Electropolishing Nitinol nickel-titanium alloy
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A discussion started in 1997 but continuing through 20192006
I'm apprentice engineer in materials and I have to perform electropolishing on very small and thin parts made of nitinol. I tried so many times to use the 20% H2SO4 & 80% methanol but it doesn't go well.
I heard that electropolishing can be done in acid-free solution, low voltage. Can someone help me or give me some advices concerning cathode, electrolyte and conditions of the experiments (current density, temperatures or else).
Thank you so much,
student - Haifa, Israel
Q. We have been electro-polishing nitinol components and have been observing surface issues. The source of the parts have very small depressions that are smooth. It almost appears like those spots were more polished than the rest of the surface. We remove all oxide from the parts before polishing using an aluminum oxide micro blasting process. Could there be some interaction with the aluminum oxide with the polishing electrolyte solution?
Any help would be appreciated.
Medical device mfgr - Woburn, Massachusetts
A. We do not think that these spots are caused by interaction of Aluminum Oxide with the surface. It looks like pitting, which is caused by changes in electrolyte composition or electropolishing regimes, or by wrong oxide removal procedure. If electrolyte contains methanol, composition of such electrolyte should be very strictly maintained.
In our methanol-free, acid-free electrolyte for electropolishing nitinol stents we never have pitting problems, and we do not need strict electrolyte composition and polishing regimes maintenance. Contact us if interested.
Electropolishing of NiTiAu2007
about use of
The internet is a giant one-room schoolhouse where people may read or overhear details about operations that they are NOT equipped or qualified to attempt. Specifics you read here may be intended for qualified chemists with haz-mat training, and working in fully equipped labs.
Q. Dear all,
I am currently looking for a suitable electropolishing solution for the ternary shape-memory alloys TiNiAu in order to have a thinned sample for electron microscopy.
I already tried several solutions that are known to work well with TiNi. Unfortunately, the added gold at a concentration around 15 at% seems to severely hamper the electro-polishing: the same conditions as for Ni-Ti give etched specimens with bad edges of the hole.
We've played with tension, temperature, fluid speed,etc.. but without success.
Solutions tried that work with NiTi but not with my sample:
80% methanol + 20% sulphuric acid (-17°C)
93% acetic acid + 7% perchloric acid (5°C)
93% methanol + 7% perchloric acid (-10°C)
75% methanol + 25% nitric acid (-22°C)
I already looked up in the literature and couldn't find anything close from my alloy. So I was wondering if you might have a suggestion of an alternative, eg, adding an extra acid to one of the above baths or maybe something completely different.
Many thanks in advance,
EMAT - Electron Microscopy for Material Science - University of Antwerp, Belgium
PhD Student - Antwerp, Belgium
December 7, 2009
A. I am polishing (Electropolishing) NiTi with high surface finish and have been doing for last three years.
Use the following recipe
90% metahnol and 10% perchloric acid solution.
Temp of polishing 0 °C.
18 Volts for 20 secs.
Before Electropolishing, manual polishing followed by diamond polishing
Try it and let me know if it works
- IIT Bombay , Mumbai , INDIA
Spec for Electropolishing Nitinol?July 14, 2010
Q. Is there an ASTM standard for electropolishing titanium alloys? (Nitinol) to be specific?Dan Rue
QA Manager - Brooklyn Park, Minnesota, USA
April 27, 2011
Q. I am getting up to speed on electropolishing and wondering if anyone can provide (or point me toward) the specific chemical equations for what is actually happening (dissolution of metal at anode, oxide layer formation, side reactions, etc.).Benjamin Seim
Engineer - Minneapolis, Minnesota, USA
How to clean and electropolish wire-knitted nitinol stentsJanuary 20, 2011
Q. I came across some discussion on Web that nitinol stents made from knitted wire, cannot be cleaned and electropolished. Is this correct? Any suggestions?Will Serv
product designer - Duram, North Carolina
January 20, 2011
? What reasons were given. While it may be difficult, I think that it can be done. The electropolish may take a lab quality setup to do it. There may be medical reasons why it is not done.James Watts
- Navarre, Florida
January 21, 2011
Q. The person that does outsourcing for nitinol stents electropolishing claims that it is difficult to electropolish areas between tightly knitted areas. There always be spots not polished where wire touches another wire.Will Serv [returning]
product designer - Duram, North Carolina
January 26, 2011
A. The wire stents can be perfectly electropolished by Ultra-Polishing method. Even the surface of contacts is shiny without holder-marks. This is an effect of Ultra-Polishing, which differs from regular electropolishing.
