Effect of Sn doping concentration on the oxidation of Al-containing MAX phase (TiAlC) combining simulation with experiment.

Sn doping is usually adopted to prepare TiAlC in mass production because it can reduce the synthesis temperature while increasing the phase purity. However, excessive Sn doping usually deteriorates the oxidation resistance of TiAlC. Therefore, an appropriate Sn doping concentration is a vital issue. In this work, the effect of Sn doping concentration on the oxidation behavior of TiAlC was systematically investigated by combining theoretical calculations and experimental methods. Density function theory calculations suggest that the oxygen adsorption mechanisms for the (001) surface of TiAlC with and without Sn doping are similar, and Ti-O bonds are always preferentially formed. The molecular dynamics simulation further indicates that Al atoms have a faster diffusion rate during the oxidation process. Therefore, a continuous AlO layer can form rapidly at high temperature. Nevertheless, when the Sn doping concentration exceeds 10 mol%, the continuity of the AlO layer is destroyed, thereby impairing the oxidation resistance of TiAlC. Furthermore, oxidation experiments verify the above results. The oxidation mechanisms of TiAlC with different Sn doping concentrations are also proposed.