Corrosion behaviour of plasma sprayed coatings

It is known that Al₂O₃, Al₂O₃ +TiO₂, Cr₂C₃+NiCr, NiAl, NiCrAl, ZrO₂ and MgZrO₃ coatings are resistant to specific corrosion media which are widely employed in industry. In the material environment configuration, the component surface is a vital parameter in determining its optimum performance. For this purpose, the corrosion behaviour of ceramics, cermet and metallic coatings on AISI 304L stainless steel substrates were investigated in 1 N H₂ SO₄ solutions. A plasma spray process was employed on a substrate with deposition of ceramic, cermet, and metallic powders such as Al₂O₃, Al₂O₃ +TiO₂, Cr₂C₃+NiCr, NiCrAl, ZrO₂+NiAl and MgZrO₃+NiAl. The porosity of coatings was measured by water impregnation, electrochemical measurements and optical methods. Potentiodynamic polarization measurements were also carried out to determine the corrosion behaviour of the plasma sprayed coatings. The microstructure of coatings and corroded coatings were investigated during the corrosion test by optical microscope, SEM and X-ray diffraction (XRD). It is concluded that the corrosion resistance depends strongly on the porosity and coating type. Besides, it was found that the corrosion resistances of Al₂O₃, Al₂O₃+TiO₂, ZrO₂+NiAl and MgZrO₃+NiAl coatings are higher than those of Cr₂ C₃+NiCr, NiAl and NiCrAl coatings.