Pre-oxidation of Inconel alloys for inhibition of carbon deposition from heated jet fuel

Exposure of superalloy surfaces to jet fuel at elevated temperatures leads to the formation of carbonaceous deposits and metal sulfides. The formation of stable oxide layers on alloy surfaces can reduce the activity of the constituent transition metals that catalyze the dehydrogenation of hydrocarbons and the subsequent carbon deposit growth. The metals Ni, Cr, Fe, Mn, Al, Ti and Nb + Ta form thermodynamically stable oxide layers after oxidation above 800 degrees C under O-2 flow. In this study, we investigated the formation of oxides and spinels on three different Ni-base superalloys (Inconel 600, Inconel 718, and Inconel X750) and their activity towards carbon and sulfur deposit formation from jet fuel (JP-8) thermal stressing at 600 degrees C and 34 atm (500 psig) for 5 hr. Metal oxide formation during pre-oxidation and the behavior of pre-oxidized samples in thermal stressing were found to depend strongly on the minor element composition of these superalloys.