Effects of the TiO2 content on the mechanical properties and galvanic corrosion resistance of Al2O3 coatings

Abstract

In this study, the conventional air plasma spraying (APS) technology was employed to deposit Al2O3 coatings with varying TiO2 contents (AT coatings) on a Ti80 substrate. The coating microstructure was characterized using scanning electron microscopy (SEM), as well as the mechanical properties including fracture toughness and Vickers hardness by indentation method. Besides, the galvanic corrosion behavior of a 921A/AT coating system couples was thoroughly investigated in comparison to a 921A/Ti80 couple. The influence of TiO2 content on the resistance of Al2O3 coatings to galvanic corrosion were discussed experimentally and theoretically. Microstructural observation indicated that the introduction of TiO2 into Al2O3 coating was conducive to improving coating quality, exhibiting a decreasing value in surface roughness and porosity. Besides, improved fracture toughness and decreasing hardness were observed for samples with higher contents of TiO2. Both experimental and theorical results demonstrated that the AT coatings could potentially inhibit the galvanic corrosion which occurred on 921A/Ti80 couples, but its resistance to galvanic corrosion weakened conversely with the increase of TiO2 content. Thereinto, the volume resistivity played a decisive role.