Corrosion Properties of Plasma-Sprayed Coatings using Oxide Powders

Three different oxides of CrO₂-TiO₂, Al₂O₃ and Al₂O₃-TiO₂ were plasma-sprayed on Ti substrate to evaluate the crystal structure and the corrosion properties of the coatings. No phase change of the coatings after corrosion test in 0.5 M H₂SO₄ solution at 25°C was found regardless of the presence of the NiCoCrAlY bond layer. Electrochemical measurements and SEM results revealed that the single coatings without the bond layer were always effective against corrosion resistance due to lower current density within the passive region. Pitting corrosion of the surface was observed for the Al₂O₃ coating. It can be concluded that the Al₂O₃-TiO₂ coating without the bond layer may be the best oxide among the oxides investigated due to low porosity (5.4%), smooth surface roughness (4.5 m), low current density (6.3×10-8 A/cm²) in the passive region, low corrosion potential (Ecorr, -0.55 V) and no pitting corrosion.