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topic 47682

Electropolishing and Chemical Etching Processes for Cobalt Chromium

A discussion started in 2002 but continuing through 2019


Q. I am currently undertaking research investigating the use of electropolishing (used in CoCr metal denture manufacture) in enhancing the fit of ceramometal copings or substructures (Porcelain Fused to Metal substructures) after they have been subjected to extra expansion during the investing stage before casting the wax patterns in wilceram metal. Any information on like or similar research or related information on electropolishing will be deeply appreciated.

Tassy Pillay
- Umhlatuzana, Durban, South Africa

affil. link
"Electroplating Engineering Handbook"
by Larry Durney
from Abe Books
info on Amazon

A. Hi Tassy.

Although I am not personally familiar with the specifics of electropolishing of CoCr alloys compared to other alloys, the Electroplating Engineering Handbook =>
has an excellent 20+ page chapter on Electropolishing which explains both the whys and the hows of the process.

Metal Finishing Information Service / Finishing Publications Ltd. in Stevenage, Herts, England has a specialty computerized literature search database for the metal finishing industry which can be accessed online, or is available on CD; they also can perform the literature search for you if you prefer.

Metal Coating Process Corp. is a specialist in electropolishing chemicals, training programs, and consulting, and can surely help you.

Good luck.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha


Q. Dear Sir,
I need a solution to electropolishing a Co-Cr alloy (51:20 chemistry value). A Glycol, Sulfuric Acid, HCl has been suggested, however does anyone know of any other suitable solutions and or more suitable ratio of given chemicals.
Which glycol is more suitable?
Can you guide me for sources?

Thanks in advance. Regards, Devesh

Devesh Kothwala-


Q. I need to know a couple of pieces of information about electropolishing. First can CoCr be electropolished and if so what kind of bath is needed. Secondly we currently electropolish stainless steel, if we put the CoCr in the same bath will there be any contamination between the parts? This is a big issue due to the customer we deal with. If you have any information about this situation please let me know.

Scott Hawkins
medical instruments - Dayton, Ohio

A. Hi Devesh. Again, I don't know the idiosyncrasies of Cobalt Chromium alloys, but there is an old U.S. Patent, No. 2,607,772 which explains a sulfuric-glycolic mix for electropolishing stainless steel which may be applicable for you:
I believe that a local plating process distributor may be able to offer you a proven proprietary. Alternately you may wish to contact an electropolishing specialist which offer training, seminars, and specialized chemistry.

Hi Scott. Surely Cobalt Chromium alloys can be electropolished. Obviously your second question about cross contamination is difficult to answer conclusively but considering the mechanism and polarity of the operation, I wouldn't foresee any contamination in the electropolishing step per se.

Best of luck.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

Does electropolishing of Cr-Co dentures effect the thickness, and how?


Q. I'm studying dental technology and would like to know more to have less errors.

Nancy Almustafa
student- Jordan

A. Hi Nancy. Electropolishing selectively dissolves the asperities because the highest current density is there. If the surface was reasonably smooth before electropolishing, I think very little metal needs to be consumed to achieve the smoothing. Here's what Dean Ward had to say about that in the Electroplating Engineering Handbook:



Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

Post cleaning of Co-Cr alloy type L605


Q. Hello

I am working with a Co-Cr alloy, L605, which contains 15% Tungsten. After welding process of the alloy, followed by electropolishing treatment, I receive impurities with mushroom shape (approx. 5 µm size) on the surface of my alloy. I tried to remove it by Chemical etch, mechanical polishing, ultrasound, sandblasting, nothing was helping.

I would really like to have advice on what I should do? I think thermal treat can help, but don't know what temperature and time.

I will appreciate any help.
Thank you,

Shlomit Chapel
microprocessors - Italy


A. The possible cause of this problem is bad preparation of the surface before electropolishing. After welding there were developed oxide layers of different thickness. In locations where oxide layer thickness is max (and oxide does not conduct electrical current), electropolishing does not take place, but electropolishing does go on around such locations. That is why you see creation of the mushroom shape.
You need to add etching step after welding and before electropolishing.

Anna Berkovich
Russamer Lab
supporting advertiser 
Pittsburgh, Pennsylvania 
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thumbs up signThank you!

Shlomit Chapel [returning]
microprocessors - Italy

Etching solution for Co-Cr L605 Alloy

January 30, 2008

Q. Our company manufactures medical devices, coronary stents.
Now presently I am looking for stent Descaling Process (to remove the metal oxide created after Laser Cutting), Annealing (to refine the grain size, hardness and elongation), Electropolishing (for bright & rounded edges) and Etching (To develop the microporosity on the stent surface) processes for chromium cobalt L605 alloy.

Regarding Descaling, Annealing, Electropolishing, I have validated all processes as per our application but after polishing we need to do etching. Here I want to do microporous development after etching on the stent surface but so far I cannot achieve.

I had taken different composition of HCl, H2SO4, and DI water with different times & temperatures, and also FeCl3 10% 20% 30% 45% solution and given various times and temperatures but I cannot develop microporosity on the stent surface.

Please give me suggestion what can I do for further?



