Effect of Ti interlayer on corrosion behavior of nanostructured Ti/TiN multilayer coating deposited on TiAl6V4

To improve the corrosion properties of TiAl6V4 alloy, TiN monolayer and Ti/TiN multilayer coatings are deposited by reactive magnetron sputtering. The phase, structure, and morphology properties are investigated by grazing-incidence X-ray diffraction, field-emission scanning electron microscopy, and atomic force microscopy, respectively, and the corrosion behavior is evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization. The TiN monolayer and Ti/TiN multilayer with thickness of 1,350 and 1,410 nm have the (111) and (002) preferred orientation and crystallite size of 42.5 and 24.3 nm, respectively. Columnar growth in TiN is hindered by the Ti interlayers and no cracking is observed between the layers indicating strong adhesion. The nanostructured Ti/TiN coating forms stable surface titanium oxide which improves the corrosion resistance by approximately 80 and four times compared with TiAl6V4 alloy and TiN coating, respectively. Hindrance of the columnar structure in TiN by the Ti interlayer decreases the local corrosion rate and enhances the galvanic corrosion resistance by forming a layer on the beta-phase enriched with vanadium as well as a TiO2 stable layer. The nanostructured Ti/TiN coating demonstrates capacitive behavior with phase angles approximately -50 degrees and high impedance values at low frequency to be the corrosion resistance mechanism.