Titanium pressure case coating

Hello,

I require a surface coating for a titanium pressure case which houses oceanographic instruments. The case is an assembly of 6Al-4V and grade 2 titanium machined components. The purpose of the coating is to give a uniform, dark surface (the unit must be visually dark, ideally matte black), and must be stable and corrosion resistant at full ocean temperatures and depths (>10,000 psi, -2 degrees C). Components are close fitting parts with counterbores and threaded holes, so surface treatment must not change dimensions more than a few tenths of a thousandth of an inch.

Is there an anodizing process for titanium that gives a very dark surface? How about a nitriding process or a black chromate coating? I'm looking for a few possibilities to evaluate.

Thank you for any assistance,

I would discuss this further with General Magnaplate. Their Canadize process for Ti is probably suitable, but I am not that familiar with color availability.