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Etching of Forged Cobalt-Chromium-Molybdenum Alloy

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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

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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

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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, Massachusetts

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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.

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February 1, 2008

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

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December 30, 2010

Hi, I'm Mas Ayu, currently student in Universiti teknologi malaysia. I looking on how to etching CoCrMo for my studies. hope everyone can help me. TQ

Mas Ayu Hassan
Student - Johor, MAlaysia

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December 7, 2011

Hi, my friend
I have a research project about fsx-414 cobalt based superalloy. I have some specimens. One of them is fsx-414 that I can etch with 92%H2SO4-5%HCl-3%HNO3. But I can't etch another specimen that is:
1. fsx-414 solution anneal
2. fsx-414 solution anneal and aged in 800
3. fsx-414 solution anneal and aged in 900
4. fsx-414 solution anneal and aged in 1000 centigrade
I try a lot of etchants that can't etch them, so if you know a good etchant and method for etching them please help me.

Mohammad Najafi Birgani
- Ahvaz, Iran