Corrosion Resistance of APS- and HVOF-Sprayed Coatings in the Al2O3-TiO2 System

In this article, the results of corrosion investigations performed on thermally sprayed ceramic coatings with different compositions in the Al2O3-TiO2 system (Al2O3, Al2O3-3%TiO2, Al2O3-40%TiO2, and TiO x ) are presented. The coatings were deposited on corrosion-resistant steel substrates using atmospheric plasma spraying (APS) and high-velocity oxy-fuel (HVOF) spraying processes and characterized by means of optical microscopy, scanning electron microscopy (SEM), and x-ray diffraction (XRD). The corrosion properties were investigated in 1 N solutions of NaOH and H2SO4, at room temperature, 60 °C, and 85 °C, as well as in hydrothermal conditions with deionized water at 100 °C and 200 °C. The corrosion stability of the coatings depended on coating characteristics (spraying method, microstructure, and crystalline phase composition) and the corrosive environment (media, test temperature, and duration). In contrast to expectations, APS-sprayed coatings were found to be more corrosion-resistant than the HVOF-sprayed coatings. Addition of TiO2 to Al2O3 increased the corrosion stability, especially for the HVOF-sprayed coatings. In this work, TiO x coatings were found to be more corrosion-resistant than the Al2O3-based coatings.