Effect of connected pores on the corrosion behavior of plasma sprayed alumina coatings

Abstract

Summary The role of connected pores in plasma sprayed alumina coatings on the corrosion of the substrate was investigated. Coatings of thickness ranging from 60 to 300 μ m were prepared by plasma spraying using Fe-0.5 wt.% C commercial mild steel substrate. The density of connected pores was measured by the ferroxyl test and the anodic polarization test using 3% NaCl solution at 35 °C. Corrosion behavior of the substrate was investigated by means of the immersion test using 3% NaCl solution at 35 °C. The connected porosity was found to decrease with increasing the coating thickness. The connected porosity P can be expressed using the coating thickness t and a constant α as P = αt −0.82 . From the immersion test, the corrosion resistance of plasma sprayed alumina coatings was found to be higher for the thicker coatings. However, in the more thickly coated specimens, the formation of the iron oxide layer at the coating-substrate interface was faster and the coating layer fell off earlier.