First-principles investigation of $3d$ transition elements in $L1$ TiAl

The effect of $3d$ transition elements (such as V, Cr, Mn, Fe, Co, and Ni additions) on material properties in $L10$ TiAl has been studied using the first-principles DMol and discrete variational method within the framework of the density-functional theory. The transfer energy calculation indicates that all these $3d$ elements show a tendency to substitute for Al sites in the stoichiometric TiAl alloy, with the increasing order $V<Cr<Mn<Ni<Fe<Co$⁠. Our results show that the local distortion of crystal lattice around an impurity atom is nonuniform, and it is found that the important influencing factors on the local lattice distortion are the impurity atom size and the site preference. Based on the effects of the doped alloying elements on the structural parameters and mechanical properties, we conclude that the larger bond strength and the smaller axial ratio benefit the ductility.