Corrosion of APS- and HVOF-sprayed coatings of the Al2O3-TiO2 system

In this paper, the results of corrosion investigations performed on thermally sprayed coatings with different compositions in the Al2O3-TiO2 system (Al2O3, Al2O3-3%TiO2, Al2O3- 40%TiO2, Al2TiO5) are presented. The coatings were deposited on corrosion-resistant stainless steel substrates using APS and HVOF processes and were characterized by means of optical microscopy and SEM of metallographically prepared cross sections as well as surfaces before and after corrosion testing. The changes in phase composition occurring during spraying were studied by X-ray diffraction. The corrosion experiments were performed with 1 N solutions of NaOH and H2SO4 at room temperature, 60°C, and 85°C. In contrast to expectations, APS-sprayed coatings were found to be more corrosion-resistant than the denser HVOF-sprayed coatings.