Effect of Sn addition on the mechanical properties and high-temperature oxidation resistance of intermetallic TiAl alloys by first principles study and experimental investigation

Tin (Sn) can be used as an effective TiAl powder sintering aid, but it is unclear whether Sn will deteriorate its properties as a micro-alloyed element in TiAl intermetallic. This work focuses on the influence of Sn on the mechanical properties and oxidation resistance of TiAl alloys. The effect of Sn on the mechanical properties of TiAl alloys is investigated by experiments and first-principles calculations. Sn atoms preferentially occupy the Al sites in γ-TiAl alloys and increase the lattice volume, which is consistent with the XRD pattern. The elastic constants of TiAl alloys with different Sn contents are also systematically presented. It is found that 1.85 at.% Sn addition improves the ductility of TiAl, but a higher Sn content reduces the ductility. This result is also verified by room temperature compression test. The density of states is also used to prove the ductility improvement of TiAl alloys with a certain amount of Sn. Last, the diffusion barrier of O and Al/Ti–O bond strength were calculated to evaluate the oxidation resistance of TiAl–Sn alloys. The addition of Sn markedly increases the O diffusion barrier and Al–O bond force constant, indicating that Sn can improve the oxidation resistance of TiAl alloy.