Effect of TmCl 3 concentration on the properties of micro-arc oxidation coatings on TC4 titanium alloy

Abstract

The effects of adding TmCl₃ on the surface morphology, phase composition, wear resistance, and corrosion resistance of micro-arc oxidation (MAO) coatings were investigated using characterization techniques including scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results showed that the addition of an appropriate amount of TmCl₃ could increase the oxidation voltage and improve the surface morphology of the coating. The main phases composing the coating were Rutile TiO₂, Anatase TiO₂, and SiO₂, in which the Tm element existed in the form of Tm₂O₃. When the added concentration of TmCl₃ was 0.15 g/L, the thickness, hardness, and adhesion of the coating reached their maximum values, which were (32.4 ± 5.43) μm, (405.37 ± 10.41) HV, and (17.44 ± 3.28) N, respectively; meanwhile, the roughness and friction coefficient reached their minimum values, which were (1.678 ± 0.486) μm and (0.7454 ± 0.2808), respectively. Corrosion current density and corrosion rate both reached their minimum values, at 4.2937 × 10⁻⁸ A·cm⁻² and 1.9651 × 10⁻²mpy, and the corrosion resistance of the micro-arc oxidation coating reached its optimal level. High-temperature oxidation tests and thermal shock tests demonstrated that the addition of TmCl₃ could effectively enhance the high-temperature oxidation resistance and thermal shock resistance of TC4 titanium alloy.