Corrosion behavior of aerosol thermal sprayed ZrO sub 2 coatings

ZrO sub 2 coatings of 2-7 # mu m thickness were obtained by the aerosol thermal spraying process on 316L stainless steel. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) showed that these films consisted of nanocrystalline ZrO sub 2 aggregates with a monoclinic structure. Corrosion tests were performed in aqueous NaCl (0.5 M) and H sub 2SO sub 4 (20 wt.%) using potentiodynamic cyclic polarization curves. Surfaces and cross-sections of coated samples were compared with the uncoated substrate. This evaluation indicated decreased pitting of the steel with coating. The protection against corrosion in NaCl solution depended strongly on coating thickness. No protection was found for thicknesses < 5 # mu m. Meanwhile, a marked reduction of the current density was produced by thicker coatings that acted as an effective corrosion barrier. Coatings thicker than 5 # mu m also provided significant protection against corrosion in H sub 2SO sub 4.