Bhavesh Pastagia
- Surat, Gujarat, India

February 25, 2008

A. Hello,

Use an electrolytic etchant (10%, 2 sec, 3 mv) such as: oxalic, phosphoric, etc.

Jose Castellanos
- Minneapolis, Minnesota, USA

May 21, 2013

Q. Dear Sir,

I have found crack problem in Co-Cr L605 metal in coronary stents after Electropolishing, I have reduced laser power during cutting, variable focal points, gas pressure, but not reduced this crack problem in coronary stents.


Brijesh Ranoliya
- Surat, Gujarat, india

May 28, 2013

Russamer Lab licenses electropolishing of the Cobalt Co-Cr stents to interested companies. Contact us for testing samples arrangements.

Anna Berkovich
Russamer Lab
supporting advertiser 
Pittsburgh, Pennsylvania 
russamer labs banner

What solutions to use to Electropolish Co-Cr Alloy (L605)


Q. Hi!

Could you share your Co-Cr electropolishing solution recipe here?


Adam Pietruszko
- Warsaw, Poland


Q. Hello, I'm doing a M.S. thesis work on electropolishing Co-Cr alloy L605. I hope this question hasn't been asked yet. I don't know what solutions to use to EP L605. I read through the standard guide for electrolytic polishing of metallographic specimens by ASTM. It indicated a couple of acids that are used for SS, and other metals. But I was unable to find a specific acid for Co-Cr alloy L605. What are the appropriate solutions that I should be using to EP L605. Can I still use the solutions indicated with SS 316L and still have the same effect for L605?

Hokuto Aihara
San Jose State University - San Jose, California, USA

August 18, 2010

Q. Hi, I have the same question. I have looked and spoken to many people, but no one has been willing to help in this regard. Most people say it is proprietary and leave it at that. I also wanted to know what metal is generally used for the Cathode? Any feedback would be greatly appreciated.

Iain Kemp
- South Africa

December 4, 2013

A. Most electrolytes for Cr Co alloys are composed of:

85% EF 200 Ethylene Glycol,
10& Sulfuric Acid,
5% Hydrochloric acid. Brilliant Shine. Some corrosive fumes.
(The hydrochloric acid can be optional).


85% EF 200,
15% Phosphoric acid (Shine varies from Brilliant to mat)

This particular formula has good effect on most CrCo alloys and has a 70 year history in industry.

Bruce Dean
Technical Product Manufacturer - Central Point, Oregon, USA

Electropolishing Solution for Platinum Chromium stents?

May 12, 2011

Q. I am currently involved in research and development of platinum chromium coronary stent. Can you suggest which acids and chemicals are involved in Descaling (Acid pre-cleaning process) and Electro-Polishing Process?

We are already engaged with Co-Cr l605 and SS 316L coronary stents.

I certainly appreciate your fast help.

Looking forward to hearing from you.


Bhavesh Pastagia
Manufacturing Cardiovascular coronary stents & support devices - Surat, Gujarat, India

April 1, 2014

Q. In electropolishing CoCr, why not use Co in anodic and cathodic chemical reaction?

kinjal patel
- Ahmedabad,Gujarat, India

April 3, 2014

Hi Kinjal. Sorry, I don't understand you. Do you mean: "why not use Cobalt cathodes?" Please explain your situation. Thanks.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

Cathode and racking material for electropolishing of CoCr alloy?

April 18, 2014

Hello Sir,
I want to do electropolishing of CoCr L605 material.
Will you please suggest me the Material for Anode and Cathode?

Sanjay Patel
- Gandhinagar,Gujarat and India

May 3, 2014

A. Final finishing of Co-Cr stents faces the following challenges:

1. The surface must not be saturated by hydrogen, in order to prevent embrittlement;

2. Since Co-Cr stents are usually very thin, special holder design is required to distribute electrical current evenly;

3. Depending on the alloy composition there may be various hard-to remove molybdenum or other carbides, that do not disappear during electropolishing.

We work with cobalt-chrome material for almost 15 years, mostly with knee implants.

Our ultrapolishing method allows to remove all of the peaks of hard-to-remove carbides. However for such delicate stents the ultrapolishing method does not work.

Recently we developed two-step processing. During the first step the surface is smooth electrochemically --

(image of the stent)

The second step dissolves all carbides on the stent surface.

(SEM image)

Anna Berkovich
Russamer Lab
supporting advertiser 
Pittsburgh, Pennsylvania 
russamer labs banner


December 13, 2014

Q. I want to know etching solution composition for CoCr L605 Material.
Can you describe it?

Dhaval Kapadia
- surat, gujarat, india

December 16, 2014

Q. What is chemical etchant for Co-Cr alloy L605? Which electrolytes can be used for above?

shrikant thorat
- pune, india

December, 2014

A. Hi Dhavel; Hi, Shrikant.
Jose and Bruce already answered in very good detail. Have you tried their suggestions? Can you phrase your question in terms of the previously posted answer to keep this interesting dialog moving forward? Repeating a question which has already been answered can be the kiss of death to a thread :-)

Thanks & Regards,

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

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