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

Research highlights: → 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 - Abstract: Good high-temperature corrosion resistance of Fe-Al alloys in oxidizing environments is due to the α-Al2O3 film which is formed on the surface provided temperature is above 900 oC 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.