Can titanium be anodized?

Titanium anodizing grows the natural titanium dioxide film electrochemically, but the result is nothing like Type II or III on aluminum. The colour anodize most people mean (AMS 2488 Type III) is a film of only 30-300 nm, thinner than a wavelength of light; the colour comes from interference in that film, and the voltage sets it: roughly bronze at 10-20 V, purple and blue at 20-35 V, yellow and gold at 50-70 V, and greens and magentas above that. The film is transparent, adds no measurable dimension, and cannot chip or peel because it is the metal's own oxide. It is used for identification, part marking, medical instrument colour coding and appearance.

AMS 2488 Type II is the functional version: an alkaline anodize that builds a thicker (about 1-3 µm), matte grey oxide with good anti-galling and anti-fretting properties. It is common on aerospace fasteners, hinges and sliding titanium parts, usually followed by a dry-film lubricant. It also improves adhesion of primers and paints. Neither type provides wear resistance comparable to aluminum hardcoat; for a hard titanium surface, look at nitriding, PVD coatings or thermal oxidation instead. Type I (a high-temperature oxide) exists but is rarely used.

Colour anodizing is sensitive to surface prep. The colour is uniform only on a uniformly finished surface, so machining marks, grain and polish differences show as shade variation. Bead blasting or a chemical pickle before anodizing gives the most even result. The film is thin enough to wear off at contact points and to be scratched by steel tools, which is fine for marking and cosmetics but not for a surface that sees abrasion. Both types are done on Ti-6Al-4V, commercially pure grades and most other alpha-beta alloys; colour response is slightly different between alloys, so match alloys in a colour-matched set.