Behaviour and mechanisms of alkali-sulphate-induced hot corrosion on composite coatings at 900 °C

Three coating systems (one single MCrAlY, two composite coatings with/without the Cr-rich interlayer) have been prepared by the arc ion plating (AIP) and electroplating methods. Hot corrosion of the coatings at 900 °C by alkali sulphates shows that a composite coating with a chromium-rich interlayer exhibits the best corrosion resistance. The MCrAlY coating was severely deteriorated in 100 h since its non-productive (Ni,Co)Al2O4 and Cr2O3 scales induce internal sulfidation and oxidation. However, the microstructural involutions seldom occur within composite coatings, especially for the one with the Cr-rich interlayer. Mechanisms of hot corrosion of the three coatings are discussed.

► Three coatings have been prepared by arc ion plating and electroplating method.
► Composite coating with Cr-rich interlayer has the best hot corrosion resistance.
► Internal sulfidation and oxidation degenerate the MCrAlY coating severely.
► Microstructural involutions seldom occur on the two composite coatings.
► The coatings exhibit various corrosion processes in the incubation period.