Microstructure and coloration mechanism of TC11 aerospace titanium alloy ultra-thin thermal oxide films

Abstract

This study explores the microstructure and coloration mechanism of high-saturation structural colors in ultra-thin oxide films formed on TC11 aerospace titanium alloy near permissible engineering temperatures. Utilizing optical microscopy (OM), spectrophotometry, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), focused ion beam (FIB), transmission electron microscopy (TEM), and energy dispersive spectrometer (EDS), the optical properties, thickness, and microstructure of the oxide films were examined. The research posits a coloration theory grounded in zero-order Fabry-Pérot resonance-enhanced absorption. Key findings reveal a color transition in the oxide films from golden to light blue as oxidation conditions vary from 450 °C for 5 hours to 550 °C for 60 hours, with an average thickness ranging from 16.3 nm to 63.4 nm. Despite changes in oxidation conditions, the film's structure remains consistent and uniform. It predominantly consists of Brookite-type TiO2, TiO and Al2O3, with trace amounts of MoO2 and MoO3. The film's color is independent of its structural composition and instead related to its thickness, influencing the absorption wavelength per the Fabry-Pérot model, which closely matches the observed absorption wavelengths. Notably, oxidation acceleration between 30 to 60 hours at 550 °C heralds the commencement of a deviation from the coloration mechanism of the oxide film based on the Fabry-Pérot cavity.