The Role of Silicon in the Protection Against Type I Hot Corrosion

Hot corrosionHot corrosion dramatically lowers the life of superalloySuperalloys components by inducing pitting (Type II) or an extensive homogeneous attack (Type I), hence initiating cracks and decreasing the load bearing section. This degradation phenomena may occur in the coldest areas of high pressure turbine components, but they are commonly found in the low pressure turbine parts like in theDS200+Hf DS200 + Hf nickel-based superalloyNickel-based superalloy investigated in this work. Therefore, a Si-modified aluminide slurry coatingCoating was applied to the alloy, and its hot corrosionHot corrosion resistance was assessed under type I conditions with a Na2SO4 deposit at various temperatures and times. The comparison against simple slurry aluminide with and without Si and out-of-pack aluminide coatingsAluminide coating revealed for the first time in the literature that Si ties up W in the coatingsCoating thereby impeding acidic dissolution, which greatly improves the corrosion resistance of DS200 + Hf superalloySuperalloys. The W-free out-of-pack aluminide coatingAluminide coating forms a protective alumina scale that delays the initiation of hot corrosionHot corrosion unless the coatingCoating is damaged. In contrast, the simple slurry aluminide coatingAluminide coating without Si does not offer any protection in spite of the Cr segregationSegregation close to the surface.