Insight into the interface properties of γ-TiAl/α-TiAl with La doping obtained by first-principles calculations.

The interface strength between TiAl and α-TiAl phases is pivotal for influencing the room temperature ductility of TiAl alloys. However, it is difficult to elucidate the bonding mechanisms of the γ-TiAl/α-TiAl interface experimentally. The effects of La doping on the properties of the γ-TiAl/α-TiAl interface were investigated by using first-principles calculations in this study. The energy stability of various atoms surrounding the interface following the substitution of La atoms was calculated and a model of the γ-TiAl/α-TiAl interface was constructed. Meanwhile, the stability and electronic structure of the interface both before and after La doping were examined. The results demonstrate that the energy of the γ-TiAl/α-TiAl interface model reaches its minimum when the Al atom at the Doped 5 site is substituted by a La atom. The interface binding energies for the clear and doped models are determined to be 3.86 J m and 2.47 J m, respectively. Similarly, the corresponding interface energies are found to be 1.65 J m and 1.15 J m. The charge analysis of the interface models reveals that the primary bonding at both interface types consists of Ti-Ti and Ti-Al bonds. In the doped interface, the La atom doping results in the formation of La-Al bonds. The results from the tensile tests reveal that the tensile stresses for the undoped and doped interface models are 19.18 GPa and 11.26 GPa, respectively. The potential energy surface analysis demonstrates that the maximum potential energy values for the clear and doped interfaces are 1.605 J m and 0.816 J m, respectively. Along the minimum energy path, the energy barriers for heterogeneous sliding at the interfaces are determined to be 0.404 J m and 0.243 J m, while the ideal shear strengths are 0.286 GPa and 0.130 GPa, respectively. Therefore, the doping of La atoms enhances the ductility of the γ-TiAl/α-TiAl interface.