Degradation of Coating Alloys in Simulated Marine Environments.
Final technical rept. 1 Mar 76-1 Mar 78,
PRATT AND WHITNEY AIRCRAFT GROUP EAST HARTFORD CT MATERIALS ENGINEERING AND RESEARCH LAB
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Chloride- and SO3 induced hot corrosion of state-of-the-art and developmental coatings were studied in a program of laboratory hot corrosion testing correlated with metallographic examination of service hardware. Laboratory furnace tests showed that CoCrAlY coatings are highly susceptible to degradation by chloride-containing salt deposits the mechanism of attack involves dealloying of aluminum via formation of an interconnected network of coarse and fine pores. Sputtered platinum overlayers are an effective means of retarding the onset of this type of degradation, especially at low temperatures where dissolution of the overlayer by interdiffusion is slow. In spite of this demonstrated potential for chloride-induced degradation, dissimilar microstructures of test specimens and service hardware primarily the presence of a zone of internal attack in test specimens but not in engine-run parts indicates that chloride alone cannot account for the severity of the marine environment. Emphasis on the program was then shifted to examination of SO3 effects. It was shown that the microstructural features of service hardware could be reproduced in furnace tests with Na2SO4 deposits and SO3 in the gas.
- Coatings, Colorants and Finishes
- Properties of Metals and Alloys
- Marine Engineering