Enhanced corrosion resistance of subsonic plasma sprayed nanostructured Al 2 O 3 -13TiO 2 coating by ultrasound-assisted sealing

In this paper, the ultrasound-assisted sealing with aluminum phosphate and silicone resin was used to fill the pores in the subsonic plasma sprayed nanostructured Al 2 O 3 -13TiO 2 coating, with which the corrosion resistance of the coating can be improved. Since ultrasonic environment accelerated the penetration of the sealant, the polarization resistance of the Al 2 O 3 -13TiO 2 coating after sealing with aluminum phosphate and with silicone resin was about 6.3 times and 119.6 times that of the as-sprayed Al 2 O 3 -13TiO 2 coating, respectively. With regard to the aluminum phosphate sealant, the heat-treatment improved the stability of sealant, while the evaporation of water in sealant resulted in the occurrence of micro-cracks in the coating. Meanwhile, the evaporation route of water also created some pits in the aluminum phosphate sealant, which weakened the surface sealing effect to a certain degree. For the silicone resin, the good elasticity and low drying temperature of silicone resin provided the sealant with a dense structure and thus ensured a remarkable sealing effect. In contrast with the aluminum phosphate sealant, the nanostructured Al 2 O 3 -13TiO 2 coatings after ultrasound-assisted sealing with silicone resin possessed higher corrosion resistance in 3.5 wt% NaCl solution.