A new understanding on titanium coloration-variation of external stimuli and in-depth mechanism analysis

Surface coloring technology plays a very unique role in the diversification of Ti applications. We report our new findings using AC polarization to fabricate chromatic passive films on Ti surface. Compared to passivation films formed using DC anodization, brighter and more uniform colors could be generated in a controlled manner by simply varying the waveform of AC polarization. The colored films fabricated by AC polarization were very dense without visible cracks or defects. DC anodization, AC sine polarization, and AC square polarization exhibited high light reflectivity in the wavelength range of 380–450 nm, 500–650 nm, and 400–500 nm, respectively. The composition distribution and formation process of colored films were analyzed in depth, which enabled our further understanding of the electrochemical coloration mechanism on Ti surface. The thickness of DC anodization, AC sine polarization, and AC square polarization were 161 nm, 203 nm, and 165 nm, which corresponded to the colors of oxford blue, pale yellow, and light blue, respectively. In addition, the corrosion resistance measurements further revealed that the films with lower surface roughness prepared by AC polarization presented great protective effect on the Ti matrix. • The new external stimuli were used to fabricate colored films on Ti surface. • A new model was proposed to explain the mechanism of AC electrochemical coloration. • The fabricated colored films exhibited high corrosion resistance for Ti matrix.