Spectral and physical properties of electrochemically formed colored layers on titanium covered with clearcoats

We present the application and characterization of two commercial polymer clearcoats to electrochemically formed colored passive layers on titanium with the aim of providing physical protection required in many of titanium's applications, while allowing the unique appearance of the colored layers to show through. Thin layers of an acrylic automotive clearcoat (～3.5 μm thick) and an epoxy marine clearcoat (～6.5 μm thick) are applied to the colored titanium surfaces using spin coating, and are found to slightly modify their visual properties, while maintaining their bright, well-defined sparkling colors. Both clearcoats are found to significantly reduce the surface roughness, thereby reducing potential wear from friction and the adhesion of fine dirt particles. They are also found to notably decrease the wetting properties of colored titanium, furthering its protection against damage from ambient and aqueous media. The clearcoats show the ability to protect colored titanium from physical and chemical damage, with the automotive clearcoat exhibiting superior adhesion. Our electrochemical coloring technique combined with the application of clearcoats creates a new and unique system that does not rely solely on a polymer coating for its colorful appearance and protection against corrosion.