Hot corrosion behavior of AIP NiCoCrAlY(SiB) coatings on nickel base superalloys

NiCoCrAlY(SiB) coatings were deposited on the nickel base superalloys DZ125 and DSM11 by arc ion plating (AIP). The corrosion behavior of the bare alloys and the protective coatings in molten 75 wt.% Na2SO4+25 wt.% K2SO4 at 900 °C in air was tested for 90 h. The results indicated that DZ125 superalloy suffered catastrophic corrosion after 5 h exposure and a thick porous oxide scale (500–600 μm) interspersed with Ni3S2 and alloy particles formed on the alloy. For the Cr-rich DSM11 alloy, a mild corrosion attack happened, but severe internal Al-rich oxidation occurred inside the alloy. With NiCoCrAlY and NiCoCrAlYSiB coatings, the hot corrosion resistance of the systems was improved due to the formation of an α-Al2O3 scale. The hot corrosion resistance of the coatings with additions of Si and B can be improved by promoting the growth of a dense and continuous α-Al2O3 layer in the initial stage and improving the adherence of the oxide scale to the coating in the subsequent hot corrosion process. The hot corrosion degradation mechanism of the NiCoCrAlYSiB coatings and the influence of the substrate materials on the behavior of the whole system were also investigated.