The effect of Pt on type II hot corrosion behavior of Si-aluminide coatings with lower silicon than the critical amount

In this paper, the effect of adding a low amount of platinum to slurry Si-modified aluminide coatings containing silicon less than the amount required to provide complete protection in these coatings is investigated. In addition to the coatings characterization, the role of platinum on the type II hot corrosion behavior of coatings has been discussed. To create silicon and silicon-platinum aluminide coatings, a slurry silicoaluminzing method was applied to samples of Ni-base superalloy GTD-111 specimens, which was previously Pt-electroplated on some of them with a thickness of 2 μm. The amount of silicon in the slurry was 10% by weight relative to total solid of the slurry, so that the amount of silicon in the coating is less than the critical amount required for complete protection. The type II hot corrosion test was carried out using a furnace method with Na2SO4-60mol% V2O5 at 700 °C. After 20 hours of hot corrosion, Al2O3 protective oxide and non-protective oxide NiAl2O4 were detected in silicon-platinum- and silicon-aluminide coatings, respectively. In the absence of platinum, the Ni3V2O8 phase was also found to be a product of NiO and NiAl2O4 dissolution in type-II hot corrosion condition. At the end of the 80-hour hot corrosion, unlike the silicon-aluminide coating, silicon remained in the silicon-platinum-aluminide coating structure.