Anodic Dissolution Behavior and Electrochemical Turning of Ti80 Alloy in NaCl Solution

Electrochemical turning is an efficient machining method for machining Ti80 pressure-resistant structures owing to its low tool cost and high machining flexibility. However, research has yet to explore the electrochemical turning of the Ti80 alloy, limiting its widespread application in ocean engineering. Accordingly, this study examined the anodic dissolution behavior and electrochemical turning of the Ti80 alloy in NaCl solution. Ti80 specimens underwent electrochemical tests, namely, potentiodynamic polarization and potentiostatic polarization. X-ray photoelectron spectroscopy was employed to characterize the composition of the passive film formed on the Ti80 surface when Ti80 was placed in a 20 wt % NaCl solution; this film's structure was investigated through electrochemical impedance spectroscopy (EIS) and transmission electron microscopy (TEM). The results revealed that the passive film mainly contained TiO₂, Al₂O₃, Nb₂O₅, ZrO₂, and MoO₃ and comprised two layers: a compact inner layer and a loose outer layer. The measured thickness of the passive film was about 18 nm from TEM, which was near the predicted value (21.6 nm) calculated by EIS data. The diffraction spots obtained from Fast Fourier Transform (FFT) with interplanar spacings of 0.1238, 0.2399, 0.1039, and 0.1888 nm indicated the (024), (201), (521), and (231) crystal planes of TiO₂, respectively, showing a relatively high crystallinity of TiO₂ in the passive film. The dissolution morphologies of Ti80 at different current densities and processing times were analyzed; the dissolution mechanism of Ti80 in 20 wt % NaCl solution was identified. Finally, grooves with relatively sharp edges were machined on a Ti80 cylindrical workpiece through electrochemical turning at rotation speeds of 0.011 and 0.005 r/min.