Effect of Atmosphere and Sample Thickness on Kinetics, Microstructure, and Compressive Stresses of Chromia Scale Grown on Ni–25Cr

Abstract

Most high-temperature alloys rely on the formation of a protective chromia scale during service. Generally, the oxidation resistance is mainly influenced or limited by corrosive environments around the alloy. In the present study, the evaluation of kinetic data is connected to microstructural analyses and stress measurements of the Cr2O3-layer formed on the Ni–25Cr model alloy after 1000 °C of isothermal exposure to atmospheres with and without water vapor and a varying (1 and 0.01%) oxygen content. Significant differences in oxide morphology, scale thickness, and oxide grain appearance could be observed. The results, with respect to oxidation kinetics and microstructures, showed a high tendency of variation when water vapor is present in the test gas. It was found that the addition of water vapor to the dry gas leads to decreased oxidation rates and reduced chromia scale thicknesses. The influence of the gas composition on the defect structure, the chromium flux, and diffusion of gas species is discussed on the basis of classical oxidation theory.