Scaling Kinetics and Scale Microstructure of Chromia Scales Formed on Ni-25%Cr Model Alloy during Oxidation in H2o-Containing High and Low pO2 Test Gas at 1000°C

Abstract

The isothermal oxidation behaviour of a Ni25Cr model alloy was studied employing the JuSie-methodology, i.e. using specimens of different thickness for each specific test gas composition at 1000°C in dry and wet N2-1%O2 as well as in Ar-7%H2O. The oxidation mechanisms were evaluated using thermo-gravimetry and SEM/EBSD analyses of oxide scale cross sections. The ion beam polished oxide cross-sections were analysed in terms of oxide grain growth and nucleation rates of new oxide at the oxide-gas interface. The findings can be explained by considering the effect of H-defects and in-scale stress state on point defect concentrations in the chromium sub-lattice.