Abstract
Low temperature Type II hot corrosion is a serious problem for low cycle fatigue (LCF) failure of advanced turbine disk alloys operating at increased temperatures. Accordingly, the present effort studied 15–20µm corrosion resistant Cr2AlC sputter coatings on Low Solvus High Refractory (LSHR) disk alloy LCF test specimens. These were cycled to failure at 840/−430MPa and 0.33Hz, after 500h oxidation and 50h of Mg-Na2SO4 hot salt corrosion, all at 760°C. The coating successfully prevented hot corrosion pitting that was responsible for a 90% decrease in uncoated LCF specimens. However, fractography identified unintentional 15–30µm deep defects produced by grit blast surface preparation of coated samples. These acted as failure origins and introduced anomalous life reduction for some coated test specimens. Furthermore, the presence and growth of an undesirable Cr7C3 second phase diminished protectiveness by promoting internal oxidation and embrittlement of the coating.
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