Structure, mechanical properties and corrosion resistance of amorphous Ti-Cr-O coatings.

In this work, titanium‑chromium oxide (TCO) coatings were investigated aiming to produce a functional hard-corrosion resistance coating based on the well-known properties of the individual TiO 2 and Cr 2 O 3 oxides. The TCO coatings were deposited on low carbon steel and Si substrates using reactive magnetron sputtering from a crystalline TiCr target. Amorphous TCO coatings with increasing oxygen content up to 65 at.% were obtained by rising the oxygen flow rate during the reactive deposition. Coatings deposited using constant O 2 flow rate of 1.5 (6.2% of oxygen) were selected to evaluate the corrosion resistance, hardness and to determine the effect of annealing treatments. Electrochemical evaluation was done using impedance spectroscopy and potentiodynamic polarization in 3.5 wt% NaCl solutions showing a significant protection efficiency. The coatings were heat treated at different temperatures (200, 400, 500, 600 and 800 °C) for 2 h in air. The coatings were analyzed by X-ray photoelectron spectroscopy to obtain the composition, X-ray diffraction (XRD) and scanning electron microscopy for microstructural and morphological characterization, respectively. The XRD results show that the heat-treated coatings maintained the X-ray amorphous structure up to 500 °C. Above this temperature, the coatings crystallize forming large Cr 2 O 3 crystals segregated to the surface leaving an amorphous TiCr bottom layer. • Amorphous Ti-Cr-O coating reached 30 GPa hardness. • Annealing at and above 500 °C led to segregation into Cr 2 O 3 and TiO 2. • Amorphous Ti-Cr-O coatings were deposited on low carbon steel. • The corrosion of the steel was significantly reduced under simulated sea water. [ABSTRACT FROM AUTHOR]