Effect of chromium and silicon additions on the hot corrosion resistance of nickel aluminide coatings

The effects of chromium and silicon modification on the microstructure and hot corrosion resistance of slurry aluminide coatings applied on pure nickel was studied by in-depth microscopic analyses. The simple and the Cr-modified aluminide coatings provided limited protection in Type II hot corrosion conditions but the Si-modified coating exhibited outstanding resistance with no sign of attack after 300 h of isothermal exposure at 700 °C. The synergistic dissolution between NiO and Al2O3/Cr2O3 appears responsible for the onset of the corrosion attack for the simple and Cr-modified coatings while silicon is shown to extend the incubation period. [Display omitted] •Experimental evidence for a two-stage corrosion mechanism following initiation and propagation.•Onset of hot corrosion attack occurs after an incubation period and is triggered by NiO.•Chromium improves resistance through formation of Cr2O3 and promoting α-Al2O3.•Silicon significantly improves the resistance of the aluminide coating by prolonging the incubation period.•Aluminium surface concentration of the coating also plays a role, mainly by delaying the formation of NiO.