Microstructure and corrosion resistance of TiN/TiO2 nano-composite film on AZ31 magnesium alloy

Abstract

The high corrosion rate of Mg alloy restricts its application. In this paper, a nano-composite film as TiN/TiO2 was introduced to Mg alloy to improve the corrosion resistance. The nano-composited film was fabricated by atomic layer deposition (ALD) and in-situ oxidation (20 SCCM oxygen flow, at 250 °C, duration ≥ 20 min). When oxygen is introduced, the initial ALD-ed crystalline TiN layer is rapidly oxidized till the amorphous TiO2 layer is saturated. A stable TiN/TiO2 nano-composited film would be obtained then. X-ray photoelectron spectroscopy depth (XPS-depth) and transmission electron microscopy image (TEM) show that the nano-composite film has an interlayer structure. The nano-composite film shows good adhesion to the Mg alloy substrate in the nano-indentation analysis. Moreover, the nano-indentation scratches heal to a certain degree after 48 h, which means the film could self-heal. With the film, the surface potential mapping is not only overall higher but also less fluctuating by scanning Kelvin probe (SKP) analysis. There is a higher Ecorr (increasing ~0.42 V) and a much lower icorr (decreasing ~1/200) for potentiodynamic polarization (PDP) measurement. Equivalent circuit fitting for electrochemical impedance spectroscopy (EIS) profile changes from Rs(CPE1Rct) to Rs(CPE2(Rf(CPE1Rct))). The film makes less corroded withing a more uniformed corroded mode during neutral salt spray test (NSS). All these indicate that Mg alloy corrosion resistance is greatly improved. The work not only provides a flexible method for the interlayer composite film fabrication but also make an effective surface modification for Mg alloy corrosion resistance.