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Titanium Anodize Thickness vs Color

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Q. Anodizing Nitinol (nickel titanium). I am interested in finding out whether anyone has successfully anodized nickel titanium and what were the results of this.

Glen Roberson
hobbyist - Las Vegas, Nevada
2006

I am from the aerospace welding world. We have requirements that allow certain coloration for welds in titanium. The thicker the oxide layer the lower the weld ductility. Specifications list various colors in order of how bad they are and give acceptance/rejection criteria. Unfortunately, there is an argument going on whether the green color is worse than blue or the other way around. Some specification list blue as worse and others list green as worse. I figure you finishing guys could help end the stalemate.

Since we know that the thicker the oxide film the lower the weld ductility all we need to know is which color is produced by a thicker oxide film. I personally am on the side that thinks the green is the result of a thicker oxide layer and therefore more detrimental.

I am looking for a chart/graph/table/list that shows the color that titanium appears for different thicknesses of titanium dioxide. Any assistance would be greatly appreciated.
Thanks
Dave Bezaire

David Bezaire David
Aerospace Engineer - Lakewood, California USA
November 20, 2010

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Hi, David.

I would say that green is thickest. I can't refer you to a peer-reviewed chart offhand, but letter 7926 lists one enthusiast's colors vs. voltages.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 22, 2010

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I was a weld evaluator for an overhaul company that worked on several major OEM engines. I have never seen green on a weld.
A blue/purple thin line outside of the bead was normally a function of the part not being clean and/or the TIG gas/backup gas was not being done correctly.
We welded 6-4 Ti in a bubble and rarely saw any blue. If we did, the purge cycle was shortcut or there was a leak in the lines that let oxygen venturi into the line.
My opinion is that it is all color is -not good- and what you are doing is assigning levels of not good.

James Watts
- Navarre, Florida
November 22, 2010