First-principles study of shear deformation in TiAl and Ti₃Al

The phase transition of titanium aluminides during the shear deformation is one of the most interesting issues. Using the DFT calculations, the shear deformation behaviors in γ-TiAl and α₂-Ti₃Al were investigated to understand the intrinsic mechanisms of phase transitions. The stress-strain curves present that, the 1 / 6 [11 over(2, -)] (111) shear deformation, whose maximum internal strength is 4.30 GPa, is the easiest way in γ-TiAl. Meanwhile, the shear deformation in TiAl is more difficult than that of 1 / 3 [10 over(1, -) 0] (0001) shear process in Ti₃Al, whose maximum internal strength is 2.86 GPa. These results reveal that the α₂ → γ phase transition happens more easily than the reverse transformation. The further analysis of the elastic constants and the partial density of states (PDOS) exhibits the main reasons as (i) TiAl has larger shear constants than Ti₃Al, and (ii) the Ti-Al bonding is stronger than that of Ti-Ti in TiAl, while Ti₃Al shows the contrasting feature.