Effect of Sn doping concentration on the oxidation of Al-containing MAX phase (Ti₃AlC₂) combining simulation with...

Sn doping is usually adopted to prepare Ti₃AlC₂ 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 Ti₃AlC₂. Therefore, an appropriate Sn doping concentration is a vital issue. In this work, the effect of Sn doping concentration on the oxidation behavior of Ti₃AlC₂ 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 Ti₃AlC₂ 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 Al₂O₃ layer can form rapidly at high temperature. Nevertheless, when the Sn doping concentration exceeds 10 mol%, the continuity of the Al₂O₃ layer is destroyed, thereby impairing the oxidation resistance of Ti₃AlC₂. Furthermore, oxidation experiments verify the above results. The oxidation mechanisms of Ti₃AlC₂ with different Sn doping concentrations are also proposed.