SEALING TREATMENT OF PLASMA SPRAYED Cr3C2-NiCr/Al2O3-TiO2 COATING BY ALUMINUM PHOSPHATE SEALANT CONTAINING Al2O3 NANOPARTICLES

A typical structure of thermal spray coatings consists of molten particles, semi-molten particles, oxides, pores and cracks. These factors cause the porosity of the coating, which have a great influence on the properties of the coatings, especially on their wear-corrosion resistance. In this study, a post spray treatment of the Cr₃C₂-NiCr/Al₂O₃-TiO₂ coating by sealing method was realized and the corrosion properties of the coating were evaluated. The coating was fabricated by atmospheric plasma spraying. Aluminum phosphate (APP) containing aluminum oxide (Al₂O₃) nanoparticles (~10 nm) was applied as the sealant. The permeability of APP into the coating was analyzed by scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). The porosity treatment efficiency and the corrosion resistance of the coatings were evaluated by electrochemical measurements including potentiodynamic polarization and electrochemical impedance spectroscopy. In addition, the wear-corrosion resistance of the sealed coating was tested in 3.5 wt.% NaCl circulation solution containing 0.25 wt.% SiO₂ particles. The obtained results showed that APP has the ability to penetrate deeply in the coating. Included Al₂O₃ nanoparticles demonstrated positive effect on porosity treatment efficiency by the APP sealant. The research results on the corrosion protection of the coating will be presented specifically in this paper.