High temperature oxidation of Fe–Al and Fe–Cr–Al alloys: The role of Cr as a chemically active element

► We have found a correlation between chemical potentials in surface–bulk atomic exchanges and oxides formed on the surface of Fe–Cr–Al alloys in high temperature ► In Fe–Cr–Al alloys the addition of Cr changes the chemical potentials to drive Al to the surface to improve the formation of protective Al-oxide scales ► The described mechanism sheds light on the phenomenon called Third Element Effect (TEE), which does not have a generally accepted explanation so far ► Our research deals with the analysis of the experimental results from the point of view of atomic scale quantum mechanics, which represents a new kind of approach to the problem ► Our first-principles computational investigation covers also an exceptionally wide concentration range of Fe–Cr–Al alloys Good high-temperature corrosion resistance of Fe–Al alloys in oxidizing environments is due to the α-Al 2O 3 film which is formed on the surface provided temperature is above 900 °C and the Al-content of the alloy exceeds the critical value. Ab initio calculations combined with experiments on Fe–13Al, Fe–18Al, Fe–23Al and Fe–10Cr–10Al alloys show that the beneficial effect of Cr on the oxidation resistance is significantly related to bulk effects. The comparison of experimental and calculated results indicates a clear correlation between the Fe–Cr chemical potential difference and the formation of the protective oxide scales.