-10 minutes, swab and neutralize/dispose of when done (it does not store) also works well.