Oxidation Lifetime Modeling of 625 and 120 Foils After Long-term Exposure in Flowing Air + 10% H2O at 700 and 800 ∘C

Abstract

A model describing oxidation kinetics considering simultaneous oxidation and volatilization of external oxide scales was integrated with a CALPHAD-based coupled thermodynamic and kinetic approach to predict the oxidation-induced lifetime of foils of alloys 625 and 120. Long-term exposures in flowing air +10% H2O at 700 and 800 ∘C under two flow velocities were used to validate the modeling results. The time to a critical Cr concentration of 10 wt% at the oxide/alloy interface, t10, was shown to correlate with the breakdown of the Cr2O3 scale for the studied experimental conditions. Finally, the modeling approach was extended to consider time-dependent oxidation and volatilization rate constants to develop a more appropriate lifetime criterion for microturbine recuperator foils.