Salt-induced hot corrosion is an accelerated mode of degradation that is known to occur in various high temperature engineering applications, including marine gas turbines. In order to improve the life of hot-section superalloy components, they are often coated with an aluminide. In this study, the hot-corrosion resistance of different types of β-NiAl aluminides and CoCrAlY-based coatings on nickel-based superalloys 247 and 792 was assessed. The coatings were tested under cyclic high-temperature (HTHC-900°C) and low-temperature (LTHC-705°C) hot corrosion conditions using a laboratory-based Dean rig. The hot corrosion conditions were simulated by depositing Na2SO4 salt on the coated samples and then exposing the samples to a O2 + 0.1%SO2 flowing gas environment. HTHC testing was performed for up to 500 hours, while LTHC testing was performed for up to 200 hours. The effect of pre-oxidation on LTHC resistance was also studied. Coating performances under both HTHC and LTHC conditions were ranked by assessing the extents of attack around the circumference of each coated sample, together with maximum depth of attack. The corrosion products and phases present in the as-received and corroded coatings were characterized. Finally, was found that pre-oxidizing at 1050°C improved the resistance of the coatings to LTHC.

Subject
Hot corrosion, Nickel coatings, Test methods, Coatings, Salts, Substrates, Nickel based alloys, Liquids, Corrosion attacks, Superalloys, Aluminides, Corrosion resistance, Samples
Keywords:
hot corrosion, aluminide coatings, CoCrAlY coatings, nickel-based superalloys, pre-oxidation
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2005
Association for Materials Protection and Performance (AMPP)
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