Anodizing of titanium: Type II alkaline vs. Type I decorative?

A. See AMS 2488. The anodizing is performed in an alkaline solution of pH >= 13. Unlike anodizing of aluminum, the colour is not uniform and almost not controllable. Depending on the alloy (and solution?!), we are getting yellow to blue through grey appearance.
Max

! With titanium in a bath of trisodium phosphate ⇦ this on eBay or Amazon [affil links] you get the most beautiful color of blue imaginable. All you need to do is to immerse the part, turn on the current and voilà, bright blue. Not gray but close?

A. A true grey from TSP (trisodium phosphate ⇦ this on eBay or Amazon [affil links] ) is not probable.

Brown, blue, silver, yellow, purple and green are possible at voltages up to 200. There are several different shades possible for each. Precise color requires precise voltage control. It anodizes nearly instantly. Surface prep makes a significant difference in the luster or look of the product. Does not need any further protection after anodize.

From 10% to 3% solutions are recommended.

A. Hi David. Anodizing of aluminum is an utterly different process bearing virtually no similarity to anodizing of titanium. In aluminum anodizing the color comes from the application of dyes; whereas in titanium anodizing no pigments or dyes of any sort are involved, as is discussed further on. We have countless threads about anodizing of aluminum if you search the site, and you can get bright red dyes for aluminum. Luck & Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey

A. The color red is not possible with titanium anodizing nor is black. Apparently neither exists in the spectrum created by the oxide layer formed on the surface. The color exists only as reflected light.

A. Hi. Black is not possible from diffraction coloration, but somewhat red-ish or at least pink is possible on titanium -- some of these colors are low saturation pastels, not bright and vivid.

The anodized layer is actually translucent white, almost transparent, rather than any color. What happens is that when light hits the component, part of the light reflects off the top surface of the anodized coating, and some of it penetrates the coating and reflects off of the bottom surface of the coating and back through the coating again. The result is that the portion of light that travelled through the coating travels further and is out of sync and the two reflected waves "interfere", canceling out some of the colors from the white light, leaving these tones. Depending on what voltage was applied, the coating thickness varies, and thus the color. The term 'partial wavelength' is sometimes given to such coatings.

Regards,

adv.
We can produce and reproduce stable and controllable colors for titanium anodizing. Technology is ready for licensing.

You can see shades available on our web site. Black color can be obtained also, but this is a different technology.

A. Hi, Vicki. I know this sounds rather strange but ...
... even though the alkaline anodizing process is covered by that AMS spec, some of the details for successful alkaline anodizing are proprietary trade secret.

You have to either:
• send the parts to a shop which knows how to do it. Tiodize is the best known but there are several others,
• retain a consultant who will give the information to you, or
• figure out these details for yourself

Unfortunately, even though the process is loosely described in the AMS spec, you will not find the required details in published literature nor in public forums. Sorry, but there it is :-)

Regards,

A. I see several comments pertaining to Grade II Titanium and obtaining green color.

Grade II in volume on racks can be vexing.
A common defect is a failure to obtain even color.
Color can have a 'Ghosty" appearance when viewed inclined and under a bright light.

A coupon was anodized, resulting in an uneven green color. When measured, the oxide thickness is uniform over the coupon.

Theories are, a change while anodizing of the um/Volt applied, and/or the um/second.

According to theory, these changes result in an anodized layer of mixed Titanium Oxide of TiO2, TIO3----X

Another theory is a change in cubic structure; i.e., anatase to rutile.
I call it "The Grade II Blues".

A. Hello Fun. If you understand where the color comes from, as described above, you understand why pink is relatively easy and a bright red does not seem possible. However, James Watts suggests that surface preparation is very important; and it seems to me that if the surface is very highly polished and thus highly reflective before anodizing, you should get somewhat more vivid colors.

Regards,

A. Type II titanium anodizing will have uniform gray color. Some companies produce anodized parts covered by "fur" that requires additional removal step.

adv. We produce hard anti-galling coating clean and ready for use. There is a possibility to grow the coating very thick for application where dielectic surface is required.

The color anodizing is always thin, and can serve mostly for color coding. The uniformity and consistency of color anodizing depends only on initial surface activation. This step can be conducted either electroless or under electrical current in a separate tank. Both methods are fine. As soon as the titanium surface is ready, it does not matter what anodizing solution you select for the final coloring. It can be oxalic acid or sodium wolframat or similar solutions available from the vendors. Be sure to final rinse the colored parts in diluted alkali solution, in order to prevent colors fading.

A. Hi Penni. Jon Quirt has specifically discussed your particular problem of consistent green anodizing above and, although he doesn't offer an exact answer, he does offer food for thought.

Also, please see letter 7926, "Anodizing titanium to green color -- Q&A's". Good luck.

Regards,

Hi cousin Raju. Penni is standing in line immediately in front of you, also hoping for a prompt reply to a problem that you say you've already solved :-)
While we await an expert who can help you, can you please offer her some tips? Thanks!

Regards,

A. Grey type II anodizing for color or for hard surface quality -- these are completely two different processes.

Grey color can be obtained in sulfuric acid. This process is easy and fast. Customers for disposable medical parts are quite happy with such anodizing.

Grey hard titanium anodizing 2488 type II is more complicated, requires proprietary conditions. Some companies advertise their equipment and chemicals for hard titanium anodizing. However in reality they hardly produce reliable and repeatable coating on more than one titanium part.

Concerning green coloring - anodizing green goes on high voltage (starting 70V). In order to reach this voltage without gassing, titanium surface must be free of iron (from cutting tools), and must be heavy saturated by fluorides. Saturation can be conducted either by electroless method, or under electrical current is special proprietary solutions. Some titanium alloys are not prepared well for coloring by standard electroless methods, and require careful preparation in electrolytic bath. Such bath does both -- removes remaining iron, and loads titanium with fluorides.

adv. Contact us for more information.

