High-temperature torsion induced gradient microstructures in high Nb-TiAl alloy

Abstract The high temperature torsion deformation of a duplex microstructure high Nb-TiAl alloy was investigated at 850 °C. The experimental results showed that the hardness and the density of twins increased with radial distance from the center to rim of 180° torsion sample. Besides, the “recrystallized”, “substructured” and “deformed” microstructures were also presented gradient and forming sub-grains was the transition stage between recrystallization and deformation. Moreover, γ grain recrystallization at twin-twin junctions occurred and the observation of dislocation-twin interactions revealed the formation of secondary twins by dissociating of the dislocation at twin-twin boundary. The dissociation of such dislocations interacting with twin boundaries and γ grain recrystallizations at twin-twin boundaries avoided excessive stress concentration, which allowed the alloy to continue plastic deformation.