Deformation-induced γ → DI-α₂ phase transformation occurring in the twin-intersection region of TiAl alloys

Deformation-induced γ → DI-α₂ phase transformation was verified to occur in the twin-intersection region of a Ti–45Al–8Nb (at.%) alloy compressed at room temperature. High-resolution image observations of the deformation-induced DI-α₂ phase suggested that the orientation relationship between the DI-α₂ and γ phases remained the typical one: (0001)_{DI−α₂}//{111}_γ, [11^¯₂0]_{DI−α₂}//〈101]_γ. The conversion of stacking sequence from ordered face-centered tetragonal to ordered nonequilibrium hexagonal close-packed structure was accomplished by the movement of a/6〈11^¯₂] Shockley partial dislocations on every other {111}_γ plane. Compositional analysis based on energy dispersive spectra revealed that the DI-α₂ phase had the same composition as the matrix γ phase. No compositional diffusion occurred because the plastic deformation was carried out at room temperature. The strong stress concentration in the intersection region was the major force to induce the γ → DI-α₂ phase transformation in the process of room-temperature compression.