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

摘要

The high temperature torsion deformation of a duplex microstructure high Nb-TiAl alloy was investigated at 850 degrees C. The experimental results showed that the hardness and the density of twins increased with radial distance from the center to rim of 180 degrees 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, gamma 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 gamma grain recrystallizations at twin-twin boundaries avoided excessive stress concentration, which allowed the alloy to continue plastic deformation. (C) 2017 Elsevier B.V. All rights reserved.