Competition between Stress Generation and Relaxation in Iron Oxide Films. Experiments and Modelling

Abstract

In the present work, the calculated growth stresses arising from iron oxide layers are compared to measurements of the macroscopic residual stresses. High temperature x-ray diffraction was used for determining the stress created in thin iron oxide layers formed on phosphated α-Fe, as a function of the oxidation time. Experiments are conducted both in situ during oxidation and after cooling, allowing us to derive respectively, growth and thermal stresses. A numerical model was developed to calculate the growth stress and the relaxation phenomena occurring during isothermal oxidation. This model takes into account the mechanical behaviour of both the substrate and the oxide, and parameters such as oxide growth kinetics, substrate thickness, etc. The elasto-viscoplastic model correlates the experimental results with the various parameters of the study.