A Critical Compressive Stress for Increasing the Oxidation Kinetics of Fe-20Cr Alloy Oxidized at 900 A°C

The effects of compressive stresses on the oxide-scale morphologies formed on an Fe-20Cr alloy were investigated by comparison of the oxidation behavior in air under classical conditions, i.e., without any applied mechanical stresses and under static compressive stresses, at 900 A degrees C. The study was carried out mainly by comparisons of oxidation kinetics gained by thermogravimetric analysis (TGA), surface morphologies of oxidized specimens observed by scanning electron microscopy (SEM), oxidized products examined by X-ray diffraction (XRD). It was found that the application of compressive stresses induced an increase in oxidation rate, but a decrease of oxide grain size. When the stresses are in the range of 5-8 MPa, both chromium- and iron-oxides formed but, at other stresses, only chromia was present. In particular, there was a maximum in oxidation rate when the applied stress was 5 MPa. The paper places emphasis on analyzing the cause of this phenomenon.