Effect of NdCl₃ on characteristics of micro-arc oxidation coating formed on TC4 alloy

To study the effect of adding NdCl₃ on the characteristics of micro-arc oxidation coating of TC4 titanium alloy, micro-arc oxidation was performed by adding different concentrations of NdCl₃ to the base electrolyte. The changes in the surface morphology, phase composition, abrasion resistance, corrosion resistance and erosion resistance of the MAO coating after the addition of NdCl₃ were investigated, utilizing SEM, XRD, XPS, multifunctional material surface tester, electrochemical workstation and autoclave testing methods. The results showed that adding an appropriate amount of NdCl₃ can increase the oxidation voltage and improved the surface morphology of the coating, and the main constituent phases of the coating were rutile TiO₂, anatase TiO₂ and Nd₂O₃. When the concentration of 0.06 g L⁻¹ was added, the thickness and hardness of the coating reached the maximum value of 25.1 μm and 540 HV, and the roughness and coefficient of friction reached the minimum value of 1.022 μm and 0.281. In addition, the corrosion current density and the corrosion rate reached the minimum value of 5.028 × 10^–9 A cm⁻² and 1.673 × 10^–3 mm a⁻¹. Therefore, the coating had excellent abrasion and wear resistance. The erosion experiments indicated that the titanium alloy substrate and the corrosion rate of the MAO coating increased with the extension of the erosion time, and the addition of NdCl₃ could effectively improve the erosion resistance of the TC4 titanium alloy substrate.