Evolution of the defect substructure in V-4Ti-4Cr alloy under severe plastic deformation

Abstract

The evolution of the defect substructure in V-4Ti-4Cr alloy under its severe plastic deformation by torsion in Bridgman anvils is studied by transmission electron microscopy. Nanoband structural states with a dipole or multipole character of misorientations and a crystallite (or nanoband) size varying from several to several tens of nanometers form in the true logarithmic strain range e ≈ 3.0−6.6. Such crystallites form inside 100-nm submicrocrystallites or coalesce (at e ≥ 6) to yield mesobands with a pronounced vortex character of their propagation. The formation of these states is related to the activation (by the flows of nonequilibrium point defects in stress fields) of quasi-viscous deformation and lattice reorientation mechanisms, which provide the generation and propagation of partial disclination nanodipoles followed by the development of collective effects in a disclination substructure. These effects lead to the group motion of nanodipoles inside the mesobands.