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Etching of Forged Cobalt-Chromium-Molybdenum Alloy [Turkey] 

February 21, 2007

I am currently conducting a research about plasma nitriding of forged CoCrMo alloy (Low carbon). I have to etch the treated specimens in order to observe the microstructure of the alloy. The etchants should reveal the grains but not harm the compound and/or diffusion layer. I have tried;
1. 97%H2O2 + 3%HCl
2. 50%H2O2 + 50%H2O2
3. 75%HCl + 25% Nitric Acid
4. Pure HCl
and I have heated the specimens (about 80 deg. cel.), heated the etchants etc. so far. But none of these methods/etchants worked out for me. Unfortunately electroetching is not an option since I don't have the required system nor time. I would appreciate your suggestions. Thanks in advance.

Ozgu Bayrak
Ataturk University - Erzurum, TURKEY

I´m doing and researching for new etchants for Co-Cr-Mo-C alloys, none of those availables on the literature seems to work out for me neither but, I tried 100ml H2O2+50ml HCl, to reveal the macrostructure the time was aprox. 10 hours or so, others authors used the same etchant but in an 6:1 HCl+H2O2 for 8 seconds, didn´t work for me.

Try to get this paper "Selection methods for etching carbides in MAR-M509 co-base superalloy and acquisition of their images" Materials characterization, 56 (2006) pp325-335. Other etchant: 1.5g CuCl2+33ml H2O+ 33ml HCl+ 33ml ethanol Another one: two stages etching SOLUTION A: 21ml H2SO4+15ml HCl+21ml HNO3+21ml HF+22ml H2O SOLUTION B: 40ml of solution of 1gCuCl2.2H2O + 5ml H2O+40ml HCl+ 20ml HF 5minutes in solution A and then 5 minutes in solution B but times can vary you should try your own (Vander Voort book), if neither of them seems to work out let me know, I´ll send you another etchants, or at least try to. Jessica Giacchi - Tandil, Buenos Aires, Argentina

Hi
Try this etchant:
15 ml HNO3+ 15 ml acetic acid + 60 ml HCl + 15 ml H20
I have successfully etched with HC Co-Cr-Mo alloy but u can also try for LC and see how it works. In my secimens the grains of the matrix etch and the carbides are not affected. I would love to know if you find an etchant that etches grain boundaries- it would be convinient.
Most researchers try electroplatting but I understand how cumbersome it can be. Good luck and let me know if you come up with any success with this or something else.

Sudesna Roy
Researcher - Boston, MA

I recently had success with another etchant
6:1 HCl -H2O2
it is a good one etches the grain boundary.
again I tried it with HC alloy.
See how it works for your alloy.

Sudesna Roy
- Boston, MA, U.S.A.

We want to develop the uniform Microporous structure by etching prior to drug coating on L 605 cobalt chromium tungston alloy,we are using the fecl3 solution as a etchent.

Abhishek Masalawala
product designer - Surat, Gujarat, India