Process of ultra polishingJuly 15, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. I would like to have details of the process of 'Ultra polishing' of surgical instruments of SS grade 410/420. How do I undertake this process? Would also appreciate response from people carrying out this process in Mumbai. Of late some of our customers have been complaining of rust in instruments like scissors, artery forceps & some other types of forceps.Varsha Shetty
- Navi Mumbai
July 16, 2015
There are different ways to make ss alloy 410 or ss alloy 420 corrosion resistant after numerous sterilization processes.
adv. One way is to electropolish in Universal electrolyte. Our tests indicate that electropolished by UA surface of stainless alloy 400-series withstand even impact of diluted hydrochloric acid for 10 minutes (normally 400-ss does not stand impact of diluted HCl) . We have licensed our UE to various medical companies all over the world. Sorry we do not have any division in Mumbai.
Another way is to plasma electropolish instruments. Plasma can be of high voltage and of low voltage original This is more expensive method for mass production. We use it only for high-yield products or for parts that require sharpening while electropolishing.
March 16, 2017
Q. Give me the methods of electropolishing of nitinol stent and heart valve to make surface area clean and smooth. And give the proper parameters of EP. We have the parameters but from that we have not getting proper result so please kindly provide me best parameter.dheeraj mishra
Metal to contact NiTi-anode during electropolishingOctober 26, 2017
Q. Hello everybody,
I'm doing my student research project on electropolishing small NiTi structures. I have several electrolytes like sulfuric acid + methanol. As cathode I use stainless steel.
Can someone recommend a metal to me, which is suitable to contact the NiTi workpiece? (The metal is going to be in touch with the electrolyte as well)
- Germany, Stuttgart
A. Hi Matthias. Bare copper rack tips are often used in installations for stainless steel electropolishing, and I'm not immediately seeing any particular reason they cannot be used for electropolishing NiTi in a sulphuric + methanol solution. Except for the exposed racking tips, the rest of the device should probably be made of copper but plastisol coated. Good luck.
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha
June 4, 2019
Q. Hi I'm currently working on an electropolishing station for a nitinol implant. I'm using an ethylene glycol solution with a 2% concentration of sulfuric acid and 1 mol of salt, all of the substances reagent grade.
Right now I'm using a stainless steel mesh and platinum coated tweezers as anode and cathode -- are those materials okay?
I'm running at a temp of 20 °C; should I go colder?
For power settings I'm using an amp control with adaptive voltage, should it be the other way around?
Thanks in advance!
- Salt Lake City, Utah, USA
November 18, 2019
A. Hi Juan, I missed this post back in June.
Nitinol (NiTi) stents electropolishing is not as easy as electropolishing stainless steel stents. If you go with traditional methanol-containing solutions, you have either to invest in special expensive equipment that maintains strict temperature and concentration control, plus prevents harm to you, especially to eyes or
you can buy the safe process from the company who licenses and teaches how to use their proprietary technologies to the medical cutting shops.
Contact us directly.
Racking for Electropolishing Nitinol Medical DevicesNovember 22, 2019
Q. Good day everyone! I'm manufacturing engineer at a small company for implantable medical devices. We're improving our electropolishing process as best as we can, but I find that we're getting "clip marks" from using reverse action tweezers on our metals (Nitinol mostly). Does anyone have advice for a better fixturing method / clipping device that doesn't give us this under-polished surface where the tweezers lie.Nicole Jones
- New Jersey, USA
December 4, 2019
If you are using a proprietary EP solution, check with the manufacturer for a recommended material.
If a home-brew, consider copper or copper based alloys.
Maybe post a picture or sketch of the contact area(s) for possible design recommendations.
- Green Mountain Falls, Colorado