A. Hola, la mayoria de los anodizadores de titanio utilizan soluciones acidas, pero nosotros estamos utilizando soluciones alcalinas, el color del anodizado es mas firme pero esta desfasado con cerca de d0s volts, por ejemplo para el azul con acido es de 18 volts, mientras que con solucion alcalina es de 20 volts, con soluciones alcalinas es mas lento el anodizado y lo puedes controlar mejor. victor solis neri - guadalajara, jalisco, mexico September 29, 2014 ---- Ed. note: Hola Victor. ¡Gracias! We appreciate your response, but we've found that if most of the readers and the site curator don't understand the messages, the forum just doesn't work. I wish I knew Spanish, but I don't. I can basically understand your posting, and I thank you for it, but I can't pretend to actually understand Spanish :-( Please try to post in English. Thanks again!

A. Type I anodizing is color spectrum processing on titanium.
Type II anodizing is the hard coat process on titanium.
Implant alloys are mainly Ti6Al4V material specifications. The process is listed under AMS 2488 I believe.

Type II Ti hard coat processing is very much proprietary in both process and chemistry parameters. Takes a bit of patience and research but it can easily enough be figured out. I put together two different bath chemistries that produce high production numbers of high quality product. I can process many pieces at the same time with no shade variance in the grey coating. Most OEM's are looking for a lustrous dark grey in the final finish.
If you anodize then you already know that green is the hardest spectrum to maintain repeatability on. Different chemistries produce different colors at different voltages. My green spectrum hits between 92 and 95 volts before I go into pinks. Hot pink as well. Blue ghosting or spots I think is the biggest issues with the greens. Teals are within a very small voltage parameter and have nothing to do with the blue problem in green. Oxide growth is uniform so surface roughness can play a factor in higher voltage colors. Shorter etch times can leave the surface too smooth to achieve the perceived green color over the entire substrate. Too rough of a substrate can cause interference in light refraction because the peaks and valleys are too far apart for an even refraction. The oxides created are still uniform in thickness which creates highs and lows in the oxide finish causing the interference or crossing of rays that may appear as spotting or ghosting. Maintaining close tolerances in chemistry and voltage parameters is very important in achieving green repeatability. I run several shades of every color to include green. Organic and inorganic oxide removal before the color tank is a major player in high voltage green. Most cleaners will not remove the organic contaminant of the oxide formed due to heat created in the milling processes of the part. I process implant geometries so etch removal of the contaminants can cause undersized critical dimensions. My etch rates are slower so pre-cleaners and deoxidizers are a must before etching even begins.
I believe the grey color you are looking for in type I Ti color anodizing is called 'grey green'. I run that color quite often. In my chemistries, it's found between silver and sea foam. Cold baths create better colors!

A. Lawrence --

regarding why it happens in the head: it is likely due to the intricate nature of the features there. Also, you said it happens more on smaller parts, which could support this hypothesis. From that vantage point, it is probably a cleaning, bubble surface tension or parts orientation situation.

I have not experienced this exact issue yet but here are some ideas that might bring you closer to finding the issue:

Do the parts pass a water break test prior to anodizing? Check your cleaning process, maybe you are not removing all substances from manufacturing left in the screw head.

How are the parts oriented during the process? Does this orientation allow any bubbles that might form to break off and float to the surface? If you can see into the tank during or after processing: can you see bubbles that adhere to the parts?

Depending on the type of your agitation and how much it may jiggle smaller parts, it could be the part's contact areas are only intermittently in contact with your fixture or the contact areas are getting anodized, increasing electrical resistance. Although, this would only explain parts with a low layer thickness but would not explain the patchiness so I wouldn't expect this to be a real problem.

In any case, our operators do a mid-cycle agitation to free any bubbles formed after approx. half the anodization time, but we do colored oxide layers with a low voltage so the risk is much smaller, as you stated earlier.
I do not know of a commercial solution for a mid-cycle hammer whack or similar to break away formed bubbles, but maybe someone else here can point you in the right direction.

Keep us updated!

Eric

A. Lawrence,

adv.
If you are interested in investing some money into upgrading the type II anodizing for titanium, you will have a reliable and fool-proof process for any size and shape.

Different alloys, different colors

Anodized 3-D printed titanium rings

These parts can pass AMS 2488 test on durability. You will definitely save money and time in a long run, skipping the frustration of anodizing process going wrong. Bonus: the anodized parts do not require additional "fur" removal step. Contact me for details.

Hi Chen,

adv.
Please contact me directly. We license the know-how of the 2488 proprietary titanium type II anodizing process. Also upon request we provide the know-how of black titanium technology.

Both technologies require off-shelf equipment and cheap chemicals.

Our metal finishing technological processes successfully work all over the world. References upon request.

A. Hi.
Many different grades/alloys, maybe all, including CP (chemically pure), can be anodized. Apologies but your question is abstract and requires a lot of guessing, so it's hard to proceed.

What type of anodizing are you doing and why? Decorating earrings, making watch dials, building wear-resistant machine parts, medical implants? Am I correctly guessing that you are currently unsuccessful in reliably etching it? Maybe some parts are etching properly and others aren't but you don't know what grade/alloy they are, and you're guessing that the problem is that they are different grades?

Please try your best to forthrightly describe exactly what you are trying to do and in what way it isn't working. If you would rather not do that for proprietary reasons, you can view topic 50566, "Titanium chemistry in HF and HNO3 chemical milling" which attempts to explain what goes on chemically in Nitric-HF etching of titanium; it may be helpful to you in sorting out whatever problem you are having. Thanks!

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey