High-Temperature Oxidation Resistance of Solid-Solution and Gamma-Prime Strenghthened Alloys in the Presence of Water Vapor

Abstract Water vapor often present as a by-product in many combustion environments is known to accelerate oxidation rates of wrought high-temperature alloys. This paper is focused on the comparative cyclic oxidation resistance of several solid-solution and gamma-prime strengthened alloys in humidified air. The cyclic oxidation testing was conducted for 1,008 hours at 760°C and 871°C in air with 10 vol. % H2O for a set of solid-solution and gamma-prime strengthened Ni-base alloys. In addition, another set of Ni- and Fe-base solid-solution strengthened alloys were tested in more aggressive air with 20 vol. % H2O at 760°C and 871°C. Alloy performance was ranked by assessing weight-change behavior and metal recession measurements, which includes metal loss, average internal penetration, and maximum internal penetration. The types of oxide scales evolved and Cr depletion behavior were studied using SEM equipped with EDS. It was found that gamma-prime strengthened alloys showed comparable oxidation resistance to solid-solution strengthened alloys at 760°C, while at 871°C gamma-prime strengthened alloys underwent greater oxidation attack. Among solid-solution strengthened chromia-forming alloys, it is seen that alloys with a low amount of Fe such as N06230, N06617, N06625 alloys exhibited excellent oxidation resistance. The S34700 alloy underwent catastrophic oxidation attack resulting in the formation of non-protective Fe-rich oxides in air + 20% H2O environment.